OLLUTION PREVENTION VIBRATORY SOLUTION PROCESS PROFILE: . RECOVERYINA WNCDIECASTDNG OPERATION

Transcription

1 OUTION PREVENTION PROCESS PROFIE: VIBRATORY SOUTION. RECOVERYINA WNCDIECASTDNG OPERATION For more nformaton, contact: RI Department of Envronmental Management Offce of Envronmental Coordnaton Polluton Preventon Program 83 Park Street, Provdence, RI Phone: CEAN RI (RI only) or

2

3 I Foreword Ths report s publshed by the Rhode Island Department of Envronmental Management's Offce of Envronmental Coordnaton (OK). OEC provdes on-ste assstance and techncal nformaton to Rhode Island busness and ndustry. The nformaton and data presented n ths report are the drect result of a cooperatve effort by the Rhode Island Department of Envronmental Management, the Unversty of Rhode Island's Chemcal Engneerng Department, and Mnature Castng Corporaton. Ths document s ntended as advsory gudance only n developng approaches for polluton preventon. Complance wth envronmental and occupatonal safety and health laws s the responsblty of each ndvdual busness and s not the focus of ths document. In addton, any and all products and companes dentfed n ths report are for example only. No endorsements are mpled nor should any be nferred. The Offce of Envronmental Coordnaton advses that pror to mplementaton of any polluton preventon methods and technologes, companes should consult wth approprate Federal, State, and ocal regulatory agences. Users are encouraged to duplcate ths publcaton as needed to mplement a polluton preventon program. Fundng for ths project was provded by the Unted States Envronmental Protecton Agency and the Rhode Island Department of Envronmental Management. Questons or comments may be addressed to: Rhode Island Department of Envronmental Management Offce of Envronmental Coordnaton Polluton Preventon Program 83 Park St. Provdence, RI (401) or CEANRI (RI only) Prnted on Recycled Paper 4040% Preansumer, 10% Post-Consumer

4 Y

5 c Contents Abstract 1 Introducton Project Descrpton I Procedure II Results 6 III Economcs 7 IV Conclusons 8 E! 1 Glossary Appendx 9 10 l e

6

7 . 1 - Abstract In ths project, membrane technology was appled to a vbratory soluton recyclng proccss used for the cleanng and polshng of mnam znc de-casts. Before the project was ntated, all process water was dscharged nto the sewer system through ten mcron cartrdge flters. Two to three hundred gallons per day of vbratory waste soluton had been dluted wth approxmately one thousand gallons per day of non-contact coolng water. Hydrochlorc acd (HCl) had been used only occasonally when necessary to adjust the soluton ph to below 10. Mneral sprts had also been used to preclean heavly contamnated parts. Whle the orgnal project objectve had been to rely on the use of acds and fltraton methods to "ze waste dscharges, development testng and mprovements obtaned throughout the year-long project ndcated that acd s no longer needed and the need for membrane fltraton s much less than orgnally antcpated. Polluton preventon has been acheved through 1.) the elmnaton of mneral sprts to preclean parts, 2.) the elmnaton of hydrochlorc acd used to settle and remove sludge, 3.) the elmnaton of a 60,OOO gdyear sewer dscharge of metal-bearng wastewater, 4.) the recovery of znc metal for off-ste recyclng, and 5.) the recyclng of an aqueous-based soap. The only fltraton needed s occasonal cleanng by the membrane system. Except as a preflter for the membrane, cartrdge flters axe no longer used and a rnsng step has been elmnated. Product rejecton rates have actually decreased as compared to before the project. The work was carred out n conjuncton wth Mnature Castng Corp. of Cranston, RI, and funded by an EPA Small Busness Polluton Preventon grant. 1

