流化床冷渣器流化特性的研究
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摘要
受我国燃用煤种和现有煤粉制备系统的限制,风水联合冷渣器经常遇到一风室流化恶化结焦的问题。将风水联合冷渣器传统的板式布风装置改为管式布风,可以有效避免风室结焦。风水联合冷渣器风室处于鼓泡流化状态,本文将对鼓泡流态化下混合颗粒的流化特性进行研究。
本文搭建截面尺寸125×250mm,高1200mm的冷态实验台。实验选取粒径分别为150-250μm和1-2mm的两种粒径电厂灰颗粒,研究混合颗粒的初始流化风速和大小颗粒的混合与分层特性。
实验结果表明,双组分混合颗粒的初始流化风速介于大小颗粒初始流化风速之间,更接近于小粒径颗粒,并随大颗粒质量分数的增加而增大,增大的趋势先慢后快;混合物料床层膨胀比随流化风速的提高而增大,增大的趋势先快后慢,实验结果与经验公式计算结果有较大误差;二元组分颗粒之间的混合程度随大颗粒组分和流化风速的增大而增强;颗粒的分层受时间的影响,当加入物料大小颗粒完全分离时,颗粒之间的混合主要发生在前10s,30s后颗粒之间的混合情况与充分流化时基本相同。
实验条件有限,本文利用Fluent软件对二元组分颗粒的流化状态数值模拟,弥补某些工况的不足,同时也是对实验结果的验证。数值模拟发现,提高流化风速有利于颗粒的混合,二元组分颗粒之间的混合与分层速度很快,前10s内已基本完成,模拟结果与实验结果吻合。本文还对同一流化风速不同粒径二元组分颗粒的混合情况进行了比较,计算发现两种粒径颗粒的粒径越接近,混合情况越好。最后,通过分析床内颗粒速度分布,发现鼓泡床内颗粒的运动方式在轴向为中心处向上、贴壁处向下的内循环流动,而颗粒在横截面是中心处向壁面运动的。
Fluidization deterioration and agglomeration often occur in the first wind box of the wind-water cooler used in the circulating fluidized bed (CFB) boilers in China, because of the limitations of coal quality and coal preparation systems. Replacing the traditional plate type distributor of the cooler with the pipe type one is deemed as an effective way to improve the fluidization and avoid agglomeration. Fluidization characteristics, especially the particle mixing in the new type cooler that operating in the bubbling bed condition is important for the cooler design and operation, and hereby has been studied in the thesis.
A cold experimental rig was built with a section area of 125×250 mm and 1200mm in height. In the experiments, ash particles with diameters of 150-250μm and 1-2mm are chosen as the bed material to study the minimum fluidization velocity, mixing and segregation characteristics of particles.
The experimental results showed that the minimum fluidization velocity of mixed particles was between those of the large and small particles, closer to that of smaller particles. The velocity increased with the increasing of mass faction of the larger particles in the bed material. As the fraction of larger particles increased, the velocity increased gradually as the fraction was of a small percentage, and then increased rapidly as the fraction exceeded a certain value. It was also found that the bed expansion ratio of bed material increased with the superficial velocity, first rapidly and then gradually. There is a noticeable discrepancy between the results obtained from present experiments and the empirical formula given in the literatures. In addition, the mixing intensity between two-component particles increased with the superficial velocity and the mass fraction of larger particles. Furthermore, the segregation of particles showed a spatial-dependent behavior. When larger and smaller particles were completely separated in the beginning of the experiment, the mixing of particles mainly completed in the first 10s, and segregation phenomena was hardly detected after 30s and the bed turned into full fluidization.
Numerical simulation of fluidization with the two-component particles was conducted by using Fluent software to verify the experimental results and to make up for deficiency of some operating modes. The results of numerical simulation show that the increase of air velocity is in favor of the mixing of particles. The mixing and segregation of particles complete in a short period, e. g., in the first 10s. The results are in accordance with experimental data. For a fixed superficial velocity, simulation results showed that the uniformity of the mixing increases as the size deviation of two-component particles decreases. Moreover, the simulation found that the internal recirculation exists in the bubbling bed, with particles move upwards in center and downwards near the wall. In the cross section of the bed, particles move toward wall from the center region.
