Abstract:
A combustion device in the form of an elevated fixed-grate that includes arcuately shaped solid refractory brick with ribs placed thereunder so as to allow horizontal air flow for fuel combustion. The brick are arranged atop one another in a stacked concentric configuration that forms a central fuel passageway and allows cascading of a fuel pile throughout the combustion stages. The device provides the benefit of proper de-ashing online while distributing the underfire air radially around the fuel pile. The elevated design of the bricks allows the air to be evenly distributed throughout the fuel pile and further allows the isolation of overfire and underfire air. Segregating overfire and underfire air in an evenly distributed manner allows the burner to combust a wide range of fuel moisture contents without modifying the mechanical components of the burner.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to carbon-based fuel furnaces. More particularly, the present invention relates to an improved grate configuration to enhance combustion of fuel of varying quality. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the art of wood and waste combustion systems, a variety of well known techniques and devices are available for heat generation of various kinds. In particular, the wood products manufacturing industry includes combustion techniques and devices which include heat sources for drying equipment. Oftentimes, such combustion techniques and devices are intended to burn all kinds of wood and potentially other solid-carbon-based fuel sources. Such varying fuel sources include waste that is sourced from wood products manufacturing. Not only do the fuel sources vary in composition and physical form, but such fuel sources also vary considerably in terms of moisture content. Accordingly, within this field, there have been many devices seeking to provide improved combustion. 
         [0003]    U.S. Pat. No. 2,444,985 discloses a fuel burner for the combustion of solid fuels comprising a blower, a conveyor screw, a cast iron heater surrounded by a sheet metal jacket provided with one or more hot air outlets, cold or return air inlets, a smoke pipe, a furnace base which forms the ash pit, an ash conveyor trough carrying a conveyor screw, refractory walls to enclose a gas chamber, and a burner wherein the usual grates normally provided in the bottom of the heater may be removed or omitted and wherein the inside of the base is lined with a refractory wall forming an interior circular chamber lined with heat refractory material. The burner of this device is installed so that its center axis is offset from the center of the circular chamber. 
         [0004]    U.S. Pat. No. 4,074,680 discloses a fireplace structure for burning a combustible fuel comprising an adjustable hood, a stationary smoke pipe, a fire support base, a lowermost base portion for operable mounting of the fireplace base upon a floor surface, a cylindrical support means with a upwardly opening plenum spaced within the fireplace base, a firebrick lining, and a grating means made of a plurality of fire brick laterally and vertically spaced to define updraft air passages for ambient air supplied from a bottom portion of the plenum, wherein the fire brick are laterally and vertically spaced to define updraft passages in addition to supporting any form of combustible material such as coal, wool, charcoal versions of the same, and an ash auger. 
         [0005]    U.S. Pat. No. 3,812,794 discloses a combustion furnace having a grate formed as a plurality of downward leading steps from an upper to a lower region with a number of separated, outwardly flaring openings among the steps including a material ram plate, and a stair-step grate formed of a number of refractory bricks which each extend slightly beyond the one above it wherein each of the refractory bricks has a passageway extending through it parallel to the horizontal surface and terminating in an upwardly flaring opening. 
         [0006]    U.S. Pat. No. 4,377,117 discloses a furnace for burning dry or wet wood waste products such as hogged bark and the like encompassing a storage bin which contains particulate wood waste material to be burned, a rotary screw conveyor, an intermediate hopper, a rotary feeder, an air flow conduit for a blower, a boiler furnace, a grating structure or grate with spaced-apart support beams having a plurality of parallel rows of bricks positioned thereon with at least some of the rows of bricks maintained a uniform distance from other rows of bricks by spacers, hot air inlet conduits positioned below the grate, and an adjustable intake. 
         [0007]    Traditionally, combustion devices have included a fixed grate furnace, though improved versions have displaced the fixed grate types with the walking grate system. This style offers online de-ashing and elevated metal grate bars. The online de-ashing avoids problems associated with a fixed floor furnace, but creates a furnace that cannot burn excessive amounts of dry fuel without the need of wetting the fuel or something similar that drastically complicates the fuel supply arrangement to these combustion devices. In addition, this style of combustion device is typically extremely expensive due to the metal bars in the floor. This is impractical for small wood products manufacturing operations to purchase. Some variations on the fixed grate include a fixed yet sloped floor grate. 
