Energy and exergy analysis of an ideal molten carbonate fuel cell (MCFC) and reheat & regenerative braysson cycle hybrid system

Abstract

Direct energy conversion devices are gaining prominence because of their high efficiency, as the process involves the direct conversion of chemical energy to its electrical counterpart, bypassing the thermal energy phase. Fuel cells work on the principle of a chemical reaction between fuels like Hydrogen, Methane, propane, ammonia, and an oxidizer. The working temperature of the fuel cell is as high as (600 °C–700 °C). Generally, waste heat liberated from the fuel cells was used to generate power by running the Brayton (or) Rankine cycle. This work involves exergy and energy analysis on a hybrid system made of a Molten Carbonate Fuel Cell and reheat & regenerative Braysson cycle. Combining a molten carbonate fuel cell (MCFC) with a Braysson cycle results in a novel hybrid system that offers exciting possibilities for power generation. In the analysis, Molten Carbonate Fuel Cell is assumed to operate at 650 °C, and the turbine inlet temperature (TIT) range of the Braysson cycle is taken as 400 to 600 °C. It has been noticed that different optimum pressure ratio values exist to obtain maximum output of power and maximum efficiencies. Both the exergy and energy efficiencies of the combined cycle increase with the increase in turbine inlet temperature. This combined system depicts maximum energy and exergy efficiency of 96.84% and 95.13%, respectively. Destruction rates of exergy for individual equipment and the total system are also obtained as a function of TIT and pressure ratio. The exergy destruction rates are found to be maximum in the fuel cells. An optimum pressure ratio is found to be 1.4, where fuel consumption is the least and efficiencies are the maximum.