chemical processing nov-10

8/8/2019 Chemical Processing Nov-10

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N o v e m b e r 2 0 1 0

Treat Tanks with Care Understand the Shocking Truth Consider Dynamic Simulation orSteam System Design Refnery Pumps Up Energy Savings

The number o openings is reboundingin both the U.S. and Western Europe

Better times Beckon forcontract engineers


2/44

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4/44

B E

N O M

E

X R E A D

Y .

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5/44 5 chemicalprocessing.com november 2010

N v b 2010 | v u 73, Issu 11

contents

252116

Chemical Proce ing (IssN 0009-2630) i p li hed monthly y P tman edia Inc., 555 We t Pierce oad, s ite 301, Ita ca, I 60143. Phone (630) 467-1300. Fax (630) 467-1109. Periodical po tage paid at Ita ca,I , and additional mailing of ce . P sT AsT : send addre change to Chemical Proce ing, P. . box 3434, North rook, I 60065-3434. subsC IPTI Ns: Q ali ed reader cription are accepted fromoperating management in the chemical proce ing ind trie at no charge. To apply for a q ali ed cription, ll in the cription card. To nonq ali ed cri er in the united state , cription are $68per year. single copie are $14. Canadian and foreign ann al cription are accepted at $115 rface per year. single copie are $16. Canada Po t International P lication ail Prod ct sale Agreement No.40028661. Canadian ail Di tri tor informat ion: Frontier/bWI, P box 1051, Fort rie, ntario, Canada, 2A 5N8. Copyright 2010 P tman edia Inc. All right re er ed. The conten t of thi p lication may not

e reprod ced in whole or in part witho t the con ent of the copyright owner. P INTs: eprint are a aila le on a c tom a i . For price q otation, contact Fo ter eprint , (866) 879-9144, www.fo tereprint .com al o p li he Control, Control De ign, Food Proce ing, Pharmace tical an fact ring and Plant ser ice . Chemical Proce ing a me no re pon i ility for alidity of claim in item reported.

columns7 From the Editor: Dont Slight the Simple

Stu .

9 Chemical Processing Online: KeepCommunication Lines Open.

10 Field Notes: Keep Con ned Space Work Safe.

14 Energy Saver: Train Plant Managers onEnergy E ciency.

15 Compliance Advisor: New IUR Report-ing Heads Our Way.

36 Plant InSites: Dont Err with Air-FinExchangers.

42 End Point: Chemical Processes MakeFashion Statement.

departments

11 In Process: Nanocatalyst Gains GreaterReactivity | Light Simpli es Synthesis

34 Process Puzzler: Deal with a Decanter

that Cant.

38 Equipment & Services

39 Product Spotlight/Classifeds

41 Ad Index

cover story16 Better Times Beckon or Contract Engineers

e number of openings is rebounding in both the U.S. and Western Europe. However, much of the work focuses on rela-tively short term assignments.

Features

D sI N AND PTI IzATI N

21 Consider Dynamic Simulation or Steam SystemDesignModels can provide crucial insights for dealing with upsets andtransient conditions. Here are some pointers for steam systemdesign and tips for staying out of hot water.

AINT NANC AND P ATI Ns

25 Understand the Shocking TruthDissipating static electricity is crucial for avoiding ignition risksin hazardous areas. is demands a rigorous approach to plant,process and personnel safety.

s IDs AND F uIDs HAND IN

29 Treat Tanks with CareA variety of easily avoided problems can cause vessel failure. Yet,

many people who design, construct, operate and maintain low-pressure storage tanks dont appreciate how frail they are.

A IN IT W

33 Refnery Pumps Up Energy SavingsReplacing an old electrical pump with a new one with appropri-ate safety classi cation would be expensive. So, the plant optedfor a steam-driven pump to enhance condensate return.


6/44

You have the choice, we have the options. Let Siemens show youhow to fully protect the investment in your current APACS+ system.

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Answers for industry.

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7/447 chemicalproc essing.com november 2010

From The eDiTor

Articles clearly

point up the

hazards and how

to address them.

Ma y a s now boast markedly better per or-

mance and reliability than they were able to achieve inthe past. A major reason or such gains has been increas-ing reliance on sophisticated equipment and so twarethat have become available thanks to the continuingevolution o technology.

O course, many actors contribute to improvementsin equipment efciency and durability includingadvances in materials, the ability to make more preciseparts, and greater condition-monitoring capabilities.Such developments underpin the technical and eco-nomic viability o producing more complex but betterper orming devices.

Meanwhile, developments in so tware, spurredby the availability and a ordability o more power ulcomputers, are trans orming how we design and operateunits. For instance, check out what simulation now o ers in Consider Dynamic Simulation or SteamSystem Design, p. 21, online at www.ChemicalProcess-ing.com/articles/2010/186.html and Consider DiscreteEvent Simulation, www.ChemicalProcessing.com/articles/2010/178.html.

Likewise, todays process control so tware promisesa host o bene ts besides tighter control. For example,it provides a way to address the alarm overload thata icts many plants (Adroitly Manage Alarms, www.ChemicalProcessing.com/articles/2009/074.html).

Another but o ten-overlooked opportunity is to use thecontrol system to improve overall operational e ective-ness (Consider State-Based Control, www.Chemical-Processing.com/articles/2010/051.html).

Further gains in plant per ormance are inevitable,as sites increasingly adopt digital eldbuses (see Take

Advantage o Fieldbus, www.ChemicalProcessing.com/articles/2010/149.html) and wireless technology (Whither Wireless, www.ChemicalProcessing.com/

articles/2009/112.html).eres no question that emerging developmentsare attracting signi cant interest at sites because o theirbene ts. However, we mustnt let the increasing ocus onsophisticated equipment and systems cause us to ignoreless exciting plant assets like tanks and piping. Twoarticles in this issue make convincing cases or payingadequate attention to such mundane items.

Treat Tanks with Care, p. 29, online at www.ChemicalProcessing.com/articles/2010/191.html, pointsout some common problems, e.g., over lling, and over-pressure or under-pressure, that have led to tanks being

reduced to scrap or even more severe consequences. e

article stresses that its easy to avoid such dangers and

o ers a number o recommendations about tank layoutand design.

I that article isnt persuasive enough, read DontUnderestimate Over llings Risks, www.ChemicalPro-cessing.com/articles/2010/143.html, which recounts thatloss o level control in tanks contributed to three majorindustrial catastrophes. It outlines seven simple steps toavoid dangers.

Another hazard that can occur with tanks andcommon plant hardware is spark generation due to thebuildup o static electricity. Understand the Shock-ing Truth, p. 25, www.ChemicalProcessing.com/articles/2010/192.html, warns that the absence o a goodpath to ground may result in the buildup o electrostaticcharges on mundane items like metal anges, ttings,valves and vessels that can lead to res and explosions.Here, too, some simple steps can avoid risks.

O course, tank ailures and static-electricity-causedres have a icted plants since the earliest days o the

industry. Sa ety guru Trevor Kletz notes in BhopalLeaves a Lasting Legacy, www.ChemicalProcessing.com/articles/2009/238.html, that the same mistakesun ortunately recur regularly: Chemical makers inves-tigate and report on accidents and make changes butthen le away and soon orget the reports. Moreover,they dont always share them with other rms.

Some companies are conscientiously trying toimprove their institutional memory (Companies KeepKnow-how in Place, www.ChemicalProcessing.com/articles/2009/114.html). Sophisticated technology undoubtedly can play an important role in capturingknowledge about plant equipment and operations. Itsparticularly valuable or documenting subtle issuesuncovered over the years by veteran sta now leaving a

rm.

eres no excuse, however, or not appreciatingright now and acting against the common risksposed by tanks and other run-o -the-mill equipment.

eyve been well documented or ages. Articles such asthe two in this issue clearly point up the hazards as wellas how to address them.

