Abstract:
A granular biomass burning furnace for use with any appropriate granular biomass, such as grains, cherry pits, etc. The furnace includes a three stage heat exchanger, a fuel injector, a fuel stirrer, an ash ejector, a wash down system, a three stage air inducer, a fuel igniter, and supporting components. The unit includes a computer controller which controls all aspects of the operation of the unit based on information from sensors located throughout the unit. The unit includes a smart logic thermal controller to adjust the output heat of the unit via a variable speed air inducer. The three stage heat exchanger system includes a spiral water jacket surrounding the burn pot, a plurality of heat exchanger baffles in the unit, and a fine finned heat exchanger at the top of the unit. The air inducer provides air to the burn pot from three directions to promote complete combustion.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a granular biomass burning heating system. Any type of granular biomass can be used as fuel. Grains, such as corn and wheat, have become popular fuel sources for furnaces and stoves. Various stoves and furnaces of a type to burn such materials are known. 
   In any type of solid fuel burning system, regardless of the type of fuel being used, it is desired to increase the efficiency of the system so that the amount of heat produced and utilized by the system is relatively high. It is further desired to decrease the lag time between unit start up and when heat is evident to the user. Further, some known biomass fuel furnaces have problems with incomplete burning of the fuel. Therefore it is desirable to provide a biomass furnace which provides for complete burning of the fuel. 
   One of the problems associated with some grain burning heating systems is back burning. Many granular biomass burning heating systems include an auger-type fuel feed. Back burning occurs when fuel located in this auger begins to burn before it is introduced to the burn pot. It is desirable to provide a granular biomass burning heating system with a fuel feed designed to prevent back burning. 
   Some known biomass furnaces have problems associated with the controls. For example, the heat of the furnace can be difficult to control. It is therefore desirable to provide a user friendly furnace, which utilizes a computer control unit to function on its own with very little human intervention. It is further desirable to provide a system which utilizes a smart logic thermal controller to reduce the human intervention necessary to keep the output of the furnace at a consistent or desirable temperature. 
   Additional problems included fly ash build up in previous furnaces. Fly ash can decrease the efficiency of the system, so it is desirable to include a way to remove the build up of ash from a biomass furnace. Additionally, incomplete combustion can clog the system by creating clinkers, or hardened lumps of unburned material, and can also decrease efficiency. Therefore it is desirable provide a biomass furnace which removes clinkers and also promotes complete combustion. 
   Although many designs for granular biomass burning heating systems have been considered, improved designs are continually being sought to improve the technology. It is an object to the present invention to provide a novel granular biomass burning heating system. 
   SUMMARY OF THE INVENTION 
   The present invention provides an improved granular biomass burning heating system. The apparatus includes a three stage heat exchanger, wherein the heat exchanger stages are connected in parallel relation to each other. 
   The apparatus may further include a linear fuel infeed system including a self closing door to minimize back burning. The apparatus may also include a venturi design to direct smoke and fire away from the self closing door when the unit is in operation. 
   The apparatus may further include an air inducement system by which air is supplied to the burn pot from the side, center, and bottom of the burn pot. 
   The apparatus may further include a wash down system which includes a water supply pump, a water filter, a baffled water sediment tank, and a rotatable shaft with a plurality of holes formed there to remove ash and other debris from the furnace. The apparatus may recycle water and cleaning solution within the process. 
   The invention may include a computer controller which automatically controls features of the furnace to automatically operate the system. 
   The invention may include a smart thermostat and a variable speed air inducer fan. The unit may utilize the smart thermostat to determine when and how long to use the high burn status before selecting the intermediate burn, low burn, burnout, or wash down status. This allows the unit to adjust itself to use the minimum amount of fuel to achieve maximum heating results. The computer chooses the heat status required for to further increase efficiency of the unit. The computer also decreases the lag time between the call for heat and actual heat. This units starts at high burn to generate maximum heat initially and through the process the unit turns down heat output when necessary to limit wasted heat. 
   The invention may further include a plurality of sensors connected to the computer controller such that the system is controlled based on input from the plurality of sensors. 
   Additional objects and advantages of the invention will be set forth in the following description, or may be learned through practice of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified side plan view of the furnace of the present invention. 
       FIG. 2  is an interior view of lower portion of the furnace of the present invention, including the fuel infeed system. 
       FIG. 3  is an interior view of the top portion of the furnace of the present invention. 
       FIG. 4  is an interior view of the furnace of the present invention. 
       FIG. 5  is an interior view of the bottom portion of the furnace of the present invention showing the air intake system. 
       FIG. 6  is an interior view of the bottom portion of the furnace of the present invention showing the water intake system, the ash auger, and the baffled sediment tank. 
       FIG. 7  is a simplified interior view of the furnace of the present invention which shows the locations of the system sensors. 
       FIG. 8  is an interior view of the fuel hopper attached to the fuel infeed system. 
       FIG. 9  is a top view of a portion of the air intake system. 
       FIG. 10  is an interior view from the top of the baffled sediment tank and the ash auger. 
       FIG. 11  is a top view of the ignition plate. 
       FIG. 12  is a flow chart depicting the initial safety protocol. 
       FIG. 13  is a flow chart depicting the ignition sequencing protocol. 
       FIG. 14  is a flow chart depicting the high burn sequencing protocol. 
       FIG. 15  is a flow chart depicting the choosing sequence. 
       FIG. 16  is a flow chart depicting the low burn sequencing protocol. 
