JPH08100184A - Carbon monoxide removing system - Google Patents

Abstract

PURPOSE: To provide the subject system stably exhibiting a high electric power- generating performance by assuredly reducing the carbon monoxide concentration in a hydrogen-rich fuel gas fed to a fuel cell to <=100ppm. CONSTITUTION: This carbon monoxide-removing system 34 is so designed that a 1st reaction section 40 and a 2nd reaction section 42 are arranged in series on the upstream side and downstream side of a fuel gas, respectively, the 1st reaction section has a cooling bed to cool a selectively oxidizing catalyst for it to be kept within its active temperature range, the 2nd reaction section has a cooling bed to cool a combustion catalyst for it to be kept within its active temperature range, and an oxidizing agent feed means 26 for the feeding oxidizing agent to the 1st reaction section/2nd reaction section. Carbon monoxide is removed by passing a fuel gas through both the 1st and 2nd reaction sections.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide removing device, and more particularly to a device for removing hydrogen rich gas supplied to a fuel cell operating at a relatively low temperature such as a phosphoric acid fuel cell or a solid polymer electrolyte fuel cell. The present invention relates to a carbon monoxide removing device used for always maintaining a low concentration of carbon monoxide.

[0002]

2. Description of the Related Art In a fuel cell power generation device in which a fuel electrode and an oxidation electrode are arranged on both sides of an electrolyte, and hydrogen and oxygen are supplied to the fuel electrode and the oxidation electrode, respectively, to obtain a cell reaction, power generation efficiency is improved. In order to increase the temperature and prevent air pollution, it is desirable to supply a gas as rich as hydrogen in the fuel electrode.

For this reason, a reforming device for producing a hydrogen-rich reformed gas by reforming a raw fuel gas containing hydrocarbons such as methanol or alcohols as a main component by the action of a reforming catalyst is provided in a fuel cell. Although it is provided in advance, carbon monoxide produced as a by-product of this reforming reaction poisons the electrode catalyst (Pt) of the fuel cell and deteriorates the performance of the fuel cell. In particular, high-performance phosphoric acid fuel cells and solid polymer electrolyte fuel cells, which have been developed in recent years, operate in a relatively low temperature range, so that the characteristics are greatly deteriorated due to catalyst poisons.

Therefore, it is necessary to reduce the concentration of carbon monoxide contained in the reformed gas immediately after the reforming reaction to about 1% to 100 ppm or less at the time of supplying it to the fuel electrode of the fuel cell. In JP-A-3-276577, a carbon monoxide removing device is provided between a reforming device and a fuel cell, which is filled with a combustion catalyst that preferentially burns carbon monoxide in the reformed gas. Is proposed.

[0005]

A combustion catalyst such as Pt / Al ₂ O ₃ is used in the carbon monoxide removing apparatus in the above-mentioned prior art, and the activation temperature range of the carbon monoxide combustion reaction is 70 to 150. If the combustion catalyst is kept in this temperature range, it is possible to reduce the carbon monoxide concentration in the reformed gas to 100 ppm or less and supply it to the fuel electrode of the fuel cell.

However, in order to maintain the temperature of the combustion catalyst in the above-mentioned combustion reaction activation temperature range, it is necessary to provide the combustion catalyst carrier with a temperature control device having both a cooling function and a heating function. Even if the control device is provided, until the temperature of the combustion catalyst carrier incorporated in the carbon monoxide removing device reaches 70 ° C. immediately after the reforming device and the carbon monoxide removing device are activated, the carbon monoxide removing device is It cannot exert its carbon monoxide removing ability. Further, even when the reformer is operated intermittently, the catalyst temperature fluctuates due to the intermittent start-up and stop of the carbon monoxide removing device, which causes the same problem as described above.

[0007]

Therefore, the present invention solves the problems of the prior art described above, and the carbon monoxide concentration in the reformed gas is set to 100 even immediately after the activation of the carbon monoxide removing device.
It is an object of the present invention to provide a carbon monoxide removing device capable of reducing the concentration to ppm or less and preventing poisoning deterioration of an electrode catalyst of a fuel cell.

