Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTI ON
This invention relates generally to a burner assembly
and ~n~re particlllarly tc~ an improved burnex a5semb1y which
operates in a manner to reduce the for~nation o nitrogen ox~des
as a result of fuel c:ombustion.
Considerable attention and efforts haYe recently been
directPd to the reduction of nitrogen oxides resulting from th
cosnl~ustion o fuel,.and especia~ly ir~ connec:tion wi~h t~e ~;e o:~
coal an ~he furl~ace sectio~s of relatiYely large install a~ orls-
10 such . a.s vapor generators and ~he li3ce. I~ a ~ypical arrang~
., . , . . , . ~or burning coal in a ~apor g~erator, se~eral bu~ ers are dis-
posed in co~ i ca~ion wlth the irlterior of ~he fuxrlac~ a~d operate
to burn a-mixture of air and pul~rerized coal. The burners used
in these arrangemen~s are y~nerally o the type in whic~ a fuel
air mixture is con~inuously ~njected ~hrough a nozzle so as ~o
form a.single re1ativPly.lar~e f~ame. As a result, the surface
ara~ of ~he fl~me is relativel~ small in compar~son to its
volumeO and therefore the average flame ~mperature is relatively
high~ ~owever, in the burning of coal, nitrosen oxides are formed
by the rixation o~ atmospheri~ nitrogen available in the com-
bustion supporting air, which is a function of the flame
temperatu~e. When the flame temperature exceeds 2800F, th~
amount of fixed nikrogen removed from the combustion supporting
air xises exponentially with increasPs in the temperature. This
condition leads to the p~oduction of high levels of nitrogen
oxides in the final combustion products, which causes severe air
pollution proble~s.
Nitroyen oxides are also formed fro~ the fuel bound
nitrogen available in the fuel itself, which is not a direct
function o the flame tempe.rature, but is related to the quantity
of available oxygen during the combustion process.
--2--
:~"
In view of the foregoing~ attempts have been made to
suppress the burner and flame temperatures and reduce the
quantity of available oxygen during the combustion process
and thus reduce the formation of nitrogen oxides. Attempted
solutions have included techniques involving two stage
combustion, flue gas recirculation, the introduction of an
oxygen-deficient fuel-air mixture to the burner and the
breaking up of a single large flama into a plurality of
smaller flames. However, although these attempts singularly
may produce some beneficial results they have not resulted
in a reduction of nitrogen oxides to minimum levels. Also,
these attempts have often resulted in added expense in terms
of increased construction costs and have led to other related
problems such as the production of soot and the like.
SUMMARY OF THE INVENTION
The present invention seeks to provide a burner assembly
which operates in a m~nner to considexably reduce the product~
ion of nitrogen oxides in the combustion of fuel without any
significant increase in cost ox other related problems, and
in which the surface area of the flame per unit volume is
increased which results in a greater flame radiation, a
lower flame temperature, and a shorter residence time of
the gas component within the flame at maximum temperature.
The invention in one aspect pertains to a burner
assembly comprising means defining an annular passage with
an inlet located at one end of the annular passage for
receiving fuel and an outlet located at the other end of the
passage for discharging the fuel. Means disposed within the
annular passage split up the fuel discharging from the opening
so that upcn ignition of the fuel, a plurality of flame
patterns are formed. A register assembly is associated with
the burner, the register assembly comprising an enclosure
extending over the annular passage for receiving air. Means
for directing the air from the enclosure towards the outlet
~3--
~7~
in two parallel paths extends around the annular passage and
register means respectively are disposed in each of the paths
for regulating the quantity o~ air flowing through the paths.
The invention in another aspect comprehends a burner
assembly comprising means defining an annular passage with
an inlet located at one end of the annular passage for re-
ceiving fuel and an outlet located at the other end of the
passage for discharging the fuel through the opening and into
the furnace. Means disposed within the annular passage split
up the fuel discharging from the opening so that upon ignition
of the fuel, a plurality of flame patterns are formed. An
enclosure extends around the annular passage for receiving
air and a sleeve is movable across the inlet to the enclosure
to vary the size of the inlet and the quantity of air entering
the enclosure, the air flowing towards the outlet mixing with
the fuel.
