Abstract:
A combustion system for extracting thermal energy from biomass or other formable fuels that does not require densification or other processing of the biomass prior to combustion. This system continuously feeds the biomass fuel from an auger or other conveyance system while simultaneously causing the biomass fuel to be formed with a hollow core. The biomass fuel is ignited from within the hollow core and burns primarily radially outward due to negative pressure surrounding combustion chamber thus facilitating and containing the combustion process. This system also utilizes pre-heating the fuel, primary and secondary air pre-heating, insulated combustion chambers, and carefully control combustion air to ensure substantial combustion is achieved even with fuels having high moisture content. In the preferred embodiment, a heat exchanger is utilized to capture thermal energy of combustion products for use as an energy source for additional processes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Provisional application Number 61196132, filed on Oct. 15, 2008. 
         [0002]    Provisional application Number 61199027, filed on Nov. 12, 2008. 
         [0003]    Provisional application Number 61271544, filed on Jul. 22, 2009. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0004]    Not applicable to this application. 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Field of the Invention 
         [0006]    The present invention relates generally to biomass combustion which comprises a suitably formable fuel and more specifically it relates to a continuous-fed biomass combustion system for efficiently extracting heat energy from unprocessed or processed biomass material of varying moisture content. 
         [0007]    2. Background 
         [0008]    Combustion of biomass has been used by humankind to generate heat and light for thousands of years. Biomass was the world&#39;s predominant energy source until fossil fuels took over during the industrial revolution. Modern biomass can include, for example: wood, wood waste, agricultural waste, energy crops, municipal solid waste, sewage sludge and cellulostic-type industrial waste. 
         [0009]    The burning of nondensified, loose grass has been one of the most utilized sources of biomass to generate heat and has been used for centuries. Many settlers on the Great Plains in the late 19th century stayed alive with grass heat. Hay was actually the fuel of choice in central and northern Nebraska until the corn culture supplanted it. However, feeding loose hay into a stove produced excessive smoke and required constant monitoring. These disadvantages led to various methods of processing the biomass prior to combustion. 
         [0010]    One of the first processing methods was to densify the biomass. In the case of hay, in order to make the hay more compact, it was twisted into twig-like bundles called “cats.” This process was successful in reducing many of the disadvantages. New “stove” technology also became more advanced and produced hay-burning devices in four basic types: stove attachments, piston-driven stoves, drum stoves, and Russian furnaces. A common hay burning stove attachment was shaped like copper boilers used for washing but were twice as deep, holding about twenty pounds of hay. Lids on a cook stove were removed and the hay-filled attachment was placed with the open end down on the cook stove. A filled attachment could provide enough heat for two to four hours. Local blacksmiths made most of these stove attachments from sheet iron riveted together. 
         [0011]    To address some of the above issues, most of the grass-burning devices currently under development are designed to use a much more densified version such as pellets or briquettes. The problem with densified biomass is that the equipment to compress biomass is very expensive to buy, requires significant maintenance, and requires significant power to operate. 
         [0012]    A recent development is stoves that burn a single round bale of hay in a large chamber. The issues with this type of hay-burning stove include difficulties in modulating temperature as well as having a significant ash clean-out problem. The stove has to be completely shut down and allowed to cool before the ashes can be safely removed. 
         [0013]    In the last decade, gasification has gotten a lot of attention. Gasification can be defined as a thermal process of changing a solid fuel such as coal, biomass, or municipal solid waste into combustible gas and oil vapors. Almost all kinds of biomass with moisture content of 5% to 30% can be gasified. Under controlled conditions that are characterized by low oxygen supply and high temperatures, most biomass materials can be converted into a gaseous fuel known as “producer gas”, which consists of combustible mixture of nitrogen, carbon monoxide, and hydrogen. Biomass gasification and/or combustion applications include water boiling, steam generation, drying, motive power applications such as using the producer gas as a fuel in internal combustion engines, and electricity generation. 
         [0014]    Combustion problems with wood and other biomass fuels have been generally due to not enough heat for drying and ignition, uncontrolled cycles of drying and ignition, with either excess air or insufficient air, too much fuel burning at once or too little, and incomplete mixing of air and fuel. At the low burn rates generally required for domestic use exhaust emissions increase dramatically, because of incomplete combustion, which causes creosote and soot buildup on heat exchangers, and in turn fire hazards and even more inefficient heat transfer. 
