Waking to the smell of brewing coffee may be a sensory pleasure for many of us, but it is a different story for neighbors of coffee-making factories.
Needing to neutralize the odor of roasting beans and destroy emissions from a new roaster that increased production, an East Coast processor steered away from the traditional approach.
Most often, bean roasting odors and emissions are treated with an afterburner that incinerates the roaster exhaust with natural gas or other fuels. While effective in air-pollution control, it is not economical or energy efficient. Rising fuel costs and the growing green movement prompted the company to find a more energy-efficient and cost-effective means of emission destruction.
Anguil Environmental Systems Inc., Milwaukee, recognized the coffee manufacturer’s need and developed a system that accounts for the unique application requirements. The maker of pollution control-equipment says the solution also achieves environmental compliance with less operating costs than the traditional afterburner approach.
Anguil recommended an 8,000 scfm regenerative thermal oxidizer (RTO) to handle the roaster, nip grinder and alkalizer at the facility. With the two-bed oxidizer, contaminated process gas is preheated as it passes through beds of ceramic media located in the energy-recovery chambers. The process gas moves from the preheated 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 direction of the process gas so both energy-recovery beds are fully utilized, providing 95 percent thermal efficiency and reducing auxiliary fuel requirements. Under normal operating conditions, the unit is self-sustaining and does not require fuel to achieve destruction.
Water vapor was a major concern during the design phase of this project; therefore, provisions were taken to handle the high moisture airstream coming from the roaster. Water is a byproduct of bean roasting, and it also is added for flavor. The water can accelerate corrosion of carbon steel parts and freeze during winter, causing system components to seize. Either of those conditions can cause unplanned oxidizer shutdowns.
To head off the potential problem, Anguil engineers recommended a knock-out drum with removal pump just upstream of the oxidizer. The fresh-air damper also was modified to introduce less water vapor, and portions of the ductwork were insulated to prevent freezing.
Special consideration was given to the oxidizer 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 kitchen oven. Organic particulate is regularly burned out during a high temperature cycle to ensure the media does not plug. The bake-out feature also helps reduce pressure drop and lower 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 waste heat from the oxidizer’s exhaust stack to the roof’s makeup air unit, saving the company more than $80,000 a year in plant heating costs during winter months, Anguil says. On similar applications, Anguil has returned waste heat back to the roasters, further reducing natural gas consumption and operating costs.
The bean processor has purchased two similar Anguil systems for its other U.S. plants.