Distillate Fuel Processing for Marine Fuel Cell Applications

FuelCell Energy, Inc. FCE is developing a 625 kW fuel cell power plant for marine applications based on its Direct Carbonate Fuel Cell DFCTrademark technology. The power plant is designed for operation on Mil-F-16884J Naval distillate fuel designated as NATO F-76. This fuel is characterized as a 385 deg C max end boiling point diesel fuel with up to 1 sulfur by weight. The development is part of the U.S. Navy 2500 kW Ship Service Fuel Cell Program, sponsored by the Office of Naval Research and administered by the Naval Surface Warfare Center Carderock Division. The technical approach is based on adapting FCEs commercial Direct Fuel Cell technology for marine applications. This fuel cell system utilizes a mixture of alkali metal carbonates as the electrolyte and operates at 1100-1250 deg F where internal reformation of hydrocarbon fuels is feasible. Because the process waste heat is captured by the endothermic fuel reforming reaction, the DFCTrademark stack provides unsurpassed overall power plant efficiency. Processing of this distillate fuel in the marine power plant design includes a high-pressure hydrodesulfurizing first stage producing desulfurized liquid fuel. The second stage employs an adiabatic prerefomer, which reacts the desulfurized distillate with steam producing a methane rich fuel gas. The converted fuel is expanded through a turbo generator, reheated and directed to the anodes in the DFCTrademark stacks. The methane is then converted to hydrogen in the DFCTrademark stacks which in turn is electrochemically converted to water, thereby producing DC power. Water for steam is recovered from ftiel cell exhaust making the process self-sufficient in its water needs. Tests on sample batches of NATO F-76 supplied by the U.S. Navy have confirmed the processes of desulfurizing and adiabatic prereforming. Subscale tests of the hydrodesulfurizing process have reduced sulfur levels in the fuel to less than 100 ppb.