Report of Commitl:ee on

Boiler-Furnace Explosions

James K. Lafontaine, Chairman Penelec

W. H. Axtman, Secretary American Boiler Manfacturers Assn.

R. R. Beal, Bailey Controls Inc. Paul L. C io f f i , Babcock & Wilcox C. W. Conaway, Industrial Risk Insurers William E. Cunningham Jr., Riley Stoker Corp~ John L. Edler, Baltimore Gas & Electric Co. Humphrey Fedorak, E I duPont de Nemours & Co. Frank H. Fishlock, Fenwal Inc.

(Rep. Fire Suppression Systems Assn.) Robert L. Gruehn, Kemper Group

(Rep. Alliance of American Insurers) T. B. Hamilton, Milton Head, SC

(Rep. Combustion Engineer Inc.) Albert L. Lake, In t ' l Union of Operating Engineers Kenneth N. Lawrence, Honeywell Inc.

(Rep. NEMA) Richard Leone, Factory Mutual Research Corp. Donald J. L. Lin, Quilin Inc. Robert M. Lundberg, Los Altos, CA Peter B. Matthews, Hartford Steam Boiler Inspection & Insurance Co. James J. McCauley, Public Service Electric & Gas Co. Raymond J. Murphy, Forney Engineering Robert P. Richmond, Exxon Co. USA Enno Toomsalu, Underwriters Laboratories Inc. Charles E. Trask, Kansas City Power & Light Co.

(Rep. Edison Electric Inst.) Albert J. Zipay, Foster.Wheeler Energy Corp.

Alternates

Phi l l ip A. Davis, Kemper Group (Alternate to R. L. Gruehn)

M. J. Karlowitz, American Petroleum Inst i tute Robert D. Lynch, Empire State Petroleum Assn. Inc.

(Alternate to Petroleum Marketers Assn. of America Rep.) Russell N. Mosher, American Boiler Manufacturers Assn.

(Alternate to W. H. Axtman) C. Dudley Orr, American Petroleum Inst i tute

(Alternate to J. H. Oannemaier) J. M. Simmons, Factory Mutual Research Corp.

(Alternate to R. Leone) J. V. Sweeney, Ebasco Services Inc.

(Alternate to Instrument Soc of America Rep.) J. C. Waung, Babcock & Wilcox Co. :

(Alternate to P. L. C io f f i )

This l i s t represents the membership at the time the Committee was balloted on the text of this ed i t i on . Since that time, changes in the membership may have occurred.

The Report of the Committee on Boiler Furnace Explosions is presented for adoption in 3 parts.

Part I of this Report, was prepared by the Technical Committee on Boiler Furnace Explosions and proposes for adoption a complete revision to NFPA 85A-1982, Standard for Explosion Prevention Single Burner Boiler-Furnaces Oi l - or Gas--Fired or Simultaneous Firing of Oil and'Gas. NFPA 85A-1982 is published in Volume 3 of the 1986 National Fire Codes and in separate pamphlet form.

Part I of this Report has been submitted to le t te r bal lot of the Technical Committee (}n Boiler Furnace Explosions which consists of 26 voi:ing members; of whom 21 voted aff i rmatively and 5 ballots were not returned (Messrs. Conaway, Edler, Karlowitz, Lynch and Trask}.

Part I I of this Report, was prepared by the Technical Committee on Boiler Furnace Explosions and proposes for adoption a complete revision to NFPA 85F-1982, Standard for the Instal lat ion and Operation of Pulverized Fuel Systems. NFPA 85F-1982 is published in Volume 3 of the 1986 National Fire Codes and in separate pamphlet form.

41

Part I I of this Report has been submitted to l e t te r ballot of the Technical Committee on Boiler~Furnace Explosions which consists of 26 voting members; of whom 14 voted af f i rmat lvely, 5 negatively (Messrs. Cunningham, Gruehn, Matthews, McCauley, and.Sweeney), 2 abstained (Messrs. Richmond and Toomsalu), and 5 ballots were not returned (Messrs. Conaway,'Edler, Karlowicz, Lynch, and Trask).

Mr. Cunningham voted negatively stating:

"I have reviewed the draft of NFPA 85F standard and with regret must vote against the release of this standard. "~

I do not object to some of the new requirements of NFPA 85F. This would include: i

(a) That b r i t t l e materials (cast iron) shall not be used in piping except as linings (paragraph 2-6.2.1.5).

I understand this to mean only piping between the pulverizer and the burner. I t would not effect the pulverizer design.

(b) Provision shall be made for ver i f i ca t ion of the flow of f i r e extinguishing or inert ing media (paragraph 2-6.8.2)."

I assume that this would be a common alarm to indicate that the media is flowing to the pulverizer, at or above a minimum rate. I

(c) I do not object to the new valve r~quirements per paragraph 5-2.3, this would require two valves in the coal piping l ines.

I am very concerned with the following design changes made by the NFPA: !

Paragraph 2-6.1.I and 2-6.1.6 - This sec~tion wi l l require al l hot and tempering a i r ducts, fan's and pulverizer to be designed for 50 psig.

Paragraph 2-6.2 - This section would require piping and valves to be designed For 200 psig. ~

The present requirement is for a l l equipmentwhich contains fuel-laden a i r to be designed for 50 psig.

I am aware that NFPA is trying to improve safety based on some recent studies. However, i t m~y be premature to incorporate these changes into NFPA 85F.

I have participated in these studies designed and conducted the explosion tests at the "CEGB f a c i l i t y in England, and considers that there is not yet suf f ic ient information that indicates that strengthenin~ the system is" the correct precautionary measure.

I have found that a key to safety is the system design and geometry. Volume change and direction change in the piping system are factors which wil l tr igger a detonation in the system. Increas'ing the design pressures, wi l l not eliminate or contain explosions and may only make them more powerful.

The NFPA requirement to inert a l l pulverizer sys tems.

.!

Paragraph 3-5.1 - When a f i r e is present', the code allows the introduction of inerting or extinguishing and increasing fuel flow. These acts can be dangerous. The pulverizer system is a complicated group'of equipment. The type of f i re , the location of the f i r e and the type of fuel wi l l dictate the extinguishing procedures. In addition, inert ing agents have not been known to extinguish f i res and ~nerting agents wi l l make f i r e temperatures hard to detect. They make i t appear that the f i res are extinguished.

I f a general statement must be used, the~operator should water deluge and t r ip the system.

Paragraph 3-5.I - Inerting is required b~ the proposed change when the unit is tripped. However, in our experience explosions occur when a unit ! s ' i n a transient condition, not stopped.

There are three inert ing media l is ted plus others. Since the inert ing is required, the code must only l i s t the acceptable media. The word "others" can be a problem.

In general, the code has confused extinguishing and inert ing creating a sense of security that is not founded experimentally or in the f i e ld . Finally, NFPA 85F constantly refers to NFPA 68 and NFPA 69 for design compliance. NFPA 69 (Appendix B) gives data for CO 2 as an inert ing agent with dusts. There is no information for N2 or steam. As for any practical application NFPA 68 (2-2.1.9) recommends against steam as an inertant for dusts. These standards do not address the specific coal problem (at this time) and cannot be used as general guidance."

Mr. Gruehn voted negatively stating:

"Considerable industry concern has been expressed concerning the 200 psi piping design change (subsection 2-6.2.1) as to warrant additional discussion and reconsideration."

Mr. Matthews voted negatively stating:

"Based upon comments received from Iowa Public Service and also from Pennsylvania Power and Light, as well as discussions at Hartford Steam Boiler, the 200 psi design change (subsection 2-6.2.1) may be inappropriate."

Mr. McCauley voted negatively as he feels design changes in the report are premature as evidenced by comments from Pennsylvania Power and Light and negative comments from Mr. Cunningham.

Mr. Sweeney voted negatively stating:

" I do not agree with the mandated increases in valving or coal pipe design pressure as the best method for reducing the hazard from pulverized coal explosions because:

(a) No rel iable test information is available to support the recommended values as being enough to solve problem by beefing up.

(b) Greatly increased cost and d i f f i c u l t y with plant maintenance..

(c) The correction of basic problems l ies in system design, measurement monitoring and operation; and should be tackled from that point.

(d) The double valving would complicate operations and would require consideration and modification of NFPA 85.

(e) Editorial comment Figure 2-5.1.1 reference in "No Valves" should be 2-5.1.2.9 rather than 2-5.1.1.9.

( f ) Figure 2-5.1.1 contains many errors and requires rework so that i t agrees with text . "

Mr. Toomsalu abstained from voting stating:

"Since my experience with pulverized fuel systems is rather l imited, I believe I am not qual i f ied to vote on the extensive revisions being proposed to this standard."

Mr. Richmond abstained from voting stating:

"Subsection 2-6.2.1 of this proposed revision of NFPA 85F sets out a requirement that piping normally operated at no more than 2 psig shall be designed to withstand an internal explosion pressure of 200 psig for containment of possible explosion pressures. Available information suggests that this wi l l provide protection against some explosions, but not every possible event. Hence, the protection achieved appears to be a matter of degree only.

For most explosion hazards, the most ef fect ive approach has been to improve the preventive features of the system rather than to attempt to achieve containment at excessive cost. Designing equipment for lO0 times normal operating pressure appears to be

42

excessive. However, since I have had no direct operating experience with this type of equipment, I choose to abstain from voting at this time."

Part I I I of this Report, was prepared by the Technical Committee on Boiler Furnace Explosions and proposes for adoption a complete revision to NFPA 85G-1982, Standard for the Prevention of Furnace Implosions in Multiple Burner Boiler-Furnaces. NFPA 85G-1982 is published in Volume 3 of the 1986 National Fire Codes and in separate pamphlet form.

Part I I I of this Report has been submitted to le t te r bal lot of the Technical Committee on Boiler Furnace Explosions which consists of 26 voting members; of whom 18 voted af f i rmat ively, 2 abstained (Messrs. Leone and Toomsalu), and 6 ballots were not returned (Messrs. Conaway, Edler, Gruehn, Karlowicz, Lynch, and Trask).

Mr. Cunningham voted aff i rmatively and stated:

I. I disagree with the requirement as outlined in paragraph 4-3.2.2, shich i t appears would require three furnace presure transmitters.

I would l ike to return to the wording in the present NFPA 85G paragraph 2-3.2.2 (a), which reads:

(a) At least two (preferably three) furnace pressure transmitters (B), each on a separate pressure sensing tap and suitably monitored (C), to minimize the poss ib i l i ty to operating with a faulty furnace pressure measurement.

The existing NFPA 85G has already suf f i c ien t ly stressed the need for redundancy in the measurement. To impose the use of a part icular redundancy arrangement with higher procurement and insta l la t ion costs unnecessarily burdens specially the smaller user.

The proposed wording is also misleading. Do we want to use two transmitters or three transmitters? Or two out of three signals of the installed transmitters? Is a median calculation where al l the three signals are used not acceptable?

2. I would l ike to note that very few units sold in today's market have multiple induced draft and forced draf t fans.

I feel i t was a mistake to remove the present wording, which is:

NOTE: During any individual fan start ing sequence, i ts associated dampers may be closed.

I t would appear that "fan control devices" (paragraph 5-].2 (a)) means in let vanes. Therefore, i t would appear that a single IO and FD fan would have to be started with al l dampers wide open. This would increase the horsepower to start a fan and may result in an unsafe condition.

The proposed wording in 5-1.2 (a) requires that on a single ID and FD fan trains, each fan needs to be started with i ts associated dampers wide open something which is only possible with a grossly oversized motor. The only remedy seems to be the use of bypass ducts around both the ID and FD fans.

As proposed, paragraph 5-I.2 (a) seems to override or be in conf l ic t with the opening paragraph 5-I.2 which allows for other than wide open paths, thus, we feel the need for completion of the note with the reference to the single fan train.

NFPA may wish to add to the proposed note (below paragraph 5 - l . l (a)) in order to deal with a single fan t ra in, which would read:

"On instal lat ions with single induced and forced draft fans, the induced draft fan's associated damper may be closed for fan star t up. The forced draft fan's associated dampers may be brought to the minimum position that insures purge a i r flow during fan operation and low start ing current conditions for this fan start up."

PART I

(LOG #12) 85A - I - ( I - I . I ) : Accept in Principle SUBMITTER: Thomas Kuhta, American Insurance Service Group Inc. RECOMMENDATION: Revise f i r s t sentence of subsection I -1.1 to read:

"This standard applies to boilers" with fuel input ratings of 12,500,000 Btuh (3663 kW) or greater." SUBSTANTIATION: We recently had reason to compare the scopes of ASME CSD-I and NFPA 85A,:' 85B, 85D, and 85E; this comparison revealed a number of inconsistencies and areas needing c l a r i f i c a t i o n . '

The scope of NFPA 85A (Section l - l ) indicates that the standard "applies to boilers with fuel input greater than 12,500,000 Btuh"; ASME CSD-I has a scope which excludes boilers "with fuel input ratings of 12,500,000 Btuh or above". Technically, this means that a 12.500,000 Btuh boi ler is not covered by either standard. The proposd change would place such boilers under the scope of NFPA 85A.

This may appear to be a minor matter, but i t could become quite important i f one has a 12,500,000 Btuh boi ler. COMMITTEE ACTION: Accept in Principle. COMMITTEE COMMENT: Refer to proposal 85A-4.

(LOG #13) 85A - 2 - ( I - I . I ) : Accept in Principle ~ : Thomas Kuhta, Americe:n Insurance Service Group Inc. RECOMMENDATION: Revise subparagraph (a) subsection I-1.1 to read:

(a) Natural gas only or another similar gaseous fuel SUBSTANTIATION: We recently had reason to compare the scopes of ASME CSD-I and NFPA'85~, 85B, 85D, and 85E; this comparison revealed a number of inconsistencies and areas needing c la r i f i ca t ion .

NFPA 85A's scope indicates thai:, among the fuels to be used, natural gas is under the standard's scope; the standard defines, natural gas as a "gaseous fuel occurring in nature consisting mostly of a mixture of organic compounds". This leaves open to question whether or not use of another gas fuel comes under the standard. NFPA 85B is much c learer ' in this regard in that i t states (subsection I - I .2 ) that the standard applies only "to f i r i ng of.natural gas as defined in Chapter 3 and other similar gases)us fuels . . . ". NFPA 85B uses the same def in i t ion of "natural gas" as NFPA 85A.

The proposed change would c la r i f y what fuels may be used within the parameters of the standard. COMMITTEE ACTION: Accept in Principle. COMMITTEE COMMENT: Refer to Proposal 85A-4.

(LOG #14) 8SA - 3 - (Appendix G): Accept SUBMITTER: Robert P. Richmond, Exxon Company, U.S.A, Baton Rouge Refinery RECOMMENDATION: Change the words "Natural Gas" to "Fuel Oil" in the subt i t le beneath the schematic diagram which begins, "Typical Schematic Arrangement . . .". SUBSTANTIATION: Correction of apparent mistake to give agreement with Appendix t i t l e and schematic. COMMITTEE ACTION: Accept. COMMITTEE COMMENT: See Committee Proposal 85A-4.

8SA - '4 - (Entire Standard): Accept SUBMITTER: Technical Committee on Boiler Furnace Explosions RECOMMENDATION: Completely revise the 1982 edition of NFPA 85A, Standard for Prevention of Furnace Explosions in Fuel Oil and Natural Gas-Fired Single Burner Boiler-Furnaces as sho~.n in the following text. SUBSTANTIATION: To ref lect changed fuel u t i l i za t ion patterns and bring safety requirements up to the standard of the industry. COMMITTEE ACTION: Accept.

NFPA 85A

Standard for Prevention of FurnaceExploslon in Fuel Oi l - and Natural Gas-Fired

Single Burner Boiler-Furnace

1987 Edition

Chapter I Introduction

Information on referenced publications can be found in Chapter 11.

1-1" Scope.

1-1.1 This standard app l i es to b o i l e r s wi th a fue l input r a t i n g of 12,500,000 Btuh (3663 kW) or g rea te r . This standard app l ies on ly to b o i l e r - f u r n a c e s using

s i n g l e burners f i r i n g :

(a) Natural gas only as def ined in Chapter 3.

(b) Other gas with a Btu value and c h a r a c t e r i s t i c s s i m i l a r to na tura l gas.

(c) Fuel o i l only o f No. 2, 4, 5 or 6 grade.

(d) Simultaneous f i r i n g o f gas and o i l f o r fue l t r a n s f e r .

(e) Simultaneous f i r i n g o f gas and o i l con t inuous ly .

I-2 Purpose. !

l-2.1 The purpose of this standard is to establish minimum standards for the design, instal lat ion,. operation, and maintenance of single burner boi ler furnaces, their fuel-burnlng systems, and related systems, to contribute to operating safety and, in part icular, the prevention of furnace explosions.

I-2.2 No standard can be promulgated that wi l l guarantee the elimination of boiler-furnace explosions. Technology in this area is under constant development, reflected in part by revisions to this standard. The user of this standard must recognize the complexity of fuel f i r ing as to the type of equipment and the characteristics of the fuel. Therefore, the designer is cautioned that the standard is not a design handbook, and does not do away with the need for competent engineering judgment. I t is intended that a designer capable of applying more complete and rigorous analysis to special or unusual problems shall have lat i tude in the development of such designs. In such cases, the designer is responsible for the va l id i ty of the approach.

I-2.3 This standard is applicable to new instal lat ions and to major alterations or extensions of existing equipment for the preparation and burning of fuel contracted for use subsequent to June l , 1987. The standard is not retroactive.

I-2.4 Furnaces such as those of process heaters used in chemical and petroleum manufacture, wherein steam generation is incidental to the operation of a processing system, are not covered by this standard.

I-2.5 Since this standard is based upon the present state of the art, i t sapp l i ca t ion to existing instal lat ions is not mandatory. Nevertheless, operating companies are encouraged to adopt those features of this standard that are considered applicable and reasonable for exist ing instal lat ions.

I-2.6 Emphasis is placed upon the importance of operation and maintenance procedures, combustion control equipment, safety interlocks, alarms, tr ips, and other related controls that are essential to safe boi ler operation.

43

Chapter 2 General

2-I Basic Cause of Furnace Explosions.

2-1.1 The basic cause of furnace explosions is the ignition of an accumulated combustible mixture within the confined space of the furnace or the associated boiler passes, ducts, and fans that convey the gases of combustion to the stack.

2-I.2 A dangerous mixture within the boiler-furnace enclosure of the accumulation of an excessive quantity of combustibles mixed with ai r in certain proportions wi l l result in rapid or uncontrolled combustion when an ignition source is supplied. A furnace explosion may result from ignition of this accumulation i f the quantity of combustible mixture and the proportion of a i r to fuel are such that an explosive force is created within the boiler-furnace enclosure. The magnitude and intensity of the explosion wi l l depend upon both the relative quantity of combustlbles that has accumulated and the proportion of a i r mixed therewith at the moment of ignit ion. Explosions, including "furnace puffs," are the result of improper procedures by operating personnel, improper design of equipment or control systems, or equipment or control system malfunction.

2-1.3 Numerous situations can arise in connection with the operation of a boiler-furnace, that wil l produce explosive conditions. The most common experiences are:

(a) An interruption of the fuel or air supply or ignition energy to the burner(s), sufficient to result in momentary loss of flames, followed by restoration and delayed re-ignition of an accumulation.

(b) Fuel leakage into an idle furnace and the ignition of the accumulation by a spark or other source of ignit ion.

(c) Repeated unsuccessful attempts to l ight-of f without appropriate purging, resulting in the accumulation of an explosive mixture.

(d) The accumulation of an explosive mixture of fuel and a i r as a result of a complete furnace flameout and the ignition of the accumulation by a spark or other ignition source, such as attempting to relight the burner.

2-1.4 The conditions favorable to a boiler-furnace explosion described in 2-1.3 are typical examples, and an examination of numerous reports of boiler-furnace explosions suggests that the occurrence of small explosions, furnace puffs, or near misses has been far more frequent than is usually recognized. I t is belived that improved instrumentation, safety interlocks and protective devices, proper operating sequences, and a clearer understanding of the problem by both designers and operators can greatly reduce the risks and actual incidents of furnace explosions.

2-1.5 In a boiler-furnace, upset conditions or control malfunction may lead to an air/fuel mixture that may result in a flameout, followed by reignition after a combustible air/fuel ratio has been restablished. There may exist, in certain parts of the boiler-furnace enclosure, dead pockets where combustible mixtures can accumulate under upset furnace conditions. These accumulations may ignite with explosive force in the presence of an ignition source.

2-2 Manufacture, Design, and Engineering.

2-2.1 The purchaser or the purchaser's agent shall, in cooperation with the manufacturer, assure that the unit is not deficient in the apparatus required for proper operation, so far as practical, with respect to pressure parts, fuel burning equipment, a i r and fuel metering, and safe l ighting and maintenance of stable flame.

2-2.2 All fuel systems shall include provisions to prevent foreign substances from interfering with the fuel supply to the burner.

2-2.3 An evaluation shall be made to determine required provisions for optimum integration of manual and automatic safety features including the advantages and disadvantages of each t r ip function.

NOTE: The maximum number of automatic t r ip features does not necessarily provide for maximum overall safety. Some t r ip actions result in additional operations that increase exposure to hazards.

2-2.4 Although this standard requires a minimum degree of automation, the trend toward more complex plants with increased automation requires added provisions for:

(a) Information about significant operating events that permits the operator to make a rapid evaluation of" the operating situation.

(b) In-service maintenance and checking of system functions without impairing the re l i ab i l i t y of the overall control system.

(c) An environment conducive to proper decisions and actions.

2-2.5 The burner-front piping and equipment shall be designed and constructed to prevent the formation of hazardous concentrations of combustible gases that may exist under normal operating conditions.

2-3 Installation.

2-3.1 The boiler shall not be released for operation before the instal lat ion and checkout of the required safeguards and instrumentation system.

2-3.1.1 The constructor responsible for the erection and instal lat ion of the equipment shall see that a l l pertinent apparatus is properly installed and connected.

2-3.1.2 The purchaser, the engineering consultant, the equipment manufacturer, and the operating company shall avoid boiler operation until such safeguards have been tested to operate properly as a system. In some instances i t may be necessary to instal l temporary interlocks and instrumentation to meet these requirements. Any such temporary system'shall be reviewed by the purchaser, the engineering consultant, the equipment manufacturer, and the operating company, and agreement shall be reached on its su i tab i l i t y in advance of start-up.

2-3.1.3 Testing and checkout of the safety interlock system and protective devices shall be accomplished jo in t l y by the organization with the system design responsibility and those who operate and maintain such systems and devices during the normal operating l l f e of the plant. These tests and checks shall be accomplished before in i t i a l operation.

2-4 Coordination of Design, Construction, and Operation.

2-4.1 Statistics indicate that human error is a contributing factor in the majority of furnace explosions. Therefore, i t is important to consider whether the error was the result of:

(a) Lack of proper understanding of, or fai lure to use, safe operating procedures.

(b) Unfavorable operating characteristics of the equipment or i ts control.

(c) Lack of functional coordination of the various components of the steam generating system and i ts controls.

2-4.2 Furnace explosions have occurred as a result of unfavorable functional design. Frequently, the investigation has identif ied human error, and has completely overlooked contributive causes that resulted in the incident. Therefore, the design, instal lat ion,

44

and functional objectives of the overall system of components and their controls shall be integrated. Consideration shall be given to the human-machine relationships that wi l l exist during the operating l i f e of the system.

2-4.3 In the planning and the engineering phases of plant construction, designs shall be coordinated with operating personnel.

2-4.4 The integration of the various components consisting of boiler, burner, fuel, and air supply" equipment, combustion controls, interlocks and safety devices, operator functions, operator communication and training shall be the responsibil ity of the operating company, and shall be accomplished by:

(a) Providing design and operating personnel who possess a high degree of competence in this f ie ld, and are required to bring about these objectives. Periodic analysis to compare the plant to evolving technology so that deficiencies can be corrected to make the plants safer and more rel iable.

2-5 Maintenance Organization.

2-5.1 A program shall be provided for maintenance of equipment at intervals consistent with type of equipment, service requirements, and the manufacturer's recommendations. (See Chapter IO).

2-6 Basic Operating Objectives.

2-6.1 Basic operating objectives shall include the following:

(a) Establish operating procedures that wi l l result in the minimum number of manual operations.

(b) Standardize al l operating procedures. The use of interlocks is essential to minimize improper operating sequences and to stop sequences when conditions are notproper for continuation. I t is part icularly important that purge and start-up procedures with necessary interlocks be established and r ig id ly enforced. Chapters 5 and6 describe operating sequences that have proven effective in boiler-furnace operation.

2-6.2 Written operating procedures and detailed checklists for operator guidance shall be provided for achieving these basic operating objectives. All manual and automatic functions shall be described.

2-7 Gas and Oil Firing - Special Problems.

2-7.1 Common hazards are involved in the combustion of solid, l iquid, or gaseous fuels. Each of these fuels has special hazards related to i ts physical characteristics. The following items shall be considered in the design of the f i r ing systems.

2-7.2 Hazards Peculiar to Gas Firing.

2-7.2.1 Characteristics of gas and gas-firing that require special consideration are as follows:

(a) Gas is colorless; therefor'e, a leak usually cannot be visually detected. Also', reliance cannot be placed on detection of a gas leak'by the presence of odor.

(b) Potentially hazardous conclitions are,most l ike ly to occur within buildings, particularly where the gas piping is routed through confined areas. In the la t ter instance, adequate venti lation shall be provided. Outdoor boilers tend to minimize confined area problems.

(c) The nature of gas fuel makes i t possible to experience severedepartures from safe air-fuel ratios without any visible evidence at the burners, furnace, or stack, and to cascade into a progressively worse condition. Thus, combustion control systems that respond to reduced boiler steam pressure or steam flow with an impulse for more fuel, unless protected or interlocked to prevent a fuel-rich mixture, should be

considered potentially hazardous. The same applies to manual f i r ing without the above mentioned ihterlocks or alarms. (See Section 4-5 for requirements to avoid such hazards). ' •

(d) Particularly with respect to natural gas systems, the gas may be either "wet" or "dry". A wet gas usually implies the presence of d i s t i l l a te , which may be characteristic of a particular source. In the case of such a wet gas, the carryover of d i s t i l l a te into the burners could result in a momentary flameout and possible reignition. Reignition Could result in a furnace explosion. Therefore, special precautions shall be taken with wet gas supply systems. (For details, see NFPA 54, National Fuel Gas Code).

(e) Widely different characteristics of gas from either a single source or multiple sources may result in a significant change in Btu (kJ) input rate to the burner(s) without an equivalent change in airflow.

