CFD-DEM simulation of a pseudo-two-dimensional spouted bed comprising coarse particles

In the present study, computational fluid dynamics (CFD) and the discrete element method (DEM) are used in conjunction with the Eulerian-Lagrangian method to simulate a pseudo-two-dimensional spouted bed comprising coarse 6-mm particles. The open-source OpenFOAM code is used to solve the governing equations. The predicted vertical particle velocity along the bed axis, particle velocity profiles in the radial directi on, power spectral den sity, time-averaged particle velocity vectors, bed pressure drop, and solid flow pattern are evaluated and compared with existing experimental data. Good agreement is found between the CFD-DEM results and the measured data. It is also shown that the present CFD-DEM model accurately predicts the particle flow pattern throughout the bed. It is found that the drag force, solid stresses, and gravity play important roles in the CFD-DEM simulation of a spouted bed comprising coarse particles.

Numerical simulation of two-dimensional spouted bed with draft plates by discrete element method

A discrete element method(DEM)-computa-tional fluid dynamics(CFD)two-way coupling method was employed to simulate the hydrodynamics in a two-dimensional spouted bed with draft plates.The motion of particles was modeled by the DEM and the gas flow was modeled by the Navier-Stokes equation.The interactions between gas and particles were considered using a two-way coupling method.The motion of particles in the spouted bed with complex geometry was solved by com-bining DEM and boundary element method(BEM).The minimal spouted velocity was obtained by the BEM-DEM-CFD simulation and the variation of the flow pat-tern in the bed with different superficial gas velocity was studied.The relationship between the pressure drop of the spouted bed and the superficial gas velocity was achieved from the simulations.The radial profile of the averaged vertical velocities of particles and the profile of the aver-aged void fraction in the spout and the annulus were stat-istically analyzed.The flow characteristics of the gas-solid system in the two-dimensional spouted bed were clearly described by the simulation results.

Progress in research of process intensification of spouted beds:A comprehensive review

The development of intensification technology for spouted beds has become a current research focus,and an effective way to improve the efficiency of spouted beds is to reform their structure.Although numerous studies have been conducted on conventional beds,there are few reviews on the comprehensive application of intensification technology for spouted beds.In this paper,we comprehensively review the role of intensification technology in spouted beds for use in hydrodynamics,drying,desulfurization,pyrolysis,coating,biomass and waste gasification,and biomass drying from the perspective of experiment and simulation.Finally,potential problems and challenges in current spouted-bed research are summarized.

Numerical Simulation of Pressurized Spouted Fluidized Bed for Coal Semi-Gasification

Numerical simulation study is conducted for a pressurized spouted fluidized bed coal carbonizer, in which hydrodynamics of pressurized spouted fluidized bed, chemical reactions and energy balance are taken into account. The effect of operating conditions such as bed pressure, air and steam mass flow ratio, temperature on product compositions in the bed is investigated. According to the calculated results, bed pressure and bed temperature have the key effects on coal semi gasification.

Analysis of Gas-Solid Flow Characteristics in a Spouted Fluidized Bed Dryer by Means of Computational Particle Fluid Dynamics

In order to grasp the particle flow characteristics and energy consumption of industrial fluidized spouted beds,we conduct numerical simulations on the basis of a Computational Particle Fluid Dynamics(CPFD)approach.In particular,the traction model of Wen-Yu-Ergun is used and different inlet conditions are considered.Using a low-speed fluidizing gas,the flow state of the particles is better and the amount of particles accumulated at the bottom of the bed wall becomes smaller.For the same air intake,the energy loss of a circular nozzle is larger than that of a square nozzle.

Catalytic Partial Oxidation of Methane with Air to Syngas in a Pilot-Plant-Scale Spouted Bed Reactor

On the basis of hydrodynamic and scaling-up studies, a pilot-plant-scale thermal spouted bed reactor (50 mm in ID and 1500 mm in height) was designed and fabricated by scaling-down cold simulators. It was tested for making syngas via catalytic partial oxidation (CPO) of methane by air. The effects of various operating conditions such as operating pressure and temperature, feed composition, and gas flowrate etc. on the CPO process were investigated. CH4 conversion of 92.2% and selectivity of 92.3% and 83.3% to CO and H2, respectively, were achieved at the pressure of 2.1 MPa. It was found that when the spouted bed reactor was operated within the stable spouting flow regime, the temperature profiles along the bed axis were much more uniform than those operated within the fixed-bed regime. The CH4 conversion and syngas selectivity were found to be close to thermodynamic equilibrium limits. The results of the present investigation showed that spouted bed could be considered as a potential type of chemical reactor for the CPO process of methane.

