JP2007005134A - 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 is installed in the close vicinity of the lower part of the housing 2 and has a heat exchanger 20 using exhaust gas from the fuel cell stack 3 as a heat source, and a water passage through which supply water from the outside passes in the lateral direction along the bottom surface of the housing 2 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 water vapor generator provided in a fuel cell, and more particularly to a water vapor generator that can efficiently use exhaust heat and 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 introduced more to a required temperature and supply them to the power generation cell. In addition, in 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 such preheating of the reaction gas. In general, a water vapor generator for obtaining water vapor is provided.
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 stable 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. When this unreformed gas is supplied as a fuel gas to the power generation cell, carbon is deposited on the electrode, and the battery There arises a problem that the performance (output) is lowered.

  The present invention has been made in view of the above problems, and an object thereof is to provide a steam generator that efficiently uses exhaust heat and always obtains a stable amount of water vapor. Is to provide a high-performance fuel cell using the water vapor generator.

  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. And a steam generator for use in a fuel cell that exhausts the exhaust gas generated by the power generation reaction to the outside, provided near the end (upper or lower) of the housing, from the fuel cell stack The heat exchanger is provided with a water flow path through which water supplied from the outside flows in a planar direction along the end face of the housing. It is characterized in that a heat conductive bead is filled in the road.

  Moreover, the present invention described in claim 2 is characterized in that, in the steam generator according to claim 1, a plurality of baffle plates facing the water flow direction are provided in the water flow path of the heat exchanger. .

  Moreover, this invention of Claim 3 is equipped with the waste gas distribution | circulation space in which the said waste gas distribute | circulates in the plane direction toward the other end from the water vapor generator in any one of Claim 1 or Claim 2. In addition, the heat exchanger is characterized in that it is held at an intermediate part in the exhaust gas circulation space so that the exhaust gas flows above and below the heat exchanger.

  The present invention described in claim 4 is characterized in that in the steam generator according to any one of claims 1 to 3, a plate fin type heat exchanger is used as the heat exchanger. Yes.

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

  Further, the present invention according to claim 6 is the fuel cell according to claim 5, wherein the fuel cell has a sealless structure in which the remaining gas that has not been used in the power generation reaction is discharged from the outer periphery of the power generation cell. It is a solid oxide fuel cell.

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

According to the present invention, by providing the water flow path that circulates in the planar direction along the end face of the housing, the radiant heat from the end of the housing can be absorbed more efficiently than a wide range, so that the heat transfer performance of the heat exchanger Will improve.
In addition, by filling the water flow path with heat transfer beads, the heat transfer area for the fluid can be increased, and the fluid flowing through the water flow path is mixed as a turbulent flow, so the heat exchange performance is It is possible to obtain a high-temperature water vapor amount that is further improved and always stable.

  Further, by providing a baffle plate facing the water flow direction in the water flow path, a vertical water flow can be generated in the horizontal water flow, and the heat transfer to the fluid is further improved by this upstream and downstream.

  In addition, by holding the heat exchanger at an intermediate part in the exhaust gas circulation space, the exhaust gas introduced from inside the housing flows through the upper and lower parts of the heat exchanger, and the fluid flows up and down by the upper and lower exhaust gas flows. It will be heated efficiently from the direction.

  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 the steam generator according to the present invention, FIG. 3 is a top view of the steam generator, and FIG. The main part structure of a battery stack is shown.

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. 4, 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.

  In addition, the solid oxide fuel cell 1 has a sealless structure in which a gas leakage prevention seal is not 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.

  Further, in the lower center of the housing 2, a horizontal installation type steam generator that uses high-temperature exhaust gas discharged from the fuel cell stack 3 installed in the upper portion in the vicinity of the bottom plate 13 as a heat source for heat exchange. 30 is disposed.

As shown in FIGS. 2 and 3, the steam generator 30 includes heat that is contained and held in an intermediate portion of a horizontally long box-shaped exhaust gas circulation space 31 that is surrounded and formed by a casing 28 in the heat insulating material 21. It consists of the exchanger 20. The heat exchanger 20 includes a water flow path 25 meandering in the plane direction along the upper bottom plate 13 inside, and externally supplied water is introduced from the lower right end of the heat exchanger 20 through the water supply pipe 17. 3, the high-temperature exhaust gas in the housing 2 introduced from the upper exhaust gas inlet 22 in the heat exchanger 20 and the radiant heat conducted through the bottom plate 13 in the process of flowing while flowing through the water flow path 25 as indicated by the arrows in FIG. Heat exchange results in high-temperature steam that is guided into the fuel cell stack 1 through the pipe 23 at the upper left end. Further, the exhaust gas introduced from the exhaust gas inlet 22 finishes heat exchange with the supply water in the process of flowing in the exhaust gas circulation space 31 in the plane direction, becomes a low-temperature gas of 150 to 250 ° C., and the exhaust pipe at the lower end. It is discharged to the outside from 19b.
As described above, the steam generator 30 can be flattened by arranging the steam generator 30 sideways and performing heat recovery in the bottom space of the housing 2 in a planar manner. It is possible to reduce the height (miniaturization) of the module.

