Exergy Analysis of a Novel SOFC Hybrid System with Zero-CO2 Emission

Abstract

Now, climate change due to the emission of greenhouse gases, especially the emission of CO2, is becoming more and more serious. Though many countries have taken all kinds of measures to control and reduce the emission of CO2, in the short term, CO2 emission still maintains a rapid growth trend. Power industry is the biggest CO2 emission sector. So, there exists the greatest CO2 emission reduction potential in the power industry. Now, many kinds of fossil fuel power generation systems with CO2 recovery are usually based on the chemical absorption method or the oxygen combustion method. The former demands a chemical absorption and separation unit to recover CO2 from the flue gas of power systems. The latter demands a special oxygen combustion technology, equipment and a larger ASU (air separation unit). And these technologies all consume great energy and result in the huger equipment investment and higher operating cost. Now, people are eager to develop the high-efficiency power generation technology with the less energy consumption for CO2 capture. Fuel cell can satisfy the above requirements, with the higher energy conversion efficiency and less energy consumption of CO2 capture, so it has attracted considerable interest in recent years. Solid Oxide Fuel Cell (SOFC) is an attractive power-generation technology that can convert the chemical energy of fuel directly into electricity while causing little pollution (Kartha & Grimes, 1994). Because the anode fuel gas is naturally separated from the cathode air by the solid electrolyte, the CO2 gas with the higher concentration can be obtained in the anode exhaust gas. In addition, SOFC can employ all kinds of fuels, including various hydrocarbon fuels. Compared with the traditional power generation systems, the SOFC hybrid system power plant has the higher system efficiency (net AC/LHV). Even after CO2 is captured, the efficiency of SOFC hybrid system still can be greater than or equal to that of the traditional power systems without CO2 capture. In order to further improve the CO2 concentration of anode exhaust gas, SOFC can employ the O2/CO2 combustion mode in the afterburner. Because the required mass flow of pure O2 is less, the energy consumption is lower. After capturing the CO2, the SOFC hybrid system does not result in a bigger efficiency reduce. So the SOFC hybrid power system with zero CO2 emission become a new way which can