U.S. patent application number 11/585473 was filed with the patent office on 2008-04-24 for low nox staged fuel injection burner for creating plug flow.
Invention is credited to Mahendra Ladharam Joshi, Xianming Jimmy Li, Aleksandar Georgi Slavejkov.
Application Number | 20080096146 11/585473 |
Document ID | / |
Family ID | 38920560 |
Filed Date | 2008-04-24 |
United States Patent
Application |
20080096146 |
Kind Code |
A1 |
Li; Xianming Jimmy ; et
al. |
April 24, 2008 |
Low NOx staged fuel injection burner for creating plug flow
Abstract
A burner for producing a plug-like flow and low NOx emissions.
The burner has a central air jet and plural staged fuel jets
surrounding the central jet. The ratio of the sum of the momentums
of vector components of the staged jets along respective axes
parallel to the central longitudinal axis of the central jet to the
momentum of the central jet along that axis is within the range of
0.5 to 1.5 and most preferably 0.8.
Inventors: |
Li; Xianming Jimmy;
(Orefield, PA) ; Joshi; Mahendra Ladharam; (Katy,
TX) ; Slavejkov; Aleksandar Georgi; (Allentown,
PA) |
Correspondence
Address: |
AIR PRODUCTS AND CHEMICALS, INC.;PATENT DEPARTMENT
7201 HAMILTON BOULEVARD
ALLENTOWN
PA
181951501
US
|
Family ID: |
38920560 |
Appl. No.: |
11/585473 |
Filed: |
October 24, 2006 |
Current U.S.
Class: |
431/9 ;
431/187 |
Current CPC
Class: |
F23D 14/48 20130101;
F23D 14/22 20130101; F23C 2201/20 20130101; F23C 2900/06043
20130101; F23D 14/58 20130101; F23D 23/00 20130101; F23D 2900/14003
20130101; F23C 6/045 20130101 |
Class at
Publication: |
431/9 ;
431/187 |
International
Class: |
F23C 7/00 20060101
F23C007/00 |
Claims
1. A staged fuel burner for establishing a plug-like flow in a
furnace, said staged burner comprising: a central nozzle and plural
staged nozzles, said central nozzle having an orifice for producing
a jet comprising air directed along a central longitudinal axis,
said staged nozzles surrounding said central nozzle, each of said
staged nozzles having at least one orifice for producing a staged
jet comprising fuel, each of said staged jets being directed along
a respective longitudinal axis and having a vector component in a
direction parallel to said central longitudinal axis, whereby the
sum of the momentums of said vector components of said staged jets
parallel to said central longitudinal axis is approximately 50% to
150% of the momentum of the central jet along said central
longitudinal axis.
2. The staged fuel burner of claim 1 wherein said sum of the
momentums of said vector components of said staged jets parallel to
said central longitudinal axis is approximately 80% to 100% of the
momentum of the central jet along said central longitudinal
axis.
3. The staged fuel burner of claim 2 wherein said sum of the
momentums of said vector components of said staged jets parallel to
said central longitudinal axis is approximately 80% of the momentum
of the central jet along said central longitudinal axis.
4. The staged fuel burner of claim 1 additionally comprising means
for supplying fuel to said staged nozzles and means for supplying
air to said central nozzle.
5. The staged fuel burner of claim 4 additionally comprising means
for supplying air to said staged nozzles, whereupon said staged
jets comprise fuel and air.
6. The staged fuel burner of claim 4 wherein said burner
additionally comprises means for supplying fuel to said central
nozzle.
7. (canceled)
8. The staged fuel burner of claim 1 wherein each orifice includes
a respective exit plane and wherein the ratio of the sum of the
momentums of the vector components of said staged jets parallel to
said central longitudinal axis to the momentum of the central jet
along said central longitudinal axis is a ratio (MR) defined by the
formula: MR = m . s , i V i cos .theta. i m . c V c ##EQU00002##
where {dot over (m)} is mass flow rate of the identified jet, V is
velocity of the identified jet at the exit plane of the orifice
from which the jet projects, .theta. is the included angle between
the central longitudinal axis and the respective longitudinal axes
of said staged nozzles, and the subscripts s, c, I represent
staged, central and i-th number of staged nozzles.
