Effects of ellipsoidal and regular hexahedral particles on the performance of the waste heat recovery equipment in a methanol reforming hydrogen production system

Hydrogen production from methanol has attracted attention due to its wide range of raw material sources and mature technology. Using waste heat of industrial high temperature solid particles like blast slag and steel slag etc. To provide vaporization heat and reaction heat for the reaction between methanol and water is an emerging technology for hydrogen production from methanol, which can save additional thermal energy resources. Herein, the performances of equipment that uses the waste heat of ellipsoidal and regular hexahedral particles to provide a heat source for methanol to hydrogen were explored by the DEM-CFD method. Compared with spherical particles of the same equivalent diameter, ellipsoidal and regular hexahedral particles have poor fluidity in the stagnant area, and the empty area is enlarged and irregular in shape. The average velocity peaks of the ellipsoidal and regular hexahedron particles are larger than those of spherical particles, and the overall mean velocity fluctuation of ellipsoidal particles is similar to that of spherical particles while the regular hexahedron particles' is larger. The average temperature drop rate of the ellipsoidal and regular hexahedral particles is slower than that of spherical particles, the uniformity of temperature distribution is worse than that of spherical particles. The ellipsoidal and regular hexahedral particles’ average effective heat transfer coefficient is smaller than that of spherical particles, and the heat transfer effect is weaker than that of spherical particles. The effective heat transfer coefficient of ellipsoidal particles is 2.95 W/(m⁻²∙K⁻¹) lower than that of spherical particles and the effective heat transfer coefficient of hexahedral particles is 6.09 W/(m⁻²∙K⁻¹) lower than that of spherical particles. Therefore, compared with the spherical particles of the same equivalent diameter, ellipsoidal and regular hexahedral particles produce less hydrogen.     

Improved utilization of desiccant material in packed bed dehumidifier using composite particles

Solid desiccant dehumidifiers are widely used in drying processes. In most of these dehumidifiers, the desiccant material is used as packed bed of granule or spherical particles. Investigations of intra-particle heat and mass transfer processes has shown that the entire portion of the particle is not participating effectively during adsorption as well as desorption processes [Pesaran AA, Mills F. Moisture transport in silica gel packed beds-I. Theoretical study. International Journal of Heat and Mass Transfer 1987; 30: 1037–49]. This is because the diffusion rate is very small compared to that of convection. In the present work, a new desiccant composite particle, in which the unutilized portion of the spherical desiccant particle is replaced with an inert particle, is proposed. By replacing the conventional particles with composite particles for the same mass of desiccant material, the available area for heat and mass transfer increases and more amount of desiccant material is effectively utilized. Further, in order to ascertain the improvement in the performance of the desiccant bed using the composite particles, various factors like thermo-physical properties of the inert material, composite particle thickness ratio, bed configuration, bed volume, the pressure drop and the increase in total adsorbed or desorbed mass have to be considered. In view of this, a theoretical investigation of the operation of vertical solid desiccant packed bed dehumidifier, using both conventional silica gel particles as well as the new proposed composite silica gel particles has been reported. A modified solid side resistance (MSSR) model is developed for the prediction of intra-particle temperature and water content profiles. Results of the present theoretical models, when applied to packed bed of conventional silica gel particles, agree well with the experimental results from the literature for both desorption and adsorption processes. From the theoretical results, more utilization for the desiccant material is obtained when ordinary silica gel particles are replaced by composite silica gel particles. For the same amount of desiccant material and same mass flow rate of air, using particles of 0.2 thickness ratio the pressure drop decreases by about 60% for the case investigated. In addition, an increase of about 11.07% and 20.46% in total mass adsorbed and desorbed respectively are obtained. At the time when adsorption process ends, an increase of 15.5% in the bed effectiveness has been obtained. In addition, the expected improvement in total mass adsorbed and desorbed is observed to be dependent on the inert material thermo-physical properties for thickness ratio less than 0.5. An optimization technique relating the composite particle design, resulting savings in pressure drop and bed volume increase is proposed.     

Flow characteristics of circulating gas–solid fluidized bed heat exchanger with multiple vertical pipes

Flow characteristics of a circulating gas–solid fluidized-bed heat exchanger with multiple vertical pipes were studied. The glass beads were circulated inside the vertical pipes of the heat exchanger with fluidizing air. The pressure drop and the circulation rate of solid particles were measured. In addition, one-dimensional velocity distribution of solid particles and the pressure distribution inside the vertical pipe were analysed. The prediction on the pressure drop with the circulation of solid particles was proved to be reasonably accurate by comparing with the measured results. © 1998 John Wiley & Sons, Ltd.     

