Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02538784 2006-03-07
Docket No.: RPAK-0010
DUAL FUEL BOILER WITH
BACKFLOW-PREVENTING VALVE ARRANGEMENT
BACKGROUND OF THE INVENTION
The present invention generally relates to combustion apparatus
1o and, in a preferred embodiment thereof, more particularly relates to a
specially designed dual fuel burner system for a fuel-fired heating
appliance such as, for example, a boiler.
Dual fuel boilers have been supplied, primarily by power burner type
boiler manufacturers, for many years. The ability to selectively operate a
boiler, or other type of fuel-fired heating appliance, with one or the other
of two different fuels (such as, for example, natural gas or propane) is
desirable to provide operation if and when the primary fuel source is
interrupted. Often the pricing of the primary fuel source can be
discounted if the customer agrees to accept interruption of the fuel
supply by the supplier when so requested. In this event, the customer
simply switches to the secondary or "backup" fuel source until the source
of primary fuel is re-established by the supplier.
Conventional power burner practices are (1) to have two separate
burner heads that can be interchanged to accommodate the switch back
and forth between the two different types of fuel, or (2) to have back-up
fuels with essentially the same Wobbe indexes such as propane-air to back
up natural gas. The first listed conventional design, of course, requires a
mechanical modification to the overall burner structure each time that a
different fuel is to be used to fire the boiler.
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A desirably simplified technique for switching back and forth
between two alternative fuel sources (a primary fuel source and an
alternate or secondary fuel source) in a dual fuel boiler is illustrated and
described in U.S. Patent 6,904,873 to Ashton which is assigned to the same
assignee as the assignee of this application,
In further developing the dual fuel boiler illustrated and described
in U.S. Patent 6,904,873 a goal was established to provide it with a
modified primary fuel/secondary fuel switching system having a valving
1o arrangement that even more effectively prevents secondary fuel back
pressure from potentially contaminating the primary fuel source with
secondary fuel.
SUMMARY OF THE INVENTION
In carrying out principles of the present invention, in accordance
with a preferred embodiment thereof, a specially designed dual fuel
heating appliance is provided. The heating appliance is representatively a
dual fuel boiler and comprises fuel burner apparatus having an inlet
portion, and fuel delivery apparatus operative to deliver to the fuel
2o burner apparatus a selectively variable one of a first fuel
(representatively
natural gas) from a source thereof, and a second fuel (representatively
propane) from a source thereof.
The fuel delivery apparatus includes a main fuel supply line
connected to the inlet portion of the fuel burner apparatus, a first fuel
supply branch line connected to the main fuel supply line and
connectable to the first fuel source, first valve apparatus connected in the
first fuel supply branch line and being openable and closable to selectively
permit and preclude flow of the first fuel therethrough, a second fuel
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supply branch line connected to the main fuel supply line and
connectable to the second fuel source, and second valve apparatus
connected in the second fuel supply branch line and being openable and
closable to selectively permit and preclude flow of the second fuel
therethrough.
According to a key aspect of the invention, the first valve apparatus
includes first and second electromechanical two position, two-way valves
connected in series, and in opposite normal flow orientations, in the first
fuel supply branch line. When these two valves are closed, second fuel
1o backpressure on one of the valves is added to the diaphragm closing
spring force thereof to more positively preclude the pressurized second
fuel from backfiowing into and contaminating the first fuel source.