To achieve this object, the present invention provides:
The combustion catalyst (Pt / Al
_{2 O 3)} is known as an excellent selective oxidation catalyst reaction efficiency to selectively oxidize carbon monoxide in the reformed gas at different activation temperature range and the _{Au / α-Fe 2 O 3} / Al 2
It is proposed to use O ₃ together.

Selective oxidation catalyst Au / α-Fe ₂ O ₃ / Al
The activation temperature range of ₂ O ₃ is room temperature to 100 ° C. According to this selective oxidation catalyst, the reaction of selectively oxidizing carbon monoxide to generate carbon dioxide is activated in a low temperature range of 100 ° C. or lower, but hydrogen is selectively oxidized in a high temperature range of 100 ° C. or higher. As a result, the reaction of producing water is activated and the hydrogen content is reduced. Therefore, the carrier carrying the selective oxidation catalyst can be made to function immediately after starting, but it is necessary to control the temperature to 100 ° C. or lower.

Therefore, the selective oxidation catalyst carrier is installed in series on the upstream side of the combustion catalyst carrier, and the selective oxidation catalyst carrier is parallel to the combustion catalyst carrier until the combustion catalyst reaches, for example, 70 ° C. After the operating temperature is reached, the operation of the selective oxidation catalyst carrier is stopped and only the combustion catalyst carrier is operated. By switching the operation of the two catalyst carriers in this way, each catalyst carrier operates within its respective activation temperature range, and even immediately after the activation of the carbon monoxide removing device or in the intermittent operation. The carbon monoxide concentration in the reformed gas can be reliably reduced to 100 ppm or less.

Moreover, the combustion catalyst has a predetermined temperature (for example, 7
(0 ° C.), the fuel gas after passing through the upstream selective oxidation catalyst carrier is introduced into the combustion catalyst carrier,
Since the oxidation reaction by the selective oxidation catalyst is an exothermic reaction, the temperature of the fuel gas rises, which increases the rate of temperature rise of the combustion catalyst. Further, when the combustion catalyst temperature is lower than 70 ° C., although it has not reached the activation temperature range, unreacted residual carbon monoxide in the selective oxidation catalyst carrier generates heat due to the combustion reaction by the combustion catalyst. The temperature is kept higher than that of the selective oxidation catalyst.

That is, the carbon monoxide removing device according to the present invention is arranged on the upstream side of the fuel gas and holds the selective oxidation catalyst supporting portion for supporting the selective oxidation catalyst, and holds the selective oxidation catalyst within its activation temperature range. A first reaction part having a cooling layer for cooling as much as possible, a combustion catalyst support part arranged in series with the first reaction part on the downstream side of the fuel gas and carrying a combustion catalyst, and the combustion catalyst. A second reaction part having a cooling layer for cooling the supporting part so as to keep it within the activation temperature range, and an oxidant for supplying an oxidant gas to the first reaction part and / or the second reaction part. A gas supply means, a first fuel passage that allows the fuel gas to pass through the first reaction section and then a second reaction section, and a first fuel path that bypasses the first reaction section and be directly introduced into the second reaction section to pass therethrough; Fuel gas switching means for switching to the second fuel path, and the second reaction section Temperature detecting means for detecting a definitive combustion catalyst temperature, when the combustion catalyst temperature detected by the temperature detecting means is below a predetermined value selects the first fuel path,
And a control means for controlling the fuel gas switching means so as to select the second fuel path when the combustion catalyst temperature is equal to or higher than a predetermined value.

The control means supplies the oxidant gas to the first reaction section and the second reaction section when the first fuel path is selected, and supplies only the second reaction section when the second fuel path is selected. The oxidant gas supply means is controlled so that the oxidant gas is supplied.

A fuel gas on-off valve is provided between the first reaction section and the second reaction section. When the first fuel path is selected, the fuel gas on-off valve is opened and the second fuel path is selected. The fuel gas on / off valve is closed when
It can be controlled by the control means.

It is preferable to use Au / α-Fe ₂ O ₃ / Al ₂ O ₃ as the selective oxidation catalyst in the first reaction section and Pt / Al ₂ O ₃ as the combustion catalyst in the second reaction section. is there.

