Research On Dry Calibration Method Of Ultrasonic Flowmeter For Flue Gas

In recent years,with the global climate change,people pay more and more attention to greenhouse gas emission reduction.It is a great challenge for human beings to effectively control and reduce greenhouse gas emissions.In China,the emission of carbon dioxide mainly comes from the combustion of fossil fuels and the emission of industrial flue gas.Therefore,it is of great significance for China to accurately measure the emission of carbon dioxide in flue gas in order to achieve the commitment of greenhouse gas emission reduction.Because of its simple structure,high measurement accuracy,no pressure loss,non-contact measurement and complex flow field,ultrasonic flowmeter can be widely used in the measurement of flue gas flow,especially in the measurement of large-diameter pipeline flow.According to the regulations,the ultrasonic flowmeter should be calibrated before use.For ordinary flow meters,the real flow can be calibrated through the verification department.However,due to the limitations of the laboratory environment,there is no flow calibration device for the large-diameter flue gas ultrasonic flowmeter in China at present,so it is impossible to carry out the real flow calibration for the large-diameter ultrasonic flowmeter applied in the flue gas.In order to solve this problem,this paper proposes the dry flow calibration of the large-diameter gas ultrasonic flowmeter,and studies the dry flow calibration of the ultrasonic flowmeter from three aspects: geometric parameters,time parameters and the accuracy of the flow integration method.The main work and research results are as follows:(1)Based on the measurement principle of ultrasonic flowmeter,the factors that affect the flow measurement are analyzed theoretically.The geometric parameters of DN1000 gas ultrasonic flowmeter are calibrated by three coordinate measuring arm.The measured parameters include channel length,channel angle and pipeline radius.The uncertainty of each geometric parameter to flow measurement is evaluated.The uncertainty of flow measurement introduced by geometric parameter is 0.087%.(2)For the calibration of ultrasonic signal propagation time of large-diameter ultrasonic flowmeter,a new calibration method for the accuracy of ultrasonic time measurement is proposed,and a set of calibration device for the accuracy of time measurement of flue gas ultrasonic flowmeter is set up under the laboratory conditions.The measurement uncertainty of ultrasonic propagation time error(35)t is 0.2% by using the device.The uncertainty of velocity measurement introduced by ultrasonic propagation time is 0.28%.(3)By using CFD numerical simulation technology,the numerical simulation models of circular single bend,double bend and rectangular single bend,reducer and diffuser are established respectively,and the flow characteristics and velocity distribution of ultrasonic flowmeter in different pipe forms are analyzed.The influence of different velocity,angle of sound channel,integration method,sound volume of sound channel and installation angle of ultrasonic flowmeter on the flow integration error of ultrasonic flowmeter with the increase of downstream straight pipe distance is studied and analyzed.A small database of the influence of installation conditions on the flow integration error is established,which can provide the flow integration error correction value of ultrasonic flowmeter under different installation conditions,which has guiding significance for the field installation and use of ultrasonic flowmeter.(4)The expanded uncertainty of dry flow calibration method is 0.82%,which shows the effectiveness of dry flow calibration method.