Abstract:
An improved boiler for generating steam includes a housing that has a proximal end and a distal end, with a water-entry port at the proximal end. A plurality of firetubes are disposed lengthwise in the housing, and the firetubes extend substantially the length of the housing between the proximal end and the distal end. The firetubes are used to pass the heated flue gas through the housing. A pair of side baffles are affixed to the inner surface of the housing that extend at least partially down the length of the housing to separate a portion of the last pass of firetubes near the housing from the remaining firetubes in the housing. At least two cross-sectional baffles are positioned adjacent the side baffles to direct the flow of water opposite to the flue gas flow in the separated part of firetubes.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims priority from U.S. Provisional Application Ser. No. 61/086,039, filed on Aug. 4, 2008, said application being relied upon and incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     A firetube steam boiler as illustrated in  FIG. 1  is commonly known in the art as used for steam generation. A conventional firetube steam boiler  6  may have a Scotch Marine design. The boiler has a closed housing or tank in which water or another fluid is vaporized. The vaporized fluid exits the boiler at saturation temperature for use in various processes or heating applications. Water partially fills a boiler tank or housing with a small volume left above to accommodate steam. 
     Various heat sources for steam generation may be used, such as a product of combustion of any type of fossil fuel (in a gas, liquid or solid condition) or waste gases of any process. With the first case, different type of burners may be used to perform fossil fuel combustion in the furnace. In the last case, the device for steam production names as a Heat Recovery Steam Generator. Usually (for example, Scotch Marine design) the furnace is immersed in the same water-filled vessel where also the steam generation occurs. Hot flue gas passes are generated in the furnace and pass through tubes (also named as firetubes, because hot flue gas travels inside of the tubes) that extend through the same water-filled closed vessel as furnace. 
     Water in the vessel of a conventional boiler is always saturated and has an almost uniform temperature through the vessel volume. Usually fresh water enters into the vessel at temperature much less than saturation temperature. However, due to a small ratio of fresh water mass to the mass of water inside of vessel, the temperature uniformity has only local character and does not impact to the heat transfer intensity. The flue gas passes through the furnace and firetubes to an exhaust port, such that the heat transferred by convection and radiation from the flue gas to the saturated water generates steam. The steam then extracts from the top segment of the housing of the boiler for use as desired. 
     Firetube boilers may include several bundles of firetubes through which the flue gas travels back and forth in the housing. For example, if the boiler includes two bundles of firetubes, the flue gas passes in one direction through a first bundle of firetubes, and then in an opposite direction through the second bundle of firetubes. This is typically referred to as a “three-pass” boiler, since the furnace is used to organize fossil fuel combustion and is considered as a first pass before traveling through the firetubes. 
     BRIEF SUMMARY OF THE INVENTION 
     A improved firetube steam boiler is disclosed herein for generating steam using a heat source affixed to the boiler distributing heated flue gas into the boiler. The improved boiler includes a housing that has a proximal end and a distal end, with the housing further having an inner or interior surface and an outer or exterior surface. A water-entry port is positioned at the proximal end and a water outlet port at the distal end. A plurality of firetubes are disposed lengthwise in the housing, and the firetubes extend substantially the length of the housing between the proximal end and the distal end. The firetubes are used to pass the heated flue gas through the housing. 