本文搭建截面尺寸125×250mm,高1200mm的冷态实验台。实验选取粒径分别为150-250μm和1-2mm的两种粒径电厂灰颗粒,研究混合颗粒的初始流化风速和大小颗粒的混合与分层特性。
实验结果表明,双组分混合颗粒的初始流化风速介于大小颗粒初始流化风速之间,更接近于小粒径颗粒,并随大颗粒质量分数的增加而增大,增大的趋势先慢后快;混合物料床层膨胀比随流化风速的提高而增大,增大的趋势先快后慢,实验结果与经验公式计算结果有较大误差;二元组分颗粒之间的混合程度随大颗粒组分和流化风速的增大而增强;颗粒的分层受时间的影响,当加入物料大小颗粒完全分离时,颗粒之间的混合主要发生在前10s,30s后颗粒之间的混合情况与充分流化时基本相同。
实验条件有限,本文利用Fluent软件对二元组分颗粒的流化状态数值模拟,弥补某些工况的不足,同时也是对实验结果的验证。数值模拟发现,提高流化风速有利于颗粒的混合,二元组分颗粒之间的混合与分层速度很快,前10s内已基本完成,模拟结果与实验结果吻合。本文还对同一流化风速不同粒径二元组分颗粒的混合情况进行了比较,计算发现两种粒径颗粒的粒径越接近,混合情况越好。最后,通过分析床内颗粒速度分布,发现鼓泡床内颗粒的运动方式在轴向为中心处向上、贴壁处向下的内循环流动,而颗粒在横截面是中心处向壁面运动的。
Fluidization deterioration and agglomeration often occur in the first wind box of the wind-water cooler used in the circulating fluidized bed (CFB) boilers in China, because of the limitations of coal quality and coal preparation systems. Replacing the traditional plate type distributor of the cooler with the pipe type one is deemed as an effective way to improve the fluidization and avoid agglomeration. Fluidization characteristics, especially the particle mixing in the new type cooler that operating in the bubbling bed condition is important for the cooler design and operation, and hereby has been studied in the thesis.
A cold experimental rig was built with a section area of 125×250 mm and 1200mm in height. In the experiments, ash particles with diameters of 150-250μm and 1-2mm are chosen as the bed material to study the minimum fluidization velocity, mixing and segregation characteristics of particles.
The experimental results showed that the minimum fluidization velocity of mixed particles was between those of the large and small particles, closer to that of smaller particles. The velocity increased with the increasing of mass faction of the larger particles in the bed material. As the fraction of larger particles increased, the velocity increased gradually as the fraction was of a small percentage, and then increased rapidly as the fraction exceeded a certain value. It was also found that the bed expansion ratio of bed material increased with the superficial velocity, first rapidly and then gradually. There is a noticeable discrepancy between the results obtained from present experiments and the empirical formula given in the literatures. In addition, the mixing intensity between two-component particles increased with the superficial velocity and the mass fraction of larger particles. Furthermore, the segregation of particles showed a spatial-dependent behavior. When larger and smaller particles were completely separated in the beginning of the experiment, the mixing of particles mainly completed in the first 10s, and segregation phenomena was hardly detected after 30s and the bed turned into full fluidization.
Numerical simulation of fluidization with the two-component particles was conducted by using Fluent software to verify the experimental results and to make up for deficiency of some operating modes. The results of numerical simulation show that the increase of air velocity is in favor of the mixing of particles. The mixing and segregation of particles complete in a short period, e. g., in the first 10s. The results are in accordance with experimental data. For a fixed superficial velocity, simulation results showed that the uniformity of the mixing increases as the size deviation of two-component particles decreases. Moreover, the simulation found that the internal recirculation exists in the bubbling bed, with particles move upwards in center and downwards near the wall. In the cross section of the bed, particles move toward wall from the center region.
