JP2004262689A - Fuel reformer and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit decrease in reforming reaction efficiency caused by carbon deposited on a reforming catalyst. <P>SOLUTION: In a fuel reformer 10, a liquid reformed fuel is intermittently injected into a fuel-introducing chamber 22 by an injector 20. Meanwhile, a reforming gas comprising air and steam is heated and subsequently fed to the fuel-introducing chamber 22. When the reformed fuel is injected, it is mixed with the reforming gas, vaporized by heat of the reforming gas and introduced into the reformer 24. While injection of the reformed fuel is suspended, oxidation and removal of carbon deposited on the reforming catalyst is performed by oxygen present within the reforming gas. The fuel-introducing chamber 22 has a volume smaller than the amount of the reforming gas fed while the injection of the reformed fuel is suspended. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel reforming apparatus that generates hydrogen from a hydrocarbon-based reformed fuel by utilizing a reforming reaction, and a method of operating the same.
[0002]
[Prior art]
As a method for generating hydrogen, a method for generating hydrogen from a hydrocarbon-based fuel by a reforming reaction is known. For example, Patent Literature 1 discloses a technique in which a steam reforming reaction and a partial oxidation reaction are used in combination as a reforming reaction to generate hydrogen from gasoline and supply the generated hydrogen to a fuel cell.
[0003]
[Patent Document 1]
JP-A-11-79703
[Patent Document 2]
JP 2001-139301 A
[0004]
[Problems to be solved by the invention]
However, when reforming a hydrocarbon-based fuel such as gasoline, there is a problem that carbon is deposited on a catalyst that promotes the reforming reaction in the course of the progress of the reforming reaction. If carbon is deposited on the reforming catalyst, the reforming reaction may be hindered by the deposited carbon, and the efficiency of the reforming reaction may be reduced.
[0005]
The present invention has been made in order to solve the above-mentioned conventional problems, and when reforming a hydrocarbon-based fuel to generate hydrogen, a modification caused by carbon precipitation on a reforming catalyst. The purpose of the present invention is to suppress a decrease in efficiency of the quality reaction.
[0006]
[Means for Solving the Problems and Their Functions and Effects]
In order to achieve the above object, a first fuel reformer of the present invention intermittently supplies a hydrocarbon-based reformed fuel to a reforming catalyst and utilizes the reforming reaction to perform the reforming. A fuel reformer that generates hydrogen from fuel,
A reformed fuel discharge unit that intermittently discharges the reformed fuel,
An oxidizing gas supply unit that discharges an oxidizing gas containing oxygen when at least the reformed fuel discharging unit stops discharging the reformed fuel;
A fuel introduction chamber into which the reformed fuel discharged by the reformed fuel discharge unit and the oxidant gas discharged by the oxidant gas supply unit are directly introduced;
A catalyst unit that is provided connected to the fuel introduction chamber, includes the reforming catalyst, and is supplied with the reformed fuel and the oxidizing gas via the fuel introduction chamber;
While controlling the reformed fuel discharge unit to discharge the reformed fuel in an amount suitable for the reforming reaction, every time the reformed fuel discharge unit stops discharging the reformed fuel, the fuel A control unit that controls the oxidizing gas supply unit so as to discharge the oxidizing gas in an amount equal to or greater than the volume of the introduction chamber;
The gist is to provide
[0007]
According to the first fuel reforming apparatus of the present invention configured as described above, the discharge of the reformed fuel is stopped when the operation of discharging the reformed fuel and the operation of stopping the discharge are alternately repeated. Occasionally, carbon deposited on the reforming catalyst can be oxidized and removed by supplying an oxidizing gas to the catalyst section. Here, every time the discharge of the reformed fuel is stopped, an amount of the oxidizing gas equal to or larger than the volume of the fuel introduction chamber is discharged into the fuel introduction chamber. The gas can be scavenged well. By sufficiently scavenging the fuel introduction chamber, a state in which the concentration of the reformed fuel in the gas supplied to the catalyst section is extremely low is realized, and the oxidized removal of deposited carbon can be favorably performed.
[0008]
In the first fuel reforming apparatus of the present invention, the control unit is supplied to the catalyst unit via the fuel introduction chamber while the reformed fuel discharge unit stops discharging the reformed fuel. It is preferable to control the discharge amount of the oxidizing gas from the oxidizing gas supply unit such that the concentration of the reformed fuel in the gas becomes 1 vol% or less. With this configuration, the carbon deposited on the reforming catalyst can be oxidized and removed more reliably.
[0009]
In the first fuel reforming device of the present invention, the control unit varies an amount of the oxidizing gas discharged from the oxidizing gas supply unit according to an amount of hydrogen to be generated by the fuel reforming device. In addition, the reformed fuel discharging unit and the oxidizing gas are oxidized such that the smaller the amount of the oxidizing gas discharged from the oxidizing gas supply unit, the longer the operation for stopping the discharge of the reformed fuel is performed. Control with the agent gas supply unit may be performed.
[0010]
With such a configuration, even when the supply amount of the oxidizing gas decreases due to a change in the amount of hydrogen to be generated by the fuel reformer, the scavenging of the fuel introduction chamber by the oxidizing gas can be reliably performed. Can be.
