JP2018060627A - Multistage fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multistage fuel cell system in which reheat for using anode off-gas for removing steam as regenerative fuel gas after cooled temporarily can be carried out without using waste-heat of the fuel cell, by a simple configuration of solid oxide fuel cell, while ensuring sufficiently high reliability during long term use.SOLUTION: A multistage fuel cell system 10 by solid oxide fuel cell using an oxide conductor in electrolyte layer, includes a fuel cell stack 11a on the prestage side and a fuel cell stack 11b on the latter stage side, a heat exchanger 12 performing heat exchange between the upstream side and downstream side of a gas line 22 for supplying anode off-gas, discharged from the fuel cell stack 11a to the fuel cell stack 11b, and a heat exchanger 13 performing heat exchange between the midstream part of the gas line 22 and cooling fluid supplied externally.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a multi-stage fuel cell system having a multi-stage fuel cell stack, and in particular, a multi-stage fuel cell using a solid oxide fuel cell (hereinafter sometimes referred to as “SOFC”). About the system.

  In a solid oxide fuel cell, an anode (fuel electrode) and a cathode (air electrode) are arranged with an electrolyte layer using an oxide conductor interposed therebetween. The operating temperature is, for example, about 700 to 800 ° C.

  In a solid oxide fuel cell, a fuel such as hydrogen is supplied to the anode side and air is supplied to the cathode side to cause an electrochemical reaction and take out electric power. Oxygen in the air supplied from the air supply pipe becomes oxide ions at the cathode, and reaches the anode through the electrolyte layer. Here, it reacts with the fuel supplied from the fuel supply pipe and emits electrons to generate electricity and reaction products (water and carbon dioxide).

  In order to improve the efficiency of a fuel cell system such as a solid oxide fuel cell, a multi-stage fuel cell stack has been proposed as a technique for improving the fuel utilization rate (see, for example, Patent Document 1 and Patent Document 2). ). That is, using a plurality of fuel cell stacks, water vapor and carbon dioxide are removed from the unreacted fuel gas in the preceding fuel cell stack, and the regenerated fuel gas having a higher concentration of fuel gas contributing to the reaction is used as the subsequent fuel gas. Used for battery stacks.

JP 2006-031989 JP-A-2006-115495

  In the SOFC system described in Patent Document 1, in order to remove water vapor from the anode off gas, the anode off gas is cooled to a dew point temperature or less and condensed. In order to remove water vapor from the anode off-gas and use it as a regenerated fuel gas, it is necessary to reheat this regenerated fuel gas to the power generation temperature of the fuel cell stack, and the exhaust heat of the fuel cell is used as a heat source for that purpose. It was.

  On the other hand, in the multi-stage fuel cell system described in Patent Document 2, since the water vapor is removed from the anode off gas in a gaseous state by the water vapor separation membrane, it is not necessary to cool the anode off gas to the dew point temperature or less necessary for water condensation. Absent. However, in order to remove water vapor in a gaseous state, it is necessary to create a pressure difference on both sides of the water vapor separation membrane. This water vapor separation membrane is a kind of filter that does not allow other gases to pass through water vapor, and clogging may occur when the surface of the water vapor separation membrane is contaminated by rust or dust during long-term use at high temperatures. If it does so, it will become difficult to ensure the water required for a driving | operation, and the reliability at the time of long-term use is not necessarily enough.

  In view of such problems of the prior art, the object of the present invention is to temporarily cool the anode off-gas in order to remove water vapor by a simple configuration using a solid oxide fuel cell using an oxide conductor as an electrolyte layer. To provide a multistage fuel cell system that can be reheated for later use as a regenerated fuel gas without using the exhaust heat of the fuel cell and has sufficiently high reliability during long-term use. .

  In order to achieve the above object, a multistage fuel cell system according to the present invention is a multistage fuel cell system using a solid oxide fuel cell that uses an oxide conductor in an electrolyte layer, and includes a power generation cell and an interconnector. At least one front-stage fuel cell stack and at least one rear-stage fuel cell stack, each of which is configured by alternately stacking a plurality of layers, and anode off-gas discharged from the front-stage fuel cell stack, A first heat exchanger that exchanges heat between an upstream portion and a downstream portion of a gas path to be supplied to the first gas exchanger, and a heat exchanger that exchanges heat between a midstream portion of the gas path and a cooling fluid supplied from the outside. And 2 heat exchangers.

