JP2006114413A - Water quality management method of fuel cell generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a management method in which the quality of recovered water is maintained at a prescribed level even if operated for a long time in a fuel cell generator in which reaction-generated water of a fuel cell stack 1 and combustion-generated water of a reformer 2 are recovered in a recovery tank 3, and in which the water is used as cooling water of the fuel cell stack 1 and steam for reforming of the reformer 2. <P>SOLUTION: An electric conductivity of the recovered water is measured by an electric conductivity measuring sensor 21 installed at the recovery tank 3, its detected signal is sent to a controller 22, and when the measured value exceeds a specified value, a part of the recovered water is discharged by opening a flow rate adjusting valve 23, and simultaneously, pure water of the same amount as that of discharged water is supplied from a pure water supply means 6 to the recovery tank 3 by opening the flow rate adjusting valve 24. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a water quality management method for a fuel cell power generation apparatus that recovers and uses reaction product water and reformer combustion product water.

A polymer electrolyte fuel cell (PEFC) is a fuel cell using a polymer membrane as an electrolyte, and has excellent characteristics such as high output density and long battery life. In this type of fuel cell, a porous membrane having functions of a current collector and a gas diffusion layer on both sides of a membrane / electrode assembly (MEA) formed by arranging a catalyst layer (electrode) on both sides of a solid polymer electrolyte membrane A single cell is configured by arranging a porous substrate and sandwiched by a separator with a gas flow groove, and a fuel cell stack is configured by stacking a plurality of such single cells. Normally, air as an oxidant gas and a reformed gas as a fuel gas are supplied to the fuel cell stack, and electric power is generated by an electrochemical reaction using these gases.
FIG. 2 is a system configuration diagram of a gas system and a water system of a fuel cell stack of this type of fuel cell power generator. In the figure, 1 is a fuel cell stack, 2 is a fuel gas reformer, 3 is a recovered water tank, 4 is a water treatment device, 5 is a pure water tank, and 11 to 16 are for air supply or water supply, respectively. It is a pump. The fuel electrode of the fuel cell stack 1 is supplied with reformed gas containing high-concentration hydrogen reformed by the reformer 2, and the air electrode is supplied with the reaction air sent by the pump 13 to generate power. Is done. The fuel electrode exhaust gas discharged from the fuel electrode is sent to the combustor of the reformer 2, and the remaining hydrogen is mixed with the combustion air taken in by the pump 12 and burned. It plays the role of heating to the reforming temperature. The combusted gas is sent to the recovered water tank 3, and the contained combustion product water is recovered. On the other hand, the air electrode exhaust gas discharged from the air electrode contains reaction product water generated along with the electrochemical reaction, and is sent to the recovery water tank 3 to recover the reaction product water. These recovered produced water is purified by the water treatment device 4 and then sent to a pure water tank 5 constituting a cooling water circulation system that functions to maintain the fuel cell stack 1 at a constant operating temperature. A part of the pure water stored in the pure water tank 5 is added to the raw fuel introduced into the reformer 2 as steam for performing steam reforming.

As described above, in the fuel cell power generation apparatus, the reaction product water and the combustion purified water of the reformer 2 can be recovered and used for cooling the fuel cell stack 1 and steam reforming of the raw fuel, and thus can be operated efficiently. It is configured as follows. In order to ensure stable operation in the fuel cell power generation device of this configuration, the water levels of the recovered water tank 3 and the pure water tank 5 need to be kept constant. Therefore, only when the water level falls, a system is adopted in which pure water is supplied from the external pure water supply means 6 to the recovered water tank 3 to keep these water levels constant. However, even when such an operation method is adopted, if the continuous operation period is long, the water quality is gradually reduced due to concentration, and the performance of the water treatment device 4 disposed in the front stage of the pure water tank 5 deteriorates. Or the foreign matter accumulated in the recovered water tank 3 has a problem that the pump 16 is clogged.
As a method for solving such a problem associated with the deterioration of the quality of recovered water, Patent Document 1 discloses that an ion-exchange type purifier is installed in parallel with an electrodeionization apparatus for purifying recovered water, and the recovered water tank is recovered. An apparatus is disclosed that measures the electrical conductivity of water and switches between the operation of an electrodeionization apparatus and an ion exchange type purifier according to the measured value.
JP 2001-176535 A

