JP2008262727A - Phosphoric acid type fuel cell power-generating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phosphoric acid type fuel cell power-generating device capable of continuing an operation above a minimum load where the fuel cell power-generating device can be thermally self-supported at a midnight power rate time zone offered at a power rate cheaper than a power-generating cost of the fuel cell power-generating device. <P>SOLUTION: When a commercial power rate is cheaper than the power-generating cost of the fuel cell power-generating device per unit electric power at night, the power generation of the fuel cell body is stopped, a fuel reforming device continues its operation at a load where the fuel reforming device is thermally self-supported, and a standby operation in which electric power necessary for the power of auxiliary accessories during operation, the generation of steam used for reforming a reaction, and retaining the heat retention of a fuel cell is supplied from commercial electric power is carried out. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell power generator installed in a site where power demand fluctuates between daytime and nighttime, and in particular, it is inexpensive at times when power demand is low using inexpensive external power such as midnight power. The present invention provides a phosphoric acid fuel cell power generator capable of performing efficient standby operation and restarting power generation in a short time.

  A fuel cell power generator includes a desulfurizer that desulfurizes a hydrocarbon-based raw fuel such as city gas, a reformer that reacts the desulfurized gas with water vapor to produce a reformed gas rich in hydrogen, and one of the reformed gases. A fuel reformer for generating a fuel gas used for power generation in a fuel cell from a raw fuel with a carbon monoxide transformer that reduces the carbon oxide concentration, and a fuel that performs a power generation reaction by supplying the fuel gas and air It consists of a battery body.

The fuel reformer is provided with a burner, and the fuel gas discharged from the fuel electrode without being used in the fuel cell is supplied to the burner, and the reformer is heated to about 700 ° C. by the combustion heat to reform gas. Promotes the reaction to produce.
The operating temperature of the fuel cell body varies depending on the type of fuel cell, and the operating temperature of the phosphoric acid fuel cell is about 200 ° C.

When installed in buildings or commercial facilities, fuel cell power generators that operate as on-site power generation systems operate at high loads during the day with high power demand, but there is very little or no power demand at night. It is put in a state of disappearing.
On the other hand, there is a growing demand for a so-called DDS (Daily Startup Shutdown) operation in which the fuel cell power generator is operated only during the daytime when there is a great demand for electric power and is stopped at night.

Since the fuel reformer is operated at a high temperature as described above, if the operation is stopped, it takes time and energy to raise the temperature at the time of restart, and the creep deformation proceeds due to the temperature change accompanying the start and stop. Since the life is remarkably shortened, the fuel reforming apparatus is kept at a predetermined temperature or more after the power generation of the fuel cell is stopped until the next power generation is started.
For example, in Patent Document 1, a fuel cell power generator is operated in the DSS mode, and a sheath heater provided in the reformer is operated using power at midnight during a power generation operation stop time of the fuel cell. It is described that the material is heated and held above the creep transition temperature of the member.

Further, in Patent Document 2, in a method for operating a hydrogen generator for producing a reformed gas for use in purification by a pressure swing adsorption device (PSA), a hydrogen-rich gas generated in the hydrogen generator during the stoppage of the PSA is disclosed. It is described that the standby operation of the reformer is performed by burning with the burner of the reformer.
By the way, the fuel cell is characterized by low voltage and high current when the load is high, and high voltage and low current when the load is low. In a state where the current is high (high load state), so much hydrogen reacts, and as the reaction increases, resistance polarization (loss due to electrical resistance), active polarization (loss due to reaction activity), concentration polarization (Loss caused by insufficient movement of reactant or product) increases, and the proportion of energy that causes loss of power generation reaction in the fuel cell increases. And this energy loss appears in the form of thermal energy.

  That is, under a high load state, the heat of combustion of the reformer burner (A) + the heat of reaction accompanying the power generation reaction in the fuel cell (B) ≧ the heat required for the reaction in the fuel reformer (C) + the steam for reforming Heat required for generation (D) + heat radiation (E). The higher the load condition, the greater the reaction heat (B). Therefore, when the operating temperature of the fuel cell is controlled to be constant, the ratio of heat energy recovered from the fuel cell increases under high load conditions, and the reforming steam required for the system is produced. Not only the required heat (D), but also the amount of exhaust heat recovery that can be taken out of the fuel cell power generator as a cogeneration system and used.

