粗颗粒在锥型床中的流化特性

通过Ｇｅｌｄａｒｔ－Ｄ类粗颗粒在三种锥形床中的实验表明：随着入口的表观气速的增加,在床中依次出现固定床流区,部分流化区和喷动流区。在固定床区内,压降和表观气速关系可以通过Ｅｒｇｕｎ公式求得：在部分流化床区内;实验和理论计算均表明了由于颗粒所受到的曳力档的轴向高度增加而减小,造成床层轴向上部未流化的颗粒对下部硫化颗粒膨和压制作用,在喷动流化区内,给出了预测锥形床的初始喷动气速和喷动压降的经验公式。     

耦合传质的羰基化固定床反应器传热模拟分析

固定床反应器中进行强放热反应时, 反应器的热点温度对操作参数变化敏感,容易引起飞温,导致转化率下降,影响催化剂寿命。为强化羰基化固定床反应器内热质传递与化学反应的协同性,建立考虑颗粒内扩散影响的羰基化固定床反应器拟均相一维传热模型,考察操作参数对床层热点温度、反应转化率、床层温升的影响。不仅体现传热传质和反应的协同作用,而且影响关系明晰、求解方便。为保证反应转化率,本实验条件下确定催化剂颗粒直径小于等于1.5 mm。反应器入口温度/冷却剂油温既要满足床层热稳定性需求,又要使反应转化率和床层温升都在合理范围内。模拟结果表明在床层入口温度升高的同时,可通过降低冷却剂油温获得良好的反应转化率和较小的床层温升。在此基础上,考察入口环氧乙烷浓度对反应转化率和床层温升的影响。本研究可为固定床反应器满足转化率要求、床层合理温升而选择催化剂颗粒直径、床层入口温度、冷却剂油温和床层入口浓度等操作参数提供计算依据。     

上流式反应器气液相间传质特性的实验研究

上流式反应器设置在固定床渣油加氢反应器前有利于提高渣油原料适用性,延长装置运行时间。实验研究了上流式反应器气液相间传质,采用五齿柱形氧化铝催化剂模拟工业催化剂颗粒,水溶液模拟渣油,空气模拟氢气,采用无氧水物理吸收和亚硫酸钠化学吸收的方法,测定了在高气液比的条件下上流式反应器床层气液相间传质特性实验。考察了表观气速、表观液速、填料粒径、内构件、催化剂级配和床层高径比对液相体积传质系数和气液相界比表面积的影响规律。实验数据表明,液相体积传质系数随着气、液速的增大而增大;随填料颗粒增大而减小;在床层内安装合适的内构件或增大反应器高径比,能够促进气液相间传质。基于实验数据拟合了适合上流式反应器液相体积传质系数和气液相界比表面积的经验关联式,拟合误差最大分别为12%和24%;表明所建气液相间传质的经验关联式能更好地预测上流式反应器中的气液相间传质特性。     

上流式反应器气液相间传质特性的实验研究

上流式反应器设置在固定床渣油加氢反应器前有利于提高渣油原料适用性,延长装置运行时间。实验研究了上流式反应器气液相间传质,采用五齿柱形氧化铝催化剂模拟工业催化剂颗粒,水溶液模拟渣油,空气模拟氢气,采用无氧水物理吸收和亚硫酸钠化学吸收的方法,测定了在高气液比的条件下上流式反应器床层气液相间传质特性实验。考察了表观气速、表观液速、填料粒径、内构件、催化剂级配和床层高径比对液相体积传质系数和气液相界比表面积的影响规律。实验数据表明,液相体积传质系数随着气、液速的增大而增大;随填料颗粒增大而减小;在床层内安装合适的内构件或增大反应器高径比,能够促进气液相间传质。基于实验数据拟合了适合上流式反应器液相体积传质系数和气液相界比表面积的经验关联式,拟合误差最大分别为12%和24%;表明所建气液相间传质的经验关联式能更好地预测上流式反应器中的气液相间传质特性。     