[0016]

[Function] When the combustion catalyst does not reach the activation temperature immediately after the activation of the carbon monoxide removing device, the fuel gas is
After being subjected to the oxidation reaction by the selective oxidation catalyst in the first reaction section, it is introduced into the second reaction section carrying the combustion catalyst. Since the selective oxidation catalyst is activated at a temperature of room temperature or higher, the carbon monoxide concentration in the fuel gas during the passage through the first reaction section is 10
It is reduced to 0 ppm or less. After the temperature of the combustion catalyst rises and enters the activation temperature range, the fuel gas bypasses the first reaction section and is directly introduced into the second reaction section, and the combustion reaction by the combustion catalyst causes the removal of the contained carbon monoxide. To be done.

[0017]

FIG. 1 shows a system configuration of a fuel cell power generator using a carbon monoxide removing device according to an embodiment of the present invention.

Liquid methanol is introduced into the combustion section 12 of the fuel reforming apparatus 10 from the tank 22 by the pump 24, and air from the air pump 26 is introduced into the combustion section 12 of the fuel reformer 10. A heat source gas is generated by burning methanol. In this embodiment, the catalyst combustion section 12 is composed of the combustion catalyst, so that the heater 14 is provided to heat the combustion catalyst to the activation temperature. The heat source is not limited to the above,
For example, the heat source gas may be generated by burning hydrogen gas or liquid methanol with a burner using air as a combustion aid. The heat source gas is used as a heat source for the vaporization reaction, the reforming reaction, and the shift reaction in the vaporization section 16, the reforming section 18, and the shift conversion section 20, which will be described later.

A mixed liquid fuel of methanol and water (mixing ratio 1: 1 to 1: 4), which is a reforming raw material, is contained in a tank 28, and is directly supplied from the tank 28 or a carbon monoxide removing device as described later. After passing through the cooling layer of the catalyst carrier 34 as a refrigerant, the fuel reformer 1 is pumped by the pump 30.
0 is introduced into the vaporization section 16, and the reformed fuel gas sequentially vaporized in the vaporization section 16 is introduced onto the reforming catalyst of the adjacent reforming section 18 to reform the reforming reaction (CH ₃ OH (g)). + H ₂ O
(G) → 3H ₂ + CO ₂ ) produces a hydrogen-rich reformed gas. The reforming section 18 is a carrier for a reforming catalyst,
For example, a reforming catalyst made of Cu / Zn is supported on the reforming section structure by impregnation, thermal spraying, electrodeposition, sputtering, coating or the like. The reforming section structure is maintained by the heat source gas in the activation temperature range of the reforming catalyst of 250 to 300 ° C. The reformed gas produced by the reforming reaction under the reforming catalyst is rich in hydrogen, but contains surplus steam, carbon dioxide, and a trace amount (about 1%) of carbon monoxide.

The reformed gas generated by the reforming reaction is introduced from the reforming section 18 into the adjacent shift conversion section 20 and is monoxidized by the shift reaction (CO + H ₂ O → H ₂ + CO ₂ ) under the shift conversion catalyst. Carbon is removed, and the concentration of carbon monoxide in the reformed gas is reduced to about 1000 ppm. The active temperature range of the shift reaction is 150 to 200 ° C., and the heat source gas is used as the heat source in the shift conversion section.

The reformed gas that has undergone the shift reaction in the shift conversion section 20 passes through the fuel gas line A or C which is switched by the switching valve 32, and enters either the gas introduction manifold 36 or 38 of the carbon monoxide removing device 34. be introduced.

An example of the structure of the carbon monoxide removing device 34 is shown in FIG. Adjacent to the gas introduction manifolds 36 and 38, a first reaction section 40 and a second reaction section 42 having substantially the same configuration
Is provided. The first reaction part 40 is a selective oxidation catalyst Au / α-Fe ₂ O ₃ / A having an activation temperature range of room temperature to 100 ° C.
It is configured as a laminated body in which a catalyst packed layer 44 filled with 1 ₂ O ₃ and a cooling layer 46 through which a refrigerant passes are alternately laminated, and the second reaction part 42 has an activation temperature range of 70 to 150 ° C. The catalyst packed layer 48 filled with the combustion catalyst Pt / Al ₂ O ₃ and the cooling layer 50 through which the refrigerant passes are configured to be alternately stacked. The configuration of the first reaction section 40 and the second reaction section 42 shown in FIG. 2 is not limited, and for example, one catalyst packing 4
The cooling tubes 46 and 50 through which the refrigerant flows may be arranged around the valves 4 and 48.

