U.S. patent number 3,574,507 [Application Number 04/846,548] was granted by the patent office on 1971-04-13 for air/fuel mixing and flame-stabilizing device for fluid fuel burners.
This patent grant is currently assigned to General Electric Company. Invention is credited to Paul H. Kydd.
United States Patent |
3,574,507 |
Kydd |
April 13, 1971 |
AIR/FUEL MIXING AND FLAME-STABILIZING DEVICE FOR FLUID FUEL
BURNERS
Abstract
Baffle means are located in the paths of fluid fuel streams
issuing at high velocity from a plurality of jet orifices in an
elongate burner pipe. These downstream baffles significantly
laterally deflect the fuel streams and result in both the promotion
of fuel/air mixing and the provision of low-velocity
flame-stabilizing regions.
Inventors: |
Kydd; Paul H. (Scotia, NY) |
Assignee: |
General Electric Company
(N/A)
|
Family
ID: |
25298252 |
Appl.
No.: |
04/846,548 |
Filed: |
July 31, 1969 |
Current U.S.
Class: |
431/350; 60/749;
432/222 |
Current CPC
Class: |
F23D
14/20 (20130101) |
Current International
Class: |
F23D
14/20 (20060101); F23D 14/00 (20060101); F23d
013/24 () |
Field of
Search: |
;60/39.72 ;431/350
;263/19 (A)/ |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dority, Jr.; Carroll B.
Claims
I claim:
1. In an apparatus for heating a gas stream by the combustion of
fluid fuel wherein the gas stream supports the combustion process
and flows past the burner construction at velocities of the order
of 1,500 to 6,000 f.p.m., fluid fuel is emitted from the burner,
mixes with the gas stream, is burned and thereby heats the gas
stream, the improvement comprising:
a. a hollow elongate burner body;
b. a row of spaced fuel orifices extending along and penetrating
the wall of said burner body on the downstream portion of said
wall;
c. at least one baffle strip located downstream of said burner
body, mounted spaced therefrom and supported thereby having as
opposite major surfaces thereof:
1. an upstream imperforate laterally extending major surface area
facing and in register with each of said orifices for laterally
spreading all fluid fuel flow impinging thereon into the adjacent
high-velocity airflow for passage around said baffle strip; and
2. a downstream laterally extending major surface area facing
downstream from said orifices for maintaining thereon a physically
unconfined low-velocity flame-stabilizing region, said baffle strip
extending substantial distances transversely to the direction in
which fuel flow emanates from said burner body.
2. The improvement recited in claim 1 in which the baffle strip
extends along the burner body in a wavy configuration and is
connected directly thereto.
3. The improvement recited in claim 1 in which a separate baffle
strip is mounted over each fuel orifice.
4. The improvement recited in claim 3 in which a plurality of
baffle strips are connected to a pair of wing structures extending
along and attached to the burner body, said wing structures having
apertures therethrough for the passage of air.
5. The improvement recited in claim 1 in which the downstream major
surface area is at least about three-fourth inch in least
dimension.
Description
BACKGROUND OF THE INVENTION
The use of fluid fuel burners broadly encompasses two types of
application: (a) equipment in which the amount of air admitted to
the combustion system is at most only slightly larger than that
required to sustain combustion and (b) systems in which the flow of
air admitted to the combustion system is considerably in excess of
the amount required to sustain combustion and the object is to
raise the temperature of the flow. Gas burners for firing
industrial and domestic heating equipment is an example of the
first type of application, while the burner for a fired exhaust
heat-recovery steam generator (used in conjunction with a gas
turbine) is an example of the second type of application.
This invention is primarily of interest for the latter type of
application and, when the term "air" is employed herein, both
normal air and oxygen-containing gas streams are encompassed.
The problems encountered with the latter type of burner application
differ in many respects from those encountered in the former type.
Examples of difficult, but desirable, conditions to achieve and
maintain in the presence of grossly excessive airflows are: (a)
operating with a short flame length (about 1-2 feet) with jet
orifices having diameters in excess of 0.050 inches; (b) providing
acceptable fuel/air mixing; (c) operating with positive flame
retention and stable combustion at air velocities from 1,500 to
6,000 f.p.m., and (d) adjusting to a wide range of fuel flows.
