JPH0256866A - Fuel cell power generating system - Google Patents

Abstract

PURPOSE:To suppress the fluctuation of the cell output when fuel is switched by providing a fuel switching device storing a hydrogen absorbing alloy absorbing and desorbing hydrogen. CONSTITUTION:A fuel switching device 39 storing a hydrogen storing device 43 made of a hydrogen absorbing alloy is provided on a fuel feeding system to switch two or more kinds of fuel for the ordinary use and the emergency use. When a fuel cell is operated by the ordinary fuel, most of the reformed gas containing much hydrogen by a reform is fed to the fuel cell, and part of it is absorbed by the hydrogen storing device 43 via a gas refining system for storage as required. When the fuel is switched, the hydrogen stored in the hydrogen storing device 43 is discharged, the output reduction due to the response delay or the like of a reforming device is supplemented, and the cell output is kept constant when the fuel is switched. Hydrogen can be fed to the fuel cell main body with no deficiency and the output reduction can be suppressed when the fuel is switched by utilizing the characteristic of the hydrogen absorbing alloy.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a fuel cell power generation system that switches between two or more types of fuel, and particularly relates to a fuel cell power generation system that has little output fluctuation when switching fuels. .

(Conventional technology) In the conventional fuel cell power generation system, as shown in Figure 3,
Fossil fuel A (alphabetic codes indicate fuels, etc. and their routes, etc.; the same applies hereinafter), which is relatively easy to obtain and secure, such as city gas, is used as a regular fuel. After the commonly used fossil fuel A is heated in the heat exchanger 1,
The desulfurization device 2 removes sulfur that causes poisoning of the reforming catalyst and fuel type catalyst. When the catalyst is poisoned with sulfur, the efficiency of the reformer 6 is reduced, and the efficiency of the entire fuel cell is also reduced. Note that if the fossil fuel A does not contain sulfur, such as methanol, this desulfurization process is not necessary.The desulfurization gas is mixed with steam G from the steam generator 20 and further heated in the heat exchanger 3. , reaction section 4 of the reformer 6
The gas is reformed into a gas containing a large amount of hydrogen. After the temperature of this fuel gas is lowered in a heat exchanger 7, it flows into a shift converter 8, where carbon monoxide in the gas is converted into carbon dioxide in order to prevent poisoning of the fuel electrode catalyst of the battery main body 12. Thereafter, this reformed gas is cooled by a heat exchanger 9, and then flows into a steam/water separator 10 to remove moisture. The reformed gas containing a large amount of hydrogen from which water has been removed is transferred to the heat exchanger 1.
After being heated at step 1, the fuel is supplied to the fuel electrode 13 of the fuel cell main body 12. The fuel cell main body 12 includes a fuel electrode 13. electrolyte 1
4. It consists of an oxidizer electrode 15, and the DC power obtained by the battery reaction is converted into AC power by an orthogonal converter 16. Note that since the cell reaction is an exothermic reaction, the fuel cell main body 12 is cooled with cooling water O. The exhaust gas F flowing out from the fuel electrode 13 is auxiliary fuel B heated in the heat exchanger 21.
It is also supplied as heating fuel C to the burner 5 of the reformer 6 and used to obtain the combustion heat necessary for the reforming reaction.

Air J is supplied to the oxidizer electrode 15 of the fuel cell main body 12 through the heat exchanger 17 and used as an oxidizer, and is also supplied to the reformer N6 and used as combustion air. The exhaust gas M flowing out from the oxidizer electrode 15 is cooled by a heat exchanger 18, and then flows into a steam/water separator 19 to remove moisture, and then is released into the atmosphere.

Further, the exhaust gas E flowing out from the reformer 6 is transferred to the heat exchanger 2
After being used to preheat auxiliary fuel B in step 1, it is released into the atmosphere. Note that the generated water H and I separated by the steam separators 10 and 19 are supplied to the steam generator 20, heated N, and become steam G, which is used for reforming fuel.