Mark r s zw , Editor in Chie

[email protected]

Dont slight the simple stuff Vessels and other mundane assets can pose signifcant risks


8/44

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chemical processing online

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E-mail: [email protected]/Customer Service:(888) 644-1803 or (847) 559-7360

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ndrew S o ey, Troubleshooting Columnist

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Vic Edwards, Aker Solutionstim frank, Dow Chemical

ben Pa erson, Eli Lillyoy Sanders, Consultant

E en turner, Eastman Chemicalben Weins ein, Procter & Gamble

Jon Wors e ,ConsultantShei a Yang, Bayer

M St t VE St ff

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ose Sou hard, IT Directorrry C ark, Vice President of Circulation

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EP tS

Ka e ha , eprin Marke ing Manager ji k@ os erprin ing.com866-879-9144 ex . 168

fax 219-561-20334295 S. hio S ree ,

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way with e-newsletters.Chemical Process-ing sends out its e-newsletters on a regularschedule. I youre not receiving them asyou should, help is on the way.

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10/44November 2010 chemicalpr ocessiNg.com 10

field Notes

K C n n S c W k S fRigorous attention to detail is essential to minimize risks and enhance response

The operaTor was frantic as he choked

down hot acid fumes. He had sat through a sternlecture on the need for a gas mask but apparently thought Real men dont need em. In desperationhe grabbed for others masks; my crew was splitbetween rescuing him and slamming the boom back into the roaster.

My operator learned a hard lesson; he was lucky.Some chemicals are less obnoxious and even moredeadly. Lets consider how you should approach acon ned space entry job the next time one comes up.

First, understand what constitutes a con nedspace. Worldwide standards uniformly agree that it:1) is totally or partially enclosed; 2) isnt normally occupied; 3) has limited egress; and 4)could containa hazard. And thats the rub. Assessing the actualrisk is a challenge. Another dilemma is de ninga space where one or more walls are open. Gener-ally, this is best left to continuous measurement: if oxygen level is below 19.5% or above 23.5%, or ahazardous chemical isever present, its a con nedspace. Some people say to ignore a periodic dangerbut I disagree. In much of the world plants arerequired to compile a con ned space registry thatincludes: the danger, with material safety data sheet(MSDS) references; the personal protection gear(PPG) required; and a rescue plan. Tis registry usually is available to the local re marshal.

Now, lets consider what documents youll needbefore conducting con ned space work: 1) the PPGlist; 2) a roster of equipment needed for the work; 3)the MSDSs; 4) a detailed l ist of monitoring equip-ment along with their calibration requirements; 5)an escape plan; 6) the location of emergency equip-ment and vehicles and their entry plan; 7) lightingrequirements; 8) shift rotation plans and break

schedules; 9) a liaison blueprint for keeping opera-tions and others informed; 10) a communicationplan with multiple alternatives; and 11) the Per-mit to Work (P W) and the preceding Job Safety

Analysis ( JSA), hot work permits, etc. Obviously,permits will take days, maybe weeks, to completethe rst time.

With a green light on the permit, youll want toschedule the work with production. By the time the

work is ready to begin things may have changed. So, walk down the con ned space area to ensure thereare no con icts with other work or production.

Ten youre ready to start.

wo people the sentry and work leader

must be chosen carefully for any con ned space work. Of the two, the sentry must be the mostexperienced. You need someone with the wisdomto realize safety comes from teamwork not anindividual act of heroism, and who can watch oth-ers work without becoming bored or distracted. Iam reminded of the death of the contract foremanin the nitrogen asphyxiation accident at ValerosDelaware plant in November 2005. Dont go intoa con ned space without proper PPG! o be e ec-tive, a sentry must: 1) be aware of the area, equip-ment and other work going on; 2) know how to userescue equipment, including harnesses and lifts,as well as environment monitors and be physi-cally able to operate the lift; 3) know directionsto the site for emergency responders; 4) have spareradios and batteries; 5) understand the work beingdone; and 6) be a stickler for procedures. Tis nalpoint is crucial because the sentry should inspectPPG for each person entering the space usu-ally wearing a harness is mandatory and test a ll

work equipment and communications gear priorto space entry and in the space before work begins.Once work is underway the sentrys job settles intorecordkeeping who enters and leaves the spaceand the environmental conditions in the space.Under no circumstance should the sentry enter thespace, including breaking the plane isolating it. Insome cases, this plane extends outward from theentry. Te job foreman is in charge of safety in thehole; the sentry is in charge of work outside andthe job itself.

Now, lets consider some special circumstances. Where heat stroke is a possibility, keep ice availableand exposure times short. Tis means rotating peo-

ple. If re is a possibility, a re blanket works bestbecause ue gases, including steam, resulting froma re could cause asphyxiation. Air tools are betterthan electr ic ones but make sure theyre driven by breathable air, not nitrogen. Protect ears in con nedspaces where sound dissipation isnt possible.

As chemical engineers, it is our responsibility, asthe best educated and most knowledgeable people ina chemical facility or re nery, to look after others.Lets do our duty.

dirK Willard , Contributing Editor

[email protected]

Choose the

sentry and the

work leader very

carefully.



in process

P d right sur ace coverage o sub-

nanometer clusters o tungsten oxide on a zirconiumoxide support (Figure 1) makes the catalyst fve timesmore reactive or n-pentane isomerization, reports aninternational group o researchers. And the strategy promises to bolster a variety o other acidic reactions,says Michael Wong, a pro essor at Rice University,Houston, a part o the team.

Refneries certainly stand to gain rom moree cient production o isopentane, which is used ingasoline. We have a way to make a better catalystthat will improve the uels they make right now,says Wong. At the same time, a lot o existingchemical processes are waste ul in terms o solvents,precursors and energy. Improving a catalyst can alsomake the chemical process more environmentally

riendly.Te key is achieving the optimum sur ace cover-

age o the nanocatalyst on the support, notes Wong, whose team at Rice collaborated with researchers atLehigh University, Greeces Centre or Research and

echnology Hellas, and the DCG Partnership o exas. Details appear in a recent paper in the Journal

of the American Chemical Society .Te greater reactivity or n-pentane isomerization

translates into a higher concentration o isopentaneand, at the same time, a lower concentration o by-products. Te benefts rom this double e ect (higherturnover rates and higher selectivity) are great and

we believe we can signifcantly reduce industrialseparation-unit costs i we can urther improve ourmaterial synthesis techniques, Wong notes.

He says that the catalyst ormula now is justright.

Recent studies show that a ter two catalyticcycles, overall activity remained practically the same,

adds Wong, a pro essor o chemical and biomolecu-lar engineering and o chemistry. We expect thecatalyst to have a longer li e due to the absence o chloride species (used in industrial isomerizationcatalysts) that eventually leach out causing seriousregeneration issues, he says.

Besides pentane isomerization, other chemicalreactions that might beneft rom the catalyst includeacidic reactions such a para n, olefn and aromaticcompound isomerization, dehydration o para nsto olefns, esterifcation reactions, hydrolysis andmetathesis.

Tese are reactions o great importance or

the petrochemical industry,

especially in uel enrichmenttechnologies. We are startingto investigate metathesis in ourlab, because we think that other

orms o the sur ace tungstencan be good or this reaction,says Wong.

Wong and his team are alsoinvestigating optimization o the sur ace coverage o othercatalytic nanomaterials thatare used on supports. Wevestarted putting molybdenumoxide and vanadium oxide inplace o tungsten oxide using anew synthesis technique we aredeveloping, he says.

Producing the catalyst on a large scale shouldbe straight orward, notes Wong. Lab samples weremade using conventional dry impregnation themost common method used commercially. Industrial

anocatalyst ains reater eactivityAcidic reactions such as pentane isomerization or gasoline stand to beneft

Sept 09 Oct 09 Nov 09 Dec 09 Jan 10 Feb 10 Mar 10 Apr 10 May 10 June 10 July 10 Aug 10

$ M i l l i o n

79.0

78.0

77.0

76.0

75.0

74.0 %

Shipments (NAICS S325) Capacity utilization

52,000

80.0

53,000

54,000

55,000

56,000

57,000

58,000

81.0

82.0

59,000

60,000

73.0

72.071.0

70.0

69.0

68.051,000

50,000

61,000

67.0

66.0

conomic Snapshot

Both shipments and capacity utilization increased slightly.