Experimental study on factors that influence the diameter of dry granulated particles

The development of heat recovery methods for dry granulation processes from blast furnace slag in the iron and steel industry is limited because of the high consumption of granulation energy during these processes. To determine the factors that influence the diameter of granulated particles, a paraffin test platform for gas quenching granulation was established. The influences of air velocity, air flow rate, liquid mass flow rate, and liquid pipe diameter on the final particle size and mass distribution were studied. Experimental results showed that the final particle size decreased (from 1.07 mm to 0.81 mm) with increasing air velocity (from 28.3 m/s to 113.2 m/s). However, when air velocity was higher than 60 m/s, its influence on particle diameter decreased significantly. The experimental data were analyzed using SPSS Statistics software, which indicated that the effect of air velocity on particle diameter was the most significant, followed by those of air flow and liquid pipe diameter. The effect of liquid mass flow was the least significant.     

A study of solid particle flow characterization in solar particle receiver

The solid particle receiver (SPR) is a direct absorption receiver in which solar energy heats a curtain of falling ceramic particle to a temperature in excess of 1000 °C. A small scale test platform was built to investigate particle flow properties. The curtain was comprised of approximately 697 μm ceramic particles that were dropped within the receiver cavity of the test platform. Tests were conducted to experimentally determine the distribution of particles velocity, curtain thickness, and curtain opacity along a drop length of approximately 3 m. Velocity data were measured using a high speed digital camera to obtain images of the particle flow at 1000 frames per second with an exposure time of 100 μs. Five mass flow rates ranging from 1 kg/s-m to 22 kg/s-m were examined, and it was found that all flows approached a terminal velocity of about 6-7 m/s in a vertical drop distance of 3 m. The experimental results were validated with computational results and were found in excellent agreement with the simulation results. In addition, a similar study was performed with various sizes of the particles to better understand how the particle flow characteristics were affected by the size of the particles.     

Theoretical approach for a pressure drop in two-phase particle-laden flows

The purpose of this research is to develop an analytical model for a pressure drop per unit pipe length due to the turbulence modulations of a carrier phase which results from the presence of a dispersed phase in various types of diluted two-phase flows. The wake behind a particle, a particle size, the loading ratio and the density difference between two phases of a particle-laden flow were considered as significant parameters, which have an influence on the turbulence of a particle-laden flow, and the relative velocity of the laden particles was calculated by using a terminal velocity. The frictional pressure drop was formulated by using the force balance in the control volume by considering the shear stresses due to the presence of particles and an analogy of the shear stresses in the solid surfaces. The numerical results show a good agreement with the available experimental data and the model successfully predicted the mechanism of the pressure drop in the particle-laden flows.     

柴油机喷油器喷孔磨粒流加工过程中颗粒形状影响的数值模拟

以喷油器喷孔为对象,基于欧拉-拉格朗日法和磨蚀模型对磨粒流研磨过程中的流场及颗粒运动进行了数值模拟,分别得出采用不同形状颗粒时的动压力、湍流动能、颗粒速度、磨蚀速率,探究了颗粒形状因子对研磨结果的影响。研究表明,磨蚀速率同颗粒形状因子成反比关系,采用形状因子较小的颗粒可加快研磨速度,形状因子为0.3的颗粒在喷孔入口处的磨蚀速率最大,比形状因子为0.7的磨蚀速率高出86.6%,颗粒形状对工件表面的磨蚀位置也有较大影响。     

Forced Convective Heat Transfer in a Porous Plate Channel

INTRODUCTIONHeattransferenllancen1enttechniquesplayaveryimportantroleintllermalcontroltechnologies1lsedwithnlicroelectronicchips,powerfullasermirrors,aerospacecraft,thermalnuclearfusion,etc.Itiswidelyrecognizedthattl1eheattransfercanbein-creasedbyil1creasingthesurfaceareaincontactwiththecoolant.TuckermanandPease[1,2]pointedoutthatforlaminarflowinconfinedchannels,theheattransfercoefficientisinverselyproportionaltothewidthofthechannelsincethelimitingNusseltnum-berisconsta11t.Theybuiltawate…     

