U.S. patent application number 10/326272 was filed with the patent office on 2003-07-10 for burner for hydrogen generation system and hydrogen generation system having the same.
Invention is credited to Asou, Tomonori, Maenishi, Akira, Mukai, Yuji, Yoshida, Yutaka.
Application Number | 20030129555 10/326272 |
Document ID | / |
Family ID | 19188503 |
Filed Date | 2003-07-10 |
United States Patent
Application |
20030129555 |
Kind Code |
A1 |
Mukai, Yuji ; et
al. |
July 10, 2003 |
Burner for hydrogen generation system and hydrogen generation
system having the same
Abstract
To provide a burner for a hydrogen generation system having an
excellent combustion stability which can be achieved at low costs,
and a hydrogen generation system having such a burner. A burner for
hydrogen generation systems according to the present invention
includes a combustion chamber that has a taper that enlarges in a
flame radiation direction, and a distributor having an upper-stage
gas injection ports for injecting utility gas and off-gas into the
combustion chamber. Air injection ports are formed in the tapered
side wall of the combustion chamber for injecting combustion air
into the combustion chamber. The air injection ports are generally
opposed to the upper-stage gas injection ports formed in the
distributor.
Inventors: |
Mukai, Yuji; (Kadoma-shi,
JP) ; Maenishi, Akira; (Ikeda-shi, JP) ; Asou,
Tomonori; (Kitakatsuragi-gun, JP) ; Yoshida,
Yutaka; (Nabari-shi, JP) |
Correspondence
Address: |
STEVENS DAVIS MILLER & MOSHER, LLP
1615 L STREET, NW
SUITE 850
WASHINGTON
DC
20036
US
|
Family ID: |
19188503 |
Appl. No.: |
10/326272 |
Filed: |
December 23, 2002 |
Current U.S.
Class: |
431/187 ;
431/10 |
Current CPC
Class: |
F23D 14/20 20130101;
C01B 3/363 20130101; Y02E 60/50 20130101; C01B 2203/066 20130101;
C01B 2203/0255 20130101 |
Class at
Publication: |
431/187 ;
431/10 |
International
Class: |
F23C 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2001 |
JP |
2001-391322 |
Claims
What is claimed is:
1. A burner for a hydrogen generation system comprising: a
combustion chamber that has a taper that enlarges in a flame
radiation direction; and a distributor that is placed in said
combustion chamber to supply to said combustion chamber a fuel gas
containing a compound made up of at least carbon and hydrogen and
an off-gas that is released from a fuel cell, said distributor
being projected in the flame radiation direction, said combustion
chamber having multiple combustion air injection ports formed in
said combustion chamber to inject combustion air into said
combustion chamber, said distributor having multiple gas injection
ports formed in said distributor to inject the fuel gas and the
off-gas into said combustion chamber, at least some of the
combustion air injection ports and at least some of the gas
injection ports being arranged in such a manner that a jet flow of
the combustion air collides with jet flows of the fuel gas and the
off-gas.
2. The burner as claimed in claim 1, wherein the combustion air
injection ports and the gas injection ports that are arranged to
achieve the collision are aligned with each other in a generally
colinear manner from the perspective of the flame radiation
direction.
3. The burner as claimed in claim 1 or 2, wherein the combustion
air injection ports that are arranged to achieve the collision are
formed in the tapered side wall of said combustion chamber.
4. The burner as claimed in claim 1 or 2, wherein the combustion
air injection ports that are arranged to achieve the collision are
formed in the tapered side wall of said combustion chamber, the
combustion air injection ports being passed through the side wall
in a direction generally perpendicular to the side wall, and
wherein the gas injection ports that are arranged to achieve the
collision is passed through said distributor in a direction
generally perpendicular to said distributor.
5. The burner as claimed in claim 1, wherein the combustion air
injection ports that are arranged to achieve the collision are
formed in the bottom wall of said combustion chamber.
6. The burner as claimed in claim 1, wherein the combustion air
injection ports that are arranged to achieve the collision are
formed in the tapered side wall of said combustion chamber and in
the bottom wall of said combustion chamber.
7. A burner for a hydrogen generation system comprising: a
combustion chamber that has a taper that enlarges in a flame
radiation direction; and a distributor that is placed in said
combustion chamber to supply to said combustion chamber a fuel gas
and an off-gas that is released from a fuel cell, said distributor
being projected in the flame radiation direction, said combustion
chamber having multiple combustion air injection ports formed in
the tapered side wall of said combustion chamber to inject
combustion air into said combustion chamber, said distributor
having multiple gas injection ports formed in said distributor to
inject the fuel gas and the off-gas into said combustion chamber,
at least some of the combustion air injection ports and at least
some of the gas injection ports being generally opposed to each
other.
8. The burner as claimed in claim 7, wherein the combustion air
injection ports that are generally opposed are formed in the
tapered side wall of said combustion chamber, the combustion air
injection ports being passed through the side wall in a direction
generally perpendicular to the side wall, and wherein the gas
injection ports that are generally opposed are passed through said
distributor in a direction generally perpendicular to said
distributor.
9. The burner as claimed in claim 1 or 7, wherein a taper angle of
said combustion chamber is in a range of from 10 degrees to 90
degrees, both inclusive.
10. The burner as claimed in claim 1 or 7, wherein the combustion
air injection ports are arranged in such a manner that a larger
amount of the combustion air is injected into said combustion
chamber on the downstream side than on the upstream side of said
combustion chamber.
11. The burner as claimed in claim 10, wherein the density of the
combustion air injection ports is higher on the downstream side
than on the upstream side of said combustion chamber.
12. The burner as claimed in claim 10, wherein the diameter of the
combustion air injection ports is larger on the downstream side
than on the upstream side of said combustion chamber.
13. The burner as claimed in claim 1 or 7, wherein the gas
injection ports comprising a first gas injection port and a second
gas injection port, the first gas injection port being for
injecting the fuel gas, and the second gas injection port being for
injecting the off-gas, the second gas injection port being located
downstream of said combustion chamber relative to the first gas
injection port.
14. The burner as claimed in claim 1 or 7, wherein said combustion
chamber is formed by pressing or draw-pressing a sheet-like
material.
15. The burner as claimed in claim 1 or 7, wherein said combustion
chamber is cylindrical in shape having a flange member that is
projected outward in the radial direction, the flange member having
a turned-up portion along the periphery thereof.
16. The burner as claimed in claim 1 or 7, further comprising: an
electrode that is placed in said combustion chamber; and a flame
detection circuit that is connected to said electrode.
