U.S. patent application number 10/759324 was filed with the patent office on 2004-12-09 for low nox emissions, low noise burner assembly and method for reducing the nox content of furnace flue gas.
This patent application is currently assigned to John Zink Company, LLC. Invention is credited to Jayakaran, Jaiwant D., Poe, Roger L., Schnepper, Carol A..
Application Number | 20040248054 10/759324 |
Document ID | / |
Family ID | 26880321 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040248054 |
Kind Code |
A1 |
Poe, Roger L. ; et
al. |
December 9, 2004 |
Low NOx emissions, low noise burner assembly and method for
reducing the NOx content of furnace flue gas
Abstract
A burner assembly for a furnace or like device having a firebox
defining a combustion zone. The burner assembly includes a first
annular tile defining a centrally located path for a flow of
combustion air and a second annular tile concentric with the first
annular tile. The second annular tile has an internal diameter
which is larger than an external diameter of said first annular
tile, and the second annular tile is positioned in surrounding
relationship relative to at least a portion of said first annular
tile so that a ring-shaped conduit is defined therebetween. The
tiles are adapted for placement in the combustion zone of the
furnace with the conduit in direct fluid communication with flue
gases surrounding the combustion zone. The arrangement is such that
combustion air flowing along said path induces a flow of flue gas
through the conduit for entrainment by the flow of combustion air.
The assembly may also include a gas jet positioned adjacent an
inlet to said conduit providing a flow of gas for admixture with
said flow of flue gas. A method is also disclosed whereby the
burner assembly is used for introducing RFG into the combustion
zone to thereby efficiently and effectively reduce the NO.sub.x
content of furnace flue gas produced when air and fluid fuel are
combusted in a combustion zone of a furnace.
Inventors: |
Poe, Roger L.; (Beggs,
OK) ; Jayakaran, Jaiwant D.; (Tulsa, OK) ;
Schnepper, Carol A.; (Tulsa, OK) |
Correspondence
Address: |
STINSON MORRISON HECKER LLP
ATTN: PATENT GROUP
1201 WALNUT STREET, SUITE 2800
KANSAS CITY
MO
64106-2150
US
|
Assignee: |
John Zink Company, LLC
|
Family ID: |
26880321 |
Appl. No.: |
10/759324 |
Filed: |
January 16, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10759324 |
Jan 16, 2004 |
|
|
|
09781817 |
Feb 12, 2001 |
|
|
|
60184615 |
Feb 24, 2000 |
|
|
|
Current U.S.
Class: |
431/116 |
Current CPC
Class: |
F23C 2900/09002
20130101; F23D 14/24 20130101; F23C 2202/40 20130101; F23C 9/08
20130101; F23M 5/025 20130101 |
Class at
Publication: |
431/116 |
International
Class: |
F23L 001/00 |
Claims
I claim:
1. A burner assembly for a furnace having a firebox defining a
combustion zone, said assembly comprising: a first annular tile
defining a path for flow of combustion air; a second annular tile
concentric with said first annular tile, said second annular tile
having an upstream portion with an internal diameter which is
larger than an external diameter of a downstream portion of said
first annular tile, said upstream portion being positioned in
surrounding relationship to said downstream portion, whereby a
ring-shaped conduit which extends along said path is defined
between said tiles, said tiles being adapted for placement in a
combustion zone of a furnace with said conduit in direct fluid
communication with flue gases surrounding said zone, the
arrangement of the tiles being such that combustion air flowing
along said path past a downstream end of the conduit induces a flow
of said flue gas through said conduit for entrainment by said flow
of combustion air; and a gas jet positioned adjacent an inlet to
said conduit providing a flow of fuel gas for admixture with said
flow of flue gas.
2. A recirculated flue gas inducing burner assembly comprising: a
fuel nozzle arrangement including a nozzle positioned to direct a
flow of fluid fuel along a flow path and into a combustion zone
inside a furnace firebox; a first tile having an elongated central
opening, said first tile being located so that said central opening
surrounds said nozzle and directs an annular flow of combustion air
past said nozzle in surrounding relationship to said flow path,
said first tile having an outer peripheral face which extends
therearound in surrounding relationship relative to said opening; a
second tile having a an elongated central passageway, said second
tile being located so that said central passageway surrounds said
path, said second tile having an internal face which extends around
said central passageway, said internal face being disposed in
spaced, facing relationship relative to said peripheral face of the
first tile, said faces defining therebetween an annular space which
extends in a direction along said path, said tiles being arranged
such that said annular space is in direct intercommunication with
an interior area of a furnace firebox when the burner is
operationally installed relative to a furnace, the arrangement of
said tiles being such that a flow of recirculated flue gas from
said interior area and through said annular space is induced by
combustion air flowing through said opening of said first tile; and
a gas jet positioned adjacent an inlet to said conduit providing a
flow of fuel gas for admixture with said flow of flue gas.
