Nonlinear temperature control of a batch suspension polymerization reactor

This paper concerns nonlinear temperature control of a batch polymerization reactor where suspension polymerization of methyl methacrylate (MMA) takes place. For this purpose, four control algorithms, namely, a fix proportional‐integral (PI) controller, an adaptive proportional‐integral‐derivative (PID) controller and two globally linearizing control (GLC) schemes, one for known kinetic model (GLC‐I) and the other for unknown kinetic model (GLC‐II), are selected. The performances of these controllers are compared through simulation and real‐time studies in the presence of different levels of parameter uncertainty. The results indicate that GLCI and GLC‐II have better performances than fix PI and adaptive PID, especially in case of strong gel effect. The worst performance belongs to adaptive PID because of rapid model changes in gel effect region. GLC‐II has a simpler structure than GLC‐I and can be used without requiring the kinetic model. In implementation of GLC‐I the closed loop observer should be used because of model uncertainties.     

Nonlinear state estimation and control of a batch reactive distillation

This paper deals with the advanced adaptive control of a batch reactive distillation (RD) column for the production of ethyl acetate. The nonlinear adaptive control law consists of the generic model controller (GMC) and an adaptive state estimator (ASE). In the first part of the present work, the design approach of the ASE scheme in two different forms, namely ASE1 and ASE2, has been addressed for a batch reactive rectifier. The predictor model of both the ASE estimators includes only a component mole balance equation around the condenser-reflux drum system and an extra state equation having no dynamics, and therefore, there is a large process/predictor mismatch. In presence of this structural discrepancy, the adaptive estimation schemes compute the imprecisely known parameters quite accurately based on the measured distillate composition under initialization error, disturbance and uncertainty. In the subsequent part, the adaptive GMC–ASE1 control structure has been formulated for the sample reactive column. This nonlinear control strategy shows comparatively better closed-loop performance than the gain-scheduled proportional integral (GSPI) controller due to the exponential error convergence capability of the estimation scheme and the high-quality control of the GMC law.     

Control System Design for a Single Feed ETBE Reactive Distillation Column

Reactive distillation (RD) is advantageous for the Ethyl Tert‐Butyl Ether (ETBE) synthesis. The steady state model of an ETBE reactive distillation column created using the simulator HYSYS is analyzed to synthesize effective control structures. Since the column exhibits input multiplicity with the dual process objectives of ETBE RD (isobutene conversion and ETBE purity), inferential variables are selected. A control structure that organizes a sensitive tray temperature in the stripping section using the reboiler duty and maintains the temperature difference of reactive trays using the reflux flow, is found to be most suitable. A decentralized PI controller and constrained Model Predictive Controller (MPC) are implemented, and performances are compared for set point tracking and disturbance rejection. MPC control algorithms are implemented in MATLAB and interfaced with HYSYS. Constrained MPC (CMPC) is found to be effective for load disturbance rejection, which frequently occurs in the single feed configuration.     

Optimal two point control of a binary distillation column

Optimal two point control and operating policies have been developed for a semi-works scale 10 tray distillation column separating methanol and water. Two controllers, based on different control philosophies were synthesized. They are:

• 1 The controller that will bring the product compositions to their desired values while keeping off-specification products to a minimum.
• 2 The controller that will bring the product compositions to their desired values while maintaining the average product composition of the control period at the desired level.

Two types of disturbances were studied, namely disturbances in the feed stream and changes in product specifications. The column operation was represented by a linearized dynamic mathematical model based on a component material balance. The solution of the problem was obtained by application of the minimum principle of Fontryagin and the modified Riccati transformation technique. Simplified optimal control schemes can be developed from the results of this work. These control schemes are simple enough to be used for direct digital computer control.     

