Cathode flow control for fuel cell power plant

Claim 2

A cathode air flow control system for use in a fuel cell power plant to minimize oxygen starvation of fuel cells in the power plant, said system comprising: a) means forming a fresh air inlet for admitting air into the cathodes of the fuel cells in the power plant; b) means in said fresh air inlet for varying the amount of air admitted to said cathodes; c) means forming an exhaust outlet for exhausting oxygen-depleted gas from said cathodes; d) sensor means in said exhaust outlet for measuring the oxygen content of the oxygen-depleted gas therein; e) means forming a recirculating loop for recirculating oxygen-depleted gas from said exhaust outlet to said air inlet; f) monitoring means in said air inlet to measure the combined flow of incoming air and recirculated oxygen-depleted gas in said air inlet so as to effectively measure the total amount of oxygen fed to the cathodes; g) means for continuously measuring the electrical current output of the power plant; and h) control means operably connected to said means for varying, to said sensor means, to said monitoring means, and to said means for continuously measuring, said control means being operable to calculate total oxygen utilization in said cathodes and cause said means for varying to increase or decrease the amount of air in said air inlet in response to changes in the total measured oxygen utilization.

Claim 3

The system of Claim 1 wherein said control means is a microprocessor which is preprogrammed to continuously calculate the optimum oxygen utilization for existing current output, and wherein said microprocessor is further operable to adjust said means for varying to compensate for differences between the optimum oxygen utilization and the total measured oxygen utilization to minimize differences therebetween.

Claim 4

For use in a fuel cell power plant having a power section with an cathode inlet portion and a cathode exhaust portion, a method for minimizing the risk of oxygen starvation in individual cells in the power section during periods of operation thereof at partial current output, said method comprising the steps of: a) providing a stream of fresh air for said cathode inlet portion; b) providing from said power section a stream of oxygen-depleted exhaust air in said cathode exhaust portion; c) continuously measuring the oxygen content of said exhaust air; d) continuously measuring the current output of said power section; e) circulating at least some of said exhaust air to said cathode inlet portion for admixture with said stream of fresh air to form a gas mixture for use in said power section cathodes during periods of partial current output, the amount of exhaust air recirculated to said cathode inlet increasing as current output decreases; f) continuously measuring the flow rate of said gas mixture in said cathode inlet portion to calculate the oxygen content of said gas mixture; g) continuously calculating the oxygen utilization in the power section as a function of the calculated oxygen content of said gas mixture and the measured oxygen content in the exhaust air; h) comparing the calculated oxygen utilization with known-optimal oxygen utilization corresponding to the measured electrical current output values; and i) varying the amount of air being admitted through said fresh air inlet so as to reduce noted differences between said calculated oxygen utilization and said optimal oxygen utilization.

Claim 5

For use in a fuel cell power plant having a power section with an cathode inlet portion and a cathode exhaust portion, a method for minimizing the risk of oxygen starvation in individual cells in the power section during periods of operation thereof at partial current output, said method comprising the steps of: a) providing a stream of fresh air for said cathode inlet portion; b) providing from said power section a stream of oxygen-depleted exhaust air in said cathode exhaust portion; c) continuously measuring the oxygen content of said exhaust air; d) continuously measuring the current output of said power section; e) circulating at least some of said exhaust air to said cathode inlet portion for admixture with said stream of fresh air to form a gas mixture for use in said power section cathodes during periods of partial current output, the amount of exhaust air recirculated to said cathode inlet increasing as current output decreases; f) continuously measuring the flow rate of said gas mixture in said cathode inlet portion to calculate the oxygen content of said gas mixture; g) continuously calculating the oxygen utilization in the power section as a function of the calculated oxygen content of said gas mixture and the measured oxygen content in the exhaust air; h) comparing the calculated oxygen utilization with known-optimal oxygen utilization corresponding to the measured electrical current output values; and i) varying the amount of air being admitted through said fresh air inlet so as to reduce noted differences between said calculated oxygen utilization and said optimal oxygen utilization.