Abstract:
A steel sided double-walled bottom fed sawdust, woodchip and other particulate matter burning furnace where combustion air is pre-heated by passing around the combustion area between the double walls and further having an automatic fuel shut-off feature.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to furnaces. 
     BACKGROUND OF THE INVENTION 
     In the past, numerous furnaces have been proposed which have bottom particulate fuel feeding systems. Additionally, furnaces have been proposed which have a pre-heating of the combustion air. 
     While these furnaces have been used extensively in the past, they do have some drawbacks. These furnaces often are expensive to manufacture. 
     Consequently, there exists a need for improved methods and apparatus for economically burning particulate matter. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an apparatus and method for burning particulate matter in an efficient manner. 
     It is a feature of the present invention to include a bottom fed particulate fuel furnace with an automatic fuel height-limiting mechanism. 
     It is an advantage of the present invention to economically control the provisioning of fuel into a furnace. 
     It is another feature of the present invention to include a tangential combustion air pre-heating structure. 
     It is an advantage of the present invention to achieve improved efficiency in burning solid fuels in a furnace. 
     The present invention is an apparatus and method for burning solid fuels designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features, and achieve the already articulated advantages. 
     Accordingly, the present invention is an apparatus and method including a fuel height level limiting mechanism in a bottom fed particulate matter burning furnace, and in another embodiment, a tangential pre-combustion air heating structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more fully understood by reading the following description of the preferred embodiments of the invention, in conjunction with the appended drawings wherein: 
         FIG. 1  is a line drawing side view of the furnace of the present invention. 
         FIG. 2  is a cross-sectional view of the furnace of  FIG. 1  taken on line  2 - 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Now referring to the drawings wherein like numerals refer to like matter throughout, and more specifically referring to  FIG. 1 , there is shown a furnace system, generally designated  100 , which includes a furnace main body  110 , which has a solid fuel supply mechanism  120 , an exhaust system  130 , a combustion air intake  140  and a fuel level limit controller  150 . 
     With the furnace main body  110 , there can be an outer layer  112  and an inner layer  114 , both of which can be made of some metal such as steel, aluminum, iron, copper, or other metallic material. Outer layer  112  and inner layer  114  could also be non-metallic such as concrete, fire brick, ceramic, etc. Furnace main body  110  may include observation doors  116  and  118  which can be a mere hinged or removable segment of the outer layer  112  and inner layer  114  respectively. 
     Solid fuel supply mechanism  120  includes a supply pipe  122  with an auger  124  therein. Solid fuel supply mechanism  120  could be a conveyor system, pressurized system or any other mechanism for transporting solid matter. The solid fuel supply mechanism  120  provides the fuel into a hole in the bottom  128  of or through an opening (not shown) near the bottom, but in the side of furnace main body  110 . In some applications, the fuel feed could be top fed or near top fed. 
     Exhaust system  130  comprises an outlet port  132  and an internal heat exhaust tube  134  which extends into the furnace main body  110  through a central hole in the top. The materials for exhaust system  130  and heat exhaust tube  134  may be steel or any suitable material which is capable of withstanding the high temperatures produced in the furnace main body  110 . The bottom  128  and the top may provide sufficient structural support for maintaining the respective placement of the bottom, top, outer layer and inner layer, exhaust system, and fuel level limit controller. However, internal or additional structural support members may be desirable, depending upon design choices of size, materials, shape, etc. 
     Combustion air intake  140  is the source of combustion air, and it includes a tapered region  142 , as well as a generally cylindrical pre-combustion heating chamber  144  disposed between outer layer  112  and inner layer  114 . Air may be forced into tapered region  142  and pass through the chamber  144  where it is heated by the combustion in furnace main body  110 . The pre-heated combustion air enters into the central combustion zone of the furnace main body  110  at air inflow region  146  along a substantially tangential line near the inner layer  114 . This heated and rotating air enhances combustion of the solid fuel augered into by auger  124 . 
     The solid fuel is augered in until it reaches the desired level, where it engages the inside portion  152  of fuel level limit controller  150 . Fuel level limit controller  150  could be a simple lever that is caused to be lifted upward when material strikes the inside portion  152  which transmits the resulting force on intermediate bar  154  to an external free end  156 , which could be coupled to a switch or other linkage configured to facilitate switching the auger  124  on and off based upon the fuel height inside of furnace main body  110 . Alternatively, other fuel level limiting systems could be employed, including electronic or optical systems. 
     In operation, the furnace  100  functions as follows: fuel is augered in, filling the central region until engaging the inner portion  152  of fuel level limit controller  150 . The operator opens the doors  116  and  118  and throws in some diesel fuel, followed by a match. The diesel fuel and the solid fuel begin to burn, and the exhaust rises and passes up the heat exhaust tube  134  and out an exhaust port  132 , where it is used to provide heat for various purposes, such as a boiler, etc. The air is either naturally drawing into the furnace or blown in from a blower. In either case, the air is pre-heated by passing around the tangential air intake port  144  found between the outer layer  112  and the inner layer  114 . When the furnace is operating at peak performance, the combustion is intense, and very little fuel is unburned. Any remaining ash is expelled out the exhaust system  130 . 
     Throughout this description, reference is made to a solid fuel or particulate matter furnaces or burning apparatuses, because it is believed that the beneficial aspects of the present invention would be most readily apparent when used in connection with solid fuel and particulate matter furnaces; however, it should be understood that the present invention is not intended to be limited to solid fuel and to particulate matter furnaces, and should be hereby construed to include other types of fuel and other structures that generate heat in a confined area. 
     Throughout this description, reference may be made to cylinders, circles, centers, etc. because many of the beneficial aspects of the present invention are realized with a furnace with a cylindrical overall shape. However, it should be understood that furnaces with rectangular cross-sections or other shapes may be substituted if they achieve many of the same advantages. 
     It is thought that the method and apparatus of the present invention will be understood from the foregoing description and that it will be apparent that various changes may be made in the fowl, construct steps and arrangement of the parts and steps thereof, without departing from the spirit and scope of the invention or sacrificing all of their material advantages. The form herein described is merely a preferred exemplary embodiment thereof.