(f) Discharges from rel ief valves or from any other form of atmospheric vents can become hazardous unless special precautions are taken. (See Appendix P).

(g) Maintenance and repair of gas piping can be hazardous unless proper methods are used for purging and recharging the line, respectively, before and after making the repairs. (See NFPA 54, National Fuel Gas Code).

2-7.3 Hazards Peculiar to Oil Firing.

2-7.3.1 Characteristics of fuel oi l and fuel oi l f i r ing that require special considerations include:

(a). Fuel oi ls have high volumetric heats of combustion, therefore, even small leaks can create potential f i re hazards.

(b) When f i r ing oi ls that require preheating, the viscosity of oi l flowing to the burners shall be held within l imits to maintain proper atomization.

(c) Water or sludge in fuel oi l storage tanks or improperly located suction takeoffs from the storage tank may result in hazardous interruptions~or pulsations of the fuel supply to the burners. A flameout, either immediately or at a later time, may result because of plugged strainers or burner tips.

(d) Widely different characteristics of'fuel oi l from either a single source or multiple sources may result in a significant change in Btu (kJ)~input rate to the burner(s) without an equivalent change in ai r flow, or without an appropriate'change in fuel oi l temperature to restore the flowing viscosity to the proper value. Different shipments of fuel 'oil with dissimilar characteristics can cause a precipitation of sludge that can lead to hazards as described in 2-7.3.1(c).

(e) On installations designed to f i re both heated and unheated fuel oi ls, conslderation shall be given to the design of the burner control system to'ensure proper interlocks are activated for the selected fuel o i l . Similar consideration shall be given to the fuel oi l piping supply to the burner as well as'oi l recirculating piping to the fuel storage tanks, depending on the arrangement of the equipment provided.

(f) There is the ever present hazard of inserting an oi l gun in the burner assembly without a t ip, new gaskets, or sprayer plate. This can result in an unsafe operating condition.

(g) Proper pumping and atomization of fuel oi ls are dependent uponcontrol of viscosity. Changes in viscosity in relation to temperature vary for different oi ls and blends of oi ls. Very close attention to the design and operation of viscosity control systems shall be followed.for each fuel when the source or properties are variable.

45

(h) Clean d i s t i l l a t e fuels have low conductivities and wi l l generate stat ic electr ical charges in the fuel stream that may be dangerous unless flowing velocit ies are limited. (See NFPA 77, Static Electr ic i ty , and API-RP 2003, Protection Against Ignitions Arising Out of Static Lighting and Stray Currents.)

( i ) The incompressibility of fuel oi l can create very rapid transients in o i l flow through operating burners upon:

( I ) Rapid operation of o i l supply valve.

(2) Rapid operation of individual burner shutoff valves.

(3) Rapid operation of regulating valve in the return oi l l lne from the burner header (on systems using this type control).

Chapter 3 Definit ions

Air Change. A quantity of a i r , provided through the burner, equal to the volume of furnace and boi ler gas passes.

Air/Fuel Ratio.

I. Air-Rich. A rat io of a i r to fuel supplied to a furnace, which provides more a i r than that required for an optimum a i r / fue l rat io.

2. Fuel-Rich. A rat io of a i r to fuel supplied to a furnace, which provides less a i r than that required for an optimum a i r / fue l rat io.

3. Excess, Air. Air supplied for combustion in excess of theoretical a i r .

NOTE: This is not "Air Rich" as previously defined.

4. Theoretical Air (Stoichiometric Air ) . The chemically correct amount of a i r required for complete combustion of a given quantity of a specific fuel.

Alarm. An audible or v is ib le signal indicating an off-standard or abnormal condition.

Annunciator. A device indicating an off-standard or abnormal condition by both visual and audible signals.

Approved. Acceptable to the "authority having ju r isd ic t ion . "

NOTE: The National Fire Protection Association does not approve, inspect or cer t i fy any instal lat ions, procedures, equipment, or materials nor does i t approve or evaluate testing laboratories. In determining the acceptabil i ty of instal lat ions or procedures, equipment or materials, the authority having jur isd ic t ion may base acceptance on compliance with NFPA or other appropriate standards. In the absence of such standards, said authority may require evidence of proper ins ta l la t ion, procedure or use. The authority having jur isd ic t ion may also refer to the l is t ings or labeling practices of an organization concerned with product evaluations which is in a position to determine compliance with appropriate standards for the current production of l is ted items.

Atomizer. That device in an o i l burner which emits l iquid fuel in a f ine ly divided state.

Mechanical Atomizer. That device in an o i l burner which emits l iquid fuel in a f ine ly divided state without using an atomizing medium.

Atomizing Medium. A supplementary f lu id , such as steam or a i r , that assists in breaking down oi l into a f ine ly divided state.

Authority Having Jurisdiction. The "authority having jur isd ic t ion" is the organization, of f ice or individual responsible for "approving" equipment, an insta l la t ion or a procedure.

NOTE: The phrase "authority having jur isd ic t ion" is used in NFPA documents in a broad manner since jur isdict ions and "approval" agencies vary as do their responsibi l i t ies. Where public safety is primary, the "authority having jur isd ic t ion" may be a federal, state, local or other regional department or individual such as a f i r e chief, f i r e marshal, chief of a f i r e prevention bureau, labor department, health department, building o f f i c i a l , electr ical inspector, or others having statutory authority. For insurance purposes, an insurance inspection department, rating bureau, or other insurance company representative may be the "authority having ju r i sd ic t ion . " In many circumstances the property owner or his designated agent assumes the role of the "authority having jur isd ic t ion" ; at government instal lat ions, the commanding o f f i ce r or departmental o f f i c i a l may be the "authority having j u r i s d i c t i o n . "

Boiler. A closed vessel in which water is heated, steam is generated, steam is superheated, or any combination thereof, by the application of heat from combustible fuels in a self-contained or attached furnace.

Burner. A device or group of devices for the introduction of fuel and a i r into a furnace at the required veloci t ies, turbulence, and concentration to maintain ignit ion and combustion of fuel within the furnace.

Burner Control Systems:

Automatic (Recycling). A system by which a furnace is purged and a burner is started, ignited, and stopped automatically and which recycles on a preset pressure range.

Automatic (Nonrecycling). A system by which a furnace is purged and a burner is started, ignited, and stopped automatically but does not recycle automatically.

Manual. A system by which a furnace is purged and a burner is started, ignited, and stopped manually.

Supervised Manual. A system by which a furnace is purged and a burner is started, ignited, and stopped manually, with interlocks to ensure that the operation follows established proper procedures.

Drip Leg. A chamber of ample volume, with suitable cleanout and drain connections, into which gas is discharged so that l iquids and solids are trapped.

Excessive Steam Pressure Switch. A pressure-actuated device arranged to effect a safety shutdown of the burner when the steam pressure exceeds a preset pressure.

Excessive Water Temperature Switch. A temperature-actuated device arranged to effect a safety shutdown of the burner when the water temperature exceeds a preset temperature.

Flame. The v is ib le or other physical evidence of the chemical process of rapidly converting fuel and a i r into products of combustion.

Flame Detector. A device that senses the presence or absence of flame and provides a usable signal.

Fuel Oil. Fuel o i l complying with ASTM D-396 Standard, Specifications for Fuel 0 i l s .

Fuel Trip. The automatic shutoff of a specific fuel as the result of an interlock or operator action.

4B

Furnace. An enclosure designed for the combustion of fuel.

Gas. (See definit ions of LP-Gas and Natural Gas).

High Gas Pressure Switch. A pressure actuated device arranged to effect a safety shutdo~n or prevent starting when the gas pressure exceeds the present value.

High Oil Temperature Switch. A temperature actuated device that in i t ia tes a signal when oi l temperature rises above the l imits required to maintain the viscosity range recommended by the burner manufacturer.

"High Steam Pressure Switch. A pressure actuated device arranged to effect a normal burner shutdown when the steam pressure exceeds a preset pressure.

High Water Temperature Switch. A temperature actuated device arranged to effect a normal burner shutdown when the water temperature exceeds a preset temperature.

Igniter. A device that provides proven ignit ion energy to immediately l i gh t -o f f the main burner.

Class l (Continuous Igni ter) . An igni ter applied to ignite the fuel input through the Burner and to support ignit ion under any burner l i gh t -o f f or operating conditions. I ts location and capacity are such that i t

w i l l provide suf f ic ient ignit ion energy, generally in excess of 10 percent of fuel load burner input, at i ts associated burner to raise any credible combinat'ion of burner inputs of both fuel and a i r above the minimum ignit ion temperature.

Class 2 (Intermittent Igni ter) . An igni ter applied to ignite the fuel input through the burner under prescribed l l gh t -o f f conditions. I t is also used to support ignit ion under low load or certain adverse operating conditions. The range of capacity of such igniters is generally 4 percent to 10 percent of fu l l load burner fuel input. I t shall not be used to ignite main fuel under uncontrolled or abnormal conditions. The burner shall be operated under controlled conditions to l imi t the potential For abnormal operation, as well as to l imi t the charge of fuel to the furnace in the event that ignit ion does not occur during l i gh t -o f f . Class 2 igniters may be operated as Class 3 igniters.

Class 3 (Interrupted Igni ter) . An igni ter applied part icular ly to gas and oi l burners to ignite the fuel input to the burner under prescribed l i gh t -o f f conditions. The capacity of such igniters generally does not exceed 4 percent of the fu l l load burner fuel input. As a part of the burner l i gh t -o f f procedure, the igni ter is turned o f f when the time t r i a l - f o r - i gn i t i on of the main burner has expired. This is to ensure that the main f lamels self-supporting, is stable, and is not dependent upon ignit ion support from the igni ter. The use of such igniters to support ignit ion or to extend theburner control range shall be prohibited.

Class 3 Special (Direct E lect r lc ' Ign i ter ) . A special Class 3 high energy electr ical igni ter capable of direct ly ignit ing the main burner fuel. This type igni ter shall not be used unless supervision of the individual burner flame is provided.

Inerting. The process of rendering a combustible mixture noncombustible through the addition of an inert gas or steam.

Interlock. A device or group of devices arranged to sense a l imi t or o f f - l im i t condition or improper sequence of events and to shut do~,n the offending or related piece of equipment, or to prevent proceeding in an improper sequence in order to avoid a hazardous condition.

Labeled. Equipment or materials to which has been attached a label, symbol or other identifying mark of an organization acceptable to the "authority having jur isdict ion" and concerned with product evaluation,

tha t mainta ins p e r i o d i c i nspec t i on o f p roduc t ion o f labe led equipment or ma te r i a l s and by whose l a b e l i n g the manufacturer i nd i ca tes compliance wi th a p p r o p r i a t e standards or performance in a s p e c i f i e d manner.

L i g h t - O f f . The es tab l ishment o f the combustion o f fue l e n t e r i n g the furnace.

L i g h t - O f f Time L imi t Timer. A dev ice used on superv ised manual systems, which l i m i t s the a l l owab le t ime between complet ion o f purge and l i g h t - o f f . This t ime sha l l be no more than f i v e minutes.

L i s ted . Equipment o r m a t e r i a l s inc luded in a l i s t publ ished by an o r g a n i z a t i o n acceptab le to the " a u t h o r i t y having j u r i s d i c t i o n " and concerned wi th product e v a l u a t i o n , tha t ma in ta ins p e r i o d i c i nspec t i on o f p roduct ion o f l i s t e d equipment o r m a t e r i a l s and whose l i s t i n g s ta tes e i t h e r t ha t the equipment o r mater ia l meets app rop r i a te standards or has been tes ted and found s u i t a b l e f o r use in a s p e c i f i e d manner.

NOTE: The means f o r i d e n t i f y i n g l i s t e d equipment may vary for each organization concerned with product evaluation, some of which do not recognize equipment as l is ted unless i t is also labeled. The "authority having ju r isd ic t ion" should u t i l i ze the system employed by the l i s t i ng organization to ident i fy a l is ted product.

Low Fire. The minimum f i r e rate resulting in stable combustion.

Low Gas Pressure Switch. A pressure actuated device arranged to effect a safety shutdown or prevent start ing when the gas pressure f a l l s below the preset value.

Low Oil Pressure Switch. A pressure actuated device arranged to effect a safety shutdown or prevent start ing when the oi l pressure fa l l s below the preset value.

Low Oil Temperature Switch. A temperature actuated device that in i t ia tes a signal when the oi l temperature fa l l s below the l imits required to maintain the viscosity range recommended by the burner manufacturer.

Low Water Cutout. A device arranged to effect a shutdown of the burner when water level in the boi ler f a l l s to a predetermined low level.

Auxi l iary Low Water Cutout. A device that is arranged to effect a safety shutdown (requires manual reset, see: shutdown, safety) of the burne~ when the water level in the boi ler f a l l s to a predetermined low level.

LP-Gas. A material composed predominantly o f any of the following hydrocarbons, or mixtures of them: propane, propylene, normal butane, isobutane, and butylenes.

Main Burner Establishing Period. (See defi,nition of T r ia l - fo r - Ign i t ion period.)

l

Modulate. To gradually vary the fuel and a i r flows to the burner in accordance with load demand.

Monitor. To sense and indicate a condition without i n i t i a t i ng automatic corrective action.

Natural Gas. A gaseous fuel occurring in nature consisting mostly of a mixture of organic compounds (normally methane, ethane, propane, and butane). The Btu value of natural gases varies between about 700 and 1,500 Btu per c u f t (26.1 and 55.9 MJ/m3), the majority averaging 1,000 Btu per c u f t (37.3 MJ/m3).

Normal Fuel Supply Pressure. The pressure'at the fuel service connection for which the fuel burning system has been designed.

Oil. (See def in i t ion of Fuel Oi l ) .

47

Operating Range. The region between the maximum fuel input and minimum fuel input in which the burner flame can be maintained, continuous and stable.

Outlet Draft. The flue gas pressure at the outlet of the last convection pass of the boi ler.

Prove. To establish by measurement or test the existence of a specified condition such as flame, level, flow, pressure, or position.

Purge. A flow of a i r through the furnace, boiler gas passages, and associated flues and ducts that wi l l e f fect ive ly remove any gaseous combustibles and replace them with a i r . Purging may also be accomplished by an inert medium.

Recycle. A start-up in i t ia ted by steam pressure or water temperature following a normal shutdown.

Repeatability. The ab i l i t y of a device to maintain a constant set point characteristic.

Re-start. A manually in i t ia ted start-up.

Safety ShutoFf Valve (Safety Trip Valve). A fast closing valve that automatically and completely shuts o f f the fuel supply to main burner(s) or igni ter(s) in response to a normal or a safety shutdown signal.

Semiautomatic. The terms "automatic (nonrecycling)" and "supervised manual" are used in this Standard to describe the functions conventionally attributed to "semiautomatic."

Service Connection. A point at which fuel, atomizing medium, or power is connected to the boi ler, f i r i ng equipment, or controlled devices.

Set Point. A predetermined value to which an instrument is adjusted and at which i t shall perform i ts intended function.

Shall. Indicates a mandatory requirement.

Should. Indicates a recommendation or that which is advised but not required.

Shutdown.

Normal. Stopping burner operation by shutting o f f al l fuel and ignit ion energy to the furnace.

Safety. Stopping burner operation by shutting o f f al l fuel and ignit ion energy to the furnace by means of a safety interlock or interlocks, and requiring a manual restart.

Soot Blower. A mechanical device for introducing steam or a i r to clean heat-absorbing surfaces.

Supervise. To sense and indicate a condition requiring attention, and automatically in i t i a te corrective action.

T r ia l - fo r - Ign i t ion Period ( Ign i ter ) . That interval of time during l i gh t - o f f in which a safety control c i rcui t permits the igni ter fuel safety shutoff valve(s) to be opened before the flame detection system is required to supervise the igni ter flame.

Tr ia l - fo r - Ign i t ion Period (Main Burner). That interval of time during l i gh t - o f f in which a safety control c i rcu i t permits the main burner fuel safety shutoff valve(s) to be opened before the flame detection system is required to supervise the main burner flame only.

Chapter 4 Equipment Requirements

4-I Fuel Supply (Oi l) .

4- I . I Fuel shall be properly stored, prepared, and delivered to the oi l service connection under anticipated operating conditions in accordance with the applicable portions of NFPA 31, Instal lat ion of Oil Burning Equipment.

4-1.2 Operation of the burner shall not be attempted unti l a satisfactory fuel supply is assured.

4-I.3 Fuel shall be continuously delivered to the combustion chamber in a f ine ly atomized form that can be readily ignited and consumed.

4-I.4 All equipment associated with pumping, heating, and straining the fuel from storage to the service connection shall be properly designed, sized, and interconnected so as to provide a suitable fuel supply over a fu l l range of conditions. Relief valves shall be installed af ter the pump to prevent overpressure in the system.

4-I.5 Fuel being burned shall be delivered to the burner at proper temperature and pressure.

NOTE: Excessively heated oi l may create vapor-lock, which can prevent continuous operation. Cold o i l may prevent satisfactory atomization.

4-I.6 Where the fuel must be heated, care shall be taken to ensure that the interlocks and instruments ref lect correct values of the variable being measured, part icular ly in dead-end lines where heavy oi l wi l l tend to sol id i fy .

4-1.7 The operation of a burner system that has the capability to burn heated and unheated oi ls shall include a procedure to ensure that the proper type of o i l , compatible with the selected mode of operation, is being supplied to the burner. Precautions shall include the intended routing of recirculated o i l .

4-I.8 Two safety shutoff valves in series, each with proof of closure, shall be provided in the oi l l ine to the main burner (see Appendix G).

CAUTION: Means shall be provided to prevent or relieve excess pressure between these valves.

4-2 Fuel Supply (Gas).

4-2.1 The gas supply at the gas service connection shall be controlled at the pressure for which the fuel burning system has been designed.

4-2.2 Gas piping shall be of ample size to maintain the desired constant pressure for the maximum burner flow.

4-2.3 Two safety shutoff valves in series, each with proof of closure, shall be provided in the gas l ine to the main burner. An automatic vent valve shall be provided between the two valves (see Appendix F).

4-2.4 Foreign matter such as welding beads, chips, scale, dust, and debris shall be removed from the gas piping.

4-2.5 A drip leg shall be provided in the gas piping (see Appendices E, and F).

4-3 Alternate Fuel Firing.

4-3.1 Manual Fuel Selection. When oi l and gas are to be burned alternately, a manually positioned fuel selector switch shall be provided to permit operation of the necessary interlocks, fuel safety shutoff valves, and controls for the fuel to be f i red.

4-3.2 Automatic Fuel Selection. When oi l and gas are to be burned alternately, an automatic change from one fuel to the other shall be accomplished only af ter a shutdown. Provision for manual changeover of the system shall be provided in accordance with 4-3.1 and Chapter 8. For simultaneous f i r i ng of o i l and gas fuels see Chapter 7.

48

4-4 Fuel Burning Equipment.

4-4.1 Ignition.

4-4.1.I The main burner shall be equipped with a permanently installed igniter. I f an intermittent igniter (Class 2) is used and is not operated as an interrupted igniter, the main burner flame shall be proven independently of the igniter.

4-4.1.2 The igniter flame or arc shall impinge on the main burner air/ fuel mixture and supply sufficient ignition energy to provide immediate ignition of al l fuel discharge from the main burner under l ight -of f conditions.

4-4.1.3 Two safety shutoff valves in series shall be provided in the gas l ine to the igniter.

4-4.1.4 The igniter shall be designed for periodic removal, cleaning, and maintenance.

4-4.2 Main Burner.

4-4.2.1 The main burner shall direct the fuel and a i r into the furnace so as to provide a stable flame and eff ic ient combustion over i ts entire operating range.

i

4-4.2.2 The burner shall be provided with at least one convenient observation port of a size to permit visual inspection of the igniter and main burner flames.

4-4.2.3 The l imits of stable flame for the burner shall be determined by test. These tests shall be performed without the igniter in service and shall include the intended range and grade of fuel(s).

The tests shall veri fy that tran:~ients generated in the fuel and a i r systems do not adversely affect burner operation. Such transients are generated by burner control valves, dampers, and other equipment that operates at speeds faster than the speed of response of other components in the system.

4-4.2.4 Each manual adjustment feature on the burner shall be provided with means for securing i t in i ts intended position.

4-4.2.5 The atomizing equipment for oi l burners shall be designed for periodic removal, cleaning, and maintenance,

4-4.2.6 Any procedure for clearing the atomizer and piping into the furnace prior to shutdown, shall be accomplished while the fan is operating and the igniter is re-established or the main flame is continuously proven during this operation.

4-4.2.7 Clearing of the oi l passages of the atomizer into the furnace immediately after a shutdown shall be prohibited.

4-4.3 Atomizing Medium for Oil Burners.

4-4.3.1 When the fuel is to be atomized with the assistance of another medium, this atomizing medium shall be supplied free of contaminants that could cause an interruption of service.

4-4.3.2 The atomizing medium shall be provided at the pressures required for proper operation.

4-4.3.3 Provisions shall be made to ensure that fuel cannot enter the atomizing medium line during or after operation.

4-4.4 Combustion Air Supply.

4-4.4.1 The combustion air supply equipment shall be capable of supplying combustion air for the optimum air/fuel rat io over the entire operating range of the burner.

4-4.4.2 Provision shall be made for periodic cleaning of the combustion a i r supply equipment.

4-4.5 Furnace.

4-4.5.1 The furnace shal l be designed to promote main burner s tab i l i t y while minimizing zones that cannot be purged.

4-4.5.2 At least one observation port in addition to the requirements of 4-4.2.2 shall be provided to permit observation of the burner flame and furnace.

4-4.6 Combustion Products Removal. :

4-4.6.1 The ou t le td ra f t equipment shall be capable of removing combustion products without adversely affecting stable flame conditions.

CAUTION: Tall stacks can produce furnace draft conditions adversely affecting flame s tab i l i ty and may require special draft control provisions. c

4-4.6.2 When two or more boilers are connected to a common stack, each connection shall be equipped with a damper system. All boiler outlet dampers shall be equipped with accessible operating and locking devices. This equipment shall be compatible'with the combustion control system of the boiler. Interlocks shall be provided to prevent f i r ing against a closed damper. Provision shall be made to prevent rendering the interlock nonfunctional i f the linkage becomes disconnected. This can be accomplished by,any of the following:

(I) placing the interlock on the driven member,

(2) u t i l i z ing a furnace pressure sw i t ch ,

(3) or other appropriate means.

Exception: Dampers are not required on boiler outlets of a type in which maintenance operations are performed from outside of the boiler.

4-5 Combustion Control System,

4-5.1 The combustion control system shall maintain air/fuel mixtures at pre-established ratios throughout the operating range of the burner and during changes in f i r ing rate.

4-5.2 The system shall provide l imits on fuel and air to prevent reducing furnace input below the point of stable burner operation. The minimum and maximum points of stable burner operation shall be defined by the burner manufacturer and verif ied by operational tests.

4-6 Interlock System. '

4-6.1 The system shall be equipped with a method of determining the operating state of each interlock without disassembling any of the interlock devices.

4-6.2 Each interlock shall be provided with a method of establishing the set point. The set point shall be repeatable within prescribed l imits.

4-6.3 Interlock devices shall be designed for anticipated environmental conditions, such as temperature, humidity, vibration, and corrosive agents.

4-6.4 The interlocks on the low water cut-outs may be bypassed for blowdown purposes only. This bypass shall be of a type that is temporarily held during blowdown.

4-6.5 Interlocks shall not be manually bypassed at any time during normal operation.

- t

Exception: See 4-6.4 and Chapter 5.

4-6.6 Each safety control AC circui t shall be two wire, one side grounded, preferably not exceeding nominal 120 volts, and shall be protected with a suitable fuse or circuit breaker in the hot side only.

49

4-6.7 Safety control DC circuits shall be arranged as called for in 4-6.6 when grounding is possible. When grounding is not possible and the circuit voltage exceeds 50 volts, the circuit shall have switching contacts in one side of the line and ground fault c i rcui t interrupters provided.

4-7 Flame Safety Shutdown System.

4-7.1 The time interval between loss of flame and stopping the fuel flow to the burner shall be not more than four seconds.

4-7.2 Permanent means shall be provided for making periodic tightness tests of the main burner gas safety shutoff valves.

Chapter 5 Starting a Cold Boiler

5-I Starting of a cold boiler shall be accomplished in conformance with the manufacturer's recommendations. In no case shall a boiler that has been taken out of service for maintenance, repair, or extended shutdown be started from a cold condition without a qualified operator present.

5-2 Applicable start-up procedures for the burner control system provided shall be followed. Firing rate shall be limited in accordance with the boiler manufacturer's instructions.

5-3 When steam is not available for heating o i l , or as an atomizing medium, or for driving auxil iary equipment, one of the starting methods described in 5-3.1, 5-3.2 or 5-3.3 shall be used.

5-3.1 Auxiliary Air Atomizing of Oil.

5-3.1.1 Equipment Required.

(a) FD fan.

(b) Approved auxil iary oil heater for start-up fuel flow with a capacity not less than that required for minimum f i re with stable flame.

(c) Compressed air supply.

(d) Check valves in steam and air lines to the atomizer.

5-3.1.2 Faci l i ty Required.

(a) An atomizing air supply (see Appendix G).

5-3.1.3 Starting Procedure.

(a) Circulate and heat o i l , using auxil iary heater and recirculating system, to satisfy al l interlocks, where included.

(b) Follow normal start-up procedure described in Chapter 6 using air as the atomizing medium.

(c) Set combustion control at l ight -of f f i r ing rate.

(d) When steam pressure is raised to a point where i t is adequate For heating and atomizing the o i l , shut' down in accordance with the normal shutdown procedure described in Chapter 6.

(e) Close atomizing air supply and open atomizing steam supply, making certain that dry steam is available.

i f ) Change over from auxil iary oi l heater to steam oil heater.

(g) Follow normal start-up procedure.

5-3.2 Auxiliary Mechanical Atomizing of Heavy Oil.

5-3.2.1 Equipment Required.

(a) FD fan.

(b) Approved auxil iary oi l heater for start-up fuel flow with a capacity not less than that required for minimum f ire with stable flame.

(c) Mechanical atomizer.

(d) Means to bypass atomizing medium interlocks. The fact that these are bypassed shall be made evident to the operator with adequate warning devices.

5-3.2.2 Starting Procedure.

(a) Circulate and heat oi l using auxil iary heater and recirculating systems to satisfy oi l interlocks, where included.

(b) Bypass atomizing medium interlocks (See 5-3.2.1(d)).

