Organic rankine cycles (ORCs) for energy recovery from molten carbonate fuel cells

Waste heat from molten carbonate fuel cell plant (MCFC) is available in quantities and at temperatures suitable for generation of additional power by means of a recovery Rankine cycle. The moderate capacity of the first commercial plants suggest the use of an organic working medium rather than steam, A number of fluids are examined; they all share adequate technical and thermodynamic characteristics and exhibit a sufficient level of thermal stability. A MCFC plant is simulated with an appropriate program and the performance of energy recovery cycles using different fluids is evaluated by means of an optimization software. Power and efficiency gains of about 13% seem possible by means of an ORC unit having a specific cast lower than that of the fuel cell plant itself. The use of mixtures as working fluids is examined in its thermodynamic and practical implications. Siloxanes mixtures, in particular, are found to be particularly attractive.