Design and analysis of compact hotbox for solid oxide fuel cell based 1 kW-class power generation system

Abstract For solid oxide fuel cell (SOFC) based stationary power generation systems, a compact and efficient design of the hotbox is crucial. The prime objective of this work is to examine a novel and compact hotbox design that is appropriate for a full-scale 1 kW class SOFC system. The endothermicity of the processes including steam generation, reforming, and cathode air preheating is maintained by the exothermicity of an integrated fuel processor and heat recovery by heat exchangers. To achieve higher conversion efficiency, we propose a design that incorporates a fuel processor embedded in the hotbox to combust the off-gases from the fuel cell stack. The thermal energy from the fuel processor is utilized in the steam generator, reformer, and heat exchangers to balance the heat requirements of the SOFC system. The numerical simulations are executed in two steps: in the first step, a comprehensive numerical model is implemented on a standalone reformer to determine the heat duty required for the reforming process. The developed numerical model is further validated with experiments performed on a standalone reformer at different conditions. The validated model is subsequently employed on the integrated hotbox components (reformer, afterburner) to determine the efficacy and performance of the system. In the second step, two different heat exchanger designs are numerically examined to determine their effectiveness in terms of waste heat recovery of the stack and the BOP components. The numerical results show that the integrated reformer gives the same gas composition and methane conversion as that of a standalone reformer but the integrated design is more compact and offers improved efficiency for the SOFC system.