Source: American Chemistry Council.

ungsten xi e Clusters

Figure 1. An atomic-level image o

tungsten oxide nanoparticles (greencircles) on zirconia support. Theother circles show the less-active

orms o tungsten oxide. Source:Wu Zhou/Lehigh University



iN process

rms already have expressed interest in cooperatingon further development.

Using the catalyst in existing reactors doesntrequire any major modi cations, he adds.

L gh S mpl f sSyn h s sULt vi Let (Uv) light provides a simpler, moreenvironmental friendly way to attach phosphorus toorganic compounds, report researchers at the Massa-chusetts Institute of Technology, Cambridge, Mass.

eir approach avoids the use of chlorine, whichcan pose health and safety risks, and produces anorganophosphorus compound in a single step.

e surprising thing about this work is that it was not discovered long ago. ere is nothing compli-cated about it, and the starting materials are readily available and needed only to be mixed together and ir-radiated with UV light, says Christopher Cummins,a chemistry professor at the school.

e elimination of chlorine would be a hugeadvantage for the industry, he notes. However,another intermediate in the phosphorus industry that

would be good to avoid is PH3, and our process may allow this as well to be circumvented.

He drew inspiration from a 1937 paper detail-ing that white phosphorus, also known as P4, couldbe broken into two P2 molecules with UV light. Hedecided to see what would happen if he broke apartP4 with UV light in the presence of organic molecules

that have an unsaturated carbon-carbon bond (1,3-di-enes). He and graduate student Daniel Tofan (Figure2) exposed the white phosphorus to UV light for 12hours and produced a tetra-organo diphosphane.

Its amazing to realize that nobody thoughtearlier about such a simple approach to incorporatephosphorus into organic molecules, notes Guy Bertrand, chemistry professor at the University of California, Riverside. Such a synthetic approach toorganophosphorus compounds is indeed urgent, sincethe old (chlorine-based) phosphorus chemistry has alot of undesirable consequences on our environment.

e new reaction cant produce industrial quanti-ties of compounds, says Bertrand, who was notinvolved in the research, but may prompt research thatcould lead to such prospects.

One near-term goal of Cummins ongoingresearch is probing the properties of the new organo-diphosphorus compounds as ligands for a range of

transition metals including nickel. e preliminary results suggest possible applications as building blocksfor supramolecular chemistry in addition to precursorsto new materials, he says.

Other goals include looking for other organicmolecules that may accept phosphorus under the samephotochemical conditions, and synthesizing a polymercontaining P-P bonds in its main chain and determin-ing its properties.

A key challenge, notes Cummins, is to improvecurrently low yields by optimizing reaction condi-tions. is will involve a careful study of the wave-

length dependence of the process.

12.1%No

63.6% Yes

3.0%Doesnt apply

21.2%Dont know

Responses (%)

Has your plan s d wh h r dus s n yourdus -coll c on sys m ar xplos ?

Most respondents say that their plants have tested theirdusts. To participate in this months poll, go to Chemical-Processing.com.

S ng h L gh

Figure 2. Graduate student Daniel Tofan stands next

to UV light apparatus. Source: MIT.


13/44



eNergY saver

Quick and con-

cise information

an help get your

lant manager on

board.

This is the last of four articles on energy training.

W v dy dealt with getting yourprocess specialist, operators and project managerto contribute to energy efficiency. Theres one lastperson you must get involved in the efforts your plant manager.

I went to dinner recently with a refinery man-ager of a large gulf coast complex. The conversa-tion ranged from safety issues, projects, person-nel, budgets, and an assortment of problems andopportunities. He was a busy man hundredsof things at the plant commanded his attention.However, I was mildly surprised when the conver-sation turned to energy. He knew exactly wherehis plant stood relative to the industry and wasmaking strides in reducing energy use. The plantefficiency has improved 3% versus last year, heboasted. I thought to myself, this is a well-trainedmanager.

To get maximum benefit from your energy program, you must present it in a way that cap-tures the plant managers attention while takinglittle or no time. Its important to present infor-mation that doesnt require the plant manager tosift through the data or try to decipher a bunchof raw numbers. Organizing the information in arepetitive fashion has benefits.

Th P T T M Th dI find the best presentation method is to set upa system of information. The system is meant togive the plant manager the right dose at the righttime.

Daily report:I would start first with the daily report your plant manager sees each morning.

This report, which usually includes everythingabout the plant, should contain two numbers thatsummarize overall consumption of energy. Thesenumbers must be something the manager is usedto looking at. The first is straight energy unitsin a certain time period (BTU/yr, Kcal/hr, MW,or kJ); the second is the relat ive number, basedon product, feed or whatever the most commonmethod you use (BTU/lb, MW/klb, etc.). Presentthese two numbers daily or weekly and display them with a reference number either the goalfor the plant or the budgeted amount.

Weekly progress report:Keep this to no more

than two paragraphs so the plant manager can

read it in less than 3 minutes. Follow energy consumption information with any explanation of

why the number is what it is. Then tel l the plantmanager what energy-related items happened thelast week and what should be expected next week.

Monthly progress report:Here, provide moredetail about individual systems and include moreinformation about projects, maintenance andenergy concerns. If you have an energy team, putin items from team meetings. The report shouldnever exceed one page. It doesnt have to break down each individual energy contributor butlarge groups (steam, electrical, furnace efficien-cies, etc.). The monthly report is a look back at

what was expected last month and what really happened. It also tells the plant manager whatto expect in the daily and weekly reports for thenext month.

Quarterly report:Hold a 60-to-90-minutemeeting with the plant manager and other key staff. Include presentations by the energy team onimplementations that took place during the quar-ter. Also mention any failures or setbacks, thereason they occurred, and how they will be fixed.Discuss new problems and pitch ideas for new projects. This is your chance to show any progressand get feedback. Use the meeting to discuss bud-get concerns and show that the energy team hasspent capital well. Dont throw quarterly meet-ings together at the last minute. It may take timeto compress material into less than 90 minutes. If you plan ahead, your report will be more conciseand will keep the attention of the audience.

Fiscal year report:Here, show the entire pro-grams accomplishments and outline how energy

projects will be implemented during the new fis-cal year. Include what you want to see in the nextbudget and your justification for that spending.Present problems that were found and resolved,projects that were implemented and whether they met expectations, and give individuals or teamstime to present what they did to save energy.

By improving the way you present informa-tion, you stand to make your plant manager abetter advocate for your energy program.

y f U , Energy Columnist

[email protected]

Train Plant Managers on nerg ciencPresent your energy program in a way the plant manager can quickly comprehend



compliance advisor

N w IUR R porting H ads Our WayProposed rule will signi cantly impact reporting functions

THe U.S. Environmental Protection Agency (EPA)

proposed important revisions to the Toxic SubstancesControl Act (TSCA) Inventory Update Rule (IUR).Chemical manu acturers and other stakeholders must beaware o the proposal and plannow or its implications.

BACKGROUNDe IUR requires manu acturers (including import-

ers) o certain chemicals listed on the TSCA Inven-tory to report site and manu acturing in ormation orchemicals produced in amounts o 25,000 lb or more ata site during a reporting year. Additional in ormationon domestic processing and use must be reported orchemicals produced in amounts o 300,000 lb or moreat a single site. e next reporting cycle will end Sep-tember 30, 2011, or chemicals manu actured in 2010.

EPA, states, and other entities have expressedconcern with the relative lack o chemical processing,use and exposure in ormation, which, they claim, hashampered regulators ability to assess risks o chemicals.Others question the utility o IUR data and the absenceo a uni orm IUR electronic reporting ormat. Publichealth and environmental activists claim that TSCAsin ormation gathering authorities are limited and proce-durally challenging to implement. Changes to the IUR are in response to these and other concerns.

KeY PROVISIONS TO PROPOSeD RULeReporting information to EPA Require use o electron-ic reporting so tware to submit all IUR in ormation;and must report i production volume o a chemicalsubstance met or exceeded the 25,000-lb threshold inany calendar year since the last principal reporting year.

Manufacturing-related information Requirereporting o certain manu acturing data, including:

whether an imported chemical is physically at the

reporting site; the volume o the chemical substanceexported and not domestically processed or used; whether a manu actured chemical, such as a byproduct,is being recycled, remanu actured, reprocessed, reusedor reworked; and reporting o production volume or allyears since the previous principal reporting year (2005).

