Note: Descriptions are shown in the official language in which they were submitted.
CA 02848681 2014-04-10
TITLE
OXY-SOLID FUEL BURNER
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of U.S. Provisional
Application No.
61/811,175, filed on April 12, 2013, which is incorporated by reference herein
in its
entirety.
BACKGROUND
[0002] This application relates to a burner for combustion of solid fuel with
oxygen.
[0003] Due in part to its variable volatile matter content, solid fuel can be
a very difficult
fuel to ignite in a flowing stream. Hence, typically the solid fuel undergoes
a significant
ignition delay that results in a flame front which is substantially detached
from the fuel
nozzle. This is an inherently unstable situation that can lead to high levels
of unburned
carbon, unstable process heating conditions (heat transfer, melting, etc.)
and, potentially,
blow-off of the flame that can lead to a very rapid and unsafe degradation in
combustion.
[0004] It is desirable to have a burner capable of forming of a solid fuel
flame front that
is attached to the burner tip. This is an inherently desirable condition that
maximizes
heat transfer, carbon burnout and flame stability.
SUMMARY
[0005] Described herein is a burner having a center oxygen conduit surrounded
by an
outer fuel (pulverized solid fuel / transport gas) conduit. The outer fuel
conduit may, in
turn, be surrounded by an outer oxygen conduit. The outer fuel conduit
includes an
upstream section in which an inner annular flow passage terminates prior to
the tip end
of the burner and abruptly discharges into a larger, intermediate annular
section between
the outer fuel conduit and the center oxygen conduit. The intermediate section
is
followed by a downstream annular section that includes an inner annular
diffuser and an
outer annular nozzle on either side of a truncated conical divider (diffuser /
nozzle
combination). The intake to the diffuser / nozzle combination is separated
from the
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discharge of the inner annular flow passage by a distance, X, that influences
the flow
distribution entering said diffuser / nozzle combination. The distance X must
be greater
than 0. The diffuser a plurality of radial guide vanes distributed around its
periphery for
the purpose of controlling flow separation within the diffuser.
[0006] Divergence of the diffuser lowers the velocity of a first fraction of
the solid fuel
stream in a controlled manner without appreciable flow separation. A second
fraction of
the solid fuel stream in the converging annular nozzle to a relatively high
velocity. The
combination of relatively high velocity and low velocity streams flowing
adjacent to one
another creates a large flow recirculation pattern that substantially aids in
sustaining
stable combustion at the fuel nozzle tip.
[0007] The diffuser may also include a bluff body (static mixing device)
positioned
immediately upstream of the radial guide vanes.
[0008] Center oxygen may flow through the central oxygen conduit, while outer
oxygen
may flow through the outer oxygen conduit. The solid fuel / transport gas
stream, having
flowed through the outer fuel conduit, discharges from the diffuser! nozzle
combination
having a velocity distribution characterized by a low inner velocity
(generated in the
diffuser) and a high outer velocity (generated in the annular converging
nozzle). The
combination of oxygen, fuel and transport gas produces a stable solid fuel
flame of
nominally circular cross-section.
[0009] The various aspects of the system disclosed herein can be used alone or
in
combinations with each other.
[0010] Aspect 1: A solid fuel / oxygen burner comprising: a central oxygen
conduit
extending toward a tip end of the burner; an outer fuel conduit surrounding
the oxygen
conduit and extending toward the tip end of the burner; an inner fuel conduit
positioned
between the oxygen conduit and the outer fuel conduit to form an inner annulus
between
the oxygen conduit and the inner fuel conduit and an outer annulus between the
inner
fuel conduit and the outer fuel conduit, the inner fuel conduit having an
outlet end
upstream of the tip end of the burner; a truncated conical divider positioned
within the
outer fuel conduit and surrounding the oxygen conduit downstream of the inner
fuel
conduit, the divider being configured to divide a fuel stream in the outer
fuel conduit into
an inner annular conical diffuser and an outer annular converging nozzle; and
at least
three radial guide vanes positioned within the diffuser; wherein the outlet
end of the inner
fuel conduit is spaced apart from an inlet end of the divider by a distance,
X.
