沉浸管式流化床的多相流模拟与结构优化
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摘要
本文针对大型流化床反应器存在进气不均、易产生大气泡和颗粒团聚体,对于强放热或吸热反应须在流化床内设置管式内构件以及时取热或加热,出口气体带出的固体颗粒量较大等弊端,进行了流场模拟与实验研究。内容包括:
设计了双锥导流式进气分布器,并利用FUENT软件对不同结构参数下分布器的流场进行了数值模拟。模拟结果表明:外锥的设立,避免了不能使气体均布的弊端;合理调整导流口的位置与尺寸能确保流体沿分布器内锥表面压力均布;分布器内气体分布不均匀度随内锥开孔率的增加先减小后增大,并沿流体的流动方向有降低的趋势;当内锥开孔率为0.8~1%,锥角采用60°时气体分布器的不均匀度小、压降低。并且利用实验验证了上述模拟结果。
对三种不同外形的流化床进行了模拟。结果显示,流化床的扩大段对床内部流场的影响显著。三种拥有扩大段的床形在降低密相床层高度、颗粒速度方面要好于普通圆筒形流化床。圆锥形流化床,降低了颗粒扬析,但容易出现沟流;当静床床面低于扩大段下端的流化床时,不适宜的结构尺寸会造成内部气泡尺寸较大、易聚并发生节涌;对静床床面位于扩大段下端,床层尺寸比例设计合理时,密相床层高度低,内部气泡尺寸较小、颗粒的扬析量少、流场稳定,与实验结果吻合。
作者对加入垂直与水平两种沉浸管的流化床内部流场进行了研究。对垂直沉浸管式流化床的模拟表明:垂直管上方与下方床层内的颗粒有从流化中心向边壁运动的趋势,而垂直管区域内的颗粒沿轴向向上运动;垂直管的加入破碎了流化床内的大气泡、减缓了气泡上升速度、减弱了气泡聚并;降低了垂直管上方床层区域内的颗粒固含率,减少了颗粒的扬析;适当加大垂直管间距可以有效降低壁面处的颗粒固含率及密相床层高度。对水平沉浸管式流化床的模拟发现:床内一定数量的管道被“气穴”包围,且管间距减小后,“气穴”增多;床内管束采用正三角与正方形两种排列方式均能降低管束上方区域内的颗粒固含率;管束呈三角形排列时密相床层高度较低,且颗粒在中心区域具有较高的轴向速度,有助于减少“气穴”现象。
In this paper, a flow field simulation and experimental study were researched because of uneven intake and easy to have a big bubble and particle aggregates, setting up baffle for transferring heat and heating in strong exothermic or endothermic reaction, bringing out a larger number of solid particles by air-out in the industrial synthesis of organic silicon monomer reaction. To solve the above problem, the specific research as follow:
The writer designed the double cone diversion inlet distributor and simulated various structural parameters of the flow field distribution with CFD simulation software. Simulation results show that outside cone could avoid the drawbacks of asymmetric gas distribution; Reasonable adjustments to diversion trench location and size could ensure the uniform pressure distribution along the inner surface of inner cone. While the ratios of aperture in inner cone increased, gas distribution uneven distribution increased after the first decrease; When the value of ratios of aperture and inside cone angle was 0.8~1% and 60°,pressure drop and uniform gas distribution reached perfect. Above all analog value corresponded with the experimental data.
The flow field distribution of three different external shape fluidized bed was simulated. According to the simulation results, conical fluidized bed was prone to channeling flow, reducing gas utilization; The fluidized bed that static bed height is lower than the bottom of the expanding section that internal flow field was volatile, When inappropriate size of it was easy to grow large bubble and had slugging phenomenon; The fluidized bed that static bed height at the bottom of the expanding section had lower dense bed height, smaller bubble size, less elutriation. The simulation results corresponded with experimental results.
