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Smoke Stack Simulator


Today, inconsistencies between measured CO2 emissions and emissions calculated from coal consumption are on the order of 10% to 20%. Either a carbon tax or cap-and-trade regulations will generate a financial incentive to accurately measure the CO2 flux emitted by flue gas stacks. The objective of this project is to develop the technical basis for measuring the CO2 flux with an uncertainty on the order of 1% at a reasonable cost. [1,2,3]


The Flow Metrology Group is using the smoke stack simulator shown in Fig. 1 to critically test conventional and alternative ways of measuring the flow of stack gases. The inlet cone and reference (upstream) section of the simulator draw in ambient (outside) air and generate a swirl-free, fully-developed turbulent flow. The reference section features an 8-path ultrasonic flow meter that NIST calibrated with an uncertainty of 0.5% (at a 95% confidence level) while it was installed in the inlet section.

Diagram of NIST's Smoke Stack Simulator test bed
Figure 1. NIST's smoke stack simulator. The test section has a length of 28 m and a diameter of 1.2 m (4 feet) which is approximately 1/10th the diameter of a power plant stack.

Figure 1 shows a right-angle bend with a “dead” volume between the reference section and the downstream test section. The bend simulates a typical connection between a power plant’s pollution control system and its stack. The bend generates counter-rotating vortices in the test section. Obstacles (such as perforated plates) can be inserted in the test section to further complicate the flow. The exhaust fans generate flows of 6 m/s to 25 m/s in the 28 m-long test section which has a diameter of 1.2 m (4 ft).

The test section is instrumented to quantify the errors and uncertainties encountered when EPA-approved Continuous Emission Monitoring (CEM) protocols are used to measure the CO2 flux. Thus, it accommodates 1-path and 2-path ultrasonic flow meters at various angles as well as automated surveys using S-probes and 3D-probes following EPA Relative Accuracy Test Audit protocols.

We seek to reduce the errors in flow measurements by using

  • a laser doppler anemometer to measure interference between pitot tubes and the walls
  • computational fluid dynamics to model/predict flow-dependence of swirl generated at stack entrance
  • computational fluid dynamics to model/predict meter responses to swirling flows
  • 3-path and 4-path ultrasonic flowmeters

We are exploring alternative methods of measuring flue gas flows such as

End Date:


Lead Organizational Unit:


Aaron Johnson
301-975-5954 Telephone

John Wright
301-975-5937 Telephone