     The improved boiler includes a pair of vertical, side baffles that affixed to the inner surface of the housing. The side baffles extend at least partially down the length of the housing, and perhaps the whole length, and separate a portion of said last pass firetubes near the housing from the remaining firetubes in the housing. In addition to the side baffles, the improved boiler will include at least two cross-sectional or substantially horizontal baffles adjacent the side baffles. The horizontal baffles are positioned in the housing between the distal end and the proximal end of the housing, with the horizontal baffles directing the flow of water in said housing from said inlet port proximate the tubes with the coolest gasses to draw or extract the most heat from the coolest tubes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective cross-sectional view of a four-pass boiler of the prior art; 
         FIG. 2   a  is a front elevational view of a boiler described herein; 
         FIG. 2   b  is a side elevational view of the boiler illustrated in  FIG. 2   a;    
         FIG. 2   c  is a rear elevational view of the boiler illustrated in  FIG. 2   a;    
         FIG. 3   a  is a front sectional view of the boiler having improved efficiency of  FIG. 2   b  taken along lines  3 - 3 ; 
         FIG. 3   b  is a second view corresponding to  FIG. 3   a , with the illustrations of the firetubes removed to show the internal baffles; 
         FIG. 4  is a side sectional view of the boiler illustrated in  FIG. 2   c  taken along lines  4 - 4 ; 
         FIG. 5  is a side sectional view of the boiler, the view illustrating the water travel pattern in the boiler illustrated in  FIGS. 3 and 4  taken along the lines  5 - 5 ; 
         FIG. 6  is a front sectional view of a second embodiment of the boiler having improved efficiency; 
         FIG. 7  is a side sectional view of the embodiment illustrated in  FIG. 6 ; 
         FIG. 8  is a further side sectional view of the embodiment illustrated in  FIG. 6 ; 
         FIG. 9  is a front sectional view of a third embodiment of the boiler having improved efficiency; 
         FIG. 10  is a side sectional view of the embodiment illustrated in  FIG. 9 ; and 
         FIG. 11  is a further side sectional view of the embodiment illustrated in  FIG. 9 . 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Looking to the attached  FIGS. 2-5 , a four-pass boiler  10  is illustrated having a design to efficiently improve the heating and evaporating of a heat transfer liquid  11 , such as water, held in the boiler  10  using heated flue gasses from a furnace  13 . The boiler  10  includes a shell or housing  12  having a lateral length between a proximal endplate  14  and distal endplates  16   a  and  16   b . The housing  12  may have cylindrical shape as illustrated in  FIGS. 2   a  and  2   c  and is used to hold the heat transfer liquid  11 . The housing  12  is further supported by a frame  25  to securely position the housing  12  on a ground surface. 
     The boiler  10  includes a means for heating and boiling the liquid  11  which includes a conventional heat source  15  for generating high temperature flue gas (combustion products) into a furnace  13 . High temperature flue gas passes through the series of tube-bundles  17 ,  18  and  19  positioned in the housing (shell)  12  and extending the length of the housing  12  from the proximal endplate  14  to the distal endplates  16   a  and  16   b  (as best shown in  FIG. 1 ). The heat source may be any type known in the art, such as a combustible fuel-fired burner  8  (see  FIGS. 2 and 4 ). In the case of a Heat Recovery Steam Generator, alternative high temperature waste gas from any process may be employed as a heat source. 
     The tube-bundles  17 ,  18  and  19 , as illustrated in  FIGS. 3   a ,  4  and  5 , are assembled into three bundles for a four-pass boiler  10 . As a result, the flue gas after furnace  13  passes through a first bundle of firetubes  17  in a first direction A from the distal endplate  16   a  to the proximal endplate  14 , a second bundle of firetubes  18  in a second direction B from the proximal endplate  14  to the distal endplate  16   b , in the third bundle of firetubes  19  flue gas travels in the same direction A as in first bundle of firetubes  17 . After passing through the third bundle of firetubes  19 , the flue gas will be released in an exhaust port  20  located near the proximal endplate  14 . Further, the temperature of the flue gas will decrease as the flue gas passes through each set of tubes  17 ,  18 ,  19 , such that the temperature of the flue gas in the third bundle  19  will be at its lowest temperature before exiting through exhaust port  20 . 
     All of the tube-bundles in a conventional firetube boiler  6  are immersed in water and are not divided by any baffles from each other. So in conventional firetube boiler  6 , heat transfers from flue gas to the water at a certain saturation temperature which depends only from pressure in the vessel. The small portion of fresh water mixes with the heated water in the boiler housing, which is a large amount of already saturated water. Further, usually in a conventional boiler there is only an inlet port  22   a  in the middle of the housing. As a result, at the fresh water inlet  22   a  and distribution ports H, the influence of the fresh water on water temperature level in the boiler is negligible. Consequently, the fresh water (in spite of being at much less than saturation temperature) simply loses its ability to extract additional heat from flue gases. 
