JP2007005133A - Steam generator and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam generator capable of constantly obtaining a stable amount of steam. <P>SOLUTION: The steam generator 30 is used for a fuel cell 1 formed by housing a fuel cell stack 3 constituted by stacking many power generation cells in a heat insulating housing 2. The steam generator 30 has a heat exchanger 20 installed in the lower part of the housing 2 and using exhausted gas from the fuel cell stack 3 as a heat source, and a water passage through which supply water from the outside is passed from the lower part to the upper part is installed in the heat exchanger 20, and heat conductive beads are filled in the water passage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a steam generator used in a fuel cell, and more particularly to a steam generator that can obtain a stable amount of water vapor.

  In recent years, fuel cells that directly convert chemical energy of fuel into electrical energy have attracted attention as highly efficient and clean power generators. In particular, solid oxide fuel cells have many advantages such as high power generation efficiency and effective use of exhaust heat, and therefore research and development are underway as third-generation fuel cells for power generation. .

This solid oxide fuel cell has a laminated structure in which a solid electrolyte layer made of an oxide ion conductor is sandwiched between an air electrode layer (cathode) and a fuel electrode layer (anode) from both sides. As described above, an oxidant gas (oxygen) is supplied to the air electrode layer side, and a fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode layer side. The air electrode layer and the fuel electrode layer are both porous layers so that the reaction gas can reach the interface with the solid electrolyte layer.

In the power generation cell, oxygen supplied to the air electrode layer passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer. It is ionized to (O ²⁻ ). The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode layer. Oxide ions that have reached the vicinity of the interface with the fuel electrode layer react with the fuel gas at this portion to generate reaction products (H ₂ O, CO _2, etc.), and discharge electrons to the fuel electrode layer. Electrons generated by the electrode reaction can be taken out as an electromotive force at an external load on another route.

By the way, in the solid oxide fuel cell, the electrochemical reaction of the power generation cell is performed in a high-temperature oxidizing atmosphere at about 650 to 1000 ° C. It is necessary to preheat oxygen (air) and fuel gas supplied more to a required temperature. In addition, in the case of an internal reforming fuel cell having a fuel reformer inside the module, it is necessary to supply high-temperature steam for fuel reforming in addition to the preheated reaction gas, so that steam is obtained. It is common to have a steam generator for this purpose.
Patent Document 1 discloses a reformer that is integrally provided with a steam generator for supplying high-temperature steam necessary for the reforming reaction.
JP 2003-63803 A

  By the way, since the reforming reaction in the reformer is an endothermic reaction, it is necessary to stably supply high-temperature steam to the reformer in order to generate a sufficient reforming reaction and obtain a hydrogen-rich fuel gas. There is. When the supply amount of water vapor fluctuates, the reforming reaction becomes unstable and unreformed gas is generated. This unreformed gas is supplied as fuel gas to the power generation cell, so that carbon is deposited on the electrodes. There arises a problem that the battery performance (output) is lowered.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a water vapor generator that can always obtain a stable amount of water vapor, and another object is to provide a high water vapor generator using the water vapor generator. It is to provide a high-performance fuel cell.

  That is, according to the first aspect of the present invention, a fuel cell stack formed by stacking a large number of power generation cells is housed in a heat insulating housing, and a reaction gas is supplied into the fuel cell stack during operation to generate a power generation reaction. A steam generator for a fuel cell that exhausts exhaust gas generated by a power generation reaction to the outside, and is provided at a lower portion of the housing and introduces exhaust gas from the fuel cell stack as a heat source The heat exchanger is provided with a water channel through which water supplied from the outside flows from the lower part to the upper part, and the water channel is filled with heat conductive beads. Yes.

  Further, according to a second aspect of the present invention, in the water vapor generator according to the first aspect, the beads are filled from an upstream portion of the water flow path to a height at which the supply water can be vaporized. Further, vaporized water vapor guiding means is provided in the bead non-filling portion in the downstream portion.

