Better Burning

Regenerative thermal oxidizers (RTOs) are effective pollution control devices widely used to destroy up to 99.9% of VOCs in paint shop process air streams by burning at temperatures to 1,500°F.

Heating air to those kinds of temperatures requires a lot of energy, so RTO suppliers are constantly developing new ways to make their RTO units more energy-efficient. Typically, RTOs are equipped with heat recovery devices that recycle that vast majority of thermal energy that would otherwise vent up the exhaust stack. The recovered, heated air can be used for warehouse or plant heating and process make-up air, or even for curing or drying applications in the process.

How much difference can an energy-efficient RTO make? Consider the case of Central Motor Wheel of America Inc. (CMWA; Paris, KY). The company, a manufacturer of steel and aluminum automotive wheels, wanted to improve efficiency on its two aluminum finishing lines.

Each line consists of primer and topcoat booths that recirculate some air and exhaust some to an RTO. Air from primer and topcoat ovens also exhausts to the oxidizer. CMWA contracted with Dürr Systems, Inc. (Plymouth, MI) to equip one of the lines with a 15,000-scfm, high-efficiency RTO. The Dürr Ecopure RL15 unit had a thermal energy recovery rating of 95% and an average temperature increase across the unit of 100°F.

The other line treated its emissions with a 13,000-scfm RTO with a thermal energy recovery rating of about 55% and a temperature increase across the unit of about 580°F. Because both oxidizers treated relatively the same air volume and emission concentration—11,675 scfm and 21 lb/hr on average—installing the Dürr RTO provided a simple way to compare energy consumption on the two lines.

The results were clear: fuel costs for the relatively inefficient unit approached $500,000/yr, while fuel costs on the aluminum line equipped with the more efficient RTO were closer to $65,000/yr. That's an 80% reduction in fuel consumption and a projected $427,000 annual savings based on current fuel costs and production hours of operation. Energy savings on the aluminum lines led CMWA to similarly equip its steel wheel finishing line.