Waste heat management of direct carbon fuel cell with advanced supercritical carbon dioxide power cycle – A thermodynamic-electrochemical modeling approach

Abstract

This study evaluates the performance of a hybrid supercritical carbon dioxide (SCO2) power cycle, which uses the waste heat of a direct carbon fuel cell (DCFC). Three different configurations including a standalone DCFC, an integrated system consisting of a DCFC coupled with a simple SCO2, and another hybrid system consisting of a DCFC and a partial cooling SCO2 are examined and characterized. In the proposed systems, the effects of the electric current density, operating temperature, anode dimensions, and the pinch point temperature difference in the SCO2 evaporator are then discussed. Considering the optimum operational region of the supercritical cycle, the partial cooling SCO2 was found to be a very promising power cycle for coupling with DCFC. Integrating a supercritical CO2 cycle with DCFC can compensate for the loss of efficiency and power density caused by decrease in fuel cell temperature. There is even an operating window in which the performance of the introduced integrated systems is practically independent of the fuel cell temperature. Results show that at the current density of 1000 A/m2, the rate of change in power density and efficiency of the standalone DCFC system is 0.47 W/m2 and 0.058% per unit of fuel cell temperature, respectively. For the integrated DCFC and partial cooling SCO2 system, however, those rates reduce to 0.13 W/m2 and 0.02% per unit of temperature.