Note: Descriptions are shown in the official language in which they were submitted.
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H-TIP
LOW NOX FORr~ATION FU~L BURNING MErr~ODS AND APPARATUS
Background of the Invention
1. Fie d of the Invention
The present invention relates yenerally to methods and
burner apparatus for combusting fuel-air mixture.s, and more
particularly, to rnethods and burner apparatus for combusting
fuel and air while inhibiting the Eormation of nitrogen
oxides.
2. Description of the Prior Art
A variety of rnethods and burner apparatus for combusting
fuel and air ~ixtures have been developed and utilized
heretofore. Such burner apparatus are used in a great
variety of applications where fuel is co~busted to provide
heat for a particular purpose, e.g., heating process
s-treams, generating steam, drying materials, etc. The
burning of fuels, however, can result in the formation of
nitrogen oxides (NOX) whicn when released to the a-tmosphere
constitute pollutants. As a result, environ~ental emission
standards have been imposed by various governmental
authorities and agencies which require the inhibition of the
formation of nitrogen oxides during fuel-air combustion.
Various methods and burner apparatus for combusting
fuel-air mixtures while suppressing the formation of
nitrogen oxides have been developed. For example, United
States Patent No. 4,004,875 issued January 25, 1977~ is
directed to a low NOX burner wherein the fuel is first
burned in a zone in which there is less than a
stoichiometric concentration of air thereby producing a
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reducing environ-rnent that suppresses NOx formation wit~ the
deficiency in air being made up in a subsequent burning
~one.
Fuel staging has atso been employed Eor suppressing
NOx formation. That is, a portion of the uel is burned in
a first zone with air bein~ supplied at a rate in excess of
the stolchiometric rate required with the remaining fuel
being burned in a second zone. The presence of excess air
in the first zone lowers the temperatura o~ the combustion
reaction and suppresses NOx formation. The fuel in the
second zone reacts with the excess oxygen resulting from the
co~bustion in the first zone and is diluted with surrounding
co~bustion gases which lowers the combustion reaction
temperature and suppresses the formation of NOx in the
second zone. A multi-stage combustion method of -this type
is described in United States Patent No. 4,395,223 issued
3uly 26, 1983.
While methods and burner apparatus u-tili~ing staged
~ombustion have been successful in reducing NOx e~nissions
heretofore, the methods have required elaborate burner
apparatus to carry out, i.e., apparatus including a
plurality of fuel nozzles and/or complex air or recycle gas
distribution systems making the apparatus expensive to
install and operate.
By the presen-t invention improved methods and burner
a~paratus for combusting fuel-air mixtures while inhibiting
the formation of nitroyen oxides are provided which are
simple and inexpensive as compared to prior art methods and
apparatus.
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Summary of the Invention
Methods of combusting fuel-air mixtures whereby the
Eormation of nitrogen oxides is inhibited are provided. In
accordance with the methods, fuel is discharged ~rom a
nozzle disposed within a burner housin~, air is'introduced
into the housing which is mixed with the fuel and the
resulting fuel-air rnixture is ignited and cornbusted. A
first portion of the fuel is discharged from the nozzle
through one or more orifices therein whereby the fuel mixes
with air and provides an igni-tion zone adjacent the nozzle.
A second portion of the fuel is discharged Erom the nozzle
by way of one or more additional orifices whereby the second
portion of fuel is distributed in a turbulent pattern which
exposes the uel to a quantity of air in excess of that
required Eor the stoichiometric burning thereof and causes
the fuel to burn in a primary col~bustion zone. The
remaining portion of the fuel is dlscharged froln the nozzle
by way of one or more additional orifices whereby the fuel
is distributed wit`nin and downstream of the primary combus-
tion zone. The remaining portion of fuel is mixed withexcess air from the primary cornbustion zone and combustion
products and is burned in a secondary co~bustion zone
substantially shielded from direct contact with incoming air
by the primary combustion zone. ~urner apparatus for
carrying Ollt the methods are also provided.
