JP2004002162A - Carbon monoxide removal method, carbon monoxide removal system and fuel cell system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an elimination method of carbon monoxide by which the life of a carbon monoxide elimination catalyst can be extended while the concentration of carbon monoxide in a mixture gas containing hydrogen and carbon monoxide is kept to an extremely low level. <P>SOLUTION: In the elimination method of carbon monoxide by allowing a mixture gas containing hydrogen and carbon monoxide to react with an oxidizing agent on a carbon monoxide elimination catalyst so as to eliminate the carbon monoxide, the ratio of the oxidizing agent added to the mixture gas is increased in response to the decrease in the performance of the carbon monoxide elimination catalyst. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a carbon monoxide removal method for removing a carbon monoxide by reacting a mixed gas containing hydrogen and carbon monoxide with an oxidant on a carbon monoxide removal catalyst. As the mixed gas, for example, a reformed gas obtained by reforming (steam reforming, partial combustion reforming, etc.) a carbohydrate such as natural gas, naphtha, kerosene, or an alcohol such as methanol is used. Can be.
[0002]
[Prior art]
Conventionally, as a carbon monoxide removal system for carrying out this type of carbon monoxide removal method, a mixed gas (for example, reformed gas) containing hydrogen and carbon monoxide and an oxidant are used to remove carbon monoxide. Reacting on a catalyst, a carbon monoxide remover containing a carbon monoxide removal catalyst for removing the carbon monoxide, and the oxidizing agent for the reformed gas so as to be able to contact the carbon monoxide removal catalyst. And a means for adding an oxidizing agent for adding the compound.
[0003]
As the carbon monoxide removal catalyst, a carbon monoxide removal catalyst in which ruthenium (Ru), rhodium (Rh), platinum (Pt), palladium (Pd), or the like is supported on a carrier such as alumina has been known. These carbon monoxide removal catalysts convert and remove carbon monoxide into carbon dioxide mainly by an oxidation reaction represented by the following reaction formula.
[0004]
Embedded image
CO + 1 / 2O₂→ CO₂
[0005]
A gas obtained by adding an oxidizing agent (oxygen or air containing oxygen) to the reformed gas through the oxidizing agent adding means is introduced into a catalyst layer composed of the carbon monoxide removing catalyst to remove the carbon monoxide. The catalyst was brought into contact with a catalyst, whereby carbon monoxide in the reformed gas was converted into carbon dioxide. In the carbon monoxide removal catalyst, when the temperature of the catalyst layer is about 80 to 200 ° C., the reaction of selectively oxidizing carbon monoxide easily proceeds, so that the temperature adjusting means (heater, cooler, etc.) May be attached to the housing to keep the temperature of the catalyst layer in the temperature range.
[0006]
This type of carbon monoxide removal system has been provided in a fuel cell system on the upstream side of the fuel cell in order to supply a reformed gas serving as fuel for the fuel cell.
[0007]
In general, the fuel cell system is configured by connecting a desulfurizer, a reformer, a carbon monoxide converter, a carbon monoxide remover, and a fuel cell in the stated order as necessary. The sulfur content in the raw fuel containing fossil fuels (hydrocarbons such as natural gas or naphtha or kerosene) or alcohols (methanol or the like) is removed by the desulfurizer. In the reformer, a reformed gas containing hydrogen is generated from the raw fuel by a steam reforming reaction, a partial combustion reforming reaction, or a combination thereof. In the carbon monoxide converter, carbon monoxide contained in the reformed gas was converted into carbon dioxide by a carbon monoxide modification reaction. At this time, the reformed gas is a gas containing hydrogen as a main component (70% by volume or more), and a gas containing carbon dioxide (about 20% by volume) and carbon monoxide (0.5 to 1% by volume). Become.
[0008]
Further, in a fuel reforming system for producing a reformed gas to be supplied to a polymer electrolyte fuel cell, since the polymer electrolyte fuel cell operates at a low temperature of about 80 ° C., even a small amount of carbon monoxide is used. Since the electrode catalyst is poisoned, it is necessary to further reduce the carbon monoxide. Therefore, in the carbon monoxide removal system, the oxidant is added to the reformed gas using the oxidant addition means, and the mixed gas containing hydrogen and carbon monoxide is acted on by the action of the carbon monoxide removal catalyst. A reformed gas obtained by further removing carbon monoxide from the certain reformed gas (for example, a gas containing 10 vol% or less of carbon monoxide and 40 vol% or more of hydrogen (dry base)) has been obtained.
[0009]
[Problems to be solved by the invention]
Conventionally, the operation of the above-described carbon monoxide removal system and the fuel cell system using the same are still in the test stage, and data on continuous operation for a long period of time has not been obtained. Therefore, a method for continuously removing carbon monoxide for a very long period has not been established.
However, the inventors have succeeded in performing a continuous operation for as long as several thousand hours, and have studied the long-term stability of the carbon monoxide removal catalyst. Here, when the inventors operate the carbon monoxide remover for a long time in a temperature range suitable for the action of the carbon monoxide removal catalyst, the carbon monoxide remover is gradually discharged from the carbon monoxide remover. It has been found that the carbon monoxide concentration in the reformed gas increases to reach several tens of ppm, and that the performance of the catalyst for carbon monoxide removal deteriorates due to continuous use for a long period of time.
