On-line monitoring assembly for detection of sulfur breakthrough in a desulfurizer assembly and sulfur breakthrough detection method

A fuel cell system comprising:

• a fuel cell including an anode and a cathode, said anode being adapted to receive fuel and said cathode being adapted to receive oxidant gas;
• a controller for controlling one or more components of said fuel cell system;
• a monitoring assembly for detecting sulfur-containing compounds in said fuel after said fuel is passed through a desulfurizer assembly,
• wherein said monitoring assembly comprises an indicator assembly for passing said fuel therethrough, said indicator assembly including a housing and a bed of indicator material in powder or bead form disposed in the housing, wherein the bed of indicator material has a predetermined length and the housing is situated on-line in one of a main path receiving substantially all the fuel and a bypass path receiving only a portion of the fuel in the fuel cell system such that the monitoring assembly continuously detects changes in the sulfur concentration in the fuel as the fuel is conveyed through the indicator assembly, and the indicator material is such that at least one physical property of the indicator material changes when the indicator material is exposed to sulfur-containing compounds in the fuel of the fuel cell system, and the indicator assembly being additionally adapted to allow detection of the change in the physical property of the indicator material;
• wherein:
• the at least one physical property of the indicator material includes a color of the indicator material and a predetermined concentration of the sulfur-containing compounds corresponds to a predetermined color of the indicator material;
• the monitoring assembly further includes a sensor assembly for detecting a rate of the color change along the predetermined length of the bed of indicator material;
• the controller is programmed to estimate when the predetermined concentration of sulfur containing compounds will be present in the fuel based on the detected rate of the color change along the predetermined length of the bed of the indicator material;
• and
• the fuel cell system further comprises a fuel flow control member for controlling the flow of fuel to the indicator assembly separately from a fuel flow control member to the desulfurizer assembly, so that the desulfurized fuel is conveyed through the indicator assembly at a predetermined flow rate.