Patent Application
20050217663
The present invention generally relates to heating apparatus and, in an illustrated embodiment thereof, more particularly relates to a fuel-fired heating apparatus having a specially designed staged fuel burner system incorporated therein.
Multiple burner combustion systems are commonly utilized in a variety of fuel-fired heating appliances such as water heaters, pool heaters and boilers. In this type of combustion system, a plurality of mutually spaced apart, parallel, horizontally oriented tubular burners are disposed in a combustion chamber portion of the heating appliance. Each burner is typically of the “premix” type in which, during firing thereof, fuel from a source thereof, and fan-supplied primary combustion air are flowed through the tube to form therein a fuel/air mixture which is discharged through burner outlet openings and combusted without the use of secondary combustion air.
Many multiple burner combustion systems of this type are operated in a “staged” manner in which for low heating loads only some of the burners are fired, with the remaining burners remaining in an unfired state. When the heating load increases, some or all of the remaining burners are also fired to correspondingly increase the heating capability of the appliance. Conventional multiple burner combustion systems of this general type have associated therewith a variety of well known problems, limitations and disadvantages.
For example, when only some of the burners are being fired, uncombusted fuel being discharged from the firing burners tends to undesirably circulate under the unfired burners, and then is discharged from the heating apparatus, resulting in poor overall fuel combustion which is undesirable from an environmental emission standpoint. Further, during firing of a given burner of this type, a substantial temperature differential exists between the (hotter) top side of the burner and its (cooler) bottom side. This temperature difference causes differential longitudinal expansion of the burner during firing, thereby subjecting the burner to a substantial amount of thermal stress during its operation. Additionally, under certain operating conditions, the burners may harmonically resonate—a condition which undesirably increases the operating noise level of the appliance.
As can readily be seen from the foregoing, it would be desirable to provide in a fuel-fired heating appliance a multiple burner combustion system in which the above mentioned burner-related problems, limitations and disadvantages are eliminated or at least substantially reduced.
In carrying out principles of the present invention, in accordance with an illustrated embodiment thereof, fuel-fired heating apparatus is provided which is representatively a boiler and has a combustion chamber with a bottom interior side portion. A heat exchanger structure horizontally extends through the combustion chamber and is adapted to receive a through-flow of a fluid, such as water, to be heated. A plurality of tubular fuel burners, representatively premix-type gas burners, longitudinally extend horizontally through the combustion chamber in a laterally spaced apart mutually parallel orientation, the burners being positioned below the heat exchanger structure and having bottom side portions spaced upwardly apart from and facing the bottom side portion of the combustion chamber.
The fuel-fired heating apparatus also has control apparatus operative to provide for staged firing of the fuel burners to heat fluid flowing through the heat exchanger structure. A resilient insulation structure is sandwiched between and contacts the bottom interior side portion of the combustion chamber and the bottom side portions of the fuel burners. Preferably, but not by way of limitation, the bottom interior side portion of the combustion chamber is of a relatively rigid insulation material, representatively a fiberboard material, and the resilient insulation structure is representatively a ceramic fiber insulation blanket structure.
In the representatively illustrated embodiment of the fuel-fired heating apparatus, the resilient insulation structure sandwiched between and contacting the bottom sides of the burners and the underlying bottom interior side portion of the combustion chamber provides several desirable functions.
First, during low stage firing of the heating apparatus when only some of the burners are being fired, it substantially blocks migration of uncombusted fuel from the firing burners to the non-firing burners via any portion of the vertical space between the bottom sides of the burners and the bottom interior side portion of the combustion chamber. This lessens the pollution emission level of the heating apparatus.
Second, the sandwiched resilient insulation structure reduces the thermal stress in the burners during firing thereof by elevating the operating temperature of the bottom sides of the burners, which reduces the temperature difference across the burner and reduces differential expansion.
Third, the resilient insulation structure allows differential expansion of the burners without impeding it, thus avoiding additional mechanical stresses in the burner. Specifically, when any of the burners thermally expands in a lateral direction it simply compresses the underlying resilient insulation structure. When the burner later cools and returns to its original lateral dimension, the resilient insulation structure simply expands to its original thickness dimension under the burner to remain engaged therewith.
Fourth, the resilient engagement of the burners by the underlying resilient insulation structure acts as a damper to any harmonic vibrations created in the burners during firing thereof. This, in turn, desirably reduces any operational noise of the fuel-fired heating apparatus.
