JP2945667B1 - Fuel cell power plant - Google Patents

Abstract

An object of the present invention is to prevent a reduction in work efficiency of an air compressor and a cathode blower and a decrease in power generation efficiency of a plant due to an increase in power during the operation of a plant of a molten carbonate fuel cell. A humidification line provided between an exhaust heat recovery boiler and a cathode supplies a part of the steam from the exhaust heat recovery boiler to the cathode. Since the battery cooling capacity can be increased by humidification, the capacity of the air compressor can be made constant, and the increase in the capacity of the cathode blower can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power plant utilizing a molten carbonate fuel cell.

[0002]

2. Description of the Related Art Fuel cells have higher power generation efficiency and superior environmental characteristics than conventional thermal power plants, and are currently being developed in various fields. In particular, a molten carbonate fuel cell has attracted attention as an alternative power source for thermal power, because it has the highest efficiency among fuel cells and can use various fuels such as coal gasified fuel.

FIG. 5 shows a power plant using a general molten carbonate fuel cell. First, the natural gas 1 and steam are mixed and heated to 800 to 1000 ° C. in the fuel reformer 10 to produce hydrogen as a fuel. About 580 ° C containing hydrogen
Of the reformed gas of the battery 1 through the anode supply line 12A.
1 to the anode 12. The anode exhaust gas at about 680 ° C. is cooled by the heat exchanger 14 to condense water vapor in the gas, and the condensed water is separated by the steam separator 15, and then guided to the combustion chamber of the fuel reformer 10. Here, the unreacted hydrogen is burned together with the air pressurized by the air compressor 16, and the fuel reforming 1
0 is required as a heat source.

The flue gas at about 400 ° C. and the air compressor 16
Part of the air at 200 to 300 ° C pressurized at about 680 ° C
About 580 ° C by mixing a part of the cathode exhaust gas of
It is supplied to the cathode 13. The remaining cathode exhaust gas is led to the expansion turbine 18 via the cathode exhaust gas line 41A, and drives the expansion turbine 18 to generate electricity in the generator 19. An exhaust heat recovery boiler 20 is installed at a stage subsequent to the expansion turbine 18, generates steam required for fuel reforming using water recovered by the steam separator 15, and recovers thermal energy of exhaust gas from the expansion turbine. .

The gas passing through the cathode 13 is
In addition to carrying oxygen and carbon dioxide necessary for the reaction, the battery 11 which has generated heat by the reaction is cooled to suppress the gas temperature at the cathode outlet to about 680 ° C. or less. The reaction resistance of the battery 11 increases with time, the performance decreases, and the calorific value increases. In particular, when operating while keeping the output of the plant constant, the calorific value increases rapidly. Therefore, it is necessary to increase the cooling capacity of the battery 11 together with the deterioration of the battery 11.

As described above, the gas of about 580 ° C. supplied to the cathode 13 is supplied to the exhaust gas of the fuel reformer 10 at about 400 ° C. and the compressed gas of 200 to 300 ° C. by the air compressor 16.
It is a mixture of a part of air at ℃ and cathode exhaust gas at about 680 ° C. The flow rate ratio is about 1: 1: 4 at the start of operation of the plant. Even when the battery 11 is deteriorated, the flow rate of the combustion exhaust gas of the fuel reformer 10 is only slightly increased. Therefore, the cooling capacity of the battery is increased mainly by increasing the air flow rate and the cathode exhaust gas circulating flow rate.

However, the gas temperature at the cathode inlet is about 58
Since it is necessary to keep the temperature at 0 ° C., there is a relationship that as the flow rate of the low-temperature air increases, the circulation flow rate of the high-temperature cathode exhaust gas also increases. Therefore, when designing the plant, it is necessary to give a sufficient design margin to the capacity of the air compressor 16 and the cathode blower 32 in consideration of the deterioration of the battery 11.
Assuming that the battery life is 4 to 5 years, the design margin is about 1.3 times the rated capacity.