Processing and use-related information Eliminatethe 300,000-lb threshold or processing-and-use in or-mation, require all reporters o non-excluded substancesto report; revise list o industrial unction categories orreporting processing-and-use in ormation and replacingthe fve-digit North American Industry Classifcation

System (NAICS) codes with 48 Industrial Sectors (IS);

revise consumer/commercial product categories or

reporting consumer-and-commercial-use in ormation;and require up ront substantiation or in ormationclaimed as confdential business in ormation (CBI).

CONCeRNS WITH THe PROPOSALFive proposed revisions are requently cited as troublingby covered industries.

First, byproduct reporting will be especially di -fcult. Most byproducts are mixtures and reportingcomponents by their unique Chemical Abstract Servicesregistration number isnt easible even i all components

were known, which they typically are not.Second, the deadline or 2011 IUR reporting is ast

approaching. EPA has stated its intent to issue a fnalrule in the spring. Because the reporting deadline is Sep-tember 30, 2011, there will be little time to implementreporting strategies and complete reports.

ird, EPAs proposal to require production volumein ormation rom 2006 through 2010 will be di cult tosatis y. It is likely many entities dont have the means tocollect this in ormation retroactively.

Fourth, lowering the processing-and-use in orma-tion threshold to 25,000 lb would be especially burden-some or reporters o inorganic substances, who werentrequired to submit processing or use in ormation duringthe last reporting cycle in 2006, as they were newly added to the IUR reporting scheme at that time.

Fi th, requiring up ront substantiation o CBIclaims will be challenging. Some believe this require-ment could adversely impact a commercial interestscompetitive standing.

CONCLUSIONe proposal is complicated, with important changes

too numerous to discuss here. Its issuance, even i modi-

fed, will signifcantly impact chemical manu acturers.Care ul review o the proposal now is essential, as there will be little time a ter the rule is issued to adapt report-ing strategies by the September 30, 2011, deadline.

LYNN BeRGeSON , Regulatory [email protected]

Lynn is managing director of Bergeson & Campbell, P.C., a Wash-

ington, D.C.-based law rm that concentrates on chemical industry

issues. The views expressed herein are solely those of the author.

This column is not intended to provide, nor should be construed

as, legal advice.

Deadline is fast

approaching and

manufacturers

will have little

time to adapt.


16/44N v 2010 c icalp c ssiNg.c 16

Data on shipments and capacity utilizationprovided by the American Chemistry Council, Ar-lington, Va., for CP s monthly Economic Snapshot(p. 11) clearly show that the U.S. chemical industry is faring better this year than last. is recovery isbolstering demand for contract engineers.

e market [for contract engineers] in the U.S.is certainly expanding, but this is relative to theeconomic downturn of 2009. e recession hit the

whole recruitment industry hard, so the baseline

from then was pretty rough, says Tim McAward, avice president at Kelly Engineering Resources, Troy,Mich., a rm that places engineers into contract andpermanent positions. Id say demand for contractengineers is now about the same as in 2008, which

was a very good year in terms of sta ng. 2009 was adisaster and it was good to turn over the calendar onthat. Much of the demand centers on three-to-fourmonth contracts that often focus on feasibility studies,

he adds.

The number of o en n rebound nn both the U.s. nd We tern uro e

y sen ttewe , d tor t l r e

Better times Beckon for

contract engineers


17/44


18/44


19/44


20/44

cycle, and the water industry, which is poised formajor investments in new plant and infrastructureacross Europe.

Opportunities in the pharmaceutical industry

depend on where you are based, he says. Our data-base lled almost overnight with contract engineersfrom Irelands pharma sector [following a Septem-ber announcement by Schering-Plough that itsseeking 160 redundancies at its plant in West Cork]but, on the other hand, pharmaceutical commis-sioning is steady in other E.U. [European Union]countries, especially Belgium, France, Germany,Switzerland and Holland.

He particularly cites Geel, Belgium, which isbecoming a hub for pharmaceutical production anddistribution in Europe. Johnson & Johnson, whichhas already invested hundreds of millions of eurosthere has just announced that Geel now will be itsdistribution center for 11 European countries and to

J&J a liates around the world.We pick up a lot of work in these E.U. countries

because they dont tend to have the skill sets they need. Overall, I think the future of commissioning is

mainly going to be on mainland Europe rather thanthe U.K.

Interestingly, Ballard has noted an increase in per-manent posts needing to be lled a sign that pursestrings are being loosened. Permanent recruitmentfroze when the credit crunch hit. However, since Aprilthis year it has been getting busier. Not so much withthe E&C companies but rather the manufacturersdirectly which makes me feel that they are about tostart going ahead with some of the proposals. In my experience, a rise in permanent recruitment is usually followed by an expansion or new project build.

Together, we can get off theuptime-downtimerollercoaster.

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M p plants consider steam as anindispensable means o delivering energy. A ter all, ito ers many per ormance advantages including low toxicity, ease o transportability, high latent heat and low cost o production. Because most o the energy in steamis stored as latent heat, large quantities o heat can betrans erred efciently at constant temperature.

Typical steam systems encompass multiple pressurelevels connected to a number o steam producers andsteam users or consumers spread across a site. As econo-mies o scale drive operating companies to build everlarger and more integrated acilities, the design o theshared steam utility system becomes extremely critical totheir operation. e steam headers o ten run throughout

the complex, tying together myriad units. is creates ahighly non-linear control and operability challenge.Its essential to ensure that steam can be provided

to all reaches o the acility without interruption andthat the system can be controlled in the event o upsetsto maintain stable operation. Improper controls couldlead to loss o the entire steam system, trip or damage o critical equipment, o -speci cation products and, in the

worst case, loss o the entire steam system and shutdowno the complete acility. Normally, such design de cien-cies become apparent only a ter an incident thiscould be costly or potentially disastrous.

Further, with ever-increasing energy costs, better

design, control and operation o the steam system candirectly impact the entire acilitys overall efciency,translating into substantial operational savings.

Traditional steam hydraulic analyses assess demandand production issues at di erent steady-state operat-ing conditions. Such analyses cant predict the steamsystem response through multiple headers all across thecomplex during process upsets.

Understanding the response through dynamic transients and ensuring the steam system can handle allexpected events without jeopardizing the availability o the acility becomes a critical aspect o the process andcontrols design o such systems.

is article takes a look at how dynamic simulation

can assist steam system design and o ers up some tipsor staying out o hot water.

AN IMp AN LDynamic simulation is a best available technologythat can be used to evaluate the as designed processand control strategy to maximize the likelihood that itcan provide stable and uninterrupted operation ollow-ing steam system or process upsets.

A typical dynamic simulation o the steam systeminvolves building a rigorous rst-principles model thatincludes:

boilers;

onsider Dynamic imulationfor team ystem DesignModels can provide crucial insights for dealing with upsets and transient conditions

By Ian Willetts, Abhilash Nair and Charles Rewoldt, Invensys Operations Management


22/44NOVEMBER 2010 CHEMICALPROCESSING.COM 22

steam turbine generators and drivers; multiple pressure headers;

pressure letdown stations; steam consumers; and regulatory and plant master control.Today commercially available software packages

such as DYNSIM from Invensys allow steam systemmodels to be built in a fraction of the time of older pro-gramming languages or software platforms (Figure 1).

e model is built and the controls are con guredto maintain the steam system at the normal designoperating point(s). e model encompasses all regula-tory controls, including those speci cally designed tomanage expected transients resulting from steam-system

or process upsets.

e high delity model can simulate many steam-system or process upset scenarios in a matter of just days to predict the system response following such eventsin a safe and controlled environment on the computer.

e model then can be used to determine how best tocorrect any issues identi ed during the upset scenarios.

TIPS AND STRATEGIES

While dynamic simulation has become more prevalentdue to software and processor advancements, it involvesfar more than simply entering numbers into a form.Experience has shown that certain considerations andpre-planning strategies signi cantly contribute to thesuccess of steam-system simulation projects. Here aresome tips:

Make conservative assumptions.is is one of themost critical aspects of design. Its inevitable that themodel wont capture every possible nuance or featureof the process, so the models response wont fully replicate actual system response. However, if themodel is designed to the highest possible rigor andall assumptions and modeling approaches err on theside of safety and over-design, you can have con -dence in the results.