A gas exhaust manifold 52 is provided on the downstream side of the first reaction section 40. Similarly, a gas exhaust manifold 54 is provided on the downstream side of the second reaction section 42. The gas discharge manifold 52 is connected to the gas introduction manifold 3 via an airtight partition wall 56 having a fuel gas opening / closing valve 58.
8 and is configured to allow gas flow between the manifolds 52 and 38 only when the fuel gas opening / closing valve 58 is opened.

Air can be introduced from the air pump 26 into the gas introduction manifolds 36 and 38 via air opening / closing valves 60 and 62, respectively. In addition, the first reaction unit 4
0, a predetermined refrigerant is introduced into each of the cooling layers 46 and 48 in the second reaction layer in order to cool the catalysts loaded in the catalyst packed layers 44 and 48 so as to keep the catalysts in their respective active temperature ranges. As the refrigerant, cooling water or any other material can be used, but in this embodiment, the water / methanol mixed liquid material in the tank 28 is used as the refrigerant, and the cooling layer 46 is provided via the refrigerant pumps 64 and 66. , 48. The refrigerant that has passed through the cooling layers 46 and 48 is pumped by the pump 30 into the vaporization section 16 of the reformer 10.
Is supplied to. With such a configuration, the water / methanol mixed liquid that is the reforming raw fuel serves as a refrigerant in the cooling layer 4.
Since it is heated by heat exchange while flowing through 6, 48, the amount of heat required in the vaporization section 16 is reduced.

Although not shown in FIG. 2, temperature sensors 68, 70 for detecting the catalyst temperature in the catalyst packed layers 44, 46 in the first reaction section 40 and the second reaction section 42 of the carbon monoxide removing device 34. Is provided. These temperature sensors 68, 7
The catalyst temperature detected by 0 is sent to the controller 72 (FIG. 3), and the controller 72, as will be described later, based on the catalyst temperature, the fuel gas switching valve 32, the fuel gas opening / closing valve 58, and the air opening / closing valve 60. , 62
And the discharge pressure control of the refrigerant pumps 64 and 66.

The selective oxidation catalyst used in the first reaction section 40 and the combustion catalyst used in the second reaction section 42 of the carbon monoxide removing device 34 need to be temperature controlled so as to be maintained in each activation temperature range. At the same time, it is desirable to introduce the reformed gas at a space velocity SV suitable for each reaction. About 500 hr ^-1 optimum space velocity of the selective oxidation catalyst and combustion catalyst respectively, because it is about 1000 hr ^-1, the first reaction part 40 the volume of the second reaction unit 42 1: by setting 2, each reaction There is no need to adjust the flow rate of the reformed gas at the inlet of the section, and a reformed gas flow rate adjusting valve (not shown) is provided at a point between the fuel reformer 10 and the carbon monoxide remover 34. Good.

After the carbon monoxide concentration in the carbon monoxide removing device 34 is reduced to 100 ppm or less, the reformed gas is introduced into the humidifier 74 consisting of a constant temperature water tank and a heater via the fuel gas line B. , To the fuel electrode (−) of the solid polymer electrolyte fuel cell 76. Since the reformed gas is cooled and humidified in the humidifier 74, the fuel cell is kept in the optimum operating temperature range of 50 to 100 ° C., and the electrolyte membrane is rehydrated to maintain its wet state. . Air serving as an oxidant gas is supplied from the air pump 26 to the oxidizing electrode (+) of the fuel cell 76.

In the present embodiment, the carbon monoxide removing device 34
The operation of is controlled as follows. (1) When the combustion catalyst temperature is 70 ° C. or lower Immediately after the activation of the carbon monoxide removing device 34, the temperature sensor 70 detects that the temperature of the combustion catalyst used in the second reaction section 42 is 70 ° C. or lower. Then, the controller 72 receives the detection signal and controls as follows.

