气体分布器是费托合成浆态床反应器的主要内构件，影响反应器的流体力学状态和反应性能。根据已有的工程实际经验设计了多层结构的管式气体分布器，以充分利用底部封头的空间。在给定的5层气体分布器整体尺寸及基准设计条件下，采用计算流体力学方法 (CFD) 对其进行模拟计算和结构优化。首先气体按三维稳态不可压缩流体处理，由于分布器喷嘴出口处于湍流状态，因此选用SST-kω单相湍流模型以匹配分布器存在曲率流动的工况；随后在流体的连续性方程和动量方程等控制方程基础上建模，采用计算流体力学软件STAR-CCM+求解方程组，并对多层气体分布器的三维流场进行数值模拟，发现基准设计条件下的分布器存在偏流和流量分布不均的问题；最后，以各层喷嘴的数量、直径和长度为设计变量，以气体分布均匀性为目标函数，在分布器喷嘴出口气体速度不高于75 m/s的限制条件下，采用SHERPA算法，对15个设计参数进行了120次迭代计算和优化，优化过程覆盖了各参数的取值范围。优化结果为每层喷嘴数量在9～15个、喷嘴半径在9～14 mm、喷嘴长度接近150 mm的上限，调节流体通过的压降，克服分布器各层最大的静压差，使气体在各层环形分布管之间均匀分配；同时喷嘴半径应随层数的增加而增加，喷嘴数量也须与半径和长度相互协调，才能得到最优的气体均布性能。最终优化设计的分布器可以获得均匀合理的流量分配，不存在短路现象，且流线较为光滑，不存在局部漩涡等非理想流场。

Gas distributor is one of the most important internals in Fischer-Tropsch slurry bed reactor,which can affect the hydrodynamics behavior and reaction performance of the reactor. In order to fully use the bottom head space of the slurry bed reactor,a muti-layer turbular slurry bed gas distributor was designed based on existing engineering experience. Under the given size and benchmark design conditions of the 5-layer gas distributor,computational fluid dynamics (CFD) was used to simulate and optimize the distributor structure. Firstly,the gas in the distributor could be treated as three-dimensional steady incompressible fluid. Since the outlet gas of the distributor was in turbulent state,the single-phase turbulence model SST-kω was selected to match the condition of curvature flow in the distributor. Then,the modeling was established based on the controling equations such as fluid continuity equation and momentum equation,the computational fluid dynamics software STAR-CCM+ was used to solve the above equations and the three-dimensional flow field of multi-layer gas distributor was numerically simulated. The results show that the benchmark design has the problems of bias and uneven flow distribution for a given 5-layer gas distributor. Finally,the nozzle parameters (length,radius and number) in each layer of the distributor were taken as the design variables,the gas distribution uniformity was taken as the objective function,and under the restrictive condition that the gas velocity at the outlet of the distributor nozzle was not higher than 75 m/s,the SHERPA algorithm was used to iterate 120 times for 15 design parameters,the range of 15 design parameters was covered in the optimization process. The results show that the optimization range of nozzle number is 9-15,the nozzle radius ranges from 9 mm to 14 mm,and the nozzle length is close to the upper limit of 150 mm to adjust the pressure drop through the fluid,overcome the static pressure difference of each layer of the distributor and make the gas evenly distributed among the annular distribution pipes of each layer. Moreover,the nozzle radius of the distributor should increase with the increase of layers,the number of nozzles must be coordinated with the radius and length of nozzles to achieve the optimal gas distribution performance. The final optimized distributor can obtain uniform and reasonable flow distribution without short circuit,the streamline is smooth without local vortex and other non ideal flow field. 

0 引言

1 数学模型

   1.1 几何模型

   1.2 控制方程

2 优化过程

   2.1 目标函数

   2.2 设计参数

   2.3 优化算法

3 结果与讨论

   3.1 参数取值范围优化

   3.2 参数和目标函数的水平坐标

4 结论