流化床管式分布器内流场模拟和布气性能分析

Flow field simulation and distribution performance analysis of a gas pipe distributor in fluidized bed

以催化裂化装置(FCCU)再生器的管式气体分布器为研究对象,对流化床管式气体分布器的布气性能进行了分析。首先,对气体分布器分支管内的流场进行数值模拟,计算结果表明沿分支管内气体流动方向,压力逐渐增大,截面流量逐渐减少,沿程喷嘴流量逐渐增大;同时分支管上游入口还存在着明显的偏流现象,从而导致了上游喷嘴的出口流量小于设计流量,下游喷嘴的出口流量高于设计流量,造成流化床内非均匀布气。然后,依据分支管的变质量流动特点,将一般变质量流动的动量方程用于分析分支管内的流动过程,表明分支管的流动过程属于'动量交换控制模型',具有始端静压低末端静压高的特点,固有压力分布不均匀的特征。这种不均匀的压力分布导致了喷嘴布气不均匀和磨损等系列问题。最后,结合流化床内的压力特点,综合分析气体分布器的分支管压降和喷嘴压降,明确了喷嘴出口流量与分支管压力分布的关系,喷嘴临界压降与设计压降的关系,结论表明分支管的结构改进可以优化和改善分布器的布气性能。

The distributing gas performance of the pipe distributor was analyzed based on the flow field numerical simulation of pipe distributor used in FCCU（Fluid Catalytic Cracking Unit）.The result from simulation shows that the pressure increases along the branch pipe and the axial flow rate decreases,which leads to the nozzle flow rate increasing gradually.Furthermore,an obvious bias flow was found in the inlet of branch,which brings the nozzle flow rate less than the designed flow rate and causes an uneven gas distribution in the fluidized bed.Meanwhile,the momentum equation with variable-mass flow was applied to analyze the flow in the pipe distributor.The flow type in the branch pipe belongs to the ＂momentum exchange controlling model＂.The pressure in the branch pipe always increases from the inlet to the end and the pressure distribution is not consequentially uniform.The uneven gas distribution of the pipe distributor results in fluidized gas non-uniformity in the bed and the erosion in branch pipe and nozzle.Finally,according to the pressure characteristics in fluidized bed system,relationship between the pressure drop of branch pipe and pressure drop of nozzles,as well as of the critical nozzle pressure drop and the designed nozzle pressure drop,was discussed.The gas distributor performance could be optimized by means of the structural improvement of branch pipe.