17. The burner as claimed in claim 1 or 7, further comprising: an
electrode that is placed in said combustion chamber; and a flame
ignition circuit that is connected to said electrode.
18. The burner as claimed in claim 1 or 7, further comprising: an
electrode that is placed in said combustion chamber; a flame
detection circuit and a flame ignition circuit that are connected
to said electrode; and a switch circuit that is used to switch the
connection between said electrode and said flame detection circuit
and the connection between said electrode and said flame ignition
circuit.
19. The burner as claimed in claim 18, wherein said electrode is
projected from the center of said distributor in the flame
radiation direction.
20. A hydrogen generation system comprising: a reformer for
generating a reformed gas that contains hydrogen by reforming a
feed material that contains a compound made up of at least carbon
and hydrogen; and a burner for a hydrogen generation system
according to claim 1 or 7.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a burner that is used to
operate a hydrogen generation system for a fuel cell system, in
which the fuel cell system generates power by a reaction of a feed
material to produce hydrogen, the feed material containing a
compound made up of at least carbon and hydrogen. The present
invention also relates to a hydrogen generation system including
such a burner.
[0003] 2. Related Art
[0004] A first related art on burners that are used to operate
hydrogen generation systems for fuel cell systems (hereinafter,
merely referred to as a "burner for hydrogen generation systems")
includes a cylindrical burner head, a first introduction pipe and a
second introduction pipe. The burner head has an outer wall
provided with a burner port and a combustion chamber provided
inside thereof. The first and second introduction pipes through
which high BTU gas and low BTU gas, respectively, can flow into the
combustion chamber of the burner head. Thus, the gases with
different BTU values can be supplied to the combustion chamber for
combustion through the single burner port (see, for example,
Japanese Patent Laid-Open No. 2001-185186). The first related art
simplifies the configuration of the burner with the use of the
shared burner port for the combustion of the high and low BTU
gases.
[0005] A second related art on burners for hydrogen generation
systems comprises a combustion chamber that is implemented using an
air nozzle with multiple air ports through which a jet of
combustion air is injected under pressure. The diameter of the
combustion chamber gradually becomes larger from the upstream side
to the downstream side (see, for example, Japanese Patent
Publication No. 5-59325). This configuration provides stable
combustion at high combustion load.
[0006] A third related art on burners for hydrogen generation
systems comprises a burner port assembly that has a taper that
enlarges from a fuel gas injection unit (see, for example, Japanese
Patent Laid-Open No. 2001-201019). This reduces the size of the
system.
[0007] Burners for hydrogen generation systems have two
distinguishing features from other burners. Firstly, the burners
for hydrogen generation systems are designed to burn a fuel gas and
an off-gas released from a fuel cell. The fuel gas and the off-gas
are significantly different in their burning velocity. More
specifically, utility gas, which is a typical fuel gas, has a
burning velocity of about 36 cm/sec. On the other hand, hydrogen,
which is the major component of the off-gas that is released from
the fuel cell, has a burning velocity of about 320 cm/sec. It was
difficult to provide stable burning of fuels using a single burner
that are significantly different in their burning velocity. This is
because a burner design adapted to either one fuel causes a
disadvantageous consequence. A burner may be adapted to a high
burning velocity of hydrogen. Using such a burner for the
combustion of the utility gas causes the major portion of the
utility gas to be exhausted without being burnt or otherwise causes
flame blowout. This is because the burning velocity for it exceeds
that of the utility gas. On the other hand, a burner may be adapted
to a low burning velocity of the utility gas. With this
configuration, however, the hydrogen may be burnt in the close
vicinity of the fuel gas injection port. This inevitably results in
the presence of flames near the surface of the fuel gas injection
port. In such a case, the combustion may be rendered unstable due
to the transfer of heat of combustion through the fuel gas
injection port. Alternatively, a distributor may glow to redness by
the heat of combustion.
[0008] Secondly, the flow rates of the off-gas released from the
fuel cell and of the fuel gas vary according to varying loads of
electricity carried by the fuel cell system. It is necessary to use
a huge amount of feed material to produce a considerable amount of
hydrogen with a large load of electricity. The flow rate of the
fuel gas should be increased accordingly. The increase in the feed
material inevitably increases the flow rate of the off-gas. This
means that a larger load of electricity requires larger amounts of
fuel gas and, in turn, of off-gas. Likewise, a lower load of
electricity requires smaller amounts of them. It is comparatively
easy to provide stable combustion with a mixture of gases when they
are relatively less different in burning velocity from one another,
even with a slight variation of their flow rates. However, the
stability of the combustion can hardly be maintained with a
variation of gas flow rates in a burner for a hydrogen generation
system where the gases having significantly different burning
velocities are mixed for combustion.
[0009] As to the above-mentioned first related art, the increase in
gas flow rate results in the flame blowout. Thus, stable combustion
cannot be achieved when with a variation of the gas flow rate. In
addition, since a combustion region is limited to a small range
within a cylindrical combustion chamber, the temperature of the
flame rises greatly in response to the increase in amount of fuel
to be burnt. This produces a large amount of nitrogen oxides. In
addition, combustion in a narrow space precariously fluctuates the
flame shape, producing problematic combustion noise.
[0010] The second related art does not involve the problems of the
flame blowout and undesirable increase in concentration of the
nitrogen oxides, even with an increase in gas flow rate. However,
the configuration having a gradually changing combustion chamber
involves the manufacturing step of welding two or more components
having different diameters, which increases manufacturing costs.
Therefore, the second related art has been difficult to be put to
practical use regardless of its excellent feature of the highly
stable combustion.
[0011] The third related art is also hardly suffered from the
problem of the flame blowout, as in the second related art.
However, insufficient mixing of the gas and the combustion air
occurs because they are merely supplied to the burner port
assembly. The flame may be extinguished when the combustion load
suddenly varies. Thus, the third related art is also not
satisfactory in terms of the stability of combustion.
[0012] The present invention was made with respect to the
above-mentioned problems and, an object thereof is to provide a
burner for a hydrogen generation system with which a fuel gas and
an off-gas that are significantly different in their burning
velocities can be burnt in a stable condition at varying flow
rates.
SUMMARY OF THE INVENTION
[0013] In order to solve the above-mentioned problems, a burner for
a hydrogen generation system according to the present invention
comprises a combustion chamber that has a taper that enlarges in a
flame radiation direction; and a distributor that is placed in said
combustion chamber to supply to said combustion chamber a fuel gas
containing a compound made up of at least carbon and hydrogen and
an off-gas that is released from a fuel cell, said distributor
being projected in the flame radiation direction, said combustion
chamber having multiple combustion air injection ports formed in
said combustion chamber to inject combustion air into said
combustion chamber, said distributor having multiple gas injection
ports formed in said distributor to inject the fuel gas and the
off-gas into said combustion chamber, at least some of the
combustion air injection ports and at least some of the gas
injection ports being arranged in such a manner that a jet flow of
the combustion air collides with jet flows of the fuel gas and the
off-gas.