         [0015]    The main problems with the application of biomass gasification systems have been economic, not technical. For example, conventional biomass gasification systems are typically suitable only for large-scale operations and not small-scale operations. Also, the product from gasification is mainly a heat source and the low value of these products in today&#39;s market is insufficient to justify the capital and operating costs of conventional biomass gasification systems. 
         [0016]    The present invention is capable of combusting a multitude of different materials including grasses without densification, wood and wood materials, waste paper and paper products, peat, refuse derived fuels (RDF), municipal solid waste, dry animal manure, or even shredded rubber tires. 
         [0017]    The present invention also overcomes the disadvantage of combustion inefficiency. It is well documented that two-stage combustion (primary and secondary) helps minimize NOx (nitrogen oxide) formation and also has the advantage of increasing thermal efficiency by utilizing more of the fuel to product heat energy. 
         [0018]    Also, conventional biomass fuel-burners suffer from the same symptoms of inefficient combustion. Relatively dry fuels are generally required for cleaner burning, but biomass fuels with 40% or higher moisture content (percentage of damp weight) are much more available in the form of logging residue, brush and agricultural waste. These fuels are generally available at a lower cost than seasoned cordwood and lend themselves better to automatic continuous fuel feed. The present invention overcomes these shortcomings by using an internal gasification process inside the primary combustion chamber to enable use of higher moisture content feedstock. 
       BRIEF SUMMARY OF THE INVENTION 
       [0019]    In view of the foregoing disadvantages inherent in the known types of combustion and/or gasification apparatus now present in the prior art, the present invention provides a new biomass combustion system construction wherein the same can be utilized for efficiently extracting heat energy from biomass material. 
         [0020]    The general purpose of the present invention, which will be described subsequently in greater detail, is to provide a new biomass combustion system that has many of the advantages of the combustion apparatus mentioned heretofore and many novel features that result in a new biomass combustion system which is not anticipated, rendered obvious, suggested, or even implied by any of the prior art gasification apparatus, either alone or in any combination thereof. 
         [0021]    To attain this, one embodiment of the present invention generally comprises a feedstock loading hopper, a hole-forming feedstock auger, an insulated feeder chamber, a fuel pre-heating magazine, a primary combustion chamber, a feedstock end stop grate at the end of the primary combustion chamber, a primary center air feed tube, a primary air modulating valve, a primary flow meter, an ash collection chamber, a stationary fan-type directing blade assembly, a secondary combustion chamber connected to the primary combustion chamber, secondary air pre-heating tubes, a secondary air mixer manifold, an airtight, insulated heat containment chamber/firebox, a secondary air modulating valve, a secondary flow meter, an insulated cyclonic filter, a residue collection bucket, a single-pass shell and tube heat exchanger, a high-temperature vacuum blower, a programmable control unit, a battery back-up system, an exhaust stack, and an air pre-heating jacket. 
         [0022]    There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and that will form the subject matter of the claims appended hereto. 
         [0023]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the terminology employed herein are for the purpose of the description and should not be regarded as limiting. 
         [0024]    To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated and described within the scope of the appended claims. 
         [0025]    A primary object of the present invention is to provide a biomass or formable fuel combustion system that will overcome the shortcomings of the prior art devices. 
         [0026]    A second object is to provide a biomass combustion system for efficiently extracting heat energy from biomass material. 
         [0027]    A further object is to provide a biomass combustion system that provides for usage of biomass combustion technologies within small-scale operations. 
         [0028]    A further object is to provide a biomass combustion system that is capable of utilizing various types of readily available fuels. 
         [0029]    A further object is to provide a biomass combustion system that provides a cost effective alternative fuel source compared to conventional fossil fuels. 
         [0030]    A further object is to provide a biomass combustion system that is environmentally friendly and utilizes renewable resources. 
         [0031]    A further object is to provide a biomass combustion system that has high combustion efficiency. 
         [0032]    A further object is to provide a biomass combustion system that is automated and requires reduced maintenance. 
         [0033]    A further object is to provide a biomass combustion system that may be utilized to produce heat. 
         [0034]    A further object is to provide a biomass combustion system that forms a hollow feedstock for centrally introduced air whereby facilitating more complete combustion. 
         [0035]    A further object is to provide a biomass combustion system that is completely surrounded with an air pre-heating jacket to better recycle, utilize, and contain the heat generated. 
