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The Potential of Pulse-Jet Baghouses for UtilityBoilers. Part 1: A Worldwide Survey of UsersVictor H. Belba a , W. Theron Grubb b & Ramsay Chang ca Consultant , Boulder , Colorado , USAb Grubb Filtration Testing Services, Inc. , Delran , New Jersey , USAc Electric Power Research Institute , Palo Alto , California , USAPublished online: 07 Mar 2012.

To cite this article: Victor H. Belba , W. Theron Grubb & Ramsay Chang (1992) The Potential of Pulse-Jet Baghouses forUtility Boilers. Part 1: A Worldwide Survey of Users, Journal of the Air & Waste Management Association, 42:2, 209-217,DOI: 10.1080/10473289.1992.10466984

To link to this article: http://dx.doi.org/10.1080/10473289.1992.10466984

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CONTROL TECHNOLOGY

The Potential of Pulse-Jet Baghouses forUtility Boilers. Part 1: A Worldwide

Survey of Users

Victor H. BelbaConsultant

Boulder, Colorado

W. Theron GrubbGrubb Filtration Testing Services, Inc.

Delran, New Jersey

Ramsay ChangElectric Power Research Institute

Palo Alto, California

Pulse-jet fabric filters (PJFFs) are widely used inU.S. industrial boiler applications and in utilityand industrial boilers abroad. Their smaller sizeand reduced cost relative to more conventionalbaghouses make PJFFs appear to be a particularlyattractive particulate control option for utilityboilers. This paper summarizes the results of asurvey co-funded by the Electric Power ResearchInstitute and the Canadian Electric Association tocharacterize the performance of and operatingexperiences with PJFFs applied to coal-fired boilers.The survey involved site visits to interview technicaland plant personnel involved in the design,installation and day-to-day operation of PJFFsworldwide. Actual field experiences with PJFFperformance in terms of outlet emissions, pressuredrop and bag life for different types of pulse-jetcleaning methods, fabrics and boilers are compared.The second part of this series will present results ofpilot PJFF studies conducted by EPRI at differentU.S. utility sites on different fuel types tocorroborate the performance observed in thisworldwide survey. Part 3 will provide a costcomparison of PJFFs to other particulate controloptions such as electrostatic precipitators andreverse-gas baghouses.

The Clean Air Act Amendments of 1990 require utilities toreduce sulfur dioxide (SO2) emissions significantly. Certainapproaches that could be cost-effective for specific sites,

Copyright 1992—Air & Waste Management Association

February 1992 Volume 42, No. 2

such as fuel switching and sorbent injection, can severelyaffect the particulate collection performance of existingelectrostatic precipitators. Pulse-jet baghouses—because oftheir compactness and their ability to meet stringentparticulate emission limits regardless of variations in coaltype or fly ash properties—are an attractive upgrade optionfor underperforming precipitators. Pulse-jet baghouses (orfabric filters) are also a very promising option for compli-ance with possible future emission regulations of fineparticulates and air toxics.

Pulse-jet fabric filters (PJFFs) are distinguished by theiruse of periodic short, powerful bursts of air to clean thebags. This energetic cleaning allows a PJFF to operate attwo or more times the filtration velocity (as measured bythe ratio of gas flow to bag surface area, or air-to-clothratio) of a conventional reverse-gas-cleaned baghouse, with-out any increase in pressure drop. To function in thisfashion, the bags are supported by metal cages and sus-pended from a tubesheet, with ash collected on the outsideof the bags (Figure 1). Because bags can be removed fromthe top, there is no need for walkways between them, andthey can be packed closely in each compartment. ThusPJFFs require about half the footprint of reverse-gasbaghouses; an important consideration for sites with lim-ited space. Moreover, compartments often can remainon-line while the bags are being cleaned, thereby reducingthe total number of compartments required.

In 1988, EPRI began a systematic assessment of pulse-jetbaghouse technology through a worldwide survey of cur-rent users, studies of pilot baghouses, and economic analy-ses. This paper represents Part 1 of a three-part seriessummarizing EPRI's assessment to date that confirms thepotential benefits of pulse-jet baghouses for U.S. utilityapplications.

There are over 300 PJFFs installed on industrial andutility coal-fired boilers worldwide.1 This paper summa-rizes key findings of a survey sponsored by EPRI and theCanadian Electric Association of site visits to full-scalePJFF installations in the United States, Canada, Europe,

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DiaphragmValve

Pulse-airManifold

Dirty GasInlet

InletBaffle

FilterBag

Figure 1. In a pulse-jet baghouse, ash is collected on the outside of thebags, which are cleaned by short, powerful bursts of air. Source: ABB FlaktIndustriella Processer AB, Sweden.

Japan and Australia.2 The site visits were conducted tointerview technical and plant personnel involved in thedesign, installation and day-to-day operation and mainte-nance of the PJFFs. The general trends that were observedin baghouse design, performance, operation and mainte-nance are reported.

It should be noted that there are currently no PJFFsinstalled on large U.S. utility boilers and this surveyinvolved visits to industrial-boiler applications in the U.S.and utility- and industrial-boiler applications abroad. There-fore, the results from this survey should only be used as anindication of the potential performance of PJFFs whenused for U.S. utility boilers firing U.S. coals. The secondpart of this series will present results of pilot PJFF studiesconducted by EPRI at different U.S. utility sites on dif-ferent fuel types to corroborate the performance observedin this worldwide survey. Part 3 will provide a cost compar-ison of PJFFs to other particulate control options such aselectrostatic precipitators and reverse-gas baghouses.

Evolution and Trends in PJFF Technologies

The first PJFF was installed thirty-three years ago, in themid-1950s, as process equipment to collect valuable productfrom pulverizing mills.3 It wasn't until the early- to mid-1970s, twenty years later, that pulse-jet technology wasapplied to the collection of fly ash from coal-fired boilers.Since that time, the use of and design details incorporatedin PJFFs used to collect fly ash from coal-fired boilers haveevolved in distinctly different directions throughout theworld. PJFFs have been successfully applied downstream ofall types of boilers ranging from PC- and stoker-fired unitsto buhbling and circulating-fluidized-bed combustors (AF-BCs and CFBCs). Additionally, PJFFs have been installeddownstream of boilers employing spray dryer absorbers,furnace sorbent injection, duct injection of dry sorbents,and SCR deNOx units. As utilities around the world have

gained successful experience, there has been a distincttrend toward the application of PJFFs to larger units.