         [0008]    While many such solutions exist to the combustion of wood and waste, problems are common to most every configuration of walking grates, fixed floor grates, and fixed floor bins. For example, walking grates do not allow the burning of fuel below 40% moisture content without damaging the metal grates. As well, fixed floor grates often plug and are hard to clean and properly gasify the products of combustion without a mechanically large furnace area. Still further, fixed floor bins are nearly impossible to effectively de-ash while online and prove very difficult to keep air infiltration down. 
         [0009]    It is, therefore, desirable to provide improved de-ashing online while improving air distribution around the combustion pile. Moreover, it is desirable to provide a combustion device capable of burning a wide range of fuel moisture contents without the need for modifying the mechanical components of the burner for the given fuel. It is further desirable to enable the combustion of low moisture content fuel without inducing rapid wearing or requiring constant maintenance. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to obviate or mitigate at least one disadvantage of previous combustion devices. The present invention provides the benefit of proper de-ashing online while distributing the underfire air radially around the pile. The elevated design of the bricks allows the air to be evenly distributed throughout the fuel pile and further allows the isolation of overfire and underfire air. Segregating overfire and underfire air in an evenly distributed manner allows the burner to combust a wide range of fuel moisture contents without modifying the mechanical components of the burner. Using bricks eliminates the problems created by using metal based grates in the floor of the furnace, thus avoiding rapid wear and constant maintenance during the burn of low moisture content fuel. 
         [0011]    In general, the present invention includes a round vertical combustion chamber. The chamber is composed of several isolated sections that are fed through an air header and controlled through damper actuators. The grate bricks are arranged in a radial fashion and elevated to allow smooth airflow throughout the pile. This also allows proper three-stage combustion of the wood fuel whereby drying, gasifying, and heat release all occur in an appropriate fashion across the grate area. Thus, this grate area is specifically designed for a wide range of moisture in the fuel supplied. The inventive configuration of elevated bricks is arranged in a radial pattern so as to solve the problems of both isolating underfire/overfire air and of automatic de-ashing. The elevated configuration allows maximization of the air flow through the grate area without compromising the high heat capability of refractory. This allows the inventive device to burn low moisture fuel without damaging the grate. Moreover, the present invention as claimed provides an invention that materially enhances the quality of the environment by materially contributing to the more efficient utilization and conservation of energy resources by using, with high efficiency, wood waste from the wood manufacturing industry. 
         [0012]    In a first aspect, the present invention provides an elevated fixed-grate apparatus for use in a multi-fuel furnace, the apparatus including: a first course of solid refractory bricks forming a base, more than one subsequent course of the solid refractory bricks arranged atop the base, the first course and each the subsequent course being arranged in a concentric manner, each the subsequent course having an outer peripheral dimension smaller than an immediately preceding course upon which the subsequent course is placed, the bricks each formed as an arcuate segment of a circle, and each the course being vertically spaced from one another so as to allow passage of air between each the course. 
         [0013]    In a further embodiment, there is provided a refractory brick of an elevated fixed-grate apparatus for use in a multi-fuel furnace, the refractory brick including: a solid refractory core formed as an arcuate segment of a circle; a pair of lateral ribs located at opposite extreme bottom edges of the solid refractory core; a central rib located at a center bottom of each the solid refractory core; and each the rib being oriented radially relative to the arcuate segment forming the solid refractory core. 
         [0014]    In further aspect, the present invention provides an elevated fixed-grate apparatus for use in a multi-fuel furnace, the apparatus including: a stepped arrangement of solid refractory bricks formed by circular courses of the bricks concentrically placed atop one another; each subsequent upper one of the circular courses having an outer peripheral dimension smaller than an immediately preceding course upon which a subsequent course is placed so as to form the stepped arrangement; and each the brick being formed as an arcuate segment of a circle and including at least one radially placed passageway for movement of combustion gases between the circular courses of the bricks. 
