JPS63231878A - Power generating method by fuel cell and its system - Google Patents

Abstract

PURPOSE:To increase a reforming rate of fuel by resupplying non-reformed gas in reformed hydrocarbon fuel to a fuel reformer. CONSTITUTION:Hydrocarbon fuel introduced into an indirect type fuel reformer built-in fuel cell system 1 is reformed in hydrogen-rich gas with a fuel reformer 6 and supplied to hydrogen storage units 2, 3 which utilize metal hydride or hydrogen storage alloy. Hydrogen gas is separated and recovered, and residual non-reformed gas is reformed again with a fuel reformer 10 of the system 1 through valves 18, 19, and the reformed gas is supplied to an anode 7 together with the recovered hydrogen. By multistep reformation, a reforming rate of hydrocarbon fuel to hydrogen is increased and power generating operation having high fuel utilization can be made.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of generating electricity using a fuel cell and an apparatus thereof.

[Conventional technology]

Examples of fuel cells that use hydrogen mixed with carbon dioxide obtained by steam reforming hydrocarbons as the negative electrode active material include molten carbonate fuel cells (molten carbonate electrolyte fuel cells) and phosphoric acid electrolyte fuel cells. Are known.

The present invention relates to a power generation method using such a fuel cell and an apparatus thereof, and will be described below using a molten carbonate fuel cell as an example.

Now, in a molten carbonate fuel cell that uses molten carbonate as an electrolyte, a hydrocarbon fuel such as natural gas is mixed with steam and reformed, and the resulting hydrogen-rich gas is used as an anode. This hydrogen reacts with carbonate ions in the electrolyte to form carbon dioxide, water, and electrons. If the anode and cathode are connected through a load circuit, electrons created at the anode flow to the cathode via the load circuit, and at the cathode, oxygen and carbon dioxide gas in the air combine with the electrons inside the cathode to form carbonate ions. and enters the molten carbonate, which is an electrolyte. In this way, electrons flow from the anode to the cathode, that is, current flows from the cathode through the load to the anode, thereby generating electricity.

When generating electricity using a molten carbonate fuel cell device, when natural gas or hydrocarbon fuels such as methanol are used as fuel, a fuel reformer is required to reform these gases into hydrogen-rich gas. be. In general, there are two methods for carrying out a reforming reaction using water vapor: an external reforming method in which a reforming reactor is installed outside the fuel cell system, and a reforming method in which a reforming reactor is installed inside the fuel cell system using a high-temperature battery. There is an internal reforming method in which a reactor is installed.

The steam reforming reaction of hydrocarbon fuel gas is accompanied by a large endothermic reaction. For example, steam reforming of methane is represented by equation (1).

CH4+2H20=CO□+4112 (11
The reaction heat of this reaction is 39.44 kca 7! /mo
l is necessary. On the other hand, in fuel cells, the system efficiency when converting chemical energy into electrical energy is 45 ~
50%, and the rest is generated as thermal energy. In the internal reforming method, in which the reforming reaction is performed using heat generated inside the battery, a high power generation system efficiency of 55% or more is expected. On the other hand, in the external reforming method, it is necessary to heat from the outside with a burner or the like. For this reason, the fuel cell device with a built-in fuel reformer is attracting attention as a highly efficient power generation device.

Conventionally, there have been several types of fuel cell devices with a built-in fuel reformer, depending on the arrangement of catalysts required for the reforming reaction and the method of supplying fuel gas. FIG. 4(A) shows a schematic diagram of a fuel cell device with a built-in fuel reformer of a direct type in which a reforming catalyst is disposed in a part of the gas supply path of the anode. Figure 4 (
B) shows a schematic diagram of a fuel cell device with a built-in fuel reformer of an indirect type in which a reforming catalyst is arranged in a reaction chamber adjacent to an anode chamber. In these figures, 31a and 3'lb are fuel cell devices with a built-in fuel reformer, 32a and 32b are introduction pipes for hydrocarbon fuel gas and steam, 33a and 33b are catalytic combustors, and 34a and 34b are air introduction pipes. Tube, 35a.

35b is a fuel reforming reaction device, 36a and 36b are anodes, 37a and 37b are electrolyte plates, and 38a and 38b are cathodes.

[Problem that the invention seeks to solve]

However, such conventional fuel cell devices with a built-in fuel reformer have the following drawbacks, regardless of whether they are of the direct type or indirect type.