(c) Insert mechanical atomizer.

(d) Follow normal start-up procedure described in Chapter 6.

(e) Set combustion control at l ight -of f f i r ing rate.

i f ) When steam pressure is raised to a point where i t is adequate for heating and atomizing the o i l , shut down in accordance with the normal shutdown procedure described in Chapter 6.

(g) Remove mechanical atomizer.

(h) Insert steam atomizer.

( i ) Make atomizing medium interlocks operable.

( j ) Change over from auxil iary oi l heater to steam oi l heater.

(k) Follow normal start-up procedure.

5-3.3 Auxiliary Mechanical Atomizing of Light (Unheated) Oil.

5-3.3.1 Equipment Required.

(a) FD fan.

(b) Mechanical atomizer.

(c) Check valves in the heavy and l ight oi l lines.

(d) Means to bypass oi l and atomizing medium interlocks. The fact that these are bypassed shall be made evident to the operator with adequate warning devices.

5-3.3.2 Faci l i ty Required.

(a) A l ight oi l 'supply.

5-3.3.3 Starting Procedure.

(a) Shut off heavy oi l to system.

(b) Insert mechanical atomizer.

(c) Bypass oi l and atomizing medium interlocks.

(d) Open l ight oi l supply into the system.

(e) Follow normal start-up procedure described in Chapter 6.

i f ) Set combustion control at l ight -o f f rate.

(g) When steam pressure is raised to a point where i t is adequate for heating and atomizing the heavy o i l , shut down in accordance with normal shutdown procedure described in Chapter 6.

(h) Shut off l ight oi l supply to the system.

( i ) Remove mechanical atomizer.

50

( j ) Insert steam atomizer.

(k) Make oi l and atomizing medium interlocks operable by removing bypasses.

(1) Open heavy oi l supply to the system.

(m) Follow normal start-up procedure.

Chapter 6 Operating Systems

6-I Chapter 6 and Appendices E and G i l lust rate typical arrangements of operating systems for automatic (recycling), automatic (nonrecycling), supervised manual, and manual systems to meet the intent of this standard. Different arrangements are permissible i f they provide equivalent protection and meet the intent of this standard.

6-2 Automatic (Recycling) Systems for Watertube Boilers.

6-2.1 An automatic (recycling) unit shall not be started from a cold condition unless a qualified operator is present. In this section, i t is assumed that the unit is hot and that steam pressure and operating water level have been established.

6-2.2 I t is further assumed that the fuel to be fired has been manually selected. The alternate fuel system shall be placed in a nonfiring condition, and the manual burner valve(s) shall be closed.

6-2.3 An igniter as specified in 7-4.1.1 shall be provided.

6-2.4 An automatic (recyling) unit shall recycle on a preset pressure and perform four major functions:

(a) Pre-firing cycle.

(b) Light-off cycle.

(c) Modulation, where provided.

(d) Shutdown cycle.

6-2.4.1 The pre-f ir ing cycle shall accomplish the following in the order l isted:

(a) Prove the fuel safety shutoff valve closed. For gas f i r ing, this shall be the down:;tream valve.

(b) Prove no flame present at the burner.

(c) Start fan.

(d) Satisfy fan interlock.

(e) Where atomizing medium is u:~ed and i f not already on, admit medium to main burner.

i f ) Where atomizing medium is u:;ed, satisfy atomizing medium interlocks.

(g) Satisfy appropriate fuel interlocks.

NOTE: The order of items (e), ( f ) , and (g) in the sequence is optional.

(h) Prove purge air flow by satisfying: ( l) a i r pressure and "open damper" interlocks for al l dampers in the flow path or (2) a i r flow interlock. Purge a i r flow shall reach no less than 70 percent of the a i r flow required at maximum continuou:~ capacity of the unit.

( i ) The purge shall be sufficient for at least eight a i r changes. Air flow during the time to open the damper and return i t to l ight -o f f position may be included in computing the time for eight a i r changes.

( j ) Set controls to l igh t -o f f position.

(k) Prove dampers and fuel control valve in l ight-of f position.

6-2.4.2 The l ight-of f cycle for a burner with an interrupted igniter shall accomplish the following in the order l isted:

(a) Energize igniter. L

(b) Prove igniter flame within 10 seconds (for direct electr ic igniter, proof of igniter operation is not required).

I) I f proven, admit fuel to main burner. For an oi l burner other than return flow type, simultaneously shut off oi l recirculating flow.

2) I f not proven, establish safety shutdown.

(c) After a maximum of lO seconds for gas and Nos. 2 and 4 oi ls or 15 seconds for Nos. 5 and 6 oi.ls, shut off igniter. For gas igniters vent the gas piping between igniter safety shutoff valves to atmosphere.

(d) Prove main flame.

I) I f proven, release to modulating control where provided.

2) I f not proven, establish safety shutdown.

6-2.4.3 The l ight-of f cycie for a burner width an intermittent igniter shall accomplish the following in the order listed:-

(a) Energize igniter.

(b) Prove igniter flame within 10 seconds.

l) I f proven, admit fuel to main burner. For an oi l burner other than return flow type, simultaneously shut off recirculating flow.

2) I f not proven, establish safety shutdown.

(c) Prove main flame within 10 seconds.

l) I f proven, release to combustion control for modulation where provided.

2) I f not proven, establish safety shutdown.

6-2.4.4 Modulation where provided shall be accomplished by a combustion control system.

6-2.4.5 The normal shutdown cycle shall accomplish the following in the order l isted:

t

(a) Shut off fuel supply to main burner.

(b) Interrupt spark and shutoff fuel supply to igniter.

(c) For o i l :

I) "Where used, open recirculating valve.

2) Shut off atomizing medium, i f desired.

(d) For gas vent piping between safety shutoff valves to atmosphere.

(e) Perform a post purge of the boiler furnace enclosure.

i f ) Shut down fan, i f desired.

6-2.4.6 For automatic (recycling) boilers, high steam pressure or high water temperature shall accomplish a normal shutdown, and the burner shall be allowed to recycle when steam pressure or water temperature has dropped to within the preset operating range.

6-2.4.7 The safety shutdown cycle shall accomplish the following in the order l isted and activate an alarm:

(a) Shut off fuel supply to main burner.

(b) Shut off fuel supply and interrupt spark to the igniter i f in operation.

51

(c) For o i l :

l) Where used, open recirculating valve.

2) Where used, shut off atomizing medium, i f desired.

(d) For gas:

I) Vent gas piping between safety shutoff valves to atmosphere.

(e) Where used, the inerting system shall be simultaneously energized with 6-2.4.7(a) above.

i f ) After post purge, shut down fan, i f desired.

(g) Require manual reset.

6-2.4,8 Any of the following conditions shall accomplish a safety shut down, and the burner shall not be allowed to recycle until a qualified operator determines the cause of the shutdown and takes the necessary corrective action to assure that safe operating conditions prevail before restarting:

(a) For o i l :

I) Low fuel pressure.

2) Low temperature of heated oi ls.

3) Loss of combustion air supply.

4) Loss of or failure to establish flame.

5) Loss of control system actuating energy.

6) Power fai lure.

7) Low water level.

8) Loss of atomizing medium, where used, as interlocked by flow or two pressure switches, one located at the service connection and the other at the burner, either one of which shall in i t ia te a safety shutdown on low pressure.

9) Excessive steam pressure or water temperature.

(b) For gas:

I) High gas pressure.

2) Low gas pressure.

3) Loss of combustion air supply.

4) Loss of or failure to establish flame.

5) Loss of control system actuating energy.

6) Power fai lure.

7) Low water level.

B) Excessive steam pressure or water temperature.

Caution: Excessive recycling to achieve a burner l lght-of f can lead to accumulation of a hazardous amount of fuel in the furnace and shall be avoided.

6-3 Automatic (Nonrecycling) Systems for Watertube Boilers.

6-3.1 The provisions of 6-2.1, 6-2.2, 6-2.3, and 6-2.4 shall apply except for 6-2.4.6 (see 6-3.1.I).

6-3.1.1 When high steam pressure or high water temperature establishes a normal shutdown, the burner shall not be allowed to recycle. A qualified operator shall in i t ia te the re-start.

6-4 Automatic (Recycling) Systems for Firetube Boilers.

52

6-4.1 In this section, i t is assumed that the equipment is in accordance with Chapter 4, the boiler has been placed in service in accordance with Chapter 5, and that the operating water level has been established.

6-4.2 An automatic (recycling) unit shall recycle on a preset pressure or temperature and perform four major functions:

(a) Prefiring cycle.

(b) Light-off cycle.

(c) Modulation, where provided.

(d) Shutdown cycle.

6-4.2.1 The prefiring cycle shall accomplish the following in the order l isted:

Ca) Prove the fuel safety shutoff valves closed.

(b) Prove no flame present at burner.

(c) Start fan.

(d) Satisfy fan interlock.

(e) Where atomizing medium is used and i f not already on, admit medium to main burner.

i f ) Where atomizing medium is used, satisfy atomizing medium interlocks.

(g) Satisfy appropriate fuel interlocks.

NOTE: The order of items (e), i f ) , and (g) in the sequence is optional.

(h) Prove purge air flow by satisfying:

I) Air pressure and "open damper" interlocks for al l dampers in the flow path, or

2) Air flow interlock.

( i ) The purge of the furnace and boiler gas passes shall be sufficient for at least four a i r changes. During the purge, the air damper shall be driven to the ful l open position. Air flow during the time to open the damper and return i t to l ight -of f position may be included in computing the time for four a i r changes.

( j ) Prove control system in l ight-of f position.

6-4.2.2 The l ight-of f cycle shall accomplish the following in the order l isted:

(a) Energize interrupted igniter.

(b) Prove igniter flame within lO seconds (for direct electric igniter, proof of igniter operation is not required).

l) I f proven, admit fuel to main burner.

2) I f not proven, establish safety shutdown.

(c) After a maximum of IO seconds for gas and Nos. 2 and 4 oi ls, or 15 seconds for Nos. 5 and 6 oi ls, shut off igniter.

(d) Prove main flame.

I) I f proven, release to modulating control where provided.

2) I f not proven, establish safety shutdown.

6-4.2.3 Modulation where provided shall be accomplished by a combustion control system.

6-4.2.4 High steam pressure, high water temperature or low water (not determined by the auxil iary low water cutoff) shall accomplish a normal shutdown, and the burner shall be allowed to recycle when steam pressure, water temperature, or water level has returned to within the preset operating range.

6-4.2.5 The normal shutdown cycle shall accomplish, the following in the order l isted:

(a) Shut off fuel supply to main burner.

(b) For o i l :

I) Where used, open recircu~ating valve.

2) where used, shut off atomizing medium, i f desired.

(c) For gas:

I) Vent gas piping between safety shutoff valyes to atmosphere.

(d) After post purge, shut down fan, i f desired.

6-4.2.6 The safety shutdown cycle shall accomplish the following'in the order l isted:

(a) Shut off fuel supply to main burner.

(b) Shut off fuel supp!y and interrupt spark to the igniter i f in operation.

(c) For o i l :

l) Where used, open recirculating valve.

2) Where used, shut off atomizing medium, i f desired.

(d) For gas:

I) Vent gas piping between safety shutoff valves t o atmosphere.

(e) Where used, energize inerting system simultaneously with 6-4.2.6(a).

(f) After post purge, shut down fan, i f desired.

(g) Require manual reset.

6-4.2.7 Any of the following conditions shall accomplish a safety shutdown, and the burner shall not be allowed to recycle until a qualified operator determines the cause of the shutdown and takes the necessary corrective action to assure that safe operating conditions prevail before restarting:

(a) For el ! :

I) Low oil pressure.

2) Low temperature of heated oi ls .

3) Loss of combustion air supply.

4) Loss of or failure~ to establish flame.

5) Loss of control system actuating energy.

6) Low water level as determined by the auxi l iary low water cutout.

7) Loss of atomizing medium where used.

8) Excessive steam pressure or water temperature.

(b) For gas:

I) High gas pressure.

2) Low gas pressure.

3) Loss of combustion a i r sgp~ly.

4) Loss of or failure to establish flame.

5) Loss of control system actuating energy.

6) Low water level as determined by the auxil iary low water cutout.

7) Excessive steam pressure or water temperature.

CAUTION: Excessive recycling to achieve a burner l ight -of f can lead to accumulation of a hazardous amount of fuel in the furnace and shall be avoided.

6-5 Automatic (Nonrecycling) Systems for Firetube Boilers.

6-5.1 The provisions of 6-4.1 and 6-4.2 shall apply, except for 6-4.2.4 (see 6-5.1.1).

6-5.1,1 When a high steam pressure or high water temperature operating control establishes a normal shutdown, the burner shall not be allowed t 9 recycle. A qualified operator shall in i t ia te the restart.

6-6 Supervised Manual Systems for Oil Fired Watertube Boilers.

6-6.1 The fol~owing steps shall be taken by the operator when starting a supervised manual unit and the indicated interlocks shall be satisifed at each step. I t is assumed that fuel pressure and temperature, atomizing medium, control system energy, power, and water level have been established. When interlocks have been sat isi f ied, this fact shall be indicated to the operator~

6-6.2 Select the fuel to be f ired. The alternate fuel system shall be placed in a nonfiring condition, and the manual burner valve(s) shall be closed.

6-6.3 An igniter as specified in 4-4.1.1 shall be provided.

6-6.4 Prefiring Cycle (in order

Operator Functions I. Check manual fuel shut- I.

off valve(s) closed.

2. Start fan. 2.

3. Where used, open 3. atomizing medium valve.

4. Open damper(s) to purge 4. position.

5. Start purge timer. 5.

6. Place damper and fuel 6. control valve in l igh t - off position.

7. None. 7.

6-6.5 Light-off cycle.

Operator Functions

I. Energize igniter. l .

2. Open fue l sa fe t y s h u t o f f va lve to main burner .

3. Close recirculating valve, where used.

2.

3.

l isted)

Interlock Functions Manual fuel shutoff valve(s) closed.

Fan on.

Atomizing medium supply available.

(I) Air pressure and damper(s), or (2) Air flow.

Purge complete.

Damper and fuel control valve in l ight -of f position. I f l ight - off a i r flow is less than purge air flow rate, start l ight -of f time limi~ timer.

Spark and igniter and main safety shutoff valves ready for operation.

Interlock Functions

Prove ignilter flame within I0 seconds. (For direct electr ic ignit ion, proof of igniter operation is not required.

None.

None.

53

4. Open manual fuel shut- 4. off valve

Prove main flame within lO seconds for Nos. 2 and 4 oi ls or 15 seconds for Nos. 5 and 6 oi ls. Close igniter safety shutoff valve(s). For gas igniter, vent gas piping between safety shutoff valves.

5. Bring unit to preset 5. None. operating pressure at an acceptable rate, maintaining an optimum air/ fuel ratio.

6. On reaching preset 6. None. pressure range, change to automatic combustion control.

6-6.6 Normal Shutdown Cycle.

Operator Functions

I. Shut off fuel supply to I. the main burner.

2. Open fuel recirculating 2. valve, where used.

3. Where used, shut off 3. atomizing medium.

4. Remove fuel atomizer. 4.

5. After post purge, 5. shut down fan, i f desired.

Interlock Functions

Fuel safety shutoff valve(s) to main burner closed.

None.

None.

None.

None.

6-6.7 Safety Shutdown Cycle.

1. None. I. Shutoff fuel supply to the main burner and shut off fuel supply and interrupt spark to the igniter i f in operation.

2. None. 2. With gas igniter, vent gas piping between safety shutoff valves to atmosphere.

3. After post purge, shut 3. None. down fan, i f desired.

6-6.8 Any of the following conditions shall accomplish a safety shutdown.

(a) Low pressure in the fuel supply at the service connection.

(b) Loss of combustion air supply.

(c) Loss of or fai lure to establish flame.

(d) Loss of control system actuating energy.

(e) Power fai lure.

(f} Low water level.

(g) Loss of atomizing medium.

(h) Excessive steam pressure or water temperature.

CAUTION: Excessive recycling to achieve a burner l ight -o f f can lead to accumulation of a hazardous amount of fuel in the furnace and shall be avoided.

6-6.9 The following conditions, where oi l heating is provided, shall sound alarms:

.(a) Low oil temperature.

(b) High oi l temperature.

6-7 Supervised Manual Systems for Gas Fired Watertube Boilers.

6-7.i The following steps shall be taken by the operator when starting a supervised manual unit and the indicated interlocks shall be satisfied at each step. I t is assumed that control system energy, power, and water level have been established. When interlocks have been satisifed, this fact shall be indicated to the operator.

6-7.2 Select the fuel to be f ired. The alternate fuel system shall be placed in a nonfiring condition and the manual burner valve(s) shall be closed.

6-7.3 An igniter as specified in 4-4.1.1 shall be provided.

6-7.4 Prefiring Cycle.

Operator Functions Interlock Functions

I. Check gas safety shut- I. Gas safety shutoff off valves closed, valves closed.

2. Start fan. 2. Fan motor on.

3. Open damper(s) to purge 3. (I) Air pressure and position, open damper(s), or

(2) Air flow.

4. Start purge timer. 4. Purge complete.

5. Place damper and gas 5. Damper and fuel control valve in l ight - control valve in off position, l ight -of f position.

I f l ight -of f a i r flow is less than purge air flow rate, start l ight -of f time l imi t timer.

6-7.5 Light-Off Cycle.

Operator Functions

I. Energize igniter.

2. Open gas safety shut- off valves to main burner.

3. Bring unit to preset 3. None. operating pressure at an acceptable rate, maintaining an optimum air/fuel ratio.

4. On reaching preset 4. None. range, change to automatic combustion control.

6-7.6 Normal Shutdown Cycle.

Operator Functions

I. Shutoff gas supply to the main burner and to the igniter, i f in operation, and interrupt spark.

2. After post purge, shut 2. None. down fan, i f desired.

6-7.7 Safety Shutdown Cycle

Interlock Functions

I. Prove igniter flame within I0 seconds. (For direct electr ic ignition, proof of igniter operation is not required.)

2. Prove main flame flame within I0 seconds.

Interlock Functions

I. Vent gas piping between safety shutoff valves to atmosphere.

54

Operator Functions Interlock Functions

1. None. I. Shut off gas supply to the main burner and shut off fuel supply and interrupt spark to the igniter i f in operation. Where used, simultaneously energize inerting system.

2. None. 2. Vent gas piping between safety shutoff valves to atmosphere.

6-7.8 Any of the following conditions shall accomplish a safety shutdown:

(a) High gas pressure.

(b) Low gas pressure.

(c) Loss of combustion air supply.

(d) Loss of or fai lure to establish flame.

(e) Loss of control systems actuating energy.

(f) Power failure.

(g) Low water level.

(h) Excessive steam pressure or water temperature.

CAUTION: Excessive recycling to achieve a burner l ight-of f can lead to accumulation of a hazardous amount of fuel in the furnace and shall be avoided.

6-8 Soot Blowing.

6-8.1 Soot blowing is necessary to maintain high thermal efficiency in o i l - f i red boilers. However, i f this operation is not performed with optimum air/fuel ratio, explosions may occur from the formation and ignition of air-soot dust clouds within the boiler.

64.1.1 Soot blowers shall be operated only while burners are f i r ing at rates suff iciently high to avoid extinguishing the burner flame.

6-8.1.2 Boilers equipped with automatic soot-blowing equipment shall have their controls interlocked to prevent operation when the burner is shut down or in the prefiring or l ight -of f cycles.

Chapter 7 Simultaneous Firing of Oil and Gas Fuels

7-I When i t is necessary or desirable to f i re both oi l and gas simultaneously in a single burner boiler on a continuous basis, the following equipment and procedure shall be used to avoid a hazardous furnace condition.

7 - l . l Hazards related to gas f i r ing alone and oil f i r ing alone are included in Section 2-7. In addition, the simultaneous f i r ing of gas and oi l increases the potential for:

(a) A fuel-rich condition.

(b) Abrupt change in air/fuel ratio.

(c) Over-firing of a boiler.

7-2 The following equipment shall be provided for continuous f i r ing of both oi l and gas:

(a) A burner capable of burning either oi l or gas fuel individually, or both fuels simultaneously.

(b) A combustion control system capable of performing the following functions:

I) Proportion total fuel input, each Fuel = individually or in any combination, to total a i r flow in order to obtain a proper air/ fuel ratio. A control system designed to accommodate a fixed amount of secondary fuel without metering and totall in'g al l fuels shall be acceptable provided i t maintains proper air/fuel ratios throughout the entire operating range of the burner.

2) Limit total fuel input to the maximum!capacity of the boiler-furnace.

3) Control a minimum ai r flow rate.

4) Control minimum input rates of each fuel.

5) Provide a stable return to proper air/fuel rat io after the t r ip of either one of the two fuels.

(c) A safety interlock system with the following capabil i t ies:

l) Meets the requirements of Section 4- 6 for each fuel being f ired.

2) Provides, on an interlock action peculiar to only one of the fuels being fired, that this particular fuel shall automatically shut down, with operation continuing on the unaffected fuel in a stable manner.

NOTE: Shutdown of both fuels is acceptable.

3) provides that both the f i r s t and second fuels be introduced with their flow control valves in l igh t -o f f positions.

4) Provides for the introduction of the second fuel without requiring a boiler prepurge.

5) Requires a manual reset following any interlock shutdown.

6) ,Prohibits the simultaneous l ight -o f f of both fuels.

7) Provides detector(s) to supervise any of the following conditions:

( i ) Igniter flame.

( i i ) Gas f i r ing.

( i i i ) Oil f i r ing.

(iv) Combined gas and oi l f i r ing.

7-3 Light-Off Cycles.

7-3.1 Prefiring and l ight-of f cycles for the in i t i a l fuel to be fired shall be in accordance with Section 6-6 for oi l and Section 6-7 for gas.

7-3.2 When oi l is introduced as the second fuel the procedure shall be as follows:

(a) Establish oi l fuel system to satisfy interlocks.

(b) Install oi l atomizer.

(c) Open atomizing medium shutoff valve;

(d) Place oi l control valve in l ight-of~ position.

(e) Open oil safety shutoff valve and establish oi l flow through the burner.

(f) Verify stable flame and proper air/ fuel rat io.

(g) Place the combustion control system into the desired mode for controlling input rate of each fuel.

7-3.3 When gas is introduced as the second Fuel the procedure shall be as follows:

(a) Establish gas fuel system to satisfy ~nterlocks.

55

(b) Place gas control valve in l ight -o f f position.

(c) Open safety shutoff valves, close vent valve, and establish gas flow through the burner.

(d) Verify stable flame and proper air/fuel ratio.

(e) Place the combustion control system into the desired mode for controlling input rate of each fuel.

7-4 Normal Shutdown Procedure.

7-4.1 The normal shutdown procedure for oi l while continuing to f i re gas shall be as follows:

(a) Reduce oil flow to l ight -o f f rate.

(b) Shut off oi l supply to burner and open oi l recirculating valve, where used.

(c) Purge oi l passages of oi l atomizer.

(d) Shut off atomizing medium i f required.

(e) Remove oil atomizer from burner i f required.

(f) Verify stable flame and proper air/fuel ratio of the gas f i re . ( 7-4.2 The normal shutdown procedure for gas while continuing to f i re oi l shall be as follows:

(a) Reduce gas flow to l ight -o f f rate.

(b) Shut off gas supply to the burner.

(c) Verify stable flame and proper air/ fuel ratio of the oi l f i re.

7-4.3 Safety Shutdowns.

7-4.3.1 Any of the following operating conditions shall accomplish a safety shutdown of the oi l supply to the burner (fuel t r ip ) :

(a) Low oil pressure.

(b) Low temperature of heated o i ls .

(c) Loss of atomizing medium.

7-4.3.2 Either of the following conditions shall accomplish a safety shutdown of the gas supply to the burner (fuel t r ip ) :

(a) High gas pressure.

(b) Low gas pressure.

7-4.3.3 Any of the following conditions shall accomplish a complete safety shutdown of the boiler:

(a) Loss of combustion air supply.

(b) Loss of or failure to establish flame.

(c) Loss of control system actuating energy.

(d) Power failure."

(e) Excess steam pressure or water temperature.

(f) Low water level.

(g) The occurrence of either the oi l or the gas fuel t r ip when only that fuel is being f ired.

7-4.3.4 Where oi l heating is provided the following conditions shall be alarmed:

(a) Low oi l temperature.

(b) High oi l temperature.

Chapter 8 Simultaneous Firing of 0i i and Gas for Fuel Transfer Only

8-I When i t is necessary or desirable to transfer from one fuel to another without stopping the flow of fuel to the furnace, the changeover shall be accomplished in a manner to prevent a fuel-rich condition. The following equipment and procedures shall be used to avoid a hazardous furnace condition.

8-2 When a transfer combustion control system is designed for simultaneous f i r ing of oi l and gas fuels on a continuous basis, Chapter 7 shall apply.

8-3 When a combustion control system is designed for f i r ing only one fuel at a time and no capability of biasing the air flow upward is provided, the following equipment and procedures shall be used.

8-3.1 Equipment Required.

(a) A burner capable of f i r ing the two fuels simultaneously during the transfer period.

(b) A fuel transfer system that includes the following:

I) A gas f i r ing mode in which oi l cannot be fired.

2) An oi l f i r ing mode in which gas cannot be fired.

3) A gas-oil f i r ing mode that permits simultaneous f i r ing of both fuels, provided all interlocks for both fuels are satisifed, including l ight -of f position for both fuel valves.

4) A control device, transfer timer, and an alarm for 8-3.1(b)3, above, to l imi t continuous operation in this mode.

(c) A safety interlock system with the following capabil i t ies:

I) Meets the requirements of Section 4-6 for each fuel being fired.

2) Provides, on an interlock action peculiar to only one of the fuels being fired, that this particular fuel shall automatically shut down, with operation continuing on the unaffected fuel in a stable manner.

NOTE: Shutdown of both fuels is acceptable.

3) Provides that both the f i r s t and second fuels be introduced with their flow control valves in l ight-of f positions.

4) Provides an interlock action that wi l l t r ip either fuel should i ts respective flow control valve leave a predetermined low rate during fuel transfer.

5) Provides for the introduction of the second fuel without requiring a boiler purge.

6) Requires a manual reset following any interlock shutdown.

7) Prohibits the simultaneous l ight -of f of both fuels.

8) Provides detector(s) to supervise any of the following conditions:

( i ) Igniter flame.

( i i ) Gas f i r ing.

( i i i ) Oil f i r ing.

(iv) Combined gas and oi l f i r ing.

