快速流化床截面平均空隙率轴向分布及其影响因素

根据在直径0.186m、高8m和直径0.14m、高12m两台快速流化床装置的实验结果，并综合文献研究报道，研究了操作气速、颗粒循环速率、颗粒物性、床层直径以及进口、出口结构等因素对床层截面平均空隙率轴向分布的影响。表明一般情况下，快速流化床截面平均空隙率轴向分布的基本形式是上部空隙率高、下部空隙率低的单调指数函数。在特定的床结构条件下，快速流化床截面平均空隙率轴向分布曲线可能发生变异，即在出口结构有强约束作用时，可能呈反C，在入口结构有弱约束作用时，可能呈S型。     

PP气相流化床反应器平均停留时间的计算

介绍了聚丙烯流化床反应器流化特性和卸料过程;提出了利用其料位测量机理计算平均停留时间的方法,并将实际计算结果与理论值进行了比较。     

振动流化床中床层空隙率的分布

在φ１４８ｍｍ的振动圆柱形流化床内,采用树脂、玻璃珠、小米及砂子等Ｇｅｌｄａｒｔ‘Ｂ和Ｄ类物料,测定了振动强度为１－８ｇ,流化床为１．０－３．０条件下气固流化床床层空隙率的变化,考察振动条件下床层轴向径向的空隙率分布,探讨了床层空隙率的一些影响因素,并根据实验结果对振动流化床的平均空隙率进行了无因次数式关联,此关联式对实际振动流化床的操作与工程设计具有一定的指导意义。     

用空隙率波动信号确定磁流化床的临界转换点

磁流化床由聚式流化向散式流化转化的实验判据,可以从磁流化床局部空隙率波动信号的主频率F_d随磁场强度H变化的曲线得到。该曲线的极值点就对应了从聚式流化转变为散式流化的临界转换点。由此确定的稳定流化区域与Rosensweig用微扰准则划定的稳定流化区域基本一致。     

气固流化床中气泡流运动特征和空隙率径向分布

The flow behavior of the bubble in gas/solid fluidized bed is studied in multi-scales.A hypotheses of taking dispersed bubble as the continuous medium and the hydromechanics expression based on volume flux are proposed.The mathematical model of radial porosity distribution in the dense zone is developed.The radial distribution of the porosity is parabolic in nature according to the theoretical calculation and the calculated data is consistent with experimental data satisfactorily.     

快速流化床中平均滑落速度及絮状物的特性

本文依据大量实验数据,研究快速流化床的操作条件,气固物性等参数对于床内颗粒平均滑落速度的影响。颗粒聚集为絮状物是快速流化床中气固流动的一个重要特征,文中对等效絮状物的基本特征进行了讨论,根据大量实验数据对絮状物的终端速度、絮状物当量直径,以及絮状物中的粒子个数作了推算,这对认识快速流化床气固接触机理及反应器的设计具有参考价值。     

气固流化床中空隙率信号的小波分析

在(?)90mm×000mm 的有机玻璃流化床中,采用 PV4A 颗粒测速仪对不同粒径的沙、聚氯乙稀(PVC)颗粒在操作气速为0.262～0.524 m/s 下不同轴/径向位置的空隙率波动信号进行测定。选用 db2为小波函数对信号进行多尺度分解和进行连续小波变换,计算不同尺度下分解信号的功率谱密度函数。研究表明,细节信号反映的是颗粒脉动和小气泡的运动特征,呈现宽频分布,有很强的随机性;近似信号主要反应大气泡的运动特征,有明显的主频存在,且随操作条件变化;连续小波变换表明空隙率波动信号在微观结构上具有自相似性。     

双射流流化床空隙率的分布

在 ３００ ｍｉｎ×５０ ｍｉｎ×２６００ ｍｍ的二维射流床中,采用内径为 １１ ｍｍ的对称双射流管,研究了等速射流条件下射流管间距、喷口射流气速、静床高度对床层空隙率分布的影响,发现射流管间距、喷口射流气速是双射流产生射流区合并的主要原因;并得到了具体实验条件下空隙率分布的数据．同时研究了双射流管不等速射流条件下空隙率分布的规律．     

冷态灰熔聚流化床气化器内空隙率分布的数学模型

基于固体颗粒的比表面物性法则,用改进的ＳＩＭＰＬＥ算法和微机上开发的ＣＡＳＩＣＣ软件考察了冷态灰溶聚流化床气化器内空隙率分布。     

THE ESTIMATION OF THE DENSE PHASE VOIDAGE OF A GAS FLUIDIZED BED

Dense phase voidage can be estimated by cutting gas flow and following the rate of bed collapse. Abrupt cessation of flow is not possible when excess gas in the windbox can only discharge through the bed. The magnitude of this problem is examined experimentally.     

