Study On Online Measurement Method Of Coal Water Slurry Size Based On Ultrasonic Wave

As unconventional natural gas associated with coal,coal-bed gas is abundant in our country.But compared with other countries,there is a big gap between Chinese coal-bed gas exploitation technologies and international advanced ones.In coal-bed gas exploitation system,the lifting and drainage efficiency of coal-water slurry directly affect the output of coal-bed gas.If the particle size and concentration of coal slime in coal water slurry are too large,it is easy to wear the lifting equipment,and too small,the lifting efficiency is low.Therefore,it is of great significance to carry out the research on the granularity measurement technology of coal water slurry online for the efficient exploitation of coal-bed gas.The representative size of the space occupied by particles is referred to as particle size.The coal water slurry’s particle group is composed of numerous single particles with varying particle sizes.And the particle size measured in this thesis is the particle size distribution of the particle group.Because ultrasonic measurement method has the advantages of online measurement,wide measuring range and non-contact measurement,the ultrasonic method is selected to measure the grain size of coal water slurry.This thesis is divided into three parts: theoretical research,simulation analysis and experimental verification.Firstly,based on the existing ultrasonic attenuation theoretical model,the particle size distribution function is integrated into the existing ultrasonic particle size measurement theoretical model.Then a theoretical model of ultrasonic particle size measurement under mixed particle size distribution is established.At the same time,aiming at the theoretical model of ultrasonic particle size measurement under mixed particle size,an ultrasonic attenuation method was proposed to measure the particle size of coal water slurry by inversion of particle size distribution.Based on the traditional genetic algorithm,the simulated annealing operator is added.In this way,it is beneficial to maintain the diversity of individuals in the group,prevent falling into the minimum solution,ensure global convergence,and have good practicability.Secondly,COMSOL Multiphysics software was used to set coupling parameters according to the physical properties of pure water and pulverized coal particles.Then,the pipeline model is built and the grid is divided.Simulating and analyzing the propagation characteristics of ultrasonic wave in coal water slurry,the theoretical model was combined with the primary factors influencing its attenuation coefficient.It includes measurement frequency,volume concentration,particle size,and medium temperature.When other factors are the same,the following conclusions can be drawn from the simulation results.First of all,the larger the frequency of ultrasonic signal,the greater the sound attenuation coefficient.And the attenuation coefficient of ultrasonic wave increases with the increase of solid particle volume concentration.At the same time,there is a significant nonlinear relationship between ultrasonic attenuation and particle size.As particle size grows,the sound attenuation coefficient initially drops sharply,then gradually rises.Additionally,the higher the temperature of the measured medium,the lower the sound attenuation coefficient.Finally,the experimental platform of coal water slurry particle size measurement system was built and the experimental results were analyzed.Single control variable method was used to study the influence of concentration,particle size,temperature,bubble presence,flow rate and other factors on the experimental measurement results.Compared with the simulation results,the results are basically consistent,which verifies the feasibility of ultrasonic attenuation method to measure the size of coal water slurry.Moreover,the experimental data are substituted into the simulated annealing genetic hybrid nonlinear inversion algorithm.Furthermore,the particle size distribution is calculated and compared with the design value.The results show that the correlation coefficient of particle size distribution is greater than 98.33%,the cumulative relative error is less than 11% particle concentration and the maximum absolute error is less than 3%.Therefore,it can be seen from the above data that the measurement accuracy meets the requirements of online measurement of coal water slurry particle size in coalbed methane mining system.