Preferably, the dual fuel heating appliance, which is illustrated in
both single and multiple burner embodiments, additionally incorporates
therein the relative first and second fuel pressure control technique
disclosed in U.S. Patent 6,904,873 which permits the use of either the first
fuel or the second fuel, the first and second fuels having different Wobbe
indexes, without modifying the supply orifice structure of the burner
apparatus. To accomplish this, the fuel delivery system further includes a
first pressure regulator through which both of the first and second fuels
must flow to reach the burner apparatus, and a second pressure regulator
through which only the higher Wobbe index fuel must flow to reach the
burner apparatus, the pressure regulation setting of the first pressure
regulator being higher than the pressure regulation setting of the second
pressure regulator.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a representative dual fuel-fired
boiler embodying principles of the present invention;
FIG. 2 is a schematic diagram of a specially designed dual fuel
delivery system utilized in the boiler;
FIG. 3 is a schematic diagram of a multi-burner version of the FIG. 2
fuel delivery system; and
FIGS 4A and 4B are enlarged scale schematic cross-sectional views of
lo the dashed area "4 in FIG. 2 and respectively illustrate one of the
electromechanical valves in FIG. 2 in its de-energized, normally closed
orientation and its energized, opened position.
DETAILED DESCRIPTION
Schematically illustrated in FIG. 1 is a fuel-fired heating appliance
which embodies principles of the present invention and is
representatively a dual fuel boiler 10. While a fuel-fired boiler is
representatively illustrated, the heating appliance could be a variety of
other types of dual fuel heating appliances such as, for example, a pool
2o heater or other type of fuel-fired water heater, and principles of the
present invention are not limited to boiler applications.
The dual fuel boiler 10 includes fuel burner apparatus 12 which is
representatively of a non-aspirating type, and a combustion air blower 14
used to supply the fuel burner apparatus 12 with combustion air 16.
According to a key aspect of the present invention, the dual fuel boiler 10
is provided with a specially designed fuel delivery system 18 which is
operatively associated with the burner apparatus 12 and may be utilized
to selectively supply to the burner apparatus 12 either a primary first fuel
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20 (representatively natural gas) or a secondary fuel 22 (representatively
propane) having a Wobbe index higher than that of the first fuel 20. First
fuel 20 is supplied to the boiler 10 via a branch fuel supply line 24, and the
second fuel 22 is supplied to the boiler 10 via a branch fuel supply line 26.
In FIG. 2 there is schematically shown a representative single burner
version of the burner apparatus 12 and the fuel delivery system 18. The
burner apparatus 12 is a single, non-aspirating type fuel burner 28 having
incorporated therein, in an inlet head portion thereof, a fuel discharge
orifice 30. According to a key aspect of the present invention, the fuel
lo delivery system 18, compared to the fuel delivery system incorporated in
the dual fuel boiler systems illustrated and described in U.S. Patent
6,904,873, has an improved valving arrangement, later described herein,
that more effectively prevents secondary fuel back pressure from
potentially contaminating the primary fuel source with secondary fuel.
In addition to the branch fuel supply lines 24 and 26, the fuel
delivery system 18 includes a main fuel supply line 32 coupled as shown to
the branch fuel supply lines 24,26 and extending from its juncture
therewith to the burner inlet fuel orifice 30. A manual shutoff valve 34
and a pressure regulator apparatus 36 are connected as shown in the main
fuel supply line 32 between the branch supply lines 24,26 and the fuel
discharge orifice 30.
As schematically and representatively illustrated, the pressure
regulator apparatus 36 is a combination pressure regulator and safety or
operating valve. Alternatively, the pressure regulator apparatus 36 may
comprise separate pressure regulator and valve structures operatively
connected in the main fuel supply line 32 upstream from the manual
shutoff valve 34 without departing from principles of the present
invention. A pressure regulator 38 is installed as shown in the second
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branch fuel supply line 26. Preferably, the pressure regulator 38 is a "lock-
up" type regulator, of a conventional construction, which incorporates
therein a check valve structure that prevents leftward fluid backflow
through the regulator 38.
The improved valving arrangement of the fuel delivery system 18
also includes three electromechanical normally closed, two position, two-
way, gas valves 40,42,44 of the solenoid/diaphragm type utilizing a linear
motor output motion as later described herein. Valve 40 is connected in
the branch fuel supply line 26 downstream of the pressure regulator 38,
1o and valves 42,44 are connected in series in the branch fuel supply line 24,
with valve 42 being upstream of the valve 44.
