JP2006079890A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To aim at shortening of start-up time under a low-temperature environment. <P>SOLUTION: A given number of end cells at both ends of a fuel cell stack 101 out of all cells constituting the stack 101 consist of cells in which moistening water is given to hydrogen gas and air gas through a porous plate, and center cells consist of cells using solid plates. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system in which startability in a low temperature environment is improved by supplying a medium heated at low temperature startup to a fuel cell main body.

  Conventionally, as this type of technology, for example, those described in the following documents are known (see Patent Document 1). In this document, cooling water heated by a heater circulates through a heat medium circuit arranged so as to pass through each cell of the fuel cell to raise the temperature of the fuel cell, while both ends of the fuel cell are heated. Technology that heats both ends of the fuel cell preferentially by circulating the cooling water heated by the heater intensively in the heat medium bypass path provided near the both ends of the fuel cell or the fuel cell. Yes. By heating both ends of the fuel cell, it is possible to prevent heat from being lost at both ends of the fuel cell due to heat loss due to a fastener or the like, and to raise the temperature of the entire fuel cell on average.

In this way, by circulating the heated cooling water to the fuel cell, when the water inside the frozen fuel cell is melted and the fuel cell is ready for power generation, hydrogen and air are supplied to the fuel cell. Start and start power generation with the fuel cell. At this time, since the cells at both ends of the fuel cell are preferentially heated, the power generation output at both ends of the fuel cell is prevented from decreasing and the output of each cell is stabilized.
JP 2003-331886 A

  As described above, in the conventional fuel cell system, at the time of low temperature startup, the cells at both ends of the fuel cell are preferentially heated, so that the temperature of the cells at both ends of the fuel cell is changed to the cell at the other part. As a result, the temperature of the entire fuel cell is increased on average.

  However, after the frozen water in the fuel cell was completely thawed and the fuel cell was ready for power generation, power generation by the fuel cell was started. For this reason, it takes a long time to thaw all the water that has frozen inside the fuel cell even if both ends of the fuel cell are preferentially heated. The problem of becoming.

  Accordingly, the present invention has been made in view of the above, and an object thereof is to provide a fuel cell system in which the startup time in a low temperature environment is shortened.

  In order to achieve the above object, a means for solving the problems of the present invention is to generate a power by chemically reacting a reaction gas of a fuel gas and an oxidant gas, and a cooling medium for removing the heat generated by the power generation circulates. In a fuel cell system including a fuel cell stack in which a plurality of cells having flow paths are stacked, a predetermined number of end cells at both ends of the fuel cell stack among all cells constituting the fuel cell stack are In addition, the fuel cell stack is configured by a cell in which moisture for humidification is given to the reaction gas through a porous plate, and the other cells of the fuel cell stack are configured by a cell using a solid plate.

  According to the present invention, by using a porous plate for the end cell and using a solid plate with a small amount of water in other cells, power generation of all cells can be started when the end cell is thawed. It becomes. Thereby, the starting time of the system in a low temperature environment can be shortened.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best embodiment for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a fuel cell system according to Embodiment 1 of the present invention. 1 includes a fuel cell stack 101, an end plate heater 102, a cooling water pump 103, a pure water pump 104, a pure water tank 105, a combustor heat exchanger 106, a radiator 107, a shut valve 108, 109, a three-way valve 110, thermometers 111, 112, and 113, and a control unit (not shown).

  The fuel cell stack 101 generates electricity by a chemical reaction between humidified hydrogen of the fuel gas and oxidant gas air, and is configured as shown in FIG.

  In FIG. 2, the fuel cell stack 101 is configured by stacking a plurality of cells. Among the plurality of stacked cells, each end cell 201 on both ends of the fuel cell stack 101 reacts with pure water for humidification through a flow path (groove) formed in a moisture permeable porous plate. It is given to gas hydrogen and air. On the other hand, other cells (hereinafter referred to as the center cell 202) excluding the end cells 201 of the fuel cell stack 101 have flow paths (grooves) formed in a solid-type solid plate separator that does not allow reaction gas to pass through. The hydrogen and air of the reaction gas are supplied to the power generation unit.

  The total number of end cells 201 is at least 2 (one at each end) or within a range of, for example, about 1% to 10% of the total number of cells constituting the fuel cell stack 101, and the required rated output of the system ( It is selected as appropriate based on the total number of cells, the size of the stack depending on the cell area), and the frequency of activation from below the freezing point of the system.

  The fuel cell stack 101 is provided with end plate heaters 102 at both ends thereof. The end plate heater 102 is composed of an electric heater, and is supplied with power from a secondary battery (not shown) at the time of low temperature startup to heat the end cell 201 and assist the temperature increase of the end cell 201.