In the conventional fuel cell power generation system described above, it is preferable to use city gas as fuel, which does not require large amounts of stockpiling from a safety perspective, and is easily available from a cost perspective and does not require replenishment. The supply of fuel will be cut off in the event of an earthquake with a seismic intensity of 5 or higher, so when fuel cells are used in systems that require reliability even in emergencies, such as power supply systems for communication, it is necessary to prepare emergency fuel reserves. However, in an emergency, it is required to switch from regular fuel such as city gas to stored fuel to ensure fuel cell operation.

Figure 3 shows a case where the reformer is shared, such as city gas and propane. Normally, valve 22 is open and valve 23 is closed, and commonly used fossil fuel A is supplied to reformer 6, and hydrogen A reformed gas containing a large amount of is produced, which is supplied to the fuel cell main body 12 via the shift converter 8, and power generation is performed. Flow rate with sensor 24.

When a stop in the supply of commonly used fossil fuel A is detected from a drop in pressure, etc., valve 22 is closed and valve 23 is opened, fuel P is supplied to reformer 6, and hydrogen is converted into a reformer containing a large amount of hydrogen. Quality gas is produced, which is supplied to the fuel cell body 12 via the shift converter 8 to generate electricity. At that time, the temperature of the reformer.

Reforming conditions such as the amount of fuel P supplied and the amount of water vapor supplied are set to predetermined optimal values.

Furthermore, FIG. 4 shows a case where different reformers are used for city gas and methanol. This is a case where fuels such as city gas and methanol, which have different reforming conditions such as reforming catalyst and reforming temperature, are switched and used.

By the way, in the case of natural gas (mainly composed of methane), which is widely used as city gas, the reforming temperature is 800°C2, and the reforming catalyst is old, whereas in the case of methanol, the reforming temperature is 250°C, Reforming catalyst Cu-Cr type or Cu-Zn
It is a system. In this case, it is necessary to use different reformers depending on the fuel.

Next, in the explanation of FIG. 4, parts that overlap with those of FIG. 3 will be omitted. Normally, the valve 22 is open and the valve 23 is closed, and the commonly used fossil fuel A is supplied. In that case, valve 26. Valve 28. Valve 29. Valve 31. Valve 37 closes, valve 25, valve 27
．． Valve 30. Valve 32. Valve 38 is opened and reformer 6 is used. The details are the same as in the case of FIG.

Therefore, when the sensor 24 detects the stoppage of the supply of the commonly used fossil fuel A from a drop in flow rate, pressure, etc., the valve 22 closes and the valve 22 closes.
3 is opened and fuel Q is supplied, and the reformer 6 is stopped or maintained in a preset standby state. In this case valve 26. Valve 28. Valve 29° Valve 31. Valve 37 opens, valve 25. Valve 27. Valve 30. Valve 32. Valve 38 is closed and reformer 33 is used. At this time, reforming conditions such as the temperature of the reformer, the amount of fuel Q supplied, and the amount of steam supplied are set to predetermined optimal values.

In addition, in the case of FIG. 4, the fuel Q is assumed to be a fuel that does not contain sulfur like methanol and does not generate much carbon monoxide through reforming, so the fuel Q is raised in the heat exchanger 36. After being heated, it is supplied to the reformer 33, where a reformed gas containing a large amount of hydrogen is produced. This reformed gas containing a large amount of hydrogen is transferred to the heat exchanger 9. Steam water separator 10. The fuel is supplied to the fuel cell main body 12 via the heat exchanger 11. 35 is a reaction part of the reformer, and 34 is a burner. Depending on the fuel, desulfurization and carbon oxide shift reactions may be necessary.

In that case, the system would be the same as that shown in FIG. 3, only the reformer would be different.

(Problems to be Solved by the Invention) In the conventional fuel cell power generation system described above, when the fuel is switched, even if the same reformer shown in Fig. 3 is used, new fuel is added to the reformer. There is a time delay before the reforming reaction reaches a steady state. Furthermore, if the reformer shown in FIG. 4 is different, there will be a considerable time delay in reaching the required state, particularly for the steam reforming reaction and combustion/heat transfer in the reformer. Therefore, when switching fuel,
A shortage of fuel hydrogen occurs, causing a phenomenon in which the fuel cell output temporarily decreases. For this reason, if a fuel cell is applied to a power source that requires high accuracy and high reliability, such as a power source for communication, there is a risk that the system will go down when switching fuels.

