Electrostatic Precipitator Maintenance Process Re-Engineering: Lead & Cadmium exposure control at the HamptonINASA Steam Plant.

Transcription

1 lectrstatic Precipitatr Maintenance Prcess Re-ngineering: Lead & Cadmium expsure cntrl at the HamptnINASA Steam Plant. Jhn S. Austin, P 50 Wythe Creek Rad Hamptn, Virginia lectrstatic precipitatrs (SP) cllect fine particles frm municipal waste cmbustr flue gases, which cntain significant cncentratins f heavy metals. In respnse t new OSHA standards, the HamptnlNASA Steam Plant began re<valuating expsures during semiannual maintenance shutdwns. A prinwy cncern was whether the cadmium r lead standard actin level were exceeded during SP maintenance. The initial testing cnfirmed expsure levels were abve OSHA Permissible xpsure Limits fr cadmium and lead. During the Fall f 1994, a maintenance prcess review was initiated t bring the prcess under cntrl and t minimize expsures t these hazards. The fcus fr prcess review was t develp engineering cntrls that, reduce wrker respirable expsure belw the actin level fr Cadmium(.0025 mglml) and Lead(.025 mglml). The prcess review lasted three years, fr SP maintenance is dne nly fur times each year. All f the task wrkers had mnitring fr lead and cadmium during the review. xpsures fr nn-task wrkers were crdinated with nging mnitring fr ther shutdwn tasks. During all SP entries, the task wrkers were fully suited and prtected with full face psitive pressure air purifying respiratrs. Prcedures were implemented t prevent flyash ash migratin. ach iteratin, the prcess review team incrprated imprvement that reduced expsures. The initial phase succeeded t reduce expsures by 86% t (Pb) and (Cd) mglml. Persnal expsures t lead and cadmium were still abve OSHA Subpart Z actin levels. The prcess review team cncluded the existing prcedures needed t be abandned. New prcedures fr wetting the flyash and water washing the SP were develped. During the first trial f the new wet methd, au air sampling cassettes recrded levels belw the PL. Three mre iteratins ptimized the prcess, and the prcedures had substantial cntrl ver expsures. The end result f the maintenance prcess review was an SP cleaning prcedure that cnsistently reduced wrker expsures t belw the PL fr lead and cadmium. Backgrund Infrmatin The HamptnlNASA Steam Plant is as a cperative enterprise wned by the City f Hamptn and the Natinal Aernautics and Space Administratin. The facilities tw Detrit Stker furnaces prcess 240 tns per day f municipal slid waste. High pressure steam is prvided t NASA Langley Research Center t pwer high speed wind tunnels and a variety f ther prcess and institutinal pwer needs. The facility is permitted t and perated by a Jint Bard' f Oversight wh represent the wners. The HamptnlNASA Steam Plant is an independent enterprise, much like a small business. With limited resurces, Cntinuus Prcess Imprvement methds are used by the emplyees t develp and update facility prcedures and t slve prblems. Regulatry prgrams, like respiratry prtectin are prcesses designated fr cntinuus imprvement, t help ensure cntinuus cmpliance with OSHA requirements. New standards fr cadmium expsure were issued by U.S. Occupatinal Safety and Health Administratin during The HamptnlNASA Steam Plant began t evaluate expsures during semi-annual maintenance cycles. There was cncern that the Cadmium standard actin level was being exceeded during SP cleaning and maintenance. Unlike the OSHA lead standard, rtatin f emplyees was nt allwed fr cmpliance with the 5 micrgram per cubic meter (0.005 mglml) permissible expsure limit (PL). ach f the standards set an Actin Level f ne half the PL. The standard has sme requirements effective when expsures exceed the Actin Level. A prcess that reduced emplyees expsure t lead and cadmium in flyash wuld mean tw less regulatry prgrams t incrprate int prcedures. ach f the standards require emplyers t implement engineering cntrls, if pssible, t remve the hazard. SP Maintenance Prcess Review The review fllwed a general prcess used at the Hamptn! NASA Steam Plant, by emplyee teams, t achieve the gals f cntinuus prcess imprvement. 213

