Optimization of a fuel cell system using process integration techniques

Abstract

A system model including a PEM fuel cell and its fuel preparation process has been developed. The goal was to investigate the process configurations to identify the optimal operating conditions and the optimal process structure of the system by applying modelling and energy integration techniques. The Ballard&Alstom's system has been considered as the initial process structure in order to define the major equipments to be considered. A simulation model using a commercial chemical process simulation software (BELSIM-VALI) has been developed. The model includes a catalytic reforming, CO-removal (Shift) and preferential oxidation for the fuel processing as well as a PEM fuel cell model and the combustion chain. The equation solver approach used by this software tool offered a real flexibility for the process synthesis approach that has been applied. The energy and the material flows obtained by simulation have been used to compute the process composite curves of the system. This has been used to identify the best heat exchange opportunities and to define the optimal operating conditions of the reforming system that provide the best overall efficiency for the balance of plant.The system has been studied according to the energy efficiency, the exergy efficiency as well as thermoeconomical parameters in the context of the combined production of heat and power.By improving the energy integration of the system, the efficiency can be raised from 35% for the reference system to 48%. To illustrate the results that will be presented, the following charts show, for a given reforming temperature, the influence of steam to carbon ratio on the system efficiency for two different configurations as well as the corresponding composite curves resulting for the balanced system.

Combined optimisation and process integration techniques for the synthesis of fuel cells systems

“…It should be mentioned that the optimal decision are quite different in the two situations indicating that the investment and the choice of the catalyst will be affected by the configuration decision. More results are presented in (Godat and Marechal , 2002). According to design assumptions or limits, the activation of different pinch points, that results from the LP optimisation strategy, will lead pratically to different configuration.…”

On Modeling of Heat and Mass Transfer and Other Transport Phenomena in Fuel Cells

“…There are several models employing process integration techniques combined with commercial process simulation packages, e.g., Belsim-VALI III in Godat and Marechal (2003), to analyze and improve the performance of an integrated PEMFC system including stack, fuel processing and postcombustion units. The fuel processing unit consists of a steam methane reformer (SMR), water gas shift (WGS) reactor (to transform the remaining CO into additional hydrogen at a lower operating temperature) and preferential oxidation reactor (PROX) (to convert the remaining CO into CO 2 to avoid catalyst poisoning).…”

“…The pinch point is that the maximum heat recovery by heat exchange can be realized when the hot and cold temperature difference maintains a minimum value ∆T min . Using the simplified PEMFC stack model together with the composite curve calculation, simulation of heat exchange network was performed to reveal the influence of the major decision variables and define the best system configuration (Godat and Marechal (2003)). The thermodynamic modelling of a combined SOFC and gas turbine (SOFC/GT) system was developed and implemented in the simulation software, Aspen Plus ® , for a reference design of around 500 kWe (Palsson et al (2000)).…”

Analysis of the control structures for an integrated ethanol processor for proton exchange membrane fuel cell systems

“…The inlet air conditions are 1 atm, 25 • C. The most important operating conditions are summarized in Tables 1 and 2. The ideal unit cell voltage is calculated through (1), adopted from Godat and Marechal [19]:…”