JPH0817455A - Exhaust heat recovery device for fuel cell generating unit - Google Patents

Abstract

PURPOSE:To provide an exhaust heat recovery device, serving as a steam separator capable of supplying steam stably to a fuel reformer with a fine pressure fluctuation, and serving as a supplemental water collector having high recovery efficiency with low power consumption. CONSTITUTION:An exhaust heat recovery device is constituted by connecting in series through piping a pressure regulator valve 51 regulating a a vapor flow, vapor condenser 52 heat exchanging vapor with a thermal medium circulating circuit 25 connected to a cooling system in the outside, condensed water tank 53 and a supply water pump 54 feeding a storage liquid in the condensed water tank 53 to a steam separator 21, to connect the device to the steam separator 21, so as to form a circulating circuit of steam condensed water. The exhaust heat recovery device of a supplementary water collector 41 is constituted by feeding recovery water by a cooling water circuit 45 to a cooler, set up in the outside, to collect heat, again returning the water through a nozzle 44 to the supplementary water collector 41, and by cooling reaction discharge air and combustion exhaust gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust heat recovery system for a fuel cell power generator for recovering reaction heat and heat of combustion exhaust gas during power generation of the fuel cell power generator.

[0002]

2. Description of the Related Art A phosphoric acid fuel cell uses phosphoric acid as an electrolytic solution and steam-reforms a raw fuel such as methane gas to obtain hydrogen in a fuel gas and oxygen in the air. To generate electric power by an electrochemical reaction.In a fuel cell power generator incorporating a phosphoric acid fuel cell, heat generated during power generation is removed by supplying cooling water,
The operating temperature of the fuel cell body is kept constant and the heat generated is recovered and used effectively.

Further, when reforming raw fuel into fuel gas, a method is adopted in which steam is added to the raw fuel to promote reforming with a catalyst in a fuel reforming device, but reforming is carried out constantly. It is necessary to constantly replenish the required amount of water vapor, and it is necessary to constantly replenish the water vapor supply device with water corresponding thereto. The water used must be highly pure water, and ion-exchanged water from which impurities have been removed by an ion-exchange water treatment device is usually used. On the other hand, in the electrochemical reaction of the fuel cell, generated water is generated, and in the fuel reformer, combustion generated water is generated due to the combustion for heating as described later. Since there are few impurities, the load on the ion-exchange type water treatment device can be reduced by using these generated water as raw water to the fuel reformer. The method of collection is adopted.

FIG. 3 is a basic system diagram of a gas system and a cooling water system of a conventional fuel cell power generator of this type. In this figure, the fuel cell main body 1 is schematically shown. A phosphoric acid electrolyte layer (not shown) is sandwiched between a fuel electrode 2 and an air electrode 3 to form a unit cell, and each unit cell is stacked. It is configured by arranging a cooling plate 4 having a cooling pipe in the.

Raw fuel such as methane gas is supplied to the fuel supply circuit 8
The high-pressure steam supplied from the steam separator 21 described later through the steam supply circuit 10 is mixed by the ejector pump 9 and sent to the fuel reformer 7.
The fuel reformer 7 is heated by combustion of the off gas discharged from the fuel electrode 2 and sent through the off gas supply circuit 12 and the air supplied from the combustion air supply circuit 16 under the reforming catalyst, and is rich in hydrogen. After being reformed into the soda gas, it is supplied to the fuel electrode 2 of the fuel cell main body 1 through the reformed gas supply circuit 11 to cause an electrochemical reaction.