[0011]
The second fuel reforming apparatus of the present invention intermittently supplies a hydrocarbon-based reformed fuel to a reforming catalyst and utilizes a reforming reaction to generate hydrogen from the reformed fuel. Quality device,
A reformed fuel discharge unit that intermittently discharges the reformed fuel,
An oxidizing gas supply unit that discharges an oxidizing gas containing oxygen when at least the reformed fuel discharging unit stops discharging the reformed fuel;
While the reformed fuel discharged from the reformed fuel discharging unit and the oxidizing gas discharged from the oxidizing gas supply unit are directly introduced, and the reformed fuel discharging unit stops discharging the reformed fuel. A fuel introduction chamber formed to have a volume equal to or less than the amount of the oxidizing gas discharged by the oxidizing gas supply unit,
A catalyst unit that is provided connected to the fuel introduction chamber, includes the reforming catalyst, and is supplied with the reformed fuel and the oxidizing gas via the fuel introduction chamber;
While controlling the reformed fuel discharge unit to supply the reformed fuel in an amount suitable for the reforming reaction to the catalyst unit, the amount of the reformed fuel discharged from the reformed fuel discharge unit is controlled. A control unit that controls the oxidizing gas supply unit so as to discharge the oxidizing gas in an appropriate amount;
The gist is to provide
[0012]
According to the second fuel reforming apparatus of the present invention configured as described above, the discharge of the reformed fuel is stopped when the operation of discharging the reformed fuel and the operation of stopping the discharge are alternately repeated. Occasionally, carbon deposited on the reforming catalyst can be oxidized and removed by supplying an oxidizing gas to the catalyst section. Here, since the fuel introduction chamber is formed so as to have a volume equal to or less than the amount of the oxidizing gas supplied while the discharge of the reformed fuel is stopped, the fuel introduction chamber is stopped when the discharge of the reformed fuel is stopped. Can be favorably scavenged by the oxidizing gas. By sufficiently scavenging the fuel introduction chamber, a state in which the concentration of the reformed fuel in the gas supplied to the catalyst section is extremely low is realized, and the oxidized removal of deposited carbon can be favorably performed.
[0013]
In the first or second fuel reformer of the present invention,
The reformed fuel discharging unit sprays the liquid reformed fuel into the fuel introduction chamber,
The oxidizing gas supply unit discharges the oxidizing gas, which has been heated to a predetermined high temperature at which the sprayed reformed fuel can be vaporized, even when performing the discharging operation of the reformed fuel,
The fuel introduction chamber may include a heating unit for heating the inner wall surface.
[0014]
With such a configuration, the reformed fuel sprayed into the fuel introduction chamber is vaporized by using heat of the oxidizing gas, and further heats the inner wall surface of the fuel introduction chamber heated by the heating unit. Can be vaporized using. Therefore, the reformed fuel can be efficiently vaporized, and the sprayed droplets of the reformed fuel do not stay in the fuel introduction chamber. Therefore, when the discharge of the reformed fuel is stopped, the inside of the fuel introduction chamber is quickly scavenged, and the concentration of the reformed fuel in the gas supplied to the catalyst portion can be more reliably reduced, so that the efficiency of removing deposited carbon can be reduced. Can be improved.
[0015]
In such a fuel reforming apparatus, the oxidizing gas supply unit may supply the oxidizing gas to the fuel introducing chamber so that the oxidizing gas forms a swirling flow in the fuel introducing chamber. good. Thereby, the efficiency of vaporizing the sprayed droplets of the reformed fuel by using the heat of the inner wall surface of the fuel introduction chamber can be further improved.
[0016]
In the first or second fuel reformer of the present invention,
The reformed fuel discharging unit sprays the liquid reformed fuel into the fuel introduction chamber,
The oxidizing gas supply unit is configured to supply the oxidizing gas, which has been heated to a predetermined high temperature at which the sprayed reformed fuel can be vaporized, into a turbulent state even when the reforming fuel is discharged. May be supplied into the fuel introduction chamber.
[0017]
With such a configuration, the vaporization of the reformed fuel droplets sprayed into the fuel introduction chamber can be promoted, and the efficiency of scavenging the fuel introduction chamber can be improved.
[0018]
The present invention can be realized in various forms other than the above. For example, the present invention can be realized in a form such as a fuel cell system having a fuel reformer, an operation method of the fuel reformer, and the like.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in the following order based on examples.
A. Overall configuration of the device:
B. Removal operation of deposited carbon:
C. effect:
D. Second embodiment:
E. FIG. Modification:
[0020]
A. Overall configuration of the device:
FIG. 1 is a block diagram schematically illustrating a configuration of a fuel cell system 15 including a fuel reformer 10 and a fuel cell 17 as an embodiment. The fuel reformer 10 includes an injector 20, a fuel introduction chamber 22, a reformer 24, a heat exchanger 26, a CO reduction unit 28, a heating unit 30, and a control unit 35.
[0021]
The injector 20 injects a hydrocarbon-based reformed fuel into the fuel introduction chamber 22. In the present embodiment, a liquid hydrocarbon is used as the reformed fuel, and the injector 20 includes a nozzle for spraying the liquid reformed fuel in the form of liquid fine particles. The injector 20 can be formed, for example, as an electromagnetic solenoid valve that can control the amount of reformed fuel to be sprayed by opening and closing the valve. The size of the droplet of the reformed fuel to be sprayed can be adjusted by the size of the discharge port provided at the tip of the nozzle. In the present embodiment, when injecting a predetermined amount of reformed fuel, the injector 20 is controlled so as to intermittently perform this injection operation.
