竖直降落式反应器中颗粒流流动传热的CFD-DEM模拟

CFD-DEM Modeling of Heat Transfer Characteristics of Granular Flow in a Vertical Falling Reactor

掌握竖直降落式热解反应器中污泥颗粒的流动与传热规律是设计反应器的关键.采用计算流体力学与离散元(CFD-DEM)耦合的方法模拟了竖直降落式反应器中污泥颗粒的流动与传热过程.首先,利用文献中的实验结果与传热模拟结果比对,验证了传热模型的合理性.进而考虑了热气流输入、反应器尺寸和污泥颗粒变化等对传热特性的影响.其中颗粒的质量随温度的变化规律通过热重实验测得,进而通过拟合得到颗粒的粒径与温度的关系.计算结果表明,颗粒在反应器内的流动接近于“活塞流”,气相压降较大(1329 Pa/m);颗粒与气相之间的对流传热占据主导地位,污泥颗粒热解传热过程颗粒形变的影响较大、不可忽略,反应器管径超过60 mm以后,管径增大会导致壁面传热占比急剧下降.此计算为污泥竖直降落式热解反应器的设计提供了依据.

The knowledge of the flow and heat transfer characteristics of sludge particles in a vertical falling reactor is the key to reactor design.The coupling of computational fluid dynamics and discrete element method(CFDDEM)is carried out to investigate the flow and heat transfer characteristics of sludge particles in the vertical falling reactor.First,the simulation results are compared with the experimental results from the literature,and the heat transfer model is verified.Then,the effects of hot air input,reactor size and sludge particle deformation on the heat transfer characteristics are comprehensively explored.The relationship between the mass change of particles and temperature is obtained by thermogravimetric experiment,and the function between diameter and temperature is fitted.The simulation results indicate that the flow of sludge particles approximates to a kind of plug flow.Addi-tionally,the convective heat transfer between particles and gas phase plays a leading role and the pressure drop of gas phase is relatively high(1329Pa/m).Furthermore,the impact of the deformation of particles cannot be ignored.After the reactor tube diameter exceeds 60 mm,an increase in pipe diameter will cause a sharp drop in the proportion of wall heat transfer.This simulation provides a basis for the design of the sludge vertical falling reactor.