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[0011] Aspect 2: The burner of Aspect 1, wherein the outlet end of the inner
annulus
has a height, h1; wherein the inlet end of the annular conical diffuser has a
height, h2;
and wherein h1 is greater than h2.
[0012] Aspect 3: The burner of Aspect 1 or 2, further comprising: a bluff body
positioned within the diffuser, the bluff body having a leading edge and a
trailing end
adjacent to an upstream end of the radial guide vanes.
[0013] Aspect 4: The burner of Aspect 3, wherein the bluff body has a height,
h3,
perpendicular to the flow direction as measured from the oxygen conduit;
wherein the
height of the inner annular conical diffuser at a perpendicular plane
coincident with the
leading edge of the bluff body has a height, h4; and wherein the ratio of
h3/h4 is from
about 0.2 to about 0.5.
[0014] Aspect 5: The burner of Aspect 4, wherein the radial guide vanes have
an axial
length, Lout, from the bluff body to a trailing end of the diffuser; and
wherein the ratio
Lout/h3 is from about 3 to about 25.
[0015] Aspect 6: The burner of Aspect 5, wherein the ratio of Lout/h3 is from
about 5
to about 15.
[0016] Aspect 7: The burner of any one of Aspects 3 to 6, wherein the bluff
body is
positioned with a leading end of the bluff body a distance, Lin, from the
inlet end of the
diffuser; wherein the diffuser has an inlet flow area, A2, and a flow area
immediately
upstream of the bluff body, A3; and wherein the relationship between the ratio
A3/A2 and
the normalized position of the bluff body, Lin/h2, is set to substantially
prevent flow
=
separation in the diffuser.
[0017] Aspect 8: The burner of any one of Aspects 1 to 7, wherein the divider
includes
a leading edge oriented substantially parallel to the outer fuel conduit.
[0018] Aspect 9: The burner of any one of Aspects 1 to 8, further comprising:
an outer
oxygen conduit surrounding the outer fuel conduit and extending toward the tip
end of
the burner.
[0019] Aspect 10: The burner of Aspect 9, further comprising: a secondary
oxygen
conduit spaced apart from the outer oxygen conduit and extending toward the
tip end of
the burner.
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[0020] Aspect 11: The burner of any one of Aspects 1 to 8, further comprising:
the
outer annulus forming a tertiary oxygen conduit.
[0021] Aspect 12: The burner of Aspect 11, further comprising: a secondary
oxygen
conduit spaced apart from the outer fuel conduit and extending toward the tip
end of the
burner.
[0022] Aspect 13: A method of combusting a pulverized solid fuel with oxygen,
the
method comprising: flowing a center oxygen stream through a central conduit
extending
toward a tip end of a burner, the central oxygen conduit being surrounded by
an outer
fuel conduit extending toward the tip end of the burner; flowing a fuel stream
of
pulverized fuel in a transport gas through an inner annulus formed by an inner
fuel
conduit positioned between the oxygen conduit and the outer fuel conduit;
causing the
fuel stream to exit the inner annulus at an outlet end of the inner fuel
conduit positioned
upstream of the tip end of the burner; dividing the fuel stream into two
streams including
an inner annular conical diffuser stream formed by a truncated conical divider
having an
inlet end positioned at a distance, X, downstream of the outlet end of the
inner fuel
conduit, and an outer annular converging nozzle stream formed between the
divider and
the outer fuel conduit, wherein the inner diffuser stream decelerates and the
outer nozzle
stream accelerates; and flowing the inner diffuser stream across at least
three radial
guide vanes positioned within the divider.
[0023] Aspect 14: The method of Aspect 13, wherein the outlet end of the inner
annulus has a height, h1; wherein the inlet end of the annular conical
diffuser has a
height, h2; and wherein h1 is greater than h2.
[0024] Aspect 15: The method of Aspect 13 or 14, further comprising: flowing
the inner
diffuser stream across a bluff body positioned with a trailing end of the
bluff body
adjacent to an upstream end of the radial guide vanes.
[0025] Aspect 16: The method of Aspect 15, wherein the bluff body has a
height, h3,
perpendicular to the flow direction as measured from the oxygen conduit.
[0026] Aspect 17: The method of Aspect 16, wherein the radial guide vanes have
an
axial length, Lout, from the bluff body to a trailing end of the diffuser; and
wherein the
ratio Lout/h3 is from about 3 to about 25.