Forced flow evaporative cooling of a volumetrically heated porous layer

In this paper, the temperature rise and pressure drop experienced by an evaporating coolant flowing through a volumetrically heated porous layer have been studied experimentally. Experimental data for the temperature distribution and the two-phase pressure drop along the direction of flow is obtained for water flowing through layers of inductively heated steel particles. Spherical steel particles varying in size from 590 to 4763 μm are used to form porous layers in 5 and 10 cm dia. glass jars. In these experiments the data are obtained for layer depths varying from 9 to 81 cm, volumetric heat generation rate varying from 1.44 to 44.0 W/cm³ and the mass flow rate of water varying from 510 to 18200 kg/m² h.A theoretical model for the temperature profile in the liquid region and the two phase region has been made and is found to compare well with the measurements. Vapor channels are observed to form in porous layers of particle diameter less than 1600 μm. Separate semi-theoretical models have been developed for the two phase pressure drop in particles with diameter less than and greater than 1600 μm.     

Convective heat transfer of horizontal spherical particle layer heated from below and cooled from above Part II: Effect of thickness of particle layer

Convection heat transfer and pressure drop measurements were performed with a rectangular duct, having a cooled upper and a heated lower surface, which was packed with spherical particles. Air was used as the test fluid and four kinds of spherical particles having different diameters and thermal conductivities were used as the packing materials. The ratio of the diameter of the spherical particle to the distance between the cooled and heated surfaces, d/H, was varied from 0.173 to 1. The thermal conductivity of the particle layer was also measured under the still air condition. The thermal conductivity of the particle layer was not affected by the value of d/H. In the case of the one-stage arrangement of spherical particles (d/H = 1), the flow resistance took on a remarkably small value compared with the flow resistance of a homogeneous spherical particle layer. Moreover, the flow resistance of the particle layer formed with some layers of particles could be predicted by combining the flow characteristics of the one-stage particle layer and that of the homogeneous spherical particle layer. The heat transfer coefficient of the particle layer was larger than that of turbulent air flow on a flat plate. At a constant superficial air velocity, there existed a value of d/H which gave a maximum value of the average heat transfer coefficient. Nondimensional heat transfer correlation equations were derived in terms of parameters expressing the average characteristics of the spherical particle layers. © 1998 Scripta Technica, Heat Trans Jpn Res, 26(3): 176–192, 1997     

Unsteady thermal flow analysis in a heat regenerator with spherical particles

Heat regenerator occupied by regenerative materials improves thermal efficiency of regenerative combustion system through the recovery of sensible heat of exhaust gases. By using one-dimensional two-phase fluid dynamics model, the unsteady thermal flow of regenerator with spherical particles, were numerically analysed to evaluate the heat transfer and pressure drop and to suggest the parameter for designing heat regenerator. It takes about 7 h for the steady state in the thermal flow of regenerator, where heat absorption of regenerative particle is concurrent with heat desorption. The regenerative particle experiences small temperature fluctuation below 10 K during the reversing process. The thermal flow in heat regenerator varies with inlet velocity of exhaust gas and air, configuration of regenerator and diameter of regenerative particle. As the gas velocity increases with decreasing the cross-sectional area of the regenerator, the heat transfer between gas and particle enhances and pressure losses increase. As particle diameter decreases, the air is preheated higher and the exhaust gases are cooled lower with the increase of pressure losses. At the same exhaust gases temperature at the regenerator outlet, the regenerator length need to be linearly increased with inlet Reynolds number of exhaust gases. It is confirmed that inlet Reynolds number of exhaust gases should be introduced as a regenerator design parameter. Copyright © 2002 John Wiley & Sons, Ltd.     

