SOFC-MGT hybrid power plants fuelled by methanol and DME

SOFC-MGT hybrid power plants are based on the integration of a solid oxide fuel cell and a micro-gas turbine and can achieve efficiencies of over 60% even for small power outputs (200-500 kW). The SOFC-MGT systems currently developed are fuelled with natural gas, which is reformed inside the same stack, but the use of alternative fuels can be an interesting option. Simply replacing methane with methanol, ethanol or DME in internally reformed SOFC-MGT systems slightly reduces efficiency and power output. However, owing to the lower reforming temperature of methanol and DME (250-300 °C), the reformer can be sited even outside the fuel cell stack. On the contrary, methane and ethanol are unsuitable for externally reformed SOFC-MGT systems, owing to their higher reforming temperature. External reforming in SOFC-MGT plants fuelled by methanol and DME enhances efficiency on account of improved exhaust heat recovery and of the higher voltage produced by the greater hydrogen partial pressure at the anode inlet. The study carried out in this paper shows that the main operating parameters of the fuel reforming section (temperature and steam-to-carbon ratio, SCR) must be carefully chosen in order to optimise the hybrid plant performance. In particular, the optimum reforming temperature is around 240 °C for methanol (with hybrid plant efficiencies of about 67%) and around 290 °C for DME (with hybrid plant efficiencies of about 65%). Using methanol and DME in externally reformed SOFC-MGT hybrid plants can lead to efficiency improvement with respect to internally reformed hybrid plants fuelled by methane, especially for the higher values of the fuel utilization factor. In particular, under the assumptions adopted here, the efficiency of externally reformed hybrid plants is higher that that of the internally reformed methane-fuelled plant for UF higher than 67-69% for methanol and 79-80% for DME