Thermal De-oiler Replaces Solvent Degreaser

Problem
A major manufacturer of automobile equipment uses a variety of aluminum parts in the fabrication of automobile air-conditioner evaporators. The parts are formed in stamping machines that use oil as a drawing lubricant. Brazing is accomplished in a vacuum furnace that requires clean and dry parts to prevent failure of the brazed surfaces.

The plant had been de-oiling the parts in a solvent-based vapor degreasing line. However the state environmental agency mandated that the line be shut down because it produced excessive water and air pollution.

Relieving the Dilemma
The manufacturer contracted Epcon Industrial Systems, Inc. to design and construct a waterless and solventless thermal de-oiling* system to replace the solvent line in time to meet a state-mandated deadline.

The new system was to be a one-to-one replacement for the existing cleaning line in terms of production rate, configuration, and parts carriers. After evaluating the existing line, Epson recommended a U-shaped configuration measuring approximately 100 feet in length with a working space of 8 feet. Low-pressure and high-pressure recirculation fans with variable-frequency drives were installed at critical points to provide temperature balancing within the de-oiler chamber. Air curtains and careful placement of the return-air plenums would prevent vaporized oil from escaping the entry and exit vestibules.

With this basic design in place, Epson added a thermal oxidizer to the system to eliminate any vaporized oils (VOCs). The oxidizer's operating at 1500°F with a combustion-chamber residence time of 1.0 sec demonstrated vapor destruction removal efficiencies (DREs) of greater than 95%. Two stainless-steel shell-and-tube heat exchangers were installed at the outlet of the oxidizer.

The primary exchanger heats ambient air, which supplies the heat to the de-oiler, and a secondary exchanger, saves fuel by elevating the temperature of the exhaust oil vapor prior to its destruction in the combustion chamber. The combustion of the oil provides up to 1.0 MBTU/hr of heat for the de-oiler. No heat source other than the natural-gas-fired burner and the heat of combustion of the VOCs is needed to maintain the required temperature for de-oiling.

Results
In the case of the automobile manufacturer, the de-oiling system, online since December 1998, has produced substantial cost reductions compared with the costs of vapor degreasing. The reduction of intangibles, such as safety and industrial hygiene—there is no contact of the parts with the products of combustion since they exit the de-oiler clean and dry—is unknown, but probably significant.

The manufacturers also realized thermal de-oiling's several other benefits compared with solvent de-oiling.

• Transport, storage, and chemicals' handling were eliminated.
• Fugitive emissions were eliminated and air pollution was reduced.
• Waste treatment and disposal was eliminated.
• Maintenance and operating costs were reduced.

Epcon manufactures thermal oxidizers, industrial ovens, heat exchangers, wash lines and coating lines.

*Thermal de-oiling is a process that uses indirectly heated dry air to clean parts contaminated with oils or lubricants. The difference between such thermal equipment as an oven and a thermal de-oiler is that the de-oiler burns the oil vapor in an oxidizer to provide clean, dry heat for the de-oiling chamber. A natural-gas-fired burner in the thermal oxidizer provides the balance of the heat needed for complete oxidation. Indirect heating helps avoid condensation of water or vapor in the de-oiling chamber or on the parts.

Contact: Epcon Industrial Systems, Inc, P.O. Box 7060, The Woodlands, TX 77387. Tel: 800-447-7872, 409-273-3600; Fax: 409-273-4600.

Edited by Paul Hersch