Performance Comparison of Internal and External Reforming for Hybrid SOFC-GT Applications by Using 1D Real-Time Fuel Cell Mode

Solid oxide fuel cells integrated with gas turbine (SOFC-GT) systems are considered among the most promising power generation units, not only because of the high efficiency, low emissions and carbon capture ability, but also the flexibility to use different kinds of fuels such as natural gas, syngas and biogas directly. In the case of natural gas, Previous researches have demonstrated that solid oxide fuel cells possess the ability to utilize natural gas directly by reforming it inside the anode because of the high operating temperature. But the major problem of internal reforming is that it increases the temperature gradient at the leading edge of fuel cell which may lead to high thermal stress and damage the cells. On the other side, external reforming requires an additional reformer outside of fuel cell, which may increase the investment costs. Also, the amount of air needed to cool the fuel cell is doubled, compared with internal reforming. A full comparison between internal reforming and external reforming of the pressurized SOFC is needed for the hybrids application. In this paper, a real time equilibrium reformer model based on minimization of Gibbs free energy was built to couple with 1D real time solid oxide fuel cell model. An internal on-anode reforming SOFC stack configuration for hybrid SOFC-GT system application was compared with external reforming configurations with 800K, 900K and 1000K reforming temperatures. The results show that internal reforming provides better performance of SOFC stack in the case of high fuel utilization. However, the external reforming showed a higher stack efficiency and smaller stack size compared with on-anode reforming when keeping a relatively lower SOFC stack fuel utilization, necessarily for high hybrid efficiency. Results indicated that external and internal reforming of fuel needs to be optimized depending on different design conditions of the entire hybrid system in terms of efficiency and investment cost. This paper shows that the hybrid system provides the opportunities for thermal integration on performance and efficiency improvement over fuel cell anode reforming.