基于CFD的生物三相内循环流化床优化设计

发布时间：2018-03-31 09:40

本文选题：生物三相内循环流化床　切入点：CFD　出处：《湖南大学》2015年硕士论文

【摘要】：生物三相内循环流化床具有优越的流体力学性能、良好的传质效果等特征。然而,目前其工程放大设计主要依靠经验参数,还未形成一套以数值分析、结构量化表达为基础的设计理论。利用计算流体力学(CFD)探讨操作参数、结构参数对生物三相内循环流化床性能的影响,对其放大设计具有较重要的意义。本研究借助计算流体力学,利用欧拉模型建立能够有效地描述生物三相内循环流化床反应器内部气液固三相复杂流动的数学模型,并用实例证明CFD模型能够有效地反映生物三相内循环流化床反应器内部气、液、固三相复杂的流体特征。以此为基础探讨操作参数、结构参数对生物三相内循环流化床性能的影响。操作参数的影响探讨结果显示:随着固体装载率的增大,气含率先增大后减小,在13%处取得最大值。当表观气速在0~0.05m/s的范围内时,气含率随着表观气速的增大而增大,在0.05m/s处达到最大值,表观速度大于0.05m/s时,气含率不再随着表观气速的增大而增大,而是基本保持不变。液体循环速率随着固体装载率的增大而减小,随着表观气速的增大而增大。在以气含率、液体循环速率作为约束条件的情况下,本流化床反应器的最佳固体装载速率为13%,最佳表观气速为0.05m/s。粒径大的固体颗粒更加有利于破碎气泡,同时也使得相界面积增大,所以气含率随着固体颗粒粒径增大而增大;粒径大的固体颗粒对液体循环程度的影响比较大,当实际操作中要求液体循环速率比较大时,宜采用粒径比较小的固体颗粒,对提高液体循环速率有利。结构参数的影响探讨结果显示:导流筒与反应器的直径比(Dr/D)主要影响液体的循环程度,从液体循环速率分布的均匀化以及液体循环速率峰值考虑,Dr/D取0.7时最优;高径比(H/D)主要影响气液固的流动型态,H/D比较小时应特别注重对气体分布装置进行优化设计;导流筒距液面高度(H1)主要影响上升区与液面之间的区域内的流场结构,对于高1.0m的流化床来说H1取100 mm时能达到较优的流场结构以及液速分布;导流筒距底部高度(H2)主要影响流化床反应器内底部混合区域内流体的运动以及液体对底部区域颗粒的卷带速度的大小和方向,该高度最小应该达到下降区的缝隙长度,但继续增大后液体对下降区底部区域污泥颗粒的卷带作用急剧减弱,容易导致水力死区的出现。
[Abstract]:Biological three-phase internal circulating fluidized bed has excellent hydrodynamic performance and good mass transfer effect. However, at present, the design of biological three-phase internal circulating fluidized bed mainly depends on empirical parameters and has not yet formed a set of numerical analysis. Based on the design theory of quantitative expression of structure, the effects of operating parameters and structural parameters on the performance of biological three-phase internal circulating fluidized bed are discussed by using computational fluid dynamics (CFD). In this study, with the aid of computational fluid dynamics and Euler model, a mathematical model of gas-liquid-solid complex flow in a biological three-phase internal circulating fluidized bed reactor was established. An example is given to prove that CFD model can effectively reflect the complex fluid characteristics of gas, liquid and solid in a biological three-phase internal circulating fluidized bed reactor, on the basis of which the operating parameters are discussed. The effect of structure parameters on the performance of a biological three-phase internal circulating fluidized bed. The results show that with the increase of solid loading ratio, the gas content increases first and then decreases. When the apparent gas velocity is in the range of 0~0.05m/s, the gas holdup increases with the increase of the apparent gas velocity. When the apparent gas velocity is greater than 0.05m/s, the gas holdup increases with the increase of the apparent gas velocity. The liquid circulation rate decreases with the increase of the solid loading rate and increases with the increase of the apparent gas velocity. When the gas holdup and the liquid circulation rate are taken as the constraint conditions, the liquid circulation rate decreases with the increase of the solid loading rate, and increases with the increase of the apparent gas velocity. The optimum solid loading rate of the fluidized bed reactor is 13 and the best apparent gas velocity is 0.05 m / s. The larger particle size is more favorable for the broken bubble and the larger the phase boundary area is, so the gas holdup increases with the increase of the particle size. Solid particles with large particle size have great influence on liquid circulation degree. When the liquid circulation rate is large in practical operation, solid particles with smaller particle size should be used. The effect of structural parameters on the liquid circulation rate is favorable. The results show that the diameter ratio of the diversion tube to the reactor (Dr / D) mainly affects the circulating degree of the liquid. Considering the homogenization of liquid circulation rate distribution and the peak value of liquid circulation rate, the optimum value of Dr / D is 0.7, the ratio of height to diameter (H / D) mainly affects the flow pattern of gas-liquid-solid and the optimum design of gas distribution device should be paid special attention to when the ratio of H / D is small. The flow field structure in the area between the rising area and the liquid surface is mainly affected by the height of the diversion tube from the liquid level. For the fluidized bed with a height of 1.0 m, the flow field structure and the liquid velocity distribution can be better when H _ 1 is taken at 100 mm. The height of the diversion tube from the bottom to the bottom mainly affects the movement of the fluid in the mixing zone at the bottom of the fluidized bed reactor and the size and direction of the velocity of the liquid to the particle in the bottom area. The minimum height should be the gap length of the descending zone. However, the effect of the liquid on the sludge particles in the bottom of the descending zone decreases sharply after further increasing, which leads to the emergence of the hydrodynamic dead zone.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X703

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