Fuel cell system

Patent metadata

Field	Value
Publication number	US-10938046-B2
Application number	US-201214115681-A
Country	US
Kind code	B2
Filing date	Apr 17, 2012
Priority date	May 19, 2011
Publication date	Mar 2, 2021
Grant date	Mar 2, 2021

Abstract

A fuel cell system includes a fuel cell stack, an oxygen-containing gas flow rate control device, a reformer, a raw fuel flow rate control device, and an exhaust gas flow rate control device. In the fuel cell system, the oxygen-containing gas flow rate control device includes a start-up oxygen-containing gas flow rate regulator valve for supplying an oxygen-containing gas to the reformer to perform partial oxidation reforming from start-up of fuel cells until the temperature of the fuel cell stack is raised to a predetermined temperature. After the temperature of the fuel cell stack reaches the predetermined temperature, the exhaust gas flow rate control device supplies an exhaust gas to the reformer to perform the partial oxidation reforming and steam reforming.

First claim

The invention claimed is:

1. A method of operating a fuel cell system,
wherein the fuel cell system comprises:
a fuel cell stack formed by stacking a plurality of fuel cells, the fuel cells each formed by stacking an electrolyte electrode assembly between separators, the electrolyte electrode assembly including an anode, a cathode, and an electrolyte interposed between the anode and the cathode;
an oxygen-containing gas flow rate control device configured to control a supply amount of an oxygen-containing gas supplied to the cathode;
a reformer for reforming a raw fuel to produce a fuel gas supplied to the anode;
a raw fuel flow rate control device configured to control a supply amount of the raw fuel supplied to the reformer;
a heat exchanger; and
an exhaust gas flow rate control device configured to direct a portion of a mixed exhaust gas comprising a fuel exhaust gas discharged from the anode and an oxygen-containing exhaust gas discharged from the cathode of the fuel cell stack, to flow into the reformer and the heat exchanger, and to control a supply amount of the mixed exhaust gas,
wherein the oxygen-containing gas flow rate control device comprises:
a power generation oxygen-containing gas flow rate controller configured to supply the oxygen-containing gas to the fuel cell stack; and
a start-up oxygen-containing gas flow rate controller configured to supply the oxygen-containing gas to the reformer to perform partial oxidation reforming from a time of start-up of the fuel cell stack until a temperature of the fuel cell stack is raised to a predetermined temperature, the predetermined temperature being a temperature at which the fuel gas ignites spontaneously in the fuel cell stack, and the predetermined temperature being less than a rated temperature at which the fuel cell system operates to perform power generation;
wherein, the reformer includes a partial oxidation reforming reactor and a steam reforming reactor;
wherein the exhaust gas flow rate control device includes:
an exhaust gas flow rate regulator valve provided between an exhaust gas return pipe and an exhaust gas pipe extending from the fuel cell stack to the heat exchanger, and
a flow rate meter and an air/fuel ratio sensor provided in the exhaust gas return pipe,
the exhaust gas flow rate regulator valve is configured to divide the mixed exhaust gas to direct a first divided portion of the mixed exhaust gas to flow into the reformer and to direct a second divided portion of the mixed exhaust gas to flow into the heat exchanger;

wherein the heat exchanger is configured to exchange heat between the second divided portion of the mixed exhaust gas and the oxygen-containing gas supplied to the cathode; and
wherein the method comprises:
producing the fuel gas by performing the partial oxidation reforming of the raw fuel using the oxygen-containing gas directly supplied from the start-up oxygen-containing gas flow rate controller to the partial oxidation reforming reactor and the raw fuel supplied from the raw fuel flow rate control device to the partial oxidation reforming reactor, and raising the temperature of the fuel cell stack to the predetermined temperature by supplying the fuel gas and the oxygen-containing gas that is supplied from the power generation oxygen-containing gas flow rate controller via the heat exchanger while letting heat exchange occur between the oxygen-containing gas supplied from the power generation oxygen-containing gas flow rate controller and the second divided portion of the mixed exhaust gas discharged from the fuel cell stack and divided and directed to flow to the heat exchanger by the exhaust gas flow rate regulator valve, wherein before the temperature of the fuel cell stack reaches the predetermined temperature, the mixed exhaust gas is supplied only to the heat exchanger, among the heat exchanger and the reformer, and is not supplied to the reformer and steam reforming using the steam reforming reactor is not performed;
stopping, after the temperature of the fuel cell stack reaches the predetermined temperature, supplying the oxygen-containing gas from the start-up oxygen-containing gas flow rate controller to the partial oxidation reforming reactor, switching using the exhaust gas flow rate regulator valve from a state in which the mixed exhaust gas is supplied only to the heat exchanger among the reformer and the heat exchanger to a state in which the mixed exhaust gas is supplied to both the heat exchanger and the reformer, and performing steam reforming and the partial oxidation reforming of the raw fuel supplied from the raw fuel flow rate control device to the partial oxidation reforming reactor using, as a reactant in each of the steam reforming and the partial oxidation reforming, the first divided portion of the mixed exhaust gas discharged from the fuel cell stack, and divided and directed to flow to the reformer by the exhaust gas flow rate regulator valve while the second divided portion of the mixed exhaust gas is directed to flow to the heat exchanger;
after the fuel cell stack reaches the predetermined temperature, measuring physical properties of the exhaust gas with the flow rate meter and the air/fuel ratio sensor, and regulating an opening degree of the exhaust gas flow rate regulator valve such that a molar ratio between oxygen component of the oxygen-containing gas in the first divided portion of the mixed exhaust gas supplied to the reformer by the exhaust gas flow rate control device and carbon component in the raw fuel supplied to the reformer by the raw fuel flow rate control device is within a range of 0.55 to 0.80; and
regulating the supply amount of the first divided portion of the mixed exhaust gas supplied into the reformer to be within a range between 15% to 40% of an entire mixed exhaust gas amount.

2. The method according to claim 1 , wherein, before the temperature of the fuel cell stack reaches the predetermined temperature, the start-up oxygen-containing gas flow rate controller and the raw fuel flow rate control device regulate a volume ratio of the oxygen-containing gas supplied to the reformer by the start-up oxygen-containing gas flow rate controller and the raw fuel supplied to the reformer by the raw fuel flow rate control device to be within a range between a stoichiometric air/fuel ratio×0.9 and the stoichiometric air/fuel ratio.

3. The method according to claim 1 , wherein, during operation from the predetermined temperature until the rated temperature, the exhaust gas flow rate control device and the raw fuel flow rate control device regulate a volume ratio between the oxygen-containing gas in the first divided portion of the mixed exhaust gas supplied to the reformer by the exhaust gas flow rate control device and the raw fuel supplied to the reformer by the raw fuel flow rate control device to be within a range between a stoichiometric air/fuel ratio×0.9 and the stoichiometric air/fuel ratio.

Assignees

• Kiyohiro Yukihiko
• Honda Motor Co Ltd

Inventors

• Kiyohiro Yukihiko

Classifications

• H01M8/04268

  Heating of fuel cells during the start-up of the fuel cells · CPC title

• H01M8/04097

  with recycling of the reactants (H01M8/04119, H01M8/04104 take precedence) · CPC title

• H01M8/04776

  at auxiliary devices, e.g. reformer, compressor, burner · CPC title

• H01M8/04761

  of fuel cell exhausts · CPC title

• H01M8/04753

  of fuel cell reactants · CPC title