       FIG. 17  is a flow chart depicting the intermediate burn sequencing protocol. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 
     FIG. 1  shows the furnace  2  of the presenting invention in a very simplified form. The furnace  2  has a lower portion  54  and an upper portion  52 . Within the lower portion  54  of the furnace  2  is a burn pot  6  and a first stage heat exchanger  10 . A second stage heat exchanger  12  lies in both the lower portion  54  and the upper portion  52  of the furnace. The upper portion  52  of the furnace  2  also includes a third stage heat exchanger  14 . The furnace  2  is preferably controlled by a computer  16 . A plurality of sensors (shown in  FIG. 7 ) are located throughout the furnace  2  to measure conditions. The data from these sensors is utilized by the computer  16  to run the furnace  2 . The furnace  2  includes an ash removal system  18 , an air inlet system  20 , and a fuel inlet system  22 . The furnace  2  is optionally surrounded by an insulated jacket  24 . 
   The furnace  2  is preferably cylindrical in shape. Attached to the furnace  2  is a computer controller  16 , an air infeed  20 , a fuel infeed  22 , a water infeed  62 , a water outlet  28 , a water pump  30 , fuel and ash rotator  32 , a washdown pipeshaft motor  34 , a wash down and ash removal caseway  36 , and a baffled sediment tank  38 . 
   The preferred embodiment of the present invention includes three stages of heat exchangers which can best be seen in  FIG. 4 . The first stage of the heat exchanger is a spiral shaped water jacket  40  surrounding the burn pot  6 . The second stage is a set of heat exchanger heli-coils  42  which are strapped to ash funnels  44  or heli-coils  42  supported by tripod legs  46  located in the furnace  2 . The third stage is a fine finned heat exchanger  48  open at the bottom and baffled at the top. The third stage heat exchanger is located at the top of the furnace  2 . The use of a three stage heat exchanger system increases the efficiency of the heat transfer of the system. 
   The furnace  2  preferably also includes condensation collectors. One bushel of corn at 10 percent moisture produces 5.6 pounds of water. This water can douse the flames if it is not removed from the system. The condensation collectors carry water away from the center of the burn pot  6 . The first and third ash funnels  44  can additionally suffice as a condensation collector. The condensation travels along the funnel  44  to the ash caseway  36 . In the preferred embodiment, an ash/condensate trough  50  located at the point where the lower portion  54  and upper portion  52  of the furnace  2  connect collects condensation as it travels towards and down the ash caseway  36 . An ash wiper  56  associated with the trough  50  pushes the condensation towards the ash caseway  36 . A third condensation tray  58  which is cupped upward can be located underneath the fine finned heat exchanger  48  so that water hits the tray  58  and is removed from the system by a pipe  60  which deposits the condensation in the baffled sediment tank  38 . It is desirable to remove the condensation from the furnace  2  to increase the efficiency of the furnace  2 . 
   Each stage of heat exchanger is supplied with water. The water inlet system is shown in  FIG. 6 . The water is provided to the furnace inlet pipe  62  which is connected to the heating system. It is contemplated that this water may come from a coil within a forced air furnace or heating pipes within the floor of the area to be heated by the furnace (not shown). The furnace inlet pipe  62  serves a water pump  30  which is located outside of the furnace  2 , near the bottom of the burn pot  6 . A system drain valve is preferably located in the furnace inlet pipe  62  near the water pump  30 . The water is pumped into the furnace  2  through the furnace inlet pipe  62 . In the preferred embodiment, the furnace inlet pipe  62  splits into a first supply pipe  66  and an inlet manifold  68 . The first supply pipe  66  supplies the spiral water jacket  40 . The inlet manifold  68  continues up the side of the furnace  2  on the outside of the furnace  2 , but underneath the optional insulating jacket  24 . The inlet manifold  68  supplies each heat exchanger heli-coil  42 . As seen in  FIG. 3 , near the top of the furnace  2  the inlet manifold  68  supplies the fine finned heat exchanger  48 . Through this configuration the heat exchangers are set up in parallel relation to each other such that each heat exchanger stage is provided with fresh heating system water. The inlet manifold  68  continues past the fine finned heat exchanger  48  and exits the optional insulated jacket  24 . The inlet manifold  68  ends in an air bleed off valve  70 . 
   This inlet configuration puts the stages of the heat exchanger in parallel rather than in series. Because each stage of the heat exchanger is getting fresh heating system water, rather than water which has been utilized in a previous stage heat exchanger, the efficiency of heat exchange in the system is increased. As discussed above, condensation problems are overcome by condensation collection system. This is because the efficiency of a heat exchanger depends in part on the temperature differential between the two fluids in the system. Water which has been used in a previous stage of the heat exchanger would be warmer than fresh heating system water entering the system, and therefore is able to accept less heat from the air in the furnace  2 , resulting less efficient heat exchange. The water flowing through some of the heli-coils  42  may be temperature regulated. In this case, a device would be present which would allow water to heat up in the heli-coils  42  before being allowed to flow out of the heli-coils  42 . This improves the efficiency of the system because water which is too cold can cause condensation, which if not properly removed, can douse the fire in the burn pot  6 . 
   The first stage heat exchanger is a spiral water jacket  40 . The water jacket  40  is formed on the inner wall of the burn pot  6  and extends around the lower portion  54  of the furnace  2 . The water jacket  40  forms a spiral path for the water flowing through the system. A water jacket pressure relief valve  41  is located at the top of the water jacket  40 , near the area where the lower portion  54  and the upper portion  52  of the furnace mate. 
   As seen in  FIG. 4 , the second stage heat exchanger includes a plurality of heat exchanger heli-coils  42 . The preferred embodiment includes eleven heli-coils  42 , four lower heli-coils  42  in the lower portion  54  of the furnace  2  and seven upper heli-coils  42  in the upper portion of the furnace  2 . However, it is contemplated that any other suitable number of heli-coils  42  could be utilized. Each heli-coil  42  is made of a pipe which is tightly wound, such that the rings of the heli-coils  42  are almost touching. The pipe is wound until it becomes too tight and would kink if further wound, leaving the center portion of the heli-coil  42  open (not shown). 
