Patent Publication Number: US-11662120-B2

Title: Reduced size fire tube boiler system and method of operating same

Description:
FIELD 
     The present invention relates to boiler systems that employ combustion processes and, more particularly, to improved boiler systems for hot water and steam applications and associated methods of operation. 
     BACKGROUND 
     Boiler systems that employ combustion processes to generate heat are commonly employed in a variety of environments. Fire tube boilers or boiler furnaces typically have a combustion chamber encompassed within a vessel or water tank and a plurality of heat transfer tubes passing through the vessel for conducting heated or hot combustion gases resulting from combustion of an air-fuel mixture by a burner, typically located at the front of the boiler. The hot combustion gases are typically passed from the front of the boiler, to the rear, and back to the front. Additional passes, using additional tubes, are often provided within the boiler to accomplish complete heat exchange. 
     In other systems, multiple combustion stages, particularly by using multiple combustion chambers, are used to accomplish complete combustion. For example, see U.S. Pat. No. 6,971,336, which teaches a firetube boiler furnace having two combustion sections and an in-line intermediate tubular heat transfer section between the two combustion sections and integral to the pressure vessel. This design provides a staged oxidant combustion apparatus with separate in-line combustion chambers for fuel-rich primary combustion and fuel-lean secondary combustion and sufficient cooling of the combustion products from the primary combustion such that when the secondary combustion oxidant is added in the secondary combustion stage, the NO x  formation is less than 5 ppmv at 3% O 2 . 
     It has been found the prior systems, such as the kind noted above, while capable of providing benefits, also can have drawbacks, including significant complexity, and relatively high costs of production, installation and/or maintenance. Moreover, such prior systems can take up a rather large area, or “footprint,” and have a relatively large size, creating complexity at during installation, particularly in instances in which space is limited and/or access is difficult. 
     In view of one or more such limitations that exist in relation to conventional fire tube boiler systems, it would be advantageous if improvements could be achieved in relation to such boiler systems and related methods of operation. 
     SUMMARY 
     The present disclosure, in at least some embodiments, relates to a boiler system that includes a burner and a housing having a generally cylindrical shape and extending between first and second walls to provide a generally cylindrical space. Further, a fire tube is positioned near a bottom of the generally cylindrical space the fire tube and extends longitudinally from a first wall of the cylindrical housing to a fire tube end wall, with the fire tube providing a combustion chamber where combustion of an air-fuel mixture is accomplished using the burner. Additionally, a first set of tubes is located within the housing, with the tubes of the first set extending longitudinally from and parallel with the end of the fire tube to the second wall of the housing, and a second set of tubes is located above and about a portion of the fire tube and a portion of the first set of tubes, with the tubes of the second set of tubes generally spanning a length extending between the first and the second walls of the cylindrical housing. A chamber providing a space between and connecting the first and second sets of tubes is provided as well, and heated or hot combustion gases flow from the fire tube to the first set of tubes, through the chamber space, and to the second set of tubes. The boiler system can be configured for use with steam and hot water applications. 
     Other embodiments are contemplated and considered to be within the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features of the present disclosure which are believed to be novel are set forth with particularity in the appended claims. Embodiments of the disclosure are disclosed with reference to the accompanying drawings and are for illustrative purposes only. The disclosure is not limited in its application to the details of construction or the arrangement of the components illustrated in the drawings. The disclosure is capable of other embodiments or of being practiced or carried out in other various ways. Like reference numerals are used to indicate like components. In the drawings: 
         FIG.  1    is a schematic diagram of a boiler system in accordance with one example embodiment encompassed herein; 
         FIG.  2    is a sectional view taken at about line  2 - 2  of  FIG.  1   ; 
