Abstract:
A boiler includes a cylindrical shell sealed at both ends. A working liquid, typically water, circulates inside the shell. A tube bundle is seated inside the shell. Hot combustion gases circulate inside the tube bundle, heating the water circulating inside the shell. The tube bundle includes a relatively large inlet tube that runs straight to a distal end, where hot combustion gases are turned 180° by a concave inner surface on the tube bundle header, which is not a part of the shell, and are returned by a plurality of smaller diameter return tubes and then to an exhaust stack. The tube bundle includes a front tube sheet and a distal end tube sheet that the tubes are welded to, but these tube sheets are not part of the shell. The entire tube bundle floats inside the shell without being fastened to the shell except at the front of the tube bundle, where a baffle is secured to the front opening of the shell. This allows the tube bundle to be removed from the shell as a single unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not Applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT.  
         [0002]    Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The present invention is related to an apparatus for providing a heated working liquid. More particularly, the present invention is directed to a Scotch Marine style boiler having a removable tube bundle, which has a single un-insulated metal inlet tube for receiving hot combustion gases and a plurality of return tubes that are parallel to the inlet tube and convey hot combustion gases in opposite directions, with the gases being turned 180° by a concave tube-bundle dome on the distal end of the tube bundle, which is not a part of the shell.  
           [0005]    2. Description of the Related Art Including Information Disclosed Under 37 C.F.R. 1.97 and 1.98.  
           [0006]    Scotch marine style boilers having a sealed shell with a plurality of heat exchange tubes sealed inside the shell are well known. Typically all the joints are welded. Such provides access to the interior of the shell and limited access to the tubes that comprise the tube bundle.  
           [0007]    Since the heat exchange tubes are welded into the ends of the shell, these boilers are subject to thermal shock, which can cause leaks in weld joints, from split tubes and the like unless the entire boiler is heated gradually to its equilibrium operating temperate and cooled gradually when it is removed from service. The possibility of damage from thermal shock requires careful and skillful operation of the boiler; decreases the convenience of utilizing the boiler for power, and increases fuel consumption. It also greatly increases the time required to obtain useful power from the boiler after firing begins.  
           [0008]    Repairing damaged tubes requires that a worker enter the man way and squeeze into the shell and cut out the defective tubes with a cutting torch. Thorough inspection of the tube bundle or the interior of the shell is not possible and any work inside the boiler is very labor intensive, expensive and potentially dangerous. This process is so uncertain and laborious that these types of boilers are often scraped when the tubes require significant maintenance, resulting in significant waste of resources.  
           [0009]    Therefore, there is a need for a boiler having a removable tube bundle; that is not subject to thermal shock; and that would consequently be easier to work on than prior art boilers.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    Accordingly, it is a primary object of the present invention to provide a boiler having a removable tube bundle.  
           [0011]    It is another object of the present invention to provide a boiler that is not subject to thermal shock.  
           [0012]    It is another object of the present invention to provide a boiler that is easier to work on than prior art boilers.  
           [0013]    These and other objects of the invention are achieved by providing a shell, basically cylindrical in shape, having a sealed distal end and a forward end that is sealed by a flange member connected to the tube bundle. The tube bundle is self-contained, that is, its integrity and functionality is independent of the shell. The tube bundle is inserted into the shell along sliding rails secured to the bottom of the tube bundle, which slide along rails that are secured to the lower interior surface of the shell.  
           [0014]    Because the tube bundle is a self-contained unit that is fastened to the shell only at the front header and otherwise rests on and floats on rails inside the shell, the boiler is not subject to thermal shock and so does not need to be coddled when heating and cooling the boiler.  
           [0015]    When the tube bundle is removed from the shell, the tube bundle is fully accessible to workers, who may carefully inspect it, perform a full visual inspection and work on it conveniently, while at the same time, the interior of the shell is readily accessible for inspection and repair. Further, it is easily possible to replace the entire tube bundle. In the existing Scotch marine boiler, replacement of the tube bundle is not feasible. The ability to readily replace the tube bundle in the present invention dramatically reduces repair and refurbishment costs associated with maintain boilers and can greatly extend the life of the entire boiler.  
