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. In particular, as the reforming temperature of methanol and DME (200-350 °C) is significantly lower than that of natural gas (700-900 °C) the reformer can be sited even outside the stack. 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. For the stoichiometric SCR values, the optimum reforming temperature for the methanol fuelled hybrid plant is around 240 °C, giving efficiencies of about 67-68% with a SOFC temperature of 900 °C (the efficiency is about 72-73% at 1000 °C). Similarly, for DME the optimum reforming temperature is around 280 °C with efficiencies of about 65% at 900 °C (69% at 1000 °C). Higher SCRs impair stack performance. As too small SCRs can lead to carbon formation, practical SCR values are around 1 for methanol and 1.5-2 for DME.
Externally reformed solid oxide fuel cell-micro-gas turbine (SOFC-MGT) hybrid systems fueled by methanol and di-methyl-ether (DME)
COCCO, DANIELE;TOLA, VITTORIO
2009-01-01
Abstract
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. In particular, as the reforming temperature of methanol and DME (200-350 °C) is significantly lower than that of natural gas (700-900 °C) the reformer can be sited even outside the stack. 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. For the stoichiometric SCR values, the optimum reforming temperature for the methanol fuelled hybrid plant is around 240 °C, giving efficiencies of about 67-68% with a SOFC temperature of 900 °C (the efficiency is about 72-73% at 1000 °C). Similarly, for DME the optimum reforming temperature is around 280 °C with efficiencies of about 65% at 900 °C (69% at 1000 °C). Higher SCRs impair stack performance. As too small SCRs can lead to carbon formation, practical SCR values are around 1 for methanol and 1.5-2 for DME.
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