evEPA United States Environmental Protection Agency Risk Reduction Engineering Laboratory Cincinnati OH 45268 Research and Development EPA/600/S-92/007 April 1992 ENVIRONMENTAL RESEARCH BRIEF Waste Minimization Assessment for a Manufacturer of Automotive Air Conditioning Condensers and Evaporators Gwen P. Looby and F. William Kirsch* Abstract The U.S. Environmental Protection Agency (EPA) has funded a pilot project to assist small- and medium-size manufacturers who want to minimize their generation of waste but who lack the expertise to do so. Waste Minimization Assessment Cen- ters (WMACs) were established at selected universities and procedures were adapted from the EPA Waste Minimization Opportunity Assessment Manual (EPA/625/7-88/003, July 1988). The WMAC team at the University of Tennessee performed an assessment at a plant manufacturing automotive air condition- ing condensers and evaporators - approximately 400,000 units per year. To make condensers, extrusions and steel coil are machined, degreased, welded, and painted. Header assem- blies are brazed and degreased. Fins are produced and placed inside header assemblies before final brazing, leak testing, packaging and shipping. To make evaporators, aluminum side sheet stock and coil and box extrusions are machined and degreased along with aluminum tube stock. All parts are as- sembled with the fins before brazing, cleaning, and chromate surface treatment. After leak testing, evaporators are packaged and shipped. The team's report, detailing findings and recom- mendations, indicated that the majority of waste was generated in the non-chromate waste water treatment facility but that the greatest savings could be obtained by converting to a powder coating technique in the condenser line to eliminate both con- taminated paint solids and paint liquids. This Research Brief was developed by the principal investiga- tors and EPA's Risk Reduction Engineering Laboratory, Cincin- nati, OH, to announce key findings of an ongoing research project that is fully documented in a separate report of the same title available from the authors. * University City Science Center, Philadelphia, PA 19104 Introduction The amount of waste generated by industrial plants has be- come an increasingly costly problem for manufacturers and an additional stress on the environment. One solution to the prob- lem of waste is to reduce or eliminate the waste at its source. University City Science Center (Philadelphia, PA) has begun a pilot project to assist small- and medium-size manufacturers who want to minimize their formation of waste but who lack the in-house expertise to do so. Under agreement with EPA's Risk Reduction Engineering Laboratory, the Science Center has established three WMACs. This assessment was done by engineering faculty and students at the University of Tennessee's (Knoxville) WMAC. The assessment teams have considerable direct experience with process operations in manu- facturing plants and also have the knowledge and skills needed to minimize waste generation. The waste minimization assessments are done for small- and medium-size manufacturers at no out-of-pocket cost to the client. To qualify for the assessment, each client must fall within Standard Industrial Classification Code 20-39, have gross annual sales not exceeding $50 million, employ no more than 500 persons, and lack in-house expertise in waste minimiza- tion. The potential benefits of the pilot project include minimization of the amount of waste generated by manufacturers, reduced waste treatment and disposal costs for participating plants, valuable experience for graduate and undergraduate students who participate in the program, and a cleaner environment without more regulations and higher costs for manufacturers. G$Q Printed on Recycled Paper ------- Methodology of Assessments The waste minimization assessments require several site visits to each client served. In general, the WMACs follow the proce- dures outlined in the EPA Waste Minimization Opportunity Assessment Manual (EPA/625/7-88/003, July 1988). The WMAC staff locates the sources of waste in the plant and identifies the current disposal or treatment methods and their associated costs. They then identify and analyze a variety of ways to reduce or eliminate the waste. Specific measures to achieve that goal are recommended and the essential supporting tech- nological and economic information is developed. Finally, a confidential report that details the WMAC's findings and recom- mendations (including cost savings, implementation costs, and payback times) is prepared for each client. Plant Background The plant manufactures condensers and evaporators for auto- motive air