Traceable Flue Gas Flow Rate Measurement Method for Large-Diameter Stacks of Thermal Power Plant

The tracer gas dilution method can address the issue of significant measurement errors in flue gas flow caused by the complex flow field in large-diameter stacks of power plants. The method is traceable and operates on a measurement principle different from the conventional velocity-area method, making it a promising candidate for on-site calibration of flow measurements. To this end, this paper employs numerical simulation to analyze the feasibility and accuracy of the tracer gas dilution method for measuring flue gas flow in power plant stacks. On this basis, it studies the influence of the tracer gas dilution ratio and injection cross-section on measurement results. In addition, different tracer gas sampling schemes were designed to evaluate the stability of the measurements. The results demonstrate that, at a height of approximately 9D (where D is the stack diameter), the tracer gas achieves full mixing with the flue gas; both excessively high and low tracer gas dilution ratios can negatively affect the mixing efficiency; injecting the tracer gas at the flue section can effectively reduce flow measurement errors. Under 80% load rate, when the tracer gas is injected into the stack, the measurement errors vary considerably across different sampling schemes. However, the three-point sampling method demonstrates a stable and accurate performance, with measurement errors of only -3.59%, -0.69%, and -1.05% at the 3D, 8D, and 12D cross-sections, respectively. When the tracer gas is injected into the horizontal flue, the flow measurement errors for all sampling schemes remain within ±10%. Specifically, with three-point sampling, the errors at the 3D, 8D, and 12D cross-sections are 0.98%, -0.52%, and 0.21%, respectively—all within ±1%. These results demonstrate the feasibility and accuracy of the tracer gas dilution method for flue gas flow measurement in large-diameter stacks.