  The end cell 201 is configured as shown in FIG. In FIG. 3, an end cell 201 includes a membrane electrode assembly (MEA) 301 that functions as a power generation unit, a pair of porous plates 302 that are disposed with the MEA 301 interposed therebetween, and a pair of the porous plates 302. And a pair of separators 304 that are arranged with the pair of cooler plates 303 sandwiched therebetween and that separate adjacent end cells.

  MEA 301 has an electrolyte membrane (not shown) sandwiched between both sides by a catalyst layer (not shown), and a carbon layer (not shown) and a gas diffusion layer (GDL, not shown) are arranged on the outer side. Composed. The MEA 301 generates electric power by chemically reacting the humidified reaction gas hydrogen and air, and the electric power obtained by the electric power generation is taken out and supplied to an external circuit.

  One of the pair of porous plates 302 is the anode side, and the other is the cathode side. Assuming that the porous plate 302 on the anode side, for example, the porous plate 302 disposed on the left side of the MEA 301 in FIG. 3, a groove serving as a hydrogen flow path 305 is formed on the side adjacent to the MEA 301. Circulates hydrogen, and the circulated hydrogen is supplied to the adjacent MEA 301. In addition, the anode-side porous plate 302 is provided with a groove serving as a humidifying pure water channel 306 facing the groove serving as the hydrogen channel 305, and the humidifying pure water is provided in the channel 306. Circulates, and the circulated pure water is given to the hydrogen flowing through the flow path 305 through the porous plate 302 to humidify the hydrogen. Therefore, the porous plate 302 on the anode side retains moisture by allowing the pure water for humidification to pass therethrough.

  On the other hand, when the porous plate 302 on the cathode side, for example, the porous plate 302 disposed on the right side of the MEA 301 in FIG. 3 is formed, a groove serving as an air flow path 307 is formed on the side adjacent to the MEA 301. Air flows through the path 307 and the circulating air is given to the adjacent MEA 301. In addition, the anode-side porous plate 302 is provided with a groove serving as a humidifying pure water channel 308 facing the groove serving as the air channel 307, and the humidifying pure water is provided in the channel 308. Circulates, and the circulated pure water is given to the air flowing through the flow path 308 through the porous plate 302 to humidify the air. Accordingly, even in the cathode-side porous plate 302, moisture is retained by allowing the pure water for humidification to pass therethrough.

  In the cooler plate 303, a groove serving as a cooling water flow path 309 is formed on the side adjacent to the separator 304, and the cooling water flows through the flow path 309, and the cells are cooled or heated by the flowing cooling water. That is, by cooling the cooling water flowing through the flow path 309, the end cell 201 that has generated heat due to a chemical reaction is cooled, while the end cell 201 is heated by heating the cooling water flowing through the flow path.

  Returning to FIG. 1, the cooling water pump 103 is a pump that supplies cooling water of a general antifreeze (LLC) to all cells of the fuel cell stack 101, and the pure water pump 104 humidifies the porous plate 302. It is a pump that supplies pure water.

  The pure water tank 105 stores the pure water for humidification supplied to the porous plate 302 by the pure water pump 104. In addition, when the number of end cells using the porous plate 302 is small, the pure water for humidification may not be stored in the pure water tank 105 in advance, but may be covered with moisture generated after the start of power generation. In this case, the pure water tank 105, the pure water pump 104, and the configuration for supplying pure water such as a pipe for leading the humidifying pure water to the end cell 201 become unnecessary.

  The combustor heat exchanger 106 is arranged in a cooling water circulation path circulating through the fuel cell stack 101 and the cooling water pump 103, and heats the cooling water supplied to each cell. The cooling water may be heated with an electric heater instead of the combustor heat exchanger 106.

  In the cooling water circulation path including the combustor heat exchanger 106, the fuel cell stack 101, and the cooling water pump 103, a part of the piping on the upstream side of the combustor heat exchanger 106 and the cooling water pump 103 is a pure water tank 105. It is arranged through. As a result, when the pure water in the pure water tank 105 is frozen, the heated cooling water passes through the pure water tank 105, thereby promoting the thawing of the frozen pure water.

  The radiator 107 flows in the cooling water that has been discharged from the fuel cell stack 101 and is warmed, and exchanges heat between the flowing cooling water and the outside air to cool the cooling water. The cooling water cooled by the radiator 107 flows into the cooling water pump 103.

  The shut valve 108 is provided between the cooling water pump 103 and the inlet side of the cooling water supplied to the fuel cell stack 101, and the shut valve 109 is provided on the three sides of the outlet side of the cooling water discharged from the fuel cell stack 101. Provided between the valves 110, both valves selectively control the supply of cooling water to the center cell 202 of the fuel cell stack 101. That is, by opening both shut valves 108 and 109, cooling water is supplied to all cells of the fuel cell stack 101, and by closing both shut valves 108 and 109, the center of the cooling water fuel cell stack 101 is provided. Supply to the cell 202 is interrupted, and cooling water is supplied only to the end cell 201.