conditioners. The 250 employees operate the plant 3,840 hr/yr to produce 400,000 condensers and evaporators annually. Manufacturing Process An abbreviated process flow diagram is illustrated in Figure 1. The following discussion includes complete process summa- ries. Condenser Line Raw materials used in the condenser manufacturing line in- clude aluminum coils, tube stock, header assemblies, and extrusions; steel coils; and miscellaneous hardware such as nuts, pins, clips, wire, and fittings. The first operation in the condenser line is the production of fins from aluminum roll stock on a fin machine in a proprietary process. Some of the machine oil used in this operation evapo- rates and the remaining spent oil is shipped offsite as a non- hazardous waste. The fins are then transported to the core assembly station. Aluminum extrusions and steel coils undergo cutting, bending, and piercing operations. A portion of the cutting oil used in these operations evaporates and the remaining spent oil is shipped offsite as non-hazardous waste. The steel coils and miscellaneous parts (nuts, pins, clips, wire, and fittings) are then degreased to remove dirt and oil prior to further process- ing. Other raw materials which undergo this degreasing step include the purchased aluminum tube stock and header as- semblies. Degreasing is accomplished by hand-dipping parts into small troughs of 1,1,1-trichloroethane. Spent 1,1,1- trichloroethane solvent is shipped offsite as hazardous waste, Condenser Line Rn Production Machining Degreasing Brazing Powder Coating Assembly Leak Testing Dip Painting Final Assembly Spent Brazing Compound MEK Evaporation Spent Oil Liquid and Solid Paint Waste Waste Water Treatment Waste Water 53% to Fume Scrubbers 47% to Municipal Sewer Evaporator Line Fin Production Machining Degreasing Brazing Cleaning Chromate Surface Treatment Assembly Leak Testing Chromate Waste Water Treatment Chromic Acid Sludge Chromic Hydroxide Sludge Figure 1. Abbreviated process flow diagram. ------- but the majority of the solvent consumed evaporates to the plant atmosphere. Steel coils and the nuts, pins, and clips are spot-welded and conveyed through an electrostatic powder-paint coating booth followed by a curing oven. A small amount of waste coating is disposed of as a non-hazardous material. When the part racks become excessively coated with paint overspray, they are sent through a burn-off oven where the overspray is incinerated; ash from the cleaning process is shipped offsite as non-haz- ardous waste. The steel assemblies are then transported to the final assembly area. Aluminum extrusions, aluminum tube stock, and 85% of the header assemblies, wire, and fittings are transported to a manual brazing area. The remaining 15% of the header as- semblies, wire, and fittings are first sent to the "header brazing area" for spot-brazing. Next, those areas that are spot-brazed are hand-dipped in a trough of 1,1,1-trichloroethane for degreasing. Some of the solvent evaporates to the plant atmo- sphere and any spent solvent is shipped offsite as hazardous waste. After spot-brazing, these parts and the parts mentioned previously are brazed in the manual brazing area. After this brazing operation, the parts are stretched and bent in further shaping operations and are transported to the core assembly area. The fins, aluminum tube stock, aluminum extrusions, and header assemblies are then assembled to form a condenser core. Banding wire is wrapped around the core to allow the fin contact points to touch the tube stock, thereby permitting proper brazing. Next, cores are conveyed through a brazing-compound spray booth. The plant utilizes a proprietary brazing slurry to which methyl ethyl ketone (MEK) is added for thinning. This slurry mixture acts as a brazing flux and filler metal for the product. From the spray booth, the parts are conveyed through a 4- stage brazing oven. Stack gases from the oven are directed to a fume scrubber which removes brazing compound ash from the exhaust gases by trapping it in a continuous water stream that flows to the plant's non-chromate waste water treatment facility. The exhaust gases, which consist mainly of evaporated MEK, pass through the fume scrubber and are released to the outside atmosphere. Next, the product is conveyed through a spray water rinse, a compressed air blow-off station, and a dry- off oven. Waste water from the rinse stage is pumped to the non-chromate waste water treatment facility. After the dry-off oven, the products are manually de-banded and leak tested. Units which fail the pressurized leak testing are sent to the repair department. Units which pass are con- veyed through a water-based dip paint