Abstract:
A steam boiler ( 15 ) comprising a fuel burning device ( 16 ) disposed in a combustion chamber and adapted to burn a fuel to form combustion gases ( 19 ), a passage ( 30 ) extending between a water inlet ( 20 ) and a steam outlet ( 23 ), the passage having a water space ( 31 ) and a steam space ( 32 ), a flue passage ( 33 ) extending between the combustion chamber and a flue outlet ( 24 ) and having a gas heat transfer space ( 34 ), a heat exchange element ( 43 ) between the gas heat transfer space and the water and steam spaces, the heat exchange element having a gas-side surface ( 35 ) that absorbs heat from the combustion gases and an opposed water-side surface ( 38 ) that radiates heat, the water-side surface having a first portion ( 39 ) adjacent to the water space and a second portion ( 40 ) adjacent to the steam space, the gas-side surface having a first portion ( 36 ) opposite the water-side first portion and a second portion ( 37 ) opposite the water-side second portion, the water-side first portion having a surface area and the water side second portion having a surface area, the gas-side first portion having a surface area and the gas-side second portion having a surface area, and a heat shield ( 41, 42, 45, 48 ) covering at least some of the surface area of the gas-side second portion. The surface area of the gas-side first portion may be greater than the surface area of the water-side first portion and the surface area of the gas-side second portion may be less than or approximately equal to the surface area of the water-side second portion.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to the field of steam boilers, and more particularly to a corrosive resistant steam boiler. 
       BACKGROUND ART 
       [0002]    Steam boilers are well-known in the prior art and have been used in residential heating applications for years. Most steam boiler systems known in the prior art include a boiler connected to radiators by a pipe system. The pipe system allows steam to rise into the radiators, pushing the ambient air out of the radiators, until a steam vent valve on the radiator closes due to the temperature rise. The steam then condenses against the inside surface of the radiator and trickles back to the boiler by gravity through the same pipe system. Thus, most steam heating systems are open systems that are filled with air during the off cycle. The air is forced out the system when the boiler is steaming. At the end of a call for heat, the steam field collapses and draws air back into the system. 
         [0003]    Generally, residential steam boilers are constructed of cast iron with vertical flue passages or flue ways. These vertical flue ways pass through a steam collection volume, sometimes referred to as a steam chest or steam space. The boiler is filled with water to a defined water level inside the casting. The casting acts as a heat exchange unit and a heat source is used to heat the water inside the boiler. Steam then collects above the waterline in the steam space before exiting up through the pipe system to the radiators. Occasionally, water must be added to the boiler because of intended and unintended loses. Intended loses may include lose of water to flush or blow down the mechanical float water level control, lose of water to flush or blow down sediment from the bottom of the boiler, and lose of water due to the escape of steam through the vent valves. Unintended loses may include leaking radiator vents and leaking in the pipe system. 
         [0004]    However, prior art boilers tend to corrode or degrade over time and with use. Thus, it would be beneficial to provide a boiler which is more resistant to the corrosive effect of heat and impurities in the system. 
       DISCLOSURE OF THE INVENTION 
       [0005]    With parenthetical reference to the corresponding parts portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides a steam boiler ( 15 ) comprising a fuel burning device ( 16 ) disposed in a combustion chamber ( 52 ) and adapted to burn a fuel to form combustion gases ( 19 ), a passage ( 30 ) extending between a water inlet ( 20 ) and a steam outlet ( 22 ), the passage having a water space ( 31 ) and a steam space ( 32 ), a flue passage ( 33 ) extending between the combustion chamber and a flue outlet ( 24 ) and having a gas heat transfer space ( 34 ), a heat exchange element ( 43 ) between the gas heat transfer space and the water and steam spaces, the heat exchange element having a gas-side surface ( 35 ) that absorbs heat from the combustion gases and an opposed water-side surface ( 38 ) that radiates heat, the water-side surface having a first portion ( 39 ) adjacent to the water space and a second portion ( 40 ) adjacent to the steam space, the gas-side surface having a first portion ( 36 ) opposite the water-side first portion and a second portion ( 37 ) opposite the water-side second portion, the water-side first portion having a surface area and the water side second portion having a surface area, the gas-side first portion having a surface area and the gas-side second portion having a surface area, and a heat shield ( 41 ,  42 ,  45 ,  48 ) covering at least some of the surface area of the gas-side second portion. 
