JP2854171B2 - Makeup water recovery equipment for fuel cell power generators - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a make-up water recovery system for recovering water in exhaust gas from a fuel cell power generator including a fuel reformer and supplying the recovered water to a water treatment system, and more particularly to a recovery system recovered from combustion exhaust gas. The present invention relates to a makeup water recovery device having a function of reducing the concentration of carbon dioxide in water.

[0002]

2. Description of the Related Art Phosphoric acid type fuel cells using phosphoric acid as an electrolytic solution convert the hydrogen in the fuel gas obtained by steam reforming a source fuel such as methane gas and the oxygen in the air with the fuel in the fuel cell. The power is supplied to the electrode and the air electrode, respectively, and power is generated based on an electrochemical reaction. To reform the source fuel into fuel gas,
A fuel reformer is used in which steam is added to methane as a source fuel to promote the reaction between water and methane with a catalyst.
Therefore, it is necessary to supply water to the fuel reformer in accordance with the amount of steam used for reforming the fuel. As this water, ion-exchanged water from which impurities have been removed by an ion-exchange type water treatment device or the like is used. The use of recovered water obtained by condensing combustion water) has less impurities than tap water, and the load on the ion-exchange type water treatment device can be reduced accordingly. Measures have been taken to recover the moisture in the exhaust.

FIG. 4 is a block diagram showing a conventional make-up water recovery and treatment system in a fuel cell power generator. In a phosphoric acid fuel cell 1, a fuel electrode and an air electrode are arranged with a matrix holding phosphoric acid therebetween. By supplying a fuel gas generated by the fuel reformer 2 to the fuel electrode and supplying air to the air electrode, power generation is performed based on an electrochemical reaction. The off-gas of the fuel gas is sent to the fuel reforming burner 2B to burn the remaining hydrogen,
The combustion heat is used as reaction heat of the fuel reforming reaction.
The combustion exhaust gas 2G containing water (combustion water) generated by the combustion of the remaining hydrogen and the air off-gas 1A containing water generated by power generation (power generation water) are sent to the makeup water recovery device 3 to recover moisture. Is performed. Makeup water recovery device 3
Has a structure in which, for example, a water-cooled heat exchanger 5 is housed in a water recovery tower 4, and water condensed in the heat exchanger 5 is stored as recovered water 6 at the bottom of the water recovery tower 4. The recovered water 6 is sent to an ion-exchange type water treatment device 8 by a pump 7A, accumulated in a water tank 9 as makeup water 10 from which impurities are removed, and sent to a fuel reforming device 2 by a pump 7B as necessary. It is added to the source fuel as high-temperature steam and is used as reaction water required for steam reforming of the source fuel.

[0004]

The recovered water obtained by condensing flue gas with a heat exchanger contains carbon dioxide having a saturation concentration proportional to the carbon dioxide concentration in the flue gas.
Therefore, a large amount of carbon dioxide gas is dissolved in the conventional recovered water 6 obtained by condensing the moisture in the exhaust gas in which the combustion exhaust gas and the air off-gas are mixed by one heat exchanger.
When such recovered water is supplied to an ion-exchange type water treatment apparatus, carbon dioxide gas acts as a load on the ion-exchange resin, and the regeneration cycle of the ion-exchange resin is shortened. Is also increased. If the recovered water is configured to be degassed to remove carbon dioxide, the regeneration cycle of the ion-exchange resin can be extended, but this requires equipment and power for degassing, and equipment In addition to the increase in complexity, size, and economic disadvantage, there is a problem in that the auxiliary equipment loss of the power generation device increases and the efficiency decreases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a make-up water recovery apparatus which can generate recovered water with a small amount of carbon dioxide gas without increasing the complexity and size of the equipment and lowering the power generation efficiency, and therefore can extend the regeneration cycle of the ion exchange resin. To provide a fuel cell power generation device provided with the same.

