JP3358227B2 - Fuel cell power generation system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell and a CO
The present invention relates to a control system for a fuel cell power generation system that recovers heat generated by a transformer and uses the waste heat as steam.

[0002]

2. Description of the Related Art FIG. 1 is a system configuration diagram schematically showing a main part of a conventional fuel cell power generation system. In the figure, a fuel cell power generation system uses a fuel reformer 2 to reform a raw fuel such as natural gas or methanol into a hydrogen-rich reformed gas, and a CO converter 3 to convert carbon monoxide in the reformed gas. Is converted into carbon dioxide to produce a fuel gas, which is supplied to a fuel electrode of a fuel cell (stack) 1 configured as a single-cell stack, and is supplied with reaction air to an air electrode, thereby providing a fuel sandwiching an electrolyte layer. Power generation based on an electrochemical reaction is performed between the electrode and the air electrode. The steam reforming reaction of the fuel reformer 2 is an endothermic reaction, and the reaction heat is supplied by the combustion heat of an attached burner.
Is an exothermic reaction and requires cooling to maintain the respective reaction temperature. Therefore, a cooling water circulation system 4 including a steam separator 5 and a circulation pump 6 is provided, and cooling water 7 at a predetermined temperature is circulated through cooling plates stacked on the fuel cell 1 to collect heat generated by power generation. In addition to maintaining the operating temperature, the cooling water 7 is also circulated through the CO converter 3 to recover generated heat and maintain the reaction temperature.

[0003] A steam separator 5 for recovering generated heat and separating the high-temperature cooling water 7 into saturated water and steam (steam) 8 keeps the temperature of the saturated cooling water 7 constant. In order to maintain the pressure of the steam 8 at a constant level by maintaining the temperature, an auxiliary heat is supplied from outside when the pressure is reduced, and the heat is supplied in the form of steam or hot water when the pressure is increased. It is configured to control the temperature to be released to the air. Further, a part of the steam (steam) 8 generated in the steam separator 5 is mixed with the raw fuel supplied through the flow control valve 11 through the flow control valve 12, and is required for the steam reforming reaction. The reaction water is supplied to the fuel reformer 2 as fresh reaction water, and the amount of heat of the steam 8 is also used as a heating source of the raw fuel and a part of the reaction heat required for the steam reforming reaction. Another part of the steam 8 is sent to an external heat utilization facility 16 to effectively use the exhaust heat of the fuel cell power generation system. Furthermore, steel
Since the cooling water 7 in the steam separator 5 runs short due to the effective use of the cooling water 7 as the heat medium or the reaction water, pure water is supplied through the water supply pump 15 and the water supply regulating valve 14,
The water level in the steam separator 5 is controlled to be kept at a constant level. That is, in the conventional fuel cell power generation system, the water level in the steam separator is detected by the water level detector, and the level adjuster 17 that senses that the predetermined level is lower than the set water level by the detection signal is provided by the valve 14. There is known a feedback control method for intermittently controlling the supply of pure water by opening and closing the liquid and keeping the liquid level in the steam separator at the set level.

[0004]

By the way, the temperature of the cooling water 7 in the steam separator 5 to be maintained at a constant temperature is reduced by replenishing pure water, and the temperature of the steam separating water in equilibrium with the cooling water temperature is reduced. Since the steam pressure in the vessel decreases, the steam flow rate added to the raw fuel and the steam flow rate supplied to the heat utilization equipment decrease. In particular, in the conventional fuel cell power generation system, the replenishment of pure water is intermittently controlled, and water supply is started when the water level in the steam separator becomes low, and when the water level returns to the set level. In order to stop the water supply, the temperature and pressure in the steam separator 5 fluctuate in accordance with the cycle of the water supply, and as a result, the supply amount of the steam periodically changes, and a stable heat amount is used as the fuel as the heat load. A problem arises in that supply to the reformer 2 and the heat utilization facility 16 is not possible.

An object of the present invention is to stabilize the supply flow rate of steam to a heat load by suppressing fluctuations in the supply amount of pure water to a steam separator.

[0006]

According to the present invention, a cooling water circulation system for recovering at least heat generated by a fuel cell stack and maintaining the same at a predetermined operating temperature is provided with a steam separator. In addition, the separated steam is added to the raw fuel and supplied to the fuel reformer, and supplied as a heat medium to an external heat utilization device. Water supply control means for continuously controlling in proportion to the supply amount is provided.

Further, it is assumed that the water supply control means includes a main controller for receiving a detection signal of the steam flow detector and a detection signal of the water supply flow detector and issuing a primary operation command of the water supply regulating valve. Further, the water supply control means receives a detection signal of a water level detector provided in the steam separator and a primary operation command,
It includes a sub-regulator that outputs a secondary operation command in which the water supply amount is corrected in accordance with a change in the detected water level with respect to the set water level, toward the water supply control valve.