烧结矿余热回收竖罐内气固传热特性

以自制气固传热实验装置为操作平台,实验研究了烧结矿颗粒填充床内的气固传热特性。结果表明:气体表观流速和烧结矿颗粒直径是影响颗粒床层内气固传热过程的主要因素。气体表观流速越大,颗粒直径越小,床层内气固传热系数就越大。当烧结矿颗粒直径和气体表观流速一定时,床层内烧结矿颗粒温度的升高导致床层气固传热系数的增加和传热Nusselt数的减小。由于计算误差较大,现有的经验关联式不适用于求解烧结矿颗粒床层内的气固传热过程。基于量纲分析法,并结合实验测量数据拟合得出了能够描述烧结矿颗粒床层内气固传热特性的实验关联式,平均计算误差为4.22%,显示了良好的预测性能。     

两段气升式气固环流取热器导流筒壁与床层间的传热特性研究

在一套φ600 mm×7000 mm半圆形的大型有机玻璃两段环流实验装置上,采用FCC催化剂,在导流筒区表观气速0.101～0.670 m/s,环形区表观气速分别为0.049 m/s和0.099 m/s范围内,测定了导流筒壁与颗粒床层之间的传热系数、床层密度和颗粒环流速度的分布规律.结果表明床层密度和颗粒环流速度是影响传热的主要因素,而这两者的变化规律完全由导流筒区和环形区的气速来调控.传热系数随导流筒区气速的增加而增加,适当增加环形区气速能显著改善传热效果.实验结果表明,两段环流取热器比目前工业催化裂化装置使用的外取热器有较高的传热系数.通过理论分析,给出了两段环流取热器的传热系数关联式.     

气液固三相流化床层膨胀特性实验分析

为分析气液固三相流化床床层特性,选用两种粒径接近、密度不同的颗粒:塑料颗粒(湿堆积密度1 273 kg/m~3,平均直径750μm)和陶粒(湿堆积密度1 680 kg/m~3,平均直径800μm),以常温空气为气相、水为液相。实验装置内径0.13 m,全床高度4.75 m,实验液柱高度3.5 m,床内颗粒有足够的膨胀高度。分别测试了液速0—13 mm/s,气速0—12 mm/s条件下的床层高度,研究气液速对塑料颗粒和陶粒床层膨胀率的影响。研究结果显示液速较低时床层收缩,随着气速增加,收缩率增大;液速较高时,膨胀率大于0,随着表观气速的增加,膨胀率先降低,表观气速大于临界值后,膨胀率将增大;除高气速外,床层膨胀率总是随着液速的升高而增大。相同气速、液速条件下,大密度陶粒的床层膨胀(收缩)率大于塑料颗粒。     

竖直管气固鼓泡流化床传热机理的CPFD模拟

针对细颗粒气固鼓泡流化床中床料与竖直传热管壁面间的传热行为,在前期实验的基础上,采用计算颗粒流体力学(CPFD)方法从颗粒在传热壁面更新的角度,深入分析了传热特性与壁面气固流动行为之间的关联性。结果表明,模拟得到的传热管壁面颗粒更新通量和基于颗粒团更新模型的颗粒团平均停留时间均能很好解释实验测得的传热系数变化规律,这证实颗粒团更新是影响传热过程的控制性因素。模拟还发现随加热管从床层中心向边壁的移动,加热管周向方向上颗粒更新通量和传热系数的不均匀性都呈增大趋势。随着表观气速的增大,气泡行为导致床层颗粒内循环流率增大,这是导致颗粒团在加热管壁面上的更新频率增大以及床层与壁面间传热系数增大的根源。     