[0006]

According to the present invention, in order to solve the above-mentioned problems, water contained in air off-gas discharged from a fuel cell and flue gas discharged from a fuel reformer is recovered. Then, the recovered water is supplied to an ion-exchange type water treatment device to be used as a makeup water for fuel reforming, wherein the water in the air off-gas is condensed at a stage subsequent to a heat exchanger that condenses the water in the combustion exhaust gas. A heat exchanger is provided in series, and condensed water from the flue gas is passed along the air-off gas side heat exchange surface of the heat exchanger disposed in the latter stage, and the condensed water is cooled by the air having a low carbon dioxide gas concentration. It is to be brought into countercurrent contact with off-gas to generate recovered water with reduced carbon dioxide gas concentration.

A heat exchanger on the flue gas side and a heat exchanger on the air offgas side are housed in a single moisture recovery tower as a direct heat exchanger, and the recovered water is used as cooling water for the combustion exhaust gas and the air offgas. It should be in countercurrent contact.

Further, the heat exchanger on the flue gas side and the heat exchanger on the air off-gas side are housed in separately formed water recovery towers using the respective recovered water as cooling water. It is assumed that the recovered water collected by the vessel is passed through the heat exchanger on the air off-gas side to make countercurrent contact with the air off-gas.

[0009]

In the structure of the present invention, a heat exchanger for condensing moisture in the air off-gas is provided in a subsequent stage of a heat exchanger for condensing moisture in the flue gas, and condensed water from the flue gas is provided in a subsequent stage. Water was passed along the air-off gas side heat exchange surface of the arranged heat exchanger, and condensed water was configured to be brought into countercurrent contact with the air-off gas having a low carbon dioxide concentration, so that the condensed water was condensed in the heat exchanger at the preceding stage. In this state, the condensed water, which had been in contact with the combustion exhaust gas and had retained a high amount of dissolved carbon dioxide, spread widely on the heat exchange surface of the subsequent heat exchanger and was brought into countercurrent contact with the air off-gas. The amount is reduced to a low saturation solubility in proportion to the concentration of carbon dioxide in the air offgas, and mixed with the condensed water of the water in the air offgas condensed in the subsequent heat exchanger to produce recovered water with little carbon dioxide. Collection Ability to extend to obtain a regeneration cycle of the ion exchange resin to purify. Also, if the cooling water temperature of the two heat exchangers is configured to be higher in the subsequent stage,
By utilizing the property of water in which the saturation solubility of carbon dioxide gas decreases in inverse proportion to the temperature, it is possible to generate recovered water having a smaller carbon dioxide gas amount.

Further, the heat exchanger on the flue gas side and the heat exchanger on the air offgas side are housed in a single moisture recovery tower as a direct heat exchanger, and the recovered water is used as cooling water for the combustion exhaust gas and the air offgas. If it is configured to make countercurrent contact, the recovered water whose temperature has risen in the heat exchanger on the combustion exhaust gas side in the preceding stage will come in countercurrent contact with the air off-gas in the heat exchanger in the subsequent stage to release dissolved carbon dioxide gas, which is simplified. The recovered water with a small amount of dissolved carbon dioxide can be efficiently generated by the supplementary water recovery device.

Further, the heat exchanger on the combustion exhaust gas side and the heat exchanger on the air off-gas side are housed in separately formed water recovery towers using the respective recovered water as a cooling medium, and the heat exchanger on the combustion exhaust gas side is provided. If the recovered water collected in step (1) is passed through the heat exchanger on the air off-gas side and is brought into countercurrent contact with the air off-gas, mixing of both exhaust gases is completely avoided, and recovered water with a smaller dissolved carbon dioxide gas amount can be obtained. It can be generated at the bottom of the flue gas side moisture recovery tower.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 is a cross-sectional view schematically showing a make-up water recovery device for a fuel cell power generation device according to an embodiment of the present invention. Omitted. In the figure, a makeup water recovery device 13 is composed of a water recovery tower 14 and a plate-type indirect heat exchanger 15 housed therein and cooled by cooling water 19. The water recovery tower 14 has an inlet 16 for the combustion exhaust gas 2G at an intermediate position in the height direction, an inlet 17 for the air off-gas 1A below it, and outlets 18 for both exhaust gases at the upper part thereof. The half functions mainly as a first-stage heat exchanger 15A for collecting moisture in the flue gas 2G as condensed water 2W, and the lower half functions as a second-stage heat exchanger 15B for collecting water in the air off-gas 1A as condensed water 1W. I do. Further, a recovery water reservoir 20 is provided at the bottom of the water recovery tower 14, and a predetermined amount of recovered water 6A in which condensed water 2W and 1A are mixed is stored, and the collected water 6A is supplied to an ion-exchange type water treatment apparatus 8 (see FIG. 4) by a pump 7A. Supply recovered water 6A.