引文
[1] 张庆国. 大型循环流化床锅炉调试研究. [工程硕士学位论文]. 北京: 清华大学, 2004
[2] 陈汉平 , 陆继东 , 金星等 . 流化床锅炉水冷绞龙冷渣器的试验研究 .热能动力工程,1998,76(13):264-266
[3] 孙即涛, 张勇, 王京波, 等. 大型 CFB 锅炉采用滚筒冷渣机的运行效果分析. 电站系统工程, 2006, 22(1): 37, 58
[4] 程乐鸣, 王勤辉. 流化移动叠置式冷渣器的发展与运行经验. 动力工程, 2000, 20(6): 974-979
[5] 姜孝国, 张缦, 杜守国. CFB 锅炉冷渣器及渣的热量回收. 锅炉制造, 2002, 4: 20-22
[6] S.L.Darling, Xiong Li. Design of 135 MWe CFB boiler. Proceeding of 14th Int. Conf. on FBC, ed. F.D.Preto, Canada, 1997: 205-212
[7] 刘朋杰, 杨守春. 循环流化床锅炉风水联合冷渣器的存在问题及改进方向. 见: 2002-2004CFB 协作网论文集萃, 234-237
[8] 刘升, 李广平, 张宏彪. 风水联合式冷渣器在工程实践中的应用. 中国电力, 2003, 38(4): 71-73
[9] 杨海瑞, 吕俊复, 岳光溪. 一种风水联合冷渣器. 中国专利, 申请日: 2004.6
[10] 陈亮. 新型城市生活垃圾流化床焚烧炉—管式布风流化床的开发研究. [硕士论文]. 浙江: 浙江大学, 2002
[11] 杨富军. 气固流化床的实验与模拟研究. [硕士论文]. 浙江: 浙江大学, 2005
[12] Rietema K. Proc intern symp on fluidization, [s.l.]: Eindhoven, 1967: 154
[13] Yerushalmi J, Cancurt N. Further studies of the regimes of fluidization. Powder Technology, 1979, 24: 187
[14] 李佑楚. 快速流态化的研究. 化工冶金, 1980, 4: 114
[15] 白丁荣. 循环流态化(1). 化学反应工程与工艺, 1991, 2: 208
[16] 陈甘棠, 王樟茂. 多相流反应工程. 浙江大学出版社, 1996: 14
[17] C Y Wen, Y H Yu. Mechanics of Fluidization. Chem Eng Prog Symp Series, 1966, 62: 100-111
[18] Laihong Shen, Mingyao Zhang. Effect of particle size on solids mixing in bubbling fluidized beds. Powder Technology 1998, 97:170-177
[19] 郭慕孙. “用床层塌落法判别流态化特性研究”的说明. 化工冶金, 1983, 4(3): 1-3
[20] 杨子平, 董元吉, 郭慕孙. 应用床层塌落法判别流态化特性. 化工冶金, 1983, 4(3): 5-15
[21] 秦绍宗, 刘广源, 孙绍林. 床层塌落过程的料面动态测定仪. 化工冶金, 1983, 4(3): 17-21
[22] 钱梓文. 鼓泡流态化床床层塌落参数的计算机数据采集和处理. 化工冶金, 1983, 4(3): 23-28
[23] 钱梓文, 陈强, 李洪钟. 鉴别流态化特性的两种控制算法. 化工冶金, 1997, 4(18): 332-335
[24] S.Y.Wu, J.Baeyens. Segregation by size difference in gas fluidized beds. Powder Technology, 1998, 98: 139-150
[25] Lu Huilin, He Yurong. Size segregation of binary mixture of solids in bubbling fluidized beds. Powder Technology, 2003, 134: 86-97
[26] Manfred Wirsum, Franz Fett, Natalia Iwanowa, et al. Paritical mixing in bubbling fluidized beds of binary particle systems. Powder Technology, 2001,120: 63-69
[27] Cheung Lucia, Nienow A W, Rowe P N. Minimum fluidization velocity of a binary mixture of different sized particles. Chem Eng Sci, 1974, 29: 1301-1303
[28] 清华大学电力系锅炉教研组. 流化燃烧锅炉. 科学出版社, 1972: 26-31
[29] 周力行. 湍流气粒两相流动和燃烧的理论与数值模拟. 科学出版社, 1994: 126
[30] 陈俊. 液态化合成氮化硅的鼓泡冷模实验与 CFD 模拟研究. [硕士论文]. 南京: 南京工业大学, 2004
[31] 徐祥. 循环流化床流动特性的数值模拟. [硕士论文]. 南京: 东南大学, 2004
[32] Cundall P A, Strack O D L. A discrete numerical model for granular assemblies. Geotechnique, Powder Technology, 1979, 29(1): 47-65.
