Abstract:
A corn-burning stove provides cooling for the corn in-feed auger and other adjacent components by combustion inlet air flow patterns. The inlet air flow transports pellet fuel through a distance within the fire pot which varies responsive to the flow rate of the inlet air flow. A fire pot and agitator ensure, in combination with the inlet air flow, complete burning of the corn, with almost no ash production and while avoiding the formation of clinkers. The agitator is toothed, having teeth closely adjacent the burn pot for moving burning corn kernels or solid pellets across the fire pot. Retractable ignitors have handles and furnace function interlocks. A process control is associated with the corn burner that includes some logic, including interlock, power control, speed controls, sensing inputs/devices, and user interface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. provisional patent application Ser. No. 60/401,281 filed Aug. 5, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention pertains generally to furnaces, and more particularly to furnaces that incorporate screw-type fuel feeders. In a particular manifestation of the invention, corn kernels are used as a fuel source. 
   2. Description of the Related Art 
   Thermal energy has many fundamental applications, ranging from basic necessities such as adequate warmth within a shelter to comfort and pleasantries such as hot water used in baths, spas and swimming pools. Representative of the breadth of applications are the diverse apparatus that have been devised to provide desired thermal energy. Common modern sources of thermal energy include electricity such as is typically produced at large electrical generation power plants, propane, kerosene, fuel oil, other petroleum-derived compounds, coal, natural gas, and wood. More recently, various easily renewable materials have been pursued which might provide the necessary fuel source for production of thermal energy. Among the fuel sources considered, which are too great to individually list herein, are biomass pellets which may be manufactured from diverse organic-based sources such as plant materials and crop residues. Corn, which is available naturally as kernels, has presented another opportunity for a readily renewable resource. 
   In spite of ready availability, and often times extremely competitive pricing per unit of energy produced, the use of corn as a fuel source has presented several challenges. One such challenge is the delivery of the corn kernels to the combustion chamber, hereinafter referred to as the fire pot. Unlike prior art liquid fuels, which may be delivered absent air or oxygen, corn kernels will, if not further processed, present small spaces and gaps between kernels which in turn entrap air. As some prior art burners have demonstrated, the temperature within a fire pot is sufficient to heat and ultimately ignite kernels within an auger feeder, owing to the availability of the air therein. One approach has been to vent air directly through the fuel source, in this case corn kernels, and into the fire pot. Exemplary of such air flow through the auger tube is illustrated in U.S. Pat. Nos. 4,619,209 to Traeger et al and 5,123,360 to Burke et al, the contents which are incorporated herein by reference. By such technique, the kernels will desirably be cooled sufficiently to prevent the back-spreading of fire into the hopper area of the furnace. Unfortunately, it is not always possible to control how tightly the kernels may be packed within the auger. Consequently, it is also not possible to reliably control the flow of air there through, nor to predict the temperature therein. 
   Another limitation of pellet furnaces in general, and also corn burners, is the difficulty with initial ignition and start-up of the furnace. Solid pellets or kernels are not readily mixed within an air stream, and so consequently cannot simply be sprayed and ignited with a spark or the like. Instead, the solid fuel is more commonly decomposed within a very hot fire pot, and the resultant gases combusted to produce the desired thermal energy. In order to obtain this sequence, the fire pot must be at a sufficiently elevated temperature to enable thermal decomposition. One method of obtaining this temperature is to use an electric heater, referred to commonly as an ignitor, to heat a location within the fire pot to the substantial temperature required for proper combustion. Once the localized region heats and ignites, the energy released therefrom will similarly be useful to support combustion across an even larger area within the fire pot. Eventually, it is desirable to have as large a region within the fire pot heated as possible, though using the prior art burners this has not been practical. In some prior art designs, ignitors have remained within the fire pot for the entire operation of the furnace. Unfortunately, this exposes the ignitor to continuously elevated temperatures, which tends to degrade the ignitor unnecessarily. Furthermore, the physical placement of the ignitor, which is usually selected to be in as close a proximity to the solid fuel as is reasonably practical, will interference once the combustion process has actually begun and attained a self-supporting status. Commensurate therewith, there have been a few designs in the prior art that have provided for the removal of these ignitors once combustion has become self-sustaining with the fuel pellets. Nevertheless, the control of these ignitors has heretofore required expensive equipment which has been of little use or benefit other than for the few seconds of use inserting or removing the ignitor. Owing to the time lag typical with the proper ignition of these types of furnaces, they may be ignited only once or a few times during an entire heating season. Consequently, the additional hardware and mechanics that add cost are most undesired. Exemplary prior art ignitors are illustrated by U.S. Pat. Nos. 5,000,100 to Mendive et al and 5,263,642 to Orchard, the contents which are incorporated herein by reference in entirety. 
