JPH08339815A - Fuel cell generator - Google Patents

Abstract

(57) [Summary] [Objective] The amount of steam used in the reformer is reduced by using the steam generated by the cell reaction in the reformer. A first fuel control valve 41 and a second fuel control valve 42 for distributing the fuel gas 1 into the first fuel gas 1a and the second fuel gas 1b are provided, and the fuel cell 20 is connected to the first fuel cell 20a and the second fuel control valve 42.
A fuel cell 20b is used, and the reformer 10 is a first reformer 10
a and the second reformer 10b, the first reformer 10a receives the supply of the first fuel gas 1a and the steam 9 to generate the first anode gas 2a, and the first fuel cell 20a includes the first anode gas 2a. Electric power is generated by the gas 2a and the cathode gas 3 from the circulation line 14, and the second reformer 10b receives the anode exhaust gas 4 and the second fuel gas 1b of the first fuel cell 20a to generate the second anode gas 2b. , The second fuel cell 20b includes the second anode gas 2b and the cathode exhaust gas 7 of the first fuel cell 20a.
The steam / carbon ratio of the steam 9 and the first fuel gas 1a is set to 2-3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power generator capable of reducing the amount of steam used in a reformer.

[0002]

2. Description of the Related Art Molten carbonate fuel cells have characteristics that conventional power generators do not have, such as high efficiency and little impact on the environment, and have attracted attention as a power generation system following hydropower, thermal power, and nuclear power. , Research is currently underway.

FIG. 2 is a diagram showing an example of power generation equipment using a molten carbonate fuel cell using natural gas as a fuel. In the figure, the power generation facility generates power from a reformer 10 that reforms a fuel gas 1 mixed with steam 9 into an anode gas 2 containing hydrogen, a cathode gas 3 containing oxygen, and an anode gas 2 containing hydrogen. The reformer 10 is provided with a fuel cell 20.
The anode gas 2 produced by is supplied to the fuel cell 20,
Most of the fuel cell 20 is consumed to become the anode exhaust gas 4, and the combustion chamber Co of the reformer 10 is used as combustion gas.
Supplied to

In the reformer 10, combustible components (hydrogen, carbon monoxide, methane, etc.) in the anode exhaust gas 4 are burned in the combustion chamber Co to generate high temperature combustion gas, and the combustion gas causes the reforming chamber Re to flow. The fuel gas 1 is heated and reformed into the anode gas 2 in the reforming chamber Re by the reforming catalyst. Anode gas 2
Is heat-exchanged with the fuel gas 1 by the fuel preheater 11, cooled, and then supplied to the anode A of the fuel cell 20. Further, the combustion exhaust gas 5 that has left the combustion chamber Co is cooled by the air preheater 32, then has its moisture removed, and joins with the air 6 to become the cathode gas 3. A part of the cathode gas 3 reacts in the fuel cell 20 to become the high-temperature cathode exhaust gas 7, a part of which is supplied to the combustion chamber Co of the reformer 10, and another part of which compresses the air 6. After recovering the power with the compressor 36,
Further, a heat energy recovery steam generator (not shown) recovers heat energy and discharges it out of the system. The steam 9 generated by the exhaust heat recovery steam generator is mixed with the fuel gas 1 and sent to the reformer 10.

Natural gas is used as the fuel gas 1, and it reacts with steam in the reformer to generate an anode gas containing hydrogen as a main component. The reaction is represented by the following formula. CH ₄ + H ₂ O → CO + 3H ₂ (1) The main component of natural gas is methane CH ₄ , and the molar ratio of the vapor component H ₂ O to methane is called the steam / carbon ratio (S / C ratio). According to the equation (1), the S / C ratio is 1 in the reaction in the reformer, but methane CH ₄ is converted into CO and H.
_In order to achieve ₂ , the S / C ratio needs to be about 2-3. When the S / C ratio becomes small, carbon is deposited on the reforming catalyst surface of the reformer and the reforming reaction does not proceed.

[0006]

In order to generate the anode gas in the reformer, steam is required, and this steam amount is consumed in large proportion in proportion to the fuel gas. The steam is generated by the exhaust heat recovery steam generator, but if the steam generation amount is large, the exhaust heat energy used for other equipment of the power generator is used, and the efficiency of the power generator as a whole decreases. Therefore, it has been desired to reduce the amount of steam used in the reformer without causing carbon deposition.