[0022]
In the fuel introduction chamber 22, in addition to the reformed fuel injected from the injector 20, steam and air (hereinafter, steam and air supplied to the fuel introduction chamber 22 are collectively referred to as a reforming gas). Is supplied through a reforming gas flow path 32. The reforming gas supplied to the fuel introduction chamber 22 is heated in the heating unit 30 prior to the supply. In order to adjust the amount of the reforming gas supplied from the heating unit 30 to the fuel introduction chamber 22, a valve 31 is provided in a reforming gas flow path 32 connecting the heating unit 30 and the fuel introduction chamber 22. Have been. In the fuel introduction chamber 22, the reformed fuel and the reforming gas are mixed to form a mixed gas, and the mixed gas is sent to the reformer 24. In the fuel reforming apparatus 10 of the present embodiment, the amount of the reforming gas supplied when the injector 20 described above stops the injection of the reformed fuel is greater than the volume of the fuel introduction chamber 22. This will be described in detail later.
[0023]
The reformer 24 includes a reforming catalyst that promotes a reforming reaction. The reforming catalyst may be appropriately selected according to the reforming fuel to be used. Since the steam and the air are supplied to the reformer 24 of the present embodiment as described above, the steam reforming reaction and the partial oxidation reaction proceed as the reforming reaction. By performing the steam reforming reaction, which is an endothermic reaction, and the partial oxidation reaction, which is an exothermic reaction, at least a part of the heat required for the steam reforming reaction can be supplied by the partial oxidation reaction. The reformer 24 may further include a heat source such as a heater, and the temperature in the reformer 24 is controlled so as to be in a predetermined temperature range suitable for the reforming fuel and the reforming catalyst to be used. . In this specification, the gas containing hydrogen generated in the reformer 24 is referred to as a reformed gas. In the reformer 24, a reaction for oxidizing the carbon deposited on the reforming catalyst also proceeds, which will be described later.
[0024]
The heat exchanger 26 is a device for lowering the temperature of the reformed gas discharged from the reformer 24 by exchanging heat with a predetermined refrigerant. The reformed gas cooled in the heat exchanger 26 is supplied to the CO reduction unit 28. Note that, as the refrigerant used in the heat exchanger 26, at least one of air and water to be supplied to the fuel introduction chamber 22 may be used.
[0025]
The CO reduction unit 28 is a device that reduces the concentration of carbon monoxide in the reformed gas supplied from the reformer 24. The reformed gas supplied from the reformer 24 usually contains a predetermined amount of carbon monoxide. When the gas containing carbon monoxide is supplied to the fuel cell 17 in this manner, the platinum catalyst included in the fuel cell 17 may be poisoned by the carbon monoxide, and the cell performance may be reduced. Therefore, a CO reduction unit 28 is provided to reduce the concentration of carbon monoxide in the reformed gas supplied to the fuel cell 17. The CO reduction unit 28 includes a catalyst that promotes a shift reaction that produces carbon dioxide and hydrogen from carbon monoxide and water vapor, and can be a shift unit that reduces the concentration of carbon monoxide in the hydrogen-rich gas by the shift reaction. . Alternatively, a carbon monoxide selective oxidizing unit that includes a catalyst that promotes a selective oxidation reaction that oxidizes carbon monoxide in preference to hydrogen and that reduces the concentration of carbon monoxide in a hydrogen-rich gas by the carbon monoxide selective oxidation reaction. Can be. Further, the CO reduction unit 28 may include both the shift unit and the carbon monoxide selective oxidation unit. Alternatively, the CO reduction unit 28 can be a device that selectively extracts hydrogen using a hydrogen separation membrane containing, for example, palladium.
[0026]
The reformed gas whose carbon monoxide concentration has been reduced by the CO reduction unit 28 is supplied to the anode of the fuel cell 17 as a fuel gas. Further, air is supplied as an oxidizing gas from the blower 34 to the cathode of the fuel cell 17, and an electrochemical reaction proceeds in the fuel cell 17.
[0027]
The control unit 35 is configured as a logic circuit centered on a microcomputer, and includes a CPU, a ROM, a RAM, and input / output ports for inputting and outputting various signals. The control unit 35 inputs detection signals from various sensors included in the fuel cell system 15 and outputs drive signals to the injector 20 and the valve 31 described above. As described above, the control unit 35 controls the operating state of the entire fuel cell system 15 including the fuel reformer 10.
[0028]
Although the fuel reformer 10 of the present embodiment supplies hydrogen to the fuel cell 17, the hydrogen generated by the fuel reformer may be supplied to different types of hydrogen consuming devices. good.
[0029]
B. Removal operation of deposited carbon:
In the fuel reforming apparatus 10 of the present embodiment, the operation of removing deposited carbon is performed by intermittently injecting reformed fuel from the injector 20 into the fuel introduction chamber 22. That is, when the reforming reaction proceeds, carbon may be deposited on the reforming catalyst, but a period in which fuel injection is stopped is provided. By supplying only carbon, the carbon deposited on the reforming catalyst is oxidized and removed. Further, in the fuel reforming apparatus 10 of the present embodiment, the volume of the fuel introduction chamber 22 is equal to or less than the amount (volume) of the reforming gas supplied to the fuel introduction chamber 22 while the fuel injection is stopped. It is formed as follows. This makes it possible to more reliably remove the deposited carbon. Hereinafter, control for intermittently performing fuel injection will be described.
[0030]
FIG. 2 is a flowchart illustrating an operation control processing routine that is repeatedly executed at a predetermined timing in the control unit 35 during operation of the fuel reforming apparatus 10.
[0031]
When this routine is executed, the control unit 35 first inputs a required hydrogen amount (step S100). The required hydrogen amount is the amount of hydrogen to be generated by the fuel reformer 10, and can be determined based on, for example, the amount of power required for the fuel cell 17.
