U.S. patent application number 09/896823 was filed with the patent office on 2002-01-17 for method and apparatus for mixing combustion gases.
Invention is credited to Hugens, John R. JR..
Application Number | 20020006591 09/896823 |
Document ID | / |
Family ID | 26911300 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020006591 |
Kind Code |
A1 |
Hugens, John R. JR. |
January 17, 2002 |
Method and apparatus for mixing combustion gases
Abstract
A gas mixing device for use with a combustion burner assembly is
disclosed. The gas mixing device includes an elongate gas expansion
nozzle adapted to be positioned within a burner housing, the gas
expansion nozzle defining a gas expansion chamber therein extending
from a first end to a second end thereof. An inlet port and an
outlet port are defined at the respective ends of the gas expansion
nozzle. At least one oxidizing gas passageway formed separately of
the gas expansion chamber extends from the first end of the second
end thereof, and has an oxidizing gas outlet at the second end of
the gas expansion nozzle. At least one fuel gas passageway is also
formed separately of the gas expansion chamber and extends from the
first end to the second end of the gas expansion nozzle, and has a
fuel gas outlet at the second end thereof. An elongate gas inlet
nozzle is also positioned within the burner housing and is spaced
from the first end of the gas expansion nozzle. A portion of the
oxidizing gas is passed through the gas inlet nozzle and into the
gas expansion chamber, with another portion of the oxidizing gas
being passed through the at least one oxidizing gas passageway. A
portion of the fuel gas is also passed into the gas expansion
chamber and mixes with the oxidizing gas to form a premixed
combustion gas stream, with a portion of the fuel gas also being
passed through the at least one gas passageway. The separate
oxidizing gas and fuel gas streams jacket and surround the premixed
combustion gas stream passed from the mixing device.
Inventors: |
Hugens, John R. JR.;
(Suwanee, GA) |
Correspondence
Address: |
NEEDLE & ROSENBERG, P.C.
The Candler Building, Suite 1200
127 Peachtree Street, N.E.
Atlanta
GA
30303-1811
US
|
Family ID: |
26911300 |
Appl. No.: |
09/896823 |
Filed: |
June 29, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60216753 |
Jul 7, 2000 |
|
|
|
60222450 |
Aug 2, 2000 |
|
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Current U.S.
Class: |
431/8 ;
431/354 |
Current CPC
Class: |
F23D 14/62 20130101;
F23C 6/047 20130101; F23N 5/003 20130101; F23N 2221/06
20200101 |
Class at
Publication: |
431/8 ;
431/354 |
International
Class: |
F23D 014/06; F23D
014/62 |
Claims
I claim:
1. A gas mixing device for use with a burner assembly, the burner
assembly including an elongate housing, an oxidizing gas supply
line in fluid communication with the housing, and a fuel gas supply
line in fluid communication with the housing, the gas mixing device
comprising: an elongate gas expansion nozzle adapted to be
positioned within the housing, said nozzle having a first end and a
spaced second end; a gas expansion chamber defined within the gas
expansion nozzle and extending from the first end of the gas
expansion nozzle to the second end thereof; an inlet port at the
first end of the gas expansion nozzle in communication with the gas
expansion chamber, and an outlet port at the second end of the gas
expansion nozzle in communication with the gas expansion chamber;
at least one oxidizing gas passageway formed separately of the gas
expansion chamber and extending from the first end to the second
end of the gas expansion nozzle, with at least one oxidizing gas
outlet at the second end of the gas expansion nozzle; and at least
one fuel gas passageway formed separately of the gas expansion
chamber and extending from the first end to the second end of the
gas expansion nozzle, with at least one fuel gas outlet at the
second end of the gas expansion nozzle.
2. The gas mixing device of claim 1, further comprising an elongate
gas inlet nozzle spaced from the first end of the gas expansion
nozzle, the gas inlet nozzle having a first end and a spaced second
end.
3. The gas mixing device of claim 2, said gas inlet nozzle defining
a gas flow passageway therein extending from the first end to the
second end thereof, a gas inlet port at the first end of the gas
inlet nozzle in communication with the gas flow passageway, and a
gas outlet port at the second end of the gas inlet nozzle in
communication with the gas flow passageway.
4. The gas mixing device of claim 3, wherein the gas inlet port of
the gas inlet nozzle is formed to be larger than the gas outlet
port thereof.
5. The gas mixing device of claim 2, further comprising a
corresponding at least one oxidizing gas passageway formed within
the gas inlet nozzle and extending from the first end to the second
end thereof.
6. The gas mixing device of claim 5, further comprising an elongate
tube positioned within the at least one oxidizing gas passageway of
the gas inlet nozzle and extending into the at least one oxidizing
gas passageway of the gas expansion nozzle.
7. The gas mixing device of claim 2, wherein the gas inlet nozzle
is adapted to be sealed to the housing upstream of the gas
expansion nozzle.
8. The gas mixing device of claim 2, wherein the gas inlet nozzle
directs at least a portion of the oxidizing gas into the inlet port
of the gas expansion nozzle.
9. The gas mixing device of claim 2, wherein the gas inlet nozzle
directs at least a portion of the oxidizing gas into the at least
one oxidizing gas passageway of the gas expansion nozzle.
10. The gas mixing device of claim 2, wherein the gas inlet nozzle
is constructed and arranged to increase the velocity of the
oxidizing gas as it flows therethrough.
11. The gas mixing device of claim 1, further comprising at least a
pair of oxidizing gas passageways spaced radially from one another
about the housing axis.
12. The gas mixing device of claim 1, the gas expansion chamber
being formed as a conical expansion chamber opening toward the
outlet port of the gas expansion nozzle.
13. The gas mixing device of claim 1, further comprising an
elongate gas inlet nozzle spaced from the first end of the gas
expansion nozzle, the gas inlet nozzle having a first end, a spaced
second end, a gas flow passageway defined therein and extending
from the first end to the second end thereof, a gas inlet port at
the first end of the gas inlet nozzle in communication with the gas
flow passageway, and a gas outlet port at the second end of the gas
inlet nozzle in communication with the gas flow passageway.
14. The gas mixing device of claim 13, wherein the gas outlet port
at the second end of the gas inlet nozzle is sized smaller than the
inlet port at the first end of the gas expansion nozzle.
15. The gas mixing device of claim 1, further comprising a gas
manifold extending at least partially about the gas expansion
nozzle.
16. The gas mixing device of claim 15, the gas manifold being
constructed and arranged to direct the fuel gas circumferentially
about the gas expansion nozzle.
17. The gas mixing device of claim 1, wherein the gas expansion
chamber is circular in cross section about the housing axis.
18. The gas mixing device of claim 1, further comprising a gas
sampling device spaced from the second end of the gas expansion
nozzle and positioned with respect to the outlet port of the gas
expansion chamber.
