TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Apparatus: The reforming stack and the purification stack include cylindrical vessels. The cylindrical vessels are stackable without the need for connecting piping between each vessel. The reforming stack is aligned vertically and comprises a shift vessel (136), an autothermal reforming vessel (128), and an anode tail gas oxidation vessel (104). The purification stack comprises a preferential oxidation vessel (144), a first desulfurization vessel (116) and a second desulfurization vessel (132). The anode tail gas oxidation vessel comprises an oxidation core containing a water gas shift catalyst for oxidizing fuel cell anode tail gas to produce a hot exhaust gas, and a finned heat exchanger (102) having several external vertical fins surrounding the oxidation core for dissipating the heat of reaction produced within the core. The hydrocarbon fuel feed is preheated in the heat exchanger (102) to produce preheated hydrocarbon fuel (114). The autothermal reforming vessel comprises a reforming core containing an autothermal reforming catalyst for reacting the desulfurized hydrocarbon fuel feed (118), the preheated water stream (124), and air (122) to produce the first intermediate hydrogen stream, and a spiral exchanger section surrounding the reforming core, containing two channels for preheating the desulfurized hydrocarbon fuel feed with the first intermediate hydrogen stream. The shift reactor vessel comprises a shift core containing a water gas shift catalyst for reacting the desulfurized intermediate hydrogen stream (134) and water (124) to produce the second intermediate hydrogen stream, and a second finned section having several external vertical fins surrounding the shift core for dissipating the heat of reaction produced in the shift core. The desulfurized intermediate hydrogen stream is preheated in the second finned section prior to being introduced to the shift core. The first desulfurization vessel comprises a desulfurization catalyst bed for desulfurizing the preheated hydrocarbon fuel feed to produce a desulfurized hydrocarbon fuel feed. The second desulfurization vessel comprises a desulfurization catalyst bed for substantially desulfurizing the first intermediate hydrogen stream to produce a desulfurized intermediate hydrogen stream. The preferential oxidation vessel comprises a preferred oxidation catalyst bed for reacting air and the second intermediate hydrogen stream to produce the hydrogen-rich gas and a heat exchange chamber for cooling the hydrogen-rich gas with water in a cooling coil. Alternatively, the fuel processor comprises a reforming module for converting hydrocarbon fuel feed into hydrogen-rich gas and oxidizing module for oxidizing fuel cell anode tail gas to produce a hot exhaust gas which preheats the hydrocarbon fuel feed to the reforming module. The oxidizing module comprises a first heat exchanger core, an oxidation core vessel containing an oxidation catalyst and a first desulfurizing vessel surrounding the oxidation core vessel and forming a first annular space filled with desulfurization catalyst. The preheated hydrocarbon fuel feed is desulfurized in the first annular space to create a desulfurized hydrocarbon fuel feed. The oxidation core vessel has a set of external vertical fins for further preheating the preheated hydrocarbon fuel feed to produce a second preheated hydrocarbon fuel feed which is introduced into the first annular space. The reforming module comprises second heat exchanger coil, reforming core vessel containing autothermal reforming catalyst bed, a second desulfurizing vessel forming annular space filled with desulfurization catalyst, shift vessel surrounding second desulfurizing vessel and preferential oxidation vessel surrounding shift vessel. The desulfurized hydrocarbon feed is preheated by hydrogen-rich gas in second heat exchanger coil to produce preheated hydrocarbon fuel feed which is then introduced into reforming core vessel, then to annular spaces to produce hydrogen-rich gas.    TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: The hydrocarbon fuel feed is sequentially introduced to the anode tail gas oxidation vessel to produce a preheated hydrocarbon fuel feed, then to first desulfurization vessel to produce a desulfurized hydrocarbon fuel feed. The desulfurized hydrocarbon fuel feed is then fed to the autothermal reforming vessel to produce a first intermediate hydrogen stream and then to the second desulfurization vessel to produce a desulfurized intermediate hydrogen stream which is then fed to shift vessel to produce a second intermediate hydrogen stream. The second intermediate hydrogen is fed to preferential oxidation vessel to produce the hydrogen-rich gas.