In the United States, PJFFs have been used primarily forsmaller industrial boilers as opposed to the reverse-gasfabric filters more conventionally applied to utility boilers.Virtually all the PJFF installations in Japan are on rela-tively small industrial boilers, with the largest treating255,000 acfm (120 m3/s). By comparison, in Canada,Europe and Australia, PJFFs have seen a wider applicationto small industrial as well as larger-sized utility boilers.

For example, retrofits of PJFFs in operation on the350-MW Munmprah Station Units 3 and 4 in Australia areeach rated to handle 1.02 Macfm (481 m3/s). The retrofitscurrently procured for the four 500-MW units at the LiddellStation of the Electricity Commission of New South Wales(ECNSW) are becoming the largest PJFF installations inthe world, with each unit treating 1.8 Macfm (850 m3/s).The first of these units is currently in operation.4 InEurope, it is common to see PJFFs, both as retrofits andnew installations, designed to treat flue gas volumes rang-ing from 730 kacfm to 1.15 Macfm (345 to 543 m3/s).

The largest PJFF installation on a PC-fired utility boileron the North American continent was started up in 1979 onthe 150-MW unit of the Milner Station of Alberta PowerLimited in Canada. This unit remained for many years thelargest boiler PJFF installation in the world until rivaled bylarger installations in Europe and the retrofits at theMunmorah Station in Australia. Another installation byFlakt Canada was on Unit #1 of the Wabamun Station ofTransAlta Utilities Corporation. The retrofit on this 70-MW, PC-fired unit started up in 1983.

Due to success of reverse-gas baghouses on utility boilers,the utility industry in the United States has become quitecomfortable with the reverse-gas technology for applicationto coal-fired boilers. Although pulse-jet technology hasexisted, it has not been applied to U.S. utility boilersbecause of concerns regarding the mechanical complexity ofPJFFs and thus the potential for excessive maintenancerequirements. Further, data were not available to confirmthat these units could deliver the bag life and emissioncontrol levels needed by utility companies.

Today, PJFFs are competitive with more-conventionalreverse-gas and shake-and-deflate baghouses due to ad-vances in bag cleaning technology, and the availability ofimproved filter bag designs and materials. However, withthe exception of three quite small and atypical installationson utility boilers, the bulk of PJFF installations in theUnited States has been on industrial boilers. The tendencystill is for these installations to be small; the PJFFstypically handling 200,000 acfm (94 m3/s) or less. Thelargest installation treats the combined exhausts of 772,000acfm (364 m3/s) from five stoker- and pulverized-coal-firedboilers.1

The Trend Toward More Conservative Air-to-Cloth Ratios

An early perceived benefit of pulse-jet collectors, due totheir higher energy cleaning method, was the use ofexceptionally high air-to-cloth ratios of from 5 to 7 ft/min(0.025 to 0.036 m/s). Since the first boiler PJFFs, there hasbeen a trend towards operating at lower air-to-clpth ratiosto ensure reasonable pressure drops, less frequent cleaningand thus longer bag lives and lower outlet emissions.

Figure 2 is a plot of design, gross air-to-cloth ratio versusstartup date for the population of PJFF sites visited; anddemonstrates the apparent trend towards lower air-to-clothratios. In general, the higher air-to-cloth ratios still beinginstalled as of late involve applications of felt in Europe.The general trend for a conservative design is towardsair-to-cloth ratios of about 4 ft/min (0.02 m/s) for feltedbags, and lower for woven fiberglass applications.

However, factors other than the type of fabric must also

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be considered when selecting an air-to-cloth ratio. Thesefactors include: the type of fuel and firing method and theresultant ash properties; the duty cycle of the boiler andPJFF; the inlet ash loading; the cleaning method; and theinteraction of these factors and others with the selectedfabric.

Design and O&M Issues

Pulse-jet cleaning methods have evolved into three basictypes that can be generally characterized in terms of thepressure and volume of the pulse air used.5 These methodsare high-pressure/low-volume (HP/LV), intermediate pres-sure and volume (IP/IV) and low-pressure/high-volume(LP/HV) pulsing. The range of pulse air pressures requiredby each method are summarized in Table I.

The original PJFF design used the HP/LV cleaningmethod; and traditionally, pulse-jet applications in theUnited States have been primarily of the HP/LV type. Bycontrast, in Canada, Australia and Europe, the predomi-nant cleaning modes on larger boilers have been the IP/IVand LP/HV designs.

Bag Length. PJFF installations on utility boilers benefitfrom the use of long filter bags since longer bags meanfewer bags to provide the same air-to-cloth ratio. Fewerbags require less plan area and fewer parts such as cages,pulse pipes, diaphragm and solenoid valves and bags thatrequire placement.

It is possible to use filter bags that are 20 ft (6.1 m) orlonger to minimize plan area requirements for retrofits intoconstricted sites. Filter bags up to 20 ft in length have beensuccessfully used in properly designed low- and high-pressure PJFFs, while bags up to 26 ft (8.0-m) have provedthemselves in intermediate-pressure units. The successfulretrofit of 24-ft bags at the Munmorah Station and pilottesting of 26-ft (8.0-m) bags have given the ECNSWconfidence to retrofit an IP/IV type PJFF with 26-ft-longbags on four 500-MW units at the Liddell Station.4 The firstof these Liddell units is currently in operation.

This suggests that all three cleaning methods couldoperate with filter bags up to 20-ft (6.1-m) long or evenlonger. However, in contemplating the installation of aPJFF that uses bags with lengths between 16 to 20 feet (4.9to 6.1 m) and longer, one should ensure that the biddershave current field experience and/or extensive pilot investi-gations to prove the applicability of their cleaning methodsto long bags with the type of fabrics anticipated andtreating dust of similar properties and difficulty.

Reliability Concerns. Potential PJFF users have beenconcerned that there will be increased operation and main-tenance problems and costs due to short bag lives andincreased number of components such as solenoids, dia-phragm valves and cages. To the contrary, few installationswe visited reported any problems with baghouse compo-nents. However, this survey demonstrates that design,fabrication and construction details cannot be ignored ifperformance and long component and bag life are to beensured. Poor gas flow distribution into compartments,high velocities between bags, misaligned and poorly madepulse pipes, cheap construction materials and components,misapplication of fabrics and poor startup and shutdownprocedures are factors that have contributed to excessivecomponent failure, pressure drop, outlet emissions and bagreplacement rates in the few installations that reportedsuch problems.

