NOVELTY - A reactor of the autothermal reformer is purged with a fuel above the upper explosive limit of a process feed stream. A non-pyrophoric shift catalyst is maintained at a specific temperature to prevent condensation of the water. The air is supplied to the reactor which is heated to a light off temperature of the catalyst, for generating air fuel mixture. The reactor is heated again to a temperature about 400-800degreesC.    USE - For starting autothermal reformer used in power plant such as natural gas power plant.    ADVANTAGE - Enables to covert process stream into synthesis gas containing hydrogen and carbon monoxide. The shutdown of the autothermal reformer is performed correctly after the ending of the operational cycle.    DETAILED DESCRIPTION - The process feed stream is produced by lighting off an oxidizer. A reactor (224) of the oxidizer is purged below 50degreesC using air of initial temperature. The fuel such as natural gas containing feed stream is supplied into a heated region of the oxidizer so as to produce air and fuel mixture. The ratio of the air and fuel in the air fuel mixture is set up to 6. The concentration of the natural gas in air is 26%. A catalyst bed (257) is heated to a light off temperature or a spark source is actuated to generate an ignition heat of about 280degreesC. The air is supplied to the heated autothermal reactor for generating air fuel mixture such that the ratio between air and fuel is set between 0.4-0.65.    INDEPENDENT CLAIMS are also included for the following:    (1) method of lighting off oxidizer in fuel processor;    (2) shutting down method of autothermal reformer, which involves stopping flow of water to the reactor of the autothermal reformer, after stopping flow of air to the reactor. The reformer is purged with the fuel and is cooled to less than 50degreesC; and    (3) shutting down method of oxidizer in autothermal reformer, which involves purging oxidizer reactor with air until the temperature of the reactor reaches shutdown temperature, after stopping flow of fuel to the reactor. The flow of air to the purged oxidizer reactor is stopped.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a fuel processor.    fuel cell (104)    check valves (210)    reactor of oxidizer (224)    electric heaters (233)    catalyst bed (257)