On the other hand, the reaction air is the reaction air supply circuit 14
Supplied to the air electrode 3 of the fuel cell main body 1 to cause an electrochemical reaction. Of the gas discharged after the electrochemical reaction has occurred in the fuel cell body 1, the off gas discharged from the fuel electrode 2 contains hydrogen that has not contributed to the electrochemical reaction. It is sent to the vessel 7 and used for combustion and heating. The exhaust gas containing water after combustion is sent to the makeup water recovery unit 41 through the combustion exhaust gas circuit 18, and the combustion product water is recovered. On the other hand, the air discharged from the air electrode 3 contains water generated by the electrochemical reaction, and is sent to the makeup water recovery unit 41 through the reaction air discharge circuit 15 to the makeup water recovery unit 41 in the same manner as the combustion exhaust gas described above. The produced water is collected.

The cooling water from the steam separator 21 is sent to the cooling pipe provided on the cooling plate 4 of the fuel cell main body 1 through the cooling water circulation circuit 20 by the cooling water circulation pump 22. The discharged water, which is a two-phase flow of steam and water that cools the heat generated by power generation and has a high temperature by receiving the heat, is sent to the heat recovery heat exchanger 23 and then returned to the steam separator 21. ,
It is separated into steam and cooling water. The separated water vapor is
The fuel is reformed through the steam supply circuit 10, and the cooling water is sent again to the cooling pipe provided on the cooling plate 4 of the fuel cell body 1. The cooling water reduced corresponding to the steam used for the fuel reforming is compensated by the makeup water sent through the ion exchange type water treatment device 47.

The heat recovery heat exchanger 23 is for recovering the heat stored in the high-temperature discharge water, and is a heat medium circulation circuit 2
The heat medium supplied in 5 is heat-exchanged with the high-temperature discharge water to raise the temperature and cool the discharge water, and at the same time, the heat is recovered to the outside for effective utilization. The heat recovery heat exchanger 23 is provided with a bypass pipe 26 and a three-way adjustment valve 27. By operating the three-way adjustment valve 27, the flow rates of the bypass pipe 26 and the heat recovery heat exchanger 23 are adjusted, The pressure of the steam separator 21, which is known by the pressure gauge 28, is controlled to be constant to suppress the fluctuation of the amount of steam sent from the steam separator 21 to the fuel reformer 7.

Make-up water collector 4 supplied with air exhausted from air electrode 3 through reaction air exhaust circuit 15 and exhaust gas containing moisture after combustion from combustion exhaust gas circuit 18.
In No. 1, these gases are cooled by directly contacting with the recovered water stored in the bottom portion, and circulated by the recovered water circulation pump 42, the recovered water cooler 43, and the nozzle 44 to recover each produced water. There is. The exhaust gas after collecting the generated water is
The gas is exhausted to the outside through the gas exhaust circuit 19.

A cooling water circuit 45 is incorporated in the recovered water cooler 43 to cool the recovered water and take out heat to the outside for effective use. On the other hand, makeup water collector 41
The recovered water stored at the bottom of the water is supplied to the water vapor separator 21 by the makeup water pump 46 via the ion exchange type water treatment device 47 as required, and is used for fuel reforming as described above. It is used as make-up water for the cooling water reduced corresponding to the generated steam.

[0011]

As described above, in the conventional fuel cell power generator, the two-phase flow of the discharged water discharged from the cooling pipe of the cooling plate 4 of the fuel cell body 1 is separated into the water vapor separator 21.
Is separated into steam and cooling water by the steam generator, and the separated steam is sent to the ejector pump through the steam supply circuit 10 to be mixed with the raw fuel for fuel reforming, but when the pressure of the steam separator 21 fluctuates, the ejector pump Since the amount of water vapor supplied to the air fluctuates, the mixing ratio of water vapor and raw fuel fluctuates,
Alternatively, since the pressure of the fuel gas fluctuates, it also affects the composition and pressure of the reformed gas sent to the fuel electrode 2,
Eventually, the operating conditions of the fuel cell fluctuate, which leads to shortening the life of the fuel cell. Therefore, it is necessary to keep the pressure of the steam separator 21 as constant as possible.

