Modeling of a three-stage low temperature ethanol steam reforming reactor for fuel cell applications

Abstract

Ethanol is a promising source of hydrogen as it is a renewable source when obtained from biomass, and hence, catalytic steam reforming of ethanol to produce hydrogen is acquiring increasing interest. The catalytic aspects of the ethanol reforming have been extensively studied giving different possibilities. However, the research of design and control for the ethanol reformers in real applications is in the beginning. These aspects are addressed in this work, and the application of interest is for a PEMFC, which at the same time feeds a variable charge. The main objective of this work is to obtain a dynamic model of a catalytic steam reforming reactor based on detailed kinetic experimental data over well-defined samples. This model will be a basic tool in the process of designing the tubular reactor and its control system, taking into account the operation temperatures. The model is based on the coupling of mass and energy balance equations and calculates the concentration and temperature profiles along the reactor and as a function of time. It considers the volumetric flow rate variation over the tubular reactor, and the heat exchange. The influence of the volume discretisation is analysed. The model developed corresponds to one new ethanol steam reformer (pathway?) carried out in three separated stages. A first stage, where ethanol dehydrogenation into acetaldehyde and hydrogen over an appropriate catalyst occurs, followed by the reforming of acetaldehyde over the cobalt catalyst. Finally, a third stage can be introduced after the reforming step for a specific water gas shift module at lower temperature in order to eliminate minute amounts of CO resulting from the reforming step over the cobalt catalyst. The simulation results for ethanol conversion were found to be in accordance with the experimental data obtained at various operating conditions. This validates the simulation model.