Abstract:
The present invention provides an improved gasifier, consisting of two separate and functionally different combustion zones within a common insulated chamber. Solid carbonaceous fuel enters the gasifier through an input feed. A spindle assembly, which is affixed to one end of the chamber, rotates, causing a mixing of the fuel and facilitating its movement through the chamber. The portion of the chamber nearest the input feed acts as a first combustion zone, partially oxidizing the raw fuel and carbonizing the fuel particles. A second combustion zone completes combustion of the char produced in the first zone. One end of the spindle assembly, located between the first and second combustion zones, includes a gas collection device for removing combustible product gas from the gasifier. The gas collector is circumscribed by an auger which, rotating with the spindle, actively transports charcoal from the first to the second combustion zone.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Solid fuels, including coal, coke, wood, charcoal, and agricultural residues, may be converted to combustible gases by processes involving heating and/or partial burning of these fuels. Such combustible gases may be burned to produce heat in more or less conventional furnaces or boilers, or, if they are adequately cleaned of ash and other solid fuel residues and tars, they may be burned in internal combustion engines, such as diesel or gas engines, or gas turbines, to produce mechanical or electrical energy. The conversion of a solid fuel to a gaseous fuel is performed in a device called a gasifier.  
         [0002]     Coal and coke gasifiers were widely used in the 19 th  and early 20 th  centuries to produce combustible gas for heating, cooking, and illumination in towns and cities and for industrial energy needs. Smaller vehicle mounted gasifiers were used in Europe during the First and Second World Wars to propel these vehicles using wood or wood charcoal as fuel. While powering vehicles with solid fuel gasifiers is not convenient by present standards, the increasing cost and environmental effects of burning petroleum fuels are encouraging people to reconsider solid fuel gasifiers for stationery applications, including boiler firing and the production of electricity. Low grade wood, agricultural residues and other forms of biomass are particularly attractive gasifier fuels because they are inexpensive, they are renewable, and their combustion does not contribute to global warming.  
         [0003]     Gasifiers may be classified according to whether they have a fixed or fluidized fuel bed, and also as to whether they produce a relatively high calorific content tar containing gas, which may only be burned in furnaces and boilers, or a lower calorific content gas, which has a low tar content and may be used to fuel engines. The present patent covers a new type of fixed bed gasifier, intended to produce a lower calorific value gas that is suitable for powering engines. The patent provides solutions to a number of problems commonly encountered with this type of gasifier, particularly when burning biomass fuels of non-uniform particle size, or having high ash content.  
         [0004]     One specific problem that is encountered with all types of gasifiers is that solid fuel residues, including carbon, ash, and fuel particles are transmitted into the product gas. All gasifiers require gas cleaning equipment to remove these impurities before the gas may be introduced into an engine. The service requirements of this cleaning equipment, the disposal of residues, and the service requirements and durability of the engine are nonetheless sensitively affected by the particulate content of the gas leaving the gasifier.  
         [0005]     The problem of particle entrainment in the gas arises because the solid fuel particles are consumed during their conversion to combustible gas. In gasifiers designed to produce gas having a low tar content, suitable for engines, gas is typically removed from the gasifier at the end opposite to where the fuel is introduced. This is because tars are released during heating and charring of the raw fuel, and can only be broken down by passing through the charcoal bed of the gasifier, where charcoal particles are also consumed in the production of combustible gas. Passing the gas through a bed containing many fine particles inevitably causes many such particles to be transported out of the gasifier by the product gas. Ash particles or carbon particles that have been largely consumed and contain high ash content are particularly detrimental to engines because ash is an abrasive material.  
         [0006]     Another issue associated with biomass gasifiers is the tendency of the charcoal bed of the gasifier, where the production of combustible gas principally occurs, to become choked with fine char and ash particles. Choking of the charcoal bed, which is typically located between the combustion zone of the gasifier and a gas collection screen or grate, interferes with the withdrawal of combustible gas from the gasifier. Reduced gas flow proportionally reduces the amount of air or oxygen that may be injected into the gasifier, causing it to drop in temperature below the temperature required for gas production. More fundamentally, the permeation of the charcoal bed with hot combustion gas (CO 2  and H 2 O) is what causes that gas to be converted to combustible gas (CO and H 2 ). Choking or densification of the charcoal bed with fine char and ash particles inhibits production of combustible gas. Choking or densification of the charcoal bed is more severe with natural fuels having random particle size, containing dust, or having high ash content. Such fuel characteristics were carefully controlled by users of earlier biomass gasifiers.  
         [0007]     In some embodiments the grates or screens are adapted to vibrate or move with the intent to minimize the densification or choking of the charcoal bed. These methods have not however been found to be effective, the charcoal quickly resealing itself due to fine char migration with the briefly established gas flow. Furthermore, vibration and grate motion discharge fine char and ash into the product gas stream, from which it must subsequently be removed.  