19. The gas mixing device of claim 1, further comprising a test
burner spaced from the second end of the gas expansion nozzle, said
test burner being constructed and arranged to measure the
composition of the mixed gases passed from the gas expansion
nozzle, the at least one oxidizing gas passageway, and the at least
one fuel gas passageway, respectively.
20. The gas mixing device of claim 1, wherein a first oxidizing gas
stream and a first fuel gas stream, respectively, are passed into
the gas expansion chamber and mixed with one another into a
premixed combustion gas stream, a second oxidizing gas stream is
passed through the at least one oxidizing gas passageway and a
second fuel gas stream is passed through the at least one fuel gas
passageway, respectively, and the premixed combustion gas stream,
the second oxidizing gas stream, and the second fuel gas stream are
mixed with one another externally of the gas expansion nozzle.
21. A gas mixing device for use with a burner assembly, the burner
assembly including an elongate housing, a first gas supply line in
fluid communication with the housing, and a second gas supply line
in fluid communication with the housing, the gas mixing device
comprising: an elongate gas expansion nozzle adapted to be
positioned within the housing, said nozzle having a first end and a
spaced second end; a gas expansion chamber defined within the gas
expansion nozzle and extending from the first end to the second end
thereof; and an inlet port at the first end of the gas expansion
nozzle in communication with the gas expansion chamber, and an
outlet port at the second end of the gas expansion nozzle in
communication with the gas expansion chamber.
22. The gas mixing device of claim 21, further comprising at least
one first gas passageway formed separately of the gas expansion
chamber and extending from the first end of the gas expansion
nozzle to at least one first gas outlet port at the second end
thereof.
23. The gas mixing device of claim 22, further comprising an
elongate gas inlet nozzle spaced from the first end of the gas
expansion nozzle, the gas inlet nozzle having a first end, a spaced
second end, a gas flow passageway defined therein and extending
from the first end to the second end thereof, a gas inlet port at
the first end of the gas inlet nozzle in communication with the gas
flow passageway, and a gas outlet port at the second end of the gas
inlet nozzle in communication with the gas flow passageway.
24. The gas mixing device of claim 23, further comprising a
corresponding at least one first gas passageway defined within the
gas inlet nozzle and extending from the first end to the second end
thereof.
25. The gas mixing device of claim 24, further comprising an
elongate tube positioned within the at least one first gas
passageway of the gas inlet nozzle and extending into the at least
one first gas passageway of the gas expansion nozzle.
26. The gas mixing device of claim 22, further comprising at least
one second gas passageway formed separately of the gas expansion
chamber and extending from the first end of the gas expansion
nozzle to at least one second gas outlet port at the second end
thereof.
27. The gas mixing device of claim 21, further comprising an
elongate gas inlet nozzle spaced from the first end of the gas
expansion nozzle, the gas inlet nozzle having a first end, a spaced
second end, a gas flow passageway defined therein and extending
from the first end to the second end thereof, a gas inlet port at
the first end of the gas inlet nozzle in communication with the gas
flow passageway, and a gas outlet port at the second end of the gas
inlet nozzle in communication with the gas flow passageway.
28. The gas mixing device of claim 27, wherein the gas outlet port
of the gas inlet nozzle is formed to be smaller than the inlet port
of the gas expansion nozzle.
29. The gas mixing device of claim 21, wherein the inlet port of
the gas expansion nozzle is formed to be smaller than the outlet
port thereof such that the gas expansion chamber opens toward the
outlet port of the gas expansion nozzle.
30. The gas mixing device of claim 21, further comprising a fuel
gas manifold extending at least partially about the gas expansion
nozzle.
31. The gas mixing device of claim 30, the fuel gas manifold being
constructed and arranged to direct the fuel gas about the gas
expansion nozzle.
32. A gas mixing device for use with a burner assembly, the burner
assembly including an elongate housing, a first gas supply line in
fluid communication with the housing, and a second gas supply line
in fluid communication with the housing, the gas mixing device
comprising: an elongate gas expansion nozzle adapted to be
positioned within the housing and having a first end, a spaced
second end, a gas expansion chamber defined therein and extending
from the first end to the second end thereof, an inlet port at the
first end thereof in communication with the gas expansion chamber,
and an outlet port at the second end thereof in communication with
the gas expansion chamber; and an elongate gas inlet nozzle spaced
from first end of the gas expansion nozzle, the gas inlet nozzle
having a first end, a spaced second end, a gas flow passageway
defined therein and extending from the first end to the second end
thereof, a gas inlet port at the first end thereof in communication
with the gas flow passageway, and a gas outlet port at the second
end thereof in communication with the gas flow passageway.
33. The gas mixing device of claim 32, the gas inlet port of the
gas inlet nozzle being formed larger than the gas outlet port
thereof, the inlet port of the gas expansion nozzle being formed
smaller than the outlet port thereof, and the gas outlet port of
the gas inlet valve being formed smaller than the inlet port of the
gas expansion nozzle.
34. A method of mixing combustion gases within a burner assembly,
the burner assembly including an elongate housing, an oxidizing gas
supply line in fluid communication with the housing, and a fuel gas
supply line in fluid communication with the housing, said method
comprising the steps of: passing at least a portion of the fuel gas
as a first fuel gas stream into an inlet of a gas expansion chamber
positioned within the housing; passing at least a portion of the
oxidizing gas as a first oxidizing gas stream into the inlet of the
gas expansion chamber; combining the first fuel gas stream and the
first oxidizing gas stream, respectively, into a premixed
combustion gas stream within the gas expansion chamber; passing the
premixed combustion gas stream from the gas expansion chamber;
passing at least a portion of the oxidizing gas as a second
oxidizing gas stream outside of the gas expansion chamber; passing
at least a portion of the fuel gas as a second fuel gas stream
outside of the gas expansion chamber; and combining the second fuel
gas stream and the second oxidizing gas stream, respectively, with
the premixed combustion gas stream externally of the gas expansion
chamber.
35. The method of claim 34, including the step of sampling the
premixed combustion gas stream downstream of the gas expansion
chamber.
36. The method of claim 34, including the step of selectively
adjusting any one or combination of the first oxidizing gas stream,
the first fuel gas stream, the second oxidizing gas stream, and the
second fuel gas stream, respectively.
37. The method of claim 34, including the step of matching the
oxidizing gas to fuel gas proportions of the unmixed second
oxidizing gas and fuel gas streams, respectively, to the oxidizing
gas to fuel gas proportions of the first oxidizing gas and fuel gas
streams, respectively, forming the premixed combustion gas
stream.
38. The method of claim 34, including the steps of combusting the
premixed combustion gas stream for forming a first flame, and then
combusting the respective second oxidizing gas and fuel gas streams
for forming a second flame that is combined with and jackets the
first flame.
