Modular Simulation of Fluidized Bed Reactors

Simulation of chemical processes involving nonideal reactors is essential for process design, optimization, control and scale‐up. Various industrial process simulation programs are available for chemical process simulation. Most of these programs are being developed based on the sequential modular approach. They contain only standard ideal reactors but provide no module for nonideal reactors, e.g., fluidized bed reactors. In this study, a new model is developed for the simulation of fluidized bed reactors by sequential modular approach. In the proposed model the bed is divided into several serial sections and the flow of the gas is considered as plug flow through the bubbles and perfectly mixed through the emulsion phase. In order to simulate the performance of these reactors, the hydrodynamic and reaction submodels should be integrated together in the medium and facilities provided by industrial simulators to obtain a simulation model. The performance of the proposed simulation model is tested against the experimental data reported in the literature for various gas‐solid systems and a wide range of superficial gas velocities. It is shown that this model provides acceptable results in predicting the performance of the fluidized bed reactors. The results of this study can easily be used by industrial simulators to enhance their abilities to simulate the fluidized bed reactor properly.     

气液固三相流化床反应器测试技术

在简述已有三相流化床测试技术的基础上,着重对近年来开发的测试新技术的基本原理及优缺点进行了分析,包括光纤探头技术、超声探头技术、放射颗粒跟踪技术、X射线颗粒跟踪测试技术、颗粒图像测速技术、电容层析成像技术、激光多普勒测速技术和相多普勒测速技术等,同时,展望了三相流化床测试技术的新方向.     

Modeling of Shallow Fluidized Bed Reactors: I. analytic solution of a simplified model

A fairly general dynamic model for shallow fluidized bed reactors is developed, and analytic solutions for the governing equations of the model are obtained after some simplification. The bubble size, the lateral dispersion coefficient of solids, the level of the excess fluid reactant and the structure of the bed are examined to determine their effects on the conversion of solids. It has been shown that the conversion of solids is influenced profoundly by the bubble size and that it is advantageous to employ a shallow fluidized bed reactor if a high conversion of solids is required.     

乙烯氧氯化流化床反应器的模型化及操作条件优化

对工业乙烯氧氯化挡板流化床反应器建立了以两相理论为基础的多釜串联反应器模型,利用大量工业数据求解模型参数并检验模型,计算结果表明模拟值与工业值基本吻合.在此基础上,对反应器操作条件进行优化,得到不同生产负荷下的最优操作条件.     

流化床反应器过程强化技术

Fluidized beds enable good solids mixing, high rates of heat and mass transfer, and large throughputs, but there remain issues related to fluidization quality and scale-up. In this work I review modification techniques for fluidized beds from the perspective of the principles of process intensification (PI), that is, effective bubbling sup-pression and elutriation control. These techniques are further refined into (1) design factors, e.g. modifying the bed configuration, or the application of internal and external forces, and (2) operational factors, including altering the particle properties (e.g. size, density, surface area) and fluidizing gas properties (e.g. density, viscosity, or velocity). As far as two proposed PI principles are concerned, our review suggests that it ought to be possible to gain improve-ments of between 2 and 4 times over conventional fluidized bed designs by the application of these techniques.     

Dynamic Behavior of Industrial Gas Phase Fluidized Bed Polyethylene Reactors under PI Control

A mathematical model describing the UNIPOL process for the production of polyethylene in the gas phase using a Ziegler‐Natta catalyst in a bubbling fluidized bed is used to analyze the major processes determining the behavior and performance of these industrially important units. The investigation shows that both static bifurcation (multiplicity of the steady states) as well as dynamic bifurcation (stable/unstable periodic attractors) behavior cover wide regions of the design and operating parameter domain. A conventional proportional‐integral (PI) control policy is suggested to stabilize the behavior of the system. The control philosophy covers both aspects of stabilizing unstable steady states as well as compensating for external disturbances. It is shown that for some controller configurations and set points the controlled process can go through a period doubling sequence leading to chaotic strange attractors. The industrial implications of the phenomena discovered for both the open loop (uncontrolled) as well the closed‐loop (controlled) systems are analyzed.     

Dynamics and Predictive Control of Gas Phase Propylene Polymerization in Fluidized Bed Reactors

A two-phase dynamic model, describing gas phase propylene polymerization in a fluidized bed reactor, was used to explore the dynamic behavior and process control of the polypropylene production rate an...     