2 _ The prcess review fllwed fur distinct steps. 1) Dcument and review current prcess. 2) Implement imprved prcedures. 3) valuate results and ptential imprvements 4) Critical Prcess Decisin - Re-ngineer? The review lasted three years, and was fllwed by a year f independent validatin f the new prcedures. A prcess review team was fnned that included the Steam Plant, Operatins and Maintenance Managers. Team Leaders frm each maintenance team and thse currently invlved with the SP maintenance als participated with the review team. Meetings f the team ccurredjust prir t and after each iteratin f the prcedures. Team members met with the industrial hygienist nly n the days the tasks were being perfnned and mnitred. The fcus gal fr the review was t develp engineering cntrls t reduce task wrker respirable expsure belw the actin level fr Lead (.025 mglm3) and Cadmium (.0025 mglm3). All prcess reviews include ther safety, envirnmental and ecnmic gals, as did this prcess review. A cncurrent gal was t keep the stack pacity at 0% during the SP cleaning prcess. Initial attempts at inductin fan ventilatin cntrl nly relcated the hazard up the smkestack. Anther fcus gal was t ensure that the SP cntainment and prcedures prtect the nn -task emplyees frm expsure t fugitive flyash. Task cst impact had nly small imprtance, fr the facility's respiratry prtectin prgram already incrprates mst cmpnents f a Subpart Z prgram. mplyees have full medical surveillance, including mnitring bld lead level. Mechanics and peratrs are all issued pwered air purifying respiratrs (p APR) with high efficiency particulate and aersl (RP A) level prtectin. Pssible cst effects fr any cntractr perfnned wrk were nt cnsidered. All cntractrs are required t use the prcedures, and special prcedures typically raise cntract cst. Initial SP Maintenance Prcess Review Initial review f the SP cleaning included reviewing current maintenance and safety prcedures, persnal prtectin levels, OSHA regulatins, and current literature and experience frm similar facilities. With each trial f the prcedure, imprvements were made. Changes included cmplete mechanical cleaning prir t using air lances, air lancing tp t bttm between plates and manually cleaning all wire weights. HPA vacuums were used when pening the until, and each task wrker is vacuumed upn exit f the SP. The task was dne by tw r three wrker teams that tk turns as entrants and attendants, s t balance the wrklad. Fr sme tests, a nn-entrant attendant was prvided s the data wuld reflect n emplyee rtatin. Imprvement f the SP maintenance prcess had tremendus results. xpsures were reduced by mre than 86%. Increased labr and cntract cst was attributed cmpletely t industrial hygiene testing and increased team meetings. Yet tw factrs required that the current prcess be abandned. Imprved Dry Cleaning Prcess Lead xpsures O.6 Q r ,, Cadmium xpsures 1.,.---.S -r-----a---- ' 0.6-0) t , A_-- / The tw SP units are each entered twice annually. The units are thrugbly cleaned, inspected and then required repairs are made. The infrequency f the tasks made a cmprehensive prcess review challenging. Ultimately, 20 emplyees were invlved in the prcess review. Five data pints represent the authr's wn expsure while perfrming the tasks being reviewed S 9 IndividualS hrtwa Figure 1: Wrker eipsure during dry cleaning SP. 214

