M. Cabassud

Application of iterative learning control to an exothermic semibatch chemical reactor

Focuses on the temperature control of a semibatch chemical reactor used for fine chemicals production. Such a reactor is equipped with a heating/cooling system composed of different thermal fluids. Without extensive modeling investigations, a feedback-feedforward control strategy is proposed for ensuring the tracking performance of the desired temperature profile. Such a strategy is derived from a family of the iterative learning control (ILC) algorithms named batch model predictive control (BMPC). Learning is achieved without requiring a detailed knowledge of the system, which may be affected by unknown but repetitive disturbances. The learning control solution is based on the minimization of a linear quadratic cost function. The synthesis of the proposed strategy is studied, and improvements of the algorithm features are proposed. First, guaranteed convergence of the algorithm is illustrated in a few experimental runs. Second, some practical considerations for the removal of high-frequency disturbance effects are outlined to improve the achieved performance. Third, a robust supervisory control procedure is employed to choose the right fluid and to reduce the superfluous fluid changeovers, mainly when different fluids are available. Finally, experimental results are presented to illustrate the practical appeal and effectiveness of the proposed scheme.

Adaptive control of a multipurpose and flexible semi-batch pilot plant reactor

Abstract Semi-batch operation is currently used in the pharmaceutical or fine chemical industry. Control of such an operation is difficult to ensure by conventional PID as operating conditions and operations change a lot even for the same apparatus. So it is very important in the fine chemical industry to maintain the flexible and multipurpose characters of batch reactors during their automation. This study deals with adaptive thermal control of different kinds of operation (heating, cooling, exothermic reactions carried out in a semi-batch jacketed pilot reactor. Experimental results show the robustness of the algorithm in respect to strong disturbances, its ability of tracking high nonlinear setpoint trajectories and its good control qualities during various chemical reactions.

A new strategy for temperature control of batch reactors: experimental application

In this paper, a new strategy for temperature control of multipurpose batch reactors using a cascaded model based control is presented. This strategy is based on the use of the thermal flux as the manipulated variable. At each sampling time, the master controller computes the thermal flux to be exchanged between the reactor content and the thermal fluid flowing inside the jacket. This information is then used to determine the right fluid and to evaluate the opening value of the control valve. For this purpose a physical modelling of the thermal system has been developed. Finally, the control valve opening degree is computed and applied to the plant.

Use of neural networks for liquid-liquid extraction column modelling: an experimental study

Abstract This paper presents a new application of neural networks to the modelling of a chemical pilot plant: a pulsed liquid–liquid extraction column. This separation process presents a highly non-linear behaviour and time-varying dynamics. Usually, physical simulation models of chemical plants describing some aspects of hydrodynamics and mass transfer are static or very complex and need excessive computer time. It is proposed that improved predictions can be obtained using a multilayer artificial neural network instead of the physical model of the process. The results obtained illustrate the successful application of such a neural network modelling approach.

Adaptive Model Predictive Control

This paper gives an overview of our studies on adaptive control performed in our laboratory for more than ten years enlightened by results of practical applications on different pilot plants. Applications have been made in two fields: continuous processes such as liquid-liquid extraction columns and batch processes, typically batch or semibatch reactors. Formerly a classical adaptive controller based on a “black-box” model: the Generalized Predictive Controller with Model Reference (GPCMR) has been used. Results were very good in the case of continuous processes but showed the limits of this type of algorithm when applied to batch processes with large changes of dynamics and long time delay. So, a special part is devoted to focus on the important advantages and improvements brought by the use of an Adaptive Model-based Controller in comparison with the classical GPCMR.

Realistic model-based predictive and adaptive control of batch reactor

Abstract This paper presents an original approach which makes use of a realistic thermal model for adaptive predictive control and supervision of a semibatch jacketed reactor. The first part is devoted to the development of an adaptive controller based on a reaUstic model established by thermal balances on the reactor and its jacket. As a first interest, an on-line deterministic estimator of the heat generated during the reaction is developed. In a second part a realistic model is used for model supported supervision to prevent temperature overshoot, especially in the case of industrial reactors, the temperature control being ensured by the adaptive controller.

