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A fuel cell (10) system in which a nitrogen (N2) gas is used on the anode section (11) and a nitrogen/oxygen (N2/O2) gaseous mix is used on the cathode section (12) to maintain the cathode at an acceptable voltage potential during adverse conditions occurring particularly during off-power conditions

A fuel cell (10) system in which a nitrogen (N2) gas is used on the anode section (11) and a nitrogen/oxygen (N2/O2) gaseous mix is used on the cathode section (12) to maintain the cathode at an acceptable voltage potential during adverse conditions occurring particularly during off-power conditions, for example, during power plant shutdown, start-up and hot holds. During power plant shutdown, the cathode section is purged with a gaseous mixture of, for example, one-half percent (0.5%) oxygen (O2) and ninety-nine and a half percent (99.5%) nitrogen (N2) supplied from an ejector (21) bleeding in air (24/28) into a high pressure stream (27) of nitrogen (N2) as the primary of majority gas. Thereafter the fuel gas in the fuel processor (31) and the anode section (11) is purged with nitrogen gas to prevent nickel (Ni) carbonyl from forming from the shift catalyst. A switched dummy electrical load (30) is used to bring the cathode potential down rapidly during the start of the purges. The 0.5%/99.5% O2N2 mixture maintains the cathode potential between 0.3 and 0.7 volts, and this is sufficient to maintain the cathode potential at 0.3 volts for the case of H2 diffusing to the cathode through a 2 mil thick electrolyte filled matrix and below 0.8 volts for no diffusion at open circuit conditions. The ejector meters high pressure nitrogen gas with a choked orifice or venturi and uses the energy in the gas from the orifice or venture to suck ambient air into the nitrogen stream before entering the cathode section.

대표청구항 ▼

A method of controlling the cell potential in a fuel cell system, which fuel cell system includes an anode section, a cathode section having a maximum allowed voltage potential, and an electrolyte providing electrochemical communication between said anode and said cathode sections, comprising the fo

A method of controlling the cell potential in a fuel cell system, which fuel cell system includes an anode section, a cathode section having a maximum allowed voltage potential, and an electrolyte providing electrochemical communication between said anode and said cathode sections, comprising the following step(s): (a) purging said cathode section with a gas mix having a dilute gas component and a majority gas component during at least some off-power conditions, causing the cathode potential to be limited to a voltage potential less than said maximum voltage limit; and (b) ejecting said dilute gas component into a stream of said majority gas component upstream of the fuel cell using a small, limited area ejector to form said gas mix. The method of claim 10, wherein there is included the step of: using an oxygen (O2) and nitrogen (N2) gas mix, with oxygen being the dilute component and nitrogen being the majority component. The method of claim 11, wherein there is included the step of: using as the source of said gas mix an ejector bleeding in air as the oxygen source into a stream of high pressure nitrogen as the primary, majority gas component. The method of claim 12, wherein there is included the step of: using the ejector to meter high pressure nitrogen gas with a choked orifice or venturi and using the energy in the gas from the orifice or venture to suck ambient air into the nitrogen stream before entering the cathode section.