         [0036]    A further object is to provide a small biomass combustion system that may be ganged together for larger heat output demands. 
         [0037]    A further object is to provide a biomass combustion system that completely removes products of combustion such as ashes and residues from the combustion area. 
         [0038]    A further object is to provide automatic feeding of feedstocks and hollowing of feedstocks at the same time. 
         [0039]    A further object is to utilize the compacted biomass to greatly reduce any uncontrolled air to enter the combustion area. 
         [0040]    A further object is to collect any and all by-products of combustion by gravity into central collection areas for easy removal and disposal. 
         [0041]    A further object of the invention is to provide an airtight heat containment chamber to enclose the combustion area and provide draft for complete combustion. 
         [0042]    A further object of the invention is to use a high temperature blower in the exhaust stream to provide negative draft pressure for a heat containment chamber. 
         [0043]    A further object of the invention is to utilize channels on the inside diameter of the combustion chamber to collect products of combustion and provide a flow path to the secondary combustion chamber. 
         [0044]    A further object of the invention is to introduce combustion air to the hollow center of biomass and other feedstocks. 
         [0045]    A further object of the present invention is to preheat all combustion air using an air jacket surrounding the combustion process. 
         [0046]    A further object of the present invention is to monitor incoming combustion air with a flow meter in order to control it completely. 
         [0047]    A further object of the present invention is to use high temperature insulating refractory materials to insulate the combustion chamber to effectively combust even with fuels containing almost half their weight in water. 
         [0048]    A further object of the present invention is to capture most of the heat from the escaping exhaust gases by exhausting through a high efficiency heat exchanger. 
         [0049]    A further object of the present invent is to provide combustion residue collection buckets that may easily be emptied at periodic intervals. 
         [0050]    A further object of the present invention is to reduce the combustion mass as much as possible in order to modulate or shut down temporarily the burning (burn rate) when heat is not called for. 
         [0051]    A further object of the present invention is to operate both primary and secondary combustion chambers at a very high temperature to ensure a substantially smokeless, clean exhaust. 
         [0052]    A further object of the present invention is to use the screw auger and protruding rod to extrude the biomass into a hollow form that will retain shape as it is burned. 
         [0053]    A further object of the present invention is to utilize the grate as a method to control where the combustion is taking place. 
         [0054]    A further object of the present invention is to use a vertical grating system whereby gravity assists in removing ashes. 
         [0055]    A further object of the present invention is to use the continuous pressure of the feedstock against the grate to remove ashes effectively. 
         [0056]    Other objects and advantages of the present invention will become obvious to the reader and it is intended that these objects and advantages be within the scope of the present invention. 
         [0057]    To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated and described within the scope of the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0058]    Various other objects, features and attendant advantages of the present invention will become fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein: 
           [0059]      FIG. 1  is a side cross sectional view of the present invention with heat exchanger and stack not shown for clarity. 
           [0060]      FIG. 2  is a side view of the heat exchanger and stack of the present invention. 
           [0061]      FIG. 3  is a view of the programmable control unit. 
           [0062]      FIG. 4  is an end view of the present invention. 
           [0063]      FIG. 5  is a discharge end view of the primary combustion chamber terminus with the grate and formed fuel shown. 
           [0064]      FIG. 6  is a cross sectional side view of the primary and secondary combustion chamber. 
           [0065]      FIG. 7  is an end view of the primary combustion chamber terminus. 
           [0066]      FIG. 8  is a cross sectional view of the primary combustion chamber. 
           [0067]      FIG. 9  is the fuel input and effluent stream discharge end view of the primary combustion chamber. 
           [0068]      FIG. 10  is the inlet end view of the secondary combustion chamber. 
           [0069]      FIG. 11  is a cross sectional side view of the secondary combustion chamber. 
           [0070]      FIG. 12  is the exhaust discharge end view of the secondary combustion chamber. 
           [0071]      FIG. 13  is a side view of the heat exchanger. 
           [0072]      FIG. 14  is an exhaust input end view of the heat exchanger 
           [0073]      FIG. 15  is an exhaust discharge view of heat exchanger. 
           [0074]      FIG. 16  is a cross sectional view of the heat exchanger. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0075]    In the following detailed description, reference is made to the accompanying drawings which form a part thereof, and in which is shown by way of illustration specific embodiments in which the invention is practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents. 