[33] Tsuji Y, Tanaka T, Ishida T. Lagrangian numerical simulation of slug flow of cohesionless particles in a horizontal pipe. Powder Technology ,1992,71: 239-250
[34] Tsuji Y, Kawaguchi T, Tanaka T. Discrete particle simulation of two-dimensional fluidized bed. Powder Technology, 1993, 77: 79-87
[35] Grienberger J, Hofmann H. Investigation and modeling of bubble columns. Chem Eng Sci, 1992, 47(9): 2215-2220
[36] Kuipers, JAM. A numerical model of gas-solid fluidized beds. Chem Eng Sci, 1992,47(8): 1913-1924
[37] Gidaspow D. Multiphase Flow and Fluidization: Continuum and kinetic Theory Description. Boston: Academic Press
[38] Tsuo Y D, Gidaspow D. Computation of flow patterns in circulating fluidized beds. AICHE J, 1990, 36(6): 885-896
[39] 洪若瑜, 李洪钟, 程圩, 等. 基于双流体模型的流化床的模拟. 化工学报, 1995, 46(3): 349-355
[40] Kuipers JAM, Prins W, Van Saij W P M. Numerical calculation of wall to bed transfer coefficients in gas fluidized beds. AICHE, 1992, 38: 1079-1091
[41] Gelperin N E, Einstein V G. Heat transfer in fluidized bed. Davidson J F, Hamson D, Fluidization New York: Academic Press, 1971: 471
[42] Li J, Doug Y, Kwauk M. Mathematical modeling of particle fluid two phase flow. Science China, 1990, 33(5): 523-534
[43] Gao Jinsen, Xu Chunming, Yang Guanghua, et al. Numerical simulation on gas-solid two-phase turbulence flow in FCC riser reactor(I) turbulent gas-solid flow reaction model. Chinese Jue of Chemical Engineer, 1998, 6(1): 12-20
[44] Ding J, Lyczkowski R W. Three dimensional kinetic theory modeling of hydrodynamic and erosion in fluidized beds. Powder Technology, 1992, 73: 127-138
[45] J R Richardson, W N Zaki. Sedimentation and Fluidization: Part I. Trans. Inst. Chem. Eng, 1954, 32: 35-53
[46] M Syamlal, T J O’Brien. Computer simulation of bubbles in a fluidized bed. AICHE Symp Series, 1989, 85: 22-31
[47] J M Dalla Valle. Micromeritics. London: Pitman, 1948
[48] J Garside, M R Al-Dibouni. Velocity-voidage relationships for fluidization and sedimentation. I & EC process Des Dev, 1977, 16: 206-214
[49] C Y Wen, Y H Yu. Mechanics and fluidization. Chem Eng Prog Symp Series, 1966, 62: 100-111
[50] S Ergun. Fluid flow through packed columns. Chem Eng Prog, 1952, 48(2): 89-94
[51] M Syamlal. The particle-particle drag term in a multiparticle model of fluidization. National technical information service, Springfield, VA, 1987, DOE/MC/21353-2373, NTIS/DE87006500
[52] Gidaspow D. Multiphase flow and fluidization: continuum and kinetic theory description. Academic Press, San Diego, 1994
[53] Fluent, Inc, Fluent 6.1: Fluent user’s guide, 2003
