摘要:

The purpose of the paper is to demonstrate aspects of control for biotechnological processes, to introduce both the control engineer and the chemical engineer or biologist to this interdisciplinary field. Starting with an analysis of aspects and problems which arise during automation of biotechnical processes, some of the modern control principles are presented and the perspectives of their use in control of fermentations are discussed. The methods have been known for years, and theoretical research on most of these may be assumed to be complete; however, the availability of inexpensive microcomputers during recent years has also enabled an economical application for small plants. Moreover, the presented algorithms may be used for the optimal design of reactors and plants.

DOI:10.1049/ip-d.1986.0033

出版商:IEE    

年代:1986

数据来源: IET

摘要:

Based on the experimental measurements of Hecht and Rosen in previously published papers, mathematical models were developed for the continuous and semibatch cultivations ofChaetomium cellulolyticumon glucose and cellulose.

DOI:10.1049/ip-d.1986.0034

出版商:IEE    

年代:1986

数据来源: IET

摘要:

Recent technological developments allow the measurement of segregated parameters of cell populations (cell size; protein, DNA and RNA contents) on significant samples of the population (105–106cells). To exploit this information and to develop control approaches based on these parameters, which are more directly related to the growth metabolism, it is necessary to use structured mathematical models of cell populations. In the paper a more general version of a growth-controlled structured model previously developed is presented, which is able to describe cell growth, unequal division and genealogical heterogeneity of budding yeast (Saccharomyces cerevisiae), and, from the model, age and size distributions for populations in steady states of growth are derived. In several conditions, both in batch and in continuous cultures, the experimental protein distributions, obtained by flow cytometry, are shown to accurately fit those predicted by the model and to contain relevant information on the conditions of growth of the microbial biomass. Furthermore, these distributions have a predictive value on process dynamics, being very sensitive to changes in synthesis and division rates, as experiments in batch reactors and in chemostats have shown, and may, therefore, find a use in the development of new control approaches for microbial reactors.

DOI:10.1049/ip-d.1986.0035

出版商:IEE    

年代:1986

数据来源: IET

摘要:

In complex or nonlinear processes the identifiability of classical models fails because of too many parameters. To reduce this number and to keep a description which is significant to the user in pharmacokinetics or bioprocessing a modular representation model is built up. To define all parameters and internal variables of those models, the authors have chosen an electrical equivalent representation. This electrical representation leads to linear and nonlinear associative modules, and this strategy allows them to realise a computer-aided design well suited to biological processes. On the one hand, it allows optimal therapeutic drug control after defining optimal criteria. On the other hand, it may be used for biomedicine, ecology and bioprocessing problems. The CAD system is conceived like a ‘Lego’ game and it can be used with minimal or no knowledge of programming and computer science. Its main goals are to formulate, resolve and simulate quickly any linear or nonlinear hypothesis of biological processes, and give time for innovation in biological research. Pharmacokinetic models are founded on the hypothesis of transmembrane drug transfer and modelled by differential equations. These differential equations allow the description of drug kinetics orin vivodrug behaviour by a compartment model. This compartment model, which is a representative or descriptive model, tries to give a concrete physiological picture of transmembrane drug transfers. In the usual pharmacokinetic studies, the compartment model is a satisfactory approach to the treatment of simple linear diffusion and elimination processes. In these cases, the canonical form (diagonal form Σ aie-λit) deduced from those models includes a number of parameters approaching the number of parameters of the representative model. Then, for a set of experimental data, when the canonical form is identified, it is possible to reconstruct the original compartment model with few structural hypotheses. For more complex or nonlinear processes, the compartment model fails because of its large number of parameters with regard to the number of identified parameters in the diagonal form. To treat these processes, the paper presents a modular model which is a representative model. In such a model, the number of parameters approach the number of canonical form parameters. On the other hand, this modular network allows a simple extension to nonlinear functions included in the linear network. The definition of this model leads to a computer-aided-design tool, suitable for any linear or nonlinear pharmacokinetic problem. To define all components of the modular model it is necessary to unify all pharmacokinetic parameters; so the authors have established an analogy table between classical pharmacokinetic and electrical parameters. This equivalence table suggests an electrical representation with physiological meaning similar to the physiological compartment concept. In this electrical model, the physiological parameters, such as elimination clearance, volume of distribution and transfer clearance between several diffusion areas, are the constitutive parameters of the model. Then, this analogy allows the inclusion of major limiting parameters like arterial or hepatic blood flow in the model.

