JP2972261B2 - Nitrogen purge method and heating method for fuel cell power generation system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a fuel cell power generation system for producing hydrogen soot by reacting a raw fuel, for example, a hydrocarbon fuel with water vapor.

[Conventional technology]

2. Description of the Related Art A reformer for producing a hydrogen gas by reacting a raw fuel, for example, a hydrocarbon fuel with water vapor, is widely used in industries such as a city gas plant and an ammonia synthesis plant.
Reformers have also been used in fuel cell power plants that have been actively developed recently for practical use. The reforming apparatus includes a desulfurizer that removes a sulfur (S) component in fuel as a pretreatment step, in addition to a reformer that performs the above-described reaction (reforming reaction) using a catalyst. As a conventional technology of a fuel cell power generation system using such a reformer, there is, for example, one disclosed in the New Energy Comprehensive Development Agency in September 1988, "Research Information Information [II] for 1987. An outline is shown in Fig. 3. In Fig. 3, (1) is a fuel cell body composed of a fuel electrode (1a), an air electrode (1b), and cooling (1c), and (2) is a hydrocarbon fuel (raw fuel). Reactor that reacts with steam to generate reformed gas containing a large amount of hydrogen, and is composed of a reaction section (2a) and a burner section (2b).
Is a desulfurizer that removes runoff (S) component in raw fuel, (4)
Is an ejector that mixes and pressurizes raw fuel with steam, (5) is a steam separator, (6) is a battery cooling water pump, (7) is an air blower, (8) and (9) are raw fuel supply pipes, (10) ) Is a shutoff valve provided on the raw fuel supply pipe (8), (11) is a nitrogen equipment, (12) is a nitrogen supply pipe, (13) is a shutoff valve provided on the nitrogen supply pipe (12), (14) ) Is a steam supply pipe, (15) is a mixed gas supply pipe, (16) is a reformed gas supply pipe, (17) is a combustible gas pipe, (18) is an exhaust gas pipe, (19) is a reaction air supply pipe, (20) is the exhaust air pipe, (21) is the combustion air supply pipe, (2)
2) is a battery cooling water pipe.

Next, the operation of the conventional system configured as described above will be described. The fuel cell body (1) has a fuel electrode (1a),
It consists of an air electrode (1b) and a cooler (1c). The reformed gas containing a large amount of hydrogen is supplied to the fuel electrode (1a), and the air is supplied to the air electrode (1b) to cause an oxidation-reduction reaction to generate electric power. Take it out. The fuel electrode (1a) requires hydrogen for the reaction, and therefore, a reformer (2) for reforming the hydrocarbon fuel into a hydrogen-rich gas is combined. First, a hydrocarbon fuel (raw fuel) such as natural gas is supplied to a desulfurizer (3) via a raw fuel supply pipe (8) at an inlet. Since the sulfur (S) content in the raw fuel may poison the reforming catalyst,
A desulfurizer (3) is installed, where sulfur (S) in the raw fuel is adsorbed and removed. Desulfurizer (3) shown in FIG.
Is a normal-temperature adsorption type, in which activated carbon or a metal-based catalyst is used as an adsorbent for sulfur (S). The raw fuel leaving the desulfurizer (3) passes through the raw fuel supply pipe (9) and ejector (4)
Sent to The ejector (4) has a function of mixing and raising the pressure of the raw fuel with the steam using the high-pressure steam supplied from the steam separator (5) as a driving force. Ejector (4)
After the raw fuel and steam are mixed in the reactor, the mixture passes through the mixed gas supply pipe (15) and the reaction section (2a) of the reformer (2)
Sent to The reaction section (2a) is filled with a reforming catalyst, where the mixed gas is given heat from the burner section (2b) to cause a reforming reaction and is converted into a reformed gas containing hydrogen as a main component. The obtained reformed gas is supplied to the fuel electrode (1a) of the fuel cell body (1) through the reformed gas supply pipe (16), where it is consumed for the reaction. The remaining surplus fuel that has been consumed passes through an exhaust combustible gas pipe (17) and burners (2) of a reformer (2).
b), where it is burned and heat is given to the reaction section (2a). The combustion exhaust gas discharged from the burner section (2b) is discharged to the atmosphere via an exhaust gas pipe (18). Part of the air from the air blower (7) is supplied to the air electrode (1b) of the fuel cell body (1) via the reaction air supply pipe (19), where it is subjected to an oxidation reaction. By supplying the reformed gas to the fuel electrode (1a) and the air to the air electrode (1b),
An oxidation-reduction reaction is performed in the fuel cell body (1), and an electric output is taken out. The remaining air consumed in the air electrode (1b) passes through the exhaust air pipe (20), joins the exhaust gas pipe (18) from the burner section (2b), and is discharged to the atmosphere. The remaining air from the air blower (7) is supplied to the burner section (2b) of the reformer (2) through the combustion air supply pipe (21), where it is consumed as combustion air. The fuel cell body (1) has a cooler (1c) for the purpose of removing reaction heat
Is disposed, and the battery cooling water is passed through this. Battery cooling water circulates through a loop composed of a steam separator (5), a battery cooling water pump (6), and a battery cooling water pipe (22), and was taken away by the cooler (1c) of the fuel cell body (1). The heat is recovered in the form of steam in the steam separator (5). The generated steam passes through the steam supply pipe (14) and ejector (4).
And used for mixing with the aforementioned raw fuel.