It is, therefore, a general object of the present
invention to provide low NOX for~ation fuel burning ~nethods
and apparatus.
A further object oE the present invention is the
provision of improved me-thods oE cornbusting fuel-air
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mixtures whereby the Eor~ation of nitroyen oxides is
inhibited which can be carried Ollt in relatively simple and
inexpensive burner apparatus.
Another vbject of the present invention is the provision
of i~proved burner apparatus for cornbusting fuel-air
mixture~s while inhibiting the for~ation of nitroyen oxides.
other and further objects, features and advantages of
the present invention will be readily apparent to those
skilled in the art upon a raading of the description of
preferred embodiments which follows when taken in
conjunction with the accompanying drawings.
Brief Description Of The Drawings
FIGURE l is a slde cross-sectional view of the low
NOX for~ation fuel burning apparatus of the present
invention.
FIGURE 2 is a top plan view of the apparatus of FIGURE
1.
FIGURE 3 is an enlarged partly sectional view of a
portion of the apparatus of FIGU~E 1 includin-~ the fuel
discharge nozæle thereof.
FIGURE 4 is a top plan view of the apparatus of FIGVRE
3.
FIGURE 5 is a side cross-sectional view of the burner
apparatus of FIGURE 1 illustrating the operation of the
apparatus.
~escription Of Preferred Embodiments
Referring now to the drawings and particularly to
FIGI]RES l and 2, a burner apparatus of the present invention
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is illustrated and generally designated by the numeral lO.
The burner apparatus lO is shown connected in an c~pening 1~
provided in the floor or wall 12 of a furnace chamber such
as the furnace chamber of a process heater containing heat
S exchange tubes or a steam generator. The burner apparatus
lO is designecl Eor use in applications where gaseous fuels
such as hydrocarbon gases are combusted. However, it will
be appreciated by those skilled in the art that burner
apparatus includin~ the present invention can take a variety
of forms.
The burner lO includes a housin~ which is comprised of
an external cylindrical ~ousing member 16 attached over the
opening 14 in the wall 12, such as by a plurality of bolt
members 18, and a heat resistant me~ber 20 formed of
refractory material mounted within the furnace cha~nber
defined by the wall 12. The interior oE the wall 12
includes an insulating layer of refractory material 22 in
which an opening is formed for receiviny the member 20 oE
the burner lO. The member 20 can he attached to the wall 12
and/or refractory material 22 oE the furnace chamber as
illustrated or it can be attached to the cylindrical housing
member 16 in any convenient manner.
The housing member 16 functions as an air re~ister, and
for this purpose, includes a plurality of air inlet openin~s
26 disposed in and around the sides thereof. ~ wall 24
closes the end of the housing member 16 and a cylindrical
damper 28 is rotatably positioned over the housing member.
The damper 28 includes air openings (not shown) therein
complementary to the air openings 26 in the housing member
30 15. A handle 30 is attached to the damper 28 so that the
4~ 3
damper can be rotated be-tween a position whereby the
openings 26 are closed by solid portions of the damper 28
and a position ~hereby the openings in the damper 28 are in
reyistration with the openlngs 26 to provide full air flow
as shown in FIGURE 1.
~ guide tube 32 is disposed coa~ially within the
cylindrical housing member 16, the outer end of which is
riyidly attached throuf~h an opening in the wall 24, such as
by welding. The inner end of the guide tube 32 has a
shieldin~ cone 34 attached thereto. A fuel supply conduit
36 extends through the guide tube 32 and has a fuel
discharge nozzle 38 connected at the inner end thereof. The
exterior end of the conduit 36 is threaded for connection to
a source of fuel and the condui-t 36 is sealingly at-tached to
a plate 39 which is in turn removably connected by means of
bolt members 40 to the wall 24.
