Research And System Design On Gas Flow Velocity And Temperature Measurement Based On Acoustic Method

The measurements of flow and temperature have been widely used in power plants,coal mines,metallurgy and chemical industries,which plays a decisive role in modern industrial production.Although there are many methods of velocity or temperature measurement in the industrial field,in some applications where the measurement area is larger,conventional singlepoint measuring equipment cannot accurately measure the average gas flow rate and average temperature of the area to be measured,and simultaneous measurement of gas flow velocity and temperature cannot be achieved in the large measurement space such as the monitoring process of total flue gas emission from coal-fired power plant and ventilation volume in coal mine roadway.In coal-fired power plants,the velocity and temperature of flue gas are important monitoring parameters of the Continuous Emission Monitoring System(CEMS),which is of great significance for the total amount of statistical pollutants discharged and the operating status of the inspection equipment.At present,for the measurement of flue gas velocity,the single-point velocity measurement methods such as pitot tube are easily affected by factors such as the installation angle of the device,which makes the measurement accuracy reduced.Moreover,the measurement error of Pitot tube is large in some regions with low velocity.For the measurement of flue gas temperature,thermocouples and other methods are easily affected by thermal inertia,and the temperature measuring components are prone to scale in the flue,which has a great influence on measurement accuracy and service life.In addition,the average flow velocity and average temperature are more engineering value,while the measurement method above can only obtain a single point of flue gas parameters.The accurate monitoring of the ventilation volume of coal mine roadway is of great significance for effectively eliminating toxic gases and dust particles in the roadway,purifying the roadway air and ensuring the safe production of coal mines in daily operations of coal mines.Therefore,the measurement of the average speed of the roadway airflow is very important for the roadway ventilation monitoring system.However,the measurement results of the velocity measuring equipment such as the mechanical flow meter have hysteresis and the average flow velocity of the roadway gas cannot be obtained.Based on acoustic measurement technology,the measurement of gas parameters in coal-fired power plants and coal mine roadways was studied.The main work and innovations are as follows:1.Aiming at the gas parameter measurement problems of the average velocity and temperature of flue gas cannot be obtained by conventional contact single-point measurement method and the problem of abrasion and blockage in the measurement environment.A simultaneous measurement of gas velocity and temperature by acoustic method was proposed and the traditional measurement structures were optimized.It is common to place a microphone next to the speaker to collect reference signals in existing acoustic measurement method.The electrical signal driving the speaker was used to replace the reference signal with poor signal correlation,which avoids the influence of reference signal distortion on the delay estimation.The experimental results showed that compared with the traditional acoustic measurement method,the measurement accuracy of the improved structure is significantly improved;The influence of the sweep frequency range on the delay calculation result was analyzed.The result of calculation was better when the sweep signal of 4~8kHz was used as the source signal.2.In order to solve the problem of large amount of computation and long timeconsuming in the existing acoustic velocity measurement method,a method for measuring the velocity and temperature of acoustic gas based on the interpolation of non-contact acoustic signal correlation functions was proposed.Accurate acquisition of time delay estimation was achieved by interpolating the cross-correlation function at the lower signal sampling rate.The numerical simulation results showed that the time of flight obtained by cubic spline interpolation method is more accurate than the linear interpolation method.The results of the backflow wind tunnel test showed that the cubic spline interpolation of the correlation function can obtain higher measurement accuracy.3.Based on the acoustic velocity measurement method above,a flow velocity and temperature measurement system was designed and a field gas flow velocity and temperature measurement was realized in power plant and coal mine roadway.In order to meet the requirements of gas parameter measurement in different occasions,the design of signal conditioning circuit module and the development of software processing program were carried out,and preliminary test verification was carried out on three occasions.For the measurement of flue gas flow velocity and temperature in power plant,an acoustic waveguide structure suitable was designed.The gas parameter measurement experiments were carried out in SCR outlet of “Key technology and engineering demonstration pilot platform for near-zero emission control of large coal-fired power plants” in Sanhe Power Generation Co.,Ltd and SCR entrance of #2 unit in Dangtu Power Generation Co.,Ltd.For the measurement of ventilation in coal mine roadway,gas flow velocity measurement was carried out in tunnel in KaiLuan Coal Mine in Tangshan.After the reliability and stability of the gas flow velocity and temperature measurement system were verified by the above three applications.An acoustic flow meter was developed and the product measurement experiment was carried out in Wuxi Metrology and Testing Institute.