Comparison of numerical simulations and experiments in conical gas–solid spouted bed

Flow behavior of gas and particles in conical spouted beds is experimentally studied and simulated using the twofluid gas-solid model with the kinetic theory of granular flow.The bed pressure drop and fountain height are measured in a conical spouted bed of 100 mm I.D.at different gas velocities.The simulation results are compared with measurements of bed pressure drop and fountain height.The comparison shows that the drag coefficient model used in cylindrical beds under-predicted bed pressure drop and fountain height in conical spouted beds due to the partial weight of particles supported by the inclined side walls.It is found that the numerical results using the drag coefficient model proposed based on the conical spouted bed in this study are in good agreement with experimental data.The present study provides a useful basis for further works on the CFD simulation of conical spouted bed.

Experiments and Modeling of the Preparation of Ultrafine Calcium Carbonate in Spouted Beds with Inert Particles

A novel reaction-drying process was carried out in a spouted bed reactor with inert particles and used to prepare ultrafine CaCO3 particles. Effects of concentrations of CO2 and Ca(OH)2, and reaction temperature on Ca(OH)2 conversion were experimentally investigated. The particle sizes and composition of CaCO3 produced were characterized with transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results indicated that ultrafine CaCO3 particles with mean size of 80 nm could be obtained with this novel process.By modifying the Arrhenius Equation and considering the Ca(OH)2 state, a kinetic model was established to describe the process in the spouted bed. The model parameters estimated from the reaction-drying experiments were found to fit well the experimental data, indicating the applicability of the proposed kinetic model.

Gas Residence Time Distributions in a Spouted Bed

In a spouted bed of 80mm in ID and 1700mm in height, the gas residence time distributions at different radial positions in both spout and annular area were measured with five different kinds of particles as spouting material, air as spouting gas, and hydrogen as tracer. The effects of superficial gas velocity, operating pressure, particle size and its category on gas residence time distribution were discussed. It was found that the gas velocity profile in spout was more uniform than that in annulus. It could be concluded that the gas flow in the spout could be treated as a plug-flow, while that in the annulus inhibited a strong non-ideal flow behavior. Increasing the superficial gas velocity and decreasing the operating pressure, the particle density and its size gave rise to spouting disturbance, thus the measured tracer concentrations vs. time curves fluctuated. The variances of residence time distribution curves could be taken as a measure of the gas fluctuation degree.

Optimization of Draft Tube Position in a Spouted Bed Reactor using Response Surface Methodology

Optimization of draft tube position in a spouted bed reactor used for treatment of wastewater containing low concentration of heavy metals is investigated in this paper. Response surface methodology is used to optimize the draft tube height, the draft tube width and the gap between the bottom of the draft tube and the inlet nozzle. It is observed that the draft tube with a height of 60 millimeter, width of 12 millimeter and the gap of 13 millimeter between its bottom and inlet nozzle, results in optimum value of minimum spouting velocity, measured 45 cubic centimeter per second (2.7 Liter per minute) .

CFD-DEM simulation of high density particles fluidization behaviors in 3D conical spouted beds

The spouted bed has been used in the coating process of high-density nuclear fuel particle.The particle fluidization behaviors in pseudo-2D and 3D spouted beds were simulated and validated.The effects of four independent variables(cone angle,particle density,inlet gas velocity,and particle loading)on particle fluidization behaviors in the 3D spouted bed were investigated systematically.The cone angle effect on fluidization mechanism was studied quantitatively first time.A new fluidization quality index was proposed based on the particle entrainment principle,and an extreme value was obtained when the cone angle was 60°,considered to be the optimum value for the 3D conical spouted bed.It was indicated the gas–solid contact efficiency can be kept up if the gas velocity was proportional to ρ_(p)^(0.65) and N_(p)^(0.78) when the particle density or loading was increased.These results will be useful for geometry and operation parameters design of the 3D conical spouted bed and helpful for developing the fluidization mechanism of high-density particles.