  Here, specific examples of the first heat exchanger and the second heat exchanger include a plate-type heat exchanger, a shell-and-plate heat exchanger, and a shell-and-tube heat exchanger. Although it is mentioned, it is not restricted to these.

  According to the multistage fuel cell system having such a configuration, the anode offgas is once cooled to remove water vapor, and then reheated for use as a regenerated fuel gas is performed by the anode offgas itself before cooling. It is not necessary to use the exhaust heat of the battery. Thereby, the exhaust heat of the fuel cell can be used as a heat source such as hot water supply, and the efficiency of the entire multistage fuel cell system can be improved.

  In the multistage fuel cell system of the present invention, it is preferable that the number of the front-side fuel cell stacks is larger than the number of the rear-stage fuel cell stacks.

  In the multistage fuel cell system of the present invention, examples of the member constituting the first heat exchanger include, but are not limited to, a stainless steel material or a titanium material. The joints between the members may be joined by welding using a welding material to which at least one of molybdenum, chromium, or nickel is added, or by brazing using a nickel-based brazing material. It may be joined or may be joined by laser welding. However, it is not restricted to such a joining method.

  According to the multistage fuel cell system of the present invention, the anode offgas is once cooled to remove water vapor, and then reheated for use as a regenerated fuel gas is performed by the anode offgas before cooling. It is not necessary to use heat. Thereby, the exhaust heat of the fuel cell can be used as a heat source such as hot water supply, and the efficiency of the entire multistage fuel cell system can be improved.

1 is an overview configuration diagram of a multistage fuel cell system 10 according to a first embodiment of the present invention. It is a general | schematic block diagram of 10 A of multistage type fuel cell systems which concern on 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment>
FIG. 1 is a schematic configuration diagram of a multistage fuel cell system 10 according to a first embodiment of the present invention. As shown in FIG. 1, a multi-stage fuel cell system 10 using solid oxide fuel cells includes a fuel cell stack 11a on the front side (left side in the drawing) and a fuel cell stack 11b on the rear side (right side in the drawing). And a first heat exchanger 12 and a second heat exchanger 13.

  Each of the fuel cell stack 11a and the fuel cell stack 11b (referred to as “fuel cell stack 11” when there is no particular distinction) is configured by alternately stacking a plurality of power generation cells and interconnectors.

  In these fuel cell stacks 11, electric power can be taken out by supplying a fuel such as hydrogen to the anode side and supplying air to the cathode side to cause an electrochemical reaction. Oxygen in the air becomes oxide ions at the cathode, reaches the anode through the electrolyte layer, reacts with the fuel, emits electrons, and generates electricity and reaction products (water and carbon dioxide).

  In this multistage fuel cell system 10, a fuel gas line 21 that supplies preheated fuel gas to the fuel cell stack 11a, and a gas line 22 that supplies anode off-gas discharged from the fuel cell stack 11a to the fuel cell stack 11b, An anode offgas line 23 for discharging the anode offgas discharged from the fuel cell stack 11b is provided.

  The anode off-gas discharged from the fuel cell stack 11a contains fuel that has not reacted, but the fuel concentration is reduced by water vapor as a reaction product. Therefore, in order to reuse the fuel cell stack 11b as a regenerated fuel gas, it is necessary to remove water vapor from the anode off gas.

  The gas line 22 further includes a gas line 22a, a gas line 22b, a gas line 22c, and a gas line 22d in order from the upstream side to the downstream side. The anode side outlet of the fuel cell stack 11a is connected to the high temperature side inlet of the heat exchanger 12 by a gas line 22a. The high temperature side outlet of the heat exchanger 12 is connected to the high temperature side inlet of the heat exchanger 13 by a gas line 22b. The high temperature side outlet of the heat exchanger 13 is connected to the low temperature side inlet of the heat exchanger 12 by a gas line 22c. The low temperature side outlet of the heat exchanger 12 is connected to the anode side inlet of the fuel cell stack 11b by a gas line 22d.