     The design of boiler  10  illustrated in  FIGS. 2-5  overcomes the lack of conventional boilers by means of organization of fresh water flow in the shell or housing  12  of the boiler  10 . With the boiler  10  illustrated in  FIGS. 2-5 , a pair of side baffles  21  affixed the inside of side-surface of the shell  12  separate the segments of last pass of the third tube bundles  19  from first and second bundles  17  and  18 , as well as the other parts of boiler  10  that are immersed or substantially immersed in water in the housing  12 . A pair of fresh water input ports  22   a  are positioned near the proximal endplate  14  of the separated segments of housing  12  for supplying of fresh water on opposite sides of the bundles  17 ,  18 , and  19  (flue gas exit from last pass tube-bundles  19 ). Looking to  FIGS. 3   a - 5 , a curved distribution baffle (or header)  22   b  is positioned proximate each input port  22   a , with the distribution baffle  22   b  generally parallel to the housing  12 . A series of distribution ports or holes H traverse the length of the distribution baffle  22   b , and distribute the fresh water from the input port  22   a  into the area between the distribution baffle  22   b  and the substantially vertical side baffles  21 . As a result, fresh water runs along the segments between the distribution baffle  22   b  and the side baffles  21  before entering into the main part of housing  12 . The baffles  21  allow the coolest fresh water to enter at port  22   a  and flow in direction B, counter to the flue gas flow direction A in the tube bundles  19 , before being mixed with saturated water  11  in the housing  12 . During the initial flow of water, the temperature of the water is lower (such as 228 degrees Fahrenheit, although it could be less) than within the center of the housing  12 . 
     The design of the boiler  10  provides the greater temperature differential between coolest gasses in the last pass tube-bundles  19  and the fresh water surrounding the tubes  19  due to of organization of counter flow of heat-carrier substances. In other words, the last pass of tube-bundles  19  performs the function of an economizer that is used to capture the lost or waste heat from the hot stack gas of the boiler  6  as used with conventional steam generation systems. However, the economizer is a device that has a separate housing and ductworks in addition to the boiler housing, providing a bulky assembly. In contrast, the design described herein gives the user an opportunity to save on economizer housing, ductwork and boiler room. 
     The improved boiler  10  will continue to be built as conventional boiler  6  is built, but the last pass tube-bundles  19  (whole or part of tube&#39;s length depending the water temperature at the outlet of separated segment) will be separated from other parts of boiler at the outer extremes of the boiler, and the bundles  19  are sandwiched by the cross-sectional or longitudinal, substantially horizontal baffles  23  between the side baffles  21  and the housing  12 . So the substantially horizontal baffles  23  do not extend across the whole boiler, but instead extend just from the baffles  21  to the shell  12  of the boiler  10 , and further isolate the cooler water from the inlet  22   a  with a smaller portion of the third tube bundles  19  in segments  30   a ,  30   b ,  30   c  or  30   d.    
     Looking to  FIGS. 3   a  and  3   b , additional cross-sectional or longitudinal (parallel to the tube bundles  17 ,  18 ,  19 ) internal baffles  23  may be positioned along the length of last pass tube-bundles  19 . As a result, as fresh water is introduced at the fresh water inlet  22   a  and distribution ports H (the ports H act as a header for water distribution), the flow of water  11  will be encouraged to flow past the tubes  19  in segments ( 30   a ,  30   b ,  30   c ,  30   d ) parallel to the tubes  19  before entering into the main body of the boiler housing  12  near the distal endplate  16   b  of the boiler  10 . As with conventional boilers, the steam generated in the boiler  10  leaves the housing through the port  24  located on the top of housing  12 . This will further organize the third bundles  19  to improve the differential between coolest gasses in the last pass tube-bundles  19  and the fresh water surrounding the tubes  19   
     The dimensions of the boiler  10  may vary according to the desired use. In the embodiment illustrated, the boiler  10  has a shell  12  diameter of approximately 92 inches, and a length of approximately 167 inches. The diameters of the firetubes  17 ,  18 , and  19  extending through the housing  12  are approximately two and one-half inches each. 
     Calculations were performed by computer model of this boiler  10  under typical conditions, and it was found that the this design could improve the efficiency of the boiler  10  by as much as three percent or more relative to boilers having traditional designs. 
     In a second embodiment of the boiler  10  illustrated in  FIGS. 6-8 , the boiler  10  overcomes a problem in conventional boilers by means of organization of fresh water flow in the boiler&#39;s shell or housing  12 . With the boiler  10  illustrated in  FIGS. 6-8 , the side baffles  21  are affixed the inside of side-surface of the shell  12  and separate the segments of last pass of tube-bundles  19  from other parts of boiler immersed in water in the housing  12 . In this embodiment, the baffles  21  have a substantially vertically oriented straight or curved plate that extends longitudinally along at least a portion of housing  12 . The fresh water input ports  22  are positioned near the proximal endplate  14  (flue gas exit from last pass tube-bundles  19 ) of the separated segments of housing  12  for supplying of fresh water. As a result, fresh water runs along of separated segments before entering into the main part of housing  12 . The baffles  21  allow the coolest fresh water to flow counter to the flue gas flow direction before being mixed with saturated water  11  in the housing  12 . 