A pilot 42 is provided for igniting fuel discharged fro~
the noæzle 38 and is connected to a supply conduit 44 which
in turn extends throu~h an opening in the wall 24 and a
re~ovable closure member 46 connected thereto. The outer
end of the su~ply conduit 44 is connected to a pilot fuel-
air mixer 48 which is in turn adapted for connection to a
source of pilot fuel.
Referring now to FIG~RES 3 and 4, the Euel dlscharge
noz21e 38, shielding cone 34 and related structure are
illustrated in detail. The shieldin.~ cone 34 is dish-shaped
and includes a plurality of openin,ls 50 formed therein for
allowing the passage oE a limited amount oE air
therethrough. The shielding cone 3~ functions to create a
protected space adjacent the nozzle 38 when incoming air is
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flowing in the direction indicated by the arrow 52 of FIGURE
3~ As will be understood, the creation of a pro-tected space
adjacent the nozzle 38 can be brought about by various types
and shapes of apparatus other than the shielding cone 34.
The nozzle 38 extends through a central opening in the
shielding cone 34 and includes an end wall 54 which contains
a plurality of Euel discharge orifices. More particularly,
the wall portion 54 of the nozzle 38 includes a first set o~
one or more orifices 56 disposed therein. When more than
one orifice 56 are utilized, they preferably all are the
same size and are positioned in equally spaced relationship
around the nozzle 38 in a plane preferably perpendicular to
the a~is of -the nozzle 38, i.e., the angle designated by the
letter "c" on FIGU~E 3 is 2referably 90. The axis of the
lS nozzle 38 is parallel to the a~is of the housing member 16
whereby the axes of the orifices 56 lie in a plane
substantially perpendicular to the direction of air flow
through the housin~ meTnber 16. The first set of orifices 56
discharge a first portion of the fuel supplied to the nozzle
38 which mixes with a 2ortion of the incoming air and
provides an ignition zone adjacent the nozzle 38 as will be
described further hereinbelow. The shielding cone 3~
provides a protected space adjacent the nozzle 38 which
prevents the i~nition zone frorn being moved away from the
nozzle 38, i.e., the shielding cone retains an ignition
flame adjacent the nozzle 38.
A second set of one or ~ore orifices 58 is disposed in
the wall portion 54 of -the nozzle 38. When more than one
orifice 58 are utili2ed, they preferably are all of the same
size and are positioned in equally spaced relationship
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around the wall 54 interiorly of and above the iynition
orifices 56. The axes of the oriEices 58 are also
preferably inclined in the direction of flow of air at an
angle in the range of from abou-t 15 to about 70 therewith,
i.e., the axes of -the oriEices 58 are all preferably
positioned at the same angle with respect to the axis of the
nozzle 38 (the angle designated by the letter "b" in FIGURE
3) which is in the range given above. The second set of
orifices 58 discharge a second portion of the fuel supplied
to the nozzle 38 which is distributed in a turbulent
outwardly flaring pattern. The second portion of fuel mixes
with the reMaining incoming air -~hich is in excess of that
required for the stoichiometric burning thereof and burns in
a primary combustion zone.
~ third set of one or ~ore oriEices 60 is disposed in
the wall portion 54 of the nozz~e 38 interiorly of and above
the primary combustion oriEices 58. Like the oriEices 56
and 58, when more than one orifice 60 are utilized, they are
preferably all of -the same size and are positioned in spaced
relationship around the nozzle 38. The axes of the oriEices
60 can be parallel to the axis of the noæzle 38 and to the
direction of air flow, or, as shown in FIGURE 3, the axes of
the orifices 60 can be inclined at an anyle in the range of
from about 1 to about 30 therewith (the anyle "a" shown on
FIGURE 3). It should be noted that anyle "a" can be about
equal to or less than the angle "b", but should not be
greater than the anyle "b".
The orifices 60 discharge the re~aining portion of fuel
supplied to the nozzle 38 therefrom whereby substantially
all of the remaining portion of Euel is burned in a
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secondary combustion zone within and downstream of the
primary combustlon zone created by the discharge of the
second portion of fuel from the orifices 58.