           [0016]    For example, in an 745 kilowatt (100 HP) Scotch marine boiler, re-tubing the boiler would take 32 man hours to accomplish, with not more than two men able to work on the project at the same time. Utilizing the present invention, about nine man hours of labor would be required to re-tube the boiler. Further, more than two men can work on re-tubing the boiler at the same time.  
           [0017]    The present invention is a modification of a complete boiler system, including the burner element and controls, which is fully described in my U.S. patent application Ser. No. 09/391,790, filed Sep. 8, 1999, now issued as U.S. Pat. No. ______ B1, which is hereby incorporated herein by reference.  
           [0018]    Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings, wherein is set forth by way of illustration and example, the preferred embodiment of the present invention and the best mode currently known to the inventor for carrying out his invention.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is right-hand front perspective view of a boiler according to the present invention.  
         [0020]    [0020]FIG. 2 is a right-hand front perspective view of the boiler of FIG. 1 with the tube bundle removed and in position for insertion into the shell.  
         [0021]    [0021]FIG. 3 is the right-hand front perspective view of the boiler as in FIG. 3 illustrating the hidden parts of the boiler.  
         [0022]    [0022]FIG. 4 is a side elevation of the boiler of FIG. 1 with the tube bundle removed and in position for insertion into the shell.  
         [0023]    [0023]FIG. 5 is a schematic front elevation of the shell of the boiler of FIG. 1, illustrating an end view of the vertically oriented rails secured to the interior of the shell and the horizontal rails that are secured to the bottom of the tube bundle that slide along the vertically oriented rails during insertion and removal of the tube bundle from the shell.  
         [0024]    [0024]FIG. 6 is a side elevation of the vertically oriented rails that are welded to the lower inside surface of the shell.  
         [0025]    [0025]FIG. 7 is a cross sectional view taken along lines  8 - 8  of FIG. 3.  
         [0026]    [0026]FIG. 8 is a perspective view of the header on the distal end of the tube bundle showing the concave interior surface of the header, or tube bundle dome.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    As required by the Patent Statutes and the case law, the preferred embodiment of the present invention and the best mode currently known to the inventor for carrying out the invention are disclosed in detail herein. The embodiments disclosed herein, however, are merely illustrative of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely to provide the proper basis for the claims and as a representative basis for teaching one skilled in the art to which the invention pertains to make and use the apparatus and process disclosed herein as embodied in any appropriately specific and detailed structure.  
         [0028]    Referring to FIG. 1, the Scotch marine style boiler, or boiler  10 , includes a shell  12  having a cylindrical main body  14  with a distal end dome  16  permanently sealed onto the cylindrical main body  14 , which seals the distal end of the cylindrical main body  14 . The structure for sealing the distal end of the shell  12  is a matter of design choice. In low pressure applications, the welded dome  16  having a perpendicular collar  17  that is welded to the shell cylindrical body  13  is adequate. In high-pressure applications, it is preferable to construct a flange on the distal end of the shell  12  and bolt a flat plate to the flange. A man way  18  consisting of a circular opening  20  in the top of the cylindrical main body  14  adjacent to the distal end dome  16  with an upstanding collar member  22  fastened to the cylindrical main body  14  about the perimeter of the circular opening  20 , which is sealed by a removable man way cover  24  in a well-known manner, which is moved along the arrow  2  during installation. Access ports  26  are provided for the insertion of various sensors essential to the safe operation of the boiler  10 . These sensors are well-known in the art.  
         [0029]    Still referring to FIG. 1, the boiler is secured to a mounting cradle  30  to keep the cylindrical boiler from rolling around. The base of the mounting cradle  30  is wide enough to provide a stable base for the boiler  10  and may itself be bolted or otherwise fastened to the floor, deck or the like and is also useful in transporting the boiler  10 .  