[0010]
This is because the reformed gas supplied to the polymer electrolyte fuel cell in order to prevent deterioration of the electrode catalyst of the polymer electrolyte fuel cell, maintain high performance, and ensure durability. It does not meet the requirement that the concentration of carbon monoxide therein must be constantly reduced to below 10 ppm.
On the other hand, it is conceivable to reduce the carbon monoxide concentration of the reformed gas by replacing the carbon monoxide removal catalyst by determining that the life has expired due to such deterioration of the carbon monoxide removal catalyst. . However, in such a countermeasure, since the carbon monoxide removing catalyst is expensive, there is a problem that the cost increases with replacement of the carbon monoxide removing catalyst. In addition, there is a problem that the power supply from the fuel cell system is hindered until the replacement of the carbon monoxide removal catalyst and the operation of the carbon monoxide removal system and the fuel cell system are stabilized.
[0011]
Accordingly, an object of the present invention is to extend the life of the carbon monoxide removal catalyst while keeping the concentration of carbon monoxide in the mixed gas at a very low concentration for a long time in view of the above problems. An object of the present invention is to provide a method for removing carbon monoxide.
[0012]
[Means for Solving the Problems]
To achieve this object, the first characteristic means of the method for removing carbon monoxide of the present invention comprises reacting a mixed gas containing hydrogen and carbon monoxide with an oxidizing agent on a carbon monoxide removing catalyst, In the carbon monoxide removing method for removing carbon monoxide, the point is that the addition ratio of the oxidizing agent to the mixed gas is increased in accordance with the performance decrease of the carbon monoxide removing catalyst.
[0013]
A second feature of the method for removing carbon monoxide of the present invention for achieving this object is to react a mixed gas containing hydrogen and carbon monoxide with an oxidizing agent on a carbon monoxide removing catalyst. In the carbon monoxide removing method for removing carbon monoxide, the ratio of the oxidizing agent to carbon monoxide contained in the mixed gas is increased in accordance with a decrease in the performance of the carbon monoxide removing catalyst. .
[0014]
A third feature of the method for removing carbon monoxide of the present invention for achieving this object is to react a mixed gas containing hydrogen and carbon monoxide with an oxidant on a carbon monoxide removal catalyst. In the carbon monoxide removing method for removing carbon monoxide, the amount of the oxidizing agent added is increased according to the usage time of the carbon monoxide removing catalyst.
[0015]
In addition, the first characteristic configuration of the carbon monoxide removal system of the present invention for achieving this object will be described with reference to the drawings. The mixed gas and the oxidizing agent are reacted on the carbon monoxide removing catalyst to remove the carbon monoxide, and the carbon monoxide removing device 4 equipped with the carbon monoxide removing catalyst is provided therein. An oxidizing agent adding means 6 for adding the oxidizing agent to the mixed gas so that the mixed gas can be contacted; a detecting means 7 for detecting performance information of the carbon monoxide removing catalyst; and the performance detected by the detecting means 7 It is determined whether or not the information satisfies a predetermined criterion, and if it is determined that the criterion does not satisfy the predetermined criterion, the oxidizing agent adding unit 6 is controlled to increase the adding ratio of the oxidizing agent to the mixed gas. And control means 8 for causing Located in.
[0016]
According to a second feature of the carbon monoxide removal system of the present invention for achieving this object, as described in claim 5, a mixed gas containing hydrogen and carbon monoxide and an oxidizing agent are used. Reacting on the carbon monoxide removing catalyst, a carbon monoxide removing device equipped with a carbon monoxide removing catalyst for removing the carbon monoxide, and contactable with the carbon monoxide removing catalyst; Oxidizing agent adding means for adding the oxidizing agent, and controlling the oxidizing agent adding means based on performance information of the carbon monoxide removing catalyst obtained in advance in association with the operation time of the carbon monoxide removing device, Control means for increasing the ratio of the oxidizing agent to the mixed gas.
[0017]
Further, in the first and second aspects, it is preferable that the mixed gas is a reformed gas obtained by reforming a hydrocarbon or an alcohol.
[0018]
Further, the characteristic configuration of the fuel cell system of the present invention for achieving this object will be described with reference to the drawings, as described in claim 7, according to any one of claims 4 to 6. The described carbon monoxide remover system 1 is provided upstream of a polymer electrolyte fuel cell 5, and the outlet gas of the carbon monoxide remover 4 or a gas derived therefrom is used as an anode gas to form the polymer electrolyte fuel cell. 5 to supply.
Furthermore, in the above-mentioned characteristic configuration, as described in claim 8, it is preferable that the performance information is output information of the polymer electrolyte fuel cell 5,
As described in claim 9, the detection means 7 detects an output voltage of the polymer electrolyte fuel cell 5 as the performance information, and the control means 8 determines that the detected output voltage is a predetermined value. It is preferable to control the oxidizing agent adding means 6 to increase the adding ratio of the oxidizing agent to the mixed gas when the value falls below the reference value.
And these effects are as follows.
[0019]
The carbon monoxide removal method proposed in the present invention and the carbon monoxide removal system and the fuel reforming system using the same are characterized in that the carbon monoxide removal catalyst housed in the carbon monoxide remover is resistant to deterioration due to sintering of the catalyst. In addition, it is based on a new finding that it is poisoned by iron or iron compounds (iron poisoning).
