基于蒙特卡罗法的脱硫塔内气固流动数值模拟

Numerical Simulation of Gas-solid Flow Behaviours in Desulfurization Tower Based on Monte Carlo

用欧拉法处理气相场的同时用基于拉格朗日法的直接数值模拟蒙特卡罗(direct simulation Monte Carlo,DSMC)法处理离散颗粒场,对循环流化床烟气脱硫塔内气固两相流动特性及其优化进行了数值模拟。基于非结构网格进行数值求解,采用四向耦合方法严格地考虑颗粒–流体、颗粒–颗粒、颗粒–器壁间相互作用,并应用高效的非结构网格搜索法,实现气固相间一一映射的耦合作用与反馈。获得了加装导流板组前后,脱硫塔内气固流动特征、轴向速度分布以及固相颗粒浓度分布,同时对影响颗粒停留时间及颗粒碰撞率的关键因素进行了分析。结果证实了调节脱硫塔内多相流动的必要性与有效性;调节后,塔内两相流动及其分布呈理想对称状态,塔内空间得到了充分利用,各粒径档颗粒停留时间比较一致;颗粒停留时间与气相场分布及颗粒物性密切相关;调节后,床内颗粒碰撞率明显低于调节前。

The optimization of gas-solid flow behaviors in circulating fluidized bed for flue gas desulfurization （CFBFGD） was simulated. The particles trajectories were calculated by the direct simulation Monte Carlo （DSMC） method, and the gas motion was modeled by the improved k-ε two-equation turbulent model. All equations were solved numerically on the unstructured meshes. Interactions of particle-fluid, particle-particle and particle-wall were considered rigorously based on the four-way coupling method. An effective model for searching the local unstructured mesh in which the individual particle lay was proposed to achieve ＇one-to-one＇ interaction between phases. Gas-solid flow patterns before and after adjustment were obtained, as well as the distributions of the particle concentration and the gas/particle axial velocity. Further, critical factors that strongly influenced the residence time and collision frequency of particles were analyzed. Final results highly confirm the feasibility and effectiveness of the scheme chosen to optimize the gas-solid flow behaviors within the tower. After adjustment, the gas-solid flow field appears symmetrical ideally, and the interior space of the tower is utilized in full. Residence time of the particles with the same radius comes to be in chorus relatively. The particle residence time is related closely to the continuum flow field and the particle .physical properties. Particle collision frequency decreases distinctly compared with that before adjustment.