Effect of Sudden Increase of Solid Feed Rate on the Arching in Hoppers Connected to a Standpipe with Interstitial Gas Flow

In this paper , a model is proposed for the prediction of the width of arching in hoppers resulted from sudden changes in solid feed rates. Such changes in solid feed rate usually come from the collision on the surface of the moving-bed in the standpipe. The model also takes into account the effect of the powder height in the standpipe of the hopper. The model proves to be adaptable for predicting operational conditions to avoid arching by keeping constant powder height in the main standpipe with interstitial gas flow.     

负压差料斗中静态架拱机理实验研究

通过实验测量散体颗粒在负压差立管料斗中的静态拱宽度,验证本文模型的正确性,并分析了散体颗粒的无约束屈服强度、料斗形状、操作条件和延时效应对静态拱宽度的影响,提出负压差移动床立管料斗孔口最小直径的理论预测方法.     

CFB煤燃烧／热解双反应器立管内气固流动模型分析

在循环流化床（CFB）煤燃烧／热解双反应器冷态实验装置上,以硅胶和电厂锅炉灰为实验物料,考察了立管内的气固流动特性,其中立管的内径44mm、高3m。研究结果表明,立管内的气固流动形态为移动床流动,Leung的立管流动模型适合对该系统中立管内移动床流动的描述,经拟合分别得到了立管内气、同速率以及气同相对速率与固体速率之间的经验方程,对热态实验过程中判断立管内的气固流动型态以及料封的稳定性均具有一定的参考价值。     

散体颗粒架拱研究现状

把在立管中形成的拱分成气泡拱和颗粒拱两类，重点讨论了影响颗粒拱形成的因素，如散体的流动函数、气压及立管流动因子等，指出各种理论模型的优劣，对今后工作提出了建议．     

负压差立管下料过程压力脉动的传递性实验与分析

在高13m大型循环流化床装置上,对φ150 mm×900 mm负压差立管内气固两相流的动态压力进行了轴向多点测量,并用标准偏差进行了分析,主要研究立管下料过程的动态传递特性.实验表明负压差立管内存在明显的压力脉动现象,这种压力脉动具有一定的传递性.颗粒质量流率比较小时是稀密两相共存流态,稀相区的压力脉动主要受进料流量振荡的影响,向下传递;密相区的压力脉动主要受立管的波动性排料影响,向上传递;随着颗粒质量流率的增加达到浓相输送流态时,上部是连续式浓相输送流态,下部是密相波浪式输送流态,立管的压力脉动主要受进口流量振荡和排料过程压缩气体作用,向下传递.对立管的压力脉动进行标准偏差分析表明脉动压力传递沿颗粒的流动方向上具有幅值增大特性.在立管内流态从稀密两相共存流态转变为浓相输送流态时,由于颗粒压缩气体分量最大,压力脉动幅值最大,减小或增加颗粒质量流率,压力脉动幅度均降低.     

循环射流流化床立管中气固流动实验研究

立管是气固循环系统的重要组成 ,其复杂性在于存在着各种流动体系。实验中循环射流流化床选用的循环立管结构是在其末端安置水平挡板作为限流构件 ,考察了水平挡板高度、加料量、射流气速等对立管料柱平衡高度的影响 ;采用气体示踪法测定了颗粒在立管中的流动速度和气体速度 ,并与立管中空隙率进行了关联 ,进而提出预测循环立管移动床流动状况的方法     

Hydrodynamic characteristics of fine particles in the riser and standpipe of a circulating fluidized bed

The hydrodynamic properties in the riser and standpipe. and the cyclone efficiency have been determined in a circulating fluidized bed (CFB) unit consisting of a riser (0.05 m-IDX3.8 m high), a standpipe (0.068 m-IDX2.5 m high) as a primary cyclone/bubbling fluidized bed, and a secondary cyclone. Silica gel powder (mean diameter = 46 μm) was used as the bed material. The effects of gas velocity in the riser and initial solid loading on the solid circulation rate, and the solid holdups in the riser and standpipe have been determined. The effects of gas velocity in the standpipe on the efficiencies of primary and secondary cyclones have been also determined as functions of solid circulation rate and solid entrainment rate. The solid circulation rate increases with increases in the gas velocity in the riser and in the initial solid loading. The efficiencies of primary and secondary cyclones increase with an increase in the gas velocity in the riser. However, the efficiency of primary cyclone decreases and that of secondary cyclone increases slightly, with an increase in the gas velocity in the standpipe.     

