Gilbert Casamatta

A General Simulation Model and a Heating/Cooling Strategy to Improve Controllability of Batch Reactors

This paper describes the development of a dynamic simulation model for stirred tank batch or semi-batch chemical reactor and its heating/cooling system. Heat and mass balances are established for the reactor and its jacket. As the general purpose is the thermal control of the reactor, special attention is devoted to the behaviour of the heating/cool-cooling system. The control strategy is based on the use of the thermal flux as manipulated variable. At each sampling time, the controller computes the thermal flux to be exchanged with the fluid flowing inside the jacket to get the desired reactor temperature set-point. This information is then used to select the thermal fluid on the basis of the maximal and minimal thermal flux capacities of each utility. The computer simulation program is flexible, enabling simulation of a batch or semi-batch reactor vessel, ranging from a laboratory pilot plant to full-scale production plant. To demonstrate the good performance of both simulation model and control methodology, experimental results are presented for a pilot plant and simulation studies have been performed for both pilot plant and industrial reactors.

Semi-batch reactor optimization and control for the epoxidation of furfural

Abstract In attempting to optimize a chemical systhesis, competing side reactions often interfere, which degrades the reactants into other undesired subtances. In those cases, the course of the reaction can be influenced by acting on the manipulated variables temperature and feedrate as the reaction proceeds. The determination of such strategies is usually referred to as optimal control. In the present paper, a methodology of optimal control of batch reactors, the main processing tool in fine chemistry, is presented. The implementation of the methodology involves two phases: (i) an optimization phase where a dynamic mechanistic model is determined and used to optimize the process based on a technical—economic objective function and (ii) a control phase where a dynamic empirical model is used to optimize a performance objective function which penalizes deviations of process variables from their optimum values given by the optimization phase. The first part of the paper presents the global strategy and the necessary theoretical developments. The second part of the paper is an illustration of the strategy using the epoxidation of furfural as a model reaction. The optimization based upon an approximate mechanistic model is compared to a more conventional approach involving the response surface methodology. Then, control studies by simulation and experimentation on a 21 pilot plant reactor for the epoxidation of furfural are performed. The previously determined optimal trajectories are implemented in practical operation.

Single-drop transport in a kühni extraction column

Abstract In any solvent extraction column, the global efficiency of the process is partly conditioned by the contact time of the two phases involved, between which the mass transfer occurs. The present paper deals with the prediction of the drop residence time inside a single compartment of a rotary agitated column, the Kuhni column. A single-drop walk model has been developed with a view to predicting the more probable drop trajectory according to the operating conditions (agitation intensity, drop size). This approach is based on the description of the mean flow patterns generated around the impeller by means of a 3D model. The single-drop motion is calculated by combining the local velocity components of the continuous phase and the axial rise velocity of the drop. The validation of the model has been achieved by comparison between the simulation results and the experiments performed in a small-scale device, devoted to the study of single-drop transport inside a representative Kuhni compartment. The single drop is detected at the inlet and the outlet of the compartment by means of infrared cells. The mean drop residence time is derived from this technique and successfully compared to the one calculated by the walk model for laminar or intermediate regimes.

MODELING AND OPTIMIZATION OF LACTIC ACID SYNTHESIS BY THE ALKALINE DEGRADATION OF FRUCTOSE IN A BATCH REACTOR

ABSTRACT The present work deals with the determination of the optimal operating conditions of lactic acid synthesis by the alkaline degradation of fructose. It is a complex transformation for which detailed knowledge is not available. It is carried out in a batch or semi-batch reactor. The “Tendency Modeling” approach, which consists of the development of an approximate stoichiometric and kinetic model, has been used. An experimental planning method has been utilized as the database for model development. The application of the experimental planning methodology allows comparison between the experimental and model response. The model is then used in an optimization procedure to compute the optimal process. The optimal control problem is converted into a nonlinear programming problem solved using the sequencial quadratic programming procedure coupled with the golden search method. The strategy developed allows simultaneously optimizing the different variables, which may be constrained. The validity of the methodology is illustrated by the determination of the optimal operating conditions of lactic acid production.

Optimisation of global pharmaceutical syntheses integrating environmental aspects

Publisher Summary Pharmaceutical synthesis optimization, because of its complexity, is often reduced to the optimization of the reaction step. This chapter discusses the dynamic model, allowing simulating the different synthesis steps and, particularly start-up and shut-down phases involved. This model connected to an optimization method is able to provide the optimal operating conditions satisfying a global objective. The application to an industrial process highlights the benefits of the proposed methodology. The chapter describes the operating conditions involving the optimization of the global synthesis, satisfying economical and environmental criteria, to develop sustainable methodologies. For this purpose, a framework based on a simulation program, modeling a global synthesis (reaction and separation steps), has been developed. Besides global synthesis treatment, the main features of this work lie in the modeling of batch units and of dynamics, particularly during the start-up and the shut-down involved in the different step.

Thermosensitive Probe Based Technique of Local Investigation of ultrasonic reactors

A thermosensitive probe, on the basis of a thermocouple embedded in ultrasound absorbing material, is developped for measuring the local ultrasound power. This paper describes the influence of the height and the nature of the liquid medium on the power consumption, and the results of local absolute power in different ultrasonic reactors.

A model-based supervisory control routine for temperature control of batch reactors: experimental results

Publisher Summary This chapter describes the application of a model-based strategy for the supervisory temperature control of a 12 liters industrial pilot-batch reactor. The reactor is equipped with a multifluid heating/cooling system. The automation of this type of heating/cooling system requires a supervisory control to handle automatically the utility fluids fed into the reactor jacket as well as the intermediate air purge and the refilling after the changeover of the fluid. The objective is to obtain good control of the process even during transient operating conditions, such as refilling of the jacket, which cannot be neglected on industrial scale. The supervisory control is based on the dynamic model of the reactor pilot plant. Once the utility fluid being chosen by the supervisory routine, its flowrate is computed by a controller, which is a nonlinear model predictive control algorithm. Different experiments are presented to demonstrate the performances of the supervisory control of the pilot-plant reactor.

Simulation-aided implementation of supervisory control of industrial batch reactors

Temperature control of batch reactors equipped with a multifluid type heating/cooling system containing an intermediate thermal fluid (pressurised water) is presented. By means of this intermediate fluid the heating/cooling system gains monofluid type behaviour over a wide temperature range. Hereby operation of the reactor is improved. The control strategy consists in using a GPC algorithm to calculate the thermal flux that has to be transferred between the heating/cooling system and the reaction mixture. The thermal flux is then introduced into a model based supervisory algorithm that automatically chooses on-line the appropriate utility. Testing the intervening software is partially carried out by connecting the original plant control software to a simulator of the process. Hereby the software validation procedure is accelerated and utility consumption is reduced, too. Experimental validation of the presented approach on an industrial 160 litres batch reactor gives satisfying performances.