CFB提升管等效反应器网络模型

对气固循环流化床(CFB)提升管内的非均相流动行为进行了计算流体力学(CFD)模拟。基于CFD时均流场数据与信息,搭建了用于描述提升管内非理想流动过程的等效反应器网络(ERN)模型。在ERN模型建立过程中提出了反应器网络的6个拓扑结构参数和一个等效判据,并系统地分析了等效反应器网络结构六参数的性质与确定方法,从而形成了一套CFB提升管流动模型建模方法。     

小型提升管反应器流动-反应耦合模拟

在提升管气固两相湍流流动模型和重油反应动力学集总模型的基础上,利用Fluent软件建立了催化裂化提升管反应器气固两相流动与反应耦合模型,对实验室小型提升管反应器进行了数值模拟,考察了气固两相的流动、传热、传质与反应过程。结果表明,提升管反应器内气固两相在轴向和径向的流动、传热与反应的分布不均匀。在入口附近。原料和催化剂温度变化显著,各组分的浓度变化剧烈,在提升管上部,变化平缓。反应器出口各组分质量分数的模拟值和实验值基本吻合。说明该模型对提升管反应器出口参数和反应结果具有较好的预测性。     

催化裂化提升管反应器流动反应耦合模型研究进展

催化裂化(FCC)工艺在重质油轻质化过程中发挥着重要作用, 而FCC提升管反应器的模型化是催化裂化新工艺与新装备的开发、催化裂化装置稳定操作与生产调优等常需做的工作。本文首先根据流动模型与反应模型不同的集成方式对提升管反应器流动-反应耦合模型进行了归纳与分类, 并回顾了国内外流动-反应耦合模型的研究历程, 指出了耦合模型的发展趋势;随后对当前研究较多的计算流体力学(CFD)流动-反应耦合模型进行了较为全面的阐述, 包括对耦合模型的应用场合、模型求解解耦方法的研究情况等均作了介绍, 同时还分析了该类耦合模型所存在的不足之处, 并指出工业提升管反应器在线采样技术的开发在耦合模型的验证工作上的必要性;最后, 对FCC提升管反应器流动-反应耦合模型研究进行了总结与展望, 以期能够为FCC提升管反应器模型化新方法的提出以及耦合模型的验证工作等研究给予借鉴和指导。     

渣油催化裂化提升管反应器组成分布的数值模拟

在流动模型和集总反应动力学模型的基础上,将流动、传热、反应综合考虑,建立了渣油催化裂化提升管反应器的数学模型,通过对4套不同工况进行数值模拟,考察了反应器内气相组成分布和催化剂颗粒的温度、速度分布,得到了与工业装置基本一致的提升管出口参数,从而验证了模型的可靠性.     

湍流气固两相流动状况的数值模拟

应用已建立的提升管反应器固两相流动反应模型,对工业催化裂化提升管反应器内在有传热及裂化反应时的湍流气固两相流动进行了数值模拟,得到了气固两相湍充动状况的详细信息,揭示了提升管内部有反应和传热时气固两相湍流流动的基本特征。模拟结果表明,在轴向,径向和圆周方向都存在着流动,湍能与率剂颗粒浓度的不均匀分布,进料段内的流动是整个反应器最复杂的部分。工业提升管反应器内这一复杂的气固两相湍流流动必将对传热和裂     

基于EMMS曳力模型的提升管进料混合段模拟

提升管进料混合段是催化裂化提升管反应器最关键的区域。为找到一种合理的方法以改善提升管进料段内油剂两相流动及混合状况,采用了EMMS曳力模型,对提升管进料混合段气固两相流混合及流动进行三维计算流体力学(CFD)模拟,并与实验数据进行了对比;分析了气固两相流动及混合特性,还模拟分析了不同进料角度对提升管进料混合段内二次流的影响以及两相流动、混合状况。结果表明,EMMS/Matrix曳力模型能够较为准确地模拟进料混合段内气固两相流动、混合过程;当喷嘴斜向上喷射进料时,射流影响区颗粒流混合不均匀,颗粒流恢复稳定流型所需时间长,且边壁受二次流影响,出现"高浓度、高返混"区域,工业过程中易引起结焦。由此提出了一种新型提升管进料段结构的改进方案,能合理利用二次流,实现颗粒流均匀混合和流动。     