Now, in such a fuel cell power generation system, when the system is stopped, there is a safety problem if flammable gas is left in the system. Therefore, a nitrogen facility (11) is installed for purging nitrogen in the system. . When the system stops, shut off the shutoff valve (10) on the raw fuel supply pipe (8) and open the shutoff valve (13) on the nitrogen supply pipe (12) to allow nitrogen from the nitrogen facility (11) to flow through the system. To expel flammable gas in the system to the outside. By supplying nitrogen from the upstream side of the desulfurizer (3), it is possible to perform nitrogen purging on almost all devices and piping including combustible gas. In order to sufficiently perform the nitrogen replacement of the combustible gas system, a nitrogen purge of an amount several times the system volume is performed. After the start of the nitrogen purge, steam is continuously supplied through the ejector (4) until the purge of the volume of the desulfurizer (3) is completed, and after the purge of the volume of the desulfurizer (3), the steam is supplied. To stop. (The illustration of the steam supply shut-off mechanism is omitted.) This is to ensure that the hydrocarbon fuel pushed out from the desulfurizer (3) by the nitrogen purge continues the normal reforming reaction with an appropriate amount of steam. As expected, when the purge for the volume of the desulfurizer (3) is completed, the steam is stopped as it is unnecessary.
If hydrocarbon fuel is supplied to the reaction section (2a) of the high-temperature reformer (2) without steam, the hydrocarbon is decomposed there and carbon deposits on the reforming catalyst. Can bring the ill effects. When the required amount of nitrogen has been supplied, the shut-off valve (13) is closed to terminate the nitrogen purge, and the system shifts to a stop state. While the system is stopped after the nitrogen purge is completed, keep the system filled with nitrogen,
Alternatively, a measure such as performing a slight amount of nitrogen purging so that air does not enter from the outside or intermittently purging the nitrogen by opening the shutoff valve (13) is taken. At system startup,
First, the shutoff valve (13) on the nitrogen supply pipe (12) is opened to supply nitrogen into the system, and at the same time, the burner section (2b) of the reformer (2)
The raw fuel is directly burned (the circuit is not shown) to raise the temperature in a system using nitrogen as a thermal catalyst, so-called nitrogen heating.
After the temperature in the system including the reformer (2) has been raised, the shutoff valve (13) of the nitrogen supply pipe (12) is closed, and the shutoff valve (10) on the raw fuel supply pipe (8) is closed. Open and introduce raw fuel.
Thereby, the reforming reaction is started, and power generation is performed.

[Problems to be solved by the invention]

In the conventional fuel cell power generation system described above, a nitrogen purge is performed from the upstream side of the desulfurizer (3) when the system is stopped, and a normal temperature adsorption type catalyst (desulfurization catalyst) used in the desulfurizer (3) Has the property of adsorbing hydrocarbon fuel, so that there is a problem that it takes time to purge nitrogen in the desulfurizer (3). Desulfurizer using metal catalyst (3)
FIG. 4 shows an example of the result of measuring the gas components at the outlet of the desulfurizer (3) when nitrogen gas was purged after operating with the city gas 13A as the raw fuel. Gas component city gas 13A is methane (CH ₄₎ 88%, ethane _{(C 2 H 6) 6%} , propane _{(C 3 H 8) 4%} , butane _{(C 4 H 10) 2%} , desulfurizer (3 ) The volume is about 0.6 m ³ and the nitrogen purge flow rate is about 20 Nm ³ / h. If the desulfurization catalyst does not have adsorptivity, the removal of combustible gas in the desulfurizer (3) by nitrogen purge should be completed in about a few minutes. However, according to FIG. Over a few hours, indicating that nitrogen replacement is still not sufficient after several hours. This is based on the phenomenon that the desulfurization catalyst has the property of adsorbing high molecular weight components (such as butane) in city gas, and slowly removes the adsorbed hydrocarbons during nitrogen purge.

