JP2009117044A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently lower concentration of hydrogen contained in fuel offgas. <P>SOLUTION: A control part 5 determines whether a temperature detected by a temperature sensor T is below a given temperature, whether a moisture content contained in the offgas is above a given moisture content, and whether an exhaust valve 45 of a hydrogen offgas flow channel 42 is opened. If 'YES' holds on either of these requirements included in the determination, the control part 5 increases a flow volume of oxidizing gas supplied from a first compressor 31 more than a flow volume supplied at normal times. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

In recent years, a fuel cell system using a fuel cell that generates electric power by an electrochemical reaction between a fuel gas, which is a reactive gas, and an oxidizing gas as an energy source has been developed. In such a fuel cell system, it is necessary to appropriately discharge impurities such as nitrogen and hydrogen from the anode electrode of the fuel cell in order to stably generate power. However, since the hydrogen offgas discharged from the anode electrode contains unreacted hydrogen, it is necessary to dilute the hydrogen below the flammable limit when discharging the hydrogen offgas to the outside. Conventionally, various hydrogen concentration reduction processes have been performed in order to dilute hydrogen below the flammable limit. For example, in the fuel cell system described in Patent Document 1 below, hydrogen concentration reduction processing using a catalytic combustor is performed to reduce the concentration of hydrogen contained in the hydrogen offgas.
JP 2005-174757 A

  By the way, in the hydrogen concentration reduction process using the catalyst combustor, if the humidity of the catalyst combustor becomes too high, moisture adheres to the surface of the catalyst, and the catalyst cannot react with hydrogen. As a result, the concentration of hydrogen contained in the fuel off-gas cannot be reduced by the catalytic combustor.

  The present invention has been made to solve the above-described problems caused by the prior art, and an object of the present invention is to provide a fuel cell system capable of efficiently reducing the concentration of fuel contained in fuel offgas.

  In order to solve the above-described problem, a fuel cell system according to the present invention includes a fuel cell that receives supply of an oxidizing gas and a fuel gas, which are reactive gases, and generates electric power through an electrochemical reaction of the reactive gas, and an oxidizing gas. A plurality of compressors that supply the fuel cell; and a catalyst combustor that uses a catalyst to combust the fuel contained in the fuel off-gas discharged from the fuel cell, the plurality of compressors supplying the oxidizing gas to the fuel cell. The catalyst combustor is provided in series on a supply flow path, and the catalyst combustor is provided between a plurality of compressors.

  According to the present invention, the catalyst in the catalytic combustor can be dried with the oxidizing gas sent from the compressor provided on the upstream side of the catalytic combustor, so that the reaction between the fuel and the catalyst can be promoted. Further, since the pressure of the oxidant gas supplied to the fuel cell can be increased by the compressor provided on the downstream side of the catalyst combustor, the backflow of the oxidant gas can be prevented.

  In the fuel cell system, when a temperature sensor that detects a temperature in the catalytic combustor and a temperature detected by the temperature sensor is equal to or lower than a predetermined temperature, at least upstream of the catalytic combustor among the plurality of compressors. And a flow rate control means for increasing the flow rate of the oxidizing gas supplied from the compressor provided on the side.

  As a result, when the temperature detected by the temperature sensor falls below a predetermined temperature, the flow rate of the oxidizing gas supplied from the compressor provided upstream of the catalytic combustor can be increased. Even when the temperature in the vessel is lowered and the catalyst is covered with water, the catalyst can be dried with the oxidizing gas supplied from the compressor.

  In the fuel cell system, the predetermined temperature can be set to a temperature at which the catalyst cannot react with the fuel.

  This increases the flow rate of the oxidizing gas supplied from the compressor provided on the upstream side of the catalytic combustor when the temperature in the catalytic combustor falls below the temperature at which the catalyst cannot react with the fuel. Can be made.