That is, in the case of methane steam reforming reaction, (1)
In addition to the formula, the reaction also occurs according to the formula (2).

CH4+1 (20=CO+ 3H2 (2) Furthermore, since -carbon oxide, water vapor, or carbon dioxide gas and hydrogen coexist, the equilibrium relationship of equation (3) is established.

CO+■, O=CO□+H2 (31 In the direct method, the hydrogen produced by the reforming reaction is immediately consumed in the cell reaction, so the equilibrium relationship between equations (2) and (3) shifts to the right. This has the advantage of increasing the reforming rate of methane, etc. However, in this case,
Exposure to highly corrosive electrolyte vapor causes a decrease in catalytic performance. Therefore, there is a drawback that stable battery performance over a long period of time cannot be obtained.

On the other hand, in the indirect method, the reforming catalyst is not directly exposed to the electrolyte vapor, so no deterioration of characteristics occurs. Customary catalysts can be used for this purpose. but,
This indirect method has the disadvantage that the reforming rate of methane and the like cannot be increased very much because the generated hydrogen is not consumed immediately.

[Means for solving problems]

The present invention has been made in view of the above-mentioned conventional problems, and is aimed at reforming hydrocarbon fuel in a fuel cell device that uses hydrogen mixed with carbon dioxide gas obtained by reforming hydrocarbon fuel as a negative electrode active material. The purpose is to improve the rate.

That is, the power generation method of the present invention involves reforming a hydrocarbon fuel such as natural gas or methanol into a hydrogen-rich gas in a power generation device equipped with a fuel reforming reaction device and a fuel cell device. Supplying the reformed gas to a reaction device to produce a reformed gas, supplying the reformed gas to a hydrogen storage device using a metal hydride or a hydrogen storage alloy, and separating and recovering hydrogen gas in the reformed gas to the hydrogen storage device; The unreformed gas discharged from this hydrogen storage device is returned to the fuel reforming reaction device, or is supplied to a fuel reforming reaction device installed separately from this reaction device for a reforming reaction. The present invention is characterized in that gas is introduced into the anode of the fuel cell device.

Further, the power generation device of the present invention is a power generation device equipped with a fuel reforming reaction device for reforming hydrocarbon fuel such as natural gas or methanol into hydrogen-rich gas, and a fuel cell device, in which the fuel cell device is installed in an indirect method. In addition to having a built-in fuel reformer, a plurality of the fuel reforming reaction devices are arranged in series, and a metal hydride or a hydrogen storage alloy is used in the flow path connecting the adjacent reaction devices for hydrogen storage. A device is provided, and the reformed gas outflow side of the most downstream reaction device in the reformed gas flow path among the plurality of fuel reforming reaction devices is connected to the anode of the fuel cell device. It is.

C Example] Embodiments of the present invention will be described based on the drawings.

Figure 1 shows a schematic diagram of a power generation device equipped with a molten carbonate fuel cell device, and 1 in the figure is a fuel cell device with a built-in indirect fuel reformer in which a large number of unit cells and a fuel reformer are arranged. , 2.3 is metal hydride (LaNis) 16+ FeT
4 is a catalytic combustor, 5 is a hydrogen cylinder, 6.10 is a fuel reforming reaction device (fuel reformer), 7 is an anode, 8 is a carbonate electrolyte plate, 9 is a cathode, 11.12 is a heat exchanger, 13 is a natural gas and steam introduction pipe, 14 is an air introduction pipe, and 15' to 22 are valves.

In this way, in this embodiment, there are two fuel reforming reactors 6.
．． 10 are arranged in series with each other, and two hydrogen storage devices 2 and 3 are installed in parallel with each other in a pipe connecting these, and a pipe is installed in the pipe so that these hydrogen storage devices can be switched and used. A valve is installed.

Next, to explain the operation procedure of this power generation device, when the temperature rises at the time of starting the fuel cell device 1, the valve 16
．． 17, 19.21 are closed, valve 20.22 is opened, and the hydrogen in the hydrogen cylinder 5 is poured into the hydrogen storage bag W3 using metal hydride.