The time required for purging nitrogen in the desulfurizer (3) in this way causes some problems as described below. First, when the system is shut down, the hydrocarbons discharged from the desulfurizer (3) due to the nitrogen purge are guided to the reactor (2a) of the high-temperature reformer (2) without steam. Then, hydrocarbons are decomposed there and carbon deposition occurs on the reforming catalyst. Carbon deposition has a serious adverse effect on the operation of the reformer (2), such as decreasing the activity of the reforming catalyst and increasing the pressure loss. Conventionally, carbon deposition was prevented by simultaneously supplying steam from the steam separator (5) until the nitrogen purge for the volume of the desulfurizer (3) was completed (about several minutes). As described above, since the hydrocarbons from the desulfurizer (3) are continuously discharged after the completion of the purging for the volume, the problem of carbon deposition has occurred after the steam was stopped. Since the nitrogen purge covers the volume of the entire system including the combustible gas, it is necessary to continue purging the required amount even after the purging of the volume of the desulfurizer (3) is completed. If the supply of steam is continued even after the purging of the desulfurizer (3) is completed, there is no problem of carbon deposition, but it is difficult to adjust the amount of steam appropriately to match the amount of residual hydrocarbons. If it is, a gas with a high humidity is supplied to the fuel cell body (1), and the fuel cell body (1)
However, there is a problem that it causes inconvenience.

Secondly, the combustible gas system is not sufficiently purged with nitrogen, or a sufficient nitrogen purge requires a lot of time and a large amount of nitrogen. If the desulfurization catalyst had no adsorption action, the purging of combustible gas in the system was sufficient with a nitrogen purge several times the system volume, which only took about ten minutes. However, as shown in FIG. 4, the combustible gas remains for a long time even after the nitrogen purge is started due to the adsorbing action of the desulfurization catalyst. The combustible gas remained, causing a safety problem. If the combustible gas is to be satisfactorily removed, it is necessary to purge nitrogen for at least several hours, and there is a problem that it takes a long time to stop the system and consumes an enormous amount of nitrogen during that time.

Third, when the temperature of the nitrogen rises at the time of system startup, the hydrocarbons discharged from the desulfurizer (3) are guided to the reactor (2a) of the high-temperature reformer (2) without steam. Then, carbon precipitation similar to that at the time of stopping occurs.
When the system is started, nitrogen is supplied from the upstream side of the desulfurizer (3), and the internal temperature of the system is increased by the combustion of the burner section (2b) of the reformer (2). The hydrocarbon adsorbed on the catalyst was discharged together with the nitrogen gas at the next start-up while the nitrogen purge at the time of stop was insufficient, and was led to the reformer (2) as it was. During the temperature rise at start-up, steam supply is not possible because the temperature inside the system has not been sufficiently increased yet, and in the absence of steam, hydrocarbons easily come into contact with the reforming catalyst during temperature rise. Carbon deposition was occurring.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a fuel cell power generation system that can prevent carbon deposition when the system is stopped and that can prevent carbon deposition when the temperature is raised when the system is started. I do.

Means for Solving the Problems A nitrogen purging method for a fuel cell power generation system according to the present invention includes a fuel cell main body, a reformer that generates hydrogen gas by reacting raw fuel with steam, and the reformer. A desulfurizer disposed on the upstream side, and on the upstream and downstream sides of the desulfurizer,
A nitrogen purge method for a fuel cell power generation system having a nitrogen supply pipe connected to a nitrogen facility via a shutoff valve, without releasing the air immediately after the desulfurizer to the atmosphere when the fuel cell power generation system is stopped. After opening the upstream shutoff valve and performing a nitrogen purge for the volume of the desulfurizer from the upstream side of the desulfurizer, closing the upstream shutoff valve and opening the downstream shutoff valve, The reformer is purged with nitrogen from the downstream side of the desulfurizer.