[0008]

In the present invention, water supply control means for continuously controlling the amount of water supply to the steam separator required by supplying steam to the heat load in proportion to the supply amount of steam, for example, By receiving a detection signal of the steam flow rate detector and a detection signal of the feed water flow rate detector, and providing a main controller for issuing a primary operation command of the water supply regulating valve,
It is possible to continuously control the water supply amount so as to match the steam supply amount, and to eliminate the periodic fluctuation of the steam supply amount caused by intermittently controlling the water supply amount.
The function of stably supplying the steam to the heat load is obtained.

The water supply control means receives a detection signal of a water level detector provided in the steam separator and a primary operation command,
If it is configured to include a sub-regulator that outputs a secondary operation command that corrects the water supply amount corresponding to the change in the detected water level with respect to the set water level toward the water supply amount control valve, for example, to keep the pressure in the steam separator constant If the water level drops due to the discharge of hot water to maintain the water level, the secondary regulator that senses this will cascade control the water supply amount with the secondary operation command corrected to increase the primary operation command by a certain amount. It is possible to continuously control the amount of water supply without causing a sudden change in the temperature of the saturated water in the separator, eliminating the periodic fluctuations in the amount of steam supply and adding steam to the heat load. A stable supply function is obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 is a system configuration diagram schematically showing a main part of a fuel cell power generation system according to an embodiment of the present invention. The same components as in the prior art are denoted by the same reference numerals, and redundant description is omitted. . In the figure, the steam 8 generated by the steam separator 5 of the cooling water circulation system 4 is
To the fuel reformer 2 via the system flow control valve 12 and to the steam reformer 2.
The steam flow is supplied to the heat utilization equipment 16 through the steam flow control valve 13.
And 26, and the detection signals 25S and 26S are input to the main controller 21. Further, the flow rate of pure water supplied to the steam separator 5 via the feed water control valve 24 is detected by the flow rate detector 27, and the detection signal 27S is also supplied to the main controller 2
1, a primary operation command 21S for amplifying the difference between the sum of the steam detection signals 25S and 26S and the feedwater flow rate detection signal 27S and controlling the feedwater quantity so that the two coincide with each other is directed to the sub-regulator 22. Output.

The water level in the steam separator 5 is detected by a water level detector 28, and the detected water level signal 28S is compared with a water level set value by the sub-controller 22, and a primary operation is performed so that the detected water level matches the set water level. A secondary operation command 22S obtained by correcting the command 21S is output to the water supply control valve 24. Therefore, the water supply control valve 24 supplies water in an amount corresponding to the supply amount of the steam 8 and performs cascade control so that the water level in the steam separator 5 matches the set water level. This makes it possible to suppress dynamic fluctuations and rapid fluctuations, and therefore, it is possible to obtain an advantage that the supply of steam to a heat load such as a heat utilization facility or a fuel reformer can be stabilized.

[0012]

In the fuel cell power generation system having the water supply control means configured as described above, the water supply amount can be continuously controlled so as to match the steam supply amount. In this manner, the periodic fluctuation of the steam supply amount which has conventionally occurred can be eliminated, and the advantage that the steam can be stably supplied to the heat load can be obtained. In addition, by providing a sub-regulator that issues a secondary operation command to correct the water supply amount in accordance with the change in the detected water level with respect to the set water level,
The secondary regulator, which senses the decrease in the water level, cascade-controls the opening of the water supply valve according to the secondary operation command corrected so as to increase the primary operation command flow rate by a certain amount. Provide a fuel cell power generation system that can continuously control the amount of water supply without causing significant changes, eliminate the periodic fluctuation of the amount of steam supply, and stably supply the steam to the heat load. can do.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram schematically showing a main part of a fuel cell power generation system according to an embodiment of the present invention.

FIG. 2 is a system configuration diagram schematically showing a main part of a conventional fuel cell power generation system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fuel cell (stack) 2 fuel reformer 3 CO transformer 4 cooling water circulation system 5 steam separator 6 circulation pump 7 cooling water 8 steam (steam) 11 raw fuel control valve 12 steam flow control valve 13 steam -Water flow control valve 14 water supply valve 15 water supply pump 16 heat utilization equipment 21 main controller 21S primary operation command 22 sub-controller 22S secondary operation command 24 water supply control valve 25 steam flow detector 26 steam flow detector 27 Water supply flow rate detector 28 Water level detector

Claims (3)

(57) [Claims] A cooling water circulating system for recovering at least heat generated by a fuel cell stack and maintaining it at a predetermined operating temperature is provided with a steam separator, and the separated steam is added to a raw fuel to provide a fuel reformer. A water supply control means for continuously controlling the amount of water supplied to the steam separator in proportion to the amount of steam supplied to the steam separator. A fuel cell power generation system, characterized in that: 2. The water supply control means includes a main controller for receiving a detection signal from the steam flow detector and a detection signal from the water supply flow detector and issuing a primary operation command to the water supply regulating valve. The fuel cell power generation system according to claim 1. 3. The water supply control means receives a detection signal of a water level detector provided in a steam separator and a primary operation command, and issues a secondary operation command in which a water supply amount is corrected in accordance with a change in the detected water level with respect to a set water level. 3. The fuel cell power generation system according to claim 2, further comprising a sub-regulator that outputs the water to the water supply control valve.