Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~0434Z
This application is a division of Canadian Serial No.
378,443, filed May 27, 1981.
BACKGROUND OF THE INVENTION
This invention relates generally to a burner assembly
and more particularly to an improved burner assembly which
operates in a manner to reduce the formation of nitrogen oxides
as a result of fuel combustion.
Considerable attention and efforts have recently been
directed to the reduction of nitrogen oxides resulting from
the combustion of fuel, and especially in connection with the use
of coal in the furnace sections of relatively large installations
such as vapor generators and the like. In a typical arrangement
for burning coal in a vapor generator, several burners are dis-
posed in communication with the interior of the furnace and op-
erate to burn a mixture of air and pulverized coal. The burners
used in these arrangements are generally of the type in which a
fuel air mixture is continuously injected through a nozzle so
as to form a single relatively large flame. As a result, the
surface area of the flame is relatively small in comparison to
its volume, and therefore the average flame temperature is rel-
atively high. However, in the burning of coal, nitrogen oxides
are formed by the fixation of atmospheric nitrogen available in
the combustion supporting air, which is a function of the flame
temperature. When the flame temperature exceeds 2800F, the
amount of fixed nitrogen removed from the combustion supporting
air rises exponentially with increases in the temperature. This
condition leads to the production of high levels of nitrogen
oxides in the final combustion products, which causes severe air
pollution problems.
Nitrogen oxides are also formed from the fuel bound
nitrogen available in the fuel itself, which is not a direct
function of the flame temperature, but is related to the quantity
of available oxygen during the combustion process.
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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 com-
bustion, flue gas recirculation, the introduction of an oxygen-
deficient fuel-air mixture to the burner and the breaking up
of a single large flame 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 invention to which this divisional application is
directed pertains to a burner assembly which operates in a
manner to considerably reduce the production of nitrogen oxides
in the combustion of fuel without any significant increase in
cost or other related problems.
The invention in this divisional application in one
aspect pertains to a burner assembly comprising means defining
an annular passage with an inlet located at one end of the
passage for receiving fuel and an outlet located at the other
end of the passage for discharging the fuel. A divider member
is dlsposed within the annular passage for dividing the stream
of fuel passing through the passage into two radially-spaced
parallel streams. Means are provided for splitting up one of
the streams as it discharges from the opening so that, upon
ignition of the fuel, a plurality of flame patterns are formed.
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The invention in this divisional application also
comprehends a burner assembly of the type above including
a register assembly associated with the burner, the register
assembly comprising an enclosure extending over the passage
for receiving air, and means for directing the air from the
enclosure towards the outlet in two parallel paths extending
around the passage. A plurality o vanes are respectively
disposed in each of the paths for regulating the spin and/or
quantity of air flowing through the paths.
The invention still further 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.
Inlet means is located at one end of the passage for
directing a fuel stream mixture of pulverized coal and air
into the passage in a tangential relation relative to the
passage. An outlet is located at the other end of the
passage for discharging the fuel stream. Means are disposed
with the annular passage for dividing the stream of fuel pass-
ing through the passage into two radially spaced parallel
streams. A substantial portion of the coal flows into the
outer of the spaced parallel streams by centrifugal forces,
means regulate the flow rate of at least one of the streams,
and an air inlet opening is formed in a portion of the
outer tubular member for admitting air to the outer stream
as the outer stream discharges from the outlet.
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BRIEF DESCRIPTION OF THE 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 front elevational view of the nozzle of
Fig. 6; and
Fig. 8 is a longitudinal cross-sectional view of
the nozzle of Fig. 6.
DESCRIPTION OF THE_PREFERRED EMBODIMENTS
Referring in general to the embodiment of Figs. 1-4 of
the drawings and specifically to Fig. 1, the reference
numeral 10 refers in general to a burner assembly which is
disposed in axial alignment with a through opening 12 formed
in a front wall 14 of a conventional furnace. 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 for acco~modating
additional burner assemblies identical to the burner assembly
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10. The inner surface of the wall 14 as well as the other
walls of the furnace are lined within an appropriate thermal
insulation material 18 and, while not specifically shown, it
is understood that the combustion chamber 16 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 producin~ 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, bottom 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 10 includes a nozzle 20 having an
inner tubular member 22 and an outer tubular member 24. The
outer tubular member 24 extends over the inner tubular
member 22 in a coaxial, spaced relationship thereto to
define an annular passage 26 which extends towards the furnace
opening 12.
