Note: Descriptions are shown in the official language in which they were submitted.
CA 02498538 2001-10-11
Docket No.: RPAK-0004DIV 1 CN
VARIABLE FIRING RATE FUEL BURNER
BACKGROUND OF THE INVENTION
The present invention generally relates to combustion apparatus and, in a
preferred embodiment thereof, more particularly relates to a specially
designed
variable firing rate fuel burner.
Fuel burners are utilized in a variety of heating applications in which the
burner operates to transfer combustion heat to a heat exchanger to thereby
heat a
1o fluid being flowed through the heat exchanger during firing of the burner.
In some of
these heating applications it is desirable that the pattern of the flame
emanating
from the outlet of the burner be considerably elongated parallel to the axis
of the
burner to suit the interior geometry of the heat exchanger and/or to satisfy
certain
heat transfer efficiency desigri parameters.
One previously proposed technique used to provide the burner flame with the
requisite elongated shape was to coaxially attach to the outlet end of the
burner a
tubular ceramic flame shaper that axially projected a considerable distance
beyond
the outlet end of the burner body. While this technique provided the burner
flame
with the desired elongated shape, it had certain problems, limitations and
disadvantages such as being fragile, relatively expensive, and undesirably
increasing
the overall length of the burner body.
In burner-fired heat exchanger applications of this general type it is often
desirable to vary the firing rate of the burner. However, in conventional fuel
burner
design it is often difficult to substantially reduce the firing rate of the
burner without
potentially creating undesirable flame "flashback".
CA 02498538 2001-10-11
In view of the foregoing it can be seen that a need exists for an improved
fuel
burner which eliminates or at least substantially reduces the above-mentioned
problems, limitations and disadvantages commonly associated with fuel burners
of
conventional constructions. It is to this need that the present invention is
directed.
SUMMARY OF THE INVENTION
In carrying out principles of the present invention, in accordance with a
preferred embodiment thereof, an improved fuel burner apparatus is provided
which
comprises a body having an outlet end and including a pilot conduit extending
along
an axis and through which a pilot fuel/air mixture may be flowed, discharged
through
the outlet end, and ignited to create a pilot flame. An inner firing conduit
circumscribes the pilot conduit and laterally defines therebetween a first
flow space
communicating with the body outlet end. An outer firing conduit circumscribes
the
inner firing conduit and laterally defines therebetween a second flow space
communicating with the body outlet end.
The fuel burner apparatus also includes a fuel/air delivery system operative
to
force fuel and air through each of the first and second body flow spaces, for
discharge
through the body outlet end and ignition by the pilot flame, to responsively
create a
main burner flame. Accordirig to a key aspect of the present invention, the
burner
body is configured in a manner such that the flow of fuel and air discharged
from the
second body flow space functions to laterally constrain the main burner flame,
representatively providing the main burner flame with a relatively thin,
axially
elongated configuration. The inner and outer firing conduits have downstream
ends,
and the downstream end of the outer firing conduit is preferably axialLy
offset from
the downstream end of the inner firing conduit in a downstream direction to
aid in
the shaping of the main burner flame.
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CA 02498538 2001-10-11
According to other aspects of the present invention, the fuel/air delivery
system is operative to force separate first and second fuel/air mixtures
respectively
through the first and second burner body flow spaces, and the fuel/air
delivery
system is operative to utilize different fuels in the separate first and
second fuel/air
mixtures.
In an illustrated preferred embodiment of the fuel burner, the fuel/air
delivery
system includes first and second fuel injectors respectively communicated with
the
first and second flow spaces and operative to receive fuel from at least one
source
thereof. An air inlet plenum structure is carried by the burner body, and
first and
second mixing plenum structures extend through the air inlet plenum structure,
the
first and second mixing plenum structures being respectively coupled to the
first and
second fuel injectors, having air inlet openings therein, and respectively
communicating with the first and second burner body flow spaces. The fuel
burner
further includes an air delivery structure operatively coupled to the first
and second
flow spaces, the air delivery structure representatively including an air
supply fan
having an outlet communicated with the interior of the air inlet plenum
structure.