   Another challenge of corn burners is the requirement for proper temperature, mixing and oxygen exposure. If a mass of corn is left relatively undisturbed during the burning process, there is a great likelihood that a clinker will form. Clinkers are large, very hard clumps of spent fuel. Unfortunately, owing to the hardness and solid mass formed, a clinker will not typically further burn, and it will instead interfere with the combustion of other kernels. Finally, the presence of these clinkers represents a waste product which is undesirable, and will require further disposal. No effective solution has been provided heretofore, though U.S. Pat. No. 4,947,769 to Whitfield, the contents which are incorporated herein by reference, illustrates a rotating member to remove ash and clinkers from the combustion grate. 
   Yet another challenge of the prior art pellet and corn burners is that of maintaining optimum temperature control. In liquid-fueled furnaces, the furnace will generally be sized to have excess heat capacity, where the time on and off is used to determine the actual heat output. Since the flame is formed through the simple generation of a spark, starting and stopping the heating cycle is very simple. The building or space being heated is used as a thermal mass which evens out the temperature between operating cycles of the furnace. While this has in the past been associated with draftiness and lack of comfort, the approach is nevertheless made possible by the easy ignition of the fuel source. In contrast, and as aforementioned with respect to the ignitors, the starting cycle for a corn fueled furnace may be measured by many minutes or hours. Furthermore, the start-up of a corn burner is less precise and may require user intervention. Both the time and intervention required will interfere with or prevent the cycling found in liquid or gas furnaces. Instead, the furnace will preferably stay lit and will use other technique for controlling heat output. In the past, this control has either been absent, meaning the furnace has been simply run at full capacity non-stop, or there has been only limited control provided. In practice, a user has been required to select a proposed heat output for the day, based upon anticipated heating needs. For a closed building of large thermal mass, this technique can provide the necessary level of control. However, when a larger door, such as an overhead door commonplace in factory loading docks and where large machinery is stored and removed for use, there may be substantial heat loss in short time periods. The present thermal regulation of corn burners is inadequate to compensate for these short period loads. Some furnaces which attempt to include speed control are illustrated by U.S. Pat. Nos. 5,873,356 to Vossler et al and 4,856,438 to Peugh, the contents of each which are incorporated herein by reference for their teachings with regard to control systems. 
   SUMMARY OF THE INVENTION 
   In a first manifestation, the invention is a pellet fuel burner operative to combust pellet fuel and thereby produce thermal energy. A fire pot is operative to contain pellet fuel during combustion. A fuel auger introduces pellet fuel into the fire pot, and a variable gas stream is coupled to the fuel auger. The variable gas stream receives the pellet fuel and transports it across the fire pot by an amount which varies responsive to a variance within the variable gas stream. 
   In a second manifestation, the invention is a solid fuel burner having variable energy output responsive to a variable demand. The burner has a combustion chamber, a means for supplying oxygen to the combustion chamber, and a means for introducing solid fuel into the combustion chamber. A means is provided for variably controlling at least one of the oxygen supply means and solid fuel introducing means. A means detects a threshold magnitude of variable demand, and a means responsive to threshold magnitude detection causes the variable control means to vary at least one of the oxygen supply means and solid fuel means. 