[0014] With the combustion chamber having the taper that enlarges
in the flame radiation direction, the flow velocity of the
combusted gas decreases sequentially in the flame radiation
direction. This makes it possible to coincide the flow velocity of
the combusted gas with the flow velocities of the fuel gas and the
off-gas in different spaces within the combustion chamber, even
when the fuel gas and the off-gas that are different in burning
velocities are mixed together for combustion. Thus, stabler
combustion can be made. The collision between the jet flows of the
fuel gas and of the off-gas with the jet flow of the combustion air
facilitates the mixing of the fuel gas and the off-gas with the
combustion air, achieving stable combustion.
[0015] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the combustion
air injection ports and the gas injection ports that are arranged
to achieve the collision are aligned with each other in a generally
colinear manner from the perspective of the flame radiation
direction.
[0016] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the combustion
air injection ports that are arranged to achieve the collision are
formed in the tapered side wall of said combustion chamber.
[0017] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that combustion air
injection ports that are arranged to achieve the collision are
formed in the tapered side wall of said combustion chamber, the
combustion air injection ports being passed through the side wall
in a direction generally perpendicular to the side wall, and
wherein the gas injection ports that are arranged to achieve the
collision is passed through said distributor in a direction
generally perpendicular to said distributor.
[0018] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the combustion
air injection ports that are arranged to achieve the collision are
formed in the bottom wall of said combustion chamber.
[0019] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the combustion
air injection ports that are arranged to achieve the collision are
formed in the tapered side wall of said combustion chamber and in
the bottom wall of said combustion chamber.
[0020] In addition, a burner for a hydrogen generation system
according to the present invention comprises a combustion chamber
that has a taper that enlarges in a flame radiation direction; and
a distributor that is placed in said combustion chamber to supply
to said combustion chamber a fuel gas and an off-gas that is
released from a fuel cell, said distributor being projected in the
flame radiation direction, said combustion chamber having multiple
combustion air injection ports formed in the tapered side wall of
said combustion chamber to inject combustion air into said
combustion chamber, said distributor having multiple gas injection
ports formed in said distributor to inject the fuel gas and the
off-gas into said combustion chamber, at least some of the
combustion air injection ports and at least some of the gas
injection ports being generally opposed to each other.
[0021] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the combustion
air injection ports that are generally opposed are formed in the
tapered side wall of said combustion chamber, the combustion air
injection ports being passed through the side wall in a direction
generally perpendicular to the side wall, and wherein the gas
injection ports that are generally opposed are passed through said
distributor in a direction generally perpendicular to said
distributor.
[0022] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that a taper angle
of said combustion chamber is in a range of from 10 degrees to 90
degrees, both inclusive.
[0023] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the combustion
air injection ports are arranged in such a manner that a larger
amount of the combustion air is injected into said combustion
chamber on the downstream side than on the upstream side of said
combustion chamber.
[0024] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the density of
the combustion air injection ports is higher on the downstream side
than on the upstream side of said combustion chamber.
[0025] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the diameter
of the combustion air injection ports is larger on the downstream
side than on the upstream side of said combustion chamber.
[0026] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the gas
injection ports comprising a first gas injection port and a second
gas injection port, the first gas injection port being for
injecting the fuel gas,and the second gas injection port being for
injecting the off-gas, the second gas injection port being located
downstream of said combustion chamber relative to the first gas
injection port.
[0027] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that said
combustion chamber is formed by pressing or draw-pressing a
sheet-like material.
[0028] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that said
combustion chamber is cylindrical in shape having a flange member
that is projected outward in the radial direction, the flange
member having a turned-up portion along the periphery thereof.
[0029] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the burner
further comprises an electrode that is placed in said combustion
chamber; and a flame detection circuit that is connected to said
electrode.
[0030] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the burner
further comprises an electrode that is placed in said combustion
chamber; and a flame ignition circuit that is connected to said
electrode.
[0031] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that the burner
further comprises an electrode that is placed in said combustion
chamber; a flame detection circuit and a flame ignition circuit
that are connected to said electrode; and a switch circuit that is
used to switch the connection between said electrode and said flame
detection circuit and the connection between said electrode and
said flame ignition circuit.
[0032] In the burner for hydrogen generation systems according to
the above-mentioned invention, it is preferable that said electrode
is projected from the center of said distributor in the flame
radiation direction.
[0033] A hydrogen generation system according to the present
invention comprises a reformer for generating a reformed gas that
contains hydrogen by reforming a feed material that contains a
compound made up of at least carbon and hydrogen; and a burner for
a hydrogen generation system according any one of claims 1 to
18.
[0034] This configuration makes it possible to continue stable
burning with the burner for the hydrogen generation system even
when the flow rates of the fuel gas and of the off-gas are varied.
It ensures to generate a necessary amount of hydrogen.
[0035] This object, as well as other objects, features and
advantages of the present invention will become more apparent to
those skilled in the art from the following description taken with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a cross-sectional view showing an essential
configuration of a hydrogen generation system including a burner
for a hydrogen generation system according to a first embodiment of
the present invention;
[0037] FIG. 2 is a plan view showing a configuration of a burner
according to the first embodiment of the present invention;
[0038] FIG. 3 is a cross-sectional view taken along line III-III in
FIG. 2;
[0039] FIG. 4 is a cross-sectional view for explaining the
combustion state in the burner according to the first embodiment of
the present invention;
[0040] FIG. 5 is a cross-sectional view for explaining the
combustion state in a modified version of the burner according to
the first embodiment of the present invention;
[0041] FIG. 6 is a cross-sectional view for explaining the
combustion state in a modified version of the burner according to
the first embodiment of the present invention;
[0042] FIG. 7 is a cross-sectional view for explaining the
combustion state in a modified version of the burner according to
the first embodiment of the present invention;
[0043] FIG. 8 is a cross-sectional view for explaining the
combustion state in the burner according to the first embodiment of
the present invention;
[0044] FIG. 9 is a cross-sectional view showing a configuration of
a modified version of the burner according to the first embodiment
of the present invention;
[0045] FIG. 10 is a cross-sectional view showing a configuration of
a modified version of the burner according to the first aspect of
the present invention;
[0046] FIG. 11 is a cross-sectional view showing a configuration of
a modified version of the burner according to the first embodiment
of the present invention;
[0047] FIG. 12 is a graphical representation of the carbon monoxide
concentration as a function of the excess air ratio between the
burner of this embodiment and a conventional burner;
[0048] FIG. 13 is a graphical representation for explaining of the
existence of a fluctuating combustion zone;
[0049] FIG. 14 is a cross-sectional view showing a configuration of
a modified version of the burner according to the first aspect of
the present invention;
[0050] FIG. 15 is a cross-sectional view showing a configuration of
a modified version of the burner according to the first embodiment
of the present invention;
[0051] FIG. 16 is a cross-sectional view showing a configuration of
a burner according to a second embodiment of the present invention;
and
[0052] FIG. 17 is a cross-sectional view showing a configuration of
a burner according to a third embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] An embodiment of the present invention is described in
detail below with reference to the drawings.