39. The method of claim 34, including the step of distributing the
first fuel gas stream at least partially about an elongate gas
expansion nozzle in which the gas expansion chamber is defined.
40. The method of claim 34, including the step of passing a
pulverized solid within a selected one of the respective gas
streams.
41. A method of controlling a combustion burner assembly, the
burner assembly including an elongate housing, an oxidizing gas
supply line in fluid communication with the housing, and a fuel gas
supply line in fluid communication with the housing, said method
comprising the steps of: combining a first stream of the oxidizing
gas and a first stream of the fuel gas, respectively, into a
premixed combustion gas stream; obtaining a sample of the premixed
combustion gas stream through a sampling device extended into said
gas stream; performing a composition analysis of the sampled
premixed gas stream; calculating an ideal oxidizing gas to fuel gas
ratio under the then current combustion burner operating
conditions; comparing the calculated ideal ratio to an actual
oxidizing gas to fuel gas ratio as determined by the composition
analysis of the premixed combustion gas stream; and regulating the
oxidizing gas to fuel gas ratio by adjusting the pressure of the
oxidizing gas passed into the gas expansion chamber.
42. The method of claim 41, the step of performing a composition
analysis of the sampled premixed gas stream comprising the step of
burning the premixed gas stream sample and then analyzing the
products of combustion.
43. The method of claim 41, the step of performing a composition
analysis of the sampled premixed gas stream comprising the step of
directly analyzing the oxidizing gas and the fuel gas proportions
in the unburned premixed gas stream sample.
44. The method of claim 41, the step of performing a composition
analysis of the sampled premixed gas stream comprising the steps of
burning the premixed gas stream sample and analyzing the products
of combustion, and then analyzing the oxidizing gas and the fuel
gas proportions in the unburned premixed gas stream sample.
45. The method of claim 41, the step of calculating an ideal
oxidizing gas to fuel gas ratio comprising the step of using
predetermined data to calculate the ideal ratio.
46. The method of claim 41, the step of calculating an ideal
oxidizing gas to fuel gas ratio comprising the step of using
chemical calculations to calculate the ideal ratio.
47. The method of claim 41, the step of calculating an ideal
oxidizing gas to fuel gas ratio comprising the step of using
predetermined data and chemical calculations to calculate the ideal
ratio.
48. The method of claim 41, further comprising the step of
repeating the process during the operation of the combustion burner
for maintaining the ideal ratio.
49. The method of claim 41, further comprising the step of
combusting the premixed combustion gas stream in stages.
50. The method of claim 41, further comprising the step of
combusting the premixed combustion gas stream at the center of a
combustion flame exiting from an expansion chamber formed as a part
of the combustion burner.
51. The method of claim 50, further comprising the step of passing
a second oxidizing gas stream and a second fuel gas stream into a
mixing head, mixing the separate oxidizing gas stream and the
separate fuel gas stream together, combusting the oxidizing gas and
the fuel gas of said second gas steams, and forming the combusted
second gases as an outer jacket about the combustion flame.
52. The method of claim 51, comprising the step of delaying the
combustion of the respective second oxidizing and fuel gas streams
with respect to the combustion of the premixed combustion gas
stream.
53. The method of claim 51, comprising the step of using the
sampled premixed combustion gas stream to indicate the overall
combustion chemistry of the combustion flame produced by the
combustion of all of the oxidizing gases and fuel gases comprising
the combustion flame.
54. The method of claim 51, further comprising the step of
adjusting the proportions of the second oxidizing gas stream to the
second fuel gas stream entering the mixing head so that the second
oxidizing gas stream to the second fuel gas stream proportions are
equal to the proportions of the oxidizing gas to the fuel gas
within the premixed combustion gas stream.
55. The method of claim 51, further comprising the step of
regulating the pressure of the oxidizing gas relative to the
pressure of the fuel gas such that the overall ratios of the
oxidizing gas to the fuel gas of the premixed combustion gas stream
and of the second gas streams, respectively, are at the desired
proportions for combustion.
56. The method of claim 51, further comprising the steps of
checking the overall burner combustion ratio by measuring the
composition of the combusted and non-combusted gases at a test
burner positioned downstream of the mixing head, and then comparing
the results thereof to the composition of the premixed combustion
gas stream measured at an outlet of the expansion chamber.
57. The method of claim 51, further comprising the step of
introducing the oxidizing gas and the fuel gas into the mixing head
at substantially the same pressure for each such gas.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims priority to U.S. provisional
Patent Application Number 60/216,753 filed on Jul. 7, 2000, in the
United States Patent and Trademark Office, and to U.S. provisional
Patent Application Number 60/222,450 filed on Aug. 8, 2000, in the
United States Patent and Trademark Office.
FIELD OF THE INVENTION
[0002] The invention relates in general to combustion burner
assemblies of the type used in the production of molten metals, for
example copper and aluminum. More particularly, the invention
relates to an improved gas mixing device, and a method of mixing
combustion gases practiced thereby, adapted for use with a
combustion burner assembly.
BACKGROUND OF THE INVENTION
[0003] The use of shaft furnace burners with the type of shaft
furnace disclosed in U.S. Pat. No. 3,199,977 to Phillips et al.,
for melting metals, to include copper and aluminum, is well known.
As known to those of skill in the art, the combustion burner of
Phillips et al. is commonly referred to as a shaft furnace burner,
and more particularly to a premix burner of the type that burns an
oxidizing gas and a fuel gas that have been mixed with one another
prior to ignition within a combustion burner. When the furnace
burner is operated in a slightly reducing mode, i.e., where less
oxygen than required for complete combustion is used in the
combustion process, as is typically desirable for the operation of
a metal melting shaft furnace, the pre-mixed and substantially
homogenous oxidizing gas to fuel gas mixture or ratio utilized
produces a flame with a relatively high adiabatic flame
temperature.
[0004] Although the flame temperature of this type of burner is
desirable from the standpoint of melting a metal or metals, the
elevated flame temperature also leads to the production of
extensive amounts of nitrogen oxide (NO.sub.x) in the off gas,
i.e., the exhaust or waste gas emitted from the burner, which is
undesirable. Additional examples of premix burners are disclosed in
U.S. Pat. No. 3,299,940 to Phillips et al., as well as in U.S. Pat.
No. 4,536,152 to Little, Jr. et al., respectively.
[0005] Moreover, In a shaft furnace of the type used to melt or
refine a metal, it is oftentimes necessary to control the
concentration of certain combustion gases, for example oxygen,
within the raw molten metal in order to control the mechanical
properties of the finished product. The known types of shaft
furnace combustion burners normally operate in a combustion region
where between 90 to 99 percent of theoretical combustion oxygen is
supplied to the burners. This oxygen ratio is controlled strictly
by measuring, i.e., sampling, and controlling the products of
combustion sampled from the combustion of the premixed oxidizing
and fuel gas streams, also known as the combustion gas stream.
