Note: Descriptions are shown in the official language in which they were submitted.
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Docket No.: RPAK-0009
HEATING APPARATUS HAVING
INSULATION-CONTACTED FUEL BURNERS
BACKGROUND OF THE INVENTION
The present invention generally relates to heating apparatus and, in
~o an illustrated embodiment thereof, more particularly relates to a fuel-
fired heating apparatus having a specially designed staged fuel burner
system incorporated therein.
Multiple burner combustion systems are commonly utilized in a
variety of fuel-fired heating appliances such as water heaters, pool heaters
and boilers. In this type of combustion system, a plurality of mutually
spaced apart, parallel, horizontally oriented tubular burners are disposed
in a combustion chamber portion of the heating appliance. Each burner is
typically of the "premix" type in which, during firing thereof, fuel from a
source thereof, and fan-supplied primary combustion air are flowed
2o through the tube to form therein a fuel/air mixture which is discharged
through burner outlet openings and combusted without the use of
secondary combustion air.
Many multiple burner combustion systems of this type are operated
in a "staged" manner in which for low heating loads only some of the
25 burners are fired, with the remaining burners remaining in an unfired
state. When the heating load increases, some or all of the remaining
burners are also fired to correspondingly increase the heating capability
of the appliance. Conventional multiple burner combustion systems of
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this general type have associated therewith a variety of well known
problems, limitations and disadvantages.
For example, when only some of the burners are being fired,
uncombusted fuel being discharged from the firing burners tends to
s undesirably circulate under the unfired burners, and then is discharged
from the heating apparatus, resulting in poor overall fuel combustion
which is undesirable from an environmental emission standpoint.
Further, during firing of a given burner of this type, a substantial
temperature differential exists between the (hotter) top side of the
~o burner and its (cooler) bottom side. This temperature difference causes
differential longitudinal expansion of the burner during firing, thereby
subjecting the burner to a substantial amount of thermal stress during its
operation. Additionally, under certain operating conditions, the burners
may harmonically resonate - a condition which undesirably increases the
15 operating noise level of the appliance.
As can readily be seen from the foregoing, it would be desirable to
provide in a fuel-fired heating appliance a multiple burner combustion
system in which the above mentioned burner-related problems,
limitations and disadvantages are eliminated or at least substantially
2o reduced.
SUMMARY OF THE INVENTION
In carrying out principles of the present invention, in accordance
with an illustrated embodiment thereof, fuel-fired heating apparatus is
25 provided which is representatively a boiler and has a combustion chamber
with a bottom interior side portion. A heat exchanger structure
horizontally extends through the combustion chamber and is adapted to
receive a through-flow of a fluid, such as water, to be heated. A plurality
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of tubular fuel burners, representatively premix-type gas burners,
longitudinally extend horizontally through the combustion chamber in a
laterally spaced apart mutually parallel orientation, the burners being
positioned below the heat exchanger structure and having bottom side
s portions spaced upwardly apart from and facing the bottom side portion
of the combustion chamber.
The fuel-fired heating apparatus also has control apparatus
operative to provide for staged firing of the fuel burners to heat fluid
flowing through the heat exchanger structure. A resilient insulation
~o structure is sandwiched between and contacts the bottom interior side
portion of the combustion chamber and the bottom side portions of the
fuel burners. Preferably, but not by way of limitation, the bottom interior
side portion of the combustion chamber is of a relatively rigid insulation
material, representatively a fiberboard material, and the resilient
insulation structure is representatively a ceramic fiber insulation blanket
structure.
In the representatively illustrated embodiment of the fuel-fired
heating apparatus, the resilient insulation structure sandwiched between
and contacting the bottom sides of the burners and the underlying
2o bottom interior side portion of the combustion chamber provides several
desirable functions.
First, during low stage firing of the heating apparatus when only
some of the burners are being fired, it substantially blocks migration of
uncombusted fuel from the firing burners to the non-firing burners via
2s any portion of the vertical space between the bottom sides of the
burners and the bottom interior side portion of the combustion chamber.
This lessens the pollution emission level of the heating apparatus.
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Second, the sandwiched resilient insulation structure reduces the
thermal stress in the burners during firing thereof by elevating the
operating temperature of the bottom sides of the burners, which reduces
the temperature difference across the burner and reduces differential
s expansion.
Third, the resilient insulation structure allows differential expansion
of the burners without impeding it, thus avoiding additional mechanical
stresses in the burner. Specifically, when any of the burners thermally
expands in a lateral direction it simply compresses the underlying resilient
~o insulation structure. When the burner later cools and returns to its
original lateral dimension, the resilient insulation structure simply expands
to its original thickness dimension under the burner to remain engaged
therewith.
Fourth, the resilient engagement of the burners by the underlying
resilient insulation structure acts as a damper to any harmonic vibrations
created in the burners during firing thereof. This, in turn, desirably
reduces any operational noise of the fuel-fired heating apparatus.