A tangentially disposed inlet 28 communicates with the
outer tubular member 24 for introducing a stream of fuel
into the annular passage 26 as will be explained in further
detail later.
A pair of spaced annular plates 30 and 32 extend around
the burner 20, with the inner edge of the plate 30 terminating
on the outer tubular member 24. A liner member 34 extends from
the inner edge of the plate 32 and in a general longitudinal
direction relative to the burner 20 and terminates adjacent
the insulation material 18 just inside the wall 14. An
additional annular plate 38 extends around the burner 20 in
a spaced, parallel relation with the plate 30. An air
divider sleeve 40 extends from the inner surface of the
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plate 38 and between the liner 34 and the nozzle 20 in a
su~stantially parallel relation to the burner 20 and the liner
34 to define two air flow passages 42 and 44.
A plurality of outer register vanes 46 are pivotally
mounted between the plates 30 and 32 to control the swirl of
secondary air from the wind box to the air flow passages 42
and 44. In a similar manner a plurality of inner register
vanes 48 are pivotally mounted between the plates 30 and 38
to further regulate the swirl of the secondary air passing
through the annular passage 44. It is understood that
although only two register vanes 46 and 48 are shown in Fig.
1, several more vanes extend in a circumferentially spaced
relation to the vanes shown. Also, the pivotal mounting of
the register vanes 46 and 48 may be done in any conventional
manner, such as by mounting the vanes on shafts (shown
schematically in Fig. 1) and journalling the shafts in proper
bearings formed in the plates 30, 32 and 38. Also, the position
of the vanes 46 and 48 may be adjustable by means 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.
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 bur-
ner nozzle 20. An elongated worm gear 52 is provided for mov-
ing the sleeve 50 and is better shown in Fig. 2. The worm gear
52 has one end portion suitably connected to an appropriate
drive means (not shown) for rotating the worm gear and the other
end provided with threads 52a. The worm gear 52 extends through
a bushing 54 (Fig. 1) which is attached to the plate 30 to
provide rotatable support. The threads 52a of the worm gear 52
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mesh with appropriate apertures 56 formed in the sleeve 50 so
that, upon rotation of the worm gear, the sleeve moves long-
itudinally with respect to the longitudinal axis of the burner
20 and across the air inlet defined by the plates 30 and 32.
In this manner, the quantity of combustion 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 plates
30 and 32 immediately downstream of the sleeve 50 to permit
the air flow to the burner 20 to be independently determined
by means of static pressure differential movements, in a
conventional manner.
As shown in Fig. 3, which depicts the details of the
burner nozzle 20, the end portion of the outer tubular member
24 and the corresponding end portion of the inner tubular
member 22 are tapered slightly radially inwardly toward the
furnace opening 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 Fig. 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 corresponding
curved surfaces of the tubular members 22 and 24 and the blocks
are tapered radially inwardly. As shown in Figure 4, the
leading end portion of each block 60 is configured in a curved
relationship so that the fuel flowing in the passage 26 and
impinging against the leading ends of the blocks 60 will be
directed into the adjacent spaces defined between the blocks
to facilitate the splitting of the fuel stream into four
separate streams.
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In operation of the burner assembly of the present
invention, the movable sleeve 50 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 50 are needed since normal control of
the secondary air to the burners is accomplished by operation
of the outer register vanes 46.
Fuel preferably in the form of pulverized coal suspended
or entrained within a source of primary air, is introduced into
the tangential inlet 28 where it swirls through the annular
chamber 26 and is ignited by suitable igniters (not shown)
appropriately positioned with respect to the burner nozzle 20.
The stream of fuel and air encounters the blocks 60 at the
end portion of the nozzle 20 whereby the stream is split into
four equally spaced streams which, upon ignition, form four
separate flame patterns. The igniters are shut off after steady
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 and 32. The axial and radial
velocities of the air is controlled by the register vanes 46
and 48 as it passes through the air flow passages 42 and 44 and
into the furnace opening 12 for mixing with the fuel from the
burner 20.
