Abstract:

The tracer gas dilution method can overcome the issue of significant errors in flue gas flow measurements resulting from the complexity of the flow field in large-diameter stacks in power plants. The method is traceable and the measuring principle differs from that of the conventional velocity-area method, thus offering the potential for utilization as an on-site calibration method for flow measurements. This paper thus analyses the feasibility and accuracy of the tracer gas dilution method in flue gas flow rate measurement of thermal power plant stacks based on numerical simulation. Furthermore, it studies the influence of the tracer dilution ratio and the tracer injection cross-section on the measurements, in addition to setting up different tracer sampling schemes to assess the stability of the measurements. The results demonstrate that at a height of approximately nine times the diameter of the stack (9D), the tracer and flue gas can be fully mixed to satisfy the measurement requirements of the tracer gas dilution method. An excessively high or low tracer dilution ratio will impair the mixing efficiency of the tracer and the flue gas. When the tracer is injected at the flue can effectively reduce the flow measurement error. When the tracer is injected at the stack, the error fluctuation range of each sampling method is considerable. However, the three-point sampling method demonstrates a stable and reliable measurement performance, with measurement errors on 3D, 8D and 12D being only -3.59%, -0.69% and -1.05%, respectively. When the tracer is injected at the flue, the flow measurement errors of each sampling method are not greater ±10%, and the measurement errors of the three-point sampling method are only 0.98%, -0.52% and 0.21%, which are all within ±1% on the cross section of 3D, 8D and 12D, respectively. This study demonstrates the feasibility and accuracy of the tracer gas dilution method in flue gas flow measurement in thermal power plants.

Key words: large diameter stack, flue gas flow field, flow rate measurement, traceability, tracer gas dilution method