ON THE DESIGN OF ROBUST CONTROL SYSTEMS FOR DISTILLATION COLUMNS

The distillation column dynamics is very nonlinear, especially at high purity. Multivariable control system designs, which are essentially linear, may not be able to perform well at different operating conditions. This paper looks at three different multivariable design techniques—decoupling control, optimal state feedback and pole assignment as applied to distillation column control. Robustness of these techniques are analyzed by looking at the performance of these controllers at different operating conditions. Some interesting results are obtained.     

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.     

负载型催化剂溶液浸渍制备专家系统的初步研究

浸渍过程的分析表明,浸渍制备涉及到大量的经验规律。因此,预测浸渍制备的条件参数是一个比较复杂的不确定性问题,使用专家系统方法有助于此类问题的解决。实现专家系统的关键在于知识的合理表述和系统框架的建造。在文中我们构成了一个浸渍制备的专家系统原型,该系统具备处理数值和非数值信息的功能。此外,讨论了浸渍知识的智能化处理问题。     

SYNTHESIS OF TWO-POINT LINEAR CONTROLLERS FOR BINARY DISTILLATION COLUMNS

The two-point composition control problem of binary distillation columns is addressed. First, the exact model-based inventory control problem is studied, yielding the underlying solvability conditions with physical meaning, the limiting behavior attainable with any controller, and its equivalence with nonlinear geometric and MPC controllers. This control behavior is recovered via a measurement-driven linear controller made of a pair of decoupled PI loops and a static interaction compensator. A closed-loop dynamics study formally shows the recovery feature and provides stability conditions coupled with conventional-like tuning rules. The controller implementation needs only four static parameters that have direct physical meaning and can be estimated from plant data and/or simulation packages. The proposed technique is tested with two representative examples in the presence of actuator errors, measurement delays, and load disturbances, matching or improving the behavior obtained with previous schemes.     

精馏过程专家系统用数据库系统的设计与实现

化工物性数据内容庞杂，数据库的设计是化工软件的重点和难点，本文提出一种用ＴＵＲ－ＢＯＰＲＯＬＯＧ语言外部数据库技术实现基于磁盘的数据库管理系统的设计方法，解决了数据库庞大与微型机内存不够的矛盾，通过接口计算模块可方便地从本数据库中调用数据；实现了友好的用户界面，提高了数据库管理的效率和透明性。     

GAIN SCHEDULING FOR COMPOSITION CONTROL OF DISTILLATION COLUMNS

Composition control loops for high purity distillation columns are highly non-linear, particularly their gain characteristics. A simple gain scheduling approach suggested by Shinskey is evaluated. This approach involves a linear approximation to the process gain when product purity increases and the assumption of constant gain when purity drops. Total loop gain is kept constant when purity increases. Digital simulations show that gain scheduling yields significant improvements in control performance.     

预防混凝土碱－集料反应智能系统

简要地介绍预防混凝土碱－集料反应智能系统（ＰＡＡＲＩＳ）的结构、功能和设计技术。     

ON THE EXERGY ANALYSIS OF BINARY DISTILLATION COLUMNS WITH HEAT INTEGRATION

The exergy analysis is done for the conventional distillation, the VR (Vapor Recompression) distillation, and the SRV (Secondary Reflux and Vaporization) distillation with the aid of computer simulation. It is shown that the careful use of thermodynamic diagrams helps us for the exergy analysis.     

DESIGN OF A COMPOSITION ESTIMATOR FOR INFERENTIAL CONTROL OF DISTILLATION COLUMNS

In distillation column control, secondary measurements such as temperatures and flows are widely used in order to infer product composition. This paper addresses the design of the linear static estimators using the secondary measurements for estimating product compositions of distillation columns. Based on the unified framework for the estimator design, the relationships among various static estimators are discussed in terms of the estimator structure. Il is shown that the projection estimator is equivalent to the regression estimators in the special cases. Since the projection estimator heavily depends on the measured inputs such as reflux flow and heat input to the reboiler due to its structural characteristic, the estimation performance is far more sensitive to measurement noise and nonlinearity of them, compared wiih the regression estimators based on the PCR or PLS method. It is also found that the use of the measured inputs leads to performance deterioration of both the projection and regression estimators because of their nonlinear effects on the product compositions especially in high-purity columns. Design guidelines for the PCR and PLS estimators are presented by analyzing the results of the simulation studies on a high-purity column example. The estimator based on the guidelines is robust to sensor noise and has a good predictive power     

分离五组分含复杂精馏塔流程的研究

以年费用为目标函数，对22个分离5组分混合物的精馏流程进行了研究．除了简单塔的14个序列之外，还包含8个含复杂塔（侧线汽提和／或侧线精馏塔）的流程.以不同的物系在不同的进料组成下，对流程的分离费用进行实例研究，通过分析得出构造含复杂塔精馏流程的实用规则.     