Fuel gas switching valve 32: Passing through fuel gas line A Fuel gas opening / closing valve 58: Open Air opening / closing valve 60: Open Air opening / closing valve 62: Open Refrigerant pump 64: Holding selective oxidation catalyst in active temperature range Refrigerant pump 66 By this, the reformed gas from the fuel reformer 10 passes through the fuel gas line A, and together with the air from the air pump 26, the gas introduction manifold 36 of the carbon monoxide remover 34.
Of the selective oxidation catalyst (Au / α-Fe ₂ O ₃ / Al ₂₎ while being introduced into the first reaction section 40 and passing through the catalyst packed bed 44.
Oxidation reaction under O ₃ (CO + 1 / 2O ₂ → CO ₂ )
Thereby, carbon monoxide in the reformed gas is oxidized and removed to carbon dioxide. Since the discharge pressure of the refrigerant pump 64 is properly adjusted by the controller 72 that receives the detection signal from the temperature sensor 68, the selective oxidation catalyst in the first reaction section 40 is held in its active temperature range. The carbon monoxide concentration in the reformed gas leaving the first reaction section is reduced to 100 ppm or less.

The reformed gas that has been subjected to the carbon monoxide removal treatment by the selective oxidation catalyst in the first reaction section 40 in this manner is then subjected to the gas discharge manifold 52, the fuel gas open / close valve 58 in the open state, and the gas introduction manifold 38. Through the second reaction section 42. At this time, the combustion catalyst in the second reaction section 42 has not reached its activation temperature range, but a certain degree of combustion reaction (CO + 1 / 2O ₂ → CO ₂ ) progresses while passing through the catalyst packed bed 48. The carbon monoxide concentration in the reformed gas is further reduced. (2) When the combustion catalyst temperature reaches 70 ° C. When the carbon monoxide removing device 34 is operated in the state of (1) above, the oxidation reaction by the selective oxidation catalyst in the first reaction section 40 is an exothermic reaction. Therefore, the temperature of the reformed gas introduced into the second reaction section 42 gradually rises, and the combustion reaction by the combustion catalyst in the second reaction section is also an exothermic reaction. The temperature of the combustion catalyst also rises. When it is known from the detection signal from the temperature sensor 70 that the combustion catalyst temperature has reached 70 ° C., the controller 72 changes the control as follows.

Fuel gas switching valve 32: Passing through fuel gas line C Fuel gas opening / closing valve 58: Closed Air opening / closing valve 60: Closed Air opening / closing valve 62: Open Refrigerant pump 64: Holding selective oxidation catalyst in active temperature range Refrigerant pump 66 : Keeping the combustion catalyst in the active temperature range, that is, when the combustion catalyst temperature reaches 70 ° C., the fuel gas switching valve 32 is switched, and the reformed gas does not pass through the first reaction section 40 and the fuel gas line C And is directly introduced into the gas introduction manifold 38. The reformed gas undergoes the above combustion reaction by the combustion catalyst while passing through the catalyst packed bed 48 of the second reaction section 42 from the gas introduction manifold 38, and the carbon monoxide concentration contained is reduced to 100 ppm or less. Since the temperature of the combustion catalyst has already reached the activation temperature range, if the discharge pressure of the refrigerant pump 66 is adjusted to cool the combustion catalyst temperature so that it does not exceed the upper limit value (150 ° C.) of the activation temperature, the combustion The catalyst is maintained in the active temperature range, and the carbon monoxide concentration in the reformed gas can be surely reduced to 100 ppm or less.

At this time, although the first reaction section 40 is in the inoperative state, the selective oxidation catalyst in the catalyst packed bed 44 is controlled by the refrigerant pump 64 so as to always maintain the activation temperature range (100 ° C. or lower). The refrigerant is sent to the cooling layer 46. (3) When the combustion catalyst temperature again becomes 70 ° C. or lower When the carbon monoxide removing device 34 is also intermittently operated due to the intermittent operation of the fuel reforming device 10, the combustion catalyst temperature is once activated. The temperature may fall to 70 ° C. or lower again after rising to the temperature range. When this is detected by the temperature sensor 70, the control by the controller 72 is switched to the state (1) again.

