NOVELTY - A fuel processor comprises a desulfurizer (110) having a housing (111) with an inlet (111a) and an outlet (111b); a first sulfur sensor (113a) disposed near the inlet; and a second sulfur sensor (113b) disposed near the outlet. The housing contains an adsorbent (112) for adsorbing sulfur compounds in a fuel, to purify the fuel. The sulfur sensors are installed in the adsorbent. The first and second sulfur sensors, respectively determine a first sulfur saturation state and a second sulfur saturation state of the adsorbent.    USE - As a fuel processor for purifying a fuel via an adsorbent; useful in a fuel cell system for generating electricity using the fuel supplied from the fuel processor (claimed).    ADVANTAGE - The fuel processor allows the desulfurizer to appropriately indicate the time to replace the fuel-purifying adsorbent, by correctly and accurately measuring the adsorption state of sulfur compounds in the adsorbent. The saturation state of the adsorbent is detected using the variation of signals between sulfur sensors, respectively installed at the inlet and outlet of the desulfurizer. The time to replace the adsorbent is determined using the result of detection, and the determination of the time is made more accurately as compared to prior-art methods using only one sulfur sensor. Since the concentration of sulfur is measured at multiple locations, the possibility of causing measurement error is reduced, as compared to the measurement performed at only one location, thus ensuring stable and smooth fuel processing. The fuel processing can be performed without stopping, by using multiple desulfurizers in the fuel cell system, where the desulfurizers are operated alternately.    DETAILED DESCRIPTION - A fuel processor comprises a desulfurizer (110) having a housing (111) with an inlet (111a) and an outlet (111b); a first sulfur sensor (113a) disposed near the inlet; and a second sulfur sensor (113b) disposed near the outlet. The housing contains an adsorbent (112) for adsorbing sulfur compounds in a fuel, to purify the fuel. The sulfur sensors are installed in the adsorbent. The first and second sulfur sensors, respectively determine a first sulfur saturation state and a second sulfur saturation state of the adsorbent. The first and second sulfur sensors detect at least one of an electrical, physical and chemical characteristic variation. The fuel processor further comprises a controller (200) to determine a saturation state of the adsorbent, based on a difference between the first and second sulfur saturation signals measured by the sulfur sensors. An INDEPENDENT CLAIM is included for operating the fuel processor involving providing sulfur sensors at an inlet and an outlet of the desulfurizer, to produce sulfur concentration signals; measuring signal variations between the sulfur concentration signals according to time; and determining sulfur saturation state of an adsorbent in the desulfurizer, using the signal variations.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a structure of a desulfurizer employed by a fuel processor.    Desulfurizer (110)    Desulfurizer housing (111)    Inlet of housing (111a)    Outlet of housing (111b)    Adsorbent (112)    Sulfur sensors (113a, 113b)    Controller. (200)