         [0006]    The heat shield ( 41 ) may cover all of the surface area of the gas-side second portion and the heat shield ( 42 ,  45 ,  48 ) may cover some of the surface area of the gas-side first portion. The surface area of the gas-side second portion may be less than or approximately equal to the surface area of the water-side second portion. The surface area of the gas-side first portion may be greater than the surface area of the water-side first portion. The surface area of the gas-side second portion may be greater than the surface area of the water-side second portion and the surface area of the gas-side first portion may be greater than the surface area of the water-side first portion. The gas-side first portion may comprise a pin deck ( 44 ). The heat exchange element may comprise a cast iron section ( 26 - 29 ) having an interior volume and the interior volume may comprise the water space and the steam space. The heat exchange element may comprise a first cast iron section ( 26 ) connected to a second cast iron section ( 27 ), the first cast iron section and the second cast iron section may form a volume ( 34   a ) there between, and the volume may comprise the gas heat transfer space. The first cast iron section may have an interior volume and the interior volume may comprise the water space ( 31   a ) and the steam space ( 32   a ). The second cast iron section may have an interior volume and the interior volume of the second cast iron section may comprise a second water space ( 31   b ) and a second steam space ( 32   b ). The heat shield ( 45 ) may comprise a metal plate ( 46 ) covering at least some of the surface area of the gas-side second portion ( 37 ), and an air space ( 47 ) between the metal plate and at least some of the surface area of the gas-side second portion. The heat shield ( 48 ) may comprise an insulation layer ( 49 ) bonded to at least some of the surface area of the gas-side second portion. The heat exchange element may have a ratio between the surface area of the gas-side first portion and the surface area of the water-side first portion of greater than one, and the heat exchange element may have a ratio between the surface area of the gas-side second portion and the surface area of the water-side second portion that is less than the ratio between the surface area of the gas-side first portion and the surface area of the water-side first portion. 
         [0007]    In another aspect, a heat exchanger is provided comprising a first passage extending between a water inlet and a steam outlet, the first passage having a water space and a steam space, a second passage extending between a fluid or gas inlet and a fluid or gas outlet, the second passage having a heat transfer space, a heat exchange element between the heat transfer space and the water and steam spaces, the heat exchange element having a gas-side surface adapted to absorb heat from the heat transfer space and an opposed water-side surface adapted to radiate heat, the water-side surface having a first portion adjacent to the water space and a second portion adjacent to the steam space, the gas-side surface having a first portion opposite the water-side first portion and a second portion opposite the water-side second portion, the water-side first portion having a surface area and the water side second portion having a surface area, the gas-side first portion having a surface area and the gas-side second portion having a surface area, and a heat shield covering at least some of the surface area of the gas-side second portion. 
         [0008]    Accordingly, the general object of the present invention is to provide an improved steam boiler that is resistant to corrosion. These and other objections and advantages will become apparent from the foregoing and ongoing written specifications, the drawings, and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of the preferred embodiment of the improved steam boiler. 
           [0010]      FIG. 2  is an exploded view of the steam boiler shown in  FIG. 1 . 
           [0011]      FIG. 3  is a vertical sectional view of the steam boiler shown in  FIG. 1 , taken generally on line A-A of  FIG. 1 . 
           [0012]      FIG. 4  is an enlarged detailed view of the cross-section shown in  FIG. 3 , taken within the indicated circle C of  FIG. 3 . 
           [0013]      FIG. 5  is a vertical cross-sectional view of an alternative embodiment of the heat transfer walls and heat shields shown in  FIG. 3 . 
           [0014]      FIG. 6  is a vertical cross-sectional view of a second alternative embodiment of a heat transfer wall and heat shield. 
           [0015]      FIG. 7  is a vertical cross-sectional view of a third alternative embodiment of a heat transfer wall and heat shield. 
           [0016]      FIG. 8  is a perspective view of an alternative embodiment of the steam boiler shown in  FIG. 1 . 
           [0017]      FIG. 9  is a vertical sectional view of the steam boiler shown in  FIG. 8 , taken generally on line B-B of  FIG. 8 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
         [0019]    Referring now to the drawings, and more particularly to  FIGS. 1 and 2  thereof, this invention provides an improved steam boiler, of which the presently preferred embodiment is generally indicated at  15 . Boiler  15  generally includes a conventional burner  16  connected to a cast iron heat exchanger  17 . Heat exchanger  17  is connected to a water source by pipes  21 , through which a desired water level for the interior volume of heat exchanger  17  is provided. Heat exchanger  17  is also connected to pipes  23 , which are part of a pipe system between heat exchanger  17  and peripheral radiators. Heat exchanger  17  includes a combustion gas outlet vent  24  at the top. 
