Abstract:
A coal consuming boiler is provided with a combustion chamber having a divider of refractory material formed therein which separates the combustion chamber into primary and secondary combustion areas. A coal burner head for combusting coal is located in the primary combustion area. Primary combustion air is directed to the burner head while additional secondary combustion air is directed to the secondary combustion area to ensure that all combustible gases are thoroughly burnt up prior to the exhaust exiting the combustion chamber through a heat exchanger of the boiler. Exhaust tubes extending through the heat exchanger are configured in a horizontal double-pass configuration. A cleaner is provided in the form of nozzles associated with each of the exhaust tubes which are arranged to direct a high pressure flow of gas periodically therethrough for removing collected ash from the exhaust tubes to increase efficiency of the heat exchanger.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a boiler and more particularly relates to a boiler which combusts coal.  
       BACKGROUND  
       [0002]     Solid fuel boilers and furnaces are well known in the prior art in various forms for combusting wood, coal and the like. U.S. Pat. No. 6,289,266 to Payson et al, U.S. Pat. No. 4,254,715 to Lahaye et al, U.S. Pat. No. 4,323,051 to Auerbach et al and U.S. Pat. No. 4,201,185 to Black disclose variations of boilers for combusting solid fuels.  
         [0003]     A common problem occurring with solid fuel burners is incomplete combustion due to insufficient temperatures being reached or insufficient combustion air being provided. This results in combustible gases escaping which are potentially both harmful to the environment and result in an inefficiency in fuel use. Further inefficiencies arise due to common ash residue in solid fuel burners.  
       SUMMARY  
       [0004]     According to one aspect of the present invention there is provided a boiler comprising:  
         [0005]     a coal burner head for combusting coal;  
         [0006]     a combustion chamber above the coal burner head;  
         [0007]     a heat exchanger for exchanging heat between exhaust exiting the combustion chamber and a heat exchanger fluid circulated through the heat exchanger;  
         [0008]     a divider formed of refractory material separating the combustion chamber into a primary combustion area on a first side of the divider and a secondary combustion area on a second side of the divider; and  
         [0009]     air supply means for directing primary combustion air to the primary combustion area on the first side of the divider and for directing secondary combustion air to the secondary combustion area on the second side of the divider.  
         [0010]     The use of a refractory divider between primary and secondary combustion areas slows the exhaust flow and concentrates flow at a location of increased temperature due to the refractory materials. Provision of the secondary combustion air at the second side of the refractory material ensures that combustible gases are fully burnt before exiting through the exhaust.  
         [0011]     When the divider includes through holes formed therein for passage of exhaust gases therethrough, the divider preferably fully spans interior walls of the chamber so that the exhaust can only pass through the holes in the divider.  
         [0012]     The divider preferably extends generally horizontally, locating the secondary combustion area thereabove and the primary combustion area therebelow.  
         [0013]     The divider may be formed of a material including alumina and silica, for example material available under the name Firecrete™.  
         [0014]     The secondary combustion air is preferably introduced into the secondary combustion area directly adjacent the divider.  
         [0015]     The primary air may be introduced into the primary combustion area adjacent the burner head.  
         [0016]     The primary and secondary combustion air are preferably introduced under pressure.  
         [0017]     The heat exchanger may include horizontal exhaust tubes for directing the exhaust therethrough.  
         [0018]     The exhaust tubes are preferably oriented in a double-pass configuration through the heat exchanger.  
         [0019]     When the exhaust tubes include first exhaust tubes and second exhaust tubes oriented parallel to one another, they are preferably commonly joined at one end by an exhaust manifold.  
         [0020]     There may be provided an exhaust tube cleaner comprising a nozzle associated with each exhaust tube which is arranged for directing a high pressure flow of gas, for example air, therethrough for removing collected ash when activated.  
         [0021]     Coal is preferably augered up through a center of the burner head from below with an ash collection hopper including an auger for removal of ash therefrom below the burner head.  