         [0076]      FIGS. 1-16  illustrate a continuously-fed biomass combustion system according to one embodiment. Similar reference characters denote similar elements throughout the several figures.  FIGS. 1 through 16  illustrate the biomass combustion system, which comprises a feedstock-loading hopper ( 21 ), a hole-forming feedstock auger ( 22 ) and elongated shaft ( 23 ) for delivering biomass, an insulated feeder chamber ( 26 ), a fuel pre-heating magazine ( 27 ), a primary combustion chamber ( 30 ), a feedstock end stop grate ( 35 ), primary center air feed tube ( 39 ), a primary air modulating valve ( 48 ), a primary flowmeter ( 49 ), an ash collection chamber ( 44 ), a stationary fan-type directing blade assembly ( 36 ), a secondary combustion chamber ( 37 ) fluidly connected to the primary combustion chamber, secondary air pre-heating tubes ( 52 ) connected to the secondary combustion chamber ( 37 ), a secondary air mixer manifold ( 55 ), an airtight, heat containment chamber ( 41 ) containing all combustion apparatus, a secondary air modulating valve ( 50 ), a secondary flowmeter ( 51 ), an insulated cyclonic filter ( 53 ) to remove pneumatically conveyed ash products, a residue collection bucket ( 54 ), a single-pass shell and tube heat exchanger ( 56 ) to remove heat from the exhaust gases and heat water, a high-temperature vacuum blower ( 58 ) to negatively pressurize the combustion process, a programmable control unit ( 59 ), a battery back-up system ( 60 ), an exhaust stack ( 61 ), and an air pre-heating jacket ( 43 ) to pre-heat both incoming primary and secondary air, and a propane ignition device ( 62 ). 
         [0077]    The feedstock-loading hopper ( 21 ) is a typical V-shaped steel hopper that collects particles of feedstock ( 24 ) and gravity-delivers the material into the hole-forming feedstock auger ( 22 ). The feedstock-loading hopper ( 21 ) may optionally contain a slide gate, rotary lock, or manual cover ( 40 ). 
         [0078]    The hole-forming feedstock auger ( 22 ) is constructed of spiral flights that are welded to a shaft in typical fashion of any screw auger. The auger is powered by auger motor ( 70 ) and gearbox ( 25 ). At the end of the hole-forming feedstock auger is an elongated shaft ( 23 ) that forms a hollow cavity ( 29 ) in the center of the feedstock. This hollow cavity ( 29 ) stays formed in the feedstock as it moves slowly into and through the primary combustion chamber until stopped by the feedstock end stop grate ( 35 ) at the terminus of the primary combustion chamber ( 30 ). The elongated shaft ( 23 ) also serves to block air leakage into the airtight heat containment chamber ( 41 ). The formed biomass material ( 28 ) further discourages any airflow into the airtight heat containment chamber ( 41 ) by substantially forming a circumferential seal. 
         [0079]    The insulated feeder chamber ( 26 ) is located between the feedstock-loading hopper ( 21 ) and the airtight heat containment chamber ( 41 ). The insulated feeder chamber ( 26 ) is fluidly connected to the hole-forming feedstock auger assembly ( 22 ) and the pre-heating feedstock magazine ( 27 ). 
         [0080]    The fuel pre-heating magazine ( 27 ) begins to pre-heat the feedstock because it is in contact with the hot combustion gases in the inside of the airtight heat containment chamber ( 41 ). The fuel pre-heating magazine ( 27 ) is fluidly connected to the primary combustion chamber ( 30 ) and slides smoothly inside to deliver the feedstock as illustrated in  FIG. 6 . 
         [0081]    The primary combustion chamber ( 30 ) is where primary combustion occurs thereby converting the biomass to a producer gas. The primary combustion chamber ( 30 ) in this embodiment is designed for combusting formable fuel such as, but not limited to: corn stover, switchgrass, reed canarygrass, forest slash, urban wood waste, lumber waste, wood chips, sawdust, straw, firewood, agricultural residue, dung and the like. The primary combustion chamber ( 30 ) is fluidly connected with the fuel pre-heating magazine ( 27 ) and the ash collection chamber ( 44 ). It has an internal diameter consistent with the inside diameters of both the fuel pre-heating magazine ( 27 ) and the insulated feeder chamber ( 26 ). The primary combustion chamber ( 30 ) contains a plurality of longitudinal tapered gas channels ( 32 ) of varying depth around the inside diameter of the primary combustion chamber ( 30 ). These air channels serve to fluidly connect the primary combustion chamber ( 30 ) with the secondary combustion chamber ( 37 ). The tapered gas channels ( 32 ) can get progressively larger and wider if dictated by application as they approach the secondary combustion chamber ( 37 ) in order to avoid any unburned particles of biomass from blocking the flow of hot gasses. The primary combustion chamber ( 30 ) is constructed of steel tubing welded to an angle ring ( 33 ) to act as a shell or containment structure for the refractory material ( 34 ) as shown in  FIG. 7  and  FIG. 8 . The insulating refractory material ( 34 ) can be cast in place and held secure after curing using special studs ( 31 ) welded to the outside tubing. 
