Note: Descriptions are shown in the official language in which they were submitted.
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BOILER AND PILOT SYSTEM
[0001]
FIELD OF THE INVENTION
[0002] The present invention relates generally to boiler and burner
apparatuses and,
more particularly, to pilots used in connection with cylindrical premix
burners.
BACKGROUND OF THE INVENTION
[0003] Burners which combust gas or other fuel are widely known. Gas burners,
incorporated for example into indirect heating devices, utilize the combustion
of a
gas or similar fuel (e.g., propane, natural gas, or fuel oil) for heating a
work
substance, oftentimes a flowable substance such as air or water. For example,
heated water may be directed into the interior of a home for general comfort
heating purposes or for providing hot water for bathing, laundering, cooking,
and
the like.
[0004] In operation, natural gas or other fuel is controllably forced through
a nozzle
or jet portion of the burner, where it is intermixed (most typically) with air
from a
blower, forming a gas spray or aerosol for enhancing combustion. In premix
burners, some or all of the air required for combustion is mixed with some or
all of
the fuel prior to burning. To start the burner, a pilot is ignited, which in
turn is
used to ignite the main burner on demand. Known pilot systems incorporate
various ignition means, such as a spark electrode, wherein a high-voltage
electrode
is mounted so that its tip is in close proximity to the grounded pilot. As a
blower
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forces the air/ gas mixture through a pilot tube, a spark is applied and the
pilot
flame ignites. This flame is then used to ignite the main burner. In the case
of an
indirect heater, the combustion product (heated air/plasma) is directed into a
heat
exchanger, where the energy produced by the combustion process is transferred
to
the work substance to be heated. The combustion exhaust is then moved to an
exhaust exit, possibly after one or more recirculation steps or the like to
further
recapture heat from the combustion product. A cylindrical housing is often
employed to cover most or all of the components.
[oo0s] One common concern with the design of burners is the potential for
"flashback," i.e. when the flame pops back through the premix burner nozzle
and
runs upstream through the air/ gas mixture. In a worst-case scenario,
flashback can
result in an explosion. To minimize the potential for flashback, many prior
art
burners use bleed air from the main burner for the pilot to ensure that
positive flow
through the pilot is maintained at all times. However, supplying the pilot
with air
from the main burner limits flexibility in choosing main burner ignition
inputs since
pilot pressure requirements control main burner operation during the ignition
sequence.
[00061 Past practice for pilots used in connection with cylindrical premix
burners
has been to locate them within the burner or, if located outside the burner,
to use air
bled from the main blower to supply the pilot. One problem or drawback with
locating the pilot within the burner is the "shadow" created by the components
of
the pilot, which affects the burning pattern on the burner surface. This
uneven
burning pattern may lead to local hot spots within the burner and reduced
burner
life. Another disadvantage with locating the pilot within the burner is that
servicing the pilot becomes very difficult, as the fuel/ air components of the
main
burner must be removed to access the pilot.
[00071 With the forgoing problems and concerns in mind, it is the general
object of
the present invention to provide a boiler apparatus with an improved pilot
burner
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that minimizes the potential for flashback, maximizes pilot component life,
allows
flexibility in choosing main burner components, and facilitates easy servicing
of the
pilot.
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide a boiler apparatus.
[ooo9] It is another object of the present invention to provide a boiler
apparatus
with an improved pilot burner.
[00010] It is another object of the present invention to provide a boiler
apparatus
with an improved pilot burner that minimizes the potential for flashback.
[ooonn] It is another object of the present invention to provide a burner
apparatus
with an improved pilot burner that maximizes pilot blower life.
[0002] It is another object of the present invention to provide a boiler
apparatus
with an improved pilot burner that maximizes pilot component life.
[000i3] It is another object of the present invention to provide a boiler
apparatus
with an improved pilot burner that allows for flexibility in choosing main
burner
components.
