Patent Publication Number: US-11378307-B2

Title: Hybrid condensing boiler with preheater

Description:
BACKGROUND 
     Boilers are known and used to heat water or create steam for various purposes. A typical boiler includes a tank in which the water is heated. A burner may provide hot combustion gases that are used to heat the water. For example, some boilers are configured as “fire tube” designs in which the combustion gases are provided through tubes inside the tank that heat water in the tank. Other types of boilers are configured as “water tube” designs in which the water is provided through tubes and the combustion gases are provided to heat water in the tubes. 
     SUMMARY 
     A boiler according to an example of the present disclosure includes a tank, a gas circuit that has a main combustion chamber in the tank and branch tubes in the tank that extend off of the main combustion chamber, and a water circuit fluidly isolated from the gas circuit and including a first manifold and water tubes extending off of the first manifold. Each water tube extends through a respective one of the branch tubes. 
     A further embodiment of any of the foregoing embodiments includes a second manifold connected with the water tubes and water output tubes that extend off of the second manifold. Each water output tube has an outlet end opening to the interior of the tank. 
     In a further embodiment of any of the foregoing embodiments, the outlet ends at located at the bottom of the tank. 
     A further embodiment of any of the foregoing embodiments includes fins disposed inside of the branch tubes. 
     In a further embodiment of any of the foregoing embodiments, the first manifold is outside of the tank. 
     In a further embodiment of any of the foregoing embodiments, the main combustion chamber is U-shaped. 
     In a further embodiment of any of the foregoing embodiments, main combustion chamber is closed-ended. 
     In a further embodiment of any of the foregoing embodiments, the tank has domed top and bottom caps. 
     In a further embodiment of any of the foregoing embodiments, the tank has a lobed cross-sectional shape. 
     A boiler according to an example of the present disclosure includes a tank, a gas circuit that has a main combustion chamber in the tank, a water circuit fluidly isolated from the gas circuit having first and second manifolds outside of the tank at, respectively, first and second opposed ends of the tank, and water tubes extending through the tank. Each water tube has an inlet at the first manifold and an outlet at the second manifold. Water output tubes extend off of the second manifold and into the tank. Each water output tube has an outlet end in the tank, and at least one tank outlet at the top of the tank. 
     In a further embodiment of any of the foregoing embodiments, the gas circuit includes branch tubes in the tank extending off of the main combustion chamber. 
     In a further embodiment of any of the foregoing embodiments, each water tube extends through a respective one of the branch tubes. 
     A further embodiment of any of the foregoing embodiments includes fins disposed inside of the branch tubes. 
     In a further embodiment of any of the foregoing embodiments, the main combustion chamber is U-shaped. 
     In a further embodiment of any of the foregoing embodiments, the main combustion chamber is closed-ended. 
     In a further embodiment of any of the foregoing embodiments, the tank has domed top and bottom caps. 
     In a further embodiment of any of the foregoing embodiments, the tank has a lobed cross-sectional shape. 
     A boiler according to an example of the present disclosure includes a tank, a gas circuit that has a main combustion chamber in the tank to transfer thermal energy to water in the tank and branch tubes in the tank that extend off of the main combustion chamber to also transfer thermal energy to water in the tank, and a water circuit fluidly isolated from the gas circuit and that has first and second manifolds outside of the tank at, respectively, first and second opposed ends of the tank. The water tubes extend through the tank. Each water tube has an inlet at the first manifold and an outlet at the second manifold, and each water tube extends through a respective one of the branch tubes such that water in the water tube is preheated prior to being discharged into the tank. Water output tubes extend off of the second manifold and into the tank. Each water output tube has an outlet in the tank, and at least one tank outlet at the top of the tank. 
     A further embodiment of any of the foregoing embodiments includes fins disposed inside of the branch tubes, and wherein the main combustion chamber is U-shaped, the main combustion chamber is closed-ended, the tank has domed top and bottom caps, and the tank has a lobed cross-sectional shape. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
         FIG. 1A  illustrates a side view of an example boiler. 
         FIG. 1B  illustrates a top-down view of the boiler. 
         FIG. 2A  illustrates a view of the boiler with a portion of the tank cutaway. 
         FIG. 2B  illustrates a view of the boiler without the tank. 
         FIG. 3  illustrates a view of the boiler without the tank and a portion of the (branch tube) hot gas circuit. 
         FIG. 4  illustrates an isolated view of a portion of the tank. 
         FIG. 5  illustrates an alternate example of an end cap. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  illustrates a side view of an example boiler  20 , and  FIG. 1B  illustrates a top-down view of the boiler  20 . The boiler  20  is generally operable to heat water or create steam and, in this regard, may be used as a water heater, pool heater, or any other application in which boilers are used. The boiler  20  is presented to demonstrate various features. However, although example features may be demonstrated together in combination, it is to be appreciated that the features may alternatively be used in other combinations that may exclude one or more of the features or include additional conventional features. 
