JP3106552B2 - Water treatment system for fuel cell power plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment system for a fuel cell power generator, which purifies condensate and tap water containing impurities and supplies the purified water as fuel cell cooling water or raw fuel reforming reaction water. And a water treatment system provided with a device for degassing dissolved gas in mixed water.

[0002]

2. Description of the Related Art In order to operate a fuel cell with high efficiency for a long period of time, heat generated by a cell reaction is removed and the temperature distribution in a unit cell stack (called a stack) is changed to a predetermined operating temperature (phosphoric acid). It is required to keep the temperature of the fuel cell as uniform as possible at around 190 ° C. Therefore, a water-cooled fuel cell is known in which a stack is formed by stacking cooling plates between blocks with a plurality of unit cells as one block, and cooling water flowing as cooling medium flows through cooling pipes embedded in the cooling plates. Have been. Further, in a water-cooled fuel cell, the cooling water is required to have as low an electric conductivity as possible (high electric resistance) in order to prevent a liquid junction from being generated between the cooling plates at different potentials. There is known a water circulation system provided with a water treatment system for replenishing ion-exchanged water.

FIG. 3 is a configuration diagram showing a conventional water treatment system for a water-cooled fuel cell. In the figure, a fuel gas is supplied from a fuel reformer 2 to a fuel electrode of a fuel cell (stack) 1 composed of a stack of unit cells, and reaction air is supplied to a pneumatic electrode from a blower 1B. Power is generated based on an electrochemical reaction in which hydrogen and oxygen directly react between the electrodes. In the fuel cell, a cooling plate 3 is stacked for each of a plurality of unit cells, and a plurality of cooling pipes embedded in the cooling plate 3 are provided with a circulating pump 4P and a steam separator 4P arranged outside via an insulating joint. Is connected to the circulation system of the cooling water 6 containing The steam separator 4 contains cooling water 6 that is lower than the operating temperature of the fuel cell by a predetermined temperature. By circulating the cooling water 6 to the cooling plate 3 by a circulation pump 4P, the heat generated by the power generation is exhausted. Thus, the temperature of the fuel cell stack 1 is maintained at the operating temperature. Further, a large amount of water generated by power generation or combustion generated by combustion of the air off-gas 1G discharged from the air electrode and the combustion exhaust gas 2G generated by burning the residual hydrogen in the fuel off-gas 1F by the burner of the fuel reformer 2 Since water is contained, the water contained in the air off-gas and the combustion exhaust gas as water vapor is condensed into the condensate condenser 5.
To recover the condensate 7 and supply it to the water treatment system.

If the electric conductivity of the cooling water 6 is high, a short-circuit current flows between the cooling plates through the cooling water in the insulating joint connecting the cooling pipes to each other. Parts are wasted. Therefore, the water treatment system 11 is connected to the cooling water circulation system in order to maintain the electric conductivity of the cooling water 6 at 1 μS / cm or less. That is, the water treatment system 11 includes the condensing condenser 5
The condensed water 7 collected in step 2 is guided to an auxiliary water tank 12 to form a mixed water 8 to which tap water is appropriately added, and the mixed water 8 is sent to an ion-exchange type water treatment device 15 via a pump 13 and a cooler 14, thereby obtaining The low-conductivity ion-exchanged water 9 was added to the cooling water 6 as makeup water, and the electric conductivity of the cooling water 6 was 1 μS /
cm or less. The supply amount of the make-up water 9 is determined by the shortage generated when the steam in the steam separator 4 is added to the raw fuel as, for example, reforming reaction water, or by discharging the cooling water to the outside as blow water. Control is performed in accordance with the amount of replenishment of the resulting shortage.

[0005]

In the conventional water treatment system shown in FIG. 3, the condensate recovered from the flue gas 2G containing a large amount of carbon dioxide contains a large amount of bicarbonate ions and free carbon dioxide gas in equilibrium with the bicarbonate ions. And a carbon dioxide concentration of about 5% even after condensing the condensate from the air off-gas. In addition, tap water contains many chlorine ions and the like. Therefore, when the mixed water having a large amount of dissolved ions and dissolved gas is to be purified by the ion-exchange type water treatment apparatus 15, the anion-exchange load of the ion-exchange resin is significantly increased, and its usable life is shortened. In addition, there arises a problem that the cost required for the regeneration process increases and the running cost of the fuel cell power generator increases. Therefore, a method of not recovering the water vapor in the combustion exhaust gas 2G is also known. However, the water balance of the power generation device is lost, and tap water containing a large amount of mixed ions must be replenished for compensation. Contradiction that the anion load cannot be reduced.