In the make-up water recovery device 13 described above, the condensed water 2W of the moisture (combustion water) in the combustion exhaust gas condensed in the heat exchanger 15A at the preceding stage is directed to a mixed gas of the combustion exhaust gas 2G and the air off-gas 1A. Although the mixed gas contains dissolved carbon dioxide gas in proportion to the concentration of carbon dioxide gas in the mixed gas, the mixed gas is brought into countercurrent contact with the air offgas 1A having a low carbon dioxide gas concentration in the heat exchanger 15B at the subsequent stage, so that the dissolved carbon dioxide is removed. Most of the gas is discharged to the air off-gas side to reduce the dissolved carbon dioxide gas amount, and is mixed with 1 W of condensed water from the air off-gas having a low dissolved carbon dioxide gas amount and collected in the collection water reservoir 20. Further, if the cooling water 19 is configured to flow from the heat exchanger 15A in the preceding stage to the heat exchanger 15B in the subsequent stage, the temperature of the cooling water 19 rises by performing heat exchange in the heat exchanger 15A. Then, since the heat exchange temperature of the heat exchanger 15B at the subsequent stage rises, it is possible to obtain recovered water having a smaller dissolved carbon dioxide amount by utilizing the property of water in which the dissolved carbon dioxide amount is reduced in inverse proportion to the temperature. it can.

FIG. 2 is a sectional view of a makeup water recovery apparatus schematically showing a different embodiment of the present invention.
The former heat exchanger 25A and the latter heat exchanger 25B housed in the tank are both configured as direct contact heat exchangers made of Raschig rings, and the recovered water 6B collected in the collected water reservoir 20 is circulated by a circulation pump. 22 to liquid-to-liquid cooler 2
1 in that the cooling water 26 is sprayed from above the heat exchanger 25A in the preceding stage to the heat exchanger 25B in the lower stage as cooling water 26. In the makeup water recovery device 23 configured as described above, the cooling water 26 sprayed in the heat exchangers of the first and second stages come into direct contact with the exhaust gas 2G and 1A to efficiently condense the moisture in the exhaust gas, and Since the dissolved carbon dioxide in the condensed water is released into the air off-gas 1A having a low carbon dioxide concentration, the exhaust gas and the cooling water 2 are discharged.
By determining the respective flow rates so as to make good contact with the collecting water 6, the effect of further reducing the amount of dissolved carbon dioxide in the recovered water 6B recovered in the recovered water reservoir 20 is obtained. Also, 2
Since the stages of the heat exchangers 25A and 25B are of direct contact type, the structure of the heat exchanger can be simplified, and high heat transfer efficiency can be obtained by performing heat exchange to the outside by the liquid-to-liquid cooler 21. The small and simple make-up water recovery device 23 with high thermal efficiency makes it possible to obtain the recovered water 6B with a small amount of dissolved carbon dioxide gas.

FIG. 3 is a cross-sectional view of a makeup water recovery apparatus schematically showing another embodiment of the present invention, in which the direct contact heat exchangers 25A and 25B are separately provided with a separate water recovery tower 34.
A and 34B, and make-up water recovery devices are separately formed on the flue gas 2G side and the air off-gas 1A side, and the recovered waters 6C and 6D are respectively transferred to the indirect heat exchangers 21A and 21A.
B, and is sprayed as cooling water 26 and 36 to the heat exchangers 25A and 25B to condense the water. At the same time, the recovered water (combustion water) 6C on the water recovery tower 34A side is supplied to the water tank 39 and the pump 32C. Moisture recovery tower 3
This embodiment differs from the above embodiments in that it is mixed with the cooling water 36 on the 4B side and used as cooling water for the heat exchanger 25B on the air off-gas side.

