低变质煤微波热解数值模拟研究

Numerical Simulation on Microwave Pyrolysis of Low-rank Coal

采用COMSOL Multiphysics软件对低变质煤微波热解过程进行了数值模拟分析,研究了微波功率、热解时间和煤样位置对微波炉腔体内电场和煤样温度场的影响,以模拟最优工艺条件进行热解实验,并对产物收率和组成进行了表征分析。结果表明:微波功率和煤样位置对腔体内电场和煤样温度场影响十分明显;热解时间对腔体内电场几乎没有影响,而对煤样温度场影响较大。微波腔体中电场强度、煤样的升温速率和热解终温都随微波功率的增大而增大。在腔体中心靠近波导3 cm的位置(-3 cm)时,煤样处在高温区域的面积最大,热解终温最高。数值模拟低变质煤微波热解的最优工艺条件为微波功率700 W、热解时间1800 s和煤样处于-3 cm位置。在此条件下进行热解实验,其产物兰炭、煤焦油、热解水和煤气的收率(质量分数)分别为70.25%,3.99%,5.31%和20.45%,其中,煤焦油中轻质油含量为37.43%(质量分数),煤气中“富氢”气体组分含量为53.02%(体积分数)。

The present study numerically investigated the microwave pyrolysis process for low-rank coal by using the COMSOL Multiphysics software.First,the impacts of the applied microwave power,pyrolysis time duration and position of coal samples on the resulting electric field in the microwave cavity and temperature distribution of coal samples were explored,and then pyrolysis experiments were performed under simulated optimal process conditions,and the yield and composition of the products were analyzed accordingly.The results show that the electric field in the microwave cavity and temperature distribution of coal samples are affected significantly by the microwave power and coal sample position.The pyrolysis time duration shows insignificant effects on the electric field in the microwave cavity while substantial effects on the temperature distribution of coal samples.The electric field intensity,the heating rate of coal samples and the final pyrolysis temperature in the microwave cavity all increase with the increase in the microwave power.When the coal samples are located near the waveguide(-3 cm),the area located in the high temperature area is the largest in the all experiments,and the final pyrolysis temperature is also the highest.The optimal process conditions based on the numerical simulations for the microwave pyrolysis of low-rank coal are 700 W of the pyrolysis power,1800 s of the pyrolysis time duration,and the coal sample located at the position of-3 cm.Pyrolysis experiments were performed under these conditions,and the yields of the pyrolysis products of bluecoke,coal tar,pyrolysis water and coal gas are 70.25%,3.99%,5.31%and 20.45%(mass fraction),respectively.Among these products,the light oil content in coal tar is 37.43%,and the content of“hydrogen-rich”gas components in coal gas reaches 53.02%(volume fraction).