Catalytic Steam Reforming of Fast Pyrolysis Bio‐Oil in Fixed Bed and Fluidized Bed Reactors

Catalytic steam reforming of bio‐oil is an economically‐feasible route which produces renewable hydrogen. The Ni/MgO‐La₂O₃‐Al₂O₃ catalyst was prepared with Ni as active agent, Al₂O₃ as support, and MgO and La₂O₃ as promoters. The experiments were conducted in fixed bed and fluidized bed reactors, respectively. Temperature, steam‐to‐carbon mole ratio (S/C), and liquid hourly space velocity (LHSV) were investigated with hydrogen yield as index. For the fluidized bed reactor, maximum hydrogen yield was obtained under temperatures 700–800 °C, S/C 15–20, LHSV 0.5–1.0 h^–1, and the maximum H₂ yield was 75.88 %. The carbon deposition content obtained from the fluidized bed was lower than that from the fixed bed. The maximum H₂ yield obtained in the fluidized bed was 7 % higher than that of the fixed bed. The carbon deposition contents obtained from the fluidized bed was lower than that of the fixed bed at the same reaction temperature.     

流化床反应器中气相丙烯聚合反应的动力学和预测控制(英文)

A two-phase dynamic model, describing gas phase propylene polymerization in a fluidized bed reactor, was used to explore the dynamic behavior and process control of the polypropylene production rate and reactor temperature. The open loop analysis revealed the nonlinear behavior of the polypropylene fluidized bed reactor, jus- tifying the use of an advanced control algorithm for efficient control of the process variables. In this case, a central- ized model predictive control （MPC） technique was implemented to control the polypropylene production rate and reactor temperature by manipulating the catalyst feed rate and cooling water flow rate respectively. The corre- sponding MPC controller was able to track changes in the setpoint smoothly for the reactor temperature and pro- duction rate while the setpoint tracking of the conventional proportional-integral （PI） controller was oscillatory with overshoots and obvious interaction between the reactor temperature and production rate loops. The MPC was able to produce controller moves which not only were well within the specified input constraints for both control vari- ables, but also non-aggressive and sufficiently smooth for practical implementations. Furthermore, the closed loop dynamic simulations indicated that the speed of rejecting the process disturbances for the MPC controller were also acceotable for both controlled variables.     

Modeling Asd Optimization of Fluidized Bed and Rotary Dryers

Fluidized bed and rotary dryers are two popular types of dryers utilized in almost every area of dryine. In this study, both dryers are analysed regarding their design and operational performance, so that they could be compared in a straightforward way. The mathematical models describing the convective drying process were evaluated for both types of dryers. Design procedures aiming at the determination of optimum sizing and operational characteristics for each type involved were carried out by appropriately optimizing the total annual cost of each structure for a given production capacity. Both dryer types were compared explicitely by evaluating optimum configurations for a wide range of production capacity values. Once the dryer sizing parameters are defined, its operational performance can be evaluated by comparing the optimum operational cost versus production capacity for predefined optimum designed structures. Rotary dryers turn out to be rather expensive compared to fluidized bed dryers, regarding design. On operational grounds, however, it is the other way around, due to the understandably favored heat transfer achieved in rotarv dryers. Characteristic examples covering a wide range of materials - from food products to inorganic minerals -are included in order to demonstrate the performance of each process as well as the effectiveness of the proposed approach.     

Modeling Asd Optimization of Fluidized Bed and Rotary Dryers

ABSTRACT

Fluidized bed and rotary dryers are two popular types of dryers utilized in almost every area of dryine. In this study, both dryers are analysed regarding their design and operational performance, so that they could be compared in a straightforward way. The mathematical models describing the convective drying process were evaluated for both types of dryers. Design procedures aiming at the determination of optimum sizing and operational characteristics for each type involved were carried out by appropriately optimizing the total annual cost of each structure for a given production capacity. Both dryer types were compared explicitely by evaluating optimum configurations for a wide range of production capacity values. Once the dryer sizing parameters are defined, its operational performance can be evaluated by comparing the optimum operational cost versus production capacity for predefined optimum designed structures. Rotary dryers turn out to be rather expensive compared to fluidized bed dryers, regarding design. On operational grounds, however, it is the other way around, due to the understandably favored heat transfer achieved in rotarv dryers. Characteristic examples covering a wide range of materials - from food products to inorganic minerals -are included in order to demonstrate the performance of each process as well as the effectiveness of the proposed approach.     

