THESES OF THE PhD DISSERTATION SIMULATION AND CONTROL OF BATCH REACTORS dr. Lajos Nagy Supervisor: dr. Ferenc Szeifert CSc, associate professor University of Veszprém Department of Process Engineering 2005.
1. INTRODUCTION AND AIM OF THE WORK Batch systems are mainly applied when multiproduct or sterile environment is required. Generally standard equipment (e.g. glass-lined reactors), which can easily be transformed for manufacturing another product, is employed. Hence, batch and semi-batch reactors are widely used in pharmaceutical-, food-, fermentation- and fine chemical industries. Batch reactors are applied for manufacturing products in small quantities, for process development of new products, for producing special and very expensive products and in cases when continuous processes cannot be applied for technical or economical reasons. Modeling and control of batch systems, especially batch reactors is a difficult task. Difficulties primarily arise from the facts that batch processes are generally unsteady-state and mainly due to the excess heat from the chemical reactions they are non-linear. Present thesis work deals with the modeling, simulation and control of batch systems including batch reactors. The main objective was to study the models which can be used for reactors from the laboratory-size to the pilot and plant sizes, as well as the evaluation of their applicability for control purposes. The work also aimed at the development of simulation programs which allow studying the reactor control algorithms and can be used for determination the parameters of the controllers. Another objective of the research was to establish a laboratory background to test and compare the developed algorithms under real physical conditions. 2. EXPERIMENTAL METHODS AND TOOLS In the laboratory of Department of Control Engineering, University of Veszprém, two computer controlled systems were built: a one-liter automated glass reactor system for process development purposes and a process-controlled pilot-size batch unit for solving scale-up problems. Both systems include data acquisition facilities. Based on the collected data, the parameters of the developed models are determined using the appropriate modules (e.g. Optimization, Identification) of the Matlab/Simulink program package. Applying the models and the simulation programs, the control algorithms were studied and their parameters were determined in Matlab/Simulink environment too. The tuned controllers were implemented in the process control software of the physical system and the algorithms were tested this way too. 2
3. NEW SCIENTIFIC RESULT 1. A physical system was built for developing, studying and testing batch control algorithms and solving scale-up problems in the Technology Laboratory of the Department of Process Engineering. The system consists of a glass reactor and a pilot-size reactor. 2. A number of models of the two reactors, with different granularity were developed and compared. a. The parameters of the models were determined by identification from the data collected on the studied systems. b. The performance of the first order, the tendency and the detailed models were investigated and it was concluded that the tendency model, in spite of its simplicity, gives results similar to those of the detailed model. c. It was determined that, considering the thermal behavior, the description of the jacket requires more complex model than the reactor does. 3. A simulation program package was developed. The package allows the simulation studies of jacketed reactors and their environment in different batch manufacturing systems. a. Comparing the results of the simulation studies and the physical experiments it can be stated that the simulator can be applied for the adequate description of the physical system and for the design and testing of controller parameters. This statement is also justified by the fact that several industrial control problems were solved with the help of the simulator. b. Applying the described simulation method, the tuning of controller parameters can be done much faster than tuning with experiments on the physical system. 4. A recipe control program was elaborated and implemented in the Matlab/Simulink environment used throughout in this work. a. The realized system allows conducting reproducible experiments and accelerates the research and development work significantly. 3
b. The system supports the integration of simulation techniques into the process control system which in itself is not well suited for research and development purposes. 5. Algorithms (PID, dual mode, GMC, PCC) used widely for temperature control of reactors were compared. a. A controller using the PCC principle developed by the research group of our department was adapted on the studied systems. b. It can be stated that in both systems the PCC controller gives better results than the other studied methods do. 6. Two possible solutions for the application of the glass reactor as reaction calorimeter were compared a. It was found that the method based on the calculation of heat transfer rate provides more accurate results (in case of the given instrumentation). b. It was proved that the accuracy of the calculation of heat transfer rates can be significantly increased by applying the signals from thermometers with different dynamics in form of inferential measurements. 7. A control algorithm preventing the overshoot was developed for the temperature control of the glass reactor. This algorithm provides better performance than the built-in (factory) algorithm does. 8. Different split-range approaches were investigated. a. It was proved that the sign of the system gain can change when switching the heat transfer medium. b. It was found that the temperature control of reactor with monofluidic jacket cannot be solved with traditional split-range controller because the sign of the gain changes. 4