Author studied the flow field of fluidized bed joined the vertical and horizontal immersed tubes. Simulating vertical immersed tube fluidized bed showed: particles flowed from the center to the edge of wall in the top and bottom of vertical tubes, and particles in the vertical tubes bank flowed along the axial upward; Vertical tubes broken the large bubbles in fluidized bed, reduced the bubble rise velocity, weakened bubble coalescence, reduced particle concentration above the vertical pipe region, so particle elutriation decreased; Appropriate to increase the spacing can effectively reduce particle concentration along the wall and the height of dense phase bed. Simulating horizontal tube fluidized bed showed: a certain number of channels were surrounded by“cavitations”, When decreasing the tubes spacing, the number of cavitations increased; The tubes that arranged by triangular and square could reduce particle concentration at the top of the tube band; The bed that tubes were arranged by triangular had the lower bed height, and the particles in the central region had a higher axial velocity, which could reduce the“cavitations”phenomenon.
设计了双锥导流式进气分布器,并利用FUENT软件对不同结构参数下分布器的流场进行了数值模拟。模拟结果表明:外锥的设立,避免了不能使气体均布的弊端;合理调整导流口的位置与尺寸能确保流体沿分布器内锥表面压力均布;分布器内气体分布不均匀度随内锥开孔率的增加先减小后增大,并沿流体的流动方向有降低的趋势;当内锥开孔率为0.8~1%,锥角采用60°时气体分布器的不均匀度小、压降低。并且利用实验验证了上述模拟结果。
对三种不同外形的流化床进行了模拟。结果显示,流化床的扩大段对床内部流场的影响显著。三种拥有扩大段的床形在降低密相床层高度、颗粒速度方面要好于普通圆筒形流化床。圆锥形流化床,降低了颗粒扬析,但容易出现沟流;当静床床面低于扩大段下端的流化床时,不适宜的结构尺寸会造成内部气泡尺寸较大、易聚并发生节涌;对静床床面位于扩大段下端,床层尺寸比例设计合理时,密相床层高度低,内部气泡尺寸较小、颗粒的扬析量少、流场稳定,与实验结果吻合。
作者对加入垂直与水平两种沉浸管的流化床内部流场进行了研究。对垂直沉浸管式流化床的模拟表明:垂直管上方与下方床层内的颗粒有从流化中心向边壁运动的趋势,而垂直管区域内的颗粒沿轴向向上运动;垂直管的加入破碎了流化床内的大气泡、减缓了气泡上升速度、减弱了气泡聚并;降低了垂直管上方床层区域内的颗粒固含率,减少了颗粒的扬析;适当加大垂直管间距可以有效降低壁面处的颗粒固含率及密相床层高度。对水平沉浸管式流化床的模拟发现:床内一定数量的管道被“气穴”包围,且管间距减小后,“气穴”增多;床内管束采用正三角与正方形两种排列方式均能降低管束上方区域内的颗粒固含率;管束呈三角形排列时密相床层高度较低,且颗粒在中心区域具有较高的轴向速度,有助于减少“气穴”现象。
In this paper, a flow field simulation and experimental study were researched because of uneven intake and easy to have a big bubble and particle aggregates, setting up baffle for transferring heat and heating in strong exothermic or endothermic reaction, bringing out a larger number of solid particles by air-out in the industrial synthesis of organic silicon monomer reaction. To solve the above problem, the specific research as follow:
The writer designed the double cone diversion inlet distributor and simulated various structural parameters of the flow field distribution with CFD simulation software. Simulation results show that outside cone could avoid the drawbacks of asymmetric gas distribution; Reasonable adjustments to diversion trench location and size could ensure the uniform pressure distribution along the inner surface of inner cone. While the ratios of aperture in inner cone increased, gas distribution uneven distribution increased after the first decrease; When the value of ratios of aperture and inside cone angle was 0.8~1% and 60°,pressure drop and uniform gas distribution reached perfect. Above all analog value corresponded with the experimental data.
The flow field distribution of three different external shape fluidized bed was simulated. According to the simulation results, conical fluidized bed was prone to channeling flow, reducing gas utilization; The fluidized bed that static bed height is lower than the bottom of the expanding section that internal flow field was volatile, When inappropriate size of it was easy to grow large bubble and had slugging phenomenon; The fluidized bed that static bed height at the bottom of the expanding section had lower dense bed height, smaller bubble size, less elutriation. The simulation results corresponded with experimental results.
