The Advantages of SOFC Systems for Power Production from Fossil Fuels without CO_2 Emission

摘要

One possibility of reducing the amount of CO_2 that is released to the atmosphere during power generation is the permanent underground disposal of the produced CO_2. This method requires a compression and liquefaction of the CO_2 containing exhaust gas of the combustion processes. A general problem is that in the presence of significant amounts of N_2 very high pressures for complete liquefaction of CO_2 are required. Such a process is not acceptable from economic reasons. Therefore, in case of conventional combustion processes a CO_2 separation process step is required. In comparison to the conventional combustion processes all SOFC plants show in principle a very attractive system behaviour, which can solve the above mentioned problems. When hydrogen is electrochemically oxidized, the oxygen ions are separated from N_2 in the air by the electrolyte. Besides CO_2 only H_2O is produced, which can be separated by condensation. Since a high fuel utilization in the SOFC can be chosen, typically 80 to 90 %, only a small amount of pure oxygen is required to realize also an N_2-free final combustion step in the after-burner. The energy demands for pure O_2 production by ceramic membranes operating at high temperatures are estimated. As an example a tubular SOFC/gas turbine system with a pressure of 5 bar and liquefaction of CO_2 at 60 bar is simulated. The energetic analysis shows that SOFC power plants can be designed to have no CO_2 emission and nevertheless reaching electric efficiencies of more than 60%.