         [0030]    Still referring to FIG. 1, the front cover  32  of the boiler  10  is circular in plan view and includes a plurality of holes  34  adjacent to its circumference, which align with matching holes  36  about the circumference of a connecting circular flange  38  connected onto the front end of the cylindrical body  14  of the boiler  10 . The front cover  32  is fastened to the circular connecting flange  38 , which is fastened to a front edge of the shell  12 , by the nuts and bolts  40 . A high temperature gasket  42  is interposed between the circular flange  38  and front cover  32 . A high-temperature tube bundle gasket  41  fits onto the front end of the tube bundle  48  and includes apertures for the inlet tube  64  and a single aperture for the return tubes  74 , each having a front end  75 . A reinforcing and locating plate  44  has a substantially oval shape with an upper opening  46  for admitting combustion gases into the tube bundle  48  (See especially FIG. 3) and an exhaust opening  50  in the lower portion of the locating plate  44  for allowing the exhaust gases to exit the tube bundle  48 . The locating plate  44  is connected to the front cover by nuts and bolts  52  inserted through the plurality of apertures  54  adjacent to the perimeter of the locating plate  44  and the aligned apertures  56  in the front cover  32 . An upper opening  55  and a lower opening  57  in the front cover  32  align with the inlet opening  46  and the exhaust opening  50  in the locating plate  44 . Thus the front cover  32  serves to seal the tube bundle  48  into the shell  12  and to seal the front end of the shell  12  itself.  
         [0031]    A burner (not shown) is connected to the upper opening  46  to direct hot combustion gases into the tube bundle  48 . If the burner is capable of projecting a long thin flame encircled by a layer of insulating air, which is the preferred type of burner, then the flame can be projected directly into the tube bundle  48 , all of which is made from typical tube bundle steel without any insulation either inside or outside the tube material. Alternatively, an external conventional fire tube (not shown) having, for example, a lining of refractory brick, may be connected to the upper opening  46 , in which case a conventional burner on the distal end of the fire tube provides the hot combustion gases to heat the tube bundle  48 . When a conventional burner is used, the fire tube must provide combustion gases to the tube bundle  48  that are cool enough that they do not melt the tubes.  
         [0032]    The boiler  10  may be used to produce either steam or hot water from feed water that is circulated through the shell  12  by external an external pump (not shown). When used as a water heater, the feed water enters the shell  12  through the water inlet  58  (FIG.  4 ) located in the bottom of the shell  12  inward from the dome  16  by about ⅛th the length of the shell  12  and the hot water exits from the boiler  10  through the hot water outlet port  60  on the top of the shell  12  adjacent to the burner inlet end of the shell  12 . When the boiler is used to produce steam, the steam exits the boiler  10  from the same outlet port  60  as hot water does, while the feed water is introduced to the boiler  10  through the boiler feed water inlet port  62  located in the middle of the length of the shell  12  about 5 cm (2 inches) below the lowest possible firing level of water in the shell  12 . The boiler  10  may be scaled to provide power throughout a wide range and the physical size of the boiler and accompanying controls, inlets, outlets and the like are determined by the load requirements of a particular application.  
         [0033]    Referring to FIGS. 2, 3, and  4 , the tube bundle  48  includes a relatively large diameter straight inlet tube  64  having an inlet end  66  for the admission of hot combustion gases from a burner and an outlet end  68  that is welded to the distal end tube sheet  70 , which is connected to a header, or tube bundle dome,  72  having an internal surface  71  that is concave, as best shown in FIG. 8. Twenty-eight straight return tubes  74  of smaller diameter than the inlet tube  64 , with the exact number a matter of design choice, each includes a distal end  76  that is welded to the distal end tube sheet  70 . The distal end tube sheet includes aligned apertures for permitting the gases to pass through the tubes and the distal end tube sheet  70  in the conventional manner. The return tubes  74  are gathered into a bundle that collectively exhausts the spent combustion gases through the lower opening  50  in the locator plate  44 , through the front ends  75  of the return tubes  74 , which exhaust the spent combustion gases. The exhaust gas is then passed through an exhaust stack (not shown) that is connected to the lower opening (exhaust opening)  50  in the locating plate  44 . The hot combustion gases are introduced into the inlet tube  64  and flow through the inlet tube in the direction of the arrow  78 , are turned around 180° by the internal surface of the header, or tube bundle dome,  72  and then flow through the return tubes  74  along the direction of the arrow  80 . The inlet end  66  of the inlet tube  64  and the front ends  75  of the return tubes  74  are welded to the front tube sheet  82 , which has aligned apertures for allowing the passage of gases from the tubes through it in the conventional manner. The inlet end  66  of the inlet tube  64  and the front ends  75  of the return tubes  74  lie in the same plane, oftentimes facilitating installation of the boiler  10 .  