  With such connection, the heat exchanger 12 performs heat exchange between the upstream portion and the downstream portion of the gas line 22. Since the temperature of the anode off-gas passing through the upstream portion of the gas line 22 is sufficiently high, the regenerated fuel gas supplied to the fuel cell stack 11b through the downstream portion of the gas line 22 can be sufficiently reheated. The heat exchanger 13 performs heat exchange between the midstream portion of the gas line 22 and the cooling water supplied from the outside by the cooling water line 24. That is, the heat exchanger 13 performs heat exchange at a lower temperature than the heat exchanger 12 (for example, heat exchange with room temperature cooling water), quickly cools the anode off gas to the dew point temperature, and water vapor in the anode off gas. Can be efficiently condensed.

  It is not always necessary to use water for heat exchange in the heat exchanger 13, and other cooling fluids can be used. For example, an antifreeze such as ethylene glycol may be used, or a radiator that sends cooling air to the heat exchanger with a fan may be used. However, it is not limited to these.

  Examples of the member (base material) constituting the heat exchanger 12 that performs heat exchange at a high temperature include, but are not limited to, a stainless steel material or a titanium material. The joint portion between these members may be joined, for example, by welding using a welding material to which at least one of molybdenum, chromium, or nickel is added, or by brazing using a nickel-based brazing material. And may be joined by laser welding. However, it is not restricted to such a joining method.

  Specific examples of the heat exchanger 12 and the heat exchanger 13 include a plate heat exchanger, a shell and plate heat exchanger, and a shell and tube heat exchanger. When the heat exchanger 12 is a plate heat exchanger, a welding type or brazing type that does not use a gasket for sealing between plates is suitable. In particular, laser welding is extremely preferable because it is suitable for use at high temperatures because the base metals are melted and joined. However, it is not restricted to these heat exchangers.

  In the multistage fuel cell system 10, the gas-liquid separator 14 is provided in the gas line 22 c that connects the high temperature side outlet of the heat exchanger 13 and the low temperature side inlet of the heat exchanger 12. The condensate produced in the above is separated and discharged from the drain line 25. As the gas-liquid separator 14, for example, a baffle type drain separator can be used. Further, a water vapor separation membrane may be disposed between the gas-liquid separator 14 and the heat exchanger 13 to remove moisture from the anode off gas to a higher degree.

  According to the configuration of the first embodiment described above, the anode off-gas discharged from the fuel cell stack 11a is reused as the regenerated fuel gas in the fuel cell stack 11b, so that the heat exchanger 12 and the heat exchanger 13 After cooling to near normal temperature and condensing and removing water vapor, the heat exchanger 12 can be reheated to the operating temperature of the fuel cell by the anode off-gas itself before cooling. Since the exhaust heat of the fuel cell is not used for reheating the anode off gas, the exhaust heat of the fuel cell can be used as a heat source such as hot water supply, and the overall efficiency of the multistage fuel cell system 10 can be improved. Moreover, since the use of a water vapor separation membrane that may be clogged is not indispensable, the reliability during long-term use can be secured sufficiently high.

Second Embodiment
In the first embodiment described above, the flow rate of the regenerated fuel gas supplied to the downstream fuel cell stack 11b is reduced because the flow rate of the anode off-gas discharged from the fuel gas supplied to the upstream fuel cell stack 11a is reduced. May not be sufficient. Therefore, a configuration in which the number of fuel cell stacks on the front stage side is larger than the number of fuel cell stacks on the rear stage side is the second embodiment.

  FIG. 2 is a schematic configuration diagram of a multistage fuel cell system 10A according to the second embodiment of the present invention. Since the second embodiment is the same as the first embodiment described with reference to FIG. 1 except for the points described below, the same reference numerals will be given to the same constituent members, and in the following. The difference will be mainly described.

  As shown in FIG. 2, a multi-stage fuel cell system 10A using a solid oxide fuel cell has two fuel cell stacks 11a and 11b on the front side (left side in the figure) and the rear side (right side in the figure). In addition, one fuel cell stack 11c (referred to as “fuel cell stack 11” when there is no particular distinction), a first heat exchanger 12, and a second heat exchanger 13A are provided.

  In the multistage fuel cell system 10A, fuel gas lines 21 for supplying preheated fuel gas are connected to the fuel cell stacks 11a and 11b, respectively. The upstream side of the gas line 22a is connected to each anode side of the fuel cell stacks 11a and 11b.