[00014] It is another object of the present invention to provide a boiler with
an
improved pilot burner that minimizes noise and ignition losses.
wools] It is another object of the present invention to provide a boiler with
an
improved pilot burner to facilitate the direct viewing of the pilot flame,
ignition
spark and main burner.
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[00016] It is another object of the present invention to provide a boiler with
an
improved pilot burner to achieve an improved robustness of pilot ignition.
[00017] It is yet another object of the present invention to provide a boiler
with an
improved pilot burner that allows for easy servicing of the pilot.
[00018] These and other objections of the present invention, and their
preferred
embodiments, shall become clear by consideration of the specification, claims
and
drawings taken as a whole.
BRIEF DESCRIPTION OF THE DRAWINGS
[00019] The present invention will be better understood from reading the
following
description of non-limiting embodiments, with reference to the attached
drawings,
wherein below:
[00020] FIG. 1 is a schematic view of a boiler and burner assembly, in
accordance
with one embodiment of the present invention.
[00021] FIG. 2 illustrates a specific configuration of the schematic
representation
shown in Figure 1, in accordance with one embodiment of the present invention.
[00022] FIG. 3 illustrates the pilot assembly of Figure 2, as ignited.
[00023] FIG. 4 illustrates component elements of the pilot assembly of Figures
2 and
3.
[00024] FIG. 5 illustrates a enlarged view of a flame disc of the pilot
assembly, in
accordance with one embodiment of the present invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[00025] As shown in Figure 1, and in accordance with a preferred embodiment of
the
present invention, a boiler apparatus includes a housing 1 defining an
interior
boiler chamber 2 and a burner assembly 4 arranged to be in thermal
communication
with the boiler chamber 2. A fuel valve assembly 6 controls a flow of fuel
(from an
unillustrated supply of the same) to the burner assembly 4, while a blower
assembly 7 directs air through an air valve assembly 9 to the burner assembly
4.
An ignition device 8 is provided for instigating combustion of an inlet gas/
air
stream, and is arranged adjacent one edge of the burner assembly 4. This
ignition
device 8, commonly known as a "pilot" or "pilot burner" is in turn used to
light the
main burner.
[00026] Figure 1 is a schematic representation of a boiler apparatus and as
such, it
will be readily appreciated that the constituent elements of the boiler
apparatus
may be at differing locations within and around the housing 2, without
departing
from the broader aspects of the present invention.
[00027] As depicted in Figure 1, both the supply of fuel and the supply of air
are
controlled, and isolated, from the burner assembly 4 via the integrated fuel
valve
and air valve assemblies, 6 and 9 respectively.
[ooo2s] As will be discussed in more detail later, it is an important aspect
of the
present invention that the integrated fuel valve and air valve assemblies, 6
and 9,
isolate the ignited fuel / air mixture from 'blowing back' into either the air
supply or
the fuel supply, thus significantly increasing the safety and operability of
the
present invention.
[00029] Figure 2 illustrates a specific configuration of the schematic
representation
shown in Figure 1, in accordance with one embodiment of the present invention.
Turning now to Figure 2, a pilot assembly P of the present invention comprises
a
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mixing tube section 30 where a supply of fuel and air are initially mixed. A
pilot
block 32 is generally shown in Figure 2 and itself includes a pilot tube 20
and an
ignition means 26, to be described in more detail later.
[00030] In accordance with one preferred embodiment of this invention, air is
provided to the mixing tube 30 via a dedicated pilot fan 10, and is directed
through
an air funnel 12 and thereafter through an air valve 13. The air funnel 12
meters the
correct amount of air through an internal orifice . Moreover, the air valve 13
may
be one of many types known in the art, such as a solenoid valve, although the
present invention is not limited in this regard.
[00031] As indicated in Figure 2, it is another important aspect of the
present
invention that a dedicated pilot fan 10 is utilized to supply air to the
mixing tube 30
of the pilot assembly P as opposed to known apparatuses which utilize a single
blower for supplying air to the burner assembly 4, as well as directing 'bleed
air' to
the pilot assembly P.