         [0082]    The feedstock end stop grate ( 35 ) is located at the ash end of the primary combustion chamber ( 30 ) and physically stops the formed biomass material ( 28 ) from entering the ash collection chamber ( 44 ) until it has a soft and crumbly consistency consistent with resulting carbon char and ash. In this effect, the grate acts as a filter to separate the firm and more dense combusting formed biomass material ( 28 ) from the less dense ashes ( 47 ). The feedstock end stop grate ( 35 ) in this embodiment has a rectangular structure, but can be of various shapes and dimensions based on feedstock, feed rate and other system variables. 
         [0083]    The primary center air feed tube ( 39 ) is fluidly connected to the primary air modulating valve ( 48 ) and the hollow cavity ( 29 ) of the biomass feedstock ( 28 ). An angle is cut into the end of the primary center air feed tube ( 39 ) to avoid blockage by any formed biomass material ( 28 ) as well as ashes ( 47 ), carbon, and char. The primary center air feed tube ( 39 ) preferably includes a plurality of openings, not shown, within it for allowing air to pass unobstructed into the hollow biomass thereby feeding the primary combustion process. This has the effect of delivering primary combustion air directly to the hollow cavity ( 29 ) of the formed biomass material ( 28 ) so air can progress toward the outside diameter of the formed biomass material ( 28 ) induced by the negative pressure in the secondary combustion chamber ( 37 ) and heat containment chamber ( 41 ) by the vacuum blower ( 58 ) whereby insuring evenly distributed combustion air flowing through the fuel in the primary combustion chamber ( 30 ). 
         [0084]    The primary air modulating valve ( 48 ) is fluidly connected to the primary center air feed tube ( 39 ) and the primary flowmeter ( 49 ). It is in communication with the programmable control unit ( 59 ) and receives a signal from the programmable control unit ( 59 ) commanding a specific airflow rate based on process parameters. In this embodiment the primary air modulating valve ( 48 ) is continuously variable between shut off (0%) and fully open (100%). 
         [0085]    The primary flowmeter ( 49 ) is fluidly connected in series with the primary air modulating valve ( 48 ) and the air pre-heating jacket ( 43 ). In this embodiment, the primary flowmeter ( 49 ) is of the paddle wheel type and produces and sends a feedback signal proportional to flow rate to the programmable control unit ( 59 ). The programmable control unit ( 59 ) then processes this input and others to generate a new command signal for primary air modulating valve ( 48 ) and other process control elements to produce the most efficient combustion of biomass. 
         [0086]    The ash collection chamber ( 44 ) is fluidly connected with the primary combustion chamber ( 30 ) and the ash cleanout bucket ( 45 ). The ash collection chamber ( 44 ) is airtight and has a tapered bottom to assist the ashes to fall into the ash collection bucket ( 45 ). Pre-heated primary combustion air is plumbed through the ash collection chamber ( 44 ) from the primary air modulating valve ( 48 ) to the primary center air feed tube ( 39 ) and transported into the hollow cavity ( 29 ) in the formed biomass material ( 28 ). The access hatch ( 46 ) is removable to allow inspection of the feedstock end stop grate ( 35 ) and propane ignition device ( 62 ). 
         [0087]    The stationary fan-type directing blade assembly ( 36 ) is a hollow, round, formed steel mechanism that is fastened to the end of the fuel pre-heating magazine ( 27 ) that changes the course of the escaping combustion gases coming out of the tapered gas channels ( 32 ) in the primary combustion chamber ( 30 ). As the gas leaves the primary combustion chamber ( 30 ) it is deflected from a linear path to a helical path around the inside of the secondary combustion chamber ( 37 ). This serves as a centrifugal separator forcing any heavier, unburned particulates toward the wall on the inside of the secondary combustion chamber ( 37 ) where they can be mixed with the incoming heated air from the holes in the end of the secondary combustion chamber ( 37 ). 
