下降管反应器内颗粒流动升温过程数值研究

Numerical study on the heating process of biomass particles in downer

中文关键词: 升温过程；固体热载体；双流体模型  离散单元法； 下降管

英文关键词: heating process  solid heat carrier  two-fluid model  discrete element method  downer

中文摘要:

      本文采用数值模拟的手段研究了下降管反应器内包含不同尺寸及密度冷热颗粒混合物的流动传热特性。双流体模型及离散单元法分别被用于描述颗粒混合物的流动过程并与实验结果进行了对比。反应器内气固相间传热，颗粒混合物间碰撞传热，以及壁面与气/固两相间的热量传递采用计算流体力学和离散单元法相耦合的方式进行了模拟，对颗粒到达反应器出口前影响温度变化趋势的因素展开了分析研究。模拟结果表明：在V型下降管反应器内，粒度较小的颗粒主要沿壁面向下滑动为主；较大尺寸颗粒向下流动过程中在反应器截面上分布区域较广；当反应器壁面热边界条件发生变化时，颗粒升温过程变化明显，采用恒温壁面冷颗粒升温速率明显提高；同时热载体颗粒数目越多，冷颗粒在下降管反应器内升温越快。

英文摘要:

      Heat transfer and flow behavior of mixture composed of hot and cold particles in a downer reactor is studied numerically. Models of TFM and DEM have been employed to describe the flow pattern of mixture, individually, and validated by the experimental data. The heating up of biochar has been studied in detail based on the simulation work on the heat transfer processes by CFD-DEM. The simulation results indicate that the small particles are mainly sliding down to the outlet of the reactor but the large heat carriers disperse widely; the wall of constant temperature is beneficial to the heating up of biochar together with the increasing number of heat carrier.