Further, a fuel cell body, a reformer that reacts raw fuel with steam to generate hydrogen gas, a desulfurizer disposed upstream of the reformer, the desulfurizer and the reformer, A nitrogen purge method for a fuel cell power generation system, comprising: a shutoff valve provided between the fuel cell power generation system and a nitrogen supply pipe connected to a nitrogen facility via the shutoff valve on the downstream side of the shutoff valve. At the time of stop, at the same time as closing the shutoff valve provided between the desulfurizer and the reformer,
The shutoff valve provided in the nitrogen supply pipe is opened, and nitrogen purging of the reformer is performed from the downstream side of the desulfurizer.

In addition, a method for raising a temperature of a fuel cell power generation system according to the present invention includes a fuel cell main body, a reformer that reacts raw fuel with water vapor to generate hydrogen gas, and is disposed upstream of the reformer. A method for raising the temperature of a fuel cell power generation system having a desulfurizer and a nitrogen supply pipe connected to a nitrogen facility via a shut-off valve on the downstream side of the desulfurizer. The shutoff valve is opened, and nitrogen is supplied to the reformer from the downstream side of the desulfurizer to raise the temperature of the reformer.

[Action] The method of switching to the purge from the downstream side of the desulfurizer after performing the nitrogen purge for the volume of the desulfurizer from the upstream side of the desulfurizer without opening to the atmosphere immediately after the desulfurizer, Since the gas is not released directly to the atmosphere, it has the effect of reducing the effect on the environment.

In addition, the method of closing the shut-off valve (25) after the desulfurizer when the system is stopped and simultaneously purging with nitrogen from the back of the shut-off valve (25) does not discharge the gas in the desulfurizer to the atmosphere. It has the effect of little effect.

According to another aspect of the invention, there is provided a method for raising the temperature of a fuel cell power generation system, in which the shut-off valve is opened when the system is started, and nitrogen is supplied from a downstream side of the desulfurizer to the reformer to raise the temperature of the reformer.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, (1) to (22) have the same configuration as the above-described conventional system. (23) is connected to the raw fuel supply pipe (9) downstream of the desulfurizer (3) and supplies nitrogen from the nitrogen equipment (11). Nitrogen supply pipe (24) is on the nitrogen supply pipe (23). Shut-off valve installed in (25) Desulfurizer (3)
Above the raw fuel supply pipe (9) on the downstream side of the
A shutoff valve arranged upstream of the connection point of 3), (26) is an atmosphere discharge pipe provided on the raw fuel supply pipe (9) between the desulfurizer (3) and the shutoff valve (25), (27) ) Is the air release pipe (2
6) The shutoff valve provided above.

Next, the operation will be described. The operation during the system operation is the same as the operation of the prior art described with reference to FIG. During operation, the raw fuel is being introduced, and the shut-off valves (10) and (25) on the raw fuel supply pipes (8) and (9) are open.
Shut-off valves (13), (24) on nitrogen supply pipes (12), (23)
And the shutoff valve (27) on the atmosphere discharge pipe (26) is in a closed state. When the system stops, the raw fuel supply pipe (8),
(9) At the same time as closing the shutoff valves (10) and (25)
Shut-off valves (13), (24) on nitrogen supply pipes (12), (23)
Is opened and the shutoff valve (27) on the atmosphere discharge pipe (26) is opened to start nitrogen purging of the combustible gas system. That is, the flammable gas system on the downstream side including the desulfurizer (3), the reformer (2), and the fuel cell body (1) is disconnected to perform nitrogen purging.
This eliminates the possibility of charging the remaining hydrocarbon fuel in the desulfurizer (3) into the reformer (2) and depositing carbon, which are problems in the prior art. After the start of the nitrogen purge, since the hydrocarbon fuel in the desulfurizer (3) is not supplied to the reformer (2), the steam supply from the steam separator (5) may be stopped immediately. Since no hydrocarbon fuel is discharged from the desulfurizer (3) unlike the prior art,
Nitrogen purging of the flammable gas system on the downstream side including the reformer (2) and the fuel cell body (1) is sufficient for several times the system volume, and can be performed in a short time (for example, about + several minutes). finish. Nitrogen purging of the desulfurizer (3) is performed from a nitrogen supply pipe (12), and the exhaust gas is discharged to the atmosphere via an air discharge pipe (26). After all, by the adsorption of hydrocarbon fuel to the desulfurization catalyst,
Although hydrocarbon fuel is discharged for a long time, the desulfurizer (3) originally operates at room temperature, and since it is in a nitrogen atmosphere, there is no problem in terms of safety even if some combustible gas remains. Therefore, it is not necessary to drive out the combustible gas to the amount adsorbed on the desulfurization catalyst, and it is sufficient to perform the nitrogen purge for the space volume in the desulfurizer (3), and the nitrogen purge is completed in a short time. According to such a method, nitrogen purging can be effectively performed in a short time without causing carbon deposition in the reformer (2).

