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.     

Identification and control of a riser‐type FCC unit

This paper addresses the use of feedforward neural networks for the steady‐state and dynamic identification and control of a riser type fluid catalytic cracking unit (FCCU). The results are compared with a conventional PI controller and a model predictive control (MPC) using a state space subspace identification algorithm. A back propagation algorithm with momentum term and adaptive learning rate is used for training the identification networks. The back propagation algorithm is also used for the neuro‐control of the process. It is shown that for a noise‐free system the adaptive neuro‐controller and the MPC are capable of maintaining the riser temperature, the pressure difference between the reactor vessel and the regenerator, and the catalyst bed level in the reactor vessel, in the presence of set‐point and disturbance changes. The MPC performs better than the neuro controller that in turn is superior to the conventional multi‐loop diagonal PI controller.     

Partial oxidation of benzene catalyzed by vanadium chloride in novel reaction-extraction-regeneration system

This paper investigates the liquid-phase partial oxidation of benzene to phenol in a novel system consisting of reactor, extractor and regenerator. Since vanadium catalyst (V³⁺) is oxidized in the reactor and therefore deactivated, the regenerator with Pd or Pt catalyst and H₂ feed is employed to regenerate the deactivated vanadium. The V⁴⁺ ion can be reduced to V³⁺ and consequently the phenol production can be enhanced. Although the regenerator can regenerate vanadium catalyst and the reaction can proceed for over 100 h, some V⁴⁺ is still present. The feed position of benzene and catalyst solution have the influence on mixing condition in the reactor and interface area between benzene and catalyst solution. Counter current flow operation with the feeds of catalyst solution and benzene at the top and the bottom respectively shows the highest phenol production. The operating temperature of reactor, extractor and regenerator showed insignificant effect on phenol production rate.     

连续搅拌釜式丙烯聚合反应器的模拟（Ⅰ）反应器的定态模拟

以实际工业装置为背景，建立了丙烯液相本体聚合连续搅拌釜式反应器的定态数学模型。通过模拟计算，考察了诸工艺参数──进料温度、进料流量、夹套冷却水人口温度和流量、丙烯蒸汽冷凝量、催化剂浓度以及反应器中的氢浓度对聚合反应釜反应结果的影响，并对其定态操作行为作了理论上的解释和分析。     

THE EFFECT OF OPERATING VARIABLES ON THE DYNAMICS OF CATALYTIC CRACKING PROCESSES

The dynamic Characteristics of a Fluidized Catalytic Cracking Process are examined over a wide range of operating conditions. A novel Order of Magnitude Approach is introduced to successfully provide physical insight into the cause and effect relationship between operating conditions and dynamic characteristics. It is shown that the original five-dimensional dynamic model is characterized by three fast time constants and two slow ones that dominate the dynamic responses. The two most important time constants are expressed as explicit functions of the operating conditions. These formulas correctly indicate in which parameter regions the open loop response is oscillatory (underdamped) or nonoscillatory (overdamped). Extensive process variables, that are either flow or capacity, related are defined in order to provide an approximate physical meaning for the dynamic modes of the system. It is shown that the two slow modes of the process are related to the enthalpy content of the regenerator and the sensible heat content of the catalyst phase in both the reactor and regenerator.     

连续搅拌釜式丙烯聚合反应器的模拟（Ⅱ）反应器的动态模拟

建立了丙烯液相本体聚合连续搅拌釜式反应器的动态数学模型，通过计算机模拟，研究了进夹套冷却水流量、丙烯蒸汽冷凝量、催比剂浓度及进料温度４个变量在矩形波和阶跃两种干扰方式下反应器的动态行为，为反应器控制系统的设计提供了定量依据。     

A logic-based controller for the mitigation of ventilation air methane in a catalytic flow reversal reactor

The control system of a catalytic flow reversal reactor (CFRR) for the mitigation of ventilation air methane was investigated. A one-dimensional heterogeneous model with a logic-based controller was applied to simulate the CFRR. The simulation results indicated that the controller developed in this work performs well under normal conditions. Air dilution and auxiliary methane injection are effective to avoid the catalyst overheating and reaction extinction caused by prolonged rich and lean feed conditions, respectively. In contrast, the reactor is prone to lose control by adjusting the switching time solely. Air dilution exhibits the effects of two contradictory aspects on the operation of CFRR, i.e., cooling the bed and accumulating heat, though the former is in general more prominent. Lowering the reference temperature for flow reversal can decrease the bed temperature and benefit stable operation under rich methane feed condition.     

