鼓泡流化床内高灰煤气化过程的颗粒尺度特性研究

基于多相流体质点网格方法(MP-PIC)对高灰煤在三维鼓泡流化床气化过程进行了数值模拟研究。在欧拉-拉格朗日框架下将气相和固相分别视作连续介质和离散相处理。首先,将模拟得到的出口处气体组分结果与实验数据进行对比,实验数据与模拟结果具有良好的一致性。其次,研究了煤颗粒在气化炉内的温度、传热系数、速度和停留时间,从颗粒尺度揭示了鼓泡流化床气化炉内的颗粒分布特性和气固流动特征。结果表明:在气化炉入口附近煤颗粒与床层温差最大,传热系数最大;由于流化床内强非线性的气固流动,床中煤温度和传热系数的空间分布不均匀;煤颗粒和床料的瞬时速度具有稳定的波动幅度,其中垂直方向速度波动最明显,且煤颗粒的瞬时速度比床料的瞬时速度略大;由于颗粒间的剧烈碰撞,延长了煤颗粒停留时间。此外,对鼓泡流化床中煤气化过程颗粒尺度的研究,有助于深入了解固体颗粒的流动行为以及气固相相互作用特性,对鼓泡流化床反应器的设计优化具有重要意义。

Particle-scale Investigation of Gasification Process of High-ash Coal in Bubbling Fluidized Bed Gasifier

In this paper, the gasification process of high-ash coal in three-dimensional bubbling fluidized bed was simulated via the multiphase particle-in-cell(MP-PIC) approach. With the Eulerian-Lagrangian framework, the gas phase and the solid phase were treated as the continuous medium and the discrete phase, respectively. Firstly, the modeling gas composition results at the outlet of the gasifier agreed well with the experimental data. Secondly, the temperature, heat transfer coefficient, velocity, and residence time of coal particles in the gasifier were discussed, and then the particle distribution characteristics and the gas-solid flows characteristics in bubbling fluidized bed gasifier were revealed in the particle scale. The results show that the temperature difference between coal particles and the bed materials, as well as the heat transfer coefficient, is most prominent near the gasifier inlet. Due to the strongly nonlinear gas-solid flows in fluidized bed, the spatial distributions of coal temperature and heat transfer coefficient in bed are uneven. The transient velocities of coal particles and bed materials have a stable fluctuation range. The vertical velocity shows the most significant fluctuation, and the velocity of coal particles is slightly larger than that of the bed materials. The rigorous collision between inter-particles prolongs the residence time of coal particles. In addition, the particle-scale investigation of the gasification process helps provide a deep insight into the flow behaviors of solid particles and the interaction between gas and solid phases in bubbling fluidized bed, which is significant to the design and optimization of the bubbling fluidized bed reactors.