Fuel flexibility is an advantage of the carbonate Direct FuelCell® (DFC®) technology. The DFC power plant product line is specifically engineered to operate on methane-based natural gas or renewable biogas, but with varying degree of system modification, DFC power plants can operate on a wide variety of fuels, including gaseous and liquid fuels.
Early DFC system studies evaluated coal gas as a fuel source, and DFC stacks have been successfully operated on coal gas. Coal gas is not widely available as a distributed energy resource at the present time, which has limited the commercial use of this aspect of DFC fuel flexibility. DFC systems have also been operated on coal mine methane, which could present a distributed generation opportunity near coal mining facilities.
Propane is a proven fuel source for DFC power plants. One example of a DFC power plant field evaluation using propane as a fuel source was conducted at Concurrent Technologies Corporation (CTC) in Johnstown, PA. In this test a DFC300 system, with only minor fuel processing system modifications, was operated on commercial propane for a six month demonstration period. The ability to switch seamlessly from natural gas to propane and back to natural gas with no loss of power was successfully demonstrated.
Advanced technology programs have also been focused on developing fuel processing approaches that allow the use of DFC power systems with logistics fuels (fuels used for ships, aircrafts or remote bases), such as jet fuels and diesel fuels.
In conjunction with support from U.S. Defense Advanced Research Projects Agency (DARPA), a 32 kilowatt (kW) DFC stack was demonstrated for over 1,000 hours with high sulfur DF-2 diesel fuel and JP-8 jet fuel. Under a ship service fuel cell program supported by the U.S. Navy, FCE constructed and delivered a DFC fuel processor module (with 500 kW fuel processing capacity) and power plant to the Navy. The test plant produced over 17.6 megawatt hours (MWh) of clean power using high sulfur JP-5 logistic fuel. This unit was the world’s first fuel cell power plant of this size operating with high sulfur naval logistic fuel.
This research reflects the U.S. Department of Defense (DoD) interest in high efficiency clean power for military applications, although the technology can also be deployed for commercial applications in off-grid remote locations, islands, environmentally sensitive areas, embassies, and other locations where conventional fuels are not available.