[0032]
Next, the control unit 35 sets the fuel injection amount and the reforming gas amount based on the required hydrogen amount (step S110). The fuel injection amount is a reformed fuel amount required to generate an amount of hydrogen corresponding to the required hydrogen amount by the reforming reaction, and is set according to the efficiency of the reforming reaction in the reformer 24. The reforming gas amount (air amount and water vapor amount) is set to be a predetermined ratio with respect to the supplied reforming fuel amount. In this embodiment, O / C (the ratio of oxygen molecules in the reforming gas to carbon atoms in the reformed fuel) and S / C (in advance, so that the reforming reaction proceeds well in the reformer 24). (The ratio of water molecules in the reforming gas to carbon atoms in the reformed fuel). Then, the reforming gas amount is set based on the reformed fuel amount and the O / C and S / C. The reformed fuel amount and the reforming gas amount set in step S110 may be calculated each time based on the required hydrogen amount as described above, or the required hydrogen amount and the set amount may be calculated in advance. The setting may be made using the associated map.
[0033]
The fuel injection amount and the reforming gas amount may be set in consideration of parameters other than the required hydrogen amount. Such other parameters include, for example, the temperature of the reformer 24. Since the efficiency of the reforming reaction varies depending on the temperature of the reformer 24, it is possible to more accurately set the amount of reformed fuel required to obtain a desired amount of hydrogen by considering the temperature of the reformer 24. Can be. When the temperature of the reformer 24 is low (such as during warm air), the amount of water vapor in the reforming gas is reduced and the amount of air is increased, so that the oxidation reaction in the reformer 24 becomes more active. It may be performed.
[0034]
After setting the fuel injection amount and the reforming gas amount, the control unit 35 sets a period during which fuel injection is performed and a period during which fuel injection is stopped (step S120). FIG. 3 is an explanatory view illustrating the state of fuel injection in the operation of removing deposited carbon. As shown in FIG. 3, the execution cycle T includes an injection period t1 for performing fuel injection and a stop period t2 for stopping fuel injection. In the stop period t2, only the reforming gas is supplied to the fuel introduction chamber 22. In the present embodiment, the execution period T is fixed, and the time density (hereinafter, referred to as a duty ratio) between the injection period t1 and the stop period t2 is controlled according to the fuel injection amount set in step S110. Since the flow rate of the reformed fuel injected from the injector 20 is determined by the performance of the injector 20 (for example, the size of the discharge port of the nozzle, the injection pressure, etc.), the reformed fuel flow rate and the fuel injection amount set in step S120 , The injection period t1 can be set. FIG. 3A shows a case where the required power amount is larger, that is, a case where the required hydrogen amount is larger, and FIG. 3B shows a case where the required hydrogen amount and the required hydrogen amount are smaller. As shown in FIG. 3, the injection period t1 is set longer as the required hydrogen amount increases. When actually setting each of the above periods, the injection period t1 and / or the stop period t2 are determined in advance and stored in the control unit 35 as a map corresponding to the required hydrogen amount or the reforming catalyst temperature. Alternatively, this map may be referred to.
[0035]
The control unit 35 controls each unit of the fuel reforming apparatus 10 according to the various control amounts set by the above processing (step S130), and ends this routine. As a result, the operation in which the fuel injection is performed in the period t1 and the operation in which the injection is stopped is performed in the period t2 are repeated, and the reformed fuel in the amount set in step S110 is supplied as a whole, and hydrogen is generated by the reforming reaction. The reforming gas is supplied in a substantially constant state irrespective of the injection period t1 and the stop period t2 such that the supply amount thereof becomes the amount set in step S110 (hereinafter, referred to as the reforming gas flow rate Q). Supplied with. Thus, in the stop period t2, the carbon in the reforming gas is oxidized and removed using the oxygen in the reforming gas.
[0036]
Here, the fuel reforming apparatus 10 of the present embodiment is configured such that the reforming gas amount (volume) supplied during the stop period t2 is equal to or larger than the volume V of the fuel introduction chamber 22. That is, even when the required hydrogen amount fluctuates and the stop period t2 fluctuates, the following expression (1) holds for the reforming gas flow rate Q.
Q × t2 ≧ V (1)
[0037]
FIG. 4 is an explanatory diagram schematically showing a state of the fuel introduction chamber 22 and the reformer 24 when the reformed fuel is intermittently injected from the injector 20. When the injection of the reformed fuel from the injector 20 is started during the injection period t1 (FIG. 4A), the reformed fuel concentration in the fuel introduction chamber 22 increases and is supplied from the fuel introduction chamber 22 to the reformer 24. The concentration of the reformed fuel in the gas also increases (FIG. 4B). The reforming reaction proceeds in the reformer 24 using the reformed fuel thus supplied. When the injection period t1 elapses and the stop period t2 is reached, only the reforming gas is supplied to the fuel introduction chamber 22. The amount of the reforming gas supplied to the fuel introduction chamber 22 during the stop period t2 is Q × t2, which is equal to or larger than the volume V of the fuel introduction chamber 22, so that the fuel introduction chamber 22 during the stop period t2. The inside is sufficiently scavenged (FIG. 4C). As a result, the concentration of the reformed fuel in the gas supplied from the fuel introduction chamber 22 to the reformer 24 becomes extremely low, and the reformer 24 oxidizes the deposited carbon using oxygen in the reforming gas. It is.