Experimental application of nonlinear model predictive control: temperature control of an industrial semi-batch pilot-plant reactor

This paper describes the application of nonlinear model predictive control (NMPC) to the temperature control of a semi-batch chemical reactor equipped with a multi-fluid heating/cooling system. The strategy of the nonlinear control system is based on a constrained optimisation problem, which is solved repeatedly on-line by a step-wise integration of a nonlinear dynamic model and optimisation strategy. A supervisory control routine has been developed, based on the same nonlinear dynamic model, to handle automatically the fluid changeovers. Both NMPCand supervisory control have been implemented on a PCand applied to a 16 l batch reactor pilot plant. Experiments illustrate the feasibility of such a procedure involving predictive control and supervisory control. # 2002 Elsevier Science Ltd. All rights reserved.

Optimisation and scale-up of batch chemical reactors: Impact of safety constraints

This work presents a methodology in order to determine the operating conditions simultaneously optimising the chemical yield and considering the safety aspect. The aim is to determine time evolutions of the reacting mixture temperature and the feed rate of reactants which not only define a maximal efficiency but also involve an adequate generated heat which can be removed by the cooling system. The problem is converted into a non-linear programming problem which is solved by standard Non Linear Programming. The methodology is validated on an industrial synthesis of a pharmaceutical product which presents high exothermicity. Results show the influence of the safety and economical constraints on the determination of optimal operating conditions. Especially, when no constraints are considered, the optimal solution is to operate batch-wise. When the generated heat is limited, the reactant has to be introduced according to a specified feed-rate profile. Experiments carried-out in a 1 litre pilot plant reactor confirm the optimisation results. This reactor is equipped with a control methodology based on temperature control through pressure which allows to remove a large amount of heat through the condenser. Then, scale-up to a 8 m3 glass-line jacketed reactor shows the relevance of the constrained optimisation approach.

Single drop break-up in a Kühni column

Abstract In order to determine breakage abilities of droplets in a Kuhni column stage, an automatic device devoted to routine working and suitable for any industrial two-phase system was developed. The operating conditions were as follows: mother drop diameter, 1–4 mm; rotation speed of the impeller, 100–250 min −1 ; various two-phase systems were studied. Drop injection, data acquisition and data processing were achieved with a microcomputer, leading directly to the following statistical quantities: breakage probability and daughter drop size distribution. The results are discussed for the following two ternary systems recommended by the European Federation of Chemical Engineering: water-acetone-toluene and water-succinic acid-n-butanol (the aqueous phase is the continuous one). Two cases were studied: aqueous and organic phases without solute; aqueous and organic phases equilibrated with a low percentage of solute. This study affords information about drop breakage, which is necessary for establishing breakage laws. Furthermore, these laws may be introduced into a drop population balance model. In this way, it is expected that the behaviour of the dispersed phase in a Kuhni column may be predicted over a wide range of operating conditions.

Constrained optimization for fine chemical productions in batch reactors

Abstract Batch and semibatch reactors are the main device of batch processes which are still widely used to produce pharmaceuticals, polymers, biotechnologicals etc. Fine chemical transformations are characterized by quite complex reaction systems which can produce undesirable end products. As the aim of the fine chemical industry is to produce high quality and purity products, it is essential to optimize batch operating conditions, i.e. temperature profile, feed flow rate, amount of reactant and final batch time, taking into account constraints on the experimental feasibility (heating and cooling rates) or the specificities of fine chemistry productions (purity constraints, …). In this work, the optimal control problem is converted into a non-linear programming problem solved by the generalized reduced gradient procedure coupled with the golden search method, for the search of the total batch time. The efficiency of the methodology is shown by its application to different formulations of the problem for different chemical reaction schemes and with stress laid on the influence of the constraints on the limitation of temperature variations and byproduct formation.