Exergy analysis and optimisation of a steam methane pre-reforming system

In this paper we present the exergetic analysis and optimisation of a steam methane pre-reformer system for marine molten carbonate fuel cells (MCFC) fuelled by liquefied natural gas (LNG). The steam methane pre-reformer is a key component of the MCFC, reforming completely higher-chain hydrocarbons and partly methane to hydrogen. The pre-reformer system efficiency improvement is of key importance since it uses up to 10% of the fuel exergy input of the MCFC. First, we develop a dynamic mathematical model that describes the physical/chemical behaviour of the pre-reformer system using a generic process modelling framework. Then, we perform exergy analysis and we optimise the reformer with respect to its exergetic performance. The developed models and exergy balances are spatially distributed to account for the internal process characteristics, capturing the interrelation of the local exergy destruction with component design and geometry. An optimisation problem is then formulated that minimises the total irreversibility of the system subject to design, space, technical, and operational constraints. The exergy analysis and optimisation for a specific MCFC derived the sources of irreversibility and provided an optimal design of 50% less exergy destruction. The results will serve as a basis for the optimisation of the entire MCFC unit.