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Faster, More Accurate, Stack-Flow Measurements



Aaron N. Johnson, Iosif I. Shinder, Bernard J. Filla, Joey T. Boyd, Rodney A. Bryant, Michael R. Moldover, Thomaa D. Martz, Matthew Gentry


Exhaust flows from coal-fired electricity-generating-plants are determined by measuring the flue gas velocity at prescribed points in the stack cross section. These velocity measurements are made using EPA-approved differential pressure probes such as the 2-hole S-probe or the 5-hole spherical probe. Measurements using the more accurate 5-hole spherical probes require a time-consuming rotation (or nulling) of the probe to find the yaw angle. We developed a time-saving non nulling technique using a spherical probe that measures all 3 components of velocity and therefore provides better accuracy than an S-probe. We compared the non-nulling and nulling techniques at both high (16 m/s) and low (7 m/s) loads. Their excellent mutual agreement (within 0.3 % of the flow) demonstrates that the non nulling technique accurately measures flue gas flows in a coal-fired stack.
Journal of Air and Waste Management Association


stack, CO2 emissions, flow RATA, relative accuracy test audit, Non-nulling, Spherical Probe, Coal-Fired Stack


Johnson, A. , Shinder, I. , Filla, B. , Boyd, J. , Bryant, R. , Moldover, M. , Martz, T. and Gentry, M. (2020), Faster, More Accurate, Stack-Flow Measurements, Journal of Air and Waste Management Association, [online], (Accessed May 25, 2024)


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Created February 24, 2020, Updated July 21, 2020