  The three-way valve 110 selectively switches the cooling water discharged from the fuel cell stack 101 to the bypass flow path on the combustor heat exchanger 106 side or the radiator 107 side. That is, the three-way valve 110 is switched to the radiator 107 side when cooling the cooling water, and distributes the cooling water discharged from the fuel cell stack 101 to the radiator 107, while combustor when heating the cooling water. Switching to the heat exchanger 106 side causes the cooling water to flow through the combustor heat exchanger 106.

  The thermometers 111 and 112 measure the temperature of the cooling water discharged from the corresponding end cell 201 of the fuel cell stack 101, and the measured temperature is given to the control unit, and in a low temperature environment based on the measured temperature. The thawing state of the water in the end cell 201 is grasped.

  The thermometer 113 measures the temperature of pure water stored in the pure water tank 105, and the measured temperature is given to the control unit, and the pure water tank 105 in a low-temperature environment based on the measured temperature. The thawing status of stored pure water is grasped.

The control unit functions as a control center for controlling the operation of the system, and is provided with resources such as a CPU, a storage device, and an input / output device necessary for a computer that controls various operation processes based on a program, such as a microcomputer It is realized by. The control unit reads a signal from each sensor (not shown) including the thermometers 111, 112, 113 in this system, and based on a control logic (program) held in advance in advance,
A command is sent to each component of the system including the cooling water pump 103, the pure water pump 104, the combustor heat exchanger 106, the shut valves 108 and 109, and the three-way valve 110, and the system under a low temperature environment described below All operations necessary for operation / stop of this system, including start-up operation, are managed and controlled.

  In the humidification of the reaction gas in the center cell 202 of the fuel cell stack 101, the cathode side air is discharged from the fuel cell stack 101 using a known WRD (Water / Recovery / Device) (not shown). Moisture generated by power generation contained in the off-gas air thus collected is humidified by returning the collected moisture to the inlet side. On the other hand, the hydrogen on the anode side is humidified by the water contained in the off-gas hydrogen by returning the off-gas hydrogen discharged from the fuel cell stack 101 to the inlet side and circulating the hydrogen. Therefore, the anode side of the center cell 202 is not provided with a configuration for supplying pure water for humidification.

  In such a configuration, according to the procedure shown in the flowchart of FIG. 4, the present system is activated and power generation is started under a low temperature environment.

  In FIG. 4, when the system is started when the outside air temperature is below freezing (step S40), first, the end plate heater 102 of the fuel cell stack 101 is energized, and the end cell of the fuel cell stack 101 is generated by the heat generated by the end plate heater 102 201 is heated (step S41). Subsequently, based on a command given from the control unit, the shut valves 108 and 109 are closed, and the three-way valve 110 is switched so that the cooling water circulation path is on the combustor heat exchanger 106 side that bypasses the radiator 107. .

  Thereafter, the cooling water pump 103 and the combustor heat exchanger 106 are operated based on a command given from the control unit (step S43). Thereby, the cooling water heated by the combustor heat exchanger 106 and sent out by the cooling water pump 103 is supplied only to the end cells 201 of the fuel cell stack 101. Therefore, the end cell 201 of the fuel cell stack 101 is heated intensively by the end plate heater 102 and the heated cooling water to be heated. As a result, in the end cell 201, the frozen water is quickly thawed.

  Thereafter, the temperature of the cooling water discharged from the end cell 201 is measured by thermometers 111 and 112 provided on the outlet side of the cooling water of the end cell 201, and the measured temperature of the cooling water is set to a preset specified temperature. As described above, for example, it is determined whether or not the temperature is 5 ° C. or higher (step S44). As a result of the determination, when the temperature of the cooling water exceeds the specified temperature, the shut valves 108 and 109 are opened, and the heated cooling water that has been supplied only to the end cell 201 until then is added to the end cell 201. The supply to the center cell 202 is started. At the same time, the reaction gas is supplied to all the cells of the fuel cell stack 101 based on a command from the control unit to start power generation (step S45).

  Here, since the center cell 202 of the fuel cell stack 101 uses a solid plate separator, only a water content of water droplets remains due to the purge process when the system is stopped, and the water content is higher than that of the end cell 201. The amount is extremely small. When power generation is started, the end cell 201 self-heats and dissipates heat from the end cells 201 at both ends toward the center cell 202. As a result, even when the thawing of the end cell 201 is finished and the heated cooling water is supplied to the center cell 202 and the power generation is started at the same time, the thawing progresses rapidly in the center cell 202 and the power generation is immediately possible. It becomes.

