应用CFD方法对化工过程两相流问题的研究
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摘要
化工两相流包括气体-液滴、气体-固体、液体-固体与液体-气泡等多种不同体系。各体系由于受两相物性、操作条件和过程环境等的影响,其流型又是多种多样,其流体力学行为非常复杂。本文主要研究了多孔介质碳化硅塔盘的流体力学行为及催化裂化装置中流化床反应器中的气固两相流问题,研究的主要内容如下:
对于多孔介质碳化硅塔盘,使用CFX提供的多孔介质模型对多孔介质塔盘进行了二维单相模拟,得到与实验结果类似的干板压降随气相动能因子变化曲线。然后,使用软件中的双欧拉两相流模型并结合多孔介质模型,模拟得到的湿板压降与实验结果基本吻合。从液体体积分率分布和气相速度分布等方面,将多孔介质塔盘的模拟结果与筛孔塔板的模拟结果进行对比,说明多孔介质塔盘具有更好的气液分布性能,气液接触面更大,气体速度扰动更剧烈,这都更有利于气液传质的进行。
对于流化床反应器,改造前,混合碳四和原料油气进入反应器后没有任何扰动和混合,直接离开反应器。这不利于反应物与催化剂的反应,原料的利用率很低。而且催化剂颗粒在反应器内分布不均。径向上,催化剂颗粒主要集中在反应器中央,壁面处的原料无法与催化剂接触并反应;轴向上,反应器中上部颗粒体积分率很低,进入的混合原料油气几乎不能反应。根据对改造前结构模拟的结果分析,对反应器两种进料管及反应器相关尺寸做出了改进与优化。改进后,催化剂颗粒在反应器内分布状况明显得到改善,颗粒分布更均匀,而且壁面附近也有一定量的催化剂颗粒存在,促进了壁面处反应的进行,提高了原料的利用率。
There are many kinds of different systems included in chemical industrial two phase flow, such as gas-droplet, gas-solid, liquid-solid, liquid-bubble, and so on. Their flow patterns are of great difference because of their difference in the physical properties of their two phases, the operating conditions and the process environment. It’s known that flow characters of the two phase flow is very complex. Both the fluid mechanics of the porous SiC tray and the gas-solid two phase flow of the fluidised bed reactor in catalytic cracking unit were studied in this paper. The main contents are as follows:
Firstly, as for the porous SiC tray, the Porous Model provided by CFX was known to have reference value and predictive value for modelling of the flow problems in the porous/pure fluid area through the study on the the Porous Model in CFX. And then, the flow of two-dimensional single-phase on the porous tray was modelled using the Porous Model to acquire the dry pressure drop. It came to that the change curve of the dry pressure drop following the F was the same to the experimental results. The wet pressure drop from the gas-droplet two phase simulation corresponded to the experimental results. It was proved that air and water had better distribution, larger contact area and more drastic velocity disturbance on the porous tray compared to that on the sieve tray from both the water volme faction and the air velocity vector.
Secondly, as for the fluidised reactor, the mixed C4 and the raw petrol gas in the reactor before transformation depart directly without any disturbance and mixture after they enter the reactor. Therefore, not only did the structure of the previous reactor go against the reaction of the reactant and the catalyst particle, but also made low utilization ratio of the reactants. The catalyst particle had uneven distribution in the whole reactor. In the radial direction, the particles mainly concentrated on the center of the reactor so that the raw materials near the wall couldn’t contact and react with the catalyst particles. In the axial direction,the raw petrol gas nearly wasn’t able to react because of the low volume fraction of the particle in the upper part of the reactor. The two kinds of feed pipes and the relative dimension of the reactor were improved and optimized accroding to the analysis of the simulation results from modelling the structure of the previous reactor. The distribution situation of the catalyst particles in the reactor had achieved significant improvements.Not only was the distribution of the particles more even, but also involved the wall of the reactor. Such distribution could promote the react near the wall and increased the utilization rate of the raw materials.