[0038]
As described above, when the required hydrogen amount decreases, the stop period t2 is set longer, and the reforming gas flow rate Q is set smaller. Conversely, when the required hydrogen amount increases, the stop period t2 is set shorter and the reforming gas flow rate Q is set larger. Thus, even when the required hydrogen amount fluctuates, the size of the fuel introduction chamber 22 is determined so that the above equation (1) always holds. As described above, the fuel introduction chamber 22 is designed such that the above equation (1) is always satisfied when the fuel reforming apparatus 10 is operated within a preset processing capacity range.
[0039]
When designing the fuel introduction chamber 22, for example, a simulation is performed over the entire range of the assumed variation in the required amount of hydrogen, the expected minimum value of “Q × t2” is determined, and the volume of the fuel introduction chamber 22 is reduced. What is necessary is just to make it below the said minimum value. Alternatively, in an operating state in which the value of “Q × t2” is expected to be particularly small, the volume of the fuel introduction chamber 22 may be set so as to be always equal to or smaller than “Q × t2”. For example, in a fuel reformer such as that shown in this embodiment, since the above-mentioned Q × t2 generally tends to decrease as the load decreases, a typical operating state at a low load (for example, the fuel cell system 15). The volume V of the fuel introduction chamber 22 may be determined so that the expression (1) is satisfied in a case where the engine is in an idling state in which only the electric power required to maintain the activation state is generated. As long as the above formula (1) is satisfied, it is sufficient that a sufficient volume is secured to sufficiently vaporize the sprayed reformed fuel and mix it with the reforming gas.
[0040]
C. effect:
According to the fuel reformer 10 of the present embodiment configured as described above, when the supply of the reformed fuel is performed intermittently to oxidize and remove the deposited carbon on the reforming catalyst, the stop period t2 By setting the supplied reforming gas amount to be equal to or larger than the volume of the fuel introduction chamber 22, it is possible to more reliably remove the deposited carbon. By setting the amount of the reforming gas supplied during the stop period t2 to be equal to or larger than the volume of the fuel introduction chamber 22, the inside of the fuel introduction chamber 22 is sufficiently scavenged when the fuel injection is stopped, and supplied to the reformer 24. A state in which the concentration of the reformed fuel in the gas to be performed is extremely low is realized. Since the concentration of the reformed fuel in the gas supplied to the reformer 24 is extremely low, the oxidation of the deposited carbon of the reforming catalyst is effectively performed. Then, by repeatedly performing such an operation, it is possible to prevent deposition of deposited carbon on the reforming catalyst.
[0041]
FIG. 5 is an explanatory diagram showing the relationship between the fuel injection operation and the reformed fuel concentration in the gas supplied to the reformer 24. As shown in FIG. 5, the reformed fuel concentration in the gas supplied to the reformer 24 sharply increases when the combustion injection is started in the injection period t1, and becomes highest at the end of the fuel injection period t1. Then, when the stop period t2 is reached, the reformed fuel concentration sharply decreases as the fuel introduction chamber 22 is scavenged by the reforming gas. By providing a state in which the concentration of the reformed fuel in the gas supplied to the reformer 24 is reduced in this manner, it is possible to oxidize and remove the deposited carbon of the reforming catalyst in a favorable manner. Specifically, it is desirable that the time during which the concentration of the reformed fuel in the gas supplied to the reformer 24 becomes 1 vol% or less is 50 msec or more. The efficiency of burning and removing the deposited carbon depends on the amount of carbon deposited on the reforming catalyst and the amount of the reforming gas, in addition to the concentration of the reforming fuel in the gas supplied to the reformer 24. It is affected by the amount of oxygen in the medium and the temperature of the reforming catalyst.
[0042]
In the stop period t2, as described above, by providing a state in which the concentration of the reformed fuel in the gas supplied to the reformer 24 is sufficiently low, it is possible to reliably remove the deposited carbon. . Further, by lowering the reformed fuel concentration in the gas supplied to the reformer 24, even if the temperature inside the reformer 24 is lower, the deposited carbon can be oxidized. Become. Therefore, the deterioration of the reforming catalyst due to the high temperature can be suppressed, and the durability of the reformer 24 can be improved.
[0043]
In the present embodiment, when the fuel injection amount is changed, the length of the injection period t1 and the length of the stop period t2 are changed in the injector 20 while keeping the duty ratio constant. With such a configuration, even when the fuel injection amount is set smaller, the scavenging of the fuel introduction chamber 22 is sufficiently performed, and the deposited carbon can be efficiently removed. That is, when the fuel injection amount is small, the reforming gas amount is set to be small accordingly, and it becomes difficult to scavenge the fuel introduction chamber 22. However, when the fuel injection amount is small, the stop period t2 is set longer. By doing so, it is possible to sufficiently scavenge the fuel introduction chamber 22 even if the reforming gas flow rate decreases.
[0044]
It should be noted that a similar effect can be obtained when changing the cycle T in place of the duty ratio when changing the fuel injection amount. Even when the cycle T is changed instead of the duty ratio, when the fuel injection amount is set smaller, the stop period t2 becomes longer, so that the fuel introduction chamber 22 can be scavenged sufficiently.
[0045]
In the above embodiment, the injection of the reformed fuel is completely stopped in the stop period t2. However, a configuration in which the injection of the reformed fuel from the injector 20 is not completely stopped may be adopted. In this embodiment, an electromagnetic solenoid valve is used as the injector 20. However, depending on the type of the injector 20, the fuel injection may not be stopped immediately even if the fuel injection signal is turned off. Also in such a case, by providing the stop period t2 during which the fuel injection signal is turned off, a state in which the concentration of the reformed fuel in the gas supplied to the reformer 24 becomes sufficiently low as described above is realized. The same effect can be obtained.
