Biochemical reactors Controllability

Chemical Engineering, Volume 3, Third edition Chemical Biochemical Reactors Process Control Edited by J. F. Richardson and D. G. Peacock... 

Imagine that we wish to control automatically a biochemical reactor in which fermentation is taking place (Figure 9.3). 

Richardson, J.F. and Peacock, D.G. (1994) Coulson Richardson s Chemical Engineering, Vol. 3 Chemical Biochemical Reactors Process Control, Pergamon. 

Volumes 1, 2 and 3 form an integrated series with the fundamentals of fluid flow, heat transfer and mass transfer in the first volume, the physical operations of chemical engineering in this, the second volume, and in the third volume, the basis of chemical and biochemical reactor design, some of the physical operations which are now gaining in importance and the underlying theory of both process control and computation. The solutions to the problems listed in Volumes 1 and 2 are now available as Volumes 4 and 5 respectively. Furthermore, an additional volume in the series is in course of preparation and will provide an introduction to chemical engineering design and indicate how the principles enunciated in the earlier volumes can be translated into chemical plant. 

When the biochemical reactors are kinetically controlled, the batch bioreactors and the PFR are described by the same design equations (Equations (11.25) and (11.28)) and show a better performance than the CSTR in most cases, except for substrate inhibition kinetics. 

Flow dynamics predict that flow through a pipe is nonuniform with regard to velocity across the diameter of a pipe, for instance. The flow at pipe walls is assumed to be zero. In our idealized biochemical reactor, this concept is represented by a boundary layer in contact with the biofilm. It does not have, of course, a discrete dimension. Rather, it is represented as an area in the structure that has reduced flow and therefore different kinetics than what we would assume exist in a bulk liquid. The boundary layer is affected by turbulence and temperature and this is unavoidable to a degree. Diffusion within the boundary layers is controlled by the chemical potential difference based on concennation. Thus the rate of transfer of pollutant to the organisms is controlled by at least two physical chemical principles, and these principles differentiate an attached growth bioreactor from a suspended growth bioreactor. 

Chapter 5, on Biochemical Engineering, has been completely rewritten in two sections by Dr R. L. Lovitt and Dr M. G. Jones with guidance from the previous author, Professor B. Atkinson. The earlier part deals with the nature of reaction processes controlled by micro-organisms and enzymes and is prefaced by background material on the relevant microbiology and biochemistry. In the latter part, the process engineering principles of biochemical reactors are discussed, and emphasis is given to those features which differentiate them from the chemical reactors described previously. 

The effectiveness of these control schemes will depend to a great extent on how accurately the various state variables and culture parameters can be estimated on-line and under a variety of operating conditions. Several aspects of the general estimation problem have been studied in situations related to chemical reactors (J, 2). With biochemical reactors, however, the estimation problem is considerably more involved because of the growth... 

Stephanopoulos, G. San, K.Y. "State Estimation for Computer Control of Biochemical Reactors" Proc. Vlth Int. Ferm. Symp., London, Canada, 1981 p 399. 

In contrast to chemical and petrochemical reactors, biochemical reactors invariably contain aqueous phase at low pressures. This aqueous phase generally controls the overall interparticle mass-transfer rate and provides four different types of resistances to the overall mass-transfer rate (Moo-Young, 1986) ... 

Most chemically reacting systems tliat we encounter are not tliennodynamically controlled since reactions are often carried out under non-equilibrium conditions where flows of matter or energy prevent tire system from relaxing to equilibrium. Almost all biochemical reactions in living systems are of tliis type as are industrial processes carried out in open chemical reactors. In addition, tire transient dynamics of closed systems may occur on long time scales and resemble tire sustained behaviour of systems in non-equilibrium conditions. A reacting system may behave in unusual ways tliere may be more tlian one stable steady state, tire system may oscillate, sometimes witli a complicated pattern of oscillations, or even show chaotic variations of chemical concentrations. 

Chemical engineering is no longer confined to purely physical processes and the unit operations, and a number of important new topics, including reactor design, automatic control of plants, biochemical engineering, and the use of computers for both process design and control of chemical plant will be covered in a forthcoming Volume 3 which is in course of preparation. 

P. Albertos and M. Perez Polo. Selected Topics in Dynamics and Control of Chemical and Biochemical Processes, chapter Nonisothermal stirred-tank reactor with irreversible exothermic reaction A B. 1.Modelling and local control. LNCIS. Springer-Verlag, 2005 (in this volume). 

Systems tics Genetics Biochemistry Culture choice Mass culture Cell responses Reactor design Control Biochemical... 

---