As a result, heat is generated by the hydrogen storage reaction, and this heat is sent out of the reaction system by a heat medium circulating in the heat exchanger 12, thereby serving as a means for raising the temperature of the battery device 1. Next, open valves 15.1B and 20.21 and valves 16.17.19
．． Close 22. Thereby, the natural gas and steam are supplied through the introduction pipe 13 to the fuel reforming reaction device 6 built into the fuel cell device 1 and reformed. Hydrogen gas in this reformed gas is introduced into the hydrogen storage device 2, where it is separated, recovered, and stored. Since the hydrogen storage reaction of metal hydrides is an exothermic reaction, the exhaust heat emitted from inside the hydrogen storage device 2 is sent out of the reaction system of the hydrogen storage device 2 by a heat medium circulating in the heat exchanger 11 and used effectively. . The unreformed gas discharged from the hydrogen storage device 2 is again introduced into the fuel reforming/reacting device 10 in the fuel cell device 1, subjected to a sufficient reforming reaction, and then supplied to the anode 7.

On the other hand, from the hydrogen storage device 3 using a metal hydride in which hydrogen has been stored in advance, the fuel cell device 1
The temperature of the heat exchanger 12 is raised using the exhaust heat, etc., and hydrogen is released. This released hydrogen gas is transferred to the valve 20.2.
1 is passed through and supplied to the anorode. In this case, the flow rate of hydrogen gas released from the hydrogen storage device 3 is adjusted by controlling the temperature of the heat exchanger 12 in accordance with changes in the load required of the fuel cell device 1.

Unreacted gas that does not participate in the cell reaction at the anode 7 mixes with excess air supplied from the air introduction pipe 14 and is supplied to the cathode 9 via the catalytic combustor 4. Here, when hydrogen is sufficiently occluded in the hydrogen storage device 2 or hydrogen in the hydrogen storage device 3 is sufficiently released, the valve 15.1B.

Close valves 20 and 22 and open valves 16 and 17 and 19.

In this case, contrary to the above, hydrogen is separated and recovered in the hydrogen storage device 3 and stored, and hydrogen is released from the hydrogen storage device 2. The following operations are performed in the same manner as the above operating procedure.

In addition, so-called hydrogen storage alloys (Ti-Ni-based alloys, Ti-Cu-based alloys, etc.) also have a hydrogen storage function similar to the metal hydride, and have the property of releasing hydrogen gas when heated. Therefore, this hydrogen storage alloy can be applied to a hydrogen storage device.

As described above, in this example, by repeating the above operations alternately, only the hydrogen gas in the reformed gas can be continuously separated and recovered, thereby increasing the reforming rate of hydrocarbon fuel. is possible.

Note that the present invention is not limited to a power generation device equipped with a fuel cell device with a built-in indirect type fuel reformer according to the above embodiment, but also includes a power generation device equipped with a fuel cell device with a built-in direct type fuel reformer. The present invention can also be applied to a power generation device equipped with an external reforming type reforming reactor. Furthermore, the present invention is applicable not only to molten carbonate fuel cells but also to fuel cells such as phosphoric acid electrolyte fuel cells that use hydrogen mixed with carbon dioxide gas obtained by reforming hydrocarbon fuel as a negative electrode active material. In either case, there is an advantage that the reforming rate of the hydrocarbon fuel can be improved and power generation operation can be performed with high efficiency in using the fuel.

The main feature of the present invention is to recover the hydrogen in the reformed gas to the hydrogen storage device as described above, and to supply the unreformed gas flowing out from the device to the fuel reforming reaction device again. However, this is not limited to a power generation device in which two (or three or more) fuel reforming reaction devices are arranged in series as in the above example, but one such reaction device is provided and the outflow gas from the reaction device is The object of the present invention can also be achieved by providing a return flow path for returning hydrogen to the inflow side and providing a hydrogen storage device in this return flow path.

Next, the relationship between the methane reforming rate and the hydrogen recovery rate of the hydrogen storage device using metal hydride in the molten carbonate fuel cell device according to the present invention will be investigated.

In the reaction of the above equation (2+, T3+), assuming that the reaction temperature is constant within the operating temperature range of the fuel cell device (600 to 700°C), the equilibrium relationships of equations (2) and (3) are established. Now, the reaction conditions are that the reaction temperature is 648°C, and the mixing ratio (molar ratio) of methane and steam is 1.
Assuming that F2.5, the methane reforming rate is calculated numerically from the equilibrium constants of equations (21 and (31).

FIG. 2 shows the relationship between the methane reforming rate and the hydrogen recovery rate determined from calculation. Here, the methane reforming rate was determined using equation (4).

Methane reforming rate (%) −(1−(CHa,) / ((Co) +(CO
2) +(CH4,) ) ) X100 (
41 Furthermore, the recovery rate of hydrogen stored in a hydrogen storage device using a metal hydride was determined using equation (5).