[0046]
D. Second embodiment:
In the first embodiment, the amount of the reforming gas supplied during the stop period t2 is set to be equal to or larger than the volume of the fuel introduction chamber 22, so that the inside of the fuel introduction chamber 22 is sufficiently scavenged and supplied to the reformer 24. This makes it possible to sufficiently reduce the reformed fuel concentration in the gas. In the following second embodiment, in addition to such a configuration, the structure of the fuel introduction chamber promotes the vaporization of reformed fuel in the fuel introduction chamber, thereby further improving the efficiency of scavenging in the fuel introduction chamber. The reformer fuel concentration in the gas supplied to the reformer 24 is further reduced.
[0047]
FIG. 6 is an explanatory diagram showing a state of a cross section of a main part of the fuel reformer of the second embodiment. FIG. 7 is an explanatory diagram showing a cross section taken along line 7-7 in FIG. The fuel reforming apparatus according to the second embodiment is provided in a system similar to the fuel cell system 15 according to the first embodiment. In FIG. 6, the injector 20, the fuel introduction chamber 22, and the reformer 20 in FIG. Only the portion corresponding to 24 is shown. 6, the same reference numerals are given to the same parts as those in FIG. 1, and the detailed description will be omitted.
[0048]
As shown in FIG. 6, in the second embodiment, the fuel introduction chamber 122 and the reformer 24 are each formed in a substantially columnar shape. The fuel introduction chamber 122 formed as a column having a larger cross-sectional diameter and the reformer 124 formed as a column having a smaller cross-sectional diameter are connected in series, and both are integrally formed. I have.
[0049]
The reforming gas passage 32 is connected to the fuel introduction chamber 122, and the high-temperature reforming gas introduced from the reforming gas passage 32 flows through the inner wall of the cylinder inside the fuel introduction chamber 122. To form a swirling flow. Then, the reformed fuel injected from the injector 20 evaporates while being mixed with the reforming gas forming the swirling flow. A heater 121 is provided in the wall of the fuel introduction chamber 122, and the wall of the fuel introduction chamber 122 is heated by the heater 121.
[0050]
A partition 123a is provided between the fuel introduction chamber 122 and the reformer 124. The partition wall 123a is formed in a conical wall shape protruding toward the fuel introduction chamber 122, and a communication hole 123b is formed in a central portion (top portion) thereof. The mixed gas in which the reformed fuel vaporized in the fuel introduction chamber 122 and the reforming gas are mixed is introduced into the reformer 124 through the communication hole 123b.
[0051]
In the reformer 124, a reforming catalyst 125 is provided. The reforming catalyst 125 can have various shapes, such as being supported on a honeycomb carrier or formed in a pellet shape. In this embodiment, a honeycomb carrier is used. When the mixed gas is supplied to the reformer 124, the reforming reaction proceeds on the reforming catalyst, and the generated reformed gas is discharged to the heat exchanger.
[0052]
According to the fuel reforming apparatus of the second embodiment configured as described above, since the reforming gas supplied to the fuel introduction chamber 122 forms a swirl flow in the fuel introduction chamber 122, the reformed gas is sprayed. Among the high quality fuel droplets, those having a relatively large particle diameter and slow vaporization are blown off onto the wall surface of the fuel introduction chamber 122. By being blown off onto the wall surface by the swirling flow, the contact area (heat transfer area) between the reformed fuel droplet and the wall surface of the fuel introduction chamber 122 increases. At this time, since the wall surface of the fuel introduction chamber 122 is heated by the heater 121, the reformed fuel droplet blown off on the wall surface of the fuel introduction chamber 122 is quickly vaporized on the wall surface of the fuel introduction chamber 122. be able to. In this way, by promoting the vaporization of the reformed fuel droplets, it is possible to prevent the reformed fuel from staying in the fuel introduction chamber 122, and the fuel introduction chamber during the stop period t2 in which the fuel injection is stopped. The scavenging efficiency in the interior 122 can be improved. Then, by improving the scavenging efficiency of the fuel introduction chamber 122, the efficiency of oxidizing and removing deposited carbon in the reforming catalyst can be improved. When the wall of the fuel introduction chamber 122 is heated by the heater 121 and the temperature of the wall rises to a temperature at which the Leidenfrost phenomenon occurs on the wall, the droplet of the reformed fuel moves around on the wall. This promotes atomization of droplets. Thus, the vaporization of the reformed fuel can also be promoted by atomizing the droplets of the reformed fuel.
[0053]
Further, as described above, the reforming gas supplied into the fuel introduction chamber 122 forms a swirling flow in the fuel introduction chamber 122, so that unvaporized droplets flow into the reformer 124, and The effect of preventing inconvenience caused by the reformed fuel droplets adhering to the surface of the quality catalyst is also obtained.
[0054]
Furthermore, in the fuel reforming apparatus of the present embodiment, the diameter of the reforming gas passage 32 is such that the reforming gas introduced into the fuel introduction chamber 122 from the reforming gas passage 32 flows as a turbulent flow. It is preferable to set the diameter (D shown in FIG. 7). Whether the flow of the fluid is laminar or turbulent can be determined using the Reynolds coefficient Re (Re = Dv / ν, v: flow rate of the reforming gas, ν: kinematic viscosity of the fluid). It is possible. Boundary critical Reynolds coefficient Re where fluid flow becomes turbulent _c = 2000 is known.
