JPH08321316A - Fuel cell generator - Google Patents

Abstract

PURPOSE: To prevent moisture contained in fuel off gas from condensing in a gas pipe, in mixture condition with fuel gas being supplied anew, aiming at a fuel cell generator of such system that the fuel off gas discharged from the fuel cell is recycled and mixed in fuel gas prior to supply. CONSTITUTION: This is a fuel cell generator which recycles the fuel off gas of a fuel cell 1 and mixes it with the fuel gas supplied through a fuel gas supply circuit 2a by an ejector pump 5 and sends it into the fuel electrode 1a of the fuel cell. A recycle circuit 2b of fuel off gas being piped on the gas outlet side of a fuel cell is provided with a moisture separator 11 which condenses and removes the steam contained in the gas by cooling the off gas by the exchange with cooling water, as a dehumidifying means which removes the moisture (produced water accompanying battery reaction) contained in off gas. And, the flow and pressure of the fuel gas to be supplied to the fuel cell are stabilized by preventing condensed water from staying within the pipe of the mixture gas circuit 2c within an ejector pump during operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power generation system for recycling fuel off-gas discharged from a fuel cell, mixing the fuel gas newly supplied from the outside with the fuel off-gas and supplying the mixed fuel gas to the fuel electrode of the fuel cell. Regarding the device.

[0002]

2. Description of the Related Art Recently, development of an on-site fuel cell power generator which utilizes by-product hydrogen obtained in a synthetic chemical factory as a raw fuel of a fuel cell has been advanced. Further, in this fuel cell power generation device, the fuel off gas discharged from the fuel cell is recycled, and the fuel gas (site by-product hydrogen) newly supplied from the outside is mixed with the fuel off gas to form a fuel electrode for the fuel cell. Is known to reduce the consumption of raw fuel and improve the hydrogen utilization rate in the fuel cell.

FIG. 5 is a process flow diagram of a conventional fuel cell power generator which employs the above-mentioned fuel off-gas recycling system. In the figure, 1 is a fuel electrode 1a and an air electrode 1
b, a fuel cell (phosphoric acid type fuel cell) schematically showing the cooling plate 1c, 2 a fuel gas supply system, 3 a reaction air supply system,
4 is a cooling water circulation system. Here, the fuel gas supply system 2 includes a fuel gas supply circuit 2a and a fuel off gas recycle circuit 2
The ejector pump 5, which operates using the fuel gas as a driving gas, is connected to a point where the fuel gas and the fuel off-gas merge. Further, the cooling water circulation system 3 is provided with a steam separator 4a, and the steam separated by the steam separator 4a is supplied to the exhaust heat utilization equipment 6 such as a heater to utilize the exhaust heat. In addition, 7 is an air blower provided in the air supply system 3, 8 is a cooling water circulation pump of the cooling water circulation system 4, 9 is a water supply pump of the waste heat utilization facility 6, and 10 is a pressure control valve.

With this structure, fuel gas (by-product hydrogen) and air are supplied to the fuel electrode 1a and the air electrode 1b of the fuel cell 1 to generate electricity by the electrochemical reaction. In addition, heat generated by the fuel cell 1 due to power generation is removed by flowing cooling water through the cooling plate 1c to maintain the operating temperature of the cell body constant (about 180 ° C.) and recover the exhaust heat from the steam separator 4a. The waste heat utilization equipment 6 is effectively utilized.

The unreacted fuel off-gas discharged from the fuel electrode 1a of the fuel cell 1 is sucked into the ejector pump 5 through the recycle circuit 2b, mixed with the fuel gas newly supplied from the outside, and then mixed gas circuit 2c. To be supplied to the fuel electrode 1a of the fuel cell 1 through. As a result, it is possible to reduce the consumption rate of the fuel gas newly supplied from the outside and reduce the hydrogen utilization rate in the fuel cell 1 to improve the power generation efficiency.

[0006]

By the way, in the fuel cell power generator adopting the recycling system in which the fuel off gas is mixed with the newly supplied low temperature fuel gas and is supplied to the fuel cell as described above, Such problems arise. That is, in the fuel cell 1, as is well known, water is produced in association with an electrochemical reaction between hydrogen and oxygen, and this reaction-produced water is discharged from the fuel cell in the form of water vapor along with fuel off-gas and exhaust air. It Therefore, the high-temperature fuel off-gas flowing in the off-gas recycling circuit 2b contains the above-mentioned reaction-produced water in a substantially saturated vapor state. On the other hand, the fuel gas newly supplied from the outside through the fuel gas supply circuit 2b is, for example, a low temperature gas close to room temperature. Therefore, when the fuel off gas and the fuel gas are mixed by the ejector pump 5, the temperature of the fuel off gas decreases. ,
The water vapor contained in this off-gas is condensed inside the ejector pump 5 and in the mixed gas circuit 2c to become a liquid.