The present inventors have conducted intensive studies to elucidate the cause of the gradual decrease (deterioration) of the carbon monoxide removal rate by the carbon monoxide remover. As a result, the state of the surface of the catalyst whose activity was greatly reduced was found. Was analyzed by electron probe microanalysis (EPMA) and inductively coupled high-frequency plasma emission spectroscopy (ICP emission spectroscopy) to confirm that iron atoms were present on the surface in some form. The present inventors have also confirmed that even a catalyst that has undergone some sintering has maintained sufficient catalytic activity as long as the poisoning by iron is small. It was considered that not only the influence of the ring but also the presence of the iron or the iron compound or both of the iron and the iron compound was deeply involved.
[0020]
Therefore, as a result of further study on the origin of iron or an iron compound present in the catalyst whose activity has been reduced, parts (for example, a stainless steel reactor, a pipe, a heat exchanger, etc.) constituting the fuel reforming system have been examined. It was found that the iron or iron compound contained was mixed with the reformed gas, adhered to the catalyst provided in the carbon monoxide remover, closed the active site, and could lower the activity. .
[0021]
Until now, when using the carbon monoxide remover under normal conditions, it was not thought that the carbon monoxide removal catalyst would be poisoned with iron, but iron and iron compounds were mixed into the reformed gas, Considering the cause of the possibility that the carbon monoxide removal catalyst may be poisoned with iron, one of the possibilities is presumed to be the following process.
[0022]
First, a reformed gas having a reduced carbon monoxide concentration after passing through the carbon monoxide converter (for example, a typical composition is 65% hydrogen, 19% carbon dioxide, 0.5% carbon monoxide, steam 15.5%) is discharged from the carbon monoxide converter at the same temperature as the outlet temperature (about 200 ° C.) of the carbon monoxide converter, but is discharged from the carbon monoxide converter. Since the operating temperature of the remover is lower than this (about 80 to 200 ° C.), the reactor for connecting the carbon monoxide converter and the carbon monoxide remover before introducing the carbon monoxide remover. Radiates heat in pipes, pipes, heat exchangers, etc., and the temperature drops. At this time, since the reformed gas has a high concentration of hydrogen, and iron and nickel are present in stainless steel materials and the like constituting the pipes and heat exchangers, iron and carbon monoxide are combined. Carbonyl (Fe (CO)₅)) And the condition is easy to release. Therefore, it is considered that iron moves along with the reformed gas, flows into the carbon monoxide remover, and adheres to the carbon monoxide removal catalyst, thereby poisoning.
Further, an oxidizing agent added for removing carbon monoxide between the carbon monoxide converter and the carbon monoxide remover, and an oxidizer added between the carbon monoxide converter and the carbon monoxide remover. Condensed water may also be involved in the iron poisoning process.
[0023]
Therefore, the inventors have conducted intensive studies on a method for removing carbon monoxide from the mixed gas using the carbon monoxide catalyst. As a result, not only deterioration due to sintering, but also the carbon oxide removal catalyst was significantly reduced by iron. The present inventors have found that there is a method capable of sufficiently removing carbon monoxide in the mixed gas even if poisoned, and completed the present invention.
[0024]
That is, as described in claim 1, a mixed gas containing hydrogen and carbon monoxide and an oxidizing agent are reacted on a carbon monoxide removing catalyst to remove the carbon monoxide. In the removing method, it is possible to recover the carbon monoxide removing performance of the carbon monoxide removing catalyst by increasing an addition ratio of the oxidizing agent to the mixed gas in accordance with the performance decrease of the carbon monoxide removing catalyst. I knew I could do it. This makes it possible to extend the life of the carbon monoxide removal catalyst while keeping the concentration of carbon monoxide in the mixed gas at a very low level for a long period of time.
[0025]
In addition, as described in claim 2, a mixed gas containing hydrogen and carbon monoxide and an oxidizing agent are reacted on a carbon monoxide removing catalyst to remove the carbon monoxide. In the removing method, the ratio of the oxidizing agent to the carbon monoxide contained in the mixed gas is increased in accordance with a decrease in the performance of the carbon monoxide removing catalyst, whereby the carbon monoxide removing catalyst is removed. It turns out that performance can be restored. This makes it possible to extend the life of the carbon monoxide removal catalyst while keeping the concentration of carbon monoxide in the mixed gas at a very low level for a long period of time. In order to increase the addition ratio of the oxidizing agent to carbon monoxide, specifically, as described in Examples, using the addition ratio of the oxidizing agent to carbon monoxide as an index, the oxidizing agent to the mixed gas May be increased.
[0026]
Here, in the present specification, the “performance of the carbon monoxide removal catalyst” includes not only the performance of the carbon monoxide removal catalyst which is directly derived, but also the factor which is derived indirectly. For example, the performance can be determined based on the concentration of carbon monoxide contained in the mixed gas after contact with the carbon monoxide removal catalyst. Alternatively, the determination can be made based on a factor affected by the concentration of carbon monoxide contained in the mixed gas after contact with the carbon monoxide removal catalyst. As will be described in detail in Examples, the output voltage of a fuel cell using a mixed gas after contact with the carbon monoxide removal catalyst or a gas obtained by subjecting the mixed gas to some treatment as an anode gas depends on the carbon monoxide removal catalyst. Since it is inversely proportional to the concentration of carbon monoxide contained in the mixed gas after contact with the fuel cell, the performance of the carbon monoxide removal catalyst can be determined using the output voltage of the fuel cell as an index.