  The heat exchanger 13A is also used as the gas-liquid separator 14 of the first embodiment. The heat exchanger 13A is, for example, a plate heat exchanger or a shell-and-plate heat exchanger, and a plate pack is disposed so that the heat transfer plate is substantially vertical. Then, by circulating the anode gas between the heat transfer plates in a downward flow, the condensed water and the anode gas are separated and discharged from the nozzles below the plate pack. The separated condensed water is discharged through a drain line 25 branched from the gas line 22c.

  According to the configuration of the second embodiment described above, the anode off-gas discharged from the fuel cell stack 11a and the fuel cell stack 11b is reused as a regenerated fuel gas in the fuel cell stack 11c. After cooling to near room temperature by the heat exchanger 13A and condensing and removing the water vapor, the heat exchanger 12 can be reheated to the operating temperature of the fuel cell by the anode off-gas itself before cooling. Since the exhaust heat of the fuel cell is not used for reheating the anode off gas, the exhaust heat of the fuel cell can be used as a heat source such as hot water supply, and the overall efficiency of the multistage fuel cell system 10A can be improved. Moreover, since the use of a water vapor separation membrane that may be clogged is not indispensable, the reliability during long-term use can be secured sufficiently high. Since there are two fuel cell stacks 11a and 11b on the front side, a sufficient flow rate of the regenerated fuel gas supplied to one fuel cell stack 11c on the rear side can be secured.

  It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-mentioned embodiment is only a mere illustration in all points, and should not be interpreted limitedly. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  For example, the multi-stage fuel cell system of the present invention is not limited to the configuration including the two-stage fuel cell stack shown in the first embodiment and the second embodiment, and includes a configuration including three or more stages of fuel cell stacks. You can also. In that case, between the adjacent stages, the upstream side in the gas flow direction is the front stage side fuel cell stack, and the downstream side is the rear stage side fuel cell stack. And the structure shown in each embodiment is applied to the arrangement / connection relationship between the first heat exchanger and the second heat exchanger between adjacent stages.

  The present invention is particularly suitable for a multistage fuel cell system using a solid oxide fuel cell using an oxide conductor in an electrolyte layer.

10, 10A
Multistage fuel cell system 11 (11a to 11c)
Fuel cell stack 12 First heat exchanger 13, 13A
Second heat exchanger 14 Gas-liquid separator 21 Fuel gas line 22 Gas line 23 Anode off-gas line 24 Cooling water line 25 Drain line

Claims (6)

A multi-stage fuel cell system using a solid oxide fuel cell using an oxide conductor as an electrolyte layer,
At least one front-stage fuel cell stack and at least one rear-stage fuel cell stack each configured by alternately stacking a plurality of power generation cells and interconnectors;
A first heat exchanger that performs heat exchange between an upstream portion and a downstream portion of a gas path that supplies the anode off-gas discharged from the front-stage fuel cell stack to the rear-stage fuel cell stack;
A multistage fuel cell system comprising: a second heat exchanger that exchanges heat between a midstream portion of the gas path and a cooling fluid supplied from outside. The multistage fuel cell system according to claim 1,
The multistage fuel cell system, wherein the number of the front stage side fuel cell stacks is larger than the number of the rear stage side fuel cell stacks. The multistage fuel cell system according to claim 1 or 2,
The member constituting the first heat exchanger is made of a stainless material or a titanium material,
The multi-stage fuel cell system is characterized in that the joint portion between the members is joined by welding using a welding material to which at least one of molybdenum, chromium, or nickel is added. The multistage fuel cell system according to claim 1 or 2,
The member constituting the first heat exchanger is made of a stainless material or a titanium material,
The multi-stage fuel cell system is characterized in that the joint between the members is joined by brazing using a nickel-based brazing material. The multistage fuel cell system according to claim 1 or 2,
The member constituting the first heat exchanger is made of a stainless material or a titanium material,
The multistage fuel cell system, wherein the joints between the members are joined by laser welding. In the multistage fuel cell system according to any one of claims 1 to 5,
The multistage fuel cell system, wherein the first heat exchanger is a plate heat exchanger, a shell and plate heat exchanger, or a shell and tube heat exchanger.

Images