Deviations on either side of the optimal oxygen range may cause the
absorption of excess amounts of oxygen by the molten metal, either
from direct exposure to oxygen in lean combustion, or from exposure
to the unburned oxygen of the oxidizing gas/oxidizer due to an
excessively long combustion flame. A sampled premix burner control
method of the type described above is disclosed in U.S. Pat. No.
5,240,494 to Williams et al.
[0006] Shaft furnace combustion burner designs that do not premix
the oxidizing gas and the fuel gas prior to the injection of the
gases into the burner block are know as nozzle mix or non-premix
burners. These types of burners operate with a lower adiabatic
flame temperature than that of a premix burner, and thus do not
attain the melting efficiency of the premix style burners, although
they do reduce the amount of nitrogen oxide resulting from the
melting process.
[0007] What is needed, therefore, but seemingly unavailable in the
art is a gas mixing device, as well as a gas mixing method
practiced thereby, adapted for use with a combustion burner
suitable for use in the melting and production of high-quality
metals having an oxygen content in the normal process range, and
which also allows for the strict control of the combustion
chemistry of the combustion burner for the purpose of reducing the
amount of nitrogen oxide resulting from the melting process.
Accordingly, what is needed is a combustion gas mixing device and
control methodology that permits the combustion burner to act as
both a premix burner for attaining the desired oxygen content in
the flame and metal molten thereby, as well as a nozzle mix or
non-premix burner which allows for the control of the burner's
combustion chemistry, when and as desired.
SUMMARY OF THE INVENTION
[0008] The present invention provides an improved gas mixing
device, as well as a method of mixing combustion gases, for use
with a combustion burner that overcome some of the design
deficiencies of the prior art. Accordingly, the combustion burner
of the present invention comprises a gas mixing device that works
in conjunction with a conventional shaft furnace burner. The gas
mixing device, as well as the gas mixing and control methods of the
invention are suitable for use in the melting and production of
high-quality metals requiring an oxygen content in a normal process
range, and which also allow for the control of the burner's
combustion chemistry so as to reduce the amount of nitrogen oxide
resulting from the metal melting process.
[0009] The gas mixing device of the invention therefore operates
substantially as a nozzle mix type of burner, with an associated
lower flame temperature which results in a lower level of nitrogen
oxide production than that of a premix burner, while attaining the
performance characteristics of a premix burner. This is achieved by
providing a gas mixing device having an elongate gas expansion
nozzle adapted to be positioned within a housing provided as a part
of a burner assembly. The burner assembly, as known, will have an
oxidizing gas supply line in sealed fluid communication with the
housing, as well as a fuel gas supply line also in sealed fluid
communication with the housing. The gas expansion nozzle has a
first end and a spaced second end with a gas expansion chamber
defined therein and extending from the first end of the nozzle to
the second end thereof. An inlet port is defined at the first end
of the gas expansion nozzle, and an outlet port is defined at the
second end of the gas expansion nozzle, each of which is in
communication with the gas expansion chamber.
[0010] The gas mixing device also includes at least one oxidizing
gas passageway formed separately of the gas expansion chamber and
extending along the gas expansion nozzle, which is provided, and
communicates with at least one oxidizing gas outlet at the second
end of the expansion nozzle. At least one fuel gas passageway
formed separately of the gas expansion chamber is also provided,
extending from the first end to the second end of the gas expansion
nozzle. The at least one fuel gas passageway is also provided with
at least one fuel gas outlet at the second end of the gas expansion
nozzle.
[0011] The gas mixing device also comprises an elongate gas inlet
nozzle spaced from the first end of the gas expansion nozzle. The
gas inlet nozzle has a first end, a spaced second end, and defines
a gas flow passageway therein extending from the first to the
second ends thereof, respectively. A gas inlet port is defined at
the first end of the gas inlet nozzle and which is in communication
with the gas flow passageway. In like fashion, a gas outlet port is
defined at the second end of the gas inlet nozzle which is also in
communication with the gas flow passageway.
[0012] The gas flow passageway defined within the gas inlet nozzle
is formed as a venturi for increasing the velocity of the gas
passed therethrough and directed toward the inlet port of the gas
expansion nozzle. It is anticipated that the gas outlet port of the
gas inlet nozzle will be sized smaller than the inlet port of the
gas expansion nozzle so as to minimize, or eliminate, any venturi
effect that may occur where the oxidizing gas and the fuel gas
enter the inlet port of the gas expansion chamber, as discussed in
greater detail below.
[0013] As the gas inlet nozzle is spaced from the gas expansion
nozzle within the housing, a gap is defined therebetween which
functions as a fuel opening for allowing the fuel gas to be passed
from a gas manifold extending at least partially about the gas
expansion nozzle into the nozzle. The gas flows through this gap
into the gas expansion chamber, mixes with the oxidizing gas, and
is then passed from the gas expansion chamber as a premixed
combustion gas stream into a downstream mixing head, or mixing
zone, provided as a part of the burner assembly.
[0014] The gas inlet nozzle also includes at least one oxidizing
gas passageway formed therein, extending from the first end to the
second end thereof, which is positioned with respect to the at
least one oxidizing gas passageway of the gas expansion nozzle. An
elongate tube or pipe is passed through both of the respective gas
inlet nozzle and gas expansion nozzle oxidizing gas passageways,
such that the two passageways are sealed to one another for
allowing the oxidizing gas to flow therethrough, as well as through
the gap between the gas inlet nozzle and the gas expansion nozzle
without otherwise being mixed with the fuel gas.
[0015] So constructed, the gas inlet nozzle directs at least a
portion of the oxidizing gas into the inlet port of the gas
expansion nozzle, and also directs at least a portion of the
oxidizing gas into the at least one oxidizing gas passageway
fashioned within each of the gas inlet nozzle, and the gas
expansion nozzle, respectively. The fuel gas supply line, in
cooperation with the gas manifold formed about the gas expansion
nozzle, ensures that at least a portion of the fuel gas enters the
inlet port of the gas expansion nozzle, and also ensures that at
least a portion of the fuel gas passes into the at least one fuel
gas passageway that extends in the lengthwise direction of the gas
expansion nozzle.
[0016] Accordingly, oxidizing gas and fuel gas enter into the inlet
port of the gas expansion chamber, and are mixed therein to form
the premixed combustion gas flow which is passed from the gas
expansion nozzle. Simultaneously, separate oxidizing gas and fuel
gas streams, respectively, pass through their respective oxidizing
and fuel gas passageways and exit through their respective
oxidizing gas and fuel gas outlet ports such that the premixed
combustion gas stream, as well as the second oxidizing and fuel gas
streams, mix with one another in the mixing head of the device. A
premix inner combustion flame core is therefore formed, with the
second oxidizing gas and fuel gas streams forming a jacket or
envelope about the combustion gas flow stream so that when these
gases are ignited at a downstream igniter assembly, the premixed
combustion gas stream/inner combustion flame core is jacketed by a
flame core formed by the second oxidizing and fuel gas streams,
once ignited.
