Abstract
The purpose of this paper is to present an observer-based control design with application to continuous bioreactors. For this purpose, phenomenological bioreactor models were represented by identified linear models plus unknown modelling error terms. Therefore, an uncertainty-based observer with a polynomial structure capable of estimating the unknown modelling error of the reactor representation is coupled to a linear input-output controller. The proposed methodology was evaluated in a sulphate reduction bioprocess and an acetone-butanol-ethanol (ABE) fermentation process for butanol (biofuel) production, under continuous regimes. Experimentally validated mathematical models were considered for this purpose. A theoretical framework is presented to demonstrate the corresponding closed-loop stability of the systems, and numerical simulations were carried out to corroborate the satisfactory performance of the proposed methodology.
Highlights
Biochemical reactors (BRs) are important process equipment in the transformation industry, which are currently employed in biomedical, food, fuel, and waste industries with great success [1,2,3]
Nonlinear behaviour is inherent in BR, where the state multiplicity, instabilities, and multiplicity of input, among others, make the operation of this process equipment a real challenge for process engineers [4,5,6]. is situation has led to intensive research in nonlinear dynamic analysis and to the design of well performing nonlinear control techniques, such as predictive control, adaptive control, sliding-mode control, and neural control, among others [7,8,9]. e proposal of nonlinear control techniques has been very important to study the closed-loop response of BR under a theoretical framework, but the complexity of these techniques makes difficult the real-time implementation for industrial plants
A single-input single-output (SISO) control scheme is considered, in which the sulphate mass concentration was selected as a measured and controlled state variable. is is proposed due to the possibility of measuring the sulphate concentration online using a colorimetric technique based on spectrometric devices [19]. e input flow (D) to the bioreactor is considered as the control input [20]
Summary
Biochemical reactors (BRs) are important process equipment in the transformation industry, which are currently employed in biomedical, food, fuel, and waste industries with great success [1,2,3]. E continuous sulphatereducing bioreactor was simulated under the assumption of perfect mixing conditions, using the following set of initial conditions: xs1,0 6000 mg/L, xs2,0 0.1 mg/L, xs3,0 155 mg/ L, xs4,0 5250 mg/L, and xs5,0 1.5 mg/L, which were considered as nominal operating conditions. To simulate different operational scenarios, the following initial conditions were considered: xs1,0 5550 mg/L, xs2,0 0.1 mg/L, xs3,0 115 mg/L, xs4,0 5150 mg/L, xs5,0 1.5 mg/L and xs1,0 5850 mg/L, xs2,0 0.1 mg/L, xs3,0 135 mg/L, xs4,0 5550 mg/L, and xs5,0 1.5 mg/L. e nominal value of the dilution rate was set at u D 0.035 1/h.
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