高效再生催化裂化装置多稳态分析：反应温度开/闭环控制条件对热反馈机制的影响

针对催化裂化反应-再生系统在提升管反应温度开环和闭环控制条件下的输出与输入多稳态问题,分析了烧焦罐式高效再生催化裂化反应-再生系统在两种条件下随着CO助燃剂添加量变化时的多稳态分布。在反应温度开环条件下,因再生温度与反应温度的耦合程度较低,使系统移热曲线呈单调递增,导致了系统出现3个稳态操作点。在反应温度闭环控制条件下,提升管反应器和再生器间热反馈机制发生改变,由于再生剂循环量可以作为额外的自由度对再生温度和反应温度之差进行补偿,再生器和提升管反应器的耦合程度增强,使得系统只会在助燃剂添加量极低时才会出现多个稳态点,而在基准操作条件下只有一个稳态点,规避了系统在提升管反应温度开环时的多个稳态点的问题。     

Dynamics and stability of ethylene polymerization in multizone circulating reactors

Multizone circulating bed reactors (MZCR) have the exclusive characteristics of producing polymers of different molecular weights in a single particle. Traditional fluidized bed reactors, on the other hand, can produce only one kind of molecular weight with relatively narrow distribution. A dynamic model for the MZCR is used to illustrate the basic dynamic behavior of the new reactor design used for polyethylene production. The model is used to study the copolymerization of ethylene with butene. Several parameter sensitivity analyses are performed to show the computer-simulated time responses for reactor temperature, number-average molecular weight, weight-average molecular weight, catalyst feed rate and the monomer/comonomer concentration along the reactor length. At certain operating conditions dynamic instability is observed and the results for the effect of cooling water temperature, catalyst feed rate, monomer and comonomer initial feed concentration on the reactor temperature and polymer molecular weight reveal that the system is very sensitive to disturbances in the heat exchanger coolant temperature. Also, at some operating conditions, the reactor temperature oscillates above the polymer melting temperature. Temperature runaway above polymer softening point is a serious problem which may cause polymer melting and hence reactor shutdown. The oscillatory behavior of the reactor temperature necessitates a suitable temperature control scheme to be installed.     

Steady state multiplicity in an UOP FCC unit with high-efficiency regenerator

The possibility of existence of multiple steady states in fluid catalytic cracking (FCC) units has a major impact in the supervision of these systems. The origins of these behaviours are usually due to the exothermicity of the catalyst regeneration reactions and to the strong interactions between the reactor and the regenerator system.Prior work has focused on modelling and control problems of different operating FCC units. However, none of these studies have considered a high-efficiency regenerator. This paper presents an analysis of the existence of output and input multiple steady states in an UOP FCC unit with a high-efficiency regenerator.The influence of unit disturbances and model uncertainties, such as coke composition and cracking enthalpy, in the output multiplicity, was studied and the results show that the high-efficiency regenerator exhibits at least three multiple output steady states and a maximum of five output steady states, in the operating range considered. Moreover, the state multiplicity analysis revealed that input multiplicity can be present in this FCC unit, depending on the choice of the control structure, and that operating the unit in full combustion mode can prevent instabilities due to input and output multiplicities. Therefore, these results can be used to guide the design of the most appropriate control structures in industrial applications. For the FCC unit with high-efficiency regenerator the most appropriate control structure corresponds to the control of the riser reactor temperature and the oxygen level in the flue gas, with the catalyst circulation rate and the combustion air flow rate, respectively.     