  In the fuel cell system, when the moisture amount calculating means for calculating the moisture amount contained in the fuel off-gas and the moisture amount calculated by the moisture amount calculating means are equal to or greater than a predetermined moisture amount, And a flow rate control means for increasing the flow rate of the oxidizing gas supplied from a compressor provided at least on the upstream side of the catalytic combustor.

  As a result, when the amount of water contained in the fuel off-gas exceeds a predetermined amount of water, the flow rate of the oxidizing gas supplied from the compressor provided upstream of the catalytic combustor can be increased. Even when the amount of water contained in the off-gas increases and the catalyst is covered with water, the catalyst can be dried with the oxidizing gas supplied from the compressor.

  In the fuel cell system, the predetermined moisture amount can be set to a moisture amount at which the catalyst cannot react with the fuel.

  As a result, the flow rate of the oxidizing gas supplied from the compressor provided on the upstream side of the catalyst combustor when the amount of water contained in the fuel off-gas is equal to or higher than the amount of water that prevents the catalyst from reacting with the fuel. Can be increased.

  The fuel cell system further includes a gas-liquid separator that recovers moisture from the fuel off-gas, and the catalytic combustor burns fuel contained in the fuel off-gas discharged from the gas-liquid separator using the catalyst. be able to.

  By doing in this way, the dry fuel off gas after the water | moisture content was collect | recovered can be made to flow in a catalyst combustor.

  In the fuel cell system, the water recovered by the gas-liquid separator can flow into the downstream side of the catalytic combustor and the upstream side of one of the compressors.

  By doing in this way, oxidizing gas can be optimally humidified, without providing a humidification module.

  According to the present invention, the concentration of the fuel contained in the fuel off gas can be efficiently reduced.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a fuel cell system according to the invention will be described with reference to the accompanying drawings. This embodiment demonstrates the case where the fuel cell system which concerns on this invention is used as a vehicle-mounted power generation system of a fuel cell vehicle (FCHV; Fuel Cell Hybrid Vehicle).

  In the fuel cell system according to the present embodiment, the fuel off-gas discharged from the fuel cell is caused to flow into a combustor (catalytic combustor) disposed between a plurality of compressors, thereby drying the catalyst contained in the combustor, It is characterized by promoting the reaction with fuel. Hereinafter, the configuration and operation of the fuel cell system having such characteristics will be described in detail.

  First, the configuration of the fuel cell system in the present embodiment will be described with reference to FIG. FIG. 1 is a configuration diagram schematically showing a fuel cell system in the present embodiment.

  As shown in FIG. 1, a fuel cell system 1 includes a fuel cell 2 that generates electric power by an electrochemical reaction between an oxidizing gas that is a reactive gas and the fuel gas, and an oxidizing gas that supplies air as the oxidizing gas to the fuel cell 2. It has a piping system 3, a hydrogen gas piping system 4 that supplies hydrogen as fuel gas to the fuel cell 2, and a control unit 5 that performs overall control of the entire system.

  The fuel cell 2 has a stack structure in which a plurality of single cells that generate power upon receiving a reaction gas are stacked. The fuel cell 2 is provided with a current sensor A that detects the output current of the fuel cell 2 and a voltage sensor V that detects the output voltage of the fuel cell 2.

  The oxidizing gas piping system 3 compresses the air taken in through the filter 30 and sends out compressed air as oxidizing gas, and the first compressor 31 and the second compressor 32. A combustor 33 disposed therebetween, an air supply channel 34 for supplying the oxidizing gas to the fuel cell 2, and an air exhaust channel 35 for discharging the oxidizing off-gas discharged from the fuel cell 2.

  By arranging the combustor 33 between the first compressor 31 and the second compressor 32, the following effects can be obtained. First, by providing the first compressor 31 on the upstream side of the combustor 33, the catalyst in the combustor 33 can be dried with the oxidizing gas sent from the first compressor 31 to the combustor 33, and the reaction of the catalyst can be promoted. it can. Further, by providing the second compressor 32 on the downstream side of the combustor 33, the pressure of the oxidizing gas supplied from the air supply flow path 34 to the fuel cell 2 can be easily increased, so that the backflow of the oxidizing gas is prevented. be able to.