If the design margin of the equipment is large, the equipment becomes a partial load at the beginning of the operation of the plant, and the work efficiency of the equipment is reduced. On the other hand, when the deterioration of the battery 11 progresses, the power of the equipment increases, so that there is a problem that the power generation efficiency of the plant decreases. Since the work efficiency and power of the air compressor 16 and the cathode blower 32 greatly affect the power generation efficiency of the plant, it is desired to reduce the work efficiency and suppress the increase in power of these devices.

[0009]

To solve this problem, for example, Japanese Patent Application Laid-Open No. Hei 7-245117 describes, for example, with reference to FIG.
0, cathode exhaust gas circulation line 41, air supply line 4
It is proposed to install a water spray device in at least one of the two locations. If water is sprayed on the cathode gas supply line 40 or the air supply line 42, the temperature of the mixed gas decreases, and the gas temperature at the cathode inlet is reduced to about 58%.
Since the cathode exhaust gas circulation flow rate increases to maintain the temperature at 0 ° C., the gas flow rate passing through the cathode 13 increases, and the battery 1
1 increases the cooling capacity.

If water is sprayed on the cathode exhaust gas circulation line 41, the temperature of the cathode exhaust gas returning to the cathode inlet decreases, and the cathode exhaust gas circulation flow rate increases to maintain the gas temperature at the cathode inlet at about 580 ° C. And the cooling capacity of the battery 11 increases. In particular, if water is sprayed at the inlet of the cathode blower 32 installed in the cathode exhaust gas circulation line 41, the volume is reduced due to a decrease in gas temperature, and the power of the cathode blower 32 can be suppressed.

[0011] For example, Japanese Patent Application Laid-Open No. 8-96818 proposes installing a water spray device inside a battery. Water droplets are sprayed inside the cathode with this spray device, and the Leidenfrost phenomenon (a phenomenon in which water droplets on a high-temperature solid surface cannot wet a metal surface above a certain critical temperature and are insulated by a vapor layer to delay evaporation). Utilizing it to cool the battery directly with water droplets. Therefore, it is stated that the cathode blower can be eliminated.

However, in the method proposed in Japanese Patent Application Laid-Open No. 7-245117, attention is paid only to the air compressor 16, and similarly to the air compressor 16, the cathode blower 32 which has a great influence on the power generation efficiency of the plant is provided. Was not taken into account. Since water has a large latent heat of vaporization, the battery 11 can be cooled with a small amount of water and does not contribute to an increase in the gas flow rate. Therefore, since the original increase in the air flow rate is compensated for by the increase in the flow rate of the cathode exhaust gas circulation line 41, the air flow rate becomes constant, but the rate of increase in the flow rate of the cathode exhaust gas increases accordingly.

For example, even if water is sprayed at the inlet of the cathode blower 32 to reduce the volume by lowering the gas temperature, the flow rate of the cathode exhaust gas circulating line 41 increases accordingly to maintain the cathode inlet temperature at about 580 ° C. Therefore, it is not so effective in suppressing the power increase of the cathode blower 32.

On the other hand, in the method proposed in Japanese Patent Application Laid-Open No. 8-96818, it is necessary that water droplets sprayed into the cathode have a uniform and appropriate particle size. When the battery performance decreases and the battery calorific value increases, the amount of spray water drops increases,
It is necessary to increase the diameter of the water droplet, which increases the probability that water droplets in the cathode gas collide with each other. As a result, water droplets having a large particle size are generated and the water droplet diameter is disturbed,
There is a possibility that the cooling of the battery becomes uneven and the power generation efficiency of the battery 11 decreases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fuel cell in which the capacity of an air compressor can be kept constant even if the battery deteriorates and the amount of heat generated increases, the increase in cathode blower capacity is suppressed, and the power generation efficiency of a plant is prevented from lowering. A power plant is provided.