3. A burner assembly comprising an elongated tile formation having
a central axis and including first and second tiles presenting an
air passageway configured for conducting combustion air in an axial
direction toward a combustion zone, said first and second tiles
each having an axially elongated annular body segment, the annular
body segment of said first tile being disposed in surrounding
relationship to said passageway, said annular body segment of said
first tile having an outer surface and said annular body segment of
said second tile having an inner surface, said annular body
segments being arranged concentrically with said outer surface
spaced radially inwardly from said inner surface so as to define
therebetween an axially elongated recirculated flue gas conduit
having a downstream end that is in communication with said
passageway and an upstream inlet end that is disposed in a plane
that is transverse to said axis.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of and claims priority
pursuant to 35 U.S.C. .sctn.120 from co-pending application Ser.
No. 09/781,817, filed Feb. 12, 2001, which application Ser. No.
09/781,817 in turn claims priority pursuant to 35 U.S.C.
.sctn.119(e) from provisional application Ser. No. 60/184,615 filed
Feb. 24, 2000. The entireties of the disclosures of said prior
applications Ser. Nos. 09/781,817 and 60/184,615 are hereby
specifically incorporated herein by this specific reference
thereto.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to burners for large scale industrial
applications. Such burners may be adapted for burning either
gaseous fuels including natural gas or liquid fuels including fuel
oil. In particular the invention relates to a low NO.sub.x, low
noise burner assembly which provides structure for recirculating
flue gas directly from the inside of the fire box.
[0004] 2. The State of the Prior Art
[0005] Environmental concerns today fuel a continuing search for
burners which operate efficiently, economically, with a minimum
amount of noise, and with a minimum amount of contamination, such
as NO.sub.x, in the flue gases. It has been determined previously
that NO.sub.x contamination may be reduced by recirculating flue
gases back into the combustion zone. Various methods have been
envisioned and/or developed for accomplishing this recirculation,
including motor driven fans and eductor devices. Generally
speaking, conventional burners utilize only the motive force of
combustion fuel to entrain furnace flue gas. This prior methodology
is limiting in that the gas has high velocity but low mass
resulting in low entrainment rates.
[0006] In addition, prior methodology has involved the use of
burners including internal structural conduits for transporting the
recirculated flue gases back to a place where the same may be
reintroduced into the combustion zone. The structural requirements
are extensive adding greatly to the cost to the overall
installation. Accordingly there has been a need for structural
features which will simplify the recirculation of flue gases.
SUMMARY OF THE INVENTION
[0007] The present invention provides a novel burner assembly which
addresses the problems and shortcomings of the prior art. In
particular, the invention provides a burner assembly that is of
simple construction and facilitates the use of a simple and
effective motive force for recirculating flue gases. In accordance
with the concepts and principles of the present invention, it has
been determined that the use of combustion air for entrainment of
flue gases is much more efficient than the use of fuel gases for
this purpose due to the tremendous difference in mass. The mass of
combustion air is typically 10 to 12 times that of the combustion
fuel gases. The invention also contemplates the simultaneous use of
both combustion air and fuel gases to provide even greater motive
forces for recirculating flue gases.
[0008] The burner assembly of the invention is adapted for being
mounted on a wall or floor or roof of a furnace or fire box or the
like which defines a combustion zone. In accordance with the
concepts and principles of the invention, the burner assembly
comprises a tile formation that has a portion which protrudes
beyond the furnace wall and into the combustion zone. The tile
formation presents an air passageway configured for conducting
combustion air into the combustion zone and a recirculated flue gas
(RFG) conduit that intercommunicates the air passageway and an area
within the furnace adjacent the combustion zone when the burner
assembly is mounted on the wall. In accordance with the invention,
the RFG conduit is preferably located entirely within the
protruding portion of the tile formation, whereby it is unnecessary
to provide RFG conduits built into the furnace structure.
[0009] In a preferred form of the invention, for ease of assembly,
the tile formation may include first and second tiles with the RFG
conduit defined between the tiles. In this preferred form of the
invention, the second tile may be mounted on a seating structure
provided on the first tile. The first and second tiles may each
have an annular body segment and the tiles may be arranged such
that the annular body segment of the first tile is disposed in
surrounding relationship to the combustion air passageway and the
annular body segment of the second tile is disposed in surrounding
relationship to at least a portion of the annular body segment of
said first tile. Preferably, in accordance with the principles and
concepts of the invention, the annular body segment of the first
tile may have an outer surface and the annular body segment of the
second tile may have an inner surface, and these surfaces may be
arranged and positioned such that the RFG conduit is defined
between them. Ideally, the annular body segments may be arranged
concentrically with the outer surface of the first tile spaced
radially from the inner surface of the second tile such that the
RFG conduit is essentially annular in shape.
[0010] In a particularly preferred mode of the invention, the
second tile may have an annular edge which sits on a seating
structure of the first tile. In this preferred mode, the seating
structure may include at least one, preferably at least two and
ideally four evenly circumferentially spaced shoulder members which
extend radially outwardly from the outer surface of annular body
segment of the first tile. In a most preferred embodiment of the
invention, the shoulder members each include a notch configured for
receiving and securing the annular edge of the second tile. Such
structure facilitates the positioning of the tiles relative to one
another and insures concentricity.