Hydrogen recovery rate (%) - ((Amount of hydrogen recovered stored in the hydrogen storage device using metal hydride) / (Amount of hydrogen in the initial reformed gas)) x 100 (51 From Figure 2, methane It can be seen that the reforming rate increases almost linearly as the hydrogen recovery rate increases.

On the other hand, FIG. 3 compares the relationship between pressure and methane reforming rate for a power generation device equipped with a conventional fuel cell device with a built-in indirect fuel reformer and a power generation device according to the embodiment of the present invention. This is what was shown.

From FIG. 3, it can be seen that according to the power generation method of the present invention, the reforming rate of methane is significantly improved compared to the conventional power generation method.

〔Effect of the invention〕

As described above, the present invention separates and recovers the hydrogen gas in the reformed gas discharged from the fuel reforming reaction device into a predetermined hydrogen storage device, and supplies the remaining gas to the fuel reforming reaction device again for reforming. Since this gas is introduced into the fuel cell device, the reforming rate of hydrocarbon fuel to hydrogen in the power generation device is improved, and power generation operations can be performed with high efficiency in using the fuel. There is.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a power generation device equipped with a molten carbonate fuel cell device according to the present invention, that is, a power generation device equipped with a fuel cell device with a built-in indirect fuel reformer, and Figure 2 is a schematic diagram of a power generation device equipped with a fuel cell device with a built-in indirect fuel reformer. Figure 3 is a graph showing the relationship between the hydrogen recovery rate and the hydrogen recovery rate in a hydrogen storage device using metal hydrides. It is a graph showing the relationship with the methane reformation rate in comparison. Figure 4 (AL) (B) is a schematic diagram of a conventional fuel cell device with a built-in fuel reformer, and Figure (A) is a direct type in which a reforming catalyst is placed in a part of the gas supply path of the anode. The things of
Figure CB) shows an indirect method in which the reforming catalyst is placed in the reaction chamber adjacent to the anode chamber. 1...Fuel cell device with built-in indirect fuel reformer, 2.
3...Hydrogen storage device, 4...Catalytic combustor, 5...
Hydrogen cylinder, 6... Fuel reforming reaction device, 7... 7 node, 8... Electrolyte plate, 9... Cathode, 10...
・Fuel reforming reaction device, 11.12...Heat exchanger, 13
．． 14...Introduction pipe, 15-22...Valve, 31a
, 31b...Fuel cell device with built-in fuel reformer, 32a, 32b-introduction pipe, 33a,' 33b...
-Catalytic combustor, 34a, 34b...introduction pipe, 35a,
35b...Fuel reforming reaction device, 35a, 36b-anode, 37a, 37b-electrolyte plate, 38a, 38b...
・Cathode. Patent applicant: Director of the Institute of Industrial Technology Patent applicant: Ebara Corporation (OLO) Fenghuan η? ω
Pressure on Otsu 6 (ATM)

Claims (3)

[Claims] (1) In a power generation device equipped with a fuel reforming reaction device and a fuel cell device that reform hydrocarbon fuel such as natural gas or methanol into hydrogen-rich gas, hydrocarbon fuel is supplied to the fuel reforming reaction device. This reformed gas is supplied to a hydrogen storage device using a metal hydride or a hydrogen storage alloy, and the hydrogen gas in the reformed gas is separated and recovered to this hydrogen storage device. The emitted unreformed gas is returned to the fuel reforming reaction device, or is supplied to a fuel reforming reaction device provided separately from this reaction device for a reforming reaction, and this reformed gas is sent to the fuel cell. A power generation method using a fuel cell, characterized by introducing the fuel cell into an anode of a device. (2) In a power generation device equipped with a fuel reforming reaction device and a fuel cell device that reform hydrocarbon fuel such as natural gas or methanol into hydrogen-rich gas, the fuel cell device is built into an indirect fuel reformer. type, a plurality of the fuel reforming reaction devices are arranged in series, and a hydrogen storage device using a metal hydride or a hydrogen storage alloy is provided in a flow path connecting these mutually adjacent reaction devices, A power generating device characterized in that a reformed gas outflow side of the most downstream reactor in the reformed gas flow path among the plurality of fuel reforming reactors is connected to an anode of the fuel cell device. (3) The power generation device according to claim 2, wherein the hydrogen storage devices are arranged in parallel with each other in a flow path that connects the fuel reforming reaction devices that are adjacent to each other.