  The compressor is not limited to the two compressors described above, and three or more compressors may be provided. In this case, the combustor 33 may be provided between any one of the plurality of combustors on the upstream side of the fuel cell 2.

  The air supply channel 34 and the air discharge channel 35 are provided with a humidifier 36 (humidification module) that humidifies the oxidizing gas pumped from the second compressor 32 using the oxidizing off-gas discharged from the fuel cell 2. ing. Oxidized off-gas that has undergone moisture exchange or the like by the humidifier 36 is finally exhausted into the atmosphere outside the system as exhaust gas. The combustor 33 is provided with a temperature sensor T that detects the temperature in the combustor 33. Furthermore, pressure sensors P1 and P2 for detecting the pressure of the air supply flow path 34 are provided on the downstream sides of the first compressor 31 and the second compressor 32, respectively.

  The hydrogen gas piping system 4 includes a hydrogen tank 40 as a fuel supply source storing high-pressure hydrogen gas, and a hydrogen supply channel 41 as a fuel supply channel for supplying the hydrogen gas in the hydrogen tank 40 to the fuel cell 2. And a hydrogen off-gas flow path 42 for allowing the hydrogen off-gas discharged from the fuel cell 2 to flow into the combustor 33. The hydrogen gas piping system 4 is an embodiment of the fuel supply system in the present invention. Instead of the hydrogen tank 40 in the present embodiment, for example, a reformer that reforms a hydrocarbon-based fuel into a hydrogen-rich fuel gas using water vapor, and a fuel gas reformed in the reformer with a high pressure A high-pressure gas tank that accumulates pressure in a state can be employed as a fuel supply source. A tank having a hydrogen storage alloy can also be employed as a fuel supply source.

  The hydrogen supply passage 41 is provided with a main stop valve 43 that shuts off or allows the supply of hydrogen gas from the hydrogen tank 40 and a regulator 44 that adjusts the pressure of the hydrogen gas to a preset secondary pressure. .

  A discharge channel 48 is connected to the hydrogen off-gas channel 42 via a gas-liquid separator 46 and an exhaust / drain valve 47. The gas-liquid separator 46 collects moisture from the hydrogen off gas and flows the dried hydrogen off gas to the combustor 33. The exhaust / drain valve 47 discharges the water collected by the gas-liquid separator 46 to the discharge channel 48 in accordance with a command from the control unit 5. The hydrogen off gas flow path 42 is provided with a discharge valve 45 that blocks or allows discharge of hydrogen off gas from the fuel cell 2. Further, a pressure sensor P <b> 3 that detects the pressure of the hydrogen off-gas flow path 42 is provided on the downstream side of the gas-liquid separator 46.

  The control unit 5 detects an operation amount of an acceleration operation member (for example, an accelerator) provided in the fuel cell vehicle with a sensor, and requests an acceleration request value (for example, a required power generation amount from a power consumption device such as a traction motor). Receives control information and controls the operation of various devices in the system. In addition to the traction motor, the power consuming device includes, for example, an auxiliary device (for example, a compressor motor) necessary for operating the fuel cell 2 and various devices (transmission, Wheel control device, steering device, suspension device, etc.), occupant space air conditioner (air conditioner), lighting, audio, etc. are included.

  When the temperature detected by the temperature sensor T is equal to or lower than a predetermined temperature, the control unit 5 increases the flow rate of the oxidizing gas supplied from the first compressor 31 as compared with the flow rate supplied at normal time. The predetermined temperature corresponds to a temperature at which the catalyst cannot react with hydrogen, for example. This is because when the temperature of the combustor 33 falls below a predetermined temperature, the catalyst is more likely to be covered with water compared with when the temperature is high, and the reaction with hydrogen becomes dull. When it is assumed that such a situation will occur, the flow rate of the oxidizing gas supplied from the first compressor 31 is increased to dry the catalyst.