[0011] In a further preferred form of the invention, the burner
assembly may include a fluid fuel burner nozzle disposed in the
combustion air passageway. In this form of the invention, the fluid
fuel burner nozzle may be adapted for delivering a gaseous fuel,
preferably natural gas or a specially blended combustible mixture
of gases, to the combustion zone. In accordance with the invention,
the fluid fuel burner nozzle may preferably be adapted for
accommodating pressurized gaseous fuels at various pressures within
a given range. Alternatively, the fluid fuel burner nozzle may be
adapted for delivering a liquid fuel, preferably a fuel oil, to the
combustion zone.
[0012] The burner assembly of the invention may also comprise at
least one fluid fuel burner nozzle disposed adjacent an entrance to
the RFG conduit. In addition, or alternatively, the burner assembly
of the invention may include a fluid fuel burner nozzle disposed on
an outer peripheral surface of the annular body segment of the
second tile.
[0013] In further accordance with the concepts and principles of
the invention, the burner assembly may be adapted for use in
connection with a furnace having a firebox defining a combustion
zone. This burner assembly may include a first annular tile
defining a path for flow of combustion air and a second annular
tile concentric with the first annular tile. The second annular
tile may have an internal diameter which is larger than an external
diameter of the first annular tile, and the second annular tile may
be positioned in surrounding relationship relative to at least a
portion of the first annular tile so that a ring-shaped RFG conduit
is defined therebetween. In this form of the invention, the tiles
may be adapted for placement in the combustion zone with the RFG
conduit in direct fluid communication with flue gases in an area
surrounding the combustion zone. The assembly may preferably be
such that combustion air flowing along the flow path induces a flow
of flue gas through the RFG conduit for entrainment by the flow of
combustion air. Ideally the assembly may include a gas jet
positioned adjacent an inlet to the RFG conduit providing a flow of
gas for admixture with the flow of flue gas.
[0014] In still further accord with its concepts and principles,
the invention provides an RFG inducing burner assembly. The
assembly comprises a fuel nozzle arrangement that includes a nozzle
positioned to direct a flow of fluid fuel along a flow path and
into a combustion zone inside a furnace firebox. The assembly also
includes a first tile structure having a central opening and which
is located so that the central opening surrounds the nozzle and
directs an annular flow of combustion air past the nozzle in
surrounding relationship to the fluid fuel flow path. The first
tile structure desirably has an outer peripheral face that extends
there around in surrounding relationship relative to the central
opening. Also included is a second tile structure that has a
central passageway. The second tile structure desirably is located
so that its central passageway surrounds at least a portion of the
first tile structure. The second tile structure may have an
internal face which extends around its central passageway and such
internal face may be disposed in spaced, facing relationship
relative to the peripheral face of the first tile structure. An
annular space is defined between the outer peripheral face of the
first tile structure and the internal face of the second tile
structure. Preferably, the tile structures are arranged such that
the annular space therebetween is in direct intercommunication with
an interior area within the firebox adjacent the combustion zone
when the burner is operationally installed relative to the furnace.
In accordance with the principles and concepts of the invention,
the assembly of the tile structures may desirably be such that a
flow of RFG from the interior area and through the annular space is
induced by combustion air flowing through the opening of the first
tile structure. In this regard it is to be noted that the assembly
of the present invention may be used to augment flue gas
recirculation in existing applications which employ a forced air
design.
[0015] In another form the invention provides a low NO.sub.x
furnace that includes an RFG inducing burner assembly and a firebox
providing a combustion zone. In this form of the invention, the
burner assembly is operationally installed on a wall or roof or
floor of the furnace to provide combustion air and a fluid fuel to
the combustion zone. In accordance with the invention, the burner
assembly preferably comprises a fuel nozzle arrangement that
includes a nozzle positioned to direct a flow of fluid fuel along a
flow path and into the combustion zone within the firebox, a first
tile structure that has a central opening, and a second tile
structure that has a central passageway. The first tile structure
may be located so that its central opening surrounds the nozzle and
directs an annular flow of combustion air past the nozzle in
surrounding relationship to the fluid fuel flow path. The first
tile structure may also have an outer peripheral face which extends
there around in surrounding relationship relative to the central
opening thereof. The second tile structure may be located so that
its central passageway surrounds at least a portion of the first
tile structure. The second tile structure may also have an internal
face which extends around the central passageway thereof.
Desirably, in accordance with the concepts and principles of the
invention, the internal face of the second tile structure is
disposed in spaced, facing relationship relative to the peripheral
face of the first tile structure, and the faces are preferably
arranged so as to define an annular space therebetween. The tile
structures further may be arranged such that the annular space
therebetween is in direct intercommunication with an interior area
of the firebox adjacent the combustion zone when the burner
assembly is operationally mounted. Desirably, the arrangement of
the tile structures is such that a flow of RFG from an area in the
firebox adjacent the combustion zone and through the annular space
is induced by combustion air flowing through the opening of the
first tile structure. Again, the assembly of the present invention
may be used to augment flue gas recirculation in existing
applications which employ a forced air design.
[0016] In further accord with the concepts and principles of the
invention, a method is provided for efficiently and effectively
reducing the NO.sub.x content of furnace flue gas produced by
combusting air and a fluid fuel in a combustion zone of a furnace.