         [0008]     A third problem, which is related to the problem of char bed densification, is that efforts to reestablish gas flow by increasing the force of gas suction or by moving or vibrating the char bed tend to create channels or gas vents through the charcoal bed. As before, fine particles are discharged into the product gas, but the result is a channel through the charcoal bed. In this case combustion gas (CO 2  and H 2 O) bypasses the charcoal bed and passes directly into the product gas stream without conversion to combustible gas (CO and H 2 ).  
         [0009]     There is therefore a need to provide a gasifier capable of providing a gaseous output nearly devoid of particles with high efficiency of conversion of solid fuel to combustible gas. Furthermore, there is a need to provide a gasifier capable of operating continuously without degradation caused by char and ash buildup within the charcoal bed. Problems with fixed bed gasifiers, as described above, in combination with cheap petroleum, have prevented their commercial application worldwide since World War II.  
         [0010]     Much more practical and experimental progress has been made with fluidized bed gasifiers, in which the particles of biomass or other carbonaceous fuel are held in suspension by high gas flow rates. Such gasifiers are operationally complex, and often produce high loadings of fine particulates and tars in the product gas. They often require large electricity consumption to run the large blowers that provide the high gas velocity needed to keep the particles in suspension. They also tend to be very tall in order to maintain stratification of operating conditions.  
         [0011]     In contrast with the above, the fixed bed gasifier has the potential to greatly simplify the process of biomass conversion to gaseous fuel, and to permit this to be done on a smaller, more decentralized scale. The present invention enables the potential promise of the fixed bed gasifier to be fully realized. The application of this technology to coal needs to be explored, and is included under the present invention. A second preferred embodiment involves enclosing multiple functional units within a common gasification chamber, thereby increasing the capacity of the device.  
       SUMMARY OF THE INVENTION  
       [0012]     The problems with the prior art have been overcome with the present invention, which provides an improved gasifier. Briefly, the gasifier is fed with biomass through an input feed, such as an auger. A spindle assembly, which is affixed to one end of the chamber, rotates, causing a mixing of the biomass and facilitating its movement within the chamber. The portion of the chamber nearest the input feed acts as a first combustion zone, having a rotating grate, air nozzles, and rotating hearth mounted upon the spindle assembly. Air nozzles inject air into the newly added biomass, causing the biomass to partially burn and be substantially converted to charcoal before moving further into the chamber.  
         [0013]     As the charcoal passes past the rotating hearth, it moves between the surface of a gas collection device and the insulated walls of the gasifier chamber. Gas can be drawn through the surface of the gas collection device into the interior of the spindle assembly through the action of a suction blower located outside the gasifier and communicating with the spindle assembly at its open end. The charcoal bed that occupies the volume between the gas collector and the surrounding insulated walls of the gasifier chamber is made to move gradually due to the rotation of one or more augers surrounding the cylindrical gas collector.  
         [0014]     In the preferred embodiment, the gas collector comprises a set of adjacent vertically stacked concentric rings. Gases are able to pass between the rings into the collector along with only very small char particles. The rotary movement of alternate rings relative to adjacent fixed rings prevents the very narrow gaps that naturally occur between such rings from becoming clogged.  
         [0015]     Once charcoal has moved past the gas collector, it enters a second combustion zone, where additional air is introduced. Thermal energy (heat), the combustion gases CO 2  and H 2 O, and tars are generated in the first combustion zone, located upstream from the gas collector. Heat and CO 2  are generated in the second combustion zone, located downstream from the gas collector. Since the second zone is fueled by dry, already hot carbon, rather than raw biomass, very elevated temperatures are achieved in the second zone where air or oxygen is introduced. The very hot CO 2  gas produced in the second combustion zone is converted to the combustible carbon monoxide gas as it moves through the charcoal toward the gas collector.  
         [0016]     Optionally, combustion gas consisting of CO 2  and H 2 O, but also containing tar and other combustible substances, produced in the first combustion zone may be drawn from the gasifier and injected by a blower into the second combustion zone. This “vapor reinjection” has the effect of accelerating combustion in the first zone and thus increasing the rate of conversion of raw biomass into charcoal. This occurs both because of the removal of water vapor from the first combustion zone, and also because removing combustion gas from the fuel feed end of the gasifier causes a propagation of the flame toward the fuel feed. It also reduces the amount of tar and also noncombustible gases that may reach the gas collector. Injecting these gases into the second combustion zone, where temperatures are much higher than in the first zone, enables the noncombustible gases to be more effectively converted to combustible gas and also enables thermal cracking of the undesirable tar molecules. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  illustrates a vertical sectional view of a first embodiment of the gasifier of the present invention;  
         [0018]      FIG. 2  is an exploded view of the gas collector in accordance with the present invention; and  
         [0019]      FIG. 3  illustrates a second embodiment of the gasifier of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]      FIG. 1  illustrates a first embodiment of the gasifier in accordance with the present invention. While this embodiment comprises a preferred embodiment in which the biomass fuel is fed into the top of a vertically oriented chamber and the fuel descends into the chamber as it is burned, the invention is not so limited. Those skilled in the art will appreciate that it is within the skill in the art to configure the chamber in other ways. For example, the biomass fuel can be fed into the bottom of a vertically oriented chamber and moved upward during burning. In another embodiment, the chamber can be configured horizontally or at some angle, such that the biomass is fed into one end of the chamber and moved to the other end.  