In the conventional fuel cell power generator, as described above, the heat recovery heat exchanger 23 is provided with the bypass pipe 26,
The three-way adjusting valve 27 is used to adjust the flow rate of the heat recovery heat exchanger 23 to keep the pressure of the steam separator 21 constant. That is, when the pressure of the steam separator 21 becomes higher than the set value, the bypass pipe 26
To increase the flow rate to the heat recovery heat exchanger 23 to reduce the proportion of water vapor in the cooling water returning to the water vapor separator 21 to reduce the pressure, and conversely the pressure becomes lower than the set value. In such a case, it is possible to increase the pressure by increasing the flow rate of the bypass pipe 26 and decreasing the flow rate of the heat recovery heat exchanger 23 to increase the proportion of steam in the cooling water returning to the steam separator 21. Has been done.

By this method, the pressure fluctuation of the water vapor separator 21 can be suppressed within a certain range. However, in this method, the pressure is controlled by increasing / decreasing the amount of steam in the returning cooling water, so that the three-way regulating valve is used. The responsiveness of the pressure change of the steam separator 21 to the movement of 27 is slow, and it is difficult to suppress the pressure fluctuation of the steam separator 21 to ± 0.05 [kg / cm ³ ] or less.

Further, as described above, in the conventional fuel cell power generator, the reaction exhaust air containing the power generation water and the combustion exhaust gas containing the combustion water are brought into direct contact with the stored recovered water to cool the direct contact type. The makeup water recovery device 41 is used. This type of makeup water collector is less expensive than the indirect heat exchange type makeup water collector that indirectly cools reaction exhaust air and combustion exhaust gas via a heat exchanger, and Although it has the advantage that the molten carbon dioxide gas in the exhaust gas can be removed efficiently, on the other hand, this method requires extra power for the recovered water circulation pump 42 and cooling for recovering the exhaust heat. Since the difference between the temperature of the water circuit 45 and the temperature of the recovered water stored at the bottom of the makeup water recovery device 41 increases, the amount of recovered water decreases, and the temperature of the makeup water of the water treatment device 47 decreases as the temperature of the makeup water increases. There is a problem that the life of the ion exchange resin is shortened.

The present invention has been made in consideration of the above problems, and its objects are: (1) The pressure of a steam separator as an exhaust heat recovery device connected to the steam separator of a fuel cell power generator. (EN) Provided is an exhaust heat recovery device which has fast control response and can suppress pressure fluctuation within a minute range of ± 0.05 [kg / cm ³ ] or less. (2) In addition, as an exhaust heat recovery device connected to the makeup water recovery device of the fuel cell power generator, a makeup water recovery device is inexpensive, can efficiently remove the molten carbon dioxide gas in the combustion exhaust gas, and collects the recovered water. Provided is an exhaust heat recovery device that suppresses the temperature of the exhaust gas to a low level to achieve high recovery efficiency.

There is one thing.

[0017]

In order to solve the above-mentioned problems, in the present invention, (1) cooling water is supplied to the fuel cell main body and steam is supplied to the fuel reformer, and heat is discharged. In the steam separator which introduces the cooling discharge water of the phase flow and separates it into steam and water, a pressure adjusting valve,
A steam condenser for exchanging heat with a heat medium circulation circuit connected to an external cooling circuit, a condensed water tank integrally connected to this steam condenser or connected only by piping, and a condensed water tank kept at about atmospheric pressure, and condensed water. A waste water heat recovery device, which is configured by connecting a feed water pump that feeds the stored liquid in the tank to the steam separator in series via a pipe, is connected to form a circulation circuit of steam condensed water with the steam separator. I shall.

(2) The reaction exhaust air discharged from the fuel cell body and the combustion exhaust gas discharged from the fuel reformer are
Directly lead to the make-up water collector to directly contact the bottom collected water to collect water, and circulate this collected water between the heat exchanger of the cooling device outside the fuel cell power generator to recover heat. An exhaust heat recovery device shall be provided.