In this form of the invention, the method involves the use of a
burner assembly as described above for introducing RFG into the
combustion zone.
[0017] In yet another aspect of the invention, a method is provided
for efficiently and effectively reducing the NO.sub.x content of
furnace flue gas. This method may comprise providing a flow of a
fluid fuel to a combustion zone in a firebox of the furnace,
providing a flow of combustion air to the combustion zone,
combusting the fluid fuel and the air in the combustion zone to
thereby produce a flame, and using the motive force of the flow of
combustion air to induce a flow of RFG directly from an area in the
firebox adjacent the combustion zone and cause it to interact with
the fluid fuel and the combustion air in the combustion zone. The
formation and emission of NO.sub.x in the furnace is thus reduced.
Preferably, in accord with the concepts and principles of the
invention, the combustion air flows along a longitudinal axis of an
elongated burner assembly.
[0018] The invention also provides a method for operating a burner
for a gas fired furnace having a fire box. In accordance with this
aspect of the invention, the method preferably includes providing a
flow of combustion air, providing a flow of combustion fuel,
admixing the fuel and air, combusting the admixture of air and fuel
in a combustion zone in the firebox, and inducing a flow of flue
gas directly from an area in the fire box adjacent the combustion
zone and into the admixture of combustion air and fluid fuel, and
thus the flame, using the motive force of the flow of combustion
air. Desirably, the foregoing method may further include a step of
using the motive force of the flow of combustion gas fuel to
further induce a flow of flue gas from the area adjacent the
combustion zone. Desirably, in this form of the invention also, the
combustion air flows along a longitudinal axis of an elongated
burner assembly.
[0019] One of the important features of the invention involves the
use of primary air flowing axially through the burner assembly for
entrainment of RFG directly from an area at the periphery of the
combustion zone. The axial entrainment system of the invention
enables the provision of a much more uniform and homogenous
combustible gas mixture leaving the burner whereby typical
stratification problems and resultant flame instability are
alleviated. The advantages of the invention over prior art burner
assemblies include, but are not limited to, (1) shorter flame
length (0.5 to 1.1 foot per MMBtuh vs. 1.5 to 2 feet per MMBtuh);
(2) larger turn down ratios (10 to 1 vs. 3 to 1); (3) much lower
noise around burner; (4) tiles are not subjected to hot spots
caused by burning jets piercing through the tile; (5) coking
tendencies are reduced if not eliminated completely; (6) stability
is greatly improved facilitating operation under substoichiometric
conditions; (7) flame anchoring in an oxidizing zone is
facilitated; (8) homogenous mixtures are provided leading to
uniformity of flame patterns; (9) both prompt and thermal NO.sub.x
are lowered; (10) potentially both air and fuel gas may be used for
flue gas entrainment; (11) flue gas entrainment is much more
efficient; and (12) axial flame patterns reduce burner to burner
interaction; (12) the assembly of the invention may be coupled with
RFG in forced air applications; (13) the assembly of the invention
is even more efficient when used in connection with a forced air
design.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a side elevational view of a burner assembly which
embodies the concepts and principles of the present invention;
[0021] FIG. 2 is a plan view looking upwardly at the lower end of
the burner as it is positioned in FIG. 1;
[0022] FIG. 3 is an enlarged plan view looking downwardly at the
upper end of the burner as it is positioned in FIG. 1;
[0023] FIG. 4 is an enlarged detail view illustrating the portion
of the burner assembly within the Circle 4. of FIG. 2;
[0024] FIG. 5 is an enlarged detail view illustrating the portion
of the burner assembly within the Circle 5. of FIG. 3;
[0025] FIG. 6 is an enlarged detail view illustrating the portion
of the burner assembly within the Circle 6. of FIG. 3;
[0026] FIG. 7 is an enlarged view, partly in cross-section
illustrating the tile formation of the burner assembly of FIG.
1;
[0027] FIG. 8 is a top plan view of the lower (upstream) tile of
the tile formation of FIG. 7;
[0028] FIG. 9 is a side elevational view of the lower tile of FIG.
7;
[0029] FIG. 10 is a side elevational view, partly in cross-section,
illustrating the upper (downstream) tile of the tile formation of
FIG. 7; and
[0030] FIGS. 11 through 16 are side elevational schematic views
illustrating several alternative embodiments of the burner assembly
of the invention.