[0027]
Also, as described in claim 3, a mixed gas containing hydrogen and carbon monoxide and an oxidizing agent are reacted on a carbon monoxide removing catalyst to remove the carbon monoxide. In the removal method, it was found that the carbon monoxide removal performance of the carbon monoxide removal catalyst can be restored by increasing the amount of the oxidizing agent added according to the usage time of the carbon monoxide removal catalyst. . This makes it possible to extend the life of the carbon monoxide removal catalyst while keeping the concentration of carbon monoxide in the mixed gas at a very low level for a long period of time.
Here, in the present specification, the "use time of the carbon monoxide removal catalyst" means the elapsed time from the start of the treatment when the carbon monoxide removal catalyst is used for the carbon monoxide removal treatment. I do.
[0028]
Further, in order to carry out the carbon monoxide removal method, a carbon monoxide removal system according to a fourth aspect can be employed. That is, referring to the drawings, in a carbon monoxide remover 4 equipped with a carbon monoxide removing catalyst for removing carbon monoxide, a mixed gas containing hydrogen and carbon monoxide and an oxidant are mixed with carbon monoxide. When reacting on the removing catalyst, the oxidizing agent is added to the carbon monoxide removing device 4 by the oxidizing agent adding means 6 so as to be able to contact the carbon monoxide removing catalyst. Here, the state of the carbon monoxide removing catalyst can be grasped by the detecting means 7 detecting the performance information of the carbon monoxide removing catalyst. Then, the control means 8 determines whether or not the performance information detected by the detection means 7 satisfies a predetermined criterion. If it is determined that the performance information does not satisfy the predetermined criterion, the oxidizing agent adding means 6 Is controlled to increase the ratio of the oxidizing agent to the mixed gas, the performance of the carbon monoxide removal catalyst is restored. Therefore, it is possible to stably supply the mixed gas having a very low carbon monoxide concentration (for example, the carbon monoxide concentration is 10 ppm or less) over a long period of time while extending the life of the carbon monoxide removal catalyst. it can.
[0029]
Further, as described in claim 5, the performance information may be acquired in advance in association with the operation time of the carbon monoxide remover, and may be used. That is, in a carbon monoxide remover equipped with a carbon monoxide removal catalyst for removing carbon monoxide, when reacting a mixed gas containing hydrogen and carbon monoxide with an oxidant on the carbon monoxide removal catalyst, The oxidizing agent is added to the mixed gas by an oxidizing agent adding means so as to be able to contact the carbon monoxide removing catalyst. Then, based on the performance information acquired in advance, the control means controls the oxidizing agent adding means to increase the ratio of the oxidizing agent to the mixed gas. Recover. Therefore, steps and configurations for removing the carbon monoxide can be reduced.
[0030]
Furthermore, as described in claim 6, when the mixed gas is a reformed gas obtained by reforming hydrocarbons or alcohols, use in which mixing of carbon monoxide is restricted (for example, , Fuel cell anode gas production, etc.). Therefore, it is preferable that the carbon monoxide removal system according to the present invention can greatly reduce the carbon monoxide concentration.
[0031]
Also, with reference to the drawings, as described in claim 7, the carbon monoxide remover system 1 according to any one of claims 4 to 6 is a polymer electrolyte fuel cell 5 The outlet gas of the carbon monoxide remover 4 having a very low carbon monoxide concentration (for example, 10 ppm or less) can be obtained for a very long time. Therefore, by supplying the outlet gas or a gas derived therefrom as the anode gas to the polymer electrolyte fuel cell 5, poisoning of the electrode catalyst constituting the polymer electrolyte fuel cell 5 is prevented, , And stable operation is possible. Further, as will be described in detail in the embodiment, since the output voltage of the polymer electrolyte fuel cell 5 can be increased by reducing the concentration of carbon monoxide in the anode gas, the utilization efficiency can be improved. it can.
[0032]
Further, referring to the drawings, as described in claim 8, a voltmeter or an ammeter conventionally provided if the performance information is output information of the polymer electrolyte fuel cell 5 Can be used as the detection means 7.
[0033]
Specifically, referring to the drawings, as described in claim 9, the detecting means 7 detects an output voltage of the polymer electrolyte fuel cell 5 as the output information, When the detected output voltage is lower than a predetermined reference value, the control means controls the oxidant adding means to increase the ratio of the oxidant to the mixed gas.
[0034]
In addition, although reference numerals are given to facilitate comparison with the drawings, the present invention is not limited to the structure of the drawings.
[0035]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a fuel cell system according to the present invention including the carbon monoxide removal system 1 according to the present invention. This fuel cell system can be roughly classified into a reforming process in which hydrocarbons such as natural gas (city gas), naphtha, and kerosene are used as a raw fuel and hydrogen that is used as an anode gas for the polymer electrolyte fuel cell 5 is used as a main component. A fuel reforming system for producing gas; and a polymer electrolyte fuel cell 5 for generating electricity by supplying the reformed gas supplied from the fuel reforming system as an anode gas and supplying air (oxygen) as a cathode gas. And
[0036]
In the fuel reforming system, a reformer 2, a carbon monoxide converter 3, and a carbon monoxide remover 4 constituting the carbon monoxide removal system 1 are connected in series through a pipe. The reformed gas that has passed through them is supplied to the anode of the polymer electrolyte fuel cell 5.
Hereinafter, each component will be described.
[0037]
The reformer 2 contains a reforming catalyst and is provided with a burner for heating the reforming catalyst. In the reformer 2, the raw fuel and steam separately supplied are mixed and brought into contact with the reforming catalyst. By the action of the reforming catalyst, hydrocarbons such as methane in the raw fuel are mainly reformed into hydrogen, and carbon monoxide and carbon dioxide are produced as by-products.