Manual shutoff valves (not shown) are connected in the branch fuel
supply lines 24 and 26, respectively upstream of the pressure regulator 38
and the electromechanical valve 42. The manual shutoff valve 34 may be
optionally installed, where shown, in addition to these non-illustrated
manual shutoff valves.
Each of the valves 40,42,44 has a normal or intended internal flow
direction as indicated by the arrow 46 thereon. When it is desired to
supply natural gas to the boiler 10, the electromechanical valve 40 is left
closed, and the electromechanical valves 42 and 44 are electrically opened
to permit natural gas to flow to the burner 12 via the lines 24 and 32.
When it is desired to supply propane to the boiler 10, the
electromechanical valves 42 and 44 are closed and the electromechanical
valve 40 is electrically opened to permit propane to flow to the burner 12
via the lines 26 and 32.
FIG. 4A cross-sectionally depicts the electromechanical valve 42
(which is configured similarly to the valves 40 and 44) in its de-energized
normally closed orientation, and FIG. 4B cross-sectionally depicts the valve
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42 in its energized or opened configuration. Like valves 40 and 44, valve
42 has an inlet end 48, an outlet end 50, and an internal flow passage 52
extending therethrough between the ends 48 and 50. Internal flow
passage 52 extends through an orifice 54. When the valve 42 is in its
normally closed FIG. 4A orientation, the orifice 54 is blocked by a closure
diaphragm 56 which is coupled to the vertically movable core 58 of the
solenoid portion of the valve and spring-driven downwardly against the
top side of the orifice 54 to close it against gas flow therethrough. When
the valve 42 is electrically energized to open it (see FIG. 4B), the solenoid
io core 58 is electrically driven upwardly to thereby open the orifice 54 and
permit gas flow in either direction through the internal passage 52
between the valve's inlet and outlet ends 48,50.
According to a key aspect of the present invention, the
electromechanical valves 42,44 connected in series in the natural gas
branch supply line 24 are "oppositely" connected therein such that their
normal flow arrows 46 are oppositely directed. Because of this unique
opposite normal flow orientations of the electromechanical valves 42,44 in
the branch line 24, when propane is being delivered to the boiler 10 via
the branch supply line 26, propane back pressure on the natural gas valve
2o 44 adds to the spring pressure on its diaphragm 56 so that such propane
back pressure cannot lift the diaphragm off the orifice of valve 44 and
permit propane backflow through the valve 44. With the valves 42,44 in
such opposite normal flow orientations in the line 24, natural gas flowing
rightwardly through the (opened) valves 42,44 sequentially passes through
the normal inlet 48 of the valve 42, the normal outlet 50 of the valve 42,
the normal outlet 50 of valve 44, and the normal inlet 48 of valve 44. Note
that if valve 44 were omitted, the propane back pressure exerted on the
diaphragm 56 of valve 42 would be exerted thereon in a direction
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opposite to that of its diaphragm closure spring, thereby potentially
lifting the diaphragm and permitting undesirable propane backfiow
through the single electromechanical valve 42.
Natural gas pressure on valve 42 in its normally closed position (for
example, when propane is being supplied to the boiler 10), adds to the
closure force on the diaphragm of valve 42 to thereby more positiveiy
preclude natural gas flow rightwardiy through the branch line 24. Natural
gas backfiow through the propane branch supply line 26 when the valve
40 is in its normally closed position, is prevented by the check valve
1o structure in the pressure regulator 38, and by the diaphragm spring
closure force within the valve 40.
