VOC Destruction Generates Auxiliary Steam for Heating

A Midwestern coatings producer had plans to expand and needed maximum achievable control technology (MACT) to comply with U.S. EPA air-pollution regulations.

The company also had to satisfy some special conditions:

1. Its coating lines had to run at 3% lower explosive limit (LEL) and as high as 25% LEL.
2. It wanted to avoid the repetitive failures (due to heavy solvent loads' causing temperature fluctuations) of the heat exchangers used with its existing recuperative oxidizers.
3. It had need for additional steam to run the process dryers.

The company contracted with Controlled Environment Systems (Waukesha, WI) in search of achieving its objectives.

CES provided an air-pollution-control and energy-recovery system—a twin-bed regenerative thermal oxidizer that generates auxiliary steam for in-plant process heating.

Premising the coating company's choosing CES was the "flexibility [the CES system] provided for energy-efficient operation between 0% and 26% lower explosive-limit solvent concentrations from the coatings and mix-room process sources," said David Swinehart, VP of engineering at CES. He added "the system provides 99% volatile organic compound, hydrocarbon, and odor control for the entire range of coatings formulations—as well as loadings and flow rates from 1,000 to 13,300 standard cubic feet per minute."

A variety of solvent vapors, including xylene, methyl ethyl ketone, heptane, phenolics, aromatics, toluene, and alcohols are oxidized in the combustion chamber of the oxidizer system at 1600°F to 2000°F with a 1-sec retention time.

The flow of exhaust gases passes through twin beds of durable, high-temperature, inert ceramic heat-transfer media that provide 95% primary heat recovery.

The first bed preheats the VOCs on their way to the combustion chamber. The combustion chamber burns away the VOCs, and the heat released during combustion keeps the ceramic beds hot. The cleaned gas then passes through the second bed to recharge its heat energy before being directed into an integral waste-heat-boiler system, which generates steam and hot water for the plant's process systems.

"The higher the solvent loading, the higher [the] levels of steam [that] are generated," says Swinehart. "For example, VOC inlet loadings of approximately 245 pounds per hour generates 1-million Btus per hour of steam. At approximately 600 pounds per hour of inlet solvent loadings, the waste-heat boiler [receives] in excess of 5-million Btus per hour of steam."

According to Swinehart, what truly makes this air-pollution control and energy-recovery system efficient is that with rare exception it only requires auxiliary fuel during the initial, cold startup of the burner.

"The system is designed for minimal maintenance without any [periodic] addition of catalyst, carbon, or biological compost that [many] other air-pollution technologies require," Swinehart says.

The integrated incinerator and waste-heat-boiler system provide low operating costs combined with extremely high VOC/hydrocarbon destruction to meet both current and future environmental air-pollution control regulations.

Contact: Controlled Environment Ltd., Kevin Summ, 1337 Pearl St., Waukesha, WI 53186. Tel: 262-547-0662; Fax: 262-549-3366; E-mail: ces1@execpc.com.