According to another aspect of the present invention, the outlet end of the
2o burner body is operatively cciupled to a heat exchanger through which a
fluid to be
heated may be flowed, the heat exchanger having an interior space for
receiving the
main burner flame from which combustion heat may be transferred to the fluid
being
flowed through the heat exchanger. Representatively, the heat exchanger has a
series of interior heating tubes through which the fluid to be heated may be
flowed,
the series of interior heating tubes circumscribing the burner flame-receiving
interior
space of the heat exchanger and longitudinally extending parallel to the axis
of the
burner body. The axial elonglation of the main burner flame injected into the
interior
of the heat exchanger parallel to the heat exchanger tubes substantially
enhances the
overall heat transfer efficiency of the overall fuel-fired heat exchange
apparatus.
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CA 02498538 2007-02-28
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(Prior Art) is a simplified cross-sectional view of an outlet end
portion of
a conventional fuel burner;
FIG. 2 (Prior Art) is a view similar to that in FIG. 1, but with a tubular
ceramic
flame shaper operatively connected to the outlet end of the conventional fuel
burner;
FIG. 3 is a simplified cross-sectional view of an outlet end portion of a
specially
designed variable firing rate fuet burner embodying principles of the present
invention; and
FIG. 4 is a simplified, somewhat schematic full cross-sectional view through
the
variable firing rate fuel burner of the present invention operatively
connected to a
representative heat exchanger, only a portion of which is iliustrated.
DETAILED DESCRIPTION
As iliustrated in FIGS. 3 and 4, this invention provides a specially designed
variable firing rate fuel burner 10. Burner 10 is illustratively depicted in a
downfire
orientation and is representatively connected at its outlet to the upper end
of a
schematically depicted, vertically elongated heat exchanger structure 12 (see
FIG. 4),
only a vertical portion of which is illustrated. Burner 10 constitutes a
substantiat
improvement of the prior art fuel burner 14 shown in FIG. 1, burner 14 being
similar
in some regards to the burner shown in FIG. 12 of U.S. Patent 5,658,139.
The prior art burner 14 had several
problems such as (1) its main outlet flame 16 being too laterally divergent
(i.e., wide)
for use in, for example, the vertically elongated heat exchanger structure 12
(see FIG.
4), and (2) its firing rate being difficult to modulate.
To a certain extent the desirable narrowing of the burner outlet flame 16 was
sotved, as itlustrated in FIG. 2 (Prior Art), by attaching to the outlet of
the prior art
burner 14 a tubular ceramic flame shaper 18 which "shapes" the outlet flame 16
to
the indicated narrower configuration 16a. However, the ceramic flame shaper 18
was
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CA 02498538 2001-10-11
expensive, fragile, and undesirably increased, the overall burner length.
Additionally,
the flame shaper did nothing to add firing rate modulation capabilities to the
burner
14.
Turning now to FIGS. 3 and 4, the improved, variable firing rate fuel burner
10
of the present invention incorporates the general structure of the FIG. I
burner 14 as
a tubular inner body portion of the improved burner 10 which comprises an
inner
firing tube or conduit 20, a pilot tube or conduit 22 outwardly circumscribed
by the
firing tube 20 and creating an annular flow space 24 therewith, a bluff body
26
carried on the lower end of the pilot tube 22, and an annular array of
circumferentially spaced flame-holding swirl vanes 28 disposed at the lower
end of
the annular flow space 24.
Burner 10 also includes an outer firing tube or conduit 30 that outwardly
circumscribes the inner firing tube 20 and creates an annular flow space 32
therewith.
As illustrated, the open lower end of the outer firing tube 30 is preferably
downwardly offset from the open lower end of the inner firing tube 20.