[0038]
Although the reformed gas thus obtained is rich in hydrogen, it contains more than ten percent of carbon monoxide as a by-product, so that when directly supplied to the polymer electrolyte fuel cell 5, the electrode catalyst is significantly poisoned. I do. Therefore, in the carbon monoxide converter 3, the outlet temperature is about 200 ° C., and the carbon monoxide is converted into carbon dioxide by contacting with a carbon monoxide conversion catalyst such as a copper-zinc catalyst. At the outlet gas of the carbon monoxide converter 3, the carbon monoxide concentration is reduced to 0.3 to 1%. However, in order to stably operate the polymer electrolyte fuel cell 5 for a long period of time, it is necessary to reduce the concentration of carbon monoxide to about 10 ppm. (Reformed gas) is further introduced into the carbon monoxide remover 4 provided downstream.
[0039]
The carbon monoxide remover 4 detects an oxidant adding means 6 for adding the oxidant to the mixed gas so as to be able to contact the carbon monoxide removal catalyst, and performance information of the carbon monoxide removal catalyst. And the control means 8 for controlling the oxidizing agent adding means 6 based on the performance information detected by the detecting means 7 to constitute the carbon monoxide removal system 1 according to the present invention. Carbon monoxide is removed from the outlet gas of the carbon monoxide converter 3.
[0040]
The carbon monoxide remover 4 contains a carbon monoxide removal catalyst capable of removing carbon monoxide contained in the outlet gas of the carbon monoxide converter 3. As such a catalyst, for example, a catalyst in which ruthenium (or a noble metal such as platinum, rhodium, or palladium) is supported on a carrier such as alumina spheres can be used. For example, for removing carbon monoxide used in the present method, a catalyst in which 0.1 to 5.0% by weight, preferably 0.5 to 2.0% by weight of ruthenium is supported on an alumina carrier can be used. . Carbon monoxide in the reaction gas is mainly combined with oxygen to form carbon dioxide by an oxidation removal reaction promoted by the carbon monoxide removal catalyst. At the same time, carbon monoxide can be removed by a methanation reaction. By these actions, the reformed gas having a very low carbon monoxide concentration can be obtained.
[0041]
The reaction temperature of the carbon monoxide removal catalyst may be within a temperature range in which the carbon monoxide removal proceeds, but is preferably carried out at 80 to 180 ° C. where the methanation reaction of carbon dioxide can be suppressed. Is preferred.
[0042]
The performance information of the carbon monoxide removal catalyst detected by the detection means 7 is, for example, the concentration of carbon monoxide in the reformed gas before contacting with the carbon monoxide removal catalyst, the carbon monoxide removal catalyst, It is information on a factor that reflects the concentration of carbon monoxide in the reformed gas after contact, or the concentration of carbon monoxide in the reformed gas after contact with the carbon monoxide removal catalyst. Specifically, there are information on the carbon monoxide concentration itself in the reformed gas before or after contact with the carbon monoxide removal catalyst, information on the output of the fuel cell (output information), and the like. The detection means 7 includes, for example, a carbon monoxide gas detection sensor. The carbon monoxide gas detection sensor may be provided in the flow path of the reformed gas and configured to acquire data in real time, or a history may be obtained from data previously acquired by the carbon monoxide gas detection sensor. The history may be created and the history may be used as performance information. The control method of the fuel cell includes various methods such as a constant output power method, a constant output current method, and a constant output voltage method.The output information such as a voltage value and a current value obtained according to these methods is provided. Can be used.
[0043]
The detection means 7 may be any means capable of acquiring the performance information. For example, when the performance information is an output voltage which is output information, a voltmeter can be employed as shown in FIG. Alternatively, if the performance information is the carbon monoxide concentration, a known carbon monoxide sensor, a flame ionization detector (FID), a thermal conductivity detector (TCD), or the like can be used. As these detecting means 7, those previously provided in the carbon monoxide removal system 1 or the fuel cell system can also be used.
[0044]
The control means 8 can be composed of a microcomputer, a control device for controlling various controls of the entire fuel cell system, and the like. The control unit 8 receives the performance information signal sent from the detection unit 7 and performs an arithmetic process based on the performance information. The control unit 8 performs the oxidation based on a result of the arithmetic process performed by the arithmetic unit. A control unit for issuing a signal for controlling the amount of the oxidizing agent added to the agent adding means 6;
A control example of the oxidizing agent adding means 6 by the control means 8 will be described later.
[0045]
As the oxidizing agent adding means 6, a known configuration such as a blower or a pump can be adopted, and air is conveyed by the blower or the pump. The destination of the oxidant may be any place where the carbon monoxide removal catalyst can contact the oxidant in the presence of the reformed gas. For example, as shown in FIG. The oxidizing agent can be introduced from the pipe on the upstream side of the carbon remover 4. Alternatively, the oxidizing agent may be introduced into the carbon monoxide remover 4.
[0046]
The reformed gas discharged from the carbon monoxide remover 4 is introduced into the polymer electrolyte fuel cell 5 as an anode gas. The polymer electrolyte fuel cell 5 has a polymer electrolyte membrane interposed between a fuel electrode (anode) and an air electrode (cathode). When the anode gas is supplied to the fuel electrode and the cathode gas (air) is supplied to the air electrode, hydrogen in the anode gas and oxygen in the cathode gas combine to generate water on the air electrode side. Electricity is generated. The off-gas of the cathode gas after power generation is released into the atmosphere. The off-gas of the anode gas can be returned to the reformer 2 in order to use unreacted hydrogen and remaining methane as fuel.
