Reuse of Wood Finishing Overspray

Case Study, Minnesota Technical Assistance Program, University of Minnesota

Company: Medallion Kitchens; Waconia, Minnesota

Industry: Woodworking industry: manufacturing kitchen cabinets and bathroom vanities.

Waste stream: Solvent-based wood sealer overspray.

Change: Install wood finish reclamation system in sealer spray booth to catch overspray material.

Savings: 11/5 gallons of sealer overspray are reclaimed from the system each day. This saves $92 per day ($8 per gallon) or an estimated $23,000 per year in raw material costs. Sealer booth sludge was reduced by 50 percent (25 gallons per day) which reduced hazardous waste disposal costs by $120 per day or $30,000 per year. Estimated total annual cost savings = $53,000.

Process Background

Medallion Kitchens is a leading woodworking company manufacturing a variety of kitchen cabinets and bathroom vanities at a daily rate of approximately 900 cabinets. Wooden cabinet parts are stained and then finished with a solvent-based catalyzed sealer and topcoat before they are assembled into completed cabinets. The process of spraying the sealer and topcoat finishes onto the cabinets is automated; a central computer controls a conveyor belt system, two water-wash spray booths and two drying ovens, and sensor-automated spray guns apply coatings to cabinet parts in each spray booth. Overspray, the finish that misses cabinet parts during application, is wasted raw material. Overspray generates waste by: (1) volatilizing, which releases volatile organic compounds (VOCs); (2) landing on conveyor bands, which must then be cleaned off and disposed of as hazardous sludge; or (3) falling into a tank containing recirculating water, which collects and floats in the water until manually removed and disposed of as hazardous sludge. Before any changes were made, this application process used approximately 75 gallons of sealer per day in the sealer spray booth, and generated approximately 50 gallons per day of hazardous waste sludge.

Incentives for Change

Medallion Kitchens was interested in reducing raw material and hazardous waste disposal costs by reusing overspray material and reducing sludge waste. Overspray is wasted raw material and is expensive to dispose of as a hazardous waste sludge. In addition, Medallion Kitchens wanted to reduce labor costs associated with sludge removal, dewatering and handling, along with potential liabilities after the sludge leaves the facility.

Process Change

Medallion Kitchens began experimenting with various designs for a reclamation system in 1989. With the assistance of a MnTAP intern during the summer of 1992, Medallion Kitchens developed a reclamation system to collect sealer overspray material. During the development of the reclamation system, various modifications were investigated to optimize the system:

After completing the modifications listed above, an overspray reclamation system was fabricated and installed inside the sealer spray booth. The system consists of two collection trays, a support assembly, a pump, a holding reservoir and minor plumbing (see figure 1). The collection trays were installed directly below a metal-band conveyor system in-line with the rotating spray guns, and were designed to catch most of the overspray material before it fell into the water-wash tank.

To minimize evaporation of the coating solvents collected in the trays, cooling water is circulated under the trays. Collected material is then recirculated through a pumping system to prevent it from curing. When approximately five gallons of overspray material has accumulated, it is manually removed from the spray booth and transferred to the mixing area. Solvent and catalyst are then added to the collected overspray to obtain the proper viscosity and chemical formulation before it is combined with new sealer, added to the spray system and reused.

Cost Savings and Results

With the assistance of a MnTAP intern, Medallion Kitchens designed, built, installed and is now operating an effective reclamation system which collects and reuses overspray material and reduces hazardous waste. The cost to Medallion Kitchens to install the system was approximately $2,000 for materials per booth, and $500 for labor (50 hours at a rate of $10 per hour).

During October and November 1992, an average of 11.5 gallons per day of overspray material was collected from the sealer spray booth reclamation system. Based on this average daily collection rate and a raw material cost of $8 per gallon, it is estimated that Medallion Kitchens will save $92 per day or $23,000 per year on raw material costs as a result of installing the overspray reclamation system in one spray booth.

Hazardous waste sludge resulting from overspray in the sealer spray booth has been reduced from an average of 50 gallons per day to 25 gallons per day. Consequently, hazardous waste disposal costs have been reduced from $240 per day to $120 per day, which will save Medallion Kitchens approximately $30,000 annually in hazardous waste disposal costs.

The estimated total savings to Medallion Kitchens as a result of installing the overspray reclamation system in one spray booth is $53,000 annually. Medallion Kitchens currently is in the process of building an additional reclamation system which will be installed in the topcoat finishing spray booth.

Some additional time is now required by Medallion Kitchens' employees to service the new reclamation system including removing collected material from the reservoir, remixing finishes and cleaning up the spray booth. However, less time is needed to service the water-wash spray booth because the amount of sludge to manage has been reduced, and water chemistry needs fewer adjustments because of lower rates of overspray contamination.

Prior to installing and using the reclamation system, the solids transfer efficiency was approximately 40 percent. After the system was installed, the solids transfer efficiency was raised to 80 percent due to reuse of the reclaimed material.

Early results indicate that VOC emission levels remained the same due to volatilization of solvents in the spray booth. Volatilization also caused material in the reclamation system to thicken. Solvent was then added to thin the material before it could be reused. The use of solvent for tray cleaning was eliminated when a nonstick coating was applied to the trays; however, care must be taken when cleaning the trays to ensure that the nonstick coating is not scratched. Currently, only a small amount of solvent is used to clean-out the hoses in the reclamation system.

Additional Information

If you have questions about this project, or if you would like assistance with your waste reduction efforts, call MnTAP at 612/624-1300 or 800/247-0015.