Still further~ the invention herein comprehends a
burner assembly comprising an inner tubular member with an
outer tubular member extending around the inner tubular
member in a coaxial relation thereto to define an annular
passage. An inlet is located at one end of the annular
passage Eor receiving fuel and an outlet is located at the
other end of the passage for discharging the fuel through
the opening into the furnace. A plurality of blocks extend
in a circumferentially spaced relationship in the annular
passage, one end of each of the bl~ck extending in the outlet,
and the other end of the blocks having a curved surface again-
st which the fuel impinges. The curved surfaces direct the
fuel into the spaces between the blocks for splitting up the
fuel discharging from the opening so that upon ignition of
the fuel, a pluxality of flame patterns are ~ormed. The blocks
extend between the tubular members and are tapered in a
direction from the outer tubular member to the inner tubular
member.
-4--
L3
More particularly, the burner assembly as disclosed
herein includes an annular passage having an inlet located
at one end thereof for receiving fuel, and an outlet located
at the other end of the passage for discharging the fuel.
A plurality of members are disposed in the path of the
outer stream for splitting up the stream so thatl upon
ignition of the fuel, a plurality of flame patterns are
formed. Secondary air is directed towards the outlet in
two parallel paths extending around the burner, and a
plurality of register vanes are disposed in each of
the paths for regulating the quantity and swirl of the
air flowing through the paths. According to an alternative
embodiment, a divider cone. is disposed within the annular
passage for dividing the stream of fuel passing through
the passage into two parallel coaxial streams and additional
secondary air is introduced into the outer stream.
-4a-
~7~g~3
BRIEF DESCRIPTION OF THF DRAWINGS
Fig. 1 is a sectional view depicting the burner
assembly of the present invention;
Fig. 2 is a partial perspective view of a component
of the burner assembly of Fig. l;
Fig. 3 is an enlarged elevational view, partially
cut-away, of the burner portion of the assembly of -the
present invention;
Fig~ 4 is a perspective view of a component of the
burner portion of Fig. 3;
Fig. 5 is a sectional view depicting the burner
assembly according to an alternative embodiment of
the present invention;
Fig. 6 is an enlarged elevational view, partially
cut-away, of the nozzle of the assembly of Fig. 5;
Fig. 7 is a ~ront elevational view of the nozzle
of FigO 6; and
Fig. 8 is a longitudinal cross-sectional view of the
nozzle of Fig. 6.
20DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring in general to the embodiment of Figs.
1~4 of the drawings and specifically to Fig. 1, the reference
--5--
43
nurneral lO refers in general to a burner assembly which is
disposed i~ axial alignment with a through opening 12 forrned
in a front wall 14 of a conventional fuxnace. It is understood
that the furnace includes a back wall and side walls of an
appropriate configuration to define a combustion chamber 16
immediately adjacent the opening 12. Also similar openings
are provided in the furnace front wall 14 ~or accommodating
additional burner assemblies identical to the burner assembly
lO. The inner surface of the wall 14 as well as the other
walls of ~he furnace are lined within an appropriate thermal
insulation material 18 and, while not specifically shown, it
is understood that the combustion chamber lS can also be
lined with vertically extending boiler tubes through which a
heat exchange fluid, such as water, is circulated in a
conventional manner for the purposes of producing steam.
It is also understood that a vertical wall is disposed
in a spaced parallel relationship with the furnace wall 14
in a direction opposite that of the furnace opening 12 along
with correspondingly spaced top, ~ottom and side walls to
form a plenum chamber, or wind box, for receiving combustion
supporting air, commonly referred to as "secondary air", in
a conventional manner.
The burner assembly lO includes a noæzle 20 having an
inner tubular member 22 and an outer tubular member 24. The
outer tubular member 24 extends over ~he inner tubular
member 22 in a coaxial, spaced rela~ionship thereto to
define an annular passage 26 which extends towards the
furnace opening 12.