对于多孔介质碳化硅塔盘,使用CFX提供的多孔介质模型对多孔介质塔盘进行了二维单相模拟,得到与实验结果类似的干板压降随气相动能因子变化曲线。然后,使用软件中的双欧拉两相流模型并结合多孔介质模型,模拟得到的湿板压降与实验结果基本吻合。从液体体积分率分布和气相速度分布等方面,将多孔介质塔盘的模拟结果与筛孔塔板的模拟结果进行对比,说明多孔介质塔盘具有更好的气液分布性能,气液接触面更大,气体速度扰动更剧烈,这都更有利于气液传质的进行。
对于流化床反应器,改造前,混合碳四和原料油气进入反应器后没有任何扰动和混合,直接离开反应器。这不利于反应物与催化剂的反应,原料的利用率很低。而且催化剂颗粒在反应器内分布不均。径向上,催化剂颗粒主要集中在反应器中央,壁面处的原料无法与催化剂接触并反应;轴向上,反应器中上部颗粒体积分率很低,进入的混合原料油气几乎不能反应。根据对改造前结构模拟的结果分析,对反应器两种进料管及反应器相关尺寸做出了改进与优化。改进后,催化剂颗粒在反应器内分布状况明显得到改善,颗粒分布更均匀,而且壁面附近也有一定量的催化剂颗粒存在,促进了壁面处反应的进行,提高了原料的利用率。
There are many kinds of different systems included in chemical industrial two phase flow, such as gas-droplet, gas-solid, liquid-solid, liquid-bubble, and so on. Their flow patterns are of great difference because of their difference in the physical properties of their two phases, the operating conditions and the process environment. It’s known that flow characters of the two phase flow is very complex. Both the fluid mechanics of the porous SiC tray and the gas-solid two phase flow of the fluidised bed reactor in catalytic cracking unit were studied in this paper. The main contents are as follows:
Firstly, as for the porous SiC tray, the Porous Model provided by CFX was known to have reference value and predictive value for modelling of the flow problems in the porous/pure fluid area through the study on the the Porous Model in CFX. And then, the flow of two-dimensional single-phase on the porous tray was modelled using the Porous Model to acquire the dry pressure drop. It came to that the change curve of the dry pressure drop following the F was the same to the experimental results. The wet pressure drop from the gas-droplet two phase simulation corresponded to the experimental results. It was proved that air and water had better distribution, larger contact area and more drastic velocity disturbance on the porous tray compared to that on the sieve tray from both the water volme faction and the air velocity vector.
Secondly, as for the fluidised reactor, the mixed C4 and the raw petrol gas in the reactor before transformation depart directly without any disturbance and mixture after they enter the reactor. Therefore, not only did the structure of the previous reactor go against the reaction of the reactant and the catalyst particle, but also made low utilization ratio of the reactants. The catalyst particle had uneven distribution in the whole reactor. In the radial direction, the particles mainly concentrated on the center of the reactor so that the raw materials near the wall couldn’t contact and react with the catalyst particles. In the axial direction,the raw petrol gas nearly wasn’t able to react because of the low volume fraction of the particle in the upper part of the reactor. The two kinds of feed pipes and the relative dimension of the reactor were improved and optimized accroding to the analysis of the simulation results from modelling the structure of the previous reactor. The distribution situation of the catalyst particles in the reactor had achieved significant improvements.Not only was the distribution of the particles more even, but also involved the wall of the reactor. Such distribution could promote the react near the wall and increased the utilization rate of the raw materials.
引文
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[2]李万平,计算流体力学,武汉:华中科技大学出版社,2004.7~8
[3]中国人民解放军总装备部军事训练教材编辑工作委员会,计算流体力学及应用,北京:国防工业出版社,2003.1~80
[4]陈材侃,计算流体力学,重庆:重庆出版社,1992.1~148
[5]陶文铨,数值传热学(第二版),西安:西安交通大学出版社,2001.42~50
[6]H.K. Versteeg, W. Malalasekera, An Introduction to Computational Fluid Dynamics: The Finite Volume Method, New York: Wiley, 1995.50~76