Moreover, when the gas is supplied to the fuel cell in such a state, the condensed water accumulates everywhere in the gas pipe and hinders the flow of the fuel gas. For this reason, the flow rate and pressure of the fuel gas sent to the fuel cell fluctuates, and stable power generation cannot be performed. Further, the pulsating changes in the gas flow rate and pressure receive mechanical stress on the fuel cell main body, and even intermittent A gas shortage occurs, the electrode catalyst is deteriorated, and the life of the fuel cell is shortened.

The present invention has been conceived in view of the above points, and an object thereof is to solve the above-mentioned problems and to introduce water contained in fuel off-gas into a gas pipeline in a mixed state with fuel gas newly supplied. It is an object of the present invention to provide a fuel cell power generation device capable of preventing condensation and avoiding an adverse effect on the fuel cell due to condensed water accumulated in the gas pipeline.

[0009]

The above object can be achieved by the present invention by constructing a fuel cell power generator as follows. 1) The first invention: a fuel cell power generator that recycles fuel off-gas discharged from a fuel cell, mixes fuel gas newly supplied from the outside with fuel off-gas, and supplies the mixed fuel gas to a fuel electrode of a fuel cell. A dehumidifying means for removing water contained in the offgas is provided in the fuel offgas recycling circuit which is provided between the gas outlet side of the battery and the gas mixing point.

The dehumidifying means is specifically constituted as a steam separator for cooling by heat exchange with cooling water to condense and remove water vapor in the fuel off-gas, and such steam separator is also used. Is a combination of a steam separation chamber and a heating chamber that heats the low-temperature fuel off-gas passing through the steam-separation chamber with the high-temperature fuel off-gas before being introduced into the steam-water separation chamber to raise the temperature. It can also be implemented.

2) Second invention: A fuel cell power generator which recycles the fuel off-gas discharged from the fuel cell, mixes the fuel gas newly supplied from the outside with the fuel off-gas, and supplies the mixed fuel gas to the fuel electrode of the fuel cell. At, in at least one of the fuel off-gas recycling circuit, the fuel gas supply circuit, and the downstream mixed gas circuit upstream of the gas mixing point, the water contained in the fuel off-gas condenses in the mixed gas. A gas heating means for preventing the above is provided.

Further, the above-mentioned gas heating means is a heat exchange provided in the gas pipeline using the cooling water extracted from the water cooling system of the fuel cell main body or the steam extracted from the steam separator in the water cooling system as a heat medium. Or a high-temperature fuel off-gas discharged from the fuel cell can be used as a heat medium in a heat exchanger provided in the gas pipeline. Further, the dehumidifying means according to the first aspect of the invention and the gas heating means according to the second aspect of the invention may be provided together with the fuel gas supply system including the fuel off-gas recycling circuit.

[0013]

According to the first invention described above, the fuel off-gas discharged from the fuel cell is dehumidified by the steam separator which is a dehumidifying means in the process of flowing through the recycle circuit, and the liquid component condensed and separated from the off-gas is drained. As a result, it is discharged from the steam separator to the outside of the system. Therefore, since the off-gas is mixed with the fuel gas newly supplied from the outside in a state where the absolute humidity is lowered and contains almost no water, the inside of the ejector pump provided at the gas confluence point and the subsequent mixing. The formation of condensed water in the gas line of the gas circuit can be prevented. In this case, the gas after dehumidification in the steam separation chamber of the steam separator is heated by heat exchange with high-temperature off-gas in the next heating chamber, whereby the relative humidity of the off-gas decreases, so the low-temperature fuel Even in a state of being mixed with the gas, the water remaining in the gas becomes more difficult to condense.

According to the second invention, the fuel off gas, the fuel gas flowing through the fuel gas supply system, or the mixed gas of the fuel off gas and the fuel gas is heated and heated by the gas heating means. Even in the state where the fuel off gas containing water and the fuel gas to be newly supplied are mixed, the mixed gas is kept at a high temperature and the wetness thereof does not exceed the saturated liquid line. As a result, it is possible to prevent the water contained in the fuel off gas from condensing in the mixed gas circuit to generate condensed water. In this case, by using cooling water of the fuel cell, excess steam, or high-temperature off-gas as the heat medium of the gas heating means, the heat required for heating the gas can be provided in the system of the fuel cell power generator.

