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Reducing Solvent
Emissions in Painting Operations
Process
Background
Crenlo Inc. is a metal fabricator that manufactures electronic
and electrical enclosures, and off-road vehicle cabs. During
the manufacturing process, materials are sheared, welded,
painted and then assembled. Crenlo has two primary painting
lines: the enclosure line and the cab line.
In the enclosure line, parts
are manually painted in spray booths using electrostatic spray
guns. Both smooth and textured finishes are produced. This
line changes color over 16 times per day and uses approximately
100 gallons of paint daily. Paint is delivered to the spray
booths in reusable five-gallon pails. When the pails are empty,
they are sent to a pail-washing system developed by Crenlo.
In the cab line, cabs are manually
painted using conventional air-atomizing spray guns. Most
of the paint for the cab line is pumped to the spray booths
directly from 55-gallon drums. However, some colors are applied
at each spray booth using pressurized pots. Color changes
are not as frequent on this line as in the enclosure line.
Paint used in the two lines
are thinned with solvents that release volatile organic compounds
(VOCs) as the paint cures. Additional VOCs are released as
fugitive emissions when solvents are used to clean equipment.
Solvent contaminated with paint during cleaning processes
is shipped off-site for distillation and then returned for
reuse at Crenlo. In 1992, Crenlo released over 130,000 pounds
of VOCs, as reported on its Toxic Release Inventory (TRI)
Form R.
Incentives for Change
Crenlo was interested in reducing its solvent emissions in order to:
- Meet anticipated lower allowable VOC emission levels in the future.
- Address employee health and safety concerns.
- Achieve Minnesota-50 Project goals. By participating in this project, Crenlo made a voluntary commitment to achieve a 50 percent reduction in emissions of targeted priority chemicals by 1995.
Intern Activities
The intern project focused on three options for reducing VOC emissions:
- Improve the design of an existing paint pail-washing system to reduce the amount of cleaning solvent used.
- Evaluate the feasibility of using a high-volume, low-pressure (HVLP) paint spray system.
- Evaluate two types of low-VOC coatings: high-solids and waterbased paints.
1. Paint Pail-Washing System.
One source of VOC emissions at Crenlo is the paint pail washer.
The old pail washer operated like a dishwasher with two cleaning
stages followed by a solvent rinse. The solvent remained in
a shallow tray on the bottom of the washer until it was sprayed
into the pails. The tray exposed a large surface area of solvent
to the air each time the washer was opened. Approximately
13 gallons of new solvent were added to the washer each day.
The intern helped construct
a new pail-washing system that was designed to minimize the
surface area of solvent exposed to the air. The new system
holds the solvent in an enclosed container under the washer
until it is needed, rather than holding it in a shallow tray
within the cleaning compartment. A funnel in the bottom of
the washer directs the solvent back into the container where
a recirculating pump system directs it back into the washer.
The new design allows less solvent to evaporate into the atmosphere,
and reduces the amount of new solvent added to the washer.
The intern also developed a list of suggested procedures for
improving the handling of paint pails and solvents
2. HVLP Spray System.
Paint consumption tests were run on the tractor cab line,
which compared Crenlo's existing conventional spray system
to the HVLP system. Tests were performed on identical parts
that were sprayed with the same coatings by the same operators.
The average amount of paint used to cover each cab was measured
for each system and results were compared.
3. Low-VOC Coatings.
High-solids and waterbased paints were evaluated as substitutes
for the solvent-based paints. All paints tested on production
parts required approval from the finishing engineer and the
customer to ensure that product specifications were met. In
the tractor cab line, four high-solids paints were tested
on production cabs as replacements for the current paint.
High-solids and waterbased paints were also tested on nonproduction
panels as potential replacements for solvent-based paints
used in the enclosure line. Line speeds, part configuration
and operating procedures were kept similar to current practices.
Results
1. Paint Pail-Washing System. Although
the intern did not measure the amount of solvent used in the
new washer, it was estimated that solvent use would be reduced
by nearly 50 percent or 1,600 gallons per year. This would
save Crenlo nearly $2,000 annually through reduced solvent
purchase and reclamation costs. The redesigned pail washer
was constructed for $2,200 and is currently in use at Crenlo.
2. HVLP Spray System.
The HVLP spray guns required 10 percent less paint to cover
the same parts as the conventional spray system due to reduced
overspray. At this reduced rate, Crenlo would reduce its use
of thinned paint in the tractor cab line by 2,100 gallons,
saving $37,000 annually. The finish applied with HVLP guns
exhibited a uniform dry-film thickness. Crenlo has purchased
14 HVLP guns and pressurized pumping equipment for its cab
line at a total cost of approximately $24,000.
3. High-Solids, Low-VOC
Coatings. Crenlo has converted approximately 90 percent
of its coatings from conventional to high-solids paint in
the cab line. Converting to a high-solids system will save
approximately $37,000 annually and reduce annual VOC emissions
by 45,000 pounds. No additional equipment will be required
for the conversion.
In the enclosure line, reduced
VOC emissions and cost savings could result by converting
to either the high-solids or water-borne paint systems. At
a negligible cost for conversion, using high-solids paints
in the enclosure line would reduce VOC emissions by an estimated
70 percent (40,000 pounds) and save $86,000 annually with
an almost immediate payback.
Converting to a waterbased
painting system for the enclosure line would cost an estimated
$132,000, but would reduce VOC emissions by an estimated 70
percent. This would also result in annual savings of about
$120,000 annually, with a payback of approximately one year.
Tests revealed that the transfer efficiency of waterbased
paint was 52 percent, followed by high-solids paints at 39
percent, and solvent-based paints at 32 percent. However,
tests showed that the waterbased paints tended to blister
on the nonproduction panels, and the high-solids paints caused
excessive paint thickness. Further testing for each system
will be required to address these concerns.
Summary
Approximately $162,000 in total annual cost savings could
result from using the new paint-pail washer and converting
to an HVLP spray system and low-VOC coatings, assuming Crenlo
selected a high-solids paint system. The one-time cost for
these modifications is estimated at $26,000.
The above changes could also
reduce annual VOC emissions by 109,000 pounds. Additional
low-cost ways to further reduce VOC emissions include improving
procedures for solvent handling and equipment cleaning.
Since the project ended, Crenlo
has decided to implement both water-borne and high-solids
paint systems on the enclosure line. Six stainless steel pumps
have been purchased to pump the water-borne paint. In addition,
another paint pail washer is being built for the cab line.
More
Information
MnTAP has a variety of technical assistance services available
to help Minnesota companies manage and reduce their industrial
waste. If you would like assistance or more information about
MnTAP's Intern Program, call 612.624.1300 or 800.247.0015
in greater Minnesota.
This project was conducted in
1993 by MnTAP intern Joe Berns, a civil engineering student
at the University of Minnesota.
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