[7]陶文铨,数值传热学,西安:西安交通大学出版社,1988.30~45
[8]Thompson J F, Warsi Z U A, Boundary-Fitted Coordinate System for Numerical Solution of Partial Differential Equations-A Review, Journal of Computational Physics, 1982, 47: 1~108
[9]Mastin C W, Thompson, J F, Elliptic System and Numerical Transformations, J. Math Anal. Application., 1978, 62: 52
[10]张涵信,沈孟育,计算流体力学-差分方法的原理和应用,北京:国防工业出版社,2003.347~420
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[13]万晓涛,郑雨,魏飞等,循环流化床提升管气固湍流的计算流体力学模拟—k ?ε和k p ?εp ?θs参数双流体模型,化工学报,2002,53(5):461~468
[14]Murat K, Gas mixing and flow dynamics in circulating fluidized beds with secondary air injection: [Doctoral Dissertation], Dalhousie University, 2001
[15]张政,谢灼利,流体-固体两相流的数值模拟,化工学报,2001,52(1):1~12
[16]Gidaspow, D. Multiphase Flow and Fluidisation, Boston: Academic Press, 1994, 120~200
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[22]Foumeny E A, Benyahia F, Can CFD improve the handling of air,gas and gas-liquid, Chem. Eng. Progress, 1993,(2): 21~26
[23]Nathalie Hamill, Chem. Eng., 1996. 68~72
[24]Nield D A, Bejan A, Convection in Porous Media, New York: Springer-Velag Inc, 1999,425~500
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[30]Nield D A, Bejan A, Convection in Porous Media, New York: Springer-Velag Inc., 1999, 300~410
[31]Seguin D, Montillet A, Comiti J. Experimental Characterization of Flow Regimes in Various Porous Media-Ⅰ: Limit of Laminar Flow Regime, Chemical Engineering Science, 1998, 53(21): 3751~3761
[32]Seguin D, Montillet A, Comiti J, Experimental Characterization of Flow Regimes in Various Porous Media-Ⅱ:Transition to Turbulent Regime, Chemical Engineering Science, 1998, 53(22): 3897~3909
[33]李亨,张锡文,何枫,多孔介质中流体的数值计算方法及其发展状况,石油大学学报,2000(5):111~116
[34]Sha W T, Yang C I, Kao T T, Cho S M, Multidimensional numerical modelling of heat exchangers, J. Heat Transfer, 1982, 104: 417~425
[35]Karayannis N, Markatos N C G, Mathematical modelling of heat exchangers, Proceedings of the Tenth International Heat Transfer Conference, Brighton. U K: The Industrial Sessions Papers, 1994, 13~18
[36]Huang L Y, Wen J X, Karaynannis T G, Mathews R D, CFD modelling of fluid flow and heat transfer in a shell-and-tube heat exchanger, Phoenics J. CFD Appl, 1996, 9(2): 189~209
[37]姚朝晖,核电站中的若干热工水力问题的研究:[博士学位论文],北京:清华大学,1995
[38]张锡文,李亨,姚朝晖,多孔介质/纯流体耦合区域内可压缩气体的流动,化工学报,2003(9):1209~1214
[39]杨杰,多孔介质塔盘的流体力学性能研究:[学士学位论文],天津:天津大学,2007
[40]刘德新,精馏塔板气液两相流体力学和传质CFD模拟与新塔板的开发:[博士学位论文],天津:天津大学,2008
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[2]李万平,计算流体力学,武汉:华中科技大学出版社,2004.7~8
[3]中国人民解放军总装备部军事训练教材编辑工作委员会,计算流体力学及应用,北京:国防工业出版社,2003.1~80
[4]陈材侃,计算流体力学,重庆:重庆出版社,1992.1~148
[5]陶文铨,数值传热学(第二版),西安:西安交通大学出版社,2001.42~50
[6]H.K. Versteeg, W. Malalasekera, An Introduction to Computational Fluid Dynamics: The Finite Volume Method, New York: Wiley, 1995.50~76
[7]陶文铨,数值传热学,西安:西安交通大学出版社,1988.30~45
[8]Thompson J F, Warsi Z U A, Boundary-Fitted Coordinate System for Numerical Solution of Partial Differential Equations-A Review, Journal of Computational Physics, 1982, 47: 1~108
[9]Mastin C W, Thompson, J F, Elliptic System and Numerical Transformations, J. Math Anal. Application., 1978, 62: 52
[10]张涵信,沈孟育,计算流体力学-差分方法的原理和应用,北京:国防工业出版社,2003.347~420
[11]栾茹,白保东,刁芬,一种三维网格全自动生成的新方法,电工电能新技术,2004(4):63~67
[12]Ding J, Gidaspow D, A bubbling fluidization model using kinetic theory of granular flow, America Institute of Chemical Engineering Journal, 1990, 36(4): 523~538
[13]万晓涛,郑雨,魏飞等,循环流化床提升管气固湍流的计算流体力学模拟—k ?ε和k p ?εp ?θs参数双流体模型,化工学报,2002,53(5):461~468
