Patent ID: 7018732

Claim:
A fuel cell system comprising: (a) a fuel cell having a first reactant inlet, a first reactant outlet, a second reactant inlet, a second reactant outlet, a coolant inlet and coolant outlet; (b) a first reactant supply subsystem for supplying a first reactant incoming stream to the first reactant inlet of the fuel cell; (c) a second reactant supply subsystem for supplying a second reactant incoming stream to the second reactant inlet of the fuel cell; (d) an enthalpy shifting subsystem comprising a first enthalpy shifting device that comprises an integral unit for both extracting at least a portion of the heat and moisture from the first reactant exhaust stream and transferring heat and moisture to the first reactant incoming stream in the first reactant supply subsystem, and a second enthalpy shifting device that comprises an integral unit for both extracting at least a portion of the heat and moisture from the first reactant exhaust stream and transferring heat and moisture to the second reactant incoming stream in the second reactant supply subsystem; (e) a first reactant circulation subsystem for circulating at least a portion of a first reactant exhaust stream from the first reactant outlet through the enthalpy shifting subsystem for transfer of heat and moisture from the first reactant exhaust stream to the first reactant incoming stream in the first reactant supply subsystem and the second reactant incoming stream in the second reactant supply subsystem; wherein the first and second enthalpy shifting devices are connected in the series in the enthalpy shifting subsystem, such that the heat and moisture from the first reactant exhaust stream is first transferred to the second reactant incoming stream through the second enthalpy shifting device and then to the first reactant incoming stream through the first enthalpy shifting device, and wherein the enthalpy shifting system further comprises a bypass line that bypasses the second enthalpy shifting device so that a portion of the first reactant exhaust stream in the first reactant circulation subsystem flows to the first enthalpy shifting device without passing through the second enthalpy shifting device.