   Each of the heli-coils  42  in the lower portion  54  of the furnace  2  are strapped to the bottom side of an ash funnel  44 . The ash funnels  44  are attached to the internal wall of the furnace  2 . The ash funnels  44  are removable for maintenance of the furnace  2 . Each heli-coil  42  is fed from the inlet manifold  68 . After the water flows through a heli-coil  42 , the water flows to the outlet manifold  80 . The lower portion  54  of the furnace  2  also includes heat deflectors  72  attached to the second and fourth sets of ash funnels  44 . The heat deflectors  72  have a shape similar to a funnel, and force the air from the furnace  2  to take a less direct path, thus exposing the air to more of the heat exchanger heli-coils  42 , which will increase the efficiency of the furnace  2 . 
   The upper portion  52  of the furnace  2  includes several upper heli-coils  42 ; in the preferred embodiment seven heli-coils  42  are utilized. The upper portion  52  heli-coils  42  are strapped to three tripod legs  46  which rest into recessed notches formed in the furnace  2  inner wall. The tripod legs  46  rise upward toward the washdown rotator shaft sleeve  74 . The tripod legs  46  are also attached to washdown rotator sleeve  74 . The tripod legs  46  are hingedly attached to the rotator sleeve  74 . Each heli-coil  42  is fed from the inlet manifold  68 . After the water flows through a heli-coil  42 , the water flows to the outlet manifold  80 . 
   A plurality of heat deflecting baffles  76  are also located in the upper portion  52  of the furnace  2 . In the preferred embodiment of this invention, seven baffles  76  are disclosed. The baffles  76  are aligned such that each baffle  76  is located just below a heli-coil  42 . The configuration of the baffles  76  and heli-coils  42  is such that the air in the furnace  2  does not have a straight path up the height of the furnace  2 . Rather, the air will be deflected by the baffle  76  and forced to flow around the baffles  76 . In this manner, the hot air from the furnace  2  will have more contact with the heat exchanger heli-coils  42 , which will result in more efficient heat transfer. 
   In the preferred embodiment of the invention, the third stage of the heat exchanger system is a fine finned heat exchanger  48 . However, it is contemplated that any other suitable type of heat exchanger could be utilized as a third stage heat exchanger. The fine finned heat exchanger  48  is formed of a pipe which has a diameter which is smaller than the diameter of the heli-coils  42 . This pipe is bent to create banks of finned tubes. The fine finned heat exchanger  48  is surrounded around its circumference by a removable shroud  78 . This shroud  78  forces the air from the furnace  2  to flow through the fine finned heat exchanger  48 , rather than flow around it. Water enters the fine finned heat exchanger  48  from the inlet manifold  68 . After the water has flowed through the heat exchanger it flows into the outlet manifold  80 . After the air from the furnace  2  flows through the fine finned heat exchanger  48 , the air exits the system through a pitched down exhaust  82 . 
     FIG. 5  shows the air inlet system  20 . The preferred embodiment of the furnace  2  has a three part air inducer system. A variable speed blower  84  is located on the outside of the furnace  2 . The blower  84  is connected to an air duct  86 . The air duct  86  extends around the diameter of the burn pot  6 . The air duct  86  is located near the bottom of the burn pot  6 , within the water jacket  40 , but below the spirals of the water jacket  40 . An air inducing donut  88  is formed with a plurality of air holes such that air is inducted to the burn pot  6  from the outer walls of the burn pot  6 . The air inducing donut  88  is immersed in the water jacket  40  and stands up from bottom of the water jacket  40  approximately ½ inch away from water jacket  40  to provide a cooling effect on three sides or the air inducing air inducing donut  88 . This configuration eliminates warping of the steel. The air duct  86  is provided with a split union  90  before the air inducing donut  88 , such that air is supplied through a secondary air duct  86  to the ash tray  92  below the burn pot  6 . 
   The air which is supplied to the ash tray  92  below the burn pot  6  is induced to the burn pot  6  in two manners. First, a central air inducer pipe  94  extends through the ignition plate  96  into the base of the burn pot  6 . This air inducer pipe  94  is preferably 1½ inches in diameter and has a pattern of small air holes thereon. The air holes are preferably ¼ inch holes which introduces air to the center of the burn pot  6 . Second, the ignition plate  96  is formed with a plurality of slots  98 . The air can travel up from the ash tray  92  through the slots  98  to enter the burn pot  6 . The ignition plate  96  stands off ⅛ inch from the water jacket  40 . This gap also allows air to enter the burn pot  6 . By this configuration, air is introduced from the sides, bottom, and center of the burn pot  6 . This configuration provides air nearest to the combustion, which increases efficiency. The speed of the blower  84  rotation is determined by desired heat output set forth by smart thermostat or by the manual setting. 
   A safety door  100  stops air flow in event of system malfunction. The safety door  100  is controlled by a normally closed solenoid  102  which opens the safety door  100  for operation. An electromagnet  104  holds the safety door  100  open during operation. By utilizing an electromagnet, rather than the solenoid to hold the safety door  100  open for extended periods of time, the amount of noise created by the unit is reduced. If power is cut, the electromagnet  104  will release the safety door  100  and the safety door  100  is returned to its normally closed position which will prevent air infeed. 
