负压差立管中散体颗粒循环量突变对动态拱宽度的影响

以预测静态拱宽度模型为基础，结合立管中气固之间相互作用特征，推导出散体颗粒循环量突变对料斗中形成的动态拱宽度影响的理论模型．利用散体颗粒在无压差条件下通过孔口流落来模拟其循环量突变，实验证明模型可以预测立管中散体颗粒循环量突变时料斗中动态拱宽度，指出了今后工作的主要方向．     

负压差移动床立管料斗架拱实验研究

通过测量散体颗粒在负压差移动床立管料斗中静态拱宽度及分析散体性质、料斗形状和操作条件对料斗静态拱宽度的影响，得出当散体颗粒６４３．５ｋｇ／ｍ３≤ρｂ≤１０８５ｋｇ／ｍ３２６．７°≤θｒ≤３２．９°２２．４°≤δ≤３４．６°在负压差移动床立管的锥形料斗０°＜α≤２８．１°中形成静态拱时，其宽度可以通过下面的关联式求得：ＤｃａｌＤｓ＝０．２３８θｒδ０．１５８α－０．２７２（－ｄｐ／ｄｈ）ρｂｇ０．３８８     

负压差移移动床立管料斗架拱实验研究

通过测量散体颗粒在负压差移动床立管料斗中静态拱宽度及分析散体性质，料斗形状和操作条件对料斗静态拱宽度的影响，得出当散体颗粒６４３．５ｋｇ／ｍ＾３≤ρｂ≤１０８５ｋｇ／ｍ＾３ ２６．７°≤θｒ≤３２．９° ２２．４°≤δ≤３４．６°在负压差移动床立管的锥形料斗０°〈α≤２８．１°中形成静态时，其宽度可以通过下面的关联式坟得：（Ｄｃａｌ／Ｄｓ）＝０．２３８（θｒ／δ）＾０．１５８（α／Φ）＾－０．２７     

负压差散体颗粒无约束屈服强度实验测量方法

根据Ｇｅｌｄａｒｔ－Ａ类散体颗粒在移动床充气条件下气体均匀分布的特点，结合散体力学和两相流理论，提出理论模型并导出散体颗粒的无约束屈服强度与静态拱宽度的关系式，通过实验测量在负压差条件下与移动床立管联接的料斗中Ｇｅｌｄａｒｔ－Ａ类散体颗粒的静态拱宽度来计算其无约束屈服强度．对于Ｇｅｌｄａｒｔ－Ａ类散体颗粒，此方法的测量结果比Ｊｅｎｉｋｅ测量结果能更准确地描述散体颗粒的无约束屈服强度．     

负压差移动床立管料斗中散体颗粒流动特征Ⅰ流区研究

通过对负压差移动床立管料斗中的散体颗粒流动状态的观察，结合散体颗粒通过料斗的平均质量流率和压力波动信号分析，将散体颗粒流动分成压力控制区、气泡控制区、气栓控制区以及悬料区，并分析了孔口直径、料斗的半锥角和物料特性对流区的影响，给出流区划分界限。     

负压差移动床立管料斗中散体颗粒流动特征：Ⅰ流区研究

通过对负压差移动床立管料斗中的散体颗粒流动状态的观察，结合散体颗粒通过料斗的平均质量流率和压力波动信号分析，将散体颗粒流动分成压力控制区，气泡控制区，气栓控制区以及悬料区，并分析了孔口直径，料斗的半锥角和物料特性对流区的影响，给出流区划分界限。     

负压差移动床立管料斗中散作颗粒流动特征──Ⅳ立管中科面高度对流落特征的影响

通过负压差移动床立管中料面高度对散体颗粒通过其下方连接的锥形料斗流落特征影响的研究，结果表明：当锥形料斗的半锥角不大于10．2°及料面高度大于0．30m时，立管中料面高度对散体颗粒流落时的流区特征、压力波动特征和散体颗粒平均质量流率等影响甚微；而当料面高度不大于0．30m时．料斗中压力波动强度减小。当锥形料斗的半锥角大于10．2°，无论立管中料面高度为0．55m还是0．30m，散体颗粒流落特征满足压力控制区，而立管中料面高度为1．65m时，散体颗粒流落时出现气泡控制区特征。     

负压差移动床上管料斗中散体颗粒流动特征──Ⅱ散体颗粒平均质量流率研究

本文给出利用料斗中体均压力梯度与立管压力梯度的关系判别压力控制区、气泡控制区、气栓控制区和悬料区的方法。在气栓控制区，料斗中体均压力梯度有如下关系[（一dP／dz）]hplug=0．241pbmfg而且，散体颗粒平均质量流率可以用Beverloo方程来预测。在此基础上，讨论了料斗中体均压力梯度对散体颗粒通过孔口平均质量流率的影响，并给出预测平均质量流率的关联式。给出一种新的立管约束条件，即料斗阀的设计方法和操作范围。     

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．     

负压差移动床立管料斗中散体粒流动特征

本文给出利用料斗中体均压力梯度与立管压力梯度的关系判别压力控制区，气泡控制区、气栓控制区和悬料区的方法，在气栓控制区，料斗中体均压力梯度有如下关系「（－ｄｐ／ｄｚ）ｖ」ｈｐｌｕｇ＝０．２４１ρｂｍｆｇ而且，菜体颗粒平均质量流率可以用Ｂｅｖｅｒｌｏｏ方程来预测，在此基础上，讨论上料斗中体均压力梯度对散体颗粒通过孔口平均质量流率的影响，并给出预测平均质量流率的关联式，给出一种新的立管约束条件，即料斗阀     

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 accountthe effect of the powder height in the standpipe of the hopper. The model proves to be adaptable for predicting operational conditions to avoid vxching by keeping constant powder height in the main standpipe wlth interstitial gas flow.     

