High Efficiency Carbon and Hydrogen Fuel Cells for CO2 Mitigated Power

Abstract

Hydrogen fuel cells have been under development for a number of years and are now nearing commercial applications. Direct carbon fuel cells, heretofore, have not reached practical stages ofdevelopment because of problems in fuel reactivity and cell configuration. The carbon/air fuel cell reaction (C + O2 = CO2) has the advantage of having a nearly zero entropy change. This allows atheoretical efficiency of 100% at 700-800°C. The current approach at LLNL to overcome the historical failures is to employ a low ash, high surface area (turbostratic) elemental carbon fuel produced by pyrolysis of hydrocarbons derived from the processing of fossil fuels and biomass. This carbon particulate fuel, once wetted with molten salt, acts like a rigid anode when in contact with an inert metal screen. The high efficiency direct carbon fuel cell (DCC) and the solid oxide hydrogen fuel cell (SOFC) integrated with fuel processing to carbon and hydrogen in a combined cycle and using a back-end Rankine steam plant, maximizes the power generation efficiently. Based on current and projected costs of fossil fuels and estimates of unit capital investment of fuel cells and conventional power plants, estimates of the cost of power generation for each of the integrated fuel cell plants and for typical current and advanced conventional plants are made including CO2 emissions. The direct carbon fuel cell provides multiple advantages—a significant increase in thermal efficiency of combined cycle direct carbon fuel cell power plants; a significant decrease in CO2 emissions, a pure CO2 stream, which can be directly sequestered or utilized; and a lower production cost than conventional plants.