3 The prcess was still ut f cntrl. Individual task wrker expsure varied greatly; standard deviatin f the samples fr bth lead an cadmium were greater then the PL's. xpsures were reduced 86% t mg/mlf lead and mg/ml f cadmium, these expsures were still abve OSHA Subpart Z actin levels. SP Maintenance Prcess Re-ngineering The critical decisin t abandn a current set f prcedures, and t start frm scratch, is never taken lightly. A wrk envirnment f cntinuus prcess imprvement can easily becme chatic with neverending trials f "new & imprved" prcedures. If a current prcedure has had sme success, why risk a radical change. If a new prcedure was wrth trying, it als shuld be wrth imprving n. At the HamptnINASA facility wet methds and HPA vacuum prcedures have wrked successfully with thers ash related tasks, but the SP flyash has much higher cncentratins f lead and cadmium. Vacuuming the large surface areas within the SP wuld have been difficult. Vacuum cleaning methds mve dust in the air, but the fcus gal was t get the dust ut f the air. The review tearn quickly explred the idea f wet cleaning. Many tearn members thught this was a bad idea. Infrmatin was gathered frm literature the SP riginal equipment manufacturer and experience at ther pwer plants. While sme cal cmbustr plants had been successfully using wet cleaning, many facilities experienced prblems and equipment failure. Mst waste t energy plants used mechanical r air cleaning. Wet cleaning weighted wire SP units similar t these had caused serius prblems with wire weight alignment and guide crrsin. There were als sme cncerns abut the crrsin recnditining f the SP's crten steel husing. Then there is the lessn we all seem t have t relearn: if yu are ging t get the ash wet, yu better wash it all ut. Otherwise, it will fuse and harden. / SP Wet Cleaning Prcedure The emplyee tearn prepared a draft wet cleaning prcedure that required nly minr imprvements ver the first three iteratins. Task wrkers use a 1112 inch fire hse t wash their way frm tp t bttm, and frm inlet t utlet. During initial trials water wash emuent was pumped t a tanker truck fr analysis and ff-site dispsal. The wash dwn water is nw allwed t flw t the wet trench system and then pumped t the wastewater strage tank fr future system make-up water. The cleaning prcess cntinues thrugh the flyash system t the wet trench. The entire SP and flyash cnveyer maintenance prcesses are nw dne in a single 12 hur day. The mechanic labr fr the cmbined maintenance prcess has been cut in half; an annual savings f $6000. The prcess review tearn met with task wrkers befre each time the SP maintenance prcedure was dne. Industrial hygiene services were prvided by LabCrp Analytical, f Richmnd Virginia. Persnal expsure data was taken fr Lead and Cadmium. Only ne data pint was affected by the water washing. The result f the re-engineered prcess was tremendus. After the first prcedure trial all cadmium test cassettes have been cllecting less than the analytic detecting limit (NO). Fr the secnd entry, it is decided t hse thrugh the man way prir t entering. The instant results were amazing. The SP envirnment previusly was very dusty; a flashlight beam wuld disappear int the dust. After a brief misting f water, the air inside the SP was visibly clean. Light traveled t far cmers, and n dust particles were seen in the air. After ne wet cleaning the SP wire weights frze in their guides, causing the prcedure t be repeated. Great detail is nw fcused n ensuring all ash is washed ut f the wire guides. That is nw dne with a garden hse, fr the frce f the fire hse wuld bend the guides leading t additinal wrk. During all f 1996, wet cleaning expsures were mnitred, and expsures were cnsistently belw the lead and cadmium actin levels (see Table I). The prcedure prved very repeatable. Ttal labr time fr the wet cleaning prcedure was half f the previus drycleaning methd. Inspectin and repairs after the wet cleaning prcedure als became less hazardus. A mre thrugh inspectin can be made after wet cleaning. Table I: Wet Cleaning xpsures Cadmium Lead Average (mg/cm) High xpsure % Cnfidence Standard Deviatin % f PL 20% 10% 215