   The preferred embodiment of the fuel inlet system is shown in detail in  FIG. 2 . The fuel inlet system has a linear actuator dosing mechanism. A furnace hopper  108  feeds fuel into a fuel channel  112 . The fuel channel  112  extends from the furnace hopper  108  into the burn pot  6 . A deflecting shroud  114  is formed inside the burn pot  6  and is connected to the inner wall of the burn pot  6  near the outside of the fuel channel  112 . The deflecting shroud  114  extends from the sidewall of the burn pot  6  and is angled up towards the center of the furnace  2 . The shroud  114  extends past the door  116  to the fuel channel  112 , and then has a slight cutback before extending vertically upward past the fuel channel door  116 . After the fuel channel door  116 , the shroud  114  extends back towards the inner wall of the furnace  2 . This configuration deflects the air from the door  116  of the fuel channel  112 , and increases the airspeed until the air is past the door  116  of the fuel channel  112 . A plunger  118  is disposed within the channel  112  to advance the fuel into the burn pot  6 . The plunger  118  is attached to a lead screw  120  which is in turn connected to a motor  122 . The motor&#39;s  122  function is to rotate the lead screw  120  in a first direction to advance the plunger  118  and to rotate in a second direction to retract the plunger  118 . The fuel channel  112  includes a pair of plunger stop sensors  124 , 125 . The fuel inlet further includes a fuel channel door  116  hingedly attached to the end of the fuel channel  112  disposed within the furnace  2 . The fuel channel door  116  is attached to a closure rod  126  by means of a pivotal linkage  128 . The closure rod  126  is attached to a compression spring  130 . 
   In use, a dose of fuel is delivered to the fuel channel  112  from the furnace hopper  108 . The fuel channel  112  is pitched upward toward the burn pot  6  to prevent fire from entering the fuel channel  112 . In the preferred embodiment, the angle of the fuel channel  112  is 22 degrees. The motor  122  rotates the lead screw  120  to advance the plunger  118 . As the plunger  118  advances the fuel dose is advanced within the fuel channel  112 . The fuel channel door  116  is pushed open by the force from the advancing dose and plunger  118 . The dose of fuel is pushed into the furnace  2  and lands on the ignition plate  96  at the bottom of the burn pot  6 . When the plunger  118  reaches the plunger advancement stop sensor  124 , the motor  122  reverses its direction and rotates the lead screw  120  in the opposite direction to retract the plunger  118 . As the plunger  118  retracts the fuel channel door  116  returns to its sealed closed position by the force of the compression spring  130  pulling on the door closure rod  126 . As a measure of safety the door  116  has a weight  129  attached thereon, such that if the closure rod linkage  128  were to break, the weight of the door  116  will force it to close. The plunger  118  continues to retract into the until the plunger  118  reaches the plunger retraction stop sensor  125  at which point the plunger  118  is at its original position and the fuel channel  112  is ready to again receive a dose of fuel. 
   Safety sensors on the lead screw  120  and dose motor  122  provide elements of safety and will shut down the motor  122  if the unit is malfunctioning. Specifically, a strike  132  is associated with the motor end of the dosing channel  112 . The strike  132  engages a normally closed limit switch  134 . A mechanical malfunction will move the strike  132  and open the limit switch  134  will causes the motor  122  to stop. There are three mechanical failures which will cause the limit switch  134  to be opened. First, if the door closure rod linkage  128  breaks, the compression spring  130  will force the door closure rod  126  into the strike  132  to open the limit switch  134 . Second, if the dose plunger  118  retracts too far a tab  119  on the plunger  118  will push against the strike  132  and open the limit switch  34 . Third, a holddown bearing  136  is located on the lead screw  120  of the dose plunger  118 . If the dose plunger  118  exceeds the shearing force for the holddown bearing bolts and the lead screw  120  will move towards the strike  132 , and the limit switch  134  will be opened. As an additional measure of safety, the lead screw  120  includes a lobe  121  near the end of the screw  120  which is associated with a rotation limit switch counter  138 . This rotation limit switch counter  138  will measure the number of times the lead screw  120  has been rotated anticipate the number of rotations in a cycle so that if there is a mechanical problem and the lead screw  120  is rotating too many times, the motor  122  will be shut down. 
   The hinged self closing fuel channel door  116  minimizes back burning in the fuel channel  112 . The deflecting shroud  114  also aids in minimizing back burning in the fuel channel  112  by causing a vacuum effect which prevents air from the furnace  2  from being pushed into the fuel channel  112 . The channel  112  is pitched up towards the burn pot  6 , further preventing fire from entering the fuel channel  112 . It should be noted that although the preferred fuel for this unit is grain, it is also contemplated that this invention could utilized with any biomass fuel. 
   Additionally, the furnace hopper  108  attached to the furnace  2  could also be automatically filled by a larger maxi-bin  140 . The furnace hopper  108  includes a sensors which would actuate an auger  144  affixed to the furnace hopper  108 . The furnace hopper  108  includes a funnel  146  which is attached to a pivoting arm  148  and a limit switch  150  located above the pivoting arm  148 . That pivoting arm  148  is attached to a pull spring  152 . When the furnace hopper  108  is full of fuel, the funnel  146  is depressed and which pushes the end of the pivoting arm  148  up against the limit switch  150 . When the fuel in the furnace hopper  108  reaches a low level, the funnel  146  is lifted up and the end of the pivoting arm  148  is pulled down by the spring  152 , removing the pivoting arm  148  from contact with the limit switch  150  which activates an auger  144  in an associated maxi-bin (not shown) to provide fuel to the furnace hopper  108 . The top of the furnace hopper  108  has a plastic covering  154  and a limit switch  156  held above the furnace  108  hopper by an arm  155 . As the furnace hopper  108  is filled with fuel, the plastic cover  154  rises. When the plastic cover  154  engages the limit switch  156 , the auger  144  supplying fuel from the maxi-bin is turned off. The furnace hopper  108  may also include a sliding door  157  near the fuel channel  112 , in order to easily remove the fuel from the furnace hopper  108  if maintenance to the furnace  2  is required. 
