A bread and bun bakery was faced with installing air pollution control equipment to control the volatile organic compounds (VOCs) emitted during their baking process. The local regulatory agency requires bakeries that generate over 25 tons of ethanol per year to reduce emissions by 95% by installing control devices on their ovens. The air stream that needed to be treated included ethanol (a VOC released during the fermentation of yeast breads), particulate (bread crumbs), grease, oil and a high level of moisture. The airflow balance in a bakery oven is crucial to the quality of the final product, therefore the installation of any pollution control equipment could not create adverse effects on the oven balance.
After thorough technical evaluation, Anguil Environmental was selected and contracted to solve the VOC problem and meet the regulatory requirements. Anguil's unique approach toward particulate control and oven balance were crucial factors in the bakery's decision process.
Anguil first analyzed the characteristics of the bakery exhaust. At the time of evaluation, the dual exhaust bread oven discharged approximately 3,000 SCFM (4,730 Nm3/Hr) and the single exhaust bun oven discharged slightly over 3,000 SCFM (4,730 Nm3/Hr). They determined that the best solution for this application was a Model 75, 7,500 SCFM (11,830 Nm3/Hr) catalytic oxidizer. A low temperature precious metal catalyst was utilized that allowed for a 500°F inlet temperature and a 625°F catalyst outlet temperature. The oxidizer also incorporated a 65% efficient, stainless steel shell and tube heat exchanger which was designed to be easily cleaned to lower maintenance costs. The heat exchanger pre-heats ability to heat the incoming process stream combined with the low temperature catalyst allowed Anguil to minimize the operational costs incurred by the bakery.
The engineering analysis revealed a high level of vaporized water in the process stream. To prevent corrosion from the water vapor, Anguil used stainless steel to manufacture the collection plenum, system fan and heat exchanger. Although components made of carbon steel would have been less expensive, the long-range cost of equipment maintenance would have greatly increased. The presence of water in the process stream also required sizing the system burner to account for the water vapor.
Another consideration was controlling the particulates from the bakery ovens. Bread particulates, grease, and oil have a tendency to coat or mask monolithic precious metal catalysts, decreasing their effectiveness over time. Anguil designed the system using its patented Self Cleaning Ceramic Filter (SCCF) to eliminate the particulate from the air stream.
The SCCF is located after the oxidizer burner and the burner continuously heats the face of the ceramic filter. When the particulates or grease come in contact with the ceramic filter, they are volatilized. The clean air passes on to the catalyst where the VOCs are oxidized.
In this case, as in many other bakery applications, the process air contained trace amounts of flour. If the process air was used as combustion air, the flour may have caused "coking" to the burner. To maintain the effectiveness of the burner, Anguil used ambient air as combustion air.
The final consideration was maintaining the oven balance. The dual exhaust from the customer's bread oven was individually ducted to an Anguil-supplied collection plenum. The single exhaust from the customer's bun oven was also diverted to the collection plenum. By taking individual exhaust runs to the oxidizer's collection plenum and holding this plenum at a constant negative pressure, the shutdown of one oven would not affect the balance of another oven.
Anguil's knowledge of the bakery industry and the unique needs associated with the baking process provided the customer the confidence to select Anguil as their solution for their emission control needs. The result is another satisfied Anguil client.
Comparison of Space Velocity Ethanol Oxidation
Effects of Ethanol Concentration on Ethanol Oxidation
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Milwaukee, Wisconsin 53223
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