~ ~7~3
I
A tangentially disp~sed inle~ 28 co~ unica~es with the
outer tubular member 24 for introduc:irg a stream of fuel
into the annular passage 26 as will be explained in further
detail ~ater.
~ pair af spaced annular pla~es 30 and 32 extend arour~d,
the b-~lrner 20, with the inner edge of the plate 3û t~ofm;n~ting
on the . outer tubular n~PTr~3er 24 . A ~i~er ~her 34 ext~ds
, ~ . . . , , . : .
rom; -khe inner edge ol~ the pla~e 32 - and in a general lorlgit
direc~ior~ relataYe ~o ~e burner 20 and ~ min~ es a~ac:e~t
the ~sulatio~ matexial 18 jtlSt ;nci~le ~he wall 14. . A~ .
additional an~ula~ plate 38 ex.~,e~ds around {:he buI~er-20 :i~.:
a spàced, psra~lel ~elat~on wi ~ ~he plate 30. A~ air
di~ider sleeve 40 eætends fro~ the inner surf~ce o~ th@
.
plate 38 and between ~he liner 34 and t~e nozzle 20 in a
substan~ialiy paralle~ relatio~ to ~he burner 20 in a sub- -
stantially parallel relation to the burner 20 and the li~er
34 ~o defin~ two air flow p~ssages 42 and 44~
A plurality o ou~ex regis~er vanes d6 are pi~otally
moun~ed between the plates 30 and 32 t~ contro~ the swirl of
secondaxy air ~rom the wind box to ~he air flow passages 42
~nd 44. In a 5i~;1 ~r m~nner a plurali~y o~ inner register
Yanes 48 are pivo.ally moun~ed between the plates 30 and 38
to further regulate the swirl of ~he secondary air passing
through the annular pas~age ~4, Xt is understood ~hat
although only two regîs~er vanes 4 6 and 4 8 are shown 1 n ~ig O
l, several more vanes extend in a circumferentially spaced
relation to the vanes shown. Also, the pivotal mo~mtirlg of
the register vanes 46 and 48 may be done in 2ny conven~ional .
manner, such as by mounting the vanes on shafts tshown-
schematically in Fig. 1~ and journalling the shafts in
proper bearings formed in the plate-~ 30, 3~ and 38. Also,
the position of the vanes 46 and ~8 may be adjustable by
means of cr~n~s or the like. Sir.ce these ty?es of compon~
ents arc conventional they are no~ shown in the drawings nor
~:ill be described in any ft~rthex (~e! ail.
The quantity of air flow from the wind box into the
register vanes 46 is controlled by movement of a sleeve 50
which is slidably disposed on the outer periphery of the plate
32 and is movable parallel to the longitudinal axis of the burner
burner nozzle 20. An elongated worm gear 52 is provided for mov~
ing the sleeve 50 and is better shown in Fig. ~. The worm gear
52 has one end portion s~litably connected to an appropriate drive
maans (not shown~ for rotating the worm gear and the other end pro-
vided with threads 52a~ The worm gear 52 extends through a bushin~
54 (Fig. 1) which is attached to the plate 30 to provide rotatable
support. The threads 52a of the worm gear 52 mesh with appropriate
apertures 55 formed in the sleeve 50 so that, upon rotation o the
worm gear, the sleeve moves longitudinally with respect to the
longitudinal axis o the burner 20 and across the air inlet defined
by the plates 30 and 32. In this manner, the quantity of combus~
tion supporting air from the wind box passing through the wind box
passages 42 and 44 can be controlled by axial displacement of the
sleeve 50. A perforated air hood 58 extends between the plate~
30 and 32 immediately downstream of the slee~e 50 to permit the
air flow to th~ burner 20 to be independently determined by means
of static pressure differential movements, in a conventional
ma~ner.