       FIG. 2A  illustrates a partial cutaway view of selected portions of the boiler  20 . In general, the boiler  20  includes a tank  22 , a water circuit  24 , and a gas circuit  26 . The boiler  20  is also shown in  FIG. 2B , but without the tank  22 . The tank  22  is a closed vessel that includes a first end  22   a  and an opposed second end  22   b . For example, the tank  22 , as well as all of the components of the boiler  20  described below, may be composed of stainless steel or other material that is corrosion resistant under conditions that are typical of boilers. In the illustrated example, the first end  22   a  is the bottom of the tank  22  and the second end  22   b  is the top of the tank  22 . For instance, the tank  22  is defined by a tank side wall  22   c  and first and second (bottom and top) domed end caps  22   d / 22   e  that are sealed with the side wall  22   c . Together, the side wall  22   c  and end caps  22   d / 22   e  define a hollow interior  22   f .  FIG. 3  illustrates another view of the boiler  20 , but without the side wall  22   c  and without portions of the water circuit  24 . For purposes that will be discussed herein below, each of the caps  22   d / 22   e  includes a respective flange  23  that defines a plurality of through-holes  23   a . The through-holes  23   a  may be of the same diametric size or of different sizes, depending on the size of the tubes extending therein. 
     The water circuit  24  circulates water and the gas circuit  26  circulates hot combustion gases from a burner  28  ( FIG. 1A ). The water circuit  24  and the gas circuit  26  are fluidly isolated from each other such that the water and the combustion gases do not mix or even come into direct contact. 
     The water circuit  24  includes an inlet pipe  30 , which may be outfitted with a flange  30   a  or other type of fitting for attaching the boiler  20  to a water source. As an example, the inlet pipe  30  is the sole or exclusive inlet for water into the boiler  20 . 
     The water circuit  24  further includes a first manifold  32 , which is connected to the inlet pipe  30 . In this example, the first manifold  32  is generally U-shaped or “8” shaped and may be formed of a single piece or multiple pieces. The first manifold  32  includes first and second legs  32   a / 32   b  (see  FIG. 2B ) that straddle the first end cap  22   d . The first manifold  32  is generally horizontally oriented and the legs  32   a / 32   b  are elongated in the horizontal direction. The inlet pipe  30  opens into the first manifold  32  at the bottom of the “U” such that water entering the first manifold  32  from the inlet pipe  30  is generally equally divided to flow into both legs  32   a / 32   b.    
     The water circuit  24  additionally includes water tubes  34  that extend off of the first manifold  32 . For instance, the water tubes  34  include inlets  34   a  that open on the top of the first manifold  32  such that the water tubes  34  extend substantially vertically from the first manifold  32 . As an example, a first group of the water tubes  34  extend off of the first leg  32   a  and a second group of the water tubes  34  extend off of the second leg  32   b . The legs  32   a / 32   b  of the first manifold  32  are closed-ended such that water provided into the first manifold  32  must flow into the water tubes  34 . 
     The water tubes  34  extend vertically from the first manifold  32  through the through-holes  23   a  of the flange  23  of the first end cap  22   d  ( FIG. 2B ). As shown in  FIG. 2A , the water tubes  34  extend into and through the tank  22  and then through the through-holes  23   a  of the flange  23  of the second end cap  22   e . The water tubes  34  then connect to a second manifold  36  that is located adjacent the second end  22   b  of the tank  22 , i.e., adjacent the second end cap  22   e.    
     Similar to the first manifold  32 , the second manifold  36  is also generally U-shaped or ″8 shaped and may be formed of a single piece or multiple pieces. The second manifold  36  includes first and second legs  36   a / 36   b  (see  FIG. 2B ) that straddle the second end cap  22   e . The second manifold  36  is generally horizontally oriented and the legs  36   a / 36   b  are elongated in the horizontal direction. The water tubes  34  include outlets  34   b  that open on the bottom of the second manifold  36 . Unlike the legs  32   a / 32   b  of the first manifold  32 , the legs  36   a / 36   b  of the second manifold  36  have openings  36   c  at the ends and sides for injecting water into the tank  22 , and openings on the bottom for receiving the water tubes  34 . 
     The openings  36   c  are connected to water outlet tubes  38  that thereby extend off of the second manifold  36 . The water outlet tubes  38  include an outlet section  38   b  coming out of the second manifold  36  and a substantially vertical section of the water outlet tube  38  that extends through another one of the through holes  23   a  of the flange  23  and into the tank  22  ( FIG. 2B ). As shown in  FIG. 2B , the water outlet tube  38  (one shown) extends substantially the entire vertical length of the tank  22  to a location that is adjacent the first end cap  22   d , i.e., the bottom of the tank  22 . At its terminal end, the water outlet tube  38  has an outlet  38   c  that opens to the interior of the tank  22 . The outlet  38   c  does not bottom-out on the bottom of the tank  22 , but rather extends to a location that is near the bottom. In general, this location will be in at least the bottom 25% of the height of the tank  22 , but more preferably in the bottom 15% or 10%. 