  Further, according to a third aspect of the present invention, in the steam generator according to the first or second aspect, as the heat exchanger, the exhaust gas flow channel and the water flow channel are crossed or opposed to each other. The plate fin type heat exchanger provided is used.

  According to a fourth aspect of the present invention, there is provided a fuel cell comprising the water vapor generator according to any one of the first to third aspects.

  According to a fifth aspect of the present invention, there is provided the fuel cell according to the fourth aspect, wherein the fuel cell releases a residual gas that has not been used for a power generation reaction from an outer peripheral portion of the power generation cell. It is a solid oxide fuel cell.

  According to a sixth aspect of the present invention, there is provided the fuel cell according to the fourth or fifth aspect, comprising a multi-stage reformer connected in series, and at least the foremost stage. The reformer is disposed apart from the fuel cell stack.

According to the present invention, the heat transfer area for the fluid (externally supplied water) can be increased by filling the water vapor generator (in the water flow path) with the heat conductive beads, thereby improving the heat exchange performance and utilizing the exhaust heat. Thus, high temperature water vapor can be obtained efficiently.
Moreover, since the fluid flowing through the water flow path is mixed as a turbulent flow by filling the beads, the heat exchange performance is further improved, and a stable water vapor amount can always be obtained.
In addition, when externally supplied water is circulated from the lower part to the upper part of the steam generator, the bead filling needs to be a vaporizable height, so that stable high-temperature steam can be obtained using the minimum necessary beads. It becomes possible.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows the internal structure of a solid oxide fuel cell to which the present invention is applied, FIG. 2 shows the internal structure of a steam generator according to the present invention, and FIG. 3 shows the main structure of a fuel cell stack. Yes.

In FIG. 1, reference numeral 1 is a solid oxide fuel cell, reference numeral 2 is a housing (can body) in which a heat insulating material 18 is attached to the inner wall, and reference numeral 3 is disposed inside the housing 2 with the stacking direction being vertical. It is a fuel cell stack. In the present embodiment, a plurality of (for example, eight) fuel cell stacks 3 are assembled and arranged in the housing 2 to constitute a high output type fuel cell module. The fuel cell module (solid oxide fuel cell 1) is installed on the mount 40. Each fuel cell stack 3 in the housing 2 has a fuel gas supply pipe 15 for introducing a fuel gas and an oxidant gas (air) supplied from the outside as reaction gases into the fuel cell stack 3. An oxidant gas supply pipe 16 is connected.
The fuel gas supply pipe 15 is connected to each fuel cell stack 3 in the housing 2 via a preheating fuel heat exchanger 33, a reformer 32, etc., and the oxidant gas supply pipe 16 is used for preheating. Each fuel stack 3 is connected via an air heat exchanger 34.

  As shown in FIG. 3, the fuel cell stack 3 includes a power generation cell 7 in which a fuel electrode layer 5 and an air electrode layer (oxidant electrode layer) 6 are disposed on both surfaces of a solid electrolyte layer 4, and an outer side of the fuel electrode layer 5. A structure in which a fuel electrode current collector 8, an air electrode current collector (oxidant electrode current collector) 9 outside the air electrode layer 6, and a large number of separators 10 outside each current collector 8, 9 are stacked in order. Have

Here, the solid electrolyte layer 4 is composed of stabilized zirconia (YSZ) to which yttria is added, the fuel electrode layer 5 is composed of a metal such as Ni or a cermet such as Ni—YSZ, and the air electrode layer 6 is LaMnO _3. , is composed of LaCoO ₃ or the like, the fuel electrode current collector 8 is composed of a sponge-like porous sintered metal plate such as Ni, the air electrode current collector 9 sponge-like porous sintered metal plate such as Ag The separator 10 is made of stainless steel or the like.

  The separator 10 electrically connects the power generation cells 7 and has a function of supplying a reaction gas to the power generation cells 7. The fuel gas supplied through the fuel gas supply pipe 15 is supplied to the outer peripheral surface of the separator 10. The oxidant gas supplied through the oxidant gas supply pipe 16 and the fuel gas passage 11 that is introduced from the outlet and discharged from the substantially central portion of the separator 10 facing the fuel electrode current collector 8 is supplied from the outer peripheral surface of the separator 10. An oxidant gas passage 12 is provided that is introduced and discharged from substantially the center of the surface of the separator 10 that faces the air electrode current collector 9.