As shown in Fig. 3, which depicts the details of the burner
nozzle 20, the end portion of the outer tubular me~ber 24 and the
corresponding end portion of the inner tubular member 22 are
tapered slightly radially inwardly toward the furnace open-
ing 12. A plurality of divider blocks 60 are circumferentially
spaced in the annular space between the tubular members 22 and
24 in the outlet end portion of the burner. As shown in FigO 3,
four such blocks are spaced at 90 intervals and extend from the
outlet to a point approximately midway the tapered portions
of the members 22 and 24. The side portion of the blocks 60
are curved to complement the corresponcirg curved surfaces
of the tubular members 22 and 24 and t-e blocks are tapered
--8--
radially inwardlyO As shown .in Figure 4q.the leading end
portion of each block 60 is configured in a curved xelation~
ship s~ tha~ the fuel ~lowing in the passage 26 and impinging
ayainst the lead~ng ends of the bloc~s 60 will be directed into
the adjacent spaces de~ined be~ween the blocks to facilitate ~h~
splitting of ~h~ ~uel stxeam in~o four separate streams.
In opexation of th~ burner assembly of ~he present inven-
tion, the movable sle~ve 50 associated with each burner is
ad~usted during ini~ial start up to accurately k~l~n~e the air
t~ each burner. After ~he initial b~l~n~ing~ no fur~he~ move-
ment of ~he slee~es 5U are needed since ~orm~l ~o~ oi o~ the .
.
seconA~ry air to ~he b~rners is accomplished by operakion of
~he outer register vanes 46.
. Fuel, preferab~y in the ~m o pulverized coal suspended
or entrained within a source of primary air~ îs introduced
into the tangential inlet 28 where it swirls through the
annular chamber 26 and is ignited by suitable igniters (no~ ~
shown~ appropriately positioned with respect to the burner
nozzle 20. The stream of.fuel and air enc~untexs the blocks
- 60 at the end portion of the nozzle 20 whereby ~he 5tream is
split into f our equally spaced streams which, upon ignition,
form four separate flame patte~ns. The igniters are shut of~
after s~eady state combustion has been achieved and secondary
air from the wind box is admitted through the perforated hood
58 and into the inlet between the plates 30 a~d 32. The axial
and radial velocities of the air is con~rolled by the register
vanes 46 and 48 as it passes through the air flow passage 42
and 44 and into the furnace opening 12 for mixing with the
fuel from the burner 2 0 .
As a result of the foregoing, several advantages result
from the burner assembly of the p-esent invention. For e.Yample,
since the pressure drop across th~ ~erforated air hoods 58 asso-
ciated with burne~ assemblies ca~. be e~ualized by balancing
_ g _
~7~3
the secondary air f 1QW to each burner by initially adjusting
the sleeves 50, a subs~antially uniform gas distribution can
be obtained across the fur~ace. This also permits a common
wind box to be used and enables the unit to operate at lower
excess air with sisnificant reductions in both nitrogen
oxides and carbon monoxides. Also, the provision of separate
register vanes 46 and 48 fo~ the outer and inner ai~ flow
passages 42 and 44 enables secondary air distribution as
well as flame shape to be indepe~dently controlled resulting
in a significant reduction of nitrogen oxides, and a more
gradual mixing of the primary air coal stream with the
secondary air since both streams enter the furnace on parallel
paths with controlled mixing.
Further, the provision of multiple flame patterns
results in a greater flame radiation, a lower average flame
temperature and a shorter residence time of the gas com-
ponents within the rlame at a m~; mllm tempera~ure, all of
which, as stated abo~e, contribute to r~duce the formation
of nitric oxides.
Also, the use of the curved surface 60a on the blocks
results in a more streamline ~low of the fuel stream before
it discharges from the outlet of the nozzle 20. Still
further, the provision of the tangential inlet 26 ~rovides
excellent distribution of the fuel around the annular space
26 in the burner 20 resulting in more complete combustion
and reduction of carbon loss and making it possible to use
individual burners with capacities significantly higher than
otherwise could be used.