The present invention has been made in view of the above-mentioned demand, and an object thereof is to reduce the amount of steam used in the reformer by using the steam generated by the cell reaction in the reformer.

[0008]

In order to achieve the above object, in the invention of claim 1, a fuel cell for generating electricity from a cathode gas containing oxygen and an anode gas containing hydrogen, and an anode exhaust gas of the fuel cell is used as a cathode exhaust gas. A reformer that burns in a part of the fuel gas and uses the heat to reform the fuel gas containing steam to the anode gas, a circulation line that circulates a part of the cathode exhaust gas of the fuel cell to the cathode, and the combustion exhaust gas of the reformer In a fuel cell power generator having an exhaust gas supply line for dehumidifying and degassing and supplying air to a circulation line, a fuel distribution valve for distributing a fuel gas to a first fuel gas and a second fuel gas is provided, and the fuel cell Is composed of a first fuel cell and a second fuel cell, the reformer is composed of a first reformer and a second reformer, and the first reformer supplies a first fuel gas and steam. First to receive
Anode gas is generated, the first fuel cell generates electricity by the first anode gas and the cathode gas from the circulation line, and the second reformer supplies the anode exhaust gas and the second fuel gas of the first fuel cell. In response, the second fuel cell generates a second anode gas, the second fuel cell generates electricity by the second anode gas and the cathode exhaust gas of the first fuel cell, and the steam / carbon ratio of the steam and the first fuel gas is 2 to 2 Set to 3.

According to the second aspect of the present invention, the fuel distribution valve distributes the first fuel gas and the second fuel gas so as to have substantially the same amount.

In the invention of claim 3, the first reformer and the second reformer burn with the anode exhaust gas and cathode exhaust gas of the second fuel cell to perform a reforming action, and the combustion exhaust gas is converted into the first exhaust gas. The reformer is via the first flow control valve and the second reformer is the second
The exhaust gas is discharged to the exhaust gas supply line via a flow control valve.

In the invention of claim 4, the exhaust gas supply line has an air preheater for cooling the combustion exhaust gas and heating the supply gas to the circulation line, and the first flow control valve and the second flow control valve are the above-mentioned. It is provided on the discharge side of the cooling combustion exhaust gas of the air preheater.

[0012]

In the first aspect of the invention, the first fuel gas and steam are supplied to the first reformer at an S / C ratio of 2-3. The first anode gas generated in the first reformer is supplied to the anode of the first fuel cell, and the vapor and the second fuel gas generated by the cell reaction are supplied to the second reformer to generate the second anode gas. It is supplied to the anode of the second fuel cell to generate electricity. Since the amount of steam supplied to the first reformer is the S / C ratio to the first fuel gas, for example, if the first fuel gas is half the total fuel gas, the steam supplied to the first reformer The amount may be half that in the conventional case where there is only one reformer and one fuel cell.

At the anode of the first fuel cell, steam is generated according to the following equation. H ₂ + CO ₃ ^2- → H ₂ O + CO ₂ (2) That is, for each mole of hydrogen gas H ₂ , vapor H ₂ O, 1
Mole is generated. Further, according to the equation (1), the fuel gas (C
3 moles of hydrogen gas H ₂ per 1 mole of H ₄ ), is generated from the first reformer and supplied to the first fuel cell. That is, the first
When 1 mol of the first fuel is supplied to the reformer, 3 mol of vapor is generated from the first fuel cell. Therefore, if the first fuel gas is almost the same as the second fuel gas, the second reformer is used. Also in the above, the S / C ratio is secured to be 2 to 3, and carbon deposition can be prevented without supplying steam to the second reformer. As described above, since it suffices to supply the steam only to the first reformer according to the first fuel gas amount, the steam consumption can be significantly reduced, and the efficiency of the entire fuel cell power generation device is improved.

In the invention of claim 2, the first fuel gas and the second fuel gas
Distribute so that the amount of fuel gas is almost the same. If the first fuel gas is more than the second fuel gas, as is apparent from the above description, the steam supplied from the first fuel cell is excessive in the second reformer, and the first fuel is used in the first reformer. Steam is required depending on the amount of gas. If the first fuel gas is less than the second fuel gas to some extent, the second reformer lacks steam. Therefore, if the first fuel gas and the second fuel gas are made to have substantially the same amount, it is possible to reduce the amount of steam supplied to the first reformer and prevent carbon deposition in any of the reformers. It will be possible.