DOI:10.1049/ip-d.1986.0036

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The development of a Kalman filter for state and parameter estimation of a biotechnical process is discussed. Because of the large complexity of biotechnical processes, mathematical models for online estimation are based on extensive simplifications. Therefore model errors in the structure and parameters cannot be avoided. In such situations, simulations of the process in combination with the estimator are very helpful during the design phase: these permit fast examinations of the different behaviour of linear filters compared to nonlinear algorithms and also investigations of the influence of sampling interval and initial values of state and filter variables on the estimation. By the use of such simulations, the suitability of process models with various degrees of simplifications can also be easily tested. Based on the simulations, an extended Kalman filter with iteration of the output equations was chosen. Besides the states, two parameters of a third order process model are estimated online. The filter algorithm was tested during batch processes and worked well after a slight modification. The filter behaviour observed in the experiments was very similar to the simulations.

DOI:10.1049/ip-d.1986.0037

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper describes progress in the development of reliable and practicable online estimations of biomass and secondary product (idiolite) formation in batch processes. Earlier work using data from cellulose and sorbose fermentations is reviewed, describing the success of the application of the Kalman filter to biomass estimation in batch culture. Progress in model development for secondary product formation is also reviewed. Results of investigations into the application of estimation to the batch growth ofStreptomyces clavuligerus(a typical industrial lactam antibiotic producer) are given. A large data base of experimental results for offline model development has been established, and the effects of oxygen-limited growth, stirrer speed and other possible interactions causing deviations from Monod-type growth are discussed. The interactions between process variables are considered, and investigated by corresponding alternative exploratory changes in the model. Implications for control and estimation strategies are explored and preliminary results given for the application of these to the batch process, using prototype hardware and software for online estimation.

DOI:10.1049/ip-d.1986.0038

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper describes an investigation into the application of state estimation and adaptive control to fed-batch fermentation for penicillin production. The work forms part of an industrial collaborative project, the aim of which is the optimising control of large fed-batch fermenters. Estimates of biomass are made using an extended Kalman filter from on-line measurements of carbon dioxide production rate and fermentation volume. The estimated biomass is controlled to a reference trajectory by an adaptive generalised predictive controller manipulating the sugar feed rate. A comparison of performance is made with control by conventional proportional plus integral (PI) techniques. The results presented are obtained from simulation studies while validation studies are carried out on both a 30 1 pilot plant fermenter and the industrial plant.

DOI:10.1049/ip-d.1986.0039

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper describes an ongoing investigation into the application of a multivariable adaptive control technique to a fed-batch baker's yeast fermentation. The application of conventional 3-term controllers provides poor control due to problems in tuning individual loops, owing to the time-variant and nonlinear properties of the process. Furthermore, the main process variable, cell mass, cannot be measured directly and hence control must be effected by either estimating the cell mass online or, alternatively, by controlling the environment for optimal cell growth. The latter approach requires the simultaneous optimisation of two or more process variables, requiring multivariable techniques. Results are presented describing the practical problems of establishing a suitable structure for the adaptive technique and the experience gained in using recursive least-squares estimation of process variables. The paper also includes results of the online application of multivariable adaptive control on a pilot-plant fermenter.

DOI:10.1049/ip-d.1986.0040

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The biological processes of waste-water treatment have often been regarded in practice as largely self-controlled and somewhat inflexible in their operation. The paper reviews some of the reasons why it has been difficult to apply the methods of control theory to these processes, and what the future role of control in waste-water treatment might be. Attention is restricted to three processes: the activated sludge process, the oxidation ditch and anaerobic digestion. In contrast to many biotechnical processes, these processes are characterised by a heterogeneous culture of micro-organisms and by multiple substrates degraded along several reaction pathways. Their dynamics are extremely difficult to identify, their observed input/output relationships frequently exhibiting substantial stability punctuated by abrupt instabilities. Other aspects of their behaviour are relatively well defined, in particular the dynamics of dissolved oxygen in the activated sludge process, and have been equally well studied from the point of view of online state-parameter estimation and adaptive control. There is still, however, a large gap between practice and theory, and, in looking briefly at an agenda of problems for the future, the paper places special emphasis on,inter alia, issues of fault detection and diagnosis and the use of plant operator experience in generating novel approaches to control.

DOI:10.1049/ip-d.1986.0041

出版商:IEE    

年代:1986

数据来源: IET