Author studied the flow field of fluidized bed joined the vertical and horizontal immersed tubes. Simulating vertical immersed tube fluidized bed showed: particles flowed from the center to the edge of wall in the top and bottom of vertical tubes, and particles in the vertical tubes bank flowed along the axial upward; Vertical tubes broken the large bubbles in fluidized bed, reduced the bubble rise velocity, weakened bubble coalescence, reduced particle concentration above the vertical pipe region, so particle elutriation decreased; Appropriate to increase the spacing can effectively reduce particle concentration along the wall and the height of dense phase bed. Simulating horizontal tube fluidized bed showed: a certain number of channels were surrounded by“cavitations”, When decreasing the tubes spacing, the number of cavitations increased; The tubes that arranged by triangular and square could reduce particle concentration at the top of the tube band; The bed that tubes were arranged by triangular had the lower bed height, and the particles in the central region had a higher axial velocity, which could reduce the“cavitations”phenomenon.
引文
[1]李晓光,赵宏伟,吴茵等.国内外有机硅工业进展[J],吉林化工学院学报[J],2006,23(2):30~31
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[6]陈国南.有机硅单体流化床的冷态研究[硕士论文].浙江:浙江大学,2004
[7]时钧,汪家鼎,余国琮等.化学工程手册(第二版)下卷[M].化学工业出版社(1996)
[8]王树楹,李锡源,魏建华等.现代填料塔技术指南,北京:中国石化出版社:1998.1
[9]董谊仁,张剑慈.填料塔孔口型液体分布器液体穿孔流量系数实验研究,化学工程, 2000,28(3).10~12,42
[10] Otero, A. R., Munoz, R. C. Fluidized bed distributors of bubble cap type [J]. Power Technology, 1974, 9:279.
[11] Mori, S., Wen, C. Y. Estimation of bubble diameter in gas fluidized beds [J]. AIChE, 1975, 21:109.
[12] Kouri R J, Sohlo J J, Chem.E.Symp.Ser, 1987, 104:B193
[13]董谊仁,侯章德.填料塔气体分布器及其塔内件[J],化工生产与技术1996,(4):6~13
[14]化学工程师手册编辑委员会.化学工程师手册[M].机械工业出版社(2001)
[15] Chen G K, Recent developments in distillation Hydrocarbon Processing.1989, 2:37
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[17] L.T.Fan, THO-CHING HO, S.HIRAOKA, W.P.WALAWENDER.Pressur Fluctuations in a Fluidized Bed [J], AICHE, 1981, 27(3):388-396
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[19] R.J.H.Voothoeve, J.A.Lips, J.C.Vlugter.Mechanism and kinetice of the Metal Catalyzed Synthesis of Methylehlorosilanes: The Kinetice of the Copper Catalyzed Reaction of Methyl Chloride and Silicon, Journal of Catalysis, 1965(4):43-55
[20]王福军.计算流体动力学分析[M].北京:清华大学出版社,2004.9
[21]张锴,毕继诚,Brandani Stefano.气固密相流化床的多相流CFD模拟进展.中国颗粒学会2006年年会暨海峡两岸颗粒技术研讨会.2006.8:652~656
[22]Van Wachem B G M, Almstedt A E. Methods for multiphase computational fluid dynamics [J].Chem. Eng. J., 2003, 96:81-98.
[23] Van der Hoef M, A, Van Sint Annaland M, Kuipers J A M.Computational fluid dynamics for dense gas-solid fluidized beds: A multi-scale modeling strategy [J].Chem. Eng. Sci., 2004, 59: 5157~5165.
[24] Chiesa M, Mathiesen V, Melheim J A, et al. Numerical simulation of particulate flow by the Euleriao-Lagrangian and the Euleriao-Eulerian approach with application to a fluidized bed [J] .Compt Chem Eng., 2005, 29: 29~304.
[25] Tanaka T,Yonemura S,Kiribayshi K,Chen W.Cluster Fomration and Particle-induced Instability in Gas-solid Flows Predicted by the DSMC Method[J].JSME International Journal Series B-Fluid sand Thernal Engineering,1996,39(2):239~245.
[26] Ouyang J, Li J.Particle-motion-resolved Diseerte Model for Simulating Gas-solid Fluidization [J].Chem Eng Sci, 1999, 54:2077~2083.