[0031] FIG. 17 is a side elevational view, partly in cross-section,
illustrating an alternative form of a burner assembly which
embodies the concepts and principles of the present invention;
[0032] FIG. 18 is a top plan view of the burner of FIG. 17;
[0033] FIG. 19 is a cross sectional view taken substantially along
the line 19-19 of FIG. 17;
[0034] FIG. 20 is a cross sectional view taken substantially along
the line 20-20 of FIG. 18;
[0035] FIG. 21 is a cross sectional view taken substantially along
the line 21-21 of FIG. 18;
[0036] FIG. 22 is a side elevational view, partly in cross-section,
illustrating yet another alternative form of a burner assembly
which embodies the concepts and principles of the present
invention; and
[0037] FIG. 23 top plan view of which is similar to FIG. 18 but
illustrates an alternative embodiment of a burner embodying the
concepts and principles of the invention which is rectangular in
shape rather than circular.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0038] A burner assembly which embodies the concepts and principles
of the invention is illustrated in FIG. 1 where it is identified
broadly by the reference numeral 20. The assembly 20 is
particularly adapted for being mounted as shown on a wall 22 of a
fire box of a furnace or the like. Wall 22 defines a combustion
zone 24 disposed generally at and around the upper end 26 of
assembly 20 as the latter is depicted in FIG. 1. It will be
appreciated by those skilled in the burner art, however, that the
orientation of the assembly 20 is not necessarily critical and the
same may be used in any one of a variety of positions such that the
flame generated thereby is projected upwardly, downwardly,
horizontally or at an angle relative to horizontal. Accordingly,
defining end 26 as an upper end is done only for convenience of
reference. Moreover, it will be appreciated that the principles and
concepts of the invention are not limited to use with round burner
tiles. In this regard, the principles and concepts of the invention
may also be applied to burners having rectangular shaped burner
tiles, flat flame burners and burners with an axisymetric
design.
[0039] Burner assembly 20 includes the conventional accessories
needed for operation, including an air inlet 28 adapted for
connection to a source of air for combustion, an air box 30, and a
manifold system 32 adapted for connection to a source of fuel and
distributing the same to respective individual burner nozzles of
the burner assembly. These devices are conventional and well known
to those skilled in the burner art. Assembly 20 may include a
flange 33 for attaching the same to wall 22 as can be seen in FIGS.
1 and 7. The flange 33 may be secured to the wall 22 using a
conventional nut and bolt (or stud) arrangement (see FIG. 4).
[0040] Burner assembly 20 is particularly adapted for inducing a
flow of flue gases from an area 34 adjacent combustion zone 24 and
recirculating the same for diluting the air and fuel mixture
combusting in the combustion zone 24. These recirculated flue gases
are often referred to as RFG (or FGR), and it is a well known
phenomena that when RFG is mixed in with the combusting air and
fuel in the combustion zone, NO.sub.x emissions are reduced.
[0041] In accordance with the invention, assembly 20 includes a
tile formation 36 having a portion 38 which protrudes beyond wall
22 and into the combustion zone 24 as shown in FIG. 1. That is to
say, portion 38 of tile formation 36 protrudes into and is
positioned essentially within combustion zone 24. Formation 36
includes a first, lower, upstream, inner tile structure 40 and a
second, upper, downstream outer tile structure 42. As can
particularly be seen viewing FIG. 7, tile 42 is mounted on a
seating structure 44 of tile 40.
[0042] As can best be seen viewing FIGS. 7, 8 and 9, in the
preferred embodiment of the invention depicted in the drawings,
tile 40 includes a generally annular body segment 46 which
surrounds a central opening 48, a base 50, and a plurality of
shoulder members 52 which preferably are essentially identical and
evenly spaced about the periphery of body segment 46. As shown in
the drawings, the depicted assembly includes four of the shoulder
members 52; however, those skilled in the art would recognize that
the assembly could just as well be designed to employ only three
shoulder members 52. As can be seen, the shoulder members 52 extend
radially outwardly from the outer peripheral surface 54 of annular
body segment 46, and together, they provide the seating structure
44 for tile 42 mentioned above. To this end, the shoulder members
52 are each provided with a notch 56 which is configured to receive
and secure an annular edge portion 58 of tile 42. That is to say,
when the tiles 40 and 42 are assembled so as to present the tile
formation 36, the edge portion 58 of tile 42 sits on a generally
horizontal ledge 60 which is part of the corresponding notch 56.
The manner in which the edge portion 58 is received and secured by
the notches 56 is best illustrated in FIG. 7. As can be seen,
surface 54 essentially extends around tile 40 and surrounds opening
48. The tiles 40, 42 of the tile formation 36 may be connected
together using well known conventional attachment devices. If the
tile formation 36 is mounted on a bottom wall of a furnace, tile 42
may simply rest on the seating structure 44. On the other hand, if
the tile formation 36 is mounted in some other position, tile 42
may be attached to tile 40 using elongated studs that are cast into
tile 42 at positions that correspond to the locations of the
notches 56. Stud receiving holes may then be provided to extend
downwardly through shoulder members 52 from the notches 56 to the
flange 33 where nuts may be used to secure the tiles 40, 42 to
flange 33 via the elongated studs.
[0043] With reference to FIGS. 3, 7 and 10, in the preferred
embodiment of the invention depicted in the drawings, tile 42 has
an annular body segment 62 that surrounds a central opening 64
thereof. The internal diameter of tile 42 is greater than the
external diameter of tile 40. Thus, as can particularly be seen in
FIG. 7, when tile 42 is mounted on tile 40, annular body segment 62
of tile 42 surrounds at least a portion of annular body segment 46
of tile 40. In particular, the lower edge portion 58 of annular
body segment 62 surrounds the upper frusto-conical portion 68 of
annular body segment 46. Thus, it can be seen that the annular body
segments 46 and 62 are arranged concentrically with the outer
annular surface 70 of the upper frusto-conical portion 68 of tile
40 spaced radially inwardly from the inner annular surface 72 of
lower edge portion 58 of tile 42. Manifestly, therefore, inner
surface or face 72 of tile 42 is disposed in a surrounding
relationship relative to frusto-conical portion 68 of tile 40.
