JP7790224B2 - fuel cell module - Google Patents

Description

This disclosure relates to a fuel cell module.

Conventionally, fuel cell modules have been proposed that include a fuel cell that generates electricity from anode gas and cathode gas, a vaporization section (evaporator) that vaporizes reforming water supplied from a reforming water supply pipe to generate steam, and a reforming section that steam-reforms reforming material supplied from a raw material supply pipe to generate anode gas. For example, Patent Document 1 discloses a fuel cell module in which the vaporization section and reforming section are housed in a housing and communicate with each other, with the reforming material supply pipe and reforming water supply pipe arranged in a double-pipe structure at one end of the housing.

Patent No. 6477085

In the fuel cell module described above, if more water vapor than expected is generated in the vaporization section, the pressure on the supply side of the reforming section may rise, making it impossible to supply sufficient raw reforming material from the raw reforming material supply pipe. This may result in a shortage of anode gas being supplied to the fuel cell, which may have a negative impact on the fuel cell module.

The primary objective of this disclosure is to mitigate excessive pressure increases that occur when reforming water vaporizes, thereby stabilizing the gas flow rate.

This disclosure takes the following measures to achieve the above-mentioned primary objective:

The fuel cell module of the present disclosure comprises:
a fuel cell that generates electricity based on the anode gas and the cathode gas;
a vaporization section that introduces reforming water to generate steam;
a reforming section that introduces the raw fuel gas and the steam derived from the vaporizing section and generates the anode gas by steam reforming;
a combustion unit that heats the vaporization unit and the reforming unit with combustion heat;
Equipped with
The vaporization section has a double-pipe structure in which a reforming water inlet pipe for introducing reforming water is an inner pipe, and a steam outlet pipe for guiding steam is an outer pipe.

In the fuel cell module disclosed herein, the vaporization unit has a double-pipe structure, with a reforming water inlet pipe serving as the inner pipe for introducing reforming water and a steam outlet pipe serving as the outer pipe for discharging steam. This allows the steam to be discharged through an annular gap (steam outlet pipe) on the outside of the double-pipe structure, thereby increasing pressure loss. As a result, even if more steam than expected is generated in the vaporization unit, the amount of steam discharged through the steam outlet pipe can be reduced, thereby mitigating excessive pressure increases on the introduction side of the raw fuel gas to the reforming unit. This allows the raw fuel gas and steam to be stably introduced into the reforming unit, stabilizing the anode gas flow rate.

The fuel cell module of the present disclosure may include a cylindrical section that forms a cylindrical closed space to accommodate the vaporization section and the reforming section, and the vaporization section may have a double-pipe structure in which the reforming water inlet pipe penetrates one end wall of the cylindrical section and the steam outlet pipe opens just before the end wall. The cylindrical section may be provided with a raw fuel gas inlet pipe that penetrates the end wall and introduces raw fuel gas, and may have a mixing space formed in which the steam discharged from the steam outlet pipe and the raw fuel gas introduced from the raw fuel gas inlet pipe are mixed and introduced to the reforming section. This allows the steam and raw fuel gas to be appropriately mixed before being introduced to the reforming section, thereby more stabilizing the anode gas flow rate.

In the fuel cell module of the present disclosure, the combustion section may include a combustion device that ignites and burns offgas introduced from the fuel cell, and the tubular section may be formed to surround the combustion section across a predetermined gap, with the combustion device located on the opposite side of the one end wall, the vaporization section disposed inside the combustion section, and the reforming section disposed in the predetermined gap. This allows for a compact configuration in which the vaporization section, reforming section, and combustion section are housed within the tubular section.

1 is a schematic diagram of a fuel cell module 10. FIG. FIG. 2 is a schematic diagram of a reforming unit 20. 3 is a cross-sectional view taken along line AA in FIG. 2. 3 is a cross-sectional view taken along the line B-B in FIG. 2.