[0047]
As an example of the arithmetic processing in such a fuel cell system, a case where the performance information is an output voltage of the polymer electrolyte fuel cell will be described.
As shown in FIG. 1, electric power generated by the polymer electrolyte fuel cell 5 is supplied to the outside via a power transmission line 9. A voltmeter 7 as detecting means 7 is connected to the transmission line 9 or the internal wiring of the polymer electrolyte fuel cell 5. As described above, the voltage of the polymer electrolyte fuel cell 5 detected by the voltmeter 7 is affected by the carbon monoxide removing ability of the carbon monoxide removing catalyst. That is, when the performance of the carbon monoxide removing catalyst is reduced and the carbon monoxide concentration in the outlet gas of the carbon monoxide remover 4 is increased, the output voltage of the polymer electrolyte fuel cell 5 is reduced. The data of the voltage detected by the voltmeter 7 is recorded as the performance information and sent to the control means 8. The control unit 8 determines in the arithmetic unit whether the performance information (voltage data) exceeds a predetermined voltage value. If the result of the determination is that the voltage data is lower than a predetermined voltage value, the control unit receives this determination and issues a command signal to the oxidizing agent adding means 6 to increase the amount of the oxidizing agent added. . The oxidant adding means 6 receiving this command signal increases the amount of the oxidant added. As a result, [O] in the carbon monoxide remover 4 is removed.₂] / [CO] is increased, the oxidation reaction of carbon monoxide by the carbon monoxide removal catalyst is accelerated, and the carbon monoxide concentration at the outlet gas of the carbon monoxide remover 4 can be reduced.
[0048]
Here, the addition ratio of the oxidizing agent is a theoretical lower limit of the oxidation reaction of the carbon monoxide [O₂] / [CO] needs to be 0.5 or more. Further, in order to suppress the combustion of hydrogen contained in the mixed gas, it is preferable to reduce the oxygen addition rate as much as possible. Therefore, [O₂] / [CO] is preferably 3.0 or less. In the case where long-term stable operation is more important than the power generation efficiency of the fuel cell system described above, it is equal to or lower than the explosion limit of hydrogen (for example, when the concentration of carbon monoxide at the inlet of the carbon monoxide remover 4 is 1%). When [O₂] / [CO] is 5.0 or less).
[0049]
Therefore, the carbon monoxide removal system 1 has been proposed previously [O₂] / [CO] low [O]₂] / [CO], and [O] with the decrease of the voltage value₂] / [CO] is increased.
[0050]
【Example】
Hereinafter, examples of the present invention will be described.
[Example 1]
An example in which the addition amount of the oxidizing agent is controlled using the concentration of carbon monoxide contained in the outlet gas of the carbon monoxide remover as the performance information of the carbon monoxide removal catalyst will be described below.
8 ml of a Ru / alumina catalyst in which 1% by weight of ruthenium (Ru) is supported on an alumina carrier is filled into a stainless steel reaction tube (housing) having a sheath tube for inserting a thermocouple therein, and then subjected to monoxide oxidation. A carbon remover was made. This carbon monoxide remover monitors the temperature of the carbon monoxide removal catalyst with a thermocouple inserted into the thermocouple insertion sheath tube, operates a heater having the reaction tube outside, and operates the reaction tube. Is configured to be controllable.
[0051]
This carbon monoxide remover has H₂6%, N₂The temperature of the reaction tube was raised to 250 ° C. while introducing a gas having a composition of 94% at a rate of 1,000 ml / min, and the temperature was kept at 250 ° C. for 2 hours (pretreatment). This pretreatment is a treatment for increasing the initial activity of the Ru / alumina catalyst at a low temperature.
[0052]
Then, after lowering the temperature of the reaction tube, a gas obtained by adding air to the outlet gas of the carbon monoxide converter ([O₂] / [CO] = 1.5) (0.5% carbon monoxide, 0.5% methane, 20.9% carbon dioxide, 0.75% oxygen, 3.0% nitrogen) A gas obtained by adding water vapor so that the concentration of water vapor in the humid gas becomes 5% to a mixed gas whose balance is hydrogen) at a space velocity (GHSV) of 7,500 / hour (dry base) at the carbon monoxide remover. The carbon monoxide was removed while controlling the maximum temperature of the catalyst layer formed by the carbon monoxide removal catalyst to be 140 ° C.
[0053]
The oxygen concentration in the reaction gas was configured to be manually changeable.
The concentration of carbon monoxide contained in the outlet gas discharged from the carbon monoxide remover was detected by a flame ionization detector (FID). The detection limit (lower limit) of this FID was 1 ppm.
The oxygen concentration in the reaction gas introduced into the carbon monoxide remover is determined by the operator by checking the detection data of the carbon monoxide concentration by the FID. Was increased.
[0054]
The result of continuously operating the carbon monoxide remover under the above conditions for about 2,600 hours is shown in FIG.
Until about 900 hours had passed since the start of the operation of the carbon monoxide remover, the concentration of carbon monoxide in the outlet gas was below the detection limit (less than 1 ppm). However, after this, the concentration of carbon monoxide in the outlet gas began to rise and reached 1 ppm after 1793 hours. Therefore, the oxygen concentration in the reaction gas is changed to [O₂] / [CO] = 3.0, the concentration of carbon monoxide in the outlet gas decreased below the detection limit. Thereafter, [O₂] / [CO] = 3.0, the operation was continued, and this state could be maintained for 2,500 hours or more.