DECOUPLER DESIGN AND CONTROL SYSTEM TUNING BY INA FOR DISTILLATION COMPOSITION CONTROL†

Six distillation column models have been used in studies of the usefulness of the Inverse Nyquist Array (INA) method for design of dual composition control for distillation. Five of the column models are experimental, one describing an industrial column, the others four pilot plants. One column model is obtained by modeling from first principles.

The control strategies investigated and compared are multiloop SISO, 2-way decoupling and l-way decoupling. The control variables are the standard ones, i.e. reflux flow and boilup.

In most of the cases INA has been found to be a useful tool for design of the loops and for comparison of the different control approaches. INA has also been found to be useful for simultaneous tuning of the decouplers and the feedback controllers.

For 2-way decoupling the criterion to minimize interaction at the critical frequency for each primary feedback loop has been found useful in most, but not all, cases. The scheme can be designed by pure gains in the decouplers and there is no reason to introduce dynamics into the decouplers—the systems studied are already sufficiently rich in dynamics.

INA has been found to be a suitable vehicle for the choice between the two possible l-way decoupling schemes.

With the design approach taken, l-way decoupling has been found to provide considerably better control quality than 2-way decoupling in two of the six systems, the differences in control quality being small in the other cases.

The effect of model mismatching on the results, caused e.g. by process nonlinearities, is discussed and simple rules to decrease the parameter sensitivity for 2-way decoupling schemes are given. When model mismatching is considered, the advantage of l-way decoupling over 2-way decoupling seems to increase.

One deficiency of the INA design as used in this paper is that it does not single out the design which is to be preferred on the grounds of robustness.     

A FUZZY MATCH BASED EXPERT SYSTEM FOR SYNTHESIS OF SEPARATION PROCESSES

A predictive parallel search algorithm,the fuzzy match inference strategy,is implemented ina prototype expert system.Selection of separation technologies and sequencing of separators are beingapproached in an integrated manner.The fuzzy match mechanism results in a relatively smaller subsetof favored schemes,constituting a hyperstructure for further quantitative evaluation and combinationoptimization.An industrial application example of aromatics extraction separation is presented.     

预防碱—集料反应的专家系统

混凝土碱－集料反应及其防治已成为全世界共，研究和重视的问题。“预防混凝土碱－集料反应的专家系统”是针对我国现状而研制的用于解决我国ＡＡＲ预防问题的计算机智能系统。它以唐明述教授几十年来积累和收集的ＡＡＲ预防知识为主，同时吸收和补充了国内外其他ＡＡＲ专家的知识和经验。知识收集经历了“整体－具体－一般”的过程；知识整理采因素层次化分析法，并设计：可装卸式框架结构”来表示知识。ＰＡＡＲＣＥ采用模块化...     

计算机智能控制系统在精馏装置中的应用

介绍了计算机智能控制系统在１氟１,１二氯乙烷（ＨＣＦＣ１４１ｂ）精馏装置上的应用。采用ＧＥＮＥＳＩＳ工控软件,在１台工业控制计算机上实现了ＤＤＣ和ＳＣＡＤＡ功能,并将工艺要求以人工智能的方式综合进ＳＰＣ级,构成计算机智能控制系统。系统投运后,产品纯度从不足９９．９０％提高到９９．９０％以上,产量从２５００ｔ／ａ提高到５０００ｔ／ａ。     

AN INNOVATIVE PROJECT INVOLVING AN APPROPRIATE HYBRID DISTILLATION SYSTEM FOR SMALL-SCALE ETHANOL FUEL PRODUCTION

A yield increase in the distillation step reveals a promising way to guarantee technical and economic feasibility for small-scale ethanol production (SSEP), up to 30 L · h^?1. The objective of this study is to assess a differentiated distiller, a hybrid composition involving a Vigreux column and a packing (Raschig rings) column in the stripping and rectifying sections, respectively. To evaluate the distiller, seven tests were performed in a continuous operation system. The feed and vaporization rates were varied so that their influence on the operational performance of the distiller could be measured. Specifically, the ethanol concentration in the distillate and bottom products, the operational capacity, and the energy factor were measured. The results prove the technical feasibility of the hybrid distiller, and the application of the hybrid distiller in small-scale distilleries is promising. To improve the distillation step, construction of a pilot-scale column is recommended.     