(d) Manual shutoff valves at the burner, downstream of the safety shutoff valves in each fuel l ine.

(e) A pressure gage in each fuel l ine downstream of the manual shutoff valve.

56

/

8-3.2 Procedure required for changing from gas to o i l :

(a) When a Class I or I I igni ter is available, place i t in service.

(b) Check that the manual oi l valve at the burner is closed.

(c) Establish o i l fuel system to sat isfy interlocks.

(d) Instal l o i l atomizer.

(e) Open atomizing medium shutoff valve.

( f ) Place combustion control system in manual position.

(g) Reduce gas f i r i ng rate to l i gh t -o f f flow.

(h) Place oi l control valve in the normal l i gh t -o f f position.

( i ) Place fuel transfer switching system into oi l-gas position. I f the oi l safety interlocks are sat isf ied, the oi l safety shutoff valve wi l l open. Fuel oi l pressure now wi l l be upstream of manual oi i valve at the burner.

( j ) Observe the gas pressure downstream from the manual gas shutoff valve and slowly close valve unti l the gas pressure starts to drop. At this point the gas flow rate is controlled by the manual valve instead of by the normal control valve.

(k) Simultaneously and slowly close the manual gas valve while opening the manual oi l valve to l ight the o i l flame from the gas flame. Continue to increase oi i f i r i ng rate while cutting back on (jas f i r ing rate to keep'a constant~heat input of the combined fuels to the burner unti l the manual gas valve is closed and manual oi l valve is fu l l y open. Care must be taken to maintain an adequate amount of excess a i r at al l times by continuously observing the burner flame, or by observing the a i r / fue l rat io or ox~,gen indicator, i f provided. During this period, a i r flow is maintained at a constant rate, with only the manual fuel valves operated.

(1) Place the fuel transfer system in the oil. position.

(m) Return the combustion control system and burner f i r i ng rate to automatic operation.

8-3.3 Procedure required for changing from oi l to gas:

(a) When a Class I or I I igni ter is available, place i t in service.

(b) Check that the manual gas valve at the burner is closed. ,,

(c) Establish gas fuel system to sat is fy inter locks.

(d) Place combustion control system in manual pos i t ion.

(e) Reduce oi l f i r i ng rate to l i gh t -o f f flow.

( f ) Place gas control valve in the normal l i gh t -o f f position;

(g) Place fuel transfer switching system in the gas-oil position. I f the gas safety interlocks are sat isf ied, the gas safety shutoff valves wil l open. Gas pressure now wi l l be upstream ,)f manual gas valve at the burner.

(h) Observe the oi l pressure downstream from the manual oi l shutoff valve and slowly close valve unti l the o i l pressure starts to drop. ,~t this point the oi l flow is controlled by the manual v,llve instead of by the normal control valve.

( i ) Simultaneously and slowly close the manual o i l valve while opening the manual gas valve to l ight the gas flame from the oi l flame. Continue to increase gas f i r ing rate while cutting back on o i l f i r i ng rate to keep a constant heat input of the combined fuel to the burner unti l the oi l valve is closed and manual gas valve is fu l l y open. Care must be taken to maintain an adequate amount of excess a i r at al l times by continuously observing the burner flame, or by observing'the a i r / fue l rat io or oxygen indicator, i f provided. During this period, a i r flow is being maintained at a constant rate, with only the manual fuel valves operated.

( j ) Place the fuel transfer system in the gas position. The oi l safety shutoff valve wi l l now close.

(k) Return the combustion control system and burner f i r i ng rate to automatic operation.

(1) Shutoff atomizing medium, i f required. ~

(m) Remove oi l atomizer from burner, i f required..

8-4 When a combustion control system is designed for f i r ing only one fuel at a time and the capabi l i t ies have been provided enabling the a i r flow to be automatically biased up a preset amount when ei ther fuel is f i red at a predetermined low rate, the following equipment and procedures shall be used.

8-4.1 Equipment Required.

(a) A burner capable of f i r i ng the two fue ls simultaneously during the transfer period.

(b) A fuel transfer system that includes the following:

I) A gas f i r ing mode in which oi l cannot be f i red (except during fuel transfer).

2) An oi l f i r i ng mode in which gas cannot be f i red (except during fuel transfer).

3) A momentary contact push button enabling fuel transfer.

(c) A safety interlock system with the following capabil'ities:

l) Meets the requirements of Section 4-6 for each fuel being f i red. :

2) Provides, on an interlock action peculiar to only one of the fuels being f i red, that th is /par t icu lar fuel shall automatically shut down, with operation continuing on the unaffected fuel in a stable manner.

NOTE: Shutdown of both fuels is acceptable.

3) Provides that both the f i r s t and second fuels be introduced with their flow control valves in l i g h t - o f f posit ions.

4) Provides an interlock action that wi l l t r ip either fuel should i ts respective flow control valve leave the predetermined low rate described in 8-4 during fuel transfer.

5) Provides for the introduction of the second fuel without requiring a boi ler purge.

6) Requires a manual reset following any(interlock shutdown. ! ,

-. 7) Prohibits the simultaneous l i g h t - o f f of both

fuels.

8) Provides detector(s) to supervise any of the following conditions:

( i ) Igniter flame.

( i i ) Gas f i r i n g .

57

( i i i ) Oil f i r ing.

(iv) Combined gas and oil f i r ing.

9) Provides a momentary contact fuel transfer push button (see 8-4.1.b(3)) to simultaneously bias the air flow by a preset value and opens the safety shut-off valveCs) of the fuel being introduced.

8-4.2 Procedure required for changing from "gas to o i l :

Ca) Establish oi l fuel system to satisfy interlocks.

(b) Install oi l atomizer.

(c) Open atomizing medium shutoff valve.

(d) Place combustion control system in manual position.

(e) Reduce gas f i r ing rate to l ight -of f flow.

(f) Place oi l control valve in the normal l ight -of f position.

(g) Depress fuel transfer push button.

(h) Observe that oi l f i r ing has commenced.

( i ) Move fuel selector switch to the oi l f i r ing position.

( j ) Release fuel transfer push button, which automatically tr ips the gas safety shutoff valves.

(k) Return the combustion control system and burner f i r ing rate to automatic operation.

8-4.3 Procedure required for changing from oi l to gas:

(a) Establish gas fuel system to satisfy interlocks.

(b) Place combustion control system in manual position.

(c) Reduce oi l f i r ing rate to l ight -of f flow.

(d) Place gas control valve in the normal l ight -o f f position.

(e) Depress fuel transfer push button.

(f) Observe that gas f i r ing has commenced.

(g) Move fuel selector switch to the gas f i r ing position.

(h) Release fuel transfer push button, which automatically tr ips the oi l safety shutoff valves.

( i ) Return the combustion control system and burner f i r ing rate to automatic operation.

( j ) Close atomizing medium shutoff valve, i f required.

(k) Remove oi l atomizer, i f required.

Chapter g Dual Oil Atomizers in a Single Burner

9-I When a burner is equipped with main and auxi l iary oi l atomizers for the purpose of changing atomizers for maintenance without affecting the boiler load, the changeover of atomizers shall be carried out under stable f i r ing conditions by a qualifed operator.

CAUTION: Care shall be taken to prevent a fuel-rich condition during the changeover period.

9-2 The following procedure for changing atomizers shall be followed:

(a) When an intermittent igniter is available, place i t in service.

(b) Install auxi l iary atomizer.

(c) Slowly open atomizing medium valve to auxil iary atomizer until pressure reaches that required for l ight-of f .

(d) Slow close manual fuel valve on main atomizer until i t is in control of oi l flow.

(e) Slowly open the manual valve admitting oi i to the auxil iary atomizer until i t ignites.

(f) Divert the atomizing medium the main atomizer to the auxil iary main atomizer is out of service.

and oi l flow from atomizer until the

(g ) To place a main atomizer back into service and to remove auxil iary atomizer, repeat the procedure outlined in Section 9-2(a) through (f) substituting the main atomizer for the auxi l iary atomizer.

Chapter 10 Inspect ion and Maintenance

lO-I Since the effective operation of al l safety and control devices depends upon their ab i l i t y to respond quickly to their activating impulses, i t is important that they be in proper operating condition at al l times. Systematic and thorough inspection and maintenance are required.

10-2 An inspectlon and maintenance schedule shall be established and performed on a periodic basis.

10-2.1 Operability and set points on al l devices, where applicable, shall be verified by periodic testing and the results shall be recorded in the log book.

I0-2.2 Any defects found shall be corrected immediately.

10-2.3 During in i t i a l operation, more frequent inspection, adjustment, and cleaning are required.

10-3 I t is essential that individuals making inspections and tests be thoroughly familiar with al l operating procedures and equipment functions and be capable of rendering sound judgement as to when equipment is in reliable operating condition.

10-4 I t is not practical to preestablish a single schedule for al l installations. Therefore the following typical schedule is a guide only, subject to adjustment according to the specific plant operation and equipment involved.

10-4.1 Daily:

Ca) Flame failure detection system.

(b) Low water level cutout and alarm.

10-4.2 Weekly:

Ca) Igniter and burner operation.

I0-4.3 Monthly:

(a) Fan and a i r flow interlocks.

(b) Fuel safety shutoff valveCs) for leakage.

(c) Low f i re start interlock.

(d) High steam pressure interlock.

(e) For o i l : Fuel pressure and temperature interlocks.

(f) For gas:

I) Gas strainer and drip leg.

2) High and low fuel pressure interlocks.

58

10-4.4

(a)

(b)

(c)

(d)

Semiannually or annually, as required:

Igniter and burner components.

Combustion air supply system.

Flame failure system components.

Piping, wiring, and connections of al l interlocks and shutoff valves.

(e) Combustion control system.

(f) Calibration of indicating and recording instruments.

10-4.5 As required for o i l f i r ing:

(a) Atomizers.

(b) Strainers.

Chapter II Referenced Publications

l l - I The following documents or portions thereof are referenced within this standard and shall be considered part of the requirements of this document. The edition indicated for each reference is current as of the date of the NFPA issuance of this document. These references are l isted separately t(~ fac i l i ta te updating to the latest edition by the user.

l l - l . l NFPA Publications. Nation~Ll Fire Protection Association, Batterymarch Park, Quincy, MA 02269.

NFPA 30-1984, Flammable and Combustible Liquids Code o

NFPA 31-1983, Installation of Oil Burning Equipment

NFPA 54-1984, National Fuel Gas (Zode

NFPA 58-1986, Liquefied Petroleu~ Gases

NFPA 70-1987, National Electrical Code

11-I.2 Other Publications.

American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103.

ASTM D396-80, Standard Specifications for Fuel Oils

American National Standards Insti tute, 1430 Broadway, New York, NY I0018.

ANSI B31.I-81, Code for Pressure Piping--Power Piping

American Petroleum Institute, 211]I L Street, NW, Washington, DC 20037

API-RP 500, Recommended Practice for Classification of Areas for Electrical Installations in Petroleum Refineries.

API-RP 2003, Recommended Practice for Protection Against Ignitions Arising out of Static Lighting and Stray Currents.

Appendix A Manual Systems for Watertube Boilers

This Appendix is not a part of the requirements of this NFPA document, but is included for information purposes only.

A-I The Manual Systems are not recommended; however, i t is recognized that with adequate and uninterrupted supplies of fuel and air . certain operating functions can be performed by a qualified operator as well as by control devices.

A-2 Controls and interlocks.

A-2-1 Interrupted or intermittent igniter.

A-2-2 Safety shutoff valves, as follows:

(a) Gas f i r ing. Two automatic safety shutoff valves, spring closing, in gas l ine to the main burner, with intermediate spring opening automatic v~nt valve.

(b) Oil f i r ing. Automatic spring closing safety shutoff valve in oi l l ine to ~he burner.

(c) Gas fired igniter. Two spring closing automatic safety shutoff valves in the gas l ine to the igniter, with intermediate, spring opening automatic vent valve.

A-2-3 Manual shutoff valve(s) in the fuel line(s) adjacent to the burner. For gas f i r ing th isshutof f valve should be proved closed before the spark to the igniter can be energized and the igniter and main gas safety shutoff valves can be opened.

A-2-4 Changes in f i r ing rate are made by the simultaneous adjustment of fuel and a i r supplies at a pre-established optimum air/ fuel rat io by the manipulation of a single control device.

A-2-5 Limits on fuel and a i r to prevent reducing furnace input below the point of stable burner operation are provided. The minimum and maximum points of stable burner operation are defined by the burner manufacturer and verif ied by operating investigation.

A-2-6 Safety shutdown interlocks include the following:

(a) Low oi i pressure.

(b) High gas pressure.

(c) Low gas pressure.

(d) Loss.of combustion air supply.

CAUTION: Excessive recycling to achieve a burner l ight -of f can lead to accumulation of a hazardous amount of fuel in the furnace and should be avoided.

A-2-7 Where oi l heating is provided the following conditions sound an alarm:

(a) Low oi l temperature.

(b) High oi l temperature.

Appendix B Fuel Oil Firing - - General Considerations

This Appendix is not a part of the requirements of this NFPA document, but is included for information purposes only.

B-l The term fuel oil refers to l iquid fuel's with widely dif fer ing characteristics. A fuel oi l burning system is designed for a specific range of oi l characteristics. Attempting to burn an oil,whose characteristics di f fer widely from those for which the system was designed can cause serious operating d i f f i cu l t ies and potential safety hazards. Hence, care must be exercised to ensure that oi ls recieved at a plant are within the specific ranges of the fuel handling and burning equipment. '~

B-2 The more important characteristics of fuel o i ls are defined in ASTM D396, Standard Specifications for Fuel Oils. Thus i t is relat ively simple to identify oi ls that require special provisions for storing, heating, pumping, atomizing, etc. Generally speaking, grades l , 2, and 4 have lower viscosities and less water and sediment than grades 5 or 6; hence they require fewer special provisions to ensure proper handling and burning. However, most power boiler fuel oi l systems are designed for the heavier grades 5 and 6; hence such systems include provisions foe preheating these usually viscous fuels. Furthermore, more care is required in design and operation of fuel oi l systems supplied with grade 6 oi l than with the other ASTM grades, to avoid flameouts attributed to interruptions or pulsation of the fuel supply, or plugging of strainers, or burner tips.

59

B-3 All of the following characteristics may have a bearing upon the problem of properly and safely burning fuel oi ls.

B-3.1 Fuel oi l is a complex mixture of hydrocarbons of differing molecular weights, boiling and freezing points. When fuel oi l is subjected to sufficiently high temperature i t wi l l par t ia l ly decompose or vaporize, thus creating new l iquid, gaseous, and solid fuels with unpredicable properties.

B-3.2 Fuel oi l is introduced into the furnace as an extremely fine mist to intimately mix with the combustion a i r in order to burn quickly and completely. In power boilers this is accomplished by spraying through small or i f ic ies with high pressure drops (mechanical atomization) or by using steam or air to break up small oi l streams. Viscosity and v o l a t i l i t y are characteristics of the oi l that indicate ease of atomization.

B-3.3 Flash point is an indicator of vo l a t i l i t y and, thus, of potential for flammable vapors. I t is a function of pressure and fuel composition.

B-3.4 Some fuel oi ls contain constituents which, when overheated, may decompose, forming solids, or may sol id i fy when exposed to low ambient temperature. The presence of such solids in the fuel may cause interrupt ions.

B-3.4.1 When storing, handling, or burning fuel oi ls that may have flash points below IO0°F (38°C) (Class I liquids as defined in NFPA 30, Flammable and Combustible Liquids Code) or that may be heated above their flash point, consideration should be given to electrical installations in areas where flammable vapors or gases may be present in the atmosphere. Typical locations are burner areas, fuel handling equipment areas, fuel storage areas, pits, sumps, and low spots where fuel leakage or vapors may accumulate. Art icle 500 of NFPA 70, National Electrical Code®, provides for classifying such areas and defines requirements for electr ical installations in the areas so classified.

B-3.5 Purging the burner atomizer before removal wil l minimize the probability for hazardous concentrations of flammable vapors at the burner front during maintenance operations. With such provisions, the burner front is not normally classified more restr ict ively than Class I, Division 2.

B-3.6 The operating company is responsible for classifying areas where fuel is stored, handled, or burned, and for revising the classification i f conditions are changed. Installations should conform to NFPA 30, Flammable and Combustible Liquids Code; NFPA 31, Installation of Oil Burning Equipment; and NFPA 70, National Electrical Code. Guidance can be obtained from API-RP 500, Recommended Practice for Classification of Areas for Electrical Installations in Petroleum Refineries.

Appendix C Low NOx Operation - - Special Problems

This Appendix is not a pa r t o f the requirements o f t h i s NFPA document, but i s inc luded f o r i n fo rmat ion purposes on ly .

C-1 General Considerations.

C-1.1 Air pollution control regulations require that new installations meet NO, emission l imits lower than emissions now obtained from many of the presently installed f i r ing systems and furnace designs using past operating procedures. In addition, air quality regulations in some local areas require a reduction of NOx emissions from existing boilers.

C-1.2 In order to achieve these reductions, one or more of the following methods are used.

C-1.2.1 Low excess air f i r ing, i .e . , less than the "normal" 10 percent to 25 percent excess air .

C-1.2.2 Multistage air admission involving the introduction of combustion a i r in two or more stages partly at the fuel nozzle (may be less than stoichiometric air) and partly by independent admission through (I) special furnace ports, (2) a second stage of a i r admission within the same burner housing.

C-I.2.3 Flue gas reclrculatlon into al l or a portion of the secondary air.

C-I.2.4 Reduced secondary ai r temperature.

C-I.2.5 Fuel Staging.

C-I.2.6 On new units, the equipment manufacturers may also introduce new burner and furnace designs.

C-1.3 The e f f e c t o f a l l o f these methods i s g e n e r a l l y to produce lower f lame temperatures and l onge r , less t u r b u l e n t f lames, which r e s u l t in lower NOx.

C-2 Hazards of Low NOx Firing Methods.

C-2.1 The methods discussed in C-I.2 may have important implications with regard to furnace safety, particularly for existing units, and may introduce unacceptable risks i f proper precautions are not taken.

C-2.1 Fuel f i r ing systems designed to reduce NO~ emissions tend to reduce the margins formerly available to prevent or minimize accumulations of unburned fuel in the furnace during combustion upsets and/or flameouts. Thus, i t is important to t r ip fuel on loss of flame.

C-2.1.2 The methods of C-l.2 may narrow the l imits of stable flames produced by the burner system. The tests specified in 4-4.2.3 should be repeated on,existing units when any of these methods are employed.

C-2.1.3 When flue gas recirculation is used, equipment should be provided to assure proper mixing and uniform distribution of recirculated gas and the combustion air . When flue gas recirculation is introduced into the total combustion air stream, equipment should be provided to monitor either the ratio of flue gas to a i r or the oxygen content of the mixture. When flue gas recirculation is introduced so that only ai r and not the mixture is i~roduced at the burner, proper provisions should be made to ensure the prescribed distribution of a i r and the recirculating flue gas/air mixture.

C-2.1.4 All of the methods tend to increase the possibi l i ty of an unstable flame and unburned combustibles throughout the unit and ducts; therefore, recommendations of the boiler, burner, and instrument manufacturers should be followed, or tests to verify operating margins should be conducted.

C-2.2 Any change in flame characteristics to reduce NO~ emissions may require changing either or both the type and location of flame detectors on existing units.

Appendix O

This Appendix is not a pa r t o f the requi rements o f t h i s NFPA document, but i s inc luded f o r i n f o rma t i on purposes on ly .

D-1 Supplemental Recommendations and Precaut ions .

D- I .1 Excessive recyc l i ng to ach)eve a burner l i g h t - o f f can lead to accumul t ion o f a hazardous amount o f fue l in the furnace and should be avo ided.

D-1.2 Recovering from a Fuel -Rich Furnace Cond i t i on . I f an a i r d e f i c i e n c y should develop wh i le f lame is mainta ined at the burners , reduce the fue l u n t i l the normal a i r / f u e l r a t i o has been res to red . I f fue l f l ow cannot be reduced, s lowly increase a i r f l ow u n t i l normal a i r / f u e l r a t i o has been res to red .

60

D-I.3 I t should be recognized tha~ fuels available today contain unexpected constituents. Therefore, engineering systems and material designs must take into consideration these potential variables.

D-I.4 Heavier-than-Air Gases.

D=I.4.1 Gas-Fired Igniters. Many o i l - f i r e d boilers are equipped with propane or other l iquefied petroleum gas (LPG)-fired igniters. Special precautions are required in locating the vent pipe from the automatic bleed valve so that heavier-than-air, vented gases do not accumulate in depressions or in confined areas. An alternative to the automatic venting of heavier-than-air gases is to eliminate the ign i ter vent valve from between the two igni ter Safety shutoff va lves.

0 -1 .4 .2 Main Burner Gas Supply. Host natura l gas suppl ied to b o i l e r s t y p i c a l l y is l i g h t e r than a i r and presents no special problems in atmosphere over and above those addressed in t h i s s t a n d a r d . Because of developing energy cost cons idera t ions , many bo i l e r s are using a gas or a mix ture of gases ,#ith h e a v i e r - t h a n - a i r c h a r a c t e r i s t i c s . These heav ie r - t han -a l r gases, such as propane/a i r mixtures and re f i ne ry 9ases, e t c . , requ i re special cons iderat ion in s to r i ng , handl ing, and vent ing to prevent accumulations in depressions or in conf ined areas.

An alternative to the automatic venting of heavler-than-air gases is to eliminate the Kent valve from between the two main gas safety shutof~ valves.

D-I.4.3 For additional information, see NFPA 54, National Fuel Gas Code, and NFPA 58, Liquefied Petroleum Gases.

Appendix E

This Appendix is not a part of the requlrements of this NFPA document, but is included for information purposes only.

H J Natural Gas Supply •

H

S Vent to Atmosphere

~ l g n i t o r

Light Oil Pilot Supply

A Safety shutoff valve, spring closing (NC) C Vent valve, spring opening (NO) H Gas star strainer J Constant gas pressure regulator N Drip leg S Pressure gauge T Manual shutoff valve O ignitor oil strainer S Pressure gauge T Manual shutoff valve V Pilot oil safety shutoff valve, spring closing

O ¥

S

~ l g n i t o r

NC = normally closed, deenergized NO = normally open, deenergized

Figure E-I Typical Ignit ion Systems for Gas/Oil-Fired Burner

61

Appendix F

This Appendix is not a part of the requirements of this NFPA document, but is included for information purposes only.

Vent to Atmosphere

Vent to Atmosphere

S R

Gas m /~'~ ~ m ~ z J IT M ~ m ~ Z ( ~

Q

Burner

A Safety shutoff valve, spring closing (NC) C Vent valve, spring opening (NO) D Gas flow control valve H Gas strainer I Closed position interlock on downstream safety shutoff J Constant gas pressure regulator valve K Vent line manual shutoff valve for leakage testing N Drip leg Q High gas pressure switch R Low gas pressure switch S Pressure gauge T Manual shutoff valve X Low fire start switch

Safety Controls not Shown

Flame detector(s) Purge air flow switch Forced draft fan discharge pressure switch and

fan damper position switch (alternative to purge air flow switch)

Excessive steam pressure interlock (excessive water temperature and pressure interlock for hot water boilers)

Low boiler water level interlock(s) (steam and hot water)

Note: NC = normally closed,deenergized NO = normally open, deenergized

Figure F-1 Typical Fuel Supply Systems and Safety Controls for Gas Burners.

62

Appendix G

This Appendix is not a par t of the requirements of t h i s NFPA document, but is included for in format ion purposes only .

Clearing J Line

S R U F

~n Atomizing ~ " ~ . , " N ~ ~ ' ~ k ' ~ ~ Irner

, _ _ Y Alternate I I

AtOd? ~zyng ~ . _ 1 ' TrlTIT~ap I Drain

A Safetv shutoff valve, spring closing (NC) B Oil re~:irculation valve atomizing medium(NO)

(optional for unheated oil) D Oil fh)w control valve F Low oil temperature switch (not applicable for unheated oil) I Closed position interlock on safety shutoff valve

' J Atomizing medium differential control valve " L Automatic atomizing medium pressure switch M Oil meter (optional) N Low atomizing medium pressure switch O Oil strainer P Atomizing medium flow interlock differential switch, or pressure interlock switch R Low pressure switch

• S Pressure gauge T Manual shutoff valve U Oil temperature gauge (optional for unheated oil) W Atomizing medium strainer X Low fire start switch Y Atomizing medium flow orifice

~;~fety Control~ not Shown

Flame detector(s) Purge air flow switch Forced draft fan discharge pressure switch and fan damper

position switch (alternative to purge air flow switch) Excessive steam pressure interlock Low boiler water level interlock(s)

Figure G-1 Typical Fuel & Atomizing Hedium Supply fo r Oi l Burner.

63

PART II

85F - ] - (Entire Standard): Accept ~ : Technical Committee on Boiler Furnace Explosions RECOMMENDATION: Completely revise the 1982 edition of NFPA 85F, Standard on Instal lat ion and Operation of Pulverized Fuel Systems as shown in the following text. SUBSTANTIATION: To ref lect changed fuel u t i l i za t ion patterns and bring safety requirements up to the standard of the industry. COMMITTEE ACTION: Accept.

NFPA 85F

Standard for the Instal lat ion

and Operation of Pulverized Fuel Systems

1987 Ed i t ion

Chapter I Introduction

I- I Scope.

I-1.1 This standard specifies requirements for pulverized fuel systems, beginning with the raw fuel bunker ahead of the pulverizer and the point at which primary a i r enters the pulverizing system and terminating at the point where the transport a i r and fuel enter the furnace or other apparatus. The pulverized fuel system is defined to include the primary a i r ducts upstream of the pulverizer to a point where pressure can be relieved by application of a suitable vent or other means.

I - I .2 This standard covers only those fuels having react iv i t ies greater than that of Pennsylvania anthracite with a vo la t i le content of eight percent on a dry basis. Reactivity of a fuel re lat ive to this base shall be determined by the pulverizer manufacturer u t i l i z ing his own technique, and appl icabi l i ty of the standard shall be determined and agreed to by user.

I - I .3 In the case of pulverized fue l - f i red boi ler furnaces, a related work is NFPA 85E, Standard for Prevention of Furnace Explosions in Pulverized Coal-Fired Multiple Burner Boiler-Furnaces. Users of this type of equipment, therefore, are referred to both standards.

I-1.4 Those systems with an oxygen-enriched atmosphere are excluded from this standard.

I-2 Purpose.