[54] C Lun, S Savage, D Jeffrey, N Chepurniy. Kinetic theories for granular flow: inelastic particles in coquette flow and slightly inelastic particles in a general flow field. Journal of Fluid Mechanics, 1984, 140: 223-256
[2] 陈汉平 , 陆继东 , 金星等 . 流化床锅炉水冷绞龙冷渣器的试验研究 .热能动力工程,1998,76(13):264-266
[3] 孙即涛, 张勇, 王京波, 等. 大型 CFB 锅炉采用滚筒冷渣机的运行效果分析. 电站系统工程, 2006, 22(1): 37, 58
[4] 程乐鸣, 王勤辉. 流化移动叠置式冷渣器的发展与运行经验. 动力工程, 2000, 20(6): 974-979
[5] 姜孝国, 张缦, 杜守国. CFB 锅炉冷渣器及渣的热量回收. 锅炉制造, 2002, 4: 20-22
[6] S.L.Darling, Xiong Li. Design of 135 MWe CFB boiler. Proceeding of 14th Int. Conf. on FBC, ed. F.D.Preto, Canada, 1997: 205-212
[7] 刘朋杰, 杨守春. 循环流化床锅炉风水联合冷渣器的存在问题及改进方向. 见: 2002-2004CFB 协作网论文集萃, 234-237
[8] 刘升, 李广平, 张宏彪. 风水联合式冷渣器在工程实践中的应用. 中国电力, 2003, 38(4): 71-73
[9] 杨海瑞, 吕俊复, 岳光溪. 一种风水联合冷渣器. 中国专利, 申请日: 2004.6
[10] 陈亮. 新型城市生活垃圾流化床焚烧炉—管式布风流化床的开发研究. [硕士论文]. 浙江: 浙江大学, 2002
[11] 杨富军. 气固流化床的实验与模拟研究. [硕士论文]. 浙江: 浙江大学, 2005
[12] Rietema K. Proc intern symp on fluidization, [s.l.]: Eindhoven, 1967: 154
[13] Yerushalmi J, Cancurt N. Further studies of the regimes of fluidization. Powder Technology, 1979, 24: 187
[14] 李佑楚. 快速流态化的研究. 化工冶金, 1980, 4: 114
[15] 白丁荣. 循环流态化(1). 化学反应工程与工艺, 1991, 2: 208
[16] 陈甘棠, 王樟茂. 多相流反应工程. 浙江大学出版社, 1996: 14
[17] C Y Wen, Y H Yu. Mechanics of Fluidization. Chem Eng Prog Symp Series, 1966, 62: 100-111
[18] Laihong Shen, Mingyao Zhang. Effect of particle size on solids mixing in bubbling fluidized beds. Powder Technology 1998, 97:170-177
[19] 郭慕孙. “用床层塌落法判别流态化特性研究”的说明. 化工冶金, 1983, 4(3): 1-3
[20] 杨子平, 董元吉, 郭慕孙. 应用床层塌落法判别流态化特性. 化工冶金, 1983, 4(3): 5-15
[21] 秦绍宗, 刘广源, 孙绍林. 床层塌落过程的料面动态测定仪. 化工冶金, 1983, 4(3): 17-21
[22] 钱梓文. 鼓泡流态化床床层塌落参数的计算机数据采集和处理. 化工冶金, 1983, 4(3): 23-28
[23] 钱梓文, 陈强, 李洪钟. 鉴别流态化特性的两种控制算法. 化工冶金, 1997, 4(18): 332-335
[24] S.Y.Wu, J.Baeyens. Segregation by size difference in gas fluidized beds. Powder Technology, 1998, 98: 139-150
[25] Lu Huilin, He Yurong. Size segregation of binary mixture of solids in bubbling fluidized beds. Powder Technology, 2003, 134: 86-97
[26] Manfred Wirsum, Franz Fett, Natalia Iwanowa, et al. Paritical mixing in bubbling fluidized beds of binary particle systems. Powder Technology, 2001,120: 63-69
[27] Cheung Lucia, Nienow A W, Rowe P N. Minimum fluidization velocity of a binary mixture of different sized particles. Chem Eng Sci, 1974, 29: 1301-1303
[28] 清华大学电力系锅炉教研组. 流化燃烧锅炉. 科学出版社, 1972: 26-31
[29] 周力行. 湍流气粒两相流动和燃烧的理论与数值模拟. 科学出版社, 1994: 126
[30] 陈俊. 液态化合成氮化硅的鼓泡冷模实验与 CFD 模拟研究. [硕士论文]. 南京: 南京工业大学, 2004
[31] 徐祥. 循环流化床流动特性的数值模拟. [硕士论文]. 南京: 东南大学, 2004
[32] Cundall P A, Strack O D L. A discrete numerical model for granular assemblies. Geotechnique, Powder Technology, 1979, 29(1): 47-65.