   In a third manifestation, the invention is an agitated solid fuel burner. A combustion chamber has a trough shaped fire pot and a solid fuel inlet. An agitator extends longitudinally within the combustion chamber and rotates thereabout. The agitator has a plurality of teeth extending from a central agitator axis. A drive operatively rotates the agitator relative to the fire pot. 
   In a fourth manifestation, the invention is, in combination, a fire pot, fuel pellets and an ignitor which produces temperatures sufficient for ignition. The improvement comprises a means to manually position the ignitor between a first position operative to ignite fuel pellets and a second position removed from interference with combustion. 
   OBJECTS OF THE INVENTION 
   Exemplary embodiments of the present invention solve inadequacies, of the prior art by providing a corn burner having a cooled auger, retractable ignitors, a helically toothed agitator, and heat demand anticipation. 
   A first object of the invention is to provide thermal energy through the combustion of corn kernels or like fuels. A second object of the invention is to convert a pellet fuel efficiently. Another object of the present invention is to generate a minimum amount of ash and prevent the formation of clinkers. A further object of the invention is to anticipate thermal demand, and adjust thermal output appropriately. Yet another object of the present invention is to distribute combustible fuel throughout a combustion chamber, whereby the total capacity of the furnace for a given volume is maximized. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, advantages, and novel features of the present invention can be understood and appreciated by reference to the following detailed description of the invention, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  illustrates a preferred embodiment corn furnace designed in accord with the teachings of the invention from projected view, with some of the components shown by partial cut-away and by schematic block diagram, the selection of block or cut-away made where appropriate to best illustrate the internal workings of the preferred embodiment. 
       FIG. 2  provides an enlarged view of some of the components of the preferred embodiment corn furnace of  FIG. 1 , taken along line  2 ′. 
       FIG. 3 , illustrates a first alternative embodiment corn furnace designed in accord with the teachings of the invention from side, schematic view. 
       FIG. 4  provides an enlarged view of some of the components of the first alternative embodiment corn furnace of  FIG. 3 , taken along line  4 ′. 
       FIG. 5  illustrates a first alternative embodiment fire pot designed in accord with the teachings of the invention from end view.
           FIG. 5   a  illustrates a first preferred embodiment concentric arrangement of auger and auger interior tube with respect to auger exterior tube, while  FIG. 5   b  illustrates auger and auger interior tube in an offset position with respect to auger exterior tube.       
       FIG. 6  illustrates a preferred embodiment furnace controller designed in accord with the teachings of the invention schematically. 
       FIG. 7  illustrates the preferred auger of  FIG. 1  from a side plan view. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A most preferred embodiment corn burner  100  designed in accord with the teachings of the present invention is illustrated in  FIG. 1 . A fire chamber wall formed by cover  110  and fire pot  200  isolates combustion gases from an exterior thereof, while providing a compartment within which safe and controlled burning may occur. Passing through the fire chamber wall is an exhaust  112 , which most preferably encloses and directs combustion gases to a safe exterior vent. The overall efficiency of corn burner  100  may be improved from the schematic illustration of  FIG. 1  if, for example, the exhaust is brought through the interior of furnace exterior wall  102 , such as, for example, by adding two right angle bends therein which would run exhaust  112  parallel to fire pot  200 . This provides more surface area for heat to be exchanged through from an exhaust gas stream and the room air being heated. 