I-2.1 The purpose of this standard is to establish minimum standards For design, insta l la t ion, operation, maintenance, and personnel safety in connection with pulverized fuel systems, to contribute to operating safety, and to minimize the probabi l i ty of pulverized fuel system explosions and the effects of those explosions which do occur.

I-2.2 No standard can be promulgated which wi l l guarantee the elimination of pulverized fuel system explosions. Technology in this area is under constant development which wil l be reflected in revisions to this standard. The users of this standard must recognize the complexity of pulverized fuel systems as to the type of equipment and the characteristics of the fuel. Therefore, the designer is cautioned that the standard is not a design handbook. The standard does not do away with the need for the engineer or competent engineering judgment. I t is intended that a designer capable of applying more complete and rigorous analysis to special or unusual problems shall have lat i tude in the development of such designs. In such cases, the designer is responsible for the va l id i t y of the approach.

I-2.3 This standard is applicable to new instal lat ions and to major alterat ions or extensions of exist ing equipment for the preparation and burning of fuel in pulverized Form contracted for subsequent to June I, 1987. The standard is not retroactive.

I-2.4 Since this standard is based upon the present state of the art , i ts application to existing instal lat ions is not mandatory. Nevertheless, operating companies are encouraged to adopt those features of this standard which are considered applicable and reasonable for existing insta l la t ions.

I-3 Basic Principles.

I-3.1 Functional Requirements.

I-3.1.I The various types of pulverized fuel systems convert a solid fuel to pulverized fuel and del iver i t continuously, and at controlled rates, to burners, storage bins, or other apparatus.

I-3.1.2 The principal requirement of pulverized fuel systems and their components is that they be capable of long-term continuous and proper operation. I t is essential that unwanted interruptions be kept to an absolute minimum because of the general combustible and explosive nature of the pulverized fuels. Experience shows that f i res and explosions are most l i ke ly to occur during start-up or shutdown or af ter an emergency shutdown.

Pulverized fuel systems shall incorporate al l necessary equipment and controls to provide For repeated safe cycles of start-up, operation, and shutdown, whether these cycles are of long or short duration.

I-3.1.3 I t is necessary that the pulverized fuel system be sized and arranged to meet the demands of the system i t serves over the required range of operation.

I-3.2 Hazards in Pulverized Fuel Systems.

I-3.2.1 Recognition of certain inherent hazards in a pulverized fuel system is important in the design, operation, and maintenance of the system, such as:

I-3.2.1.I An uninterrupted controllable raw fuel supply is essential to minimize f i res and explosions within the system. These interruptions and control problems in the fuel supply may be caused by worn equipment, excessive surface moisture, large or unusual fuel sizing, or foreign substances including iron, wood, rags, excelsior or rock. Compositions of certain clays (Bentonitic or mixed layers) contained in some coal seams may cause interruptions in coal flow which should be guarded against.

I-3.2.1.2 To f ac i l i t a te the discharge of fuel from the raw fuel bunker at a controlled rate, the bunker shall be designed in accordance with principles stated in 2-6.7.1. These principles require a bunker design that provides for mass flow and self-cleaning flow characteristics. The purchaser or his agent should be aware of the wide range in material handling characteristics of fuel that are related to differences in moisture, size consist, and consolidation characteristics. The probable range in these characteristics for the fuels to be used and a determination of time consolidation shear values over these ranges are prerequisites for obtaining a bunker design that provides the desired flow characteristics over the range of fuels to be used. I f the fuel is of a nature that spontaneous combustion in the raw fuel bunker is l i ke ly to occur even when equipment is in service, the bunker design shall be a mass flow instead of self-cleaning design.

I-3.2.1.3 A f i re , ahead of or in the pulverizer, usually causes an abnormal increase in temperature of the equipment or of the mixture leaving the pulverizer. Fires are caused by feeding burning fuel from the raw fuel bin, by spontaneous combustion of an accumulation of fuel or foreign material in the pulverizer, piping, or burners, or by operating at abnormally high temperatures.

64

1-3.2.1.4 Fires in burner pipes or other paris of pulverized fuel systems af ter the pulverizer wi l l generally not be detected by an abnormal increase in pulve~zer outlet temperature. Temperature sensors on pipes or in or on other components of the system can be used to detect these f i res.

I-3.2.1.5 I t is not desirable to feed abnormally hot, smoldering, or burning raw fuel to pulverizers. Where the feeding of such fuel is unavoidable, the procedures outlined in Section 3-5 shall be followed.

I-3.2.1.6 Transport velocit ies shall be adequate to prevent set t l ing of the fuel particles in the system or flashback from the burners.

I-3.2.1.6.1 Pulverized fuel is conveyed through pipes from the pulverizer in transport air . Malfunction or maloperation may introduce several hazards. For example, improper removal of a burner from service can introduce: ( l ) the set t l ing out of pulverized fuel in the burner pipes; (2) a leakage of pulverized fuel from the operating pulverizer through the burner valve into an idle burner pipe; or (3) leakage of gas or a i r through a burner valve, thereby causing a f i r e in an idle pulverizer. In Chapter 3 Operation, necessary precautions are established to avoid such hazards.

I-3.2.1.7 Pulverizers tripped under load wi l l have fuel remaining in the hot pulverizer, burner piping, and burners. These accumulations can cause spontaneous combustion of the fuel or an explosion.

1-3.2.1.8 Fuel systems are hazardous when fuel escapes into the surrounding atmosphere or a i r enters an inerted system.

1-3.2.1.9 The characteristic of fuel to oxidize can raise i ts temperature to a point where auto- or spontaneous combustion can occur. This characteristic can constitute a special hazard with certain fuels and fuel mixtures.

1-3.2.1.I0 Accumulations of fuel in the pulverlzer can cause f i res. This is usually due. to insuff ic ient drying which can be indicated by too low a pulverizer outlet mixture temperature.

1-3.2.1.II Excessive pulveri.zer outlet mixture temperatures increase the possibi l i ty of pulverizer f i res and can cause coking of burner parts.

I-3.2.1.12 Gases can be released from freshly crushed fuel and accumulations of flammable or explosive mixtures can occur in bins or other enclosed areas.

I-3.2.1.13 Hot a i r flowing back into the fuel bunker constitutes a hazard.

I -3.2. i .14 To ensure compatibility of the equipment and the type of fuel to be pulverized, i t is desirable to have a quality def in i t ion of the fuel. This shall be acceptable to the equipment designer, the agency responsible for procurement of the fuel, and the operating department. Vo la t i l i t y , moisture, ash content, maximum size and distr ibut ion, gr indabi l i ty , and other fuel characteristics shall be given close attention. Some fuels are much more abrasive than others and some can be corrosive.

I-3.2.1.15 A pulverized fuel sy!item is designed for a specific range of fuel characteristics. Fuels which d i f f e r widely from the design range can cause serious operating d i f f i cu l t i e s and produce a potential safety hazard. Care shall be exercised to make sure that al l fuels received are within the specific range of the fuel handling and burning equipment.

I-3.2.1.16 Improperly trained personnel, inadequate maintenance programs, or operati,}n of abnormally worn equipment can cause f i res and explosions.

I-3.2.1.17 Accumulation of pulverized fuel in a i r ducts or pipes, part icular ly those shared by a group of pulverizers, is hazardous.

I-3.3 Pulverizing and Fuel System Component Functions.

]-3.3.1 Drying and Conveying of Fuel. PuIyerizer a i r is used to continuously convey the pulverized fuel from the pulverizer. Normally, heated pulverizer a i r evaporates some of the moisture from the raw fuel while fuel is being pulverized, and elevates the a i r / fue l mixture to the desired temperature. The temperature and quantity of pulverizer a i r used is controlled to obtain the degree of dryness and pulverizer temperature desired, depending on the type of fuel being burned.

I-3.3.2 Classifying the Pulverized Fuel. An essential characteristic of the pulverized product is i ts fineness. I t is desirable that the pulverized fuel system minimize variat ion in fineness as pulverizer parts wear, and as fuel properties change over the anticipated range. For this purpose most pulverizers are equipped with adjustable c lass i f iers , or achieve some adjustment of fineness by.varying a i r flow or other means.

1-3.3.3 "Transporting and Distr ibuting the Pulverized Fuel. The pulverized fuel may be transported d i rect ly to one or more burners or to one or more a i r / fue l separation devices or to one to more bins or lock hoppers for intermediate storage.

I-3.3.4 Refuse Removal. I t is desirable that foreign, hard-to-grind material be removed from the fuel before i t is fed to the pulverizers; however, i t is ~ advisable that the pulverizers, reject or tolerate reasonable amounts of such materials so that damage or interruption of service do not result.

I-3.4 Manufacturing, Design, and Engineering.

I-3.4.1 The equipment manufacturer and the purchaser or the purchaser's agent shall cooperate in determining requirements for equipment design and operation so that the purchaser or agent can be assured that the system is not deficient.

I-3-4.2 An evaluation shall be made to determine the optimum integration of manual and automatic safety features considering the advantages and disadvantages of each t r ip function.

Note: The maximum number of automatic t r ip features does not necessarily provide for maximum safety. Some t r ip actions result in additional operations which increase exposure to hazards.

I-3.5 Coordination of Design, Insta l la t ion, and Operations.

I-3.5.1 The pulverized fuel system shall not be released for operation before the ins ta l la t ion and checkout of the required safeguards and instrumentation system.

(a} The constructor responsible for the erection and instal lat ion of the equipment shall see th@t a l l pertinent apparatus is properly instal led and connected.

(b} The purchaser, the engineeing consultant, the equipment manufacturer, and the operating company shall avoid pulverized fuel system operation unt i l such safeguards have been tested to operate properly as a system. In some instances i t may be necessary to instal l temporary interlocks and instrumentation to meet these requirements. Any such temporary system shall be reviewed by the purchaser, the engineering consultant, the equipment manufacturer, and the operating company, and agreement reached on i ts su i tab i l i t y , in advance of start-up.

(c} Testing and checkout of the safety interlock system and protective devices shall be accpmplished j o i n t l y by the organization with the system design responsibi l i ty and those who operate and. maintain such system and devices during the normal operating l i f e of the plant. These tests shall be accomplished before i n i t i a l operation.

65

I-3.5.2 I t is essential that proper coordination of design, insta l la t ion, operation, maintenance, and training be accomplished.

I-3.6 Operation, Maintenance, and Training.

I-3.6.1 The pulverized fuel system handles erosive materials that can cause rapid rates of wear of system components, thus creating a potential explosion hazard. Special maintenance measures are required to safeguard the system. A preventive maintenance program, using c r i t e r i a such as tonnage or hours of service based on plant experience, shall be put into effect. The manufacturer's recommendations shall be considered in establishing these maintenance c r i te r ia , especially in those plants with l i t t l e or no experience handling pulverized fuel .

I-3.6.2 For safe operation, proper coordination of the overall design and functional objectives are important. I t cannot be assumed that correctly designed equipment and the manufacturer's operating instructions can be wholly relied upon to ensure a safe operating system without the benefit of a competent technical, operating, and maintenance plant organization.

I-3.6.3 Continued competence can only be achieved by maintenance of technical training and operator proficiency as a continuing act iv i ty throughout the l i f e of the plant a f ter i n i t i a l training.

I-3.6.4 Control equipment including interlocks and alarms shall be properly maintained at al l times to ensure proper and rel iable operating condition of the system. All control equipment shall operate over a period of time consistent with the equipment being controlled without requiring maintenance.

I-4 Definit ions. For the purpose of this standard, the following def in i t ions shall apply.

Air

Auxi l iary Air. Air or inert gas supplied from an auxi l iary source to maintain a minimum fuel mixture velocity in the burner piping.

Primary Air. The a i r or inert gas used to convey the pulverized fuel to te burners.

Note: In some d i rec t - f i red pulverized fuel systems, the primary a i r services the same function as pulverizer a i r .

Pulverizer Air. Air or inert gas introduced into the pulverizer to convey the pulverized fuel from the pulverizer and to dry the fuel i f required.

Seal Air. Air or inert gas supplied to any device, at an adequate pressure for the specific purpose of preventing contamination.

Tempering Air. Air or inert gas at a lower temperature added to hot primary a i r or gas to modify i ts temperature.

Transport Air. Air or inert gas used to convey pulverized fuel.

Approved. Acceptable to the "authority having j u r i s d i c t i o n . "

NOTE: The National Fire Protection Association does not approve, inspect or cer t i fy any insta l lat ions, procedures, equipment, or materials nor does i t approve or evaluate testing laboratories. In determining the acceptabil ity of insta l lat ions or procedures, equipment or materials, the authority having jur isd ic t ion may base acceptance on compliance with NFPA or other appropriate standards. In the absence of such standards, said authority may require evidence of proper insta l la t ion, procedure or use. The authority having jur isd ic t ion may also refer to the l is t ings or labeling practices of an organization concerned with product evaluations which is in a position to determine compliance with appropriate standards for the current production of l isted items. 66

Authority Having Jurisdiction. The "authority having jur isdict ion" is the organization, o f f ice or individual responsible for "approving" equipment, an insta l la t ion or a procedure.

NOTE: The phrase "authority having jur isd ic t ion" is used in NFPA documents in a broad manner since jur isdict ions and "approval" agencies vary as do their responsibi l i t ies. Where public safety is primary, the "authority having jur isd ic t ion" may be a federal, state, local or other regional department or individual such as a f i r e chief, f i r e marshal, chief of a f i r e prevention bureau, labor department, health department, building o f f i c i a l , electr ical inspector, or others having statutory authority. For insurance purposes, an insurance inspection department, rating bureau, or other insurance company representative may be the "authority having ju r isd ic t ion . " In many circumstances the property owner or his designated agent assumes the role of the "authority having jur isdict ion"; at government instal lat ions, the commanding o f f i cer or departmental o f f i c i a l may be the "authority having jur isd ic t ion. "

Annunciator. A device which indicates an off-standard or abnormal condition by both visual and audible signals.

Bin. An enclosure to store pulverized fuel.

Bunker. An enclosure to store raw fuel.

Burner. A device or group of devices for the introduction of fuel and a i r into a furnace at the required velocit ies, turbulence and concentration to maintain ignit ion and combustion of the fuel within the furnace.

Classif ier. A device to control pulverized fuel part ic le size distr ibut ion.

Confined Space. Any work location or enclosure in which any of the following may exist:

(a) The dimensions are such that a person 6 f t (1.8 m) ta l l cannot stand up in the middle of the space or extend his arms in al l directions without h i t t ing the enclosure.

(b) Access to or from the enclosure is by manhole, hatch, port or other re la t ive ly small opening which l imits ingress and egress to one person at a time.

(c) Confined spaces may include but are not limited to pulverizers, ducts, heaters, windboxes, cyclones, coal dust collectors, furnaces, bunkers or bins, etc.

Cyclone. A device which by centrifugal action separates the pulverized fuel from a i r or inert gas.

Damper.

Auxil iary Air Control Damper. A controllable damper for regulating the flow of auxi l iary a i r .

Hot Air Control Damper. A controllable damper for regulating the flow of hot a i r as required to control pulverizer outlet temperature.

Primary Air Control Damper. A control lable damper for regulating the flow of primary a i r or pulverizer a i r .

Primary Air Shutoff Damper. A t ight-seating damper usually located upstream from primary a i r regulating damper to prevent flow.

Tempering Air Control Damper (Cold Air Damper). A damper used to control tempering a i r .

Tight Shutoff Damper. A close f i t t i n g damper to minimize a i r or gas passing into any system component.

Direct-Fired System (Unit System). One in which the fuel is pulerized and delivered suspended in the primary a i r , direct ly to the burner(s).

Distr ibutor/Divider. A device which spl i ts a single fuel and primary a i r stream into two or more streams.

Dust Collector. An auxi l iary separator used to separate the fuel dust from the a i r or inert gas prior. to discharge of the l a t t e r from the system.

Exhauster. The fan located at the pulverizer out let used to draw the pulverizer a i r through the,pulverizer and to del iver the a i r / fue l mixture to the burner(s) or other apparatus.

Feeder, Fuel. A device for supplying a controlled amount of fuel to a system or subsystem.

Flame. The y is ib le or other physical evidence of the chemical process of rapidly converting fuel and a i r into products of combustion.

Gate, Fuel. A shutoff gate between the fuel bunker or bin and the fuel feeder.

Grindabil i ty. The characteristic of solid fuel representing i ts re lat ive ease of pulverization. (See ASTM D 409.')

Igniter. A device which provide:~ adequate igni t ion energy to immediately l ight o f f the main burner.

Inerting. The di lut ion of the oxygen content of an a i r / fue l mixture to a point where i t is no longer explosive through the addition of an inert gas or vapor.

Interlock. A device or group of devices arranged to sense a l imi t or o f f - l i m i t condition or improper sequence of events and to shut do~n the offending or related piece of equipment, or to prevent proceeding in an improper sequence to avoid a h,~zardous condition.

Labeled. Equipment or materials to which has been attached a label, symbol or other ident i fy ing mark of an organization acceptable to the "authority having jur isd ic t ion" and concerned with product evaluation, that maintains periodic inspection of production of labeled equipment or materials and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.

Listed. Equipment or materials included in a l i s t published by an organization acceptable to the "authority having jur isd ic t ion" and concerned with product evaluation, that maintains periodic inspection of production of l is ted equipment or materials and whose l i s t i ng states either that the equipment or material meets appropriate standards or has been tested and found suitable for use in a specified manner.

NOTE: The means for identi fying l is ted equipment may vary for each organization concerned with product evaluation, some of which do not recognize equipment as l isted unless i t is also labeled. The "authority having jur isd ic t ion" should u t i l i ze the system employed by the l i s t ing organization to ident i fy a l is ted product.

Lock Hopper. A vessel with valves and controls, used for transferr ing fuel from a low pressure containment to a higher one.

Pressure/Air Lock. A device for" transferr ing pulverized fuel between zones of d i f ferent pressure without permitting appreciable flow of a i r or gas in either direction.

Primary Air Fan (Pulverizer Air Fan). The fan used to supply the pulverizer a i r to the pul'verizer or to supply the a i r to the burner l ines of a storage system.

Pulverized Fuel. Solid fuel reduced to a size such that more that 50 percent wi l l pass through a 200 mesh sieve (74 microns),

Pulverized Fuel Pump. A device or system for transporting fuel mechanically olr pneumatically u t i l i z i ng minimum a i r flow.

Pulverizer. A machine to convert solid fuel to pulverized Fuel.

Shall. Indicates a mandatory requirement.

Should. Indicates a recommendation or that which is ' advised but not required.

Valve

Barrier Valve. A valve, not necessarily dust~tight, to impede furnace gases traveling back into any system component opened for inspection or maintenance.

Check Valve. A self-operating valve used, to prevent reverse flow through any portion of the system.

Dust-Tight Valve. A t ight-seating valve intended to stop flow. i

Flow Control Valve. A device capable of regulating quantity of throughput to a controlled range.

Vent Valve. A valve used to permit'venting of a i r or gas from the system.

Vent. An outlet through which a i r or gas can be discharged from the system or to rel ieve explosion pressures.

Chapter 2 Design

2-1 Introduction. General requirements for pulverized fuel systems are covered in this section. ;Specific requirements for only the more commonly used d i rect - f i red unit systems,and storage systems are covered in deta i l . For other types of systems, refer to Chapter 5.

2-2 System Arrangement Requirements.

2-2.1 The system arrangement shall be such that i t provides only one possible direction of flow, i .e . , from the points of entrance of fuel and a i r to the point of discharge, which may be either a furnace or a transport and collection system.

2-2.1.I. Means shall be provided to resist the passage of a i r or gas from the pulverizer through the feeder into the bunker.

Note: A vert ical and cylindrical column of fuel of suf f ic ient height is one way to sat isfy this requirement.

2-2. l .2 Primary a i r (or f lue gas) supply ~hall be taken from a source with a pressure equal to or higher than that against which fuel wi l l be discharged from the system.

2-2.2 The system shall include indicators and annunciators that wi l l provide the operator with adequate information about signif icant operating conditions, both normal and abnormal, throughout the system.

2-3 Piping Arrangement.

2-3.1 Piping shall,be arranged to minimize hazardous accumulation of fuel .

2-3.2 Where the a i r / fue l stream is directed into multiple pipes, the system shall divide the a i r / fue l mixture in the proper rat io amoung the various pipes.

2-3.3 Positive means shall be provided to'rassure that al l pipe veloci t ies are equal to 'o r above the minimum velocity required for fuel transport. Testing during i n i t i a l start-up and retesting as appropriate shall be performed to ver i fy that indiv idual pipe velocit ies are adequate.

2-3.4 All piping system components shall be capable of being cleared of pulverized fuel using available primary a i r veloci t ies. '

67

2-4 Inerting Arrangement.

2-4.1 Where an inerting system is required in accordance with 2-6.8 i t shall be permanently installed and equipped with suitable connections which shall be a minimum of one inch diameter. Injection shall be con t ro l l ed by r e a d i l y operable valves or dampers. (See NFPA 69.)

Note: I t is p re fe rab le that operat ion of these valves be accomplished at a location remote from the pulverized fuel system to reduce personnel hazard.

2-5 System Arrangements.

2-5.1 Direct-Fired Systems.

2-5.1.I This system may have the fan located either following or ahead of the pulverizer. I f auxi l iary ai r is used, a damper is required in this l lne. The usual d i rect - f i r ing pulverized fuel system is comprised of the following components (see Figures 2-5.1 (a) through ( f ) ) :

(a) Raw fuel bunker.

(b) Raw fuel gate.

(c) Raw fuel feeder.

(d) Flow control of raw fuel.

(el Feeder discharge piping.

(f) Air-swept pulverizer.

(g) Classifier.

(h) Foreign material collecting hopper.

( i ) Pulverizer a i r fan or exhauster.

( j ) Source of hot air .

(k) Source of tempering air .

(I) Temperature control of air .

(m) Flow control of a i r .

(n) Piping and ducts.

(o) Valves.

(p) Dampers.

(q) Burners.

(r) Means of inerting.

(s) Safety interlocks and alarms.

2-5.1.2 Valve Requirements.

2-5.1.2.1 For a suction furnace that can be fired by other main fuels or is connected to two or more pulverizers or exhausters, barrier valves shall be installed to isolate al l burner lines (see Figures 2-5.1.1 (c ) , (d) , ( e l , ( f ) , (g) , (h) , and ( i ) ) . In add i t i on , a d u s t - t i g h t va lve or equ iva lent shal l be i n s t a l l e d in the burner pipe as close to the furnace as p rac t i cab le . The valves shal l be closed p r i o r to enter ing a p u l v e r i z e r or exhauster.

2 -5 .1 .2 .2 For a pressure furnace that can be f i r e d by Other main fue ls or is connected to two or more pu lve r i ze rs or exhausters, a d u s t - t i g h t va lve shal l be i n s t a l l e d to i s o l a t e a l l burner l i nes (see Figures 2-5.1.1 ( j ) , ( k ) , and (1 ) ) . In add i t i on , a second d u s t - t i g h t va lve or equ iva len t sh l l be i n s t a l l e d as close to the furnace as p rac t i cab le . Both valves shal l be closed p r i o r to en ter ing a p u l v e r i z e r or exhauster.

Note: I t is recommended that one or both valves descr ibed in 2-5.1.2.1 and 2 - 5 . l . 2 . 2 be quick c los ing .

- FEE DER DISCHARGE RAW- FUEL FEEDER PIPING

HOT-AIR RAW-FUEL f / A U X I L I A R Y AIR OR DUNKER + | / AUXILIARY AIR FLUE GA! \ RAW-FUEL~/ /'DAMPER

~,/~GATE / / / "°+" '+ CONTROL,, DAMPER \ ~'I3iJST TIGHT

~/VALVE " TEMPERING~ ~IR DAMPER .~ I / t I P " /

/ t SUCTION / FURNACE AIR /

/ PRIMARY AIR BARRIER SHUT OFF DAM PE R ~ " VAL VE

/ PULVERIZER. I~. ~ _ ~

~ _ OTHER PRIMARY AIR'J L FUELS CONTROL DAMPER "EXHAUSTER

Figure 2-5.1 (a): Direct Firing Pulverized Fuel Exhauster System for Negative Pressure Furnance

~WV;~C ~TN~ER \ /RAW FUEL FEEDER ~ ~ / IAUXILIARY AIR

/ ~-DUST TIGHT VALVE

CONTROL DAM PER ~ I TEMPERING AIR\ "%, " DAMPER " ~ , -

TEMPERING A I R ~ i

PRIMARY AIR ~ SHUT OFF DAMPER / " I

AUXILIARY AIR / " I SUCTIO'Iq ~'ONTROL D A M P E ~ / ~ : I~ [5~ ~ / F U R N A C E

;RIk~ARoY AD[ARM;ER PR (IMARY ] /1\\ , , , , , \ , , RR,,:2 "s

, ' , , L , , ,

Figure 2-5.1 (b) : Direct Firing Pulverized Fuel for Furnace Negative Pressure

AW fUEL DUNKER ~ AW FUEL O~TE

RAW FUEL FEEDER

MJXlL IARY AUXILIARY Am CONTROL ~IIPER • * m /

_

. , J - / I # Tm.T / ~ I

ro.c~o I fEud.me ~ I \ I r-"J ~ / ] m*rr I " " \ .o ' \ I. \ I V l f 5,

]7 >+ °

~-PRIMARY Am ShUTOFI r DAMPER

PC'3rTIV( PRESSURE FUAWACE

/ / / / ,

Figure 2-5.1 (c): Direct Firing Pulverized Fuel Exhauster System for Positive Pressure Furnace

68

RAil FUEL BURliER

I~U4W P-U~L 0ATE

J~AW FU~L FEEDE~

AUXILI~Y

. . . . . .

VALVES

CONTROL O~PER

SHU~'OF F DAMPER

klR CONTROL 0AM~ER

Figure 2-5.1 (d): Oirect Firing Pulyerized Fuel Hot Primary Air Fan System for Positive Pressure Furnace

I~W RUIIL ll'¢OR~d~i suw~t~s

g~COX~Ry rEEOERS

R~R~N/drT TE . . . . . . IR

I I~IM~y AIR NI~T[R

Figure 2-5.1 (e): Direct Firing Pulverizer Fuel Cold Primary Air Fan System for Positive Pressure Furnace

SO VALV l l

SlWeLE SOURCE OF FUEL NO INOWI~UAI. BURNERS OFF (S ( ( Z.§.l,l,Sl

hi)

I

FURNACE

~,...

lUCTIOi l • F1At l I I~ I I~I[SSUlql -Ir tJ~14Cl

MULTIPLE SOURCE OF FUEL

mE 0~ Wine BUYERS o~r. MULTIPLE SOURCE :OIIEEC~ION TO lORE OF FUEL IWE e~JRN~': OR WULT]~.E

:ol~¢llOX "to OwE eURNEn

Y,,J

OUST r~ TIOHT ~,, "

VALVES L

(f) B ~ n I E R v,u.~ E ; ~ " ~¢" ST

I I , - - ~.

