Modeling and Performance Analysis of the Rolls-Royce Fuel Cell Systems Limited: 1 MW Plant

Abstract

This paper is focused on the performance of the 1 MW plant designed and developed by Rolls-Royce Fuel Cell Systems Limited. The system consists of a two stage turbogenerator coupled with pressure vessels containing the fuel cell stack, internal reformer, cathode ejector, anode ejector, and off-gas burner. While the overall scheme is relatively simple, due to the limited number of components, the interaction between the components is complex and the system behavior is determined by many parameters. In particular, two important subsystems such as the cathode and the anode recycle loops must be carefully analyzed also considering their interaction with and influence on the turbogenerator performance. The system performance model represents the whole, and each physical component is modeled in detail as a subsystem. The component models have been validated or are under verification. The model provides all the operating parameters in each characteristic point of the plant and a complete distribution of thermodynamics and chemical parameters inside the solid oxide fuel cell (SOFC) stack and reformer. In order to characterize the system behavior, its operating envelope has been calculated taking into account the effect of ambient temperature and pressure, as described in the paper. Given the complexity of the system, various constraints have to be considered in order to obtain a safe operating condition not only for the system as a whole but also for each of its parts. In particular each point calculated has to comply with several constraints such as stack temperature distribution, maximum and minimum temperatures, and high and low pressure spool maximum rotational speeds. The model developed and the results presented in the paper provide important information for the definition of an appropriate control strategy and a first step in the development of a robust and optimized control system.