  Further, the solid oxide fuel cell 1 has a sealless structure in which no gas leakage prevention seal is provided on the outer peripheral portion of the power generation cell 7, and during operation, as shown in FIG. The fuel electrode layer 5 and the air electrode layer are diffused while the fuel gas and the oxidant gas (air) discharged from the substantially central portion of the separator 10 through the agent gas passage 12 toward the power generation cell 7 are diffused in the outer peripheral direction of the power generation cell 7. 6 is distributed over the entire surface with a good distribution to generate a power generation reaction, and the remaining gas (exhaust gas) that has not been consumed by the power generation reaction is freely released from the outer periphery of the power generation cell 7 to the outside. . Then, as shown in FIG. 1, high temperature exhaust gas discharged into the internal space of the housing 2 at the top of the housing 2 (450 to 600 ° C. in the case of a solid oxide fuel cell having an operating temperature of around 700 ° C.) An exhaust pipe 19a is provided for discharging the gas to the outside.

  In addition, a steam generator 30 that uses high-temperature exhaust gas discharged from the upper fuel cell stack 3 as a heat source is disposed at the lower center of the housing 2.

  The water vapor generator 30 is composed of a heat exchanger 20 accommodated in a space surrounded by a heat insulating material 21, and externally supplied water is introduced from the lower part of the heat exchanger 20 through a water supply pipe 17. In the process of circulating upward, heat exchange with the high-temperature exhaust gas in the housing 2 introduced from the upper exhaust gas inlet 22 in the heat exchanger 20 results in high-temperature steam, and enters the fuel cell stack 1 through the pipe 23 at the upper end. It is supposed to be guided. The exhaust gas introduced from the upper exhaust gas inlet 22 finishes heat exchange with the supply water in the process of flowing downward, becomes a low-temperature gas of 150 to 250 ° C., and is discharged to the outside from the lower exhaust pipe 19b. The

  In the present embodiment, as shown in FIG. 2, the heat exchanger 20 has an exhaust gas passage 24 with fins 26 through which exhaust gas from the fuel cell stack 3 circulates and a fin 26 with fins 26 through which externally supplied water circulates. A plate fin type heat exchanger is used in which the water flow paths 25 are arranged in a cross-like manner or opposed to each other in units of plates, and the gaps between the fins 26 in the water flow paths 25 are filled with beads 27. Yes. As this bead 27, an alumina bead having a diameter of 1 to 2 mm and excellent in thermal conductivity is used.

Thus, by filling the heat exchanger 20 (in the water flow path 25) with the heat conductive beads 27, the heat transfer area in the water flow path 25 can be increased, so the heat capacity as the heat exchanger increases, Heat exchange performance can be improved. Thereby, the supply water from the outside can be efficiently heated and vaporized to obtain a large amount of high-temperature steam.
Further, when the water flow path 25 is narrowed by filling the water flow path 25 with the beads 27, the heated water in the bead filling area is mixed in a turbulent flow, so that the heat exchange performance is further improved. In addition to the improvement, the water flow in the flow path is made uniform, so that a stable amount of water vapor can always be obtained.

  In addition, the water vapor generator 30 of the present embodiment is installed at the bottom of the housing 2 to circulate high-temperature exhaust gas serving as a heat source downward from above, and externally supplied water from below (upstream) of the heat exchanger 20. The bead 27 is vaporized at least from the upstream portion in the water flow path 25 because it is configured to circulate upward (downstream) and to release water vapor evaporated in the distribution process from the downstream end of the heat exchanger. It is sufficient to fill up to a possible height. Therefore, it is possible to obtain a stable amount of water vapor using a minimum number of beads. In addition, the water vapor | steam vaporized in the water flow path 25 can be taken out from the bead non-filling area | region which is the most downstream part.