         FIG.  3    is a schematic diagram of boiler system, similar to the boiler system of  FIG.  1    but showing an alternative burner arrangement, in accordance with one example embodiment encompassed herein; 
         FIG.  4    is a sectional view taken along line  4 - 4  of  FIG.  3   ; 
         FIG.  5    is a schematic diagram of a boiler system in accordance with another example embodiment encompassed herein; 
         FIG.  6    is a sectional view taken along line  6 - 6  of  FIG.  5   ; 
         FIG.  7    is a schematic diagram of boiler system, similar to the boiler system of  FIG.  5   , but showing an alternative burner arrangement, in accordance with one example embodiment encompassed herein; 
         FIG.  8    is a sectional view taken along line  8 - 8  of  FIG.  7   ; 
         FIG.  9    is a diagrammatic illustration of a prior boiler system showing typical furnace lengths L f  and typical boiler lengths, L b , of such a prior boiler system; and, 
         FIG.  10    is a diagrammatic illustration of a new boiler system provided in accordance with embodiments of the present disclosure, and showing typical furnace lengths L nf  and typical boiler lengths, L nb  of such boiler systems. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    shows a schematic diagram of a boiler system (or “boiler”), generally referenced by numeral  10 , in accordance with one example embodiment encompassed herein, and  FIG.  2    is a sectional view taken at about line  2 - 2  of  FIG.  1   . With reference to these Figures, the boiler  10  employs, in accordance with at least some embodiments, a housing or shell  12  with, as shown in the present embodiment, a generally cylindrical shape, and includes a circumference, and is mounted upon an appropriate base structure  14 . At or near its front end  16  ( FIG.  1   ), the boiler  10  is formed or otherwise provided with an outer front end wall  18  ( FIG.  1   ) and an inner front end wall  20  ( FIG.  1   ), which can in at least some embodiments take the form of a tube sheet, spaced longitudinally of the boiler with respect to the outer front end wall. Similarly, at or near its rear end  22  ( FIG.  1   ), the boiler is formed or otherwise provided with an outer rear end wall  24  ( FIG.  1   ) and an inner rear end wall  26  ( FIG.  1   ) and which again can in at least some embodiments take the form of a tube sheet. As described further below, the shell  12 , together with the inner front and rear end walls  20 ,  26  form the substantially tank or vessel that contains water that is to be heated. 
     Extending longitudinally (and as shown horizontally) of the boiler  10  and generally mounted within the shell  12  and generally near its bottom  28  is a main or fire tube or furnace  30 , which provides a combustion chamber  32  ( FIG.  1   ). The combustion chamber  32  is generally bounded by a shell structure  34 , which in the present embodiment takes a cylindrical shape having a circumference. The shell structure  34  extends longitudinally from the front furnace end wall  35  which, in the present embodiment is a portion of the front inner end wall  20 , and to a furnace end wall,  36  ( FIG.  1   ), where the rear end wall  36  can, in at least some embodiments, take the form of a tube sheet. 
     At or near its front end wall  35 , the fire tube  30  opens to accommodate a burner  50  ( FIG.  1   ), described in greater detail herein. At or near its rear end wall  36 , the fire tube  30  extends and opens to a first set of tubes, generally referenced by numeral  40 , which are located, in the embodiment illustrated, rearward of the fire tube and which further extend longitudinally (and as shown horizontally) of the boiler  10 . In other words, the tubes of the first set of tubes  40  extend to be contained within the circumference of the shell structure  34  when viewing the sectional views of  FIGS.  2  and  4   , or contained within a projection of the circumference of the shell structure longitudinally. The first set of tubes  40  further extend to and through the inner rear end wall  26  to a turnaround space  42  ( FIG.  1   ) between the rear outer and inner end walls  24 ,  26 , respectively, of the boiler  10 . In accordance with at least some embodiments, the rear outer end wall  24  is constructed so that it can be opened, for example as a hinged door, to permit access to the turnaround space  42  and other features or structures of the boiler  10 , and thus in at least such embodiments can be described as an access door. 