I (g) OUST TII~I4T

I VALVES .

V/~. V~S IINTERL NKEN

~ I~ ~, '=' k'-~.~ i-

V ~ . V E S

, E I IA I p I P " , t / / t l

{ | ]

Figure 2-5.1.1: Direct Firing Pulverized Fuel System's Valve Requirements in Burner Piping 6g

2-5.1.2.3 I f one valve is used to isolate more than one burner l ine, means shall be provided to prevent circulation between those lines or burners (see Figure 2-5.1.I (c).

2-5.1.2.4 Two dust-t ight valves or one dust-t ight valve and one barr ier shall be instal led in each burner pipe at the pulverizer or exhauster outlet for a suction furnace designed for operation with one or more pulverized fuel nozzles shut o f f (see Figure 2-5.1.I ( f ) ) .

2-5.1.2.5 Two dust-t ight valves or one dust-t ight valve and one barr ier valve, or equivalent, shall be provided in each burner pipe i f one or more pulverizers is connected to more than one furnace at a time (see Figure 2-5.1.1 (h)).

2-5.1.2.6 When two or more pulverizers are'each connected to two or more furnaces at the same time, valve requirements of 2-5.1.2.1 or 2-5.1.2.2 shall apply (see Figures 2-5.1.1 (g) and (1)).

2-5.1.2.7 Two dust-t ight valves or one dust-t ight valve and one barr ier valve shall be instal led in the burner piping when the discharge pipes form separate exhausters or pulverizers are connected to the same burner nozz le (see Figure 2-5.1.1( i ) ) . i

2-5.1.2.8 The valve located nearest to the pulverizer shall be so positioned that pulverized fuel" accumulations above the valve wi l l drain into the exhauster or pulverizer when the valve is opened. Other valves shall be located so as to prevent accumulation of pulverized fuel.

2-5.1.2.9 Figures 2-5.1 (a) through ( f ) and Figures 2-5.1.I (a) through (1), and the,accompanying text i l l us t ra te and specify requirements for the usual combinations of equipment; i f other combinations are used, thpy shall conform to the principles set forth in this standard.

Note: No valves are required between the pulverizer and the burners for a single pulverizer or exhauster connected to one Or more burners in a furnace that cannot be f i red by any other means, provided that the combustion a i r to individual burners cannot be shut o f f (see Figures 2-5.1.1 (a) and 2-5.1.1 (b)). "

2-5.1.3 Isolation Requirements.

2-5.1.3.1 For pressurized pulverizer and suct ion pulverizer with pressurized air-supply insta l la t ions, there shall be a means for t ight shutoff of hot a i r supply and means for shutting o f f the primary a i r supply to each pulverizer.

Note: This may be the total primary a i r control damper i f t ight seating.

2-5.1.3.2 For suction pulverizer instal lat ions with atmospheric tempering a i r supply, there shall be a means for shutting o f f the hot a i r supply.

Note: This may be the hot a i r control damper i f t ight seating.

2-5.2 Storage Firing Systems.

2-5.2.1 This system may be aranged for part ial or complete venting of the pulverizer a i r and water vapor af ter separating the pulverized fuel in cyclones or other types of dust collectors, The separated Fuel is usually transported to storage bins for subsequent supply to the burners. In addition to the components of a d i rect - f i red system as l is ted under 2-5.1, a typical storage system includes some or al l of the following special equipment (see Figures 2-5.2.1.I (a) and (b) and 2-5.2.1.2 (a) through (d)).

(a) Cyclone separator.

(b) Dust col lector (e.g.. cyclone vent Collector).

(c) Vent fan.

(d) Cyclone pressure lock. ,

(e) Transport system (e.g., pulverized fuel pump, piping and valves).

(f) Pulverized fuel bins.

(g) Pulverized fuel feeders.

(h) Auxiliary a ir damper.

( i ) Primary air fan.

2-5.2.2 Valve Requirements.

2-5.2.2.1 Barrier valves shall be provided in the piping between pulverized fuel feeders and burners of a storage system connected to one or more burners of a suction furnace (see Figures 2-5.2.1.1 (a) and 2-5.2.1.2 (a) through (d)).

2-5.2.2.2 A check valve shall be installed in each vent pipe connecting the cyclone or dust collector of a storage system to the primary air fan or to any portion of the furnace or stack of a suction furnace (see Figures 2-5.2.1.2 (a) and (d)).

2-5.2.2.3 A dust-tight valve shall be installed in each burner pipe, between pulverized fuel feeder and burner For a storage system connected to one or more burners of a pressure furnace (see 2-5.2.3 and also Figure 2-5.2.1.1 (b)). These valves shall not be opened until the primary air pressure is established.

2-5.2.2.4 A pressure lock shall be installed at each fuel outlet of a pulverized fuel bin connected to a pressure furnace to permit feeding of fuel into the burner lines at higher pressure, and to prevent flow of primary air into the bin (see Figure 2-5.2.1.1 (b)).

2-5.2.2.5 A pressure lock shall be installed at each cyclone outlet i f more than one cyclone is connected to a single pulverized fuel pump, or i f the cyclone is arranged for direct gravity discharge into the pulverized fuel bin.

Note: A pressure lock is not required at the cyclone outlet i f only one cyclone is connected to the pulverized fuel pump.

2-5.2.3 Primary Air Connections of Pressure Furnace Firing.

2-5.2.3.1 For pressure furnace f ir ing, a dust-tight valve shall be installed between the forced draft system and the inlet of the primary air fan (see Figure 2-5.2.1.1 (b)). A minimum stop shall be provided on the primary air control valve to prevent its being completely closed unless the shutoff valves in the burner pipes are closed.

VEST V~LVE (CO~TR~LLEm~

~O: *m CONTROL o~eee

TEMPE R |ll 0 -- ~. ~)

PULVERIZER Am / / ~ ' ~ ' ~ ~ COWXROL 0 ~

PULVI[RIZER ~]R FA4~ / /

FEEDER DISCHAR~ j PIPINO

R*W FUEL BUNItER

~/I AW FUEL GATE ~LV~RIZED FUEL SIN

VEN~ r ~ t C~CK VALVEII EWT OUST

PRESSURE =ULVER IZER LOCi(

vi i

pR)MAAy AIR ¢O~TROL DAMPER \

~LV [R [ I [ ° FUEl. OATE

Figure 2-5.2.1.2 (a): Pulverized Fuel Storage Firing System (Partial Recirculation- Vented Air to Stack)

\ S . . . .

I * w - ~ L

NOTENI£NT DUST COLLECTOR MAY ~1[ OMITTED.

Figure 2-5.2.1.2 ( b ) : Storage Firing System (Partial Recirculation--Vented Air to PA Fan)

PULVERIZEO /BIN VENT F~E CER FUEL BIM

, O ISCH~0E / PIPIND . VENT ~ t "

.OT .R EO.TROL ~ : " " \ . . . . .

HOT.Am RAW- C CLONE OR FUEL Y~

FLUE GAS% / TE COL PUL¥.

nEAM[ RPE R I N 0 ~ IMIARy C ~;4-TR ()I. ~MPER ~LUE GAS i i AIR rAN

PULVERIZER AIR PULVERIZED

AIR FAN . ~ # J w ~ PULV. fUEL (D) ,~ATE PULVERIZER PRESSURE

PRESSURE~ _.LOCK'~ ~FUELFEEDER ~ FURNACE

/ ~ - - - - 7 ~__ : [ ~ HOT A,R / ~C~OT TIGMT VALVES )

CONTROL C~kMP(R ~ • t~ ' ~ . .~HOT AIR

PRIMARY AIR F'AN AIR HEATER

r~ ~CED TE MPER IN6 Am ~ r~ FT

NOTE ~ULVERIZER FA~ OR VENT FAN DAMPER MAY NOT BE REOUIRED, TEMP[R|

Figure 2-5.2.1. I (a) and (b): Pulverized Fuel Storage Firing System

70

R~ F~IL ~ . ~ R

~ . T r ~

Figure 2-5.2.1.2 (c): Storage Firing System (Partial Recirculation--Vented Air to Furnace)

Au~,oulc Arm IWL[T. *T OUST

- VEMT FAN " L [ C T ~ / T ,

RAW r u ~ u BUW~R • cYcLo~t

eeESSUF ~ Locx i

RAW '~ .... I1 / 1 ' \ I i / , fEEDER ~ ~ m ~ v '

Am s H u T o f f ; r e e v e . o ~ e ~ e r r - -

= AIR COWTR~ AIR rAW f ~M~RINe Am

........... ~ I " , ' \ / I / r--:::[Z],~.~J " ' HOT AIR AIFI HEATER

, Figure 2-5.2.1.2 (d): Storage Firing System (Partial Recirculation)

2-5.2.4 Venting.

2-5.2.4.1 Partial venting shall be used to control humidity in the pulverized fuel system, to minimize quantity of vented a i r or gas, or Lo conserve heat.

2-5.2.4.2 Total venting shall be used where there is no further use for the transport a i r or gas.

2-5.2.4.3 Both vent systems have these common requirements:

(a) There shall be no venting to a pressure furnace because of the probabil i ty of revel-se flow of furnace gases.

(b) Venting to a suction furnace shall be permitted when i t is delivered to a zone where combustion is active and injection l ine velocit ies are maintained at least 50 percent abovethe maximum flame propagation rate of the fuel.

(c) Venting to a stack, flue or breeching shall be permitted when i t is done to a zone where the temperature does not exceed two-thirds of the ignit ion temperatu're of the fuel in degrees Fahrenheit and the design of the entire vent system i ; such that there wi l l be no hazardous accumulation of combustible fuel dust.

(di Venting to theprimary a i r fan shall be permitted when the primary a i r fan is operating i f : some means is provided to prevent reverse flow; the primary a i r system can handle the total amount of a i r ; and the primary a i r fan is discharging to a zone of active combustion.

(e) When venting to atmosphere, the vented a i r or gas shall be suf f ic ient ly clean of combustible material as to create no f i r e or explosion hazard. The vented a i r or gas shall not interfere with the proper opertion of other systems within the area.

( f ) Check valves (when required) shall be located as near as practicable to the source or possible reverse flow into the system.

2-5.2.4.4 When the vented a i r from the cyclone is discharged to the atmosphere as in Figure 2-5.2.1.I, the vent shall discharge at an adequate height above the building roof.

2-5.2.4.5 When the vented a i r is discharged into the stack, f lue or breeching, the connection shall be made at a point where the pressure is less than that of the room in which the pulverizer is located, and each vent l ine shall have a check valve opening in the direction of the flow.

71

2-5.2.4.6 Vent connections shall be located downstream of the recirculated gas in le t connection in such a manner that any combustible dust carried by the vented a i r cannot be entrained in the recirculated gas for possible introduction into a zone of high furnace temperature.

2-6 Pulverizer System Component Design Requirements.

2-6.1 Strength of Equipment.

2-6.1.1 All components of the pulverized fuel system as described below that are normally operated at no more than 2 psig (13.8 kPa) pressure shall be designed to withstand an internal explosion pressure of 50 psig (344 kPa) for containment of possible explosion pressures. For operaLing pressures in excess of 2 psig (13.8 kPa), the equipment as described below'shall be designed to withstand an internal explosion presure of 3.4 times the absolute operating pressure.

2-6.1.2 Equipment design strength shall incorporate the combined stresses from mechanical loading, operating, and explosion pressures plus an allowance for wear which shall be determined by agreement between the manufacturer and purchaser. Implosion pressures shall also be considered.

2-6.1.3 Some parts of the pulverized fuel system such as large f l a t areas, sharp corners, etc., may be subjected to shock wave pressures, and special consideration shall be given to their design based on their locations in the system.

2-6.1.4 The components fa l l i ng within the requirements of 2-6.1.1, 2-6.1.2 (6.1 m) and 2-6.1.3 for a

d i r ec t - f i r ed system shall begin at a point two feet above the in let of the raw fuel feeder and at the seal a i r connections to the pulverizer system, and end at the discharge of the pulverizer, external c lass i f le r or exhauster. These shall include, but are not limited to, the following:

(a) Raw fuel feeding devices, discharge hoppers, and feed pipes to the pulverizer.

(b) All parts of the pulverizer required for containment o f internal pressure.

(c) Exhauster and connecting piping from the pulverizer.

(d) External c lass i f iers and connecting piping from the pulverizer.

(e) Foreign material col lecting hoppers connected to the pulverizer.

Note: Not included in the scope of these requirements are the raw fuel bunker or mechanical components such as seals, gears, bearings, shafts, drives, etc.

2-6.1.5 Explosion vents shall not be used on any component of the system described in 2-6.1.4.

2-6.1.6 All ductwork, from the hot and tempering a i r supply ducts to individual pulverizers including damper frames, expansion jo in ts , supports, and hot primary a i r fans, shall be designed to contain explosion pressure as defined in 2-6.1.I or shall be vented in accordance with NFPA 68. Ductwork and components upstream of the vents do not have to meet this requirement.

2-6.1.6.1 Atmospheric tempering a i r in lets, i f present, can serve as vents i f designed and applied in accordance with NFPA 68.

2-6.1.7 I f a pulverized fuel storage system is started and operated with an inert atmosphere in al l parts of the system in accordance with NFPA 69, the strength requirements of 2-6.1.1 shall not apply. Any component of the system started and operated with an inert atmosphere need not comply with the strength requirements of 2-6.1.1.

2-6.1.8 A pulverized fuel storage system that is not started and operated with an inert atmosphere in accordance with NFPA 69 shall meet the requirements of 2-6.1.1. The components fa l l i ng within these requirements are those l is ted in 2-6.1 plus:

(a) lock hoppers

(b) vent fans

(c) circulat ing fans

(d) transport systems

(e) pulverized fuel feeders

( f ) primary a i r fans handling fuel laden a i r .

2-6.1.9 In a pulverized fuel storage system that is not started and operated with an inert atmosphere in accordance with NFPA 69, the following equipment shall meet the requirements of 2-6.1.1 or shall be equipped with suitable vents in accordance with NFPA 68:

(a) cyclone

(b) dust collectors

(c) pulverized fuel bins.

2-6.1.10 Explosion vents shall not be used on the feeder or pulverizer of any system.

2-6.2 Piping.

2-6.2.1 For systems normally operated at no more than 2 psig (13.8 kPa) the pulverized fuel piping from the outlet of the equipment defined in 2-6.1.4 and 2-6.1.9 to the pulverized fuel burner or storage bin shall be designed to withstand an internal explosion pressure of 200 psig (1379 kPa) for containment of possible explosion pressures. Systems operated at greater than 2 psig (13.8 kPa) shall be designed to withstand an internal explosion of 13.6 times the absolute operating pressure.

2-6.2.1.1 There shall be an a11owance for wear in excess of the strength requirements of 2-6.2.1 which shall be determined by agreement between manufacturer and purchaser.

Note: Elbows are especially vulnerable to wear but a l l parts of the system need consideration.

2-6.2.1.2 Pulverized fuel piping shall provide smooth flow and have bend radii of not less than I pipe diameter. Wherever possible, radii in excess of I pipe diameter shall be used.

2-6.2.1.3 Flexible jo in ts and sp l i t clamp couplings shall conform to 2-6.4.1 except that the junction of two sections may be sealed with f lex ib le material. There shall be no separation of the pipe jo in t in case of fa i lu re of the f lex ib le material. Positive mechanical connections shall be provided between the two sections to prevent serious misalignment or separation.

2-6.2.1.4 Piping materials shall satisfy the strength requirements of 2-6.4.1 at temperatures normally encountered in the service of the equipment and shall comply with 2-6.6.2 for allowable stresses.

2-6.2.1.5 Br i t t l e materials shall not be used for piping except as abrasion resistant l inings and where no credit is taken for the structural strength of the l ining.

2-6.2.1.6 Piping support systems shall be designed and installed in accordance with ANSl B31.1, Power Piping Code, Chapter 2, Part 5, so that combined stresses wil l not be in excess of those specified in 2-6.6.2.

2-6.2.1.7 Pipe which is lined with abrasion resistant material shall have casing thickness and flange size designed for the strength requirements in 2-6.2.1 with no allowance required for wear.

2-6.2.1.8 Prior to i n i t i a l operation or af ter piping system renovation, an in-service leak test shall be performed in accordance with the following procedure:

(a) The system shall be gradually brought up to normal operating pressure and temperature.

(b) The system shall be continuously held at the conditions described in (a) for IO minutes.

(c) Examination for leakage shall be made of a l l jo ints and connections.

(d) The system shall show no visual evidence of weeping or leakage.

2-6.3 Valves.

2-6.3.1 All valves in the pulverized fuel system from a point within two feet (6.1 m) above the in le t of raw fuel feeder to the point of consumption of the pulverized fuel shall have construction capable of withstanding pressures as defined in 2-6.1.1 or 2-6.4.1 depending on application. These shall include but not be limited to the following:

(a) Barrier valve.

(b) Dust-tight valve.

(c) Check valve.

(d) Pressure/air lock.

(e) Raw fuel gate.

2-6.4 Interconnections.

2-6.4.1 Valves at points of interconnection between pulverized fuel system components requiring d i f ferent design pressures shall comply with the strength requirements of the lower pressure of the two.

2-6.5 Bunker and Hopper Designs.

2-6.5.1 The raw fuel bunker structural material shall be made of noncombustible material. I t shall be designed to provide:

(a) An uninterrupted flow of fuel being handled at a controlled rate.

(b) A flow pattern in which arching and ratholing (piping) are avoided.

2-6.5.1.I The bunker out let feeder(s) shall be coordinated with the bunker to avoid the probabi l i ty that improper feeder selection wi l l result in a l ter ing the bunker flow characteristics specified in 2-6.5.1 (a) or (b).

2-6.5.1.2 Provision shall be made to prevent accumulation of flammable mixtures of a i r and fuel dust and combustible gases within the bunker.

2-6.5.2 Pulverized fuel bins shall conform to strength requirements as specified in 2-6.1 (see 2-6.1.7 and 2-6.1.g). These bins shall be designed to permit fuel discharge at an uninterrupted, controlled rate. Internal construction shall minimize stat ic deposits. Open top bins shall not be used.

2-6.5.2.1 Provision shall be made to prevent accumulation of flammable mixtures of a i r and fuel dust and combustible gases within the bin.

2-6.5.2.2 Bins shall be equipped with high and low level fuel detectors (see 2-2.2).

2-6.5.3 Pulverized fuel lock hoppers shall be designed for 3.4 times the absolute operating pressure. These hoppers shall be designed to permit fuel discharge at an uninterrupted controlled rate. Internal construction shall minimize accumulations.

2-6.5.3.1 Lock hoppers shall be equipped with high and low level fuel detectors (see 2-2.2).

72

2-6.6 Materials Of Construction.

2-6.6.1 Materials of contruction used shall sat isfy the strength requirements of 2-6.1 at temperatures normally encountered in the service of the equipment.

2-6.6.2 I f made of steel or other ducti le metals, the allowable stress values shall be determined as follows:

(a) Tension. The maximum, allo~,able direct (membrane) stress shall not exceed the lesser of I/4 of the ultimate, or 5/8 of "the yield strength of the material.

(b) Combined Bending and.Membr,~ne Stress (where bending stresses are not se l f - l im i t ing) . The maximum allowable value of combined bending and membrane stress shall not exceed the lesser of the yield strength or I/2 the ultimate strength of the material.

(c) Combined Bending and Membrane Stress (where bending streses are ~e l f - l imi t ing) . The maximum allowable values of combined se l f - l im i t ing and non-self- l imit ing bending stresses plus membrane stress shall not exceed the ultimate strength of the material.

(d) Compressive Stress. For components where compressive stresses occur, in addition to the requirements of (a), (b), and (c) above the cr i t i ca l buckling stress shall be taken into account.

(e) Fatigue Analysis. On components subject to cyclic loading, fatigue analysis shall be made to guard against possible fatigue fai lures. Both mechanical and thermal loading shall be considered.

2-6.6.3 I f made of cast iron or other nonductile materials, the allowable stress shall not exceed I/4 of the ultimate strength of the material for al l parts. When cast iron or other nonductile materials are used for f l a t areas exceeding one foot square, the surface shall be strenthened by ribbing, or other means. The poss ib i l i ty of buckling and fatigue fai lures shall also be considered.

2-6.6.3.1 To assure casting quality, suitable nondestructive examination shall be made at locations of high stress, at abrupt changes of section, and at sharp angles, to detect significa.nt defects. The choice of such a quality assurance program shall be the responsibi l i ty of the designer.

2-6.6.4 The jus t i f i ca t ion of ne~, materials or improved analytical methods which may be ~eveloped shall be the responsibi l i ty of the designer. I f such materials and methods are used for the design'of pulverized fuel ' system components, they shall meet the requirements of 2-6.1 and 2-6.2.

2-6.7 Electrical Equipment.

2-6.7.1 All e lectr ical equipment: and wiring shall conform to NFPA 70 (ANSI), National Electrical Code.~

2-6.7.2 Locations where completely dus t - t i gh t pulverized fuel systems are instal led in compliance with this standard shall .not be considered a hazardous location for electr ical equipment as defined in NFPA 70.

2-6.8 Inerting System.

2-6.8.1 Pulverizers and pulveri;:ed fuel storage systems shall be equipped with an inerting system

" capable of maintaining an inert iltmosphere, as required to meet the provisions of 3-5.2.1 (see also NFPA 69).

2-6.8.2 Provision shall be made for ver i f icat ion of flow of inert ing media when the :~ystem is activated.

2-6.9 Fire Extinguishing System.

2-6.9.1 Pulverizers and pulverized fuel collecting systems shall be equipped with suitable connections'for f i r e extinguishing. These connections shall be at least one inch (25 mm) diameter and shall be adequate to pass the amount of extinguishing material required.

2-6.9.2 Provision shall be made for ver i f icat ion of flow of f i re extinguishing media when the system is activated.

2-7 Safety Interlock Systems.

2-7.1 The safety interlocks required by th~ pulverizer system shall be coordinated with the boi ler, furnace or other related devices.

2-7.1.I Interlock devices shall be designed for anticipated environmental conditions such as temperature, humidity, vibration, and corrosive agents.

L 2-7.1.2 These components shall be inst~lled in a manner to fac i l i t a te testing and maintenance.

2-7.2 Interlocks for d i rect - f i red pulverized.fuel systems shall be arranged to t r ip in the following sequence:

(a) Failure of primary a i r fan or exhauster tr ips burner shutoff valve or equivalent and feeder. Follow

"manufacturer's requirements regarding pulverizer tr ipping.

(b) Failure of pulverizer t r ips feeder.

(c) Closure of al l fuel l ine valves tr ips pulverizer, primary a i r flow and raw fuel feed.

(d) Failure of feeder shall i n i t i a te an alarm; restart ing is blocked unti l feeder start-up conditions are re-established.

Note: Several means are available to indicate loss of fuel feed through the pulverizer, loss of fuel feed t o t h e pulverizer, loss of fuel stored within the pulverizer, and loss of fuel input to. the burners. At least one, but preferably a combination of means, should be re l iably established and used to actuate l oss -o f= fue l interlocks.

(e) Primary a i r flow below manufacturer's recommended minimum tr ips the pulverizer.

2-7.3 Permissive sequential start ing interlocks for ~ i rect f i red systems shall be arranged so that af ter appropriate furnace interlocks have been satisf ied in accordance with NFPA 85E, Pulverized Coal~Fired Multiple Burner Boiler-Furnaces, the pulverizer can be started only in the following sequence: :

(a) Ignit ion system in service in accordance with NFPA 85E.

(b) Start primary a i r fan or exhauster.

(c) Establish minimum a i r flow.

(d) Start pulverizer.

(e) Start raw fuel feeder.

Exception: Items (b) and (d) above can be~simultaneous when dictated by system design.

2-7.4 Interlocks for pulverizers of storage systems shall be arranged to t r ip as follows:

(a) Full pulverized fuel bin tr ips fuel pump or conveyor and raw fuel feeder.

(b) Failure of fuel pump or conveyor tr ips vent fan on cyclone or dust col lector and pressure locks upstream of fuel pump or conveyor.

(c) Failure of vent fan tr ips pulverizer exhauster or a i r fan.

(d) Failure of pulverizer exhauster or a i r fan tr ips raw fuel feeder.

(e) Failure of pulverizer t r ips raw fue3 feeder.

73

2-7.5 Permissive sequential starting interlocks for pulverized fuel storage systems shall be arranged so that the system components can be started only in the following sequence:

(a) Start pulverized fuel pump or conveyor

(b) Start cyclone and dust collector pressure-locks

(c) Start vent fan

(d) Start pulverizer exhauster or air fan

(e) Start pulverizer

(f) Start raw fuel feeder.

2-7.6 For pressure furnace f i r ing from storage or seml-storage systems, the dust-tight valve in the burner pipe after the pulverized fuel feeder shall be interlocked so that i t cannot be opened unless the primary a i r shutoff valve is open.

Chapter 3 Operation

3-I Introduction.

3-1.1 Operating principles and sequence applicable to al l pulverized fuel systems are covered in 3-2. Sequences for the most common systems are given in 3-3 and 3-4. Other arrangements require different sequences of operating events. Abnormal conditions are covered in Section 3-5.

3-1.2 Since this chapter covers only the operation of the pulverized fuel system as indicated in I- I .1, the user is referred to the NFPA standard covering the particular application, e.g., NFPA 85E, Pulverized Coal-Fired Multiple Burner Boiler-Furnaces. I f the particular application is not covered by NFPA standards, the user is referred to the equipment manufacturer's operating instructions.

3-2 Operation of al l Pulverized Fuel Systems.

3-2.1 Functional Requirements.

3-2.1.1 The purchaser's consultant or engineering staff or, preferably, the operating staff, shall prepare written operating instructions and check l is ts to coordinate the operation of the pulverized fuel equipment with the other associated apparatus or systems.

3-2.1.2 Correct sequence of operating events shall be followed regardless of whether the unit is operated manually or certain functions are accomplished by interlocks or automatic controls.

3-2.1.3 Normal practice shall be to operate al l parts of the system within the established fuel, air, pressure and temperature limitations.

3-2.1.4 Every effort shall be made to establish operating procedures for the process or system in which the fuel is consumed that wil l permit continuous operation of the pulverized fuel system.