9. The staged fuel burner of claim 1 wherein said respective
longitudinal axes of said staged jets extend parallel to said
central longitudinal axis.
10. The staged fuel burner of claim 1 wherein said longitudinal
axis of at least one of said staged jets extends at an outward
diverging angle to said central longitudinal axis.
11. The staged fuel burner of claim 10 wherein said longitudinal
axes of all of said staged jets extends at an outward, diverging
angle to said central longitudinal axis.
12. The staged fuel burner of claim 1 wherein said longitudinal
axis of at least one of said staged jets extends San inward,
converging angle to said central longitudinal axis.
13. The staged fuel burner of claim 10 wherein said longitudinal of
all of said staged jets extends at an inward, converging angle to
said central longitudinal axis.
14. The staged fuel burner of claim 1 wherein said orifices of said
staged burners have a common exit plane.
15. The staged fuel burner of claim 14 wherein said orifice of said
central nozzle has an exit plane that is located forward of said
common exit plane of said staged burners.
16. The staged fuel burner of claim 14 wherein said orifice of said
central nozzle has an exit plane that is located rearward of said
common exit plane of said staged burners.
17. The staged fuel burner of claim 14 wherein said orifice of said
central nozzle has an exit plane that is coplanar with said common
exit plane of said staged burners.
18. The staged fuel burner of claim 1 wherein said orifices of said
staging nozzles are the same size and shape.
19. The staged fuel burner of claim 1 wherein said orifices of said
staging nozzles are different sizes and/or shapes.
20. A method of establishing a plug like flow of burning fuel in a
furnace comprising: (A) providing staged burner comprising a
central nozzle and plural staged nozzles surrounding said central
nozzle, said central nozzle having an orifice arranged for
producing a jet comprising air directed along a central
longitudinal axis, said staged nozzles surrounding said central
nozzle, each of said staged nozzles having at least one orifice and
arranged for producing a staged jet comprising fuel, each of said
staged jets being directed along a respective longitudinal axis and
having a vector component in a direction parallel to said central
longitudinal axis, (B) providing a fluid comprising air to said
central nozzle, whereupon said central nozzle produces a jet
comprising air directed along said central longitudinal axis, and
(C) providing a fluid comprising fuel to said staged nozzles,
whereupon said staged nozzles produce respective staged jets
comprising fuel along said respective longitudinal axes, whereby
the sum of the momentums of said vector components of said staged
jets parallel to said central longitudinal axis is approximately
50% to 150% of the momentum of the central jet along said central
longitudinal axis.
21. The method claim 20 wherein said sum of the momentums of said
vector components of said staged jets parallel to said central
longitudinal axis is approximately 80% to 100% of the momentum of
the central jet along said longitudinal axis.
22. The method of claim 21 wherein said sum of the momentums of
said vector components of said staged jets parallel to said central
longitudinal axis is approximately 80% of the momentum of the
central jet along said longitudinal axis.
23. The method of claim 20 additionally comprising supplying air to
said staged nozzles, whereupon said staged jets comprise fuel and
air.
24. The method of claim 20 wherein additionally comprising
supplying fuel to said central nozzle, whereupon said central jet
comprises air and fuel.
25. The method of claim 20 additionally comprising providing
combustion products to said central nozzle, whereupon said central
jet comprises air and combustion products.
26. The method of claim 20 wherein each orifice includes a
respective exit plane and wherein the ratio of the sum of the
momentums of the vector components of said staged jets parallel to
said central longitudinal axis to the momentum of said central jet
along said central longitudinal axis is a ratio (MR) defined by the
formula: MR = m . s , i V i cos .theta. i m . c V c ##EQU00003##
where {dot over (m)} is mass flow rate of the identified jet, V is
velocity of the identified jet at the exit plane of the orifice
from which the jet projects, .theta. is the included angle between
the central longitudinal axis and the respective longitudinal axes
of said staged nozzles, and the subscripts s, c, i represent
staged, central and i-th number of staged nozzles.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to burners for furnaces, and
in particular to staged burners for creating a plug-type flow
pattern with low nitrogen oxides (NOx) emissions.