In this embodiment, a water recovery tower 34A on the flue gas side and a water recovery tower 34B on the air off-gas side are used.
Is formed separately, the mixing of the exhaust gas can be avoided, and the carbon dioxide concentration of the air offgas 1A in the air offgas side moisture recovery tower can be maintained at the original low concentration.
The recovered water 6C having a large amount of dissolved carbon dioxide on the A side is mixed with the cooling water 36 to raise the temperature of the cooling water 36 somewhat, and the heat exchanger 25B
The dissolved carbon dioxide gas is efficiently discharged to the air off-gas side, and the recovered water 6D having a low dissolved carbon dioxide amount equilibrated with the carbon dioxide concentration of the air off-gas 1A can be recovered at the bottom of the water recovery tower 34B. Further, by repeatedly circulating the collected water 6D as the cooling water 36, the collected water 6D
Since the amount of dissolved carbon dioxide gas therein can be further reduced, the load on the ion exchange resin can be further reduced, and the regeneration cycle of the ion exchange resin can be extended.

[0017]

According to the present invention, as described above, a heat exchanger for condensing moisture in the air off-gas is provided at the subsequent stage of the heat exchanger for condensing moisture in the flue gas, and condensed water from the flue gas is provided. Was passed along the heat exchange surface on the air-off gas side of the heat exchanger disposed in the subsequent stage, so that the condensed water was brought into countercurrent contact with the air-off gas having a low carbon dioxide gas concentration. As a result, the condensed water of the flue gas in the flue gas, which had maintained high saturation solubility in contact with the flue gas when condensed in the first heat exchanger, spread widely on the heat exchange surface of the second heat exchanger and became air. The countercurrent contact with the offgas reduces the amount of dissolved carbon dioxide to a low saturation solubility that is proportional to the concentration of carbon dioxide in the air offgas, and mixes with the condensed water in the air offgas condensed in the subsequent heat exchanger. Since the recovered water with a small amount of dissolved carbon dioxide gas is generated, it is possible to extend the regeneration cycle of the ion-exchange resin, which has been a problem with conventional make-up water recovery systems that use the water in the combustion exhaust gas as recovered water. In addition, it is possible to provide a fuel cell power generator equipped with a make-up water recovery device having a large effect of reducing the working cost required for the regeneration treatment and maintenance work of the ion exchange resin.
In addition, if the cooling water temperature of the two heat exchangers is configured to be higher in the subsequent stage, the amount of carbon dioxide gas is smaller by utilizing the property of water in which the saturation solubility of carbon dioxide becomes smaller in inverse proportion to the temperature. The advantage that recovered water can be generated is obtained.

Further, the heat exchanger on the flue gas side and the heat exchanger on the air off-gas side are housed in a single moisture recovery tower as a direct contact heat exchanger, and the recovered recovered water is used as a cooling medium for the flue gas and air off-gas. In this case, the recovered water whose temperature has increased in the heat exchanger on the combustion exhaust gas side in the preceding stage comes into countercurrent contact with the air off-gas in the heat exchanger in the subsequent stage to release dissolved carbon dioxide gas. Recovered water with a small amount of gas can be obtained, and the heat exchanger can be housed in one water recovery tower as a direct contact type with a simple structure, and the heat transfer efficiency can be increased by cooling the cooling water as a liquid-liquid cooler. Therefore, it is possible to provide a fuel cell power generation device capable of efficiently recovering recovered water having a small amount of dissolved carbon dioxide gas with a simplified makeup water recovery device.