     Also extending longitudinally (and as shown horizontally) of the boiler  10  is a second set of tubes, generally referenced by numeral  44 , located generally above the fire tube  30  and above the first set of tubes  40 , and generally span a length extending from the inner rear end wall  26  to the inner front end wall  20 . Moreover, the second set of tubes  44  are open to a space forward of the front inner end wall of the boiler, generally referenced by number  46  ( FIG.  1   ), which space provides access to an exhaust or stack outlet  48 . 
     In accordance with at least some embodiments, the shell structure  34  of the furnace  30  is centered with respect to the housing  12  of the boiler system  10  with respect to a vertical plane P, and the tubes of the first set of tubes and the tubes of the second set of tubes are symmetrically positioned with respect to the vertical plane P. Moreover, in accordance with at least some embodiments, the shell structure  34  of the furnace  30  is positioned with respect to the housing  12  of the boiler system  10  such that the shell structure of the furnace, and all of the tubes of the first set of tubes  40  are below a horizontal plane H of the housing  12  of the boiler system  10 . Finally, the tubes of the second set of tubes are circumferentially disposed about the shell structure of the furnace (and therefore the tubes of the first set of tubes) such that they are located above a horizontal plane H f  of the shell structure  34  of furnace  30 . The second set of tubes  44  is disposed symmetrically with respect to the vertical plane P of the boiler housing  12  of the boiler  10 . 
     The burner  50  ( FIG.  1   ) is provided to accomplish combustion within the main tube  30 . In at least some embodiments, the burner  50  can take the form an air-fuel burner having a burner head  52  ( FIG.  1   ) often taking the form of a cylinder adapted to receive a combustible air-fuel mixture. Air for the air-fuel mixture is provided by way of: an air inlet  54  ( FIG.  1   ) formed in a housing  56  ( FIG.  1   ), which includes or provides for a damper  58  ( FIG.  1   ) for opening or closing the air inlet to selectively provide an air flow, indicated by arrows  59  ( FIG.  1   ). Fuel, such as gas (e.g., natural gas) is provided, as indicated by arrows  60 , to the burner  50  from a fuel source (not shown) by way of a fuel inlet  61 . In accordance with at least some embodiments, the burner  50  can be described as a “pre-mix” burner. In the embodiment illustrated in  FIGS.  1  and  2   , burner  50  the takes the form of a “gun” style burner arrangement. It is contemplated that, in at least some embodiments, the burner head  52  is configured to discharge the combustible air-fuel mixture into the combustion chamber. The discharged combustible air-fuel mixture is ignited to produce a flame in the combustion chamber  32 . 
     In at least some embodiments, and as shown (in  FIG.  1   ), the burner head  52  is incorporated or provided with respect to the main or fire tube  30  by mounting the burner  50  to the main or fire tube front wall  35 , so that the burner head extends into the main or fire tube. With this arrangement, the combustion chamber  32  is at least in some sense integrated with and used as part of the burner  50 . 
     In a further embodiment, as shown in  FIGS.  3  and  4   , with  FIG.  4    being a sectional view taken at about line  4 - 4  of  FIG.  3   , the boiler  10 ′ includes an integrated burner  50 ′ that is integrally provided with the boiler system. More particularly, as shown, boiler  10 ′ includes an additional front housing or head portion  80 ′ in which the burner  50 ′ is provided and which an air passage  81 ′ is provided. Air for the air-fuel mixture is provided, indicated by arrows  82 ′, by way of: an air inlet  54 ′ ( FIG.  3   ) formed or provided in the front housing  80 ′ ( FIG.  3   ). The air is drawn, via a combustion air fan  83 ′ ( FIG.  3   ) and as shown by arrows  84 ′, towards the damper  58 ′ ( FIG.  3   ) via the passage  81 ′. The damper  58 ′ provides again for opening or closing of the air inlet  54 ′, or more generally the air passage  81 ′, to selectively provide an air flow, indicated by arrows  59 ′ ( FIG.  3   ). Fuel, such as gas (e.g., natural gas) is provided, as indicated by arrows  60 ′, to the burner  50 ′ from a fuel source (not shown) by way of a fuel inlet  61 ′. In accordance with at least some embodiments, the burner  50  can again be described as a “pre-mix” burner. In general, the overall components of the boiler system  10 ′ are similar or the same as those provided with respect to  FIGS.  1  and  2   . Like parts are labeled with like numbers. 
     Also as shown, with reference to  FIGS.  1 - 4   , various regions of the boiler  10 / 10 ′, including over portions of its outer housing  12 / 12 ′ (e.g., as shown at and near its rear outer wall  26 / 26 ′), is provided with insulation  62 / 62 ′ ( FIGS.  1  and  3   ). Additionally, as shown, the fire tube  30 / 30 ′, is, over a portion of its length, provided with an insulation  64 / 64 ′ that surrounds a portion of the burner head  52 / 52 ′. 
