导向管液固喷动床的数值模拟研究

本文以液-固两相流理论为基础,用颗粒动力学理论描述颗粒与颗粒间的碰撞,用标准湍流方程模拟液相和颗粒相的湍动,并且考虑液-固两相的相互作用,旨在探索一种工程设计和放大的新方法。对比颗粒循环速率和密相区真实液相流速的模拟结果与实验值,结果吻合较好。     

导向管喷动床内单相流场及声波对流场影响的数值模拟

为阐明超细粉在声场导向管喷动流化床内的流化机理,并为进一步优化和完善床层结构及操作条件提供基础,采用标准k-ε湍流模型计算了导向管喷动流化床内的单相气体流场,考察了进口流化气速和射流气速对气体流动规律的影响,以及声场对导向管喷动流化床内气体轴向速度分布及其脉动均方根的影响。结果表明:在高速射流条件下,导向管喷动流化床内气体呈内循环流动,气体循环流量随流化气速度的增加而减小,但随射流气速度的增加而增加;外加声场使环隙区和喷泉区的气体流动更加均匀,显著增加环隙区和喷泉区气流的湍动程度,且湍动程度随声压级的增大而显著增大,随声波频率的升高而小幅度降低。     

导向管喷流床的最小喷动速度的研究

在内径９２ｍｍ的有机玻璃床内,使用四种没的物料,以空气作为喷动相流气体,综合考虑了床层的几何尺寸,以及气体和固体本身的物性,研究了导向管喷流床的最小喷动速度,得出了导向管喷流床的最小喷动速度的经验公式,以便对其设计和操作提供参考     

导向管充气喷动床流体力学性能

在内径92mm的有机玻璃床内,对导向管充气喷动床的操作相图、床层压降、最小喷动速度及最大弃气速度进行了研究.实验采用4种颗粒为实验物料并采用空气为 喷动和弃气气体,通过对实验数据的回归得到用于计算或判别导向管弃气喷动床最小喷动速度和最大充气速度的计算式,以便为其设计和操作提供依据.     

超细粉在导向管喷动床中的固体循环速率

Ultra-fine powders are difficult to be fluidized due to the strong particle to particle cohesiveness.However, the authors‘ experiments showed that the ultra-fine powder CaCO3 could be stably fluidized in a spouted bed with a draft tube. The effects of geometric and operating parameters on solid circulation rate of ultra-fine powder CaCO3 were investigated in a 120 mm diameter transparent semicircular spouted bed with a draft tube. Three draft tubes with different sizes were used in this study. It was found that the solids circulation rate was mainly dependent on the drawing rate of the gas jet from the nozzle, then on the gas transport capacity in the draft tube. With increasing gas feed rate, distance between the nozzle and the draft tube inlet and draft tube diameter, the solids circulation rate could be increased. Based on the jet theory, a quantitative correlation was proposed for predicting the solid circulation rate of ultra-fine powders in a spouted bed with a draft tube by taking into account the gas transport capacity in the draft tube.     

锥底喷动床内气固两相流的数值模拟

为了得到喷动床内流场分布的详细信息,给进一步的实验研究和工业放大提供理论依据,对锥底喷动床内气固两相流的流动状况进行数值模拟.使用欧拉模型进行计算,得到稳定的喷动区、环隙区和喷泉区等喷动床典型流动特征.考察喷动床内颗粒相在喷动区、环隙区和喷泉区的速度分布以及空隙率和颗粒体积分率的分布.计算结果同实验观察得到的结果相符.     

导向管喷动流化床内颗粒停留时间模型

通过对导向管喷动流化床的喷动区和流化区分别进行质量平衡和动量平衡,得出了描述连续流动条件下其床层内粒子停留时间的数学模型。本模型所得计算结果与以前报道的实验结果一致。     

导向管喷动床床层与埋管表面的换热特性研究

以石英砂作为循环颗粒,研究了颗粒与换热管束壁面的换热特性.在导向管喷动床环隙内,砂子以移动床的形式向下移动.为测定移动床层与埋管表面的换热系数,自制了组合热探头,并用调压器调节组合热探头的功率,使其稳定在不同温度下工作.分别考察了不同电压、不同吹松气量和不同床层轴向位置等对换热系数的影响.通过电压递增与递减的验证性实验,考察了两种方式对实验结果的影响.通过实验可知,换热系数随颗粒循环量的增加而增加.实验在常温常压下进行,喷动床材质为有机玻璃,移动床层与埋管换热壁面的平均换热系数在300 W/(m2·K-1)～400W/(m2·K-1)之间.     