The relationship between the time during the fuel switching, the output (power generation amount) of the fuel cell, and the amount of hydrogen supplied is as shown in FIG. The solid line in FIG. 4(a) and FIG. 4(a) respectively show the fuel cell output and hydrogen supply amount of the conventional technology at the time of fuel switching. From this figure, it can be easily understood that the prior art has the disadvantage that the hydrogen supply amount is insufficient for a period of Δ when switching fuels, and the battery output is accordingly reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell power generation system that eliminates the drawbacks of the prior art described above and can suppress fluctuations in battery output during fuel switching.

(Means for Solving the Problems) In order to achieve the above object, the present invention consists of a fuel cell main body, a fuel supply system, an oxidizer supply system, a cooling system, and ancillary equipment, and provides hydrogen for fuel cells by converting fossil fuels into In a fuel cell power generation system obtained by quality, in order to switch between two or more types of fuel for regular use or emergency use, the fuel supply system is equipped with a fuel switching device that has a built-in hydrogen storage device made of a hydrogen storage alloy, and the regular fuel During fuel cell operation, most of the reformed gas containing a large amount of hydrogen obtained through reforming is supplied to the fuel cell, and if necessary, a portion is stored in the hydrogen storage device after passing through the gas purification system. and
A fuel characterized in that when switching fuels, the hydrogen stored in the hydrogen storage device is released to compensate for a decrease in output due to a response delay of the reformer, etc., and the battery output is held constant when switching fuels. The main topic is battery power generation systems. In a fuel cell power generation system consisting of a fuel cell main body, a fuel supply system, an oxidizer supply system, a cooling system, and ancillary equipment, hydrogen is taken in and out by heating and cooling the fuel supply system using a heating medium and a cooling medium. A fuel switching device 39 containing a hydrogen storage alloy is provided.

(Example) Embodiments of the present invention will be described below along with the drawings.

It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention.

FIG. 1 is a system diagram of a fuel cell power generation system showing one embodiment of the present invention, and FIG. A fuel switching device 39 is provided between the water separator 10 and the heat exchanger 11.
A fuel cell power generation system equipped with That is, the present invention provides fuel electrode 13. Electrolyte 14. Oxidizer electrode 1
5, a fuel cell body 12 consisting of a fuel cell main body 12, a reformer that supplies fossil fuel A; Shift converter 8. Fuel supply system including steam/water separator IO, air supply system that supplies air J, cooling water 0
In the cooling system and attached supply device, the fuel switching device 39
It has been established.

Note that among the symbols shown in FIG. 1, the same symbols as those in FIGS. 3 and 4 indicate the same parts, and their explanations will be omitted.

In the fuel switching device 39, 43 is a hydrogen storage device incorporating a hydrogen storage alloy that takes in and out hydrogen by heating and cooling with a heating medium S and a cooling medium T. An example of a hydrogen storage alloy is the well-known lanthanum-nickel system.

Examples include metal hydrides such as magnesium/nickel type, iron/titanium type, etc. Hydrogen storage alloys take in and out hydrogen through the following reaction.

2M+H house → 2MH+q That is, when hydrogen is stored, hydrogen is stored by removing generated heat q with a cooling medium, and when hydrogen is released, hydrogen is released by applying heat q from the outside with a heating medium. Reference numerals 40 and 41 refer to a flow meter and a hydrogen sensor equipped with a flow meter and a hydrogen sensor for monitoring the reformed gas flow rate and the hydrogen concentration in the reformed gas so as to keep the amount of hydrogen supplied to the fuel electrode 13 of the fuel cell main body 12 constant. This is a hydrogen concentration monitoring device. In addition, 50 is a flow rate and hydrogen concentration monitoring device, which measures the hydrogen concentration at the outlet of the reformed gas sent to the hydrogen storage device for element storage to grasp the state of the hydrogen storage alloy and store hydrogen. It is used to adjust the amount of reformed gas supplied to the device 243. Further, when hydrogen is supplied from the hydrogen storage device 43 to the fuel cell main body 12, the flow rate is measured and used to adjust the hydrogen supply amount to an appropriate value. An example of a method for measuring hydrogen concentration using a hydrogen sensor is metal oxides (oxides such as W, Mo+Cr+Pa, TI+In) and active catalysts (Pt, Ir, etc.).