Fabrics

The types of fabrics, their durabilities and their qualitieshave evolved considerably since the first PJFF was installedon an industrial process in the mid-1950s. This evolutionhas differed markedly among countries, due largely to

o

1• 0.02 m/s

•

• • Felt

O Woven Glass

• • f

• o •

-

1974 1976 1978 1980 1982 1984 1986 1988 1990 1992

Year of Start Up

Figure 2. Design air-to-cloth ratio vs year of start up.

differences in startup dates and process or environmentalrequirements. In the United States, the most commonfabric has been woven fiberglass, which has operatingtemperature limits of about 500°F (260°C). There is arecent trend toward the use of either needle felts orpolytetrafluoroethylene (PTFE) membranes (such asGORE-TEX) on woven glass. These materials are favored inCFBC applications, where woven glass bags have performedinadequately, or in new installations, where very stringentemission limitations have dictated the use of media that aremore efficient than conventional woven glass.

Experience in Canada, Australia and Europe has beenprimarily with various felted fabrics. Homopolymer acrylic(Dralon T) has proved to be a very good fabric for peaktemperatures of less than 284°F (140°C) such as down-stream of spray dryers or with boilers firing low sulfur coaland which use air tempering systems or other techniques toavoid high temperature excursions. Felts that are made ofpolyphenylene sulfide (PPS or Ryton) and aramid (Nomex)fibers are operated at temperatures of less than 400°F(204°C). Glass (Huyglas), polyimide (P84), and Teflon feltscan operate at somewhat higher temperatures, perhaps upto500°F(260°C).

Woven Fiberglass Versus Synthetic Felts. Recently in theUnited States, and paralleling the success of felts in othercountries, more PJFF installations are using syntheticfelts. However, for early applications of PJFFs in theUnited States, fiberglass was the only material of reason-able cost that could withstand flue gas conditions. This, inconjunction with the favorable experience gained withwoven fiberglass in reverse-gas installations, prompted anevolution in the U.S. toward woven fiberglass PJFF bags,primarily in HP/LV units. Woven fiberglass fabrics wereappealing due to their ability to withstand gas tempera-tures of up to 500°F (260°C) and to be more forgiving ofupset temperatures for larger boilers employing regenera-tive-type air heaters. Some early attempts at using the fewfelts available at the time in the U.S. resulted in prematurefailures of the bags. Since these early PC applications, bagsmade of Huyglas, Teflon and Ryton felts have been usedwith varying degrees of success in a range of coal-firedboiler applications. More recently, the use of PJFFs down-stream of spray dryers and FBCs has provided moreopportunities to apply felts made of Nomex and Dralon T.

This study indicates that by observing proper design and

Table I. Ranges of pulse pressure vs. cleaning method.

Cleaning Method

HP/LVIP/IVLP/HV

Typical Pulse Pressure

psig

40 to 10015 to 307.5 to 10

bar

2.8 to 6.91.0 to 2.10.5 to 0.7

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construction tolerances, woven fiberglass bags can workand provide reasonable bag lives and pressure drops whilestill maintaining very low outlet emissions comparable withthose achieved by felts. However, fiberglass is less forgivingthan synthetic felts and care must be taken in ensuringproper bag and cage fit and in installing the filter bags. Also,fiberglass bags are more susceptible to abrasion and relateddesign and construction problems that may exacerbateabrasion such as pulse pipe misalignment, flue gas maldis-tribution and hopper dust removal problems. Off-line clean-ing, in which compartments are isolated from the flue gasstream for cleaning, was developed in part to accommodatethe more fragile woven fiberglass fabric.

There are two basic types of woven fiberglass in use inboiler PJFFs. The conventional double-warp face 16 oz/yd2

(540 g/m2) woven fiberglass fabric is not a particularlysuitable fabric for a facility that must consistently achieveNew Source Performance Standards or lower. On the otherhand, bags that are made of fiberglass cloth of 22 oz/yd2

(750 g/m2) or heavier and properly woven in the conven-tional double filling-face weave are quite capable of achiev-ing lower emission levels comparable to levels from syn-thetic felts. However, the heavier weight fiberglass tends toexhibit lower operating permeabilities than felts; and thus,higher pressure drops for a given air-to-cloth ratio can beexpected. Thus, PJFFs using woven glass should be sizedmore conservatively and operated at lower air-to-clothratios than those using felts.

Comments from some sites suggest that quality controlproblems in felting and in bag manufacturing in NorthAmerica have sometimes resulted in disappointing perfor-mance of felted bags. This points, at a minimum, to a needfor increased efforts at specification and quality controlduring the bag and felt fabrication process.

Retrofit of PJFFs into ESP Casings. Recent Clean Air ActAmendments make many existing ESPs undersized asutilities contemplate coal switching and using dry sulfuroxide control technologies. PJFFs have been retrofitted intoexisting ESP casings in utility boilers abroad and onindustrial process applications in the United States. Ingeneral, these retrofits have performed quite well. Suchretrofits are a viable option for reducing particulate emis-sions where sufficient precipitator plan area is available.The first utility applications of PJFFs involved retrofitsinto existing electrostatic precipitator (ESP) casings inAustralia. These PJFFs were retrofitted due to limitedspace in which to install new baghouses. Today, retrofitsinto ESP casings of two 350-MW units of the ECNSW'sMunmorah Station are operating successfully. Similar ret-rofits into ESP casings of four 500-MW units at theECNSW's Liddell Station are being installed; the first unithas started up. Also, unique retrofits into ESP casings inEurope demonstrate the viability of such an option toupgrade particulate control on this continent.

Performance

This survey involved visits to gather operating, mainte-nance and performance data at 36 sites representing 71separate boiler/baghouse units, including concurrent andhistorical information regarding outlet emissions, pressuredrop and bag life experience. The data are summarized inTable II. The information is grouped by boiler type andPJFF cleaning method. The major findings of this surveywith respect to PJFF performance are summarized below.

Pressure Drop

Consistent with previous literature, this survey confirmsthat pressure drop characteristics of well-designed andwell-built PJFFs are reasonable and in general lower thanexhibited by conventional reverse-gas baghouses operating

at equivalent air-to-cloth ratios. Figure 3 is a plot offlange-to-flange pressure drop versus operating air-to-clothratio for all data gathered during the site visits to PJFFinstallations on pulverized coal- (PC) and stoker-fired boil-ers. The air-to-cloth ratios are based on the cloth area inservice and on actual flue gas volumes observed at the timeof the visit. In most cases, the observed flue gas volumeswere calculated stoichiometrically based on boiler operatingparameters and flue gas conditions at the time of the visit.

Superimposed on Figure 3 are distinct data values and ashaded area that represent the range of pressure dropversus air-to-cloth ratio for shake-and-deflate (S/D) andreverse-gas-with-sonic-assist (RG/S) baghouses on utilityboilers.6 Figure 3 indicates that for a given air-to-clothratio, flange-to-flange pressure drops are lower for PJFFinstallations on PC-fired boilers than for RG/S and S/Dapplications. This enables PJFFs to be sized and operatedat higher air-to-cloth ratios than RG/S and S/D baghouses.