   Auger  140 , through outer auger tube  144 , also passes through the fire chamber wall. Auger  140  provides a controlled feed of combustible fuel into fire pot  200 . Agitator  150  similarly passes through the fire chamber wall. Agitator  150  ensures a gentle stirring of fuel within fire pot  200 , thereby ensuring complete combustion of fuel. Ignitor elements  130 , only one of which is numbered in the figures, similarly passes through the fire chamber wall. At least one ignitor element is most preferably provided to initiate combustion when corn burner  100  is first started. Several sources of inlet air which bring necessary oxygen to the fuel for combustion to occur are also provided which pass through the fire chamber wall. In addition to the fire chamber and contents therein, a blower  120  is provided to circulate inlet air. Through ducts which will be discussed in more detail herein below, inlet air  120  is most preferably pre-heated during circulation, serving as cooling air for critical components. A hopper  142  serves as a container bin for solid fuel, which in the preferred embodiment is most preferably corn. Hopper  142  may be a relatively small hopper directly attached to the furnace, or may be a separate, more remotely located and much larger hopper which uses an auger to not only feed fuel into fire pot  200 , but also to transport the fuel. Using the larger, remote hopper enables the hopper bin to be filled by a delivery person in a manner similar to the, present LP gas tank refills. A thermostat  172  and associated control circuitry  170  provide control over power for igniter elements  130 , fuel auger  140 , agitator motor  158 , combustion air blower fan  120 , and a heated air outlet fan not illustrated, but typically adjacent room air outlet  104 . Second exterior chamber wall  102  is typically provided outside of the fire chamber, forming a second enclosure through which air will pass and be circulated by a blower fan. This air, which is heated through heat exchanged from the fire chamber walls, is then passed to the point of demand. For exemplary purposes only, and not intended to be limiting, the heated air may be passed into heat ducts for distribution throughout an enclosure such as a building or the like. 
   As illustrated in  FIG. 1 , combustion air is provided by blower  120  through main plenum  122  which most preferably extends underneath the fire pot from end to end. Most preferably prior to fire pot  200 , a first branch plenum  124  directs air upwards to an access hole  152  into the core of optionally hollow agitator  150 , and additionally further upward to fuel auger exterior tube  144 . Most preferably, there will be sufficient airflow about or through fuel auger exterior tube  144  to ensure that the temperature within auger  140  is maintained at a level safely below the combustion point of the fuel passing through. In the illustrated and preferred embodiment of  FIGS. 1 and 2 , the cool inlet air will pass through auger exterior tube  144  which surrounds the auger interior tube  147 . The use of two concentric tubes ensures that auger interior tube  147  is continually surrounded by relatively cool inlet air rather than the much hotter combustion chamber gases. The auger exterior tube  144  need not be concentric with the auger interior tube  147 , such as illustrated in  FIGS. 5 and 5   a  nor does it have to form a complete enclosure about the auger interior tube  147 . As illustrated in  FIG. 5   b , auger interior tube  147  and auger exterior tube  144  may also be adjusted to offset from concentric, which will in turn cause the relatively cool inlet air to be offset with respect to auger  146 . Nevertheless, in the preferred embodiment this auger exterior tube  144  does completely surround auger interior tube  147 . 
   The air flowing around auger interior tube  147  is most preferably controlled to distribute fuel within fire pot  200 . This distribution of fuel is controlled in the preferred embodiment through the varying of a butterfly valve  160  within first branch plenum  124  leading to auger exterior tube  144 . Butterfly valve  160  may be varied in the preferred embodiment of  FIGS. 1 and 2  by a cam  154  mounted for rotation in association with agitator tube  150 . Cam  154  will most preferably be designed to vary the air flow with position of agitator tube  150 , so that when butterfly valve  160  is in an open position, kernels are carried within the inlet air to the opposite end of fire pot  200 . Consequently, as butterfly valve  160  closes, kernels are dropped more closely to the auger outlet. In this way, fuel is more evenly be distributed within fire pot  200 , which in turn makes optimum use of fire pot  200 , thereby increasing the maximum BTU output for a given size fire pot while also helping to minimize the formation of ash and clinkers. In order to calibrate the burner for most efficient distribution of fuel using air flow through auger exterior tube  144 , an adjustment screw  167  passing through fixed block  166  may be provided as shown in  FIG. 2  which varies the position of butterfly valve  160  by a preset amount relative to cam  154 . This calibration may be made at the factory or at a later date during servicing, inspection or the like, as will be determined appropriate for a particular burner design at the time of manufacture or installation. Adjustment screw  167  may be provided merely to set a minimum air flow through auger exterior tube  144 , which is as shown in  FIG. 2 , or adjustment screw  167  may alternatively be designed to provide an overall offset of air flow. In other words, rotation in a first direction would increase air flow at all positions of cam  154 , while rotation in a second direction opposite the first would then decrease air flow at all positions of cam  154 . The specific embodiment to be implemented will be readily selected by one reasonably skilled in the art, in light of the remaining disclosure herein. 