[0055]
Further, the operation of the carbon monoxide remover was continued, and the activity (carbon monoxide concentration in the outlet gas) of the carbon monoxide removal catalyst was measured after 6000 hours. Under the condition that the maximum temperature of the catalyst layer is 120 ° C., [O₂] / [CO] was varied to 1.5, the carbon monoxide concentration in the outlet gas increased to 212 ppm. After this, [O₂] / [CO] = 3.0, the concentration of carbon monoxide in the outlet gas of the carbon monoxide remover 1 returned to below the detection limit (less than 1 ppm).
After operating as described above, the carbon monoxide removal catalyst was taken out of the carbon monoxide remover, and the amount of iron attached to the carbon monoxide removal catalyst was measured by ICP emission spectroscopy. As a result, it was found that about 0.64 mg of iron was increased per 1 g of the carbon monoxide removal catalyst. At this time, the carbon monoxide adsorption amount of the carbon monoxide removal catalyst was 46% smaller than before the start of the operation.
Thus, the carbon monoxide removal system controlled by the present method maintained a high carbon monoxide removal ability over a long period of time even when a deteriorated carbon monoxide removal catalyst was used.
[0056]
[Example 2]
An example in which an output amount of a fuel cell using an outlet gas (reformed gas) of a carbon monoxide remover is used as performance information of the carbon monoxide removal catalyst to control an oxidant addition amount will be described below.
The effect of the concentration of carbon monoxide contained in the anode gas (reformed gas) on the cell performance of a polymer electrolyte fuel cell (using MEA manufactured by E-Tek) was tested. The operating temperature of the fuel cell was 70 ° C., and the current density was 300 mA / cm.²The fuel utilization was 60%.
The result is shown in FIG.
[0057]
When the concentration of carbon monoxide in the anode gas was less than 1 ppm (shown as 0 ppm in the figure), the single cell voltage was 634 mV. However, when the concentration of carbon monoxide in the anode gas became 10 ppm, it decreased to 546 mV, and when it was 20 ppm, it decreased to about 430 mV. Therefore, the output voltage of the fuel cell was inversely proportional to the concentration of carbon monoxide contained in the anode gas, that is, the outlet gas of the carbon monoxide remover.
Therefore, information on the output voltage of the fuel cell can be used as the performance information of the carbon monoxide removal catalyst.
[0058]
[Another embodiment]
Hereinafter, another embodiment will be described.
(A) In the carbon monoxide removal system according to the present invention, for example, when a carbon monoxide converter is provided on the upstream side, it can be said that the composition of the outlet gas affects the performance of the carbon monoxide removal catalyst. Therefore, the concentration of carbon monoxide in the inlet gas of the carbon monoxide converter, which depends on the quality of the raw fuel, or the concentration of carbon monoxide in the outlet gas of the carbon monoxide converter due to the deterioration of the carbon monoxide conversion catalyst over time. It is also possible to determine the performance information of the carbon monoxide removal catalyst in consideration of the rise of the carbon monoxide. In this case, the performance information can be acquired by, for example, a carbon monoxide gas detection sensor. The carbon monoxide gas detection sensor may be provided in the flow path of each gas and configured to acquire data in real time, or may create a history from data previously acquired by the carbon monoxide gas detection sensor. Then, the history may be used as performance information. When the output information of the fuel cell is used as the performance information of the carbon monoxide removal catalyst, it can be said that the state of the fuel cell affects the performance of the carbon monoxide removal catalyst. Therefore, it is also possible to determine the performance information of the carbon monoxide removal catalyst in consideration of the voltage drop due to the deterioration of the fuel cell over time.
(B) In the fuel cell system, the carbon monoxide removal system is feedback-controlled based on the performance information acquired in real time by the detection means, but the method for acquiring the performance information is limited to such a method. Not done. For example, the same carbon monoxide removal system, the same carbon monoxide removal system, the same fuel cell system, the same fuel cell system, the same carbon monoxide removal catalyst, or the same carbon monoxide removal catalyst The performance information at the time of use is stored in association with the operation time of the carbon monoxide removal system or the fuel cell system, and arithmetic processing is performed on the control means based on the performance information obtained in advance. Thus, the oxidizing agent adding means can be controlled. The accumulation of the performance information may be performed manually, or the control means may be set to automatically collect and accumulate the information.
[0059]
For example, using the history of the concentration of carbon monoxide in the outlet gas obtained in Example 1, 1793 hours after the operation of the carbon monoxide remover was started, [O₂] / [CO] was increased from 1.5 to 3.0, and a carbon monoxide removal system in which an apparatus for adding oxygen gas was controlled by control means such as a microcomputer could be constructed.
[0060]
Further, when the carbon monoxide removal system is operating at a partial load output, an oxidizing agent is added in an amount corresponding to the operating state based on performance information acquired in advance for each operating state. Control may be performed as follows.
For example, with respect to the amount of the mixed gas (outlet gas of the carbon monoxide converter) and the amount (concentration) of carbon monoxide contained in the mixed gas, information obtained in advance for each operation state (rated or partial load, etc.) , And an oxidizing agent can be added in an amount depending on the operating conditions.