[0054] First Embodiment
[0055] FIG. 1 is a cross-sectional view showing an essential
configuration of a hydrogen generation system including a burner
for a hydrogen generation system according to a first embodiment of
the present invention.
[0056] FIG. 1 shows a hydrogen generation system 100 that generates
hydrogen to be supplied to a fuel cell system, by reforming a feed
material containing a compound, such as utility gas, made up of at
least carbon and hydrogen. The hydrogen generation system 100
comprises a burner 5, a catalyst container 12, and a combustion
cylinder 13. The burner 5 is enclosed in an air chamber 11 from
which a combustion air is drawn. The catalyst container 12 is for
holding a catalyst bed 3 in, which the catalyst bed 3 is filled
with a catalyst based on nickel or ruthenium. The combustion
cylinder 13 is placed above the burner 5 in order to prevent the
flame coming from the burner 5 from being directly contacted with
the catalyst container 12. The combustion cylinder 13 also has the
function of defining a gas flow passage. The hydrogen generation
system 100 generates a produced gas 4 that is made up of hydrogen,
carbon dioxide, and carbon monoxide by through the reaction of a
feed gas 2 in the catalyst bed 3 in the catalyst container 12. The
feed gas 2 is made up of the utility gas and steam. This generation
is based on an endothermic reaction that occurs at a high
temperature of about 700.degree. C. To this end, a hot gas is fed
by the burner 5 to heat the feed gas 2 and the catalyst bed 3.
[0057] Examples of the compound that is made up of at least carbon
and hydrogen include, besides the utility gas, hydrocarbons such as
methane, ethane, and propane, natural gas, alcohols such as
methanol, kerosene, and LPG.
[0058] As will be described later, the burner 5 has a combustion
chamber 9, and a distributor 8 that sends the gas to the combustion
chamber 9. The distributor 8 mixes a utility gas 6, which is a feed
gas, and an off-gas 7 that is released from a fuel cell before
injecting the mixed gas into the combustion chamber 9. On the other
hand, the combustion air that is drawn from the air chamber 11 is
then injected into the combustion chamber 9 through an air
injection port which will be described later. The burner 5 mixes
the gases and the air sufficiently in the combustion chamber 9 for
the combustion and produces the flame in an upward direction. The
mixture of the utility gas 6 and the off-gas 7 is hereinafter
referred to as a combusted gas.
[0059] A combusted gas 1 that has been used in the burner 5 flows
around the catalyst container 12 through the combustion cylinder
13. Then, it is exhausted outside the hydrogen generation system
100.
[0060] Details of the burner 5 according to the present invention
are described with reference to FIGS. 2 and 3. FIG. 2 is a plan
view showing a configuration of the burner according to the first
embodiment of the present invention. FIG. 3 is a cross-sectional
view taken along line III-III in FIG. 2. In FIG. 3, the combustion
cylinder 13 and the air chamber 11 are illustrated for the
convenience of description.
[0061] As shown in FIGS. 2 and 3, the cylindrical combustion
chamber 9 surrounding the flame has a taper that enlarges in the
direction in which flame radiates (flame radiation direction)
indicated by "X". The upper end of the combustion chamber 9 is open
to the air. The tapered side wall of the combustion chamber 9 has
multiple air injection ports 16 through which the air combustion
air 10 is injected under pressure into the combustion chamber 9.
The air injection ports 16 are arranged with a spacing between
adjacent ports 16 decreasing along a flame radiation direction "X",
i.e., upwardly. The pitch P in the up-and-down direction of the air
injection ports 16 in FIG. 3 satisfies the relation
P1>P2>P3>P4>P5. The bottom wall of the combustion
chamber 9 has multiple lower air injection ports 19 which are
similar to the air injection ports 16, to inject the combustion air
10 under pressure.
[0062] The upper open end of the combustion chamber 9 has a flange
member 17 that extends in the radial direction. The flange member
17 has a rib 20 at the end thereof to increase the strength.
[0063] The cylindrical tubular distributor 8 is coaxial with the
combustion chamber 9. One end of the distributor 8 is projected
into the combustion chamber 9. The other end of it is connected to
a pipe through which the utility gas 6 and the off-gas 7 are fed.
The end of the distributor 8 located within the combustion chamber
9 includes eight upper-stage gas injection ports 14 and eight
lower-stage gas injection ports 15 that are arranged in the radial
direction of the distributor 8 to inject the combusted gas into the
combustion chamber 9. The combusted gas, which has been generated
by mixing the utility gas 6 and the off-gas 7 in the pipe, is
radially injected under pressure in the radial direction through
the upper-stage and lower-stage gas injection ports 14 and 15 into
the combustion chamber.
[0064] The above-mentioned air injection ports 16 and the lower air
injection ports 19 pass through the side wall and the bottom wall,
respectively, of the combustion chamber 9 in the direction
perpendicular to the associated wall. Likewise, the upper-stage and
lower-stage gas injection ports 14 and 15 pass through the
distributor 8 in the direction perpendicular to it. Thus, the jet
flow direction of the combustion air that is injected through the
air injection ports 16 is rendered perpendicular to the side wall
of the combustion chamber 9. The jet flow direction of the
combustion air that is injected through the lower air injection
ports 19 is rendered perpendicular to the bottom wall of the
combustion chamber 9. In addition, the jet flow direction of the
combusted gas that is injected through the upper-stage and
lower-stage gas injection ports 14 and 15 is rendered perpendicular
to the distributor 8.