Cocurrent Downflow Fluidized Bed Dryer: Experimental Equipment and Modeling

Product damage, high energy consumption, and nonhomogeneous final properties are present in typical drying operations such as pneumatic drying, fluidized-bed dryers, and upward circulating fluidized-bed dryers. The downer bed has been shown to be a good technique for this processes. The objective of this work is to test an experimental downflow dryer and model its operation. The equipment consists of a 5-m-high stainless steel duct with 0.17 m i.d. Gas velocity was varied between 0.3 and 8 m/s in co-current solid flow varying between 0 and 50 kg/m²s. Drying rates, pressures, and total flux for solid and gas are determined. Temperature profiles for gas and solid along the radial and axial directions are determined and tested with model predictions. The solid particles were previously dried turnip (Brassica napus) seeds. The equipment shows good operational conditions and facilities for parameter determination, but must be complemented with better equipment for particle concentration determinations. The model's predictions of pressure, gas velocity, solid concentration, and temperature are compared with our experimental values or those reported in the literature.     

Cocurrent Downflow Fluidized Bed Dryer: Experimental Equipment and Modeling

ABSTRACT

Product damage, high energy consumption, and nonhomogeneous final properties are present in typical drying operations such as pneumatic drying, fluidized-bed dryers, and upward circulating fluidized-bed dryers. The downer bed has been shown to be a good technique for this processes. The objective of this work is to test an experimental downflow dryer and model its operation. The equipment consists of a 5-m-high stainless steel duct with 0.17 m i.d. Gas velocity was varied between 0.3 and 8 m/s in co-current solid flow varying between 0 and 50 kg/m²s. Drying rates, pressures, and total flux for solid and gas are determined. Temperature profiles for gas and solid along the radial and axial directions are determined and tested with model predictions. The solid particles were previously dried turnip (Brassica napus) seeds. The equipment shows good operational conditions and facilities for parameter determination, but must be complemented with better equipment for particle concentration determinations. The model's predictions of pressure, gas velocity, solid concentration, and temperature are compared with our experimental values or those reported in the literature.     

循环流化床半干法脱硫床体建模以及稳床措施研究

循环流化床半干法脱硫工艺技术要求高,建立和稳定流化床是两个关键点,只有做好恰当的流化床设计和配置合理的输送设备,才可保证脱硫系统的稳定高效运行。     

Mathematical Modeling of the Fluidized Bed Drying of Cubic Materials

The unsteady‐state simultaneous heat and mass transfer between gas and potato cubes during the drying process in a batch fluidized bed was described by a mathematical model. Mass transfer was considered to occur in three dimensions whereas heat transfer between the gas and dried material was assumed to be lumped. It was found that the model could describe the drying process with acceptable accuracy. The moisture profile inside the material at any cross‐section and at any time can be predicted by the model.     

Some Issues on Core‐Annulus and Cluster Models of Circulating Fluidized Bed Reactors

The one‐dimensional cluster model and the core‐annulus model are examined based on existing correlations. The core‐annulus model is found to give reasonable agreement with ozone decomposition data when the effective interphase mass transfer rate constant is equal to about 0.1 1/s, which is one order smaller than the reported values based on gas tracer tests. The prediction from the core‐annulus model that the reactor performance decreases with increasing the riser diameter is found to be inconsistent with limited experimental data The one‐dimensional cluster model predicts that a riser reactor performs very close to the pseudo‐homogeneous plug flow reactor because of the high mass transfer rate between the cluster and the dilute phase. The improvement of model predictions lies in the better characterization of the cluster shape, size and the mass transfer rate between the cluster and the dilute phases.     

Effect of Polymer Particle Size and Inlet Gas Temperature on Industrial Fluidized Bed Polyethylene Reactors

Static and dynamic bifurcation behaviors dominate the operation of fluidized bed catalytic reactors for the production of polyethylene (UNIPOL Process) and have important implications on the safe operating temperature and polyethylene production rate. The investigations show that the multiplicity of the steady state phenomenon covers a wide range of parameters together with the phenomenon of periodic oscillations with sharply changing amplitudes with a change of the chosen bifurcation parameter. In some cases, the periodic branches terminate through periodic limit point (PLPs), while in other cases it terminates homoclinically. A detailed parameteric investigation using two-parameter continuation diagrams for the loci of static and Hopf bifurcation points as well as one parameter bifurcation diagrams shows that it is possible to increase the productivity of the unit considerably without exceeding the constraints of the polymer melting point. Gas feed temperature, catalyst feed rate, and polymer particle size distribution are important operating parameters in polyethylene fluidized bed reactors. Gas velocity plays a significant role in keeping the fluidized bed bubbling in addition to the fact that it acts as a cooling media by removing excess heat generated from the polymerization reaction. The kinetic behavior of the catalyst and effect of reactor temperature on product properties require, in some cases, operating just below the softening point of the polymer which requires a suitable controller to avoid polymer melting.