A new method for identifying flow pattern of spouted fluidized bed by coupling Hilbert-Huang transform characteristics of differential pressure signals in different zones

On a cold spouted fluidized bed,this study compares the characteristic differences in intrinsic mode function(IMF)energy and Hilbert–Huang spectrum between the spout zone and annulus zone under different combinations of spouted gas and fluidized gas flow rates for five typical flow patterns.The energy distribution characteristics under different flow patterns are also analyzed.The Hilbert–Huang spectrum and IMF energy of pressure difference signals exhibit distinct variations in different zones as the flow pattern changes.Moreover,there exists a correlation between the energy in the middle-frequency range and the flow pattern.Leveraging the K-means algorithm,the middle-frequency range energy of IMFs in the spout zone and annulus zone is subjected to clustering analysis,leading to the identification of partition boundaries for each flow pattern.Based on this,a flow pattern identification method of spouted fluidized bed coupled with middle-frequency range energy in spout zone and annulus zone is proposed,which has very high identification accuracy.

A Preliminary Research on a Plasma Spout-Fluid Bed Reactor

A laboratory-scale plasma spout-fluid bed reactor with a 10 kW DC plasma torch was developed and tested using quartz sand particle and rice hull. The preliminary experimental results including particle recirculation and attrition, bed temperature distribution and stability, as well as biomass gasification system energy balance were presented in this paper. Research results indicated that plasma spout-fluid bed reactor may be a technically feasible reactor for carbonaceous organic material gasification.

非球形湿颗粒导向管喷动流化床流动特性

实际工业生产中颗粒多为非球形颗粒,对颗粒形状效应和液相作用机制的研究不足,是导向管喷动流化床在颗粒涂层改性、包膜等工业应用的关键限制因素。选取粒径、密度相似的球形和圆柱形非球形颗粒为实验物料,对比两种颗粒在不同气速和雾滴引入量下的压力脉动信号频谱分析、信息熵分析,并结合床内气固流动对流型进行划分,绘制非球形湿颗粒流动相图,进而探究喷动流化过程中颗粒形状效应及液相作用机制。相比于球形颗粒,粒径、密度相似的非球形颗粒有较小的最小喷动速度,在喷动过程中有两个及以上较低的主频峰且信息熵较大,显示出非球形颗粒在系统内较高的混乱程度,颗粒之间摩擦、碰撞等降低了导向管内颗粒的固体循环速率。液体的引入增大了环形区颗粒间液桥力,使最小流化速度变大,但液体挥发引起喷动气量增大,使最小喷动速度与最小喷动流化速度减小。在喷动流化流型下引入液体,球形颗粒导向管两端压降ΔpDT的脉动主频降低,而非球形颗粒ΔpDT的主频升高。而且非球形颗粒黏附液体后频谱分析结果显示幅值较大的单一主频峰,表明非球形湿颗粒压力脉动规律性的增强。

咖啡豆红外喷动床干燥对其粉末物性品质、干燥能耗及挥发性成分的影响

为获得高品质干燥咖啡豆,采用红外喷动床组合干燥技术对咖啡豆进行干燥处理,研究不同进口温度和进口风速对咖啡粉色泽、堆积密度、休止角、得粉率、持水能力和水溶性指数、微观结构、干燥能耗及挥发性成分的影响。结果表明,提高进口温度和进口风速可以加快干燥速率,缩短干燥时间,降低干燥能耗。采用顶空固相微萃取-气相色谱质谱联用共检测出7大类(酸类、酯类、醛类、醇类、酮类、杂环类及其他类)挥发性化合物,其中酸类、酯类、醇类、杂环类4类为咖啡豆主要挥发性化合物且含量较高。综合对比得出最佳干燥条件为进口温度75℃,进口风速7.5 m/s,在此条件下,L*值和堆积密度取得最大值,分别为106.59和0.65 g/mL,休止角取得最小值36.87°,得粉率、持水能力和水溶性指数取得最大值,分别为43.43%、5.4 g/g和41.27%,干燥能耗取得最小值336.53 kJ/g,形态结构保存较为完整,壁面光滑平整,检测到的挥发性成分种类最高达70种,含量为38 487.028 49 ng/g(以干基计),咖啡豆综合品质最佳。该研究可为红外喷动床干燥技术在咖啡豆干燥加工及工业化生产中的应用提供参考。