[0065] The upper-stage gas injection ports 14 formed in the
distributor 8 are generally opposed to the lowermost set of the air
injection ports 18 of the multiple air injection ports 16 formed in
the combustion chamber 9. Thus, the jet flow of the combusted gas
coming out through the upper-stage gas injection ports 14 collide
with the jet flow of the combustion air 10 coming out through the
air injection ports 18. The upper-stage and lower-stage gas
injection ports 14 and 15 formed in the distributor 8 and some of
the lower air injection ports 19 formed in the combustion chamber 9
are arranged in such a manner that the jet flow direction of the
combusted gas is crossed with the jet flow direction of the
combustion air 10. Accordingly, the jet flow of the combusted gas
that is injected through the upper-stage gas injection ports 14 and
the lower-stage gas injection ports 15 collides with the jet flow
of the combustion air 10 injected through the lower air injection
ports 19.
[0066] The physical relationship among the air injection ports 18,
the lower air injection ports 19, and the upper-stage gas injection
ports 14 is described more in detail with reference to FIG. 2. In
FIG. 2, the area where the upper-gas injection ports 14 are formed
is shown in cross section only for the distributor 8 for the
purpose of making a clear view of the position of the upper-stage
gas injection ports 14. In the figure, the arrow "A" drawn from the
center in the radial direction indicates the jet flow direction of
the combusted gas that is injected through the upper-stage gas
injection ports 14. The arrow "B" towards the center indicates the
jet flow direction of the combustion air that is injected through
the lowermost set of the air injection ports 18 indicated by the
dotted line "C", of the air injection ports 16. As apparent from
the above, according to this embodiment, the positions of the
injection ports are adjusted in such a manner that the jet flow
direction of the combusted gas is aligned with the jet flow
direction of the combustion air in a generally colinear manner from
the perspective of the flame radiation direction. In addition, in
this embodiment, the position of some lower air injection ports 19
is adjusted in such a manner that the jet flow direction of the
combustion air that is injected through the lower air injection
ports 19 is crossed with the jet flow direction "A" of the
above-mentioned combusted gas.
[0067] The combustion chamber 9 is made by pressing a
heat-resistant stainless steel of 2 mm thick to provide the opening
having a taper angle .theta. of 30.degree. after the air injection
ports 16 and the lower air injection ports 19 are formed in it.
Alternatively, the combustion chamber 9 may be formed by drawing
press instead of the press working.
[0068] Next, flows of the gases and the flame condition are
described with reference to FIG. 4, for the case where the
combusted gas as a mixture of the utility gas 6 and the off-gas 7
is burnt using the burner 5 having the above-mentioned
configuration according to this embodiment.
[0069] First, the jet flow of the combusted gas A that is radially
injected into the combustion chamber 9 through the upper-stage gas
injection ports 14 formed in the distributor 8 collides with the
jet flow of the combustion air B that is injected through the
lowermost set of the air injection ports 18 that are generally
opposed to the upper gas injection ports 14. They collide at the
position indicated by "D" in the figure. As a result, the combusted
gas A and the combustion air B are mixed thoroughly. At the
position "D" immediately after the upper-stage gas injection ports
14 formed in the distributor 8, the flow of the combusted gas A has
its highest flow velocity. Thus, only the hydrogen component having
a high burning velocity of the combusted gas is burned at this
position "D" to generate flames. The combusted gas "E" based on the
utility gas, which is still not burnt, flows in the flame radiation
direction "X". In this case, since the combustion chamber 9 has a
taper that enlarges in the flame radiation direction "X", the
cross-section of the gas flow passage continuously increases. This
decreases the flow velocity of the combusted gas "E". When the flow
velocity of the combusted gas "E" becomes equal to or lower than
the burning velocity of the utility gas, then the flame "F" is
generated for combustion.
[0070] On the other hand, an increased amount of fuel to be burnt
results in the increase in flow velocity of the combusted gas A. It
may exceed the burning velocity of the utility gas at the position
corresponding to the flame "F". In such a case, however, the
tapered shape of the combustion chamber 9 continuously decreases
the gas flow velocity. The flame "G" is produced at a more
downstream position. The volume of the flame G may be increased
arbitrarily in the flame radiation direction "X". The temperature
of the flame may be kept to be generally equal to the temperature
achieved when the amount of fuel to be burnt is relatively small.
Thus, generation of the nitrogen oxides can be suppressed which
otherwise are easily produced during the combustion at a high
temperature.
[0071] In the above-mentioned second related art, the diameter of
the combustion chamber is gradually increased towards the opening.
Accordingly, the flow of the combusted gas significantly varies at
the step portions. In addition, the step portions disturb the flow
of the gas. Therefore, the stability would be lost with a large
amount of fuel to be burnt. In contrast to this, the present
invention employs the combustion chamber 9 having a taper that
enlarges in the flame radiation direction "X". The flow rate of the
combusted gas can be varied continuously from a high rate to a low
rate. This allows for the burning of the gases that are different
in burning velocity in different spaces within the combustion
chamber 9. Accordingly, the stability of the combustion does not
deteriorated.
[0072] In addition, the upper-stage gas injection ports 14 are
generally opposed to the lowermost set of the air injection ports
18. This arrangement causes the jet flow of the combusted gas "A"
to collide with the jet flow of the combustion air "B",
facilitating the mixing of the combusted gas "A" and the combustion
air "B". Thus, hydrogen that has a higher burning velocity and is
highly flammable is mixed with the air thoroughly at the collision
position "D". Therefore, the flame at the position "D" is always
present in a stable condition. The fuel cell system should increase
or decrease the production of electricity according to the load of
electricity. The fluctuation of the load of electricity occurs when
an electric-powered device is turned ON or OFF. The fluctuation
thus occurs within a fraction of a second. This means that the
amount of fuel to be burnt in the burner for a hydrogen generation
system also fluctuates significantly in a very short period of
time. Conventional burners have the problem of the flame blowout
due to the sudden change in amount of fuel to be burnt. On the
contrary, the flame is not blown out at the position "D" in the
burner of the present invention. The flame is kept and serves as a
pilot flame. No flame blowout will occur accordingly.
[0073] In this embodiment, only the upper-stage gas injection ports
14 formed in the distributor 8 are generally opposed to the air
injection ports 18. However, the lower-stage gas injection ports 15
may be generally opposed to the air injection ports 18, if
necessary. It goes without saying that the air injection ports that
are generally opposed to the upper-stage gas injection ports 14 or
the lower-stage gas injection ports 15 are not limited to those
formed in the side wall of the combustion chamber 9 at the
lowermost portion of it.
