分解炉内气固两相流动特性的数值模拟

采用Eulerian—Eulerian气固两相双流体模型、大涡模拟方法模拟气相湍流流动、颗粒动力学理论模拟颗粒相流动,数值模拟分解炉内气固两相流体的动力特性。用小波分析方法研究分解炉内气固两相湍流特性。在分解炉中心区域形成高浓度-高速度的上升颗粒流、在壁面区域形成高浓度、低速度的下降颗粒流,构成颗粒的内循环流动。     

轻烧氧化镁气流床煅烧炉热工过程及煅烧风量研究

轻烧氧化镁气流床煅烧炉热工行为研究是其热工参数优化、实现节能降耗的必需的基础性工作之一。基于Euler-Lagrange理论建立了某企业轻烧氧化镁气流床煅烧炉数值计算模型,籍此研究了炉内气固流动、传热及分解过程基本规律,并确定了现有产量下的适宜煅烧风量。结果表明：主炉内煅烧烟气旋流上升,温度中心高、壁面低;副炉内旋流效应骤减,温度趋于均匀;距离烟气入口4~18 m行程范围内,气固换热剧烈,物料快速分解,分解率达96%,而后于24 m处分解完全。将煅烧风量降至原有风量的91.22%、气料体积质量比降至1.46 Nm³/kg,不但提高了炉窑空间利用率,同时吨产品燃耗降低了8.78%。     

Characteristics and applications of flash metakaolins

This paper presents physical, chemical and mechanical characteristics of metakaolins obtained from an industrial flash calciner, in order to compare their properties with standard industrial metakaolin produced in a rotary kiln calciner. Three kaolins, with three levels of purity, were calcined by these two different methods to give six different metakaolins for the study. The results showed that the method of calcination did not affect the chemical composition of the metakaolins formed but did influence their physical properties and performance as a supplementary cementitious material when blended with Portland cement, and in geopolymer synthesis. Flash metakaolins have a lower water demand than rotary metakaolins, which can be explained by the morphological properties of the flash metakaolin, induced by the calcination process. Traditional rotary-calcined metakaolins tend to be angular layered particles, whereas flash metakaolins contain spherical particles. Mechanical test results showed that the two methods of calcination can lead to metakaolins with equivalent performance in the synthesis of construction materials.     

分解炉内煤矸石悬浮煅烧的数值模拟

煤矸石制备水泥辅助胶凝材料的应用研究对水泥行业的节能减排与大宗固废的高值利用均具有重要意义。本文以河北某地不同矿区的6种煤矸石为原料，采用XRD，热重等方法分析判断其化学成分和矿物组成，通过静态煅烧实验研究了其煅烧活化条件，并通过胶砂实验测定其胶凝活性。结果表明，煅烧温度和时间会影响产品的胶凝活性，煤矸石经过适当的热处理后，可用作辅助胶凝材料替代部分水泥熟料，在实现煤矸石资源化利用的同时，也为水泥工业碳减排提供了新路径。但煤矸石成分复杂，活化煅烧需要注意煅烧制度。采用CPFD（Computational Particle Fluid Dynamics）数值模拟方法模拟了分解炉内煤矸石传热、传质及化学反应，分析了不同工况下分解炉内气固两相流场。结果表明：入炉空气的温度较低时无法点燃煤矸石中的可燃组分，通过高温烟气点火和分级司料可有效解决这一问题。     

Measurement of residence time distribution in a rotary calciner

Rotary calcination is widely used in catalyst manufacturing and many other industrial processes. In this article, the influence of operational variables and material properties on the mean residence time (MRT), hold up, and axial dispersion was investigated in a pilot plant rotary calciner. Residence time distributions (RTD) of spherical, cylindrical, and quadrilobe catalyst particles were measured and contrasted. The Saeman's model was successfully applied to predict the experimental bed depth and the MRT as particles flowed through the calciner. It was observed that increasing the feed rate did not significantly affect the MRT. Results for the different particles indicated that cylinders and quadrulobes exhibited less axial dispersion than spheres due to the decreased flowability. A reliable method was developed to provide a reasonable RTD prediction in rotary calcination systems. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4068–4076, 2013     