[33] Tsuji Y, Tanaka T, Ishida T. Lagrangian numerical simulation of slug flow of cohesionless particles in a horizontal pipe. Powder Technology ,1992,71: 239-250
[34] Tsuji Y, Kawaguchi T, Tanaka T. Discrete particle simulation of two-dimensional fluidized bed. Powder Technology, 1993, 77: 79-87
[35] Grienberger J, Hofmann H. Investigation and modeling of bubble columns. Chem Eng Sci, 1992, 47(9): 2215-2220
[36] Kuipers, JAM. A numerical model of gas-solid fluidized beds. Chem Eng Sci, 1992,47(8): 1913-1924
[37] Gidaspow D. Multiphase Flow and Fluidization: Continuum and kinetic Theory Description. Boston: Academic Press
[38] Tsuo Y D, Gidaspow D. Computation of flow patterns in circulating fluidized beds. AICHE J, 1990, 36(6): 885-896
[39] 洪若瑜, 李洪钟, 程圩, 等. 基于双流体模型的流化床的模拟. 化工学报, 1995, 46(3): 349-355
[40] Kuipers JAM, Prins W, Van Saij W P M. Numerical calculation of wall to bed transfer coefficients in gas fluidized beds. AICHE, 1992, 38: 1079-1091
[41] Gelperin N E, Einstein V G. Heat transfer in fluidized bed. Davidson J F, Hamson D, Fluidization New York: Academic Press, 1971: 471
[42] Li J, Doug Y, Kwauk M. Mathematical modeling of particle fluid two phase flow. Science China, 1990, 33(5): 523-534
[43] Gao Jinsen, Xu Chunming, Yang Guanghua, et al. Numerical simulation on gas-solid two-phase turbulence flow in FCC riser reactor(I) turbulent gas-solid flow reaction model. Chinese Jue of Chemical Engineer, 1998, 6(1): 12-20
[44] Ding J, Lyczkowski R W. Three dimensional kinetic theory modeling of hydrodynamic and erosion in fluidized beds. Powder Technology, 1992, 73: 127-138
[45] J R Richardson, W N Zaki. Sedimentation and Fluidization: Part I. Trans. Inst. Chem. Eng, 1954, 32: 35-53
[46] M Syamlal, T J O’Brien. Computer simulation of bubbles in a fluidized bed. AICHE Symp Series, 1989, 85: 22-31
[47] J M Dalla Valle. Micromeritics. London: Pitman, 1948
[48] J Garside, M R Al-Dibouni. Velocity-voidage relationships for fluidization and sedimentation. I & EC process Des Dev, 1977, 16: 206-214
[49] C Y Wen, Y H Yu. Mechanics and fluidization. Chem Eng Prog Symp Series, 1966, 62: 100-111
[50] S Ergun. Fluid flow through packed columns. Chem Eng Prog, 1952, 48(2): 89-94
[51] M Syamlal. The particle-particle drag term in a multiparticle model of fluidization. National technical information service, Springfield, VA, 1987, DOE/MC/21353-2373, NTIS/DE87006500
[52] Gidaspow D. Multiphase flow and fluidization: continuum and kinetic theory description. Academic Press, San Diego, 1994
[53] Fluent, Inc, Fluent 6.1: Fluent user’s guide, 2003
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