   As described above, the ignition plate  96  is located at the bottom of the burn pot  6 . The ignition plate  96  is shown in  FIG. 11 . The ignition plate  96  includes two annular recesses  158  which house an electrical ignition mechanism  159 . Four tabs  160  are located on the surface of the ignition plate  96  to loosely hold the ignition elements  159  in place. These tabs  160  are installed in recesses in the plate  96 , such that the tabs  160  are flush with the surface of the ignition plate  96 . The ignition plate  96  also includes a plurality of slots  98 . In the preferred embodiment, these slots  98  are beveled such that the slot is wider on the lower side of the ignition plate  96 . In the preferred embodiment, the slots  98  are approximately 9/64 of an inch. The bevels improve the ash drop out which will be described below. The ignition plate  96  must be of a material that is tolerant to reach combustion temperatures of 1600 degrees F. The material must also be tolerant to abrasion and the impact of the biomass fuel. In the preferred embodiment, the ignition plate  96  is made of a metal material, however any other suitable material could also be used, as would be obvious to one of skill in the art. 
   The ash removal system can be best seen in  FIG. 2 . An ash tray  92  is located beneath the ignition plate  96 . As the fuel is burned, ashes fall through the slots  98  in the ignition plate  96  into the ash tray  92 . A shaft  162  extends through the bottom of the furnace  2 , the ash tray  92 , and the ignition plate  96  and extends into the burn pot  6 . A fuel stirrer  32  is located just above the ignition plate  96  and is attached to the shaft  162 . The fuel stirrer  32  has two sets of arms  164 , 165 . The first set of arms  164  is located just above the surface of the ignition plate  96 . The second set of arms  165  is located approximately halfway up the shaft  162 . The blades on the arms  164 , 165  are beveled and sharp and extend close to, but not touching the water jacket  40  to avoid damaging the water jacket  40 . The fuel stirrer  32  includes rotatable cutting wheels or projections  166  which engage the slots  98  of the ignition plate  96  to clean the slots  98  during rotation of the fuel stirrer  32 . The fuel stirrer  32  is attached to the shaft  162  at the T-head  168  at the top of the shaft  162 . There is an air gap between the top of the shaft  162  and the T-head  168  to give a margin of flexibility to the shaft  162  in a vertical direction. The shaft  162  is attached to a small spring in the bottom of the ash tray  92 . This allows the shaft  162  to move slightly up and down and allows the cutter wheels or projections  166  to engage and disengage the slots  98 . The shaft  162  is connected by a drive mechanism  173  to a rotator motor  174 . When the motor  174  drives the shaft  162  to rotate, the fuel stirrer  32  is rotated which causes additional ashes to fall through slots  98  in the ignition plate  96 . Removal of debris from the ignition plate  96  ensures proper air flow for combustion. The fuel stirrer  32  also serves to agitate the fuel to increase complete combustion of the fuel and further increase efficiency of the furnace  2  and break up any clinkers which may form. A clinker is a fragment of incombustible matter left after a wood, coal or charcoal fire. 
   Inside the ash tray  92 , an ash arm  176  is attached to the shaft  162  just above the bottom surface of the ash tray  92 . When the shaft  162  is rotated the ash arm  176  rotates and pushes any ashes which have accumulated into the removable ash slide  178 . The removable ash slide  178  may include a mechanism such as an auger  180  to remove the ashes from the furnace  2 . In the preferred embodiment, the ash auger  180  would run for approximately 30 seconds after 60 minutes of cumulative furnace  2  operation. The auger is located near the baffled sediment tank  38  and the base of the auger  180  is constantly immersed in water. This water acts as a dam to prevent unwanted air to flow to or from the furnace  2 . The auger  180  runs relatively slowly, so that the debris is dried by the time it reached the end of the auger  180 . However, it is also contemplated that the ash slide  178  may simply deposit ashes into an appropriate disposal container. 
   The furnace  2  includes a wash down system which can best be seen in  FIG. 4 . The wash down system functions to clean ash and other debris from the furnace  2 . The wash down system includes a pipeshaft  182  which is attached to a pipeshaft motor  34 . The pipeshaft motor  34  is provided outside of the furnace  2  to rotate the pipeshaft  182 . The pipeshaft  182  is attached to a water supply  184 ; the water supply pipe  184  includes electric solenoid valves (not shown). The pipeshaft  182  has numerous washdown holes provided thereon. The holes can be of any size which provides adequate volume and pressure of fluid to achieve sufficient washdown of the furnace  2 ; however the preferred embodiment provides holes which are approximately 1/16″ in diameter. The water supplied to the washdown cycle can optionally include an additive, such as a cleaning agent, to aid in cleaning the unit. The water solution is pumped, filtered, and reused in subsequent cycles. 
   In the preferred embodiment, the water solution is stored in a baffled sediment tank  38  of approximately 18 gallons, shown in  FIGS. 6 ,  7  and  10 . It is important to use enough water for adequate cleaning of the system without using too much water, which can flood out key components of the system. The baffled sediment tank  38  allows the ash to sink in the tank. In this manner, most of the solids are removed from the water solution before reaching the filters and pump  190 . The baffled sediment tank  38  includes a removable cover for access to clean the tank  38 . The washdown cycle can be initiated either manually or automatically. 
   As described above, the furnace  2  is formed with a number of ash funnels  44  and tripod legs  46  to which the heat exchanger heli-coils  42  are attached. In the preferred embodiment four sets of ash funnels  44  are provided in the lower portion  54  of the furnace  2  and seven sets of tripod legs  46  are provided in the upper portion  52  of the furnace  2 . The ash funnels  44  and tripod legs  46  are attached to the inner wall of the furnace  2 . 