高效喷旋分解炉SWC的开发研究

在和类典型分解炉特点的基础上开发了一种独具特色的高效分解炉SWC，通过优化研究，使炉内气体的喷腾、旋流效应得到较理想的配合，能够既保证良好的气固混合效果，为煤粉燃烧和碳酸盐分解反应提供良好的环境条件，又具有优良的低阻特性，该炉的料气停留时间比值超过国内现有的各同类炉型，可达到很高的空间利用率，有利于新型干法厂增产降耗。为我国资源状况复杂的实际情况和利用低质燃料提供了一种优良的选择方案，也为性能不理想的分解炉的改造提供了方向。     

A coupled fluid dynamic-discrete element simulation of heat and mass transfer in a lime shaft kiln

In the present study heat and mass transfer related to the chemical conversion of limestone to quicklime in a shaft kiln are investigated by means of a coupled numerical scheme for gas and solid phase transport. The three-dimensional transport of mass, momentum and energy in the gas phase is modelled by computational fluid dynamics (CFD), while a discrete element method (DEM) is employed for the mechanical movement and the conversion reactions of the solid material. The DEM simulation readily describes the mechanical and thermal particle-to-particle interactions of a large number of differently sized particles. Novel aspects addressed in this work are the simultaneous effects of inner particle heat-conduction and pore-diffusion of the gaseous product of the calcination reaction (CO₂) modelled by a shrinking core approach. Simulations of laboratory scale experiments of single reacting spheres show good agreement with the measured conversion rates. Simulations of an idealised vertical shaft kiln including pressure drop calculations demonstrate the suitability of the proposed approach for the modelling of industrial scale systems.     

Micromechanic modeling and analysis of the flow regimes in horizontal pneumatic conveying

Pneumatic conveying is an important technology for industries to transport bulk materials from one location to another. Different flow regimes have been observed in such transportation processes, but the underlying fundamentals are not clear. This article presents a three‐dimensional (3‐D) numerical study of horizontal pneumatic conveying by a combined approach of discrete element model for particles and computational fluid dynamics for gas. This particle scale, micromechanic approach is verified by comparing the calculated and measured results in terms of particle flow pattern and gas pressure drop. It is shown that flow regimes usually encountered in horizontal pneumatic conveying, including slug flow, stratified flow, dispersed flow and transition flow between slug flow and stratified flow, and the corresponding phase diagram can be reproduced. The forces governing the behavior of particles, such as the particle–particle, particle‐fluid and particle‐wall forces, are then analyzed in detail. It is shown that the roles of these forces vary with flow regimes. A general phase diagram in terms of these forces is proposed to describe the flow regimes in horizontal pneumatic conveying. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Mathematical modeling of an in-line low-NOx calciner

The reduction of the NO_x content in in-line-calciner-type kiln systems can be made by optimization of the primary firing in the rotary kiln and of the secondary firing in the calciner. Because the optimization of calciner offers greater opportunities the mathematical modeling of this reactor is very important. A heterogeneous, dynamic mathematical model for an in-line low-NO_x calciner based on non-isothermal diffusion-reaction models for char combustion and limestone calcination has been developed. The importance of the rate at which preheated combustion air was mixed into the main flow was particularly studied. The results of the simulations indicate that the external heat and mass transfer to the char particles is not limiting. Internal diffusion of O₂, CO, NO and CO₂ is important especially in the reducing zone and the first part of the oxidizing zone of the calciner and the internal heat transport limitation is significant for the endothermic limestone calcination. The rate at which preheated combustion air is mixed into the main flow directly influences the coal combustion rate, and thereby through the rate of heat release from combustion, it also influences the calcination rate and the temperature profile. The mixing rate has some influence on the CO concentration profile and an important influence on the overall degree of fuel-N to NO conversion.     