   Air flow is further combined with rotation of agitator tube  150 , resulting in better distribution of fuel and more complete exposure of fuel to air. In the case of corn as a fuel, kernels are spread about fire pot  200  and then stirred by agitator teeth  151  to prevent the formation of large unburned carbon structures commonly referred to in the industry as clinkers. Consequently corn is reduced by the present corn burner  100  beyond prior art corn residual to ash in the present invention, and then the ash is allowed to burn free of agitation in the last portion of the fire pot, in turn leading to more complete combustion and reduced ash residual. 
   In the preferred embodiment, air passing adjacent auger interior tube  147  performs another important function. During operation of corn burner  100 , this air provides oxygen at the top of fire pot  200 . The top of fire pot  200  is mainly filled with combustion gases, typically not fully burned. The introduction of additional oxygen into this part of the chamber may be accompanied by substantial further combustion, sufficient to form a blue flame or ring adjacent the auger outlet. The added combustion of course increases the overall efficiency of corn burner  100 . 
   An air inlet  152  may, as aforementioned, also be provided within agitator  150  which permits the flow of cool inlet air therein, which in turn may extend the life of agitator  150 . Without cooling air, agitator  150  may be prone to thermal warp. Consequently, it is desirable to circulate sufficient cooling air to prevent such warping, or to design agitator  150  from thermally resistant materials such as stainless steel or the like. As an added benefit of air passing through first branch plenum  124 , agitator  151  adjacent agitator motor  158  is cool to the touch, thereby protecting agitator motor  158  and all associated bearings from any heating effect from fire pot  200 . 
   Additional air inlets  222  are provided along the bottom of fire pot  200 , passing inlet air up into fire pot  200  under the pressure of blower  120 . Most preferably, the inlet pressure will be equivalent to several inches of water, which tends to prevent fuel and ash from settling over or blocking air inlets  220 ,  222 . Air inlets  220 ,  222  are also preferably relatively small, to prevent the passage of fuel from fire pot  200  into main plenum  122 . In the preferred embodiment, these air inlets  220 ,  222  are approximately one-eighth of an inch in diameter, though a designer will recognize the most appropriate size for these openings for a given application. 
   Solid fuel burners typically require a certain amount of pre-heating in order for the fuel to be combusted within the fire pot. While other known means of initiating combustion may be suitable for use in the present invention, the use of one or more electric heating ignitors is most preferred. Two ignitors  130  are illustrated in  FIGS. 1 and 2 , and as shown therein ignitors  130  are in an ignition position. As shown, ignitors  130  extend through tubes  131  that pass through fire pot  200  wall, and extend into fire pot  200 . Most preferably, there is a minimum of clearance between the ignitor elements and the tubes, which when combined with corrosion, soot or the like will prevent the escape of combustion gases through these tubes  131 . Seals could alternatively be provided between ignitors  130  and tubes  131 , as required or when desired. 
   The ignitor tubes  131  could, depending upon the exact positioning, interfere with the rotation of agitator tube  150 . Consequently, safety switches  134  are provided which must be closed for agitator tube  150  to be rotated. These safety switches  134  are activated by ignitor handles  132  when ignitors  130  are fully retracted from fire pot  200 . Consequently, ignitors  130  may be moved from fire pot  200  by manually gasping handles  132  and sliding these into engagement with safety switches  134 , at which time agitator tube  150  will be enabled by switches  134  for rotation. When control box  170  is otherwise signaled, agitator tube  150  may then be rotated. 
