Method and arrangement for utilizing recirculation for high temperature fuel cell system

Abstract

An arrangement utilizing recirculation for high temperature fuel cell system, each fuel cell including an anode side, a cathode side, and an electrolyte between the anode side and the cathode side, wherein the fuel cell system can perform anode side recirculation flow of reactants. The arrangement can accomplish a recycle ratio of 70% or more for the recirculation flow, feed to the recirculation a feed-in flow, which can include substantially high oxygen content, the feed-in flow being 30% or less of entire flow, perform heat exchanging to provide substantially reduced low temperature conditions in the recirculation flow, perform catalytic partial oxidation in the recirculation flow to produce a substantially high amount of hydrogen for the recirculation flow in fuel cell system start-up or shutdown situations, and exhaust 30% or less of the entire flow from the anode side recirculation.

Description

RELATED APPLICATION(S)[0001]This application claims priority as a continuation application under 35 U.S.C. §120 to PCT / FI2013 / 050118, which was filed as an International Application on Feb. 5, 2013, designating the U.S., and which claims priority to Finnish Application No. 20125147 filed in Finland on Feb. 10, 2012. The entire contents of these applications are hereby incorporated by reference in their entireties.FIELD[0002]The present disclosure relates to a method and arrangement for utilizing recirculation for high temperature fuel cell systems.BACKGROUND INFORMATION[0003]Most of the energy of the world can be produced by oil, coal, natural gas or nuclear power. All these production methods have their specific issues as far as, for example, availability and friendliness to environment are concerned. As far as the environment is concerned, for example, oil and coal can cause pollution when they are combusted. The issue with nuclear power is, at least, storage of used fuel.[0004]Be...

AI Technical Summary

Benefits of technology

This patent talks about a way to recycle a flow of gas in a fuel cell system with a high level of oxygen or air. By using a heat exchanger to cool down the gas, the system can produce hydrogen and steam for use in the system. This helps to control the production of carbon dioxide and steam in start-up or shutdown situations. The system can also operate without the need for expensive purge gases, resulting in cost and space savings.

Problems solved by technology

All these production methods have their specific issues as far as, for example, availability and friendliness to environment are concerned.

As far as the environment is concerned, for example, oil and coal can cause pollution when they are combusted.

The issue with nuclear power is, at least, storage of used fuel.

One issue with an SOFC device can be the high operating temperature, which results in long start up and shutdown times and mechanical and chemical compatibility issues.

The harmful carbon compound produced in the coking can coat some of the active surface of the fuel cell device, thus significantly deteriorating the reactivity of the fuel cell process.

The harmful carbon compounds can even completely block the fuel passage.

If nickel oxide formation is severe, the morphology of electrode can be changed irreversibly causing significant loss of electrochemical activity or even break down of cells.

In practical systems, the amount of purge gas has to be minimized because an extensive amount of, for example pressurized gas containing hydrogen, can be expensive and problematic as space-requiring components.

Fuel cell system start-up or shutdown operation can include sufficient steam and hydrogen production, where CO production in large amounts can be harmful.

Using higher air, for example, oxygen amounts for more complete oxidation can produce too much heat making temperature raise excessive in the start-up situation or cooling process too slow in the shutdown situation.

This gas mixture can be used for various chemical industry purposes, and the operating temperature of CPOx can be above 700° C. The known product gas product can be unsuitable for fuel cells due to coke formation in the system heating / operating temperatures.

Start-up or shutdown gas can include sufficient steam and hydrogen production, whereas CO production in larger amounts can be harmful.

Using higher air, for example, oxygen amounts for more complete oxidation, can produce too much heat making the temperature raise excessive in regards to normal SOFC operating conditions, thermal management, thermal stresses and material selection.

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