The scatter in Figure 3 is due mostly to the wide varietyof coal types, fabrics, inlet loadings, ash characteristics andoperation history of the bags. Also, the mechanical lossesover and above the pressure drop across the tubesheet canvary significantly from one design to another. The nature ofthe pulse-jet cleaning cycle is such that it also can affect thepressure drop of a PJFF depending upon how the cycle isinitiated and its timing and sequencing. Overall, the relation-ship between flange-to-flange pressure drop (AP) and air-to-cloth (A/C) ratio can be reasonably approximated for PCapplications by:

Flange-To-Flange AP = (1.7) x (A/C) ± 40% (1)

where air-to-cloth ratio is expressed in ft/min and pressuredrop is expressed in inches H2O.

Figure 4 is a plot of available tubesheet pressure dropinformation versus air-to-cloth ratio for PJFFs applied toPC- and stoker-fired boilers. The tubesheet pressure dropcan be approximated for PC applications by the relation-ship:

Tubesheet AP = (1.3) x (A/C) ± 50% (2)

where air-to-cloth ratio is expressed in ft/min and pressuredrop is expressed in inches H2O.

Effect of Boiler Type on Pressure Drop. Boiler type affectspressure drop performance of PJFFs. Note that the PJFFdata values plotted on Figures 3 and 4 represent both PC-and stoker-fired units. In general, the PJFFs on stoker-fired boilers visited in the survey operate at lower pressuredrops for a given air-to-cloth ratio than PC-fired applica-tions. This was expected since the fly ash particles gener-ated by stoker firing tend to be coarser and more irregularthan the ash produced by PC boilers.

Figure 5 shows flange-to-flange pressure drop versusair-to-cloth ratio for PJFFs applied to both circulating-fluidized-bed (CFBC) and bubbling-bed (AFBC) combus-tors. Figure 5 compares these FBC datapoints compiled bythis survey to data values for reverse-gas baghouses withand without sonic assist and shake-and-deflate baghousesapplied to FBCs as compiled by other EPRI-sponsoredwork.7'8 Also, equation 1 is plotted on Figure 5 to allow acomparison of PJFF performance on FBCs to PC-firedboilers.

Figure 5 suggests superior pressure drop performance byPJFFs when compared to conventional reverse-gas, reverse-gas with sonic assist, and shake-and-deflate fabric niters forFBC applications. These plots indicate surprisingly similarPJFF pressure drop performance for AFBCs and PC-firedboilers. However, average PJFF pressure drops for CFBCsare considerably higher than for PC-fired boilers (e.g.,about 2 in Wg or 0.5 kPa difference at an air-to-cloth ratio of4 ft/min).

In addition to boiler type, other upstream conditions can

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Table II. Pulse-jet baghouse performance data.

SiteNo.

6A6B917

20A20B20C20D212324252630235

10A10B10C10D10E323536A36B36C41A41B41C421

1B4

22

38A38B38C333443A43B1112131A

19A19B19C19D28143716

1829A29B31A31B3940

44A44B44C15

Start UpDate

19751975198319871983198319831983198619841987198219831985197919831988198319831983198319831986198619781979197919861986198619861979197919901980

19841984198419821982198719871983198319831981

19861986198619861984198519841988

19881988198919881988198819881986198619861989

DesignVolume(Kacfm)

32032019217896969613282

2056050488486053010171271271271271274632202972972977297297294923203201017180

19419419417817894941338989110

919191911465916156

203182182111111165165999999128

BoilerType

PCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPCPC

PC/WBPC/WBPC/WBStokerStokerStokerStokerStokerStokerStokerStoker

AFBCAFBCAFBCAFBCAFBCAFBCAFBCAFBC

CFBCCFBCCFBCCFBCCFBCCFBCCFBCCFBCCFBCCFBCCFBC

PrimaryCoals

ABABCMABEBEBEBEBEB

WB/EBEBEBEBEB

SAnWWBABABABABABABPB

PB/SABPB/BB/RBPB/BB/RBPB/BB/RB

PBPBPBPBr

WSBWSBAB

WB/EB

GB/PBGB/PBGB/PBRB/ABRB/ABAuBrAuBrABABAB

WSB

LWLWLWLWEBAB

GB/BrAB

WBEBEB

An/BrAn/BrGSBGSBECBECBECBAB

CoalSulfur

(%)

0.350.350.480.502.201.002.200.760.680.700.66

0.820.580.160.260.380.400.400.400.400.400.80

0.5-0.60.7-1.50.7-1.50.7-1.5

0.750.750.750.600.510.510.380.76

0.320.321.301.300.400.400.400.51

;*:W:W:-:!&&::S:;

1.191.191.191.193.110.90

1.2-3.20 3-0 4

0 634 284.280.840,84

8.008.008.00

Flue Gas/AshModifications

SCR:NH3DFSDA:LimeDFSDA:LimeDFSDA:Lime

DFSDA:Lime/2yrs PC

MCMC

MC

FSI:LS/FU I/ESPDFSDA:Lime

SCR-.NH3SCR:NH3SCR:NH3

FSI:LS/DSI:Na/SCR:U

AS I

ESP/RASDA Lime

FSI:Dolomite/CycFSI:Dolomite/Cyc

RASDA:LimeRASDA:Lime

LS/2ndary MCLS/2ndary MCLS/2ndary MCLS/2ndary MC

LSLS

LS/FARSand

LS/NH3/FARLSLSLSLSLSLSLSLSLSLS

PJFFCleaningMethod

HP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IVIP/IV

LP/HVLP/HVLP/HVLP/HV

IP/IVIP/IVIP/IV

HP/LVHP/LVHP/LVHP/LVIP/IVIP/IVIP/IV

LP/HV

HP/LVHP/LVHP/LVHP/LVHP/LVIP/IVIP/IV

LP/HV

HP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVHP/LVLP/HV

Fabric

Dralon T FeltDralon T Felt

Ryton Felt27 oz WGGlass Felt22 oz WG

Nomex/Ryton FeltRyton Felt16 02 WG16ozWG22 oz WG16 oz WG22 oz WG16ozWGNomex FeltNomex Felt

Dralon T FeltTeflon FeltTeflon FeltTeflon FeltTeflon FeltTeflon FeltNomex Felt -Nomex FeltDralon T FeltDralon T FeltTeflon FeltNomex FeltTeflon FeltRyton FeltNomex FeltDaytex FeltDaytex Felt

Dralon T FeltDaytex/Ryton Felt

Polyester FeltTefaire FeltGlass Felt

Dralon T FeltDralon T FeltNomex FeltRyton FeltTeflon FeltTeflon FeltTeflon FeltRytonFelt

16 oz WGNomex FeltNomex FeltRyton Felt

16ozWG/G-TNomex FeltNomex FeltRyton Felt

22 oz WG22 oz WG22 oz WGRyton FeltRyton FellRyton FeltRyton FeltRyton FeltP84 Felt

16ozWGNomex Felt

DesignA/C

(ft/min)

6.746.743.713.844.004.004.005.523.663.833.703.422.503.236.446.093.944.463.353.353.353.355.535.156.696.696.695.445.444.775.235.565.563.355 30

4 884 884.884.924.922.762.764.334.334.335.73

,,.v.v,.™g,.,,.