Next, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a schematic diagram of a fuel cell module 10. As shown in FIG. 1, the fuel cell module 10 of this embodiment includes a fuel cell stack 11 that generates electricity through an electrochemical reaction between hydrogen in the anode gas and oxygen in the cathode gas; a reforming unit 20 that reforms raw fuel gas (e.g., natural gas or LPG) by steam reforming to produce anode gas; first and second heat exchangers 41, 42; and a condenser 50. The fuel cell stack 11, reforming unit 20, and first and second heat exchangers 41, 42 are housed in a thermally insulated, box-shaped module case 12. The fuel cell module 10, together with a raw fuel gas supply device, a reforming water supply device, an air supply device, and a hot water storage tank (not shown), constitute a fuel cell system. The raw fuel gas supply device supplies raw fuel gas to the reforming unit 20 (reforming section 22), the reforming water supply device supplies reforming water required for reforming (steam reforming) raw fuel gas into anode gas to the reforming unit 20 (evaporation section 21), and the air supply device supplies air as cathode gas to the fuel cell stack 11. The hot water storage tank recovers heat generated by the fuel cell module 10 and stores it in water.

The fuel cell stack 11 comprises multiple solid oxide unit cells arranged vertically, each having an electrolyte such as zirconium oxide and an anode electrode and a cathode electrode sandwiching the electrolyte. An anode gas passage is formed within the anode electrode of each unit cell. In addition, a cathode gas passage is formed within the cathode electrode of each unit cell.

As shown in Figures 1 and 2, the reforming unit 20 has a vaporization section 21, a reforming section 22, a combustion section 23, and a pressure equalization section 24 (see Figure 2). As shown in Figure 2, these are covered by an outer tube 25 that is cylindrical and has closed ends at both ends in the axial direction.

The vaporization unit 21 is connected to the reforming water pipe 32 of the reforming water supply device, and reforming water is introduced through the reforming water pipe 32. The vaporization unit 21 heats the introduced reforming water with heat (combustion heat) from the combustion unit 23, evaporating the reforming water to generate steam. The steam generated by the vaporization unit 21 is mixed with the raw fuel gas introduced into the pressure equalization unit 24 in the pressure equalization unit 24, and the mixed gas flows into the reforming unit 22.

The reforming unit 22 has a Ru-based or Ni-based reforming catalyst 221 (see Figure 2) filled therein. In the presence of heat from the combustion unit 23, the reforming catalyst 221 generates hydrogen gas and carbon monoxide through a reaction (steam reforming reaction) of the mixed gas. The reforming unit 22 then generates hydrogen gas and carbon dioxide through a reaction (carbon monoxide shift reaction) between the carbon monoxide generated in the steam reforming reaction and steam. This results in the reforming unit 22 generating anode gas containing hydrogen, carbon monoxide, carbon dioxide, steam, unreformed raw fuel gas, and the like. The anode gas generated by the reforming unit 22 flows through the anode gas piping 33 into the anode gas passage of each unit cell of the fuel cell stack 11 and is supplied to the anode electrode.

Air serving as a cathode gas flows from an air supply device through cathode gas piping 34 into the cathode gas passage of each unit cell of the fuel cell stack 11 and is supplied to the cathode electrode. Oxide ions (O ^2- ) are generated at the cathode electrode of each unit cell, and these oxide ions permeate the electrolyte and react with hydrogen and carbon monoxide at the anode electrode to generate electrical energy. An input terminal of a power conditioner (not shown) is connected to the output terminal of the fuel cell stack 11, and the power generated by the fuel cell stack 11 is converted to AC power by the power conditioner and supplied to an electrical load.

Anode gas (hereinafter referred to as "anode off-gas") not used in the electrochemical reaction (power generation) in each unit cell is temporarily discharged outside the module case 12 through the anode off-gas piping 35 and supplied to a condenser 50 (cooler) installed outside the module case 12. The anode off-gas supplied to the condenser 50 is then cooled by heat exchange with hot water from the hot water storage tank, and the water vapor contained in the anode off-gas is removed. The anode off-gas is then reintroduced into the module case 12 and supplied to the combustion section 23 of the reforming unit 20. The water obtained by condensing the water vapor contained in the anode off-gas is stored in a reforming water tank and used as reforming water.