         [0022]     The heat exchanger may include a pressure relief tank coupled in communication therewith.  
         [0023]     According to a second aspect of the present invention there is provided a boiler comprising:  
         [0024]     a coal burner head for combusting coal;  
         [0025]     a combustion chamber above the coal burner head;  
         [0026]     air supply means for directing combustion air to the combustion chamber;  
         [0027]     horizontal exhaust tubes communicating with the combustion chamber for directing exhaust gases therethrough;  
         [0028]     a heat exchanger for exchanging heat between the exhaust tubes and a heat exchanger fluid circulated through the heat exchanger; and  
         [0029]     an exhaust tube cleaner comprising a nozzle associated with each exhaust tube which is arranged for directing a high pressure flow of gas therethrough for removing collected ash from the exhaust tubes.  
         [0030]     Minimized residue in the exhaust can be achieved with further efficiencies resulting from provisions of an air cleaner using high pressure flows of air to remove ash residue from heat exchanger components.  
         [0031]     A manifold is preferably coupled in communication with all of the nozzles for supplying air under pressure to all of the nozzles when air under pressure is introduced therein.  
         [0032]     The exhaust tubes may comprise first exhaust tubes and second exhaust tubes communicating in series with one another through an exhaust manifold wherein all of the nozzles are located at the exhaust manifold.  
         [0033]     The nozzles are preferably oriented in at least some of the exhaust tubes to direct the flow of air under pressure towards the burner head.  
         [0034]     The exhaust tube cleaner may be operated automatically at periodic intervals to periodically direct a high pressure flow of gas through the exhaust tubes. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]     In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:  
         [0036]      FIG. 1  is a partially exploded perspective view of the boiler.  
         [0037]      FIG. 2  is a partly sectional perspective view of the assembled boiler.  
         [0038]      FIG. 3  is a side elevational view of the boiler.  
         [0039]      FIG. 4  is an end elevational view of the boiler.  
         [0040]      FIG. 5  is sectional view along the line  5 - 5  of  FIG. 3 .  
         [0041]      FIG. 6  is a sectional view along the line  6 - 6  of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION  
       [0042]     Referring to the accompanying drawings, there is illustrated a boiler generally indicated by reference numeral  10 . The boiler is particularly suited for combusting solid fuels, for example coal and the like.  
         [0043]     The boiler  10  includes a housing having a burner section  12  and a heat exchanger section  14 . The burner section generally comprises a vertically oriented cylindrical wall formed in double layers to define a water jacket  16  between the layers.  
         [0044]     A burner head  18  is supported within the hollow interior of the burner section spaced above the bottom end thereof. The burner head  18  is a round flat supporting surface having a diameter which is smaller than the diameter of the interior of the burner section to define an annular space therebetween for receiving excess ash subsequent to combustion above the burner head.  
         [0045]     Solid fuel is fed onto the burner head  18  up through a hole  20  formed in the center of the plate in communication with a feed tube  22  which supplies the fuel to the burner head. The burner head  18  further includes a plurality of air holes distributed thereacross in communication with a pair of air supply tubes  24  extending horizontally beneath the burner head along opposing sides of the feed tube  22  therebetween.  
         [0046]     The burner section includes a hopper bottom  26  locating an ash removal auger  28  in communication therewith which extends at an upward incline from a center of the hopper bottom to location external of the housing. The ash auger  28  is operated periodically and automatically by a timer to remove ash at preset intervals when the boiler is operating.  
         [0047]     A stoker  30  is provided spaced outwardly from a front side of the boiler. The stoker  30  includes an air box  32  coupling a fan (not shown) thereto which supplies air under pressure in a flow to the air box  32 . The air box communicates with the air supply tubes  24  to feed the air under pressure as primary combustion air to the burner head.  
