The coffee roasting process consists of cleaning, roasting, cooling, grinding, and packaging operations. Particulate matter (PM), volatile organic compounds (VOC), organic acids, and natural gas combustion products are the primary emissions from the roasting of coffee beans. Green coffee beans contain chemical compounds including proteins, fats, sugars, dextrin, cellulose, caffeine, and organic acids. During the roasting process some of these compounds volatize, oxidize, or decompose. As a result, toxic compounds such as alcohols, aldehydes, organic acids and nitrogen and sulfur compounds are emitted.
Gaseous emissions from roasting operations are typically ducted to a thermal oxidizer or thermal catalytic oxidizer following particulate matter removal by a cyclone. Some facilities use thermal catalytic oxidizers, which require lower operating temperatures to achieve control efficiencies that are equivalent to standard thermal oxidizers. Catalysts are also used to improve the control efficiency of systems in which the roaster exhaust is ducted to the burners that heat the roaster. When particulate matter is a concern, some roasters utilize Recuperative Thermal Oxidizers.
Coffee roasting equipment ranges from small 25 pound per hour batch roasters located at coffee shops to large industrial, continuous roasters at larger facilities. Below is a review of the types of oxidizers typically implemented for coffee roasting:
Catalytic treatment of VOC's and other air pollutants works by reacting the harmful air pollutants over a specially designed catalyst where VOC's are converted to CO2, water vapor (H2O), and usable heat. These harmless byproducts are passed through a heat exchanger where the gas stream’s energy is transferred to the incoming exhaust.
The CPI VANGUARD Catalytic Oxidizer utilizes a unique condensate evaporation section in conjunction with a high velocity mixing chamber. The process starts as emissions are drawn into the condensate evaporation section and forced through the burner’s flame. This direct flame impingement systematically breaks down the stream and keeps particulate (coffee chaff) to an absolute minimum. In the rare instance that particulate is present a unique chaff guard extracts the unwanted particulate.
An integral part of the VANGUARD Catalytic Oxidizer’s performance is the high velocity mixing chamber at the burner, which creates the turbulence needed to ensure proper mixing of the air stream. By designing for the highest mixing, the system can deliver the highest temperature uniformity before the catalyst bed. Temperature uniformity ensures that 100% of the catalyst is efficiently oxidizing the VOC’s. No other manufacturer of catalytic oxidizers can incorporate the advantages of temperature uniformity before the catalyst bed and controlled thermal expansion in a user-friendly system. The CPI VANGUARD Catalytic Oxidizer provides a minimum 99% VOC destruction of the emissions from the roasting process.
Recuperative Thermal Oxidizers are appropriate for process applications, like coffee roasting, where particulate matter may be present. The integration of a heat exchanger with ah combustion chamber can handle a wide range of process flow rates and VOC concentrations.
The CPI QUADRANT SR Thermal Oxidizer process begins with a booster fan designed to draw the volatile organic compound (VOC) laden process exhaust to the QUADRANT System. From there, the VOC-laden process air stream is then directed into the condensate evaporate section where it is preheated to eliminate any vapor droplets before entering the FLOATING TUBE primary heat exchanger. This step protects the leading edge of the heat exchanger from condensate build-up and subsequent preignition. When the stream enters the FLOATING TUBE heat exchanger, it is continuously preheated at close to the ignition temperature before being sent to the pre-heat burner. The exchange of energy in the primary heat exchanger makes up the basis for fuel savings and economical operation.
Regenerative Thermal Oxidizer (RTO) treatment of VOC’s and other air pollutants works by passing the harmful air pollutants through a combustion chamber where it is heated to the setpoint temperature and oxidation of the VOC’s is completed. Regenerative Thermal Oxidizers (RTO’s) offer the most efficient thermal oxidation due to the high thermal energy recovery of the heat exchanger media. The general operation of an RTO consists of passing process exhaust air (with VOC’s) through a heat exchange media where it is pre-heated. This pre-heated air enters a combustion chamber where it is heated to the setpoint temperature where oxidization of the VOC’s is completed. Hot treated clean air is cooled as it passes through the heat exchange media, which absorbs the heat to used during the pre-heat cycle.
The CPI TRITON Regenerative Thermal Oxidizers (RTOs) are two-tower systems engineered to provide long, efficient operation. Each system incorporates specialized ceramic media in the regenerator (heat transfer bed) to allow thermal rate efficiencies up to 97%, making TRITON RTO Systems among the world's most cost-effective air pollution control alternatives. TRITON RTOs take advantage of our unique valve technology to deliver greater than 98% destruction rate efficiency. Designed around the world’s most stringent emission requirements, TRITON RTOs can confidently assure you of exceptional performance and reliability.