A REACTIVE DISTILLATION PROCESS FOR AN AZEOTROPIC REACTION SYSTEM: TRANSESTERIFICATION OF ETHYLENE CARBONATE WITH METHANOL

A reactive distillation process is proposed for manufacturing dimethyl carbonate (DMC) through the transesterification reaction of ethylene carbonate (EC) with methanol. Modeling and simulation of the reactive distillation column have been carried out to study the effects of operating conditions, such as the reflux ratio, the number of theoretical plates, the feed ratio, the top effluent, the liquid holdup, and the feed location, on EC conversion and product composition at the top of the reactive distillation column. The calculated results show that a complete EC conversion can be achieved. The model reliability is analyzed under different Murphree tray efficiencies, showing no considerable difference between the equilibrium and nonequilibrium models for this system. And the calculated results are verified by experimental data and commercial operation of a dimethyl carbonate plant of 10,000 tons per year.     

DEVELOPMENT OF A FUZZY EXPERT SYSTEM FOR THE SELECTION OF BATCH DRYERS FOR FOODSTUFFS

The selection of dryers is an art in which knowledge, experience and science all play important roles. Historically, dryer selection has been made by experts on the basis of their extensive knowledge. However, in recent years, computer-based techniques have been developed, which have the potential of at least partially deskilling this process. Of the various possibilities, fuzzy expert systems, in which the selection qualifiers are represented as linguistic rather than numerical variables, are the most promising. This paper describes the development of a fuzzy system for the selection of batch dryers for food products. It featured a novel modular approach in which independent selection goals for dryer type, atmospheric, vacuum or freeze operation, and single or multiple units were adopted. This made the system particularly flexible and amenable to adaptation. The program starts from a ' drying process checklist“ in which the principal process variables are specified, and provides a ranked list of feasible alternative dryers. The algorithm was extensively tested and provided quite plausible results. Four representative case studies are presented and discussed.     

DEVELOPMENT OF A FUZZY EXPERT SYSTEM FOR THE SELECTION OF BATCH DRYERS FOR FOODSTUFFS

ABSTRACT

The selection of dryers is an art in which knowledge, experience and science all play important roles. Historically, dryer selection has been made by experts on the basis of their extensive knowledge. However, in recent years, computer-based techniques have been developed, which have the potential of at least partially deskilling this process. Of the various possibilities, fuzzy expert systems, in which the selection qualifiers are represented as linguistic rather than numerical variables, are the most promising. This paper describes the development of a fuzzy system for the selection of batch dryers for food products. It featured a novel modular approach in which independent selection goals for dryer type, atmospheric, vacuum or freeze operation, and single or multiple units were adopted. This made the system particularly flexible and amenable to adaptation. The program starts from a ‘ drying process checklist“ in which the principal process variables are specified, and provides a ranked list of feasible alternative dryers. The algorithm was extensively tested and provided quite plausible results. Four representative case studies are presented and discussed.     

A REACTIVE DISTILLATION PROCESS FOR AN AZEOTROPIC REACTION SYSTEM: TRANSESTERIFICATION OF ETHYLENE CARBONATE WITH METHANOL

A reactive distillation process is proposed for manufacturing dimethyl carbonate (DMC) through the transesterification reaction of ethylene carbonate (EC) with methanol. Modeling and simulation of the reactive distillation column have been carried out to study the effects of operating conditions, such as the reflux ratio, the number of theoretical plates, the feed ratio, the top effluent, the liquid holdup, and the feed location, on EC conversion and product composition at the top of the reactive distillation column. The calculated results show that a complete EC conversion can be achieved. The model reliability is analyzed under different Murphree tray efficiencies, showing no considerable difference between the equilibrium and nonequilibrium models for this system. And the calculated results are verified by experimental data and commercial operation of a dimethyl carbonate plant of 10,000 tons per year.