line. Contaminated paint solids and liquids are shipped offsite as hazardous waste. The product is then conveyed through a compressed air blow- off station and a curing oven and then to final assembly where the steel assemblies are added to the cores. Evaporator Line Several operations and wastes involved in the evaporator line are similar to those in the condenser line with the exception of the painting operation; paint is not applied to the evaporators. Raw materials for the evaporator line consist of several differ- ent aluminum parts including roll stock, side-sheet stock, extru- sions, tube stock, and miscellaneous materials including nuts, pins, and clips. Fins are produced from the aluminum roll stock on a fin machine. A portion of the cutting oil utilized in this operation evaporates and the remaining spent oil is shipped offsite as non-hazardous waste. Fin units are then transported to a core assembly station. Side-sheet stock and extrusions undergo cutting, bending, and piercing operations. A portion of the cutting oil utilized in these processes evaporates and the remaining spent oil is shipped offsite as non-hazardous waste. The extrusions and tube stock are then cleaned with solvent to remove dirt and oil. The spent 1,1,1-trichloroethane solvent is shipped offsite from this opera- tion as hazardous waste; most of the solvent evaporates to the plant atmosphere. A hand-brazing operation follows degreasing and then the extrusions and tube stock are transported to the core assembly station. At that station, aluminum fins, sheet stock, extrusions, and tube stock are assembled into an evapo- rator core. Banding wire is fastened around the unit to allow the fins to touch the tubing stock at the points where brazing is to occur. From core assembly, the cores are first conveyed through a booth for spray application of brazing compound in a manner similar to that Described for the condenser process line. After the brazing oven, parts are de-banded and 95% are transported immediately to a 2-stage ultrasonic cleaning tank. The remaining 5% undergo a secondary brazing operation before being transported to the ultrasonic cleaning tanks. A 4- stage water rinse and a 2-stage air blow-off follow the ultra- sonic cleaning. Waste water from these three steps is pumped to the waste water treatment facility. Next, parts are conveyed through a chromate surface treatment process which will be discussed next. Parts are then blown dry and moved through a dry-off oven from which they are transported to final assembly. The assembled product is then tested for leaks, the core face is blown dry, and units are sent to shipping. Chromate Surface Treatment , The chromate surface treatment process is one of the steps in the evaporator production process. Parts from the 2-stage compressed air blow-off station in the evaporator line enter the #1 tank, a pre-wash tank which contains hydrogen peroxide, sulfuric acid, and water. This solution microscopically etches the surface of the metal in preparation for chromium treatment. Contaminated water from tank #1 is pumped to 2 underground treatment pits in the chromate treatment facility which will be discussed. Next, the parts are conveyed through 2 water rinse tanks (tanks #2 and #3). A continuous flow of water passes through tank #2 and is directed to the non-chromate waste water treatment facility. Water is added to tank #3 daily in batch fashion and is subse- quently emptied nightly during a non-production period. This waste water, similar to that drained from tank #2, is pumped to the non-chromate waste water treatment facility. Tank #4 is the chromate conversion tank. In this tank, a phosphate coating is formed on surfaces for corrosion resis- tance and improved surface wettability. Three different chrome phosphate chemicals are used. Water from this tank is dgmped periodically directly to the waste acid holding tank in the chro- mate treatment facility. From the chromate conversion tank, parts are conveyed through two counterflowing rinse tanks (tanks #5 and #6). Make-up ------- water is added to rinse tank #6 and overflow from this tank cascades back to tank #5. Waste water from both tanks is pumped to an underground pit located beneath the chromate line before being pumped to the waste acid holding tank in the chromate treatment facility. A wetting agent, which causes water to bead up and roll off the finished product, is added to tank #7. Waste water from this tank is dumped periodically to the underground treatment pits in the chromate treatment facil- ity. The product is then conveyed to the next step in the evaporator line process, a compressed air blow-off station. Chromate Waste Water Treatment Waste water