Research On Measurement Method Of Flue Gas Velocity And Gas Pollutant Emission From Coal-fired Power Plants

The efficient control of the gas pollutants discharged from coal-fired power plants depends on the accurate measurement of the pollutant emissions,but instantaneous measurement techniques and concentration limits nowadays are mainly based on data from some sample sources rather than all sources,and its lack of effective means to measure total pollutants makes it difficult to reflect the level of emission control technology in the industry.What's more,the straight pipe leading to chimneys after desulfurization in coal-fired power plants are relatively short,the internal flow is difficult to fully develop and it forms many back flows and secondary flows,so it is difficult to determine the position of the sampling point which can represent the average cross-section velocity.In addition,the corner of the flue destroys the stability and symmetry of the flue gas flow,as a result,the velocity distribution of the flue gas in the flue is extremely uneven,and there are high,medium and low speed areas at the same time,so it is impossible to construct an accurate mathematical model and calculate the position of average velocity.From this point of view,this paper put forward the idea of looking for suitable positions of velocity measuring points in the flue pipe by experiment means and the calculation and simulation functions of CFD software.The purpose of this method is to study the locations of measuring points which can represent the average cross-section velocity in flue,and to analyze whether these locations have a general rule for the change of flue gas velocity,so as to overcome the limitations of traditional single-point measurement methods and achieve accurate measurement results of flue gas velocity and total amount of gas pollutants emitted from coal-fired power plants.By structing models of the horizontal flue in coal-fired power plants and the numerical simulation of flue gas flow,this paper analyses the flue gas flow condition and the velocity distribution in horizontal flue,finds that the flow pattern in horizontal flue is similar to that in different inlet flue gas velocities,and the locations of the measuring points which can represent the set values of flow velocities are approximately the same.On this basis,this paper determines four suitable velocity measurement points by velocity simulation and calculation with the help of Chebyshev numerical integration method and Gauss numerical integration method,and verifies that these points can adapt to different set values of flow velocity theoretically,it is shown that the measured results at these four locations can well reflect the actual flow velocity of flue gas in the case of flow velocity variation.In order to extend the simulation results to the actual situation,this paper designs a series of simulation tests and model experiments,makes scaled-down experimental models and builds corresponding experimental platforms.After that,this paper analyses and compares the differences between laboratory conditions and field conditions by CFD simulation.And it proves that these differences will not affect the positions of the measuring points which can represent the actual value of the flue gas velocity too much.On this basis,this paper determines and vertifies the suitable positions of velocity measuring points by actual measurement experiments,and finally obtains the suitable positions of velocity measuring points in horizontal flue of coal-fired power plants.For rectangular horizontal flue structures with dimensions of a 600 MW unit,the appropriate velocity measuring points are located at the cross-section of 1.6m away from the exit of flue,1.88 m away from the front wall of flue,0.93m?0.97m?3.13 m and 3.17 m away from the bottom of flue.In addition,on the basis of emphasizing how to measure the flue gas velocity discharged from coal-fired power plants accurately,this paper also takes some researches on relevant gas composition and concentration measurement methods,and explains the method and process of calculating the specific value of gas pollutant emission when gas velocity and corresponding component concentration is obtained by Nondispersive Infrared Spectroscopy,and contract the Gas Pollutant Emission Measurement System of Coal-fired Power Plant,which lays the fundation for the effective control of the gas pollutants discharged from coal-fired power plants.