--10--
7~3
An alternative embodiment o~ the present invention is
depicted in Figs. 5 8. Referring specifically to Fig. 5 the
reerence numeral 110 refers in general to a burner assembly
which is dispo~ed in axial alignment with a throuyh opening
112 formed in a front wall 114 o~ a conventional furnace.
It is understood that the furnace includes a back wall and a
side wall of an appropriate configuration to define a
combustion chAmh~r 116 ; ~ ely adjacent ~he ope~ing 112.
Also, similar openings are provided in the furnace front
wall 114 for accommodating additional burner assemblies
identical to the burner assembly 10. The inner surface of
the wall 114 as well as the other walls of the furnace are
lined within an appropriate thermal insulation material 118
and, while not specifically shown, it is understood that the
combustion chamber 116 can also be lined with boiler tubes
through which a heat ex~hange fluid, such as water is
circulated in a conventional manner ~or the purposes of
producing steam.
It is also understood that a vertical wall is disposed
in a parallel relationship with the furnace wall 14 along
with connecting top, bottom, and side walls to form a plenum
ch?mher, or wind box, for receiving combustion supporting
air, commonly referred to as "secondary air", in a convention~l
manner.
The burne~ assembly 110 includes a nozzle 120 having an
inner tubular member 122 and an outer tubular member 124.
The outer tubular member 124 extends over the inner tubular
member 122 in a co~xial, spaced relationship thereto to
define an annular passage 126 which extends towards the
furnace opening 112. A tangentially spaced inlet 128 com-
municates with the outer tubular mem~ber 124 for ~ntroducing
a stream of fuel and air into the annular passage 126 as
will be explained in further detail later.
A pair of spaced annular plates 130 and 132 extend
around the noæzle 120, with the inner edge of the plate 13~
terminating on the outer tubular member 124. A liner member
134 extends from the inner edge of the plate 132 and in a
genexal longitud;n~l direction relatlve to the nozzle 120
and terminates adjacent the insulation material 11~ just
inside the wall 11~. An additional annular plate 138
extends around the nozzle 120 in a spaced, parallel relation
with the plate 130. An air divider sleeve 140 ex~ends from
the inner surface of the plate 138 and between the liner 134
and the nozzle 120 in a substantially parallel relation to
the nozzle and the liner 134 to define two air flow passages
142 and 144.
A plurality o~ outer register vanes 146 are pivotally
mounted between the plates 130 and 132 to control the swirl
of secondary air from the wind box to the air flow passages
142 and 144. In a similar manner a plurality of inner
register vanes 148 are pivotally mounted between the plates
130 and 138 to further regulate the swirl of the secondary
air passing through the annular passage 144~ It is under
stood that although only two register vanes 146 and 143 are
shown in Fig. 5, several more vanes extend in a ~ircum
ferentially spaced relation to the vanes shown. Also, the
pivotal rnounting of the vanes 146 and 143 may be done in any
conventional manner, such as by mounting the v~nes on shaf~s
(shown schematically~ and journallir.g the shafts in proper
bearings formed in the plates 130j 132 and 138. Also, the
~0 position of the vanes 146 and 148 mav be adjustable by means
-12-
of cranks or the like. Since these types of components are
conventional they are not shown in the drawings nor will be
described in any further detail.
It is understood that the quantity of air flow from the
wind box into the vanes 146 is controlled by movement of a
sleeve 150 which is slidably disposed on the outer pexiphery
of the plate 132 and is mo~able parallel to t~e longitudi~al
axis of the nozzle 120. This movement can be achieved by
using an elongated worm gear and associated apparatu~ in a
manner identical ~o that disclosed in the previous embodi-
ment. Thus, the quantity of combustion supporting air from
the wind box passing through the air flow passages 142 and
144 can be controlled by axial displacement of the sleeve
150. A perforated air hood 156 extends between the plates
130 and 132 ;mm~ tely downstream or the sleeve 150 to
permit determination of the secondary air 10w to the burner
~s in the previous embodiment.