As a result of the foregoing, several advantages result
from the burner assembly of the present invention. For example,
since the pressure drop across the perforated air hoods 58 asso-
ciated with burner assemblies can be equalized by balancing
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the secondary air flow to each burner by initially adjusting
the sleeves 50, a substantially uni~orm qas distribution can
be obtained across the furnace. ~h~s also permits a common
wind box to be used and enables the un~t to operate at lower
excess air with significant reduction~ ~n both nltrogen
oxides and carbon monoxides. Also, the provision of separate
register vanes 46 and 48 for the outer and inner air flow
passages 42 and 44 enablès ~econdary air distribution as
well as flame shape to be independently controlled resulting
in a significant reduction of nitrogen oxides, and a more
gradual mixing o~ the primary air coal stream with the
secondary air since both streamq enter the furnace on parallel
paths with controlled mixing.
Further, the provision of multiple flame patterns
results in a greater ~lame radiation, a lower average flame
temperature and a shorter residen~e time of the gas com-
ponents within the flame at a maximum temperature, all of
which, as stated above, contribute to reduce the formation
of nitric oxides.
Also, the use of the curved surface 60a on the blocks
results in a more streamline flow of the fuel stream before
it discharges from the outlet of the nozzle 20. Still
further, the provision of the tangential inlet 26 provides
excellent distribution of the fuel around the annular space
26 in the burner 20 resulting in more complete c~mbustion
and reduction of carbon loss and ma~ing it possible to use
individual burners with capacities significantly higher than
otherwise could be used.
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An alternative embodiment of the present invention is
depicted'in Fig~. 5-8. Referring specifically to Fig. S the
reference numeral 110 refers in general to a burner assembly
which is disposed in axial alignment with ~ through 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 configur~tion to define a
combustion chamber 116 immediately adjacent the opening 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 speci~ically shown, it is understood that the
combustion chamber 116 can also be lined with boiler tubes
through which a heat exchange fluid, such as water is
circulated in a conventional m2nner for the purposes of
producing steam.
It is also understood that a vertical wall is disposed
in a parallel relationship with the ~urnace wall 14 along
with connecting top, bottom, and side walls to form a plenum
chamber, or wind box, for receiving combustion supporting
air, commonly referred to as "secondary air", in a convention~l
manner.
The burner assembly 110 includes a nozzle 120 having an
inner tubular me~'oer 122 and an outer tubular member 124.
The outer tubular member 124 extends over the inner tubular
member 122 in a coaxial, 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 mer~er 124 for .ntroducing
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a stream of fuel and air into the annu}ar passage 126 as
will be explained in further detail later.
A pair of spaced annular plates 1 0 and 132 extend
around the nozzle 120, with the inner edge of the plate 130
terminating on the outer tubular member 124. A liner member
134 extends from the innex edge of the plate 132 and in a
general longitudinal direction relative to the nozzle 120
and terminates adjacent the ~nsulation material 118 ~ust
inside the wall 114. An additional annular plate 138
extends around the nozzle 120 in a spaced, parallel relation
with the plate 130. An air divider sleeve 140 extends 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 of outer register vanes 146 are pivotally
mounted between the plates 130 and 132 to control the swirl
of secondary air ~xom 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 148 are
shown in Fig. 5, several more vanes extend in a circum-
ferentially spaced relation to the vanes shown. Also, the
pivotal mounting of the vanes 146 and 148 may be done in any
conventional manner, such as by mounting the vanes on shafts
(shown schematically) and journallir.g the shafts in proper
bearings formed in the plates 130, 132 and 138. Also, the
position of the vanes 146 and 148 mav be adjustable by means
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of cranks or the like. Since these types of components are
conventional they are not shown in the drawings nor will be
descxibed in any further detail.
It is understood that the quantlty o~ 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 periphery
of the plate 132 and is movable parallel to the longitudinal
axis of the nozzle 120. This movement can be achieved by
using an elongated worm gear and associated apparatus in a
manner identical to that disclosed in the prevlous embodi-
ment. Thus, the quantity o~ 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 immediately downstream of the sleeve 150 to
permit determination of the secondary air flow to the burner
as 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 corresponding end portion of the inner tubular
member 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 portions of inner tubular
member 122 and the outer tubular 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.
