Maintaining Optimum Combustion

Doug Simmers, global product manager in the Rosemount Analytical Combustion Gas business of Emerson Process Management, the Austin, Texas-base supplier, believes that combustion flue gas analysis is the key in reducing greenhouse gas emissions.

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His thoughts were first reported on the “Emerson Process Experts” blog (www.emersonprocessxperts.com) written by Emerson Process Management Systems Communications Manager and “chief blogger” Jim Cahill.

Simmers notes that in analyzing the relationship between excess air, carbon monoxide (CO), carbon dioxide (CO2), and oxygen (O2), the counterintuitive point is that maximum combustion efficiency actually occurs at the point of maximum CO2 production. Less energy is produced as you move away from this point, which in turn causes the combustion process to run longer to produce the same amount of energy. The extra time required actually means more CO2 is produced.

To operate in the area of maximum combustion efficiency, it’s important to continuously analyze the flue gas and close the fuel/air ratio control loop. Unfortunately, the flue gas does not always have a homogeneous distribution, especially when multiple burners are involved.

A stratification profile, developed using an array of Emerson Oxymitter transmitters of varying lengths, is used for balancing the burners, detecting burner fouling, discovering poor fuel distribution and spotting variations among units. Oxygen probes made with zirconium dioxide (ZrO2) “fuel cell” technology are well suited for the job, according to Simmers, because they operate well at elevated temperatures, which permits an in-place design. Plus, the accuracy of these sensors actually improves at lower O2 levels. The result is better information for optimum combustion, leading to reduced greenhouse gas emissions.

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