For example, Gandhi et al. [1] discuss the model-ing of steam systems (speci cally boilers followinga trip) and the phenomenon of self-boiling in whichresidual heat in the boiler continues to generatesteam long after fuel is cut o . While it might bepossible to rigorously model the boiler to the level of detail to capture the self-boiling phenomenon, it may be more prudent instead to take a more conservativeapproach assuming steam generation stops shortly after fuel is cut o . A control system that can handlea rapid loss of steam certainly can deal with the situ-ation where the steam supply decays more slowly.

On the other side of the coin is modeling theramp-up of boilers when more steam is needed. eboiler manufacturer will supply the design maxi-

mum rate of change of steam production up to themaximum continuous rating. e vendor may give a20% per minute ramp but what if its actually only 10% or 15% due to unforeseen issues. e dynamicsimulation platform provides a perfect environmentto run multiple cases to test the sensitivity to key parameters.

Employ strict quality-assurance procedures.eaccuracy of simulation results depends upon many factors, including the modeling approach, assump-tions, data mining and data input. Experts follow strict procedures when executing a project to ensure

the model is built to the highest possible standard

AVOID COMMON DESIGN ERRORS

Dynamic simulation can aid in a number of areas of steamsystem design, including:

Properly sizing lines. One of the common errors encoun-tered in steam system design is incorrectly sized distributionpiping. Undersized lines have higher velocities and pressure

drops, leading to insufcient ow and pressure of steam tousers. Undersized lines also increase the risk of erosion, noiseand hammering. On the other hand, oversized lines are ex-pensive and cause higher heat losses, impacting the qualityof steam. In addition, ows through steam pipes can undergodrastic changes. Understanding this phenomenon throughsimulation is crucial for accurately estimating and verifyingline sizes.

Getting the system control loop right. Feedback loopsalone might not sufce to control the steam system through awide range of upsets. Scenarios where s team supply exceedsdemand can be handled by disposing of excess s team fora short while until feedback loops bring the system undercontrol. However, when theres a sudden shortage of steam,the feedback control actions might be too late. Appropri-ate feedforward control actions must be initiated before theshortage affects operation of the facility. Understanding theextremely non-linear characteristics of a steam system bysimulation is critical for successful design of these feedfor-ward controls.

Setting correct priorities in steam shedding . Situationswhere theres likely to be a severe shortage of steam requirean emergency steam-shedding plan to avoid a full-scaleshutdown. But which units should be shed and in whichorder? Such situations require a carefully designed strategythat prioritizes shedding of steam users based on the impacton the overall operation. As with designing feedforward con-trols, a simulation model can be used to evaluate differentsteam-shedding strategies in a cost effective and safe man-ner, thereby ensuring the best possible emergency sheddingstrategy is determined and deployed in the master controller.


23/44

and model inputs are correct. Its crucial to establishquality-assurance procedures that will certain results

obtained are meaningful and trustworthy.e main focus should be on checking the data

input into the model. Discuss assumptions made andcon rm theyre conservative enough that the results

wont compromise any objectives of the study. Forinstance, using a larger steam header volume thanactual in the model could yield a slower responsethan actual; this could lead to inaccurate results andconclusions for the design of pressure controls.

In addition, have experts from operations review scenarios that are tested on the model to ensure the

worst case is considered.Such a quality-assurance process guarantees the

model developed includes all the right inputs andassumptions, making the results more reliable andcredible.

With a high-quality steam system model,engineering and operating companies can begin toreap the bene ts of dynamic simulation in di erent

aspects and phases of the design process.Validate steam-network piping design.e piping

network often is designed for the ows and pres-sure pro le at steady-state conditions. In the eventof process upsets and the transients that may follow,these parameters undergo rapid changes that normalhydraulic analysis cant discern.

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Steam System

Figure 1. Dynamic simulation can serve to validate controlsystems, check control valve sizes and response times, andprovide initial controller tuning parameters.



Some pipes within acceptable limits at normalconditions could exceed design limits during tran-sients and become potential bottlenecks to the steady operation or startup of the facility. Identifying such

bottlenecks during startup, commissioning or afteran incident could lead to expensive eld changes thatimpact the project schedule for new plants or opera-tion of an existing facility.

A dynamic simulation analysis of the steam systemhelps precisely understand transients in the system.Simulating upsets enables monitoring ows and pressuredrops across pipe segments as a function of time, toidentify violations of design criteria during the tran-sients. e greatest bene t from this type of analysisoccurs when its performed closely with the engineeringdesign of the system. At that point, incorporating neces-sary design corrections incurs the lowest possible costand impact on schedule.

Con rm steam system controls.Dynamic simula-tion also can be used to evaluate the proposed controlstrategy around the integrated steam system. It can helpget the control system right the rst time, thereby savingvaluable time during commissioning, helping ensurestable operation during day-to-day operations andkeeping the system up and healthy during some of the

worst-case scenarios the facility could experience. An upset, like loss of a boiler, has the potential to

bring down the entire steam system, causing shutdownof critical process units. Because a dynamic simulationmodel incorporates all the controls, analysis can deter-mine if the as-built controls can maintain stable opera-tion after an upset. e model allows easy con gurationand testing of control alternatives that might improvesteam-system response. Feedforward signals to boilercontrols, low/high selector clamps on letdown stations,priority settings on steam headers, set-point staggeringacross the facility on various control loops are some of the important handles that can be quickly changed and

ne-tuned using a dynamic simulation analysis. ese

parameters can prevent nuisance trips and shutdownsand can accelerate startup.Identify steam load-shedding strategies.A critical

outage of major steam producers for scheduled main-tenance or due to an unforeseen trip requires adjustingsteam demand to balance supply and demand across thecomplex. If backup boilers cant make up the di erenceor are slow to respond to the upset, it will become neces-

sary, for example, to switch from steam-driven turbinesto electric drivers (if available) or to identify which less-critical units should be taken o ine and for how long toprotect the more-critical equipment and units.

When transient demand exceeds transient produc-tion, as in the case of multiple boiler trips, a steamshedding strategy must be initiated quickly to counterthe upset before steam networks reach unacceptablepressures. Developing a steam shedding plan that couldbe implemented during a major upset is critical to main-taining the availability and un-interrupted operation of the steam system.

Dynamic simulation can be a great help with thisevaluation as it can be used to test and evaluate criticalshed lists and to develop a strategy prior to startupand operation that least impacts the economic pro t-ability of the overall complex. It allows analysis of eitherreducing steam consumption or dropping steam usersoutright based on priority and criticality. Both feedback pressure-driven and feedforward event-based sheddingstrategies can be easily con gured and tested.

KEEP OUT OF HOT WATER

Dynamic simulation quickly is becoming an accept-ed technology for performing in-depth steam systemanalyses that cant otherwise be done except by trialand error in the plant. Engineering companies canbene t greatly from performing such analyses by following the tips described here and other best prac-tices as early in the process lifecycle as possible.

Moreover, the simulation software platform mod-els become assets within the company and can be re-used beyond the design environment to support plantcommissioning and for the development of operator

training systems.IAN WILLETTS is a director of Invensys Operations Manage-

ment (IOM), Carlsbad, Calif. ABHILASH NAIR is a principal

consultant for IOM in Carlsbad. CHARLES REWOLDT is

an application engineer for IOM in Carlsbad. E-mail them at

[email protected], [email protected] and

[email protected].


Do Your Own Steam Survey, www.ChemicalPro-cessing.com/articles/2009/039.html

Steam Projects Provide Fast Payback, www.ChemicalProcessing.com/articles/2008/111.html

Simulation Gets a New Dynamic, www.Chemical-Processing.com/articles/2006/048.html

REFERENCE

1. Gandhi, S.L., Graham, J., Dufeld, M.A., and Cortes, R.M., Dynamic Simulation Analyzes Expand-

ed Renery Steam System, p. 3, Hydrocarbon Processing (Nov. 1995).



