循环浆态床气体停留时间分布的研究

研究了循环浆态床气流段的气流量和液体循环量对气体停留时间分布的影响。实验结果表明,减小气流量或者增加液体循环量,气体返混程度变大,气体平均停留时间增长。建立模型模拟循环浆态床气流段气体停留时间分布,得到停留时间分布密度函数和物料分率p与射流相似准数Ct和气液动量比准数Cr的关联式。从关联式看出,气液动量比准数Cr越小,物料分率p越大,表明循环液体流量越大,气体停留时间分布越接近于全混流。这一结论与实验结果相符。     

加压喷动床中细颗粒喷动特性

在内径分别为 186mm和 80mm的加压喷动床中 ,以空气为喷动介质 ,在 10 1～ 70 0kPa的压力范围内考察了几种不同粒度的细颗粒在加压下的喷动特性 .研究结果表明在不同的Re_t 内压力对最小喷动速度的影响不同 .实验还发现 ,随着压力的升高 ,喷动区直径增大 ,稳定操作区域增大 ,加压可明显改善喷动床的操作稳定性     

带导流管液固喷动床的最小喷动速度研究

在截面为矩形有机玻璃喷动床内，使用四种粒径的窄筛分球形玻璃珠，以常温水作为喷动和辅助液体。综合考虑床体的几何尺寸、操作参数以及液体和颗粒的物性特征，系统研究带导流管喷动床的最小喷动速度，得出最小喷动速度的经验公式，为设计和操作提供参考。     

复合床反应器中液体停留时间分布模拟研究

在对置式复合床液停留时间分布的实验研究基础上,对2喷嘴对置式复合床液体停留时间分布的三维模型进行了研究。使用压力喷嘴模型,水-氮气系统,用Fluent模拟了气量、液体流量对液体停留时间分布的影响,与实验值进行了比较。结果表明,尽管实验值与模拟值的平均停留时间tm之间存在一定差别,但在整个停留时间分布上,二者吻合较好。通过对模拟结果分析,发现喷嘴撞击区有较强混合,但在撞击区之后较长的空间,气体保持平推流,与实验结果一致。     

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。     

多气体入口的喷动床的喷动过程

本文叙述了一种适合于颗粒涂覆用的,具有特殊的多气体入口的喷动床。研究了这种喷动床在不同气流量和松装体积时的五种特征状态,给出了各种状态下的颗粒循环特点,并描述了在不同气流量和松装体积区间内出现不同喷动状态的相图。     

喷动床内气固两相流体动力行为的数值模拟

引　言喷动床被广泛应用于不同工业领域中 ,如石油裂解反应 -再生器、煤和农业废弃物气化和燃烧 ,喷动床还被应用于粮食和药品的干燥等[1] .因此 ,喷动床设计应满足不同应用的要求 .喷动床内气相反应物的反应时间和停留时间依赖于床体几何结构和运行参数 .尽管已有许多的实验对喷动床内气固两相流动进行了研究 ,得到了喷射区、环形区和喷泉区内的气固两相流动流体动力特性 ,然而由于喷动床内气固两相流动的复杂性 ,人们对床体几何结构和运行参数对喷动床动力学的影响至今并不清楚 .因此 ,床体几何结构和运行参数等对喷动床动力学的影响成为…     

密相输运床径向颗粒体积分数分布的研究

在提升管高17 m,内径0.102 m的密相输运床冷态实验装置中,采用B类石英砂颗粒,针对径向颗粒体积分数分布进行了研究。结果表明,径向颗粒体积分数分布不均匀:提升管中心至近壁面附近(r/R=0—0.7),颗粒体积分数较低且基本一致;近壁面处(r/R=0.7—0.9)颗粒体积分数显著升高;壁面附近(r/R=0.9—0.97)达到最大。增加固体循环流率或降低提升管气量,各径向位置颗粒体积分数都增加。其中壁面附近最为明显,提升管中心至近壁面附近变化较小。文中建立了径向颗粒体积分数分布描述关系式,对于A类颗粒和B类颗粒实验结果都能较好地预测。     