3.163.163.164.522.823.572 973 603 153.154.594.593.943.943.543.543.543.12

O b s e r v e dA/C

(ft/min)

6.746.744.172.71

3.851.992.832.01

1.562.824.043.183.804.403.893.953.693.555.535.152.14

2.664.10

4.65

3 384.13

2.982.98

1.805.095.135.136.37

«x.x.K.:.x«*.>:

3.562.573.571.843 29

3 982 68

3.402.37

3.54

F-to-FAP TS AP(in Wg)

10.405.91

4.023.606.903.80

3.003.753.905.686.008.835.426.135.265.466.225.62

5.636.02

8.90

5 00

5.664.424.424.428.70

«««««««.:.:

4.504.805.602.41

9 414 65

6.586.02

7.00

(in Wg)

2.808.005.845.31

3.002.766.213.10

3.73

4.40

2.811.73

2 43

5 82

3.233.23

3.573.213.213.21

2.803.80

1.412 36

7 253 27

4.78

ParticulateEmissions(Lb/MBtu)

0.08080.0808

0.00800.08490.06360.0446

0.05340.0280

0.01700.02100.01590.10500.01800.0050

0.06950.19810.07350.12630.01620.00320.01060.01060.01270.02690.02690.02690.01800.02300.0230

0 0920

0 02410.02410.0062

0.00260.00200.00240.00240.0024

*x«.x.>:*TOx.x*x.:*

0.01280.01680.0185

0.00410.00950 0057

0 00640 00300.00070.01140.01890.0095

0.3200

InstalledBag Life(Years)

4.1

0.90.54

6.2

3.12.81.96.83.5

2.25

4.5

3.14.54.511

63

3.5

2 30.81.51.50.7

2.52.52.5

0.2

2.5

2 52.5

2.52.50.1

ServiceBag Life(Years)

2.3

0.90.54.36.7

3.22.01.75.43.8

2.1

0.80.82.4

6.33.1

2 4

1 90.81.11.10.5

0.2

2.5

2 32.1

0.1

Boiler Type: PC (Pulverized Coal); PC/WB (PC w/ Wet Bottom); AFBC ( Bubbling Fluidized Bed Combustor); CFBC (Circulating Fluidized Bed Combustor).Coal Type: WSB (Western Subbituminous); SAnW (Semi-Anthracite Waste); WB (Western Bituminous); AB (Australian Bituminous); CM (Coke Midlings); LW (Lignite Waste);

EB (Eastern Bituminous); An/Br (German Anthracite & Brown); PB (Polish Bituminous); SAB (South American Bituminous; Venezuelan & Columbian); BB (British Bituminous);RB (Russian Bituminous); GB/Br (German Bituminous & Brown); GSB (German Subbituminous); PBr (Polish Brown); AuBr (Austrian Brown); ECB (Eastern Canadian Bituminous).

Flue Gas/Ash Modifications (Upstream of PJFF): ASI (Alcohol & Sludge Incineration); MC (Mechanical Collector); LS (Limestone in FBC Bed or Injected Into Furnace);(Sand in FBC Bed); SCR:NH3 (Selective Catalytic DeNOX w/ Ammonia Injection); FAR ( PJFF Flyash Reinfection Into FBC); DFSDA:Lime (Dual Fluid Spray Dryer Absorber w/Lime sorbent); FSI:LS (Furnace Sorbent Injection of Limestone); FUI (Furnace Urea Injection for NOX Control); ESP (Electrostatic Precipitator); Cyc (Cyclone);RASDA (Rotary Atomizer Spray Dryer Absorber); DSI:Na (Duct Sorbent Injection of Sodium Bicarbonate); SCR:U (SCR DeNOX w/ Urea Injection).

PJFF Cleaning Method: LP/HV (Low Pressure/High Volume); IP/IV (Intermediate Pressure/Intermediate Volume); HP/LV (High Pressure/Low Volume).Fabric: 16 oz WG (16 oz/square yard Woven Fiberglass); 22 oz WG (22 oz/square yard Woven Fiberglass); G-T (Gore-Tex Membrane); Nomex/Ryton (Nomex and Ryton Felt Bags).F-to-FAP (Flange-to-Flange Pressure Drop); TSAP (Tubesheet Pressure Drop).Installed Bag Life: Time that bag set installed from time of startup to time of failure/changeout (See Text & Reference 2).Service Bag Life: Actual time that bag set exposed to flue gas from time of startup to time of failure/changeout normalized to 8064 hours of operation per year (See Text & Ref. 2).

affect particle properties and hence drag and operatingpressure drop. The site visits included several installationsthat combine SO2 removal with the PJFF; e.g., spray dryerabsorbers and duct and furnace sorbent injection. Theseunits tended to operate at lower pressure drops whencompared to PC-fired applications operating at equivalentair-to-cloth ratios. This suggests that units employingeither spray dryers or duct and furnace sorbent injection

should not in general be a problem for pulse-jet applica-tions.

Effect of Fabric on Pressure Drop. Fabric selection canaffect PJFF pressure drop. Figure 6 compares tubesheetpressure drop versus air-to-cloth ratio for PC and FBCPJFFs employing felted fabrics to those using conventionalwoven fiberglass in weights of 16 oz./yd2 (540 g/m3) and 22oz./yd2 (750 g/m3) or greater. This graph suggests that, for

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14

u10

QT Q

6 4c

-PJFFs I

•

A

•1.5 kPa

i1I

•«•

•

0.02 m/s. . . . i i . . . . i. .

• PC

O Stoker

H RG/S FF

• S/DFF

1 O

•

12

0 1 2 3 4 5 6 7Air-To-CIoth Ratio, ft/mln

Figure 3. Flange-to-flange pressure drop vs. air-to-cSoth ratiofor PJFFs on PC- and stoker-fired boilers compared to reverse-gas with sonic assist and shake-and-deflate baghouses on PCboilers.

a given air-to-cloth ratio, PJFFs using felted fabrics per-form at pressure drops that are 1 to 2 in Wg lower thanPJFFs using woven fiberglass bags. In other words, anair-to-cloth ratio of 4 ft/min (0.020 m/s) is adequate formany felted applications, whereas an air-to-cloth of 3ft/min (0.015 m/s) may be necessary for woven glass tooperate at the same pressure drop.