Comparison of Two Types of Control Structures for Benzene Chlorine Reactive Distillation Systems

The “neat” operation of the two-reactant reactive distillation column has better steady-state economics, while it presents a challenge for design, optimization, and control of the process. Based on the optimal economic design, the dual-composition control structure and dual-temperature control structure are designed respectively for the benzene chlorine consecutive reactive distillation process. The effectiveness and robustness are analyzed comparably for the disturbance resistance in terms of changes of production rate and feed composition. Results show that dual-temperature control with propose selection of tray temperatures and the optimal profile of the set point can provide better transient process performance than the composition control structure.     

基于神经网络和多模型的非线性自适应PID控制及应用

针对一类未知的单输入单输出离散非线性系统,提出了基于神经网络和多模型的非线性自适应PID控制方法。该方法由线性自适应PID控制器、神经网络非线性自适应PID控制器以及切换机构组成。采用线性自适应PID控制器可保证闭环系统所有信号有界;采用神经网络非线性自适应PID控制器可改善系统性能;通过引入合理的切换机制,能够在保证闭环系统稳定的同时,提高系统性能。理论分析表明,该方法能够保证闭环系统所有信号有界,如果适当地选择神经网络的结构和参数,系统的跟踪误差将收敛于任意给定的紧集。将所提出的方法应用于连续搅拌反应釜,仿真结果验证了所提出方法的有效性。由于该方法基于增量式数字PID控制器,在工业过程中有着广阔的应用前景。     

基于自适应神经模糊推理系统的间歇反应精馏组分估算(英文)

Composition estimation plays very important role in plant operation and control. Extended Kalman filter (EKF) is one of the most common estimators, which has been used in composition estimation of reactive batch distillation, but its performance is heavily dependent on the thermodynamic modeling of vapor-liquid equilibrium, which is difficult to initialize and tune. In this paper an inferential state estimation scheme based on adaptive neuro-fuzzy inference system (ANFIS), which is a model base estimator, is employed for composition estimation by using temperature measurements in multicomponent reactive batch distillation. The state estimator is supported by data from a complete dynamic model that includes component and energy balance equations accompanied with thermodynamic relations and reaction kinetics. The mathematical model is verified by pilot plant data. The simulation results show that the ANFIS estimator provides reliable and accurate estimation for component concentrations in reactive batch distillation. The estimated states form a basis for improving the performance of reactive batch distillation either through decision making of an operator or through an automatic closed-loop control scheme.     

板式塔发展的新方向—并馏塔

并馏塔是国外近年来发展起来的一种新塔盘。它以在同样塔径和塔高条件下增加30％—50％的传质理论级数的优秀结果而引人注目。本文介绍了这种塔盘的结构,概述了目前的研究状况,对其理论基础进行了探索,并以某一塔设想改造为例,初步揭示了并馏塔的应用前景。     

CLOSED-LOOP DATA RECONCILIATION FOR THE CONTROL OF A BINARY DISTILLATION COLUMN

Data reconciliation is a procedure that makes use of process models along with process measurements to give more precise and consistent estimates for process variables. Data reconciliation has been traditionally used to provide a more representative set of data to calculate steady-state inventories and process yields. For dynamic systems, the use of data reconciliation is relatively nascent. This article examines the potential use of data reconciliation in closed-loop control as a filter to attenuate the noise in measurements of the controlled variables so that the controllers can access more accurate sets of data. Data reconciliation filters were implemented in simulations of a PID control system for a binary distillation column. Results showed that data reconciliation could efficiently reduce the propagation of measurement noise in control loops, so that the overall performance of the controller is enhanced.     

CLOSED-LOOP DATA RECONCILIATION FOR THE CONTROL OF A BINARY DISTILLATION COLUMN

Data reconciliation is a procedure that makes use of process models along with process measurements to give more precise and consistent estimates for process variables. Data reconciliation has been traditionally used to provide a more representative set of data to calculate steady-state inventories and process yields. For dynamic systems, the use of data reconciliation is relatively nascent. This article examines the potential use of data reconciliation in closed-loop control as a filter to attenuate the noise in measurements of the controlled variables so that the controllers can access more accurate sets of data. Data reconciliation filters were implemented in simulations of a PID control system for a binary distillation column. Results showed that data reconciliation could efficiently reduce the propagation of measurement noise in control loops, so that the overall performance of the controller is enhanced.     