In the third aspect of the invention, the first reformer and the second reformer burn with the anode exhaust gas and cathode exhaust gas of the second fuel cell to perform the reforming action, but the flow rate of the fuel gas has changed. In this case, the flow rate of the combustion gas is changed accordingly so that the combustion temperature becomes a temperature suitable for the reforming action. Therefore, the flue gas is passed through the first reformer through the first flow control valve and the second reformer through the second reformer.
The gas is discharged to the exhaust gas supply line through the flow control valve. This discharge lowers the pressure in the combustion chamber of the reformer, so the inflow of anode exhaust gas and cathode exhaust gas increases, but since the anode exhaust gas containing combustion components has a constant flow rate, there is almost no change, and the cathode exhaust gas is the same as the anode exhaust gas. Since the flow rate is about 10 times, the flow rate of the exhaust gas from the causal mixture increases mainly. The cathode exhaust gas contains oxygen,
Since the combustion component is not included so much, the concentration of the combustion component is consequently reduced and the combustion temperature can be controlled.

In the invention of claim 4, the exhaust gas supply line has an air preheater for cooling the combustion exhaust gas and heating the supply gas to the circulation line, and the first flow rate control valve and the second flow rate control valve are air preheaters. Is provided on the discharge side of the cooled combustion exhaust gas.
Accordingly, the first flow rate control valve and the second flow rate control valve may have specifications for low temperatures, and thus cost can be reduced.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of a fuel cell power generator according to an embodiment. In this figure, elements having the same functions as those in FIG. 2 are represented by the same reference numerals. The fuel cell power generator includes a reformer 10 for reforming a fuel gas 1 containing steam into an anode gas 2 containing hydrogen, and a fuel cell 20 for generating power from an anode gas 2 and a cathode gas 3 containing oxygen and carbon dioxide. Equipped with
The anode exhaust gas 4 discharged from the fuel cell 20 is supplied to the combustion chamber Co of the reformer 10 through the discharge line 12,
The cathode exhaust gas 7 burns together with a part thereof, and the combustion exhaust gas 5 is supplied to the cathode C of the fuel cell 20 as the cathode gas 3 containing carbon dioxide and oxygen through the exhaust gas supply line 13 and the circulation line 14.

The fuel gas 1 containing natural gas passes through the stop valve 40 and the first fuel control valve 41 causes the first fuel gas 1 to flow.
a and the second fuel gas 1b by the second fuel control valve 42. First fuel control valve 41 and second fuel control valve 42
The distribution ratio is designated by the output command P. The first fuel gas 1a is the steam 9 from the exhaust heat recovery steam generator 39 described later.
Are mixed at an S / C ratio of 2 to 3, usually 2.5 to 3, heated by the fuel preheater 11, and supplied to the first reformer 10a. The first reformer 10a is a second fuel cell 20 described later.
Anode exhaust gas 4 and cathode exhaust gas 7 discharged from b
And a reforming chamber Re for reforming the first fuel gas 1a to generate the first anode gas 2a by heat transfer from the combustion chamber Co. The combustion chamber Co is provided with a temperature sensor 45 for measuring the temperature inside the chamber, and the measured value controls the first flow rate control valve 43 described later. Combustion chamber C
o is filled with a combustion catalyst for sufficient combustion,
The reforming chamber Re is filled with a reforming catalyst for reforming the first fuel gas 1a into the first anode gas 2a mainly containing hydrogen.

The first fuel cell 20a is supplied with the first anode gas 2a at the anode A and the cathode gas 3 at the cathode C to generate electricity. In the anode A, the reaction represented by the formula (2) is performed and the anode exhaust gas 4 containing vapor is discharged. The second reformer 10b has the same structure as the first reformer 10a, is supplied with the second fuel gas 1b and the anode exhaust gas 4 in the reforming chamber Re, and transfers heat from the combustion chamber Co to the second fuel gas 1b. Is reformed to generate the second anode gas 2b. The combustion chamber Co is provided with a temperature sensor 46 for measuring the temperature inside the chamber, and the measured value controls the second flow rate control valve 44 described later.

A temperature sensor 48 is provided at the cathode C outlet of the first fuel cell 20a, and is compressed by a turbine compressor 36 described later in order to lower the temperature of the cathode exhaust gas 7 to the cathode C inlet temperature and supply oxygen. The air 6 is supplied by the air control valve 47. Second fuel cell 20
In b, the cathode C is supplied with the mixed gas of the cathode exhaust gas 7 and the air 6, and the anode A is supplied with the second anode gas 2b to generate electricity.