3-2.1.5 Unless the pulverizer-burner system is specif ically designed for operation with less than the fu l l complement of burners served by a pulverizer, such operation shall be prohibited.

3-2.2 Preparation for Starting.

3-2.2.1 Preparation for every start-up shall include checks for:

(a) Pulverizer system sealing air , i f required, in service.

(b) Energy supplied to control system and to safety interlocks.

(c) All pulverizer system gates, valves and dampers in start-up positions.

3-2.2.2 After an overhaul or after significant maintenance or outage the following inspections and checks shall be made:

(a) Pulverizers, ducts and fuel piping in good repair and free from foreign material.

(b) Pulverizers, ducts and fuel piping evacuated by al l personnel; al l access and inspection doors closed; al l personnel protection devices reinstalled.

(c) All pulverizer a i r or flue gas dampers operated through ful l operating range.

(d) Pulverizers, feeders, controls, and associated equipment in'good condition, adjusted properly and ready for service.

(e) A complete functional check of al l safety interlocks.

3-3 Operation of Direct-Fired Systems.

3-3.1 Starting Sequence.

3-3.1.1 The starting sequence shall consist of the following steps. All steps shall be included. The sequence of steps (b) through ( i) can vary as recommended by the system designer.

(a) Start all necessary l ight -of f equipment in proper sequence.

(b) Open tempering air damper.

(c) Start primary ai r fan or exhauster, i f driven separately from the pulverizer.

(d) Open primary air flow control damper to a predetermined setting which is at least sufficient to provide minimum burner line velocity.

(e) Open burner l ine valves, i f any, on the pulverizer to be started.

(f) Start pulverizer.

(g) Open hot a i r damper and maintain pulverizer outlet temperature within the normal range.

(h) Start raw fuel Feeder.

( i ) Place pulverizer outlet temperature control, primary ai r flow control, and raw fuel feed control on automatic.

3-3.2 Normal Operation.

3-3.2.1 The pulverizer output shall be regulated by increasing or decreasing i ts fuel and a i r supplies in accordance with the manufacturer's procedures or as determined by f ield tests.

3-3.2.2 The individual burner shutoff valves, i f provided, shall be wide open or completely closed (never as intermediate settings).

3-3.2.3 For operation at reduced pulverizer loads, the auxil iary ai r dampers, where provided, shall be used to maintain minimum burner line velocit ies.

3-3.2.4 A pulverizer shall not be operated below i ts minimum air or fuel stop setting.

3-3.3 Normal Shutdown.

3-3.3.1 The shutdown sequence shall consist of the following steps. All steps shall be included. The sequence of steps can vary as recommended by the system designer:

(a) Reduce pulverizer output to not less than 25 percent of rated pulverizer capacity and establish required combustion system conditions for shutdown (.see NFPA 85E).

74

(b) Shut off the hot a i r and open up the cold air to cool down the pulverizer.

(c) When the pulverizer is cooled, stop the feeder and continue operation of the pulverizer with sufficient air flow to remove all fuel from the pulverizer and associated burner lines. Continue cooling i f required.

(d) Shut the pulverizer down when the pulverizer system is empty.

(e) Burner l ine shutoff valves shall be positioned in accordance with the manufacturer's instructions.

(f) Stop primary a i r flow when desired system conditions are reached.

3-4 Operation of Storage Systems.

3-4.1 Operation of Fuel Burning Equipment.

Note: Operation of the fuel burning and pulverizing sections of storage systems are v i r tual ly independent of each other.

3-4.1.1 Starting Sequence.

3-4.1.1.1 The starting sequence shall be as follows:

(a) Th e fuel burning portion shall be coordinated with the furnace (see NFPA 85E).

(b) Start primary a i r fan(s).

(c) Open al l burner l ine valve!~ for the burners to be started.

(d) Open pulverized fuel gate, i f not already open, and start pulverized fuel feeders for these burners.

3-4.1.2 Normal Operation.

3-4.1.2.1 Individual burner valves shall be wide open or completely closed (never at intermediate settings).

3-4.1.2.2 Fuel flow shall be controlled by adjusting the pulverized fuel feeder speed.

3-4.1.2.3 Primary a i r flow shall be sufficient at al l times to prevent sett l ing of coal dust in burner pipes;

3-4.1.3 Normal Shutdown.

3-4.1.3.1 The shutdown sequence .~hal3 be as follows (see also NFPA 85E):

(a) Establish required combustion system conditions for shutdown.

(b) Stop pulverized fuel feeder.

(c) When burner flame is extinguished, close burner and primary ai r shutoff valves.

(d) Stop primary ai r fan after last burner served by that fan is shut down.

3-4.2 Operation of Pulverizing Equipment of Storage Systems.

3-4.2.1 Starting Sequence.

3-4.2.1.I The basic principle to be followed is that of starting equipment in sequence from the storage bin "upstream" toward the point of pulverizer a i r supply and then f inal ly raw fuel supply. (Se~ Figures 2-5.2.1.I and 2-5.2.1.2 (a), (b), (c), and (d).) The starting sequence shall be:

• (a) Start pulverized fuel pump or conveyor, i f provided.

(b) Start cyclone pressure lock, i f provided.

(c) Start cyclone or dust collector vent fan or exhauster in accordance with 2-5.2.4.

(d) Start pulverizer exhauster or fan and adjust control dampers to obtain proper ai r flow and temperature.

(e) Start pulverizer.

(f) Start raw fuel feeder.

(g) Readjust control damper(s) to obtain required pulverizer air/fuel outlet temperature and air flow.

3-4.2.2 Normal Shutdown.

3-4.2.2.1 The shutdown sequence shall be as follows:

(a) Close hot air damper and open cold air (or flue gas) damper to cool down pulverizer.

(b) Stop raw fuel feeder.

(c) When pulverizer is empty of fuel and is cool, shut i t down.

(d) Stop pulverizer exhauster or fan.

(e) Stop cyclone and dust collector vent fan or exhauster.

(f) Stop cyclone pressure lock.

(g) Stop pulverized fuel pump or conveyor.

3-5 Abnormal Pulverizer System Conditions.

3-5.1 When a f i re is suspected in the pulverizer system and abnormal operating conditions are encountered, al l personnel shall be cleared From the area near the pulverizer, primary ai r duct, burner pipes, burners and feeder or other pulverized fuel system components before the operating conditions are changed except for introduction of inerting or f i re exinguish4ng media and increasing fuel flow.

3-5.2 Pulverizer Tripping.

3-5.2.1 Inerting.

3-5.2.1.1 A pulverizing system tripped under load shall be inerte d and maintaiqed under an inert atmosphere until the pulverizer and i ts contents have cooled or the fuel is removed.

3-5.2.1.2 The inerting procedure shall be'as prescribed by agreement between the pulverizer equipment manufacturer and the purchaser. They shall consider fuel characteristics, pulverizer temperature, size, and arrangement of the pulverizer.

3-5.2.1.3 Inerting media shall be selected from the following:

(a) Carbon dioxide.

(b) Steam.

(c) Nitrogen.

(d) Other inert media.

3-5.2.2 Fuel Clearing Procedures.

3-5.2.2.1 For pulverizers that are tripped and inerted while containing a charge of fuel in accordance with 3-5.2.1.I, the following procedure shall be used to clear fuel from the pulverizer and sweep the transport lines clean as soon as possible after i t has been tripped and there is confirmation that there is no burning or smoldering fuel.

(a) Isolate, from the furnace, al l shutdown or tripped pulverizers.

75

(b) Start up one pulverizer in accordance with the principles and sequences l is ted in 3-3.1.I (a) through ( f ) .

(c) Continue to operate the pulverizer unti l empty and in normal condition for shutdown. When the operating pulverizer is empty of fuel, proceed to another pulverizer and repeat the procedure unti l a l l are cleared of fuel.

Exception: Furnace conditions permitting, rather than running the pulverizer unti l empty, restart feeder and return pulverizer to normal operation.

3-5.2.2.2 In the event that there are indications of burning or smoldering fuel in an out-of-service pulverizer, the pulverizer shall not be restarted under the normal procedure. Fire extinguishing procedures ' shall be followed or removal of residual fuel shall be accomplished under inert conditions by:

(a) Removing fuel through the pyrites removal system.

(b) Starting the pulverizer with inert primary a i r using the starting sequences in 3-3.1.I (a) through ( f ) .

Due to the danger of an explosion when opening and cleaning, pulverizers shall not be cleaned manually unti l they and their contents have been cooled to ambient temperature.

3-5.3 Pulverized Fuel System Fires.

3-5.3.1 Fire in any part of a pulverized fuel system shall be considered serious and dealt with promptly. Extinguishing media shall be in accordance with 3-5.2.1.3 or water or inert solids.

3-5.3.2 The following procedures for f ighting f i res shall be considered with modifications for specific systems, specific locations of f i re , or requirements of the equipment manufacturer.

(a) I f suf f ic ient inertant flow capacity is provided (at least 50 percent by volume of the minimum primary a i r flow for the system), inert the pulverizer a i r / fue l flow, shut o f f the fuel feed, empty the pulverizer of fuel, shut down and isolate the pulverizer.

(b) Stop the primary a i r flow, t r ip the pulverizer and feeder, isolate the system and inert. Avoid disturbing any accumulation of dust within the pulverizing equipment. Do not open any access doors to the pulverizer unti l the f i r e is extinguished and al l temperatures have returned to ambient. After isolat ion of the pulverizer is ver i f ied, follow procedures outlined in 3-5.3.6.

(c) A f i re detected in an operating low-storage pulverizer may generally be extinguished by shutting o f f the hot a i r , increasing the raw fuel feed as much as possible without overloading the pulverizer, and continuing to dperate with tempering a i r . I f the temperature at the pulverizer outlet does not drop within a few minutes, introduce water into the raw fuel or a i r tempering streams or both. However, the water must be added in such quantities and at such locations as not to cause hang-up or interruption of the raw fuel feed nor to s t i r up any deposits of combustible material. When al l evidence of f i r e has disappeared, shut o f f the water, t r ip the pulverizer, isolate and inert.

(d) When following either procedure in (b) or (c) above, the pulverizer shall be tripped by stopping a i r flow before or simultaneously with fuel flow.

3-5.3.3 In the event of f i res detected in other parts of a d i rect- f i red system, such as burner l ines, the appropriate procedures as outlined in 3-5.2.2 (a), (b) or (c) shall be followed.

3-5.3.4 In the event of f i res detected in components such as cyclones, dust coilectors, pulverized fuel bins, etc., of pulverized fuel systems other than d i rect- f i red systems, the affected components shall be isolated and inerted.

3-5.3.5 I f f i r e is found in a pulverizer which is out of service, i t shall be kept out of service and isolated. All a i r supply to the pulverizer shall be shut o f f , and the pulverizer shall be inerted. Access doors to a pulverizer shall not be opened unt i l the f i re is extinguished and al l temperatures have returned to ambient and isolat ion ver i f ied.

3-5.3.6 Following f i res in pulverizing systems, the pulverizing equipment shall be in ternal ly inspected and al l coke formations and other accumulations shall be removed to avoid future f i res, and i f the pulverizer is wet i t shall be dried. In no case shall a compressed a i r j e t be used. All components shall be inspected, and damaged items, such as gaskets, etc., shall be replaced.

Chapter 4 Personnel Safety

4-I Confined Spaces.

4 - I . I Specific procedures shall be developed and used for personnel entering confined spaces which shall :

(a) Posit ively prevent inadvertent introduction of fuel, hot a i r , steam, gas or any inerting medium.

(b) Posit ively prevent inadvertent start ing or moving of mechanical equipment or fans.

(c) Prevent accidental closing of access doors or hatches.

(d) Include tags, permits or locks to cover confined space entry.

(e) Determine need for vent i lat ion or self-contained breathing apparatus where the atmosphere may be stagnant, depleted of oxygen, or contaminated with i r r i t a t i n g or combustible gases. Test for an explosive or oxygen deficient atmosphere shall be made.

( f ) Provide for a safety attendant. The safety attendant shall remain outside of the confined space with appropriate rescue equipment and shall be in contact, preferably visual contact, with those inside.

(g) Provide for the use of proper safety belts or harnesses that shall be properly tied o f f when such use is practical.

4-2 Raw Fuel Bunkers.

4-2.1 In addition to the general provisions of 4-I , additional specific provisions for entering and working in fuel bunkers or bins l isted in 4-2.2 through 4-2.11 shall be made that recognize the high probabi l i ty of the presence of combustible or explosive gases, and the hazards associated with shi f t ing or s l id ing coal.

4-2.2 No one shall be permitted to enter fuel bunkers or bins without f i r s t not i fy ing the responsible supervisor and obtaining appropriate permits, tags, clearances, etc.

4-2.3 The responsible supervisor shall inspect the bunker, see that al l necessary safety equipment is on hand, and see that a safety attendant, who wi l l have no other duties during the job, is also on hand. The supervisor shall review with the safety attendant and the workers the scope of the job and safety procedures to be followed.

4-2.4 No smoking, flames, or open l ights shall be permitted. All lamps shall be suitable for Class I I , Division I location as defined in NFPA 70, National Electrical Code.

4-2.5 Tests shall be made for the presence of an explosive and oxygen deficient atmosphere in a bunker or bin. I f such an atmosphere is found, posit ive vent i lat ion shall be provided, and entry prohibited unti l the atmosphere returns to safe l imi ts . Suff icient retests shall be made during the course of the work to ensure a safe atmosphere and, i f i t is not maintained, the bunker shall be evacuated.

7B

Exception: A non-explosive, oxygen deficient atmosphere may be entered with suitable breathing apparatus.

4-2.6 No person shall enter a bunker containing burning fuel.

4-2.7 No person shall enter a bunker or walk on the fuel unless the safety attendant is present and the person is equipped with a safety belt or harness and l i f e l ine. The l i f e l ine shall be secured to an adequate support above the person~ and shall have only sufficient slack to permit limite(l movement necessary to performance on the job. The l i f e line shall be Manila rope at least one-half incll (12.7 mm) in diameter, or equivalent, in good (:ondition.

4-2.8 The safety attendant shall remain outside or above the bunker and shall keep the workers in ful l view at al l times. An adequate means of communication shall be provided to the safety attendant in case additional help is needed.

4-2.9 Whenever practical, work shall be done from platforms, ladders, scaffolds, etc., rather than from the surface of the fuel i t se l f .

4-2.10 No one shall walk on or w,)rk on a fuel surface that is more than three feet (0.9 m) lower than the highest point of the surrounding Fuel, in order to avoid the possibi l i ty of beingcovered by sliding fuel.

4-2.11 Full-face respirators or respirators and goggles shall be worn when dust conditions require them, as directed by the responsible supervisor or the safety attendant.

4-3 Maintenance Rules.

4-3.1 Housekeeping.

4-3.1.1 Good housekeeping is essential for safe operation and prevention of fires or explosions; therefore, provision shall be made for periodic cleaning of horizontal ledges or surfaces of buildings and equipment to prevent the acculnulatlon of appreciable dust deposits.

4-3.1.2 Creation of dust clouds shall be minimized during cleaning. Compressed air shall not be used to dislodge coal dust accumulations; water washing or vacuum cleaning methods are preferred.

4-3.2 Cleaning Plugged Equipment.

4-3.2.1 Severe injury and property damage can result from careless handling of unconfined pulverized fuel; therefore, extreme caution shall be used in cleaning out plugged burners, burner piping, pulverized fuel bins, feeders, or other parts'of the system.

Note: Pulverized fuel that may flood out or spi l l from such places can be ignited by a random spark or hot surfaces on which i t fal ls, or may already be smoldering and can produce an intensely hot f i re or explosion without warning. Since pulverized fuel dr i f ts freely in air , ignition may take place at considerable distance from the point of in i t ia l disturbance.

4-3.3 Welding and Flame Cutting (see also NFPA 51, Oxygen-Fuel Gas Systems for Cutting and Welding, and NFPA 51B, Fire Prevention in Use of Cutting and Welding Processes).

4-3.3.1 Emphasis shall be placed'on the hazard associated with welding or flame cutting on pulverized fuel equipment; such operations shall be properly supervised with use of f i re fighting equipment and watches. Written procedures shall be established which specify the precautions and permits required for welding and cutting on or near the pulverized fuel system.

4-3.3.2 Prior to welding or flame cutting, a l l deposits of pulverized fuel shall be removed by washing down or vacuuming, as far as practical, by approved methods from exterior and inter ior surfaces that could be affected. No work shall commence until the area has been ventilated sufficiently to minimize the possibi l i ty of f i re or explosion. Equipment shall not be returned to service until any area that has been sqbjected to welding or cutting has been cooled.

4-3.3.3 Fire-resistive blankets or other approved methods shall be used in such manner as to confine weld spatter or cutting sparks.

4-3.3.4 A careful inspection of al l areas near where welding or cutting has been done, including~the floors above and below, shall be made when the job ' is finished or interrupted and such "area patrolled for a period long enough'to make certain that no smoldering fires have developed.

4-3.4 Explosion-Operated Tools and Forming Techniques.

4-3.4.1 These tools and techniques shall not be used where flammable dust or dust clouds are present. When these operations become necessary, al l equipment, floors, and walls shall be cleaned and all dust accumulation removed by an approved method.' A~careful check shall be made to be sure that no cartridges or charges are le f t in the work area.

4-4 Electrical Tools and Lighting.

4-4.1 Where flammable dusts or dust clouds are present, sparking electrical tools shall not be used. All lamps shall be suitable for Class I f , D!vision I locations as defined in NFPA 70 (ANSI), National Electrical Code.

4-4.2 Either ground fault protected or spe~iflcally approved low voltage (6 to 12 volts) extension cords or l ights shall be used for al~ confined spaces where moisture may be a hazard.

Chapter 5 Special Systems

5-I Introduction. Specific requirements of some special systems, as well as operation of these special systems, are covered in this chapter. For general design, operating and safety requirements of these systems, refer to Chapters 2, 3 and 4.

5-2 Semi-Direct Firing System.

5-2.1 Description. This system is one in which the fuel is pulverized near the point of use in,an air-swept pulverizer. The fuel is separated from the air in a cyclone or other type dust collector. Fuel discharges from the cyclone through a rotary valve and is picked up by air from a primary ai r fan and blown into the furnace. The primary ai r fan may take i ts suction from the pulverizer a i r fan or from other sources. I f the primary air fan does not u t i l i ze al l of the pulverizer air, a vent fan is required. (See Figures 5-2 (a) and (b)~)

5-2.2 System Arrangement.

This system includes the following special equipment:

(a) Cyclone separator or other type dust•collectors.

(b) Pressure !oc k.

(c) Primary air fan.

(d) Vent fan and dust collector ( i f required).

(e) Pulverized fuel pick up.

5-2.3 Valve Requirements (see 2-5.].2).

5-2.3.l A barrier valve and a dust-tight valve shall be installed between each fuel pickup point and the burner for a suction furnace that can be fired by other fuels (see 2-5.] .2.]) .

7

C

RAW FUEL BUNmCER

RAW r U ( L

fEEDER R DISCHARE PRESSU E

PXPINO LOCK SUCTION

FURNACE

5 ...... <:0 : : : : ° ' m OAMF~R m I

I AIR ~ ~ r DAMPER I . . . . .

li - -

TEMPIERIWO AIR HOT AIR

Figure 5-2 (a): Semi-Direct Firing Pulverized Fuel System

f •

RAW FUEL BUWXEn

~AW fU(L gUS T TIGHT ~ T I ~ W . W I / .

rUnW~E

r i E ~ m - ~ ~ ~LVSRI2I~ P~ZW= Rt2I~ o l s c H / ~ a ¢ p l c P

( ) , F-1 VEoII.=_ ~( . . . . = r ,w

f / ? ' / \ . . . . . . . . . . . . __ \ i v%, ~o,o,o o, ,~ , , , =

L : ' C - I / ~ . . . . . . . . . . . --..~-.. v.o , ,,, ~o.,,~. - - . , ~ • • .

Figure 5-2 (b): Semi-Direct Firing Pulverizer Fuel System

5-2.3.2 Two dust-tight valve(s) shall be installed between the fuel pickup point and the burner for a pressurized furnace i f the furnace can be fired by other fuels. (See 2-5.1.2.2.)

Note I: I t is recommended that one or boh valve(s) described in 5-3.3.1 and 5-3.3.2 be quick closing.

Note 2: No valves are required between the pulverizer outlet and cyclone.

5-2.4 Isolation Requirements (see 2-5.1.3).

5-2.5 Operation.

5-2.5.1 Starting Sequence. The starting sequence shall be as follows:

(a) Start up al l necessary combustion system auxil iaries in the proper sequence. (See 3-3.1.1.)

(b) Start forced draft fan (for pressure furnace o n l y ) .

(c) Start primary ai r fan.

(d) Open all valves in lines to burners to be started (includes barrier valves and dust-tight valves).

(e) Adjust primary ai r flow to desired value, at least sufficient to provide minimum burner line velocity.

(f) Start pressure locks.

(g) Start pulverizer a i r fan.

(h) Start pulverizer.

( i) Start vent fan ( i f required).

( j ) Start raw fuel feeder.

(k) Adjust dampers and controls as in 3-3.1.1 ( i ) .

5-2.5.2 Normal Operation (see 3-3.2).

5-2.5.3 Normal Shutdown. The normal shutdown procedure shall be as follows:

(a) Follow procedures of 3-3.3.1.

(b) When the pulverizer is empty and cool, stop the pulverizer and pulverizer a i r fan or exhauster.

(c) Stop pressure locks.

(d) Stop vent fan.

(e) Stop primary ai r fan.

5-2.5.4 Interlocking (see 2-7).

5-3 Pulverized Fuel System for Blast Furnace Injection.

5-3.1 Description. This system is one in which the fuel is pulverized in an air-swept pulverizer. collected, stored, and batch pressurized to a pressure higher than the blast furnace pressure, transported, and distributed to the furnace tuyeres (see Figure 5-3). This system has three major subsystems.

(a) Fuel grinding and collecting system.

(b) An inert gas pressurized fuel storage and feeding system.

(c) Pulverized fuel transportation and distr ibution system.

5-3.2 System Arrangement. The pulverizer, pulverized fuel collecting, pressurizing, and feeding equipment may be remotely located from the blast furnace. I t is recommended that the distr ibution system be located close to the blast furnace. The pulverizer fan may be located ahead of the air heater and pulverizer, between the air heater and pulverizer, at the pulverizer outlet, or at the cyclone or dust collector vent.

The special equipment includes:

(a) Pulverizer airheater.

(b) Cyclone separator or other type dust collector.

(c) Cyclone pressure lock.

(d) Pulverized fuel bin.

(e) Pulverized fuel feed tanks.

(f) Pressure=tight isolation valves.

(g) Injection a i r system.

(h) Inert gas system.

( i ) Fuel injection lances.

( j ) Flow control of a i r (or flue gas).

(k) Vent dust collector.

78

5-3.3 Valve Requirements.

5-3.3.1 Pressure locks shall be installed at the pulverized fuel discharge of the cyclone separator or vent dust collector return lines.

To ous t v ~ , v ~ v E q . T o ~ s T cY Lo.~ C~LtCTOA V ' ~ ! i COLLECTm U ~ * T O A

. ~u~r,~,~L

. . . . t I

Figure 5-3: Blast Furnace Fuel Injection System

5-3.3.2 Special dust-tight valves shall be installed at each fuel outlet of the pulverized fuel bin, at the fuel discharge outlet of each feed tank, and at each fuel outlet of the pulverized fuel distributors. These valves shall be t ight at a pressure 1.5 times that required in the feed tanks.

5-3.4 Isolation Requirements. Isolation damper(s) shall be provided upstream of the pulverizer and at the discharge of the cyclone separator to permit inerting in this system.

5-3.5 Operation.

Note: Pulverized fuel is injected into the blast furnace tuyeres where the blast a i r carries this fuel into a furnace zone of extremely high temperature. The injection of fuel into an operating blast furnace presents no explosion hazard but precautions in handling pulverized fuel must be observed to avoid fires and explosions in the pulverizer fuel injection system.

5-3.5.1 Operation of Fuel Pulverizing Equipment. This is a storage grinding system and the principles and procedures in 3-4..2 shall apply.

5-3.5.2 Operation of fuel injection equipment shall be as follows:

(a) Ascertain the blast furnace is in service before starting the pulverized fuel injection system.

(b) Start inert gas source.

(c) Start injection a i r system blower or compressor and pressurize injection l ine to distr ibutor.

(d) Pressurize f i l l ed pulverized fuel feed tank with inert gas.

(e) Open dust-tight valves in lines leaving distributors.

(f) Establish transport air flow.

(g) Open discharge dust-tight valves from pulverized fuel feed tank.

Note: This sequence wi l l start pulverized fuel flow to the blast furnace. This systemdescription uses pu!verized fuel feed tank sequencing to maintain the feed; however, other means for doing this may be used. Because of the f i re hazard, inert gas is used to f luidize and pressurize the

• feed tank system. In normal operation, pulverized fuel flow to the furnace is controlled by regulating the pressure drop across thelsystem.

5-3.6 Normal Shutdown.

5-3.6.l The shutdown sequence shall be as follows:

(a) Empty fuel bin and feed tanks of pulverized fuel.

(b) Purge the injection and distr ibution system.

(c) Close the distr ibutor dust-tlght valves. l

5-3.6.2 I f al l pulverized fuel cannot be removed from the system, inert gas shall be provided for the feed hoppers and pulverized fuel bin when the system is idle.

5-3.7 Interlocking. In addition to the interlocking requirements of 2-7.4, the following shall be included:

(a) Failure of pulverizer a i r flow trips separately fired air heater.

(b) Failure of the cyclone separator or other type dust collector pressure lock tr ips raw coal feeder.

(c) Power failure closes al l valves required to isolate system.

5-4 Direct Firing System for Rotary Kilns.

5-4.1 Description. This system is a form of direct f i r ing. (See 2-5.1, and Figures 5-4 (a) and 5-4 (b).) The only special equipment is a dust collector with pressure lock for cleaning hot a i r or gas (optional).

5-4.1.1 Isolation Requirements.

5-4.1.1.1 When a by-pass air system is used, a by-pass control damper shall be installed.

5-4.1.I.2 Tempering damper shall be installed near the kiln hood to protect the hot gas duct.

5-4.2 Operation.

5-4.2.1 Starting Sequence. The starting sequence shall be as follows: (See 3-3.1.1.)

(a) Start pressure lock.

(b) Start the primary ai r fan or exhauster.

(c) Start a i r heaters, i f furnished.