基于计算流体力学的气相烯烃聚合反应器模拟综述

气相聚合过程以流化床为核心反应器,其混合、传递和化学反应过程规律对工艺研发具有指导意义。计算流体力学是一种模拟流体流动的方法,可节省大量人力和物力并提供更全面的反应过程信息,在气固流态化领域得到广泛应用。基于计算流体力学的流态化模拟的难点在于如何建立能够恰当描述颗粒团聚过程的曳力模型,关于热量传递甚至聚合反应过程的模拟工作都是基于此发生的。随着计算机运算能力的提高,研究工业尺度的流化床反应器以及由粒径分布而带来的传递过程的影响可能成为模型广度及深度发展的方向。     

Calcination of phosphate in impinging streams. Part II. Phosphates with high organic matter and with pulverized coal

Calcination of a high organic matter phosphate and a phosphate containing pulverized coal up to 10 wt % was performed successfully in an impinging stream calciner. The results re-established previous conclusions that the present calciner is a useful device. A simplified model has been developed for exploring the effect of various operating parameters on the concentration of phosphate particles at the impingement plane of the streams. It also assisted us in explaining the effect of the phosphate flow rate on the efficiency of calcination. It was established that the calcination rate of phosphate is governed by the internal resistance of the particle to the heat transfer, which was consistent with previous results.     

Multiphase CFD Simulation of a Solid Bowl Centrifuge

This study presents some results from the numerical simulation of the flow in an industrial solid bowl centrifuge used for particle separation in industrial fluid processing. The computational fluid dynamics (CFD) software Fluent was used to simulate this multiphase flow. Simplified two‐dimensional and three‐dimensional geometries were built and meshed from the real centrifuge geometry. The CFD results show a boundary layer of axially fast moving fluid at the gas‐liquid interface. Below this layer there is a thin recirculation. The obtained tangential velocity values are lower than the ones for the rigid‐body motion. Also, the trajectories of the solid particles are evaluated.     

RFC分解炉的性能研究

分析了RFC分解炉内的气固流动、阻力特性以及炉内物料停留时间分布等 ,研究表明炉内大部分区域气体流动表现出明显的旋流流动特点 ,炉内湍流强度分布比较均匀 ,并沿轴向流动方向逐步增强。RFC分解炉的料气停留时间比值约为 3.7,如果考虑炉出口与C5进口之间的垂直连接管道 ,则物料依次通过分解炉系统的平均停留总时间约为 13.3s。RFC分解炉的 3次风旋流流动的阻力系数为 74,窑气喷腾流动的阻力系数为 13。研究结果与工厂实际生产情况完全符合 ,为改进分解炉的设计和优化工厂的操作提供参考。     

Dynamic modeling of a multiple hearth furnace for kaolin calcination

A dynamic model of a multiple hearth kaolin calciner has been developed and is presented in this article. This model describes the physical‐chemical phenomena taking place in the six furnace parts: the solid phase, gas phase, walls, cooling air, rabble arms, and the central shaft. The solid phase movement, in particular, is described by a novel mixing model. The mixing model divides the solid bed in a hearth into volumes and the distribution of their contents, after one full central shaft rotation, is identified by the pilot experiments. First, the model is validated by the industrial data, and then the dynamics of the multiple hearth furnace is studied by introducing step changes to the three manipulated variables: the feed rate, and the gas, and air flows supplied. The responses of the gas phase temperature and solid bed component profiles are analysed and the results are discussed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3683–3698, 2015     

An open-source population balance modeling framework for the simulation of polydisperse multiphase flows

Polydispersity is a challenging feature of many industrial and environmental multiphase flows, influencing all related transfer and transport processes. Besides their size, the fluid or solid particles may be distributed with respect to other properties such as their velocity or shape. Here, a population balance model based on the method of classes is combined with a multifluid solver within the open source computational fluid dynamics library OpenFOAM. The model allows for tracking the evolution of one or more size-conditioned secondary properties. It is applied to two different problems, the first being bubbly flow of air and water in a vertical pipe, where considering the velocity as a secondary property allows to resolve the size-dependent radial segregation. The second application is the gas phase synthesis of titania powder, where non-spherical particle aggregates appear whose shape is modeled through a collision diameter, leading to an improved prediction of the size distribution.     