FIG. 4 is a block diagram showing an improved conventional water treatment system. A waterfall type deaeration tower 16 is provided between a condensate condenser 5 and an auxiliary water tank 12, and a condensate is recovered by a pump 5P. The mixed water 7 and the tap water sent from the water condenser 7 are brought into direct countercurrent contact with fresh air sent from the blower 17, and the amount of dissolved gas in the mixed water is reduced using the waterfall effect to determine the gas concentration in the fresh air. A mixed water 18 of low saturation solubility equilibrated with
It is configured to be stored in the auxiliary water tank 12. However, in order to obtain a sufficient waterfall effect with this method,
It is necessary to increase the height of the degassing tower to 2M or more, which not only increases the size of the apparatus, but also increases the pressure loss and increases
There is a drawback that causes an increase in size and power consumption. A heater (not shown) is provided on the outlet side of the blower 17 so that the mixed water 8
There is also known a configuration in which the degassing effect is enhanced by utilizing the property of air (heating degassing effect), in which the amount of dissolved gas decreases in inverse proportion to the temperature rise by bringing the gas into countercurrent contact with high-temperature air. Have been. However, since the heated mixed water evaporates and is discharged into the exhaust gas, the evaporation loss of the mixed water increases, and as a result, the heating temperature of the mixed water stops at about 80 ° C. and is inversely proportional to the temperature. However, since the properties of water that can lower the saturation solubility of carbon dioxide and hydrogen chloride cannot be fully utilized, there is a disadvantage that the usable life of the ion exchange resin cannot be sufficiently extended.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a water treatment system for purifying mixed water of condensed water and tap water to make up makeup water, and to highly remove ions mixed in the mixed water which becomes an anion load on the ion exchange resin. Accordingly, the life of the ion exchange resin is prolonged, and the maintenance management cost is reduced.

[0008]

According to the present invention, a condensate obtained by condensing at least water vapor in a combustion exhaust gas of a fuel reformer with a condensate condenser is ion-exchanged. A low-conductivity make-up water through a water treatment system, which is supplied to a fuel cell or a fuel reformer, wherein the condensate and the fuel cell are disposed between the condensing condenser and the ion-exchange type water treatment device. And a direct contact type deaerator for directly countercurrently contacting the air off-gas.

[0009] Further, it is provided with means capable of supplying an arbitrary predetermined amount of the air off-gas to the direct contact deaerator and supplying the remaining air off-gas to the condensing condenser.

[0010] Further, the air off-gas which has been brought into countercurrent contact with the condensate in the direct contact deaerator is returned to the condensate condenser. Further, tap water is supplied to the condensing condenser.

[0011]

With the above construction, 150 ° C.
And an air off-gas having a high temperature of as low as 200 ° C. and a low carbon dioxide concentration, and condensed water obtained by condensing water vapor in the combustion exhaust gas of the fuel reformer or a mixed water containing at least the condensed water. By contact, the deaeration effect of the waterfall method and the heating method can be obtained at the same time, so that the mixed ions of the condensate or the mixed water are efficiently released into the air off-gas to obtain a mixed water having a low saturated gas concentration. be able to.
In the case of a phosphoric acid fuel cell, the air off-gas contains phosphoric acid scattered from the air electrode of the fuel cell, and the phosphoric acid acts to convert hydrogen carbonate ions in the condensed or mixed water into carbon dioxide. Therefore, the concentration of mixed ions can be significantly reduced. Furthermore, since degassing can be performed using the differential pressure of the air off-gas with respect to atmospheric pressure,
A blower for supplying air to the direct contact deaerator becomes unnecessary, and the configuration of the water treatment system can be simplified and power consumption can be reduced.

[0012] Further, if a predetermined amount of the air off-gas is supplied to the direct contact deaerator and the remaining air off-gas is supplied to the condensate condenser, for example, a variable damper may be provided. The flow rate of the air off-gas introduced into the direct contact deaerator can be easily adjusted.