[0044] When tile 42 is seated on tile 40 in an operational position
as shown in FIGS. 3 and 7, it can be seen that central opening 48
of tile 40 together with central opening 64 of tile 42 present a
passageway 74 defining a path 76 along which combustion air from
air box 30 is conducted into combustion zone 24. As can be seen
viewing FIGS. 3 and 7, passageway 74 is surrounded by the
respective annular body segments 46 and 62 of tiles 40 and 42 as
well as by annular face 72 (not seen in FIG. 3) which extends there
around.
[0045] As mentioned above, outer annular surface 70 of the upper
frusto-conical portion 68 of tile 40 is spaced radially inwardly
from the inner annular surface 72 of lower edge portion 58 of tile
42. Thus, surfaces 70 and 72 are disposed in spaced, facing
relationship relative to one another. The annular space 78 between
surfaces 70 and 72 (see FIG. 3) provides an annular or ring-shaped
RFG conduit 80 which intercommunicates air passageway 74 with the
area 34 which is adjacent combustion zone 24. Thus, RFG conduit 80,
which is defined between upper and lower tiles 40, 42, is in direct
communication with flue gases in the area 34 surrounding combustion
zone 24 so that combustion air flowing along path 76 is able to
induce a flow of flue gas from area 34 and through conduit 80 for
entrainment by the combustion air and dilution and cooling of the
gases combusting in combustion zone 24 to thereby reduce the
production of NO,. That is to say, the arrangement of the tiles 40,
42 is such that a flow of RFG from area 34 and through annular
space 78 is induced by the action of the combustion air flowing
along passageway 74 and through the openings 48 and 64. The
combustion air flowing past the downstream end 81 of conduit 80
creates a motive force for inducing a flow of RFG through conduit
80. Thus, the arrangement of the tiles provides an action much like
an eductor or an ejector. That is to say, the mass of combustion
air flowing in the direction of arrow 76 entrains RFG directly from
the area 34 in the interior of the firebox which surrounds the tile
assembly 20 of the invention. The RFG flows in the direction of the
arrows 85 from the area 34, through the ring-shaped conduit 80 and
past end 81 of the latter where it joins and is entrained by the
combustion air flowing along path 76. The mass of combustion air
flowing in the direction of the arrow 76 thus provides the motive
force for entraining the flue gases directly from the area 34 along
the path of the arrows 85 and delivering it to the outlet end 83 of
gas nozzle 82 where it is diffused and admixed with the combustion
mixture, thus slowing the rate of reaction of the fuel with oxygen
from the combustion air.
[0046] In accordance with the invention, the downstream tile 42 is
located around the upstream tile 40 so as to form the ring-shaped
conduit 80 which is open to the furnace gases in the interior of
the furnace. These furnace gases are able to interact with the air
flowing along path 76 through the center of tile 42 to create a
combined flow leaving the tile system of approximately 118% of
inlet air quantity (volume). This added furnace gas is swept around
the flame in combustion zone 24 slowing the diffusion of air into
the main flame in a very uniform and homogenous manner.
[0047] At this point it is to be noted that although tile 40 is
shown as having four shoulder members 52, the number actually
desired and/or required for a given application may vary depending
upon, for example, such things as the overall dimensions of the
tiles, the orientation of the assembly, the weight of tile 42
and/or the flow areas required for passageway 74 and conduit
80.
[0048] In the preferred embodiment of the invention illustrated in
FIGS. 1 through 10 of the drawings, burner assembly 20 may include
primary, secondary and tertiary fluid fuel burner nozzles. Primary
nozzle 82, which is illustrated particularly in FIGS. 3 and 7, is
surrounded by tiles 40 and 42 and is generally centrally located in
passageway 74, whereby an annular flow of combustion air is
directed past nozzle 82 in central opening 64. Accordingly, the
combustion air initially flows in a surrounding relationship
relative to the flow of fuel emanating from nozzle 82. Although the
nozzle 82 as shown is particularly adapted for delivering a gaseous
fuel to the combustion zone, it is to be understood that in
accordance with the concepts and principles of the invention,
nozzle 82 may be adapted for delivering either a liquid fuel, for
example a fuel oil, or a gaseous fuel, for example natural gas,
along a path which is generally parallel to path 76 to the
combustion zone.
[0049] In the preferred embodiment of the invention, burner
assembly 20 may also include a plurality, preferably four (4),
secondary burner nozzles or gas jets 84. These nozzles 84, which
are particularly illustrated in FIGS. 1, 3, 5 and 7, are disposed
adjacent the inlet 86 of RFG conduit 80 whereby fuel gas is admixed
with RFG. In addition, the gas emanating from nozzles 84 provides a
motive force for further inducing a flow of RFG from area 34. As
will be appreciated by those skilled in the burner art, there is
nothing critical about the number of nozzles 84, and for any given
application, the number thereof may vary from zero (0) to eight (8)
or more. However, when the assembly includes a multiplicity of such
secondary nozzles, the same should be spaced evenly about the outer
periphery of annular tile segment 46 as shown.