As shown in Figs. 6-8, which depict the details of the
nozzle 120, the end portion of the outer tubular member 124
and the corres~ondiny end portion of the inner tubular
mPmher 122 are tapered slightly radially inwardly toward the
furnace opening 112. A divider cone 158 extends between the
inner tubular member 122 and the outer tubular member 124.
The divider cone 158 has a straight portion 158a (Fig. 8)
which extends between the straight portlons of inner tubular
member 122 and the outer tu~ular member 124, and a tapered
portion 158b which extends between the tapered portions of
the tubular members for the entire lengths thereof. The
function of the divider cone 158 will be described in
greater detail later.
13-
A plurality of V-shaped splitters 160 are circumferen-
tially spaced in the annular space between the outer tubular
member 124 and the divider cone 158 in the outlet end portion
of the nozzle 120. As shown in Figs. 6 and 7, four such
splitters 160 are .spaced at 90 intervals arld extend from
the outlet to a po.i~t approximately midway between the
tapered portions of the tubular ~m~Prs i22 and 124. Each
spli~ter 160 is formed by two pla~e ~pmh~rs welded together
at theix ends to ~orm a V-shape. The plate m~mh~rs are al~o
welded along their respective longi~u~;n~l edges to the
outer tubular mPmhP~ 124 and the divider cone 158 to support
the splitters and the divider cone i~ the noz21e 120. The
apex of each splitter 160 is ~isposed upstream of the nozzle
outlet so that the ~uel-air stream flowing in the annular
space between the divider cones 158 and the outer tubular
member 124 will be directed into the adjacent spaced defined
between the splitters to facilitate the splitting of the
fuel.stream into four separate streams.
Four pie-shaped openings 162 are formed through the
outer tubular me~er 124 and respectively extend i~mediately
over the spli~ters 160. These openings are for the purpose
of admltting secondary air from the inner air flow passage
144 (Fig. l) into the annular space defined between the
divider cone 158 and the outer tubular member 124 for
reasons that will be explained in detail later.
As shown in Fig. 8, a tip 164 is formed on the end of
the tapered portion of the inner tubular member 122 and is
movable relative to the latter member by means of a ~lurality
of rods 166 extending within the tubular member and affixed
--14--
~ca7~3
to the inner wall of the tip. The other ends of the rods
166 can be connected to any type of actuator device (not
shown) such as hydrauli cylinder or the like to effect
longitudinal movement of the rods and therefore the tip 164
in a conventional manner.
It ~an be appreciated from a view of Fig. ~ that the
longit~l~in~l l"o~ le~lt of the tip 164 varies the effeckive
outlet opening defined between the tip and the divider cone
158 so that the amount of fuel-air flowing through this
opening can be regulated. Since the divider cone 158
divides the fuel-air mixture flowing through the annular
passage 126 into two radially spaced parallel streams
extending to either side of the divider cone 158, it can be
appreciated that movement of the tip 164 regulates the
relative flow of the two streams while varying their
velocity.
It is understood that appropriate igniters can be
provided adjacent the outlet of the no7zle 120 for igniting
the coal as it discharges from the noz21e. Since these
igniters are of a conventional desisn they have not been
shown in the drawings in the interest of clarity.
In operation of the embodiment of Figs. 5-8, the
movable sleeve 150 associated with each burner is adjusted
during initial start up to accurately balance the air to
each burner. After the initial balancing, no further
movement of the sleeves 150 are needed since normal control
of the secondary air flow to the buxners is accomplished by
operation of the outer burner vanes 146. However, if desired,
flow control can be accomplished by the sleeve.