         [0015]    Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures. 
           [0017]      FIG. 1  is a generalized schematic of a multi-fuel furnace with an elevated fixed-grate in accordance with the present invention. 
           [0018]      FIG. 2  is a top-view showing the concentric arrangement of the elevated fixed-grate in accordance with the present invention. 
           [0019]      FIG. 3  is a cross-sectional side view illustrating the concentric arrangement of the elevated fixed-grate in accordance with the present invention. 
           [0020]      FIG. 4  is a top-view illustrating the three primary fuel stages of a combustion pile as seen atop the concentric arrangement of  FIG. 2 . 
           [0021]      FIG. 5  is a prior art illustration showing a side view of one type of prior art cast brick. 
           [0022]      FIG. 6  is an illustration showing a side view of a single fixed-grate brick in accordance with the present invention. 
           [0023]      FIG. 7  is a perspective view of the single fixed-grate brick of  FIG. 6  in accordance with the present invention. 
           [0024]      FIG. 8  is an illustration showing a cross-sectional view of the stepped support structure underlying the concentric arrangement of the elevated fixed-grate in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Generally, the present invention provides a combustion apparatus in the form of a multi-fuel furnace with an inventive fixed-grate that is elevated and center-fed with wood fuel. With specific reference to  FIG. 1 , there is shown a generalized schematic of a multi-fuel furnace  100  with an elevated fixed-grate  14  in accordance with the present invention. It should be understood that a variety of furnace configurations may be possible without straying from the intended scope of the present invention and that the configuration shown in  FIG. 1  is only one possible configuration. Here, basic furnace elements are illustrated including an auger mechanism  12  powered by motor  13  for providing a center-fed input of combustible fuel such as, but not limited to, waste wood, sawdust, wood chips, bark, or any residual waste product from wood manufacturing. The inventive fixed-grate provides enhancements a multi-fuel furnace which helps to improve the overall quality of the environment. This is accomplished via increased efficiency in the utilization and conservation of energy resources by better use of wood waste from the wood manufacturing industry as described in more detail herein below. Flue gases exit the furnace  100  primarily via a flue  15  and usable heat exits via a heat conduit  10 . 
         [0026]    Though not shown, the auger mechanism  12  itself may be preceded by another mechanism to provide fuel in any manner such as via a simple chute or a more complex conveyor system depending upon the given configuration. It should be readily apparent to one of skill in the art of wood manufacturing that any other device or process may, if desired, be attached to the heat conduit  10  such as a rotary dryer or any other common heat processing element. Though not shown, heat may be extracted from the combustion process via the heat conduit  10  or in any conventional manner including, without limitation, a thermal water jacket surrounding the refractory, fluid pipes within the flue gas stream, or any heat transfer mechanism suitable for the given configuration. 
         [0027]    In operation, combustible fuel is center-fed into the elevated fixed-grate  14  via the auger mechanism  12  through a central feed conduit  16 . Although alternative shapes are possible without straying from the intended scope of the present invention, the round shape of the vertical combustion chamber  11  lends itself to uniform heating of the combustion pile. As well, this round shape coincides with the concentric courses of grate bricks described further herein below. Due to the arrangement of concentric courses of grate bricks, the formation and subsequent burning of the combustion pile thereupon provides for residual ash to come to rest at the outer peripheral base of the fixed-grate  14 . 
         [0028]    The basic structural elements of the furnace  100  including the heat conduit  10 , combustion chamber  11 , auger mechanism  12 , motor  13 , and flue  15  are well-known elements and are therefore not further described herein. The combustion chamber  11  can be composed of several isolated sections (not shown) that are fed through an air header and controlled through damper actuators in any known manner. Indeed, each of these basic structural elements may vary in known shape, form, or complexity without impacting upon the novelty of the present invention. Such novelty rests in the combination of the aforementioned structural elements with a unique arrangement, as discussed in further detail herein below, of concentric brick courses which form the elevated fixed-grate  14 . 