From at least thermal stress and operational noise reduction
standpoints, the disclosed placement of a resilient insulation material in
2o engagement with only a side portion of a fuel burner could also be used
to advantage in applications where only a single burner is employed in a
fuel-fired heating apparatus. Moreover, principles of the present
invention could also be utilized to advantage with burners positioned in
non-horizontal orientations and positioned in other locations within a
2s combustion chamber portion of a fuel-fired heating appliance.
It should be noted that while in a preferred embodiment of the
present invention a resilient, insulative material is sandwiched between
and resiliently contacts the burners and a facing surface portion of the
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combustion chamber, and is operative to block the flow of uncombusted
fuel between the burners and the facing combustion chamber surface
portion, the invention could provide some of the above-described
advantages without incorporating therein all of the structural and
s operational features present in the preferred invention embodiment.
For example, if a non-resilient insulation material were to be used,
the sandwiched structure would still desirably increase the temperature
of a side of the firing burner it contacts. As another example, if a
resilient,
non-insulative sandwiched structure were to be used, burner operational
~o noise that may occur would still be reduced, and the thermal expansion of
the burners during firing thereof would still be resiliently resisted. Also,
even if the sandwiched structure did not substantially block the flow of
uncombusted fuel between the burners and the facing combustion
chamber surface, the sandwiched structure could still provide some or all
of the other benefits that it does in the preferred embodiment of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic, partially phantomed side elevational view of a
2o fuel-fired heating apparatus having incorporated therein a staged fuel
burner system incorporating principles of the present invention;
FIG. 2 is a perspective view of a longitudinal portion of one of the
fuel burners removed from the heating apparatus;
FIG. 3 is an enlarged scale schematic cross-sectional view through a
2s lower portion of the heating apparatus; and
FIG. 4 is an enlarged scale schematic cross-sectional view through the
heating apparatus taken along line 4-4 of FIG. 3.
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DETAILED DESCRIPTION
Referring initially to FIGS. 1 -3, the present invention provides fuel-
fired heating apparatus 10 which is representatively a boiler. However,
principles of the present invention are not limited to boilers, and could
s alternatively be incorporated to advantage in a variety of other types of
fuel-fired heating appliances such as, for example, water heaters and pool
heaters.
As illustrated in FIGS. 1 and 3, the fuel-fired heating apparatus 10 has
a metal housing 12 within which a combustion chamber 14 is disposed,
~o the combustion chamber 14 being operatively communicated at its top
side 16 with a suitable flue pipe 18. Extending across a top interior
portion of the combustion chamber 14 is a heat exchanger structure 20
through which a fluid to be heated, such as water 22, may be suitably
flowed. The interior of the combustion chamber 14 is lined with panels,
such as bottom panel 24 and side panels 26, of a relatively rigid insulation
material, representatively a fiberboard insulation material (see FIG. 3). A
fuel burner system 28 is operatively associated with the combustion
chamber 14 and is used to heat the water 22 flowing through the heat
exchanger structure 20.
2o The fuel burner system 28 includes a plurality of tubular metal fuel
burners 30 (representatively six premix-type gas burners 30a-30f) which
longitudinally extend horizontally through the combustion chamber 14 in
a mutually spaced, parallel relationship, and suitable controls 32
permitting a staged firing of the burners 30 - for example, firing only the
2s burners 30a-30c under low fire conditions or firing all or the burners 30a-
30f under high fire conditions. Other firing stage combinations may be
alternatively utilized if desired, and there may be a greater or .lesser
number of burners incorporated in the burner system 28. Both the
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premix-type burners 30 and the associated burner controls 32 may be of a
suitable conventional construction well known to those of ordinary skill in
this particular art. As best illustrated in FIG. 3, the burners 30 are spaced
downwardly apart from the heat exchanger structure 20, and are also
s spaced upwardly apart a smaller distance from the top side of the bottom
relatively rigid insulation structure 24 within the interior of the
combustion chamber 14.
Burners 30 have open inlet end portions (not shown) which are
suitably anchored to a vertical wall portion of the combustion chamber
~0 14, and have closed outlet ends 34 (see, for example, the representative
burner 30a in FIG. 2) and top and bottom body side portions 36,38.
Formed in the top side 36 of each burner 30 are fuel/air mixture discharge
openings such as slots 40 or outlet holes 42 (or both as representatively
shown in FIG. 2). During firing of the heating apparatus 10 a fan portion 44
15 thereof draws combustion air 46 inwardly through a conduit 48 and forces
the air 46 (via a non-illustrated air plenum) into the inlet ends of all of
the
burners 30a-30f. Alternately, the blowers can be staged to operate only
when the respectively staged burners are operating. At the same time,
the controls 32 operate to force fuel 50 (representatively natural gas) from
2o a source 52 thereof inwardly through the inlet ends of the burners 30
which are being fired (for example the burners 30a-30c).
