Research On Gas-solid Two-phase Flow Concentration Base On Ultrasound

The mixed flow of air and pulverized coal in the primary air duct of coal-fired boilers is a complex gas-solid two-phase flow with sparse solid-phase characteristics.The realization of solidphase concentration detection is one of the technical difficulties for boiler combustion optimization.For a long time,due to the different milling systems and the complexity of the gas-solid two-phase flow,there has been a lack of reliable and effective solid-phase concentration measurement methods.Ultrasonic-based gas-solid two-phase flow concentration measurement has attracted widespread attention because of its good penetration,simple structure,and high reliability.This paper mainly studies the ultrasonic-based gas-solid two-phase flow concentration measurement method,and lays the foundation for the development of a reliable gas-solid two-phase flow parameter measurement system.The main research work and innovation results are as follows:(1)The propagation law of ultrasonic waves in sparse gas-solid two-phase flow was studied.It was found that the ultrasonic attenuation coefficient and speed of sound were related to the solid phase concentration,solid particle size,ultrasonic frequency,and physical property parameters.In addition,the numerical simulation shows that the influence of changes in the physical properties of solid particles on the ultrasonic attenuation coefficient and the speed of sound is negligible.Compared to the ultrasonic attenuation coefficient,the changes in the solid-state concentration,solid-phase particle size,and ultrasonic frequency change are very fast.Small,so the ultrasonic attenuation coefficient is used as the concentration calculation feature.(2)A free-fall gas-solid two-phase flow concentration test bed was designed and constructed,and the ultrasonic measuring device,powder feeding,and measurement system related equipment were selected or manufactured.The test bench can reduce the influence of uneven solid concentration and particle size distribution on the measurement result by setting the mixing pipe section.By designing an automatic control program to realize program-controlled feeding,automatic measurement,reducing the error caused by manual operation,and improving the repetition and accuracy of experiments.(3)The effect of ultrasonic frequency,solid phase concentration and particle size on ultrasonic attenuation coefficient was systematically studied.A solid-phase concentration and solid particle size calculation model based on ultrasonic attenuation coefficient at multiple frequencies was proposed and was verified by experimental data.Experimental results show that the particle size calculation model has nothing to do with the solid phase concentration,and can clearly distinguish particle sizes of different sizes.The measurement error is less than 20%.The concentration calculation model needs the known particle size and the measurement error is below 15%.The verification results prove the validity and accuracy of the above model under condition of the solid phase concentration range is 0.03%~0.6%,and the solid particle size range is 40?m~120?m.(4)A set of gas-solid two-phase flow concentration measurement system based on LabVIEW is designed,and an excitation signal that can generate multiple specific frequency spurious waves within a single emission cycle is designed to facilitate the use of ultrasonic attenuation coefficient at multiple frequencies.The specific part of the model calculation is developed by MATLAB,and the MATLAB script is called by LabVIEW.The system test results show that the concentration measurement system has better stability and real-time performance,and its response to concentration changes is within 1 second.