Anode exhaust gas 4 of the second fuel cell 20b is provided in the combustion chamber Co of the first reformer 10a and the second reformer 10b.
And cathode exhaust gas 7 are supplied. Since the fuel utilization rate of the fuel cell is about 80%, the anode exhaust gas 4 contains about 20% of the fuel component. The cathode exhaust gas 7 contains oxygen necessary for combustion. The combustion exhaust gas 5 from the combustion chamber Co contains carbon dioxide gas, which is necessary for the cell reaction at the cathode C, so that an exhaust gas supply line 13 described later is provided.
Is supplied to the cathode C through the circulation line 14.

Combustion exhaust gases 5a and 5b are discharged to the exhaust gas supply line 13 from the combustion chambers Co of the first reformer 10a and the second reformer 10b. An air preheater 32 is provided in the exhaust gas supply line 13 to cool the combustion exhaust gas 5a, 5b. A first flow rate control valve 43 and a second flow rate control valve 44 are provided at the cooling side outlet of the air preheater 32, and the first flow rate control valve 43 controls the flow rate of the combustion exhaust gas 5 a based on the temperature sensor 45. The second flow rate control valve 44 controls the flow rate of the combustion exhaust gas 5b based on the temperature sensor 46. The flue gas 5 cooled by the air preheater 32 is dewatered by the condenser 33 and the steam separator 34, pressurized by the low temperature blower 35, mixed with the air 6, heated by the air preheater 32, and circulated. Enter line 14.

A part of the cathode exhaust gas 7 drives the turbine of the turbine compressor 36, and then the exhaust heat recovery steam generator 3
9 is supplied. The exhaust heat recovery steam generator 39 uses the water separated by the steam separator 34 to generate steam 9 in the cathode exhaust gas 7 that has driven the turbine of the turbine compressor 36, and is supplied by the S / C control command Q. The steam control valve 49 supplies the first reformer 10a with a steam amount having a predetermined S / C ratio with respect to the first fuel gas 1a. Further, the air 6 compressed by the turbine compressor 36 is the low temperature blower 3
It merges with the combustion exhaust gas 5 at the outlet of 5. Turbine compressor 3
6 has a backup line 37 having an electric blower 38
Is provided and is used as a backup when the capacity of the turbine compressor 36 is insufficient.

A part of the cathode exhaust gas 7 is a part of the air preheater 3.
2 is mixed with the combustion exhaust gas 5 and the air 6 heated to produce cathode gas 3, and the circulation line 14 causes the cathode C
Is supplied to. The circulation line 14 circulates the cathode gas 3 by the high temperature blower 23.

Next, the operation of this embodiment will be described. Since the output command P indicates the distribution ratio of the fuel gas 1, the first fuel control valve 41 supplies the first fuel gas 1a accordingly,
The second fuel control valve 42 supplies the second fuel gas 1b. The S / C ratio for the first fuel gas 1a according to the output command P is
For example, the S / C control command Q in which the amount of steam is set to 3
Accordingly, the steam control valve 49 supplies the steam 9. Output command P
Makes the first fuel gas 1a and the second fuel gas 1b substantially the same amount, and minimizes the consumption amount of the steam 9. The amount of steam 9 thus supplied and the first fuel cell 20
The amount of vapor generated at the anode A of a is almost the same,
The second reformer 10b is supplied with substantially the same amount of vapor as the first reformer 10a, so that carbon deposition can be prevented. When the first fuel gas 1a and the second fuel gas 1b are made to have substantially the same amount in this way, the S / C ratio of the vapor to the entire fuel gas 1 becomes half of the S / C ratio to the first fuel gas 1a. The steam consumption is also half that of the conventional case shown in FIG. As a result, the efficiency of the entire power generator is improved by about 1.5%.

In the combustion chamber Co of the first reformer 10a and the second reformer 10b, the combustion temperature is measured by the temperature sensors 45 and 46, and the amount of the fuel gas 1 and the vapor supplied to the reforming chamber Re changes. Even so, the flow rates of the combustion exhaust gases 5a and 5b are controlled by the first flow rate control valve 43 and the second flow rate control valve 44 so that the reforming reaction temperature becomes constant. When the flow rate of the combustion exhaust gas 5 is increased when the temperature of the combustion chamber Co is increased, the pressure of the combustion chamber Co is reduced, so that the cathode exhaust gas 7 mainly increases and flows in. The cathode exhaust gas 7 contains oxygen but does not contain combustion components, and the combustion temperature is lowered by thinning the anode exhaust gas 4 containing combustion gas. In addition, combustion exhaust gas 5
The inflow of the cathode exhaust gas 7 into the combustion chamber Co increases as the flow rate of the exhaust gas increases. The reason is that if the inflow amount of the combustion exhaust gas 5 into the exhaust gas supply line 13 increases, the gas supply amount to the circulation line 14 increases and This is because the amount of cathode exhaust gas 7 in the line 14 increases.

