Fuel processor - PEM fuel cell systems for energy generation

Abstract

In the last few years, increasing attention has been paid to PEM fuel cells, as promising device for decentralized energy production, both in stationary and automotive field, thanks to high compactness, low weight (high power-to-weight ratio), high modularity, good efficiency and fast start-up and response to load changes. The high efficiencies that can be obtained with a PEM fuel cell, however, require a high purity hydrogen feed at the anode. Hydrogen, though, is not a primary source, but it is substantially an energy carrier, that can be stored, transported and employed as gaseous fuel, however, it needs to be produced from other sources. The main hydrogen source is actually represented by hydrocarbons, through classical Steam Reforming or Partial Oxidation industrial scale processes. However, the limitation of hydrogen storage and transport due to its chemico-physical properties has pushed toward the concept of decentralized hydrogen production; in this way, the hydrogen source, such as methane, is distributed through pipelines to the small-scale plant, installed nearby the users, and the hydrogen produced in situ is fed directly to the energy production system, avoiding hydrogen storage and transportation. In this sense, research is oriented toward the optimization of the decentralized hydrogen production unit, generally named as fuel processor, for residential and automotive applications, for achieving fuel conversion into hydrogen with high efficiencies and high compactness. Since the efficiency of the integrated fuel processor – fuel cell system strongly depends on system configuration and on the heat integration, a system analysis of the most promising configurations is performed, in order to identify the best solution for energy production in a PEM fuel cell system. Analysis of global system efficiency of fuel processor – PEM fuel cell systems is performed by means of the software AspenPlus®, with identification of best configuration and best operating conditions. Moreover, since the application of fuel processor – PEM fuel cell system is foreseen for small and medium scale, an important characteristic that must me associated to the high efficiency is the compactness of the system. The PEM fuel cell, indeed, is generally characterized by high efficiency and compactness, therefore, in order to keep its standard, also the fuel processor coupled with it must be efficient and as compact as possible. In order to have an idea of the encumbrance of the reactors, a detailed mathematical model for fixed bed reactors was developed in this work, in order to size and compare conventional fixed bed reactor and membrane catalytic reactors. The software employed was Mathematica®.