[0055]
In this way, by making the reforming gas supplied to the fuel introduction chamber 122 turbulent, the vaporization of the sprayed reformed fuel droplets is further promoted, and the efficiency of scavenging from the fuel introduction chamber 122 is improved. be able to. It is considered that the vaporization of the reformed fuel droplets is promoted by making the reforming gas turbulent for the following reasons. When the atomized reformed fuel droplets evaporate, the area around the reformed fuel droplets is covered by the layer of the evaporated reformed fuel vapor. As a result, heat conduction to the reformed fuel droplets is hindered, and the thermal energy of the reforming gas may lower the efficiency of vaporizing the reformed fuel droplets. Here, by making the flow of the reforming gas turbulent, the effect of removing the vapor layer covering the reformed fuel droplets can be obtained, and the vaporization of the reformed fuel can be promoted.
[0056]
In the second embodiment, the heater 121 is provided to heat the wall surface of the fuel introduction chamber 122. However, a different type of heating unit may be provided. When a high-temperature gas (for example, a combustion gas) is generated in a system including the fuel reformer, the high-temperature gas flow path is routed so that the high-temperature gas can heat the wall surface of the fuel introduction chamber 122. It is good.
[0057]
E. FIG. Modification:
The present invention is not limited to the above-described examples and embodiments, but can be implemented in various modes without departing from the gist of the invention, and for example, the following modifications are possible.
[0058]
E1. Modification 1
In the first and second embodiments, the flow rate of the reforming gas is controlled to be substantially constant during the injection period t1 and the stop period t2, but the flow rate of the reforming gas is controlled between the injection period t1 and the stop period t2. May be changed. Also in this case, the same effect can be obtained if the amount of the reforming gas supplied into the fuel introduction chamber during the stop period t2 is equal to or larger than the capacity of the fuel introduction chamber.
[0059]
E2. Modified example 2:
In the first and second embodiments, the reforming gas consisting of air and water vapor was supplied during the stop period t2. However, if the oxidizing gas containing at least oxygen was supplied, the oxidation of the deposited carbon was prevented. Removal can be performed similarly. For example, during the stop period t2, the supply of steam may not be performed. When air is used as the oxidizing gas supplied to the fuel introduction chamber during the stop period t2, the amount of air supplied during the stop period t2 may be equal to or larger than the volume of the fuel introduction chamber.
[0060]
E3. Modification 3:
Further, in the above-described embodiment, air and steam are supplied together as the reforming gas into the fuel introduction chamber, but both may be separately supplied to the fuel introduction chamber. For example, instead of supplying pre-generated steam to the fuel introduction chamber, liquid water may be sprayed into the fuel introduction chamber using a nozzle, and may be vaporized together with the reformed fuel using the heat brought in by the heated air. . In this case, when supplying the heated air to the fuel introduction chamber during the stop period t2, spraying of water may be performed simultaneously, or spraying of water may not be performed.
[0061]
Alternatively, at least a part of the air to be supplied may be supplied from the injector 20 instead of supplying the entire amount of the air together with the steam as the reforming gas to the fuel introduction chamber. For example, the reformed fuel may be sprayed by the injector 20 configured as a two-fluid nozzle, and air may be used as the assist gas used in the two-fluid nozzle.
[0062]
E4. Modification 4:
Further, in the embodiment described above, the fuel introduction chamber and the reformer are provided separately, but a configuration in which the two are not provided is also possible due to the structure. FIG. 8 is an explanatory diagram schematically illustrating a configuration of a fuel reforming apparatus as a modification. The reformer 224 in the fuel reforming apparatus of FIG. 8 includes a reforming catalyst 125 and a spray / mixing unit 222 formed as a space having a predetermined size upstream of the reforming catalyst 125 and provided with a heater 221. ing. The reforming fuel is injected from the injector 220 into the spray / mixing unit 222, and the reforming gas is supplied into the spray / mixing unit 222. The reformed fuel injected from the injector 220 is vaporized by the heat of the heater 221 and the heat of the reforming gas, and is guided to the reforming catalyst 225 by the flow of the reforming gas while being mixed with the reforming gas. . In such a fuel reforming apparatus, the spraying / mixing unit 222 corresponds to a fuel introduction chamber into which reformed fuel is directly introduced, and the amount of the reforming gas supplied during the stop period t2 is changed by the spraying / mixing unit. What is necessary is just the volume of 222 or more.
[0063]
E5. Modification 5:
Various hydrocarbon-based fuels can be used as the liquid reformed fuel injected from the injector 20. For example, those containing gasoline, alcohol, or aldehyde can be used. Further, in the embodiment, the liquid fuel is used as the reforming fuel, but a gaseous fuel may be used. In this case, instead of spraying the liquid fuel into the fuel introduction chamber, the gaseous fuel may be introduced into the fuel introduction chamber as it is. If the reforming fuel is intermittently discharged into the fuel introduction chamber and an amount of the oxidizing gas equal to or larger than the volume of the fuel introduction chamber is supplied into the fuel introduction chamber while the discharge of the fuel is stopped, the same applies. The effect can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically illustrating a configuration of a fuel cell system 15 including a fuel reforming apparatus 10 as an embodiment.
FIG. 2 is a flowchart illustrating an operation control processing routine.
FIG. 3 is an explanatory diagram exemplifying a state of fuel injection in a removal operation of deposited carbon.
FIG. 4 is an explanatory diagram schematically showing a state of a fuel introduction chamber 22 and a reformer 24 when reformed fuel is intermittently injected from an injector 20.
FIG. 5 is an explanatory diagram showing a relationship between an operation of fuel injection and a reformed fuel concentration in a gas supplied to a reforming catalyst.
FIG. 6 is an explanatory diagram showing a state of a cross section of a main part of a fuel reforming apparatus according to a second embodiment.
