Video: Ratioing Fresh Air and Fuel Flow to Furnace

By Cecil Smith, president of Cecil L. Smith, Inc.

The scrubber duct inlet temperature controller adjusts the opening of the fuel gas valve. Opening only the fuel gas valve affects the hot air temperature. To increase the heat input at a constant hot air temperature, both the fuel gas valve and the fresh air damper must open. This video presents a ratio control configuration that enables the scrubber duct inlet temperature controller to simultaneously change the openings of the fuel gas valve and the fresh air damper, the objective being to minimize the effect on the hot air temperature.

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Cecil Smith is president of Cecil L. Smith, Inc., Houston, a firm specializing in automation technology that he founded after leaving the faculty of Louisiana State University. Also cited as one of the 50 most influential people in the field, he teaches courses on control topics and has authored or co-authored 14 books, including “Digital Control of Industrial Processes and more than 100 articles. You can email him at cecilsmith@cox.net. He is also one of our experts in our Ask the Experts forum. You can pose your instrumentation and control questions to him here. http://www.chemicalprocessing.com/experts/instrumentation-control/