催化裂化提升管反应器模型的建立

工业催化裂化提升管反应器内既存在着气固两相的湍流流动,又存在着传热和裂化反应,而且这些过程是相互影响,高度耦合在一起的。本文全面系统地考虑湍流气因两相流动,传质,传热及反应等复杂因素及其相互影响,建立了催化裂化提升管反应器三维气固两相流动反应模型,形成了相应的数值解法,编制了大型的模拟计算程序。由此可对工业催化裂化提升管反应器内湍流气固两相流动进行系统的数值模拟研究。     

FCC反应过程的CFD模拟进展

流化催化裂化（fluid catalytic cracking,FCC）工艺是石油炼制中的重要转化工艺,用于生产汽油、柴油、轻质烯烃等重要化工原料。FCC反应过程的CFD模拟有助于理解FCC反应器中流动和反应行为,辅助设计和优化FCC工艺设备,最终指导工业生产和实现虚拟调控和放大。从与FCC反应模拟相关的多相流动模型、反应动力学模型以及流动与反应之间耦合等方面做了回顾和总结。在流动与反应耦合研究方面,从湍流模型的使用、流动结构的影响、精细化模型的发展以及原油汽化模型的重要性这4个角度做了分析比较及总结。基于已有的研究工作,认为虽然很多研究表明CFD模拟能较好地揭示工业FCC提升管反应器内的流动和反应行为,但缺乏采用同一方法实现从小试到工业反应器模拟放大的实例,从侧面反映了当前的FCC理论模型和模拟技术还远未达到可以代替实验的水平。展望未来的FCC反应模拟,建议从模型精细度和计算效率上加强研发,并在此两方面寻求平衡,最终实现虚拟调控。     

汽油催化改质反应过程数值模拟

在汽油催化反应动力学模型和气固两相流动模型的基础上,建立了汽油改质反应过程流动-反应耦合模型。针对不同的转化反应器构型（提升管、提升管-床层反应器）,对汽油改质过程进行了数值模拟。模拟结果表明,对提升管反应器而言,汽油经过低温改质反应后,烯烃含量可以从35.1%降低到18%左右,烯烃降低幅度可达48%,汽油中烯烃主要转化为异构烷烃。另外,随着反应温度的升高,汽油转化反应中的裂化反应增强,导致汽油收率下降。对于提升管-床层反应器而言,汽油中的烯烃含量可以降得更低,在床层空速4时,烯烃含量可以降低到5%左右,汽油收率为80%左右。     

CFD方法在固定床反应器传热研究中的应用

固定床反应器是一种常见的化学和生化反应器,由于内部结构十分复杂,固定床内的局部流动和传热过程研究一直是一个颇具挑战性的问题。有效参数法是长期以来固定床传热研究的常用方法,但是由于对固定床内温度场缺乏准确的了解,目前为止许多基于有效参数法的传热模型的普适性仍然存在问题。计算流体力学（CFD）的数值模拟方法是近年来应用于固定床流动和传热研究的一种新的研究方法,它通过数值方法求解流动和传递的微分方程组而获得流场和温度场。CFD数值模拟方法能够提供精确的局部流动和传递信息如速度分布、压力分布、温度分布、组分浓度分布等。本文综述和分析了CFD方法在固定床反应器的流动和传热研究领域的最新进展,讨论了CFD方法在该领域的应用前景。     

Computational fluid dynamics of a circulating fluidized bed under various fluidization conditions

A computational fluid dynamics (CFD) model was developed to simulate the hydrodynamics of gas-solid flow in a circulating fluidized bed (CFB) riser at various fluidization conditions using the Eulerian-Granular multiphase model. The model was evaluated comprehensively by comparing its predictions with experimental results reported for a CFB riser operating at various solid mass fluxes and superficial gas velocities. The model was capable of predicting the main features of the complex gas-solids flow, including the cluster formation of the solid phase along the walls, for different operating conditions. The model also predicted the coexistence of up-flow in the lower regions and downward flow in the upper regions at the wall of the riser for high gas velocity and solid mass flux, as reported in the literature. The predicted solid volume fraction and axial particle velocity were in good agreement with the experimental data within the high density fast fluidization regime. However, the model showed some discrepancy in predicting the gas-solid flow behavior in the riser operating in dense suspension up-flow and low density fast fluidization regimes.     