One example of prior-art solutions to the above problems is
described in U.S. Pat. No. 3,051,464, Yeo et al., wherein an array
of spaced air jets is provided adjacent a gas supply means, the air
jets having varying air-supplying capacity such that a greater or
lesser portion of the air jet array contributes to the combustion
depending upon the amount of gas supplied. The air jets are located
in at least one mixing wall flanking the gas supply means. Flame
retention is accomplished by the provision of shielded eddy pockets
adjacent certain ports for the discharge of gaseous fuel, called
ignitor ports, as distinguished from main gas ports. These eddy
pockets are in part defined by projections, which extend into paths
of the fuel gas streams leaving the ignitor ports, but not the main
gas ports from which the gas streams flow unimpeded. As described
in the Yeo et al. specification, it is necessary to supply various
raw gas or gas/air mixtures to the burner to vary the stage of
operation. For example, at "high fire operation" either raw gas or
a rich gas/air mixture is supplied. For "minimum and low rates of
operation" the burner ports are supplied with a combustible mixture
of gas and air containing all or substantially all the air required
for combustion. This requirement of premixing of fuel gas and air
poses a distinct problem. It is inconvenient to mix fuel gas and
external air for admission to a burner and fuel cannot be mixed
with hot air sources, such as hot turbine exhaust air.
In contrast to the Yeo et al. mixture, which is used for fluid
fuel-burning operations in the presence of great excesses of air,
U.S. Pat. No. 3,037,553, Jackson, describes a gas burner for
heating equipment specifically designed to operate without any
excess flow of air and to provide for close proportioning of the
air/gas mixture. Unaerated gas jet streams exiting at high velocity
from the burner pipes strike a gas-impingement structure consisting
of bars disposed within an air injection duct. This combined
structure is provided to break up the gas jet streams and aerate
the gas. The air injection duct permits the ejected gas to induce
the proper airflow for combustion to pass therethrough and is
apparently relied upon to provide a zone of relatively low-velocity
flow for gas ignition and flame propagation. Although the gas jet
streams are high-velocity flows, the airstream must not have any
significant velocity, because of the construction disclosed.
Therefore, there is no indication that the combination of
gas-impingement and air-injection duct structures would function in
the presence of high-velocity airflows. Further, this combined
structure is not suitable for use in applications in which a wide
range of fuel flows and fuel jet velocities are encountered.
What is needed in the art is a mechanically simple and rugged
burner construction with a turndown ratio of at least 5:1 with
which unaerated fluid fuel may be burned with a short, nonluminous
flame with positive flame retention in the presence of great
excesses of air having velocities ranging up to 6,000 f.p.m.
SUMMARY OF THE INVENTION
The instant invention solves the above-mentioned need and, in
addition, enables the utilization of larger fuel jet orifices
having diameters in the 0.050 inches--0.150 inches range, thereby
increasing the capability of the burner to combust "dirty" fuel, a
major problem in the field. These objectives are attained by
placing flame-holding baffle structures of significant lateral
dimension downstream of the jet orifices to provide significant
lateral deflection of each fluid fuel stream whereby the desired
fuel/air mixing is achieved and a low-velocity flame-stabilizing
region is provided thereover for each flame. In addition, the
lateral spread of the baffles into the airstream provides a more
uniform flame temperature distribution.
BRIEF DESCRIPTION OF THE DRAWING
The exact nature of this invention as well as objects and
advantages thereof will be readily apparent from consideration of
the following specification relating to the annexed drawing in
which:
FIG. 1 is a perspective view showing a single burner element with a
pair of flame-holder wings affixed thereto representative of the
prior art;
FIG. 2 is an elevational view of the preferred construction of the
gas burner/flame-holder unit of the instant invention;
FIG. 3 is a sectional view taken on line 3-3 of FIG. 2;
FIG. 4 is a plan view of a modification of the prior-art gas burner
device to embody the flame holders of the instant invention;
FIG. 5 is a sectional view taken on line 5-5 of FIG. 4; and
FIG. 6 is a sectional view through an array of the burners of FIGS.
2, 3 showing the flame profiles and low-velocity regions provided
by the instant invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A single prior-art burner/flame-holder unit 10 is shown in FIG. 1,
which in its simplest construction includes hollow cylindrical tube
11 closed at one end by cap 12 and open at the opposite end thereof
for connection to a source (not shown) of fluid fuel, such as gas
or vaporized oil. A typical mounting plate arrangement 13 is
employed to mount the burner unit 10 so that it projects into a
combustion chamber.