[0074] As described above, the air injection ports 16 including the
air injection ports 18 are penetrating the side wall of the
combustion chamber 9 at right angles. The combustion chamber 9 is
then formed by press working to have a tapered-shape. Thus, as
shown in FIG. 4, the jet flow direction of the combustion air "B"
that is injected through the air injection ports 16 is inclined by
a predetermined angle in the exhaust direction of the combusted gas
(i.e., the flame radiation direction "X"). On the other hand, the
upper-stage gas injection ports 14 are penetrating the distributor
8 at right angles. The distributor 8 is projected in parallel to
the flame radiation direction "X". Thus, as shown in FIG. 4, the
jet flow direction of the combusted gas "A" that is injected
through the upper-stage gas injection ports 14 is rendered
perpendicular to the flame radiation direction "X". Accordingly,
the jet flow of the combustion air "B" and the jet flow of the
combusted gas "A" do not collide head-on with each other. Rather,
they are slightly crossed with each other. This configuration is
advantageous from the viewpoint of the stable combustion as
described below. This point is described with reference to FIG. 5
in which a modified version of this embodiment is shown.
[0075] FIG. 5 is an enlarged cross-sectional view around a
distributor when air injection ports and gas injection ports are
formed in such a manner that the jet flow direction of the
combustion air coincides with the jet flow direction of the
combusted gas. As shown in FIG. 5, air injection ports 18' are
provided on the side wall of the combustion chamber as being
inclined with respect to the side wall at a certain angle.
Consequently, the jet flow direction of the combustion air "B"
coincides with the jet flow direction of the combusted gas "A".
This causes the jet flow of the combusted gas "A" to directly
collide with the jet flow of the combustion air "B". A portion of
the combusted gas that has been produced flows towards the bottom
of the combustion chamber 9 in the opposite direction to the
exhaust direction of the combusted gas, as indicated by the symbol
"Q" in the figure. Then, the portion of the combusted gas returns
in the exhaust direction of the combusted gas. The returned portion
of the combusted gas flows across the jet flow of the combusted gas
"A" or of the combustion air "B", or across the flame at the
position "D". The returned portion can disturb these flows,
deteriorating the stability of the combustion. The combustion
becomes stabler when the jet flow direction of the combustion air
is displaced at a certain angle towards the exhaust direction of
the combusted gas as shown in FIG. 3 than when the jet flow of the
combusted gas directly collides the jet flow of the combustion air,
because the jet flow of the combustion air is crossed with the jet
flow of the combusted gas.
[0076] In this embodiment, the crossed collision between the jet
flows of the combustion air and the combusted gas is achieved by
means of forming the air injection ports 16 in the side wall of the
tapered combustion chamber 9, passing through the side wall at
right angles. However, the crossed-collision of the jet flows may
be achieved by other ways than the above. For example, the
upper-stage gas injection ports 14 may be passed through in the
direction displaced towards the exhaust direction of the combusted
gas, thereby to cause the crossed-collision of the jet flows.
[0077] As shown in FIG. 4, the combustion air "H" is also fed
through the lower air injection ports 19 in the burner 5 of this
embodiment. As described above, the combustion air "H" is injected
from a position that crosses from the bottom with the combusted gas
"A" and the combustion air "B". This has the function of providing
the better mixing of the combusted gas and the combustion air. In
addition to the effect of improving the mixed condition with the
gases, the combustion air "H" has the function of maintaining the
flame even when the flow rate of the combustion air "B" becomes
relatively excess to the flow rate of the combusted gas "A". Thus,
the combustion air "H" significantly contributes to the
stabilization of the combustion. It should be noted that an
excellent combustion stability can also be achieved without the use
of the air injection ports that are generally opposed to the
upper-stage gas injection ports 14, as shown in FIG. 6. For
example, this may be achieved by crossing the jet flow of the
combustion air "H" that is injected through the lower air injection
ports 19, with the jet flow of the combusted gas that is injected
through the upper-stage gas injection ports 14 and the lower-stage
gas injection ports 15.
[0078] As described above, the present invention achieves the
stable combustion and reduction in concentration of the nitrogen
oxides by using the combustion chamber having a taper that enlarges
in the flame radiation direction. While this embodiment uses a
taper angle .theta. of 30.degree. for the combustion chamber, the
angle .theta. may be optimized according to the type of the fuel
and the amount of fuel to be burnt. A small angle .theta. results
in less reduction in flow velocity of the combusted gas in the
flame radiation direction. Consequently, flameout may occur when
the amount of fuel to be burnt is increased. In addition, the small
angle limits the size of the flame with an increased amount of fuel
to be burnt. The concentration of the nitrogen oxides tends to be
increased. Further, unstable fluctuation of the flame shape may
lead to combustion noise. On the contrary, a large angle .theta.
results in incomplete combustion because the fuel and the air are
not mixed well. This may produce yellowish flames, grime, and
carbon monoxide. Although the optimum value for the angle of the
tapered opening of the air injection port depends on the type of
the fuel, the amount of fuel to be burnt, and the volume of the
combustion chamber, the angle .theta. in a range of about
10.degree. to 90.degree. can ensure the stability of the
combustion. The angle is preferably in a range of 10.degree. to
45.degree. from the viewpoints the gas-and-air mixture and the
stability of combustion with the utility gas and hydrogen used as
the fuel.
[0079] As shown in FIG. 3, the pitch P between the air injection
ports 16 is sequentially decreased along the direction to the
downstream of the combustion chamber in this embodiment. This
configuration has a remarkable effect with a large amount of fuel
to be burnt. This point is described with reference to FIGS. 7 and
8. First, when the air injection ports 16 are aligned at equal
distances (P1'=P2'=P3'=P4'=P5') along the direction to the
downstream of the combustion chamber 9 as shown in FIG. 7, the
combusted gas flows in the direction indicated by the arrow "I".
This direction corresponds to the direction that is displaced
towards the side wall of the combustion chamber 9 from the flame
radiation direction "X". The resulting flame "J" tends to be
distributed outward as shown in the figure. However, the combustion
cylinder 13 is placed above the burner 5. It prevents the flame
from being distributed horizontally over the width of the
combustion cylinder 13. Therefore, the combusted gas is disturbed
in the combustion cylinder 13, which may disturb the combustion and
produce unstable flames.