[0027] Aspect 18: The method of Aspect 17, wherein the ratio of Lout/h3 is
from about
5 to about 15.
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[0028] Aspect 19: The method of any one of Aspects 14 to 17, wherein the bluff
body
is positioned with a leading end of the bluff body a distance, Lin, from the
inlet end of the
diffuser; wherein the diffuser has an inlet flow area, A2, and a flow area
immediately
upstream of the bluff body, A3; and wherein the relationship between the ratio
A3/A2 and
the normalized position of the bluff body, Lin/h2, is set to substantially
prevent flow
separation in the diffuser.
[0029] Aspect 20: The method of any one of Aspects 13 to 19, wherein the
divider
includes a leading edge oriented substantially parallel to the outer fuel
conduit.
[0030] Aspect 21: The method of any one of Aspects 13 to 20, further
comprising:
flowing a stream of outer oxygen through an annular oxygen passage bounded by
an
outer oxygen conduit surrounding the outer fuel conduit and extending toward
the tip end
of the burner.
[0031] Aspect 22: The method of Aspect 21, further comprising: flowing a
stream of
secondary oxygen through a secondary oxygen conduit spaced apart from the
outer
oxygen conduit and extending to the tip end of the burner.
[0032] Aspect 23: The method of any one of Aspects 13 to 20, further
comprising:
flowing a stream of tertiary oxygen through the outer annulus between the
inner fuel
conduit and the outer fuel conduit.
[0033] Aspect 24: The method of Aspect 23, further comprising: flowing a
stream of
secondary oxygen through a secondary oxygen conduit spaced apart from the
outer fuel
conduit and extending toward the tip end of the burner.
[0034] Aspect 25: The method of any of Aspects 13 to 24, further comprising:
flowing
the center oxygen stream at a velocity of less than about 20 to about 30
ft/sec.
[0035] Aspect 26: The method of any of Aspects 13 to 24, further comprising:
flowing
the center oxygen stream at a velocity of greater than about 20 to about 30
ft/sec.
[0036] Aspect 27: A regenerative furnace comprising: a burner block having at
least
one firing port mounted in a sidewall of the furnace; and one or more solid
fuel / oxygen
burners positioned near an edge of the at least one firing port, the burner
comprising: a
central oxygen conduit extending toward a tip end of the burner; an outer fuel
conduit
surrounding the oxygen conduit and extending toward the tip end of the burner;
an inner
fuel conduit positioned between the oxygen conduit and the outer fuel conduit
to form an
inner annulus between the oxygen conduit and the inner fuel conduit and an
outer
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annulus between the inner fuel conduit and the outer fuel conduit, the inner
fuel conduit
having an outlet end upstream of the tip end of the burner; a truncated
conical divider
positioned within the outer fuel conduit and surrounding the oxygen conduit
downstream
of the inner fuel conduit, the divider being configured to divide a fuel
stream in the outer
fuel conduit into an inner annular conical diffuser and an outer annular
converging
nozzle; and at least three radial guide vanes positioned within the diffuser;
wherein the
outlet end of the inner fuel conduit is spaced apart from an inlet end of the
divider by a
distance, X; wherein in an under-port arrangement, the one or more burners are
positioned beneath the at least one firing port in an under-port arrangement;
and wherein
in a side-port arrangement, the one or more burners are positioned along a
side of the at
least one firing port.
[0037] Aspect 28: The furnace of Aspect 27, wherein the one or more burners
are
positioned adjacent to an edge of the port and outside the port.
[0038] Aspect 29: The furnace of Aspect 27, wherein the one or more burners
are
positioned adjacent to an edge of the port and within the port.
