Problem
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 airstream 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.
Action
After thorough technical evaluation, Anguil Environmental
Systems, Inc. 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.
Solution
Anguil 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). Anguil
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
500F inlet temperature and a 625F catalyst outlet temperature. The
oxidizer also incorporated a 65% effective, stainless steel
shell and tube heat exchanger. The heat exchanger was designed to
be easily cleaned to lower maintenance costs. The heat exchanger's
ability to heat the incoming process stream combined with the low
temperature catalyst allowed Anguil to minimize the operational
costs incurred by the bakery.
Anguil's 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 ducted 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