     The second end cap  22   e  further includes one or more openings  40  for discharging water. For example, the openings  40  are connected to discharge tubes  42 , which are connected to a discharge manifold  44 . As an example, the discharge manifold  44  may be a pipe that is outfitted with a flange  44   a  or other type of fitting for attaching the boiler  20  to a downstream device or use. The water circuit  24  may thus include any or all of the structures described above though which water flows. 
     The gas circuit  26  includes structures that combustion gases flow through in the boiler  20 . In this regard, the gas circuit  26  may include a main combustion chamber  50  (see  FIGS. 2A, 2B, and 3 ). As best shown in  FIG. 3 , the main combustion chamber  50  is generally U-shaped and includes a first leg  50   a , a turn section  50   b , and a second leg  50   c . The “U” is oriented sideways such that the legs  50   a / 50   c  are generally horizontally oriented, while the turn section  50   b  is generally vertically oriented. The first leg  50   a  includes an opening that is connected to the burner  28 . The first leg  50   a  extends through an opening  52  in the tank  22  ( FIG. 2A ) into the interior of the tank  22 . Beyond the opening  52 , the entirety of the main combustion chamber  50  is within the tank  22 . 
     The gas circuit  26  may further include branch tubes  54  that extend off of the main combustion chamber  50 . For instance, in the illustrated example, all of the branch tubes  54  extend off of the lower portion of the turn section  50   b  and the second leg  50   c  of the main combustion chamber  50 . 
     The branch tubes  54  include elbows  54   a  that provide a turn from generally horizontal sections of the branch tubes  54  coming out of the main combustion chamber  50  and substantially vertical sections of the branch tubes  54  that extend upwards through the tank  22  and the through holes  23   a  in the flange  23  of the second end cap  22   e . The elbows  54   a  permit the branch tubes  54  to extend upwards rather than further in the horizontal lateral direction, which facilitates a reduction in the footprint of the boiler  20 . Additionally, the elbows  54   a  provide compliance to permit thermal expansion of the branch tubes  54 . In general, the is one group of branch tubes  54  that all extend off of one side of the main combustion chamber  50  (toward the leg  32   a ) and another group of branch tubes  54  that extend off of the opposed side of the main combustion chamber  50  (towards the legs  32   b ). 
     The branch tubes  54  are interrupted at the through-holes  23   a  or just beyond the through-holes  23   a  such that the vertically upward-extending sections of the branch tubes  54  terminate. Additional downwardly-extending branch tubes  56  begin at other ones of the holes  23   a  in the flange  23  of the second end cap  22   e . The branch tubes  56  extend downwards through the tank  22  to the through-holes  23   a  in the flange  23  of the first end cap  22   d . The branch tubes  56  terminate at the through-holes  23   a  or just beyond the through-holes  23   a . Enclosures  58  (see  FIG. 1A ) may be provided around each of the end caps  22   d / 22   e  such that there are gas transfer spaces  60  below and above the first and second end caps  22   d / 22   e , respectively, into which the branch tubes  54 / 56  open. Thus, combustion gases are discharged from the branch tubes  54  into the space  60  above the second end cap  22   e . The gases are subsequently drawn into the branch tubes  56  from the space  60  via a downstream draft pressure differential. If desired, elbow connectors could instead be used to directly connect the tubes  54 / 56  rather than discharging the gas into the space  60 . 
     The branch tubes  56  terminate at the same through-holes  23   a  in the flange  23  of the first end cap  22   d  which the water tubes  34  extend through such that inside of the tank  22  the water tubes  34  are disposed inside of the branch tubes  56 . For instance, each water tube  34  is concentrically arranged in a corresponding one of the branch tubes  56 . The branch tubes  56  are of larger diameter than the water tubes  34  such that there is an annular gas passage between the outer diameter surface of the water tube  34  and the inner diameter surface of the branch tube  56  for flow of the combustion gases. As shown in  FIG. 2A , there may be fins  57  disposed inside of the branch tubes  56  to provide additional surface area through which to transfer thermal energy to the water in the water tubes  34 . The fins  57  are generally thin ridges or projections that either wrap/spiral around the water tubes  34  from top to bottom as a group or individually or that extend linearly betwee the water tubes and the inner diameter of the branch tubes  56 . 