  After increasing the flow rate of the oxidizing gas, the control unit 5 increases the flow rate of the oxidizing gas supplied from the first compressor 31 when the temperature detected by the temperature sensor T becomes higher than a predetermined flow rate increase release temperature. The flow rate is returned to the normal flow rate. The predetermined flow rate increase release temperature is preferably set to a temperature higher than the predetermined temperature described above.

  The control unit 5 calculates the amount of water contained in the hydrogen off-gas, and when the calculated amount of water is equal to or greater than a predetermined amount of water, the flow rate of the oxidizing gas supplied from the first compressor 31 is supplied at normal times. The flow rate is increased. The predetermined amount of water corresponds to, for example, the amount of water that prevents the catalyst from reacting with hydrogen. The amount of water contained in the hydrogen off gas can be calculated by using, for example, the amount of hydrogen chemical reaction corresponding to the amount of power generated by the fuel cell 2. This is because when the water content exceeds a predetermined water content, the catalyst is covered with water and the reaction with hydrogen becomes dull. The catalyst is dried by increasing the flow rate of the oxidizing gas supplied from 31.

  After increasing the flow rate of the oxidizing gas, the control unit 5 calculates the amount of water contained in the hydrogen off-gas, and when the calculated amount of water becomes less than a predetermined flow rate increase canceling water amount, the first compressor 31. The flow rate of the oxidizing gas supplied from is returned to the normal flow rate. In addition, it is preferable that the predetermined flow rate increase canceling water amount is set to be smaller than the predetermined water amount described above.

  When the hydrogen off-gas is discharged, the control unit 5 increases the flow rate of the oxidizing gas supplied from the first compressor 31 and the second compressor 32 as compared with the flow rate supplied at normal time. The hydrogen off gas is discharged when the discharge valve 45 of the hydrogen off gas flow path 42 is opened. This is because when the hydrogen off-gas is discharged, the amount of oxygen necessary for power generation in the fuel cell 2 decreases, so that the oxidation supplied from the first compressor 31 and the second compressor 32 when the hydrogen off-gas is discharged. The gas flow rate is increased.

  The control unit 5 increases the flow rate of the oxidizing gas supplied from the first compressor 31 and the second compressor 32 when the discharge valve 45 of the hydrogen off-gas passage 42 is closed after increasing the flow rate of the oxidizing gas. Return to the normal flow rate.

  The control unit 5 controls the flow rates of the oxidizing gas and the hydrogen off-gas so that the pressures detected by the pressure sensors P1 to P3 satisfy the pressure P1 <the pressure P3 <the pressure P2.

  Here, the control unit 5 physically includes, for example, a CPU, a ROM that stores a control program and control data processed by the CPU, a RAM that is mainly used as various work areas for control processing, And an input / output interface. These elements are connected to each other via a bus. Various sensors such as pressure sensors P1 to P3, temperature sensor T, current sensor A, and voltage sensor V are connected to the input / output interface, and the first compressor 31, the second compressor 32, the main stop valve 43, the discharge Various drivers for driving the valve 45 and the exhaust / drain valve 47 are connected.

  The CPU receives various detection results in the pressure sensors P1 to P3, the temperature sensor T, and the like via the input / output interface according to a control program stored in the ROM, and processes them using various data in the RAM. The flow rates of the oxidizing gas and the hydrogen off gas in the fuel cell system 1 are controlled. Further, the CPU controls the entire fuel cell system 1 by outputting control signals to various drivers via the input / output interface.

  Next, the oxidizing gas flow rate control process in the fuel cell system of the present embodiment will be described using the flowchart shown in FIG. This oxidizing gas flow rate control process is repeatedly performed from when the ignition key is turned on to when it is turned off.

