Model Predictive Control for Ethanol Steam Reformers
Document typeMaster thesis
Rights accessRestricted access - author's decision
This thesis firstly proposes a new approach of modelling an ethanol steam reformer (ESR) for producing pure hydrogen. Hydrogen has obvious benefits as an alternative for feeding the proton exchange membrane fuel cells (PEMFCs) to produce electricity. However, an important drawback is that the hydrogen distribution and storage have high cost. So the ESR is regarded as a way to overcome these difficulties. Ethanol is currently considered as a promising energy source under the research for its renewable and easy-access. The modelled reformer has been divided into two stages in order to miximize the output of pure hydrogen. Specifically, the hydrogen is generated in the first stage by steam reforming (SR) over the Cobalt-based catalysts. The second stage is used to purify the hydrogen from the mixture gas through a Pd-Ag membrane separation. Unlike the conventional way, the two stages are carried out in a same module, since only one heating device is required. The main idea of the modelling approach is to develop a one-dimensional, pseudo-homogeneous and non-steady-state model based on the mass balance. Finite difference method is applied to transform the partial differential equations (PDEs) into ordinary differential equations (ODEs). Furthermore, the control of the ESR system is also discussed in this thesis. Some Model predictive control (MPC) strategies have been designed for the linear and non-linear models of the ESR. The mathematical model of the ESR by using the proposed approach is used for the design of a MPC controller. The first part of this thesis has been devoted to obtain the non-linear mathematical model with the assumptions of isothermal and isobaric conditions and perform simulations. The numerical linearisation of the mathematical model towards a controloriented model has been performed as well as the method of model-order reduction with Hankel norm approximation and temporal discretization with zero-order hold, which will be used as the prediction model of the MPC. The control objectives of the ESR system are to maximize the hydrogen yield and minimize the ethanol flow rate, which result in a multi-objective problem. Open-loop and close-loop simulations are developed to highlight the proposed controller results. The analysis has taken into account relevant indices such as the ethanol conversion,input smoothness and output error.
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