In addition, cathode gas (hereinafter referred to as "cathode off-gas") that is not used in the electrochemical reaction (power generation) in each unit cell is supplied to the combustion section 23 through the cathode off-gas piping 36.

The anode off-gas that flows into the combustion section 23 is a combustible gas containing fuel components such as hydrogen and carbon monoxide, and is mixed with the oxygen-containing cathode off-gas that flows into the combustion section 23. When the mixed gas (hereinafter referred to as "off-gas") is ignited in the combustion section 23 by a burner device 235 that includes an ignition device, the combustion of the off-gas generates heat necessary for generating steam in the vaporization section 21 and for the steam reforming reaction in the reforming section 22. The combustion section 23 also generates combustion exhaust gas containing unburned fuel, which passes through the combustion exhaust gas piping 37 and the combustion catalyst before being discharged into the outside air. The combustion catalyst is an oxidation catalyst that re-burns the unburned fuel in the combustion exhaust gas.

The first and second heat exchangers 41, 42 are both installed within the module case 12. The first heat exchanger 41 exchanges heat between the anode off-gas flowing upstream of the condenser 50 in the anode off-gas piping 35 and the anode off-gas flowing downstream of the condenser 50 in the anode off-gas piping 35. The second heat exchanger 42 exchanges heat between the combustion exhaust gas flowing through the combustion exhaust gas piping 37 and the cathode gas flowing through the cathode gas piping 34.

As shown in FIG. 2 , in the reforming unit 20, the combustion section 23 has a cylindrical combustion chamber 231 whose both ends in the cylindrical axis direction are closed by end walls 232, 233, and a burner device 235 provided on the inner surface of the end wall 232 of the combustion chamber 231. An anode offgas pipe 35 is connected to the end wall 232 of the combustion chamber 231 so that anode offgas flows into the combustion chamber 231 from inside the burner device 235, and a cathode offgas pipe 36 is connected so that cathode offgas flows into the combustion chamber 231 from outside the burner device 235. Furthermore, a combustion exhaust gas pipe 37 is connected to the end wall 233 of the combustion chamber 231 opposite the end wall 232 so that combustion exhaust gas generated by combustion of the anode offgas and cathode offgas in the combustion chamber 231 flows out of the unit.

The vaporizer 21 is disposed within the combustion chamber 231, adjacent to and at a predetermined distance from the end wall 233 of the combustion chamber 231 opposite the end wall 232 on which the burner device 235 is disposed. A reforming water pipe 32 for introducing reforming water is disposed on the end wall 217 of the vaporizer 21 on the same side as the end wall 233 of the combustion chamber 231. The reforming water pipe 32 extends to the outside through the end wall 254 of the outer pipe 25 and is connected to a reforming water supply device (reforming water pump) not shown. The reforming water pump is configured as, for example, a plunger pump that discharges reforming water by intermittently driving (reciprocating) a plunger using electromagnetic force and spring force, and intermittently discharges reforming water into the reforming water pipe 32.

The interior of the vaporization section 21 is divided into three sections: a drip section 211, a filling section 212, and a buffer section 213, by mesh-like partition members 215, 216, such as punched metal, which have multiple communicating holes (through-holes). Figure 3 is a cross-sectional view taken along line A-A in Figure 2, and Figure 4 is a cross-sectional view taken along line B-B in Figure 2. In this embodiment, the drip section 211 and the filling section 212, which is separated from the drip section 211 by a partition member 215, are provided on the end wall 217 side, and the buffer section 213, which is separated from the drip section 211 and the filling section 212 by a partition member 216, is provided on the end wall 218 side opposite the end wall 217.