(d) Start the pulverizer.

(e) Start the raw fuel feeder.

(f) Adjust primary a i r and fuel to desired value.

5-4.2.2 Normal Operation (see 3-3.2).

5-4.2.3 Normal Shutdown. Normal shutdown procedure. shall be as follows:

(a)

(b)

(c)

(d)

(e)

5-4.3

Shut off hot air.

When pulverizer is cool, stop raw fuel feeder.

When pulverizer is empty, stop pulverizer.

Stop primary a i r fan or exhauster.

Stop pressure lock.

Interlocking (see 2-?.I and 2-7.2).

7 9

PULV. AIR ~ R A W FUEL CONTROL - - \ B | N ~HOT AIR (OR GAS VALVE \ I DAMPER

RAW F U E L ~ /

" ~ \ / , / COLD AIR -OPTIONAL ~ J / INLET ~,AIR HEAT-ER ~ | # 0AMPER OR

PRIMARY AIR F'AN

CONTROL VALVE HOOD IAL TER NATE ) OR COOLER

Figure 5-4 (a): Direct-Fired Pulverized Fuel Systems for Rotary Kilns

RAW FUEL BIN

HOT AIR (OR GAS) --"~ RAW FUEL DAMPER ~,

X / /GATE COLD AIR OPTIONAL [ / . ~ l / INLET AIR HEATER | , ~ DAMPER OR

~ . - - i / • REGISTER --i

L OUST - ~ . / COLLECTOR--~ . . . . . l # "

RAW FUEL v ~ . I- . IFEEO R y . / L O C , ! - + " PULV.AIR k J ~ . - L CONTROL ~ W= | ! ~ I IJ-'~ .

BY -PASS SUCTION ROTARY (ALTERNATE) PULVERIZER OR KILN

COOLER

Figure 5-4 (b): Direct-Fired Pulverized Fuel Systems for Rotary Kilns

Chapter 6 Referenced Publications

6-I The following documents or portions thereof are referenced within this standard and shall be considered part of the requirements of this document. The edition indicated for each reference is current as of the date of the NFPA issuance of this document. These references are l isted separately to fac i l i ta te updating to the latest edition by the user.

6- I . I NFPA Publications. National Fire Protection Association, Batterymarch Park, Quincy, MA 02269.

NFPA 51-1983, Oxygen-Fuel Gas Systems for Welding and Cutting

NFPA 51B-1984, Fire Prevention in Use of Cutting and Welding Processes

NFPA 68-1978, Guide for Explosion Venting

NFPA 69-1986, Explosion Prevention Systems

NFPA 70-1987, National Electrical Code

NFPA 85E-1985, Prevention of Furnace Explosions in Pulverized Coal-Fired Multiple Burner Boiler-Furnaces.

6-I.2 Other Publication.

The following publication is available from the American National Standards Insti tute, 1430 Broadway, New York, NY I0081.

ANSI B31.1-1980, Power Piping Code.

Appendix A

This Appendix is not a part of the requirements of this NFPA document, but is included for information purposes only. r

A-I Direct Firing Circulating System.

A-I-I Description. This system, Figures A-l (a) and (b), is a form of direct f i r ing. The pulverizer, raw-fuel feeder, and primary air fan (exhauster) maintain the required air/fuel mixture in a circulating loop, or header, at sufficient pressure and velocity to cause the mixture to flow to the burners. Burners are connected to the circulating loop where desired. One circulating system may f i re one or more pressure furnaces or suction furnaces, or multiple circulating systems may f ire a single furnace. Where more than one furnace is fired by one circulating system, the furnaces may be of different types. The fuel supply to each burner is controlled independently of the other burners. Lighting each burner is a separate function from operation of the pulverizer.

A-2-1 System Arrangement.

A-2-1.1 Exhauster Requirements. The exhauster shall be at the outlet of the pulverizer.

A-2-1.2 Valve Requirements.

A-2-1.2.l Two dust-tight valves with seal a i r between them shall be installed between the circulating loop and each burner i t serves. One of these valves shall be located as near to the loop as practical and some means shall be provided to prevent accumulation of fuel above the valve.

A-2-I.2.2 A flow control valve shall be installed between the circulating loop and each burner i t serves.

A-2-I.3 Damper Requirements. For pressure furnace applications with multiple circulating systems, a primary air shutoff damper shall be provided ahead of the pulverizer.

A-2-2 Operation.

A-2-2.1 Starting Sequence. The starting sequence shall be as follows:

(a) Start up al l necessary combustion system components in the proper sequence (see 3-3.1.1).

(b) Start exhauster.

,=%'~, cow.u,.

TIU~LIO *m "4"-

maw WUE~. F{Zn(I

. . . . . ' ,~Z ; , =,,

R(CIRC~ATIOW C~TR~ ~ R ~

v ~ s

SUCTIO~

"f l . . . . . . . . . t - , , , /

........ Z : C

Figure A~I (a): Direct-Fired Circulating Pulverized Fuel System

)Al l rW

• / 2 80 Figure A-I (b): Direct-Fired Pulverized Fuel

Circulating System

(c) Start pulverizer.

(d) Start raw fuel feeder and place on automatic control.

(e) Open dust-tight valves in burner line.

(f) Open flow control valve in burner line.

A-2-2.2 Normal Operation.

A-2-2.2.1 Fuel rate to each burner in the system shall be regulated by the flow control valves in the burner lines.

A-2-2.2.2 The dust-tight valves in the burner lines shall be wide open or completely closed.

A-2-2.3 Normal Shutdown. Normal shutdown sequence shall be as follows:

(a) When taking burners out of service (except for the last burner on the system), close the flow control valve and the dust-tight valves in the burner lines and establish seal a i r between the valves.

(b) When taking the last burner on the circulating system out of service along with the pulverizing system, follow the procedure give in 3-3.3.1. '

(c) Interlocking, refer to 2-7.

Appendix B

This Appendix is not a part of the requirements of this NFPA document, but is included for information purposes only.

B-I Direct Firing System for Firing Zinc Fuming Furnace.

B-l-1 Description. This system is one in which the fuel is pulverized near the point of use in an air-swept pulverizer. The entire system operates at a pressure of a few pounds/square inch above atmosphere (see Figure B-I). Because of the operation pressure, primary a i r ' i s supplied by the furnace blower. This is a direct firing'system similar to that used on boilers. This special equipment includes:

(a) Lock hoppers for the raw fu~.l bin.

(b) Burners.

s r ~ RAw LrUgL P FEEDER

Z~C IrEEo[R OlSC~q 8[ FUWIWO

AIR CONTROL 'r[MPERINO AI R OAMP I[R

M~TEM • ~c I,~z. SLAO

Figure B-I: Zinc Fuming Furnace Pulverized Fuel System

B - I - I . I Because the raw fuel lock hoppers are pressurized due to the high operating pressure in the pulver izer, they shall be designed for operating presure, but not for pulverized fuel explosion pressure.

B-1-1.2 Separate controls shall keep the lock hoppers f i l l e d and presur ized.

B-1-2 Valve Requirements. Special pressure- t ight valves shall be ins ta l led at the i n le t and ou t le t of each raw fuel lock hopper.

Note: No valves are required between the ' pulver izer and burners as system cannot operate with id le pulver izers or burners.

B-l-3 Iso la t ion Requirements (see 2-5.1.3).

B-1-4 Operation.

Note: As" pulverized fuel is injected int'o a pool of molten slag, no ign i t ion problems ex is t and operation is merely a pulver iz ing and conveying system.

B-1-4.1 Start ing Sequence. The s ta r t ing sequence shall be as fol lows:

(a) Ascertain that there is a charge of molten slag in the furnace.

(b) Start the pulverizer.

(c) Open pulverizer a i r control damper to desired air flow.

(d) Start raw fuel feeder.

B-I-4.2 Normal Operation. Pulverizer output shall be regulated by varying pulverizer a i r and feedi~ng fuel in proportion to ai r flow to maintain the desired air/ fuel ratio over the operating range, or by varying feed rate alone.

B-I-4.3 Normal Shutdown. Normal shutdown procedure shall be as follows:

(a) Shut off hot a i r supply.

(b) Stop raw fuel feeder.

(c) When pulverizer is empty, stop pulverizer.

(d) Close pulverizer a i r flow control damper.

B-I-5 Interlocking (see 2-7.1 and 2-7.2).

Appendix C

This Appendix is not a part of the requirements of this NFPA document, but is included for information purposes only.

C-I Direct-Firing System for Reverberatory Furnaces (see 2-5.1).

81

PART I I I

85G - I - (Entire Standard): Accept SUBMITTER: Technical Committee on Boiler Furnace Explosions RECOMMENDATION: Completely revise the 1982 edition of NFPA 85G,'Standard for Prevention of Furnace Explosions in Fuel Air and Natural Gas-Fired Single Burner Boiler-Furnaces as shown in the following text. SUBSTANTIATION: To reflect changed fuel ut i l izat ion patterns and bring safety requirements up to the standard of the industry. COMMITTEE ACTION: Accept.

NFPA 85G

Standard for the Prevention

of Furnance Implosions in

Multiple Burner Boiler-Furnances

Information on referenced publications can be found in Chapter 8.

Chapter 1 Introduction

1-1 Scope. The scope of this standard is to establish minimum standards for the design, instal lat ion, and operation of boiler-furnaces, their fuel burning, a i r supply and combustion products removal systems, which include induced draft fans, related control equipment, and the stack, to prevent furnace implosions, and to contribute to operating safety.

1-1.l This standard is applicable to new installations and major alterations, or extensions of existing equipment of boiler-furnaces as described in Section 1-1, contracted for subsequent to June 1, 1987. This standard is not retroactive.

I - ] .2 This standard offers two methods for minimizing the risk of negative furnace draft in excess of furnace structural capability. Consideration shall be given to one or both of the following methods:

(a) Design the furnace and flue gas removal system so that the maximum head capability of the induced draft fan system with ambient a i r does not exceed the design pressure of furnace ducts and associated equipment. This design pressure is defined the same as the wind and seismic stresses of subsection 1-5.6 of Section 5 of the Manual of Steel Construction (American Institute of Steel Construction).

(b) Provide a furnace pressure control system in accordance with Section 4-3.

l-2 Purpose. The purpose of this standard is to minimize the probability of boiler-furnace'implosions. To this end, the standard requires the coordination of requirements concerned with structural reinforcement, operating procedures, control systems, and interlocks.

l -2. l Since this standard is based upon the present state of the art, application to existing installations, except as covered in 1-].1, is not mandatory. Nevertheless, operating companies are encouraged to adopt features that are applicable for existing installations where changes to the draft system are to be made.

I-2.2 Emphasis is placed upon the importance of: adequate strength of the structure, combustion and draft control equipment, safety interlocks, alarms, tr ips, and other related controls that are essential to safe boiler operation.

1-2.3 The effect of gas cleanup systems located downstream of the post-combustion gas passes of the boiler-furnace is known to be significant. Coordination of the operating procedures and design of the boiler furnace and air quality systems air gas path

is required. Such coordination shall include requirements for ensuring a continuous flow path from the forced draf t fan i n l e t to the stack. This standard offers only the genera] requirements of these systems because of the m u l t i p l i c i t y of the i r designs.

Chapter 2 General

2-1 Genera]

2-1.1 Basic Causes of Furnace Implosions

2-1.1.1 A furnace implosion is the resul t of the occurrence of excessively low gas side pressure which causes equipment damage.

2-1.1.2 Two condit ions that have caused furnace implosions are:

(a) A ma]operatlon of the equipment regulat lng the bo i le r gas flow, including a i r supply and f lue gas removal, resul t ing in the furnace being exposed to excessive induced dra f t fan head capab i l i t y .

(b) The rapid decay of furnace gas temperatures and pressure resul t ing from e i ther a rapid reduction in fuel input or a master fuel t r i p .

2-1.1.3 A combination of these two mechanisms has resulted in the most severe furnace implosion incidents.

2-1.2 Manufacturing, Design, and Engineering

2-1.2.1 On the basis of reported incidents, f i e ld tests, and simulations, the maximum negative furnace pressure is primarily determined by the maximum head characteristic of the induced draft fan; a major objective of the final design is to l imi t draft equipment maximum head capacity to that required for satisfactory operation. Special consideration shall be given to selection of fan and arrangement of duct work so as to l imi t the effect of negative head.

2-I.2.2 With scrubbers or other high draft loss equipment for removing flue gas contaminants a booster fan may be required. A bypass or other appropriate means shall be provided to counteract the potential excessively negative pressure conditions resulting from combining the suction heads of both the induced draft and booster fans.

Chapter 3 Definitions

Approved. Acceptable to the "authority having jur isdict ion."

NOTE: The National Fire Protection Association does not approve, inspect or cert i fy any installations, procedures, equipment, or materials nor does i t approve or evaluate testing laboratories. In determining the acceptability of installations or procedures, equipment or materials, the authority having jur isdict ion may base acceptance on compliance with NFPA or other appropriate standards. In the absence of such standards, said authority may require evidence of proper instal lat ion, procedure or use. The authority having jur isdict ion may also refer to the l ist ings or labeling practices of an organization concerned with product evaluations which is in a position to determine compliance with appropriate standards for the current production of l isted items.

Authority Having Jurisdiction. The "authority having jur isdict ion" is the organization, office or individual responsible for "approving" equipment, an instal lat ion or a procedure.

NOTE: The phrase "authority having jur isdict ion" is used in NFPA documents in a broad manner since jurisdictions and "approval" agencies vary as do their responsibil it ies, Where public safety is primary, the "authority having jur isdict ion" may be a federal, state, local or other regional department or individual such as a f i re chief, f i re

82

marshal, chief of a f i re prevention bureau, labor department, health department, building o f f i c ia l , electrical inspector, or others having statutory authority. For insurance purposes, an insurance inspection department, rating bureau, or other insurance company representative may be the "authority having jur isdict ion." In many circumstances the property owner or his designated agent assumes the role of the "authority having jur isdict ion"; at government installations, the commanding off icer or departmental o f f ic ia l may be the "authority having jur isdict ion."

Directional Blocking. An interlock which, upon detection of significant error in furnace pressure, acts to inhibi t the movement of al l appropriate final control elements in a direction which would increase the error.

Fan Test Block Capability. The point on the head vs. flow characteristics curve at which the fan is selected. This is the calculated operating point associated with maximum continuous rating of the boiler furnace plus head and flow margins.

Labeled. Equipment or materials to which has been attached a label, symbol or other identifying mark of an organization acceptable to the "authority having jurisdict ion" and concerned with product evaluation, that maintains periodic inspection of production of labeled equipment or materials and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.

Listed. Equipment or materials included in a l i s t published by an organization acceptable to the "authority having jur isdict ion" and concerned with product evaluation, that maintains periodic inspection of production of l isted equipment or materials and whose l is t ing states either that the equipment or material meets appropriate standards or has been tested and found suitable for use in a specified manner.

NOTE: The means for ident i fy lng l isted equipment may vary for each organization concerned with product evaluation, some of which do not recognize equipment as l isted unless i t is also labeled. The "authority having jur isdict ion" should u t i l i ze the system employed bythe l is t ing organization to identify a l isted product.

Open Flow Path. An open flow path.is defined as a continuous unrestricted path for movement of an air stream from the forced draft fan inlet to the stack.

Override Action. A control which, upon detection of significant error in furnace pressure, acts t o reposition the induced draft fan control device in a direction to reduce the error.

Shall. Indicates a mandatory requirement.

Should. Indicates a recommendation or that which is advised but not required.

Note: Notes and footnotes are for information only and are not mandatory.

Chapter 4 Equipment Requirements

4-I Furnace Structural Design

4-I . I The furnace shall be capable of withstanding without permanent deformation of any support member (at to yield or buckling), a transient design pressure [see l - l .2 (a)] of:

(a) the test block capability of the FD fan at ambient temperature, but not t6 exceed plus (+) 35 in. of water (+8.7 kPa), and

(b) the test block Capability of the induced draft fan at ambient termperature but not. less than minus (-)35 in. of water (-8.7 kPa).

4-1.2 When the induced draft fan test block;capability is less than minus (-)35 inches of water (-8~TkPa) consideration shall be givento an increased!negative transient design pressure, i f the induced draft fan head capability wi l l increase due to significant draft losses beyond the a i r heater, or for other reasons such as excessive induced draft fan test block margins.

4-2 Combustion Products Removal Subsystem. The transient internal design pressure defined in 4-1.l shall be taken into consideration in the design of the a i r and gas flow path from the FD fan discharge through the stack.

4-3 Furnace Pressure Control System

4-3.1 Functional Requirements. The furnace ~ressure control system shall control the furnace pressure of the desired set point in the combustion chamber.

4-3.2 System Requirements (see Figure 4-3.2)

4-3.2.1 The furnace pressure control sobloop (a) shall position the draft regulating equipment to maintain furnace pressure at the desired set point.

4-3.2.2 The control system shall include the following features and functions:

(a) Two out of three furnace pressure transmitters (b), each on a separate pressure sensing tap and suitably monitored (c), to minimize the possibi l i ty of operating with a faulty furnace pressure measurement.

(b) A feed forward signal (d), representative of boiler air flow demand. This may be a fuel flow signal, a boiler-master signal, or other suitable index of demand but shall not be a measured a i r flow signal.

r {D)

Feed-Forward Demand Signal

(A)

Furnace Pressure Control Subsystem

l ,

J (P) Auto/Man Transfer Station

MFT Signal

I (G) Feed-Forward from Master Fuel Trip

I(E) FanOverride J I Action or I IDirectional Blocking| I on Large Furnace|

• I Draft Error J

!(B) J i Two-out-of- I Three-Furnace I P(essure I Transmitter J

l c) I | Transmitter | Monitoring I System

Fig. 4-3.2: System Requirements

83

(c) Runback action or directional blocking (e) on large furnace draft errors introduced after the auto/manual transfer station (p).

(d) Feed forward action (g) ini t iated by a master fuel t r ip to minimize the pressure excursions, introduced after the auto/manual transfer station (P).

(e) To avoid uncontrolled changes in air or flue gas flow, axial fans, when used, shall be operated in such a manner as to avoid a stal l condition.

4-3.3 Component Requirements

4-3.3.1 Power Supplies. All reasonable precautions shall be taken to assure the ava i lab i l i t y of a failure-free power source (electric or pneumatic) to al l devices associated with the furnace pressure control and implosion protection systems.

4-3.3.2 Furnace Pressure Control Final Control Elements. The operating speed of furnace pressure control element(s) (H) (draft fan inlet damper drive, blade pitch control, speed control) shall meet the following cr i ter ia:

(a) The operating speed must not exceed the control system's sensing and positioning capabilit ies in order to avoid undesirable hunting and overshooting on automatic control. Excessive speed can create damaging negative pressure transients downstream. Excessive speed may also be unsuitable for manual control.

(b) The operating speed of the draft control equipment must not be less than that of the air flow control equipment.

(c) To ensure a rate of response satisfactory for control, special consideration shall be given to the design of furnace draft control systems with variable speed and axial fans.

Chapter 5 Sequence of Operations

5-I Functional Requirements

5-I . I The purpose of sequencing requirements is to ensure that the operating events occur in the proper order and not to provide fan operating procedures. The proper fan startup and shutdown procedures are defined by manufacturers, engineering consultants, and operating companies. These procedures shall be integrated with the operating procedures specified in this standard and in the related standard applicable to the fuel being fired as follows:

(a) "Gas-Fired", NFPA 85B

(b) "Oil-Fired", NFPA 85D

(c) "Pulverized Coal-Fired", NFPA 85E

5-1.2 An open flow path from the inlet of the forced draft fans to the stack shall be ensured under al l operating conditions. Where the system design does not permit the use of wide open air paths, the minimum open area a i r paths shall not be less than that required for purge air flow requirements with fans in operation. Principles to be observed shall include:

(a) In preparation for starting the f i rs t induced draft fan, al l fan flow control devices and shutoff dampers shall be open. In addition, sufficient isolating dampers, windbox dampers, a i r registers, and other control dampers shall be opened to assure an open flow path from the forced draft fan inlet through the furnace, induced draft fans, and the stack. Unless an open flow path is provided by other means, the open path shall be assured while starting the f i r s t induced draft and forced draft fan.

Note: On installations with multiple induced draft and forced draft fans, during any individual fan's starting sequence i ts associated dampers may be closed.

(b) Within the limitations of the fan manufacturers' recommendations, al l flow control devices and shutoff dampers on idle fans shall remain open until the f i r s t induced draft and f i r s t forced draft fans are in operation maintaining furnace pressure conditions and indicating an open flow path.

Note: After the f i r s t induced draft and forced draft fans are started and are delivering a i r through the furnace, the shutoff damper(s) of the remaining idle fans may be closed.

(c) The practice of operating with excess induced draft fan capability in relation to either forced draft fan capability or boiler load shall be discouraged.

5-1.3 The sequence for starting and stopping fans under al l conditions shall be:

Ca) Start an induced draft fan and then start a forced draft fan. Succeeding induced draft and forced draft fans shall be started in accordance with 5-1.4.

(b) Shutdown procedures shall be the reverse of 5-1.3 (a).

5-1.4 When starting and stopping fans, the methods employed and the manipulation of the associated control elements shall minimize furnace pressure excursions. The furnace pressure control subsystem shall be placed and maintained on automatic control as soon as practical.

5-1.5 Following shutdown of the last fan from any cause, opening of fan dampers shall be delayed or controlled to avoid excessive positive or negative furnace pressure transients during fan coast down.

Chapter 6 Interlock System

6-1 Functional Requirements. The functional requirements for interlock systems specified in the standard for the fuel being fired shall be followed:

(a) "Gas-Fired", NFPA 85B

(b) "Oil-Fired", NFPA 85D

(c) "Pulverized Coal-Fired", NFPA 85E

6-2 System Requirements

6-2.1 I t is possible to achieve conditions conducive to a furnace implosion that wi l l not be detected by any of the mandatory automatic t r ip devices, even though they are properly adjusted and maintained; therefore, operating personnel shall be made aware of the limitations of the automatic protection system.

6-2.2 The following interlocks shall be provided:

(a) High Furnace Pressure I. Trip master fuel t r ip when furnace pressure

exceeds the normal operating pressure by a value recommended by the manufacturer. I f fans are operating after t r ip , continue in service. DO not increase the air flow by deliberate manual or automatic control action.

2. Before main fuel f i r ing and following a five-minute period after a master fuel t r ip (furnace post purge), t r ip forced draft fans i f the furnace pressure exceeds the normal operting pressure by a value recommended by the manufacturer.

(b) High Furnace Draft (balanced-draft units)

I. Trip master fuel t r ip (not necessarily automatic) i f furnace negative pressure exceeds the normal oPerating'pressure by a value recommended by the manufacturer. I f fans are operating after t r i p , continue in service. Do not increase the a i r flow by deliberate manual or automatic control action.

84

Note: A short time delay may.be necessary to prevent tripping on rapid transients that do not present a hazard for the trip~ specified in 6-2.2 (a) 1., (a) 2. , and (b) 1.

2. Before main fuel f i r i ng and following a master fuel t r ip , t r ip a l l induced draft fans i f furnace negative pressure exceeds the no~lal operating pressure by a value recommended by the manufacturer. A short time delay is necessary to allow i:or the negative pressure transients due to loss oi: main flame. The value of negative pressure at which this t r ip is activated shall be greater than that specified in 6-2.2 (b) I.

(c) Loss of Forced Draft Fans

I. Provide an additional interlock for a variable speed fan to prove forced draft fan flow.

2. Close damper(s) on loss of an individual forced draft fan, unless i t is the last forced draf t ' fan in service.

3. Where an interlock system is provided to start , stop, and t r ip induced draft and force d draft fans in pairs, the associated induced draft fan wil l be tripped on loss of an individual forced draft fan and the dampers associated with both fans shall be closed, unless they are the last fans in service.

4. In i t i a te master fuel t r ip on loss of al l forced draft fans. All forced draft fan dampers shall be opened af ter a time delay to avoid high duct pressure during fan coast-down. Dampers shallremaln open. Gas recirculation fan system dampers shall be closed.

(d) Loss of Induced Draft Fans

( I) Provide an additional inte.rlock for a variable speed fan to prove induced draft fan flow.

(2) Close damper(s) on loss of an individual induced draft fan, uless i t is the last induced draft fan in service.

(3) "Where an interlock system is provided to start , stop, and t r ip induced draft and forced draft fans in pairs, the associated forced draft fan wil l be tripped on loss of an individual induced draft fan and the dampers associated with both fans shall be closed, unless they are the last fans in service.

(4) In i t ia te master fuel t r ip on loss of al l induced draft fans. Trip al l forced draft fans. All induced draft fan dampers shall be opened af ter a time delay to avoid high draft during fan coast-down. Dampers shall remain open and fans shall be started according to 5-I.2 to 5-I .4. Gas recircula~ion fan system dampers shall be closed.

(e) Multiple and Variable Speed Fans

( I) On start of second fan and subsequent fan(s), whether forced draft or induced draf t , the fan shall be capable of delivering a i r flow before opening i ts damper(s).

Chapter 7 Alarm System

7-I Functional Requirements. The functional requirements for alarm systems specified in the standard for the fuel being f i red shall be followed:

(a) "Gas-Fired", NFPA 85B

(b) "Oil-Fired", NFPA 85D

(c) "Pulverized Coal-Fired", NFPA 8SE

7-2 System Requirements. In addition to the alarms required in 7-I, the following separately annunciated alarms shall be provided:

(a) In i t ia t ion of directional blocking or runback action.

(b) Redundant transmitter deviations within the furnace pressure control system.

(c) Axial flow fan ( i f used) nearing sta l l l ine.

Chapter 8 Referenced Publications

The following documents or portions thereof are referenced within this standard and shall be considered part of the requirements of this document. The edition indicated for each reference is current as of the date' of the NFPA issuance of this document. These references are l isted separately to f a c i l i t a t e updating to the latest edition by the user.

8-I NFPA Publications. National Fire Protection Association, Batterymarch Park, Quincy, MA 02269.

NFPA 85B-1984, Prevention of Furnace Explosions in Natural Gas-Fired Multiple Burner Boiler-Furnaces

NFPA 85D-1984, Prevention of Furnace Explosions in Fuel Oil-Fired Multiple Burner Boiler-Furnaces

NFPA 85E-1985, Prevention of Furnace Explosions in Pulverized Coal-Fired Multiple Burner Boiler-Furnaces

8-2 Other Publication

Manual of Steel Construction, American Insitute of Steel Construction, 400 N. Michigan Avenue, Chicago, IL 60611.

85