[0002] Furnaces for ethylene cracking and other industrial
processes, e.g., steam-methane reformers, typically make use of
burners utilizing fuels such as natural gas, propane, hydrogen,
refinery off-gas and other fuel gas combinations of various
calorific values. For example, steam-methane reformer furnaces are
used to produce hydrogen and carbon monoxide by reforming a
hydrocarbon feed with steam and, at times, carbon dioxide at high
temperatures. The furnace used for steam-methane reforming can be
configured in several different structures. One of the most
conventionally used arrangements for such reformer furnaces has
vertical reformer tubes arranged in rows. The burners of the
furnace can be located on the furnace's floor, its ceiling or its
walls. As is known, operating a reformer tube above the desired
temperature can cause large decreases in tube life. This, in turn
will adversely affect the economics of the plant since the tubes
are a substantial portion of the overall cost of the plant and
require large expenditures of time and effort to replace one that
has failed. Tube hot spots can arise from undesirable furnace flow
patterns which cause flame impingement. This is particularly true
in a tightly packed furnace with relatively few rows of burners and
process tubes where the furnace geometry is such that the flue gas
extraction system causes flue gas to cross over the process tubes.
Needless to say any crossover within the flame zone should be
avoided to maintain equipment life and plant reliability. To that
end, establishing an appropriate flow pattern is critical to
uniform furnace heating and the concomitant reduction of process
tube overheating. Thus, one important criterion for the design of
burners where process tube overheating is a concern is to provide a
burner that will inherently create what is commonly referred to as
a plug-like flow.
[0003] Another important criterion for burner design is low NOx
emissions. As is known nitrogen oxides are among the primary air
pollutants emitted from combustion processes. NOx emissions have
been identified as contributing to the degradation of environment,
particularly degradation of air quality, formation of smog and acid
rain. As a result, air quality standards are being imposed by
various governmental agencies, which limit the amount of NOx gases
that may be emitted into the atmosphere. One common way of reducing
NOx emissions is by means of fuel/oxidant staging techniques, e.g.,
use of fuel staging burners making use of multiple jets outside and
surrounding a central air jet. Other techniques are known for
producing low NOx emissions from burners. The following are some
exemplary references pertinent to the field of low NOx burners:
U.S. Pat. No. 4,531,904 (Sato et al.), U.S. Pat. No. 4,946,382
(Kobayashi et al.) and U.S. Pat. No. 5,823,764 (Alberti et al.) and
U.S. Published application 2006/0040223A1 (Ghani et al.). All
references cited herein are incorporated herein by reference in
their entireties.
[0004] While the above mentioned prior art may be suitable for
their intended purposes, they nevertheless leave something to be
desired from the standpoint of creating a uniform or plug-like flow
with low NOx emissions.
BRIEF SUMMARY OF THE INVENTION
[0005] The subject invention constitutes a staged fuel burner for
establishing a plug-like flow, and is particularly useful in
furnaces, such as ethylene crackers, reformers, etc. The staged
burner comprises a central nozzle and plural staged nozzles. The
central nozzle has an orifice producing a jet of air directed along
a central longitudinal axis. The staged nozzles surround the
central nozzle and each has at least one orifice producing a staged
jet. Each staged jet comprises fuel, is directed along a respective
longitudinal axis from the nozzle and has a vector component in a
direction parallel to the central longitudinal axis. The sum of the
momentums of the vector components of the staged jets parallel to
the central longitudinal axis is approximately 50% to 150%
(preferably 100%, and most preferably 80%) of the momentum of the
central jet along the central longitudinal axis.
[0006] In accordance with another aspect of this invention there is
provided a method of establishing a plug like flow of burning fuel
in a furnace. The method entails providing a staged burner
comprising a central nozzle and plural staged nozzles surrounding
the central nozzle. The central nozzle has an orifice arranged for
producing a jet of air directed along a central longitudinal axis.
