基于EMMS的循环流化床三维全循环CFD模拟

对于循环流化床内气固两相流动,三维全循环计算流体力学(Computational Fluid Dynamics,CFD)模拟是最直观可靠的模拟方式。然而,受计算资源和模型的限制,目前的模拟工作大多对构体进行简化,如仅考虑提升管段,或采用二维长方形代替三维构体,或对实际装置几何尺寸进行成比例缩小等等。对几何结构的简化,忽略了出入口、周向结构或返料装置等因素对流动行为的影响,因而计算结果不能准确反映真实流场。采用基于结构的多流体模型(the Structure-dependent multi-Fluid Model,SFM)耦合能量最小多尺度模型(the Energy-Minimization Multi-Scale model,EMMS)修正曳力,完全依据实验参数建立构体和设定边界条件,对中试规模循环流化床进行三维全循环动态模拟。计算结果表明,三维全循环模拟不仅能定性预测快速流态化中典型的上稀下浓和边壁浓中心稀的非均匀分布,定量对比颗粒循环通量、浓度和速度信息与实验值也吻合较好。由于三维全循环模拟不存在几何结构简化,能直接表征真实工况和流场,特别适合于结构复杂的大尺寸工业装置模拟。     

加压条件下气固流化床流动特性的CFD模拟研究

本文利用CFX模拟软件,考察了加压流化床内的三维流动特性,分析压力对床层沿床压降、固含率轴径向分布、颗粒速率以及气泡行为等方面的影响。结果表明,升高压力能够提高床层膨胀高度,降低床层固含率。在床层底部,升高压力对中心区域和壁面附近的固含率都会有明显影响,而在床层中部则主要使壁面附近固含率降低。同时,升高压力会明显增加床层底部的颗粒向上和向下速率,并且会使床层内气泡数量增加,气泡会出现频繁的合并与破裂。     

微机械气体红外探测器的CFD模拟

概要地介绍了一种可工作于室温环境下的微型气体红外探测器,它基于气体吸收红外辐射后以无辐射去激励方式产生一系列热效应的物理基础,可获得包含红外辐射源信息的信号.为深入研究热效应所产生的微热信号对器件整体性能的控制和影响,建立了相应的流体力学(CFD)模型,通过数值分析方法,获得了气体物质微观行为随红外辐射源辐射特性的变化关系.     

微气体传感器结构设计和优化

设计了一种新型微气体传感器的电极结构,这种共平面型电极结构消除了加热器产生的磁场对测量信号的干扰。利用铂作为电极材料,SiO2作为隔热层,利用有限元软件分析优化,当SiO2,Si的厚度分别为50,250μm,加热电极的宽度、信号电极的宽度和间距分别为150,15,60μm时,传感器获得的中心温度较高且比较均匀的中心温度分布,有利于传感器整体性能的提高。     

湍流状态下工业流化床反应器的模型与模拟

运用７种典型的鼓泡流化床反应器模型对湍流状态下工业邻苯二甲酸酐反应器进行了模拟计算，模拟计算结果与工业数据的对比与分析表明了鼓泡流化床模型可以拓宽应用于湍流体系。     

大型电除尘器的CFD模拟及优化设计

介绍了电除尘器设计的基本过程,运用CFD流体分析软件对电除尘器的流场进行了分析,得到了流场分布的各相参数,并对除尘器结构进行了改进,分析比较了优化前后的结果,为工程中电除尘器的设计和流场的优化提供了理论依据,具有现实指导意义。     

结晶器不同进料位置混合过程的CFD模拟

用CFD模拟和电导率实验研究结晶过程。重点在不同进料位置对结晶过程的影响。CFD模拟采用FLUENT软件研究结晶器内部搅拌混合过程,分析各点的速度变化;电导率实验利用电导率仪测定搅拌过程中各点的电导率变化。CFD模拟顶部进料时收敛时间为0.75 s,底部为0.25 s;电导率实验顶部进料混合时间为40 s,中部为30 s,底部为20 s。模拟结果和实验结果都表明:以底部进料的混合时间为最短。     

摆线泵CFD模拟分析

本文应用FLUENT软件的动网格模型对某汽车用摆线泵进行仿真分析,得到了该泵内部的流动与压力分布情况,以及不同工况下该泵的流量特性曲线。     

液-液喷射器不同进料方式下混合过程的CFD模拟

利用计算流体力学(CFD)软件CFX5对液-液喷射器混合段物料的混合性能进行了模拟,确定了工作流体和引射流体都平行于混合管轴线进料时物料完全混合所需的混合管长度,并分析了三种不同进料方式:(1)工作流体和引射流体都与混合段轴线平行进料;(2)工作流体与混合段轴线平行进料,引射流体与轴线成30°进料;(3)引射流体与混合段轴线平行进料,工作流体与轴线成30°,对混合管内混合过程的影响,结果表明,工作流体和引射流体都与混合段轴线平行进料时混合效果最好。     