[0016]

In order to solve the above-mentioned problems, in the present invention, the gas supplied to the cathode inlet is humidified by steam, and the humidification amount is increased in accordance with the calorific value of the battery. By mixing water vapor into the gas supplied to the cathode inlet, the flow rate of the gas supplied to the cathode inlet can be increased without changing the capacity of the air compressor. Further, since the specific heat of steam is about twice as large as that of general gases such as nitrogen and oxygen, the specific heat of the gas can be increased by increasing the humidification amount. That is, the cooling capacity of the battery is improved. Therefore,
An increase in the circulation flow rate of the cathode exhaust gas can be suppressed, and as a result, an increase in the power of the cathode blower can be suppressed, and the design margin can be reduced. Further, since water vapor is a gas, it is easily dispersed in the gas, and the battery can always be uniformly cooled even if the amount of mixed vapor changes.

That is, a fuel cell power plant according to claim 1 of the present invention comprises a fuel cell for generating power by a potential difference generated between an anode and a cathode, an anode gas supply line for supplying anode gas and cathode gas, and A cathode gas supply line communicates with the anode and the cathode, respectively, and supplies cathode exhaust gas from the cathode to the cathode and the expansion turbine, drives the expansion turbine to generate power, and discharges the exhaust gas of the expansion turbine into an exhaust heat recovery boiler. A humidification line for supplying a part of the steam from the exhaust heat recovery boiler to the cathode is provided between the exhaust heat recovery boiler and the cathode.

The fuel cell power plant according to claim 2 of the present invention opens and closes a control valve provided in a humidification line between a cathode and an exhaust heat recovery boiler in accordance with a heat value of the fuel cell. A control device for controlling the flow rate of the fuel cell is provided.

In the fuel cell power plant according to a third aspect of the present invention, the steam supplied to the cathode is heated by a heater provided at a stage subsequent to the expansion turbine with the exhaust heat gas from the expansion turbine and the cathode exhaust gas. And supplying to the cathode via the humidification line.

In the fuel cell power plant according to a fourth aspect of the present invention, a part of the air is humidified by a humidification tower, and the humidified air is heated by a heater provided at a stage subsequent to the expansion turbine. Is supplied to the cathode via the

A fuel cell power plant according to a fifth aspect of the present invention is characterized in that a combustor is provided in a cathode exhaust gas line communicating between a cathode outlet and an expansion turbine.

In the fuel cell power plant according to claim 6 of the present invention, a combustor is provided in the cathode exhaust gas line communicating between the cathode outlet and the expansion turbine, and the cathode exhaust gas is burned by the combustor from the cathode. While passing the high-temperature exhaust gas through a heater provided in the subsequent stage of the expansion turbine, the air pressurized by the air compressor is heated by the heater,
It is characterized in that it is supplied to the cathode through the humidification line.

[0023]

(Embodiment 1) An embodiment of the present invention will be described with reference to FIG. In FIG. 1, a humidification line 43, its regulating valve 51, a control device 39, a detector 38 for detecting the calorific value of the battery, and a water recovery device 26 are installed. A humidification line 43 is provided between the two.

A change in the calorific value of the battery is detected by the detector 38, and a part of the steam generated in the exhaust heat recovery boiler 20 is supplied to the cathode gas supply line 40 through the humidification line 43 in response to the increase in the calorific value. . The change in battery calorific value is
The temperature of the gas passing through the cathode 13 may be directly measured, or may be calculated from a decrease in battery voltage or the like. By humidifying with steam, the gas flow rate can be increased without changing the capacity of the air compressor 16, and the heat capacity of the gas is also increased to increase the battery cooling capacity per unit flow rate, so that the flow rate of the cathode exhaust gas circulation line 41 is increased. Can be suppressed. As a result, an increase in the power of the cathode blower 32 can be suppressed, and the design margin can be reduced. In general, the temperature of steam generated in the exhaust heat recovery boiler 20 is 200 to 300 ° C., which is lower than the gas temperature at the cathode inlet of about 580 ° C., so it is necessary to increase the circulation flow rate of the cathode exhaust gas at about 680 ° C. However, since the heat capacity of the cathode exhaust gas is improved and offset, the circulation flow rate of the cathode exhaust gas does not greatly increase.