Particulate Emissions

Modern, well-built and properly maintained PJFFs usinga variety of fabrics are quite capable of meeting EPA's NewSource Performance Standards (NSPS) of 0.03 lb/106 Btu

14

12

10

o.E 8

JZ(00)•5 4

• PC

O Stoker

•1.5kPa

1

4

O

<

ft •

»

0.02 m/s

•

O

1 2 3 4 5 6Air-To-CIoth Ratio, ft/min

10

q

I 8

f 6CO

t 4

O#

PJFFs on CFBCs

PJFFs on AFBCs

RGFF on AFBC (Plant #1)

RG/S on AFBC (Plant #1)

•1.5 kPa *+

+

•

o

RGFF on AFBC (Plant #2)

S/DonCFBC(P!ant#3)

S/DonCFBC(Plant#4)

^ PJFFs on PC BoilersEquation 1

0.02 m/s

0.5 1 4.51.5 2 2.5 3 3.5Air-To-CIoth Ratio, ft/min

Figure 5. Flange-to-flange AP vs air-to-cloth ratio for various types of fabricfilter applied to fluidized bed combustors (Source of RGFF, RG/S, and S/Ddata: References 7 and 8).

(approximately 30 mg/Nm3). As shown on Figure 7, asignificant number of the sites surveyed reported emissionlevels of well below the NSPS and comparable to emissionlevels achieved by conventional low-ratio baghouses. Inspec-tion of the graph reveals that 75 percent of all the testresults are less than the NSPS and 35 percent of theavailable test results were less than 0.01 lb/106 Btu (approx-imately 10 mg/Nm3). Opacities were usually well below 5percent. Those units exhibiting emission levels in excess ofthe NSPS were older installations, early PJFF applicationsthat are not required to meet stringent emission regula-tions, and installations operating at high air-to-cloth ratiosand high cleaning frequencies.

The results presented in Figure 7 also have been sortedinto two fabric categories. The first category includes theconventional heavier weight (> 22 oz/yd2 or 750 g/m2)woven fiberglass bags and all needle felts except Teflon. Thesecond general category includes Teflon felt and conven-tional lightweight woven fiberglass of 16 oz/yd2 (540 g/m2).This second category was isolated from the rest since it wasfound to be more difficult to consistently achieve lowemission levels with these fabrics. The lower collectionefficiency of Teflon felts can probably be attributed to thelarge diameter Teflon fibers used. DuPont, the producer of

14

12

(3

0)

uE 8

| 6

(0

"^ 4

• PC, Felt

• PC, Woven Glass

O FBC,Felt

• FBC,Woven Glass

1.5 kPa 0

o

i •a

O

o D •

0.02 m/s

Figure 4. Tubesheet AP vs air-to-cloth ratio for PJFFs on PC-and stoker-fired boilers.

0 1 2 3 4 5 6 7Air-To-CIoth Ratio, ft/min

Figure 6. Effect of fabric on tubesheet pressure drop.

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Teflon fibers, is currently producing a finer fiber to enhancethe collection efficiency of the Teflon felt. All conventionallightweight woven fiberglass bags applied today are con-structed of double-warp face 16 oz/yd2 cloth. This clothdesign was observed to exhibit lower collection efficiencythan any other group of fabrics observed in this survey.

By contrast, the conventional, double-filling face wovenfiberglass bags of 22 oz/yd2 (750 g/m2) or greater are quitecapable of achieving lower emission levels. Test resultsfrom the installations using these conventional, double-filling face woven glass bags exhibited emission levelsconsistently less than 0.02 lb/106 Btu (approximately 20mg/Nm3).

No correlation of air-to-cloth ratio versus outlet emis-sions could be observed in the data taken as a whole;although specific case histories of individual installationsexhibited dramatic correlation between decreasing air-to-cloth ratios and decreasing emissions. Two such sites wererequired to provide additional cloth area by the installationof additional compartments to decrease emission levels tocomply with the prevailing standards.

Bag Life

The large number of different PJFF designs, filter mate-rials, operating conditions, and flue gas and ash characteris-tics makes assessment of bag life difficult based on the sitessurveyed. This difficulty is further compounded by differ-ences in interpreting what constitutes bag life at each sitesince bag replacement policies differ and not all sites replacebags only when they "fail." For example, several installa-tions observe scheduled maintenance outages and changeout sets of filter bags well before the end of their life, oftenprior to any bag failures, to avoid the necessity for shut-downs during the plant's baseloaded operation.

Defining bag failure is not a clear-cut task. The mostbasic definition of bag failure is that point at which a bagfails to perform adequately in terms of outlet emission orpressure drop requirements. However, a new installationwith stringent emission limitations will be less tolerant ofsmall pinhole leaks or bleedthrough and thus report shorterbag life than an older site enjoying relatively lax limitationsor reporting requirements. Also, a site with limited fancapacity will consider its bags to be blinded much soonerthan a plant equipped with over-sized fans.

The plant's load factor and duty cycle were found tosignificantly affect the interpretation of bag life. Some unitsoperate at low capacity factors and/ or in a seasonal mode asin the case of numerous district heating plants that werevisited in Europe. For such plants, a bag life reported in"years since installation" may be misleading. Yet, althoughthe actual in-service time of the bag is less than the totaltime since its installation, many of these installations mustendure tough duty cycles. This is because low capacityfactors often equate with cycling and peaking duty withnumerous startups and shutdowns and dewpoint excur-sions.

Therefore, two bag life definitions were developed tobracket the extremes of bag life reported and so that thedata could be interpreted consistently and in a way mostrelevant to a baseloaded generating station. Installed BagLife is defined as the time in years that a given set of filterbags was installed from the time of the bags' startup to thetime that the set of bags was removed, or through the dateof the site visit if the bags had not been removed. ServiceBag Life is defined as the actual hours that a set of bags wasin service (exposed to flue gas) divided by 8064 hours peryear operation to normalize data from cycling and peakingplants to a baseloaded operation. This definition tends toprovide a conservative bag life estimate since under theseconditions many of the P JFFs encounter severe duty nottypical of a baseloaded plant.