竖直管气固鼓泡流化床传热机理的CPFD模拟

针对细颗粒气固鼓泡流化床中床料与竖直传热管壁面间的传热行为,在前期实验的基础上,采用计算颗粒流体力学(CPFD)方法从颗粒在传热壁面更新的角度,深入分析了传热特性与壁面气固流动行为之间的关联性。结果表明,模拟得到的传热管壁面颗粒更新通量和基于颗粒团更新模型的颗粒团平均停留时间均能很好解释实验测得的传热系数变化规律,这证实颗粒团更新是影响传热过程的控制性因素。模拟还发现随加热管从床层中心向边壁的移动,加热管周向方向上颗粒更新通量和传热系数的不均匀性都呈增大趋势。随着表观气速的增大,气泡行为导致床层颗粒内循环流率增大,这是导致颗粒团在加热管壁面上的更新频率增大以及床层与壁面间传热系数增大的根源。     

流化床气固流动二维数值模拟

为了获得流化床中床层在不同气速下的流动特性,根据某一生物质发电厂中的HX220/9.8-IV1型纯烧生物质的循环流化床锅炉进行二维建模,通过FLUENT软件对床层冷态流态化进行二维数值模拟,调整一二次风入口风速以获得不同的表观气速,得到了鼓泡床、湍动床以及快速床的气固流动状态,并在快速床的基础上模拟了床层在气流作用下的稀相输送状态。模拟结果清晰展示了各个状态下的床层颗粒的分布情况。     

Modelling of batch fluidised bed drying of pharmaceutical granules

This paper presents a mathematical model based on a three-phase theory, which is used to describe the mass and heat transfer between the gas and solids phases in a batch fluidised bed dryer. In the model, it is assumed that the dilute phase (i.e., bubble) is plug flow while the interstitial gas and the solid particles are considered as being perfectly mixed. The thermal conductivity of wet particles is modelled using a serial and parallel circuit. The moisture diffusion in wet particles was simulated using a numerical finite volume method. Applying a simplified lumped model to a single solid particle, the heat and mass transfer between the interstitial gas and solid phase is taken into account during the whole drying process as three drying rate periods: warming-up, constant rate and falling-rate. The effects of the process parameters, such as particle size, gas velocity, inlet gas temperature and relative humidity, on the moisture content of solids in the bed have been studied by numerical computation using this model. The results are in good agreement with experimental data of heat and mass transfer in fluidised bed dryers. The model will be employed for online simulation of a fluidised bed dryer and for online control.     

Mathematical Model for Batch Drying in an Inert Medium Fluidized Bed

A modified three-phase model is proposed for batch drying of fine powders in an inert medium fluidized bed. The overall heat and mass transfer coefficients between the interstitial gas and solid phases have been determined by the proposed surface-stripping model in which the Biot number is a governing parameter. The effects of gas velocity, inlet gas temperature and mass ratio of starch to inert particles on the drying characteristics of starch in a 0.083 m ID × 0.80 m high medium fluidized bed have been determined. Based on the proposed model, the internal resistance of mass transfer at the powder is equal to the external resistance. The model predicts well the bed temperature, humidity of outlet gas, moisture content of solid particles, heat and mass transfer in an inert medium fluidized bed.     

流化床氛围下多孔物料干燥传热传质的数值模拟

用有限差分法数值求解一个热、质传递耦合模型,理论研究多孔物料流化床干燥过程。方程离散采用全隐格式的控制容积方法,三对角矩阵法（TDMA）用来求解线性方程组。选用球形的苹果丁作为多孔物料。在典型操作条件下,通过分析温度、饱和度和压力的分布侧形,讨论了物料内部的热、质传递机理。在对比条件下,考察了气体入口温度、气速和床面积因子对干燥过程的影响。结果表明：干燥过程受气、固相间的耦合传热传质的影响十分明显,干燥时间随气体入口温度和气速的提高而减少;随床面积因子的增大而增加。     

DRYING OF BIOMASS PARTICLES IN FIXED AND MOVING BEDS

ABSTRACT

The drying of biomass fuel particles in fixed and moving beds with hot gas or steam is considered both experimentally and theoretically. A single particle drying model is coupled with a model describing beat and moisture transfer in The gas phase of the bed. The size of the bed to reach a certain degree of drying depends mostly on the following parameters: particle size, panicle moisture content, gas inlet temperature, gas inlet moisture content and gas mass flow rate.     