In each of the firing burners (such as burner 30a partially illustrated
in FIG. 2) this creates an interior flow 54 therethrough of premixed fuel
and air which upwardly exits the top side discharge openings 40 and 42
25 and is suitably ignited to create burner flames 56 within the combustion
chamber 14. The non-firing burners 30 (if any) have only air traversing
their interiors. Combustion gases 58 from the burner flames 56 pass
upwardly and exteriorly across the heat exchanger structure 20 to heat
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water 22 being flowed therethrough, and are then discharged upwardly
through the flue pipe 18 as shown in FIG. 1.
With reference now to FIGS. 3 and 4, in accordance with a key aspect
of the present invention, the pollutant discharge level of the heating
s apparatus 10 is diminished by sandwiching a resilient insulation structure,
representatively a blanket 60 of ceramic fiber insulation material,
between the bottom sides 38 of the burners 30a-30f and the top side of
the relatively rigid bottom interior insulation structure 24 within the
interior of the combustion chamber 14. The ceramic fiber insulation
~o blanket 60 contacts both the bottom sides 38 of the burners 30a-30f and
the top side of the relatively rigid bottom insulation structure 24, and
representatively extends along essentially the entire top side of the
bottom insulation structure 24.
The sandwiched ceramic fiber insulation blanket 60 serves several
15 functions in the representatively illustrated fuel-fired heating apparatus
10. First, it basically °plugs" the space within the interior of the
combustion chamber 14 between the bottom sides 38 of the burners 30a-
30f and the top side of the underlying relatively rigid bottom insulation
structure 24. During low fire operation of the heating apparatus 10 in
2o which, by way of non-limiting illustration and example, only the burners
30a-30c are being fired, this prevents migration of uncombusted fuel from
the firing burners 30a-30c to the non-firing burners 30d-30f via any
portion of the vertical space between the bottom sides 38 of the burners
30a-30f and the top side of the underlying relatively rigid bottom interior
25 insulation structure 24 within the combustion chamber 14. This
substantially lessens the amount of unburned fuel discharged through the
flue pipe 18 during low fire operation of the heating apparatus 10,
thereby reducing its pollutant emissions.
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Second, during firing of any of the burners 30 there exists a
substantial temperature differential between its (hotter) top side 36 and
its (cooler) bottom side 38. This top-to-bottom temperature differential
causes the burner (such as the burner 30a depicted in FIG. 2) to thermally
s expand, as indicated by the double-ended arrow 62 in FIG. 4., thereby
subjecting the burner to substantial thermal stress during its firing.
However, because a bottom side portion 38 of each burner 30 is
contacted by the ceramic fiber insulation blanket 60, during firing of the
burner the operating temperature of its bottom side portion 38 is
~o increased, thereby reducing the top-to-bottom temperature differential
of the firing burner and correspondingly reducing the differential
expansion of the burner. This, in turn, desirably reduces the thermal
stress imposed on the burner during firing thereof.
Third, this reduction of thermal stress on each firing burner 30 is
achieved without substantially impeding the differential longitudinal
expansion (i.e., bowing down) of the burner. When a firing burner 30
expands during firing thereof, as indicated by the double-ended arrow 62
in FIG. 4, the ceramic fiber insulation blanket 60 is simply resiliently
compressed between the bottom side 38 of the burner 30 and the
zo underlying relatively rigid insulation structure 24 in a manner moving the
top side 64 of the blanket 60 downwardly from its solid line position in
FIG. 4 to its dotted line position therein. When the firing of the burner 30
ceases, and the burner 30 cools, the lateral dimension of the burner
diminishes and the top side 64 of the ceramic fiber blanket 60 resiliently
25 returns to its solid line burner-engaging position shown in FIG. 4.
Fourth, the resilient engagement of the ceramic fiber insulation
blanket 60 with the bottom sides 38 of the burners 30a-3of acts as a
damper to any harmonic vibrations created in the burners during firing
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thereof. This, in turn, desirably reduces the operational noise of the fuel-
fired heating apparatus 10.
As previously mentioned, a greater or lesser number of burners 30
could be utilized in the fuel burner system 28 if desired, and the multiple
s burners could be grouped for staging purposes in a variety of different
manners. Additionally, the disclosed placement of a resilient insulation
material in engagement with only a side portion of a fuel burner could
also be used to advantage (at least from thermal stress and operational
noise reduction standpoints) in applications where only a single burner is
~o employed in a fuel-fired heating apparatus. Further, while the interior of
the combustion chamber is representatively lined with a relatively rigid
fiberboard insulation material, and the sandwiched insulation material is
illustratively a ceramic fiber insulation blanket structure, a variety of
other
types of resiliently compressible and relatively rigid insulation materials
could be alternatively utilized if desired without departing from principles
of the present invention. Moreover, principles of the present invention
could also be utilized with burners positioned in non-horizontal
orientations and positioned in other locations within a combustion
chamber.
2o the foregoing detailed description is to be clearly understood as
being given by way of illustration and example only, the spirit and scope
of the present invention being limited solely by the appended claims.
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