超细粉在导向管喷动床中的流化行为

以料径5μm的CaCO3超细粉为物料，对其在半圆形导向管喷动床中的流化行为进行研究，考察床层压降特性及喷嘴直径、导喷距及导向管直径对起始流化行为的影响。     

喷动流化床流动特性数值模拟

为了捕捉喷动流化床中微观层次上的颗粒运动信息,建立了基于CFD的二维非稳态喷动流化床欧拉-欧拉两相流模型。分析了不同流化气速对喷动流化床气固流动特性的影响,即不同工况下的炉内压力降、颗粒浓度、床内空隙率分布、气体速度分布和固体颗粒速度分布。数值模拟研究结果表明:随流化气速的增大,压降和炉内平均空隙率逐渐增大,密相床层高度逐渐增加,沿着轴向方向的气体流量增大,喷动气的射流深度逐渐增加,同时射流半径也逐渐增加。     

Hydrodynamics of a gas-driven gas-liquid-solid spouted bed with a draft tube

A cylindrical gas-liquid-solid spouted bed, driven exclusively by gas flow, has been developed with a high potential for use in biochemical processes, such as a biological wastewater treatment. A plexiglass column with a 152 mm inner diameter was used in combination with a 53 mm inner diameter plexiglass draft tube. Three particle types were studied with densities ranging from 1044 kg/m³-1485 kg/m³ and average particle sizes ranging from 0.7-2.5 mm. Four flow regimes were observed when increasing the gas velocity, including fixed bed, semispouted bed, full spouted bed, and internal circulating fluidized bed. The transition gas velocities between those regimes were experimentally measured and termed as minimum spouting velocity, full spouting velocity, and minimum circulating velocity, respectively. A measurement of the downward particle flux in the annulus was used to identify the minimum spouting velocity, while the particle velocity and dense phase retraction in the annulus were monitored for the full spouting and minimum circulating velocities. All regime transition velocities increased with more dense particles and longer draft tubes. The minimum spouting velocity and full spouting velocity were not affected when varying the nozzle-tube gap, while the minimum circulating velocity increased with longer nozzle-tube gaps. Experiments without a draft tube were carried, though the spouting stability was significantly reduced without the draft tube.     

双喷嘴矩形导流管喷动床脱硫性能的研究

针对半干法烟气脱硫方法,提出了一种新型的双喷嘴矩形导流管喷动床半干法烟气脱硫装置。在不同的钙硫摩尔比、静床层高度、表观气速、绝热饱和温差下,以消石灰为脱硫剂,研究了该装置的脱硫性能,并与未加导流管的双喷嘴矩形喷动床的脱硫性能进行了比较;研究了不同脱硫剂流量下导流管喷动床的喷动压降。实验结果表明:脱硫率与钙硫摩尔比、静床层高度成正比,与绝热饱和温差、表观气速成反比;喷动压降与脱硫剂流量成反比。并最终得出了实验条件下双喷嘴矩形导流管喷动床的最佳操作范围和脱硫率关联式。     

Study of the hydrodynamics within a draft tube spouted bed system

Two dimensional Darcy and Ergun models are used to describe the hydrodynamics within the annulus of a spouted bed equipped with a draft tube. Experimental pressure and stream function data for water spouting are shown to be in good agreement with theoretical predictions. Verification of a general spout-annulus interfacial boundary condition is also established and it is shown that the entry region below the draft tube functions as a classical spouted bed. In addition, an experimental procedure for determining the location of the spout-annulus interface is presented. Fluid residence time distributions are calculated for a few cases of practical interest.     