In addition, the combined use of the off-gas dehumidifying means and the gas heating means further enhances the effect of preventing the generation of condensed water.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings of the respective embodiments, the same members corresponding to those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. Embodiment 1 FIG. 1 shows a first embodiment corresponding to claims 1 and 2 of the present invention.
5 shows an embodiment of the invention of FIG. 5, and in comparison with the configuration of FIG. 5, a fuel-off gas circuit 2b is additionally equipped with a steam separator 11 as a dehumidifying means. This steam separator 1
Reference numeral 1 includes a cooling coil 11a, which cools fuel-off gas discharged from the fuel cell 1 by heat exchange with cooling water flowing from the outside to the cooling coil 11a, and condenses and separates water contained in the gas. It functions as a drain to drain the water outside the system.

With this structure, most of the water contained in the fuel off-gas (water vapor generated by the cell reaction of the fuel cell 1) is removed, and the absolute humidity of the off-gas itself decreases. As a result, even when the low-temperature fuel gas supplied from the outside to the fuel gas supply circuit 2a and the fuel off gas are mixed via the ejector pump 5, the inside of the ejector pump 5 and the mixed gas circuit 2c following the ejector pump 5 Thus, the fuel cell 1 can be operated in a state in which condensed water is hardly generated. As a result, condensed water does not accumulate in the gas pipe, and it is possible to avoid adverse effects such as unstable flow rate and pressure of the fuel gas supplied to the fuel cell 1 due to the generation of the condensed water.

Second Embodiment: FIG. 2 shows an application example of the first embodiment corresponding to claim 3 of the present invention. In this embodiment, the steam separator 11 is the cooling coil 11
The gas-water separation chamber 11b is a combination of a gas-water separation chamber 11b containing a and a heating chamber 11d containing a heating coil 11c for flowing the high-temperature off-gas discharged from the fuel cell 1.
The low-temperature fuel off-gas, which has been separated into steam and water by passing through the chamber, heat-exchanges with the high-temperature fuel-off gas before being introduced into the steam-separation chamber in the process of flowing through the next heating chamber 11d to raise the temperature. Has been done.

With this structure, the fuel off gas discharged from the fuel cell 1 is separated into the steam separation chamber 11b of the steam separator 11.
After being cooled and dehumidified in, the temperature is raised again by exchanging heat with high-temperature off-gas in the next heating chamber 11d. Therefore, the relative humidity of the off-gas that has left the steam separator 11 is further lowered, which further enhances the effect of preventing the condensed water generated when the off-gas is mixed with the fuel gas.

Embodiment 3 FIG. 3 shows an embodiment of the second invention corresponding to claims 4 and 5 of the present invention.
Compared with the configuration described above, the mixed gas circuit 2c of the fuel gas supply system 2
In addition, a gas heater 12 that functions as a heat exchanger is newly added. In this gas heater 12, the steam extracted from the steam separator 4a provided in the cooling water circulation system 4 of the fuel cell 1 flows as a heat medium to the heating coil 12a wound around the pipe of the mixed gas circuit 2c as a steam trace. I am trying.

With such a configuration, when the fuel cell 1 is in operation, the steam separator 4a has a temperature of 165 ° C. and a pressure of 6
Water and water vapor are stored at about Kg / cm ² , and the fuel mixture flowing through the gas mixture circuit 2c is exchanged by heat exchange with water vapor extracted from this and supplied to the heating coil 12a of the gas heater 12. The gas is heated and heated. As a result, the relative humidity of the mixed gas is lowered, and even after the fuel off gas containing water and the fuel gas supplied through the fuel gas supply circuit 2a are mixed by the ejector pump 5, the water contained in the mixed gas is condensed. Is less likely to occur, the above-mentioned Example 1
An effect equivalent to is obtained.

Although FIG. 3 shows an example in which the gas heater 12 is installed in the mixed gas circuit 2c, a fuel gas supply circuit 2a or a fuel off gas recycling circuit 2b may also be used.
The same effect can be obtained by providing the above. Also, the gas heater 12
As the heat medium flowing through the heating coil 12a, the high temperature side cooling water extracted from the cooling water circulation system 4 of the fuel cell 1 in place of the steam extracted from the steam separator 4a (water temperature of about 170
Alternatively, it is possible to use blowdown water extracted from the steam separator 4a. Further, the steam-water separator 11 described in the first embodiment can be used together with the Hi-gas heater 12 in the recycle circuit 2b.