         [0034]    The specific diameters of the tubes  64 ,  74  and the number of return tubes  74  is calculated in accordance with the total volume of combustion gases that have to be extracted from the from the return tubes, which are equipped with turbulators in the conventional manner to maintain a desired velocity of gas throughout all the tubes  64 ,  74 .  
         [0035]    Referring to FIGS. 2, 3,  4 , three spaced apart baffles  84  include apertures  86  that the inlet tube  64  and return tubes  74  pass through. The tubes  64 ,  74  are not fastened to the baffles  84 , but are free to float within the apertures  86 . The apertures  86  help to support the tubes  64 ,  74  and to maintain the proper spacing of these tubes, but the principal purpose of the baffles is to help direct the flow of water or steam throughout the shell  12  to improve heat transfer. The baffles  84  have a profile in the broad dimension that is 63% of the surface area of a cross section of the shell  12 . The principal purpose of the baffles  84  is to slow the velocity of the working fluid that flows through the shell  12  and to maximize the time of contact between the water or steam and the tubes  64 ,  74  to increase the efficiency of the heat transfer from the tubes  64 ,  74  to the working fluid. The greater the desired flow rate of the working fluid through the shell  12 , the greater the number of desired baffles is.  
         [0036]    Welded to the lower surfaces of the baffles  84  are a pair of skid rails  88 , which are parallel spaced apart metal bar stock members oriented with the width of the rails being horizontally oriented (See especially FIG. 5). These skid rails  88  allow the tube bundle  48  to be slid into the shell  12  by riding along the skid members  90 , that are welded into the shell  12  along the lower portion of the shell  12  at regular intervals of about 3 cm (See especially FIG. 5), and that consist of metal bar stock members that are oriented so that width is vertical and the skid rails  88  ride on the edge of the bar stock. That is, the skid rails  88  can slide along the top of the aligned skid members  90 , with the skid rails  88  being welded to the baffles  84  and the skid members  90  being welded to the lower surface of the inside of the shell  12 . This system allows the tube bundle  48  to be slid into the shell  12  in the direction of the arrow  92  and to be removed by reversing this direction. Referring in particular to FIG. 6, each skid member  90  has a lower edge  91  with drainage notches  93  formed in it at regular intervals throughout the length of the skid members  90 , which may be semi-circular as shown or another shape. There drainage notches prevent stagnant areas near the skid members  90 , thereby preventing the accumulation of sludge along the skid members  90 . FIG. 7 illustrates an end elevation of the tube bundle  48 .  
         [0037]    A front tube bundle flange  94  is circular and includes an upper circular opening  96  that the inlet tube  64  penetrates and a large roughly half-moon opening  98  that holds the outlet end of the return tubes  74 . The tube bundle flange  94  seals the tube bundle  48  against the mounting flange collar  38  on the front edge of the cylindrical portion of the shell  12 , with the high-temperature gasket  42  being seated between these two surfaces.  
         [0038]    Utilizing the preferred burner, the boiler  10  achieves a fuel to product efficiency of 85%+ and an NOX emission level of 1 on the conventional NOX scale of 1-800. Many boilers are capable of NOX emissions of only 350 and government regulations will soon require levels of 10 or fewer, which the boiler  10  can easily meet.  
         [0039]    While the present invention has been described in accordance with the preferred embodiments thereof, the description is for illustration only and should not be construed as limiting the scope of the invention. Various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention as defined by the following claims.