THE RADIAL DISTRIBUTION OF HEAT TRANSFER COEFFICIENT IN FAST FLUIDIZED BED

This paper presents an experimental study on the axial and radial distributions of heat transfer coefficients in a fastfluidized bed operated at ambient temperature.The following formula is recommended to correlate the local heat transfer coefficients in fast fluidized beds:where a,n_1 and n_2 are functions of radial positions.     

EFFECTS OF PARTICLE CHARACTERISTICS ON THE PERFORMANCE OF A FAST FLUIDIZED BED REACTOR

A heterogeneous model for the fast fluidized bed reactor which carries out a gas-solid non catalytic reaction is presented. The hydrodynamics of the fast fluidized bed is characterized by the model of Kwauk et al. (1985) which assumes the existence of two phases; a dense phase and a dilute pneumatic transport phase. For a given solid flowrate, the length of the reactor occupied by each phase depends on gas velocity, particle diameter and density and average voidage within the reactor. The gas-solid reaction is assumed to follow the shrinking core model. The solids are assumed to be completely backmixed in the dense phase and move in plug How in the dilute pneumatic transport phase. The gas phase is assumed to be in plug flow in both phases

For given gas and solid flowrates, the transition from the dense phase flow to the fast fluidized bed (containing two regions) as functions of particle size and density is determined using the model of Kwauk et al. (1985). The numerical solution of the governing mass balance equations show that for given solid and gas flowrates, (and average voidage) the gas phase conversion shows an unusual behavior with respect to particle diameter and density. Such behavior is resulted from the effects of particle diameter and density on the reactor volume occupied by each phase and the effect of particle diameter on the apparent reaction rate. The numerical results show that a fast fluidized bed gives the best conversion at large particle density and for the particle diameter which results the fast fluidized bed to be operated near the pure dense phase flow.     

EFFECT OF HIGH VOIDAGE ON MASS TRANSFER COEFFICIENT IN A FLUIDIZED BED

Experiments were carried out to determine the gas-solid mass transfer coefficient for the air-naphthalene system under fast-fluidized conditions. The data were obtained under conditions of high voidage (as high as 98%) and high gas velocities (0·5 m/s-2·2 m/s). The results indicate that the correlation for the mass-transfer coefficient in a gas-solid fluidized bed under low voidage conditions established by previous investigators can be extended to the fast fluidization regime. Significantly lower mass transfer coefficients were, however, obtained under high voidage compared to low voidage conditions.     

THE EFFECT OF RADIAL DISTRIBUTION OF VOIDAGE ON THE BURNING RATE OF A CARBON SPHERE IN A FLUIDIZED BED

The local void around a sphere in a packed bed or in the emulsion phase of a fluidized bed has been calculated theoretically; and measured as a function of the radial distance from the centre of the sphere. Effects of this distribution on the burning rate and Sherwood number have been investigated for two types of bed e.g. where inerts are of the same size as the carbon particle and where the inerts are smaller than the carbon particle. Even though the present analysis studies the effect on the diffusive component of the mass transfer alone, the results suggest that the distribution of voidage will yield Sherwood numbers higher than that calculated from the constant voidage assumption. The voidage distribution explains the increase in burning rate of carbon with increasing size of the inerts.     

快速流化床内颗粒速度的关联

颗粒速度是快速流化床内重要的流体力学参数,直接测定是困难的,一般都是通过测定其他参数,来计算颗粒的速度。本研究在内径6.6cm 和9.7cm,高3m 的快速流化床内测定颗粒的轴向滞留量分布及压头损失,分析床层内颗粒速度及其影响因素,对三种不同颗粒进行测定,将实验数据进行关联,得出颗粒速度的关联式:适用范围:气体流速:1.4～6.0m/s颗粒循环速度:30～130kg/m~2·s颗粒终端速度:0.133～0.880m/s将实验值与计算的结果比较,基本一致。故可认为该式在实验范围内,可用于推算快速流化床内的颗粒速度。     

循环流化床锅炉快速床流体动力学结构研究

论述了快速床区流体动力学的结构，研究了快速床区纵向和横向悬浮密度分布的规律及相应的计算公式。对影响快速床区动力学结构的主要因素，如固体颗粒的循环率、气体速度等进行了试验研究，对循环流化床锅炉的设计和运行有一定的指导意义。     

THE TEMPERATURE OF BURNING CARBON PARTICLES IN A FAST FLUIDIZED BED OF FINE PARTICLES

The temperature of coarse (6–8 mm) carbon particles burning in a fast fluidized bed was measured. The burning carbon particle was found to be 50–70^°C hotter than the bed solids. The convective heat transfer coefficient on the particle was also measured in a separate experiment to help predict the temperature of the carbon particle using a mathematical model which considered both combustion kinetics and heat transfer on the particle. A good agreement between the predicted and measured values of temperature was found.