Reformer for a fuel cell

Details Reformer for a fuel cell Reformer for a fuel cell

1998-11-04

2001-09-04

Kalafut, Stephen (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Having magnetic field feature

C422S211000, C422S218000, C422S236000

Reexamination Certificate

active

06284398

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reformer for a fuel cell using a partial oxidation reaction (also called autothermal) as a reforming reaction, and more particularly to a reformer for a fuel cell comprising a container provided with an inlet for introduction of a vapor of a methanol solution as a raw fuel and an outlet for discharge of a reformed gas, and a catalytic layer which divides the inside of the container into an inlet space communicating with the inlet and an outlet space communicating with the outlet end which is constructed such that a passing cross section of the catalytic layer at the side of the outlet space becomes larger than a passing cross section at the side of the inlet space.
2. Description of the Related Art
Although a reformer is often used for a conventional hydrogen supply apparatus to a fuel cell, for improvement of starting properties, responsiveness, and miniaturization, a reforming reaction using a partial oxidation method is effective in a conventional hydrogen generating apparatus as disclosed in Japanese Patent Unexamined Publication No. Hei. 8-231201.
In reforming by a partial oxidation reaction, a reaction in which excess water is added is generally used, and reaction proceeds according to the following equations, in which equation 1 indicates a partial oxidation reaction, equation 2 indicates a methanol decomposition reaction, and equation 3 indicates a shift reaction.
CH
3
OH+0.5O
2
→CO
2
+2H
2
−192KJ (kilojoules)  [Equation 1]
CH
3
OH→CO
2
+2H
2
+91KJ  [Equation 2]
CO+H
2
O→CO
2
+H
2
−41KJ  [Equation 3]
In an actual reforming unit, the partial oxidation reaction of methanol occurs, and the decomposition reaction of methanol progresses by heat generation in the former reaction, and the shift reaction occurs by CO obtained in the former reaction and excess water. In this case, while the partial oxidation reaction and the methanol decomposition reaction progress at a relatively high temperature of 300 to 400° C., the shift reaction progresses at a relatively low temperature of, for example, 150 to 250° C. so as to lower the unreacted CO concentration, and the reaction rate of the shift reaction is low as compared with the partial oxidation reaction and the methanol decomposition reaction. Thus the shift reaction determines the rate of the total reaction.
However, as the foregoing three kinds of reactions progress, the mole number of the reaction products at the right side of the above equations becomes larger than the mole number at the left side. Thus, the volume of the product gas increases, which causes the flow velocity to increase. That is, there is a problem that the flow velocity is increased in the region where the third shift reaction occurs, so that a sufficient shift reaction cannot be performed.
In a reforming unit using a partial oxidation reaction, heat supply from the outside is unnecessary, and for example, in the conventional hydrogen generating apparatus (Japanese Patent Unexamined Publication No. Hei. 8-231201), there is proposed a structure as shown in
FIG. 10
, in which a raw fuel is directly blown into a reforming unit K.
In the paper “REFORMERS FOR THE PRODUCTION OF HYDROGEN FROM METHANOL AND ALTERNATIVE FUELS FOR FUEL CELL POWERED VEHICLE” published August 1992 by Argonne National Laboratory Co. Ltd., as shown in
FIG. 11
, the JPL autothermal reformer is constructed such that a raw fuel gas, air, and water vapor are mixed by a swirl mixer SM, and are supplied in an axial direction of a cylindrical reforming unit in which a low temperature active catalytic layer L, an oxidation catalytic layer O, and a water vapor reforming catalytic layer H are arranged in sequence along the length of the reforming unit, so that the fed raw fuel gas is reformed.
In the above hydrogen generating apparatus, it is difficult to supply a raw fuel uniformly to the catalytic layers within the reforming unit, and so to effectively use the entirety of the catalytic layers, so that a sufficient shift reaction cannot be performed. Further, it is difficult to raise the volume velocity.
In the foregoing reformer, since the passage length of the cylindrical reforming unit through which a raw fuel gas passes is large, if a volume velocity, that is, a reaction gas flow amount per unit volume of a catalyst, which is an index of catalyst efficiency, is to be raised, the flow velocity becomes high and the pressure loss rises, so that the raw fuel must be introduced at a high pressure and high power consumption results.
Moreover, in order for the shift reaction to be sufficiently performed, the volume of the water vapor reaching the reforming catalytic layer for performing water vapor reforming reaction in
FIG. 11
is required to be large, so that the pressure loss is further increased and the volume velocity is lowered.
SUMMARY OF THE INVENTION
It is an object of the present invention to enable a sufficient shift reaction by effectively using the entirety of the catalytic layer in the reformer.
It is a further object of the present invention to enable a sufficient shift reaction by raising the volume velocity in the reformer.
It is yet a further object of the present invention to enable a sufficient shift reaction by lowering the pressure loss in the reformer.
According to the present invention, the above and-other objects are achieved in a reformer for a fuel cell using a partial oxidation reaction (also called autothernal) as a reforming reaction, where the inside of a container is divided by the catalytic layer into an inlet space communicating with the inlet for introduction of a vapor of a methanol solution as a raw fuel and an outlet space communicating with the outlet for discharge of the reformed gas, and a passage cross section of the catalytic layer at the side of the outlet space is larger than a passage cross section at the side of the inlet space.
According to a first aspect of the present invention, a reformer for a fuel cell using a partial oxidation reaction as a reforming reaction comprises a container including an inlet for introduction of a vapor of a methanol solution as a raw fuel and an outlet for discharge of a reformed gas, and a catalytic layer structured such that the inside of the container is divided into an inlet space communicating with the inlet and an outlet space communicating with the outlet, in which a passage cross section of the catalytic layer at a side of the outlet space is larger than a passage cross section at a side of the inlet space.
According to a second aspect of the present invention in the first aspect, the passage cross section of the catalytic layer at the side of the outlet space is larger by a range of 20% to 250% than the passing cross section at the side of the inlet space.
According to a third aspect of the present invention in the first aspect, the passage cross section of the catalytic layer becomes gradually larger from the side of the inlet space to the side of the outlet space.
According to the fourth aspect of the present invention in the first aspect, the catalytic layer is made of a porous material hydrocarbon catalyst, such as ceramics including alumina supporting a methanol reforming catalyst.
According to a fifth aspect of the present invention in the first aspect, the catalytic layer is made up of a small diameter cylindrical wire mesh, a large diameter cylindrical wire mesh coaxially disposed with the small diameter wire mesh, and a granular catalyst disposed between the small diameter wire mesh and the large diameter wire mesh.
According to a sixth aspect of the present invention in the first aspect, the container is a hollow cylindrical container in which an opening is formed at a center of one axial end of the container and an opening is formed at a center of the other axial end, the catalytic layer is formed of a hollow cylinder with a smaller outer diameter and a shorter length in an axial direction than tho

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