         [0048]     The stoker  30  further includes a hopper  34  having an open top end formed at the top of the air box which communicates at a bottom end with an auger housed within the feed tube  22  to conduct fuel deposited into the hopper  34  to the burner head through the central hole  20  thereof upwardly from beneath the burner head responsive to water temperature of the boiler falling below a prescribed lower limit of the boiler.  
         [0049]     A suitable mounting collar  36  is coupled to the cylindrical wall of the burner section of the housing for receiving the feed tube  22  and the air supply tubes  24  therethrough to the interior of the housing. The mounting collar  36  further supports the stoker on the cylindrical wall of the housing.  
         [0050]     A suitable access panel  38  is supported in the cylindrical side wall of the burner section of the housing diametrically opposite the stoker.  
         [0051]     A combustion chamber is defined above the burner head which supports a horizontal divider  40  therein at a positioned spaced above the burner head. The divider  40  comprises a high heat resistant material available under the trade name Firecrete™ or other suitable refractory material having similar characteristics. Firecrete™ material is formed mostly of alumina while including large portions of silica and some other compounds therein.  
         [0052]     The divider  40  divides the combustion chamber into a primary combustion area  42  and a secondary combustion area  44 . The divider  40  fully spans the interior walls of the burner section and includes through holes  46  formed therein at circumferentially spaced positions thereabout such that the flow of exhaust from the primary combustion area is forced through the holes  46  to the secondary combustion area  44 .  
         [0053]     As described above primary combustion air is directed through the air supply tubes  24  directly to the burner below the divider in the primary combustion area. A branch duct (not shown) coupled to the air box  32  provides secondary combustion air directly above the divider into the secondary combustion area  44  by extending the branch duct through aperture  48  formed in the side wall of the burner section of the housing. A suitable damper control is provided on the branch duct directing the secondary combustion air therethrough for controlling how much air is directed to the secondary combustion area.  
         [0054]     The heat exchanger section  14  of the housing comprises a horizontal cylinder jointed at a first end directly above the burner section and being suspended above the ground at a second end  52  by suitable legs  54 .  
         [0055]     Adjacent the first end  50  of the heat exchanger an upper first end wall  56  spans vertically across an upper half of the cylindrical wall spaced only slightly from the first end of the cylinder to define a small exhaust chamber  58  between the upper first end wall  56  and the end wall of the cylindrical heat exchanger section of the housing. A lower first end wall  60  similarly spans vertically across the lower half of the cylindrical wall of the heat exchanger section spaced sufficiently from the first end of the cylinder to receive the burner section directly below the heat exchanger section between the lower first end wall  60  and the first end of the cylinder walls of the heat exchanger section. A horizontal wall  62  joins the upper and lower first end walls to enclose the secondary combustion area which is accordingly bound at a top end by the horizontal wall  62  along a bottom by the divider  40 , at one end by the lower first end wall  60 , at an opposing end by the end wall of the heat exchanger section and at sides by cylindrical walls of the heat exchanger section spanning the remaining sides.  
         [0056]     The exhaust chamber  58  includes a shelf  64  spanning between the upper first end wall  56  and the first end of the heat exchanger section at a position which is spaced slightly above the horizontal wall  62  to define an open space  66  therebetween which is open for communication with the second end of the housing to define a water jacket within the interior of the housing between the exhaust chamber  58  and the secondary combustion area.  
         [0057]     At the second end of the heat exchanger section of the housing, a second end wall  68  fully spans the cylindrical wall of the housing spaced inwardly only slightly from the second end  52  of the housing to define an exhaust manifold space  70  therebetween.  
         [0058]     A plurality of first exhaust tubes  72  are all oriented spaced apart and parallel to one another in a lower half of the housing in communication between the secondary combustion area and the exhaust manifold space  70 . Similarly a plurality of second exhaust tubes  74  span parallel to the first exhaust tubes spaced apart from one another in the upper half of the heat exchanger section of the housing for communication between the exhaust manifold space  70  and the exhaust chamber  58  at the first end of the housing.  