  The present invention, as described above, in a fuel cell power generator of a system that recovers reaction product water generated in a fuel cell stack and combustion product water generated in a reformer and uses it as cooling water for the fuel cell stack or steam for reforming, It is an object of the present invention to provide a water quality management method in which a decrease in the quality of recovered water is suppressed even if the operation is continued for a long time, and is maintained at a predetermined level of water quality, thereby ensuring stable operation.

In order to achieve the above object, in the present invention,
A fuel cell body that obtains electric energy through an electrochemical reaction by introducing a reformer that steam-reforms the raw fuel into a hydrogen-rich reformed gas, and an oxidant gas and the reformed gas obtained by the reformer And a recovery tank for storing recovered water generated by condensing water vapor generated in the fuel cell main body due to this electrochemical reaction and water vapor contained in the combustion exhaust gas generated by the operation of the reformer. In the fuel cell power generator using pure water obtained by purifying the recovered water stored in the tank as cooling water for maintaining the fuel cell main body at a constant temperature and steam for reforming in the reformer,
(1) The quality of the recovered water stored in the recovery tank is measured by a water quality measuring means provided in the recovery tank, for example, an electrical conductivity measuring sensor, and the recovered water is recovered by the recovered water discharging means provided in the recovery tank. A part is discharged to the outside, pure water is replenished to the recovery tank from the outside by pure water replenishing means, and the quality of the recovered water stored in the recovery tank is within a predetermined range, for example, electric conductivity is 2.0 (mS / m) Control shall be made so that

(2) In (1) above, the amount of recovered water discharged from the recovery tank by the recovered water discharging means and the amount of pure water supplied to the recovery tank by the pure water replenishing means are adjusted to substantially the same amount. I will do it.
(3) In the above (1) or (2), the amount of recovered water discharged by the recovered water discharging means and the amount of pure water supplied by the pure water supplying means are adjusted by the adjusting valve. To do.

  The reaction product water generated in the fuel cell body and the combustion product water generated by the operation of the reformer are recovered and stored in a recovery tank, and the purified water obtained by purifying the recovered water is used as cooling water for the fuel cell body. In addition, in the fuel cell power generator used as reforming steam in the reformer, if the recovery tank is provided with pure water replenishing means and pure water is replenished into the recovery tank from the outside, the quality of the recovered water in the recovery tank is It improves according to the amount of pure water supplied. Moreover, if a collection water discharge means is provided in the collection tank and a part of the collected water is discharged, the amount of the collected water in the collection tank decreases according to the amount of the discharged water. Therefore, as described in (1) above, the recovery tank is provided with the recovery water discharge means and the pure water supply means, the pure water supply means supplies the recovery tank from the outside, and the recovery water discharge means supplies the recovered water. If a part is discharged to the outside, the quality of the recovered water can be improved and the water level in the recovery tank can be adjusted. Also, for example, a water quality measuring means such as an electrical conductivity measuring sensor is provided to measure the water quality of the recovered water, and the recovered water is adjusted so that the water quality falls within a predetermined range, for example, the electric conductivity is 2.0 (mS / m) or less. By controlling the discharge means and pure water replenishment means to adjust the recovered water discharge amount and pure water replenishment amount, the quality and level of the recovered water in the recovery tank can be maintained within the specified range, and the fuel cell power generator can be stabilized Driving.