from several tanks (specifically tanks #1, 4, 5, 6 and 7) in the chromate surface treatment line is directed to the chromate waste water treatment process. Water from tanks #1 and #7 is pumped to 1 of 2 collection pits where sodium bisulfite is added to reduce the toxic hexavalent chrome level. Hydrated lime is then added to the solution to raise the pH and neutralize the acid and thereby convert the chromium to a less toxic trivalent form. Immediately after neutralization, sodium hydrosulf'rte is added to insure that all chromium remains in the trivalent form. Then the water is pumped to 1 of 2 sludge thickening tanks from which water is decanted and pumped to the non-chromate waste water treatment facility. Chromic hy- droxide sludge is removed from the thickening tank and shipped offsite as hazardous waste. In a separate operation, water from chromate line tank #4 is pumped directly to a waste acid holding tank. In addition, waste water from tanks #5 and #6 is directed to a holding pit. This water is then pumped to the waste acid holding tank, Where it becomes mixed with the water from tank #4. This mixture is not treated in any manner before being shipped off- site as hazardous waste. Non-Chromate Waste Water Treatment Several waste water streams are fed from various processes in the plant to a large outside water collection pit. From the pit, water is pumped to a pH adjustment tank where hydrated lime is added to raise the pH of the water from approximately 3 to 6.5. Water is then pumped through 2 cooling towers to lower its temperature from 95°F to about 75°F. From there, the water is treated again in another pH adjustment tank where sodium hydroxide is added to raise the pH from 6.5 to 8.5. Water is then pumped into a large clar'rfier where a small amount of hydrated lime is added to initiate the precipitation of solids. Sludge is drawn from the bottom of this tank to a filter press where the water is removed by pressing it from the solid waste; the solid waste is removed from the plant as non-hazardous waste. The water from this pressing operation is directed back Into the clarifier tank. Sludge-free water from the top of the clarifiertank is passed through a sand-filter polishing unit and a portion is recycled within the plant for operation of the fume scrubbers in the condenser and evaporator process lines. The remaining water is released to the municipal sewer system. Existing Waste Management Practices • The plant operates an extensive waste water treatment system described previously. • Small run-off troughs have been installed on the spray brazing booths to capture some of the slurry run-off from the spray process. Fume scrubbers on the brazing oven stacks cap- ture the slurry particulates from the stack gases. The slurry particulates are then directed to the water treatment facility. Toxic hexavalent chromic acid waste is converted to trivalent form before removal from the plant. Waste Minimization Opportunities The type of waste currently generated by the plant, the source of the waste, the quantity of the waste, and the annual treat- ment and disposal costs are given in Table 1. Table 2 shows the opportunities for waste minimization that the WMAC team recommended for the plant. The type of waste, the minimization opportunity, the possible waste reduction and associated savings, and the implementation cost along with the .payback time are given in the table. The quantities of waste currently generated by the plant and possible waste reduction depend on the production level of the plant. All values should be considered in that context. It should be noted that the economic savings of the minimiza- tion opportunity in most cases, results from the need for less raw material and from reduced present and future costs asso- ciated with waste treatment and disposal. Other savings not quantifiable by this study include a wide variety of possible future costs related to changing emissions standards, liability, and employee health. It should also be noted that the savings given for each opportunity reflect the savings achievable when implementing each waste minimization opportunity indepen- dently and do not reflect duplication of savings that would result when the opportunities are implemented in a package. Additional Recommendations In addition to the opportunities recommended and analyzed by the WMAC team, three additional measures were considered. These measures were not completely analyzed because of insufficient data or minimal savings as indicated below. They were brought to the plant's attention for future reference, however, since these approaches to waste reduc- tion may increase in attractiveness with changing plant