Jet orifices, or ports, 14 located at intervals along the length of
fuel tube 11 admit fluid fuel into the trough-shaped mixing space
16 defined by diverging flame-holder webs 17, 18 provided with a
plurality of apertures 19, 21, respectively, spaced longitudinally
thereof. Apertures 19, 21 direct air from the passing stream into
mixing volume 16 in distinct jets providing a multitude of small
"combustors" distributed along the burner length.
It has been shown that by replacing the flame-holder wings 17, 18
of the prior-art burner 10 (FIG. 1) with s single undulating metal
strip 31 extending along fuel tube 32 (FIGS. 2 and 3) and welded
(or otherwise attached) to the top of tube 32, a more effective
burner unit is produced. The points of attachment 33 are located
midway between fuel orifices 34 with flame-holder strip 31 arched
over each orifice 34 as shown. This distance s and h may each vary
from about 2 inches to about 6 inches. The width w of flame-holder
strip 31 will range from about three-fourths inch to about 11/2
inches and the orifice size may range from about 0.050--0.150
inches in diameter.
These relatively large orifice diameters facilitate the utilization
of gaseous or vaporized fuels containing such impurities as
particulate matter and substances, which would form soot in the
fuel tubes 32, if not passed by the orifices. Ordinarily, such
large orifice sizes must be avoided, because the discharged fuel is
not adequately mixed with the air before it is burned. With the
construction in FIGS. 2 and 3 each issuing stream of fuel is
deflected as it impinges upon wavy flame-holder strip 31 being
forced to move laterally a significant distance in order to pass
beyond flame holder 31. In traversing this path the fuel becomes
thoroughly mixed with the air streaming by tube 32 as may be seen
in FIG. 6.
In addition to promoting mixing of the fuel with air, strips 31
provide low-velocity wake regions 36 along most of the upper
surface thereof in which the flame can stabilize, while the lateral
spread of the burning gas regions 37 results in a more uniform
flame temperature distribution. The strips 31 must provide an
imperforate transversely extending width of at least three-fourth
inches in order to produce a large enough wake for flame
stabilization.
The spacing center-to-center of fuel tubes 32 (FIG. 6) may range
from about 9inches--18 inches. Using such an arrangement the flames
remain stabilized in the presence of airflows ranging as high as
6,000 f.p.s. to produce increases in air temperature as required
ranging from 100.degree. to as high as 1,000.degree. F. or even
higher. There is, of course, no need to induce airflow and the
cooling effect of the airflow minimizes oxidation of the
flame-holder strips 31.
A second embodiment is shown in FIGS. 4 and 5 wherein the prior-art
wing structures 41, 42 are relied upon, not as flame holders, but
as supports for the transversely extending spaced baffle flame
holders 43 arching over the fuel orifices 44 in fuel tube 46. In
the construction shown, an added set of wing apertures 47, 48 is
located in the space between adjacent flame holders 43, but the
critical aspect of this invention is the juxtaposition of flame
holders 43 and fuel orifices 44, whereby the emerging gaseous or
vaporized fuel strikes the undersurface of the bafflelike flame
holder and is deflected laterally to each side in order to continue
on its way.
Low-velocity regions (not shown) occur over the upper surfaces of
flame holders 43 in the same manner as is illustrated in FIG. 6 for
the simpler preferred construction of FIGS. 2 and 3 and flame
stabilization results in the same manner. The distance from orifice
44 to the underside of flame holder 43 may be 11/2 inches-- 3
inches. With this distance set at the higher end of this range
greater mixing between air and fuel can occur before impingement on
the baffle 43. Conversely with this distance set at the lower end
of this range, less air/fuel mixing can occur.
The burner construction of this invention may be disposed in the
airstream with the fuel tube extending vertically, horizontally or
at some other desired angle to the horizontal so long as the
orifice side of the fuel tube faces downstream.
The invention has particular applicability to a heat-recovery steam
generator used in conjunction with a gas turbine wherein a bank, or
banks, of burners according to this invention are disposed in a
stack or duct-receiving exhaust gases from the gas turbine. The
purpose of the burner system, which must operate under a wide range
of conditions, is to raise the temperature of the large flow of
turbine exhaust air through a controlled temperature rise and
provide a uniform temperature in the discharged airflow.
Although all baffles shown are rectangular in transverse section,
they could be formed as V-shaped (or convex) in cross section so
long as the point of the V-shape (or the convex surface) is placed
upstream. The imperforate transverse dimension seen by the gas flow
must, of course, remain at least about three-fourth inch in order
to provide the minimum size wake for flame stabilization and to
give the added benefit of lateral spreading of the hot gases.
* * * * *