Embodiment 4 FIG. 4 shows an application embodiment of the second invention corresponding to claim 6 of the present invention. In this embodiment, the gas provided in the pipeline of the mixed gas circuit 2c is shown. The high-temperature fuel off-gas discharged from the fuel cell 1 is caused to flow through the heater 12, and the mixed gas is heated and heated by heat exchange with the off-gas to prevent condensation of water.

Although each of the illustrated embodiments shows a fuel cell power generator in which by-product hydrogen obtained from a site such as a chemical factory is directly supplied as a raw fuel to a fuel cell, natural gas or the like is used. As a raw fuel, it is needless to say that the raw fuel can be applied to a fuel cell power generation device which is reformed into a hydrogen-rich gas in a fuel reforming system and supplied to a fuel cell. Then, in this case, a part of the fuel off-gas discharged from the fuel cell is supplied to the burner of the fuel reformer and consumed,
The rest is recycled and merged with the reformed gas to be supplied to the fuel cell.

[0025]

As described above, according to the present invention, when the fuel off gas discharged from the fuel cell is recycled and mixed with the fuel gas newly supplied from the outside, the dehumidifying means provided in the fuel off gas circuit. , Or by the action of the gas heating means provided in the gas circuit of the fuel gas supply system, the water contained in the fuel off-gas (water generated by the cell reaction) is provided inside the ejector pump at the gas confluence point,
It is possible to prevent condensation in the pipeline of the mixed gas circuit that follows or to prevent the condensed water from accumulating in the gas pipeline of the fuel supply system and obstructing the flow of the fuel gas, and supplying the fuel to the fuel cell. Power generation operation can be performed with the gas flow rate and pressure kept stable.

[Brief description of drawings]

FIG. 1 is a system flow diagram of a fuel cell power generation device corresponding to a first embodiment of the present invention.

FIG. 2 is a steam-water separator corresponding to Embodiment 2 of the present invention, and a peripheral circuit diagram thereof.

FIG. 3 is a system flow diagram of a fuel cell power generator corresponding to Example 3 of the present invention.

FIG. 4 is a system flow diagram of a fuel cell power generator corresponding to Example 4 of the present invention.

FIG. 5 is a system flow diagram of a conventional fuel cell power generator.

[Explanation of reference numerals] 1 fuel cell 1a fuel electrode 1b air electrode 1c cooling plate 2 fuel gas supply system 2a fuel gas supply circuit 2b fuel off-gas recycling circuit 2c mixed gas circuit 3 reaction air supply system 4 cooling water circulation system 4a steam separator 5 Ejector pump 11 Air-water separator (dehumidifying means) 11b Air-water separating chamber 11d Heating chamber 12 Gas heater (gas heating means)

Claims (7)

[Claims] 1. A fuel cell power generator that recycles fuel off-gas discharged from a fuel cell, mixes the fuel gas newly supplied from the outside with the fuel off-gas and supplies the mixed fuel gas to a fuel electrode of the fuel cell. A fuel cell power generator comprising a dehumidifying means for removing water contained in the offgas in a fuel offgas recycling circuit provided between the gas outlet and the gas mixing point. 2. The fuel cell power generator according to claim 1, wherein the dehumidifying means is a steam separator that cools by heat exchange with cooling water to condense and remove water vapor in the fuel off gas. Fuel cell power generator. 3. The fuel cell power generator according to claim 2, wherein the steam-water separator has a steam-water separation chamber and a high temperature before the low-temperature fuel off-gas passing through the steam-water separation chamber is introduced into the steam-water separation chamber. A fuel cell power generator comprising a combination of a heating chamber for exchanging heat with various fuel off-gas to raise the temperature. 4. A fuel cell power generator that recycles fuel off-gas discharged from a fuel cell, mixes fuel off-gas newly supplied from the outside with fuel off-gas, and supplies the mixed fuel gas to a fuel electrode of a fuel cell. Gas that prevents water contained in the fuel off gas from condensing in the mixed gas in at least one of the fuel off gas recycling circuit on the upstream side, the fuel gas supply circuit, or the mixed gas circuit on the downstream side. A fuel cell power generator comprising a heating means. 5. The fuel cell power generator according to claim 4, wherein the gas heating means heats the cooling water extracted from the water cooling system of the fuel cell main body or the steam extracted from the steam separator in the water cooling system. A fuel cell power generation device, comprising: 6. The fuel cell power generator according to claim 4, wherein the gas heating means is a heat exchanger using a high temperature fuel off-gas discharged from the fuel cell as a heat medium. 7. A fuel cell power generator comprising a dehumidifying means according to claim 1 and a gas heating means according to claim 4, which are provided together with a fuel gas supply system including a fuel off-gas recycling circuit.