The above will be described in more detail.
The heat generated at the cathode 13 due to deterioration of the
The analog signal is converted into a digital signal by an A / D converter (not shown). This digital signal is input to the control device 39, and the reference value (normal value) of the control device 39
The motor of the drive circuit (not shown) is rotated left and right depending on whether it is high or low, and the adjustment valve 51 (control valve) is raised and lowered by a drive operation mechanism (not shown).
The opening and closing of the adjustment valve 51 is controlled to control the flow rate of steam in the humidification line 43, and a predetermined steam flow rate is supplied to the cathode 13 via the cathode gas supply line 40. Further, the humidification line 43 may directly communicate with the cathode 13.

As a result, in the present invention, as compared with the case where the humidification line 43 is not provided, an increase in the flow rate of the cathode exhaust gas circulation line 41 can be suppressed by the amount of water vapor supplied from the humidification line 43 to the cathode 13. 3
2 can be suppressed, and the design margin can be reduced.

This means that the flow rate of gas supplied to the cathode 13 can be increased and the heat capacity can be increased without increasing the capacity of the air compressor 16 in the air supply line 42, so that the cooling capacity of the battery 11 can be increased. Can also.

When the amount of humidification increases, the flow rate of gas supplied to the expansion turbine 18 increases, and the weight flow rate per unit volume also increases. Therefore, the output of the expansion turbine 18 increases, and an effect of compensating for a decrease in battery output is expected. it can. Further, since the flow rate of the exhaust gas of the expansion turbine 18 supplied to the exhaust heat recovery boiler 20 also increases, the amount of generated steam naturally increases. Therefore, a new heating source is not required to generate steam to be supplied to the cathode gas supply line 40.

The exhaust gas from the expansion turbine 18 may be passed through the exhaust heat recovery boiler 20 and the feed water heater 21 and then discharged directly to the outside of the plant. However, as shown in FIG. The water is recovered by a recovery device 26, and the water is evaporated by an exhaust heat recovery boiler 20 to form a cathode gas supply line 4.
If it is supplied to 0, the amount of make-up water from outside the plant can be minimized.

(Embodiment 2) FIG. 2 shows another embodiment of the present invention. The basic plant configuration is the same as FIG. 1, but
FIG. 2 is characterized in that the exhaust heat line 44, its regulating valve 52, and the high-temperature heater 24 are installed.

That is, since the circulating flow rate of the cathode exhaust gas at about 680 ° C. is controlled so that the gas temperature at the cathode inlet becomes about 580 ° C., the higher the temperature of steam supplied to the cathode inlet, the higher the circulating flow rate of the cathode exhaust gas. Can be reduced. Therefore, in the plant shown in FIG. 2, a high-temperature heater 24 is installed in front of the exhaust heat recovery boiler 20, and the steam generated in the exhaust heat recovery boiler 20 is further heated by the high-temperature heater 24, and then the cathode is heated. 13 inlet. A part of the cathode exhaust gas exhausted to the expansion turbine 18 is directly supplied to the high-temperature heater 24 through the exhaust heat line 44. As a result, the power generation amount of the expansion turbine 18 is reduced, but the corresponding energy is used for heating the steam, and the temperature of the steam supplied to the cathode inlet can be increased. Since this leads to reduction and power reduction, there is no reduction in the power generation efficiency of the plant.

In the plant shown in FIG.
By making the flow rate of the cathode exhaust gas introduced into 8 constant, the design margin of the expansion turbine 18 can be made 1 so that the work efficiency does not decrease due to the partial load. However, if there is room in the temperature and flow rate of the expansion turbine exhaust gas,
It is also possible not to install the exhaust heat line 44. This is because the work efficiency of the expansion turbine 18 is smaller than that of the air compressor 16 even at a partial load, and the work efficiency is offset by an increase in the amount of gas introduced into the expansion turbine 18.