4 quipment perfrmance after wet cleaning was exceptinal; the autmatic SP cntrls ramped t full pwer with a lw spark rate fr days after cleaning. N ntable repairs have been caused by wet cleaning the units except fr the rewrk due t the weights nt being cleaned cmpletely. Crrsin depsits left after wetting has seemed t reduce the wear f sme cmpnents. By the Spring f 1997, the hazard was under cntrl with ne exceptin. ven after wet cleaning, metal grinding in the SP still caused expsures abve the PL. The review team develped a wet grinding prcedure, and it nw reduces expsures belw the PL. Grinding and welding tasks are generally dne by cntractrs, but facility staff tk n the tasks, s t imprve the prcess. Changes t the Respiratry Prtectin Prgram Initially several enhancements were made t the prcedure t increase emplyee prtectin and awareness. All mechanics were issued pwered air purifying respiratrs. Stricter cntrl and specificatin f tedlar dispsable cveralls were implemented. Task wrkers are cleaned with HPA vacuums as they exit the. SP manway. Prcedures were established fr use and cleaning fhpa vacuum equipment. Several types f vacuums were purchased, including small shulder strap HPA vacuums that were perfect fr tp end entries. The lessns learned during the prcess review led t majr changes t the 29CFR respiratry prtectin prgram that the facility had. The prgram nw incrprates many aspects f the OSHA Lead and Cadmium standards. The emplyee hazardus substance ntificatin appendices have been incrprated int the Safety Manual fr Lead and Cadmium. Substance data sheets have been included with ther material safety data infrmatin. The wet cleaning methd was included as a safety prcedure. Updating was als needed t reflect changes t persnal prtective equipment. The newly designated Fly-Ash Hazard als had t be incrprated int plicy and prcedure. All pints f prbable expsure are clearly marked with bright range signs directing wrkers t special prcedures. Training nw emphasizes lead and cadmium infrmatin, and "wash yur hands" awareness has been included fr maintenance shutdwns. Since the respiratry hazard has been reduced, additinal fcus is nw being placed n ther multi-path expsures. Dispsable tedlar suits have been prblematic, and are n lnger required under rain cats during wash dwn itself. The facility nw intends t establish a dirty cverall prgram. With special prcedures Medlar suits are nw HPA vacuumed, prir t disrbing in clear bags immediately upn disrbing and are delivered directly t the refuse feed hppers. The certified Industrial Hygienist wh validated the wet cleaning prcedure recmmended task testing as fllws: annual re-testing f the wet prcedure, and testing fr Lead ash grinding task until mre data is available t evaluate expsures. Industrial Hygiene testing will be included with the Semi-annual maintenance shutdwns t gather data n many ther "infrequent tasks." Csts fr these services have dubled t abut $4000 each year. Testing als increases time and difficulty f the tasks. Summary f Analysis and Results All expsure data was cllected and reduced t Time Weighted Averages (TWA) using apprved industrial hygiene methds and calculatins. During the initial dry cleaning task wrkers had t change filter cassettes ver a twelve hur prcedure. Data was cmbined and crrected t an 8 hur TWA with a 95% cnfidence levels. The reprted results are representative f a single wrker's expsure ver 8 hurs, 95% cnfidence. xpsure data was reprted and all calculatins were dne in micrgrams per cubic meter. The fllwing frmulas and cnstants were used: n L TC; TTask) ;-1 ( TWA= - - 8hrs 8hrs Mnitring was dne typically fr a minimum eight hur perid, and the value use fr T 1<Uk was always eight hurs r greater. The dry cleaning task tk 10 t 12 hurs, and this frmula cmpensates fr the lnger expsures. The upper cnfidence limits were calculated as a percentage f the PL with the fllwing frmula and a nrmal statistic Z value f The cefficient f variatin (CVT1l) fr lead and cadmium sampling were 0.06 and 0.07 respectively. UCL(95%) = X_ C ;, / PL n 216