E gi EE sa ety pro essionals at plantsmust work long and hard to eliminate the possibil-ity o res or explosions in areas where fammable orcombustible materials are being processed, handledor stored. Tis involves identi ying all potentialignition sources whether electrical, hot sur aces,mechanical sparks or naked fames.

However, no matter how well the workingenvironment has been designed, theres one potentialsource o spark discharges thats ever-present in virtu-ally every workplace and that has enough energy toignite all common fammable or combustible liquid

vapors and gases as well as many airborne dusts andloose solid materials. Tat energy source is static electricity , also known as electrostatic or just simply static.

Static electricity is the prime culprit or at leasttwo serious res or explosions in industry worldwideevery day o the year, according to the National FireProtection Association (NFPA) and the U.K.s Institu-tion o Chemical Engineers (IChemE). In the U.S.alone, static electricity causes on average 280 indus-trial incidents each year reported to re and emer-gency departments, resulting in injuries and atalities,

tens o millions o dollars o direct property damage,

lost production or plant downtime, and environmen-tal release issues.

Static electricity is generated continuously throughrelative motion in other words, whenever sur aceso materials come into contact and separate. Tisinteraction causes electrons to be stripped rom onesur ace to the other, creating an electrical imbalance.Te rate at which electrons are trans erred is infu-enced by a number o actors such as speed and areao contact and the characteristics o the materials ( orexample, the trans er rate will increase greatly i thematerials are dissimilar or one is an insulator). In the

workplace typical examples include liquids fowingthrough pipelines or into drums and tanks, powderdropping down a chute and even a person walkingacross an insulating foor. Charge generated in this

way o ten is lost by a combination o conduction toground and contact with atmospheric moisture (hu-midity). However, generated charge becomes a seriousproblem in hazardous areas when its allowed to ac-cumulate on objects not at ground potential. In thesecases, a signi cant potential (voltage) can develop and,depending on the characteristics o the ungroundedobject, this may have many times the surrounding

fammable atmospheres minimum ignition energy

Understand the

ShockingTruth

Dissipating static electricity is crucial for

avoiding ignition risks in hazardous areas

By Graham Tyers, Newson Gale, Inc.


26/44Nov mb 2010 ch m c oc Ng.com 26

(MIE), the minimumenergy that can ignitea mixture o a speci edfammable material withair or oxygen, measuredby a standard procedure.

PERVASIVE PROBLEMIn any typical workingenvironment hiddendangers may lurk inthe hazardous area inthe orm o isolatedconductors. ese areconductive (commonly metal) objects that areeither inherently or acci-dentally insulated rom

ground. is prevents any static electricity generatedrom sa ely discharging, resulting in accumulation

o charge on the object. ese isolated conductorsmay exist in commonly used items, including metalfanges, ttings and valves in pipework systems; por-table drums, containers and vessels; tanker trucks,rail cars and intermediate bulk containers (IBCs);and even people! Isolated conductors are probably the most likely source o static ignition incidentsin industry, ranging rom small-scale res to majordamage to plant and injury to personnel.

Paints, coatings, gaskets, seals and other non-conductive materials can be su ciently insulating to

prevent sa e static dissipation. e extent o chargegeneration current is usually very low, typically nogreater than 110-4 A; however, on isolated conduc-tors this charge can quickly build up to a very high

potential, with voltages in excess o 30 kV not uncom-mon. Depending on the capacitance o the object,this may result in signi cant levels o energy available

or discharge, well above the MIE o the surroundingfammable atmosphere. Typical MIEs vary accord-ing to whether the fammable atmosphere comprisesvapor, dust or gas, but many commonly used solventsand other fammable chemicals have MIEs well below 1 mJ (Table 1). I the isolated conductor then comesinto proximity with another object at a lower poten-tial, much o this energy could be unleashed via theair gap in the orm o an incendive spark. O course,static ignition o the fammable atmosphere alsorequires a suitable concentration o uel (vapor, dust orgas) in the air. For the purposes o sa e plant design,though, the very act theres an identi ed fammableatmosphere should suggest that this is possible orlikely.

ree main international technical standards orstatic control have been developed and maintainedby panels o re prevention and process sa ety expertsaround the globe. NFPA 77 (North America) andCenelec CLC/TR: 50404 (Europe) both draw atten-tion to a range o hazards, illustrating static controlpractices or a diverse range o industrial processes.

e American Petroleum Institute (API) 2003 stan-dard ocuses on hazards more speci c to the petro-leum industry. e guidelines propose maximumprocessing rates, recommended charge relaxationtimes or conductive and nonconductive liquids and,most importantly, the maximum level o resistancerecommended or static dissipative circuits.

e standards have a high degree o commonality concerning conductive metal grounding circuits. Forsuch circuits, which encompass the plant equip-

ment at risk o accumulating charge and the routeto ground, most standards recommend a maximumresistance o 10 . e rationale is that conductivemetal circuits in good condition have a somewhatlower resistance. I a circuit is compromised due to

aulty connections caused by long-term degradation,corrosion, damage or operators not ollowing correctprocedures, its resistance will exceed 10 . ere ore,this value becomes a good positive benchmark toveri y that circuits regularly used or eliminating static

Minimum Ignition Energy

Table 1. These values are or guidance only always veri y thespecifc MIE o any material. Source: NFPA, IChemE

material (gas/vap rr wder/Dust)

mini u niti nner y (m ), J

car n disulfde 0.009

met an l 0.14

Xylene 0.20

T luene 0.24

r pane 0.25

t yl a etate 0.46

Zir niu 5.00

p xy resin 9.00

lu inu 10.00

u ar 30.00

W eat ur 50.00

Assured Protection

Figure 1. An intrinsically sa e,sel -testing grounding clampvisually indicates proper

unctioning.


27/4427 CHEMICALPROCESSING.COM NOVEMBER 2010

hazards are performing their intended safety functione ectively, particularly in tough industrial processingenvironments.

E ective grounding and bonding best remedy

the problems associated with isolated conductors.Grounding involves linking the conductive object toa known ground point via a mechanically strong andelectrically conducting cable, thereby giving it zero(ground) potential. Bonding (or equipotential bond-ing) links adjacent conductive objects so as to equalizethe potential between them; at some point the linkednetwork also is grounded, meaning everything is atzero potential. For xed installations such as pipe-

work, storage tanks, etc, this is relatively simple toimplement. However, its more di cult for mobile/portable objects such as drums, IBCs and tankers.Such objects require use of purpose-designed tempo-rary grounding and bonding devices, along with strictprocedures to ensure theyre always in place prior tostarting of the process to prevent any static chargeaccumulation.

NFPA 77, Recommended Practice on Static Elec-tricity 2007 Edition, suggests speci c types of clampsand devices for grounding and bonding portable ormobile plant, drums and containers; these generally have to employ hardwearing sharp contacts and posi-tive spring pressure, and be universally adaptable to a

wide range of plant objects. If such units are properly speci ed and used, in most cases you can be sure of ef-fective static control through grounding and bonding.In all situations, its also important to periodically testthe control measures used, checking clamp/contact/cable condition and the all-important connection back to the ultimate grounding point. Intrinsically safe

instruments are requiredfor working live in ahazardous area.

FURTHER CONCERNSEven when the appropriate static safety equipmenthas been speci ed, those responsible for operations

within hazardous areas must address some additionalconcerns. In operational terms attaching a ground-ing clamp to a plant object is always a physicalaction. Even if diligently following company recom-mended safety procedures, an operator can neverknow whether the clamp has made good enoughcontact with the object to safely dissipate any staticgenerated before it can accumulate to dangerouslevels. Lots of conductive objects capable of ac-cumulating high static charges also have insulatinglayers e.g., paint or a coating or even productbuild-up on their surfaces that may prevent thislow resistance contact. Many common ground-ing and bonding clamps show very high resistancereadings when clamped onto conductive objects withinsulating surfaces. e problem can be even worse if a plant uses standard welding clamps or lightweight

alligator clips in place of purpose-designed devices.To solve these problems, use intrinsically safe,continuously self-testing grounding clamps (Figure 1),as recommended in NFPA 77. An operator employsthese in exactly the same way as conventional ground-ing clamps.

ese devices employ certi ed, active electronicmonitoring circuits powered by a low energy bat-tery. e circuit only is completed when the clampachieves a low resistance contact onto the object to begrounded; the operator receives visual con rmation of this via a light/indicator (usually a pulsing LED). e

self-testing grounding clamp also monitors cable con-

TAKE FOUR KEY STEPSTo achieve effective static control in hazardousareas:

1. Identify hazardous areas and processeswhere static electricity may accumulate.2. Specify conductive or static dissipative

items of plant, equipment and packaging.Only use insulating plastics after carryingout risk assessment/hazard evaluation.

