Energy analysis of the integration of a molten carbonate fuel cell for high efficiency carbon capture from internal combustion engines

Carbon dioxide emissions from fossil fuel power plants are considered among the main reasons for the greenhouse effect. Various technologies have been developed to capture CO2 from power plants, but they require a considerable consumption of energy, penalizing the plant. Molten Carbonate Fuel Cell (MCFC) technology can play an important role in CO2 capture, thanks to the operating principle based on the electrochemical reaction, through the carbonate ions CO32-, in which electricity is generated. The production of energy makes this capture system "active" thus avoiding the energy consumption typical of passive systems. The MCFC has two advantages in carbon capture: the cell removes CO2 fed at the cathode to promote carbonate ion transport across the electrolyte and any dilution of the oxidized products is avoided. The MCFC was modeled using Aspen Plus software with the implementation of one of the electrochemical models found in literature. The MCFC is retrofitted to an internal combustion engine (ICE) for CHP application achieving a reduction of 75% of CO2 emissions. The new system does not introduce important penalties to the plant, as for passive systems, managing to maintain energy efficiencies similar to the original system. Two options for CO2 purification in the CCS unit were investigated. The first uses a membrane to remove hydrogen due to the excess of chemical reactants in the fuel cell. This component does not consume energy but cannot reach a high purity of CO2 due to the presence of other impurities. The second case uses an oxy combustor which burns all the excesses of the cell, thus recovering the chemical energy not used in the cell, obtaining a high CO2 purity. However, this system requires the use of an Air Separation Unit (ASU), which consumes electricity to produce the necessary oxygen. An energy analysis was carried out for the two cases analyzed and they were compared with other possible options, which can be adopted in the context of cogeneration, showing positive results with the achievement of high-efficiency cogeneration status and drastically reducing CO2 emissions.