[0019]

[Operation] As described above, (1) The pressure regulating valve, the steam condenser for exchanging heat with the heat medium circulating device connected to the external cooling device, and the steam condenser are integrally connected or connected only by piping. An exhaust heat recovery device that is configured by connecting a condensed water tank that is maintained at approximately atmospheric pressure and a water supply pump that feeds the liquid stored in the condensed water tank to the steam separator in series via piping If the pressure of the steam separator becomes higher than the set value, the steam condensate will be condensed from the steam separator by increasing the opening of the valve for adjusting the pressure. The steam flow rate to the steam generator increases, the pressure of the steam separator immediately decreases, and on the contrary, when the pressure of the steam separator falls below the set value, decrease the opening of the valve to remove steam from the steam separator. The steam flow to the steam condenser is reduced and water Since the pressure of the gas separator immediately rises, it is possible to fast pressure control response than the conventional control method, ± pressure fluctuations 0.05
It becomes easy to control to a minute range of [kg / cm ³ ] or less.

The amount of heat recovered by the steam condenser to the external heat medium circulation circuit increases as the steam flow rate increases. Therefore, if the flow rate of the heat medium circulation circuit is kept constant, the difference in temperature between the inlet and the outlet of the steam condenser heat exchanger of the heat medium increases as the vapor flow rate increases. (2) In addition, the reaction exhaust air discharged from the fuel cell main body and the combustion exhaust gas discharged from the fuel reformer are directly guided to the makeup water collector, and are brought into direct contact with the collected water at the bottom to collect water. If an exhaust heat recovery device that circulates the recovered water between the heat exchanger of the cooling device outside the fuel cell power generator and recovers the heat is provided, the recovered water is cooled by the external cooling device. Because it is directly cooled with low temperature cooling water,
The temperature can be maintained at a lower temperature as compared with the case of cooling through a conventional collected water cooler, and the recovery efficiency is improved. Also, because the cooling water is circulated between the heat exchanger of the external cooling device, there is no need to install a recovered water circulation pump as in the case of using a recovered water cooler, and low power consumption and low cost It can be used as a make-up water collector.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a basic system diagram of a gas system and a cooling water system of a fuel cell power generator incorporating the exhaust heat recovery system of the first embodiment of the present invention. Components having the same functions as those of the conventional example shown in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted.

The difference between this embodiment and the conventional example is as follows: (1) The return pipe of the cooling water circulation circuit 20 for cooling the fuel cell main body 1 is connected to the vapor space of the water vapor separator 21 and Instead of the system composed of the heat recovery heat exchanger 23 and the three-way adjusting valve 27, a pressure adjusting valve 5 for adjusting the steam flow rate for the purpose of adjusting the pressure of the steam separator 21.
1, a steam condenser 52 for exchanging heat with the heat medium circulating device 25 connected to an external cooling device, a condensed water tank 53 connected to the steam condenser 52 only by piping, and a condensed water tank 53. Water supply pump 5 for sending the stored liquid to the steam separator 21
4 and 4 are connected in series via a pipe, and an exhaust heat recovery device is connected to form a circulation circuit of steam condensed water with the steam separator 21. The condensed water tank 53 is connected to the makeup water recovery device 41 and is maintained at substantially atmospheric pressure.

(2) Also, make-up water for directly guiding the reaction exhaust air discharged from the fuel cell main body 1 and the combustion exhaust gas discharged from the fuel reformer 7, and making direct contact with the recovered water at the bottom to recover water. The recovery device 41 is provided with an exhaust heat recovery device of a type in which the recovered water is circulated between the cooling water circuit 45 and a cooling device outside the fuel cell power generator to recover heat.