5 The results f wet methds were prcedures that cnsistently reduce expsures during and after cleaning t belw the actin levels. The wet grinding prcedure reduces lead levels t belw the PL, but abve the actin level. SP grinding tasks are very infrequent, s it may take years t accurately quantify expsures. The summary f resutts are presented in Figures 2 and 3. Figure 2: Lead xpsures 0.3., ('I) - Cl 0.1 Nn-task wrkers were perfnning there regular tasks while the SP cleaning was ccurring. These samples were all taken during planned maintenance shutdwn perids. Tw samples were taken frm mechanics that were engaged in flyash cnveyer repairs. Thse wrkers that served nly as attendants fr the SP prcedure were included with the nn-task wrker data (see Table III). The results indicate the SP cntainment in cnjunctin with exit vacuuming des prevent fugitive ash migratin. Table II Incidental xpsures Cadmium Lead Average (mglcrn) High xpsure % Cnfidence Dry Figure 3: Cadmium xpsures ('I) - ' % f PL 16% 11% T better understand the hazard, SP flyash cmpsite grab samples were taken and analyzed fr ttal txic metal cntent. Lead and cadmium were fund in significant amunts. Arsenic was nt detected in the flyash samples. The results indicated lead varied mre than cadmium, and lead was fund in cncentratins f frty times that f cadmium 9 (see Table III). Table ill Lead & Cadmium in the F1yash Lead Cadmium 7055 mglkg 160 mglkg Dry Mst cadmium samples fr the wet methds and the nntask incidental expsures were reprted at a nn-detect level. Time weighted averages fr these varied based upn the sampling and task duratins. The wet grinding prcedure cntrls cadmium, but the lead absrbed int the metal causes lead expsure abve the actin level. The wash water effluent wash als tested prir t dispsal. The water was washed t an idle wet trench then pumped up t the tank truck, s sme cntaminatin was expected. The results was ppsite f the dry sample, fr cncentratins f Cadmium (13 mgll) were higher than fr Lead (3.2 mgll). The levels f these tw metals in the effluent were nt prblematic. Hwever, Zinc levels f 137 mgll required the waste water t be shipped ut f the regin fr prcessing. 217

6 Cnclusins The prject presents hard industrial hygiene data and a pssible slutin t the lead and cadmium headache that mst municipal waste cmbustrs are experiencing. It als serves as a gd example f hw emplyee teams using Cntinuus Prcess Imprvement methds can help slve sme f ur mst challenging prblems. The incumbent prcedure, mechanical and air cleaning f the electrstatic precipitatrs, did cause expsures abve the PL fr lead and cadmium. The prcess was ut f cntrl: sme persnnel had less expsure during SP cleaning, but thers wuld get very high expsure. The current prcedures had t be abandned, and the prcess was re-engineered. References Plg, Bcubara A. et. al., Fundamentals f Industrial Hygiene, 4111 ditin, 1996, Natinal Safety Cuncil, Itasca, Illinis Cde f Federal Regulatins, 29 CFR Part 1910, 1910./35, , , current, United States Occupatinal Safety and Health Administratin, Washingtn, DC. HarnptnINASA Stearn Plant, Safety Manual and current industrial hygiene data recrds. Wet cleaning methds effectively cntrl respirable expsures t lead and cadmium. The prcedures validated during this prcess review repeatedly lwered expsures t nn-detect fr cadmium, even during fllw-up repairs and grinding. The prcedures lwered lead expsures t belw the Actin Levels with the exceptin f during grinding tasks inside the SP. Task wrkers will cntinue t be affrded full persnal prtective equipment, and many aspects f the OSHA Subpart Z standards are incrprated int the facility's respiratry prtectin prgram. Annual re-testing will be dne fr the SP wet cleaning prcedure and during grinding tasks inside the SP. The prcess review did nt try t reduce csts, but the reengineered task requires abut half f the time t cmplete. mplyee invlvement had several benefits. Training fr the new prcedure was cn-current with develpment. mplyee wnership f the prcedures enhances ur ability t ensure prcedures are being cmplied with. The prcedures will be mnitred and imprved n as needed. Prcess reviews f perating and maintenance tasks prcedures are cntinuing at the HamptnINASA Stearn Plant, and we expect critical gals t be achieved and csts reduced frm thse effrts. 218

7 Imprved Dry Cleaning Prcess Lead xpsures ce 0.6 C) t ;j Cadmium xpsures ('I) C) , t-----a Individual 8 hr TWA 219

8 Figure 2: Lead xpsures 0.3 -,--- M - C> PL Wet Grind Dry Wet Nn-Task Figure 3: Cadmium xpsures , M ao.oob Dry PL Wet Wet Grind Nn-Task 220