   Each set of ash funnels  44  in the lower portion  54  of the furnace  2  has an ash wiper  56  located in close proximity thereto. In the preferred embodiment the ash wipers  56  are magnetic; however it is also contemplated that the ash wipers  56  could have a different configuration, such as having metal bristles attached to the wiping surface. The ash wipers  56  are attached to the pipeshaft  182 , such that when the pipeshaft  182  rotates, the ash wiper  56  rotates. The ash caseway  36  is a tube positioned just inside the water jacket  40  surrounding the furnace  2 . The caseway  36  includes magnetic doors  196  located just above the point where the first and third ash funnels  44  are attached to the caseway  36 . An additional magnetic door  196  is provided at the top of the caseway  36  in the area where the lower portion  54  and the upper portion  52  of the furnace  2  are mated. This door  196  is an exit point for condensate during operation of the furnace  2 . Additionally, the debris and fluid from the washdown cycle are discharged through this door  196 . 
   In use, the pipeshaft motor  34  is operated to rotate the pipeshaft  182 . Water is supplied to the pipeshaft  182  through the water supply pipe  184 . When water is supplied to the pipeshaft  182  and the pipeshaft  182  is rotated water is flung from the pipeshaft holes to clean the furnace  2 . As the pipeshaft  182  is rotated, the ash wipers  56  which are hingedly attached to the pipeshaft  182  also rotate. The rotation of the ash wipers  56  causes any debris on the ash funnel  44  to be pushed away. The second and fourth lower funnels  44  are attached to tripod legs  46  which protrude from the funnel  44  to mate with notches formed in the inner wall of the furnace  2 . The configuration of the ash funnels  44  is such that as the water and debris from the second and fourth set of ash funnels  44  will fall onto the first and third set of ash funnels  44 . The debris and water on the first and third ash funnels  44  are pushed towards the ash caseway  36 . The trough  50  at the connection area of the lower portion  54  and upper portion  52  of the furnace  2  also collects water and debris and, as described above, contains a additional magnetic door  196 . The magnetic doors  196  of the ash caseway  36  are pushed open as the wipers  56  from the rotating shaft come in close proximity with the door. Each door  196  includes a protrusion. As the wiper  56  rotates, the wiper  56  engages the protrusion and opens the door  196  and allows the water and debris to fall down the ash caseway  36  and into the ash tray  92 . The magnetic door  196  is biased such that when the force of the water and debris recedes, the door  196  returns to its closed position. Sensors show door  196  position. An open door during burn status can be closed manually or by automatic means. A small electric solenoid is connected to each magnetic door  196  to push the door  196  shut if necessary. The steps of operation of the wash down system will be described in more detail below. 
   As is seen in  FIG. 1  the furnace  2  includes a computer  16  which controls the system. A number of sensors throughout the system provide data to the computer  16 . The locations of the primary sensors are shown in  FIG. 7 ; however additional sensors may be utilized. The sensors includes a limit switch on a normally closed electric solenoid  202 , an exhaust temperature sensor  204 , an outlet temperature sensor  206 , a plurality of monitoring temperature sensors  208 , a plurality of door position limit switches  210 , a removable burn pot temperature probe  212 , an air door position sensor  214 , an air inlet temperature sensor  216 , a water column sensor  218 , a torque clutch with reversing sensor  220 , an ignition plate current sensor  222 , a fuel channel temperature sensor  224 , a water inlet temperature sensor  226 , a door closure sensor  228 , a plunger advancement stop sensor  124 , a plunger retraction stop sensor  125 , a normally closed limit switch  134 , a rotation limit switch counter  138 . 
   There are six main sequences: a start up sequence, an ignition sequence, a high burn sequence, a selection sequence which selects between low burn, intermediate burn, burnout, and washdown, a low burn sequence, and an intermediate burn sequence. Each of the sequences combines activities including, but not limited to rotating the fuel stirrer, activating the air blower  84 , activating the igniter  159 , administering doses of fuel, ash dispensing, washdown, and selection of burn status. The computer  16  and program utilize the sensor data to determine which step of the program is to be completed. The unit also includes a smart logic thermal controller. 
     FIGS. 12-17  are flowcharts which show the various sequencing series by which the furnace  2  operates.  FIG. 12  is the First Sequencing Series, which is the initial start up and safety check protocol.  FIG. 13  is the Second Sequencing Series, which is the ignition sequencing protocol.  FIG. 14  is the Third Sequencing Series, which is the high burn sequencing protocol.  FIG. 15  is the Sequence Series, which is the low burn, intermediate burn, burnout, and/or wash down selection sequence.  FIG. 16  is the low burn sequencing protocol.  FIG. 17  is the intermediate burn sequencing protocol.  FIGS. 12-17  use a number of abbreviations of parts of the system. For example, B.P. stands for burn pot, L.S. stands for limit switch, W.D. stands for wash down, W.C. stands for water column, and SLTC stands for smart logic thermal controller. 
   As illustrated in  FIG. 12 , the computer  16  tests various elements of the unit as an initial safety protocol. Specifically, when the main power is manually on, the computer  16  tests whether the furnace hopper  108  has fuel. Whether the furnace hopper  108  has fuel is tested by the limit switch associated with the furnace hopper  108 . If the furnace hopper  108  does not have fuel, a limit switch activates the auger  144  to rotate. When the furnace hopper  108  is full an additional limit switch turns off the auger  144  to the furnace hopper  108 . The computer  16  also turns the circulator pump  30  on, tests whether it is functioning, and then turns it off. The computer  16  tests whether all water, exhaust, dose tube, and fan duct temperatures are 180 degrees F. or less. The computer  16  tests, by means of separate limit switches, whether the fuel plunger  118  is retracted, the combustion release door  201  is closed, the wash down solenoid valves are closed, and whether the wash down ash caseway doors  196  are closed. The computer  16  also rotates the fuel stirrer  32  for one minute and or greater than or equal to 12 revolutions and tests to see if it is complete. The computer  16  activates the ash auger  180  for 30 seconds, and then tests whether the cycle is complete. The computer  16  also activates the blower  84  to 100 percent power then turns off the fan and tests whether the wash down caseway sensors are ok. The computer  16  then tests whether there is a call for heat. If there is a call for heat the computer  16  proceeds to the second sequence. If there is no call for heat, the unit is put in stand by mode. If the unit fails any of the tests above, the computer  16  either attempts to solve the failure, or deactivates the unit and activates an associated alarm. If the computer  16  attempts to solve the failure and still fails, the unit is deactivated and the associated alarm is activated. 