There is one thing. When the pressure of the steam separator 21 deviates from the set value due to the configuration of (1), the steam separator 2 is adjusted by adjusting the opening degree of the pressure adjusting valve 51.
It is possible to immediately return the pressure of the steam separator 21 to the set value by changing the flow rate of steam from 1 to the steam condenser 52, and it is possible to adjust the pressure with a quick response compared to the conventional control method. Therefore, the pressure of the steam separator 21 can be accurately controlled, so that the amount of steam can be stably supplied to the fuel reformer 7, and the fuel cell power generator can be operated stably.
Further, by adopting the configuration of (2), it is possible to keep the recovered water at a low temperature and improve the recovery efficiency. Also,
It is not necessary to install a recovered water circulation pump, and it is possible to provide an inexpensive makeup water recovery device with low power consumption.

FIG. 2 is a basic system diagram of a gas system and a cooling water system of a fuel cell power generator incorporating the exhaust heat recovery system of the second embodiment of the present invention. The difference from the first embodiment is that the steam condenser 5 of the exhaust heat recovery device installed in the steam separator 21.
2 and the condensed water tank 53 are integrated, and the function thereof is the same as that of the first embodiment. FIG. 4 shows a heat medium circulation circuit 25 of the exhaust heat recovery device provided in the vapor separator 21 according to the second embodiment of the present invention shown in FIG.
1 shows a specific configuration example of a cooling water circuit 45 of the exhaust heat recovery device provided in FIG.

In the heat medium circulation circuit 25, for example, 85
The high-temperature water that has been heated by the heat exchange in the steam condenser 52 and has been heated to, for example, 90 degrees Celsius is combined with the cooling water that circulates in the cooling tower 63 and the cold-hot water that circulates in the fan coil unit 62. It is cooled by the steam-fired cold water heater 61 and is circulated again to the steam condenser 52 at a predetermined temperature. Further, in the cooling water circuit 45, for example, the recovered water having a temperature of 50 ° C. is heat-exchanged with the cooling water circulating in the cooling tower 66 by the heat exchanger 65 to be cooled to, for example, 40 ° C., and the makeup water recovery device is supplied from the nozzle 44. 41, and the water is recovered by directly contacting the reaction exhaust air and the combustion exhaust gas. It should be noted that a part of the recovered water that has been heat-exchanged by the heat exchanger 65 is adjusted in flow rate by the adjustment valve 67, if necessary, and is sent to the heat exchanger 64 to be used for cooling the heat medium circulation circuit 25. . As described above, in order to effectively use the two exhaust heat recovery devices by connecting them, the temperature of the high-temperature water supplied to the heat medium circulation circuit 25 depends on the supply water of the cooling water circuit 45 of the makeup water recovery device 41. It is necessary that the temperature is higher than the temperature, and it is more effective if the temperature of the supplied high temperature water is 60 ° C. or higher.

FIG. 5 shows a system in which the exhaust heat recovery device provided in the makeup water recovery device 41 is of the conventional type. Even in this method, the pressure response of the water vapor separator can be controlled quickly, and effective exhaust heat recovery is possible. However, compared with this method, in the above method, the recovered water cooler 4
3 and the recovered water circulation pump 42 are unnecessary, and in terms of equipment,
It is also advantageous in terms of power consumption and in terms of lowering the temperature of the recovered water.

[0028]

According to the present invention, in the exhaust heat recovery apparatus used in the fuel cell power generator, (1) the exhaust heat recovery apparatus connected to the steam separator to form the circulation circuit of the steam condensed water is A pressure control valve that controls the internal pressure of the separator, a steam condenser that exchanges heat with the heat medium circulation circuit that connects the steam to an external cooling device, and an integrated connection or only a pipe to this steam condenser. Since the condensed water tank held at approximately atmospheric pressure and the water supply pump for sending the stored liquid of the condensed water tank to the steam separator are configured to be connected in series via the pipe, Since the control of the pressure response is fast and the pressure of the steam separator can be kept constant with high accuracy, the amount of steam to the fuel reformer can be controlled stably and the fuel reforming sent to the fuel cell main unit can be controlled. Low gas pressure and flow rate Reduction is, the fuel cell system can be stably operated.