The drip section 211 is a space into which the reforming water introduced through the reforming water pipe 32 drips. The filling section 212 is a space filled with, for example, alumina spheres 212a as a spherical heat storage material with high thermal conductivity. The alumina spheres 212a are heated by the heat of combustion generated in the combustion chamber 231. The reforming water that drips into the drip section 211 can flow into the filling section 212 through the communication holes in the partition member 215. The water that flows into the filling section 212 is vaporized while being diffused in the gaps between the filled alumina spheres 212a. The drip section 211 and the buffer section 213 are not filled with alumina spheres 212a. When water accumulates on the bottom surface of the filling section 212, it flows into the buffer section 213 through the holes in the partition member 216 and is vaporized within the buffer section 213. Because the buffer section 213 is located on the end wall 218 side, i.e., the side closer to the burner device 235, it is at a higher temperature than the drip section 211 and the filling section 212. This promotes evaporation of water that flows into the buffer section 213.

The buffer section 213 is a space that is at least larger than the drip section 211 and the filling section 212, and in this embodiment, it is larger than the combined space of the drip section 211 and the filling section 212, for example, it is partitioned to be a space about 10 times the size of the filling section 212. Therefore, in the vaporization section 21, the buffer section 213 can sufficiently absorb the volume expansion that occurs when the reforming water vaporizes into steam. This suppresses fluctuations in the pressure of the steam discharged from the vaporization section 21, allowing the raw fuel gas and steam to be stably introduced into the reforming section 22, thereby stabilizing the gas flow rate of the anode gas.

Furthermore, a steam pipe 214 for discharging vaporized steam is connected to the end wall 217 of the vaporization section 21 on the same side as the end wall 233 of the combustion chamber 231, i.e., to the end walls 217, 233 where the reforming water pipe 32 is arranged. The vaporization section 21 of this embodiment has a double-pipe structure with the reforming water pipe 32 as the inner pipe and the steam pipe 214 as the outer pipe. The reforming water pipe 32 penetrates the end wall 254 of the outer pipe 25 and extends to the outside, but the steam pipe 214 is formed to a length that opens into the pressure equalization section 24 just before the end wall 254 of the outer pipe 25. Therefore, the water vapor vaporized in the filling section 212 or the buffer section 213 is discharged from the drip section 211 through the steam pipe 214 to the pressure equalization section 24 and then supplied to the reforming section 22 via the pressure equalization section 24. Because the steam pipe 214 and the reforming water pipe 32 have a double-pipe structure, the steam is guided through an annular gap to the pressure equalizing section 24. Therefore, even if the steam pipe 214 is formed to be short, the pressure loss can be made relatively large.

The reforming section 22 has a reforming catalyst 221 disposed in a cylindrical space (cylindrical space, predetermined gap) formed between the outer peripheral surface of the side wall (circumferential wall) 234 of the combustion chamber 231 and the inner peripheral surface of the side wall (circumferential wall) 251 of the outer tube 25. Steam and raw fuel gas flow into the reforming section 22 from one end of the cylindrical space in the axial direction, and anode gas generated by steam reforming flows out from the other end in the axial direction. The anode gas flowing out of the reforming section 22 is supplied to the anode electrode of the fuel cell stack 11 through an anode gas pipe 33.