Further, the heat exchanger on the flue gas side and the heat exchanger on the air off-gas side are housed in separately formed water recovery towers using respective recovered water as a cooling medium, and the heat exchanger on the flue gas side is disposed. If the recovered water collected in step (1) is passed through the heat exchanger on the air off-gas side and is brought into countercurrent contact with the air off-gas, mixing of both exhaust gases is completely avoided, and recovered water with a smaller dissolved carbon dioxide gas amount can be obtained. It is possible to provide a make-up water recovery device that can be generated at the bottom of the combustion exhaust gas side water recovery tower, so that the regeneration cycle of the ion exchange resin can be made longer, and the long-term continuous operation of the fuel cell power generation device can be maintained at a low working cost. Benefits are obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a makeup water recovery device of a fuel cell power generation device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a makeup water recovery apparatus schematically illustrating another embodiment of the present invention.

FIG. 3 is a cross-sectional view of a makeup water recovery apparatus schematically illustrating another embodiment of the present invention.

FIG. 4 is a configuration diagram showing a conventional make-up water recovery and treatment system in a fuel cell power generator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Phosphoric acid type fuel cell 1A Air off gas 1W Condensed water (moisture in air off gas) 2 Fuel reformer 2G Combustion exhaust gas 2W Condensed water (moisture in combustion exhaust gas) 3 Conventional make-up water recovery device 4 Water recovery tower 5 Heat exchanger 6 Recovered water 8 Ion-exchange type water treatment device 10 Make-up water 13 Make-up water recovery device 14 Moisture recovery tower 15 Indirect heat exchanger 15A Heat exchanger at front stage (combustion exhaust gas side) 15B Heat exchanger at rear stage (air off-gas side) Reference Signs List 20 Collected water reservoir 6A Collected water 21 Liquid-to-liquid cooler 23 Make-up water collecting device 25A Direct contact heat exchanger in front stage 25B Direct contact heat exchanger in rear stage 6B Collected water 26 Cooling water 34A Water recovery tower (combustion exhaust gas side) 34B Moisture recovery tower (air off-gas side) 6C Recovered water (combustion water) 6D Recovered water (low dissolved carbon dioxide gas)

──────────────────────────────────────────────────の Continuing on the front page (72) Kunihiro Nishizaki, Inventor 2-11-2 Kajigaya, Takatsu-ku, Kawasaki-shi, Kanagawa (72) Nobuhiro Iwasa 910-55, Katsuragi-cho, Kishiwada-shi, Osaka (72) Inventor Hiromasa Yoshida Aichi 1-9-6, Oshikiri, Nishi-ku, Nagoya, Japan (72) Inventor Tadashi Komatsu 1-1, Tanabe-Shinda, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (56) References JP-A-61-39371 (JP, A) JP-A-4-370665 (JP, A) JP-A-4-370666 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 8/00-8/24

Claims (3)

(57) [Claims] 1. An air off-gas discharged from a fuel cell,
The water contained in the flue gas and the flue gas discharged from the fuel reformer is recovered, and the recovered water is supplied to an ion-exchange type water treatment device to make up water for fuel reforming. A heat exchanger for condensing moisture in the air off-gas is provided in a subsequent stage of the heat exchanger for condensing water, and an air-off gas side heat exchange surface of a heat exchanger provided in the latter stage for condensed water from combustion exhaust gas. Wherein the condensed water is brought into countercurrent contact with the air off-gas having a low carbon dioxide gas concentration to generate recovered water having a reduced carbon dioxide gas concentration. 2. A heat exchanger on the flue gas side and a heat exchanger on the air offgas side are housed in one moisture recovery tower as a direct heat exchanger, and the recovered water is used as cooling water to convert the flue gas and air offgas. 2. The make-up water recovery device for a fuel cell power generator according to claim 1, wherein the make-up water recovery device is configured to make countercurrent contact in order. 3. A heat exchanger on the flue gas side and a heat exchanger on the air offgas side are housed in separately formed water recovery towers using the respective recovered water as cooling water, and heat exchange on the flue gas side is performed. 3. The replenishing water recovery device for a fuel cell power generator according to claim 2, wherein the recovered water recovered by the device flows through the heat exchanger on the air off gas side to make a counter current contact with the air off gas.