[00032] It will be readily appreciated that by utilizing a separate and
dedicated pilot
fan 10 (instead of having a single air blower for use in supplying both the
burner
assembly 4 and the pilot assembly P), the pilot fan 10 may be designed to the
precise requirements (pressure, and the like) of the pilot assembly P and may
be
controlled to a more precise degree.
[00033] It is yet another important aspect of the present invention that the
separate
and dedicated pilot fan 10 enables the pilot fan 10 to be wholly located
outside of
the boiler chamber 2 and the burner assembly 4, thus making repairs of the
pilot
assembly P more easily accomplished. Likewise, repair or replacement of the
burner assembly 4 may also be effectuated without disrupting the pilot
assembly P.
[00034] Still yet another important aspect of utilizing the dedicated pilot
fan 10 lies in
the ability to control the operational status of the pilot fan 10, apart and
separate
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from the operation of the blower used to supply air to the burner assembly 4.
Thus,
the pilot fan 10 may be switched off even while the blower for the burner
assembly
4 remains active, saving both power as well as increasing the operational life
of the
pilot fan 10.
[000351 Returning again to Figure 2, air from the pilot fan 10 is passed
through the
air valve assembly 13 (or, 9 in Figure 1), and mixes with fuel in the mixing
tube 30.
The fuel itself is also passed through a fuel valve assembly 15 (or, 6 in
Figure 1)
prior to entering the mixing tube 30, via an inlet port 18.
[000361 It is yet another important aspect of the present invention that both
the
supply of air, as well as the supply of fuel, are isolated from the pilot fan
10 and fuel
source 19 via the integrated air valve assembly and fuel valve assembly, 13
and 15
respectively. In this manner, any possibility of 'blow back' of the ignited
mixture of
air/ fuel within the mixing tube 30 is eliminated, and the overall safety of
the pilot
assembly P is greatly increased.
[000371 As will be understood, after the air/ gas mixes in the mixing tube 30,
it is
forced downstream to the pilot block 32. The pilot block 32 comprises a pilot
tube
20 and an operationally integrated ignition means (22, 26 and 28, as described
below).
[000381 The mixing tube 30 is connected to the pilot tube 20, which receives
the air
gas mixture and directs the flow of the air/ gas mixture out the end of the
pilot tube
20, where an adjacent ignition source 22 ignites the mixture, thus producing a
flame
40, as best shown in Figure 3.
[000391 It will be readily appreciated that the mixing tube 30, as well as the
other
components comprising the piping connecting the air/ gas mixture to the pilot
block
32, may be made of any suitable material known in the art such as steel,
aluminum,
etc, without departing from the broader aspects of the present invention.
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Aluminum is preferably utilized because this will allow the present invention
to
have two compression fittings for easy disassembly.
[00040] As again shown in Figure 2, a pressure switch and tube assembly 27 is
utilized to operationally connect the supply of fuel with the active supply of
air
from the pilot fan 10. Thus, the pressure switch and tube assembly 27 will
coordinate the activation of the fuel valve assembly 15 with the activation of
the
pilot fan 10. As will be appreciated, upon sensing air flow from the pilot fan
10, the
pressure switch and tube assembly 27 will send a signal to the fuel valve
assembly
15 to open, which will allow gas/ fuel to pass through the gas orifice 18 and
into the
mixing tube 30.
[ooo4i] A further important aspect of the present invention lies in the use of
a pilot
tube retaining collar 14, as best seen in Figures 2, 4 and 5. The pilot tube
retaining
collar 14 is provided at the end of the pilot tube 20 and includes an
integrated pilot
flame disc 16. The pilot flame disc 16 is a substantially flat disc containing
numerous holes 24 through which the air/ gas mixture from the mixing tube 30
passes.