8 Introducton Vbratory O p d n Vbratory and tubbng operatons are metal-fnshng technques that are found n a varety of ndustres. Typcal ndustry types nclude jewelry manufacturng and machne tool manufacturng. The sze of the metal parts to be fnshed range from small jewelry peces that measure fracton of an nch to large, heavy metal parts that are several nches long. In order to clean andlor polsh metal parts, aqueous-based chemcals and ceramc or plastc meda are typcally used n ether a vbratng basn or a rotatng barrel. Occasonally, metal-based meda lke steel shot s used. In most cases, the waste effluent from these operatons usually conssts of soapy water, pulverzed meda, and both soluble and nsoluble metals of the type found n the metal parts beng processed. Tradtonal waste treatment technques have ncluded chemcal flocculaton and settlng to remove metal contamnants pror to sewer dscharge. In most nstances, where other types of metal-fnshng and platng operatons exst n the plant, the vbratory waste effluent s mxed wth other metal-bearng waste streams pror to treatment and dsposal. Polluton preventon for these operatons generally conssts of source segregaton, the elmnaton of treatment chemcals, the reducton of sludge generaton, water/soap conservaton, and metal recovery. Though no two processes are exactly the same, ths report profles a typcal tubbng operaton and the types of technologes and methods that can be used by companes to reduce operatng/ envronmental costs and mprove overall operatng effcency. Company Background Snce ts foundng n the early 1960'~~ Mnature Castng Corp. has been nvolved n the manufacture of precson mnature znc de-castngs. As a fully ntegrated faclty, the company s responsble for the desgn and constructon of ther own de-castng equpment as well as the producton of castngs. In the early days of Operaton, all effluents of the de-castng process were dscharged nto the cty sewer sym ncludng loo0 gallon per day of noncontact coolng water and soapy vm cbharge. When the company relocated n 1988 to ts exstng locaton n -, FU, a conscous effort was made to undertake an effectve envronmental maaagement/polluton preventon program. In 1989, the company contacted the Rhode Island Department of Envronmental Management's Polluton hventon Offce. Mnature Castng sought to determne the most effcent and cost-effectve means of reducng and managng ts vbratory waste effluent. In late 1990, DEM's Polluton Preventon Program helped Mnature Castng apply for and wn a $24,000 U.S. EPA Small Busness Polluton Preventon Grant to carry out a year-long study on vbratory soluton recyclng usng membrane technologes. 2

9 .. I t -1tm/mth ' Rbckpn ' -10 tons/ month Me cast 1 'hbbng b Operaton Operaton, znc alloy II h8hcd 9 tons/month product I I - 10 tons/month 4 to sewer. lp flter8... Orgnal Operaton As part of the manufacturng process, precson znc decastngs are cleaned wth vbratory fnshng equpment. At the start of the project, about 10% of the de-castngs had to be precleaned wth mneral sprts pror to vbratory fnshng. All of the effluent from the tubbng machnes was mxed and dluted wth non-contact coolng water and dscharged drectly to sewer (Fgure 1). The objectve of the EPA funded study was to ncorporate membrane technologes, such as ultrafltraton, nto a workng polluton preventon program for the cleanng operaton. Prncpal nvestgators antcpated that the mneral sprts could also be elmnated and replaced wth an aqueous cleaner, membranes could be used to clean and recycle all of the spent cleanng soluton. An addtonal objectve was to recover all de-cast metal concentrate for off-ste recovery. Ten tons of znc alloy ban are melted down every month n the decastng operaton of the manufacturng process. Approxmately 109b of the de-casts exhbt notceably more "smudge" or oxde buld-up than the remanng 9ocKb of the parts. Whle all parts were cleaned n the vbratory machnes, 10% of the peces had to undergo an addtonal preclean step wth mneral sprts pror to the vbratory cleanng. The mneral sprts cleaner was changed over every month by an outsde solvent suppler. On a daly bass, two to three hundred gallons of water was used wth approxmately 2 gallons of soap concentrate n the vbratory operaton. The effluent was fltered through one mcron cartrdge flters and mxed wth lo00 gallons per day of noncontact coolng water pror to dscharge. 3