     In accordance with embodiments of the present disclosure, the main or fire tube  30 / 30 ′ provides for complete combustion of heated gases, as well as passage of such heated gases to the first set of tubes  40 / 40 ′ rearward of the fire tube, with such passage or flow indicated by arrows  66 / 66 ′. The first set of tubes  40 / 40 ′ provide for further passage of the heated gases to the turnaround space  42 / 42 ′, with such flow indicated by arrows  67 / 67 ′ and then to the second set of tubes  44 / 44 ′ located, as shown, above or vertically in relation to the first set of fire tubes, which such flow indicated by arrows  68 / 68 ′. The second set of tubes provide for further passage of heated gases in to the space  46 / 46 ′, and then to the exhaust  48 / 48 ′, as indicated by arrows  70 / 70 ′, where the gases are discharged, as indicated by arrows  72 / 72 ′. 
     As shown in  FIGS.  1  and  2   , as well as  FIGS.  3  and  4   , in accordance with at least some embodiments of the present disclosure, the boiler  10 / 10 ′ is provided for use with a steam application. The second set of tubes  44 / 44 ′ are positioned within the boiler shell  12 / 12 ′ so that they are spaced circumferentially about or around an upper portion of the fire tube  30 / 30 ′. The second set of tubes  44 / 44 ′, together with the fire tube  30 / 30 ′ and the first set of tubes  40 / 40 ′, are positioned below a level  73 / 73 ′ of water  74 / 74 ′ that that is contained within the shell, and thus are completed submerged in water. The water is heated for use in other applications. Additionally and as shown, the second set of tubes  44 / 44 ′ are positioned and oriented or disposed adjacent one another and to create additional space for steam that is created due to heat transfer from the first and second sets of tubes  40 / 40 ′,  44 / 44 ′ to the water  74 / 74 ′. Controlled discharge of such steam can be discharged via the outlet (e.g., steam outlet)  76 / 76 ′. 
       FIG.  5    is a schematic diagram of a boiler system  10 ″ in accordance with another example embodiment encompassed herein and  FIG.  6    is a sectional view taken along line  6 - 6  of  FIG.  5    and having a burner  50 ″ similar to the burner  50  of  FIGS.  1  and  2   . FIG.  FIG.  7    is a schematic diagram of boiler system  10 ″′, similar to the boiler system  10 ″ of  FIG.  5   , but showing an alternative burner  50 ″′ (similar to the burner arrangement of  FIGS.  3  and  4   ), in accordance with one example embodiment encompassed herein.  FIG.  8    is a sectional view taken along line  8 - 8  of  FIG.  7   . 
     With reference to these Figures, the boiler  10 ″/ 10 ′″ employs, in accordance with at least some embodiments, a housing or shell  12 ″/ 12 ′″ with, as shown in the present embodiment, a generally cylindrical shape, and includes a circumference, and is mounted upon an appropriate base structure  14 ″/ 14 ′″. At or near its front end  16 ″/ 16 ′″ ( FIGS.  5  and  7   ), the boiler  10 ″ 10 ′″ is formed or otherwise provided with an outer front end wall  18 ″ 18 ′″ ( FIGS.  5  and  7   ) and an inner front end wall  20 ″/ 20 ′″ ( FIGS.  5  and  7   ), which can in at least some embodiments take the form of a tube sheet, spaced longitudinally of the boiler with respect to the outer front end wall. Similarly, at or near its rear end  22 ″ 22 ′″ ( FIGS.  5  and  7   ), the boiler is formed or otherwise provided with an outer rear end wall  24 ″/ 24 ′″ ( FIGS.  5  and  7   ) and an inner rear end wall  26 ″/ 26 ′″ ( FIGS.  5  and  7   ) and which again can in at least some embodiments take the form of a tube sheet. As described further below, the shell  12 ″/ 12 ′″, together with the inner front and rear end walls  20 ″/ 20 ′″,  26 ″/ 26 ′″ form the substantially tank or vessel that contains water that is to be heated. 
     Extending longitudinally (and as shown horizontally) of the boiler  10 ″/ 10 ′″ and generally mounted within the shell  12 ″/ 12 ′″ and generally near its bottom  28 ″/ 28 ′″ is a main or fire tube or furnace  30 ″/ 30 ′″, which provides a combustion chamber  32 ″/ 32 ′″ ( FIGS.  5  and  7   ). The combustion chamber  32 ″/ 32 ′″ is generally bounded by a shell structure  34 ″/ 34 ′″, which in the present embodiment takes a cylindrical shape having a circumference. The shell structure  34 ″/ 34 ′″ extends longitudinally from the front furnace end wall  35 ″/ 35 ′″ which, in the present embodiment is a portion of the front inner end wall  20 ″/ 20 ′″, and to a furnace end wall,  36 ″/ 36 ′″ ( FIGS.  5  and  7   ), where the rear end wall  36 ″/ 36 ′″ can, in at least some embodiments, take the form of a tube sheet. 