         [0020]    As shown in  FIGS. 2-3 , heat exchanger  17  is formed from four castings, a front casting  26 , a first center casting  27 , a second center casting  28 , and a rear casting  29 . Rear casting  29  has a recessed lower portion  53  and each of front casting  26  and center castings  27  and  28  include openings  51   a - c . Front casting  26  is connected to burner  16  by a burner tube  56  and a combustion chamber connector  54 , which includes a hinged door  55  that provides access to the interior volume of heat exchanger  17 , thereby forming a combustion chamber  52  for forming combustion gases  19 . Opening  51   a  allows for open communication and passage from burner  16  through burner tube  56  and connector  54  into combustion chamber  52 . 
         [0021]    Castings  26 - 29  are joined with tie rods extending between front casting  26  and rear casting  29 , such that openings  51   a - 51   c  and recess  53  form combustion chamber  52 . The castings are also configured such that a vertically extending flue passage  33   a  is provided between adjacent castings  26  and  27 , a vertically extending flue passage  33   b  is provided between castings  27  and  28 , and a vertically extending flue passage  33   c  is provided between castings  28  and  29 , respectively. These flue passages communicate between combustion chamber  52  and flue gas exhaust outlet  24 . Vertically extending flue ways  33   a - 33   c  are defined by outer opposed vertical surfaces  35   a  and  35   b , outer opposed vertical surfaces  35   c  and  35   d , and outer opposed vertical surfaces  35   e  and  35   f , respectively, of castings  26 - 29 . These passages provide a heat transfer space  34 . 
         [0022]    Castings  26 - 29  have an upper hollow region that defines vertical passages  30   a - 30   d , respectively. Passages  30   a - 30   d  allow for water and steam to communicate between water inlets  20   a - 20   d  and steam outlets  22   a - 22   d , respectively. Vertically extending passages  30   a - 30   d  are defined by vertical inner surfaces  38   a  and  38   b , vertical inner surfaces  38   c  and  38   d , vertical inner surfaces  38   e  and  38   f , and vertical inner surfaces  38   g  and  38   h , respectively, of castings  26 - 29 . 
         [0023]    As shown in  FIGS. 3-4 , passages  30  are partially filled with water  25  to a waterline  56 . Passages  30  have a lower water space  31  and an upper steam space  32 . Water space  31  is generally filled with water  25 . Steam space  32  is a volume in which steam forms before exiting. Therefore, the two inner water side surfaces  38  of each casting each comprise a first lower portion  39  adjacent to water space  31  and a second upper portion  40  adjacent to steam space  32 . Each of these portions has in turn a certain surface area. In the preferred embodiment, water side surface  38  is a vertically extending flat planar surface. 
         [0024]    The portion of the casting between passage  30  and flue passage  33  acts as a heat exchange wall  43 . Walls  43   a - 43   f  of castings  26 - 29 , respectively, allow for the transfer of heat from combustion gases  19 , which pass through flue passage  33 , to water  25  in passage  30 , thereby heating water  25  to form steam that will pass from outlets  22  to a pipe system  23  and peripheral radiators, thereby heating the radiators and providing radiated heat to a residence or other facility. Wall  43  has two opposed outer surfaces, namely water side surface  38 ( b - g ) and gas side surface  35 ( a - f ). 
         [0025]    Gas side surface  35  has a lower portion  36  opposite lower portion  39  of water side surface  38  and an upper portion  37  opposite upper portion  40  of water side surface  38 . Each of these portions has in turn a certain surface area. 
         [0026]    In the preferred embodiment, lower portion  36  of gas side surface  35  is provided with a conventional pin deck  44 , while upper portion  37  of gas side surface  35  does not include a pin deck. Instead, upper portion  37  is a flat vertical planar surface. As a result, the enhanced outer surface area of lower portion  36  is greater than the flat outer surface area of upper portion  37 . Because inner water side surface  38  is a flat vertical planar surface on both its lower portion  39  and its upper portion of  40 , the surface area of lower portion  36  of gas side surface  35  is substantially greater than the surface area of lower portion  39  of water side surface  38 . However, the surface area of upper portion  37  of gas side surface  35  is substantially the same as the surface area of upper portion  40  of water side  38 . As a result, greater heat transfer across wall  43  will occur from lower portion  36  of gas side surface  35  to lower portion  39  of water side surface  38  relative to heat transfer between upper portion  37  of gas side surface  35  and upper portion  40  of water side surface  38 . As a result, water space  31  of passages  30  will receive greater emitted heat from wall  43 , while steam space  32  of passages  30  will not be heated to as great an extent as water space  31 . Thus the heat transfer is focused from combustion gases  19  to water  25  in water space  31 . 