Modeling the disintegration of cavitating turbulent liquid jets using a novel VOF–CIMD approach

In this article, a novel modeling approach capable of simultaneously tracking the events of cavitation, occurring within an injector nozzle, and the liquid jet breakup process, inclusive of spray formation, in the nozzle exterior is presented. A single fluid model, embedded with a Volume-of-Fluid (VOF)-based interface capturing methodology for monitoring the liquid–gas interface dynamics, is supplemented with a vapor transport model for predicting cavitation events triggered within the liquid. While the surface forces due to liquid–gas interfacial instabilities are modeled using a Continuum Surface Force model, a Cavitation-Induced-Momentum-Defect (CIMD) correction approach is employed to account for the effects of cavitation dynamics within the liquid flow. Liquid turbulence is modeled using the well-known RNG k–ε model inclusive of new source terms due to cavitation-induced turbulent kinetic energy production and dissipation. The combined VOF–CIMD methodology is validated by examining the effects of cavitation on the disintegration of turbulent planar liquid jets exiting a two-dimensional nozzle. Different flow Reynolds and Cavitation number configurations are tested. The results predicted by the model including those of the transport vapor dynamics and the liquid jet disintegration processes match, both qualitatively and quantitatively, very well with the available experimental data. In comparison with experimental observation, our model predicts different regimes of liquid jet behavior such as wavy jet, spray formation simultaneously with events of developing or super-cavitation. The numerical approach elaborated in this article can be extensively applied in the design and development of efficient spray applicators and other industrial fluidic devices.     

Numerical modelling of calcination reaction mechanism for cement production

Calcination is a thermo-chemical process, widely used in the cement industry, where limestone is converted by thermal decomposition into lime CaO and carbon dioxide CO₂. The focus of this paper is on the implementation and validation of the endothermic calcination reaction mechanism of limestone in a commercial finite volume based CFD code. This code is used to simulate the turbulent flow field, the temperature field, concentrations of the reactants and products, as well as the interaction of particles with the gas phase, by solving the mathematical equations, which govern these processes. For calcination, the effects of temperature, decomposition pressure, diffusion and pore efficiency were taken into account. A simple three-dimensional geometry of a pipe reactor was used for numerical simulations. To verify the accuracy of the modelling approach, the numerical predictions were compared with experimental data, yielding satisfying results and proper trends of physical parameters influencing the process.     

Improvement of the Uniformity of Radial Solids Concentration Profiles in Circulating Fluidized‐Bed Risers

In order to enhance the uniformity of the radial solids distribution and thereby the performance of industrial circulating fluidized‐bed (CFB) risers, an approach by using the air jet from the riser circumference is proposed. The Eulerian‐Eulerian computational fluid dynamics (CFD) model with the kinetic theory of granular flow is adopted to simulate the gas‐solids two‐phase flow in a CFB riser with fluid catalytic cracking (FCC) particles. The numerical results indicate that by employing the circumferential air jet approach under appropriate jet velocities, the maximum solids concentration in the near‐wall region can be greatly reduced, the entrance region can be shortened, and the uniformity of the flow structure can be significantly improved.     

CFD simulation of high-temperature effect on EHD characteristics in a wire-plate electrostatic precipitator☆

A computational fluid dynamics (CFD) model is carried out to describe the wire-plate electrostatic precipitator (ESP) in high temperature conditions, alming to study the effects of high temperature on the electro-hydrodynamic (EHD) characteristics. In the model, the complex interactions at high temperatures between the electric field, fluid dynamics and the particulate flow are taken into account. We apply different numerical methods for different fields, including an electric field model, Euler–Lagrange particle-laden flows model, and particle charging model. The effects of high temperature on ionic wind, EHD characteristics and collection effi-ciency are investigated. The numerical results show high temperature causes more significant effects of the ionic wind on the gas secondary flow. High viscosity of gas at high temperature makes particles follow the gas flow pattern more closely. High temperature reduces the surface electric strength, so that the mean electric strength weakens the space charging. On the contrary, there is an increase in the diffusion charging at high tem-perature compared with at low temperature. High temperature increases the ratio of mean drag force over mean electrostatic force acting on the particles which may contribute to a decline of collection efficiency.     

Modelling and simulation of heat and mass transfer in a packed bed of solid particles having high diffusion resistance

The heat and mass transfer processes between gas phase and solid particles are studied in a fixed bed throughflow dryer. The particles have a moderate size but high heat and mass transfer resistances. To describe the drying process, simple cell model approach is used. The transport resistances of the particles are taken into account by imbedding a Luikov-type distributed parameter model into each cell.

The relationships of this model to the cell model with lumped variables for the particles, as well as to the continuous two phase model are analysed. Numerical investigations show that moisture diffusion taking place inside the particles can control the drying process even at moderate Biot numbers.