The staged nozzles surround the central nozzle and each has at
least one orifice arranged for producing a staged jet. Each staged
jet comprises fuel, is directed along a respective longitudinal
axis and has a vector component in a direction parallel to the
central longitudinal axis. Air is provided to the central nozzle,
whereupon the central nozzle produces a jet of air directed along
the central longitudinal axis. Fuel is provided to each of the
staged nozzles, whereupon each staged nozzles produces a respective
staged jet of fuel along a respective longitudinal axes. The sum of
the momentums of the vector components of the staged jets parallel
to the central longitudinal axis is approximately 50% to 150%
(preferably 100%, and most preferably 80%) of the momentum of the
central jet along the central longitudinal axis.
BRIEF DESCRIPTION SEVERAL VIEWS OF THE DRAWING
[0007] The invention will be described in conjunction with the
following drawings in which like reference numerals designate like
elements and wherein:
[0008] FIG. 1 is an end view of one exemplary embodiment of a
burner constructed in accordance with the subject invention;
[0009] FIG. 2 is a sectional view, not to scale, of the exemplary
burner taken along line 2-2 of FIG. 1;
[0010] FIG. 3A is a sectional view, similar to FIG. 2, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0011] FIG. 3B is a sectional view, similar to FIG. 3A, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0012] FIG. 3C is a sectional view, similar to FIG. 3A, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0013] FIG. 4A is a sectional view, similar to FIG. 2, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0014] FIG. 4B is a sectional view, similar to FIG. 4A, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0015] FIG. 4C is a sectional view, similar to FIG. 4A, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0016] FIG. 5A is a sectional view, similar to FIG. 2, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0017] FIG. 5B is a sectional view, similar to FIG. 5A, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0018] FIG. 5C is a sectional view, similar to FIG. 5A, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0019] FIG. 6A is a sectional view, similar to FIG. 2, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0020] FIG. 6B is a sectional view, similar to FIG. 6A, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0021] FIG. 6C is a sectional view, similar to FIG. 6A, of another
exemplary embodiment of a burner constructed in accordance with the
subject invention;
[0022] FIG. 7 is a sectional view, similar to FIG. 2, but showing
still other exemplary embodiments of a burner constructed in
accordance with the subject invention;
[0023] FIGS. 8A-8E are schematic diagrams of the arrangement and
shape of several different exemplary orifices of some exemplary
burners of the subject invention; and
[0024] FIGS. 9A-9I are enlarged end views of various shaped
orifices that can be used with the burners of the subject
invention;
DETAILED DESCRIPTION OF THE INVENTION
[0025] Referring now to FIG. 1 wherein like reference characters
refer to like parts there is shown at 20 one exemplary embodiment
of a staged fuel burner constructed in accordance with this
invention. That burner exhibits good plug flow characteristics and
low NOx emissions and is what is commonly referred to as a staged
burner. To that end, the burner 20 includes a central nozzle 22
that is surrounded by a plurality of staging or staged nozzles 24.
In the exemplary embodiment of FIG. 1 ten such staged nozzles 24-1
to 24-10 are provided. That arrangement is exemplary of a multitude
of burners that can be constructed in accordance with this
invention. In particular, burners constructed in accordance with
this invention can include any number of staged nozzles surrounding
the central nozzle. Each nozzle may include a single orifice or
plural orifices. Moreover, the orifices may be of any shape and
size, as will be seen later with reference to FIGS. 8A-8D and
9A-9I. In the exemplary embodiment shown in FIGS. 1 and 2 each
nozzle includes a single, circular shaped orifice 26. Each orifice
26 is arranged to produce a stream or jet of a fluid along a
longitudinal axis from the exit plane 28 of the orifice (i.e., the
plane at the downstream end of the orifice). Thus, the orifice 26
of the central nozzle produces a jet of air and, if desired some
fuel and/or combustion products, along the central longitudinal
axis of the burner. The air, fuel and/or combustion products are
provided to the central nozzle from means (not shown). The
direction of this "central jet" is shown by the arrow designated as
V.sub.c in FIG. 2. It should be pointed out at this juncture that
the direction of the central jet need not be parallel to the
central longitudinal axis of the burner, such as shown in FIG. 2,
but rather may extend at an angle thereto as shown in FIGS. 6A-6C
(to be described later).