One example is a method in which hydrogen concentration is detected from changes in conductivity using a metal (Rh, Pd, etc.) as a detection element. 42 is a gas separation and removal device, which is used to separate gases other than hydrogen that may be adsorbed on the alloy surface etc. and have a negative effect on the hydrogen storage performance of the hydrogen storage alloy.0Separation methods include activated carbon, molecular Adsorption method using adsorbents such as sieves, activated alumina, and zeolites.

An example is a membrane separation method using a hydrogen-selective permeable membrane.

Next, the operation of the fuel switching device applied to this embodiment having the configuration as shown in FIG. 2 described above will be explained.

During fuel cell operation using regular fuel, most of the reformed gas R containing a large amount of hydrogen removed by the steam-water separator 10 passes through the flow rate and hydrogen concentration monitoring devices 40 and 41 to the heat exchanger 1.
1 and then supplied to the fuel electrode 13. A portion of the reformed fuel gas is sent to the gas separation and removal device 42 through the opened valve 44, and gases other than hydrogen that have an adverse effect on the hydrogen storage alloy are removed. Gas other than hydrogen removed by the gas separation and removal device 42 passes through the opened valve 45 to the reformer 6.
burner 5 (both shown in Figure 1) and used as a heat source for reforming. Further, the hydrogen gas purified by the gas separation and removal device 42 flows into the hydrogen storage device 43, and hydrogen is stored in the hydrogen storage alloy. At this time, as described above, heat is generated, so the cooling medium T is passed through the outside of the hydrogen storage device to remove heat and promote the hydrogen storage reaction. That is, open the control valve 47 and valve 49, and! The Ilv valve 47 is adjusted to control the supply amount of the cooling medium T to efficiently store hydrogen in the hydrogen storage device. At this time, the control valve 46 and the valve 48 are closed. After hydrogen has been stored in the hydrogen storage alloy in the hydrogen storage device 43, the exhaust gas is processed by a flow rate and hydrogen concentration monitoring device 50. Through the opened valve 52, the fuel electrode 13 of the fuel cell
The exhaust gas is supplied to the burner 5 of the reformer 6 (both shown in FIG. 1), and serves as a heat source for the reformer. Valve 52 is closed. This hydrogen storage is performed until the hydrogen storage alloy built in the hydrogen storage device 43 reaches a saturated state. When the hydrogen storage alloy reaches a saturated state, the hydrogen concentration in the exhaust gas on the outlet side of the hydrogen storage device 43 increases.
This is detected by the flow rate and hydrogen concentration monitoring device 50, and the valve 44
．． Valve 45. Valve 51 is closed.

At the time of fuel switching, the hydrogen concentration in the reformed gas R temporarily decreases due to a response delay of the reformer, etc., and the amount of hydrogen gas supplied decreases. Therefore, when this is detected by the flow rate and hydrogen concentration monitoring bag M40, the control valves 47 and 49 are closed and the supply of the cooling medium T to the hydrogen storage device f43 is stopped.
The control valve 46 and the valve 48 are opened, the heating medium S is supplied to the hydrogen storage bag 243, and hydrogen is released. The amount of released hydrogen is adjusted by controlling the supply amount of the heating medium S using the control valve 46. Further, the valve 51 is closed and the valve 52 is opened, and the hydrogen released from the hydrogen storage device 43 is mixed with the reformed gas, and this is supplied to the fuel electrode 13 of the fuel cell main body 12. The amount of released hydrogen is determined by the flow rate and hydrogen concentration monitoring devices 41 and 50, and the control valve 46 is controlled so that the amount of hydrogen supplied by the mixed gas is the same as the amount of hydrogen supplied before fuel switching.
Next, when the reformer reaches a steady state and the amount of hydrogen supplied by the reformed gas R becomes the same as the state before fuel switching, the supply of hydrogen gas from the hydrogen storage device 43 is stopped. . That is, when it is confirmed by the flow rate and hydrogen concentration monitoring device 40 that the hydrogen concentration in the reformed fuel gas R has returned to the level before the fuel switching, the control valve 46 and the valve 48 are closed, and the hydrogen storage device 43 is closed. The supply of the heating medium S to the hydrogen storage device 43 is cut off, and the release of hydrogen is stopped.Then, the control valve 47 and the valve 49 are opened, and the cooling medium T is supplied to the hydrogen storage device 43. Hydrogen is stored in the hydrogen storage device 43 as in the case of battery operation. At that time, the valve 52
is closed and valve 44. Valve 45. Valve 51 is opened.

