THE EFFECT OF TEMPERATURE ON FLUIDIZED BED BEHAVIOUR

Most published correlations for the minimum fluidizing gas velocity have been derived from tests under ambient conditions and increasing discrepancy is found in their application over wider ranges of operating conditions. Up to 1000°C the Ergun equation is reliable but it requires a knowledge of the particle shape factor and bed voidage for its application. Bed voidage is found to vary with temperature for laminar gas flow conditions.

Paralleling changes in gas flow conditions with operating temperature are changes in bed-to-surface heat transfer coefficients. There is a distinct transition from the interphase gas convective to the particle convective component of heat transfer being the dominant mechanism as the operating temperature increases and Re_mf reduces through 12,5 at Ar ～ 26000. This is thought to be a consequence of change in bed bubbling behavior.     

THE EFFECT OF RELATIVE SIZE ON THE DYNAMICS OF FLUIDIZED BED DRYERS

The dynamic characteristics of a two stage fluidized bed dryer are studied when the drying gas flows in a crosscurrent or countercurrent arrangement. The slow dynamic modes are related to such extensive thermodynamic process variables as the total mass and energy content of both dryers. The fast dynamic modes are shown to represent steady state mass and energy balances of one of the dryers.     

高温流化床结焦特性

分析了近年来高温流化床结焦研究的状况,总结了流化床结焦现象及其影响因素、流化床结焦时的最小流化速度及影响因素、流化床结焦机理,并分析了研究中存在的问题,探讨了高温流化床结焦特性研究的方向。     

温度对循环流化床径向动力学特性的影响

运用多尺度能量最小整体运动力学模型,分析了温度对循环流化床径向动力学特性的影响。结果表明,在相同的操作气速和颗粒循环量下,随着床温的升高,局部颗粒浓度将减小,真实的颗粒地速度将增加,而气固两相间的滑移速度将降低;同时真实的气体速度,颗粒通量和悬浮输送能量等动力学参数也将随床温而发生变化。     

EFFECT OF FLUIDIZED BED DRYING ON STABILIZATION OF RICE BRAN

ABSTRACT

Rice bran was treated in a batch fluidized bed at temperatures starting from 90°C up to 130°C in steps of 10°C for different treatment periods. Drying characteristics of rice bran so obtained were used in a mathematical model to predict the maximum possible storage period of rice bran treated under fluidizing conditions. It was observed that the fluidized bed treatment of rice bran requires much lower treatment times for stabilization of rice bran compared with packed bed processes and therefore could be very attractive in commercial applications.     

EFFECT OF FLUIDIZED BED DRYING ON STABILIZATION OF RICE BRAN

Rice bran was treated in a batch fluidized bed at temperatures starting from 90°C up to 130°C in steps of 10°C for different treatment periods. Drying characteristics of rice bran so obtained were used in a mathematical model to predict the maximum possible storage period of rice bran treated under fluidizing conditions. It was observed that the fluidized bed treatment of rice bran requires much lower treatment times for stabilization of rice bran compared with packed bed processes and therefore could be very attractive in commercial applications.     

多孔挡板流化床气泡行为的研究

本文在内径为(?)120mm 的多孔挡板流化床中,用光导纤维法和电容法测定了 Al(OH)_3粉、铜粉和 FCC 三种不同物料体系的气泡频率和气泡速度,对操作条件和挡板参数对气泡行为的影响作了研究和分析。结果表明,在一定的气速下,挡板的开孔率、孔径和板间距(级间高径比小于3)对气泡频率和气泡速度的影响较小;对属 B 类的 Al(OH)_3粉和铜粉物料,气速对气泡频率的影响可以忽略,而对属 A 类的 FCC 物料,气泡频率随气速的增大而增大。     

流化床煅烧低温合成粉煤灰水泥熟料的研究

本文介绍了分布板直径为120mm的锥形流化床的冷态模型试验。在此基础上,进行了放大的工业性中间试验。锥形流化床的分布板直径为600mm床高6400mm。文中讨论了流化床的最佳几何参数和操作条件以及密相区的气一固流动特性,还讨论了分布板和床层的压力降。用流化床煅烧低温合成粉煤灰水泥熟料的热耗为2900kJ/kg·c1,该水泥的28天耐压强度超过325kg/cm~3。这些结果可供工业性流化床设计时参考。     

ＣＦＢ稀相段直长对颗粒内循环流动规律的影响

采用光纤探头测定Ｄ１m射流循环流化床（半圆形）稀相区颗粒速度、颗粒浓度和颗粒流通量的径向分布规律,并考察了操作条件及其轴向的影响,实验结果表明,在循环流化床（ＣＦＢ）中,颗粒流动在床层径向有较大的不均匀性,并呈明显的内循环流动结构,进而考察了影响其流动规律的,以期进一步理解循环流化床颗料流动机理,强化和改善反应器的设计操作。     