Comparison of conventional and spherical reactor for the industrial auto-thermal reforming of methane to maximize synthesis gas and minimize CO2

Auto-thermal reforming (ATR), a combination of exothermic partial oxidation and endothermic steam reforming of methane, is an important process to produce syngas for petrochemical industries. In a commercial ATR unit, tubular fixed bed reactors are typically used. Pressure drop across the tube, high manufacturing costs, and low production capacity are some disadvantages of these reactors. The main propose of this study is to offer an optimized radial flow, spherical packed bed reactor as a promising alternative for overcoming the drawbacks of conventional tubular reactors. In the current research, a one dimensional pseudo-homogeneous model based on mass, energy, and momentum balances is applied to simulate the performance of packed-bed reactors for the production of syngas in both tubular and spherical reactors. In the optimization section, the proposed work explores optimal values of various decision variables that simultaneously maximize outlet molar flow rate of H₂, CO and minimize molar flow rate of CO₂ from novel spherical reactor. The multi-objective model is transformed to a single objective optimization problem by weighted sum method and the single optimum point is found by using genetic algorithm. The optimization results show that the pressure drop in the spherical reactor is negligible in comparison to that of the conventional tubular reactor. Therefore, it is inferred that the spherical reactor can operate with much higher feed flow rate, more catalyst loading, and smaller catalyst particles.     

一体化外置式换热器的物料流动特性

对循环流化床锅炉一体化外置式换热器在单边运行时的物料流动特性进行了冷态试验研究.结果表明:该外置式换热器具有很好的自平衡特性;各仓室流化风速的改变会引起颗粒夹带速率及各仓室压力分布的变化,通过调节各仓室的流化风速可以很好地控制进入外置式换热器和回料密封的物料流量.同时,还建立了孔口两侧压差与通过孔口处的固体流率之间的经验关系式,并定义了孔口流量系数.试验数据表明:所建立的关系式可以很好地用于预测固体流率与孔口压降之间的关系.     

Numerical investigation of the solid particle erosion rate in a steam turbine nozzle

A numerical investigation of solid particle erosion in the nozzle of 300 MW steam turbine is presented. The analysis consists in the application of the discrete phase model, for modelling the solid particles flow, and the Eulerian conservation equations to the continuous phase. The numerical study employs a computational fluid dynamics (CFD) software, based on a finite volume method.The investigation permits us to know the influence of the parameters such as: particle diameter, impact angle, particle velocity and particle distribution on the erosion rate in the surface of the nozzle. These parameters are analyzed to different operational conditions in the turbine.The results show the eroded zone which increases the throat area through the nozzle provoking changes in the operation conditions. When the throat area increases the turbine demands an increase of steam flow to maintain the power supply. On the other hand, it is shown that the solid particles flow cause the most severe the erosion rate whereas the steam mass flow rate is the most sensitive parameter. Finally it is obtained that the erosion rate decreases as the diameter of the particle increases in a nearly linear form.     

贾汪 PFBC_CC 中试电站异形煤仓设计和试验

借助詹尼克整体流动斗仓设计方法对实际斗仓中的几个特殊问题进行分析和简化处理,研究了在一个异形粒煤斗仓内产生整体流的取形问题,并通过模型试验验证了某结果的正确性。,     

Analysis of mass loss of a coal particle during the course of burning in a flow of inert material

This paper is an attempt to explain the role of erosion during the process of coal combustion in a circulating fluidized bed. Different kinds of carbon deposits found in Poland, both bituminous as well as lignite with the particle of 10 mm in diameter were the subject of the research. According to many publications it is well known that erosion plays a significant role in coal combustion, by changing its mechanism as well as generating an additional mass loss of the mother particle. The purpose of this research was to determine the influence of an inert material on an erosive mass loss of a single coal particle burning in a two-phase flow. The determination of the influence of a coal type, the rate of flow of inert material and the temperature inside the furnace on the erosive mass loss of burning coal particle was also taken into consideration. The results obtained indicate that the velocity of the erosive mass loss depends on the chemical composition and petrographic structure of burning coal. The mechanical interaction of inert and burning coal particles leads to the shortening of the period of overall mass loss of the coal particle by even two times. The increase in the rate of flow of the inert material intensifies the generation of mass loss by up to 100%. The drop in temperature which slows down the combustion process, decreases the mass loss of the coal particle as the result of mechanical interaction of the inert material. As was observed, the process of percolation plays a significant role by weakening the surface of the burning coal.     