         [0059]     In this configuration exhaust must pass from the secondary combustion area through the first tubes to the exhaust manifold space  70  and subsequently through the second tubes to the exhaust chamber  58  before exiting upwardly through a vertical exhaust tube  76  coupled to the housing in communication with the exhaust chamber  58  at the first end of the heat exchanger section. A horizontal, double-pass heat exchanger configuration results when the fluid chamber  80  surrounding the exhaust tubes  72  and  74  is filled with a suitable heat exchanging fluid, for example water and the like which can be circulated therethrough.  
         [0060]     An over pressure tank  78  is supported above the heat exchanger section of the housing in communication with the heat exchanger fluid chamber  80  surrounding the exhaust tubes  77  and  74  in the event that excessive heat results in sufficient expansion of the fluid within the fluid chamber  80  to overflow into the over pressure  78  without damage to the boiler.  
         [0061]     An exhaust tube cleaner system  82  is provided at the second end of the heat exchanger section of the housing housed within the exhaust manifold space  70 . This system includes a nozzle  84  supported in association with and aimed at the open second end of each of the first and second exhaust tubes  72  and  74 . A series of manifold tubes  86  joins all of the nozzles in communication with a source of air at high pressure so that when activated, high pressure air is directed through each of the nozzles  84  to subsequently direct a high pressure flow of air through each of the first and second exhaust tubes  72  and  74 . Any suitable gas which is not readily combustible may be used in place of air, but air is preferred as it is most readily available.  
         [0062]     Air in the first tubes at the lower half of the housing is directed towards the burner head and the combustion chamber for returning ash to the burner head and accordingly subsequently down to the hopper therebelow when the ash overflows in operation. Air in the second exhaust tubes  74  in an upper half of the housing is forced in a direction towards the exhaust chamber  58 . The main vertical exhaust tube  76  coupled to the exhaust chamber extends vertically at right angles to the second exhaust tubes  74  so that ash being forced through the second exhaust tubes by the high pressure air flow is encouraged to settle in the exhaust chamber rather than exit through the main vertical exhaust tube  76 .  
         [0063]     A suitable disposal hole  88  is provided in the shelf  64  enclosing the bottom of the exhaust chamber which permits the exhaust chamber to be selectively opened to the secondary combustion area therebelow so that any ash settled within the exhaust chamber can be periodically manually urged down through the hole  88  to similarly settle on the burner head or overflow down into the hopper and ash removal system below the burner head.  
         [0064]     Activation of the release of high pressure air through the manifold  86  and nozzles  84  is accomplished automatically by a suitable controller including a timer for periodic activation thereof automatically at preset intervals during operation of the boiler.  
         [0065]     The location of the divider of refractory material directly above the burner head to define a first combustion area and a secondary combustion area thereabove allows heat to be concentrated at the secondary combustion area so that injection of secondary combustion air immediately above the refractory material forming the divider ensures that all combustible gases are burnt up before exiting through the exhaust tubes.  
         [0066]     In summary, a boiler or hot water heater is described herein including horizontal flue tubes and a double-pass heat exchanger. The first stage of combustion is a stoker fed coal burning head surrounded by a water jacket. Above this a slab of Firecrete™ with holes for the exhaust gases to pass therethrough leading to a unique secondary combustion area. In this secondary combustion area above the divider, the highest temperatures are produced and any unburned gases are burned up. The horizontal flues are cleaned through an air manifold system using a high pressure air flow system. This clears the flues by cleaning out any fly ash and materials in the flue for increased heat exchanger efficiency. The air cleaning system is controlled by a timer and operates at regular intervals. The fly ash then falls into the ash pit below the burner head to be subsequently augured out of the boiler.  
         [0067]     While one embodiment of the present invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. The invention is to be considered limited solely by the scope of the appended Claims.