Composition estimation of multicomponent reactive batch distillation with optimal sensor configuration

An inferential state estimation scheme based on extended Kalman filter (EKF) with optimal selection of sensor locations using principal component analysis (PCA) is presented for composition estimation in multicomponent reactive batch distillation. The properties of PCA are exploited to provide the most sensitive dynamic temperature measurement information of the process to the estimator for accurate estimation of compositions. The state estimator is supported by a simplified dynamic model of reactive batch distillation that includes component balance equations together with thermodynamic relations and reaction kinetics. The performance of the proposed scheme is evaluated by applying it for composition estimation on all trays, reboiler, reflux drum and products of a reactive batch distillation column, in which ethyl acetate is produced through an esterification reaction between acetic acid and ethanol. This quaternary system with azeotropism is highly nonlinear and typically suited for implementation of the proposed scheme. The results demonstrate that the proposed EKF estimation scheme with optimal temperature sensor configuration is effective for inferential estimation of compositions in multicomponent reactive batch distillation.     

Design and control of butyl acrylate reactive distillation column system

In this study, the design and control of a reactive distillation column system for the production of butyl acrylate has been investigated. The proposed design is quite simple including only one reactive distillation column and an overhead decanter. The optimal design is selected based on the minimization of total annual cost (TAC) for the overall system. At this optimized flowsheet condition, output multiplicity was found with reboiler duty or feed ratio as the bifurcation parameter. The highest purity stable steady state was selected as the base case condition for the control study. The overall control of this system can be achieved with no on-line composition measurements. Simple single-point tray temperature control loop is designed to infer final product purity. From results of dynamic simulation, the proposed control strategy performs very well in rejecting various disturbances while maintaining butyl acrylate product at high purity. One of the important finding in this paper is that it is better to operate this reactive distillation column not at the exact feed stoichiometric balance point for better operability reason. The control performances of the proposed operating point and the operating condition right at the exact stoichiometric balance point will be compared.     

Dynamic Study of Distillation Column Operated with Tray Heat Source Combined with Reboiler

This work reports experimental tests using the distribution of energy in distillation by applying internal heat sources combined with a reboiler in order to reduce the transition time when the process is disturbed. In this way, a dynamic study was undertaken in a pilot column with ethanol and water, comparing the effects of a step disturbance in the reboiler and the same heat quantity in the intermediate tray of the column. The results showed that the use of the combined heat supply reduced the hydraulic delay in the distillation column and, consequently, the transition time. In this way, this study suggests that it is possible to use the heat distribution to control a distillation column using classical strategies and simple controllers, such as proportional-integral-derivatives (PID), and with this obtain faster responses.     

Synthesis of PID controller for unstable and integrating processes

Properly designed controllers provide stable closed-loop response for open-loop unstable processes. Internal model controller equivalent PID tuning rules for low order unstable plus dead time systems are synthesized in this work. The controller is approximated near the vicinity of zero (origin). Controller parameters are derived by equating the closed-loop response to a control-signature (desired closed-loop response) involving a user defined tuning parameter, λ. Simulations are carried out to show the performance of the proposed tuning scheme for both set point and disturbance rejection cases.     

AN INDIRECT FEEDFORWARD COMPOSITION CONTROLLER FOR DISTILLATION COLUMNS

This paper addresses the problem of designing an indirect feedforward controller, also called cascade control, to regulate the product composition of distillation columns to overcome load disturbances. The overall controller is composed of two cascaded controllers. The primary controller is basically a low-gain controller, which uses slow (delayed) composition measurements to provide servo responses (composition control). The secondary controller has the structure of a high-gain proportional-integral (PI) controller with an antireset windup scheme, which uses fast temperature measurements at a given distillation tray to track the output of the primary controller. In this way, the secondary controller also provides protection against load disturbances. A simulated example is used to illustrate the functioning of the proposed controller.     