[0017] The above-described method also includes the steps of
sampling the premixed combustion gas stream downstream of the gas
expansion chamber, and of selectively adjusting any one, or
combination, of the first oxidizing gas or first fuel gas streams
passed into the gas expansion chamber, the second oxidizing gas
stream, and the second fuel gas stream, respectively, for varying
the combustion characteristics and performance of the mixed
gases.
[0018] The method may also include the steps of matching the
oxidizing gas to fuel gas ratio or proportions of the second
oxidizing and fuel gas streams, respectively, to the oxidizing gas
to fuel gas ratio/proportions of the first oxidizing and fuel gas
streams, respectively, of the premixed combustion gas stream.
[0019] A novel method for controlling the combustion of a
combustion burner assembly also results from the unique design of
this invention, which method includes the steps of combining the
first stream of the oxidizing gas with the first stream of the fuel
gas, respectively, into the premixed combustion gas stream.
Thereafter, a sample of the premixed combustion gas stream is
obtained through a sampling device extended into the gas stream. A
composition analysis is performed of the sampled premixed
combustion gas stream, and an ideal oxidizing gas to fuel gas ratio
is then calculated using the current combustion burner operating
conditions. The calculated ideal ratio is compared to an actual
oxidizing gas to fuel gas ratio, as determined by the composition
analysis of the premixed combustion gas stream. Thereafter, the
oxidizing gas to fuel gas ratio is regulated by adjusting the
pressure of the oxidizing gas passed into the gas expansion
chamber. This method or control process is continually repeated
during the operation of the combustion burner in order to maintain
the ideal ratio of oxidizing gas to fuel gas.
[0020] A feature of the invention, therefore, is that the
combustion of the respective second oxidizing and fuel gas streams
can be delayed, having the effect of reducing the temperature of
the combustion flame, which in turn reduces the nitrogen oxide
content of the combustion burner waste gases passed from the
combustion burner assembly, and/or the shaft furnace. The
methodology of the invention also includes the steps of checking
the overall burner combustion ratio by measuring the composition of
the combusted and non-combusted gases at a test burner positioned
downstream of the mixing head, and then comparing the results
thereof to the composition of the premixed combustion gas stream
sampled and measured at the outlet of the gas expansion chamber.
Moreover, the oxidizing and fuel gases are introduced into the
mixing head at substantially the same pressure for the purpose of
minimizing the likelihood of there being a back-pressure condition
within the gas expansion nozzle.
[0021] It is, therefore, a object of the present invention to
provide an improved gas mixing device for use with a combustion
burner assembly, as well as an improved method of mixing gases
practiced thereby, and also an improved method for controlling the
gas mixing operation and the combustion of the gases. It is to this
object, as well as the other objects, features, and advantages of
the present invention, which will become apparent upon reading the
specification, when taken in conjunction with the accompanying
drawings, to which the invention is directed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a side elevational view in partial cross section
of a combustion burner within which the present invention can be
used.
[0023] FIG. 2 is a side elevational view in cross-section of an
enlarged portion of the burner shown in FIG. 1.
[0024] FIG. 3 is a side elevational view in cross-section of a
preferred embodiment of the gas mixing device of the present
invention.
[0025] FIG. 4 is a cross-sectional view taken along line 4-4 of
FIG. 3 illustrating a gas manifold.
[0026] FIG. 5 is a cross-sectional view also taken along line 4-4
of FIG. 3 of an alternate embodiment of the gas manifold.
DETAILED DESCRIPTION
[0027] Referring now in detail to the drawings, in which like
reference characters indicate like parts throughout the several
views, FIGS. 1 and 2 illustrate a known type of combustion burner
assembly adapted for use with a shaft furnace of the type
illustrated in U.S. Pat. No. 3,199,977 to Phillips et al., the
provisions of which are incorporated herein fully by this
reference. In particular, the combustion burner assembly 5 of FIGS.
1 and 2 is a premix type of combustion burner, as disclosed in the
aforementioned '977 patent to Phillips et al., and is also
disclosed in U.S. Pat. No. 3,299,940 also to Phillips et al., as
well as to U.S. Pat. No. 4,536,152, to Little, Jr. et al., the
provisions of each of which are incorporated herein fully by this
reference.
[0028] Referring, therefore, to FIGS. 1 and 2, the combustion
burner assembly 5 is illustrated for use with a shaft furnace
provided with a furnace wall 7 having a refractory lining 8 and
enclosed or encased by a steel shell 9. The combustion burner
assembly includes an igniter assembly 11 comprised of an elongate
tubular section 12 extending from and in fluid communication with a
burner outlet 13 defined within and extending through the furnace
wall. A plurality of sampling ports 15 are defined within the
tubular section of the igniter assembly, and are used for
withdrawing combustion gas samples for measuring the respective
oxidizing and fuel gas components thereof.
[0029] The igniter assembly also includes an igniter 16, which can
be any type of desired, and known, igniter. An elongate housing 17
extends upstream of the igniter assembly 11, and is in sealed fluid
communication with an oxidizing gas supply line 19, and a fuel gas
supply line 23. The oxidizing gas supply line is regulated by a
valve 20, as well as by an orifice plate 21, as described in
greater detail in the aforementioned patents to Phillips et al., as
well as to Little, Jr. et al. Additionally, it is anticipated that
the combustion burner assembly 5 of FIGS. 1 and 2, as well as the
combustion burner assembly 30 of FIGS. 3 through 5, could utilize
the control system as described in U.S. Pat. No. 5,240,494 to
Williams et al., the provisions of which are incorporated herein
fully by this reference.
[0030] The fuel gas supply line 23 extends into a gas manifold 24
which extends about the periphery of the housing 17, and in
particular a removable sleeve 25 placed therein. The sleeve 25
defines a mixing chamber or zone 27 within the housing, and is
provided with a radially spaced series of fuel gas supply openings
or inlets 28 defined therein, such that the fuel gas is passed from
the supply line into the fuel gas manifold, and from there through
the gas inlets into the mixing zone. The fuel gas stream, denoted
by the arrows with the reference character "F," mixes with the
oxidizing gas stream, denoted by the arrows with the reference
character "O," for forming a premixed combustion gas stream,
denoted by the reference character "C," which is passed from the
mixing chamber toward the downstream igniter assembly.