[0026] Each of the orifices 26 of each of the staged nozzles of
burners constructed in accordance with this invention produces a
jet of fluid (a "staged jet"), which includes fuel and may, if
desired include some air and/or combustion products, along the
longitudinal axis of the orifice from its respective exit plane.
The fuel, air and/or combustion products are provided to the staged
nozzles from means (not shown). The staged jets can all be directed
in the same direction (e.g., parallel to the central longitudinal
axis, at a converging angle to the central longitudinal axis or at
a diverging angle to the central longitudinal axis) or can be
directed in different directions to one another. For example, in
the exemplary embodiment of FIGS. 1 and 2, four of the nozzles,
namely, 24-1, 24-4, 24-6 and 24-9 are each directed at an inwardly
converging angle to an axis 30 that is parallel to the longitudinal
axis 32 of the central nozzle 22, while the other six nozzles 24-2,
24-3, 24-5, 24-7, 24-8 and 24-10 are each directed parallel to the
longitudinal axis 32 of the central nozzle 22. In FIG. 2 the jet
produced by the orifice of the nozzle 24-1 is shown by the arrow
designated as V.sub.1, and it extends at an angle .theta..sub.1 to
the axis 30, while the jet produced by the orifice of the nozzle
24-7 is shown by the arrow designated as V.sub.7 and extends
parallel to the longitudinal central axis.
[0027] As best seen in FIG. 2, all of the staged nozzles 24-1 to
24-10 of the burner 20 are disposed equidistantly from one another
about the central nozzle 22. Moreover, the exit plane of the
orifices of the staged nozzles 24-1 to 24-10 is located rearward of
the exit plane 28 of the orifice 26 making up the central nozzle
22. This arrangement is also merely exemplary of many arrangements
of the position of the nozzles of burners constructed in accordance
with this invention. Thus, the staged nozzles 24 need not be
equidistantly spaced from one another. Moreover, the relative
position of the exit plane of the orifice of the central nozzle to
the orifices of the staged nozzles need not be like shown in FIG.
2. For example, as shown in FIGS. 4A-4C the exit planes of the
orifices 26 of all of the burner's nozzles can be in the same
plane. Alternatively, as shown in FIGS. 5A-5C the exit planes of
the orifices 26 making up the staged nozzles can be located forward
of the exit plane of the orifice of the central nozzle. In fact, it
is contemplated that different orifices have different exit planes
than other orifices. Further still, the number of staged nozzles
used in any given burner is also matter of design choice, depending
upon the application for the burner. Thus, burners constructed in
accordance with this invention may include any number of plural
staged nozzles extending about the central nozzle. Further yet, the
radial distance of each staged nozzle from the central longitudinal
axis of the burner need not be the same. Accordingly, one or more
staged nozzles 24 can be at a greater or lesser radial distance
from the central longitudinal axis 32 than another staged
nozzle.
[0028] Irrespective of the arrangement, number, size and direction
of the nozzles/orifices, there exists a critical burner design
parameter which causes a drastic change in the overall furnace flow
pattern, much like laminar-to-turbulent transitions. This design
parameter is the momentum ratio (hereinafter sometimes referred to
as "MR") of the staged jets 24 to the central jet 22. In
particular, it has been found that when a burner 20 is constructed
so that the sum of the momentums of the staged jets is nearly equal
to momentum of the central jet, an even or plug-like flow profile
is observed. Most preferably this ratio is 0.8 (i.e., the sum of
the momentums of the staged jets is 80% of the momentum of the
central jet). However, it has been determined that plug-type flow
can be achieved if the ratio is within the range 0.5 to 1.5 (i.e.,
50% to 150%).