  First, the control unit 5 determines whether or not the temperature detected by the temperature sensor T is equal to or lower than a predetermined temperature, whether or not the amount of water contained in the hydrogen off gas is equal to or higher than the predetermined amount of water, It is determined whether or not the discharge valve 45 has been opened (step S1). If NO is satisfied for all the requirements included in this determination (step S1; NO), the process of step S1 is repeated.

  On the other hand, when YES is established for any of the requirements included in the determination in step S1 (step S2; YES), the control unit 5 sets the flow rate of the oxidizing gas supplied from the first compressor 31 to the normal time. The flow rate is increased from the supplied flow rate (step S2). In step S2, the flow rate of the oxidizing gas supplied from the second compressor 31 may be increased from the flow rate supplied during normal operation.

  Subsequently, the control unit 5 determines whether or not the temperature detected by the temperature sensor T is higher than a predetermined flow rate increase canceling temperature, and whether or not the amount of water contained in the hydrogen off-gas is less than a predetermined flow rate increase canceling water amount. Whether or not the discharge valve 45 of the hydrogen off-gas channel 42 is closed is determined (step S3). If NO is satisfied for all the requirements included in this determination (step S3; NO), the process of step S3 is repeated.

  On the other hand, when YES is established for any of the requirements included in the determination in step S3 (step S3; YES), the control unit 5 sets the flow rate of the oxidizing gas supplied from the first compressor 31 to the normal time. It returns to the supplied flow rate (step S4).

  As described above, according to the fuel cell system 1 in the present embodiment, the catalyst in the combustor 33 can be dried with the oxidizing gas fed from the first compressor 31 provided on the upstream side of the combustor 33. And the catalyst can be promoted. Therefore, the concentration of hydrogen contained in the hydrogen off gas can be efficiently reduced.

  Further, according to the fuel cell system 1 in the present embodiment, the pressure of the oxidizing gas supplied to the fuel cell 2 can be increased by the second compressor 32 provided on the downstream side of the combustor 33, and therefore the backflow of the oxidizing gas Can be prevented.

  Further, when the temperature detected by the temperature sensor T is equal to or lower than a predetermined temperature, the flow rate of the oxidizing gas supplied from the first compressor 31 provided on the upstream side of the combustor 33 can be increased. Even when the temperature in the combustor 33 is lowered and the catalyst is covered with water, the catalyst can be dried with the oxidizing gas supplied from the first compressor 31.

  Furthermore, when the predetermined temperature is set to a temperature at which the catalyst cannot react with hydrogen, the temperature in the combustor 33 becomes equal to or lower than the temperature at which the catalyst cannot react with hydrogen. The flow rate of the oxidizing gas supplied from the first compressor 31 provided on the upstream side of the combustor 33 can be increased.

  In addition, when the amount of water contained in the hydrogen off gas exceeds a predetermined amount of water, the flow rate of the oxidizing gas supplied from the first compressor 31 provided on the upstream side of the combustor 33 can be increased. Even when the amount of water contained in the hydrogen off-gas increases and the catalyst is covered with water, the catalyst can be dried with the oxidizing gas supplied from the first compressor 31.

  Furthermore, by setting the predetermined amount of water to a amount of water that prevents the catalyst from reacting with hydrogen, the amount of water contained in the hydrogen off-gas exceeds the amount of water that prevents the catalyst from reacting with hydrogen. When this happens, the flow rate of the oxidizing gas supplied from the first compressor 31 provided on the upstream side of the combustor 33 can be increased.

  Further, according to the fuel cell system 1 in the present embodiment, the hydrogen off-gas discharged from the gas-liquid separator can be caused to flow into the combustor 33, so that the dry hydrogen off-gas after the moisture is recovered is supplied to the combustor 33. Can flow in.

