反应器结构对多段气化炉内颗粒分布的影响
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摘要
针对多段气化炉(上部快速床、下部鼓泡床),采用MP-PIC(Multi-Phase Particle In Cell)方法模拟了多粒径煤粉颗粒的三维全循环流化过程,考察了鼓泡床与快速床床径比及鼓泡床和快速床之间的过渡段高度对气化炉内流动特性的影响。结果表明,基本工况下,大颗粒主要存在于下部鼓泡床中,细颗粒主要存在于上部快速床内,但细颗粒会通过旋风分离器和回料管再次进入鼓泡床参与循环。进入旋风分离器的大部分为半径622mm以下的小颗粒,无1216 mm以上的大颗粒。旋风分离器对小颗粒的分离效率为99.75%,分离效率良好。增大床径比(即减小快速床直径),快速床中气速增大,整个气化床更快达到稳定状态,被夹带到快速床中的颗粒增多,所夹带的颗粒粒径增大。过渡段高度存在一个适当值(炉高0.6～1.0 m),升高或降低过渡段高度,快速床中颗粒浓度均增大,颗粒通量均升高,旋风分离效率降低。
The 3 D full-loop multi-stage gasifier(upper fast fluidized bed with lower bubbling fluidized bed) was simulated with MP-PIC(Multi-Phase Particle In Cell) method successfully. To study the effect of reactor structure on the gas-solid flow in the multi-stage gasifier, the effects of diameter ratio of bubbling fluidized bed to fast fluidized bed and transition section heights on the flow characteristics of gasifier were systematically studied by simulations with MP-PIC method. The results showed that the circulating fluidization process of pulverized coal was successfully simulated by the current method. For basic case, coarse particles mainly resided in the lower bubblingbed, and fine particles mainly resided in the upper fast bed. However, fine particles can return to the bubbling bed from cyclone and stand pipe. Only the small particles with diameters less than 622 μm can enter the cyclone, where there were no particles with diameters larger than 1 216 μm. The cyclone had a separation efficiency of 99.75% for small particles, which exhibits a good separation performance. Increasing the bed diameter ratio(ie, reducing the diameter of the fast bed) led to the increase of gas velocity in the fast fluidized bed. Under this condition the gasifier tended to reach steady state much faster. And more particles can be entrained into the fast fluidized bed. The entrained particle size range also increased. Compared to the basic condition, both increasing and decreasing the height of the transition section increased the particles concentration and solid flux in the fast fluidized bed. The efficiency of the cyclone was also higher than that of the basic condition. These implied that there existed an optimum value of the transition section height(between 0.6 and 1.0 m in this case). Increasing or decreasing this value will increase the solid flux in fast fluidized bed but will reduce the cyclone efficiency. These rules can be significant and helpful to the design and optimization of multi-stage gasifiers.
The 3 D full-loop multi-stage gasifier(upper fast fluidized bed with lower bubbling fluidized bed) was simulated with MP-PIC(Multi-Phase Particle In Cell) method successfully. To study the effect of reactor structure on the gas-solid flow in the multi-stage gasifier, the effects of diameter ratio of bubbling fluidized bed to fast fluidized bed and transition section heights on the flow characteristics of gasifier were systematically studied by simulations with MP-PIC method. The results showed that the circulating fluidization process of pulverized coal was successfully simulated by the current method. For basic case, coarse particles mainly resided in the lower bubblingbed, and fine particles mainly resided in the upper fast bed. However, fine particles can return to the bubbling bed from cyclone and stand pipe. Only the small particles with diameters less than 622 μm can enter the cyclone, where there were no particles with diameters larger than 1 216 μm. The cyclone had a separation efficiency of 99.75% for small particles, which exhibits a good separation performance. Increasing the bed diameter ratio(ie, reducing the diameter of the fast bed) led to the increase of gas velocity in the fast fluidized bed. Under this condition the gasifier tended to reach steady state much faster. And more particles can be entrained into the fast fluidized bed. The entrained particle size range also increased. Compared to the basic condition, both increasing and decreasing the height of the transition section increased the particles concentration and solid flux in the fast fluidized bed. The efficiency of the cyclone was also higher than that of the basic condition. These implied that there existed an optimum value of the transition section height(between 0.6 and 1.0 m in this case). Increasing or decreasing this value will increase the solid flux in fast fluidized bed but will reduce the cyclone efficiency. These rules can be significant and helpful to the design and optimization of multi-stage gasifiers.
引文
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[13]钟汉斌,蓝兴英,高金森,等.鼓泡床内双组分颗粒流动行为的数值模拟[J].中国煤粉技术,2013,19(3):1-5.Zhong H B,Lan X Y,Gao J S,et al.Numerical simulation of hydrodynamics of binary particle mixtures in bubbling fluidized beds[J].China Powder Science and Technology,2013,19(3):1-5.
[14]唐胜利,王舯,吕红,等.鼓泡流化床流动特性的数值仿真和实验研究[J].计算机仿真,2011,28(11):396-400.Tang S L,Wang Z,Lv H,et al.Numerical simulation and experimental for flow characteristics in bubbling fluidized-bed[J].Computer Simulation,2011,28(11):396-400.
[15]Liang Y S,Zhang Y M,Li T W,et al.A critical validation study on CPFD model in simulating gas-solid bubbling fluidized beds[J].Powder Technology,2014,263:121-134.
[16]Li F,Song F F,Sofiane B,et al.MP-PIC simulation of CFB riser with EMMS-based drag model[J].Chemical Engineering Science,2012,82:104-113.
[17]Gidaspow D.Hydrodynamics of fiuidizatlon and heat transfer:supercomputer modeling[J].Applied Mechanics Reviews,1986,39:1-23.