催化裂化装置再生器主风裕量的动态分析

以某催化裂化装置为基础,建立反应-再生系统的动态机理数学模型。从生产操作和闭环控制的角度,用动态优化的方法对再生器的主风裕量进行了计算,指出过程动态特性对主风设计裕量的选取有着很大影响。在考虑工艺和设备条件变化留出的稳态裕量之外,需要留出一定的动态裕量以满足过程操作和控制的要求,其大小与控制系统设计有关。系统对控制器性能的要求愈高,所需要的主风裕量应愈大。故在进行工艺设计时需要对系统的控制性能和主风设计裕量进行综合考虑,使设计结果既能满足工艺要求,又能实现良好的自动控制。     

Integrated FCC riser—regenerator dynamics studied in a fluid catalytic cracking pilot plant

In this paper a dynamic simulator of the fluid catalytic cracking (FCC) pilot plant, operating in the Chemical Process Engineering Research Institute (CPERI, Thessaloniki, Greece), is presented. The operation of the pilot plant permits the execution of case studies for monitoring of the dynamic responses of the unit, by imposing substantial step changes in a number of the manipulated variables. The comparison between the dynamic behavior of the unit and that predicted by the simulator arise useful conclusions on both the similarities of the pilot plant to commercial units, along with the ability of the simulator to depict the main dynamic characteristics of the integrated system. The simulator predicts the feed conversion, coke yield and heat of catalytic reactions in the FCC riser on the basis of semi-empirical models developed in CPERI and simulates the regenerator according to the two-phase theory of fluidization, with a dilute phase model taking account of postcombustion reactions. The riser and regenerator temperature, the stripper and regenerator pressure drop and the composition of the regenerator flue gas are measured on line and are used for verification of the ability of the simulator to predict the dynamic transients between steady states in both open- and closed-loop unit operation. All the available process variables such as the reaction conversion, the coke yield, the carbon on regenerated catalyst and the catalyst circulation rate are used for the validation of the steady-state performance of the simulator. The comparison between the dynamic responses of the model and those of the pilot plant to step changes in the feed rate and preheat temperature reveals the ability of the simulator to accurately depict the complex pilot process dynamics in both open- and closed-loop operation. The dynamic simulator can serve as the basis for the development of a model-based control structure for the pilot plant, alongside its use as a tool for off-line process optimization studies.     

Multiplicity of the steady state in fluidized bed reactors—IV. Fluid catalytic cracking (FCC)

A mathematical model for fluid catalytic cracking units is developed. The model takes into account the kinetics of the cracking reactions, as well as the kinetics of coke combustion in the regenerator. A numerical scheme is developed for the solution of the model equations. It is found that multiplicity of the steady states extends over a wide scope of operating variables and parameters. The model investigates the effects of catalyst circulation rate and gas oil flow rate, which have a strong effect on the reactor temperature and hence yield and selectivity. The phenomenon of hysteresis has been investigated. The model can be used for yield optimization and steady state control.     

焦化加热炉出口温度的预测函数控制

采用透明控制结构,设计了焦化加热炉出口温度的预测函数控制系统.针对影响出口温度的可测扰动采用前馈控制加以补偿,实际工业应用表明该控制系统具有较好的跟踪性能和较强的鲁棒性.     

Rational design of heating elements using CFD: Application to a bench-scale adiabatic reactor

This article explores the use of computational fluid dynamics (CFD) modelling for designing an oven which enables the adiabatic operation of a chemical reactor at bench-scale. For accomplishing this scope, the oven consists of electrical heating elements, air circulation system and a control loop that uses the temperature inside the reactor as set-point for the reactor wall temperature. Depending on the spatial configuration of the air flow and the heating elements, as well as the air flow rate, different temperature profiles within a given oven section are obtained, being appropriate those leading to uniform reactor wall temperatures and fast dynamic response. The use of CFD allows, by obtaining temperature maps within the oven, the selection of appropriate configurations. The optimal configuration adopted has been experimentally validated in a lab-scale adiabatic reactor working with both particulated and monolithic catalyst beds.     