  In the above-described embodiment, the humidifier 36 is provided in the oxidizing gas piping system 3 of the fuel cell system 1, but the humidifier is not necessarily provided. With reference to FIG. 3, the structure of the fuel cell system when a humidifier is not provided will be described. As shown in the figure, the fuel cell system in the present modification is different from the fuel cell system in the above-described embodiment in that the fuel cell system 1 in the modification uses the water collected by the gas-liquid separator 46 in the first way. The water supply flow path 49 that flows into the upstream side of the two compressors 32 is further provided, and the humidifier is not provided. Thus, the oxidizing gas discharged from the combustor 33 can be made to flow into the second compressor 32 after being humidified with the moisture supplied from the moisture supply channel 49. Therefore, it is possible to supply the fuel cell 2 with the optimally humidified oxidizing gas without providing the humidifier 36.

  In the above-described embodiment, the case where the fuel cell system according to the present invention is mounted on a fuel cell vehicle has been described. However, the present invention is also applied to various mobile bodies (robots, ships, aircrafts, etc.) other than the fuel cell vehicle. The fuel cell system according to the invention can be applied. Moreover, the fuel cell system according to the present invention can also be applied to a stationary power generation system used as a power generation facility for buildings (houses, buildings, etc.).

It is a lineblock diagram showing typically the fuel cell system in an embodiment. 4 is a flowchart for explaining an oxidizing gas flow rate control process in the fuel cell system shown in FIG. 1. It is a block diagram which shows typically the fuel cell system in a modification.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel cell, 3 ... Oxidation gas piping system, 4 ... Hydrogen gas piping system, 5 ... Control part, 30 ... Filter, 31 ... 1st compressor, 32 ... 2nd compressor, 33 ... Combustor, 34 ... Air supply flow path, 35 ... Air discharge flow path, 36 ... Humidifier, 40 ... Hydrogen tank, 41 ... Hydrogen supply flow path, 42 ... Hydrogen off-gas flow path, 43 ... Main stop valve, 44 ... Regulator, 45 ... Drain valve, 46 ... gas-liquid separator, 47 ... exhaust drain valve, 48 ... discharge channel, 49 ... moisture supply channel, P1-P3 ... pressure sensor, T ... temperature sensor, A ... current sensor, V ... voltage sensor .

Claims (7)

A fuel cell that receives supply of an oxidizing gas and a fuel gas, which are reactive gases, and generates electric power through an electrochemical reaction of the reactive gases;
A plurality of compressors for supplying the oxidizing gas to the fuel cell;
A catalyst combustor for combusting the fuel contained in the fuel off-gas discharged from the fuel cell using a catalyst,
The plurality of compressors are provided in series on a flow path for supplying the oxidizing gas to the fuel cell,
The fuel cell system, wherein the catalytic combustor is provided between the plurality of compressors. A temperature sensor for detecting the temperature in the catalytic combustor;
When the temperature detected by the temperature sensor is equal to or lower than a predetermined temperature, the flow rate of the oxidizing gas supplied from at least the compressor provided upstream of the catalytic combustor among the plurality of compressors is increased. Flow rate control means,
The fuel cell system according to claim 1, further comprising:   The fuel cell system according to claim 2, wherein the predetermined temperature is a temperature at which the catalyst cannot react with the fuel. A moisture amount calculating means for calculating the amount of moisture contained in the fuel off gas;
When the moisture amount calculated by the moisture amount calculating means is equal to or greater than a predetermined moisture amount, the oxidation supplied from at least a compressor provided on the upstream side of the catalytic combustor among the plurality of compressors. A flow rate control means for increasing the gas flow rate;
The fuel cell system according to claim 1, further comprising:   The fuel cell system according to claim 4, wherein the predetermined moisture amount is a moisture amount at which the catalyst cannot react with the fuel. A gas-liquid separator that recovers moisture from the fuel off-gas,
The fuel cell system according to any one of claims 1 to 5, wherein the catalyst combustor burns fuel contained in the fuel off-gas discharged from the gas-liquid separator using a catalyst.   The fuel cell system according to claim 6, wherein the water recovered by the gas-liquid separator is caused to flow into the downstream side of the catalytic combustor and the upstream side of any one of the compressors.

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