         [0029]      FIG. 2  is a top-view that shows the arrangement  200  of concentric courses  201 ,  202 ,  203 ,  204 , and  205  of grate bricks which together form the elevated fixed-grate  14 . Here, the outer peripheral base  210  which may include a recess for collection of residual ash can be seen as well as the auger mechanism  12  which feeds fuel to the surface of the top course  205  from which such fuel cascades over subsequent courses  202 ,  203 ,  204 , and  205  towards the outer peripheral base  210 . While five courses are shown, it should be understood that any number of courses may be provided without straying from the intended scope of the invention. Indeed, a larger overall furnace would require a large arrangement of bricks which may vary in the number of courses or further may vary in the size of each brick that comprise the courses where such variation is also within the scope of the present invention. The grate bricks are arranged in a radial fashion and elevated so as to allow smooth airflow throughout the combustion pile. This also provides for proper three-stage combustion of the wood fuel whereby drying, gasifying, and heat release all occur in an appropriate fashion across the grate area. In this manner, a wide range of allowable moisture content in the fuel is possible due to the three-stage combustion. This inventive configuration of concentric courses of elevated bricks serves to both isolate underfire air from and overfire air and also to automatically de-ash the fixed-grate area. Moreover, the elevated configuration allows maximization of the air flow through the grate area without compromising the high heat capability of refractory. This allows the present inventive device to burn low moisture fuel without damaging the grate. For purposes of the present invention, allowable moisture content for the fuel entering the combustion chamber  11  can range from 1% to 60%. 
         [0030]    With regard to  FIG. 3 , the three-stages of combustion enabled by the present invention are clearly illustrated. Here, a close-up, cross-sectional side view  300  shows the concentric arrangement of the elevated fixed-grate. Fuel is fed upwardly (as shown by an upward pointing arrow) through a contiguous, cylindrical inner cavity  31  from the auger mechanism  12 . In this manner, raw fuel  34  having an elevated moisture content will enter the combustion chamber  11  for the initial drying stage. Because the brick grates are arranged concentrically in a stepped manner, the dried fuel is allowed to cascade down the outer edges of the elevated fixed-grate. The dried fuel then enters the gasifying stage (indicated by dome  33 ) whereby the majority of energy is released from the fuel into the combustion chamber  11 . Underfire air fed through holes  32  in the support structure flows through passageways (explained in further detail below) in the bricks and feeds combustion during the gasifying stage. 
         [0031]    Such underfire air is physically separated from the overfire air flow. The overfire air flow serves more to dry the fuel in the initial combustion stage. Accordingly, underfire air is typically drier and hotter which aids in the superheating aspect of the gasification stage. During combustion, the residue  35  of gasification continues to cascade down the outer edges of the elevated fixed-grate to the final burn-out stage at which time a final ash is produced. The final ash comes to rest at the base of the elevated fixed-grate against the round walls of the combustion chamber  11 . As previously suggested in regard to  FIG. 2 , an optional recess along the floor where the final ash comes to rest can be provided to allow for automatic de-ashing. It is this addition of a refractory lined chamber at the bottom allows the ash to collect in this chamber for subsequent removal. 
         [0032]    In terms of the combustion pile,  FIG. 4  is provided to show the three primary combustion stages  40  from a top down perspective.  FIG. 4  is effectively an identical illustration relative to  FIG. 2  with the addition of fuel stages overlaid there upon. Here, the manner in which the combustion pile cascades out from the center in a circular manner atop the concentric arrangement of  FIG. 2  can be seen. The innermost circular portion  41  illustrates the fresh fuel initially center-fed from below through the contiguous, cylindrical inner cavity via the auger mechanism (shown at center) and in the initial stage drying on the fixed-grate. Beyond the innermost circular portion  41  is shown a central circular portion  42  which represents the gasification stage of the fuel. Lastly, the outermost circular portion  43  represents the burn-out stage whereby residual ash will eventually accumulate at the periphery of the outermost circular portion  43 . As mentioned, such ash can then drop down into a recessed area for subsequent removal from the combustion chamber floor. In this manner, de-ashing of the fixed-grate is accomplished in a passive manner without requiring any additional mechanisms. 