  Further, since the number of end cells 201 is smaller than the number of center cells 202, and thus the number of porous plates 302 of the end cells 201 is also small, the humidifying net required for the porous plates 302 of the end cells 201 during power generation is required. The amount of water held in the pure water tank 105 is small. For this reason, when the heated cooling water is supplied to the fuel cell stack 101, the heating / cooling water is passed through the pure water tank 105 and the frozen water in the pure water tank 105 is thawed so much. Does not take much time. Therefore, there is a high possibility that a part or all of the pure water in the pure water tank 105 has been thawed before the start of power generation, and humidifying pure water can be supplied to the fuel cell stack 101 from the beginning of power generation. It becomes possible.

  However, since the porous plate 302 of the end cell 201 contains moisture supplied at the time of the previous power generation even before power generation, the thawing of pure water in the pure water tank 105 is not necessarily completed at the start of power generation. You don't have to. That is, the moisture contained in the porous plate 302 at the beginning of power generation is used as moisture for humidification.

  After the power generation is started, it is determined whether or not the temperature of pure water in the pure water tank 105 measured by the thermometer 113 is equal to or higher than a preset specified temperature, for example, 5 ° C. (step S46). . As a result of the determination, when the temperature of the deionized water is equal to or higher than the specified temperature, the deionized water pump 104 is operated (step S47), the deionized water is supplied to the porous plate 302 of the end cell 201, and the power generation is performed. Continued.

  As described above, in the first embodiment, a porous plate is used for several cells of the end cell 201 in the fuel cell stack 101, and a solid plate is used for the center cell 202. When it is thawed, power generation can be started, and the system startup time from below freezing point can be shortened.

  Further, by using a porous plate for the end cell 201, flooding of the end cell 201 can be prevented during normal operation.

  Furthermore, when the outside air temperature is below freezing point, even if the cell is once thawed, water flooding occurs in the cell's catalyst layer at the start of power generation and refreezes, which may degrade performance and cause permanent deterioration. was there. However, in the said Example 1, the said malfunction can be prevented by employ | adopting a porous plate for the end cell 201. FIG.

  Moreover, the end cell 201 can be rapidly thawed by supplying heated cooling water only to the end cell 201 at the time of starting from below freezing point. Therefore, by starting power generation in all cells after thawing the end cell 201, the system startup time in a low-temperature environment can be significantly reduced compared to the conventional case where power generation is started after all cells are defrosted. it can.

In addition, by inserting two cooler plates 303 that allow cooling water to flow into the end cells 201 only in the end cells 201, the thawing time of the end cells 201 can be shortened compared with a case where the number of the cooler plates 303 is one when starting from below freezing. can do.

  For example, when a porous plate is used for the center cell 202, only one cooler plate is required.

It is a figure which shows the structure of the fuel cell system which concerns on Example 1 of this invention. It is a figure which shows the structure of the fuel cell stack shown in FIG. It is a figure which shows the structure of the end cell shown in FIG. It is a flowchart which shows the starting procedure of the system which concerns on Example 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Fuel cell stack 102 ... End plate heater 103 ... Cooling water pump 104 ... Pure water pump 105 ... Pure water tank 106 ... Combustor heat exchanger 107 ... Radiator 108, 109 ... Shut valve 110 ... Three-way valve 111, 112, 113 ... Thermometer 201 ... End cell 202 ... Center cell 301 ... MEA
302 ... Porous plate 303 ... Cooler plate 304 ... Separator 305, 306, 307, 308, 309 ... Flow path

Claims (3)

A fuel cell stack comprising a plurality of cells stacked with a flow path through which a cooling medium for removing heat generated by power generation is generated by chemically reacting a reaction gas of a fuel gas and an oxidant gas. In the fuel cell system,
Among all the cells constituting the fuel cell stack, a predetermined number of end cells at both ends of the fuel cell stack are constituted by cells in which moisture for humidification is given to the reaction gas through a porous plate, and the fuel cell The other cell of the stack is configured by a cell using a solid plate. Heating means for heating the cooling medium;
A cooling medium supply means for selectively supplying and controlling the cooling medium heated by the heating means to the end cell;
When starting up the fuel cell system in a low temperature environment, the cooling medium heated by the heating means is selectively supplied only to the end cells by the cooling medium supply means, and the heated cooling medium in the end cells is selectively supplied. 2. The fuel cell system according to claim 1, wherein frozen water is thawed and power generation of all cells of the fuel cell stack is started immediately after thawing. 3. The fuel cell system according to claim 1, wherein the end cell has a cooler plate in which a flow path through which a cooling medium flows is formed, inserted into the anode side and the cathode side, respectively.

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