Hydrogen generator, fuel cell system, and method of operating hydrogen generator

1. A hydrogen generator comprising:

a reformer configured to generate a hydrogen-containing gas by a reforming reaction using a material gas;

a hydro-desulfurizer configured to remove a sulfur compound in the material gas;

a material gas passage through which the material gas supplied to the reformer flows;

a recycled gas passage connected between a first connection portion of a gas passage located downstream of the reformer and a second connection portion of the material gas passage located upstream of the hydro-desulfurizer;

a first on-off valve disposed on the recycled gas passage;

a second on-off valve disposed on the material gas passage between the second connection portion and the hydro-desulfurizer; and

a controller configured to open the first on-off valve, after generation stop of the hydrogen-containing gas, to supply the material gas to the recycled gas passage, and to close the second on-off valve when the controller opens the first on-off valve.

2. The hydrogen generator according to claim 1 , further comprising a processor configured to dilute a combustible gas discharged from the gas passage located downstream of the reformer when the material gas is being supplied to the recycled gas passage by the controller.

3. The hydrogen generator according to claim 1 , further comprising a processor configured to combust a combustible gas discharged from the gas passage located downstream of the reformer when the first on-off valve is opened, and the material gas is being supplied to the recycled gas passage.

4. The hydrogen generator according to claim 1 , wherein before a first operation of replacing a gas in the reformer with the material gas, the controller opens the first on-off valve to supply the material gas to the recycled gas passage.

5. The hydrogen generator according to claim 1 , wherein before a second operation of supplying the material gas to a gas passage including the reformer so as to compensate for gas contraction in the reformer or an internal pressure decrease in the reformer by a temperature decrease in the reformer, the controller opens the first on-off valve to supply the material gas to the recycled gas passage.

6. The hydrogen generator according to claim 1 , further comprising a booster disposed on the material gas passage extending from the second connection portion to the second on-off valve,

wherein the controller does not activate the booster but opens the first on-off valve to supply the material gas to the recycled gas passage.

7. A fuel cell system comprising:

the hydrogen generator according to claim 1 ; and

a fuel cell configured to generate electric power using the hydrogen-containing gas supplied from the hydrogen generator.

8. The hydrogen generator according to claim 1 , wherein:

the controller includes:

a calculation processing module; and

a storage module configured to store a control program, and

the control program, when executed by the calculation processing module, causes the controller to open the first on-off valve, after generation stop of the hydrogen-containing gas, to supply the material gas to the recycled gas passage, and to close the second on-off valve when the controller opens the first on-off valve.

9. A method of operating a hydrogen generator, comprising:

generating a hydrogen-containing gas in a reformer by a reforming reaction using a material gas;

supplying the hydrogen-containing gas generated by the reformer to a hydro-desulfurizer through a recycled gas passage;

removing a sulfur compound from the material gas to which the hydrogen-containing gas, which is supplied through the recycled gas passage, is added, by the hydro-desulfurizer;

stopping generating the hydrogen-containing gas; and

opening a first on-off valve disposed on the recycled gas passage, after the stopping generating the hydrogen-containing gas, to supply the material gas to the recycled gas passage, wherein:

the recycled gas passage is connected between a first connection portion of a gas passage located downstream of the reformer and a second connection portion of a material gas passage, through which the material gas supplied to the reformer flows, located upstream of the hydro-desulfurizer,

a second on-off valve is disposed on the material gas passage between the second connection portion and the hydro-desulfurizer, and

when the first on-off valve is opened, the second on-off valve is closed.

10. The method according to claim 9 , further comprising diluting a combustible gas discharged from a gas passage located downstream of the reformer when the first on-off valve is opened, and the material gas is being supplied to the recycled gas passage.

11. The method according to claim 10 , wherein before a first operation of replacing a gas in the reformer with the material gas, the first on-off valve is opened, and the material gas is supplied to the recycled gas passage.

12. The method according to claim 10 , before a second operation of supplying the material gas to a gas passage including the reformer so as to compensate for gas contraction in the reformer or an internal pressure decrease in the reformer by a temperature decrease in the reformer, the first on-off valve is opened, and the material gas is supplied to the recycled gas passage.

13. The method according to claim 10 , wherein:

a booster disposed on the material gas passage extending from the second connection portion to the second on-off valve is not activated;

the first on-off valve is opened; and

the material gas is supplied to the recycled gas passage.

14. The method according to claim 9 , further comprising combusting a combustible gas discharged from a gas passage located downstream of the reformer when the first on-off valve is opened, and the material gas is being supplied to the recycled gas passage.