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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 i~ the outlet end portion
of the nozzle 120. As shown in Figs. 6 and 7, four such
splitters 160 are spaced at 90 ~ntervals and extend from
the outlet to a point approximately midway between the
tapered portions of the tubular members 122 and 124. Each
splitter 160 is formed by two plate members welded together
at their ends to form a V-shape. The plate members are also
welded along their respective longitudinal edyes to the
outer tubular member 1~4 and the divider cone 158 to support
the splitters and the divider cone in the nozzle 120. The
apex of each splitter 160 is disposed upstream of the nozzle
outlet so that the fuel-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 member 124 and respectively extend immediately
over the splitters 160. These openings are for the purpose
of admi;tting secondary air from the inner air flow passage
144 (Fig. 1) into the annular space defined between the
divider cone 158 and the outer tubular member 124 for
reisons 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 plurality
of rods 166 extending within the tubular member and affixed
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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 hydraulic cylinder or the like to effect
longitudinal movement of the rods and therefore the tip 164
in a conventional mænner.
It can be appreciated from a ~iew of Fig. 8 that the
longitudinal movement of the tip 164 varies the effective
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 movemen~ 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 noz~le 120 for igniting
the coal as it discharges from the nozzle. 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 burners is accomplished by
operation of the outer burner vanes 146. However, if desired,
flow control can be accomplished by the sleeve.
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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 it swirls through the
annular chamber 126. Since the pulverized coal introduced
into the inlet 128 is heavier than the air, the pulverized
coal will tend to move radi~lly outwardly towards the inner
wall of the outer tubular member 124 under the centrifugal
forces thus produced. ~s a result, a great ma~ority o~ the
coal along with a relatively small port~on of air enters the
outer annular passage aefined between the outer tubular
member 124 and the divider cone 158 (Fig. 8) where it
encounters the apexes of the splitters 160. The stream is
thus split into four equally spaced streams which discharge
from the nozzle outlet and, upon ign~tion, form four
separate ~lame patterns. Secondary air from the inner air
passage 14~ (Pig. 5) passes through the $nlets 162 formed in
the outer tubular member 124 and enters the annular passage
between the latter member and the d~vider 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 enters the annular passage
defined between the divider cone 158 and the 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 adjusted to precisely control the relative amount, and
therefore velocity, of the air and coal discharging from the
nozzle 120 from the annular passages between the outer
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tubular member 124 and the divider cone 158 and ~etween the
divider cone and the inner ~ubular member 122.
Secondary air from the wlnd box is admitted through the
perforated hood 156 and into the inlQt 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 2nd 144 and into the
furnace opening 112 for mixing with the coal from the nozzle
120. The igniters are then shut off after steady state com-
bustion has been achieved.
As a result of the foregoing, several advantages resultfrom the burner assembly of the 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 the sleeves 150, a substantially
uniform 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 provision of 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 independe~tly 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
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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 maxLmum temperature, all of which, as
stated abovel contribute to reduce the formation of nitric
oxides.
Still further, the provision of the tangential inlet
126 pro~ides excellent d$stribution o~ the fuel around the
annular space 126 in the nozzle 120, resulting in more
complete co~bustion and reduct~ on o~ carbon loss and making
it possible to use individual burners with capacitie~
significantly higher than otherwise could be used. Pro-
vision o~ the inlet openings 162 in the outer tubular member
permits the introduction of a portion of the secondary air
to be entrained with the fuel-air stream passing through the
annular passage between the outer tubular member 124 and the
divider cone, since the majori~y of this stream will be
primarily pulverized coal. As a result, a substantially
uniform air-coal ratio across the entire cross-section of
the air-coal stream is achieved. .Also, the provision of the
movable tip 164 to regulate the flow of the coal-air mixture
passing through the inner annular passage defined between
the divider cone 158 and the inner tubular member 122
enables the air flow on both sides o~ 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 embodiments of the prevent invention
within the scope of the invention. For example, since the
arrangement of the present invention permits the admission
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of air at less than stoichiometric, overfire air ports, or
the like can be provided as needed to supply air to complete
the combustion.
As will be apparent to those skilled in the art, other
changes and modifications may be made to the embodiments of
the present invention without departing from the spirt and
scope of the present invention as defined in the appended
claims and the legal equi~alent.
3o
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