Gas: heating and illuminating – Apparatus for converting or treating hydrocarbon gas
Reexamination Certificate
1999-09-13
2001-12-25
Tran, Hien (Department: 1764)
Gas: heating and illuminating
Apparatus for converting or treating hydrocarbon gas
C048S128000, C422S105000, C422S108000, C422S172000, C422S198000
Reexamination Certificate
active
06332901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for reducing a concentration of carbon monoxide contained in reformate gas that has been obtained through reformation of a hydrocarbon such as methyl alcohol and a fuel such as water vapor. The present invention also related to a carbon monoxide reducing method.
2. Description of Related Art
As a system using this type of reformate gas, there is known a system that employs a fuel cell. For example, a typical fuel cell employing an electrolyte film permeable to protons is designed to electrochemically oxidize fuel, such as hydrogen gas, and to take out an electromotive power generated during the process.
A reformer that is used in such a system equipped with this fuel cell is designed, for example, to supply a reforming catalyst with methanol and water vapor and to obtain a reformate gas therefrom composed mainly of hydrogen, through a reforming reaction under a predetermined temperature. Basically, the reforming reaction is an endothermic reaction in which 1 mole of methanol reacts with 1 mole of water to produce 3 moles of hydrogen and 1 mole of carbon dioxide. However, a small amount of carbon monoxide is inevitably generated. The reaction is expressed by the formula (i) shown below.
CH
3
OH+H
2
O→3H
2
+CO
2
+&agr;CO−49.5(kJ/mol) (i)
In the case where reformate gas is used as a fuel gas for a fuel cell, platinum is employed as a catalyst for electrodes of the fuel cell. Therefore, if the fuel gas or reformate gas contains carbon monoxide, the carbon monoxide poisons and deteriorates the platinum. For this reason, it is preferable to gradually remove carbon monoxide from the reformate gas. Various methods for removing carbon monoxide from the reformate gas are known in the art. For example, Japanese Patent Application Laid-Open No. HEI 8-329969 discloses a device wherein an oxidation portion for oxidizing carbon monoxide contained in the reformate gas is disposed between a reforming portion for causing a reforming reaction and a fuel cell. In this device, the concentration of carbon monoxide is detected in a reformate gas feed path extending from the reformer to the fuel cell. If the concentration has become equal to or greater than a predetermined level, the amount of air supplied to the oxidation portion is increased.
In the aforementioned device of the related art, the carbon monoxide contained in the reformate gas reacts with oxygen contained in the air at an oxidation catalyst of the oxidation portion and is converted to carbon dioxide, which is not harmful to the platinum. In this manner, carbon monoxide is removed from the reformate gas. However, according to the aforementioned device of the related art, although the amount of air blown into the oxidation portion is increased with increases in concentration of carbon monoxide contained in the reformate gas, that amount of air may not always be suited for an actual amount of carbon monoxide.
That is, in principle, 1 mole of carbon monoxide reacts with 1/2 mole of oxygen to produce 1 mole of carbon dioxide. Therefore, if the amount of air supplied to the oxidation portion is insufficient with respect to an amount of carbon monoxide contained in the reformate gas, not all of the carbon monoxide is converted to carbon dioxide, and unreacted carbon monoxide is supplied to the fuel cell and poisons the platinum catalyst. Conversely, if an excessive amount of air is supplied to the oxidation portion, surplus oxygen is supplied to the fuel cell together with the reformate gas. As a result, the fuel gas for the fuel cell may burn instead of being used to generate electric power. However, in the device of the related art wherein the amount of air blown into the oxidation portion is increased simply based on a detected concentration of carbon monoxide, no effective measures may be taken to address or eliminate these problems.
SUMMARY OF THE INVENTION
The present invention has been made in light of the aforementioned circumstances, and it is an object of the present invention to provide a device capable of suitably removing carbon monoxide from reformate gas.
In order to achieve the above-stated and other objects, according to a first embodiment of the present invention, there is provided a carbon monoxide reducing device including a carbon monoxide oxidation portion, an oxygen supplying device, and an oxygen supply amount controller. The carbon monoxide oxidation portion oxidizes and thereby reduces carbon monoxide gas contained in reformate gas that is obtained through a reforming reaction. The oxygen supplying device supplies oxygen to the reformate gas so as to oxidize the carbon monoxide contained in the reformate gas. The first oxygen supply amount controller controls an amount of oxygen supplied to the reformate gas based on an amount of fuel contributing to a reforming reaction.
Thus, according to the first embodiment of the present invention, the amount of oxygen supplied to oxidize carbon monoxide is changed in accordance with an amount of fuel contributing to a reforming reaction. In other words, as the reforming reaction proceeds, carbon monoxide is generated at a certain rate and reacts with oxygen with a predetermined efficiency. Hence, the amount of supply of oxygen is determined in accordance with an amount of reformate fuel, whereby the amount of oxygen is set to a value matching the amount of carbon monoxide produced in the reforming reaction.
Further, in other embodiments, there may be provided a response delay-based adjuster in the oxygen supply amount controller that adjusts the amount of oxygen, which is supplied so as to oxidize the carbon monoxide, based on a response delay from supply of the fuel to generation of the reformate gas.
The response delay-based adjuster makes it possible to reflect a response delay of the reforming reaction on the amount of oxygen supplied to oxidize carbon monoxide. Therefore, the concentration of oxygen is prevented from becoming too high or too low at a location where carbon monoxide reacts with the oxygen. Consequently, the concentration of carbon monoxide contained in the reformate gas can be reduced effectively.
Further, there may be provided a concentration-based adjuster in the oxygen supply amount controller that adjusts the amount of oxygen, which is supplied so as to oxidize the carbon monoxide, based on a concentration of carbon monoxide flowing out of the carbon monoxide oxidation portion.
The concentration-based adjuster makes it possible to reflect a target concentration of carbon monoxide contained in the reformate gas on the amount of supply of oxygen. Therefore, the amount of oxygen supplied to oxidize and remove carbon monoxide can be set with higher precision. As a result, the quality of the reformate gas obtained can be improved.
Further, there may be provided a temperature-based adjuster in the oxygen supply amount controller that adjusts the amount of oxygen based on a temperature of the carbon monoxide oxidation portion.
The temperature-based adjuster makes it possible to reflect a temperature of the carbon monoxide oxidation portion where carbon monoxide is oxidized on the amount of supply of oxygen. Therefore, for example, if the oxidation of carbon monoxide or the like causes an extraordinary rise in temperature, the amount of supply of oxygen can be limited. As a result, it is possible to prevent the CO oxidation portion from abnormally deteriorating because of heat.
Still further, there may be provided a pressure-based adjuster in the oxygen supply amount controller that adjusts a command value for setting the amount of oxygen supplied from the oxygen supplying device, based on a quantity associated with a pressure in the carbon monoxide oxidation portion.
The pressure-based adjuster adjusts a command value for the oxygen supplying device in accordance with a pressure of oxygen supplied to the carbon monoxide oxidation portion. Therefore, even when the pressure in the carbon monoxide oxidation portion is high, a neces
Aoyama Satoshi
Araki Yasushi
Maeda Iwao
Nagamiya Kiyomi
Taki Masayoshi
Doroshenk Alexa A.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Tran Hien
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