  On the other hand, the smaller the load, the lower the ratio of energy that causes a loss of power generation reaction in the fuel cell, that is, the reaction heat (B), and the lower the ratio of thermal energy that is recovered as the load is reduced. If the operating temperature of the fuel cell is maintained at a predetermined temperature suitable for the reaction (about 200 ° C. for a phosphoric acid fuel cell) and the heat energy for producing the reforming steam is removed, the exhaust heat recovery amount becomes zero. If there is a load and the temperature is less than that, the operating temperature cannot be maintained unless the fuel cell is heated (thermal independence is not possible). That is, there is a minimum load in the fuel cell power generation device that allows the fuel cell to be thermally independent (maintaining A + B ≧ C + D + E in the above equation).

If it is attempted to operate under a condition below this minimum load, it is necessary to supply energy from outside the fuel cell power generator to heat the fuel cell to maintain the operating temperature, and the power generation efficiency is significantly reduced. Therefore, normally, the system is not operated under the condition of the minimum load (approximately 25 to 40% although it varies depending on the system configuration).
Furthermore, in fuel cells with a relatively high operating temperature, such as phosphoric acid fuel cells, it takes time to increase the temperature at startup, and purging the system with an inert gas is required by the Electricity Business Law at the time of shutdown. Therefore, even if there is little demand for power at night, power is generated at the lowest load that can stand by heat, and only insufficient power is purchased from an inexpensive commercial system at night. In addition, when introducing a phosphoric acid fuel cell, a site that has at least a power demand that allows the fuel cell power generator to continue operating at the lowest load that can stand by heat is selected and installed. There are currently no sites where this occurs.

In Patent Document 3, the power transmission to an external load is substantially stopped and the fuel cell main body is supplied with a small amount of reaction gas at night when the power is excessive as described above while maintaining the battery at the operating temperature. Thus, it is described that the electric power obtained by maintaining the power generation state is used for a heater for keeping the battery warm.
JP 2003-288929 A JP 2003-128401 A Japanese Patent Publication No. 8-28230

   As described above, conventional phosphoric acid fuel cell power generators have been selected and installed at sites with power demand that can be operated at a minimum load that allows the fuel cell power generators to stand by heat even at night, and continue to operate at night. It was. For users who have introduced a phosphoric acid fuel cell power generation system, the fuel cell power generation system can be self-sustaining even during the midnight power hours of commercial power provided at a lower price than the power generation cost of the fuel cell power generation system. Power generation had to be continued at the minimum load or higher, which was more expensive than supplying midnight power.

  Therefore, in this proposal, a phosphoric acid fuel cell power generator can be operated in DSS, and even a user who has introduced a phosphoric acid fuel cell power generator can purchase power from a commercial system at night, An object of the present invention is to provide a phosphoric acid fuel cell power generator that can be operated more economically than the operation of the fuel cell power generator is continued at the lowest load that can stand by itself.

In order to solve the above problems, in the present invention,
A phosphoric acid fuel cell power generator comprising a fuel reformer that reforms a hydrocarbon-based raw fuel gas into a fuel gas containing hydrogen as a main component and a fuel cell body that generates power using the fuel gas. When the commercial power charge is cheaper than the power generation cost of the phosphoric acid fuel cell power generator per unit of electric power (not including the depreciation cost of the power generator), the power generation of the fuel cell main body is stopped, The fuel reformer continues to operate with a heat self-supporting load, and performs standby operation for supplying from the commercial power the power required for auxiliary machinery during the operation, generation of steam for reforming reaction, and heat retention of the fuel cell body. The control means for controlling is provided.

By performing such a standby operation, a user who has introduced a phosphoric acid fuel cell power generator can operate more economically, and at night, the load that allows the phosphoric acid fuel cell power generator to be thermally independent. As described above, the phosphoric acid fuel cell power generation apparatus can be introduced even to a site where there is no power demand enough to continue operation.
The fuel gas generated in the fuel reformer during the standby operation is assumed to be burned by a burner provided in the fuel reformer after flowing through the fuel electrode of the fuel cell body. For example, it is not necessary to purge the fuel electrode during the standby operation at night, and the temperature of the fuel cell stack can be kept at a high temperature and the startup time can be shortened while suppressing nitrogen consumption.