[0029] Turning again to FIG. 2, the momentum of the central jet
produced by the nozzle 22 of the burner 20 is designated by {dot
over (m)}.sub.c, while the momentum of each of the surrounding
staged jets produced by the nozzles 24-1 to 24-10 is designated by
{dot over (m)}.sub.s,i where s designates that the momentum is of a
staged jet and i represents the particular staging jet, e.g., in
the embodiment shown in FIG. 2 i="7" since the staging jet is that
produced by the orifice making up the nozzle 24-7.
[0030] As mentioned above, the staged jets need not be all directed
along axes parallel to the longitudinal axis of the central jet. In
fact, in the exemplary preferred embodiment, shown in FIGS. 1 and 2
some staged jets, namely, the jets produced from the nozzles 24-1,
24-4, 24- 6 and 24-9, extend at an inwardly converging angle to the
longitudinal axis of the central jet. The other of the staged jets,
namely, the jets produced by nozzles 24-2, 24-3, 24-5, 24-7, 24-8
and 24-10, extend parallel to the longitudinal central axis of the
central jet. Thus, the momentum ratio exhibited by burners
constructed in accordance with this invention takes into account
angularly directed jets. In particular, the momentum ratio produced
by burners of this invention is the ratio of the combined momentums
of the components of the staging jets that are directed parallel to
the longitudinal axis of the central jet to the momentum of the
central jet. As is well known, momentum is the product of mass flow
and jet velocity and is a vector in the direction of the velocity.
Here the jet velocity is the mean or average velocity based on the
actual stream thermodynamic state (as defined by temperature,
pressure, composition, etc.) at the point of exit from the orifice
producing the jet and the area of the orifice through which the jet
will pass, e.g., the area of the exit plane 28 of the jet's orifice
26. For staged fuel jets, this velocity can be readily determined,
e.g., calculated based on the orifice area and the pressure at
design rate measured during testing or in operation. For the
central jet, the velocity is based on the area of the orifice and
the combustion air temperature, or the burner opening into the
furnace and the adiabatic flame temperature of the combustion air
and the primary fuel, whichever is higher. Numerically, MR is
defined by the following formula:
MR = m . s , i V i cos .theta. i m . c V c ##EQU00001##
where {dot over (m)} is mass flow rate of the identified jet, V is
velocity of the identified jet at the exit plane of the orifice
from which the jet projects, .theta. is the included angle between
the central longitudinal axis and the longitudinal axes of the
staged nozzles, and the subscripts s, c, i represent staged,
central and i-th number of staged nozzles, because the burner
includes multiple staged jets whose orifices have longitudinal axes
which may extend at different angles to the central longitudinal
axis of the central nozzle.
[0031] It has been observed that a smaller MR ratio means lower
staged fuel fraction and the burner resembles more closely a single
central jet. The flame is dominated by the center air jet, and a
narrow flame ensues. When such burners are used in a typical
furnace, the space between the flame produced thereby and the
process tubes or the wall of the furnace will be filled by
recirculating flue gas. A slight perturbation can cause the flame
to touch the process tubes. In the limit, the burner is represented
by a single point source. Because the point source has a high
velocity, but the neighboring firing wall has zero velocity, the
velocity differential and the resultant pressure difference create
recirculation zones next to the jet, which become the origin of a
large scale recirculation zone in the furnace.
[0032] As the MR ratio increases, more fuel is staged, and the
burner gets farther away from a single central jet. When the MR
ratio gets to approximately unity, the fuel (staged) jets and air
(central) jet have similar momentums. The combined fuel and air
jets from the burner have the best opportunity to develop a
plug-type flow pattern and maintain the forward direction down the
burner axis. If the MR is too large, the flame resembles a hollow
jet and will collapse inward to the center and become short and
bushy. Such flames tend to overheat the process tubes near the
burners.
