两段式气流床煤气化炉内气固流动数值模拟研究

Numerical simulation of the gas-solid flow in the two-stage entrained flow coal gasifier

建立了两段式气流床煤气化炉内气固两相流动的三维计算流体力学(CFD)模型,将气体视为连续介质,在Eu ler坐标系下考察气相的运动;将颗粒视为离散体系,在Lagrange坐标系下研究颗粒的运动。利用所建CFD模型对基本设计尺寸和操作条件下的两段式气流床煤气化炉内气固两相流动进行了模拟,给出了两段式气流床煤气化炉内的气固两相流动的规律和颗粒的分布规律。在此基础上,针对不同的结构(喉口直径变化)和不同的操作条件(两段气固进料量变化)进行了一系列的模拟比较。结果表明,喉口直径的变化对于炉内气固两相流动及颗粒分布有重要影响。随着喉口直径减小,喉口附近区域的气相回流增强,颗粒运动轨线变得更加曲折,颗粒分布发生明显变化。两段气固流量的改变可以明显改变炉内气固流动,随着一段反应区的气固流量增加和二段反应区气固流量减小,一段反应区内的气相回流更加显著,二段反应区气相回流减弱,颗粒螺旋上升运动增强,反应器边壁处颗粒浓度增大,颗粒沉积现象减弱。

Due to the advantages of high carbon conversion and high capacity,pressurized entrained flow gasification is of interest and becoming increasingly important in the production of synthesis gas.To improve the thermal efficiency,the entrained flow gasifiers often use two-stage feeding mode.Recently,a novel pilot scale two-stage entrained flow gasifier has been developed in China.In order to meet the requirements of the process development,a 3-D full scale（ID700 mm×H11 200 mm） mathematics model based on the Computational Fluid Dynamic（CFD） has been developed for investigating the gassolid flow characteristics in the gasifier.In the model,the gas phase was treated as continuous phase with an Euler frame of reference,while the particle phase was modeled as dispersed phase with a Lagrange frame of reference.Base on this CFD model,a simulation was performed firstly under the base designing and operating condition,which gave the kinetics regulation of the gas-solid two-phase and the distribution of particle in the gasifier.And then a series of numerical simulations were performed under several different designing and operating conditions（the throat diameters and gas-solid flow rate in the two stages） to investigate the effect of design and operation parameters on the gas-solid flow throughout the gasifier.The results showed that throat diameter was critical in the two-stage entrained flow gasifier,which might control the flow field,particle trajectory and particle distribution.The smaller throat diameter leads to not only stronger gas recirculation near the throat,swirling particle trajectories but also obviously changing of the particle distribution.The changes of feeding rate between the two-stage obviously influence the gas flow flied and particle behavior.The feeding rate increase in the first stage and the decrease in the second stage will enhance the gas recirculation in the first stage,weaken the recirculation in the second stage and leads to stronger particle swirling up movement,higher particle concentration near the wall and less particle deposition at the bottom.