Patent Application
20070154856
The present invention generally relates to combustion apparatus 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.
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. Pat. No. 6,904,873 to Ashton which is assigned to the same assignee as the assignee of this application, and which is hereby incorporated in its entirety herein by this reference.
In further developing the dual fuel boiler illustrated and described in U.S. Pat. No. 6,904,873 a goal was established to provide it with a modified primary fuel/secondary fuel switching system having a valving arrangement that even more effectively prevents secondary fuel back pressure from potentially contaminating the primary fuel source with secondary fuel.
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 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 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 backpressure on one of the valves is added to the diaphragm closing spring force thereof to more positively preclude the pressurized second fuel from backflowing 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. Pat. No. 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.
Schematically illustrated in
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 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
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 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, 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.
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 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 opposite to that of its diaphragm closure spring, thereby potentially lifting the diaphragm and permitting undesirable propane backflow 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 positively preclude natural gas flow rightwardly through the branch line 24. Natural gas backflow through the propane branch supply line 26 when the valve 40 is in its normally closed position, is prevented by the check valve 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. Pat. No. 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 advantageously 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.
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
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.
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.