From at least thermal stress and operational noise reduction standpoints, the disclosed placement of a resilient insulation material in engagement with only a side portion of a fuel burner could also be used to advantage in applications where only a single burner is employed in a fuel-fired heating apparatus. Moreover, principles of the present invention could also be utilized to advantage with burners positioned in non-horizontal orientations and positioned in other locations within a combustion chamber portion of a fuel-fired heating appliance.
It should be noted that while in a preferred embodiment of the present invention a resilient, insulative material is sandwiched between and resiliently contacts the burners and a facing surface portion of the combustion chamber, and is operative to block the flow of uncombusted fuel between the burners and the facing combustion chamber surface portion, the invention could provide some of the above-described advantages without incorporating therein all of the structural and operational features present in the preferred invention embodiment.
For example, if a non-resilient insulation material were to be used, the sandwiched structure would still desirably increase the temperature of a side of the firing burner it contacts. As another example, if a resilient, non-insulative sandwiched structure were to be used, burner operational noise that may occur would still be reduced, and the thermal expansion of the burners during firing thereof would still be resiliently resisted. Also, even if the sandwiched structure did not substantially block the flow of uncombusted fuel between the burners and the facing combustion chamber surface, the sandwiched structure could still provide some or all of the other benefits that it does in the preferred embodiment of the invention.
Referring initially to
As illustrated in
The fuel burner system 28 includes a plurality of tubular metal fuel burners 30 (representatively six premix-type gas burners 30a-30f) which longitudinally extend horizontally through the combustion chamber 14 in a mutually spaced, parallel relationship, and suitable controls 32 permitting a staged firing of the burners 30—for example, firing only the burners 30a-30c under low fire conditions or firing all or the burners 30a-30f under high fire conditions. Other firing stage combinations may be alternatively utilized if desired, and there may be a greater or lesser number of burners incorporated in the burner system 28. Both the premix-type burners 30 and the associated burner controls 32 may be of a suitable conventional construction well known to those of ordinary skill in this particular art. As best illustrated in
Burners 30 have open inlet end portions (not shown) which are suitably anchored to a vertical wall portion of the combustion chamber 14, and have closed outlet ends 34 (see, for example, the representative burner 30a in
In each of the firing burners (such as burner 30a partially illustrated in
With reference now to
The sandwiched ceramic fiber insulation blanket 60 serves several functions in the representatively illustrated fuel-fired heating apparatus 10. First, it basically “plugs” the space within the interior of the combustion chamber 14 between the bottom sides 38 of the burners 30a-30f and the top side of the underlying relatively rigid bottom insulation structure 24. During low fire operation of the heating apparatus 10 in which, by way of non-limiting illustration and example, only the burners 30a-30c are being fired, this prevents migration of uncombusted fuel from the firing burners 30a-30c to the non-firing burners 30d-30f via any portion of the vertical space between the bottom sides 38 of the burners 30a-30f and the top side of the underlying relatively rigid bottom interior insulation structure 24 within the combustion chamber 14. This substantially lessens the amount of unburned fuel discharged through the flue pipe 18 during low fire operation of the heating apparatus 10, thereby reducing its pollutant emissions.
Second, during firing of any of the burners 30 there exists a substantial temperature differential between its (hotter) top side 36 and its (cooler) bottom side 38. This top-to-bottom temperature differential causes the burner (such as the burner 30a depicted in
Third, this reduction of thermal stress on each firing burner 30 is achieved without substantially impeding the differential longitudinal expansion (i.e., bowing down) of the burner. When a firing burner 30 expands during firing thereof, as indicated by the double-ended arrow 62 in
Fourth, the resilient engagement of the ceramic fiber insulation blanket 60 with the bottom sides 38 of the burners 30a-30f acts as a damper to any harmonic vibrations created in the burners during firing thereof. This, in turn, desirably reduces the operational noise of the fuel-fired heating apparatus 10.
AS previously mentioned, a greater or lesser number of burners 30 could be utilized in the fuel burner system 28 if desired, and the multiple burners could be grouped for staging purposes in a variety of different manners. Additionally, the disclosed placement of a resilient insulation material in engagement with only a side portion of a fuel burner could also be used to advantage (at least from thermal stress and operational noise reduction standpoints) in applications where only a single burner is employed in a fuel-fired heating apparatus. Further, while the interior of the combustion chamber is representatively lined with a relatively rigid fiberboard insulation material, and the sandwiched insulation material is illustratively a ceramic fiber insulation blanket structure, a variety of other types of resiliently compressible and relatively rigid insulation materials could be alternatively utilized if desired without departing from principles of the present invention. Moreover, principles of the present invention could also be utilized with burners positioned in non-horizontal orientations and positioned in other locations within a combustion chamber.
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.