Referring now to FIGURE 5, :Ln operation of the burner
appara-tus 10, fuel under pressure, i.e., a pressure
generally in the range of from about about 3 to about 30
psig., is supplied to the condui-t 36. Pilot fuel at a
pressure in the range of from about 3 to about 15 psig. is
supplied to the air mixer 4~. The pilot fuel is mixed wi-th
air while flowing through the mixer 48 and the resul-ting
fuel-air mixture is discharged Erorn the pilot 42, ignited
and burned. The flame from tAe pilot functions to ignite
-the fuel discharged from the nozzle 38. However, it is to
be noted that other ignition means can be utilized and the
use of a pilot burner is optional.
The pressurized fuel suppliad to the condui-t 36 flows to
the nozzle 38 connected thereto and is discharged in-to the
furnace chamber through the orifices 56, 58 and 60 therein.
The first set of orifices, i.e., the ignition orifices 56,
are of a size and/or number whereby the first portion of
fuel discharged therethrough is a rate in the range of from
about 1~ to about 25~ of the total rate of fuel discharged
from the nozzle 38. Such portion of the fuel mixes with air
in the protected space adjacent the nozzle 38, is ignited by
the flame frorn the pilot 42 or other means and burns in an
ignition zone 62 adjacent the shieldiny cone 34 and nozzle
38.
The second set of orifices, i.e., the primary co~bus-tion
orifices 58, are of a size and/or number such that a second
portion of fuel is discharged therethrough at a rate in the
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ran~e o~ from about 1~ to about 60~ of the total rate o:E
fuel discharged from the nozzle 38. The second portion of
fuel i9 dis-tributed in an outwardly Elarin~ pattern from the
nozzle 38 in a turbulent manner which causes the fuel to mix
with air flowing into the housing of the burner 10 by way of
the openings 26 in the housing rnember 16 thereoE. The rate
oE air flowing into the burner 10 is adjusted by adjusting
the position of the damper 28 on the housin3 merrlber 16
whereby the total amoun-t of air is substantially equal to or
greater than that required for the s-toichiometric burning of
the total rate of fuel discharged from the nozzle 38. The
second portion of fuel and air mixture produced is combusted
in a primary combustion zone 64 which flares outwardly from
the nozzla 38. Because the second portion of fuel is mixed
with air in excess of that required for the stoichio-metric
burning of the fuel, the temperature in the primary
corabustion zone 64 is lowered and the formation of NO~ in
the primary co(nbustion zone is inhibited.
The remaining porton of the fuel supplied to the nozzle
3~ is dischar~ed therefrom by way of the third set of
orifices therein, i.e., the secondary combustion ori-fices
60. The portion of the fuel discharged through the orifices
is distributed wlthin and downstream of the primary
combustion zone 64 into a secondary cornbustion zone 66 which
is substantially shielded from direct contact with inco-ming
air by the primary combustion zone 6~. The fuel in the
secondary combustion zone is mixed with air from the primary
combustion zone which is diluted with combustion products
from the primary combus-tion zone~
Thus, because the remaining portion of fuel discharged
through the secondary cornbustion orifices 60 is burned in a
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secondary combustion zone 6~ within and downstream of the
primary combustion zone 64, and because the air mixed with
such remaining portion of fuel i5 diluted with combustion
producks, the combustion -takes place at a relatively low
S temperature whereby the formation of NOX is inhibited.