     At or near its front end wall  35 ″/ 35 ′″, the fire tube  30 ″/ 30 ′″ opens to accommodate a burner  50 ″/ 50 ′″ ( FIGS.  5  and  7   ), described in greater detail herein. At or near its rear end wall  36 ″/ 36 ′″, the fire tube  30 ″/ 30 ′″ extends and opens to a first set of tubes, generally referenced by numeral  40 ″/ 40 ′″, which are located, in the embodiment illustrated, rearward of the fire tube and which further extend longitudinally (and as shown horizontally) of the boiler  10 ″/ 10 ′″. In other words, the tubes of the first set of tubes  40 ″/ 40 ′″ extend to be contained within the circumference of the shell structure  34 ″/ 34 ′″ when viewing the sectional views of  FIGS.  6  and  8   , or contained within a projection of the circumference of the shell structure longitudinally. The first set of tubes  40 ″/ 40 ′″ further extend to and through the inner rear end wall  26 ″/ 26 ′″ to a turnaround space  42 ″/ 42 ′″ ( FIGS.  5  and  7   ) between the rear outer and inner end walls  24 ″/ 24 ′″,  26 ″/ 26 ′″, respectively, of the boiler  10 ″/ 10 ′″. In accordance with at least some embodiments, the rear outer end wall  24 ″/ 24 ′″ is constructed so that it can be opened, for example as a hinged door, to permit access to the turnaround space  42 ″/ 42 ′″ and other features or structures of the boiler  10 ″/ 10 ′″, and thus in at least such embodiments can be described as an access door. 
     Also extending longitudinally (and as shown horizontally) of the boiler  10 ″/ 10 ′″ is a second set of tubes, generally referenced by numeral  44 ″/ 44 ′″, located generally above the fire tube  30 ″/ 30 ′″ and above the first set of tubes  40 ″/ 40 ′″, and generally span a length extending from the inner rear end wall  26 ″/ 26 ′″ to the inner front end wall  20 ″/ 20 ′″. Moreover, the second set of tubes  44 ″/ 44 ′″ are open to a space forward of the front inner end wall of the boiler, generally referenced by number  46 ″/ 46 ′″ ( FIGS.  5  and  7   ), which space provides access to an exhaust or stack outlet  48 ″/ 48 ′″. 
     In accordance with at least some embodiments, the shell structure  34 ″/ 34 ′″ of the furnace  30 ″/ 30 ′″ is centered with respect to the housing  12 ″/ 12 ′″ of the boiler system  10 ″/ 10 ′″ with respect to a vertical plane P″/P′″, and the tubes of the first set of tubes and the tubes of the second set of tubes are symmetrically positioned with respect to the vertical plane P″/P′″. Moreover, in accordance with at least some embodiments, the shell structure  34 ″/ 34 ′″ of the furnace  30 ″/ 30 ′″ is positioned with respect to the housing  12 ″/ 12 ′″ of the boiler system  10 ″/ 10 ′″ such that the shell structure of the furnace, and all of the tubes of the first set of tubes  40 ″/ 40 ′″ are below a horizontal plane H″/H′″ of the housing  12 ″/ 12 ′″ of the boiler system  10 ″/ 10 ′″. Finally, the tubes of the second set of tubes are circumferentially disposed about the shell structure of the furnace (and therefore the tubes of the first set of tubes) such that they are located above a horizontal plane H f ″/H f ″′ of the shell structure  34 ″/ 34 ′″ of furnace  30 ″/ 30 ′″. The second set of tubes  44 ″/ 44 ′″ is disposed symmetrically with respect to the vertical plane P″/P′″ of the boiler housing  12 ″/ 12 ′″ of the boiler  10 ″/ 10 ′″. 
     The burner  50 ″/ 50 ′″ ( FIGS.  5  and  7   ) is provided to accomplish combustion within the main tube  30 ″/ 30 ′″. In at least some embodiments, the burner  50 ″/ 50 ′″ can take the form an air-fuel burner having a burner head  52 ″/ 52 ′″ ( FIGS.  5  and  7   ) often taking the form of a cylinder adapted to receive a combustible air-fuel mixture. Air for the air-fuel mixture is provided by way of: an air inlet  54 ″/ 54 ′″ ( FIGS.  5  and  7   ) formed in a housing  56 ″/ 56 ′″ ( FIGS.  5  and  7   ), which includes or provides for a damper  58 ″/ 58 ′″ ( FIGS.  5  and  7   ) for opening or closing the air inlet to selectively provide an air flow, indicated by arrows  59 ″/ 59 ′″ ( FIGS.  5  and  7   ). Fuel, such as gas (e.g., natural gas) is provided, as indicated by arrows  60 ″/ 60 ′″, to the burner  50 ″/ 50 ′″ from a fuel source (not shown) by way of a fuel inlet  61 ″/ 61 ′″. In accordance with at least some embodiments, the burner  50 ″/ 50 ′″ can be described as a “pre-mix” burner. 
