Control of Reactive Batch Distillation Columns via Extents Transformation

Nowadays in large-scale process industry, high purity of products is not only desired but crucial. Products must meet high-purity standards to conform with market and customers’ requirements. Two chemical processes, reaction and distillation, are essential to achieve these objectives. To overcome certain disadvantages and/or limitations that each operation unit possess, these two processes are sometimes combined in one. The combination of a separation zone with a reaction zone in the reactive distillation column, leads to complex interactions between vapor-liquid equilibrium, mass transfer rates, diffusion and chemical kinetics, which are accurately described by rigorous mathematical models. Nevertheless, this kind of models are inconvenient when it comes to parameter estimation and model-based control implementation; controllers and estimators require simpler models to perform reliably and efficiently. This situation poses a trade-off problem between model accuracy and control efficiency and implementability. The extents of reaction and flows is a mathematical framework that has been attracting a lot of attention in recent years, especially in processes with chemical reaction. This approach introduces a linear transformation to decompose the system dynamics into its reaction and flow spaces to obtain a decoupled quasi-linear representation of the system’s governing dynamics. The nonlinear model is brought to an LPV description by means of this transformation. Due to the decoupling effect on the global dynamics, the system is simplified in representation and no reduction of the state-space dimension or linearization needs to be done. The extent transformation framework is extended to the case of a reactive batch distillation column to build an LPV model for control. This model is used to develop an MPC. To test the efficiency of the LPV-based scheme, the MPC is compared against a nonlinear MPC.
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