[0050] Burner assembly 20 may also include a plurality, preferably
four (4), tertiary burner nozzles or gas jets 88. These nozzles 88,
which are particularly illustrated in FIGS. 1, 3, 6 and 7, may
preferably be mounted in respective channels 90 provided in the
outer peripheral surface 92 of annular tile segment 62. Desirably,
the shoulder members 52 may be provided with end faces 94 which
provide support for the tubes 96 supplying fuel to nozzles 88. As
will once again be appreciated by those skilled in the burner art,
there is nothing critical about the number of nozzles 88, and for
any given application, the number thereof may vary from zero (0) to
eight (8) or more. However, when the assembly includes a
multiplicity of such tertiary nozzles, the same should be spaced
evenly about the outer periphery 92 of annular tile segment 62 as
shown.
SPECIFIC EXAMPLE
[0051] A specific example of the operation of a furnace using the
embodiment of the present invention described above and shown in
the FIGS. 1 through 10 of the drawings is as follows:
[0052] Burner is fired at 8.0 MMBtuh. Excess air is 15%. Furnace
temperature is 1500.degree. F. Burner differential pressure is 0.3
inches of H.sub.2O. Burner damper is fully opened. Combustible gas
is 100% natural gas. Single central fuel nozzle configuration. The
results obtained in the flue gas include 3% measured oxygen, 0 ppm
measured CO and approximately 20 to 35 ppm measured NO.sub.x.
[0053] In the foregoing description and specific example, the fuel
has been described principally as being fuel gas or natural gas. It
is to be noted in this regard, that the burner of the invention may
also be used effectively for reducing NO, emissions when burning
other fluid fuels, such as, for example, normally liquid fuels
including fuel oil or other gas blended fuels. It is also to be
noted that existing installations may be retrofitted so as to use
the principles and concepts of the present application.
[0054] As illustrated and described above, the burner assembly 20
of the invention includes primary, secondary and tertiary burners.
Alternative embodiments are illustrated schematically in FIGS. 11
through 16. In each case, the schematically shown tile formation
including concentric tiles may be essentially the same as the tiles
40 and 42 described above. As shown in FIG. 11, the illustrated
burner assembly may include only a single centrally located primary
burner nozzle. As shown in FIG. 12, the illustrated burner assembly
may include two or more burner nozzles located adjacent the outer
peripheral surface of the upstream tile near the inlet to the RFG
induction conduit. As shown in FIG. 13, the illustrated burner
assembly may include two or more burner nozzles located on the
internal surface of the central opening in the upstream tile
adjacent the RFG induction conduit. As shown in FIG. 14, the
illustrated burner assembly may include a centrally located primary
burner nozzle and two or more burner nozzles located on the outer
peripheral surface of the downstream tile. As shown in FIG. 15, the
burner assembly may include a single centrally located primary
burner nozzle that is equipped with a premixer and conventional
swirler mechanism. As shown in FIG. 16 the burner assembly may be
arranged essentially as described above in connection with FIGS. 1
through 10, except in this case the central burner nozzle is
particularly adapted for delivering a liquid fuel. In each case,
the flow of RFG from area 34 and through conduit 80 is induced by
combustion air flowing along path 76 past end 81 of the
conduit.
[0055] An alternative form of a burner arrangement which embodies
the concepts and principles of the invention is illustrated in
FIGS. 17 through 21 where the arrangement is identified broadly by
the reference numeral 120. The burner arrangement 120 is similar in
configuration to the burner arrangement 20 except for the manner in
which the upper tile 142 sits on the lower tile 140. This in turn
changes the configuration of the annular space 178 defined between
the tiles 140 and 142.
[0056] With reference to FIGS. 17 through 21, it can be seen that
the lower tile 140 includes a plurality of shoulder members 152
which project radially outwardly from the outer peripheral surface
154 of annular body segment 146. Together the upper surfaces 153 of
the members 152 provide a seating structure 144 for tile 142. To
this end, upper tile 142 is provided with a plurality of downwardly
projecting feet 159. In accordance with the invention, the number
of feet 159 on upper tile 142 corresponds with the number of
members 152 on lower tile 140, and as can be seen, the feet 159 are
positioned to sit on the upper surfaces 153 when the tiles are
assembled. With this arrangement, the lower edge portion 158 of the
upper tile 142 is spaced vertically from the upper edge portion 161
of the lower tile 140. Such spacing provides a configuration for
the annular space 178 which is different than the configuration of
the annular space 78 of burner assembly 20. This spacing also
changes the configuration of the path 185 provided for the flow of
flue gas from the interior of the furnace and into the central
passageway 174 within the tiles 140, 142. Such flow, of course, is
induced by the flow of combustion air along the path 176 as well as
by the flow of fuel gas from nozzles 184. Tile 142 may be attached
to tile 140 using conventional means, for example, studs extending
downwardly from feet 159 through stud receiving holes extending
through the shoulder members 152.
