NOVELTY - The system has an inner reactor vessel (61) placed within an outer reactor vessel (60), and forming enclosed reaction spaces (62) between the vessels. One of the spaces and the inner vessel are filled with a methanation catalyst (63), and includes a reformed fuel/steam inlet that is in fluid communication with a reformed fuel source i.e. steam reformer. The other space and the inner vessel are filled with a desulfurization material, and includes a methane fuel outlet, where the methanation catalyst and the desulfurization material are in fluid communication with each other.    USE - Fuel processor system for converting heavier, sulfur-laden hydrocarbon fuel i.e. JP-8 to fuels, suitable for use in a high temperature fuel cell e.g. solid oxide fuel cell (claimed) such as 3 -kW solid oxide fuel cell stack, used in a portable power application. Can also be used for JP-A, diesel fuel, natural gas, propane, petrol, kerosene, and crude oil.    ADVANTAGE - The reactor vessels are separated such that the reactor vessel containing the spent desulfurization material can be simply removed and replaced with the reactor vessel containing fresh desulfurization material. The system allows sulfur-laden reformed gas stream to be introduced into and flows through one of the reaction spaces and the reactor vessel containing the desulfurization material, thus resulting in desulfurization of the stream after which the desulfurized stream flows through the other reaction space and the reactor vessel containing the methanation catalyst. The reactor vessels are arranged such that the gas streams flowing through the vessels are in a counterflow relation-ship, thus transferring heat to the desulfurization material and sulfur-laden gaseous stream by exothermic methanation process, and hence enabling temperature control over the desulfurization process and the methanation process to match the requirements of a fuel cell into which methane-containing gaseous stream output from the methanation process is ultimately introduced. The methane introduced into the solid oxide fuel cell is internally reformed in the solid oxide fuel cell and consumes a significant portion of the heat generated, thus reducing amount of cathode oxidant flow through the fuel cell needed for sensible cooling, and hence reducing oxidant-side pressure drop, and reducing parasitic power required for an oxidant blower. The system allows for removing 95 percent of excess fuel cell stack heat, and proportioned approximately 55 percent cell cooling from preheating incoming cathode air via radiation air preheating and 45 percent cell cooling from direct internal reforming, thus simplifying overall system, increasing compactness, reducing parasitic losses from air handling, eliminating additional or external heat exchangers, and consequently increasing electrical conversion efficiency of the system. The system projects cathode airflow to be only about 70 higher than that required to satisfy the electrochemical reaction compared to more than 500 percentages higher airflow in designs not incorporating radiation air preheating and direct internal reforming. The system projects lower cathode air flow rate to reduce the air pressure drop in the cell stack, thus lowering parasitic blower power, and reducing seal stresses.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a desulfurization and methanation unit.    Desulfurization/methanation unit (11)    Outer reactor vessel (60)    Inner reactor vessel (61)    Reaction space (62)    Methanation catalyst (63)    Zinc oxide bed (64)