   Just as ignitors  130  are preferred to generate the initial temperatures required for combustion of solid fuel such as corn kernels, the combustion process will most preferably be controlled to maintain combustion at rates which tend to anticipate the demands for heat. Consequently, burning of fuel will be maintained continuously, and variably controlled to match the demand for heat. This virtually eliminates the need to start and stop the burner, which is relatively more difficult with solid fuel than with prior art liquid or gas fueled heaters. In order to achieve this desirable control, thermostat  172  and control box  170  are most preferably designed to variably control auger motor  148  and blower  120 , thereby varying fuel and air introduced into fire pot  200 , and consequently varying the heat output from the burner. Most preferably, this heat output is controlled as a function of heat demanded to maintain a given temperature, and the current deviation therefrom. For exemplary purposes, but understanding that there are other implementations that will be devised by those skilled in the art that may cooperate effectively in the preferred embodiment of  FIG. 1 , an electronic record may be kept of the auger motor speed and blower speed over a time period, and the direction and amount the thermostat temperature deviated over that same time period at these motor and blower speeds. New values may be relatively accurately calculated for auger motor and inlet blower to adjust the heat output of the burner, to once more target the desired thermostat temperature by taking into account the rate of deviation at the thermostat. In other words, the heat output from the burner required to maintain a given temperature is anticipated based upon rate of deviation at the current heat output. In a more simple alternative, the amount of current temperature deviation from the desired temperature may be used to determine a threshold deviation, which, when reached, may be used to vary the blower and auger from a neutral setting. This is illustrated in  FIG. 6 , where Thermostat is used to shunt resistor R 2 , thereby changing the desired setting input into KBIC, which is a solid state SCR DC motor speed control circuit such as commercially available from KB Electronics of Coral Springs, Fla. Whatever the technique used to adjust the auger and blower speeds, most preferably there will be calculated or predetermined ratios between auger motor speed and blower speed. These ratios are used to maintain proper air-to-fuel ratio within fire pot  200  at all available levels of required heat output, to thereby maintain maximum burner efficiency and combustion cleanliness. 
   The most preferred embodiment has a minimum of sensors, thereby reducing the technical complexity of corn burner  100  and generally improving reliability. However, additional electro-mechanical and electronic controls and sensors may be incorporated into the preferred embodiment without deviating from the teachings of the present invention provided herein. More particularly, chemical and physical sensors may be provided to monitor combustion compounds and temperatures within the fire chamber and control such factors as air or fuel introduction or distribution, or other useful parameters of operation. 
     FIGS. 3 and 4  illustrate a first alternative embodiment corn burner  101  having like components numbered the same as in the preferred schematic illustration of  FIGS. 1 and 2 . As shown therein, a large auxiliary hopper  143  may be provided which feeds directly into hopper  142 . A support post  105  may be provided to support the extra weight of corn that may be received in auxiliary hopper  143 . A structural frame  106  may similarly be provided. Chamber  103  encloses fire pot  200 , and in this alternative embodiment, may be used to create a water jacket thereabout. When, as in this alternative embodiment, a water jacket is created, the preferred output of thermal energy is in the form of hot water or steam as is found in many industrial or residential boilers. In order to further boost the efficiency of operation, most preferably where a corn burner such as burner  100  is used to heat air, inlet  113  may be used to preheat room air. 
     FIG. 4  illustrates the operation of ignitor  130 , showing handle  132  in the operative and inserted position. In this position, arm  133  through roller  135  is held at an approximately eight o&#39;clock position by riding upon bracket  136 . However, when in the position illustrated by broken lines and prime number designations, arm  133 ′ pivots somewhat counter clockwise, and may then be used to trigger a switch such as a micro-switch or the like for detection of removed position. Also visible in  FIG. 4  is the bracket  149  used to support auger motor  148 . Other suitable brackets or arrangements may be sued used for each of the motors used herein, and while necessary for operation, form no consequential part of the present inventive concept. 