         [0027]    Heat transfer across wall  43  is further limited by a heat shield  41  covering upper portion  37  of gas side surface  35 . Heat shield  41  decreases heat transfer from combustion gases  19  in heat transfer space  34  to upper portion  40  of water side surface  38  of heat exchange wall  43 . In the preferred embodiment, heat shield  41  is a metal plate that extends over and covers all of upper portion  37  of gas side surface  35 . As shown, shield  41   a  comprises a horizontal plate connected at its right edge to the top edge of a vertical plate. The vertical plate covers upper portion  37   a  of gas side surface  35   a , and the horizontal plate extends over and is supported by the top of front casting  26 . This same form is employed with respect to shield  41   d  on rear casting  29 . A vertical plate covers upper portion  37   f  of gas side surface  35   f , and is connected at its top edge to the left edge of a horizontal plate that extends over and is supported by the top of rear casting  29 . Shields  41   b  and  41   c  comprise two vertically extending plates connected at their top edges by a horizontal support plate. Shield  41   b  saddles the top of casting  27  such that the first vertical plate covers upper portion  37   b  of gas side surface  35   b  and the second vertical plate covers upper portion  37   c  of gas side surface  35   c . Shield  41   c  saddles the top of casting  28  such that the first vertical plate covers upper portion  37   d  of gas side surface  35   d  and the second vertical plate covers upper portion  37   e  of gas side surface  35   e . Thus, the upper portion  37  of gas side surface  35  does not include a pin deck  44  and instead is covered by heat shield  41 . 
         [0028]    A number of unexpected benefits result from the variation in surface area between upper portion  37  and lower portion  36  of gas side surface  35  and the placement of heat shield  41  over the upper portion  37  of gas side surface  35 . Prior art boilers have been known to experience early corrosion to the upper portion  40  of water side surface  38 . One of the unexpected benefits of the improved design is that it results in less degradation, in comparison to a conventional steam boiler, to upper portion  40  of water side surface  38 . Prior art boilers have also been known to experience excessive amounts of scale build up from calcium and magnesium carbonates on upper portion  40  of water side surface  38 . This scale build up is reduced with the improved design. Thus, counter intuitively and unexpectedly, covering upper portion  37  of gas side surface  35  with shield  41 , rather than covering the upper portion  40  of water side surface  38  where corrosion was typically found in the prior art, reduced the corrosive effects of temperature and contaminants on water side surface  38 . This was found to be particularly beneficial with respect to rear casting  29 . 
         [0029]      FIG. 5  shows an alternative embodiment of heat exchange walls  43  and heat shields  41 . In the alternative embodiment shown in  FIG. 5 , water side surfaces  38  and passages  30  are generally the same as the embodiment shown in  FIG. 3 . However, heat shield  41  and gas side surface  35  have been modified. First, pin deck  44  on lower portion  36  of gas side surface  35  has been removed. Thus, all of gas side surface  35  is a flat vertical planar surface, and the surface area of lower portion  36  is generally the same as the surface area of upper portion  37 . Second, an alternative heat shield  42  is used. Heat shield  42  covers not only the upper portion  37  of gas side surface  35  but also some of lower portion  36  of gas side surface  35 . The vertical plates of the heat shield shown in  FIG. 3  have been lengthened so that they extend below the waterline level  56  in passage  30  and thereby cover at least some of lower portion  36  of gas side surface  35 . 
         [0030]    Two additional embodiments of heat exchange wall  43  and heat shield  41  are shown in  FIGS. 6 and 7 . In the alternative embodiment shown in  FIG. 6 , water side surface  38  and passage  30  are generally the same as the embodiment shown in  FIGS. 3 and 5 . However, heat shield  41  and the left gas side surface have been modified. First, a portion of the pin deck  44  on lower portion  36  of the left gas side surface  35  has been removed. Thus, the upper part of lower portion  36  of the left gas side surface  35  is a flat vertical planar surface. Second, alternative heat shield  45  is used. Heat shield  45  comprises a metal shielding portion  46  that is adapted to cover the upper gas side surfaces by extending from a point midway up the lower portion  36  of the left gas side surface  35 , over the top of the casting, and down to the waterline level  56  on the right gas side surface  35 . Shielding portion  46  is also configured to provide an air space  47  between the inner surface of shielding portion  46  and the subject outer surface of the casting. This air space acts as an insulator. 