Experimental and CFD study of wall effects on orderly stacked cylindrical particles heat transfer in a tube channel

In this study, the flow and heat transfer characteristics of regularly arranged cylindrical particles in a bed with bed-to-particle diameter ratio of 2.65 (The particle and bed diameter are 25 and 66 mm respectively and the bed height is 200 mm) have been studied in two different arrangements of particles. The first layout is coaxial particles which embrace 8 layers and 3 equilateral cylindrical particles in each layer); the second arrangement is similar to the first one but the intermittent layers have been rotated 60^o. Three dimensional CFD simulation of air flow through these arrangements of particles in bed have been carried out by the standard κ-ε turbulence model with using of FEMLAB (Multiphysics in MATLAB) software version 2.3. For two configurations, comparisons between CFD results and experimental data have been drawn. Our results have been compared with prediction of empirical correlations for pressure drop of flow through the bed. The heat transfer CFD results were validated by naphthalene sublimation mass transfer experiments. The particle Nusselt number was obtained by using analogy between mass and heat transfer. A good quantitative and qualitative agreement between hydrodynamic of CFD simulation and experimental results was gained for both arrangements. The model predicts pressure drop of channel with two arrangements, coaxial and non-coaxial particles with an average error of 10% and 15%, respectively. Moreover, the CFD simulation has predicted the average particle Nusselt numbers of these two arrangements with an average quantitative error of 7% and 14%. Furthermore, the influence of wider range of Reynolds number (2500–6800) on particle Nusselt number has been investigated.     

Numerical Investigation on the Two Phase Flow Behaviors in Supercritical Water Fluidized Bed with Swirling Flow Distributor

ABSTRACT

Supercritical water fluidized bed reactor is a promising in the clean and efficient conversion of coal, and the distributor is one of the key component for the heat and mass transfer enhancement. However, the optimization study for the distributor in supercritical water fluidized bed reactor has been seldom conducted due to the special thermal properties of supercritical water. In this work, the swirling flow distributor was designed for its optimization for heat and mass transfer inside a supercritical water fluidized bed reactor. The swirling flow can be generated by the concentric circle or triangle type hole distribution in distributor with 0 or 45° intersection angle between the fluid inlet velocity direction and the distributor plane. The computational particle fluid dynamics (SCWFB) method, which has quick calculating speed and high accuracy, was used in this work to study the particle-fluid two-phase flow behaviors inside SCWFB with swirling flow distributors. Investigations were made to reveal the influence of the hole distribution type and intersection angle on the bed pressure drop and particle volume fraction characteristics. The results showed that the triangle type distributor with 45° intersection angle has the best fluidization performance. The conclusions drawn may has potential application for continuous and stable operation of supercritical water fluidized bed reactor for coal gasification.     

气固两相Y型分支管网流量分配特性的试验研究与数值模拟

在水平Y型分支管道中,采用压缩空气作为输送动力,小米作为输送介质进行气力输送试验,对分支管道的固体流量分配特性进行了研究.试验表明,变动支管与主管中轴线夹角与气体表观速度对固相分配特性具有较大影响.同时,采用Euler-Lagrange两相流研究方法,固相采用离散相(DPM)模型,采用Fluent软件对3种不同夹角的Y型分支管内气固两相流动进行了数值模拟.模拟结果较好地预估了颗粒在分支处的流动形态、颗粒在分支管内的运动轨迹,以及重新实现颗粒相流场均匀分布所需的距离.通过对分支管内固体颗粒质量分配的数值模拟结果与试验结果比较,发现两者之间相对误差较小.     

Research of the gas-solid flow character based on the DEM method

Numerical simulation of gas-solid flow behaviors in a rectangular fluidized bed is carried out three dimensionally by the discrete element method (DEM). Euler method and Lagrange method are employed to deal with the gas phase and solid phase respectively. The collided force among particles, striking force between particle and wall, drag force, gravity, Magnus lift force and Saffman lift force are considered when establishing the mathematic models. Soft-sphere model is used to describe the collision of particles. In addition, the Euler method is also used for modeling the solid phase to compare with the results of DEM. The flow patterns, particle mean velocities, particles’ diffusion and pressure drop of the bed under typical operating conditions are obtained. The results show that the DEM method can describe the detailed information among particles, while the Euler-Euler method cannot capture the micro-scale character. No matter which method is used, the diffusion of particles increases with the increase of gas velocity. But the gathering and crushing of particles cannot be simulated, so the energy loss of particles’ collision cannot be calculated and the diffusion by using the Euler-Euler method is larger. In addition, it is shown by DEM method, with strengthening of the carrying capacity, more and more particles can be schlepped upward and the dense suspension upflow pattern can be formed. However, the results given by the Euler-Euler method are not consistent with the real situation.