         [0033]    For the sake of comparison of the present invention to standard refractory configurations,  FIG. 5  and  FIG. 6  are provided. Specifically,  FIG. 5  is a prior art illustration showing a side view of one type of prior art cast brick whereby a fuel pile rests upon a typical fire brick having air holes cast therein. In such structure, the air holes are vertical and typically plug with ash so as to require a significant amount of maintenance in the form of de-ashing procedures. Moreover, such known configurations with holes in the refractory allow the refractory itself to expand and contract, thus causing cracking and eventual premature failure. In contrast,  FIG. 6  is an illustration showing a side view of a single fixed-grate brick in accordance with the present invention. Here, the air flow is provided via a horizontally arranged air passage beneath the solid refractory brick. This horizontal orientation of the air passage advantageously alleviates plugging of the air passages without the need for holes with the refractory itself. Moreover, the concentric arrangement of overlapping courses of radially arranged bricks in accordance with the present invention in combination with the horizontal air passages facilitates the cascading characteristics of a combustion pile utilizing the present invention. In this manner, this arrangement provides the aforementioned automatic de-ashing as the combustion pile cascades from the center top of the fixed-grate as fresh fuel in the drying stage through the mid-level gasifying stage and ultimately to the bottom peripheral edge of the fixed-grate upon the burn out stage whereby final ash rests. 
         [0034]    Each individual brick in accordance with the present invention is formed generally as an arcuate segment of a circle. In  FIG. 7 , this formation is shown by way of a three-dimensional perspective view of a single fixed-grate brick of  FIG. 6  in accordance with the present invention. Here, the basic structural elements of a single fixed-brick  70  are shown to include a solid refractory section  71  held in an elevated position via ribs  72   a ,  72   b , and  72   c . The ribs  72   a ,  72   b , and  72   c  include lateral ribs  72   a  and  72   b  and central rib  72   b  located at the bottom surface of each single fixed-brick  70 . Each of the ribs  72   a ,  72   b , and  72   c  is oriented radially relative to the arc of the given brick. The voids created by the ribs  72   a ,  72   b , and  72   c  form horizontal passageways  73   a  and  73   b . In forming the elevated fixed-brick apparatus in accordance with the present invention, each single fixed-grate brick is arranged into a base forming a complete ring of bricks upon which a subsequent course of bricks with fewer bricks is placed thereby forming a progressively smaller completed ring of incrementally smaller individual fixed-grate bricks. It should be readily apparent that the inner peripheries  70   a  and outer peripheries  70   b  of each brick in each course of bricks align and the inner peripheries  70   a  surround the contiguous, cylindrical inner cavity (as previously shown in  FIG. 3 ) of the assembled elevated fixed-grate. 
         [0035]    As can further be seen by way of  FIG. 8  in a simplified cross-section  800 , the bricks  70  are situated on a stepped support structure  801  that generally mirrors the stepped arrangement of the bricks  70 . The stepped support structure  801  may be formed from steel of a thickness and quality sufficient to withstand long term use in a high heat environment. This stepped support structure  801  is tied together underneath the main brick support plates  801   a  to support the overall weight of the inventive grate. The main brick support plates  801   a  may be integrally formed with the stepped support structure  801  or may be separately formed and laid atop the stepped support structure  801 . The main brick support plates  801   a  are designed such that the combustion air supplied to the underfire air is distributed in a homogenous pattern throughout the circular pattern of the bricks  70 . These plates serve the dual purpose of distributing air flow (via holes  810 ) and structural support of the overall combustion grate made up of the bricks  70 , support plate  801   a , and support structure  801 . While one particular configuration for a stepped support structure  801  is shown in  FIG. 8 , it should be readily apparent that any suitable underlying structural support may be used so long as airflow is enabled to the brick undersides while structurally supporting the courses of bricks  70 . 
         [0036]    The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.