4. SCIENTIFIC PUBLICATIONS AND PRESENTATIONS RELATED TO THE THESES PUBLICATIONS: Abonyi J., Á. Bódizs, L. Nagy, F. Szeifert, "Hybrid Fuzzy Convolution Model Based Predictor Corrector Controller", Computational Intelligence for Modelling Control and Automation, IOS Press Holland, 265-270, ISBN 9-051-99474-5, 1999 Abonyi J., Á. Bódizs, L. Nagy, F. Szeifert, "Predictor Corrector Controller using Wiener Fuzzy Convolution Model", Hungarian Journal of Industrial Chemistry, 27(3), 227-233, 1999. Abonyi J., L. Nagy, F. Szeifert: Takagi-Sugeno Fuzzy Control of Batch Polymerization Reactors, Soft Computing In Engineering Design and Manufacturing (Eds.), P.K. Chawdry, R. Roy and R.K. Plant, Springer London, 1997, ISBN 3-540-76214-0, 1997 Madár J., F. Szeifert, L. Nagy, T. Chován, J. Abonyi: Tendency Modelbased Improvement of the Slave Loop in Cascade Temperature Control of Batch Process Units, European Symposium on Computer Aided Process Engineering -13, 467-472, (ESCAPE- 13 Lappeenranta, Finland, June 1-4, 2003), A. Kraslawski, I. Turunen (Eds.), Computer-Aided Chemical Engineering, Vol. 14, Elsevier, 2003 Nagy L., Szeifert F., Chován J. T.: Control of pilot plant size systems with adaptive control algorithms, Mérés és Automatika, 39, 220-224 (1991). Szeifert F., Vass J., Nagy L.: Predictor-Corrector Control algorithm, Automatizálás '89, Székesfehérvár, 501-511 (1989). Szeifert, F., Chován, J. T., Nagy L.: Adaptive Optimizing Control Algorithm for a CSTR, Comp. and Chem. Eng. 16-S, S197 (1992). Szeifert, F., Chován, J. T., Nagy, L.: Dynamic simulation and Control of flexible chemical technologies, Mérés és Automatika, 40, 24 (1992). 5
Szeifert, F., Chován, T., Nagy, L.: Process Dynamics and Temperature Control of Fed-Batch Reactors, Comp. and Chem. Eng. 19-S, S447 (1995). Szeifert, F., Nagy, L., Chován, T., Molnár, F.: Realistic model-based adaptive temperature control of batch reactors, Proc of ACASP '95, IFAC, 201-206, Budapest (1995). Szeifert, F., Nagy, L., Chován, T.,: Model-Based Temperature Control of Fed-Batch Reactors, Proc. of DYCORD+ '95, IFAC, Helsingor (Dánia, 1995). PRESENTATIONS: Abonyi J., L. Nagy, F. Szeifert: Fuzzy Control of Batch Polymerization Reactors, IEEE International Conference on Intelligent Systems, INES'97, pp. 251-255, 15-17 Sept. 1997, Budapest Abonyi J., L. Nagy, F. Szeifert: Fuzzy Control of Polymerization Reactors, 20. KBN, 1997, Szeged Chován T., Szeifert F., Nagy L.: Neural Network based control algorithms, MKN '94, Veszprém (1994). Érsek P., Szeifert F., Nagy L.: A priori model based control of reactors, MKN '95, Veszprém (1995). J. Abonyi, L. Nagy, F. Szeifert: Takagi-Sugeno Fuzzy Control of Batch Polymerization Reactors, 2nd On-line World Conference on Soft Computing (WSC2), June. 1997 Molnár, F., Morász, M., Szeifert, F., Nagy, L., Chován, T.: Model based control algorithms in the CHEMIFLEX system, MKN '93, Veszprém (1993). Nagy L, Szeifert F, Chován T.: Simulation program package for design of batch systems, MKN '99, Veszprém (1999). Nagy L., Árva P., Szeifert F., Chován T.: Control of pilot plant size gas purification system, MKN '91, Veszprém (1991). Nagy L., Moser, K., Árva, P.: Computer controlled crystallization system, MKN '92, Veszprém (1992). 6
Nagy L., Szeifert F., Chován T.: Control of fed-batch reactor, MKN '94, Veszprém (1994). Nagy L., Szeifert F., Chován, T., Molnár, F.: Hierarchy of batch systems, MKN '95, Veszprém (1995). Nagy L., Szeifert F., Kiss P., Kovács K,: Developing and testing system for investigation of adaptive control algorithms, MKN '93, Veszprém (1993). Szeifert F,., Chován, T., Nagy, L.: Adaptive Optimizing Control Algorithm for CSTR. ESCAPE-1, Helsingor (Denmark, 1992). Szeifert F., Chován T., Nagy L.: Control of reactors with adaptive algorithms, MKN '91, Veszprém (1991). Szeifert F., Chován T., Nagy L.: Process Dynamics and Temperature Control of Fed-Batch Reactors, ESCAPE - 5, Bled (Slovenia, 1995). Szeifert F., Nagy L., Chován T., Abonyi J.: Model-Based Control of Batch Systems, DCS 9, Lillafüred, 2003. Szeifert F., Nagy L., Chován T.,: Model-Based Temperature Control of Fed-Batch Reactors, DYCORD+ '95, Helsingor (Denmark, 1995). Szeifert F., Nagy L., Chován, T., Molnár, F.: Realistic model-based adaptive temperature control of batch reactors, ACASP '95, Budapest (1995). Szeifert, F., Chován, T., Nagy, L.: Dynamic simulation and control of flexible chemical technologies, Automation 92, Budapest (1992). Szeifert, F., Chován, T., Nagy, L.: Optimising control of reactors, MKN '92, Veszprém (1992). Szeifert, F., Nagy L., Chován T.: Using of modell based control, MKN '93, Veszprém (1993). 7