双喷嘴矩形导流管喷动床喷动压降

引言 传统的柱锥形喷动床(CSBs)的应用受到一些因素的限制,例如处理物料能力、起始压力大及难以放大等,为此,Romankov等[1]最早提出了长方形截面的矩形喷动床结构,来克服CSBs的缺点.此后,Rocha等[2]用矩形喷动床进行了片剂包衣的研究.     

循环喷动流化床颗粒抛射高度的计算

通过对循环喷动流化床顶部封闭空间气体射流及气固运动的理论分析 ,得出了循环喷动流化床中颗粒出循环管后抛射高度的计算方法 ,所得计算结果与实测结果误差小于 8% ,为循环喷动流化床的设计提供理论依据     

Side-outlet spouted bed with draft tube: Effect of varying the position of the outlet

The vector form of the Ergun equation was used to numerically predict gas phase streamlines, residence time distributions, chemical conversions and pressure drops in the annulus of a side-outlet spouted bed with an internal draft tube. By varying the position of the side-outlet, it was demonstrated that there exists an optimum location for this outlet at which conversion is a maximum and which shows a greatly improved gas phase residence time distribution in the annulus compared with a conventional spouted bed unit.     

开孔导流管喷动床烟气脱硫技术实验研究

研究了一种新型的半干法脱硫开孔导流管喷动床。在相同静床层高度下,研究了其最小喷动速度、最大喷动压降、喷动高度;在相同钙硫摩尔比、入口SO2质量浓度、进气温度、绝热饱和温差条件下,以消石灰为脱硫剂,研究了其脱硫性能。实验结果表明,与传统柱锥型喷动床相比,开孔导流管喷动床具有更好的流体力学性能和脱硫效率。实验条件下最适宜的操作条件为:钙硫摩尔比为0.9—2.5,进气温度为120—130℃,绝热饱和温差为10℃。     

Prediction of pressure drop and minimum spouting velocity in draft tube conical spouted beds using genetic programming approach

The smart method of genetic programming (GP) is used to predict the operating pressure drop (ΔP_s) and the minimum spouting velocity u_ms for conical spouted beds (CSBs) equipped with nonporous draft tubes. Accordingly, six dimensionless variables have been taken as model inputs, including crucial parameters associated with the bed and tube geometric and operating conditions. Two general correlations comprising almost all constitutive and operating variables have been derived for the first time by the GP approach. Both ΔP_s and u_ms values predicted by the GP technique are in a fair agreement with the values corresponding to the experiments, with average absolute relative errors (AARE) of 18.9 and 19.9 %, respectively. The results of the proposed correlations show that the GP method is a powerful tool to make reasonable estimates.     

摩擦-动力应力模型研究喷动床内气固两相流动过程

考虑颗粒滑动的半持续性接触应力和颗粒碰撞瞬时接触应力对颗粒相应力的贡献,建立了喷动床内气体颗粒两相流动计算模型。采用颗粒动理学和Johnson 等的摩擦应力模型,数值模拟喷动床颗粒流动过程,获得了喷动床喷射区、环隙区和喷泉区内颗粒流动特性。模拟计算与He等的实验结果进行了对比。同时分析了摩擦应力模型对颗粒相黏度变化的影响,表明中速颗粒流的颗粒相摩擦应力模型将直接影响喷动床气体颗粒两相流动的预测。     

Simulations of flow behavior of gas and particles in spouted bed with a porous draft tube

Flow behaviors of particles in a two-dimensional spouted bed with a porous draft plates are studied using a fluid dynamic computation with kinetic-frictional stresses models. Gas flow through the porous draft tube is simulated by Brinkman-Darcy-Forchheimer formulation. The distributions of concentration and velocities of particles are predicted. Simulated results predict the solid circulation rate and gas flux rate measured in the spouted bed with a porous draft tube (Ishikura et al., 2003). The solid circulation rate in the spouted bed with a porous draft tube is larger than that with a non-porous draft tube. The predicted bed pressure drop with the porous draft tube is high in comparison to the spouted bed with non-porous draft tube. The effect of the porosity of the porous draft tube on distributions of gas flux rate through the annulus and solid circulation rate are discussed.