The pressure equalizing section 24 has a space defined by the end wall 233 of the combustion chamber 231 and the end wall 254 of the outer pipe 25. The reforming water pipe 32 and combustion exhaust gas pipe 37 described above are attached to the end wall 254 of the outer pipe 25 so as to penetrate the pressure equalizing section 24, and the raw fuel gas pipe 31 is connected so that the raw fuel gas flows into the pressure equalizing section 24. The space of the pressure equalizing section 24 is also connected to the inside of the vaporization section 21 via the steam pipe 214. As a result, the raw fuel gas and steam flow into the reforming section 22 through the pressure equalizing section 24, and the pressure equalizing section 24 functions as a buffer section, enabling the raw fuel gas and steam to be supplied approximately uniformly in the circumferential direction to the cylindrical space (reforming catalyst 221) of the reforming section 22. Furthermore, due to the double-pipe structure described above, even if more water vapor than expected is generated in the vaporization unit 21, the amount of water vapor led from the vaporization unit 21 to the pressure equalization unit 24 can be reduced, mitigating excessive pressure increases in the pressure equalization unit 24. This prevents the supply of raw fuel gas to the reforming unit 22 from being hindered by pressure increases in the pressure equalization unit 24, and allows the raw fuel gas and water vapor to be appropriately supplied to the reforming unit 22, stabilizing the gas flow rate of the anode gas.

In the fuel cell module 10 of this embodiment described above, the vaporization unit 21 has a double-pipe structure with the reforming water pipe 32 as the inner pipe and the steam pipe 214 as the outer pipe. Steam is discharged through the outer annular gap (steam pipe 214) of the double-pipe structure, thereby increasing pressure loss. Therefore, even if the vaporization unit 21 generates more steam than expected, the amount of steam discharged can be reduced, mitigating excessive pressure buildup on the raw fuel gas introduction side to the reforming unit 22. This allows the raw fuel gas and steam to be stably introduced into the reforming unit 22, stabilizing the anode gas flow rate. This prevents damage to the fuel cell stack 11 due to oxidation and expansion of the anode electrode, which could occur when an insufficient flow of anode gas into the fuel cell stack 11 causes an excess of cathode gas. It also prevents misfires due to an insufficient flow of anode off-gas into the combustion unit 23.

The vaporization section 21 also has a double-pipe structure in which the reforming water pipe 32 penetrates the end wall 254 of the outer pipe 25, and the steam pipe 214 opens just before the end wall 254. The outer pipe 25 is provided with a raw fuel gas pipe 31 that penetrates the end wall 254, and is formed with a pressure equalization section 24 that mixes the steam derived from the steam pipe 214 with the raw fuel gas introduced from the raw fuel gas pipe 31 and introduces the resulting mixture to the reforming section 22. This allows the steam and raw fuel gas to be appropriately mixed before being introduced into the reforming section 22, thereby making it possible to more stabilize the anode gas flow rate.

In addition, the vaporization section 21, reforming section 22, and combustion section 23 can be housed in the outer tube 25, resulting in a compact configuration.

In the above-described embodiment, a single-unit configuration (reforming unit 20) in which the vaporization section 21, reforming section 22, and combustion section 23 are housed in the outer tube 25 is illustrated, but this is not limited to this. For example, the vaporization section 21 and reforming section 22 may be combined into one unit, with the combustion section 23 being separate.

In the above-described embodiment, the vaporizer 21 has the drip section 211 formed separately from the filling section 212 and the buffer section 213, but this is not limited to this, and the drip section 211 may be included in the filling section 212. In other words, the vaporizer 21 only needs to have its interior divided into the filling section 212 and the buffer section 213. Alternatively, the interior of the vaporizer 21 may not be divided into the filling section 212 and the buffer section 213, but may be a single space (filling section 212).

In the above-described embodiment, the vaporization section 21 is arranged inside the combustion section 23 (combustion chamber 231), and the buffer section 213 is on the burner device 235 side, but this is not limited to this. For example, the arrangement direction of the filling section 212 and the buffer section 213 may be perpendicular to the cylindrical axis direction of the outer tube 25, so that only the buffer section 213 is not on the burner device 235 side. Furthermore, the vaporization section 21 may not be arranged inside the combustion section 23 (combustion chamber 231).

In the above-described embodiment, the anode off-gas from the fuel cell stack 11 is supplied to the condenser 50, where the water vapor contained in the anode off-gas is removed, and then the anode off-gas is supplied to the combustion section 23. However, the anode off-gas from the fuel cell stack 11 may also be supplied directly to the combustion section 23. In this case, the combustion exhaust gas generated by combustion of the off-gas in the combustion section 23 is supplied to the condenser, and the water vapor contained in the combustion exhaust gas is condensed.