[0033]

EFFECTS OF THE INVENTION According to the present invention, since the carbon monoxide removal treatment is efficiently performed by the action of the selective oxidation catalyst even immediately after the activation of the carbon monoxide removal device, the carbon monoxide content is always kept below the predetermined level. The fuel gas can be supplied to the fuel cell in a state where the concentration is reduced, deterioration of the electrode catalyst of the fuel cell can be prevented, stable performance can be given to the fuel cell, and a long life can be achieved.

In the conventional carbon monoxide removing device using only the combustion catalyst, a temperature control device having a heating function and a cooling function is used in order to keep the combustion catalyst in the activation temperature range. In the present invention in which a selective oxidation catalyst and a combustion catalyst having different regions are used together, a heating source such as a heater is not required, and each catalyst can be easily held in its respective activation temperature range.

[Brief description of drawings]

FIG. 1 is a schematic system configuration diagram of a solid polymer electrolyte fuel cell including a carbon monoxide removing device according to an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing the configuration of the carbon monoxide removing device in FIG.

FIG. 3 is an explanatory diagram showing a control system of each element related to the carbon monoxide removing device in FIG. 1.

[Explanation of symbols]

 10 Fuel Reforming Device 26 Air Pump 28 Raw Fuel Tank 32 Fuel Gas Switching Valve 34 Carbon Monoxide Removing Device 40 First Reaction Part 42 Second Reaction Part 44 Selective Oxidation Catalyst Packing Layer 46 Cooling Layer 48 Combustion Catalyst Packing Layer 50 Cooling Layer 60 , 62 Air opening / closing valve 64, 66 Refrigerant pump 68, 70 Temperature sensor 76 Fuel cell

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[Procedure amendment]

[Submission date] November 15, 1994

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Fig. 2]

FIG.

[Figure 3]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C01B 3/58 // C07B 61/00 300

Claims (4)

[Claims] 1. A carbon monoxide removing apparatus for oxidizing and removing carbon monoxide in a hydrogen-rich fuel gas, comprising: a selective oxidation catalyst supporting portion disposed upstream of the fuel gas and supporting a selective oxidation catalyst; A first reaction part having a cooling layer for cooling the selective oxidation catalyst so as to keep it within its activation temperature range, and arranged in series with the first reaction part on the downstream side of the fuel gas, A second reaction part having a combustion catalyst support part for supporting a combustion catalyst and a cooling layer for cooling the combustion catalyst support part to keep it within the activation temperature range; And / or an oxidant gas supply means for supplying an oxidant gas to the second reaction part, a first fuel path for passing the fuel gas to the first reaction part and then to the second reaction part, and Bypass the first reaction section and directly to the second reaction section A fuel gas switching means for switching to a second fuel path that enters and passes through, a temperature detecting means for detecting a combustion catalyst temperature in the second reaction section, and a combustion catalyst temperature detected by the temperature detecting means is a predetermined value. A control means for controlling the fuel gas switching means so as to select the first fuel path when the temperature is equal to or less than the predetermined value and to select the second fuel path when the combustion catalyst temperature is equal to or higher than a predetermined value. A device for removing carbon monoxide, which is characterized in that 2. The control means supplies an oxidant gas to the first reaction section and the second reaction section when the first fuel path is selected and when the second fuel path is selected. 2. The carbon monoxide removing apparatus according to claim 1, wherein the oxidizing gas supplying means is controlled so that the oxidizing gas is supplied only to the second reaction section. 3. A fuel gas on-off valve is provided between the first reaction section and the second reaction section, and the control means comprises:
2. The control for opening the fuel gas on-off valve when the first fuel path is selected, and closing the fuel gas on-off valve when the second fuel path is selected. Carbon oxide removal device. 4. The selective oxidation catalyst in the first reaction section is Au / α-Fe ₂ O ₃ / Al ₂ O ₃ , and the _second oxidation catalyst is the _second oxidation catalyst.
The carbon monoxide removing apparatus according to claim 1, wherein the combustion catalyst in the reaction section is Pt / Al ₂ O ₃ .