     FIG. 5  illustrates fire pot  200  from end view looking down agitator  150  central shaft, opposite fuel auger  146 . A part of fire chamber wall is formed by wall  230 , which has several viewing windows  232 ,  234  formed therein. These viewing windows will most preferably have closures provided during operation, but are available for inspection purposes, particularly when starting combustion within fire pot  200 . Fire pot  200  is removable from corn burners such as burners  100 ,  101  through two screw or bolt holes  236 ,  237 , though other means of attachment may be provided. As will be apparent from  FIGS. 1–4 , and preferably where hopper  142  is not mechanically attached to auxiliary hopper  143 , all components associated with fire pot  200  will move therewith for ready inspection, repair, or cleaning. Fire pot internal wall  210  is generally U-shaped, but may preferably have two small ears formed therein just above the center line defined by agitator central shaft  150 . Most preferably, these will provide improved air flow from air jacket  205  which surrounds inner wall  210 . A particularly preferred double helical arrangement of agitator teeth  151  is visible in  FIG. 1  and shown in more clear detail in  FIG. 7 , which provides most preferred movement of corn and ash to the end of the fire pot opposite the auger inlet. The helical arrangement may preferably be designed to include a few teeth  153  most nearly adjacent fuel auger  146  that serve to move fuel gradual towards this wall  230 . The remaining teeth  155  will tend to move fuel away therefrom. The general direction of rotation of teeth  151  is identified by arrow R in  FIG. 5 . As may be understood best from  FIG. 7 , tooth  151  a will couple with teeth  151   b ,  151   c ,  151   d  and the remaining teeth in that direction to move corn and ash to the end of the fire pot opposite the auger inlet. Tooth  151  a couples with teeth  151   e ,  151   f ,  151   g , and the remaining teeth in that direction to move corn towards wall  230 . This opposed direction of tooth rotation may be seen from helical rotation patterns shown by lines  156  and  157 , which each originate from tooth  151   a  and follow the pattern of teeth  151  that will interact with corn in two different directions of travel. By providing a few teeth that move fuel towards wall  230 , a good fire will be maintained adjacent fuel auger  146 , which has been determined to provide improved operation. 
   The spacing between teeth  151  is also important for the clinker-free operation of corn burner  100 . When corn is used as the fuel source, approximately 5/32″ clearance is provided between adjacent teeth  151 , and also between each tooth and the inner wall  210 . This clearance may, in one embodiment, be less than the smallest average cross-sectional dimension of the fuel being used. 
   From the foregoing figures, additional features and options become more apparent. First of all, the burner may be manufactured from a variety of materials, including ceramics, refractory metals, stainless steel, carbon steel, or other suitable materials or combinations of materials. The specific material used may vary as will be recognized by those skilled in the art of burner construction. Where metal is used for the fire chamber wall, strips may be welded or tacked on to the fire chamber that extend therefrom, to increase the amount of heat exchange surface area. These strips may further be provided with holes and thereby force the channeling of air or water, as may be desired. 
   A variety of designs have been contemplated for the burner, including the fire pot within the burner. The particular fire pot illustrated herein includes a generally U-shaped burner compartment, in part dictated by the generally circular reach of the most preferred agitator. However, other shapes and geometries may be used, and more than one agitator may be provided as desired. Consequently, the exact geometries or shapes of the burner compartment and fire pot are not critical to the successful operation of the invention, provided the embodiment chosen provides adequate air flow and suitable exposure of fuel to oxygen source to adequately combust the fuel. The materials used for a particular design may be chosen not only based upon the usual requirements for a burner, but may also factor in the particular design including types of fuel, chamber size, and other factors that will be recognized by the designer. Other variations are also contemplated herein and have been only illustrated by way of selected alternative embodiments. 
   While the foregoing details what is felt to be the preferred and additional alternative embodiments of the invention, no material limitations to the scope of the claimed invention are intended. The possible variants that would be possible from a reading of the present disclosure are too many in number for individual listings herein, though they are understood to be included in the present invention. Further, features and design alternatives that would be obvious to one of ordinary skill in the art are considered to be incorporated also.