Direct Carbon Fuel Cells: Assessment of their Potential as Solid Carbon Fuel Based Power Generation Systems (2004)

Small-scale experimental work at Lawrence Livermore National Laboratory (LLNL) has confirmed that a direct carbon fuel cell (DCFC) containing a molten carbonate electrolyte completely reacts solid elemental carbon with atmospheric oxygen contained in ambient air at a temperature of 650-800 C. The efficiency of conversion of the chemical energy in the fuel to DC electricity is 75-80% and is a result of zero entropy change for this reaction and the fixed chemical potentials of C and CO{sub 2}. This is about twice as efficient as other forms power production processes that utilize solid fuels such as petroleum coke or coal. These range from 30-40% for coal fired conventional subcritical or supercritical boilers to 38-42% for IGCC plants. A wide range of carbon-rich solids including activated carbons derived from natural gas, petroleum coke, raw coal, and deeply de-ashed coal have been evaluated with similar conversion results. The rate of electricity production has been shown to correlate with disorder in the carbon structure. This report provides a preliminary independent assessment of the economic potential of DCFC for competitive power generation. This assessment was conducted as part of a Director's Research Committee Review of DCFC held at Lawrence Livermore National Laboratory (LLNL) on April 9, 2004. The key question that this assessment addresses is whether this technology, which appears to be very promising from a scientific standpoint, has the potential to be successfully scaled up to a system that can compete with currently available power generation systems that serve existing electricity markets. These markets span a wide spectrum in terms of the amount of power to be delivered and the competitive cost in that market. For example, DCFC technology can be used for the personal power market where the current competition for delivery of kilowatts of electricity is storage batteries, for the distributed generation market where the competition for on-site power generation in the range of 0.5 to 50 MW is small engines fueled with natural gas or liquid fuels or in the bulk power markets supplied usually by remote central station power plants with capacities of 250-1250 MW that deliver electricity to customers via the transmission and distribution grid. New power generation technology must be able to offer a significant cost advantage over existing technologies serving the same market to attract the interest of investors that are needed to provide funding for the development, demonstration, and commercialization of the technology. That path is both lengthy and expensive. One of the key drivers for any new power generation technology is the relative amount of pollutant emissions of all types, particularly those that are currently regulated or may soon be regulated. The new focus on greenhouse gas emissions offers a window of opportunity to DCFC technology because of its much higher conversion efficiency and the production of a very concentrated stream of CO{sub 2} in the product gas. This should offer a major competitive advantage if CO{sub 2} emissions are constrained by regulation in the future. The cost of CO{sub 2} capture, liquefaction, and pressurization has the potential to be much less costly with DCFC technology compared to other currently available forms of fossil fuel power generation.