Maximizing PEM fuel cell power plant system efficiency at optimum system pressure

Abstract

A PEM fuel cell power plant system (10) has a process air pump (26), which may be a fan, a blower or a compressor, with an adiabatic efficiency of between 40% and 70%. The process air at the inlet 27 of the cathode reactant gas flow field 16 is between 1.07 atmospheres and 1.85 atmospheres, and may be at an optimal pressure for maximum overall system efficiency P={0.45+2.6E-1.8E<2>}atms±0.2 atms where P is the air inlet pressure and E is the adiabatic efficiency of the process air pump.

Description

[0001] This invention relates to operation of a proton exchange membrane (PEM) fuel cell power plant at a pressure which is selected to correspond with the adiabatic efficiency of the reactant air pump.[0002] Heretofore, one type of PEM fuel cell power plant utilizes compressors to pump the reactant air to the cathode reactant gas flow fields, and has typically been operated with air inlet pressures of two or three atmospheres. This takes advantage of the ability of a fuel cell to operate at higher average cell temperatures, exhaust dew point temperatures and coolant temperatures as a consequence of higher operating pressures. Another type of known fuel cell power plant may utilize a fan or blower to provide the reactant air, and consequently works near ambient pressure. While this type of fuel cell power plant cannot take advantage of the efficiencies that result from higher pressure and therefore higher temperature, the overall system efficiency is higher than that of the fuel cel...

AI Technical Summary

Benefits of technology

[0006] Objects of the invention include provision of a PEM fuel cell power plant: which operates at or near maximum system efficiency; which operates at a system pressure which provides overall maximum system efficiency, taking into account thermodynamic efficiency as well as the adiabatic efficiency of the process air pump; which permits achieving the highest possible water balanced system exhaust dew point consistent with overall system efficiency; and provision of an improved PEM fuel cell power plant.

[0009] As used herein, the term "pump" includes fans, blowers and compressors of all types. By selecting a system pressure as a function of adiabatic efficiency of the process air pump, a fuel cell stack can be composed of a fewer number of cells, without sacrificing any performance; alternatively, a fuel cell stack having a usual number of cells can operate at usual performance with higher efficiency and lower fuel consumption.

Problems solved by technology

In particular, utilizing electricity generated by the fuel cell power plant to operate the pump (fan, blower or compressor) which provides the process air to the fuel cell power plant comprises a significant load of parasitic power consumption.

It has heretofore been known that a fuel cell power plant operating at or near ambient pressure utilizing a relatively low power pump has an overall system efficiency which is greater than fuel cell power plants operating at two or three atmospheres, which have higher thermodynamic efficiency, but lower overall system efficiency, due to the increased parasitic power requirement of the required air pump.

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