Furthermore, in this configuration, since the heat and steam of the steam separator are circulated in the closed circuit to recover heat to the outside, the quality of the steam and water is affected by the external equipment. Can be kept stable without. (2) An exhaust heat recovery device used for a makeup water recovery device that introduces reaction exhaust air from the air electrode and combustion exhaust gas from the fuel reformer to recover these water, and uses this recovered water in the fuel cell power generator. It is configured to supply heat to an external cooling device, cool it, return it to the makeup water recovery device, and directly contact the reaction exhaust air and combustion exhaust gas to cool them. The reactor can be constructed at low cost and the molten carbon dioxide gas in the combustion exhaust gas can be removed efficiently, and the circulating pump for the recovered water is not required, so the power consumption can be reduced and the recovered water can be cooled externally. Since it is directly cooled by the device, it is possible to set the temperature of the recovered water to a low temperature and improve the recovery efficiency.

[Brief description of drawings]

FIG. 1 is a basic system diagram of a gas system and a cooling water system of a fuel cell power generator incorporating an exhaust heat recovery device according to a first embodiment of the present invention.

FIG. 2 is a basic system diagram of a gas system and a cooling water system of a fuel cell power generator incorporating an exhaust heat recovery device of a second embodiment of the present invention.

FIG. 3 is a basic system diagram of a gas system and a cooling water system of a conventional fuel cell power generator of this type.

FIG. 4 is a specific configuration diagram of a heat medium circulation system of an exhaust heat recovery device provided in a vapor separator and a cooling water system of an exhaust heat recovery device provided in a makeup water recovery device according to a second embodiment of the present invention.

FIG. 5 is a specific example of a heat medium circulating system of an exhaust heat recovery device according to a second embodiment of the present invention provided in a steam separator and a cooling water system of a conventional exhaust heat recovery device provided in a makeup water recovery device. Diagram

[Explanation of symbols]

 1 Fuel Cell Main Body 4 Cooling Plate 7 Fuel Reformer 8 Fuel Supply Circuit 9 Ejector Pump 10 Steam Supply Circuit 14 Reactive Air Supply Circuit 15 Reactive Air Discharge Circuit 16 Combustion Air Supply Circuit 18 Combustion Gas Discharge Circuit 19 Gas Exhaust Circuit 20 Cooling Water Circulation Circuit 21 Water vapor separator 25 Heat medium circulation circuit 41 Make-up water collector 44 Nozzle 45 Cooling water circuit 46 Make-up water pump 47 Water treatment device 51 Pressure adjusting valve 52 Steam condenser 53 Condensed water tank 54 Water supply pump

Claims (2)

[Claims] 1. Steam for supplying cooling water to a fuel cell main body and steam to a fuel reformer and introducing cooling exhaust water of a two-phase flow heated and discharged in the fuel cell main body to separate steam and water. In an exhaust heat recovery device that is connected to a separator and forms a circulation circuit for steam condensed water, a pressure control valve that adjusts the internal pressure of the steam separator and a heat medium circulation circuit that connects steam to an external cooling device and heat A steam condenser to be exchanged, a condensed water tank that is integrally connected to this steam condenser or connected only by piping, and is maintained at approximately atmospheric pressure, and a water supply pump that sends the stored liquid of the condensed water tank to the steam separator. An exhaust heat recovery device for a fuel cell power generator, wherein the exhaust gas heat recovery device is connected in series via a pipe. 2. The reaction exhaust air discharged from the air electrode of the fuel cell main body and the combustion exhaust gas discharged from the fuel reformer are introduced and cooled to recover water contained therein as recovered water. In an exhaust heat recovery device used for a makeup water recovery device of a fuel cell power generation device, the recovered water is passed between the makeup water recovery device and a heat exchanger cooled by a cooling device installed outside the fuel cell power generation device. An exhaust heat recovery device for a fuel cell power generator, which circulates to recover heat.