[00042] The use of the pilot tube retaining collar 14 and integrated pilot
flame disc 16
is yet another important aspect of the present invention. The holes 24 of the
flame
disc 16 adds additional turbulence to the air/gas mixture as it passes out the
end of
the pilot tube 20. Moreover, the flame disc 16 itself provides a backstop to
the
more-perfectly mixed and ignited air/ fuel mixture, thus assisting the
direction of
the flame 40 into the burner assembly 4.
woo As indicated previously, the ignition means includes a solid state igniter
26
connected to a spark electrode 28, although other ignition means known in the
art
may be alternatively utilized without departing from the broader aspects of
the
present invention. In a preferred embodiment, a solid state igniter 26 with a
minimum output voltage of 9,000 volts is connected to the spark electrode 28.
An
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electrode tip 22 (best seen in Figure 2) extends from the electrode 28 to an
inner
periphery of the pilot tube retaining collar 14. To effect ignition, a voltage
from the
solid state igniter 26 is applied to the electrode 28 which causes as spark to
arc from
the electrode tip 22 to an inner periphery of the pilot tube retaining collar
14.
[00044] In a preferred embodiment, the spacing of the electrode tip 22 is 1/8
inch
from an inner periphery of the pilot tube retaining collar 14. The maximum
spacing
is 1/ 4 inch from an inner periphery of the pilot tube retaining collar 14.
These
settings allow the electrode tip 22 to be placed anywhere from the center of
the pilot
tube retaining collar 14, to within 1 / 8 inch from either side, and still
ignite the pilot
flame 40, while the most preferred depth of the electrode tip 22 is flush to 1
/ 16 inch
inside the pilot tube retaining collar 14.
[000451 Upon ignition, the flame 40 burns in a torch-like fashion with
approximately
a 6,000 BTU input. The pilot assembly P may then be operated at minimum gas
pressures under two inches and maximum pressures of over five inches. The fuel
valve assembly 15 has a full adjustment within these parameters and the pilot
is
easily set in the field by one simple gas pressure adjustment, preferably set
at about
three inches water column. With the present invention, the flame 40 of the
pilot
burner is extremely tolerant to maladjustment, and will ignite at full input
(about
4,000,000 BTUs) without igniting low fire first (although such a scenario is
not
preferred).
[00046] As described above, the pilot gas and air flow are isolated from the
combustion chamber, and their respective sources, via integrated valves 13 and
15
following main burner ignition. Thus, increased combustion chamber pressure
due
to variations in boiler input or downstream conditions cannot create reverse
flow,
i.e. flashback, of combustion chamber gases through the pilot assembly P. As
previously mentioned, t he fact that the pilot gas and air flow are isolated
from the
combustion chamber via valves also allows the pilot fan 10 to be turned off
during
burner operation, increasing pilot fan life.
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[000471 A further advantage of the independent pilot is that the main blower
can be
lit at optimum conditions for reduced noise and ignition losses.
[00048] In addition to the advantages described above, the pilot burner
orifice is
specifically designed with an aperture of sufficient size to allow direct
viewing of
the pilot flame, ignition spark, and main burner. Sight glass may be
positioned
directly on top of the pilot tube to allow for direct viewing of the main
flame and
pilot flame. This provides significant aid in troubleshooting pilot ignition
issues.
The pilot burner orifice is also designed to optimize fuel flow past the spark
igniter
to enhance ignition over a wide range of pilot conditions, improving
robustness of
pilot ignition.
[000491 An infra-red flame detector may also be positioned to detect the pilot
as well
as main flame.
[ooosol As the entire pilot system/ assembly P maybe mounted in a single
housing,
outside of the boiler and main burner housing, the pilot assembly P may be
easily
removed for service without disturbing other system components.
[ooosil Although this invention has been described in terms of its application
to
boiler burners, it will be apparent that it may also be applied to other types
of
burners. In addition, while the invention has been described with reference to
the
preferred embodiments, it will be understood by those skilled in the art that
various
obvious changes may be made, and equivalents may be substituted for elements
thereof, without departing from the essential scope of the present invention.
Therefore, it is intended that the invention not be limited to the particular
embodiments disclosed, but that the invention includes all embodiments falling
within the scope of the appended claims.