颗粒塞阀及其操作特性的研究

通过对粗聚丙烯和瓷球两种Geldart-D类颗粒漏斗-立管系统实验研究,发现在悬料操作区域内,漏斗-立管系统具有较高的抗压能力。因此,把在悬料条件下具有抗压特征的漏斗-立管系统(无机械转动部件阀门)称之为“颗粒塞阀”。颗粒塞阀的抗压下限可由下式-dp/dl=200(1-εmf)^2μgUmf/εmf^3(φsdp)^2(D0/D1)^2 7.0(1-εmf)ρg（Umf)^2/φsdp(D0/D1)^4沿立管高度积分求得;而抗压上限是由Ergun公式沿立管高度积分求得,但计算所用的气速是指此系统的漏斗中颗粒的有效重量等于气固之间作用的曳力时所对应的立管中气速。并指出了此阀可用于把颗粒从低压容器输送到高压容器的场合。     

Bulk coarse particle arching phenomena in a moving bed with fine particle presence

Bridging or arching of flowing solids particles is a serious hazard in the operation of moving bed systems. The mechanics of the arching has been extensively analyzed in the context of particle discharge from a hopper with conical geometry by considering the particulate layer stress distribution. However, bridging can also occur in a moving bed system with cylindrical geometry during the continuous mass flow of solids particles. Experimental work conducted in this study reveals that the appearance of solids bridging is normally accompanied by the presence of fine particles in the coarse moving particles as well as by the countercurrent interstitial gas flow. In this study, a stress analysis of the layered particles distributed in a cylindrical, vertical moving bed that flows downward opposing to upward flow of the interstitial gas is developed to quantify the bridging phenomenon. The analysis takes into account of the effects of presence of fine powder in the coarse particle flows and properties, such as particle‐size distribution, bed voidage, and interstitial gas flow rate. The experimental validation of the present stress analysis for moving bed systems with varied fine and coarse particle concentration distributions, and interstitial gas velocities is also conducted. The stress distributions of the particles under flowing and arching conditions are obtained. An arching criterion is formulated, which indicates that the critical radius of the standpipe to avoid arching phenomenon is only related to the property of the bulk solids in the present geometric configuration of the flow system. © 2014 American Institute of Chemical Engineers AIChE J, 60: 881–892, 2014     

垂直立管中催化剂流动特性的实验研究

对垂直立管中催化剂的流动性能进行了实验研究,测定了各种操作条件下立管中的轴向压力分布、催化剂循环速率以及附加吹气的影响. 实验结果表明,立管中的气固流动存在分别处于负压差下移下流区的"脱气段"和处于正压差下移下流区的"持气段"两种流动状态;下料阀开度对固体循环流率有明显的约束作用,且使"持气段"总压降增加较"脱气段"更为明显;对立管引入附加吹气有明显的增压作用,并使立管的压力分布有较大的改变. 根据实验结果及分析,对垂直立管的管形设计和催化剂在垂直立管中的密相输送提出了分析与建议.     

The control of bed height and solids circulation rate in the standpipe of a cold flow circulating fluidized bed

Circulating fluidized beds (CFBs) are used widely in the chemical industry. Knowing or estimating the bed height in the standpipe and the solids circulation rate are essential for effective control of the system. This paper incorporates a 2-region model to calculate the bed height in the standpipe with a Kalman filter algorithm to estimate the solids circulation rate (SCR). Simulations of both the standpipe bed height and SCR were compared with experimental data and shown to give good agreement.

In addition, a neural network method was applied to model the entire cold flow CFB system and measured data sets were used to train the neurons of the network. Finally, a linear controller was applied to control both the bed height and solids circulation rate to desired set points. Simulations were performed for both positive and negative step inputs for both variables and satisfactory control was demonstrated using this controller in combination with the neutral network and Kalman estimator.     

Flow of cohesive solids in standpipes against a pressure gradient

For downflow of cohesive solids in a standpipe in the absence of pressure gradient, the flow, no-flow criterion of Jenike (1964) can be applied to determine the minimum diameter for no arching to occur. In this paper Jenike's analysis is extended to account for the presence of pressure gradient in the standpipe. An equation for estimating minimum pipe diameter for smooth flow is presented. For design we suggest that the minimum diameter in the absence of pressure gradient should be measured and our equation is to be applied to extrapolate to the real situation with a finite pressure gradient.The present work is relevant to recent usage of standpipes in oil-shale processing and coal power plants.     

Study on the stress distribution and modeling of the stand pipe in a circulating moving bed

The liquid-solid circulating moving bed reactor is a novel one, which consists of two reaction chambers and a particle transport system. Particles move down to the lower reaction chamber from the upper reaction chamber through a coupling standpipe and to the particle transport system through a bottom standpipe, and are then conveyed into the upper reaction chamber through a riser. A stress distribution model based on the equations of continuity and momentum balance in the reactor is established and used for simulations which shows that the stress concentration regions are at the coupling standpipe and the bottom of the regeneration chamber. To reduce the largest stress in the stress concentration regions and to minimize catalyst consumption, the regeneration chamber should be designed to give a low ratio of height to diameter. Zoning diagrams of the flow patterns in the bottom standpipe are proposed and the flow patterns can be readily deduced from the pressure gradient.     