(Embodiment 3) FIG. 3 shows another embodiment of the present invention. The basic plant configuration is the same as FIG. 1, but
In FIG. 3, the humidification tower 23, the low-temperature heater 25, and the high-temperature heater 24
It is characterized by having been installed.

That is, when the battery 11 deteriorates and the calorific value of the battery increases, a part of the air pressurized by the air compressor 16 is humidified by the humidification tower 23, and the low-temperature heat exchanger 25 and the high-temperature heat exchanger 24 are humidified. Then, the water in the humidified air converted into water vapor is supplied to the cathode 13 inlet. Even with such a method, the same effect as in the first embodiment can be obtained. In the plant of FIG. 3, the pumps 34 and 35 and the blower 36 need extra power, but since the pumps 34 and 35 compress water, the power required is smaller than that of gas compression and is neglected. it can. Since the flow rate of the blower 36 is smaller than that of the air compressor 16 and the cathode blower 32 and the temperature is as low as about 150 ° C., the power can be offset by the increase in the output of the expansion turbine 18.

(Embodiment 4) FIG. 4 shows another embodiment of the present invention. In this plant, a molten carbonate fuel cell is added to a combined plant. The basic plant configuration is the same as that of FIG. 1, except that a combustor 29, a steam turbine 27, a condenser 28, a high-temperature heater 24, a humidification line 43 and a regulating valve 51 thereof are newly installed. .

That is, about 5 to 10% vol of oxygen sufficient for combustion remains in the cathode exhaust gas discharged from the cathode outlet. Therefore, the cathode exhaust gas is burned in the combustor 29 together with the additional fuel, and is passed through the expansion turbine 18 to generate electricity through the generator 19. Rather than using air at 200 to 300 ° C pressurized by the air compressor 16 as in a conventional combined power plant,
By utilizing the cathode exhaust gas at about 680 ° C., the power generation efficiency of the expansion turbine 18 can be increased.

About 650 discharged from the expansion turbine 18
℃ high-temperature exhaust gas, high-temperature heater 24, waste heat recovery boiler 2
0, the water is passed through the feed water heater 21, and the water in the exhaust gas is recovered by the water recovery device 26 and then discharged to the outside of the plant. The reheating of the combustor 29 raises the temperature of the exhaust gas from the expansion turbine to a high temperature, and the amount of steam generated in the exhaust heat recovery boiler 20 increases. The increased amount is supplied to the steam turbine 27 to generate power.

A part of the air compressed by the air compressor 16 is
The mixture is heated to about 580 ° C. or higher by a high-temperature heater 24 installed at a stage subsequent to the expansion turbine 18, and supplied to an inlet of the cathode 13.
By mixing this high-temperature heated air into the flue gas of the fuel reformer 10 at about 400 ° C., the temperature of the gas supplied to the inlet of the cathode 13 can be made about 580 ° C.
The cathode exhaust gas circulation line 41 in FIG. 1 can be omitted. As a result, the cathode blower 32 can also be eliminated, so that the power of the cathode blower 32 becomes unnecessary, and the power transmission end power generation efficiency is improved by that amount.

When the battery 11 has deteriorated, part of the steam generated in the exhaust heat recovery boiler 20 is supplied to the air supply line 42 according to the degree of deterioration. Thereby, the battery 11
Even if is deteriorated, the flow rate of gas supplied to the cathode 13 can be increased and the heat capacity can be increased without increasing the capacity of the air compressor 16, so that the cooling capacity of the battery 11 can be increased.

[0040]

According to the present invention, a part of the steam from the exhaust heat recovery boiler can be supplied to the cathode by the humidification line provided between the exhaust heat recovery boiler and the cathode, and the battery deteriorates. Even if the calorific value increases, the cooling capacity of the battery can be increased by humidifying the steam, so that the capacity of the air compressor can be kept constant and the increase in the capacity of the cathode blower can be suppressed. Therefore, the design margin of each device can be reduced, and a decrease in work efficiency due to a partial load at the beginning of operation and a decrease in power generation efficiency of the plant due to an increase in power at the time of battery deterioration can be prevented.