The correspondence between the main elements of the embodiment and the main elements of the present disclosure listed in the "Means for Solving the Problems" section will be explained below. The fuel cell stack 21 of the embodiment corresponds to the "fuel cell" of the present disclosure, the vaporization section 21 corresponds to the "vaporization section," the reforming section 22 corresponds to the "reforming section," the combustion section 23 corresponds to the "combustion section," the reforming water pipe 32 corresponds to the "reforming water introduction pipe," and the steam pipe 214 corresponds to the "steam discharge pipe." The outer pipe 25 corresponds to the "cylindrical section," the raw fuel gas pipe 31 corresponds to the "raw fuel gas introduction pipe," and the pressure equalization section 24 corresponds to the "mixing space." The burner device 235 corresponds to the "combustion device."

The correspondence between the main elements of the embodiments and the main elements of the invention described in the "Means for Solving the Problem" section does not limit the elements of the invention described in the "Means for Solving the Problem" section, as the embodiments are examples used to specifically explain the form for implementing the invention described in the "Means for Solving the Problem" section. In other words, the interpretation of the invention described in the "Means for Solving the Problem" section should be based on the description in that section, and the embodiments are merely specific examples of the invention described in the "Means for Solving the Problem" section.

The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to these embodiments in any way, and it goes without saying that the present invention can be embodied in various forms without departing from the spirit of the present invention.

This invention can be used in industries such as fuel cell module manufacturing.

10 fuel cell module, 11 fuel cell stack, 12 module case, 20 reforming unit, 21 vaporization section, 22 reforming section, 23 combustion section, 24 pressure equalization section, 25 outer pipe, 31 raw fuel gas pipe, 32 reforming water pipe, 33 anode gas pipe, 34 cathode gas pipe, 35 anode off-gas pipe, 36 cathode off-gas pipe, 37 combustion exhaust gas pipe, 41 first heat exchanger, 42 second heat exchanger, 50 condenser, 51 temperature sensor, 211 dripping section, 212 filling section, 212a alumina spheres, 213 buffer section, 214 water vapor pipe, 215, 216 partition member, 217, 218 end wall, 221 reforming catalyst, 231 combustion chamber, 232, 233 end wall, 234 peripheral wall, 235 Burner device, 251 side wall, 254 end wall.

Claims (3)

a fuel cell that generates electricity based on the anode gas and the cathode gas;
a vaporization section that introduces reforming water to generate steam;
a reforming section that introduces the raw fuel gas and the steam derived from the vaporizing section and generates the anode gas by steam reforming;
a combustion unit that heats the vaporization unit and the reforming unit with combustion heat;
Equipped with
The vaporization section has a double-pipe structure in which a reforming water inlet pipe for introducing reforming water is an inner pipe, and a steam outlet pipe for guiding steam is an outer pipe. 10. The fuel cell module of claim 1,
a cylindrical portion that forms a cylindrical closed space to accommodate the vaporizing portion and the reforming portion;
the vaporization section has a double-pipe structure in which the reforming water inlet pipe penetrates one end wall of the cylindrical section and the water vapor outlet pipe opens just before the end wall,
The cylindrical portion is provided with a raw fuel gas inlet pipe that penetrates the end wall and introduces raw fuel gas, and a mixing space is formed in which steam discharged from the steam discharge pipe and raw fuel gas introduced from the raw fuel gas inlet pipe are mixed and introduced into the reforming portion. 3. The fuel cell module according to claim 2,
the combustion unit has a combustion device that ignites and burns the off-gas introduced from the fuel cell,
the cylindrical portion is formed to surround the combustion portion with a predetermined gap therebetween, so that the combustion device is located on the opposite side of the one end wall,
the vaporization section is disposed inside the combustion section,
The reforming section is disposed in the predetermined gap.