As another embodiment of the nitrogen purge when the system is stopped, there is a method in which the nitrogen purge for the volume of the desulfurizer (3) is performed as in the prior art, and then the nitrogen purge is performed from the downstream side of the desulfurizer (3). is there. In this case, air release pipe (26)
The shutoff valve (27) is not required. When the system is stopped, first shut off the shutoff valve (10) on the raw fuel supply pipe (8), open the shutoff valve (13) on the nitrogen supply pipe (12), and perform nitrogen purge from the upstream side of the desulfurizer (3). . At this time, desulfurizer (3)
Since the hydrocarbon fuel inside is supplied to the reformer (2), steam is also supplied to prevent the carbon deposition in the reformer (2). When the nitrogen purge for the volume of the desulfurizer (3) is completed, the shutoff valve (13) is closed, the shutoff valve (24) is opened, and the nitrogen purge from the downstream side of the desulfurizer (3) is switched.
Then stop steaming. Nitrogen purge from the downstream side of the desulfurizer (3) may be several times the amount of the annual gas system volume on the downstream side, and is completed in a short time. After the switching of the shutoff valves (13) and (24), the nitrogen purging of the desulfurizer (3) is not performed, and the hydrocarbon fuel adsorbed on the desulfurization catalyst remains. No problem. In this embodiment, the shutoff valve (25) on the raw fuel supply pipe (9) may be omitted, but it is better to install it in order to prevent the adsorbable combustible gas in the desulfurizer (3) from diffusing and moving to the downstream side. desirable. In this case, the shut-off valve (24) is opened and the shut-off valve (25) is closed at the same time, and thereafter the shut-off valve (25) is kept closed while the system is stopped. Also in this embodiment, the nitrogen purge can be effectively performed in a short time without causing carbon deposition in the reformer (2).

As still another embodiment of the nitrogen purge when the system is stopped, there is a method in which the nitrogen purge of the desulfurizer (3) is not performed at all and the raw fuel is left in the desulfurizer (3).
In this case, the air release pipe (26), the shutoff valve (27), the nitrogen supply pipe (12), and the shutoff valve (13) become unnecessary in FIG. When the system is stopped, the shut-off valve (24) is opened, and only the nitrogen purge of the combustible gas system downstream of the desulfurizer (3) is performed, but the nitrogen purge of the desulfurizer (3) is not performed. The shutoff valve (25) closes at the start of the nitrogen purge to prevent the flammable gas in the desulfurizer (3) from diffusing and moving to the downstream side. The desulfurizer (3) operates at normal temperature, and there is no safety problem even if the desulfurizer (3) is left with flammable gas contained unless it is stopped for a long time. In this case, the same effects as those of the above-described embodiments can be obtained. In the embodiment of FIG. 1, an example is shown in which the nitrogen supply pipe (23) is connected to the raw fuel supply pipe (9) between the desulfurizer (3) and the ejector (4). It may be connected on the mixed gas supply pipe (15) on the downstream side of the ejector (4), and the same effects as in the above embodiment can be obtained.

A method for raising the temperature when the system is started, which is another invention, will be described with reference to FIG. In FIG. 2, (1)-
(11) and (14) to (22) are the same as the configuration of the conventional system described above. (28) is connected to the raw fuel supply pipe (9) downstream of the desulfurizer (3) and supplies nitrogen from the nitrogen equipment (11). Nitrogen supply pipe (29) is on the nitrogen supply pipe (28). It is a shut-off valve provided in. When the system is started, the shut-off valve (29) is opened and nitrogen for heating is supplied from the downstream side of the desulfurizer (3). As a result, the nitrogen for heating does not pass through the desulfurizer (3), and the hydrocarbon discharged from the desulfurizer (3) causes carbon deposition in the reformer (2) as in the prior art. Is completely gone. Then, as in the prior art, the raw fuel is burned in the burner section (2b) of the reformer (2) in parallel with the nitrogen supply (the circuit is not shown).
Raise the temperature inside the system. After the temperature inside the system is raised, the nitrogen supply pipe (2
8) Close the upper shutoff valve (29) and open the shutoff valve (10) on the raw fuel supply pipe (8) to introduce raw fuel. The nitrogen supply pipe (28) and the shutoff valve (29) in the present invention are the same as the nitrogen supply pipe (23) and the shutoff valve (2) shown in FIG.
Of course, 4) can also be used. The second
In the embodiment shown in the figure, the nitrogen supply pipe (28) is connected to the raw fuel supply pipe (9) between the desulfurizer (3) and the ejector (4). May be connected on the mixed gas supply pipe (15) on the downstream side, and the same effects as in the above embodiment can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the nitrogen supply pipe connected to the nitrogen equipment provided via the shutoff valve on the downstream side of the desulfurizer is provided, and the nitrogen from the nitrogen supply pipe is supplied to the desulfurizer via the shutoff valve. The fuel cell power generation system that can supply nitrogen effectively in a short time can be obtained.