[27] Gidaspow D.Hydrodynamics of fluidization and Heat Transfer: Supercomputer Modeling [J]. APPl Mech Rev, 1986, 39(l):1~22.
[28] Massoudi M, Rajagopal K R, Ekmann J M, et al.Remarks on the Modeling of Fluidized System[J],AIChEJ,1992,38:1801.
[29] Sinelair J L, Jackson R.Gas-Particle Flow in a Vertiele Pipe with Particle-Particle Interaetion [J]. AIChEJ, 1989, 35(9):1473~1486.
[30] Louge M Y, Mastorakos E,Jenkins J T .The Role of Particle Collisions in Pneumatic Transport[J]. J.Fluid Mech.1991, 231:345~359.
[31] Dasgupta S, Jaekson R, Sundaresna S.Turbulent Gas-Particle Flow in Vertical Risers [J] .AIChEJ, 1994, 40(2):215~228.
[32] Rumen D, Chavdar D, Gas flow distribution in packed column[J].Chem.Eng.and Proce.2002, 41(5):385~393
[33]洛振福,赵跃民,陈清如等.浓相高密度分选流化床气体分布参数的研究[J].中国矿业大学学报,2004,33(3):237~240
[34]张锴,赵玉龙,张济宇等.鼓泡床内气体分布器设计及其对水力学的影响[J].煤化工, 1995,23(4):11~15
[35]张文卿.大型填料塔分布器内计算流体力学行为研究及优化设计[硕士论文].浙江:浙江大学,2004.
[36]傅德熏,马延文.计算流体力学[M],高等教育出版社,2002.
[37] Ian Hulme,Eric Clavelle,Loni van der Lee.CFD Modeling and Validation of Bubble Properties for a Bubbling Fluidized Bed[J]. Ind.Eng.Chem.Res.2005, 44:4254~4266
[38] Sebastian Zimmermann, Fariborz Taghipour. CFD Modeling of the Hydrodynamics and reaction kinetics of FCC Fluidized-Bed Reactors [J]. Ind.Eng.Chem.Res.2005, 44:9818~9827
[39]周继良,邹宗树,余艾鼓.鼓泡流化床流动特性的数值模拟[J],材料与冶金学报2007(6):126~129
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[46] Y.He, H.Lu, Q.Sun, L.Yang, ET al.Hydrodynamics of gas-solid flow around immersed tubes in bubbling fluidized beds [J] Powder Technology, 2004, 145:88~105
[47]赵永志,程易.沉浸管式流化床的颗粒尺度模拟[J].化学工程,2007,35(11):21~24
[2]王皖林,王涛.中国甲基氯硅烷合成技术进展[J].有机硅材料,2008,22(1):1~5
[3]郑建军.我国三大有机硅单体生产装置发展概述[J],化工新型材料,1999:76~77
[4]幸松民,王一璐.有机硅合成工艺及产品应用[J].化学工业出版社,2000.62~63
[5]金涌,祝京旭,汪展文等.流态化工程原理[M].清华大学出版社(2001):72
[6]陈国南.有机硅单体流化床的冷态研究[硕士论文].浙江:浙江大学,2004
[7]时钧,汪家鼎,余国琮等.化学工程手册(第二版)下卷[M].化学工业出版社(1996)
[8]王树楹,李锡源,魏建华等.现代填料塔技术指南,北京:中国石化出版社:1998.1
[9]董谊仁,张剑慈.填料塔孔口型液体分布器液体穿孔流量系数实验研究,化学工程, 2000,28(3).10~12,42
[10] Otero, A. R., Munoz, R. C. Fluidized bed distributors of bubble cap type [J]. Power Technology, 1974, 9:279.
[11] Mori, S., Wen, C. Y. Estimation of bubble diameter in gas fluidized beds [J]. AIChE, 1975, 21:109.