         [0088]    The secondary combustion chamber ( 37 ) is fluidly connected with the secondary air pre-heating tubes ( 52 ), the primary combustion chamber ( 30 ), and the inside of the airtight heat containment chamber ( 41 ). Two-stage combustion helps increase combustion efficiency and minimize NOx formation. The secondary combustion chamber is preferably constructed of a welded steel shell with similar construction as the primary combustion chamber ( 30 ). It has the insulated refractory material ( 34 ) cast on to the welded refractory wall support studs ( 31 ) to better contain the high heat of the secondary combustion process. The secondary combustion chamber ( 37 ) is supported at one end by the primary combustion chamber ( 30 ) and at the other end by the fuel pre-heating magazine ( 27 ). The slightly lower pressure inside the airtight heat containment chamber ( 41 ) draws hot gasses from the primary combustion chamber ( 30 ) as well as from heated air from the secondary air pre-heating tubes ( 52 ). As the two gas streams mix, the remaining fuel is self-ignited as a secondary combustion process for more complete combustion. The gas mixture continues to rotate around the inside of the secondary combustion chamber ( 37 ) until it finds the gas exit channel ( 63 ) at the end and bottom of the secondary combustion chamber ( 37 ). This gas exit channel ( 63 ) is formed into the refractory material ( 34 ) to allow the exhaust to exit the secondary combustion chamber ( 37 ) 
         [0089]    The secondary air pre-heating tubes ( 52 ) are fluidly connected with the secondary air mixer manifold ( 55 ) and the holes ( 38 ) in the end of the secondary combustion chamber ( 37 ) as shown in  FIG. 6 . The secondary air pre-heating tubes ( 52 ) in this embodiment are a series of stainless steel convoluted tubing. The convolutions in the tubing aid in creating turbulence inside the tubing that increasing convective heat transfer inside the tubes. The secondary air pre-heating tubes ( 52 ) supply heated air containing oxygen into the effluent stream emitted from the biomass in the primary combustion chamber ( 30 ), thereby providing a much cleaner and reduced pollution exhaust stream. 
         [0090]    The secondary air mixer manifold ( 55 ) is fluidly connected to the secondary air pre-heating tubes ( 52 ) and secondary air modulating valve ( 50 ) and distributes the incoming air into several secondary air pre-heating tubes ( 52 ) thus increasing the amount of surface area available for heat transfer thereby increasing the temperature of the combustion air. The secondary air mixer manifold ( 55 ) is located inside the heat containment chamber ( 41 ) to aid heat transfer as well. 
         [0091]    The airtight heat containment chamber ( 41 ) is fluidly connected with the gas exit channel ( 63 ) in the end of the secondary combustion chamber ( 37 ), and the insulated filter ( 53 ). The airtight heat containment chamber ( 41 ) is held in negative pressure by the high temperature vacuum blower ( 58 ) located further downstream. Controlled entry for primary and secondary combustion air is maintained by negative pressure within the heat containment chamber ( 41 ). However, air movement/entry through the formed biomass material ( 28 ) is substantially prevented by the length of compacted biomass forming a circumferential seal, as well as the elongated shaft ( 23 ) that plugs the hole in the center of the formed biomass material ( 28 ). It is this predictable air intake behavior that can be adjusted/accounted for by the programmable control unit ( 59 ) when it sends signals to the primary air modulating valve ( 48 ) and secondary air modulating valve ( 50 ) to allow both primary and secondary air into the process. 
         [0092]    The secondary air modulating valve ( 50 ) is identical to the primary air modulating valve ( 48 ) and is fluidly connected with the secondary air mixer manifold ( 55 ) and the secondary flowmeter ( 51 ). It is in communication with the programmable control unit ( 59 ) control unit and receives a signal from the programmable control unit ( 59 ) commanding a specific airflow rate based on process parameters. In this embodiment the secondary air modulating valve ( 50 ) is continuously variable between shut off (0%) and fully open (100%). 