负压差立管内气固两相流的流态特性及分析

对于出口插入密相床的立管，管内气固两相的流动特点是下行的颗粒速度大于气体速度和颗粒的逆压差流动，颗粒下行是一个减速运动过程. 管内的气固两相流的流态有两种形式，当GsGsc时，流态是浓相输送流态，气流下行. 两种流态可以互相转变，主要取决于颗粒质量流率的大小. 负压差立管的流态变化与气固两相之间滑落速度和轴向压力的变化密切相关，滑落速度随颗粒质量流率的增加逐渐减小，而轴向压力则逐渐增大以平衡立管的负压差.     

Flow of fluidized solids and bubbles in standpipes and risers

Equations are presented for the densities of fluidized solid-bubble mixtures in downward and upward vertical flow. Data from a large commercial standpipe are in close agreement with calculations. Flow instability is predicted when downward solid flow is sufficient to hold a gas bubble stationary in a standpipe. Commercial experience of such instability is presented indicating the existence of slugs in a 45-in.-diam. standpipe.     

Effect of solid circulation rate on coating efficiency and agglomeration in circulating fluidized bed type coater

Circulating fluidized bed was proposed to be used as a coater, and coating experiments of glass beads with silica powder were performed in a circulating fluidized bed. Glass beads and silica powder were chosen as model particles, because their shape was almost spherical. The respective effects of gas flow rates supplied from a distributor and from an air nozzle for solid circulation, feed rate of powder suspension and particle content in the bed on coating efficiency and agglomeration are mainly discussed. Coating efficiency in circulating fluidized bed coater was correlated well with solid circulation time rather than with gas flow rates or solid circulation rate, while the agglomeration among core particles was mainly governed by solid circulation rate.     

A model for the pressure balance of a low density circulating fluidized bed

The pressure balance along the solid circulation loop of a circulating fluidized bed equipped with a solid flux regulating device has been modelled and the influence of the pressure balance on the riser behaviour has been predicted.The solid circulation loop has been divided into many sections, where the pressure drop was calculated independently: riser, cyclone, standpipe, control device and return duct. A new theoretical model, that is able to predict the pressure losses in the return path of the solid from the standpipe to the riser, has been built. A new correlation for cyclone pressure loss with very high solid loads has been found on the basis of experimental data.The pressure loss in the riser has been calculated by imposing the closure of the pressure balance, ΣΔP = 0. Once the riser pressure drop had been calculated, the holdup distribution along the riser was obtained by imposing a particular shape of the profile, according to the different fluid-dynamics regimes (fast fluidization or pneumatic transport). In the first case, an exponential decay was imposed and the bottom holdup was adjusted to fit the total pressure drop, in the second case, the height of the dense zone was instead varied.The experimental data was used to develop the sub-models for the various loop sections have been obtained in a 100 mm i.d. riser, 6 m high, CFB. The solid was made of Geldart B group alumina particles. The tests were carried out with a gas velocity that ranged between 2 and 4 m/s and a solid flux that ranged between 20 and 170 kg/m²s. A good agreement was found between the model and experimental data.     

The characteristics of particle flow in the overflow and underflow standpipe of fluidized beds

Characteristics of particle flow in the standpipes of a 10 cm I.D.×120 cm high fluidized bed were investigated. The standpipes used in this experiment were vertical overflow and vertical underflow standpipes. Sand particles and polyethylene powders were employed as the bed materials. The effects of standpipe diameter, gas velocity and particle properties on the solid flow rate were determined. The experimental results showed that the flow behaviors of solids through the overflow and underflow standpipes are different with variations of operating conditions. For both standpipes, the mass flow rate of solids was strongly dependent on the standpipe diameter. For the overflow standpipe, the increase of gas velocity increased the solids flow rate. But for the underflow standpipe it decreased the solid flow rate. From the measured pressure drops, solid fractions in the standpipes were determined by the momentum balance. The obtained experimental data of solids mass flow rate were well correlated with the pertinent dimensionless groups for underflow as well as overflow standpipes.     

气固循环流化床负压差下料立管的压力脉动特性

通过对气固循环流化床负压差下料立管的压力测量,分析了立管下料过程的压脉动特性。负压差下立管内的颗粒由立管上部的低压端流向下部的高压端的过程中,对所夹带的气体产生压缩导致了立管内气固两相流动的不稳定性,表现为立管压力的脉动以及颗粒下行速度的波动和密度分布的不均匀。压力脉动的幅度随负压差的增加而增大。     

Dynamics of jetsam layer in continuous segregation of binary heterogeneous particles in gas-solid fluidized bed

Investigations on the dynamics of height of defluidized jetsam layer were carried out during the continuous segregation studies of heterogeneous binary particles in a fluidized bed system. The effect of bottom discharge pipe, flow rates of gas and solid and composition of flotsam in the feed on the growth of defluidized layer has been studied. It is found that the steady state defluidized bed height decreases with increase in gas velocity, feed composition and bottom discharge pipe diameter, and decrease in solid flow rate. A model based on the exponential growth of the defluidized bed height is used to compare the experimental data on the dynamics of defluidized bed height. Correlations are developed for growth constant and steady state bed height in terms of operating and geometric parameters. The agreement between the model and experimental data is satisfactory.