  Further, at this time, the air electrode of the fuel cell main body is purged with an inert gas at the start of the standby operation, and the inert gas is maintained so that the cell voltage of the fuel cell is maintained at 0.1 V or less during the standby operation. Is supplied to the air electrode, even if fuel gas is introduced into the fuel electrode while the fuel cell main body is not generating power, the open circuit state is prevented and the air electrode is exposed to a high potential state, thereby preventing a decrease in life. be able to.

In the inert gas purge of the air electrode, at the start of the standby operation, an inert gas is supplied to the air flow path of the air electrode at a flow rate of 5 mm / s or more for 2 minutes or more, and thereafter, 0. What is necessary is just to let it flow continuously with the flow velocity of 05 mm / s or more.
Further, if the load of the fuel reformer during the standby operation is 4 to 8%, the fuel gas generated from the raw fuel supplied to the fuel reformer is burned by the burner of the fuel reformer. The heat provides the minimum heat necessary for the operation of the fuel reformer, the raw fuel gas consumed during the standby operation is minimized, and the flow rate of the fuel gas passing through the fuel electrode can be reduced. The amount of phosphoric acid scattered inside is also reduced.

  According to the present invention, even for a user who has introduced a phosphoric acid fuel cell power generator, it is possible to purchase low-cost power from a commercial system at night, and to generate power from a phosphoric fuel cell at the lowest load that can be heat independent at night. As a result, it was possible to obtain a fuel cell power generation device that was more economical than the continuous operation.

FIG. 1 is a schematic configuration diagram schematically showing a phosphoric acid fuel cell power generator embodying the present invention.
The fuel cell power generation system shown in FIG. 1 includes a fuel reformer 10 including a desulfurizer 1, a reformer 2, and a carbon monoxide converter 3, and a phosphoric acid fuel cell body 20. City gas as raw fuel is first desulfurized by the desulfurizer 1, and then reformer 2, carbon monoxide converter along with water vapor supplied from the steam separator 8 through the reforming steam supply pipe 7. 3 is reformed into a fuel gas mainly composed of hydrogen by a chemical reaction.

In the fuel cell main body 20, during operation, the direct current obtained by generating electricity by the reaction between the fuel gas supplied from the fuel reformer 10 to the fuel electrode 4 and the air supplied to the air electrode 5 by the reaction air blower 9. Is converted into an alternating current by the inverter 11 and supplied to the user.
The remaining fuel gas discharged from the fuel electrode 4 without being used for the reaction in the fuel cell main body 20 is supplied to the burner 6 of the reformer 2 through the fuel off-gas supply pipe 12 and supplied from the combustion air blower 13. Combustion air and the heat of combustion gas contribute to the reforming reaction in the reformer 6. The heat generated by the power generation reaction in the fuel cell main body 20 is gradually heated by the cooling water flowing through the battery cooling water circulation system pipe 15 via the fuel cell main body 20 by the battery cooling water pump 14. Water vapor is extracted from the cooling water heated by the main body 20 into a gas-liquid two-phase flow by the gas-water separator 8 and used for reforming the raw fuel as described above. The steam separator 8 is provided with a starting heater for raising the temperature of the cooling water when starting the fuel cell power generator.

Next, the nighttime standby operation of the phosphoric acid fuel cell power generator of the present invention will be described.
The phosphoric acid fuel cell power generator according to the present invention cuts off the connection to the external load and stops the supply of electric power when the midnight power charge from the commercial power supply is applied.
At the same time, the reaction air supply blower 9 and the battery cooling water pump 14 are stopped, the valve 21 provided in the reaction air supply pipe 17 is closed, and the purge nitrogen supply pipe 18 connected to the reaction air supply pipe 17 is connected. The provided valve 22 is opened, supply of nitrogen from the nitrogen cylinder 19 to the air electrode of the fuel cell main body 20 is started, and nitrogen purge is performed. A porous carbon plate is laminated with the air flow groove forming surface facing the air electrode 5, and is supplied so that the flow rate of nitrogen flowing through each air flow groove is 5 mm / s or more, and this is performed for 2 minutes. This is done.

