A
hydrocarbon fuel reformer for producing diatomic
hydrogen gas is disclosed. The reformer includes a first reaction vessel, a shift reactor vessel annularly disposed about the first reaction vessel, including a first shift reactor zone, and a first
helical tube disposed within the first shift reactor zone having an inlet end communicating with a
water supply source. The
water supply source is preferably adapted to supply liquid-phase water to the first
helical tube at flow conditions sufficient to ensure
discharge of liquid-phase and steam-phase water from an outlet end of the first
helical tube. The reformer may further include a first catalyst
bed disposed in the first shift reactor zone, having a low-temperature shift catalyst in contact with the first helical tube. The catalyst
bed includes a plurality of coil sections disposed in coaxial relation to other coil sections and to the central longitudinal axis of the reformer, each coil section extending between the first and second ends, and each coil section being in direct fluid communication with at least one other coil section.