         [0093]    The secondary flowmeter ( 51 ) is identical to the primary flowmeter ( 49 ) and is fluidly connected between the secondary air modulating valve ( 50 ) and the air pre-heating jacket ( 43 ). In this embodiment, the secondary flowmeter ( 51 ) is of the paddle wheel type and produces and sends a feedback signal proportional to flow rate to the programmable control unit ( 59 ). The programmable control unit ( 59 ) then processes this input and others to generate a new command signal for secondary air modulating valve ( 50 ) and other process control elements to produce the most efficient combustion of biomass. 
         [0094]    The insulated high temperature cyclonic filter ( 53 ) is fluidly connected to the airtight heat containment chamber ( 41 ), the residue collection bucket ( 54 ), and single-pass shell and tube heat exchanger ( 56 ). The heavier particles exit the bottom of the filter where they enter the residue collection bucket ( 54 ). Also, any fly ash, liquid, or solid debris that drips or falls from the end of the single-pass shell and tube heat exchanger ( 56 ) falls into the same residue collection bucket ( 54 ). The insulation around the filter reduces any heat loss in the combustion gases thereby increasing thermodynamic efficiency. The filter may also be comprised of other common configurations such as a high temperature baghouse or electrostatic precipitator. 
         [0095]    The residue collection bucket ( 54 ) is positioned at the lower end of the insulated cyclonic filter ( 53 ) and is meant to be emptied as necessary. 
         [0096]    The single-pass shell and tube heat exchanger ( 56 ) is constructed similar to any shell and tube heat exchanger using a plurality of stainless steel thin-wall tubes ( 69 ). At the input end an input header ( 66 ) is fluidly connected to the output of the insulated cyclonic filter ( 53 ) and accepts the hot combustion gases ready for heat removal. An alternative heat extraction method may include heating water and/or liquids, producing steam, and/or producing super-heated gases or other applications such as Stirling engines, absorption cooling, or CHP (combined heat and power) integrated into the heat containment chamber ( 41 ). The heat extraction method is not restrictive of location and may be located in the primary combustion chamber, secondary combustion chamber, heat containment chamber, filter, or any other suitable location within the device. 
         [0097]    At the other end of the single-pass shell and tube heat exchanger ( 56 ) is the output header ( 67 ). The output header section is fluidly connected to the high temperature vacuum blower ( 58 ) for final exhaust of the cooled combustion gas to the atmosphere. 
         [0098]    In the shell section is located water inlets and outlets typical of any heat exchanger. The shell section may also contain an expansion joint ( 65 ) if required. 
         [0099]    A high temperature vacuum blower ( 58 ) is fluidly connected to the output header ( 67 ) of the single-pass shell and tube heat exchanger ( 56 ) and the exhaust stack ( 61 ). This blower uses suction to create a negative pressure (vacuum) inside all of the components including; output header ( 67 ) of the single-pass shell and tube heat exchanger ( 56 ), input header ( 66 ) of the single-pass shell and tube heat exchanger ( 56 ), the cyclonic filter ( 53 ), and the airtight heat containment chamber ( 41 ), the primary combustion chamber ( 30 ), the tapered primary center air feed tube ( 39 ), the primary air modulating valve ( 48 ), the primary flowmeter ( 49 ), the secondary combustion chamber ( 37 ), the secondary air pre-heating tubes ( 52 ), the secondary air mixer manifold ( 55 ), the secondary air modulating valve ( 50 ), the secondary flowmeter ( 51 ) and finally the air pre-heating jacket ( 43 ). Additionally, it also attempts to draw air from the fuel pre-heat magazine ( 27 ) through the hollow formed biomass material ( 28 ) but is restricted as the resistance to airflow of this path is much greater than the other paths. 
         [0100]    A programmable control unit ( 59 ) as shown in  FIG. 3  of the drawings is in communication with the primary air modulating valve ( 48 ), the secondary air modulating valve ( 50 ), the auger motor ( 70 ), the high temperature vacuum blower ( 58 ), and the propane ignition device ( 62 ). The programmable control unit ( 59 ) may be in communication with these devices via direct electrical connection, radio signal or other communication means. The programmable control unit ( 59 ) also is in communication with various pressure and temperature sensors within the primary combustion chamber ( 30 ), the secondary combustion chamber ( 37 ), the single-pass shell and tube heat exchanger ( 56 ), and the exhaust stack ( 61 ) to monitor the performance of the system and adjust the components accordingly. The programmable control unit ( 59 ) may be comprised of a computer or other electronic device capable of storing various types of data including input data, program data, control signals, and similar items. 
