Analysis of theoretical efficiency in a model 10 kW direct carbon fuel cell using a coal based carbonate slurry

A detailed mass and enthalpy balance of a direct carbon fuel cell has been carried out in order to understand achievable efficiency of a 10 kW analogy. Using literature input data, a steady state model has been built which allows assessment of the final fuel cell efficiency and sensitivity of this value to several variables including the extent of parasitic gasification of the fuel (reverse Boudouard reaction). It is shown that for a hybrid DCFC system, which utilises both primary (solid oxide membrane) and secondary (molten carbonate) electrolytes, a slurry based feed of coal and carbonate could provide enough waste heat from electrochemical inefficiency to both retain the molten feed temperature, as well as provide pre-heating for inlet air streams to achieve an overall system efficiency of over 70%. Higher system efficiencies may be possible, however will depend heavily on the cell design and specifically on increasing the electrochemical efficiency at the expense of waste heat generated. Additional parasitic power input is required in these cases. A base case of assumptions has been evaluated with sensitivity of the system efficiency compared for the carbon slurry loading, the carbon and oxygen conversion per pass of the fuel cell (fuel utilisation), equipment heat losses, amount of coal char ash present and the extent of carbon corrosion within the cell. Under the base case investigated, life cycle emissions of the technology have been estimated (using several assumptions) at 647 kg CO2/MWh at 70% system efficiency, with no carbon storage, while emissions of 93 kg CO2/MWh at 66% system efficiency are potentially achievable (dependent on accuracy of assumptions) if carbon dioxide is able to be effectively sequestered. (C) 2019 Elsevier Ltd. All rights reserved.