In another invention, a nitrogen supply pipe connected to a nitrogen facility is connected to a downstream side of a desulfurizer via a shutoff valve, and when the system is stopped, the shutoff valve is opened and a nitrogen purge of a reformer is performed from a downstream side of the desulfurizer. Therefore, it is possible to obtain a nitrogen purging method for a fuel cell power generation system capable of performing effective nitrogen purging in a short time without causing carbon precipitation.

Further, in this method, the elimination of the air discharge pipe (26) means that the gas in the desulfurizer is not directly discharged to the atmosphere, that is, the influence on the environment can be reduced.

In another invention, a nitrogen supply pipe connected to a nitrogen facility is connected to a downstream side of the desulfurizer through a shutoff valve, and when the system is started, the shutoff valve is opened to supply nitrogen from the downstream side of the desulfurizer to the reformer. Since the temperature of the reformer is increased by supplying
A method for raising the temperature of a fuel cell power generation system capable of effectively raising the temperature in a short time without causing carbon deposition can be obtained.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a fuel cell power generation system according to one embodiment of the present invention and a nitrogen purging method thereof, FIG. 2 is a system diagram showing a temperature raising method of a fuel cell power generation system according to another invention, and FIG. FIG. 4 is a system diagram showing a conventional fuel cell power generation system, and FIG. 4 is a characteristic diagram showing characteristics of a conventional nitrogen purge. In the figure, (1) is the fuel cell body, (2) is the reformer,
(3) is a desulfurizer, (11) is a nitrogen equipment, (23) is a nitrogen supply pipe, (24) is a shutoff valve, (28) is a nitrogen supply pipe, and (29) is a shutoff valve. In the drawings, the same reference numerals indicate the same or corresponding parts.

Continuation of the front page (56) References JP-A-57-212774 (JP, A) JP-A-58-164167 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 8 / 00-8/24

Claims (3)

(57) [Claims] 1. A fuel cell main body, a reformer for generating hydrogen gas by reacting raw fuel with steam, a desulfurizer disposed upstream of the reformer, and an upstream side of the desulfurizer. A nitrogen purge method for a fuel cell power generation system having a nitrogen supply pipe connected to a nitrogen facility via a shut-off valve, and a downstream side, wherein when the fuel cell power generation system is stopped, the atmosphere immediately after the desulfurizer is brought to the atmosphere. Without opening, after opening the upstream shutoff valve and performing a nitrogen purge for the volume of the desulfurizer from the upstream side of the desulfurizer, the upstream shutoff valve is closed and the downstream shutoff valve is closed. A nitrogen purging method for a fuel cell power generation system, comprising opening and purging nitrogen in the reformer from a downstream side of the desulfurizer. 2. A fuel cell main body, a reformer for reacting raw fuel with steam to generate hydrogen gas, a desulfurizer disposed upstream of the reformer, and the desulfurizer and the reformer. A nitrogen purge method for a fuel cell power generation system comprising: a shut-off valve provided between the fuel cell and a nitrogen supply pipe downstream of the shut-off valve to a nitrogen facility via the shut-off valve. When the power generation system is stopped, the shutoff valve provided between the desulfurizer and the reformer is closed, and at the same time, the shutoff valve provided on the nitrogen supply pipe is opened, and the reforming is performed from the downstream side of the desulfurizer. A method for purging nitrogen in a fuel cell power generation system, comprising purging a reactor with nitrogen. 3. A fuel cell main body, a reformer for reacting raw fuel with steam to generate hydrogen gas, a desulfurizer disposed upstream of the reformer, and a downstream of the desulfurizer. A fuel supply system having a nitrogen supply pipe connected to a nitrogen facility via a shut-off valve on the side of the desulfurizer. A method for raising the temperature of a fuel cell power generation system, comprising supplying nitrogen to the reformer from a downstream side to raise the temperature of the reformer.