Abstract:
A dual fuel boiler has fuel delivery apparatus coupled to its burner section through a pressure regulator and operative to deliver to the burner section, from sources thereof, a selectively variable one of (1) a first fuel at a pressure greater than the pressure regulation setting of the pressure regulator, and (2) a second fuel at a pressure less than the pressure regulation setting, the second fuel having a Wobbe index greater that that of the first fuel. The first fuel is flowed to the burner section via a branch supply line in which first and second electromechanical two position, two-way, two position valves are installed in series in opposite normal flow orientations to thereby prevent backflow of the second fuel into the source of the first fuel.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     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.  
         [0002]     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.  
         [0003]     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.  
         [0004]     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.  
         [0005]     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.  
       SUMMARY OF THE INVENTION  
       [0006]     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.  
         [0007]     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.  
         [0008]     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.  
         [0009]     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.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic diagram of a representative dual fuel-fired boiler embodying principles of the present invention;  
         [0011]      FIG. 2  is a schematic diagram of a specially designed dual fuel delivery system utilized in the boiler;  
         [0012]      FIG. 3  is a schematic diagram of a multi-burner version of the  FIG. 2  fuel delivery system; and  
         [0013]      FIGS. 4A and 4B  are enlarged scale schematic cross-sectional views of 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  
       [0014]     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 heater or other type of fuel-fired water heater, and principles of the present invention are not limited to boiler applications.  
         [0015]     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 .  
         [0016]     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 delivery system  18 , compared to the fuel delivery system incorporated in the dual fuel boiler systems illustrated and described in U.S. Pat. No. 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.  
         [0017]     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 .  
         [0018]     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 .  
         [0019]     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 .  
         [0020]     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.  
         [0021]     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 .  
         [0022]      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  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 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&#39;s inlet and outlet ends  48 , 50 .  
         [0023]     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 .  
         [0024]     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 .  
         [0025]     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.  
         [0026]     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  reduces the pressure of the first fuel  20  that it receives to nominally 3.5″ W.C. for supply to the burner  28 .  
         [0027]     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.  
         [0028]     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 .  
         [0029]      FIG. 3  schematically illustrates modified burner apparatus  12   a  and an associated modified fuel delivery system  18   a  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  12   a  depicted in  FIG. 3  comprises two pluralities of burners  28   a  (representatively two groups of three burners  28   a ). The modified fuel delivery system  18   a  includes two branch fuel supply lines  32   a , each of which couples the main fuel supply line  32  to one of the two burner groups as shown. The modified fuel delivery system  18   a  also includes two pressure regulating apparatuses  36   a , each of which is installed in one of the branch lines  32   a . Representatively, each of the two pressure regulator apparatuses  36   a  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  18   a  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  36   a  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  28   a  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  30   a.    
         [0030]     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.