A blank-off plate 34 (see FIG. 4) internally located at an upper end portion
of
the burner 10 blocks the upper end of the outer annular flow space 32 and
separates
the flow space 32 from an upper end chamber 36 in the burner body which is
communicated at its lower side with the inner annular flow space 24. Upper end
chamber 36 and an upper end portion of the outer annular flow space 32
communicate with the interior of an air inlet plenum structure 38 disposed at
the
upper end of the burner 10 and coupled to the outlet of an air supply fan 40.
Fuel injectors 42,44 are operatively connected to mixing plenum structures
46,48 disposed in the air inlet plenum structure 38 and respectively
communicated
with the upper end chamber 36 and an upper end portion of the outer annular
flow
space 32. Each of the mixing plenum structures 46,48 has a series of air inlet
openings 50 formed therein.
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CA 02498538 2001-10-11
During operation of the burner 10, a- fuel-air mixture is flowed downwardly
through the pilot tube 22 to maintain a pilot flame 52 adjacent the lower end
of the
burner 10. Pilot flame 52 is initiated by a suitable igniter structure (not
shown). Fuel
from a source thereof is forced into the fuel injectors 42 and 44, and
combustion air
54 is forced into the inlet plenum structure 38 by the fan 40. The air 54
entering the
plenum 38 is forced into the mixing plenum structures 48,50 through their air
inlet
openings 50 and mixed with fuel discharged from the injectors 42,44 to form
(1) a
first or inner premixed fuel-air flow 56 that is forced downwardly through the
inner
annutar flow space 24 for downward discharge therefrom and ignition by the
pilot
flame 52, and (2) a second or outer premixed fuel-air flow 58 that is forced
downwardly through the outer annular flow space 32 for discharge therefrom and
ignition at the lower end of the burner 10.
This forcibLe discharge of the annular outer premixed fuel-air flow 58
outwardly around the discharged inner premixed fuel-air flow 56 causes the
outer
premixed fuel-air flow 58 to function as a flame shaping structure that takes
the
place of the previously described ceramic flame shaper 18 (see FIG. 2) and
operates
to cause the resulting main burner flame 60 to assume the desired long, narrow
shape without the use of the ceramic flame shaper 18.
Additionally, the use of the two premixed fuel-air mixture flows 56,58
provides
the burner 10 with substantially enhanced firing rate adjustment capabilities
by
simply reducing or increasing the amount of fuel supplied to the injector 44
and/or
reducing the air supply to the burner. Further, the dual premixed fuel-air
flow
capability permits the burner 10 to be simultaneously operated with two
different
types of fuel simply by supplying each injector 42,44 with a different type of
fuel.
In addition to its enhanced firing rate adjustment capability and dual-fuel
operational capability, the unique structure of the burner 10 just described
provides
it with a variety of other advantages compared to conventionally configured
fuel
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CA 02498538 2001-10-11
burners. These other advantages include lowered NOx emission rates, enhanced
stability, better fuel/air mixing characteristics and a lowered burner
pressure drop.
The unique configuration and operation of the burner 10 also enhances the
performance of the elongated heat exchanger 12 (see FIG. 4) due to the
correspondingly elongated burner flame 60. Representatively, the heat
exchanger 12
has a vertically elongated cylindrical body 62 with a header section 64 at its
upper
end, the outlet end of the burner 10 being operatively connected to the header
section 64. The elongated burner flame 60 is forced downwardly into a
vertically
io elongated firing space 66 disposed in the interior of the heat exchanger
body 62 and
surrounded by a circumferentially spaced array of vertically oriented heat
exchanger
tubes 68 disposed in the interior of the heat exchanger 12 (only two of the
tubes 68
being shown). During operation of the heat exchanger 12, a fluid (for example,
water) to be heated is ftowed through the tubes 68 and receives combustion
heat
from the burner outlet flame 60. Due to the unique flame shaping capability of
the
burner 10 described above, the elongated flame 60 is generally parallel to the
lengths
of the tubes 68, thereby desirably enhancing the heat transfer efficiency of
the heat
exchanger 12.
The foregoing detailed description is to be clearly understood as being given
by
way of illustration and example, the spirit and scope of the present invention
being
limited solely by the appended claims.
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