Research On The Method Of Determining Flue Gas Velocity Measurement Of Rectangular Gas Duct In Coal-fired Power Plant

Air pollution control is of great importance in China's environment protection. Most air pollutants, such as SO2, NOX, dust, greenhouse gas CO2 and so on, are mainly from Coal-fired power plants. Flue gas velocity is the key parameter to determining pollutants'emissions, and how to arrange the point location influences the test results greatly.In this paper, firstly summarizes the characteristics of flue gas parameter testing methods, giving the different range of flue gas temperature, humidity, oxygen content in each part of the FGD system under different working conditions in base of statistical data, which provides reference basis for flue gas velocity measurement instrument selection and the preliminary error excluding in testing field. Meantime, the pitot tube method is chosed to measure the flue gas velocity according to the flue gas features in coal-fired power plant and field testing conditions.Secondly, the first optimization scheme halving the sampling points in the sampling plane is proposed because flue geometry size of the coal-fire power plant is so big that there is no sampling gun long enough to testing; the second optimization scheme which controls sampling points in 20, appropriately lengthens the long side of small pieces in same areas because some related terms in current measurement standard don't meet the testing requirements. Result shows that, the relative error between the optimization schemes and the real value is within 10%, so both scheme have feasibility.Finally, how to determine flue gas velocity in non-standard sampling plane is discussed considering that coal-fired power plants mostly use non-standard sampling planes. This paper analyzes the applicability of increasing the number of sampling point to determine flue gas velocity through examples. Results indicate that, it is feasible whenσ=0.30; while whenσ=0.30, actual workload should be taken into account, the sampling plane is suggested to be replaced; and if there is no evident change in the measure result with the increase of sampling points, the best way is to change the sampling plane. Meanwhile, this paper shows that area weighting factor method apply to determining flue gas velocity of the non-standard sampling plane which have stratified airflow and air movement distributed uniformly in large gas velocity area.