Ethanol manufacturers use thermal oxidizers to reduce emissions of volatile organic compounds (VOCs) in dried distillers grain (DDG) exhaust. The exhaust gas flows through the thermal oxidizer and is heated to 1,600°F (871°C), at which temperature the organic molecules break down to inert components.

State and federal environmental regulations require ethanol plants to operate thermal oxidizers to within ±90°F (50°C), which ensures complete breakdown of the VOC constituents. A temperature sensor is required to control the natural gas burners and to monitor for environmental compliance.

It is critical to measure the temperature accurately and control the process precisely. If the thermometer indicates a reading that is higher than the actual temperature, then the VOCs may not be completely eliminated and the plant would violate its environmental permit. If the thermometer indicates a reading lower than the actual temperature, then the plant may be burning more natural gas than is needed.

In this type of thermal oxidizer application, engineers at Burns Engineering, Minnetonka, Minn., recommend the company’s Series 100 Type K thermocouple assembly because the mineral-insulated design can withstand temperatures up to 2,156°F (1,180°C).

They also recommend a duplex configuration, which provides a quick backup sensor should it be required. A second thermocouple located next to the control sensor is a good check to see if any drift occurs. Burns suggests a heavy-duty tapered thermowell of 316 stainless steel construction to avoid having the thermocouple element fuse to the inside of the well.In addition, Burns Engineering recommends changing out the thermocouple elements on an annual basis, noting that the documentation provided with a new thermocouple element can be filed with other permit documents.

For more temperature sensor recommendations for challenging applications, visit the technical information section of www.burnsengineering.com.

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