Power plants – Motive fluid energized by externally applied heat – Power system involving change of state
Reexamination Certificate
2000-12-20
2002-11-19
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Power system involving change of state
C422S198000, C422S198000, C422S211000
Reexamination Certificate
active
06481207
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a single-pipe cylinder type reformer for manufacturing a hydrogen-rich reformed gas by steam-reforming a hydrocarbon-based crude fuel such as town gas, natural gas, or LPG or an alcohol and, more particularly, to a reformer used in combination with a polymer electrolyte fuel cell.
2. Description of the Prior Art
A reformer is an apparatus for producing a (hydrogen-rich) reformed gas having a high hydrogen concentration by steam-reforming a hydrocarbon-based crude fuel such as town gas, natural gas, and/or LPG or an alcohol. This apparatus is widely used to produce hydrogen used in the process of manufacturing optical fibers or semiconductors and for fuel cells and the like.
In a case of methane, the reforming reaction in the reformer is expressed as:
CH
4
+H
2
O→CO+3H
2
(CH
4
+H
2
O←CO+3H
2
)
CO+H
2
O→CO
2
+H
2
(CO+H
2
O←CO
2
+H
2
)
The steam reforming reaction caused by the reformer is an endothermic reaction, and hence heating is required to sustain the reaction. In general, a combustion unit such as a burner is provided for the reformer, and heating is performed by burning surplus hydrogen from a reformation material gas or fuel cell. As a reformer for producing a relatively small amount of hydrogen, a single-pipe cylinder type reformer like the one disclosed in Japanese Unexamined Patent Publication No. No. 11-11901 is known. This single-pipe cylinder type reformer is configured to have a heating means such as a burner in a cylindrical vessel incorporating a catalyst layer between two cylinders so as to heat the catalyst layer with the heating means and steam-reform a reformation material gas passed through the catalyst layer.
FIG. 1
is a longitudinal sectional view showing the schematic arrangement of a conventional single-pipe cylinder type reformer.
In the single-pipe cylinder type reformer shown in
FIG. 1
, an upright elongated outer cylinder
1
having a circular cross-section, a circular inner cylinder
3
located inside the outer cylinder
1
, an intermediate cylinder
2
located inside the outer cylinder
1
to surround the inner cylinder
3
at a predetermined distance therefrom, and a radiation cylinder
4
located inside the inner cylinder
3
are concentrically disposed, and the annular space between the inner cylinder
3
and the intermediate cylinder
2
is filled with a reforming catalyst
5
. A burner
7
supported on a burner mount base
6
is disposed in the upper portion of a combustion chamber
9
located inside the radiation cylinder
4
. A cover plate (bottom plate) la which is a common one-piece plate is attached to the lower ends of the outer cylinder
1
and inner cylinder
3
. In the single-pipe cylinder type reformer shown in
FIG. 1
, the burner
7
is disposed in the upper portion of the combustion chamber
9
. However, the burner
7
is disposed in the lower portion of the combustion chamber
9
in some case (not shown). In such a case, the cover plate
1
a
is attached as a ceiling plate, which is a common one-piece disk, attached to the upper ends of the outer cylinder
1
and inner cylinder
3
.
The single-pipe cylinder type reformer shown in
FIG. 1
operates as follows.
The burner
7
generates a high-temperature combustion gas in the combustion chamber
9
with a combustion flame
8
. The heat is transferred outside the inner cylinder in the radial direction via the radiation cylinder
4
to heat the reforming catalyst
5
. At the same time, the high-temperature combustion gas enters the inner cylinder
3
from the lower portion of the radiation cylinder
4
to become an ascending current, thereby directly heating the reforming catalyst
5
. The combustion gas is discharged from the upper end portion of the reformer after heating. Meanwhile, the reformation material gas which is fed from the upper portion of the reformer is heated to about 700° C. while descending the annular flow path filled with the reforming catalyst
5
. As a consequence, steam reforming is sufficiently performed. The reformed material gas (reformed gas) is reversed in the lower end portion of the reformer to become an ascending current in the path formed between the outer cylinder
1
and the inner cylinder
3
. Meanwhile, the sensible heat of the reformed gas is recovered in the reforming step inside the intermediate cylinder
2
. As a result, the temperature of the reformed gas lowers, and the gas is extracted outside as a reformed gas from the upper end portion of the reformer.
The conventional single-pipe cylinder type reformer shown in
FIG. 1
suffers the following problems.
(1) Since the common one-piece cover plate
1
a
is hermetically fixed to the lower end portions of the outer cylinder
1
and inner cylinder
3
, which require a partition for a fluid, by welding or the like, the thermal stresses produced in the outer cylinder
1
and inner cylinder
3
due to the temperature difference during operation cause buckling of the inner cylinder
3
which is heated to a high temperature, in particular. The following factors due to this buckling may degrade the performance of the reformer:
a. leakage of the reformed gas due to a crack in the inner cylinder
3
;
b. damage to the reforming catalyst due to the deformation of the inner cylinder
3
; and
c. uneven heating in the circumferential direction due to the deformation of the inner cylinder
3
.
(2) Since the combustion chamber
9
is partitioned off from the outside with the one-piece cover plate
1
a
common to the inner cylinder
3
and outer cylinder
1
, the heat insulating properties are poor, and the heat radiation loss from the cover plate
1
a
portion increases.
When a polymer electrolyte fuel cell is used for a home, vehicle, or the like, a reduction in the size and weight of the overall reforming apparatus including a single-pipe cylinder type reformer is an essential condition. In addition, various improvements, e.g., efficient operation and a reduction in rise time for the start of operation, are required.
For example, the required improvements include a reduction in fuel by efficient preheating of a reformation material gas, an improvement in operability by prevention of overheating of a steam generator, an increase in efficiency by the preservation of a necessary temperature inside the reformer and the effective use of heat quantity, suppression of heat radiation to the outside by an effective heat insulating structure, realization of high durability by a reduction in heat stress due to an inner temperature difference, an increase in efficiency of steam generation by the effective use of reaction heat, and an operation method capable of efficiently coping with variations in operation state.
The reformed gas produced by the conventional single-pipe cylinder type reformer contains about 10% of CO. When such a reformed gas is to be used for a polymer electrolyte fuel cell, the CO concentration must be decreased to about 0.5% by using a CO transformer, and a CO selective oxidation reaction must be caused by using a CO selective oxidizing unit to decrease the CO concentration to about 10 ppm. However, separately providing the CO transformer and CO selective oxidizing unit for the single-pipe cylinder type reformer is not preferable in terms of a reduction in size, an increase in efficiency, and starting characteristics.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above problems in the prior art, and has as its first object to provide a single-pipe cylinder type reformer which prevents the generation of thermal stresses by liberating thermal displacement of outer and inner cylinders forming a reformer in the axial direction, prevents the occurrence of buckling of the inner cylinder and a deterioration in the performance of the reformer due to the buckling, in particular, and reduces a heat radiation loss from a combustion chamber through a cover plate.
It is the second object of the present invention to provide
Miura Toshiyasu
Shirasaki Yoshinori
Nguyen Hoang
Tokyo Gas Co., LTD
Townsend and Townsend / and Crew LLP
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