[0039] Aspect 30: A method of combusting a pulverized solid fuel with oxygen
in a
regenerative furnace, the method comprising: flowing hot combustion air
through a
regenerator firing port; providing a solid fuel / oxygen burner positioned
adjacent to an
edge of the firing port; flowing a center oxygen stream through a central
conduit
extending toward a tip end of a burner, the central oxygen conduit being
surrounded by
an outer fuel conduit extending toward the tip end of the burner; flowing a
fuel stream of
pulverized fuel in a transport gas through an inner annulus formed by an inner
fuel
conduit positioned between the oxygen conduit and the outer fuel conduit;
causing the
fuel stream to exit the inner annulus at an outlet end of the inner fuel
conduit positioned
upstream of the tip end of the burner; dividing the fuel stream into two
streams including
an inner annular conical diffuser stream formed by a truncated conical divider
having an
inlet end positioned at a distance, X, downstream of the outlet end of the
inner fuel
conduit, and an outer annular converging nozzle stream formed between the
divider and
the outer fuel conduit, wherein the inner diffuser stream decelerates and the
outer nozzle
stream accelerates; and flowing the inner diffuser stream across at least
three radial
guide vanes positioned within the divider.
[0040] Aspect 31: The method of Aspect 30, further comprising flowing a stream
of
tertiary oxygen through the outer fuel conduit.
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[0041] Aspect 32: The method of Aspect 30, further comprising flowing a stream
of
outer oxygen through an outer oxygen annulus.
[0042] Aspect 33: The method of any of Aspects 30 to 32, wherein the fuel and
oxygen streams discharging from the burner are mixed with air as it exits the
adjacent
[0043] Aspect 34: The method of Aspect 33, wherein the burner is operated with
less
than the stoichiometric amount of oxygen, with a stoichiometric ratio from
about 0.05 to
about 0.5.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] Fig. 1 is a schematic side cross-sectional view of an exemplary solid
fuel /
oxygen burner in which a central oxygen conduit is surrounded by an outer fuel
conduit,
an inner fuel conduit surrounding the central oxygen conduit discharges into
the outer
fuel conduit upstream of the tip end of the burner, and fuel exiting the inner
fuel conduit
[0045] Fig. 2 is a schematic depiction of flow patterns in the burner of Fig.
1 when the
[0046] Fig. 3 is a schematic depiction of flow patterns in the burner of Fig.
1 when the
central oxygen stream velocity is greater than the velocity of the fuel stream
exiting the
diffuser.
in Fig. 1, wherein the divider includes a straight, parallel leading edge.
[0048] Fig. 5 is a schematic side cross-sectional view of an embodiment of a
burner as
in Fig. 4, wherein the burner further includes a bluff body positioned within
the diffuser at
an upstream end of the guide vanes.
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[0050] Fig. 7 is a schematic and graphical depiction indicating a geometric
relationship
of the diffuser as in Fig. 5 to prevent flow separation from the diffuser
walls.
[0051] Fig. 8 is a series of schematic representations of alternate shapes and
forms of
bluff bodies for use in the burner as in Fig. 5.
[0052] Fig. 9 is a schematic side cross-sectional view of an embodiment of a
burner as
in Fig. 4, further including an outer annular oxygen conduit.
[0053] Fig. 10 is a schematic side cross-sectional view of an embodiment of a
burner
as in Fig. 4, in which tertiary oxygen is flowed in an outer annulus between
the outer fuel
conduit and the inner fuel conduit.
[0054] Fig. 11 is a schematic side cross-sectional view of an embodiment of a
burner
as in Fig. 9, further including a secondary oxygen conduit spaced apart from
the outer
annular Oxygen conduit.
[0055] Fig. 12 is a schematic side cross-sectional view of an embodiment of a
burner
as in Fig. 10, further including a secondary oxygen conduit spaced apart from
the outer
fuel conduit.
[0056] Fig. 13 is a schematic end view of a regenerative glass melting furnace
firing
port in which a plurality of burners, for example as any of the embodiments
described
herein, in an under-port arrangement. wherein the burners are positioned below
the
regenerator firing port. The end view is taken from the furnace chamber look
toward the
furnace sidewall.
[0057] Fig. 14 is a schematic end view of a regenerative glass melting furnace
firing
port in which a plurality of burners, for example as any of the embodiments
described
herein, in a side-port arrangement. wherein the burners are positioned along
one or both
sides of the regenerator firing port. The end view is taken from the furnace
chamber look
toward the furnace sidewall.
[0058] Fig. 15 is a schematic side cross-sectional view of an embodiment of a
burner
as in Fig. 9, further including a combustion air conduit surrounding the outer
oxygen
conduit.