The method of the present invention whereby fuel can be
discharged frorn a single nozzle or two or more nozzles and
burned wlth low NOX formation is comprised oE the steps of
discharging a first portion of euel fro~ each nozzle through
one or more orifices, or a set of orifices therein, whereby
the Euel mixes with air and provides an ignition zone
adjacent the nozzle; discharging a second portion of the
Euel through one or more additional ori~ices, or a second
set of oriEices therein, whereby the second portion of fuel
is distributed ~in a turbulent pattern which causes the fuel
to mix wi~h a rate of air in excess of tha-t required for the
stoichio~etric burnin~ thereof and to burn in a primary
combustion zone; and discharging the remaining portion of
the fuel from the nozzle through one or more additional
orifices, or a third set of orifices therein, whereby the
relnaining portion of the fuel is distributed within and
downstream of the primary cornbustion zone wherein i-t is
mixed with air frorn the primary combustion zone which is
diluted with combustion products from the primary cornbustion
zone. The resulting mixture of fuel and combustion product
diluted air is burned in the secondary cornbustion zone.
As men-tioned above, because the combuskion in the
primary cornbustion zone takes place in e~cess air, -the flame
temperature in such zone is lowered whereby the formation of
NOX is inhibited. Combustion in the secondary combustion
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zone is delayed because the secondary combustion zone is
shielded by the pri~ary zone from direct contact with
incoming air. This delay in the mixing of the fuel and air
allows for dilution of the air with corQbustion products from
the primary combustion zons, resulting in a lower co~bustion
temperature which inhihits the for~ation of NOX in the
secondary combustion zone.
While the present invention has been described as it
relates to a natural draEt burner apparatus, it is to be
understood that the inven-tion is applicable to a wide
variety of burner designs, including those utilizing forced
draft. In additionr more than one fuel discharge nozzle of
the presen-t invention can be utilized in a single burner
apparatus, as for example, the burner apparatus disclosed in
15 U.S~ Patent No. 3,033,273 issued on r~ay 8, 1362. Further,
the fuel discharge nozzls and shielding cone utilized in
burners in accordance with this invention can take various
forms and shapes so long as the functional li~itations
described above are ~et thereby.
In order to facilitate a clear understanding of th~
method and apparatus of the present invention, the following
example is ~iven.
Example
A burner apparatus 10 designed for a heat release oE
6,000,000 BTU/hr by burning natural gas having a calorific
value of 930 BTU/SC~ is firsd into a furnace char~ber. The
nozzle 38 includes a first set of 6 orifices 56 of 0.0625
inch diameter, a second set of 4 orifices 58 of 0.1405 inch
30 dia~eter and a third set of 4 orifices 60 of 0.1875 inch
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dia~eter. The axes of the oriEices 56 are at an angle of
90 with the axis of the nozzle 38, the axes of the orifices
58 are at an angle of 4~ with the axis of the nozzle 38 and
the axes of the oriEices 60 are at an angle of 10
therewith.
The fuel is supplied -to the nozzle 3~ at a pressure oE
about 15 psiq. and at a rate of about 6452 SCF/hr. The
first portion o fuel discharged through the ignition
nozzles 56 is at a rate of about 596 ~CF/hr., the second
portion of fuel discharged through the primary co~bus-tion
orifices 5~ is at a rate of about 1986 SCF/hr. and the
remaining portion of fuel discharged through the secondary
coinbustion oriEices 60 is at a rate oE about 3870 SC~/hr.
The discharged Euel is co~bined witn air in the burner
apparatus 10 and burned whereby a heat release in the
furnace chamber of about 6,000,~00 ~TU/hr. is realized. ~he
stack emissions from the simulated furnace chamber contain
an NOX concentration of less than about 40 pprn. A
conventional burner including a conven-tional nozzle fired in
the furnace chamber in the same manner and under the same
conditions creates stack emissions containing an
NOX concentration of more thar- about 70 ppm.
Thus, the present invention is well adapted to carry out
the objects and attain the advantages mentioned as well as
those inherent therein. While ~resently preferred
embodiments of the invention have been described herein for
purposes oE this disclosure, numerous changes in the
construction of parts and in the arrangenent of parts and
steps will suggest themselves to those skilled in the art,
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which changes are encompassed wi-thin the spiri-t of this
invention as defined by the appended claims.
~hat is claimed i5:
n
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