Numerical Simulation on Gas-Solid Two-Phase Turbulent Flow in FCC Riser Reactors(Ⅱ) Numerical Simulation on the Gas-Solid Two-Phase Turbulent Flow

Numerical simulation on the flow,heat transfer and cracking reactions in commercial fluid catalyticcracking(FCC)riser reactors were carried out employing the developed turbulent gas-solid two-phase flow-reac-tion model for FCC riser reactors given in Part Ⅰ of the present paper.Detailed information about the turbulentflow fields in the riser reactor obtained revealed the basic characteristics of the gas-solid two-phase turbulentflows when heat transfer and catalytic cracking reactions were co-existing in the riser.Results showed that thedistributions of the flow,the turbulence kinetic energy and the catalyst particle concentration are not uniform inthe axial,radial and tangential directions.The most complicated part of the riser reactor is the feed injectingzone.The complicated configuration of the turbulent gas-solid two-phase flows would exert a great influence onthe results of interphase heat transfer and cracking reactions.     

Modelling a circulating fluidized bed riser reactor with gas—solids downflow at the wall

A predictive model was developed for the fully developed zone of a circulating fluidized bed (CFB) riser reactor operating in the fast fluidization regime that overcomes limitations of existing models. The model accounts for the upward flow of gas and solids in the core and downward flow of the two phases in the annulus. Additionally, a numerical solution methodology for the simulation of a riser reactor employing the hydrodynamic model was devised. A simulation was performed using the fast, main Claus reaction to demonstrate the effects of backmixing in the fast fluidization regime. It was found that the molar flow rates of the reactants leaving a fast fluidized CFB riser reactor were significantly higher than those leaving an identical reactor operating in the pneumatic transport regime.     

A preliminary CFD study of the gas-solid flow fields in multizone circulating polymerization reactors

A Eulerian-Eulerian model incorporating the kinetic theory of granular flow is adopted to describe the gas-solid two-phase flows in a multizone circulating propylene polymerization reactor. Corresponding simulations are carried out in a commercial computational fluid dynamics (CFD) code Fluent. First, the model is validated by comparing simulation results with the experimental data. Entire fields in the reactor composed of a riser and a downer are also obtained numerically. Furthermore, the model is used to distinguish the flow behaviors in the riser and the downer. The effects of riser-outlet configuration and operation gas velocity on the flow behaviors in the reactor are also investigated numerically. The simulated results show that the flow behaviors in the riser of MZCR are different from those in the downer of MZCR. In addition, the simulation results also show that both the exit configuration of the riser and the operation gas velocity can significantly affect the flow behaviors in the MZCR.     

Experiment and 3D simulation of slugging regime in a circulating fluidized bed

A circulating fluidized bed (CFB) is widely applied in many industries because it has high efficiency. To develop and improve the process, an understanding of the hydrodynamics inside the CFB is very important. Computational fluid dynamics (CFD) represents a powerful tool for helping to understand the phenomena involved in the process. In this study, a CFD model was developed to represent a cold model of the laboratory scale CFB which was designed to study the hydrodynamics of a CFB using commercial CFD software. The Eulerian approach with kinetic theory of granular flow was used for simulating the hydrodynamics inside the system. After proper tuning of relevant parameters, the pressure profile along the equipment from the simulation was well agreed with that from the experiment. The simulation result expresses the hydrodynamic parameters of the slug flow such as solid volume fraction, gas and solid velocities and granular temperature in the riser.     

16m高气固提升管中的压力梯度与流动行为研究

在较宽操作条件范围对16m高提升管中气－固两相流（空气－FCC颗粒）的压力梯度进行了实验测试,进一步揭示了快速流态化和密相气力输送这两种流动形态的动力学特征及其与操作参数的关系。结果表明,在表观气速增大的过程中气固提升管中的轴向压力梯度并非总是不断趋于均匀分布;提升管高度对快速流态化到密相气力输送状态的过渡有重要影响,对于给定的表观气速,提升管高度增加将使过渡点所应的颗粒循环量和床层颗粒浓度都减小。本实验条件下所有过滤点对应的床层颗粒浓度较为一致,平均为0．0104,并由此得到过渡点操作参数Ug与Gs的关联式。本文研究表明,在以往工作基础上进一步研究提升管高度对流动行为的影响极有必要。