不同形状换热管传热性能的CFD模拟及优化选型

针对一个工业换热器管程传热强化的要求,提出基于CFD模拟的换热管选型及其结构优化方法。选择普通圆管、扁管、螺旋扭曲扁管和内置扭带圆管4种不同形状的强化传热管为考察对象,借助流体力学模拟软件Fluent6.3,对不同传热管的内部参数分布、传热系数、压降大小和综合效果等进行了模拟和比较分析,结果表明螺旋扭曲扁管的综合传热效果最佳,其中传热系数比普通圆管提高了3倍,压降小于0.5 MPa,可满足工业换热器强化传热改进的要求。通过模拟取得了螺旋扭曲扁管适宜的结构参数范围,其中扭曲程度5~15,扁度为2~2.6,通过分析管内流场的分布,证明这种特殊结构换热管对流体湍动程度和传热效果有显著强化作用。     

基于EMMS曳力的湍动床气固流动CFD模拟

湍动流化床已广泛用于费托合成、FCC催化裂化等工业过程。其主要流动特点是由底部密相鼓泡区与顶部稀相分散区两者构成。由于湍动流化的复杂性,导致目前对该类体系内非均匀结构形成与演化的研究相对较少。近年来,快速发展的计算流体力学方法为深入研究此类流化提供了一种有效的手段,然而传统的双流体模型往往不能成功捕获到湍动流化的复杂结构。为了考虑非均匀结构对曳力的影响,本文提出了一个改进的曳力模型,即将湍动流化床分为3个区域:底部鼓泡区、过渡区和顶部稀相区。其中,底部区采用气泡EMMS曳力模型进行修正,过渡区采用Wen-Yu曳力模型,顶部区采用Schiller-Naumann曳力模型。修正的曳力模型与双流体模型耦合后,再通过FLUENT商业软件平台对湍动流化床内的气固两相流动进行CFD模拟。模拟结果显示,修正的曳力模型可以较好的预测湍动流化床内的流体动力学特征。该曳力模型能够模拟底部密相鼓泡区和顶部稀相分散区的两相共存结构,颗粒浓度在径向分布上为"环-核"结构,模拟的轴向颗粒浓度分布与实验数据吻合较好。     

基于Aspen Plus软件的循环流化床烟气脱硫模型

本文研究和模拟循环流化床烟气脱硫的流程和模型.以微元分析SO2的传质为基础,建立循环流化床烟气脱硫的数学模型,模型用双膜理论分析脱硫反应对SO2传质过程的增强影响,并采用惯性碰撞理论解释浆滴的形成过程.借助Aspen Plus过程模拟平台,用FORTRAN语言编写基于该模型的用户单元模块,模拟循环流化床烟气脱硫工艺,分析Ca/S、增湿水量、塔内颗粒物浓度、水滴粒径等参数对脱硫的影响,模拟计算结果和实验数据的对比显示模型能如实反映实际的趋势.本文为应用循环流化床烟气脱硫技术提供参考.     

Control of industrial gas phase propylene polymerization in fluidized bed reactors

The control of a gas phase propylene polymerization model in a fluidized bed reactor was studied, where the rigorous two phase dynamic model takes into account the polymerization reactions occurring in the bubble and emulsion phases. Due to the nonlinearity of the process, the employment of an advanced control scheme for efficient regulation of the process variables is justified. In this case, the Adaptive Predictive Model-Based Control (APMBC) strategy (an integration of the Recursive Least Squares algorithm, RLS and the Generalized Predictive Control algorithm, GPC) was employed to control the polypropylene production rate and emulsion phase temperature by manipulating the catalyst feed rate and reactor cooling water flow, respectively. Closed loop simulations revealed the superiority of the APMBC in setpoint tracking as compared to the conventional PI controllers tuned using the Internal Model Control (IMC) method and the standard Ziegler–Nichols (Z–N) method. Moreover, the APMBC was able to efficiently arrest the effects of superficial gas velocity, hydrogen concentration and monomer concentration on the process variables, thus exhibiting excellent regulatory control properties.     

CFD assisted modeling for control system design: A case study

This paper presents a novel modeling approach of coupling transient computational fluid dynamics (CFD) simulation with system identification for control system involving fluid flow and heat transfer. In order to illuminate the feasibility of this method, a fluid flow and heat transfer related process, i.e. a three dimension (3-D) spatio-temporal air temperature distribution and input (inlet air temperature) dependent process in the desert climate chamber, is considered. The distributed parameter models of the chamber temperature are identified using transient CFD simulation results and are then validated against the results obtained from the CFD simulations with high RT² (more than 0.97) and negative Young’s information criterion (YIC, less than ?11.8). The PI controllers embedded in CFD simulation are then developed based on the models. The performance of the closed-loop systems is also evaluated within the full-scale CFD model. The results show that CFD-based system identification is feasible to model fluid flow and heat transfer related processes.     