     In accordance with these embodiments, the respective boiler systems  10 ″/ 10 ′″, respectively, are provided for use with a hot water application. Accordingly, it is contemplated that the boilers  10 ″/ 10 ′″, and particularly each of the respective shells  12 ″/ 12 ′″, are completely, or at least substantially completely filled (or “flooded”) with water  74  during operation, and so no level of water is indicated, as was shown in  FIGS.  1 - 4   . Water typically exits (for use in various applications) via outlet  92 ″/ 92 ′″ and/or is replenished (as the water is used) via inlet  90 ″/ 90 ′″ ( FIGS.  5 ,  7   ). As shown in  FIGS.  5 - 8   , the second set of tubes  44 ″/ 44 ′″, respectively, are positioned within the boiler shell  12 ″,/ 12 ′″ respectively, so that the tubes are spaced about or around an upper portion of the fire tube  30 ″/ 30 ′″, respectively, and are disposed throughout a substantial portion of the space above the respective fire tube  30 ″/ 30 ′″. Stated another way, the respective second set of tubes  44 ″/ 44 ′″ is not contained below a level of water, as discussed in reference to the embodiment described in  FIGS.  1 - 4    and the tubes of the respective second set of tubes  44 ″/ 44 ′″ now are positioned to extend within an uppermost region of the shell  12 ″/ 12 ′″. 
     With further reference to  FIGS.  5  and  6   , an exemplary boiler  10 ″ is shown for use for a water application. With the exception of the arrangement of the second set of tubes  44 ″, as described above, the remaining structures of the boiler  10 ″ are consistent with those described with reference to  FIGS.  1  and  2   , above, with like reference numbers referring to like structures. Similarly, with reference to  FIGS.  7  and  8   , an exemplary boiler system  10 ′″ is shown for use with a water application. With the exception of the arrangement of the second set of tubes  44 ′″, as described above, the remaining structures of the boiler  10 ′″ are consistent with those described with reference to  FIGS.  3  and  4   , above, with like reference numbers referring to like structures. 
     One burner type or style that is contemplated for use, or contemplated to be adapted for use, in regard to embodiment(s) of the boiler  10 / 10 ′/ 10 ″/ 10 ′″ of the present disclosure is the XPO™ Indirect burner, available from Maxon Corporation, located at 201 East 18th Street, Muncie, Ind. 47302. In such embodiments, various features of the burner  50 / 50 ′/ 50 ″/ 50 ′″ can take a specific form, for example, the burner head  52 / 52 ′/ 52 ″/ 52 ′″ can take the form of an air-fuel nozzle. Additional details regarding at least some embodiments of burners, such as the XPO™ Indirect burner, that can be used in accordance with at least some embodiments of the present disclosure are provided in U.S. Pat. No. 8,784,096, entitled “Low NOx Indirect Fire Burner”, the entirety of the teachings of which are incorporated by reference herein. In other embodiments, the burner  52 / 52 ′/ 52 ″/ 52 ′″ can take on other styles or forms, for instance a burner of the fiber mesh style (not shown), where the burner head can take the form of a burner canister, or surface burner. 
     In accordance with embodiments of the present disclosure, it is contemplated that the tubes making up the first and second sets of tubes  40 / 40 ′/ 40 ″/ 40 ′″ and  44 / 44 ′/ 44 ″/ 44 ′″, respectively, can comprise any of a variety of tubes including by way of example, plain tubes, plain tubes with extended heating surface, and rifled tubes that are generally known. One example of rifled tubes currently available and known is X-ID® tubes, available from Tektube, located at 555 West. 41 st  Street, Tulsa, Okla., 74107. Another example of tubes suitable for use in relation to embodiments of the present disclosure are aluFer® tubes, available from Hoval Aktiengesellschaft Austrasse 70, 9490 Vaduz Liechtenstein. In at least some embodiments, the tubes can comprise cylindrical smooth outer-walled outer tubes of steel into which profiled inserts made of aluminum, and having ribs, may be inserted, such as of the kind described in a in U.S. Pat. No. 6,070,657, entitled “Heat Exchanger Tube for Heating Boilers”, the entirety of the teachings of which are incorporated by reference herein. In other embodiments, it is contemplated that the tubes can take on other styles or forms. Other tube types are contemplated and considered within the scope of the present disclosure. 
       FIG.  9 A  is a diagrammatic illustration of a prior boiler system  100  showing typical furnace lengths L f  and typical boiler lengths, L b , of such a prior boiler system. A typical prior boiler system  100  is available, for example, as CleaverBrooks&#39; CBEX Elite boiler.  FIG.  9 B  is a is a diagrammatic illustration of a new boiler system  110  provided in accordance with embodiments of the present disclosure, including by way of example, those depicted and described in one or more of  FIGS.  1 - 8   , and showing typical furnace lengths L nf  and typical boiler lengths, L nb  of such boiler systems. Table A, below, indicates typical furnace and boiler lengths for boiler systems  100  of the prior design ( FIG.  9   ), as well as the reduced furnace and boiler lengths, respectively, for boiler systems  110  provided in accordance with exemplary embodiments of the present disclosure ( FIG.  10   ). 
     