[18]宋素芳,郝振华,董立波,等.Bubble-based EMMS/PFB模型的建立及在加压流化床浓相段的应用[J].化工学报,2017,68(8):2998-3005.Song S F,Hao Z H,Dong L B,et al.Establishment of bubble-based EMMS/PFB model and its application on dense section of pressurized fluidized-bed[J].CIESC Journal,2017,68(8):2998-3005.
[2]房倚天,王志青,李俊国,等.多段分级转化流化床煤气化技术研究开发进展[J].煤炭转化,2018,41(3):1-11.Fang Y T,Wang Z Q,Li J G,et al.Research and development progress in Multi-stage conversion fluidized bed coal gasification technology[J].Coal Conversion,2018,41(3):1-11.
[3]Geldart D.The size and frequency of bubbles in two and three-dimensional gas-fluidized beds[J].Powder Technology,1970,4:41-55.
[4]Rowe P N,MacGillivray H J,Cheesman D J.Gas discharge from an orifice into a gas fluidized bed[J].Transactions of the Institution of Chemical Engineers,1979,57:194-199.
[5]Rowe P N,Everett D J.Fluidized bed bubbles viewed by X-ray[J].Transactions of the Institution of Chemical Engineers,1972,50:42-48.
[6]张永民,卢春喜.床形结构对气固流化床流化质量和气体返混特性的影响[J].化工学报,2010,61(9):2296-2304.Zhang Y M,Lu C X.Fluidization quality and gas back-mixing in gas-solids fluidized beds of different shapes[J].CIESC Journal,2010,61(9):2296-2304.
[7]沈荣春,束忠明,黄发瑞.气体分布器结构对气升式环流反应器内气液两相流动的影响[J].化学反应工程与工艺,2007,23(5):422-429.Sheng R C,Shu Z M,Huang F R.Effect of gas sparger on gas-liquid two-phase flow in an airlift loop reactor[J].Chemical Reaction Engineering and Technology,2007,23(5):422-429.
[8]王涛,孟祥奎,杨慧,等.分布器结构对气固鼓泡流化床内气相分布影响的数值模拟[J].青岛科技大学学报(自然科学版),2013,34(2):160-166.Wang T,Meng X K,Yang H,et al.Numerical simulation of influence of distributor structure on gas distribution in gas-solid bubbling fluidized bed[J].Journal of Qingdao University of Science and Technology(Natural Science Edition),2013,34(2):160-166.
[9]杨世亮,罗坤,房明明,等.不同管排方式下三维鼓泡床内气固流型及埋管磨损的LES-DEM研究[J].工程热物理学报,2014,35(7):1338-1342.Yang S L,Luo K,Fang M M,et al.LED-DEM investigation of the hydrodynamics and tube erosion in 3-D bubbling fluidized bed with different tube configuration[J].Journal of Engineering Thermophysics,2014,35(7):1338-1342.
[10]许建良,赵辉,代正华,等.单喷嘴水煤浆气化炉高径比对反应流动的影响[J].化学工程,2016,44(4):68-73.Xu J L,Zhao H,Dai Z H,et al.Influences of height-diameter ratio on multiphase reaction flow of single-burner coal water slurry gasifier[J].Chemical Engineering(China),2016,44(4):68-73.
[11]王海艳,郝振华,王志雨,等.多段分级转化流化床颗粒浓度的数值模拟[J].化学反应工程与工艺,2013,29(1):42-50.Wang H Y,Hao Z H,Wang Z Y,et al.Numerical simulation of gas-solid flow in a multi-stage fluidized bed[J].Chemical Reaction Engineering and Technology,2013,29(1):42-50.
[12]樊强,刘银河,李广宇,等.载气对两段式干煤粉加压气化炉气化特性的影响[J].化工进展,2017,36(1):136-145.Fan Q,Liu Y H,Li G Y,et al.Effect of carrier gas on gasification performance of two-stage entrained-flow coal gasifier[J].Chemical Industry and Engineering Progress,2017,36(1):136-145.
[13]钟汉斌,蓝兴英,高金森,等.鼓泡床内双组分颗粒流动行为的数值模拟[J].中国煤粉技术,2013,19(3):1-5.Zhong H B,Lan X Y,Gao J S,et al.Numerical simulation of hydrodynamics of binary particle mixtures in bubbling fluidized beds[J].China Powder Science and Technology,2013,19(3):1-5.
[14]唐胜利,王舯,吕红,等.鼓泡流化床流动特性的数值仿真和实验研究[J].计算机仿真,2011,28(11):396-400.Tang S L,Wang Z,Lv H,et al.Numerical simulation and experimental for flow characteristics in bubbling fluidized-bed[J].Computer Simulation,2011,28(11):396-400.
[15]Liang Y S,Zhang Y M,Li T W,et al.A critical validation study on CPFD model in simulating gas-solid bubbling fluidized beds[J].Powder Technology,2014,263:121-134.
[16]Li F,Song F F,Sofiane B,et al.MP-PIC simulation of CFB riser with EMMS-based drag model[J].Chemical Engineering Science,2012,82:104-113.
[17]Gidaspow D.Hydrodynamics of fiuidizatlon and heat transfer:supercomputer modeling[J].Applied Mechanics Reviews,1986,39:1-23.
[18]宋素芳,郝振华,董立波,等.Bubble-based EMMS/PFB模型的建立及在加压流化床浓相段的应用[J].化工学报,2017,68(8):2998-3005.Song S F,Hao Z H,Dong L B,et al.Establishment of bubble-based EMMS/PFB model and its application on dense section of pressurized fluidized-bed[J].CIESC Journal,2017,68(8):2998-3005.