Coupling effects of fuel reforming process and fuel utilization on the system performance of a natural gas solid oxide fuel cell/gas turbine hybrid system

Abstract

A design study was undertaken of a 100 kW natural gas solid oxide fuel cell (SOFC)/gas turbine (GT) hybrid system to evaluate the impacts of the reforming process under a broad range of SOFC fuel utilizations. An equilibrium reformer model and a one-dimensional SOFC model are employed to perform system study for this hybrid, while balance of plant model is built in Ebsion to simulate the associated performance of GT cycle. Fifty design cases with varied external fuel reforming temperatures are analyzed based on different SOFC fuel utilization levels. With the decrease of reforming temperature, optimal fuel utilization in terms of efficiency shift from 90% with external reforming to 60% with internal reforming. Highest efficiency up to 74% was achieved with internal reforming, but this came with 1275 K cathode inlet air temperature and 1673 K turbine inlet temperature, which no current fuel cell and few GTs can tolerate. High fuel pre-reforming rates provided a higher design flexibility and showed opportunities of efficiency improvement with appropriate thermal integration strategy. And the feasibility of achieving high efficiencies in the hybrid system with thermally integrated external reforming will be explored in our future work. Novelty Statement Both fuel reforming process and fuel utilization could affect the heat and energy balance in the hybrid gas solid oxide fuel cell (SOFC)-gas turbine (GT) system. However, the optimal design condition considering different fuel reforming approaches and SOFC fuel utilization levels was not determined in the literature. In addition, appropriate integration strategies, used to balance the heat and power between the two subsystems (SOFC and GT), are imperative under different fuel reforming approaches and SOFC fuel utilization levels. But, the feasibility of those thermal integration strategies has not been examined in existing studies. This work studied the coupling effects of SOFC fuel utilization and fuel reforming process on system performance of a natural gas hybrid SOFC/GT cycle. Highest efficiency up to 74% was achieved with internal reforming, but this came with 1275 K cathode inlet air temperature and 1673 K turbine inlet temperature, which no current fuel cell and few GTs can tolerate. High fuel pre-reforming rates provided a higher design flexibility and showed opportunities of efficiency improvement with appropriate thermal integration strategy.