FIG. 7 is an explanatory diagram showing a state of a section taken along line 7-7 in FIG. 6;
FIG. 8 is an explanatory view schematically showing a configuration of a fuel reforming apparatus as a modification.
[Explanation of symbols]
10. Fuel reformer
15 ... Fuel cell system
17 ... Fuel cell
20, 220 ... injector
22,122… Fuel introduction chamber
24, 124, 224 ... reformer
26 ... Heat exchanger
28 ... CO reduction unit
30 ... Heating section
31 ... Valve
32 Reforming gas flow path
35 ... Control unit
121 ... heater
123a ... partition wall
123b ... communication hole
125, 225 ... reforming catalyst
221 ... heater
222: Spray / mixing unit

Claims (8)

A fuel reformer that intermittently supplies a hydrocarbon-based reformed fuel to a reforming catalyst and generates hydrogen from the reformed fuel using a reforming reaction,
A reformed fuel discharge unit that intermittently discharges the reformed fuel,
An oxidizing gas supply unit that discharges an oxidizing gas containing oxygen when at least the reformed fuel discharging unit stops discharging the reformed fuel;
A fuel introduction chamber into which the reformed fuel discharged by the reformed fuel discharge unit and the oxidant gas discharged by the oxidant gas supply unit are directly introduced;
A catalyst unit that is provided connected to the fuel introduction chamber, includes the reforming catalyst, and is supplied with the reformed fuel and the oxidizing gas via the fuel introduction chamber;
While controlling the reformed fuel discharge unit to discharge the reformed fuel in an amount suitable for the reforming reaction, every time the reformed fuel discharge unit stops discharging the reformed fuel, the fuel A control unit that controls the oxidizing gas supply unit so as to discharge the oxidizing gas in an amount equal to or greater than the volume of the introduction chamber. The fuel reformer according to claim 1, wherein
The control unit is configured to control the concentration of the reformed fuel in the gas supplied to the catalyst unit through the fuel introduction chamber to be 1 vol while the reformed fuel discharge unit stops discharging the reformed fuel. %. The fuel reformer according to claim 1 or 2,
The control unit varies the amount of the oxidizing gas discharged from the oxidizing gas supply unit according to the amount of hydrogen to be generated by the fuel reforming device, and the oxidizing gas supply unit discharges the amount. The fuel reforming that controls the reformed fuel discharge unit and the oxidant gas supply unit such that the smaller the amount of the oxidizing gas is, the longer the time for performing the operation of stopping the discharge of the reformed fuel is. apparatus. A fuel reformer that intermittently supplies a hydrocarbon-based reformed fuel to a reforming catalyst and generates hydrogen from the reformed fuel using a reforming reaction,
A reformed fuel discharge unit that intermittently discharges the reformed fuel,
An oxidizing gas supply unit that discharges an oxidizing gas containing oxygen when at least the reformed fuel discharging unit stops discharging the reformed fuel;
While the reformed fuel discharged from the reformed fuel discharging unit and the oxidizing gas discharged from the oxidizing gas supply unit are directly introduced, and the reformed fuel discharging unit stops discharging the reformed fuel. A fuel introduction chamber formed to have a volume equal to or less than the amount of the oxidizing gas discharged by the oxidizing gas supply unit,
A catalyst unit that is provided connected to the fuel introduction chamber, includes the reforming catalyst, and is supplied with the reformed fuel and the oxidizing gas via the fuel introduction chamber;
While controlling the reformed fuel discharge unit to supply the reformed fuel in an amount suitable for the reforming reaction to the catalyst unit, the amount of the reformed fuel discharged from the reformed fuel discharge unit is controlled. A control unit for controlling the oxidizing gas supply unit so as to discharge the oxidizing gas in an appropriate amount. The fuel reformer according to any one of claims 1 to 4, wherein
The reformed fuel discharging unit sprays the liquid reformed fuel into the fuel introduction chamber,
The oxidizing gas supply unit discharges the oxidizing gas, which has been heated to a predetermined high temperature at which the sprayed reformed fuel can be vaporized, even when performing the discharging operation of the reformed fuel,
The fuel reformer includes a heating section for heating an inner wall surface of the fuel introduction chamber. The fuel reformer according to claim 5, wherein
The fuel reformer, wherein the oxidant gas supply unit supplies the oxidant gas into the fuel introduction chamber such that the oxidant gas forms a swirling flow in the fuel introduction chamber. The fuel reformer according to any one of claims 1 to 4, wherein
The reformed fuel discharging unit sprays the liquid reformed fuel into the fuel introduction chamber,
The oxidizing gas supply unit is configured to supply the oxidizing gas, which has been heated to a predetermined high temperature at which the sprayed reformed fuel can be vaporized, into a turbulent state even when the reforming fuel is discharged. And a fuel reformer for supplying the fuel into the fuel introduction chamber. A method for operating a fuel reformer that generates hydrogen from a hydrocarbon-based reformed fuel using a reforming reaction,
(A) intermittently repeating the operation of discharging the reformed fuel into a predetermined fuel introduction chamber;
(B) guiding the reformed fuel discharged in the step (a) to a reforming catalyst that promotes the reforming reaction, and generating hydrogen from the reformed fuel by the reforming reaction;
(C) supplying an oxidizing gas containing oxygen in an amount equal to or larger than the volume of the fuel introduction chamber to the fuel introduction chamber when the operation of discharging the reformed fuel is stopped. When,
(D) guiding the oxidant gas supplied in the step (c) to the reforming catalyst, and oxidizing and removing carbon deposited on the reforming catalyst. Method.

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