[0033] A desired flame must balance the forward projecting power of
a large air jet at the center and the heat release capacity of the
fuel (staged) jets surrounding it. As was mentioned earlier, this
balance manifests in this form as a momentum ratio close to one,
with a ratio of 0.8 being optimum. Near the optimal MR ratio, the
combined central air jet and staging jets attain pressure balance
and produce a flame, which when used in a furnace proceeds in a
straight line along the firing axis. While the flow will tend to
change direction and cross the process tubes, at some point (e.g.,
due to the flue gas extraction system) such action occurs at a
sufficient distance from the burner so that the furnace gas
temperature at the point where it crosses the process tubes is
sufficiently low that overheating of the process tubes does not
present a hazard. The plug flow in the combustion zone prevents
flame impingement on the process tubes and discourages the
formation of a large scale high temperature recirculation zone. As
long as the combustion is complete, the combustion gases can go
wherever they prefer without causing process tube overheating. The
plug flow enables higher heat release intensity per cubic foot of
combustion space without tube overheating. The elimination of the
high temperature recirculation zone also reduces NOx emissions,
since the formation of NOx is proportional to both temperature and
retention time. The lower temperature also increases tube and
catalyst life, and reduces soot formation in the process tubes.
[0034] In FIG. 3A there is shown an alternative burner constructed
in accordance with this invention. This embodiment is similar to
the embodiment of FIG. 2, except that all of the staged nozzles are
directed so that their orifices 26 create staged jets extending
parallel to the longitudinal axis 32 of the central nozzle 22.
Thus, in the interest of brevity the common components of the
embodiments of FIGS. 2 and 3 will be given the same reference
designations. As can be seen the burner of FIG. 3 has a central
nozzle 22 that produces a central jet whose direction of flow is
shown by the arrow designated as V.sub.c while the two staged
nozzles 24-1 and 24-2 shown produce respective staged jets shown by
the arrows designated as V.sub.1 and V.sub.2. In FIG. 3B there is
shown another alternative burner constructed in accordance with
this invention. That burner is similar in construction to the
burner shown in FIG. 3A except that its staged nozzles are directed
so that the orifice of each creates a staged jet extending at an
inwardly converging angle .theta. to an axis 30 that is parallel to
the longitudinal axis 32 of the central nozzle 22. The direction of
the jets from the orifices of the staged nozzles in FIG. 3B are
shown by the arrows designated as V.sub.1 and V.sub.2. The other
details of the construction of the burner of FIG. 3B are similar to
the details of the burner of FIG. 3A and hence are given the same
reference designations and will not be reiterated herein. In FIG.
3C there is shown another alternative burner constructed in
accordance with this invention. That burner is similar in
construction to the burner shown in FIG. 3A except that its staged
nozzles are directed so that the orifice of each creates a staged
jet extending at an outwardly diverging angle .theta. to an axis 30
that is parallel to the longitudinal axis of the central nozzle 22.
The direction of the jets from the orifices of the staged nozzles
in FIG. 3C are shown by the arrows designated as V.sub.1 and
V.sub.2. The other details of the construction of the burner of
FIG. 3C are similar to the details of the burner of FIG. 3A and
hence are given the same reference designations and will not be
reiterated herein.
[0035] FIGS. 4A-4C show further embodiments of burners constructed
in accordance with this invention. The embodiments of FIGS. 4A-4C
are similar to the embodiments of FIGS. 3A-3C, respectively, except
that the exit planes of the orifices of all of the nozzles are
coplanar. Thus, in the interest of brevity the common components of
the embodiments of FIGS. 4A, 4B and 4C and FIGS. 3A, 3B and 3C,
respectively, will be given the same reference designations and no
further discussion of the details of the construction of the
burners will be given.
[0036] FIGS. 5A-5C show further embodiments of burners constructed
in accordance with this invention. The embodiments of FIGS. 5A-5C
are similar to the embodiments of FIGS. 3A-3C, respectively, except
that the exit planes of the orifices of the staged nozzles are
coplanar and located forward of the exit plane of the orifice of
the central nozzle. Thus, in the interest of brevity the common
components of the embodiments of FIGS. 5A, 5B and 5C and FIGS. 3A,
3B and 3C, respectively, will be given the same reference
designations and no further discussion of the details of the
construction of the burners will be given.