中试脉冲喷动床微波冻干山楂干燥特性与品质特性研究

该文针对传统冻干(conventional freeze-drying,CFD)存在的干燥周期长、能耗大及生产成本高等问题,探究中试脉冲喷动床微波冻干(pulse-spouted bed microwave freeze-drying,PSBMFD)山楂的干燥特性与品质特性,分析代替传统冻干进行商业化应用的可行性。以CFD山楂作为对比,研究了两者干燥时间、能耗、山楂品质及干燥均匀性等方面的差异。结果显示,和CFD相比,中试PSBMFD能耗降低72.49%,干燥周期减少62.39%,较好地保留山楂原有风味,所得山楂产品具有多孔结构和较高质构(硬度20.83 N);在水分含量、色差、收缩率方面,中试PSBMFD实现了山楂产品较高的均匀性(>90%);在营养保留方面,中试PSBMFD山楂具有较高的总酚含量[37.03 mg/g干基,以没食子酸当量(gallic acid equivalent,GAE)计]与抗氧化能力。该中试实验结果为PSBMFD商业化提供了有效的理论基础和技术支持。

Numerical simulation of uranium tetrafluoride fluorination in a multistage spouted bed using the improved CFD-DEM chemical reaction model

A CFD-DEM reaction coupling model was established to simulate UF_(4) fluorination process,in which heat and mass transfer,heterogeneous chemical reaction,and particle shrinkage model were considered.The gas behavior was described by the conservation laws of mass,momentum,and energy.The solid phase is modeled with the discrete element method,considering the gas-solid interphase force,contact force,heat transfer,and chemical reaction models based on the discretized surface.Each particle can be individually tracked and associated with specific physical properties.The proposed CFD-DEM reaction coupling model based on particle shrinking reaction model with discretized surface was validated by the experimental and literature results at first.Then a multistage conical spouted bed was proposed and the process of UF_(4) fluoridation reaction in it was investigated.The fluidization characteristics and the con-centration distribution of gaseous products in the spouted bed with an extended gas velocity range were obtained and analyzed.In addition,the effects of different parameters,such as superficial gas velocity,temperature,fluorine concentration,on fluoridation rate and the fluorine conversion rate were inves-tigated based on the proposed CFD-DEM reaction coupling model.The results obtained in this work are beneficial for method development of the chemical reaction simulation research in particle scale using the CFD-DEM model,and useful for operation and equipment parameters design of the uranium tetra-fluoride fluorinate industrial process in the future.

Hydrodynamic behaviour of Cellets^(TM)(Ph.Eur./USP)in a spouted bed using image processing method

The hydrodynamic behaviour of the spouted bed in the pharmaceutical industries has been found to be less addressed.The present paper has focused on the hydrodynamic characteristics of a spouted bed where the Cellets^(TM)(Ph.Eur./USP)is adopted as the bed material.Experiments are carried out with three different static bed heights(H_(0))of shallow depth(2D_(i)≤H_(0)<3D_(i))using two different particle sizes.The spouted bed employed with D_(i)/D_(0) of 5 has given the experimental information on external spouting(Ues)by mapping the pressure drop,and fountain height(H_(f))against the superficial gas velocity(U_(g))is rep-resented with the image contours,which show the intrinsic behaviour.All the 1000 μm and 700 μm particles have been found to exhibit symmetric and asymmetric spouting.With increasing U_(g),the fully suspended particles are limited to a certain height in the freeboard region due to the gas-solid cross-flow,which implies the clusters have identified with the image processing method.

Axial gas mixing in conical spouted beds with high density particles

Conical spouted beds operating with high-density particles(ρp>2500 kg/m^(3))have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors.In the literature,the number of axial gas mixing studies in conical and conical-cylindrical spouted beds is very limited and all axial mixing studies were carried out with relatively light particles(ρp≤2500 kg/m^(3)).Therefore,the objective of this study was to generate experimental data that can be used to explain the gas axial mixing behavior in conical spouted beds operating with both low-and high-density particles.Experiments were conducted in two(γ=30°,60°)conical spouted beds with three different types of particles:zirconia(ρp=6050 kg/m^(3)),zirconia toughened alumina(ρp=3700 kg/m^(3))and glass beads(ρp=2460 kg/m^(3)).In order to be able to compare experimental data obtained at different conditions,a 1-D convection-diffusion gas mixing model originally developed by San Joséet al.(1995)was implemented to determine the axial dispersion coefficients.The results show that the axial dispersion coefficients range between m^(2)/s and m^(2)/s,increase with superficial gas velocity and are higher than the corresponding dispersion coefficients of fixed beds,lower than the dispersion coefficients of fluidized beds and in the same range with the cylindrical spouted beds reported in the literature.The corresponding Peclet numbers were in the range of 0.6–7.8 for all operating conditions and slightly higher Peclet numbers were obtained with glass beads indicating the relative importance of gas convective transport over gas dispersion for light particles compared to heavy particles.