Further, if the air off-gas which has been brought into countercurrent contact with the condensate in the direct contact deaerator is returned to the condensate condenser, the water content in the direct contact deaerator increases. The condensate condenser cools the condensed air off-gas and recovers the water content as condensate.This makes it possible to reduce the evaporation loss of condensate and reduce the amount of tap water to be supplied while maintaining the water balance of the power generator. It becomes possible.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 is a configuration diagram showing a water treatment system of a fuel cell power generation device according to an embodiment of the present invention. The same components as those of the prior art are denoted by the same reference numerals, and redundant description will be omitted. In the figure, a water treatment system 21 has a configuration in which a direct contact deaerator 22 is added to the previous stage of a conventional water treatment system including an auxiliary water tank 12, a pump 13, a cooler 14, and an ion exchange type water treatment device 15. The mixed water 8 obtained by mixing condensed water with tap water in the condensate condenser 5 is sprayed from above the packed layer 22A of the Raschig ring in the direct contact deaerator 22 via the pump 5P. .
The branch passage 26 supplies a variable damper 23 provided on a pipe for supplying the air off-gas 1G to the condensate condenser 5 and an air off-gas 1g branched from the upstream side and branched from below the packed bed 22A. Outgoing pipe 24 and packed layer 22A
And a pipe 25 for returning 1 g of air off-gas directly in contact with the mixed water 8 to the outlet side of the variable damper 23 (the inlet side of the condenser). The amount of air off-gas supplied to 22 is controlled to a desired value by adjusting the opening of variable damper 23.

In the water treatment system configured as described above, the mixed water 8 sprayed from above on the packed bed 22A of the direct contact deaerator 22 is diverted to the branch passage 26 by the variable damper 23. Packed bed 2 via pipe 24
Direct countercurrent contact with 1 g of air off-gas supplied from below 2A. At this time, the mixed water comes into contact with the phosphoric acid in the air off-gas to convert hydrocarbon ions into carbon dioxide gas, and heat exchange with high-temperature air off-gas raises the temperature to change chlorine ions into hydrogen chloride gas, and the temperature increases. The effect of the rise of water is to increase the partial pressure of carbon dioxide and hydrogen chloride in the mixed water, thereby enhancing the effect of the waterfall that promotes the release of carbon dioxide and hydrogen chloride to the off-gas side where the gas partial pressure is low. Is stored in the auxiliary water tank 12 as the mixed water 28 in which the saturated dissolution concentrations of carbon dioxide and hydrogen chloride in the mixed water are significantly reduced.

In addition, the improvement of the degassing performance makes it possible to reduce the height of the direct contact type degassing device, which can reduce the pressure loss. It is possible to supply air off-gas to the direct contact deaerator by utilizing the pressure difference that it has, and the blower that was conventionally required to supply air to the direct contact deaerator becomes unnecessary. It is possible to simplify the configuration of the processing system and save power.

Further, if a variable damper is provided in the supply system of the air off-gas, and the branch passage is configured to return the air off-gas, which has been brought into countercurrent contact with the mixed water by the direct contact type deaerator, to the condensing condenser, the branch passage can be formed. The flow rate of air off-gas to the air can be easily adjusted, and the air-off gas containing moisture evaporated by the direct contact deaerator can be cooled by the condensing condenser and recovered as condensate. In addition to the improvement of gas performance, the evaporation loss of condensate water can be reduced, and the amount of tap water used can be reduced while maintaining the water balance of the power generator, thus further reducing the anion load of the ion exchange resin. ,
Therefore, the life of the ion exchange resin can be extended, and the cost of the regeneration treatment and the number of maintenance work can be reduced accordingly.

FIG. 2 is a system configuration diagram showing a modification of the embodiment of the present invention, in which the condensate condenser 5 and the upper part of the direct contact type deaerator 22 are directly connected by a pipe 31 and the mixed water 8 is headed. The difference from the above-described embodiment is that the pump is supplied to the direct contact deaerator using the difference, and the pump 5P in the above-described embodiment is eliminated by such a configuration. And the blower 17 for supplying air (FIG. 4)
In addition, the effect of improving the plant efficiency of the power generator can be obtained.