[0059] Fig. 16 is a schematic side cross-sectional view of an embodiment of a
burner
as in Fig. 10, further including a combustion air conduit surrounding the
outer fuel
conduit.
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[0060] Fig. 17 is a schematic plan view of a regenerative furnace into which
one or
more burners as described herein may be installed.
DETAILED DESCRIPTION
[0061] For the purposes of the description herein, the following definitions
are
provided. Transport gas is a gaseous fluid used to carry or transport solid
fuel particles,
and may comprise air, oxygen-enriched air, nitrogen, carbon dioxide, recycled
flue gas,
and combinations thereof. Oxygen is a gas containing oxygen molecules at a
concentration greater than or equal to 28 mol% 02, preferably greater than or
equal to
60 mol% 02, and more preferably greater than or equal to 85 mol% 02. Solid
fuel is a
hydrocarbon fuel in solid form and may comprise petroleum coke; all varieties
of coal
including anthracite, bituminous, sub-bituminous, and lignite; peat, wood,
grass, and
other so-called biomass materials; municipal solid waste; and combinations
thereof.
[0062] Several embodiments and variations of an oxygen / pulverized solid fuel
burner
are described herein. One embodiment of a burner is illustrated in Figure 1. A
central
oxygen conduit is surrounded by an outer fuel conduit, both the oxygen conduit
and the
outer fuel conduit extending toward a tip end of the burner. An inner fuel
conduit, having
a smaller diameter than the outer fuel conduit, is positioned between the
oxygen conduit
and the outer fuel conduit, and terminates at a location upstream of the tip
end of the
burner. A truncated conical flow divider is positioned within the outer fuel
conduit and
surrounding the oxygen conduit at a location downstream of the inner fuel
conduit. The
divider may extend to the tip end of the burner or may terminate upstream of
the tip end
of the burner. In some embodiments, one or both of the oxygen conduit and the
outer
fuel conduit extend to the tip of the burner.
[0063] Pulverized solid fuel plus a transport gas flows downstream through the
inner
fuel conduit, while center oxygen flows through the central oxygen conduit.
The outlet
(trailing) edge of the inner fuel conduit has an annular opening of height,
hi, from the
oxygen conduit. The outlet of the inner fuel conduit is separated from the
divider in the
axial direction by a length, X. The inlet (upstream) edge of the divider has
an annular
opening of height, h2, where h2 is smaller than hl. The divider gives rise to
two co-
annular flow sections: an annular diffuser located between the oxygen conduit
and the
divider, whose flow cross-sectional area increases in the direction of flow;
and an
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annular converging nozzle located between the divider and the outer fuel
conduit, whose
cross-sectional area decreases in the direction of flow.
[0064] In one embodiment, the annular diffuser contains at least three radial
guide
vanes spaced around the circumference of the diffuser passage. The guide vanes
provide controlled separation of the flow emanating from the corners formed at
the
intersection of each guide vane with the surface of the center oxygen conduit.
The
controlled separation at the inner corners in turn promotes attachment of the
flow at the
outer surface of the diffuser, thus improving diffuser stability relative to
annular diffusers
without the radial guide vanes. The radial guide vanes need not extend the
entire axial
length of the diffuser. For example, as illustrated in Fig. 1, the radial
guide vanes begin
downstream of the inlet end of the diffuser.
[0065] The fuel and transport gas stream exits the inner fuel conduit and
spreads
radially as it flows axially downstream toward the divider. Based on the
velocity of the
fuel and transport gas stream, the magnitude of the distance, X, and the
relative
magnitudes of the annular openings h1 and h2, a certain portion of the fuel
stream
enters the diffuser while the remainder enters the converging nozzle. The
portion flowing
through the diffuser experiences a decrease in axial velocity, while the
portion flowing
through the nozzle experiences an increase in axial velocity. The low velocity
portion at
the outlet of the diffuser is essential toward attaining a stable, attached
flame region,
while the high velocity portion at the outlet of the nozzle helps to create a
large scale,
torroidal, streamwise vortex between the low and high velocity regions,
improving mixing
therein, while also inducing recirculation of hot products of combustion from
the
surrounding, thereby assisting fuel ignition.