10 Project Descrpton Procedure Durng the year-long study, dfferent hypotheses were tested. In order to gan a rm understandng of the effect of each process modfcaton, only a few parameters could be vared at a tme. Also, snce a man objectve of the study was to determne the long-term cleanng effectveness of recycled water, condtons could not be vared often. The project was dvded nto three phases where several membrane fdters and acds were tred, as well as some major procedural modfcatons. Fgure 2 depcts the process flow scheme used n the fmt two phases of the project,.e., when acds were used to adjust ph and facltate sludge removal and the membrane system was used to recycle all rnse waters. Fgure 3, whch represents the fnal process desgn, shows how major procedural changes have vastly smplfed the operaton. Tap water make-up for evaporaton Sonp. -30 gal/month Tubbw Soluton Tubbng I Fnlrhed H Clenn Water -- 4 Y

11 -P. Tap vrtcr make-up for errporatton m= 1 P zn de cut. Water Ibblng Soluton Recycle I 1 7 c 4. In Phase 1 (Fgure 2), mneral sprts was elmnated entrely from the cleanng operaton. An aqueous-bascd cleaner (Oakte M3) was used as an effectve replacement. In Phase 2, dfferent acds were tested for phadjustment and sludge settlng. In Phase 3 (Fgure 3), acd use and rnsng were also elmnated. As shown n Fgure 3, the fnal process has been smplfed consderably. Not only has dscharge to the sewer been elmnated, but soap use has also been reduced by almost 90%. Tap water s actually added to the system to make up for evaporaton. A total of 100 gallons of soluton s contnuously recycled. The sludge that s perodcally removed and sent back to the metal suppler for reclamaton was also analyzed for metal content. The cleanlness of the parts resultng from the new process (Fgure 3) was montored n-house aganst normal producton qualty requrements. The followng secton provdes a more detaled dscusson of the results obtaned. 5

12 W Results Whle the orgnal project objectve ncluded the use of acds and fltraton methods to "ze waste dscharges, developmental testng and mprovements obtaned throughout the year-long project ndcated that acd was no longer requred and that the need for membrane fltraton was much less than orgnally antcpated. Polluton preventon has been acheved through: the elmnaton of mneral sprts to preclean parts by ncreasng the strength and broadenng the use of the aqueous cleaner. the elmnaton of acd used to settle and remove sludge. Whle sludge could be more easly removed through ph-adjustment and settlng, t was dscovered that elmnatng the use of acd dd not affect the cleanng and qualty of the parts; n fact, the chemstry of the soluton could be mantaned longer whle much less soap was requred. the elmnaton of a 60,oOO gallyear sewer dscharge of metalbearng wastewater. All solutons have been contnuously reused for twelve months wth absolutely no effluent sewer dscharge. the recovery of znc metal for OR-ste recyclng. All sludge s recovered from the operaton and s sent back to the metal suppler who combnes the sludge wth other scrap metal for reclamaton. the recyclng of an aqueous-bused soap. The caustc cleaner s contnually reused, whle small amounts arc added perodcally to mantan the necessary soap strength. Soap purchases have been reduced by approxmately 909b. The requred s ulaafltraton for cleanng the whole system every sx weks (Fgwe 3). Except as a preflter for the membrane, cartrdge flters axe no longer used and the rnsng step has been elmnated. Product rejecton rates have actually decreased n comparson to rejecton rates experenced before the project was ntated. 6

13 Economcs b.. In Phase 3, the process was smplfed and optmzed: acd use was elmnated, the rnsng step was elmnated, the ten mcron cartrdge flters used pror to the project and durng Phases 1 and 2 were also elmnated, less sludge was created, membrane system operaton was reduced by 90%, and the product qualty had actually mproved. In addton to the envronmental benefts acheved, many cost savngs were quckly realzed. The table below shows a drect cost comparson between the present recyclng operaton and the old, chemcal ueatment/sewer dscharge operaton of Not ncluded n the table arc the costs ncd by the test program tself,.e., Unversty chemcal engneers and analytcal test costs, whch were covered mostly by the EPA grant. Also not lstedare the savngs obtaned by ncreased productvty whch resulted f'" fewer rejected lots of product. Based on captal expense and annual operatng cost calculatons, a sgnfcant payback was observed n less than one year. Economc Anaysr af VbratorylCleanng Operaton - Captal Equpment, ncludng membrane system tanks Pump flters/hwsngs Annual operatng costs map mneralsprts. Cartrdge Nters membrane replacement enew labor water sewer fees analytcal tests 0 $5,500 (approxmate) $1526 $100 1, , neglgble 4,742 neglgble 1, Total Annual Operatng Costs $9157 $2500 7