9 Teflon Felt* WovenGlass 9 16otfsqyd

I All Other Foils &•Woven Glass S>> 22

oz/sqyd

< 0.01 0.01 to 0.02 0.02 to 0.03 >0.03

Outlet Paniculate Emissions, Lb/106 BtuFigure 7. Mass emissions for all baghouses in survey.

Figures 8 and 9 depict Installed Bag Life and Service BagLife, respectively, sorted by fabric type. These figurescannot be used alone to assess bag life. Only preliminaryconclusions can be drawn from such limited data, and eachsite must be examined in detail to determine all relevantfactors affecting bag life for the specific site. For example, aPJFF installed with an exceptionally low air-to-cloth ratiowould likely achieve a much longer bag life than a "typical"installation due to the less frequent cleaning necessary.Design or fabrication inadequacies such as poor gas flowdistribution or misaligned pulse pipes can cause severe bagabrasion due to direct impingement of flue gas and ashresulting in atypically short bag life. Likewise, useful baglife information is not provided by filter bags that haveendured extraordinary upset conditions such as hopperfires or major boiler startup problems; and such sites havenot been included in Figures 8 and 9.

This survey suggests that in a properly designed and builtPJFF, for which the appropriate fabric was selected, onecan expect good felt bags to achieve as much as three yearslife or more. The methodology used in analyzing the baghistory for each site, to develop the following preliminaryassessment of potential bag life, is presented in detail inReference 2.

Ryton (sulfar) felt bags have demonstrated the ability toachieve a bag life of 3 to 4 years or more under many fluegas conditions. One installation surveyed had experienced a6 to 7 year life on its initial set of "Ryton" bags; however,these bags were actually made of Daytex, a heavyweight,composite felt consisting of Ryton fiber needled to a Rastex(PTFE) support fabric (scrim), which is more durable thanconventional 16 oz/yd2,100 percent Ryton felt. Many of theRyton bags which achieved outstanding bag life in earlierboiler PJFFs, in both the U.S. and Europe, containedRastex scrim. The widespread use of 100 percent Ryton felt(with a Ryton scrim) is a relatively recent development, andlong-term bag life data is only just becoming available.Ryton fiber is exceptionally resistant to acidic conditions;however, it is not chemically inert and is subject to degrada-tion by some combinations of flue gas conditions whichhave not yet been well defined.

Nomex (aramid) felt bags have also achieved a life of asmuch as 3 to 4 years downstream of FGD spray dryers orFBCs, provided the bags are not subjected to "upset"conditions. DuPont guidelines state that Nomex should notbe used if any two of the following three conditions areexceeded for any prolonged period during typical baghouseoperation: 325°F, 15 percent moisture by volume, or 350ppm SO2.9 Since Nomex fiber has inherently poor resis-tance to acid hydrolysis, it should not be used in conven-tional PC- or stoker-fired boilers that are burning fuelscontaining more than 0.3 percent sulfur, and care must beexercised not to permit Nomex bags to be exposed to

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Figure 8. Installed Bag Life—years installed since startup on

untreated or improperly treated flue gas in spray dryer orFBC baghouses.

Dralon T felt appears to be an inexpensive and effectivealternative; however, temperatures must be kept low (lessthan 260°F continuous) and cooling of the flue gas is usuallyrequired. The retrofit of Unit No. 4 at the MunmorahStation of the Electricity Commission of New South Waleshas used the same Dralon T felt bags since its startup inOctober of 1988 with only three bag failures. Bag testingprojects that these bags should substantially exceed theirguarantee of three years; despite numerous startups withoil firing and one excursion in which unburned oil wasdeposited directly on the bags.4

Teflon felt bags are highly durable due to the inherentchemical inertness of Teflon fiber. The length of"uninterrupted" service obtained with Teflon bags is fre-quently dependent on their tendency to "blind," whichresults in unacceptably high operating pressure drop or

outlet emissions or both. Due to their high cost, Teflon bagswhich have become blinded but remain physically sound aretypically removed and washed and reused multiple times(up to six times over an eleven-year period in one installa-tion surveyed). In an effort to improve the filtration perfor-mance and extend the length of service which can beattained with Teflon bags before it becomes necessary towash them, DuPont has developed Tefaire, a felt consistingof a blend of Teflon with fine glass fibers, and more recently,a finer, 3.4 denier Teflon fiber which has a 30 percentsmaller diameter than the 6.7 denier fiber previously used.The information obtained during the survey for other feltssuch as P84, Huyglas and Tefaire was insufficient to projectpotential bag life.

This survey suggests that 2-year bag lives or longer arepossible for conventional woven glass bags; provided thatthe fabric and bags are fabricated properly and that thePJFF incorporates conservative air-to-cloth ratios, properbag-to-cage fit and proper design details. Figures 8 and 9indicate that conventional woven glass bags lasted any-where from 1 to 5 years. The 22 oz/yd2 (750 g/m3) orheavier woven glass fabric appears to last somewhat longerthan the lighter weight 16 oz/yd2 (540 g/m3) fabric. Oneunit employing a 16 oz/yd2 (540 g/m3) woven glass with 3.8years of service bag life operated at an air-to-cloth ratio of3.2 ft/min (0.016 m/s). One 22 oz/yd2 (750 g/m3) wovenglass application with 5.4 years of service bag life used avery conservative air-to-cloth ratio of 2.2 ft/min (0.011m/s) and 40 wire cages compared to the 20 wire cagesnormally used for woven glass bags. However, the authorsare aware of installations that apparently have observedsuch proper design and construction details but wereunable to achieve reasonable bag lives with no firm evidenceas to why the bags failed prematurely. Anyone contemplat-ing the use of woven fiberglass bags should ensure that theOEMs under consideration have successful experience withthe cloth applied to similar boiler and flue gas conditions.

Synthetic felt bags are more forgiving of inadequacies inPJFF and bag design and construction and thus consis-tently exhibit longer bag lives than most woven glassinstallations. However, woven fiberglass bags can be pur-chased at a significantly lower cost than most synthetic feltbags. Thus, the tradeoff of bag life versus bag cost should beconsidered.

Figure 9. Sen/ice Bag Life—bag fife in equivalent years ofservice based on actual hours exposed to flue gas normalizedto 8064 hours/year operation.

Conclusions

This survey has verified that PJFFs have been appliedsuccessfully to coal-fired boilers worldwide and can be anattractive option for U.S. utility particulate control needs.Although once feared to present a maintenance headachefor large utility and industrial boiler applications, well-designed and well-built PJFF installations have provensuch concerns to be unfounded. To ensure adequate perfor-mance and long component life; design, fabrication andconstruction details cannot be ignored. Poor gas flowdistribution into compartments, high velocities betweenbags, misaligned and poorly made pulse pipes, cheap con-struction materials and components, misapplication offabrics and poor startup and shutdown procedures arefactors that have contributed to excessive component fail-ure, pressure drop, outlet emissions and bag replacementrates in the few installations that reported such problems.