     The burner  28  produces hot combustion gas that is blown or otherwise provided into the main combustion chamber  50 . The combustion gas travels from the main combustion chamber  50  into the branch tubes  54 . The branch tubes  54  open into the gas transfer space  60  above the second end cap  22   e . From there, the gas travels into the branch tubes  56  and then into the gas transfer space  60  below the first end cap  22   d . The gas may then be exhausted from the boiler  20  through an exhaust structure  62  ( FIG. 1B ) and/or chimney. 
     During operation of the boiler  20  to heat water, water is initially provided in the water circuit  24  through the inlet pipe  30  and into the first manifold  32 . The water then travels vertically upwards through the water tubes  34  inside of the tank  22  to the second manifold  36 , and then to the water outlet tubes  38 , which discharge the water into the interior of the tank  22 . Thus, water is not directly provided into the tank, but rather first travels through the water tubes  34  inside the tank  22 . 
     The burner  28  provides hot combustion gases into the main combustion chamber  50 , which then flow through the branch tubes  54 / 56  as described above. The thermal energy from the gases in the main combustion chamber  50  and branch tubes  54 / 56  serves to conductively and radiantly heat the water in the tank  22  that is in contact with the outer surfaces of the main combustion chamber  50  and the outer surfaces of the branch tubes  54 / 56 . Additionally, the hot gases that flow through the branch tubes  56 , in which the water tubes  34  are disposed, transfer thermal energy to the water flowing in the water tubes  34 . The fins  57  facilitate such heat transfer. The water entering the boiler  20  is thus preheated in the water transfer tubes  34  by the hot gases in the branch tubes  56  prior to being discharged from the water outlet tubes  38  into the interior of the tank  22 . The branch tubes  56  thereby serve the dual purpose of heating the water in the tank and preheating the water in the water tubes  34 . In particular, the preheating avoids directly feeding source water, which may initially be cold, into the tank  22 . This facilitates a reduction in thermal shock to hot components in the boiler  20 , such as the main combustion chamber  50  and branch tubes  54 , which come into contact with the water in the interior of the tank  22 , i.e., the temperature difference between the components and the water is less than it would otherwise be without such preheating. 
     The water outlet tubes  38  provide additional convective heating. For instance, since the water outlet tubes  38  open at the bottom of the tank  22  and the water is discharged from the top of the tank  22 , the discharge of water from the water outlet tubes  38  serves to circulate the water in the tank  22 , thereby churning cooler water that may settle toward the bottom of the tank  22  and pushing the water toward the top of the tank  22 . The churning and mixing of the water may thus facilitate the reduction of water stagnation and steam while promoting convective heating. 
     As can be appreciated, the water can cause an elevation in pressure inside of the tank  22 . In this regard, a further feature of the boiler  20  to accommodate such pressures is that the end caps  22   d / 22   e  are domed ( FIG. 3 ). The domed shape, which may be hemi-cylindrical or near hemi-cylindrical serves to uniformly distribute pressure across the end caps  22   d / 22   e . For example, the end caps  22   d / 22   e  may be formed of relatively thin tube sheets, such as stainless steel tube sheets. The domed shape also permits compliance when under pressure or under thermal expansion, thereby also facilitating a mitigation of pressure/stress on other components, such as the main combustion chamber  50  and branch tubes  54 / 56 . 
     The configuration of the main combustion chamber  50 , branch tubes  54 / 56 , manifolds  32 / 36 , and water tubes  34  also serves to reduce the footprint of the boiler  20 . For instance, the boiler  20  as a relatively compact footprint because the tubes  34 / 54 / 56  are oriented substantially vertically rather than horizontally, which is enabled by the U-shaped configurations of the manifolds  32 / 36  and main combustion chamber  50 . In this regard, as shown in an isolated view of the side wall  22   c  of the tank  22  in  FIG. 4 , the side wall  22   c  has a lobed cross-sectional shape (in a plane that is perpendicular to vertical direction A). For instance, the side wall  22   c  defines a first lobe  64   a  and a second lobe  64   b  that meet at junctions  66 . For instance, the lobes  64   a / 64   b  may be symmetrical about a horizontal axis that intersects the junctions  66 . 
     The junctions  66  projects inwards such that the narrowest portion of the profile of the side wall  22   c  is between the junctions  66 . In the boiler  20 , the junctions  66  project toward the center of the boiler  20  and between adjacent ones of the branch tubes  56 . Such a lobed-shape further facilitates the reduction in the size the footprint of the boiler  20 , while also reducing weight. 
       FIG. 3  illustrates an example of the end cap  22   e  that has a cylindrical dome.  FIG. 5  illustrates an alternate example of an end cap  122   e  in which, rather than the cylindrical dome, the end cap  122   e  has two circular domes. Additionally, in the end cap  22   e , the openings  23   a  are exclusively in the flange  23 . In the end cap  122   e , however, a some of the openings  123   a  are in the circular domes. 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.