Experimental Study On Measurment Of Primary Air Concentration In Coal-fired Power Plant By Ultrasound

Accurate measurement of pulverized coal concentration in primary air pipeline is critical to the safety of power plant operations,but its complex fluidity and unfixed phase interface make it difficult in engineering field.Ultrasound has many advantages,such as good penetration,non-contact and easy cleaning.It is widely used in two-phase flow measurement.The paper focused on the topic of experimental study on measurement of primary air concentration in coal-fired power plant,through experiments,the measurement of primary air concentration by ultrasonic was studied.The main research contents are as follows:(1)An experimental platform for solid phase concentration measurement of sparse gas-solid two-phase flow and a test bench for simulating primary air were designed and built The experimental platform can measure the ultrasonic attenuation coefficient under different particle size,ultrasonic frequency and solid phase concentration.The negative pressure design of the system makes the material unable to leak,and the purging ensures the cleanness of the ultrasonic transducer.The control system developed by LabVIEW make the automatic powder feeding and ultrasonic measurement of the experimental bench possible,which reduces the error of manual operation and improves the efficiency of the experiment.Pulverized coal is used as material in the test bench,and closed cycle design was adopted to ensure that pulverized coal cannot leak.The test bench was mainly used to verify the results of the experimental platform for solid phase concentration measurement of sparse gas-solid two-phase flow.(2)The main interference factors of the experimental platform were studied,including ambient temperature,humidity and gas-phase velocity.The principle of each factor was explored through designing relevant experiments,and the correction method was put forward based on that.The results show that temperature and humidity can change the characteristics of ultrasonic transducer and the attenuation of ultrasound in two-phase flow.The velocity of gas phase will change the direction of ultrasonic propagation,so that the ultrasonic signal that can be received by the receiving transducer will be reduced and the calculated ultrasonic attenuation will be increased.Through correction,the attenuation coefficients of ultrasound at different temperatures,humidities and gas velocities are basically the same.(3)A signal processing method based on ultrasonic echo was proposed,which discards the general method of subtracting the logarithm of the signal amplitude before and after attenuation.By dividing the first and second waveforms,the influence of background noise on the ultrasonic signal was effectively eliminated,and the ultrasonic attenuation coefficient in the two-phase flow of wind-powder was obtained.Compared with general method,the linear correlation coefficient between the calculated attenuation coefficient and the concentration was increased from 0.774 to 0.972.(4)The effects of ultrasonic frequency,wind-powder concentration and solid particle size on the ultrasonic attenuation coefficient were systematically studied.The variation characteristics of attenuation coefficient and concentration under different frequencies and particle sizes were obtained.A wind-powder concentration inversion algorithm based on experimental data of glass beads was proposed.An error analysis of the inversion was performed on particles having a particle size of 106 μm to 250 μm.Among them,when the particle size is 120μm and the solid phase volume concentration is between 0.65‰-1.43‰,the relative error of the concentration measurement is-5.35%-3.12%..(5)On the experimental platform of the air-powder system,the pulverized coal concentration of the air-powder system was measured by the sparse phase gas-solid two-phase flow solid phase concentration inversion algorithm,and the applicability of the algorithm in the detection of pulverized coal concentration was verified.The verification results show that the proposed method can be used to detect the pulverized coal concentration of the air-powder system with particle size of 120μm and volume concentration between 0.73-1.31‰,and the relative error of the detection is within-8.32-8.86%.