Adjustment of drag coefficient correlations in three dimensional CFD simulation of gas-solid bubbling fluidized bed

Fluidized beds have been widely used in power generation and in chemical, biochemical, and petroleum industries. 3D simulation of commercial scale fluidized beds has been computationally impractical due to the required memory and processor speeds. In this study, 3D Computational Fluid Dynamics simulation of a gas-solid bubbling fluidized bed is performed to investigate the effect of using different inter-phase drag models. The drag correlations of Richardon and Zaki, Wen-Yu, Gibilaro, Gidaspow, Syamlal-O’Brien, Arastoopour, RUC, Di Felice, Hill Koch Ladd, Zhang and Reese, and adjusted Syamlal are reviewed using a multiphase Eulerian-Eulerian model to simulate the momentum transfer between phases. Furthermore, a method has been proposed to adjust the Di Felice drag model in a three dimensional domain based on the experimental value of minimum fluidization velocity as a calibration point. Comparisons are made with both a 2D Cartesian simulation and experimental data. The experiments are performed on a Plexiglas rectangular fluidized bed consisting of spherical glass beads and ambient air as the gas phase. Comparisons were made based on solid volume fractions, expansion height, and pressure drop inside the fluidized bed at different superficial gas velocities. The results of the proposed drag model were found to agree well with experimental data. The effect of restitution coefficient on three dimensional prediction of bed height is also investigated and an optimum value of restitution coefficient for modeling fluidized beds in a bubbling regime has been proposed. Finally sensitivity analysis is performed on the grid interval size to obtain an optimum mesh size with the objective of accuracy and time efficiency.     

循环流化床锅炉燃烧系统的自抗扰控制器优化设计

循环流化床锅炉燃烧系统是典型的具有非线性、大滞后、强耦合特性的系统, 很难建立准确的数学模型,常规的控制方法难以取得良好的控制效果. 自抗扰控制器具有结构简单, 不依赖被控对象具体模型等优点, 易于工业现场应用. 本文为某国产75 t/h循环流化床锅炉燃烧系统设计自抗扰控制器, 使用非支配排序果蝇算法对控制器参数进行基于ITAE指标、调节时间和最大控制量的多目标优化. 用所设计控制器进行仿真研究, 并与非优化的自抗扰控制器和基于预期动态的PI控制器进行比较. 结果表明, 所设计控制器效果最优, 可以更有效地对通道间的耦合 进行估计和补偿, 具有更强的解耦能力.     

Adaptive modeling of the drying of baker's yeast in a batch fluidized bed

This study investigates the drying of baker's yeast in a fluidized-bed dryer. Mathematical modeling of the process was performed, incorporating the important process and quality parameters of the system. Artificial neural network (ANN) and adaptive neural network-based fuzzy inference system (ANFIS) structures were used to create process and quality models. Due to uncertainty regarding the process parameters, various different ANN structures were built, and the ANN with the optimum performance results for the proposed models was selected. This study also presents an ANFIS modeling approach with adaptive structure. ANN quality modeling was performed using process output parameters, and the quality loss incurred from drying the product was determined. These proposed models are easy to apply and do not impose any additional burden on the process (or the employees). The database used in this work was gathered from large quantities of industrial data (about 570 batches) obtained under various working conditions at random times over one year.     

35t循环流化床锅炉热工控制系统的设计与运行

根据循环流化床锅炉运行的特点，结合燃煤的变化及负荷要求来控制锅炉的运行工况．实现了PLC对锅炉的控制要求，同时介绍了热工控制系统的实现过程。     

循环流化床过程仿真的数学模型

传统的循环流化床仿真的数学模型都采用反应动力学的方法。本文采用了CSTR的平衡反应算法,对循环流化床建立仿真的数学模型,已用于100MW循环流化床的实际工业装置仿真培训器中,算法比较稳定,模拟了循环流化床的开停车、事故处理和正常操作,动态趋势和实际工业装置相符。与设计值相比,模拟的稳态误差在1%以内,动态误差在5%以内。     

Optimal polymer grade transitions for fluidized bed reactors

Industrial polymerization plants experience frequent changes of products, driven by end-use properties to meet various market requirements. Efficient grade transition policies are essential to save time and materials. In this study, the gas-phase catalytic polymerization is modeled in a fluidized bed reactor by a single-phase model, and dynamic optimization is implemented to determine optimal operating sequences for grade changes. Two optimization formulations, a single-stage and a multi-stage formulation, are introduced and compared. The superiority of the multi-stage formulation is demonstrated owing to a better control on each stage during the transition and a further reduction of off-grade time. Subsequently, an on-line optimal control framework is established by incorporating shrinking horizon nonlinear model predictive control with an expanding horizon weighted least-square estimator for process states and unknown parameters. The results of a case study indicate the designed framework is able to handle process uncertainty, while reducing the transition time.