  Further, as described in (2) above, the amount of recovered water discharged from the recovery tank by the recovered water discharging means and the amount of pure water supplied to the recovery tank by the pure water replenishing means are adjusted to substantially the same amount. In this case, the level of the recovered water in the recovery tank is kept constant regardless of the amount of pure water replenished, so that the fuel cell power generator can be operated more stably.

  The best mode of the fuel cell power generator of the present invention includes a reformer that steam-reforms raw fuel into a hydrogen-rich reformed gas, an oxidant gas, and a reformed gas obtained by the reformer. The fuel cell main body that obtains electric energy by introducing an electrochemical reaction, the water vapor generated in the fuel cell main body by this electrochemical reaction and the water vapor contained in the combustion exhaust gas generated by the operation of the reformer are condensed. A recovery tank for storing the generated recovered water, and purified water obtained by purifying the recovered water stored in the recovery tank, cooling water for maintaining the fuel cell main body at a constant temperature, and the reformer In the fuel cell power generator used as steam for reforming in Japan, the quality of the recovered water stored in the recovery tank is measured by water quality measuring means such as an electric conductivity measuring sensor and the recovered water discharged in the recovery tank is discharged. A part of the recovered water is discharged to the outside by the stage, and pure water is replenished to the recovery tank from the outside by the pure water replenishing means, so that the quality of the recovered water stored in the recovery tank is controlled within a predetermined range. There is.

FIG. 1 is a system configuration diagram of a gas system and a water system of a fuel cell stack of a fuel cell power generator to which an embodiment of a water quality management method of the present invention is applied. The difference from the system configuration diagram in the conventional water quality management method shown in FIG. 2 is that the recovered water tank 3 is provided with an electrical conductivity measuring sensor 21 as the water quality measuring means of the recovered water. In addition, a discharge pipe with a flow rate adjusting valve 23 is used as a recovered water discharging means for draining the stored recovered water by controlling the flow rate, and a flow adjusting valve 24 is connected to a supply pipe from the pure water supplying means 6 to the recovered water tank 3. The two flow rate adjusting valves 23 and 24 are configured to be controlled by the controller 22 that operates in response to the detection output of the electric conductivity measuring sensor 21.
In the water quality management method of the present embodiment, when the fuel cell power generator is operated, a recovered water system is configured as shown in FIG. 1, and the measurement signal of the electrical conductivity measuring sensor 21 is sent to the controller 22 to measure the recovered amount. The flow rate adjusting valves 23 and 24 were opened and closed in accordance with the level of electrical conductivity of the recovered water in the water tank 3, that is, the level of water quality, and the quality of the recovered water was adjusted and maintained. That is, when the quality of the recovered water is good and the electric conductivity is less than the specified value of 2.0 (mS / m), the flow rate adjusting valves 23 and 24 are both kept closed, and the recovered water from the discharge pipe is maintained. Neither discharge nor supply of pure water from the pure water supply means 6 is performed, but when the electric conductivity exceeds 2.0 (mS / m), the flow rate adjusting valve 23 is opened and the recovered water having a flow rate of 50 ml / min or more is opened. At the same time, the flow rate adjustment valve 24 provided in the supply pipe from the pure water supply means 6 is opened and adjusted to supply substantially the same amount of pure water into the recovered water tank 3 as the above discharge amount. Thus, by recovering the recovered water whose water quality has been lowered and supplying pure water, the quality of the recovered water in the recovered water tank 3 is improved and maintained at a good level substantially below the specified value. In this water quality management method, the amount of discharged water through the flow rate adjusting valve 23 and the amount of supplied water through the flow rate adjusting valve 24 are adjusted to be approximately the same, so that the level of recovered water in the recovered water tank 3 is adjusted. The fuel cell stack can be stably operated without causing large fluctuations. According to the experiment results of the present inventor, by adjusting the water quality using the present water quality management method, it was possible to perform a continuous operation for a long time exceeding 3000 hours without exchanging the water treatment apparatus.