         [0031]      FIG. 7  shows a third embodiment of heat exchange wall  43  and heat shield  41 . In the alternative embodiment shown in  FIG. 7 , water side surface  38  and passages  30  are generally the same as the embodiments shown in  FIGS. 3 ,  5  and  6 . In addition, the left gas side surface  35  is generally the same as the embodiment shown and described in  FIG. 6 . However, alternative heat shield  48  is used. Heat shield  48  comprises an outer metal shielding portion  50  that is adapted to cover the upper gas side surfaces by extending from a point midway up the lower portion  36  of the left gas side surface  35 , over the top of the casting, and down to the waterline level  56  on the right gas side surface  35 , as with the embodiment shown in  FIG. 6 . However, rather then an air pocket, an insulation layer  49  is provided between shielding portion  50  and the subject outer surface of the casting. 
         [0032]    While the preferred embodiments show multiple passages  30   a - d  and multiple flue ways  33   a - c  there between, with multiple separating heat exchange walls  43   a - f , it is contemplated that only a single heat exchange wall with the improved features may be used, or the number of heat exchange walls with the improved features may be otherwise varied as desired. Also, in a boiler with multiple heat exchange walls  43 , different embodiments of the heat shield may be used on the different gas side surfaces of the heat exchange walls  43  employed. Thus, the heat shield used may vary among the multiple heat exchange walls  43   a - 43   f  within the boiler or even between the two gas side surfaces of a particular casting. 
         [0033]    Similarly, it is contemplated that the relative surface area of the upper portions and lower portions of the gas side surfaces  35  may be modified. Thus, the surface area of the gas side upper portion  37  may be less than or approximately equal to the surface area of the water side upper portion  40 , the surface area of the gas side lower portion  36  may be greater than the surface area of the water side lower portion  39 , or the surface area of the gas side upper portion  37  may be greater than the surface area of the water side upper portion  40  and the surface area of the gas side lower portion  36  may be greater than the surface area of the water side lower portion  39 . The differences in surface areas may also vary among the multiple heat exchange walls  43   a - 43   f  within the boiler or in a boiler casting (as each of center castings  27  and  28  in the preferred embodiment have two heat exchange walls  43   b ,  43   c  and  43   d ,  43   e , respectively). 
         [0034]      FIG. 8  shows an alternative embodiment of the cast iron heat exchanger  17  shown in  FIG. 1 . In this embodiment, a circular vertical tube type boiler or heat exchanger  60  is employed. Boiler  60  is of a welded steel construction having a number of vertical tubes. As shown, heat exchanger  60  includes a single inlet  61  for water and a single outlet  62  for steam together with a flue gas vent  63 . 
         [0035]    As shown in  FIG. 9 , the interior volume of heat exchanger  60  is similar to the embodiment of heat exchanger  17  shown in  FIG. 5 . Combustion chamber  64  is provided beneath three vertically extending flue passages  65   a - c . Six heat exchange walls  66   a - f  separate multiple interior passages  68   a - d  from flue passages  65   a - c . As with the previous embodiments, passages  68  comprise a lower water space  69  and a steam space  70 , with the water space  69  filled to a waterline  71  with water  25 . Heat exchange walls  66  each have a water side surface  72   a - f  and a gas side surface  73   a - f . The water side surface has a lower portion  74   a - f  and an upper portion  75 - f  each of which has a surface area. Each gas side surface  73  has a corresponding lower portion  76  and upper portion  77 . In this embodiment, water side surfaces  72  and passages  68  are generally the same as the embodiment shown in  FIG. 5 , and gas side surfaces  73  and flue passages  65  are generally the same as the embodiment shown in  FIG. 5 . Thus, all of gas side surface  73  is a flat vertical surface, and the surface area of lower portion  76  is generally the same as the surface area of upper portion  77 . Heat shield  78  covers all of upper portion  77  of gas side surface  73 . Again, heat shield  78  decreases heat transfer from combustion gases  19  in passages  65  to upper portion  75  of water side surface  72  of heat exchange walls  66 . In this embodiment, heat shield  78  is a metal plate that extends over and covers all of upper portion  77  of gas side surface  73  down to waterline  71 . 
         [0036]    Therefore, while the presently-preferred form of the steam boiler have been shown and described, and several alternative embodiments discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.