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.     

Experimental validation of polyhedral discrete element model

The flow of polyhedral granular particles in a small 3D slice hopper is studied experimentally and computationally by applying the discrete element method (DEM). A high speed camera was used to obtain the experimental results. The experimental packing structure, flow behaviour, arching and discharging in the hopper are analysed and compared with the DEM results for three hopper half angles. Reasonable agreement is shown on the static packing, flow behaviour and hopper discharge rates. The critical orifice length at which flow ceases to be smooth is investigated and arching of the material around the orifice is demonstrated experimentally and computationally. Spherical particles of nearly identical volume and density to the average of the polyhedral particles are also tested and compared to the polyhedra. The DEM is shown to be reasonably adept at modelling the interactions between polyhedral particles in a system in which there are very many possible particle geometrical interactions. Further work should consider the cohesion between the particles and the particle and the wall. Simulations of a greater number of particles in different hopper geometries should also be explored.     

Flow of sphero-disc particles in rectangular hoppers—a DEM and experimental comparison in 3D

Flows of “sphero-disc” granular particles in a rectangular hopper are studied both experimentally using high-speed video recording and mathematically using the discrete element method (DEM). The flow behaviour of particles and their arching and discharging in the hopper are analysed and compared with the DEM results for three hopper openings. In general, good agreement is shown on particle static packing, the flow behaviour and hopper discharging rates and the arching effect when flow ceases due to an inadequate hopper outlet opening. Spherical particles with a similar volume to the disc-like particles are also tested and compared and a clear effect of particle shape on flow rates is shown. Although some minor discrepancies are shown, these are likely to be caused by the practical difficulties in matching the exact particle parameters between the simulations and the experiments. The DEM is shown to be a powerful tool to analyse the interactions between irregularly shaped particles and demonstrates a great potential in analysing detailed particle packing structure and flow patterns, which may lead to the elaboration of a novel method for hopper design. Further work will focus on developing DEM to model a wider range of particle shapes and hopper geometries, use of DEM for flow and structure analysis, and the development of more sophisticated measuring tools such as tomography to validate the DEM model.     

On the theory of arching in mass flow hoppers

Experimental evidence reveals an overdesign of the critical outlet widths in mass flow hoppers, when following the standard Jenike method for the estimation. This would be expected, because Jenike did neither account for the possibility that an arch across the outlet may slide along the wall, nor for the fact that the arch, in addition to its own weight, will have to sustain the weight of the powder above.In the present analysis a modified theory is presented, where these two factors are included. Furthermore, this theory includes simplified, purely analytical expressions for the distribution of active and passive stresses in the powder in the converging hopper section of a silo. The theory yields considerably less overdesign of the critical arching width of the hopper outlet than does the original Jenike theory. The still remaining overdesign probably stems from using a straight-line extrapolation of the failure function in the region of the low stresses. In order to overcome this element of uncertainty, the true course of the failure function must be actually measured down to very low stresses. An alternative principle of measurement, probably making this possible, is presented.In addition to yielding critical arching widths across the hopper outlet, the present theory also provides a means of assessing the possibility of the formation of stable powder arches in the region of transition between the parallel and the converging part of the silo.     

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     

Geldart-D 类颗粒在长立管-漏斗系统悬料的初始条件

The incipient condition of hang-up for three Geldart-D powders has been experimentally studied in a 21 m long standpipe hopper system. Experimental results show that the pressure gradient for hang-up to occur is independent of the materials height in the hopper and the diameter of orifice and equals to (dpw/dl)a, which can be predicted by Eq. (7). While the corresponding gas velocity in the standpipe equals to the incipient fluidized velocity of particles at the high pressure and can be predicted by Kwauk‘s equation.     

Determination of standpipe pressure profiles and slide valve orifice discharge coefficients on synthol circulating fluidized-bed reactors

A Synthol Circulating Fluidized-Bed (CFB) reactor utilizes a finely divided, reduced iron oxide catalyst to convert (CO + H₂) to gaseous and liquid fuels. The reactor consists essentially of a fast-fluidized bed with a hopper and standpipe providing a pressure seal sufficient to maintain a high catalyst inventory in the reaction zone. For optimum reactor operation, the catalyst must flow down the standpipe in the dense-phase fluidized-flow regime so giving maximum pressure recovery.Tests carried out on the Sasol 1 commercial reactors showed that the dense-phase flow regime could be maintained with minimal use of added aeration. Work carried out on a large cold-model hopper and standpipe showed that added aeration was vital in maintaining dense-phase flow and in achieving a high pressure recovery. The relatively high pressure operation of the commercial reactors and consequent low compression effect going down the standpipe is such that the entrapped aeration entering the standpipe is sufficient to prevent a flow regime transition to a packed bed. Orifice discharge coefficients determined on the commercial reactors and the cold model agreed closely with values reported in the literature.