[0066] Two distinct flow regimes may be associated with the burner
configuration of
Fig. 1. First, if the center oxygen stream is flowing at relatively low
velocity, e.g., below
about 20-30 ft/sec, then upon exiting from the center oxygen conduit, the flow
pattern
immediately downstream of the burner is that which is qualitatively
illustrated in Fig. 2.
That is, a wake region is formed along the burner axis due to the weak center
momentum and strong outer momentum of the burner. Second, if the velocity of
the
center oxygen stream is relatively high, e.g., greater than about 20-30
ft/sec, then the
momentum of the center oxygen jet largely prevents the formation of an axial
wake
region, and instead induces the flow of fuel toward the axis, and the overall
flow pattern
immediately downstream of the burner is qualitatively as illustrated in Fig.
3.
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[0067] A related embodiment, shown in Fig. 4, includes a leading edge on the
divider
that is largely straight and substantially parallel to the burner axis. The
purpose of the
straight and parallel leading edge is to minimize flow disturbances at the
inlet of the
diffuser by reducing the angle of attack between the oncoming flow and the
divergent
diffuser wall.
[0068] Another embodiment of the burner includes a bluff body positioned
adjacent to
the leading edge of the radial guide vanes within the diffuser, for example as
depicted in
Fig. 5. The function of the bluff body is to "trip" the flow entering the
diffuser, facilitating
more reliable downstream attachment of the flow to the outer diffuser wall
(i.e., the
divider), while creating intense mixing that acts to reduce high velocity
peaks in the flow
field exiting the diffuser. The bluff body has a height, h3, perpendicular to
the flow
direction, and the radial guide vanes have a length, Lout, from the trailing
edge of the
bluff body to the diffuser exit.
[0069] A qualitative illustration of the effect of the bluff body on the
diffuser flow is
shown in Fig. 6. Note that a localized zone of reverse flow forms downstream
of the bluff
body adjacent the central oxygen conduit. In order to limit the extent of
deposited solid
particulate within the diffuser passage due to the reverse flow, yet still
provide sufficient
mixing length for adjustment of flow momentum, the non-dimensional length,
Lout/h3, of
the diffuser section from the trailing edge of the bluff body to the diffuser
exit (i.e.,
normalized by the bluff body height) should be from about 3 to about 25, and
is
preferably from about 5 to about 15.
[0070] Another factor in the placement of the bluff body is the relationship
between the
ratio of the diffuser cross-sectional area just upstream of the bluff body to
that at the
diffuser inlet (A3/A2 as denoted in Fig. 7), and the non-dimensional inlet
length, Lin/h2,
from the inlet of the diffuser to the leading edge of the bluff body (i.e.,
normalized by the
opening height of the diffuser).
[0071] It known that, for a fixed angle annular diffuser, increasing the
diffuser length
will eventually result in flow separation (also known as stall), which can
generate flow
instabilities and distort the velocity profile within the diffuser. Flow
instabilities and a
distorted velocity profile at the inlet to the radial guide vanes would cause
sub-standard
performance of the diffuser section downstream of the bluff body. Hence, for
optimal
operation of the burner, upstream stall can be avoided by keeping the non-
dimensional
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length, Lin/h2, as a function of the area ratio, A3/A2, within the region
below the curve
shown in Fig. 7.
[0072] It is contemplated that a similarly effective bluff body may assume
other forms
and shapes beyond the representative disk of Fig. 5. These alternative shapes
include,
but are not limited to, curved and triangular as depicted in Fig. 8.
Regardless the shape
of the bluff body, its height, h3, should be greater than nominally half of
its streamwise
thickness, W.
[0073] In a further embodiment of the present burner, an outer oxygen annulus
is
positioned to introduce a stream of outer oxygen around the outer periphery of
the fuel
stream exiting the burner, as illustrated in Fig. 9. Mixing of the outer
oxygen and fuel
streams facilitates rapid ignition of the fuel stream and increases flame
radiative heat
transfer. From an operational perspective, the outer oxygen can be utilized
with or
without central oxygen. In the latter case, the end of the central oxygen
passage may be
blocked to prevent the ingress of partially burned fuel and hot products of
partial
combustion.