[12] Kouri R J, Sohlo J J, Chem.E.Symp.Ser, 1987, 104:B193
[13]董谊仁,侯章德.填料塔气体分布器及其塔内件[J],化工生产与技术1996,(4):6~13
[14]化学工程师手册编辑委员会.化学工程师手册[M].机械工业出版社(2001)
[15] Chen G K, Recent developments in distillation Hydrocarbon Processing.1989, 2:37
[16]张吕鸿.填料塔进料气体分布器气液运动的研究[博士论文],天津;天津大学,1998
[17] L.T.Fan, THO-CHING HO, S.HIRAOKA, W.P.WALAWENDER.Pressur Fluctuations in a Fluidized Bed [J], AICHE, 1981, 27(3):388-396
[18]陈甘棠.化学反应工程,北京:化学工业出版社,1990,225
[19] R.J.H.Voothoeve, J.A.Lips, J.C.Vlugter.Mechanism and kinetice of the Metal Catalyzed Synthesis of Methylehlorosilanes: The Kinetice of the Copper Catalyzed Reaction of Methyl Chloride and Silicon, Journal of Catalysis, 1965(4):43-55
[20]王福军.计算流体动力学分析[M].北京:清华大学出版社,2004.9
[21]张锴,毕继诚,Brandani Stefano.气固密相流化床的多相流CFD模拟进展.中国颗粒学会2006年年会暨海峡两岸颗粒技术研讨会.2006.8:652~656
[22]Van Wachem B G M, Almstedt A E. Methods for multiphase computational fluid dynamics [J].Chem. Eng. J., 2003, 96:81-98.
[23] Van der Hoef M, A, Van Sint Annaland M, Kuipers J A M.Computational fluid dynamics for dense gas-solid fluidized beds: A multi-scale modeling strategy [J].Chem. Eng. Sci., 2004, 59: 5157~5165.
[24] Chiesa M, Mathiesen V, Melheim J A, et al. Numerical simulation of particulate flow by the Euleriao-Lagrangian and the Euleriao-Eulerian approach with application to a fluidized bed [J] .Compt Chem Eng., 2005, 29: 29~304.
[25] Tanaka T,Yonemura S,Kiribayshi K,Chen W.Cluster Fomration and Particle-induced Instability in Gas-solid Flows Predicted by the DSMC Method[J].JSME International Journal Series B-Fluid sand Thernal Engineering,1996,39(2):239~245.
[26] Ouyang J, Li J.Particle-motion-resolved Diseerte Model for Simulating Gas-solid Fluidization [J].Chem Eng Sci, 1999, 54:2077~2083.
[27] Gidaspow D.Hydrodynamics of fluidization and Heat Transfer: Supercomputer Modeling [J]. APPl Mech Rev, 1986, 39(l):1~22.
[28] Massoudi M, Rajagopal K R, Ekmann J M, et al.Remarks on the Modeling of Fluidized System[J],AIChEJ,1992,38:1801.
[29] Sinelair J L, Jackson R.Gas-Particle Flow in a Vertiele Pipe with Particle-Particle Interaetion [J]. AIChEJ, 1989, 35(9):1473~1486.
[30] Louge M Y, Mastorakos E,Jenkins J T .The Role of Particle Collisions in Pneumatic Transport[J]. J.Fluid Mech.1991, 231:345~359.
[31] Dasgupta S, Jaekson R, Sundaresna S.Turbulent Gas-Particle Flow in Vertical Risers [J] .AIChEJ, 1994, 40(2):215~228.
[32] Rumen D, Chavdar D, Gas flow distribution in packed column[J].Chem.Eng.and Proce.2002, 41(5):385~393
[33]洛振福,赵跃民,陈清如等.浓相高密度分选流化床气体分布参数的研究[J].中国矿业大学学报,2004,33(3):237~240
[34]张锴,赵玉龙,张济宇等.鼓泡床内气体分布器设计及其对水力学的影响[J].煤化工, 1995,23(4):11~15
[35]张文卿.大型填料塔分布器内计算流体力学行为研究及优化设计[硕士论文].浙江:浙江大学,2004.
[36]傅德熏,马延文.计算流体力学[M],高等教育出版社,2002.
[37] Ian Hulme,Eric Clavelle,Loni van der Lee.CFD Modeling and Validation of Bubble Properties for a Bubbling Fluidized Bed[J]. Ind.Eng.Chem.Res.2005, 44:4254~4266
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