NOVELTY - A fuel processor comprises a dynamic control(s) for dynamically controlling temperature of the fuel processor and providing maintenance of the temperature of the critical zone within a predetermined temperature range.    USE - For converting a fuel into a reformate, to produce hydrogen for use in fuel cells.    ADVANTAGE - The fuel processor achieves the desired conversion of the feed streams through the shortest path and yet offers the flexibility to accommodate the control algorithms during various steady and transient operating modes such as start-up, steady-state, ramp-up, ramp-down, shutdown, and other various operating modes.    DETAILED DESCRIPTION - A fuel processor comprises:    (1) a coolant stream having a variably controllable flow path;    (2) an air feed having an air feed temperature;    (3) a water feed having a water feed temperature;    (4) a steam feed having a steam feed temperature;    (5) a reformate (40) having a reformate temperatures, an oxygen to carbon ratio, and a steam to carbon ratio; and    (6) a fuel processing train (103) having an autothermal reformer (12), heat exchanger(s) (14, 16, 18, 20, 22, 24) adapted to utilize the coolant stream, water/air injector(s) (42, 44, 46, 48), water gas shift reactor(s) (26, 28, 30, 32) for controlling the carbon monoxide and hydrogen gas concentration in the reformate, preferential oxidation reactor(s) (34, 36, 38) and critical zone(s), and dynamic control(s) for dynamically controlling the temperature of the fuel processor and providing maintenance of the temperature of the critical zone within a predetermined temperature range.    An INDEPENDENT CLAIM is also included for a method of heat exchange between fluids entering and leaving an autothermal reformer comprising:    (1) mixing air and water feeds prior to entering a heat exchanger;    (2) providing longer contact time between air and water/steam;    (3) providing a greater cooling capacity in the heat exchanger;    (4) providing greater turbulence in the heat exchanger to improve heat transfer; and    (5) lowering the concentration of oxygen in a resulting mixture.    DESCRIPTION OF DRAWING(S) - The drawing shows a the integrated fuel processor.    Autothermal reformer (12)    Heat exchangers (14, 16, 18, 20, 22, 24)    Water gas shift reactor (26, 28, 30, 32)    Preferential oxidation reactor(s) (34, 36, 38)    Reformate (40)    Water injectors (42, 44, 46, 48)    Fuel processing train (103)