[0061]
(C) The application of the carbon monoxide removal system according to the present invention is not limited to use as a component of a fuel cell system. The carbon monoxide removal system according to the present invention can be used for other applications for removing carbon monoxide in a mixed gas containing hydrogen and carbon monoxide, for example, the system alone, or industrial hydrogen. It can be used in a purification process in gas production.
[0062]
(D) The origin (raw fuel) of the mixed gas introduced into the carbon monoxide removal system according to the present invention may be alcohols such as methanol. In this case, a known reforming carbon monoxide removal catalyst of a type suitable for reforming the alcohol can be used as the reforming catalyst.
[0063]
(E) In the fuel cell system, when the raw fuel contains sulfur, a desulfurizer having a known desulfurization catalyst may be provided in front of the reformer 2. By providing the desulfurizer, poisoning of the reforming catalyst, the carbon monoxide denaturing catalyst, the carbon monoxide removing catalyst, and the like can be prevented.
(F) The type of the desulfurization catalyst, the reforming catalyst, and the carbon monoxide conversion catalyst used in the fuel reforming system need not be limited, and known ones can be used. Although the polymer electrolyte fuel cell has been exemplified as the fuel cell, the present invention can also be applied to other types of fuel cells, for example, a fuel cell system using the phosphoric acid fuel cell.
(G) In the carbon monoxide removal system and the fuel cell system according to the present invention, under the use condition in which the poisoning of the carbon monoxide removal catalyst by iron is suppressed, deterioration of the carbon monoxide removal catalyst due to sintering is reduced. Even if it occurs, it is possible to extend the life of the carbon monoxide removal catalyst while maintaining the carbon monoxide concentration in the mixed gas containing hydrogen and carbon monoxide at a very low concentration for a long period of time. It is considered possible.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a fuel cell system according to the present invention.
FIG. 2 is a graph showing a relationship between a concentration of carbon monoxide in an anode gas supplied to a fuel cell and an output voltage of a single cell constituting the fuel cell.
FIG. 3 is a graph showing the concentration of carbon monoxide in the outlet gas of the carbon monoxide removal system according to the present invention.
[Explanation of symbols]
1. Carbon monoxide removal system
2 reformer
3 carbon monoxide transformer
4 Carbon monoxide remover
5 Fuel cell
6 means for adding oxidizing agent
7 Detection means
8) Control means

Claims (9)

A mixed gas containing hydrogen and carbon monoxide and an oxidizing agent are reacted on a carbon monoxide removing catalyst, and in the carbon monoxide removing method for removing the carbon monoxide,
A method for removing carbon monoxide, wherein the ratio of the oxidizing agent to the mixed gas is increased in accordance with a decrease in performance of the carbon monoxide removing catalyst. A mixed gas containing hydrogen and carbon monoxide and an oxidizing agent are reacted on a carbon monoxide removing catalyst, and in the carbon monoxide removing method for removing the carbon monoxide,
A method for removing carbon monoxide, wherein the addition ratio of the oxidizing agent to carbon monoxide contained in the mixed gas is increased in accordance with a decrease in performance of the carbon monoxide removing catalyst. A mixed gas containing hydrogen and carbon monoxide and an oxidizing agent are reacted on a carbon monoxide removing catalyst, and in the carbon monoxide removing method for removing the carbon monoxide,
A method for removing carbon monoxide, wherein the amount of the oxidizing agent added is increased according to the usage time of the carbon monoxide removing catalyst. A mixed gas containing hydrogen and carbon monoxide and an oxidizing agent are reacted on a carbon monoxide removing catalyst, and a carbon monoxide removing device equipped with a carbon monoxide removing catalyst for removing the carbon monoxide,
Oxidizing agent adding means for adding the oxidizing agent to the mixed gas so as to be able to contact the carbon monoxide removing catalyst,
Detecting means for detecting performance information of the carbon monoxide removal catalyst,
It is determined whether or not the performance information detected by the detection means satisfies a predetermined criterion, and when it is determined that the performance information does not satisfy the predetermined criterion, the oxidizing agent adding means is controlled to control the mixed gas. Control means for increasing the ratio of addition of the oxidizing agent. A mixed gas containing hydrogen and carbon monoxide and an oxidizing agent are reacted on a carbon monoxide removing catalyst, and a carbon monoxide removing device equipped with a carbon monoxide removing catalyst for removing the carbon monoxide,
Oxidizing agent adding means for adding the oxidizing agent to the mixed gas so as to be able to contact the carbon monoxide removing catalyst,
The oxidizing agent adding unit is controlled based on performance information of the carbon monoxide removing catalyst obtained in advance in association with the operation time of the carbon monoxide removing device, and an adding ratio of the oxidizing agent to the mixed gas is increased. A carbon monoxide removal system comprising a control unit. The carbon monoxide removal system according to claim 4 or 5, wherein the mixed gas is a reformed gas obtained by reforming a hydrocarbon or an alcohol. The carbon monoxide removal system according to any one of claims 4 to 6 is provided upstream of a polymer electrolyte fuel cell, and an outlet gas of the carbon monoxide remover or a gas derived therefrom is used as an anode gas. A fuel cell system for supplying the polymer electrolyte fuel cell. The fuel cell system according to claim 7, wherein the performance information is output information of the polymer electrolyte fuel cell. The detecting means detects an output voltage of the polymer electrolyte fuel cell as the output information,
9. The control method according to claim 8, wherein the control means controls the oxidizing agent adding means to increase the oxidizing agent adding ratio to the mixed gas when the detected output voltage falls below a predetermined reference value. Fuel cell system.

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