In the present embodiment, a plate fin type heat exchanger is used as the heat exchanger 20, and a plurality of baffle plates 29 (partition plates) are provided in a meandering water flow path 25 so as to face each other in the water flow direction. Each small area partitioned by the plate 29 is filled with beads 27. As the beads 27, alumina beads having a diameter of 1 to 2 mm and excellent thermal conductivity may be used. In addition, plate fins 24 serving as heat transfer portions of the steam generator 30 are provided on the upper and lower sides along the water flow path 25.
The baffle plate 29 is erected vertically from the bottom of the water flow path 25 and has an appropriate gap above the water flow path 25 in order to secure a lateral water flow.

Thus, by providing the water flow path 25 that flows in the lateral direction along the bottom plate 13 (the bottom surface of the housing), the heat radiated from the bottom of the housing can be directly and widely absorbed. The inside of the exhaust gas circulation space 31 is maintained at a suitable high temperature state by the heat and the heat of the high temperature exhaust gas introduced from the exhaust gas inlet 22, and the heat transfer of the heat exchanger 20 is extremely high.
Further, since the heat exchanger 20 is held and fixed at an intermediate portion in the exhaust gas circulation space 31, the exhaust gas introduced into the exhaust gas circulation space 31 flows through the upper and lower portions of the heat exchanger 20 and is exhausted. Thus, the water flow path 25 can be efficiently heated from both the upper and lower sides of the heat exchanger 20 by the upper and lower exhaust gas flows.

  In addition, since the heat transfer beads 27 are filled in the water flow path 25, the heat transfer area in the water flow path 25 is extremely large, the heat capacity of the heat exchanger 20 is increased, and the water flow path 25 is Since the feed water flowing through the turbulent flow is mixed as a turbulent flow, the heat exchange performance is further improved, and the water flow in the flow path is made uniform, so that a stable high-temperature water vapor amount can always be obtained. become.

  In addition, since a plurality of baffle plates 29 facing the water flow direction are provided in the water flow path 25, a vertical water flow can be generated in the horizontal water flow. The heat transfer can be further improved.

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 and mixed with the fuel gas in the fuel gas supply pipe 15 to become a mixed gas. After this mixed gas is preheated in the fuel heat exchanger 33, it is modified. It is introduced into the mass device 32. Since a sufficient amount of water vapor is always stably supplied from the water vapor generator 30 to the reformer 32, a stable reforming reaction is performed by the reforming catalyst to reform the fuel gas rich in hydrogen. By supplying this reformed gas to each fuel cell stack 3, 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. The figure which shows the upper surface view of a water vapor generator. 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)
25 Water channel
27 beads (alumina beads)
29 Baffle plate 30 Steam generator 31 Exhaust gas distribution space 32 Reformer

Claims (7)

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 near the end of the housing and uses exhaust gas from the fuel cell stack as a heat source. In this heat exchanger, water supplied from the outside extends along the end surface of the housing. And a water flow path that circulates in a planar direction, and the water flow path is filled with heat conductive beads. The steam generator according to claim 1, wherein a plurality of baffles facing the direction of water flow are provided in the water flow path of the heat exchanger. The exhaust gas has an exhaust gas circulation space in which the exhaust gas circulates in a plane direction from one end to the other end, and the heat exchanger is held at an intermediate portion in the exhaust gas circulation space so that the exhaust gas circulates above and below the exhaust gas. The water vapor generator according to claim 1 or 2, wherein the water vapor generator is provided. The steam generator according to any one of claims 1 to 3, wherein a plate fin type heat exchanger is used as the heat exchanger. A fuel cell comprising the water vapor generator according to any one of claims 1 to 4. 6. The fuel cell according to claim 5, 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. 6. The reformer having a multi-stage configuration, each connected in series, and at least the foremost reformer being disposed apart from the fuel cell stack. Item 7. The fuel cell according to any one of Items 6.

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