吸附床内气体浓度分布的测定

<正>1引言固定床内流体的轴向与径向混合作用对床层内的传质、传热和反应过程有很大的影响,研究固定床内流体的混合特性一直受到各国学者的重视。固定床中流体与固体颗粒间的传质与流体的混合作用是相互影响的。一些学者对吸附床中气体澎合特性进行了研究。l－3。,但他们所使用的固定床实验装置内径比较小（100mm以下）,一般都采用改变床层高度,在床层出口端收集气体样品进行分析,测定不同床层截面上气体浓度分布。这一检测气体浓度的方法对气、固间有较大传质速率的吸附床会产生较大的误差。为准确测定床层内气体浓度及变化,建立了气体浓度微机检测系统和内径为267nlm的气相吸附装置,催化燃烧式气体浓度传感器置于床层内,可连续检测和记录床层内历点浓度。应用该装置测定了甲烷－空气－SA分子筛物系在床层内不同横截面上甲烷浓度分布及随时间变化的数据。     

Behaviour of Cohesive Powders in a Powder‐Particle Spouted Bed

Behaviour of cohesive powders in a powder‐particle spouted Bed (PPSB) has been investigated under several operating variables and solids properties. The elutriation rate constant based on the hold‐up of fine powders in the bed decreased with a decrease in the size of fine powders, and with an increase in the size of coarse particles under a constant superficial gas velocity. This finding is quite different from the elutriation phenomena of particles more than 100 µm in size. Moreover, the mean residence time of fine powders increased with a decrease in the superficial gas velocity and the size of fine powders, and decreased with a decrease in the size of coarse particles.     

二维三相循环流化床液体停留时间分布的研究

用脉冲示踪法对二维三相循环流化床液体停留时间分布(RTD)进行了测定。在气速2～3m／s,液体循环量0～0．35m^3／h,固体循环量1．5～1．75g／s的范围内测得的液体停留时间分布曲线均有明显的3峰分布。其中前两峰分布是由于提升管中颗粒与液体之间和液体与气体之间共同作用改变了液体轴向速度分散程度的结果。第三个峰的分布是由于液体进入循环仓循环后在出口处检测的RTD曲线,并且提出一维两组分扩散物理叠加模型,模型的预测结果与实验获锝的RTD曲线平均误差小于5％,可较好地描述提升管中液体停留时间分布曲线。     

含有生物质固体颗粒进料时的扩张床稳定性评价

针对扩张床吸附进料中含有较高浓度的生物质固体颗粒的特殊性,选择特殊离子(Li+和 Br-)作为停留时间分布(RTD)示踪物,系统考察了离子选择性电极的工作范围、响应时间、流速、生物质固体颗粒浓度的影响,证明了离子选择性电极的可用性。通过优化脉冲离子浓度和脉冲量,确定了合适的脉冲条件为 0.1mol?L?1和 0.5mL。以面包酵母为模型生物质、基因重组大肠杆菌匀浆液为实际对象,进行了含有固体颗粒进料时的 RTD 测定,考察不同生物质固体颗粒浓度和扩张床吸附剂的影响,不仅证实了所建立方法的可行性,而且是一种真实操作条件下扩张床稳定性评价的有效手段。     

Residence Time Distribution of Solids in a Fluidized Bed

Experimental investigation on RTD of solids is carried out in a single‐stage fluidized bed provided with an internal, using uniformly sized particles and a binary solid mixture, varying gas flow rate, solids rate, bed height, dilution and the bed geometry. The effect of these variables on first and second moments as well as on F‐curves has been determined. Using a binary solid mixture or an internal inside the bed is found to reduce backmixing of solids. The data is fitted to FTEM and the values of N obtained were compared for different variables.     

肿胀床中蛋白质吸附性能

The influence of operation parameters on the adsorptio11 perforn1ance of protein (bovin serum albumin,BSA) in an expanded bed was studied using Streamline diethyl aminoethyl (DEAE).The result of residence timedistributions (RTD) and breakthrough curves showed that adsorption performance of the expanded bed could notbe improved by increasing the fiow velocity at the range from 16ml.min~(-l)to 26ml.min~(-1).The increase of proteinconcentration from 0.5 mg.ml~(-1) to 2mg.ml~(-l) resulted in poor adsorption performance.With increasing temperaturefrom 5℃ to 30℃ and the sedimented bed height from 11.5cm to 22.5cm,the adsorption characteristics in theexpanded bed were improved.     