烧结床层的热质分析

基于烧结生产的复杂物理化学过程,建立了烧结床层传热、传质和流动的二维非稳态数学模型,考虑了孔隙率、物料颗粒当量直径等床层结构影响参数的变化,并对气固传热系数进行了修正。通过数值计算,获得了烧结床层的温度场、结构变化和烟气的流场、温度场、浓度场等。烟气出口温度、床层总压降与生产实测值吻合较好,验证了数学模型的正确性。进一步分析了燃料配比、风量和给料温度等操作参数对烧结过程的影响。研究结果表明：燃烧带的厚度、最高温度随着烧结过程的进行而逐渐增加。床层孔隙率、颗粒当量直径的变化主要发生在燃烧带的熔融、冷凝阶段。料层压损最大的是燃烧熔融层,其次是混合料带,最小的是烧结矿层。增加焦粉含量、提高烧结混合料的初温,有利于提高成矿质量;风量过大时,会造成成矿质量下降、生产成本提高。     

循环流化床中C类颗粒的干燥

为将循环流化床(CFB)技术应用于C类颗粒(＜30μm)的干燥,在自建的循环流化床(内径0.104 m×高2.35 m)内,以玉米淀粉(dp=8 μm,ρp=800 kg/m3)为研究对象,考察了不同操作参数对其干燥特性及干湿分离情况的影响.结果表明:循环流化床适用于C类颗粒的干燥;干燥速率随气速及进风温度的增大而增大...     

循环流化床中C类颗粒连续干燥的研究

循环流化床(CFB)作为一种新兴反应器,其结构简单、气固接触效率高、处理量大,成为气固二相干燥应用研究的新方向.文中在自建的循环流化床(内径0.104 m×高2.35 m)内,以玉米淀粉(dp=8 μm,ρp=800 kg/m3)为C类颗粒,进行了连续干燥.实验初步研究了进料速率、进风温度及气速等操作参数对淀粉平均停留...     

Modelling and Simulation of Momentum, Heat, and Mass Transfer in a Deep-Bed Grain Dryer

This article concerns the modelling and simulation of a deep-bed grain dryer in a large diameter-column. Two-dimensional (2D) models of deep-bed grain dryers were built by considering simultaneously momentum, heat, and mass transfer in the drying phase together with coupled heat and mass balance in the grain phase. The dynamic equations are solved numerically by using finite difference method. The momentum equations are applied to simulate pressure drop and velocity field of the drying air across the bed. The mass and heat balance in the two phases determine the profile of temperature and moisture content in both phases. Further, drying rate curves for various temperature of inlet drying gas together with moisture content of grain were simulated. The simulated profiles are in close agreement with experimental data.     

ANALYSIS OF HEAT AND MASS TRANSFER DURING COMBINED MICROWAVE CONVECTIVE SPOUTED-BED DRYING

Heat and mass transfer phenomena during the combined microwave-convective batch spouted bed drying are analyzed. Wheat was chosen as a test material. The governing equations, including consideration of internal heat generation and thermodiffusion are formulated and solved using the numerical method of lines. The model allowed variable material transport and dielectric properties. The parameters investigated include electric field strength, electromagnetic field frequency, inlet air temperature, and superficial air velocity. Representative drying and temperature curves as well as moisture and temperature profiles are presented and discussed.     

ANALYSIS OF HEAT AND MASS TRANSFER DURING COMBINED MICROWAVE CONVECTIVE SPOUTED-BED DRYING

Heat and mass transfer phenomena during the combined microwave-convective batch spouted bed drying are analyzed. Wheat was chosen as a test material. The governing equations, including consideration of internal heat generation and thermodiffusion are formulated and solved using the numerical method of lines. The model allowed variable material transport and dielectric properties. The parameters investigated include electric field strength, electromagnetic field frequency, inlet air temperature, and superficial air velocity. Representative drying and temperature curves as well as moisture and temperature profiles are presented and discussed.