Theoretical and experimental studies concerning the application of modern adaptive techniques for the control of continuous alcoholic fermentation of glucose by a yeast strain conducted in a multistage reactor are reported. The practical control objective was the regulation of the substrate concentration in the process effluent. Mathematical expressions for the control scheme are given, with the underlying control engineering argumentation. Suitable feeding of sugar for stage 2 was controlled to minimize the effluent sugar concentration.
A kinetic model of ethanol fermentation conducted under a variety of conditions in a continuous four-stage reactor is proposed. The expressions for specific growth and product formation rates are: micro = micro0 exp(-k1P)(1- X/X1) nu P = nu0 exp(-k2P (1 - X/X2). Parameters were identified by nonlinear programming and shown to fit data correctly for steady states of seven different experiments. The product inhibition constants were of 27 and 84 g/L, respectively. Secondary inhibitions were represented by the linear biomass term. The proposed model gave a better description of phenomena than one which only took ethanol inhibition into account. The same model also fitted batch fermentation data, with only some parameters altering significantly. The use of this model for on-line purposes is discussed.
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