       
         
           
               
             
               
                 TABLE A 
               
             
            
               
                   
               
               
                 Furnace and Boiler Lengths 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Typical Prior 
                   
                 Typical Prior 
               
               
                   
                 New Design 
                 Designs* 
                 New Design 
                 Designs* 
               
               
                   
                 Furnace 
                 Avg Furnace 
                 Boiler 
                 Boiler 
               
               
                 Boiler 
                 Length 
                 Length 
                 Length 
                 Length 
               
               
                 Horsepower 
                 L nf  (inch) 
                 L f  (inch) 
                 L nb  (inch) 
                 L b  (inch) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 100 
                 57 
                 95 
                 139 
                 156 
               
               
                 125 
                 57 
                 102 
                 139 
                 163 
               
               
                 150 
                 59 
                 106 
                 141 
                 167 
               
               
                 200 
                 59 
                 125 
                 141 
                 186 
               
               
                 250 
                 59 
                 150 
                 144 
                 214 
               
               
                 300 
                 59 
                 158 
                 144 
                 222 
               
               
                 350 
                 63 
                 170 
                 148 
                 232 
               
               
                 400 
                 63 
                 179 
                 148 
                 241 
               
               
                 500 
                 65 
                 182 
                 151 
                 245 
               
               
                 600 
                 65 
                 197 
                 151 
                 260 
               
               
                 700 
                 72 
                 206 
                 158 
                 269 
               
               
                 800 
                 72 
                 213 
                 158 
                 276 
               
               
                   
               
               
                 *Typical prior design lengths taken from CleaverBrooks&#39; CBEX Elite boiler 
               
            
           
         
       