     The boiler  10  will continue to be built as conventional boiler does, but the last pass tube-bundles  19  (whole or part of tube&#39;s length depending the water temperature at the outlet of separated segment) will be separated from other parts of boiler at the outer extremes of the boiler  10 , and the last pass bundles  19  are sandwiched by cross-sectional internal baffles  27  positioned between the baffles  21  and the housing  12 . As a result, the cross-sectional baffles  27  do not extend across the whole shell  12  of the boiler  10 , but instead extend just from the baffles  21  to the boiler&#39;s shell  12 . 
     The cross-sectional baffles  27  can be positioned at predetermined locations along the length of the housing  12 . Looking to  FIG. 8 , additional cross-sectional internal baffles  27  are positioned substantially equidistantly along the length of last pass tube-bundles  19 . The internal baffles  27  are positioned substantially at right angles with respect to the tubes  19 , and they are alternately positioned either above or below the upper level of water  11  held in the boiler  10 . As a result, as fresh water is introduced at the fresh water ports  22 , the flow of water  11  will be encouraged to flow past the tubes  19  in a serpentine fashion before exiting over upper edge of last baffle  27  and entering into the main body of the boiler housing  12  near the distal endplate  16   b  of the boiler  10 . Such as in the conventional boiler, the generated in the boiler  10  steam leaves the housing through the port  24  located on the top of housing  12 . 
     It is to be noted that boilers  10  having firetube passes may incorporate the improved efficiency design. Looking to  FIGS. 9-11 , a third embodiment of the boiler  10  is illustrated corresponding to a 2-pass firetube boiler. In this embodiment, there is a single tube-bundle  19 , that is assembled for the two-pass boiler  10  so that the flue gas, after traveling through the furnace  13 , will pass in an opposite direction through the bundle of firetubes  19  and be released in an exhaust port  20  located near the proximal endplate  14 . 
     Like second embodiment, the design of boiler  10  illustrated in  FIGS. 9-11  overcomes the lack of conventional boilers by means of organization of fresh water flow in the boiler&#39;s shell or housing  12 . With the boiler  10  of this embodiment, the a pair of curved or bent substantially longitudinal baffles  21  affixed to the inside of side-surface of the shell  12  separate the segments of last pass of tube-bundles  19  from other parts of boiler immersed in water in the housing  12 . Consequently, this embodiment illustrates that the baffles  21  do not have to be substantially straight as illustrated in  FIGS. 6-8 , but can be bent to best fit around the tube-bundles  19 . The fresh water input ports  22  are positioned near the proximal endplate  14  (flue gas exit from last pass tube-bundles  19 ) of the separated segments of housing  12  for supplying of fresh water. As a result, fresh water runs along of separated segments before entering into the main part of housing  12 . The baffles  21  allow the coolest fresh water to flow counter to the flue gas flow direction before being mixed with saturated water  11  in the housing  12 . The design of the boiler  10  provides the greater temperature differential between coolest gasses on the last pass tube-bundles  19  and the fresh water surrounded the tubes due to of organization of counter flow of heat-carrier substances. 
     In this embodiment, cross-sectional internal baffles  27  are positioned substantially equidistantly along approximately half of the length of last pass tube-bundles  19  (see  FIG. 6 ). As with the prior embodiment, the internal baffles  27  are positioned substantially at right angles with respect to the tubes  19 , and they are alternately positioned either above or below the upper level of water  11  held in the boiler  10 . As a result, as fresh water is introduced at the fresh water ports  22 , the flow of water  11  will be encouraged to flow past the tubes  19  in a serpentine fashion before exiting over upper edge of last baffle  27  and entering into the main body of the boiler housing  12  near the distal endplate  16   b  of the boiler  10 . Such as in the conventional boiler, the generated in the boiler  10  steam leaves the housing through the port  24  located on the top of housing  12 . 
     Having thus described exemplary embodiments of a FIRETUBE STEAM BOILER HAVING IMPROVED EFFICIENCY, it should be noted by those skilled in the art that the within disclosures are exemplary only and that various other alternatives, adaptations, and modifications may be made within the scope of this disclosure. Accordingly, the invention is not limited to the specific embodiments as illustrated herein, but is only limited by the following claims.