CAS OpenIR
费托合成搅拌釜相分散结构的研究与优化
郑林
Subtype硕士
Thesis Advisor古芳娜
2018-12
Degree Grantor中国科学院大学
Degree Discipline化学工程
Keyword费托合成,搅拌釜,相分散结构,Cfd模拟,反应性能
Abstract

费托合成铁基催化剂的实验室小试评价装置为搅拌釜式浆态床反应器,釜内多相流动状态复杂。搅拌釜的入塔表观气速较小,受釜结构限制,釜底部的固含率较高,且分散不均匀。通过优化内构件及操作条件,均不能有效提升釜底的相分散效果,影响了催化剂反应性能的平行性和重复性。为解决搅拌釜相分散的问题,冷态实验以费托合成轻柴油-空气为实验介质,分别采用高速摄像法、光纤探针法考察不同内构件结构、表观气速、搅拌转速等对搅拌釜内相分散的影响,并对搅拌釜内的流场分布进行了计算流体力学(CFD)数值模拟,设计了热态实验装置的新型相分散结构,进行费托合成铁基催化剂反应性能的验证对比。具体工作及主要结果如下:(1)参照热态实验装置等比例设计冷态实验装置,采用高速摄像法详细研究了挡板、气体分布器、搅拌桨等内构件以及搅拌转速对气含率、气泡尺寸分布的影响。冷态实验结果表明:在高速搅拌下,流体被快速甩到边壁,挡板形成流场扰流作用,流体沿挡板向上向下流动,形成两个分散中心;加入催化剂后,挡板前后未发现催化剂沉积,但搅拌釜底部存在一定数量的催化剂沉积,并随着催化剂的增加,沉积的量逐渐增加;分布器的结构形式对相分散影响较大,烧结金属型分布器的相分散效果最好;通过改造底部进气方式及分布器形式,可以很好的解决气体分布及催化剂分散问题。(2)采用化学腐蚀法制备了光纤探针,对不同表观气速、搅拌转速及气体分布器条件下的搅拌釜内气含率进行了测量,考察搅拌釜内轴向、径向的局部气含率的分布。结果表明:搅拌釜内的局部气含率随着表观气速和搅拌转速的增大而增大;当搅拌转速达到一定值时,局部气含率不再增大;改进入口气体分布器型式对气相均匀分布的作用明显;(3)基于Euler-Euler双流体模型和标准k-ε湍流模型,并将多重参考系(MRF)的方法用于描述旋转叶轮与固定挡板之间的相对运动,对搅拌釜内的流场分布进行CFD数值模拟。模拟结果表明,改变搅拌釜的结构型式可有效改善釜底的相分散。(4)设计两种新型热态实验的搅拌釜催化剂评价装置,并在该新型搅拌釜内进行了费托合成铁基催化剂反应性能的长周期测试。结果表明,新型相分散结构的费托合成反应性能的平行性基本一致,催化剂的稳定性得到有效提高,产物选择性差异较小。;A stirred tank reactor is used as the laboratory device to test the Fischer-Tropsch synthesis (FTS) catalyst, and in the tank the flow field is very complex. The apparent gas velocity in the stirred tank is very small, so the solid holdup at the bottom of the stirred tank is relatively high due to the restriction of the structure of the tank, and the dispersion is not uniform. The phase dispersion at the bottom of the stirred tank could not be greatly improved by optimizing the internal components and operating conditions. It makes a problem that the parallelism and repeatability of the stirred tank reactor is not satisfactory. In order to solve the problem of phase dispersion in the stirred tank, the influence of different internal structure, apparent gas velocity and stirring speed on the phase distribution in stirred tank were investigated by high-speed photography method and optical fiber probe method,and the cold model experiment mediums were FTS light diesel oil and air. At the same time, the flow field of the stirred tank was simulated by computational fluid dynamics (CFD). And the new types of phase dispersion structure were designed and the reaction performance of Fe-based catalyst for FTS was investigated. The primary works and results are as follows:(1) The cold model was designed according to the hot experimental device, and the effects of internal components such as baffle, inlet gas distributor, agitator blade and stirring speed on gas holdup and bubble size were studied in detail by high-speed photography method. The results show that under the action of high speed stirring, the fluid was swiftly thrown to the side wall, and under the action of baffle disturbance, the fluid flowed up and down along the baffle, forming two dispersion centers. After adding the catalyst, there was no catalyst deposition in front of and behind the baffle, but there was a certain amount of catalyst deposition at the bottom, and the amount of deposition increased with the amount of catalyst. The form of inlet gas distributor had great influence on phase dispersion, and the dispersing effect of sintered metal distributor was the best. The problem of gas distribution and catalyst dispersion could be well solved by reforming the mode of inlet distributor at the bottom.(2) The optical fiber probe was prepared by chemical etching. It was used to study the local gas holdup of cold model experiment. And the influence of stirring speed, apparent gas velocity and inlet gas distributor on local gas holdup were studied. The local gas holdup in the stirred tank at different axial and radial directions was investigated. The experimental results show that the local gas holdup would increase with the apparent gas velocity and the stirred speed. When the stirred speed reached some value, the local gas holdup would not increase all the time. And the change of inlet gas distributor would obviously improve the uniform distribution of the gas.(3) The flow field in the stirred tank was simulated by CFD, which using the Euler-Euler two fluid model along with standard k-ε turbulence model. The relative motion between rotating impeller and stationary baffles was modeled with the multiple reference frame (MRF) approach. The simulation results show that changing the structure of the gas-liquid stirred tank could effectively improve phase dispersion of the tank bottom.(4) The new types of phase dispersion structure were designed to investigate the FTS reaction performance over Fe-based catalyst. The results show that the FTS reaction parallelism of the new phase dispersion structure was basically consistent. The stability of the catalyst was improved effectively, and the selectivity of products was relatively small. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40734
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
郑林. 费托合成搅拌釜相分散结构的研究与优化[D]. 中国科学院大学,2018.
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