[0080] On the contrary, when the air injection ports 16 are aligned
towards the downstream of the combustion chamber at a pitch that
becomes smaller as it approaches to the downstream (P1>P2
>P3>P4>P5) as shown in FIG. 8, a larger volume of
combustion air is fed at a position closer to the opening of the
combustion chamber 9. The combusted gas in this case flows in the
direction "K" which is similar to the above-mentioned direction
"I". In addition, the combusted gas also flows in the direction "L"
along the surface of the wall of the combustion cylinder 13 because
of the air that is supplied from near the opening of the combustion
chamber 9. The flow of the combusted gas in the direction "L" leads
the direction of the flame upward that is trying to be distributed
over the width of the combustion cylinder 13. Consequently, the
flame "M" is directed towards the downstream of the combustion
cylinder 13 without being distributed over the width of the
combustion cylinder 13. This prevents the combustion from being
disturbed, improving the stability of the combustion. As apparent
from the above, the more stable combustion can be achieved by
increasing the amount of air supply in the downstream direction of
the combustion chamber. Thus, the amount of the air supply is
increased towards the downstream of the combustion chamber in this
embodiment. To this end, the distance between the adjacent air
injection ports 16 is adjusted in order to provide a higher port
density on the downstream side than on the upstream side of the
combustion chamber. However, the amount of the air supply may be
increased towards the downstream of the combusted gas by any other
ways including: to increase the number of the air injection ports
16 while maintaining the distance between the ports to be equal as
shown in FIG. 9; and to increase the diameter of the air injection
ports 16 as shown in FIG. 10. The air injection ports 16 may run
like the grid of a chess board or may be in a zigzag alignment.
Moreover, the present invention does not limit the shape of the
upper-stage gas injection ports 14, the lower-stage gas injection
ports 15, and the air injection ports 16. These ports may have any
one of various shapes other than the circle. Examples of the shape
include an ellipse, an oval, a rectangle, or a slit.
[0081] As described above, in this embodiment, the combustion
chamber 9 is made by pressing a thin sheet material. Thus, the
burner 5 having the above-mentioned excellent features can be
provided at low price. However, a significant deformation may occur
with the thin sheet material because the combustion chamber 9 is
exposed to a hot combusted gas. With this respect, this embodiment
uses the rib 20 in the circumferential direction, in which the rib
is formed by turning the end of the flange member 17 that is
provided at the upper end of the combustion chamber 9. The rib 20
significantly reduces the thermal deformation of the combustion
chamber 9. Therefore, the burner of the type according to this
embodiment can be manufactured through the press working of a thin
sheet material. The position of the turned-up portion is not
limited to the end of the flange member 17 of the combustion
chamber 9. For example, as shown in FIG. 11, a turned-up portion 21
may be provided along the circumference in the middle of a flange
member 17. The turned-up portion 21 may also be used as a means to
determine the position relative to the air chamber 11. This
configuration may improve the assembling operations.
[0082] As described above, the combustion can be made stabler with
the burner according to this embodiment. FIG. 12 is a graphical
representation of the carbon monoxide concentration as a function
of the excess air ratio between the burner of this embodiment and a
conventional burner. In FIG. 12, 12A shows the relation for the
burner according to this embodiment and 12B shows the relation for
the conventional burner. As shown in FIG. 12, the burner of this
embodiment hardly produces carbon monoxide at a higher excess air
ratio as compared with a conventional burner. Carbon monoxide
typically results from incomplete combustion of the combusted gas
and the combustion air that are mixed insufficiently. From the FIG.
12, the burner of this embodiment is expected to maintain a good
mixing condition with the more stable combustion over a wider range
as compared with the conventional burner.
[0083] FIG. 13 is a graphical representation for explaining of the
existence of a fluctuating combustion zone. The ordinate represents
the flow rate of the air that is supplied from the bottom of the
combustion chamber. When the flow rate of the air that is supplied
from the bottom of the combustion chamber is low, a fluctuating
combustion zone 13A is present within a certain range of the excess
air ratio, as shown in FIG. 13. In the fluctuating combustion zone
13A, the flame in the combustion chamber may be intermittent with
instantaneous breaks as if it had caught its breath. Alternatively
or in addition to it, combustion noise may be produced. However,
the fluctuating combustion zone 13A disappears as the flow rate of
the air from the bottom increases. In the burner of this
embodiment, the lower air injection ports are provided in the
bottom wall of the combustion chamber to supply air from the bottom
in order to ensure the combustion without the fluctuating
combustion zone 13A, thereby to ensure more stable combustion.
[0084] While the present invention has thus been described in
conjunction with the embodiment wherein only a single distributor 8
is used, the number of the distributors may be varied according to
the amount of fuel to be burnt when the present invention is
applied to a large-scale hydrogen generation system. While this
embodiment is for the case where the combustion chamber 9 has a
circular opening, the combustion chamber may have an opening of a
different shape such as a polygon or oval, that fits for the shape
of the combustion cylinder.
[0085] In this way, the hydrogen generation system in a fuel cell
system that includes the burner according to this embodiment with
which the stable combustion can be achieved, can produce hydrogen
in a stable manner even with a fluctuated power generation load.
This allows a stable operation of the fuel cell system.
[0086] The same effect as the effect of the present invention can
be achieved as long as the combustion chamber 9 has a taper.
Therefore, as shown in FIG. 14 for example, a combination of a
cylindrical portion "N" and a tapered portion "O" may provide a
good burner that exhibits a stable combustion performance.
Furthermore, the taper of the combustion chamber 9 is not limited
to be defined by a straight line. Instead, as shown in FIG. 15, the
taper may be curved to provide a similar effect to the effect of
the present invention.
[0087] In addition, while the gas injection ports formed in the
distributor 8 of this embodiment are arranged into a two-stage
configuration. The number of the upper-stage and lower-stage gas
injection ports is eight for each. The number of the stages and the
number of the ports may be determined appropriately according to
the size of the distributor(s). When the gas injection ports are
arranged into a multi-stage configuration as in this embodiment,
the ports in the multiple stages may be arranged on a straight line
or may be arranged not to be on the straight line in order to
facilitate the mixing of the combusted gas and the air.
[0088] Furthermore, it is not necessary that all gas injection
ports formed in the distributor 8 are generally opposed to the air
injection ports formed in the combustion chamber 9. However, all
gas injection ports may generally be opposed to the air injection
ports in order to further facilitate the mixing of the combusted
gas and the air. Likewise, it is not necessary that all lower air
injection ports formed in the combustion chamber 9 are arranged in
such a manner that the jet flow direction of the combustion air
that is injected through the lower air injection ports is crossed
with the jet flow direction of the combusted gas that is injected
through the gas injection ports. They may be arranged in such a
manner.
[0089] Second Embodiment
[0090] A burner according to a second embodiment of the present
invention is configured to independently feed the utility gas and
the off-gas from a distributor to a combustion chamber without
mixing them together.