3. Ensure correct grounding and bonding andother prevention techniques are in place and are properly maintained.

4. Provide ongoing training and awarenessfor employees and contractors about safeworking practices in hazardous areas.

Verication and Interlock System

Figure 2. Such a system can automaticallyshut down operations if a problem develops.



dition back to the designedground point, and wontgive the visual go-ahead if the cable has worked looseor is broken. Clamps foruse in hazardous locationsshould carry the appropri-ate certi cation or approvalmark, e.g., from Factory Mutual (FM) or the Cana-dian Standards Association(CSA).

To move to an evenhigher level of security,NFPA 77 recommendsground veri cation andinterlock systems to providenot only visual veri cationto the operator but alsointerlock switching contactsthat may be linked to pro-cess pumps, valves, alarm/shutdown/control systems,etc. Such interlocks can

preclude process startup until the conductive objecthas been safely grounded; if at any time during theoperation the condition changes (due to a clampfalling o or wire breaking), the system automatically shuts down the process. Systems employing interlocksalso can prevent accidents caused by operators ap-proaching plant objects already carrying accumulatedstatic charges, as in these cases static electricity wontbe generated until the process is initiated.

Static ground veri cation and interlock systemsgenerally are line-powered. ey employ approved

intrinsically safe barriers to limit the monitoring cir-cuit to safe levels but still must have proper hazard-ous location and safety cert i cation. ese systemstypically handle ultra-safety-critical applications likeloading/unloading tanker trucks and rail cars withlow conductivity ammable liquids (Figure 2), IBCs,

uid bed dryers, mixers, transfer equipment and spe-cial process machines. ey also are useful whereverits highly likely that static charge will accumulate invery low MIE ammable atmospheres.

A static safety audit also requires us to considerthe people working in the hazardous area. If the hu-

man body is insulated from contact with the ground,

either by nonconducting shoes, insulating oors orboth, static charge can start to accumulate as theperson walks along the oor. After just a few steps, afairly high potential may develop (especially in low-

humidity atmospheres); if the person then approach-es a conductive material at either ground or a lowerelectrical potential, a spark may occur. Its generally thought such sparks can reach energies as high as 30mJ, su cient to ignite a lmost all ammable vaporsand gases, and many sensitive combustible powder(dust) atmospheres. ese sparks can be avoided by using ground wrist-straps for sedentary workers, orstatic dissipative (SD) safety shoes for personnel whoneed to move around to carry out their tasks. In thecase of the latter, its also necessary for oor materialsto be su ciently conducting to allow a ground leak-age path to safely dissipate any static charge as eachfoot contacts the ground.

In the U.S., SD footwear is manufacturedaccording to ASTM F2413-05, which speci esmaximum and minimum levels for ground leakagevia the shoe. Leakage should be low enough to allow static charges to relax to ground but high enough toprovide some protection against electric shock. SDfootwear can be checked for ongoing e ectivenessusing test stations (Figure 3). ese types of deviceshelp prevent incorrect shoes being used in static-sensitive environments.

GET GROUNDED

e dangers of static electricity in hazardous areasdemand a rigorous approach to plant, process andpersonnel safety. As the speed and scale of modernmanufacturing and distribution techniques increase,and the range of materials used and processedgrows, such an approach to safety becomes evenmore important. So, gain a greater understandingby reviewing NFPA 77 and other industry-speci ccodes of practice that provide practical guidance for

speci c situations.GRAHAM TYERS is president of Newson Gale, Inc., Jackson, N.J.

Email him at [email protected].


Static Electricity References, www.ChemicalPro-cessing.com/experts/answers/2007/109.html

Avoiding a Future Accident, www.ChemicalPro-cessing.com/articles/2006/112.html

Shoe Tester

Figure 3. Device provides aneasy way to check that staticdissipative shoes remaineffective.


29/44



SOME COMMON PROBLEMSSimple operational situations often cause tank failures.

Accidental over lling, impeding exiting vent ow, andnot allowing in-breathing as a tank is being pumped outare cardinal sins.

Over lling . A recentCP article, Dont Underesti-mate Over llings Risks, www.ChemicalProcessing.com/articles/2010/143.html, focused speci cally on thehazards posed. It cited three major industrial accidentsresulting from over lling including a massive re inDecember 2005 at the Bunce eld Oil Storage Depot inHertfordshire, England. e tank that caused the inci-dent had an independent high-level alarm and interlock but the system didnt work. e September 2006 Beaconprovided details on that disaster and related that over ll-ing has contributed to a number of serious incidents inthe chemical and oil industries in recent years.

Tanks must be engineered to provide protection

via alarms and high-high level interlocks againstover lling of hazardous materials and the resulting

spillage.Over-pressure and under-pressure.Its crucial to main-

tain the integrity of tank venting systems. Otherwise,catastrophic damage may result.

Over-pressure caused a sudden drastic failure atthe base of a 12-ft-dia., 24-ft-high ber-glass acid tank (Figure 1). e tank was equipped with a separate ventline, an over ow line and a vacuum breaker.

As a safety precaution when repairing an under-ground sewer line that would receive acid if the tank over owed, supervision had the over ow line blindedand instructed operators to run the vessel well below theover ow line. e thought was that the vent line wassized su ciently for lling purposes.

Unfortunately, a blind from a previous job had beenleft within the vent line and wasnt detected. As opera-tors started lling the ber-glass tank, the inerts had noplace to go and the tank was pressurized to destruction.Fortunately, no one was injured [4].

Under-pressure led to a well-maintained low-pressure 20-ft-dia., about-30-ft-tall carbon-steel solventtank with -in. walls ending up as scrap metal afterimprovements to the vent system. To reduce emis-sions, vent recovery compressors and more-sophisticatedinstrumentation were replacing old-style conservationvents.

While the rst batch of material after the tank conversion was being pumped out, the roof and twocourses of vertical walls were sucked in due to the lack of the nitrogen padding and the vacuum protection systembeing inadvertently isolated by a small block valve.

A simple hinged vent lid had served well for decades.e lid was replaced with a much more complex system

involving a vent compressor to recover the vapors anda nearly zero leakage pressure/vacuum device. e

REFERENCES1. Kletz, Trevor A., What Went Wrong? Case Histories of Process Plant Disasters, p. 97, 5th ed., Gulf

Publishing, Burlington, Mass. (2009). Similar details are also found in all earlier editions.2. Beacon , a free single-page monthly publication of the CCPS comes in many different languages.

To subscribe, go to: http://www.aiche.org/CCPS/Publications/Beacon/index.aspx.3. Safe Tank Farms and (Un)Loading Operations, BP Process Safety Series, BP Safety Group,

Sunbury-on-Thames, U.K. (2008).4. Sanders, Roy E., Chemical Process Safety: Learning from Case Histor ies, p. 108, 3rd ed., Elsevier

Butterworth-Heinemann, Burlington, Mass. (2005).5. Sanders, Roy, Human Factors: Case Histories of Improperly Managed Changes in Chemical

Plants, p. 150, Process Safety Progress (Fall 1996).

Tilting Tank

Figure 1. Over-pressure due to left-in-place blind causedbase of tank to give way.


31/44

operators were well trained on the new compressor butnot on the new piping arrangement. Worse yet, closureof a single small-diameter impulse valve rendered allthe well-conceived improvements worthless. Oops, a

$100,000 mistake [5].Plant designers must strive to develop user-friendly

piping, layout and control schemes, and must clearly la-bel equipment safety systems to reduce opportunities forfailure. Venting systems should ensure proper protectionduring all phases of operations.

