A Study of Integration Potential in Various Reformer Strategies for Logistical Fuels Processing

The theoretical energy efficiency of a fuel cell system is approximately three times higher than a combustion engine based generator; thus, it would provide substantial savings if alternative means of power production could be developed. Recent efforts have been focused on reforming existing logistical fuels, e.g. diesel or JP-8, for use in fuel cell systems. This is particularly important for military applications, as it would allow for the US armed forces to move towards using a single logistical fuel. To meet these ends, the Center for Microfibrous Materials Manufacturing (CM3) at Auburn University has developed a bench scale test bed to investigate powering a portable radar system with a PEM fuel cell stack by producing high purity hydrogen from steam reforming (SR) of JP-8.

In principle, a PEM fuel cell system consists of the fuel processing section and the fuel cell itself, with the former consisting of the reformer and post-combustion cleanup steps. Such systems inherently possess tremendous integration potential, not only in terms of recycling unused material, but also in terms of energy recovery. Process integration techniques can be employed to realize this potential by providing global process insights and identifying overall process performance targets. It is imperative to apply a holistic approach in order to guarantee a truly optimal solution to the problem, since optimizing each unit individually might lead to suboptimal designs as one bottleneck is replaced by another.

Using commercial process simulation software models of the reformers and reformate clean up system were developed based on data obtained from the fuel processing test bed. Once the simulation model had been developed, a process integration study was performed to identify the potential energy recovery. By employing pinch analysis methods the global flow of energy in the system was mapped and analyzed. Models have been developed for three reformation strategies: steam reforming (SR), partial oxidation (POX), and auto-thermal reforming (ATR). Since the post-reformation steps, i.e. hydrogen cleanup, do not change significantly if the reforming process is changed, it is fairly simple to compare the overall efficiency of the three reforming techniques after performing a thermal pinch analysis to identify the minimum utility requirements. A comprehensive efficiency analysis of hydrogen production from logistical fuels also requires an evaluation of effects of varying the fuel itself. Changing the fuel changes the chemical make-up of the reformer effluent; thus, the downstream processing is also affected. Therefore the simulation models described above have been modified to investigate the use of alternative logistical fuels, such as natural gas, diesel, and JP-8. Additionally, the reactor configuration for each model was changed from isothermal to adiabatic operation, so that the efficiency of the two reaction conditions could be compared.

This contribution will illustrate the results of a process integration analysis of the different reforming strategies of the various logistical fuels, including preliminary thermal management and water conservation strategies. It will also include an analysis of varying reactor configurations and operating conditions for the combinations of fuels and reforming strategies.