Model predictive control of an industrial pyrolysis gasoline hydrogenation reactor

This study focuses on the implementation of a nonlinear model predictive control (MPC) algorithm for controlling an industrial fixed-bed reactor where hydrogenations of raw pyrolysis gasoline occur. An orthogonal collocation method is employed to approximate the original reactor model consisting of a set of partial differential equations. The approximate model obtained is used in the synthesis of a MPC controller to control the temperature rising across a catalyst bed within the reactor. In the MPC algorithm, a sequential optimization approach is used to solve an open-loop optimal control problem. Feedback information is incorporated in the MPC to compensate for modeling error and unmeasured disturbances. The control studies are demonstrated in cases of set point tracking and disturbance rejection.     

半间歇反应釜先进控制系统的研究

结合乙二醇二甲醚半间歇生产工艺改造和安全自控要求,设计以IPC上位机和PLC下位机构成的先进控制系统,并对反应釜的进料和温度进行智能化控制。通过进料流量控制系统、反应釜温度控制系统和报警联锁系统的应用,确保了产品质量和生产安全。     

Control of a reverse flow reactor for VOC combustion

A flow reversal reactor for VOC combustion is controlled by the linear quadratic regulator (LQR), which uses dilution and internal electric heating as controls to confine the hot spot temperature within the two temperature limits, in order to ensure complete conversion of the VOC and to prevent overheating of the catalyst. Three phases of operation, i.e., dilution phase, heating phase and inactive phase, are identified. In dilution and heating phases, the cost functions of the LQR control are defined in quadratic forms. In the inactive phase, the controllers are inactivated. A linear model is derived by linearization of a countercurrent pseudo-homogeneous model at two nominal operating conditions in the dilution phase and the heating phase, respectively. The feed concentration and the temperature profile are estimated on-line by using a high-gain observer with three temperatures measurements and are used in the LQR feedback control. Experiments are carried out on a medium-scale reversed flow reactor to demonstrate the proposed LQR control strategy. Results show that the LQR controller is highly efficient in maintaining normal operation of the reactor.     

Circulating fluidized bed combustion reactor: Computational Particle Fluid Dynamic model validation and gas feed position optimization

A 3D Computational Particle Fluid Dynamic (CPFD) model is validated against experimental measurements in a lab-scale cold flow model of a Circulating Fluidized Bed (CFB). The model prediction of pressure along the riser, downcomer and siphon as well as bed material circulation rates agree well with experimental measurements. Primary and secondary air feed positions were simulated by varying the positions along the height of the reactor to get optimum bed material circulation rate. The optimal ratio of the height of primary and secondary air feed positions to the total height of the riser are 0.125 and 0.375 respectively. The model is simulated for high-temperature conditions and for reacting flow including combustion reactions. At the high temperature and reaction conditions, the bed material circulation rate is decreased with the corresponding decrease in pressure drop throughout the CFB for the given air feed rate.     

Development of a CH4 dehydroaromatization–catalyst regeneration fluidized bed system

A pilot-scale methane dehydroaromatization–H₂ regeneration fluidized bed system (MDARS) was developed. In the MDARS, the catalyst circulation between a fluidized bed reactor and a fluidized bed regenerator with the help of a catalyst feeder allowed methane dehydroaromatization (MDA) and H₂ regeneration to be carried out simultaneously, which is good for maintaining a stable MDA catalytic activity. A fixed bed reactor (FB) and a single fluidized bed reactor (SFB) were also used for a comparative study. The experimental results showed that the catalytic activity in the MDARS was more stable than that in the FB and SFB reactors. The effects of some parameters of MDARS on the CH₄ conversion and product selectivity were investigated. To verify the feasibility and reliability of the MDARS, an eight-hour long-term test was carried out, which demonstrated that the operation of the MDARS was stable and that the catalytic activity remained stable throughout the entire experimental period.