Tank venting systems mustnt be altered or tam-pered with without a management-of-change review.

AN OLD STORY

None of this is new. In anICI Safety Newsletter pub-lished in the 1970s, Kletz predicted a storage tank wouldbe sucked in each year. Experienced process safety people hear of such situations every so often.

CCPS has pointed out tanks vulnerability tovacuum in two issues of theBeacon. Vivid photos of failed tanks demonstrated the importance of maintain-ing proper vacuum protection.

e February 2002 Beacon, titled A Little Noth-ing Can Really be De ating VACUUM is a Power-ful Force!, showed a rail car sucked in and a tank thatcollapsed while being painted. One main message was:Whenever vacuum relief systems are removed, covered,modi ed, etc., special precautions are needed to preventan incident.

Vacuum Hazards Collapsed Tanks in theFebruary 2007Beaconstressed three key points:

1. Well-intentioned people can easily block vents.2. Never cover or block the atmospheric vent of an

operating tank.3. Routinely check for plugging of vents on tanks in

fouling service.

OTHER FUNDAMENTALS

Always keep in mind the following points about low-

pressure tank layout and design: Tank spacing and layout are critical. Various prop-erty insurance publications and pamphlets fromthe National Fire Protection Association (NFPA)o er some guidance about the proper spacing of storage tanks, especially those that contain am-mable or toxic liquids.

Tanks containing incompatible chemicalsshouldnt be allowed within the same dikingsystems.

Fire-protection features, including staticelectricity dissipation, vapor space inerting,

protective foam generators, water spray and

dike designs, demand professional handling. Venting systems not only must be well designed

but also must be inspected and maintained dur-ing the life of the equipment. Tamper-proof ventdesigns are ideal.

Tank bottoms should be sloped and associatedpiping should be laid out to facilitate completedrainage. Tanks should be checked for internaland external corrosion.

Local conditions, such as the possibility of ood-ing or hurricanes, which can a ect low-pressurestorage tanks should be considered.

Ongoing corrosion monitoring is essential. e BPbooklet [3] contains a number of photos and brief descriptions of tank failures from corrosion.


Dont Underestimate Overllings Risks, www.ChemicalProcessing.com/articles/2010/143.html

Bhopal Leaves a Lasting Legacy, www.Chemical-Processing.com/articles/2009/238.html

Its Time to Tank Complacency, www.Chemical-Processing.com/articles/2006/028.html


32/44

Many helpful references are available. Teseinclude API-650, API-620, API-510 Pressure Ves-

sel Inspection Code Maintenance, Inspection,Rating and Alteration, API-653 ank Inspec-tion, Repair, Alteration, and Reconstruction,NFPA codes and Reference 3.

VESSEL INSPECTION

o quote from the BP booklet [3], Most tanks are madeof carbon steel, which can corrode when exposed to airand water. Over time, uncontrolled rusting can weakenor destroy the components of a tank, resulting in holesor possible structural failures, and release of stored prod-ucts into the environment.

E ective timely inspections can drastically reducefailures from corrosion.

Tree di erent approaches to tank inspections are widely used.

A periodic visual inspection by operators is therst line of defense. Tis type of routine monitoring

focuses on evidence of seepage or leakage, tank set-tling, bulging or signi cant corrosion.

In-service inspections generally are less frequentthan operator reviews and typically are performed by certi ed inspectors. Such checks often start ve yearsafter commissioning, with frequency adjusted accord-ing to tank history, the risk involved and the corrosionrate. Tese most often involve taking ultrasonic thick-ness readings at key locations.

Periodic internal inspections after the tank isdrained and washed are a must (Figure 2). Tese canidentify components that have shifted, localized pit-ting, etc., that may not be apparent from an externalinspection. ypically internal inspections take placeat a frequency between annually and once every tenyears. Te exact frequency is best determined by thecorrosive nature of the uid, including its trace com-

ponents, and the past history of similar equipment onthe site.

DONT TAKE TANKS FOR GRANTED

anks can and do hold large inventories of a widevariety of raw materials, intermediates and nishedproducts safely for decades. However, if a tank and itsaccessories are poorly designed, abused by operationsor deprived of e ective inspection and basic mainte-nance, bad things can happen.

ROY E. SANDERS is a chemical process safety consultant based

in Lake Charles, La. E-mail him at [email protected].

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Figure 2. There is no substitute for an internal inspection tohelp ensure mechanical integrity.


33/4433 CHEMICALPROCESSING.COM NOVEMBER 2010

MAKING IT WORK

A SITE-WIDE steam and condensate system auditof a Midwest refinery conducted by Armstrongand its local representative, the Steam Econo-mies Company, revealed that the refinery wasdischarging condensate to the sewer through atemporary hose due to a faulty condensate pump-ing system.

As it investigated the situation fur ther, the auditteam discovered the system that returned conden-sate to the boiler house used electrically drivencentrifugal pumps. While these units worked mostof the time, they required signi cant maintenancedue to their numerous parts and sensitive sensorsthat demanded ongoing calibrations. Because thepumps were old, they also were unreliable and parts were hard to nd. Moreover, the system neededa pump-around loop to prevent burnout of thepump and motor. Also, the controls to direct thecondensate were complicated and required periodicmaintenance.

Any replacement electrical pump would have tomeet all the electrical safety requirements of a Class1 Division 1 environment and its installation cost would be high. Other drawbacks of an electricalpump in condensate service are cavitation issues dueto insu cient net positive suction head (NPSH) andleaking pump seals.

Seeking a lower cost and a more dependablesolution, the re nery was drawn to the simplicity of Armstrongs PT-516 pump (Figure 1). It uses steamfrom the plant rather than electrical power. And,unlike the centrifugal pumps that ran continuously,the PT-516 only consumes steam when the conden-sate level in the pump requires a pumping cycle.

e re nery reports there no longer are any NPSHconcerns and hotter condensate (212F versus 180F)now can be returned. e steam-driven pump canhandle up to 65,000 lb/hr of condensate.

e pump plus accessories and check valves costabout $20,000. Installation also involved removal of

unneeded piping, controls and valves. e payback period should run two to three years.

e Armstrong PT-516 steam pump has been inservice for more than a year with no interruptionsto returning condensate from the crude unit to theboiler house. is has helped the re nery maximizeenergy savings and capture an additional $75,000annually.

Now the re nery is investigating other opportu-

nities to use steam-driven technology for condensatecollection and return.

MICHAEL CALOGERO, P.E., is Allentown, Pa.-based reningand petrochemical manager for Armstrong International. E-mail

him at [email protected].

Renery Pumps Up Energy SavingsSwitching to a steam-driven pump enhances condensate return system

By Michael Calogero, Armstrong International

RELATED CONTENT ON CHEMICALPROCESSING.COMWhats Involved in Changing From an Electric Motor to a Steam Turbine?, www.ChemicalProcessing.

com/experts/answers/2010/016.htmlHow Do You Decide Between Steam or Electrical Turbines?, www.ChemicalProcessing.com/experts/

answers/2009/119.html

CHECK OUT PAST ARTICLESMaking It Work stories going back to 2005

are available at www.ChemicalProcessing.com/voices/making_it_work.html

Steam Pump

Figure 1. Unit only operates when triggered by condensate level.


34/44Nov mb 2010 h mi lp o ssiNg. om 34

p o ss p zzl

T s mo T s puzz

Deal with a Decanter that CantReaders recommend ways to save a standing separator

our decanter f r e arat n a xture f 10, 20, 30 and 40 c und fr a water/t uene ut n nt erf r n r t.T a e ace, we ted f r a 3-ft-d a eter ert ca un t w t a

en t /d a eter rat f a ut 3:1. T e f w are 6,000 under ur (pph) f r an c and 2,500 pph f aque u a e. T e

c t e are: 300 cp f r t e r an c; 0.8 cp f r t e water. T eec f c ra t e are: 0.8 f r t e r an c; 0.99 f r t e water. Feed at a ut 50% f t e tra t de en t and we u e a d er n

ayer f a ut 5%. t u t e decanter de ned t ca ture100 cr n () dr et , t e car n f ter t at u ed t er ea a water n f ter actua

chemical processing nov-10

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