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
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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.
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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
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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.
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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.
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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
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