   As illustrated in  FIG. 13 , the second sequence is the ignition sequence. The computer  16  provides three consecutive doses of fuel to the furnace  2 , and tests whether this has been completed using a limit switch with an event counter. Motor rotation is verified at each does. If the three doses are complete, the fuel stirrer  32  is then rotated for 5 seconds or greater than or equal to one revolution. Motor rotation is verified at each operation. If the fuel stirring step is complete, the computer  16  turns on the water pump  30 . If the water pump  30  has properly tuned on, the computer  16  turns the igniter  159  on. The computer  16  tests whether there is current to the igniter plate  96 . If the current sensor shows there is current to the plate  96 , the computer  16  activates the air fan  84  to 100% and tests whether the fan  84  is at 100%. If the air fan  84  is at 100% the computer  16  then tests whether the air cut out door  100  is open. This is tested via a limit switch. If the air cut out door  100  is open, the computer  16  tests whether the burn pot  6  temperature of 300 degrees F. or higher and rising within approximately 10 minutes of turning the fan  84  on. If this condition is satisfied the computer  16  turns the igniter  159  off at a burn pot  6  temperature of 300 degrees F. or more. While the burn pot  6  temperature is rising, the computer  16  proceeds to the third sequence. If the unit fails any of the tests described above, the computer  16  either deactivates the unit and activated an appropriate alarm, or attempts to fix the problem through the steps shown in  FIG. 13 . If the problem cannot be fixed by the steps shown in  FIG. 13 , the computer  16  deactivates the unit and activates an appropriate alarm. As illustrated in  FIG. 14 , the third sequence is a high burn protocol. In the high burn protocol the computer  16  tests whether the burn pot  6  temperature is 1010 degrees F. and rising. If the burn pot  6  temperature is 1010 degrees F. and rising, the computer  16  waits until the burn pot  6  temperature has fallen to 1000 degrees F. then rotates the fuel stirrer  32  for 5 seconds or greater than or equal one rotation. If the fuel stirrer  32  has successfully been rotated for 5 seconds, or greater than or equal one rotation, the computer  16  tests whether the burn pot  6  temperature has risen above 1010 degrees F. If the burn pot  6  temperature has risen above 1010 degrees F., the computer  16  repeats the previous step of rotating the fuel stirrer  32  when the burn pot  6  temperature falls to 1000 degrees F. If the burn pot  6  temperature has not risen to 1010 degrees F., the computer  16  has a dose of fuel delivered to the burn pot  6  when the burn pot  6  temperature falls to 950 degrees F. Within 30 seconds, the computer  16  tests whether the temperature has risen to over 1010 degrees F. If the temperature has reached more than 1010 degrees F., the computer  16  returns to the step of waiting for the burn pot  6  temperature to falls to 1000 degrees F. and rotating the fuel stirrer  32  for five seconds or at least one revolution and repeats above described procedure. At that point, if there is a call for low or medium burn and more than five doses have been administered in the high burn sequence, the computer  16  runs the low or medium burn sequence. The selection of burn status is determined by the smart logic thermal controller or by manual selection. As described with regard to the previous sequences, if the unit fails any of the tests described above, the computer  16  either deactivates the unit and activated an appropriate alarm, or attempts to fix the problem through the steps shown in  FIG. 14 . If the problem cannot be fixed by the steps shown in  FIG. 14 , the computer  16  deactivates the unit and activates an appropriate alarm. 
   As illustrated in  FIG. 15 , the fourth sequence is the choosing sequence after high burn protocol. In this sequence the computer  16 , with input from either the smart logic thermal controller or manual input, determines whether to run the low burn, intermediate burn, burn out status or wash down sequence. The computer  16  uses either manual input or a smart logic thermal controller to determine whether the unit is to activate low burn status. If the unit is to activate low burn status, the unit runs the low burn sequence. If the unit is not to activate low burn status, the computer  16  tests whether the unit to activate intermediate burn status. If the unit is to activate intermediate burn, the intermediate burn sequence is run. In the unit is not told to activate intermediate burn, the computer  16  goes to the burnout sequence. 
   The burnout sequence can be initiated either manually or by the smart logic thermal controller. The burnout cycle is also shown in  FIG. 15 . In the burn out sequence when the burn pot  6  temperature falls to 300 degrees F., the fan  84  is turned off and the fuel stirrer  32  is rotated for 5 minutes or 60 revolutions. The water pump  30  is turned off at 200 degrees F. The optimum washdown time is determined based on the differential between the output water temperature and the exhaust air temperature. As the differential between the two temperatures increases, the inefficiency of the unit is also increasing. The controller makes a decision on the optimum time for washdown based on the temperature differential as well as other factors. For example, if the ambient air temperature is too low, the unit will not go through the washdown process. The burnout sequence is also described in  FIG. 15 . 