Fuel, preferably in the form of pulverized coal suspended
or entrained within a source of primary air, is introduced
into the tangential inlet 128 where i~ swirls through the
annular chamber 126. Since the pulverized coal introduced
into the inlet 12~ is heavier than th~ air, the pulverized
coal will tend to mova radially ~utwardly towards the inner
wall of the outer tubular member 124 under the centrifugal
orces thus produced. As a result, a great majoxity of the
coal along with a relatively small portion of air enters the
outer a~nular pas~age defined between the outex tubular
member 124 and the divider cone 158 (Fig. 8) where it
encounters the apexes of the splitters 160. The stream i5
thus split into four equally spaced streams which discharge
from the nozzle outlet and, upon ignition, form four
sep~rate flame patterns. Secondary air from the inner air
passage 14~ (Fig. 5) passes through the inlets 162 formed in
the outer tubular member 124 and enters the annular passage
between the latter member and the divider cone 158 to supply
secondary air to the streams of coal and air discharging
from the outlet.
The remaining portion of the air-coal mixture passing
through the annular passage 126 enter~ the annular passa~e
defined between the divider cone 158 and khe inner tubular
member 122. The mixture entering this annular passage is
mostly air due to the movement of the coal radially outwardly,
as described above. The position of the movable tip 164 can
be adjus~ed to precisely control the relative amount, and
therefore velocity, of the air and coal discharging from the
noæzle 120 from the annular passages between the outer
-16-
tubular member 124 and the divider cone 158 and between the
divider cone and ~he inner tubular member 122.
Secondary air from the wind box is admitted through the
perforated hood 156 and into the inlet between the plates
130 and 132. The axial and radial velocities of the air are
controlled by the register vanes 146 and 148 as it passes
through the air flow passages 142 and 144 and into the
furnace opening 112 for mixing with ~he coal from the nozzle
i20. The igniters are then shut off after steady state oom
bustion has been achieved.
As a result of the foregoing, several ad~antages result
from the burner assembly of he present invention. For
example, since the pressure drop across the perforated air
hoods 156 associated with the burner assemblies can be
equalized by balancing the secondary air flow to each burner
by initially adjusting thP sleeves 150, a substant ially
u~ifoxm flue gas distribution can be obtained across the
furnace. This also permits a common wind box to be used and
enables the unit to operate at lower excess air with
significant reductions in both nitrogen oxides and carbon
monoxides. Also, the prcvision or separate register vanes
146 and 148 for the outer and inner air flow passages 142
and 144 enables secondary air distribution and flame shape
to be independently controlled resulting in a significan~
reduction of r.itrogen oxides, and a more gradual mixing of
the primary air coal stream with the secondary air since
both streams enter the furnace on parallel paths with
controlled mixing.
Further, the provision of multiple flame patterns
~7~3
results in a greater flame radiation, a lower average flame
temperature and a shorter residence time of the gas components
within the flame at a maximum temperature, all of which, as
stated above, contribute to reduce the formation of nitric
oxides.
Still fuxther, the provision of the tangential inlet
126 provides excellen~ distribution of the fuel around the
annular space 126 in the nozzle 120, resulting in more
complete combustion and reduction of carbon loss and making
it possible to use individual burners with capacities
significantly higher than otherwi~e could be used. Pro-
vision of the inlet openings 162 in the outer tubular membex
permits the introduction of a portion of the secondary air
to be entrained with the fuei~air stream passing through the
annular passage between the outer tubular member 124 and the
divider cone, since the majority of this stream will be
primarily pulverized coal. As a resul~, a substantially
uniform air-coal ratio across the entire cross-section of
the air-coal stream is achievea. Also, the provision of the
movable tip 164 to regulate the flow of the coal-air mixture
passing through the inner annular passage derined between
the divider cone 158 and the inner tubular member 122
enables the air flow on both sides of the divider cone to be
regulated thereby optimizing the primary air veiocity with
respect to the secondary air velocity.
It is understood that several variations and additions
may be made to both embodimen~s of ~he prevent invention
within the scope of the invention. For example, since the
arrangement of ~he present invention permits the admission
-18-
7~3
of air at less than stoichiometric, over~ire air ports, or
the like can be provided as needed to supply air to complete
the combustion.
As will be apparent to ~hose skilled in the art, other
changes and modifications may be made to the e~bodime~ts of
the present invention without departing from the spirt and
scope of the present invention as defined in the appended
claims and the legal equivalentO
-19-