Further, as will be described below, the fuel gas continues to be supplied to the fuel electrode 4 during the standby operation for stopping the power generation, so that air flows into the air electrode 5 to be in an open circuit state and exposed to a high potential. In order to prevent the lifetime from being reduced, the nitrogen purge to the air electrode 5 is continuously performed so that the cell voltage is maintained at 0.1 V or less. For this reason, during the standby operation, the supply of nitrogen is continued so as to flow through the air circulation groove of the air electrode 5 at a flow rate of 0.05 mm / s or more.

On the other hand, the fuel reformer 10 continues to generate fuel gas even during the standby operation at night. The generated fuel gas passes through the fuel electrode 4 of the fuel cell main body 20 whose power generation is stopped, and the whole amount is supplied to the burner 6 of the reformer 2 as it is.
The operating load of the fuel reformer 10 at this time is that the reaction in the fuel reformer 10 can be performed only by the heat obtained by burning the fuel gas generated from the raw fuel gas in the fuel reformer 10 by the burner 6 ( The fuel reformer 10 can self-support heat, that is, [combustion heat of the reformer burner] ≧ [heat required for reaction in the fuel reformer] + [heat radiation from the fuel reformer] However, as the amount of gas passing through the fuel electrode 4 of the fuel cell main body 20 increases, phosphoric acid in the cell scatters downstream, leading to a decrease in life, and the amount of raw fuel gas used is reduced for standby operation costs. Since it is preferable that the number is smaller, it is preferable to reduce the load to the minimum at which the fuel reforming apparatus 10 can self-support heat.

At this time, since the fuel cell main body 20 has stopped power generation, the reforming steam cannot be obtained by the heat of the power generation reaction. Therefore, midnight power is supplied to the starter heater 16 provided in the steam separator 8 to obtain reforming steam.
Similarly, midnight power is supplied to a heat retaining heater 23 provided for heat retention during storage and transportation in the fuel cell main body 20 to keep the fuel cell main body 20 at 50 ° C. to 60 ° C. Furthermore, midnight power is also used for auxiliary machinery power such as the combustion air blower 13 that is activated even during standby operation.

In the phosphoric acid fuel cell power generator according to the present embodiment, the control device for the fuel cell power generator is automatically switched to the standby operation between 23:00 and 7:00 when an inexpensive late-night power charge is applied from the power company. Programmed. The method of performing the standby operation is generally as described above, but the amount of the air electrode purge during the standby operation and the load of the fuel reformer are as follows.
The nitrogen purge of the air electrode 5 during the standby operation is performed at a flow rate at which the flow rate of nitrogen flowing through the air circulation groove is 5 mm / s at the start of the standby operation for 2 minutes, and during the subsequent standby operation, the nitrogen flowing through the air circulation groove The supply was continued at a flow rate of 0.05 mm / s.

The fuel reformer 10 controlled the load during standby operation to 4 to 8% (the raw fuel supply amount was set to 4 to 8% of the flow rate at the rated load of 100%).
If the heat inside the fuel reformer 10 is excessive and the detected temperature of the reformer 2 rises to 900 ° C or higher, the load is reduced. However, if the load is less than 4%, control becomes difficult. If the heat remains even when the load is lowered to 4%, the adiabatic flame temperature is lowered by increasing the air-fuel ratio of the burner 6 by increasing the flow rate of the combustion air supplied from the combustion air blower 13 to the burner 6.

Conversely, if the heat in the fuel reformer 10 is insufficient and the detected temperature of the reformer 2 falls below 600 ° C., the load is increased, but if the load is greater than 8%, the problem of phosphoric acid scattering occurs. However, if the load of 8% is maintained, the temperature of the reformer 2 can be recovered to the predetermined temperature.
The cost comparison between the case where the standby operation is performed in the present embodiment during the midnight power time period and the case where the power generation is continued with the load of 40% which is the lowest load capable of thermal independence of the conventional fuel cell power generator is as follows. It was as follows.

When a 100KW phosphoric acid fuel cell power generator is continuously operated with a load of 100% during the day and a load of 40% during the night (23:00 to 7:00), the city gas rate is the same as the basic rate and the basic rate of flow. It is about 65 yen / Nm ³ about Te.
The amount of city gas consumed during continuous operation at night (23:00 to 7:00) at 40% load is about 9 Nm ³ / h. Assuming 360 days, the cost of continuous operation at night is
The 65 yen ^{/ Nm 3 × 9Nm 3 / h} × 8h / day × 360 days / year = 1,684,800 yen / year.