By appropriately opening or closing the electromechanical valve 40,
or the electromechanical valves 42 and 44, either the first fuel 20 or the
second fuel 22 may be supplied to the burner 28 during firing thereof. As
in the case of the dual fuel boiler apparatus illustrated and described in
U.S. Patent 6,904,873, when the first fuel 20 is being supplied to the burner
28 the first fuel 20 is delivered to the pressure regulator apparatus 36 at a
pressure higher than its pressure regulation setting, and when the second
fuel 22 is being supplied to the burner 28 the second fuel 22 is delivered
to the pressure regulator apparatus 36 at a pressure lower than its
pressure regulation setting. Further, the pressures of the first and second
fuels 20,22 as they reach the burner 28 are related to one another in a
manner such that the firing rate of the burner 28 is essentially the same
regardless of which of the fuels 20,22 is being delivered thereto. This
advantageousiy eliminates the necessity of changing out the burner
orifice 30 each time a switch is made from either of the fuels 20,22 to the
other fuel.
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Representatively, but not by way of limitation, the setting of the
pressure regulator apparatus 36 is nominally 3.5" W.C., the first fuel (by
virtue of a non-illustrated upstream pressure regulator) is delivered to the
oppositely connected electromechanical valves 42,44 at a pressure within
the range of from about 7" to about 14" W.C., and the pressure regulator
38 is set to reduce the pressure of the second fuel 22 delivered to the
electromechanical valve 40 to about 2.0" W.C. Accordingly, for the fuel
delivery system 18 illustratively depicted in FIG. 2, when the first fuel 20
is
being supplied to the burner 28 the pressure regulator apparatus 36
1o reduces the pressure of the first fuel 20 that it receives to nominally
3.5"
W.C. for supply to the burner 28.
However, when the second fuel 22 is being supplied to the burner
28, the pressure regulator apparatus 36 does not regulate the pressure of
the second fuel downwardly (since the second fuel is delivered to the
pressure regulator apparatus 36 at a pressure lower than its setting), and
the second fuel 22 is supplied to the burner 28 at a pressure of about
1.3"W.C. due to the inherent valve and supply line pressure drops. Thus,
the pressure of the first fuel 20 being supplied to the burner orifice 30 will
be a function of the setting of the pressure regulator apparatus 36, while
the pressure of the second fuel 22 being supplied to the burner orifice 30
will be a function of the pressure of the second fuel 22 upstream of the
pressure regulator apparatus 36 and the inherent valve and supply line
pressure drops.
As can be seen, by simply adjusting the settings of the pressure
regulating devices 36 and 38 the fuel delivery system 18 can be
correspondingly adjusted to maintain the firing rate of the burner 28 at a
substantially constant level when other combinations of fuels are coupled
to the fuel delivery system for use with the burner 28.
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Fig. 3 schematically illustrates modified burner apparatus 12a and an
associated modified fuel delivery system 18a which may be alternatively
incorporated in the dual fuel boiler 10 or other fuel-fired heating
appliance. Instead of the single burner 28 defining the burner apparatus
12 shown in FIG. 2, the modified burner apparatus 12a depicted in FIG. 3
comprises two pluralities of burners 28a (representatively two groups of
three burners 28a). The modified fuel delivery system 18a includes two
branch fuel supply lines 32a, each of which couples the main fuel supply
line 32 to one of the two burner groups as shown. The modified fuel
lo delivery system 18a also includes two pressure regulating apparatuses 36a,
each of which is installed in one of the branch lines 32a. Representatively,
each of the two pressure regulator apparatuses 36a has a setting equal to
that of the single pressure regulator apparatus 36 shown in FIG. 2. In all
other regards, the modified fuel delivery system 18a is identical in
construction and operation to the previously described fuel delivery
system 18 shown in FIG. 2. As in the case of the fuel delivery system 18,
the pressure regulators 36a are representatively set at nominally 3.5" W.C.,
and the second fuel pressure regulator 38 is set to about 2.0" W.C. Thus,
by simply opening the valve 40, or the valves 42,44, the multiple burners
2o 28a may be operated at substantially equal firing rates using either of the
two fuels 20 and 22 without the necessity of changing out any of the
burner orifices 30a.
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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