丙烯精馏塔智能控制系统设计及应用

针对乙烯生产装置丙烯精馏塔的工艺特征和操作特点,利用支持向量机在小样本数据建模中的优势,提出一种基于支持向量机丙烯浓度软测量技术,解决了塔釜建模数据样本少的问题,实现了塔釜丙烯浓度在线测量。在上述软测量系统的基础上,设计了丙烯浓度智能控制系统。该系统采用模糊PID作为丙烯浓度控制器,其输出量作为灵敏板温度控制器的设定值,与灵敏板温度控制构成串级调节系统,同时为了克服进料量对灵敏板温度造成的干扰,设计了进料流量前馈控制器。丙烯浓度智能控制系统对塔釜丙烯指标进行实时控制,提高了塔釜丙烯浓度的控制平稳度,解决了塔釜丙烯浓度超标问题。现场应用效果表明,该丙烯浓度软测量系统测量精度高,控制系统可以有效控制塔釜丙烯浓度,取得了良好的控制效果,满足了工业现场运行的需要。     

Design and control of reactive distillation for hydrolysis of methyl lactate

Esterification of raw lactic acid from fermentation broth and then hydrolysis of lactate ester in reactive distillation column is an effective process for purification of lactic acid. Reactive distillation for hydrolysis of methyl lactate is studied. First, the thermodynamic properties and reaction kinetics are analyzed; then the reactive distillation column is designed based on the objective function total annual cost. The effects of tray number of rectifying section, tray number of reactive section, and feed location on the total annual cost are investigated. And a dual-temperature control structure is proposed for the optimal reactive distillation column, and the results show that it works quite well for this hydrolysis system.     

An indirect feedforward composition controller for distillation columns

This paper addresses the problem of designing an indirect feedforward controller, also called cascade control, to regulate the product composition of distillation columns to overcome load disturbances. The overall controller is composed of two cascaded controllers. The primary controller is basically a low-gain controller, which uses slow (delayed) composition measurements to provide servo responses (composition control). The secondary controller has the structure of a high-gain proportional-integral (PI) controller with an antireset windup scheme, which uses fast temperature measurements at a given distillation tray to track the output of the primary controller. In this way, the secondary controller also provides protection against load disturbances. A simulated example is used to illustrate the functioning of the proposed controller.     

19万t/a醋酸乙烯精馏装置的技术改造

应用计算机模拟了进料热状况对醋酸乙烯精馏系统的影响,并计算了不同回流比下的塔板数、能耗、冷却负荷等参数值,通过改变进料热状况消除塔内恒浓区,优选出最佳精馏方案,即进料气化率20％、同流比为2、理论板数为63。应用复合斜孔塔板代替筛板塔板,对醋酸乙烯精馏塔进行了技术改造。改造后装置生产能力提高至19万t／a,节能20％,产品质量稳定,醋酸乙烯精馏塔运行周期延长至4年。     

Temperature Inferential Control of Heat‐Integrated Distillation Column Based on Variable Sensitive Stage Temperature Set‐point

Heat‐integrated distillation is an improved distillation technique with remarkable energy‐saving potential. A control scheme with a variable sensitive stage temperature set‐point is proposed to solve the control problem of a heat‐integrated distillation column (HIDiC). An online estimator is designed to support the variation of the set‐point. The locations of the stage temperature measurements are carefully selected based on a combination strategy with three steps. First, the sensitive stages are selected. Then, the following stages are determined by a PCA‐based method. Finally, a maximum differentiation method provides the remaining measurement selections. According to the profile parameters estimated by the proposed estimator, the set‐point of the sensitive stage temperature is adjusted adaptively to reduce the influence of the disturbances. Two commonly‐used PID controllers, the sensitive temperature control and the temperature differential control, are developed as the comparative study. The simulation results show that the proposed control scheme has a distinct advantage in restraining different disturbances.