14 Concluson Ths project demonstrates a cost-effectve and envronmentally sound soluton to vbratory waste management. The project has demonstrated success n polluton preventon and the recyclng of vbratory soluton n a znc de-castng ndustry. Smlar programs at other Mode Island facltes have begun. Whle the vbratoryhbbng operaton s ubqutous, many parameters exst whch render each ndvdual operaton unque. The type of metal to be cleaned, the type of soap used, the desred fnsh on the metal, the type of vbratory meda used, and even the ncomng tap water supply must all be consdered. An economc analyss of ths project dsplays a favorable payback. Whle drect technology msfer has already been demonstrated n other Rhode Island companes, t s antcpated that the data collected and experence acqured from ths project wll facltate programs at other companes to the extent that developmental work and costs are mnmzed. As of March, 1993, ten to ffteen Rhode Island companes have successfully mplemented smlar programs at ther facltes. If more nformaton on ths EPA-funded project s desred, a detaled techncal paper s avalable from the Rhode Island DEM Polluton Preventon Offce, 83 Park St., Provdence, FU 02903, telephone (401)

15 Glossary add: one of a large class of chemcal substances whose water solutons exhbt a ph less than 7 aqueous: made from, wth, or by water caustc: alkalne materal such as sodum hydroxde; when mxed wth water, exhbts a ph greater than 7 de castng: product from a prrocess where molten metal s njected under pressure nto a colder steel mold ef fluent: any gas or lqud emergng from a ppe or smlar outlet; usually refers to waste products from chemcal or ndustral plants as stack gases or lqud mxtures fltraton: a means of separaton where consttuents are separated usually by physcal methods flocculaton: the combnaton or aggregaton of suspended collodal partcles n such a way that they form small clumps; usually used n conjuncton wth addtve chemcals (flocculants) to mat waste water membrane: a mcroporous struncture whch acts as a hghly effcent flter that allows passage of water but rejects suspended solds and collod&; dependng on the membrane type, ons and small molecules may or may not be rejected (see ultrafltraton) mneral sprts: lght petroleum dstllate used for cleanngdegreasng off-ste recovery/rechmaton: the transport of unusable materals away from the ste of operaton to a faclty that makes use of a process that transforms the unusable materal to a usable feedstock for any gven operaton ph-acjustment: the act of changng the ph of an aqueous soluton by addng acd or caustc polluton preventon: the use of materals, process, or practces that duce or elmnate the creaton of pollutants or wastes at the source source segregaton: the act of separatng process chemcal effluents or wastes at each *vdual pont of orgn to facltate materals recovery ultrafltraton: the process that utlzes membranes to acheve separaton of varous consttuents; a typcal ultrafltraton membrane wll allow water, ons, and small molecules to pass through whle rejectng large molecules and suspended solds 9

16

17 Appendx The followng s a partal lst of vendors that supply equpment and provde start-up assstance. The Mode Island Department of Envronmental Management does not endorse any partcular vendor or product. The followng lst s not complete and s provded for nformatonal purposes only. Infntex Inc Man St. Clarnce, NY ocal Dstrbutor (401) Koch Membrane Systems, Inc. 850 Man St. Wlmngton, MA ocal Dstrbutor (508) MSC qud Fltraton Corp. 10 Dusthouse Rd. Enfeld, CT ocal Dstrbutor (203) Romcon, Inc. 100 Cummngs Park Woburn, MA ocal Dstrbutor (617) Sanborn Inc. 25 Commercal Dr. Wrentham, MA ocal Dstrbutor (508) t I.!

18