NOVELTY - Apparatus for synthesizing hydrogen gas from a fuel, has a primary reactor with a catalyst; and a heat exchanger annularly disposed around the reactor. The heat exchanger has inlet conduits in fluid communication with an inlet of the reactor, and outlet conduits in fluid communication with an outlet of the reactor. The inlet and outlet conduits are adapted to provide a counter flow transfer of heat energy in between.    USE - The apparatus is used for synthesizing hydrogen gas from a fuel, by directing a fuel stream into a primary reactor portion of a combined primary reactor and heat exchanger; flowing an oxygen-containing stream through the inlet conduits of a heat exchanger portion of the combined primary reactor and heat exchanger into the primary reactor portion; subjecting the fuel stream and the oxygen-containing stream to a reforming reaction in the presence of the catalyst contained within the primary reactor portion, thus forming the product gases; directing the product gases through the outlet conduits of the heat exchanger portion, where the product gases flowing through the outlet conduits in a direction counter to the flow of the oxygen-containing stream through the inlet conduits to provide heat energy to the oxygen-containing stream (claimed). It may be used in small-scale, highly integrated fuel cell systems (claimed), such as those used in automobiles or homes.    ADVANTAGE - The apparatus provides heat exchanger mechanization to transfer reformate energy to steam and air for efficient operation of hydrocarbon fuel processors.    DETAILED DESCRIPTION - A synthesizing apparatus for synthesizing hydrogen gas from a fuel, comprises a primary reactor having a catalyst situated between an inlet adapted to receive a fuel stream and an oxygen-containing stream, and an outlet adapted to provide product gases, where one of the gases is hydrogen; and a heat exchanger annularly disposed around the primary reactor. The heat exchanger has inlet conduits and outlet conduits. The inlet conduits are in fluid communication with the inlet of the primary reactor. The outlet conduits are in fluid communication with the outlet of the primary reactor. The inlet and outlet conduits are adapted to provide a counter flow transfer of heat energy in between.    An INDEPENDENT CLAIM is also included for a fuel cell system (10), comprising a fuel cell stack (18) provided with source of hydrogen gas; and a combined primary reactor and heat exchanger in fluid communication with the fuel cell stack and adapted to provide the hydrogen gas. The combined primary reactor and heat exchanger has a primary reactor portion as above, and a heat exchanger portion as above.    DESCRIPTION OF DRAWING(S) - The figure is a schematic block diagram of a fuel cell system provided with a combined primary reactor and heat exchanger.    Fuel cell system (10)    Fuel processor (11)    Combined primary reactor and heat exchanger (12)    Fuel cell stack (18)    Exhaust or effluent (31, 33)