The battery output according to this embodiment described above is shown by the dashed line in FIG. 5(a), and the amount of hydrogen supplied from the fuel switching device is shown in FIG.
C) and (B), where FIG. 5(C) shows the shortage of hydrogen supply from the reformer corresponding to the maximum output drop ΔW during the time period Δ when the hydrogen supply from the reformer is insufficient. In this case, excess hydrogen is discharged from the fuel cell without reacting, reducing the hydrogen utilization rate, but it is easy to control (mixing Since there is no need to monitor the amount of hydrogen supplied by gas and adjust the amount of hydrogen supplied from the fuel switching device, there is an advantage that the flow rate and hydrogen concentration monitoring device 41 shown in FIG. 2 is not required. Figure 5 (
B) is a case where hydrogen is supplied from the fuel switching device to compensate for the shortage during the time Δ when the amount of hydrogen supplied from the reformer is insufficient. In any case, as shown in FIG. 5 (see Figure 5), whereas in the conventional example the battery output decreases at the time of fuel switching can be seen as Δ over time, in the present example no decrease in the battery output is observed.

(Effects of the Invention) As explained above, according to the present invention, the fuel cell consists of a fuel cell main body, a fuel supply system, an oxidizer supply system, a cooling system, and an accessory device, and hydrogen for the fuel cell is obtained by reforming fossil fuel. In a battery power generation system, in order to switch between two or more types of fuel for regular or emergency use, the fuel supply system is provided with a fuel switching device containing a hydrogen storage device made of a hydrogen storage alloy, and the fuel cell is operated using the regular fuel. In some cases, most of the reformed gas containing a large amount of hydrogen obtained through reforming is supplied to the fuel cell, and a part of the reformed gas is occluded and stored in the hydrogen storage device after passing through the gas purification system as necessary.
At the time of fuel switching, the hydrogen stored in the hydrogen storage device is released to compensate for the decrease in output due to the response delay of the reformer, etc., and the battery output is maintained constant when the fuel is switched. Utilizing this characteristic, it is possible to supply hydrogen to the fuel cell main body without shortage even when switching fuels, so it is possible to suppress a decrease in the output of the fuel cell power generation system when switching fuels.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a fuel cell power generation system showing one embodiment of the present invention, FIG. 2 is a system diagram showing a fuel switching device applied to one embodiment of the fuel cell power generation system of the present invention, and FIG. Figure 4 is a system diagram of a conventional fuel cell power generation system that can switch between fuels using one type of reformer. Figure 5 is a system diagram of a conventional fuel cell power generation system that requires a different reformer for each fuel. Figures (a) and (a) are graphs showing the relationship between time during fuel switching, fuel cell output, hydrogen supply amount from the reformer, and hydrogen supply amount from the fuel switching device. 39... Fuel switching device 4G, 41.50... Flow rate and hydrogen concentration monitoring device 42
...Gas separation and removal device 43...Hydrogen storage device Fig. 5

Claims (1)

[Claims] In a fuel cell power generation system that consists of a fuel cell main body, a fuel supply system, an oxidizer supply system, a cooling system, and ancillary equipment, hydrogen for fuel cells is obtained by reforming fossil fuels, and two or more types of fuel are used for regular or emergency use. In order to switch between uses, the fuel supply system is equipped with a fuel switching device that has a built-in hydrogen storage device made of a hydrogen storage alloy. Most of the hydrogen is supplied to the fuel cell, and part of it is stored in the hydrogen storage device after passing through the gas purification system as needed. When switching fuels, the hydrogen stored in the hydrogen storage device is released. A fuel cell power generation system comprising: compensating for a decrease in output due to a delay in response of a reformer, etc., and maintaining a constant cell output when switching fuels.