[0057] With reference to FIG. 19, it can be seen that the channels
190 are offset angularly relative to the shoulder members 152,
whereas, in the burner arrangement 20, the channels 90 are not
offset angularly relative to the shoulder members 52. In accordance
with the concepts and principles of the invention, the channels 190
are preferably offset 45.degree. relative to the shoulder members
152. This angular offset places the nozzles 184 in positions where
there is a minimum of structure to hinder the flow of fuel from the
nozzles 184 and into the annular space 178.
[0058] Another alternative form of a burner arrangement which
embodies the concepts and principles of the invention is
illustrated in FIG. 22 where the arrangement is identified broadly
by the reference numeral 220. The burner arrangement 220 is
essentially the same as the burner arrangement 120 except for the
placement of the burner nozzles 284 and the radial dimension of the
shoulder members 252. The arrangement of FIG. 22 facilitates the
employment of a burner which may be smaller in diameter than the
burner arrangement 120.
[0059] Yet another alternative form of a burner arrangement which
embodies the concepts and principles of the invention is
illustrated in FIG. 23, where the arrangement is identified broadly
by the reference numeral 320. The burner arrangement 320 is
essentially the same as the arrangement 120 described above except
for the general shape thereof which is rectangular rather than
circular. Components of arrangement 320 which correspond with
elements of arrangement 120 are designated using reference numerals
in the 300 series.
[0060] The burner arrangements of the present invention achieve low
NO.sub.x emissions, low noise, air entrainment of RFG, prompt
NO.sub.x alleviation, simplicity of construction, short flame
profile, high turndown ratios, high stability and low CO emissions.
Flow of RFG is induced without mechanical devices such as blowers
by using the combustion air as a motive force for entrainment of
RFG instead of fuel gas. In addition, the arrangement is such that
the secondary gas tips are located behind a burner tile so that jet
noise is shielded from the outside of the burner. Moreover,
diffusion of RFG directly from the interior of the furnace directly
into the gas jet prior to combustion results in reduction of prompt
NO.sub.x. The arrangement is simple resulting in low manufacturing
costs while providing ease of operation.
[0061] An important feature of the invention is the provision of a
non-powered means of supplying flue gas to a burner to reduce
NO.sub.x emissions and enhance mixing of combustion air, fuel gas
and RFG to facilitate homogeneity of the mixture. The burner
arrangement is based at least in part upon the important concept of
using the mass of the axially flowing combustion air to entrain RFG
from the furnace and mix it with the entering fuel gas in
sufficient amounts while ensuring that the mixture remains
combustible. As mentioned previously, the invention also
contemplates the use of both the mass of the axially flowing
combustion air and the mass of the fuel provided through gas jets
to entrain RFG from the furnace and mix it with the entering
fuel.
[0062] The impedance of combustion caused by the flue gas entering
the nozzle arrangement directly in accordance with the invention
lowers the flame temperature, thus inhibiting the formation and
emission of NO.sub.x. Prior to the design of the invention, only
small amounts of flue gas were entrained by individual gas jets
inspirating flue gases into the tile block. The old design proved
to be fairly inefficient with the stratification of flue gases
causing long flames and burner instability. The present invention
utilizes the energy of the large mass of flowing combustion air
leading to a greater mass of flue gas entrainment and consequent
more efficient mixing with the gas jet and flame. An important note
here is that the air induced flue gas entrainment is performed in
the furnace space and the flue gases are not required to go back
into the burner body as with some previous burner arrangements.
[0063] In the simplest configuration of the burner the flame is
ignited and stabilized in an oxidizing zone within the primary
tile. The flame envelope is quickly extended into the flue gas rich
secondary zone where NO.sub.x formation and emission is inhibited.
The flame envelope never loses stability as it enters the secondary
flue gas diluted zone as it is firmly anchored and defined in the
primary (oxidizing) zone contained in the primary tile section.
This rapid diffusion and rapid quenching without instability
conserves short flame lengths and large turndown ratios. Flame
lengths are typically 1.1 feet or less per million BTUs of firing
rate (fuel dependent) and turndown rates typical of natural draft
low NO.sub.x burners on the order of 10 to 1 may easily be
achieved. CO emissions are typically zero, but are somewhat
dependent upon furnace temperature.
[0064] Configurations of the burner of the invention other than as
shown in the drawings include staged fuel with either a gas gun
being utilized or with primary risers inserted into the ring-shaped
conduit for additional NO.sub.x abatement. When an annular primary
tile is utilized as shown in the drawings, the riser is shielded
from the outside of the burner by the primary tile greatly reducing
the jet noise emitted by the burner to the exterior. The primary
risers are set low enough in the ring-shaped conduit so that the
gas jet has sufficient time to entrain pure flue gas prior to
entering the oxidizing zone. This premixing of flue gas with the
combustion gas lowers the speed at which the combustion gas can
react thus additionally reducing the formation of NO.sub.x. Once
the gas jet starts to burn it does so in an atmosphere rich with
flue gas which is constantly being entrained by the combustion air.
The overall effect is ultra low NO.sub.x as both prompt and thermal
NO.sub.x are greatly reduced. The overall simplicity of the burner
combined with the stability achieved in the oxidizing zone make the
burner arrangements of the invention an important advance relative
to existing technologies.
* * * * *