Case study - Bean roasting

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Courtesy of Anguil Environmental Systems, Inc.

Overview

After purchasing a new Barth roaster for their East coast processing facility, a nationally known bean roasting company knew their emissions and odors would need to be addressed with the increase in production.

Action

Emissions and odors from the bean roasting process have traditionally been treated with an afterburner which simply burns the roaster exhaust with natural gas or other fuel types. This is an effective means of air pollution control but not very economical or energy-efficient. Rising fuels costs and the recent green movement prompted this company to find a more energy-efficient, cost-effective means of emission destruction.

Solution

Recognizing the need for a better solution within the industry, Anguil Environmental Systems had developed a dependable system that not only accounts for the unique needs of this application but also achieves environmental compliance at a fraction of the operating cost. Expected savings for a four bag roaster can be seen in the illustration below.

Anguil recommended an 8,000 SCFM Regenerative Thermal Oxidizer (RTO) to handle the Barth Roaster, Nip Grinder and Alkalizer at this facility. With the two-bed RTO, contaminated process gas is pre-heated as it passes through beds of ceramic media located in the energy recovery chambers. The process gas moves from the pre-heated chamber toward the combustion chamber, where the Volatile Organic Compounds (VOCs) are oxidized, releasing energy into the second energy recovery chamber before going to atmosphere. A diverter valve switches the process gas direction so both energy recovery beds are fully utilized, providing 95% thermal efficiency thereby reducing auxiliary fuel requirements. Under normal operating conditions the unit is self-sustaining, requiring no fuel use to achieve destrutction. This energy-efficient design offers significantly lower operating costs in comparison to other emission treatment methods common bean roasting facilities.

Water vapor was a major concern during the design phase of this project and therefore provisions were taken to handle the high moisture airstream coming from the roaster. Not only is water a bi-product of bean roasting but it is also added for flavor and sterilization purposes, if precautions were not taken it could have caused system components to seize during freezing weather, accelerated corrosion of carbon steel parts or even oxidizer shutdowns during high production times. Anguil engineers recommended a knock out drum with removal pump just upstream of the RTO. Modifications were also made to the fresh air damper to introduce less water vapor and portions of the ductwork were insulated to prevent freezing.

Special consideration was given to the RTO ceramic media to account for any particulate in the airstream, ensuring proper operation. The oxidizer also has a bake-out feature which works much like the self-cleaning feature on a stove. Organic particulate is regularily burned out during a high temperature cycle, this ensures that the media does not plug, reduces pressure drop and lowers electrical consumption.

In addition to the emission and odor control equipment, Anguil provided a 7,000 SCFM Plate Heat Exchanger and corresponding duct work. This sends approximately 1.5<<BTU/hr of waste heat from the RTO exhaust stack to a make-up air unit on the roof, saving the company over $80,000 a year in plant heating costs during winter months. On similar applications, Anguil has returned waste heat back to the roasters which further reduces natural gas consumption and operating costs.

The company has purchased two similar systems from Anguil for facilities in other regions of the United States. The projects have resulted in environmental compliance, lower operating costs and fewer green house gas emissions for the bean roasting company at all three plants.

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