On the other hand, the cost required for the standby operation of the present invention is as follows.
The unit price of the nighttime electricity charge at night (23:00 to 7:00) is approximately 6.3 yen / kWh, including the basic charge and the electricity charge. In addition, 40 kW generated by the phosphoric acid fuel cell power generator, 2 kW auxiliary power of the fuel cell power generator, steam generation power for reforming (8% load, S / C = 3.0 equivalent steam 7 kg / h) ) A total of 50 kW of 5 kW and battery heat insulation heater 3 kW will be purchased.

Therefore, the annual electricity charge required for standby operation at night is
6.3 yen / kWh × 50 kW × 8 h / day × 360 days / year = 907,200 yen / year.
Further, the nitrogen purge performed on the air electrode 5 during the standby operation of the fuel cell power generator of the present invention consumes about 500 liters of nitrogen per standby operation per day. The price of nitrogen is about 3,000 yen per 20MP x 47 liter cylinder (9400 liters), so the annual nitrogen consumption charge is
500 l / day × 360 days / year × 3,000 yen / 9400 l = 57,500 yen / year.

The annual cost merit of the embodiment of the present invention compared to the conventional continuous operation is
1,684,800 yen- (907,200 yen + 57,500 yen) = 720,100 yen.
Furthermore, if you prepare about 8 nitrogen cylinders,
360 (day / year) / [9400 (l / tube) × 8/500 (l / day)] = 2.4 / year, and the annual nitrogen cylinder replenishment frequency is less than 3 times. There is no level.

Schematic configuration diagram schematically showing the fuel cell power generator of the present invention

Explanation of symbols

1 Desulfurizer 2
2 Reformer 3 Carbon Monoxide Transformer 4 Fuel Electrode 5 Air Electrode 6 Burner 7 Reforming Steam Supply Pipe 8 Air / Water Separator 9 Reaction Air Blower 10 Fuel Reformer 11 Inverter 12 Fuel Off Gas Supply Pipe 13 Combustion Air Blower 14 Battery Cooling Water Pump 15 Battery Cooling Water Circulation System Piping 16 Startup Heater 17 Reaction Air Supply Piping 18 Purge Nitrogen Supply Piping 19 Nitrogen Cylinder 20 Fuel Cell Main Body 21, 22 Valve 23 Insulation Heater

Claims (5)

In a phosphoric acid fuel cell power generator comprising a fuel reformer that reforms a hydrocarbon-based raw fuel gas into a fuel gas mainly composed of hydrogen, and a fuel cell main body that generates power using the fuel gas,
When the commercial power charge is cheaper than the power generation cost of the phosphoric acid fuel cell power generation device per unit amount of power, the fuel cell main body stops generating power, and the fuel reformer is a heat self-supporting load. A control means is provided for continuing the operation and controlling to perform a standby operation of supplying power required for auxiliary power during the operation, generation of steam for reforming reaction, and heat retention of the fuel cell body from commercial power. A phosphoric acid fuel cell power generator.   The fuel gas generated in the fuel reformer during the standby operation flows through the fuel electrode of the fuel cell main body, and is then burned by a burner provided in the fuel reformer. The phosphoric acid fuel cell power generator according to claim 1.   At the start of the standby operation, the air electrode of the fuel cell main body is purged with an inert gas, and the inert gas is supplied to the air electrode so that the cell voltage of the fuel cell is maintained at 0.1 V or less during the standby operation. The phosphoric acid fuel cell power generator according to claim 2.   The inert gas purge at the start of the standby operation is to supply the inert gas to the air flow path of the air electrode at a flow rate of 5 mm / s or more for 2 minutes or more, and then during the standby operation, the inert gas is supplied to the air. 4. The phosphoric acid fuel cell power generator according to claim 3, wherein the phosphoric acid fuel cell power generator is continuously passed through the flow path at a flow rate of 0.05 mm / s or more.   6. The phosphoric acid fuel cell power generator according to claim 1, wherein a load of the fuel reformer during the standby operation is 4 to 8%.