[0031] A feature of the known type of combustion burner assembly 5
illustrated in FIGS. 1 and 2 is that the mixing of the oxidizing
gas and fuel gas can be controlled with some degree of precision
for obtaining the desired combustion gas ratios. This results in a
combustion gas flame having a relatively high adiabatic flame
temperature, but can also result, as known, in the production of
undesirable amounts of nitrogen oxide in the off gas or waste gases
passed from the combustion burner assembly, as well as the shaft
furnace, or other device with which the combustion burner assembly
is used. This type of burner assembly construction is contrasted to
those types of combustion burners known as nozzle mix burners, or
non-premix burners, which operate with a much lower adiabatic flame
temperature than that of a premix burner, but which also result in
a lesser emission of nitrogen oxide.
[0032] The present invention is illustrated in FIGS. 3 through 5.
In fashion heretofore unknown in the art, the gas mixing device 30
of FIGS. 3 through 5 provides a combustion burner assembly which
can function in many ways similar to a premix type of burner, and
yet which is also possessed of the characteristics of a nozzle mix
burner for providing a high adiabatic flame temperature, and for
also reducing nitrogen oxide emissions when contrasted with the
known types of premix burners. This is obtained by providing a
elongate gas expansion nozzle 31 which is positioned within, and
supported along the longitudinal axis, denoted by the reference
character "A," within the housing 17 of the combustion burner
assembly. The gas expansion nozzle has a first end 32 and a spaced
second end 34, and defines a gas expansion chamber therebetween
having an inlet port 36 at the first end of the expansion nozzle,
and an outlet port 38 at the second end thereof, each of which is
in communication with the gas expansion chamber.
[0033] As illustrated in FIGS. 3 through 5, at least one oxidizing
gas passageway 39 is defined within the gas expansion nozzle
separately of the gas expansion chamber, and extends from the first
end to the second end thereof. As shown in FIGS. 3 through 5, there
is at least a pair of radially spaced oxidizing gas passageways
defined within the gas expansion nozzle. The number of oxidizing
gas passageways defined within or otherwise formed as a part of the
gas mixing device 30 may be as desired, and as determined by the
combustion gas requirements of the furnace or other device with
which the combustion burner assembly will be used.
[0034] Each of the oxidizing gas passageways 39 extends to and is
in fluid communication with a respective oxidizing gas outlet 40
formed at the second end of the gas expansion nozzle. These
oxidizing gas outlets open into a downstream mixing head or zone 42
which is present externally of the outlet port 38 of the gas
expansion nozzle 31. The premixed combustion gas stream formed
within the gas expansion chamber, as discussed in greater detail
below, is mixed with separate oxidizing gas and fuel gas streams,
respectively, as described in greater detail, below.
[0035] Referring to FIG. 3, at least one fuel gas passageway 43 is
defined by the gas expansion nozzle in cooperation with the housing
17, which fuel gas passageway extends from the first end to the
second end of the gas expansion nozzle. Similar to the oxidizing
gas passageways, each of the fuel gas passageways terminates, i.e.
is in communication with, a respective fuel gas outlet 44 opening
to the mixing head 42.
[0036] Although the oxidizing gas passageway 39 is shown as being
defined within the gas expansion nozzle, and the fuel gas
passageway 43 is shown as being defined by the gas expansion nozzle
in cooperation with the interior sidewall of the housing 17, it is
anticipated that these gas passageways can be formed in any fashion
as desired, and may be defined entirely within the gas expansion
nozzle, may be defined by the gas expansion nozzle in association
with the housing in which is it placed, or may be fashioned as
separate tubes, pipes, or sealed fluid passageways otherwise
extending toward the second end of the gas expansion nozzle, and
each of which communicates with an oxidizing gas or fuel gas
outlet, respectively.
[0037] Positioned upstream of the gas expansion nozzle, and spaced
from the first end thereof, is an elongate gas inlet nozzle 46. The
gas inlet nozzle has a first end 47, a spaced second end 48, and
defines a continuous gas flow passageway therein extending from the
first to the second ends of the nozzle. A gas inlet port 51 is
fashioned at the first end of the nozzle, and a gas outlet port 52
is fashioned at the second end of the nozzle, each of which is in
communication with the gas flow passageway.
[0038] The gas inlet nozzle also includes at least one oxidizing
gas passageway 54 defined therein, and extending from the first end
to the second end thereof. As shown in FIG. 3, there are at least a
pair of radially spaced oxidizing gas passageways defined within
the gas inlet nozzle. As for the gas expansion nozzle 31, there
will be a corresponding, as well as any desired number, of
oxidizing gas passageways defined within the gas inlet nozzle, each
of which extends into sealed fluid communication with a
corresponding oxidizing gas passageway provided as a part of the
gas expansion nozzle. Accordingly, and as shown in FIGS. 3 through
5, an elongate tube or pipe 55 is passed through each of the
respective oxidizing gas passageways 39, 54, such that each
corresponding oxidizing gas passageway is in sealed fluid
communication with the other.
[0039] As described above, the gas inlet nozzle is spaced from the
first end of the gas expansion nozzle by a continuous annular gap
56, which gap defines a fuel gas supply opening leading into, and
extending toward the inlet port of the gas expansion chamber
defined within the gas expansion nozzle.
[0040] In operation, an oxidizing gas "O" is passed through the
oxidizing gas supply line 19 toward, into, and through the gas
inlet nozzle 46. This is accomplished by passing at least a portion
of the oxidizing gas through the gas flow passageway 50, and then
through the inlet port 36 of the gas expansion chamber 35. Another
portion of the oxidizing gas, in any desired amount, is passed into
the oxidizing gas passageways 54 defined in the gas inlet nozzle,
through the elongate tubes 55, and through the oxidizing gas
passageways 39 defined within the gas expansion nozzle. The
oxidizing gas passed through the oxidizing gas passageways will
exit the gas expansion nozzle through the oxidizing gas outlet
ports 40, and will be passed toward the mixing zone 42, as
described above.
[0041] In similar fashion, the fuel gas "F" is passed through the
fuel gas supply line 23 and into the annular fuel gas manifold 24
extending about the first end 32 of the gas expansion nozzle 31, as
illustrated in FIGS. 3 through 5. So constructed, at least a
portion of the fuel gas is passed through the fuel gas passageway
43 and into the gap 56 for entering the inlet port of the gas
expansion chamber, and in so doing, will be mixed with the
oxidizing gas being passed from the gas inlet nozzle and into the
gas expansion chamber. The oxidizing gas and fuel gas passed into
the gas expansion chamber will be thoroughly mixed with one another
into a premixed combustion gas stream "C," as shown in FIG. 3. The
premixed combustion gas stream is then passed downstream toward the
igniter assembly.