         [0021]     A spindle assembly  10  is located within an insulated chamber  12 , preferably along the central vertical axis of chamber  12 . The chamber  12  must withstand temperatures in excess of 2000° F., and thus its walls must be constructed of a suitable material capable of withstanding these high temperatures as well as providing thermal insulation, such as ceramic, lined with insulation, and surrounded by a steel shell. Input auger  16 , or other suitable feeding device, is used to feed biomass fuel into the top of chamber  12 , typically from a suitably designed hopper and in such a manner as to minimize air leakage into the chamber with the fuel.  
         [0022]     The spindle assembly  10  is suspended from the top or cover of chamber  12  in such a manner as to be able to rotate about a vertical axis. In the first embodiment, the spindle  10  is suspended from the center of the chamber so as to be equally spaced from the walls of the chamber  12 . A second embodiment will be described below in association with  FIG. 3 . Spindle  10  comprises an inner tube  56 , which is preferably fixed in position, such as by clamp  58 , and unable to rotate. Spindle tube  64  circumscribes inner tube  56  and rotates about a vertical axis. In the preferred embodiment, spindle tube  64  is in communication with gear  68 , which is connected via a gear assembly to a motor (not shown). Air jacket tube  20  preferably surrounds spindle tube  64  in such a manner as to allow the flow of air to occur in the space between the two tubes. Preferably, this flow of air is supplied under pressure by primary air blower  22 . Air damper  24  can be optionally used to control the flow of air entering the air jacket pipe  20 . Air damper  24  also can be used to prevent admission of air into the pipe when the gasifier is inactive. Optionally, air can be drawn through the air nozzles  18  into the gasifier chamber by maintaining the chamber at a lower pressure than the outside air. In either case, air that is pushed through the air jacket pipe  20  is forced through the air nozzles  18  into the gasifier chamber  12 . In the preferred embodiment, a circular grate  26  is affixed above air nozzles  18  and rotates with the spindle tube  64 . Optionally, stirring fingers  28  which extend outwardly from the air jacket pipe  20  can also be included. Located below the air nozzles  18  is a rotating hearth  30 , preferably constructed of refractory ceramic, or other high temperature resistant material. The rotating grate  26 , hearth  30  and fingers  28  increase the lateral mixing of the fuel material, and facilitate the downward flow of fuel, while also promoting flame penetration of the fuel above the hearth  30  and between the hearth and gasifier walls. All of these components are attached to the spindle tube  64 , causing them to rotate in unison.  
         [0023]     Below the ceramic hearth  30  lies the gas collector  14 . The gas produced by the gasifier is captured by the collector  14  and transferred out of the gasifier through gas tube  56 . Gas tube  56  is prevented from rotating by its attachment to the top of the gasifier via clamp  58 . FIG.  2  illustrates the preferred embodiment of the gas collector  14 . The collector comprises an internal frame  54 , which is attached, such as by locating pins, to inner tube  56 , and therefore unable to rotate. At the base of the internal frame  54  is a ceramic heat shield  66 . Fixed rings  50  and rotating rings  52  are placed about internal frame  54  in an alternating pattern. The rings are preferably produced from heat resistant steel alloy and fit over the internal frame. Fixed rings  50  have one or more, preferably two, internal protrusions  50   a , each of which is configured to fit between adjacent supports of internal frame  54 , thereby fixing them with respect to the internal frame. Rotating rings  52  do not have the above-mentioned protrusions and therefore are free to rotate relative to internal frame  54 . Natural imperfections in the manufacturing process create sufficient gaps between adjacent rings to allow gas to flow between them. The capacity of the gas collector can be varied by a number of techniques; an increase in the number of rings used causes an increased number of gaps through which gas can flow. Similarly, an increase in the radius of the rings also increases the area through which the gas can flow. The rings may be deformed or machined to have slightly rippled upper and lower surfaces, that, being identical for all rings, cause the rings to move slightly toward and away from adjacent rings as they turn relative to adjacent rings. Atop the uppermost ring, which is preferably a fixed ring  50 , is situated a hub  62 . Hub  62  preferably has upward facing protrusions, which interlock with corresponding lower side indentations on the ceramic hearth  30  and has locating pins or other means to ensure its rotation with spindle tube  64 . This interlocking mechanism, or any other similar interconnection, allows the hub  62 , to move in concert with the ceramic hearth  30  and spindle tube  64 . Auger  60  is attached to hub  62 , as by welding, and circumscribes the stack of rings. In the preferred embodiment, the auger  60  is attached to all rotating rings  52  by welding, but not attached to fixed rings  50 . In this way, the rotation of spindle tube  64  causes the rotation of the ceramic hearth  30 , the hub  62 , the auger  60 , and the rotating rings  52 .  
