单个球形木材颗粒热解过程数值模拟

Numerical Simulation of Pyrolysis of a Wood Particle

建立一维、非稳态单个球形木材颗粒热解模型,模型包含颗粒内部气相和固相质量、动量和能量守恒方程。颗粒内气体运动采用Darcy理论描述,传热模型包括颗粒内的导热和对流传热以及颗粒表面与外界的对流和辐射传热,热解动力学采用一步反应模型。运用文献中的实验结果对模型进行了验证,模型能够较好地预测颗粒内部不同位置处温度和固体失重率随时间的变化过程。运用模型考察进气温度和颗粒粒径对木材颗粒热解过程的影响。结果表明:进气温度越高,颗粒热解所需要的时间越短。相同无量纲直径处,小粒径的颗粒升温快,整个颗粒的温度趋于一致的时间较短,剩余固体率的变化规律与温度的变化一致。

An unsteady, one-dimensional model was developed to study the pyrolysis of a single wood particle. Mass, momentum and energy conservations of gas and solid within the particle were considered. The gas velocity in the particle was modeled using Darcy＇s law for fluid through a porous medium. The heat transfer model included heat conduction and convection inside the particle, and convection and radiation between the particle and the hot gas. The kinetic model consisted of primary pyrolysis reaction. In order to check accuracy of the model, the time-resolved predictions of temperature and residual mass fraction were compared with published experimental results, which gave good agreement. Then, the model was used to investigate the effects of inlet gas temperature and particle diameter on the wood particle pyrolysis. The results showed that the pyrolysis time decreased when the inlet gas temperature increased. At the same dimensionless diameter, the temperature of the small particle increased and reached uniform rapidly. The time-resolved variation of the residual mass fraction was similar with that of the temperature.