[0074] Yet another embodiment of the present burner eliminates the outer
oxygen
annulus, but introduces tertiary oxygen into the annulus between the outer
fuel conduit
and the inner fuel conduit, as illustrated in Fig. 10. The tertiary oxygen has
a similar
beneficial effect on ignition and heat transfer as the outer oxygen, but
accomplishes it
within a smaller diameter device.
[0075] Still another embodiment of the present burner incorporates a "staged"
oxygen
stream that is introduced adjacent to and beneath the burner body as depicted
in Figs.
11 and 12. Fig. 11 corresponds to the burner embodiment with outer oxygen
(Figure 9),
while Fig. 12 corresponds to the burner embodiment with tertiary oxygen
(Figure 10).
The principal advantages of the so-called staged oxygen is that it affords a
means of
controlling the flame length and burner NOx emissions. In particular, by
introducing less
than the stoichiometric amount of oxygen to the main body of the burner and
the balance
to the staged oxygen port, an increase in flame length and reduction of NOx
can be
obtained. The practical upper limit to the amount of staged oxygen, as a
percent of the
stoichiometric value, is reached when degradation in combustion occurs (e.g.,
the flame
becomes unstable, CO emissions and unburned carbon increase), or the flame
becomes
too long relative to the process furnace dimensions. This limit must be
determined on a
case-by-case basis.
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[0076] In another configuration, the burner can be surrounded by combustion
air.. In
this way, the burner can provide enhancement of air-fuel combustion. For
example,
Figs. 15 and 16 illustrate burner embodiments as in Figs. 9 and 10 with an
additional
outer annulus of air. Air may also be introduced around the burner in a duct
of arbitrary
cross-section.
[0077] A burner as described herein can be used in a system as a device for
heating
and / or melting operations. In particular, the burner can be utilized in a
regenerative
glass melting furnace, for example as shown in Fig. 17. In known regenerative
furnaces
burner blocks having one or more firing ports are positioned on opposite sides
or ends of
the furnace combustion chamber. Each of the firing ports typically contains
one or more
burners for delivery of fuel into the combustion chamber. The firing ports
also provide a
combustion air supply around the burners. During furnace operation, the
burners on
opposite sides of the combustion chamber are operated alternately in a cyclic
fashion.
While the burners on one side of the combustion chamber are fired, hot
combustion
products exit the opposite side of the combustion chamber. Regenerators or
refractory
checkers on either side of the furnace provide a heat transfer medium to
transfer heat
from the hot combustion gases exiting the combustion chamber to the cold
combustion
air which is delivered to the furnace. The combustion air and exhaust gas
flows are
reversed typically every 20 minutes so that each side checker can be
alternately heated
and used for preheating of combustion air. FIG. 17 shows a regenerative
furnace 10
having regenerator checkers 12 on opposite sides. During firing of the burners
22,
combustion air is delivered from the regenerator checkers 12 through the
firing ports 20,
into the combustion chamber 16 of the furnace 10.
[0078] There are many ways in which the presently disclsoed burner can be
configured
to operate in a regenerative glass melting furnace. One configuration of
particular utility
is in tandem with hot combustion air. Figs. 13 and 14, for example, illustrate
exemplary
embodiments wherein one or more burners are installed near a hot combustion
air port
(i.e., firing port) in a regenerative glass melting furnace, wherein near
means that the
burner can be either adjacent to and outside the edge of the port or adjacent
to the end
and within the port. In these embodiments, solid fuel is injected into the hot
air stream as
it discharges from the firing port. Fig. 13 illustrates an exemplary under-
port firing
arrangement, while Fig. 14 illustrates an exemplary side-port firing
arrangement. In
these embodiments, the burners can be operated with less than stoichiometric
oxygen
as a means to enhance the solid fuel combustion with hot combustion air from
the
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CA 02848681 2014-04-10
regenerator port. For example, the burners can be operated with a
stoichiometric ratio
between about 0.05 and about 0.5.
[0079] The present invention is not to be limited in scope by the specific
aspects or
embodiments disclosed in the examples which are intended as illustrations of a
few
aspects of the invention and any embodiments that are functionally equivalent
are within
the scope of this invention. Various modifications of the invention in
addition to those
shown and described herein will become apparent to those skilled in the art
and are
intended to fall within the scope of the appended claims.
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