[14]Murat K, Gas mixing and flow dynamics in circulating fluidized beds with secondary air injection: [Doctoral Dissertation], Dalhousie University, 2001
[15]张政,谢灼利,流体-固体两相流的数值模拟,化工学报,2001,52(1):1~12
[16]Gidaspow, D. Multiphase Flow and Fluidisation, Boston: Academic Press, 1994, 120~200
[17]C.K.K. Lun, S.B. Savage, The Effects of an Impact Velocity Dependant Coefficient of Restitution on Stresses Developed by Sheared Granular Materials, Acta. Mechanica., 1986, 63(1-4):15~44
[18]C.K.K. Lun, S.B. Savage, D.J. Jeffery, N. Chepurniy, Kinetic Theories for Granular Flow: Inelastic Particles in Couette Flow and Slightly Inelastic Particles in a General Flow Field, J. Fluid Mech.,1984, 140: 223~256
[19]Miller A, Gidaspow D, Multiphase Flow and Fluidization: Continuum and Kinetic Theory Descriptions, AIChE Journal, 1992, 38(11): 1811
[20]H. Enwald, E. Peirano, A.E. Almstedt, Eulerian Two-Phase Flow Theory Applied to Fluidisation, Int. J. Multiphase Flow., 1996, 22: 21~66
[21]J. Ding, D. Gidaspow, A Bubbling Fluidisation Model using Theory of Granular Flow, AIChE. J., 1990, 36: 523~538
[22]Foumeny E A, Benyahia F, Can CFD improve the handling of air,gas and gas-liquid, Chem. Eng. Progress, 1993,(2): 21~26
[23]Nathalie Hamill, Chem. Eng., 1996. 68~72
[24]Nield D A, Bejan A, Convection in Porous Media, New York: Springer-Velag Inc, 1999,425~500
[25]Prithiviraj M, Andrews M J, Three dimensional numerical simulation of shell-and-tube heat exchangers, Numerical heat transfer, 1998, 33 (8): 799~816
[26]Patankar S V, Spalding D B, A calculation procedure for the transient and steady state behavior of shell-and-tube heat exchangers, Heat Transfer Design and Theory Sourcebook, New York: McGraw-Hill, 1974, 155~176
[27]Pascal J P, Pascal H, Pressure diffusion in unsteady non-Darcian flows through porous media, Eur. J. Mech. B/Fluids., 1995, 14(1): 75~90
[28]Pascal J P, Pascal H, Non-linear effects on some unsteady non-Darcian flows through porous media, Int. J. Non-Linear Mechanics., 1997, 32(2): 361~376
[29]Marcos H J P, Marcelo J S, On the Definition of Turbulent Kinetic Energy for Flow in Porous Media, Int. Comm. Heat Mass Transfer., 2000, 27 (2): 211~220
[30]Nield D A, Bejan A, Convection in Porous Media, New York: Springer-Velag Inc., 1999, 300~410
[31]Seguin D, Montillet A, Comiti J. Experimental Characterization of Flow Regimes in Various Porous Media-Ⅰ: Limit of Laminar Flow Regime, Chemical Engineering Science, 1998, 53(21): 3751~3761
[32]Seguin D, Montillet A, Comiti J, Experimental Characterization of Flow Regimes in Various Porous Media-Ⅱ:Transition to Turbulent Regime, Chemical Engineering Science, 1998, 53(22): 3897~3909
[33]李亨,张锡文,何枫,多孔介质中流体的数值计算方法及其发展状况,石油大学学报,2000(5):111~116
[34]Sha W T, Yang C I, Kao T T, Cho S M, Multidimensional numerical modelling of heat exchangers, J. Heat Transfer, 1982, 104: 417~425
[35]Karayannis N, Markatos N C G, Mathematical modelling of heat exchangers, Proceedings of the Tenth International Heat Transfer Conference, Brighton. U K: The Industrial Sessions Papers, 1994, 13~18
[36]Huang L Y, Wen J X, Karaynannis T G, Mathews R D, CFD modelling of fluid flow and heat transfer in a shell-and-tube heat exchanger, Phoenics J. CFD Appl, 1996, 9(2): 189~209
[37]姚朝晖,核电站中的若干热工水力问题的研究:[博士学位论文],北京:清华大学,1995
[38]张锡文,李亨,姚朝晖,多孔介质/纯流体耦合区域内可压缩气体的流动,化工学报,2003(9):1209~1214
[39]杨杰,多孔介质塔盘的流体力学性能研究:[学士学位论文],天津:天津大学,2007
[40]刘德新,精馏塔板气液两相流体力学和传质CFD模拟与新塔板的开发:[博士学位论文],天津:天津大学,2008
[41]张士瑞,薛敦松,常规炼油工艺的技术进步-石油炼制技术进展综述(1),石油规划设计,2003,14(3):6~9
[42]张建芳,山红红,杨朝合等,两段提升管催化裂化新技术,中国专利,ZL00134054.9,2000-12-13
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