     
     In accordance with embodiments of the present disclosure, and as noted above with references to the Figures, tubes of the second set of tubes  44 / 44 ′/ 44 ″/ 44 ′″ are circumferentially disposed about the shell structure  12 / 12 ′/ 12 ″/ 12 ′″ of the furnace  30 / 30 ′/ 30 ″/ 30 ′″ (and therefore the tubes of the first set of tubes  40 / 40 ′/ 40 ″/ 40 ′″) such that they are located above a horizontal plane H f /H f ′/H f ″/H f′ ′″ of the shell structure  34 / 34 ′/ 34 ″/ 34 ′″ of furnace  30 / 30 ′/ 30 ″/ 30 ′″. It is of further note that, as the boiler horsepower increases (e.g., up to 800 horsepower), it has been found that, in at least some embodiments, the number of tubes also increases and the boiler is packed much tighter with tubes, or stated another way, the spacing between respective tubes is more compressed. Moreover, it has been found that at least some of the tubes of the second set of tubes  44 / 44 ′/ 44 ″/ 44 ′″ on such larger horsepower boilers are located below the horizontal plane H f /H f ′/H f ″/H f ′″ and may be considered as being located below a portion the fire tube. 
     Advantageously, disclosed in accordance with at least some embodiments of the present disclosure, is a means for providing a boiler system with a reduced size while maintaining efficiency. In accordance with at least some embodiments, the boiler comprises a tank for a supply of water to be heated. Within the lower portion of the tank, a combustion chamber is provided, having a burner assembly mounted at one end. The chamber is terminated short of the opposite end of the water tank and has a series of smoke or fire tubes to direct the combustion products through the water to a manifold at the tank end. The manifold directs the combustion products back through tubes into the water tank, generally mounted about the combustion chamber, to an exhausting manifold at the burner end of the tank. 
     Advantageously, the boiler and/or the burner-boiler system, when compared to conventional systems, has a reduced size or “footprint,” and so is better suited for a smaller boiler room, or other location where space is a substantial constraint. 
     Boiler systems provided in accordance with embodiments of the present disclosure, achieve 9 ppmv NO x  formation at 3% O 2 . In still further embodiments, the system achieves 5 ppmv NO x  at 3% O 2 . 
     Moreover, boiler systems provided in accordance with the present disclosure do not require two (or multiple) combustion stages or sections in order to accomplish complete combustion of the air-fuel mixture, let alone such two (or multiple) sections having one zone that may be considered as “fuel rich” and another that may be considered as “fuel lean.” 
     A boiler system may comprise two or more embodiments described herein. Any reference to orientation (e.g., horizontal, vertical, upper, lower, front, rear, and the like) is made with reference to the specific drawing for teaching purposes only and should not be considered limiting. 
     In accordance with at least some embodiments of the present disclosure, a boiler system is provided that comprises: a burner; a housing having a generally cylindrical shape and extending between first and second walls to provide a generally cylindrical space; a fire tube positioned near a bottom of the generally cylindrical space the fire tube and extending longitudinally from a first wall of the cylindrical housing to a fire tube end wall, the fire tube providing a combustion chamber where combustion of an air-fuel mixture is accomplished using the burner; a first set of tubes located within the housing and extending longitudinally from and parallel with the end of the fire tube to the second wall of the housing, and a second set of tubes located above and about a portion of the fire tube and a portion of the first set of tubes, the second set of tubes generally spanning a length extending between the first and the second walls of the cylindrical housing; and a chamber providing a space between and connecting the first and second sets of tubes; and wherein heated combustion gases flow from the fire tube to the first set of tubes, through the chamber space, and to the second set of tubes. 
     In accordance with at least some embodiments of the present disclosure, the fire tube includes a shell structure comprising a generally cylindrical shape having a circumference and the first set of tubes extends in-line with the fire tube. 
     In accordance with at least some embodiments of the present disclosure, the housing includes a circumference and the second set of tubes extends at least partially about the shell structure. 
     In accordance with at least some embodiments of the present disclosure, a vertical plane passing through a center of the housing also passes through a center of the fire tube and the first and second sets of tubes are each positioned generally symmetrically on either side of the vertical plane. 
     In accordance with at least some embodiments of the present disclosure, at least one of: (a) none of the tubes of the second set of tubes extend in a region or location that is below any portion of the fire tube, and (b) none of the tubes of the second set of tubes extend in a region or location that is below any portion of the tubes of the first set of tubes. 
     In accordance with at least some embodiments of the present disclosure, none of the tubes of the second set of tubes extend in a region or location that is between the fire tube and the bottom of the cylindrical housing. 
     In accordance with at least some embodiments of the present disclosure, the flow of heated combustion gases is sequential such that the heated gases flow from the fire tube directly to and through the first set of tubes, and then directly to and through the chamber space, and then directly to and through the second set of tubes, before the heated combustion gases are discharged from the boiler. 
     In accordance with at least some embodiments of the present disclosure, the second set of tubes and the first set of tubes are submerged in water. 
     In accordance with at least some embodiments of the present disclosure, either: (a) water is provided within the housing to a water level, providing space open space to remain within the housing and permitting the boiler to be configured for steam applications; or (b) water is provided within the housing so that the housing is filled with water and the boiler is configured for hot water applications. 
     In accordance with at least some embodiments of the present disclosure, the first set of tubes comprises one or more plain tubes, one or more plain tubes with an extended heating surface, or one or more rifled tubes, and where in the second set of tubes comprises one or more plain tubes, one or more plain tubes with an extended heating surface, or one or more rifled tubes. 
     In accordance with at least some embodiments of the present disclosure, the burner is integrated with respect to the fire tube. 
     In accordance with at least some embodiments of the present disclosure, the burner is integrally formed with the housing. 
     In accordance with at least some embodiments of the present disclosure, combustion of the air-fuel mixture is completed within the combustion chamber, which is the only combustion chamber. 
     In accordance with at least some embodiments of the present disclosure, the air provided with for use with the air-fuel mixture is provided from a single source. 
     In accordance with at least some embodiments of the present disclosure, there is no device provided within the chamber providing the space between and connecting the first and second sets of tubes, that is configured to close any portion or end of any of the tubes in the first set of tubes or any of the tubes in the second set of tubes. 
     In accordance with at least some embodiments of the present disclosure, there is no device provided within the chamber providing the space between and connecting the first and second sets of tubes, that is configured to reverse the flow of any portion of the heated gases in any of the tubes in the first set of tubes, or any of the tubes in the second set of tubes. 
     Notwithstanding the above description, it should be appreciated that the present disclosure is intended to encompass numerous other systems, arrangements, and operational processes in addition to those descripted above. In reference to the preceding paragraphs and the aforementioned figures, although various embodiments of the present invention have been described above, it should be understood that embodiments have been presented by way of example, and not limitation. A person of ordinary skill in the art will recognize that there are various changes that can be made to the present invention without departing from the spirit and scope of the present invention. Therefore, the invention should not be limited by any of the above-described example embodiments, but should be defined only in accordance with the following claims and equivalents of the claimed invention presented herein.