[0091] FIG. 16 is a cross-sectional view showing a configuration of
a burner according to the second embodiment of the present
invention. As shown in FIG. 16, a distributor 22 has a first gas
injection port 23 and a second gas injection port 24. The first gas
injection port 23 is for injecting the utility gas 6 that is
supplied via a pipe 25 into a combustion chamber 9. The second gas
injection port 24 is for injecting the off-gas 7 that is supplied
via a pipe 26. The second gas injection port 24 is located at a
position that is closer to the place where the flame is produced,
than the first gas injection port 23. This configuration
independently supplies the utility gas 6 and the off-gas 7 to the
combustion chamber 9 without being mixed together. Other components
and parts of the burner according to this embodiment are similar to
those described in conjunction with the first embodiment.
Accordingly, such components and parts are depicted similar
reference numerals and description thereof will be omitted.
[0092] In the first embodiment, the utility gas 6 and the off-gas 7
are mixed together before being supplied to the distributor 8.
However, the amount of the utility gas 6 to be fed may be varied
due to the variation in amount of the off-gas 7 to be fed which is
caused as a result of the fluctuation of the load of electricity in
the fuel cell system. More specifically, when the amount of the
off-gas 7 to be fed is decreased for example, the pressure across
the distributor 8 and the pressures across the gas injection ports
14 and 15 are dropped. Then, the flow rate of the utility gas 6 is
increased according to a discharge pressure-flow rate curve of a
utility gas supply pump (not shown). On the contrary, when the
amount of the off-gas 7 to be fed is increased, the utility gas
supply pump reduces the amount of the utility gas 6 to be fed. It
is possible to determine the flow rate of the off-gas 7 to control
the flow rate of the utility gas supply pump when the change in
flow rate of the off-gas 7 is gradual. However, the pump cannot
follow this change when the flow rate of the off-gas 7 varies
suddenly. Then, the flow rate of the utility gas 6 may be varied
temporarily as described above. The burner according to the first
embodiment can continue stable combustion even with such
fluctuation in flow rate of the utility gas 6. However, combustion
noise may be produced or the concentration of carbon monoxide in
the exhaust gas may be increased temporarily in some cases.
[0093] This problem can be solved by independently supplying the
utility gas 6 and the off-gas 7 to the combustion chamber 9 in this
embodiment. Furthermore, the utility gas 6 is supplied upstream of
the off-gas 7 which contains hydrogen, in a combustion chamber 9.
With this configuration, the jet flow of the utility gas 27 that is
injected through the first gas injection port 23 always crosses the
hydrogen flame "P". This ensures the utility gas to be ignited for
combustion. Therefore, the embodiment can prevent the dying out of
flames and discharge of the utility gas without being burnt
completely, even when the flow rate of the utility gas is
temporarily reduced to almost none.
[0094] Third Embodiment
[0095] A burner according to a third embodiment of the present
invention is configured to allow detection of ignition and
flames.
[0096] FIG. 17 is a cross-sectional view showing a configuration of
a burner according to the third embodiment of the present
invention. As shown in FIG. 17, a rod-shaped electrode 28 is
inserted into a distributor 8. The electrode 28 has the function of
an ignition electrode and an electrode for flame detection. One end
of the electrode 28 is projected into a combustion chamber 9 and is
bent towards the side wall of the combustion chamber 9. In FIG. 17,
the position of the flame "F" produced with a low gas flow rate and
the position of the flame "G" produced with a high gas flow rate,
as described in the first embodiment, are shown as well. The one
end of the electrode 28 is adjusted to be positioned in a space
where the flame "F" overlaps the flame "G".
[0097] On the other hand, the other end of the electrode 28 extends
to the outside of the distributor 8. It is connected to a high
voltage power supply 29 for ignition, through a switch 32. It is
also connected to a power supply 30 for flame detection and a flame
detector 31 through a switch 33. The high voltage power supply 29
for ignition and the flame detector 31 are connected to a flange
member 17 on the combustion chamber 9.
[0098] Other components and parts of the burner according to this
embodiment are similar to those described in conjunction with the
first embodiment. Accordingly, such components and parts are
depicted similar reference numerals and description thereof will be
omitted.
[0099] In the burner having the above-mentioned configuration, the
utility gas 6 and the combustion air 10 are fed in a predetermined
amount for ignition during the start-up operation of the fuel cell
system. In such a case, the switch 32 is closed and the switch 33
is opened to apply a high voltage across the electrode 28 and the
combustion chamber 9 on the distributor 8 by using the high voltage
power supply 29 for ignition, thereby to cause discharge. The
discharge occurs between the tip of the electrode 28 and the
combustion chamber 9 nearby. This portion corresponds to the place
where the utility gas is burnt and the flame "F" is produced even
with a small flow rate of the utility gas. Therefore, the burner is
ignited easily.
[0100] To detect the flame during the operation of the fuel cell
system, the switch 32 is opened and the switch 33 is closed. The
power supply 30 for flame detection is used to apply a voltage
across the electrode 28 and the combustion chamber 9 on the
distributor 8. The electric current flowing between them is
measured using the flame detector 31. The flame detector 31 is for
measuring the electric current created by charged particles that
are present in the flame. When the flame disappears, the conductive
charged particles are no more in the flame. No electric current
flows accordingly, and the flameout is detected. This approach for
detecting the flame is less precise in hydrogen flames because of
low ion current. Therefore, the tip of the flame detecting
electrode is preferably located in the flame of the utility gas.
The combustion chamber in the above-mentioned first related art is
cylindrical in shape. Therefore, the position of the flame
significantly varies depending on the flow rate of the utility gas.
When the flame is far away from the position of the detector of the
flame detecting electrode, then the detector often fails to detect
the flame even when it exists. On the contrary, the flame "G"
produced with a high gas flow rate and the flame "F" produced with
a low gas flow rate are positioned relatively closely when using
the burner of the present invention. By positioning the tip of the
electrode 28 at the position where both flames are present as shown
in the figure, the flame can be detected without fail even when the
flow velocity of the utility gas is varied.
[0101] As apparent from the above, using the burner of the present
invention, the flame can be detected with a simple configuration.
The fuel cell system can be operated more safely.
[0102] As described above, according to this embodiment, the single
electrode has the functions of both the ignition electrode and the
flame detection electrode. However, it goes without saying that two
separate electrodes may be provided that have their respective
function.
[0103] By combining the above-mentioned embodiments, various
different burners for hydrogen generation systems can be achieved
depending on the size of the hydrogen generation system and the
volume of the combustion chamber.
[0104] Numerous modifications and alternative embodiments of the
invention will be apparent to those skilled in the art in view of
the forgoing description. Accordingly, the description is to be
construed as illustrative only, and is provided for the purpose of
teaching those skilled in the art the best mode of carrying out the
invention. The details of the structure and/or function may be
varied substantially without departing from the spirit of the
invention.
* * * * *