[0019]

According to the present invention, as described above, a direct contact type deaerator for degassing dissolved gas in mixed water by bringing the mixed water and air off-gas into direct countercurrent contact with each other by ion exchange with a condensing condenser 150 ° C
The temperature is as high as 200 ° C. and the air-off gas with low carbon dioxide concentration is in direct countercurrent contact with the mixed water.
When the degassing effect of the waterfall method and the heating method is obtained at the same time, and the air off-gas contains phosphoric acid, this phosphoric acid converts hydrogen carbonate ions in the mixed water to carbon dioxide gas to facilitate degassing. As a result, mixed water in which the saturation solubility of mixed ions and mixed gas is significantly lower than that of the conventional apparatus can be easily obtained, and therefore, the life of the ion exchange resin is greatly reduced due to a significant reduction in the anion load of the ion exchange resin. And a fuel cell power generation device provided with a water treatment system that has a remarkable effect of reducing the cost of regenerating the ion exchange resin and reducing the number of man-hours for maintenance work.
In addition, since the height of the direct contact deaerator can be reduced by improving the deaeration performance, the size of the direct contact deaerator can be reduced compared to a conventional water treatment system using a deaeration tower. And the advantage that the pressure loss can be reduced.

As described above, since the pressure loss of the direct contact type deaerator is reduced, the branch passage for diverting a predetermined amount of the air off gas to the direct contact type deaerator is connected to the air off gas supply system to the condensing condenser. If it is configured to be connected to the air, the degassing process can be performed using the pressure difference that the air off gas has with respect to the atmospheric pressure, so the blower required in the conventional waterfall type degassing tower becomes unnecessary, Advantages are obtained in that the configuration of the water treatment system can be simplified and power can be saved.

Further, if a variable damper for controlling the air off-gas diverted to the branch passage is provided, and the air off-gas which has been brought into countercurrent contact with the mixed water by the direct contact type deaerator is returned to the condensing condenser, In addition to being able to easily adjust the flow rate of the air off-gas to the passage, the air-off gas whose moisture content has increased with the direct contact deaerator can be cooled by the condensate condenser and recovered as condensate. Can reduce the evaporation loss of condensate water, which is a problem with degassing towers, and can maintain the water balance of the power generator by itself. The advantage that the anion load of the exchange resin can be further reduced is obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a water treatment system of a fuel cell power generator according to an embodiment of the present invention.

FIG. 2 is a system configuration diagram showing a modification of the embodiment of the present invention.

FIG. 3 is a configuration diagram showing a conventional water treatment system for a water-cooled fuel cell.

FIG. 4 is a block diagram showing an improved conventional water treatment system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell (stack) 2 Fuel reformer 3 Cooling plate 4 Steam separator 5 Condenser condenser 6 Cooling water 7 Condensed water 8 Mixed water 9 Makeup water 11 Water treatment system 12 Auxiliary water tank 15 Ion exchange type water treatment device Reference Signs List 16 deaeration tower 17 blower 18 mixed water (degassed) 21 water treatment system 22 direct contact deaerator 22A packed bed 26 branch passage 23 variable damper 1G air off gas 2G combustion exhaust gas

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 8/00-8/24

Claims (4)

(57) [Claims] 1. A condensate obtained by condensing at least steam in a combustion exhaust gas of a fuel reformer with a condensate condenser to make-up water of low electric conductivity through an ion-exchange type water treatment apparatus.
In a fuel cell or a fuel reformer, a direct contact type degasser is provided between the condensate condenser and the ion-exchange type water treatment apparatus, in which the condensate and the air off-gas of the fuel cell are brought into direct countercurrent contact. A water treatment system for a fuel cell power generator, comprising a gas device. 2. The fuel cell according to claim 1, further comprising means capable of supplying an arbitrary predetermined amount of the air off-gas to the direct contact deaerator and supplying the remaining air off-gas to the condensing condenser. Water treatment system for power generator. 3. The fuel cell power generator according to claim 1, wherein an air off-gas in countercurrent contact with the condensate in the direct contact deaerator is introduced into the condensate condenser. Water treatment system. 4. The water treatment system for a fuel cell power generator according to claim 1, wherein tap water is supplied to said condensing condenser.