   If the smart logic controller determines that it is not an appropriate time to run the washdown cycle, the computer  16  tests whether there is a call for heat. If there is a call for heat the computer  16  runs the first sequence, the safety protocol. If there is no call for heat the unit is put to standby. The wash down cycle is also shown in  FIG. 15 . In the washdown sequence, the ash auger  180  is activated for 30 seconds. If this is completed successfully the water solenoid  186 , washdown water pump  190 , washdown pipeshaft motor  34 , wash down pipeshaft  182 , fuel stirrer  32 , and ash auger  180  are activated for 15 minutes. Water pump  190  is deactivated for 5 minutes before the next step. This allows water within the furnace  2  to drain out. This allows the unit to dry out. The fan  84  is activated and the igniter plate  96  is activated to prevent corn from entering wet furnace  2 . If this is completed successfully, the air blower  84  is activated at 100 percent for 45 minutes, the fuel stirrer  32  for 45 minutes and ash auger  180  are activated for 5 minutes and the igniter  159  is activated for 45 minutes. If this is completed successfully, the computer  16  tests whether there is a call for heat. If there is a call for heat the first sequence is run. If there is no call for heat the unit is put to standby. As described with regard to the previous sequences, if the unit fails any of the tests described above, the computer  16  either deactivates the unit and activated an appropriate alarm, or attempts to fix the problem through the steps shown in  FIG. 15 . If the problem cannot be fixed by the steps shown in  FIG. 15 , the computer  16  deactivates the unit and activates an appropriate alarm. 
   The low burn protocol is shown in  FIG. 16 . In the low burn protocol the computer  16  tests whether the burn pot  6  temperature is 410 degrees F. and rising. If the burn pot  6  temperature is 410 degrees F. and rising, the computer  16  waits until the burn pot  6  temperature has fallen to 400 degrees F. then rotates the fuel stirrer  32  for five seconds or greater than or equal one rotation. If the fuel stirrer  32  has successfully been rotated for 5 seconds, or greater than or equal one rotation, the computer  16  tests whether the burn pot  6  temperature has risen above 410 degrees F. If the burn pot  6  temperature has risen above 410 degrees F., the computer  16  repeats the previous step of rotating the fuel stirrer  32  when the burn pot  6  temperature falls to 400 degrees F. If the burn pot  6  temperature has not risen to 410 degrees F., the computer  16  has a dose of fuel delivered to the burn pot  6  when the burn pot  6  temperature falls to 375 degrees F. Within 30 seconds, the computer  16  tests whether the temperature has risen to over 410 degrees F. If the temperature has reached more than 410 degrees F., the computer  16  returns to the step of waiting for the burn pot  6  temperature to fall to 400 degrees F. and rotating the fuel stirrer  32  for five seconds or at least one revolution and repeats above described procedure. At that point, if there is a call for high or medium burn and more than five doses have been administered in the low burn sequence, the computer  16  runs the high or medium burn sequence. The selection of burn status is determined by the smart logic thermal controller or by manual selection. As described with regard to the previous sequences, if the unit fails any of the tests described above, the computer  16  either deactivates the unit and activated an appropriate alarm, or attempts to fix the problem through the steps shown in  FIG. 16 . If the problem cannot be fixed by the steps shown in  FIG. 16 , the computer  16  deactivates the unit and activates an appropriate alarm. 
     FIG. 17  shows the intermediate burn sequence. In the intermediate burn protocol the computer  16  tests whether the burn pot  6  temperature is 710 degrees F. and rising. If the burn pot  6  temperature is 710 degrees F. and rising, the computer  16  waits until the burn pot  6  temperature has fallen to 700 degrees F. then rotates the fuel stirrer  32  for five seconds or greater than or equal one rotation. If the fuel stirrer  32  has successfully been rotated for five seconds, or greater than or equal one rotation, the computer  16  tests whether the burn pot  6  temperature has risen above 710 degrees F. If the burn pot  6  temperature has risen above 710 degrees F., the computer  16  repeats the previous step of rotating the fuel stirrer  32  when the burn pot  6  temperature falls to 700 degrees F. If the burn pot  6  temperature has not risen to 710 degrees F., the computer  16  has a dose of fuel delivered to the burn pot  6  when the burn pot  6  temperature falls to 650 degrees F. Within 30 seconds, the computer  16  tests whether the temperature has risen to over 710 degrees F. If the temperature has reached more than 710 degrees F., the computer  16  returns to the step of waiting for the burn pot  6  temperature to fall to 700 degrees F. and rotating the fuel stirrer  32  for 5 seconds or at least one revolution and repeats above described procedure. At that point, if there is a call for low or high burn and more than five doses have been administered in the intermediate burn sequence, the computer  16  runs the low or high burn sequence. The selection of burn status is determined by the smart logic thermal controller or by manual selection. As described with regard to the previous sequences, if the unit fails any of the tests described above, the computer  16  either deactivates the unit and activated an appropriate alarm, or attempts to fix the problem through the steps shown in  FIG. 17 . If the problem cannot be fixed by the steps shown in  FIG. 17 , the computer  16  deactivates the unit and activates an appropriate alarm. 
   If at any time during a call for heat, whether high, intermediate, or low burn sequence, if the burn pot  6  tem falls to 300 degrees F. or less, the igniter  159  will activate and the fan speed  84  will increase to 100 percent. Both will activate for approximately 10 minutes. At this point one dose of fuel will also be administered. If the burn pot  6  temp rises to 410 degrees F. and rising within the 10 minutes the igniter  159  will be deenergized and the fan  84  speed will resume its speed based on the burn status which was its related burn status. The burn status will then continue as previously described. If combustion does not occur, an appropriate alarm will be indicated. 
   It should be noted that the entire furnace  2  can be taken apart for maintenance purposes. The top of the furnace  2  has a removable cover  200 . All of the heat exchangers can be disconnected and removed from the system. The heli-coil tripod legs  46  are hinged to allow the legs  46  to be pulled out of the furnace  2 . 
   The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.