In this embodiment, when the electrical conductivity exceeds the specified value of 2.0 (mS / m), a predetermined amount of recovered water is discharged and at the same time, approximately the same amount of pure water is supplied into the recovered water tank 3. However, if the specified value of electrical conductivity is set to a high value, it is easy to maintain the water quality, but water with relatively poor water quality flows into the system, leading to a rapid deterioration in the characteristics of the device. When the specified value is set to a low value, the water quality is maintained at a high level, but the water in the recovered water tank is frequently exchanged, and a large amount of pure water is supplied, so that the operation cost increases. Therefore, it is desirable that the specified value of electrical conductivity in the case of performing the water quality management method of the present embodiment is selected to be approximately 2.0 (mS / m) from the results of trial and error.
In this embodiment, when the electrical conductivity exceeds the specified value, the recovered water having a flow rate of 50 ml / min or more is discharged, and at the same time, substantially the same amount of pure water is supplied into the recovered water tank 3. The discharge amount of recovered water and the supply amount of pure water are not limited to this flow rate, and may be selected according to the scale of the system, particularly the scale of the recovered water tank. Further, the flow rate may be a function of the difference between the detected value and the specified value, such as a flow rate that is proportional to the difference between the detected electrical conductivity of the recovered water and the specified value.

  As described above, if the water quality management of the recovered fuel cell stack is performed using the water quality management method of the present invention, it is possible to suppress a decrease in the quality of the recovered water even if the operation is continued for a long time. Therefore, the fuel cell power generator can be stably operated. Therefore, this water quality management method can be expected to be widely used in this type of fuel cell power generation device.

FIG. 1 is a system configuration diagram of a gas system and a water system of a fuel cell stack of a fuel cell power generator to which an embodiment of a water quality management method of the present invention is applied. System configuration diagram of gas system and water system of this type of conventional fuel cell power generator

Explanation of symbols

1 Fuel cell stack
2 Reformer
3 recovered water tank
4 Water treatment equipment
5 Pure water tank
6 Pure water supply means 11-16 Pump 21 Electrical conductivity measurement sensor 22 Controller 23 Flow control valve (drainage)
24 Flow control valve (pure water)

Claims (5)

A reformer that steam-reforms the raw fuel into a hydrogen-rich reformed gas, and a fuel cell that obtains electric energy through an electrochemical reaction by introducing the reformed gas and oxidant gas obtained by the reformer A main body, and a recovery tank for storing recovered water generated by condensing water vapor generated in the fuel cell main body due to the electrochemical reaction and water vapor contained in the combustion exhaust gas generated by the operation of the reformer, In a fuel cell power generator using pure water obtained by purifying recovered water stored in the recovery tank as cooling water for maintaining the fuel cell body at a constant temperature and steam for reforming in the reformer ,
The quality of the recovered water stored in the recovery tank is measured by the water quality measuring means provided in the recovery tank, and a part of the recovered water is discharged to the outside by the recovered water discharge means provided in the recovery tank. A method for managing the water quality of a fuel cell power generator, wherein pure water is supplied to the recovery tank from the outside by water supply means, and control is performed so that the quality of the recovered water stored in the recovery tank falls within a predetermined range. The amount of recovered water discharged from the recovery tank by the recovered water discharging means and the pure water supplied to the recovery tank by the pure water replenishing means are adjusted to be substantially the same amount. 2. A water quality management method for a fuel cell power generator according to 1. The amount of recovered water discharged by the recovered water discharging means and the amount of pure water supplied by the pure water replenishing means are adjusted by an adjustment valve. Water quality management method for fuel cell power generator. 4. The water quality management method for a fuel cell power generator according to claim 1, wherein the water quality measuring means provided in the recovery tank is an electrical conductivity measurement sensor. 5. The quality of recovered water stored in the recovery tank is controlled so that the electrical conductivity measured by the electrical conductivity measuring sensor is 2.0 (mS / m) or less. The water quality management method of the fuel cell power generator described in 2.

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