[0042] Simultaneous with the passage of at least some of the fuel
gas into the inlet port of the gas expansion chamber, a desired
amount of the fuel gas is passed through the respective fuel gas
passageways 43, and through the respective fuel gas outlet ports 44
into the gas mixing head or zone 42 formed externally, and
downstream, of the outlet port of the gas expansion nozzle. Whereas
the oxidizing and fuel gases passed through the gas expansion
chamber form the premixed combustion gas stream, the "second"
oxidizing gas and fuel gas streams, respectively, passed through
their respective oxidizing gas and fuel gas passageways are used in
a nozzle-mix fashion for jacketing the premixed combustion gas
stream before it is passed into the igniter assembly. The practical
effect of this type of combustion gas stream formation is that a
two-part flame having an inner flame core comprised of the premixed
combustion gas stream is created, with the second oxidizing and
fuel gas streams, respectively, combusting and jacketing the inner
flame core. This allows for a far greater degree of precision in
controlling the gas mixing process, as well as the combustion
chemistry, for allowing a relatively high adiabatic flame
temperature to be obtained, while also controlling the amount of
nitrogen oxide that is emitted from the combustion process.
[0043] A gas sampling device 58, of known construction, is
positioned downstream of the outlet port of the gas expansion
nozzle such that the gas sampling device measures the respective
oxidizing and fuel gases which comprise the premixed combustion gas
stream. Positioned further downstream of the gas sampling device,
for example approximately 25 inches or so downstream of the mixing
head, is a conventional test burner which will sample the
combustion gases that have been passed downstream, burn same, and
determine the composition of the respective oxidizing and fuel gas
ratios therein. Accordingly, using both of the gas sampling and the
test burner devices, in association with the described construction
of the gas mixing device, a very high degree of control is
attainable over the gas mixing process, as well as the combustion
process itself, for blending, mixing and maintaining the desired
oxidizing gas to fuel gas ratios, all for the purposes of attaining
the desired flame temperature and nitrogen oxide measurements.
[0044] FIG. 4 is a cross-sectional view of the gas mixing device
taken along line 4-4 of FIG. 3, illustrating the fuel gas manifold
24 which extends about the exterior circumference of the gas
expansion nozzle 31. The fuel gas passes through the fuel gas
supply line 23 such that it is tangentially directed toward the
exterior surface of the gas expansion nozzle, and is passed
circumferencially about the exterior of the gas expansion nozzle
within the gas manifold. In so doing, the fuel gas is evenly
distributed or spread about at least the first end of the gas
expansion nozzle for uniformly distributing and supplying fuel to
the gas expansion chamber through the gap 56, and from there into
the inlet port of the gas expansion chamber.
[0045] In FIG. 5, however, the gas supply line 23 is shown
intersecting the longitudinal axis A passed through the housing 17
and the gas expansion nozzle 31, such that a deflector plate 62 is
required for directing the fuel gas circumferentially about the
exterior surface of the gas expansion nozzle, again for attaining
the results of uniformly distributing the fuel gas about the gas
expansion nozzle, or at least the first end thereof, and from there
passing the fuel gas into the gap 56 and then into the inlet port
of the gas expansion chamber.
[0046] As shown in FIGS. 4 and 5, by passing the fuel gas flow
through the gas manifold and in a direction which is tangent to the
exterior surface or periphery of the gas expansion nozzle, a
rotational velocity is imparted to the fuel gas therein. This
rotational velocity helps to ensure the desired even pressure
distribution of the fuel gas about the circumference of the gas
manifold, and results in a more uniform entry of the fuel gas into
the gap 56 as well as into the fuel gas passageways 43 of the gas
mixing device. Additionally, it is anticipated that the rotational
velocity of the fuel gas within the manifold may enhance the
capability of the gas mixing apparatus to carry pulverized solids
therein, as well as other gases or liquids, all as desired. Also,
and as one skilled in the art will appreciate, the fuel gas may be
passed through the gas inlet nozzle 46 rather than the oxidizing
gas, with the oxidizing gas being passed through the gas manifold
24, and through the gap 56 into the inlet port of the gas expansion
chamber, as well as through their separate, and respective,
oxidizing and fuel gas passageways, as desired.
[0047] The gas expansion nozzle 31, as well as the gas inlet nozzle
41 may be constructed of any desired material, and preferably of a
material which is suitable for use in a high gas flow operation
with potentially corrosive gases as well as for use in a heavy duty
or severe working environment subject to corrosive forces both
internally and externally of the burner assembly. For example, both
of the gas expansion nozzle and the gas inlet nozzle may be formed
of a ceramic or ceramic coated material, or a metallic material, or
of any desired metal or non-metallic material. It is anticipated,
however, that the tube 55 passed through the gas inlet nozzle and
into the gas expansion nozzle will preferably be formed of a
metallic material, and more preferably of a stainless steel for its
superior durability and resistance to corrosion. Also, and as shown
in FIG. 3, the gas inlet nozzle 41 is sealed to the housing 17,
such that all of the oxidizing gas, or other gas(es) must flow
therethrough, and then into either the gas expansion chamber or
into the gas mixing zone 42 through the oxidizing gas passageways,
as desired.
[0048] As described hereinabove, therefore, the gas mixing device
of this invention, and primarily the gas expansion nozzle 31 and
gas inlet nozzle 46 thereof, replace the interchangeable sleeve 25
of the known combustion assembly 5. The gas flow passageway 50 of
the gas inlet nozzle is formed as a venturi for increasing the
velocity of the gases passed therethrough. The gas expansion
chamber 35, however, is formed to be conical, and may be circular
in cross-section, for example as shown in FIGS. 4 and 5, although
any desired cross-sectional shape of the gas expansion chamber may
be used as designed for attaining the desired gas mixing
characteristics therein, i.e. for forming the premixed combustion
gas stream. Accordingly, the shape of the gas expansion chamber may
be, but is not limited to, a conical shape as shown, or may be
parabolic, or hyperparabolic, all as desired.
[0049] The control methodology practiced by the gas mixing device
utilizes a sample of the oxidizing gas and the fuel gas, which may
include, for example, the premixed combustion gas stream. The
control process thus includes the steps of obtaining a sample of
the premixed combustion gas stream through the gas sampling device
58. A composition analysis of the sampled premixed combustion gas
is then performed by burning the premixed sample and analyzing the
products of combustion, or by analyzing the ratio of the oxidizing
gas to the fuel gas components of the unburned premixed sample
directly, or by performing both steps together. Thereafter, an
ideal ratio of the oxidizing gas to fuel gas, under the current
burner operating conditions, is calculated by using either
predetermined data, or chemical calculations, or both, as
desired.
[0050] The ideal ratio so calculated is then compared to the actual
oxidizing gas to fuel gas ratio as measured in the composition
analysis of the premixed combustion gas stream. The oxidizing gas
to fuel gas ratio is then regulated, as required, by adjusting the
pressure of the oxidizing gas supply line, or the fuel gas supply
line, or both, again as desired. This control process, as described
above, is then repeated throughout the operation of the combustion
burner to maintain an ideal oxidizing gas to fuel gas ratio.