For a given air-to-cloth ratio, pressure drops are lower forPJFFs than for reverse-gas-with-sonic-assist (RG/S) andshake-and-deflate (S/D) baghouses on all types of boilers.This enables PJFFs to be sized and operated at higherair-to-cloth ratios than RG/S and S/D baghouses. Oursurvey shows that an average flange-to-flange pressuredrop of 4 to 6 in Wg (1.0 to 1.5 kPa) can be expected for

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PJFFs using needle felts and operating at an air-to-clothratio of 4 ft/min (0.020 m/s).

Modern, well-built and properly maintained PJFFs usinga variety of fabrics are quite capable of meeting EPA's NewSource Performance Standards (NSPS) of 0.03 lb/106 Btu(approximately 30 mg/Nm3). A significant number of thesites surveyed reported emission levels of well below theNSPS and comparable to emission levels achieved byconventional low-ratio baghouses. To achieve today's morestringent emission requirements, generally more conserva-tive air-to-cloth ratios than applied in the past are required.Whereas, at one time, an air-to-cloth ratio of 5 to 7 fpm wasconsidered adequate for a PJFF, these days, air-to-clothratios approaching 4 fpm or less should be considered for anew installation using felted cloth. Lower air-to-cloth ratiosin the range of 3 fpm or lower should be considered forthose installations that plan to use woven fiberglass.

For a properly designed and built PJFF with the appropri-ate fabric selection, one can expect good felt bags to reachand exceed three years of life. Bags constructed of Teflonand Ryton felt were found to provide bag lives of 3 to 4 yearsor more for a variety of flue gas conditions. Provided thebags are not subjected simultaneously to high temperatureand acid/hydrolysis conditions, Nomex bags can providesimilar lives downstream of spray dryers or FBCs. Two-year bag lives or longer are possible for woven glass bagsconstructed of conventional double-filling face cloth of 22oz/yd2 (750 g/m2) or heavier; provided that the fabric andbags are fabricated properly and that the PJFF incorpo-rates conservative air-to-cloth ratios, proper bag-to-cage fitand proper design details. The conventional double-warpface 16 oz/yd2 (540 g/m2) woven fiberglass fabric is notparticularly suitable for a facility that must consistentlyachieve New Source Performance Standards or lower.

Acknowledgments

This report was prepared based on the findings of workfunded by the Electric Power Research Institute and theCanadian Electric Association under EPRI Contract RP1129-21.2

The authors heartily thank the Electricity Commission ofNew South Wales and the Queensland Electricity Commis-sion in Australia for their sharing of valuable expertise andtime. We thank Brian Thicke of Alberta Power for provid-ing invaluable information, suggestions and guidance. Wegratefully acknowledge the exceptional assistance providedby the following original equipment manufacturers whogenerously devoted time and resources to provide assis-tance in identifying and providing introductions to theappropriate people for seeking approvals for plant sitevisits, making contacts and even in arranging for some sitevisits:

Flakt AB Stockholm and their subsidiaries worldwideincluding: Flakt Australia, Flakt USA, Flakt IndustriSweden and Gadelius KK in Japanthe Howden companies worldwide including: JamesHowden Australia, Howden Environmental Systemsand their licensee in Japan, MitsubishiEnvironmental Elements CorporationWheelabrator Air Pollution Control and their licensee inJapan, Sinto DustcollectorLurgi GmbHBiihler Brothers, Ltd. and Biihler-MiagHeinrich Liihr, GmbH and Interel in the U.S.A.

Finally, we graciously thank the owners and operators ofthe plants that allowed site visits and their innovative plantoperating, maintenance and engineering personnel whocontributed considerable amounts of time, effort and exper-tise.

References

1. "Pulse-Jet Fabric Filters for Coal-Fired Utility and IndustrialBoilers," EPRI CS-5396s; Research Project 1129-8, Preparedby Southern Research Institute.

2. Belba, V. H.; Grubb, T. "Pulse-Jet Baghouses: User's Survey,"Electric Power Research Institute Report No. GS-7457 (EPRIRP 1129-21), August 1991.

3. Gregg, W. "Pulse-Jet Dust Collectors for Utility Boiler Emis-sion Control," presented at the Joint ASME/IEEE PowerGeneration Conference, Dallas, Texas, October 22-26,1989.

4. Robertson, C; Strangert, S. "Australian Experience with Pulse-Jet Filters on Large Utility Boilers," presented at The NinthSymposium on the Transfer and Utilization of ParticulateControl Technology, Williamsburg, Virginia, October 1991.

5. Mascord, K.; Strangert, S. "The Ascendency of the Pulse-JetFilter," presented at the Third CSIRO Conference on GasCleaning, August 1988.

6. Cushing, K. M.; Merritt, R.L.; Chang, R.L. "Operating historyand current status of fabric filters jn the utility industry," J. AirWaste Manage. Assoc. 40:1051 (1990).

7. Cushing, K. M.; Bush, P. V.; Snyder, T. R. "Fabric FilterTesting at the TVA Atmospheric Fluidized-Bed Combustion(AFBC) Pilot Plant," Electric Power Research Institute ReportNo. CS-5837,1988.

8. Cushing, K. M.; Belba, V.H.; Chang R.L.; Boyd, T.J. "FabricFiltration Downstream from Fluidized Bed Combustion Boilers,"presented at The Ninth Symposium on the Transfer andUtilization of Particulate Control Technology, Williamsburg,Virginia, October 1991.

9. Personal communication by Theron Grubb with Dr. Herman H.ForstenofDuPont.

V.H. Belba, P.E. is a consultant, 4758 Edison Lane,Boulder, CO 80301. W.T. Grubb is president, Grubb Filtra-tion Testing Services, Inc., P.O. Box 1156, Delran, NJ08075. R. Chang is a project manager, Electric PowerResearch Institute, 3412 Hillview Avenue, Palo Alto, CA94303.

CONTROL TECHNOLOGYNEWS

U.S. DOC Organizes EnvironmentalTrade Mission to Eastern Europe

The U.S. Department of Commerce is organizing anEnvironmental Technologies Trade and Investment Mis-sion to Poland, Romania, and Bulgaria, March 10-21,1992.

The mission will cover air, water, and soil pollution abate-ment, waste water and hazardous waste treatment, energyrecovery, and monitoring/measuring technologies.

The mission will provide contact with Ministries of theEnvironment, Privatization, and Industry. Participatingcompanies will also meet with industrial concerns. Commer-

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