石灰投加对水厂排泥水造粒流化床处理工艺的影响

石灰作为一种传统的助凝剂,应用于水厂排泥水调质浓缩工艺,可提高污泥颗粒密度,改善污泥沉降脱水性能。本文利用造粒流化床处理工艺,以南方某水厂排泥水为处理对象进行中试试验,研究了石灰投加对工艺运行效果的影响。试验结果表明,石灰投加可减小PAM投药量,同时增大流化床最大上升流速。中试条件下,500mg／L的石灰投加量可在不影响出水水质的情况下,使流化床PAM投药量减少14％～24％,最大上升流速由38～50cm／min增至42～57cm／min。与现行常规处理工艺相比,石灰投药量可由1667mg／L降至500mg／L左右,PAM投药量可节省50％,同时出泥沉降陛能得到极大改善,含固率提高2～6倍。     

方形截面循环流化床出口效应的实验研究

在0.27 m(长)×0.27 m(宽)×10 m(高)方形截面循环流化床冷态实验台上,针对三个不同的表观气速(Ug=6.0 m/s,6.8 m/s,7.6 m/s),考察了半弯道光滑出口和T形突变出口两种不同结构对系统颗粒循环流率以及床内颗粒浓度分布的影响.实验得到的系统颗粒循环流率Gs=60 kg/m2s～170 kg/m2s.结果表明:两种出口结构下,系统颗粒最大循环流率都随主床表观气速的增加而增加;半弯道光滑出口结构下得到的最大循环流率大,其对应的最大循环流率分别为136kg/m2s,162 kg/m2s和170 kg/m2s;床内颗粒浓度为底部浓顶部稀的分布,T形出口的约束效应使出口附近产生了一个颗粒增浓的区域.     

气液固三相磁稳定流化床的操作状态对反应结果的影响

以氮气、水、铁粉为气液固三相研究了三相磁稳定流化床的床层操作状态；以重整生成油的烯烃饱和加氢过程为体系，研究了铁粉与大比表面非晶态合金催化剂混合颗粒为固相的磁稳定流化床中床层操作状态对反应结果的影响。找到了有利于气液固三相反应的磁稳定流化床床层操作状态     

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.     

EFFECT OF OPERATING VARIABLES ON BED TO WALL HEAT TRANSFER IN A CIRCULATING FLUIDIZED BED

Heat transfer coefficients were measured for 227 and 87 micron size particles of silica sand in a 102 mm dia. and 5.5 m tall circulating fluidized bed made of plexiglass. Effects of solid circulation rate, fluidization velocity, bed density and particle sizes were studied. The heat transfer coefficients were calculated from the temperatures measured along the axis of a 25 mm dia 100 mm long cylindrical heat flux meter.     

EFFECT OF FLUIDIZING PARTICLE ON DRYING CHARACTERISTICS OF POROUS MATERIAL IN FLUIDIZED BED

The drying characteristics of porous material in fluidized bed were examined theoretically and experimentally. The brick ball was used as the sample and immersed in the fluidized bed. The glass beads were used as the fluidizing particles and the particle diameters were changed. When the pore diameter of sample was relatively large, the fluidizing particles were adhered on the sample surface. In the theoretical analysis, the heat and mass transfers in adhered particle layer were considered. The fluidizing particles were adhered on the sample surface during the earlier period of drying. The sample temperature largely decreased when the mass of adhered particle decreased. The calculated results are in good agreement with experimental data. The diameter of fluidizing particle had a small effect on the drying time. The excess increments in drying gas temperature hardly contributed to shortening the drying time.     

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.     

循环复合流化床特性的研究

在直径２５０ｍｍ的循环复合流化床冷模试验装置上，研究了一、二次风速及循环率对流化床轴向浓度分布、物料停留时间的影响规律。可供设计及操作参考。     

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.     

顺流串联流化床流动特性研究

针对攀枝花钛资源钙、镁含量高的特点，研究了快速流化床—湍流床—快速流化床三级串联组成的顺流串联流化床的流动特性。采用光导纤维测速仪和压力计，研究了固相的停留时间和流动形态。对快速流化床的流化速度、湍流床的轴向和径向浓度分布以及抗粘结能力进行了考察。用功率谱密度函数表征床层的活跃程度，定性地说明了湍流床抗粘结能力提高的幅度。     

循环流化床流体特性研究

在 D2 0 0 mm× 2 560 mm自制循环流化床上利用生石灰进行了流体特性研究 .实验结果表明 :固体颗粒循环速率和表观气速是影响压力分布的两个重要因素 .降低气速、提高颗粒循环速率 ,可以提高床内颗粒浓度 ,增加颗粒停留时间 .最后经无因次分析和实验数据拟合 ,分别得到了循环流化床压降和颗粒浓度沿床轴向分布经验关联式 .