吸波剂协助低阶煤微波热解能量场分布数值模拟研究

Numerical modeling of energy field distribution of absorber-assisted microwave pyrolysis of low-rank coal

吸波剂协助煤微波热解技术可实现煤的清洁高效转化,吸波剂协助煤微波热解技术与数值模拟技术相结合,可进一步优化微波热解产物特性。将电磁场能量守恒方程、固体热传导方程和几何模型耦合,运用COMSOL软件建立了适用于吸波剂协助低阶煤微波热解反应的电磁-传热模型,考察了兰炭(BC)、Fe_(2)O_(3)和Fe_(2)O_(3)/BC三种不同种类吸波剂协助煤微波热解的微波腔体电场和煤样温度场的分布特性和强度变化,并与煤微波热解实验进行了对比验证。结果表明:吸波剂种类对微波腔体的电场和煤样的温度场的分布位置和分布区域形状没有显著影响,而对两者的分布区域面积和强度存在较大影响。吸波剂按对电场的分布区域面积和强度的影响从大到小依次为Fe_(2)O_(3)/BC、兰炭和Fe_(2)O_(3),煤样的温度场呈现出右高左低的分布趋势,且高温区域形状呈羽状。三种吸波剂中,Fe_(2)O_(3)/BC吸波剂的电场强度最大,约为9.79×10^(4)V/m,其煤样的温度场分布区域面积和煤样最高温也均最大。三种吸波剂模拟升温特性与实际微波热解升温特性相似,但Fe_(2)O_(3)吸波剂条件下热解最高温和终温模拟结果与实验结果差异最小,而Fe_(2)O_(3)/BC吸波剂条件下的模拟升温曲线与实验结果最为相似。

The microwave pyrolysis assisted by absorbers can achieve clean and efficient conversion of coal,and numerical simulation techniques are often employed to further optimize the properties of the resulting products.In this study,the electromagnetic field energy conserva-tion equation,the solid heat conduction equation and the geometric model were coupled,and the COMSOL software was used to establish an electromagnetic-heat transfer model to analyze the microwave pyrolysis reaction of low-rank coal assisted by absorbers.The distribution characteris-tics of the electric field in the microwave cavity and the temperature field of the coal sample under the effects of different types of absorbers,namely,bluecoke(BC),Fe2O3 and Fe2O3/BC were investigated via the electromagnetic-heat transfer model,and the results were verified via com-parison with the coal microwave pyrolysis experiments.The results show that the absorber type has no significant effect on the location and shape of the distribution area of the electric field of the microwave cavity and the temperature field of the coal sample.However,the absorber type has a strong impact on the distribution area and intensity,and the impact of the absorber from large to small follows the order Fe2O3/BC,BC,Fe2O3.The trend of temperature distribution of coal sample is higher on the right and lower on the left,and the shape of high temperature area is pinnate.Among these absorbers,the intensity of electric field of Fe2O3/BC is highest,which is 9.79×104 V/m,meanwhile,the distribution area of temperature field and highest temperature of coal sample also are highest.The simulated temperature rise characteristics of the three absorb-ers are similar to the experimental results.However,the difference between the highest and final temperature of the simulation results and experimental results is the smallest under Fe2O3 ab-sorber conditions,and the simulated temperature-rising curve under Fe2O3 absorber conditions exhibites a good agreement with the experimental results.