| The problem of global warming caused by excessive emissions of carbon dioxide and other greenhouse gases has aroused widespread concern in the world.At the same time,it has a serious impact on agricultural production and threatens human survival.As a big country of carbon emission,China reduces carbon emission by establishing carbon trading market.At present,the domestic carbon trading market uses the emission factor method to calculate carbon emissions,but a large number of enterprises use default values instead of actual measured values when accounting,resulting in low credibility of the accounting data.In the world,online monitoring method is the highest level method of carbon emission inventory.Online monitoring method is to install continuous emission monitoring system(CEMS)on the stack to monitor the carbon emission of enterprises in real time.In order to ensure the accuracy of CEMS,it is required to calibrate it regularly,so as to ensure the accuracy of enterprise measurement.Due to the difficulty of load adjustment,calibration is usually carried out only under one load.However,there are few studies on whether the calibration coefficient can represent the situation under different loads.Based on CFD,the paper simulated six typical stack models(straight pipe,single bend pipe,coplanar double bend pipe,non surface double bend pipe,diffuser pipe and tapered pipe)under the premise of verifying the effectiveness of the selected turbulence model,and analyzed the flow field of the above model in detail;Based on the velocity measurement method of S-type pitot tube,the calibration coefficient of S-type pitot tube under different loads is studied by coupling simulation and experiment;The optimal method of circle breaking area(OWICS)is used to calculate the simulation flow rate,and the calibration coefficient of ultrasonic flowmeter is studied under different loads by combining with experimental verification;In addition,the uncertainty evaluation of calibration of two flowmeter under the same load is carried out.The results are as follows:(1)Three kinds of pipe diameter,three kinds of upstream straight pipe length and four kinds of pipe form are selected to couple the simulation and experiment of S-type pitot tube calibration coefficient under different loads.The change law of calibration coefficient is analyzed by two quantitative methods: relative standard deviation and relative maximum deviation.The results show that: under different loads,there is no good consistency between the relative standard deviation and the relative maximum deviation of the calibration coefficient of S-type pitot tube,and the maximum difference between them is 2.18%;the relative standard deviation and relative maximum deviation decrease with the increase of pipe diameter;the relative standard deviation and relative maximum deviation decrease with the increase of upstream straight pipe length;the relative standard deviation and the relative maximum deviation vary with different pipe types,and the relative standard deviation and the relative maximum deviation are the largest among the two different curved pipes,which are 7.67% and 7.09% respectively.Under the above different conditions,the maximum values of the relative standard deviation and the relative maximum deviation of the calibration coefficient of the S-type pitot tube under different loads were 8.57%and 8.38% respectively.(2)Three path angles,three pipe diameters,four path layout forms,three upstream straight pipe lengths and six pipe forms are selected to simulate the calibration coefficient of ultrasonic flowmeter under different loads,which is verified by experiments.Two quantitative methods are used to analyze the change law.The results show that: under different loads,the relative standard deviation and the relative maximum deviation of the calibration coefficient of ultrasonic flowmeter have good consistency,and the maximum difference between them is only 0.11%,so the relative standard deviation of the calibration coefficient is mainly analyzed;the relative standard deviation of calibration coefficient of ultrasonic flowmeter at forty-five ° is the smallest,which is within 0.37%;the relative standard deviation decreases with the increase of pipe diameter;the relative standard deviation of four path ultrasonic flowmeter is smaller than that of mono path and dual path ultrasonic flowmeter.the relative standard deviation of four path ultrasonic flowmeter is within 0.37% and that of mono path ultrasonic flowmeter is within0.90%;the relative standard deviation decreases with the increase of upstream straight pipe length;the relative standard deviation is the largest among double bend pipe,which is 0.90%.Under the above different conditions,the relative standard deviation of calibration coefficient of ultrasonic flowmeter under different loads is less than 1%,and the calibration coefficient has little change.(3)The uncertainty of two kinds of flow meters was evaluated when the load was 30 m/s.The results show that the uncertainty of S-type pitot tube simulation and experiment coupling calibration is 0.42%,and the uncertainty of ultrasonic flowmeter calibration is 0.58%.In conclusion,S-type pitot tube calibration of stack can not be realized by single load calibration,but can be realized by single load calibration. |
PDF Full Text Request