[0027]

As is clear from the above description, two sets of reformer and fuel cell are provided and steam is supplied to the first set of reformer.
By supplying the steam generated by the first set of fuel cells to the second set of reformers, the steam consumption can be significantly reduced. As a result, the overall efficiency of the power generator can be improved. In this case, the same amount of fuel gas is supplied to the first and second reformers, so that the steam consumption can be reduced to about half of the conventional amount. Further, even if the flow rate of the fuel gas to the reformer changes, the reforming reaction temperature can be kept constant by controlling the flow rate of the combustion exhaust gas.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a fuel cell power generator according to an embodiment.

FIG. 2 is an overall configuration diagram of a conventional fuel cell power generator.

[Explanation of symbols]

 1 Fuel Gas 1a First Fuel Gas 1b Second Fuel Gas 2 Anode Gas 2a First Anode Gas 2b Second Anode Gas 3 Cathode Gas 4 Anode Exhaust Gas 5 Combustion Exhaust Gas 5a First Combustion Exhaust Gas 5b Second Combustion Exhaust Gas 6 Air 7 Cathode Exhaust Gas 9 steam 10 reformer 10a first reformer 10b second reformer 11 fuel preheater 12 exhaust line 13 exhaust gas supply line 14 circulation line 20 fuel cell 20a first fuel cell 20b second fuel cell 23 high temperature blower 32 air Preheater 33 Condenser 34 Steam-water separator 35 Low temperature blower 36 Turbine compressor 37 Backup line 38 Electric blower 39 Exhaust heat recovery steam generator 40 Stop valve 41 First fuel control valve 42 Second fuel control valve 43 First flow rate control Valve 44 Second flow rate control valve 45, 46, 48 Temperature sensor 47 Air control valve 4 9 Steam control valve A Anode C Cathode Co Combustion chamber Re Reforming chamber

Claims (4)

[Claims] 1. A fuel cell for generating electric power from a cathode gas containing oxygen and an anode gas containing hydrogen, and an anode exhaust gas of the fuel cell is burned with a part of the cathode exhaust gas, and the fuel gas containing steam is heated by the heat. A reformer for reforming the exhaust gas, a circulation line for circulating a part of the cathode exhaust gas of the fuel cell to the cathode, and an exhaust gas supply line for dehumidifying the combustion exhaust gas of the reformer and adding air to the circulation line. In a fuel cell power generator provided, a fuel distribution valve for distributing a fuel gas into a first fuel gas and a second fuel gas is provided, and the fuel cell is constituted by a first fuel cell and a second fuel cell, and the reformer is provided. Is composed of a first reformer and a second reformer, the first reformer receiving a supply of a first fuel gas and steam to generate a first anode gas, and the first fuel cell having a first reformer. From the anode gas and the circulation line The second reformer receives the anode exhaust gas of the first fuel cell and the second fuel gas to generate the second anode gas, and the second fuel cell generates the second anode gas and the second anode gas and the second anode gas. 1 Power generation is performed by the cathode exhaust gas of a fuel cell, and the steam / carbon ratio of the steam and the first fuel gas is 2 to
3. A fuel cell power generation device characterized in that 2. The fuel cell power generator according to claim 1, wherein the fuel distribution valve distributes the first fuel gas and the second fuel gas so as to have substantially the same amount. 3. The first reformer and the second reformer burn with the anode exhaust gas and cathode exhaust gas of the second fuel cell to perform a reforming action, and the combustion exhaust gas is fed to the first reformer by the first reformer. The fuel cell power generator according to claim 1, wherein the second reformer discharges the exhaust gas to the exhaust gas supply line via the first flow rate control valve and the second reformer. 4. The exhaust gas supply line has an air preheater for cooling the combustion exhaust gas and heating the supply gas to the circulation line, and the first flow rate control valve and the second flow rate control valve cool the air preheater. The fuel cell power generator according to claim 3, wherein the fuel cell power generator is provided on the combustion exhaust gas discharge side.