         [0101]    The battery back-up system ( 60 ) is the power source for the entire mechanism. Because efficient components are used and power requirements can be managed utilizing the programmable control unit ( 59 ), direct current electricity can be used for the programmable control unit ( 59 ), auger motor ( 70 ), high temperature vacuum blower ( 58 ), vacuum sensors (not shown), temperature sensors (not shown), and warning lights (not shown). 
         [0102]    An exhaust stack ( 61 ) is fluidly connected to the high-speed vacuum blower ( 58 ) and exits the structure. The exhaust stack ( 61 ) may have a rain cap (not shown) to keep out moisture and pests. 
         [0103]    The air pre-heating jacket ( 43 ) completely surrounds the heat containment chamber ( 41 ) using light steel such as sheet metal. Outside fresh air enters the air pre-heating jacket via in air inlet ( 42 ) and starts to warm up from the intense heat on the outside surface of the heat containment chamber ( 41 ). Air from the inside of the jacket is delivered either to the primary flowmeter ( 49 ) or secondary flowmeter ( 51 ). 
         [0104]    The propane ignition device ( 62 ) is used to automatically start the combustion process. Typically, a soft copper propane tube (not shown), thermocouple (not shown), and spark ignition wires (not shown) are placed inside the ash collection chamber ( 44 ) near the end of the primary center air feed tube ( 39 ). Since there is a negative pressure inside the primary combustion chamber ( 30 ) when the biomass is ready to ignite, the flame will begin to travel down the hollow cavity ( 29 ) of the formed biomass material ( 28 ) and start the combustion process. 
         [0105]    In use, unprocessed or processed feedstock is loaded within the feedstock-loading hopper ( 21 ). The feedstock is gravity fed to hole-forming feedstock hopper ( 22 ) and then automatically augered into the insulated feeder chamber ( 26 ), which then feeds the biomass into the fuel pre-heating magazine ( 27 ), and finally into the primary combustion chamber ( 30 ). The entire process is controlled automatically by the programmable control unit ( 59 ). The high temperature vacuum blower ( 58 ) then starts to develop a vacuum in the components it is fluidly connected to. This negative pressure then draws air into both the primary combustion chamber ( 30 ) and secondary combustion chamber ( 37 ). Ignition is started using the propane ignition device ( 62 ) and water starts to flow through the shell and tube heat exchanger ( 56 ). 
         [0106]    After the start up sequence has been completed and the temperature of the components has substantially reached a steady state temperature the biomass feed rate is controlled by the programmable control unit ( 59 ). As the biomass is consumed in the primary combustion chamber, the system temperature begins to fall slightly which is sensed by installed sensors and signal sent to the programmable control unit ( 59 ). The programmable control unit ( 59 ) then starts the auger motor ( 70 ). After waiting a few seconds to see the temperature start to rise again, the programmable control unit ( 59 ) waits for another temperature drop before commanding the auger motor ( 70 ) to add more fuel into the primary combustion chamber ( 30 ). 
         [0107]    The formed biomass material ( 28 ) burns towards the feeding auger as primary air progresses from the inside out (hollow cylindrical form with air introduced at the center). At the outside of the primary combustion chamber ( 30 ) the air channels collect the products of combustion and transfer the products to the directing blade assembly ( 36 ). The products of combustion are then spun in the secondary combustion chamber ( 37 ) to depart a cyclonic movement to them that uses centrifugal force to mix any unburned particles and unburned gasses with secondary air while directing heavier particles towards the outside of the secondary combustion chamber ( 37 ). 
         [0108]    The pre-heated secondary air is introduced to mix with the primary combustion effluent stream. This creates conditions for a second, higher temperature oxidation process that burns even more of the volatiles and particles. 
         [0109]    The hot combustion gases then exit the secondary combustion chamber ( 37 ) into the heat containment chamber ( 41 ), then into the cyclonic filter ( 53 ), then into the single-pass shell and tube heat exchanger ( 56 ) to transfer the heat to water or other heat transfer fluid, then into the high temperature vacuum blower ( 58 ), then into the exhaust stack ( 61 ), with final discharge to the atmosphere. 
         [0110]    As to a further discussion of the manner of usage and operation of the present invention, the same should be apparent from the above description. Accordingly, no further discussion relating to the manner of usage and operation will be provided. With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed to be within the expertise of those skilled in the art, and all equivalent structural variations and relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, 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, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.