Drying of Agricultural Grains in a Multiple Porous Draft Tube Spouted Bed

A multiple porous draft tube spouted bed (MPDTSB) was used to carry out drying of Ragi (Eleusine coracana), Barley, and Wheat grains. Batch experiments were conducted under varied conditions of initial moisture contents of grains, air inlet temperatures, and airflow rates. The draft tube parameters and fluid inlet sizes were also varied in the study. The results indicated that MPDTSB has the potential to be used for scale up to large-scale solids drying. In addition, two single porous draft tube spouted beds (SPDTSBs) were used for comparison with MPDTSB; the batch drying times in the MPDTSB were found to be lower when compared to those in SPDTSB under identical operating conditions.     

Performance of Fixed Bed Reactors with Two-Phase Upflow and Downflow

A time and space dependent model was developed to analyse the performance of two-phase upflow and downflow fixed bed bioreactors and was applied to biological phenol degradation. The hydrodynamic parameters were determined from residence time distribution measurements, using an imperfect pulse method for time–domain analysis of non-ideal pulse tracer response. A transient diffusion model of the tracer in the porous particle coupled with the PDE model was used to interpret the obtained RTD curves. Gas–liquid mass transfer parameters were determined by a stationary method based on the least square fit of the calculated concentration profiles in gas phase to the experimental values. The analysis of the performance of fixed bed bioreactors used for phenol biodegradation shows that for the same operating conditions two-phase upflow gives much higher conversions. Gas–liquid mass transfer is the limiting step in the rate of phenol biodegradation when the inlet phenol concentration is high. © 1997 SCI.     

Measurement of Residence Time Distributions in a Continuously Operated Spouted Bed

Continuous gas-solid processes are applied in many industries with particulate products, e.g. for granulation or coating. In this contribution, the residence time behavior in a continuously operated prismatic spouted bed was determined by applying an impulse of magnetizable tracer particles. Experiments were performed with the original configuration and with separation plates including mouse holes of varying size between the different chambers of the ProCell 25 apparatus. It is shown that the shape of the residence time distribution is influenced by the separation plates. In order to quantify the backmixing between the chambers, discontinuous experiments were performed, and the bed mass distribution and the distribution of the tracer were measured and compared to the initial conditions.     

Low‐Temperature Selective Catalytic Reduction of NO on an Iron Ore Catalyst in a Magnetically Fluidized Bed

Low‐temperature selective catalytic reduction of NO from simulated flue gas by NH₃ on admixtures of iron ore and iron catalyst in a magnetically fluidized bed was experimentally studied. It was found that iron ore exerts a prominent catalytic effect on NO removal resulting in high removal efficiency without magnetic fields. Since iron ore is insensitive to magnetic fields due to its antiferromagnetic property, NO removal efficiency with iron ore as catalyst is only slightly influenced by magnetic fields. The NO removal efficiency, however, can be greatly improved using admixtures of iron ore and iron as catalyst in a magnetically fluidized bed. At defined magnetic field intensity and the same temperature, the removal efficiency reaches higher values compared with that without magnetic fields.     

Voidage Profiles in a Slot‐Rectangular Spouted Bed

Local voidages were determined using optical fibre probes for 1.4 and 2.4 mm glass beads in slot‐rectangular spouted beds of width 150 mm. The effects of air inlet flow rate, slot width and bed thickness were investigated. Spout widths were determined from standard deviations of local voidage fluctuations. Both spout and annulus voidages increased with increasing air flow. Annulus voidages were usually higher than corresponding loose‐packed voidages and decreased with increasing height. Annulus and spout voidages were very sensitive to the air entry slot width and particle diameter. With increasing height, spouts became increasingly circular (three‐dimensional), despite the initial rectangular geometry.