In the present embodiment, the steam generator 30 is configured by a plate fin type heat exchanger, but other tube fin type heat exchangers, plate heat exchangers, and the like can be used. However, the plate fin type heat exchanger has an advantage in that a compact and high-performance steam generator 30 can be configured.
In the present embodiment, the high-power type fuel cell module configured by arranging and arranging a plurality of fuel cell stacks 3 has been described. However, the present invention also applies to a fuel cell module configured by a single fuel cell stack 3. Of course, it is possible.

  As described above, the steam generator 30 of the present invention can effectively use the thermal energy of exhaust gas and always obtain a stable amount of steam. The obtained water vapor is guided to the fuel gas supply pipe 15 through the pipe 23 as the guiding means, mixed with the fuel gas in the fuel gas supply pipe 15 to become a mixed gas, and this mixed gas is preheated by the fuel heat exchanger 33. After that, it is introduced into the reformer 32. In the reformer 32, since a sufficient amount of water vapor is always supplied from the water vapor generator 30, a suitable reforming reaction by the reforming catalyst is performed to reform the fuel gas rich in hydrogen, The fuel cell stack 3 is supplied, so that a highly efficient and high performance fuel cell can be realized.

  In the present invention, although not shown, the reformer 32 may have a multistage configuration in which the reformers 32 are connected in series. In this case, the reformer in the foremost stage is disposed at a location separated from the fuel cell stack 3 (for example, in the exhaust pipe 19a or in the vicinity thereof), and the reforming in the initial stage with a large endotherm is performed. It is preferable to carry out with a vessel. As a result, it is possible to avoid the inconvenience of cooling the fuel cell stack 3 by the large heat absorption of the reformer 32 having a single structure as shown in FIG. The steam generator 30 that uses the exhaust heat of the fuel cell stack 3 can always introduce a high-temperature exhaust gas, and thus greatly contributes to always generating a stable amount of steam. It is.

The figure which shows the internal structure of the solid oxide fuel cell to which this invention was applied. The principal part sectional drawing which shows the internal structure of the water vapor generator which concerns on this invention. It is a principal part schematic block diagram of the fuel cell stack which concerns on this invention, and shows the flow of the gas at the time of driving | operation.

Explanation of symbols

1 Fuel cell (solid oxide fuel cell)
2 Housing 3 Fuel cell stack 7 Power generation cell 20 Heat exchanger (plate fin type heat exchanger)
23 Guidance means (piping)
24 Exhaust gas channel 25 Water channel
27 beads (alumina beads)
30 Steam generator 32 Reformer

Claims (6)

A fuel cell stack formed by stacking a large number of power generation cells is housed in a heat insulating housing, and during operation, a reaction gas is supplied into the fuel cell stack to cause a power generation reaction, and an exhaust gas generated by the power generation reaction is generated. A steam generator used for a fuel cell exhausted outside,
A heat exchanger is provided in the lower part of the housing and introduces exhaust gas from the fuel cell stack as a heat source. The heat exchanger is provided with a water flow path through which water supplied from the outside flows from the lower part to the upper part. A water vapor generator, wherein the water flow path is filled with heat conductive beads. The beads are filled from the upstream portion of the water flow path at least to a height at which the supply water can be vaporized, and vaporized water vapor guiding means is provided in a bead unfilled portion in the downstream portion. The water vapor generator according to claim 1. 3. The water vapor according to claim 1, wherein a plate fin type heat exchanger provided with an exhaust gas flow channel and a water flow channel intersecting or facing each other is used as the heat exchanger. Generator. A fuel cell comprising the water vapor generator according to any one of claims 1 to 3. 5. The fuel cell according to claim 4, wherein the fuel cell is a solid oxide fuel cell having a sealless structure that discharges residual gas that has not been used in a power generation reaction from an outer peripheral portion of the power generation cell. 5. The reformer having a multi-stage configuration, each connected in series, and at least the foremost reformer is disposed apart from the fuel cell stack. Item 6. The fuel cell according to any one of Items 5.

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