CROSS REFERENCE TO RELATED APPLICATIONS
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 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.
[0005] 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.
[0006] 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.
[0007] 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 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.
[0009] It is another object of the present invention to provide a boiler apparatus with
an improved pilot burner.
[0010] It is another object of the present invention to provide a boiler apparatus with
an improved pilot burner that minimizes the potential for flashback.
[0011] It is another object of the present invention to provide a burner apparatus with
an improved pilot burner that maximizes pilot blower life.
[0012] It is another object of the present invention to provide a boiler apparatus with
an improved pilot burner that maximizes pilot component life.
[0013] 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.
[0014] It is another object of the present invention to provide a boiler with an improved
pilot burner that minimizes noise and ignition losses.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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
[0019] The present invention will be better understood from reading the following description
of non-limiting embodiments, with reference to the attached drawings, wherein below:
[0020] FIG. 1 is a schematic view of a boiler and burner assembly, in accordance with one
embodiment of the present invention.
[0021] FIG. 2 illustrates a specific configuration of the schematic representation shown
in Figure 1, in accordance with one embodiment of the present invention.
[0022] FIG. 3 illustrates the pilot assembly of Figure 2, as ignited.
[0023] FIG. 4 illustrates component elements of the pilot assembly of Figures 2 and 3.
[0024] FIG. 5 illustrates a enlarged view of a flame disc of the pilot assembly, in accordance
with one embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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
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.
[0035] 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.
[0036] 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.
[0037] 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).
[0038] 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.
[0039] 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. Aluminum is preferably
utilized because this will allow the present invention to have two compression fittings
for easy disassembly.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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 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.
[0044] 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.
[0045] 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).
[0046] 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, the 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.
[0047] A further advantage of the independent pilot is that the main blower can be lit at
optimum conditions for reduced noise and ignition losses.
[0048] 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.
[0049] An infra-red flame detector may also be positioned to detect the pilot as well as
main flame.
[0050] As the entire pilot system/assembly
P may be 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.
[0051] 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.