[0051] Accordingly, during operation of the combustion burner a
ceramic water-cooled or heat-resistant metal burner block (not
illustrated) provided as a part of the igniter assembly is affixed
to the mixing head 42, and combustion of the oxidizing gas and fuel
gas occurs in stages therein. As described above, it is anticipated
that during combustion first the premixed combustion gas stream
passed through the gas expansion chamber will be combusted, and
will burn at the center of a two-part flame. Thereafter, the second
oxidizing gas and fuel gas streams passed through their separate
oxidizing gas and fuel gas passageways, and through their
respective outlet ports and into the mixing head 42, will be mixed
with one another to form an outer core or jacket about the premixed
combustion gas stream. The second gas streams are combusted to form
the second or outer jacketing portion of the combustion flame. The
result of this process is that the delayed burning of the second
oxidizing gas and fuel gas streams reduces the flame temperature,
which results in a reduced nitrogen oxide content in the burner
exhaust or waste gases. The sampled premixed combustion gas stream,
taken at the gas sampling device 58 can also be used to indicate
the overall combustion chemistry of the flame produced by the
combustion for all of the oxidizing gas and fuel gas supplied to
the gas mixing device 30, whether a part of the premixed combustion
gas stream or the respective second oxidizing and fuel gas streams
passed into the mixing head.
[0052] The ratio or proportions of the unmixed oxidizing gas to
fuel gas entering the mixing head 42 through the oxidizing gas
outlets 40 and the fuel gas outlets 44, respectively, may be
adjusted by selecting an average diameter of the oxidizing gas
passageways, and in particular the inner diameter of the tubes 55
passed therethrough, or the fuel gas passageways 43, or by any
other form of resistance that may be placed therein to ensure that
the ratio/proportions of the unmixed oxidizing gas to fuel gas are
equal to the ratio/proportions of the oxidizing gas to fuel gas in
the premixed combustion gas stream, as measured by the gas sampling
device 58. Moreover, the oxidizing gas pressure relative to the
fuel gas pressure, at the oxidizing and fuel gas supply lines,
respectively, is regulated, in known fashion. The gap 56 formed
between the gas inlet nozzle 46 and the gas expansion nozzle 31 and
used to pass the fuel gas into the inlet of the gas expansion
chamber may also be spaced as desired for regulating the amount of
fuel gas allowed to flow into the inlet of the gas expansion
chamber.
[0053] The overall ratio of the premixed combustion gas stream to
the non-mixed or second oxidizing gas and fuel gas streams,
respectively, is set at the desired proportion for combustion
within the igniter assembly. This ratio will be maintained as long
as the oxidizing gas and fuel gas pressure differentials at the
oxidizing and fuel gas supply lines, respectively, and at the gap
56 between the nozzles, remains unchanged. The overall burner
combustion ratio may be checked by using the test burner 59,
whereupon the composition of the burned or unburned combustion
gases may be undertaken and compared to the results of the same
quantities of gases measured in the premixed combustion gas stream
at the upstream gas sampling device 58.
[0054] It is anticipated that the introduction of the oxidizing gas
and the fuel gases into the gas mixing device 30 will occur at
substantially the same pressure for each component, in order to
mitigate the effects of any back-pressure encountered at the burner
outlet, and extending into the interior of the furnace. For
example, in the event of a blockage at the burner outlet due to a
solidified process metal, the gas pressures will preclude either
component, be it the oxidizing gas or the fuel gas, from flowing
into their respective supply lines, or into any portion of the gas
mixing device normally occupied by the other one of the combustion
gas components, which will thus minimize the creation of a
dangerous explosive condition within the gas mixing device 30, and
more particularly within the gas expansion nozzle 31, and/or the
mixing head 42.
[0055] To allow for the use of relatively identical oxidizing and
fuel gas supply pressures, it is desirable that the diameter of the
gas outlet port 52 provided as a part of the gas inlet nozzle 46 be
sized smaller than the diameter of the inlet port 36 of the gas
expansion nozzle 31, or that the center line of the gas flow
passageway 56 within the gas inlet nozzle be offset laterally with
respect to the center line of the gas expansion chamber 35. By
making the diameter of the gas outlet port of the gas inlet nozzle
smaller than the inlet port of the gas expansion chamber, or by
offsetting the gas flow passageway with respect to the gas
expansion chamber, the venturi effect of the gas inlet nozzle in
association with the inlet of the gas expansion nozzle will be
minimized, if not reduced entirely, while still maintaining the
enhanced mixing characteristics created by the device.
[0056] An illustrative application of the present gas mixing device
would be in the use of a shaft furnace burner used for melting
copper or aluminum. The construction of the gas mixing device 30 as
described, allows for taking a sample of the premixed combustion
gas stream to be analyzed, and the results used to control the
combustion process within the furnace, while the secondary
oxidizing and fuel gas flow streams passed through the separate
oxidizing and fuel gas passageways, respectively, will burn at a
lower flame temperature, resulting in a decrease in the quantity of
nitrogen oxide produced by the burner.
[0057] It is also anticipated, for example, that the gas mixing
device 30 of the present invention may fit inside existing
combustion burner designs, in place of the cylindrical mixing
sleeves 25 (FIGS. 1 and 2) presently used therewith. For example,
the gas mixing device may be used in a T-thermal type 300 and 400
series burner, and other similar burners used in existing shaft
furnace applications. The ability to substitute the present
invention in place of the standard mixing sleeves of the known
types of burners allows for the retrofitting of the gas mixing
device into many existing shaft furnaces without substantial
modification of the furnace piping.
[0058] Additionally, it is anticipated that the separate oxidizing
gas and fuel gas passageways may be formed such that the
combination of the gas expansion nozzle 31 and the gas inlet nozzle
46, alone, forms a convergent or divergent nozzle allowing a
portion of the oxidizing gas and the fuel gas mixture to bypass the
nozzle as desired. In this embodiment, the gas mixing device will
premix all of the oxidizing gas and fuel gas used in the combustion
burner, prior to the introduction of the premixed combustion gas
stream into the igniter assembly.
[0059] Although several embodiments of the invention have been
disclosed in the foregoing specification, it is understood by those
skilled in the art that many modifications and other embodiments of
the invention will come to mind to which the invention pertains,
having the benefit of the teaching presented in the foregoing
description and associated drawings. It is thus understood that the
invention is not limited to the specific embodiments disclosed
hereinabove, and that many modifications and other embodiments are
intended to be included within the scope of the invention.
Moreover, although specific terms are employed herein, they are
used only in a generic and descriptive sense, and not for the
purposes of limiting the described invention, and the words "a,"
"an," or "the" can mean one or more, depending upon the context in
which the terms are employed.
* * * * *