[Brief description of the drawings]

FIG. 1 is a system diagram of a power plant using a molten carbonate fuel cell shown as one embodiment of the present invention.

FIG. 2 is a system diagram of a power plant using a molten carbonate fuel cell shown as another embodiment of the present invention.

FIG. 3 is a system diagram of a power generation plant using a molten carbonate fuel cell shown as another embodiment of the present invention.

FIG. 4 is a system diagram of a power generation plant using a molten carbonate fuel cell shown as another embodiment of the present invention.

FIG. 5 is a system diagram of a power generation plant using a conventional molten carbonate fuel cell.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fuel, 2 ... Air, 3 ... Water, 10 ... Fuel reformer, 11
... Fuel cell, 12 ... Anode, 13 ... Cathode, 14 ...
Heat exchanger, 15: steam-water separator, 16: air compressor, 18
... Expansion turbine, 19 ... Generator, 20 ... Exhaust heat recovery boiler, 21 ... Feed water heater, 22 ... Chimney, 23 ... Gas water separator, 24 ... High temperature heater, 25 ... Low temperature heater, 26 ... Water recovery device , 27 ... steam turbine, 28 ... condenser, 29 ... combustor, 30 ... fuel compressor, 31 ... anode blower, 32
... Cathode blower, 33 ... Water supply pump, 34 ... Circulation pump, 35 ... Replenishment water pump, 36 ... Blower, 38 ... Battery calorific value detector, 39 ... Control device, 40 ... Cathode gas supply line, 43 ... Humidification line, 50 , 51, 52 ... adjustment valve.

Continuation of the front page (56) References JP-A-7-245117 (JP, A) JP-A-8-96818 (JP, A) JP-A-6-215790 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) H01M 8/00-8/24

Claims (6)

(57) [Claims] 1. A fuel cell for generating electricity by a potential difference generated between an anode and a cathode, and an anode gas supply line and a cathode gas supply line for supplying an anode gas and a cathode gas, respectively, are connected to the anode and the cathode, respectively. In a fuel cell power plant that supplies cathode exhaust gas from the cathode to the cathode and the expansion turbine, drives the expansion turbine to generate power, and supplies the exhaust gas of the expansion turbine to the exhaust heat recovery boiler, A fuel cell power plant, wherein a humidification line for supplying a part of the water vapor to the cathode is provided between the exhaust heat recovery boiler and the cathode. 2. The fuel cell power plant according to claim 1, wherein a control valve provided in a humidification line between the cathode and the exhaust heat recovery boiler is opened / closed in accordance with a heat value of the fuel cell to flow steam. A fuel cell power plant, comprising: a control device for controlling a fuel cell. 3. The fuel cell power plant according to claim 1, wherein the steam supplied to the cathode is heated by a heater provided at a subsequent stage of the expansion turbine with exhaust heat gas from the expansion turbine and cathode exhaust gas. A fuel cell power plant, wherein the power is supplied to a cathode via a humidification line. 4. The fuel cell power plant according to claim 1, wherein a part of the air is humidified by a humidification tower, and the humidified air is heated by a heater provided at a stage subsequent to the expansion turbine, and is passed through the humidification line. A fuel cell power plant, wherein the fuel cell power is supplied to a cathode. 5. The fuel cell power plant according to claim 1, wherein a combustor is provided in a cathode exhaust gas line communicating between a cathode outlet and an expansion turbine. 6. The fuel cell power plant according to claim 1, wherein a combustor is provided in the cathode exhaust gas line communicating between the cathode outlet and the expansion turbine, and a high temperature is obtained by burning the cathode exhaust gas from the cathode in the combustor. While passing the exhaust gas through a heater provided at the subsequent stage of the expansion turbine, the air pressurized by the air compressor is heated by the heater,
A fuel cell power plant, wherein the power is supplied to the cathode via the humidification line.