condi- tions. Pump the 1,1,1-trichloroethane to the cleaning troughs instead of transferring the solvent from the holding tank manually in buckets. The current transfer method leads to spillage and excessive evaporative losses. Explore the possibility of using an alternate flux- ing system containing less hazardous materials. • Analyze the treated water from the non-chromate waste water process to determine if more of it is acceptable for reuse in the process. Currently only two-thirds of the treated water is reused. This research brief summarizes a part of the work done under Cooperative Agreement No. CR-814903 by the University City Science Center under the sponsorship of the U.S. Environmen- tal Protection Agency. The EPA Project Officer was Emma Lou George. ------- Table 1. Summary of Current Waste Waste Generated Evaporated 1, 1, 1-trichloroethane Spent 1, 1, 1-trichloroethane Contaminated brazing slurry Evaported methyl ethyl ketone Evaporated cutting oil Spent Cutting oil Contaminated paint solids Contaminated paint liquids Paint ash Evaporated 1, 1, 1-trichloroethane Spent 1, 1, 1-trichloroethane Contaminated brazing slurry Evaporated methyl ethyl ketone Evaporated cutting oil Spent cutting oil Chromic acid sludge Chromic hydroxide sludge Waste water sludge Generation Source of Waste Degreasing operations in the condenser process line Degreasing operations in the condenser process line Spray-brazing booth in the condenser process line Spray-brazing booth and fume scrubber in the condenser process line Machining operations in the condenser process line Machining operations in the condenser process line Dip paint line in the condenser process line. The waste consists of spent paint filters, paint-covered plastic sheets, and paint residue. Dip paint line in the condenser process line. The liquid paint waste was generated during the annual maintenance procedure. Burn-off oven for removing dried paint from the parts racks in the condenser process line Degreasing operations in the evaporator process line Degreasing operations in the evaporator process line Spray-brazing booth in the evaporator process line Spray-brazing booth and fume scrubber in the evaporator process line Machining operations in the evaporator process line Machining operations in the evaporator process line Acid holding tank in the chromate waste water treatment process Sludge thickening tanks in the chromate waste water treatment line Filter press in the non-chromate waste water treatment line Annual Quantity ' Generated 4,282 gal 2,805 gal 522 gal 12,569 gal 2, 140 gal 200 gal 38,520 Ib 5,220 Ib 1 bbl 1,428 gal 935 gal 698 gal 6,770 gal 1,160 gal 100 gal 97,500 gal 45,000 gal 576yd3 Annual Waste Management Cost $0' 2,780 5,070 0' 0' 2,320 37,820 4,450 560 0' 2,060 7,170 0' 0' 2,070 53,180 45,210 158,540 1 Plant personnel report no waste management cost associated with solvent evaporation. ------- Tfbl» 2. Summary of Recommended Waste Minimization Opportunities Annual Waste Reduction Net Annual Waste Generated Minimization Opportunity Quantity % Savings Contaminated paint Replace the dip paint 38,520 Ib 100 $133,820' Implementation Payback Cost Years $130,320 1.0 solids, Contaminated PaM Squids Waste water sludge Contaminated paint solids Evaporated 1,1,1- trichhroethane Waste water sludge system with an electrostatic epoxy powder paint coating 5,220 Ib 100 system. The proposed system will lead to more even coating of complex surfaces and easier collection and reuse of drag-out powder. Install a sludge dry-off oven in 432yd3 75 23,910* the waste water treatment line to dry the sludge processed in the filter press. Evaporation of water from the sludge will greatly reduce the volume of sludge currently hauled offsite. Modify the dip paint system to 15,408 Ib 40 19,720' increase the holding time of the dip-painted parts over the paint tank. Parts should be tilted back and forth so that maximum paint drainage into the paint tank is achieved. Cover the troughs of 1,1,1- 2,855 gal 50 14,280' trichloroethane in the condenser and evaporator process lines to reduce solvent evaporative losses. Currently the troughs are open and unused 95% of the time. Modify the brazing slurry run-off 6yd3 1 3,980' collection systems in the condenser and evaporator process lines to maximize the amount of slurry returned to the spray booth holding tanks. This WMO will make it possible to reuse approximately 40% of the slurry that is currently drained to the waste water treatment process. 28,440 1.2 25,440 1.3 1,880 0.1 4,980 1.3 ' Includes row material cost savings. ' Total cost savings have been reduced by ihe operating exist of the oven. 'US. Government Printing Office: 1992—648-060/60079 ------- |