[0037] FIGS. 6A-6C show further embodiments of burners constructed
in accordance with this invention. The embodiments of FIGS. 6A-6C
are similar to the embodiments of FIGS. 4A-4C, respectively, except
that the central nozzle and its orifice extend at an angle to the
central longitudinal axis 32 of the burner so that the central jet
extends at that angle as shown by the arrow designated V.sub.c.
Thus, in the interest of brevity the common components of the
embodiments of FIGS. 5A, 5B and 5C and FIGS. 4A, 4B and 4C,
respectively, will be given the same reference designations and no
further discussion of the details of the construction of the
burners will be given.
[0038] FIG. 7 shows still a further exemplary embodiment of a
burner constructed in accordance with this invention. FIG. 7 is
similar to FIGS. 4B and 4C, except that its staged nozzles extend
at different angles to each other. In particular, one staged nozzle
24-1 extends at an inwardly converging angle .theta..sub.1 to an
axis 30 that is parallel to the longitudinal axis of the central
nozzle 22, while another staged nozzle 24-2 extends at an outwardly
converging angle .theta..sub.2 to an axis 30 that is parallel to
the longitudinal axis of the central nozzle 22.
[0039] As mentioned earlier the orifice(s) making up the central
nozzle and/or any of the staged nozzles can be of any shape or
size. For example, as shown in FIG. 8A the central nozzle 22 can
have a single orifice 26 of circular cross section and be
surrounded by four staged nozzles 24-1, 24-2, 24-3 and 24-4. Each
of the staged nozzles has a single circular shaped orifice 26,
whose diameter is substantially smaller than the diameter of the
central orifice. Moreover, the orifices 24-1, 24-2, 24-3 and 24-4
are equidistantly spaced from each other and equidistantly spaced
from the central orifice. In FIG. 8B there is shown another nozzle
arrangement. This arrangement is similar to the arrangement of FIG.
8A, except that the central nozzle includes a square shaped orifice
26. In FIG. 8C there is shown another nozzle arrangement. This
arrangement is similar to the arrangement of FIG. 8A, except that
the central nozzle includes a hexagonal shaped orifice 26. FIG. 8D
shows another nozzle arrangement. This arrangement is similar to
the arrangement of FIG. 8A, except that the central nozzle includes
a rectangular shaped orifice 26. FIGS. 9A-9H show various other
shapes for orifices that can be used in burners of this invention,
such as the circular orifice of FIG. 9A, the square orifice of FIG.
9B, the hexagonal orifice of FIG. 9C, the rectangular orifice of
FIG. 9D, the multi-cross slotted orifice of FIG. 9E, the cruciform
orifice of FIG. 9F, and the two cross slotted orifice of FIG. 9G.
FIG. 9H shows a nozzle which can be the central nozzle 22 or any or
all of the staged nozzles 24, where the nozzle has three circular
shaped orifices 26 arranged in a triangular array in the lower half
of the nozzle. FIG. 9I shows a nozzle which can be the central
nozzle 22 or any or all of the staged nozzles 24, where the nozzle
has two circular shaped orifices 26 arranged in a linear array in
the lower half of the nozzle. It must be pointed out at this
juncture that the orifices and nozzles shown herein are merely a
few examples of a myriad of shapes and sizes that can be used in
burners constructed in accordance with this invention.
[0040] As should be appreciated by those skilled in the art the
burners of the subject invention has particular utility for use in
furnaces. However, its use is not limited to such applications.
When used in furnaces the burners of the subject invention will
eliminate the high temperature recirculation zone by creating a
plug flow like flow pattern. With the high temperature
recirculation zone eliminated, a higher firing rate can be
maintained. Furthermore, the process tubes of a furnace making use
of burners constructed in accordance with the subject invention
will have an extended life due to the lower and even surrounding
temperature. The lower temperature will also decrease the soot
formation and increase catalyst life. Finally, since NOx formation
is proportional to temperature, eliminating hot spots will decrease
NOx emissions.
[0041] While the invention has been described in detail and with
reference to specific examples thereof, it will be apparent to one
skilled in the art that various changes and modifications can be
made therein without departing from the spirit and scope
thereof.
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