         [0024]     Turning back to  FIG. 1 , a second combustion zone within the lower portion of chamber  12  includes nozzles  32  for the injection of air or oxygen into said combustion zone. In the preferred embodiment, air is injected by blower  38 , controlled by damper  42 , which, when the gasifier is inactive, may entirely prevent air leakage via nozzles  32  into chamber  12 . Optionally, nozzles  34  reinject gases produced in the first combustion zone, principally CO 2 , H 2 O, and tars, into the second combustion zone, near the bottom of gasifier chamber  12 . Such reinjection may be caused by a blower  40  and controlled by a damper  44 , or by varying the blower speed. Ash auger  36  is located at the bottom of chamber  12 , which is preferably conical in shape to require the ash to accumulate near the auger. Auger  36  enables ash and other noncombustible residues to be removed from chamber  12  to an ash receiver suitably designed to prevent air leakage into chamber  12 .  
         [0025]     Having described the physical components of the present invention, the operation of the gasifier will now be described. Referring to  FIG. 1 , biomass is fed into the gasifier via the rotation of input auger  16 . The drive motor of the input auger  16  (not shown) is equipped with a means of detecting that the gasifier chamber  12  is full of biomass fuel. In practice this may be performed by a variety of mechanisms such as electrical or mechanical detection of the torque applied to the feed auger, or by a separate paddle wheel type sensor. As the biomass enters the chamber  12 , the rotary action of fingers  28  and circular grate  26  serve to mix the biomass and ensure even penetration into the biomass of the flame originating at nozzles  18 . Air nozzles  18  provide the combustion air necessary for the biomass to burn. Air is preferably blown into the space between air jacket pipe  20  and spindle tube  64  by primary air blower  22 . Damper  24  controls the flow of air entering the air jacket pipe  20 . Alternatively, air can enter the gasifier by maintaining a negative pressure differential between the inside of the gasifier and the outside environment. The region of chamber  12  located in the vicinity of circular grate  26 , circular hearth  30  and air nozzles  18  comprises combustion zone I, where solid fuel is carbonized by vaporization and combustion of substantially all of its volatile combustible constituents.  
         [0026]     The combustion process is initiated by manually igniting the raw biomass, such as by the use of a blowtorch, or an automatic ignition device. Once ignited, the combustion of the biomass becomes a continuous, self-sustaining process, where the injection of air and additional biomass are all that is needed to maintain combustion. Spindle assembly  10  is rotated continuously or intermittently during operation of the gasifier, but at a low speed, to ensure mixing and flow of the material, but so as to avoid unnecessary breakage of the fuel and charcoal particles. As additional fuel is added and carbonized within combustion zone I, this newly carbonized fuel descends deeper into the chamber  12 . The rotation of the auger  60  ensures that the carbonized fuel continues to descend, despite the movement of gas toward the gas collector surface and the consequent migration of small char particles toward the gas collector surface. The close proximity of the surface of the gas collector to the walls of the gasifier chamber  12 , which chamber is square in its plan view or otherwise designed to prevent rotation of the charcoal particles with the spindle assembly, assists in forcing the char particles to descend toward combustion zone II. The bottom of the gasifier chamber  12 , denoted as combustion zone II, is thereby maintained full of char particles, despite the upward flow of gas from combustion zone II toward the gas collector. In a preferred embodiment of the gasifier, the outside diameter of the gas collector is approximately ten inches, while the distance between opposite walls of chamber  12  is eighteen inches, creating a distance of four inches between the gas collector surface and the nearest surfaces of the chamber  12 .  
         [0027]     The downward movement of charcoal particles in proximity to the gas collector is responsible for preventing the problem of charcoal bed choking or densification mentioned previously. This problem is caused by the rapid migration of small char and ash particles with the flow of gas toward the gas collector. These small particles remain mobile and continue to flow with the gas until their path is obstructed by somewhat larger particles, having void spaces slightly too small to allow further migration of these particles. In this way the charcoal bed acts like a filter, trapping particles that would otherwise reach the gas collector surface, the smallest of which would pass between the gas collector rings and enter the product gas. A stationery charcoal bed would necessarily and quickly clog with these smaller particles, as occurs in fixed bed gasifiers of conventional design. In the present invention, the clogging, densification, or aggregation of the charcoal bed is counteracted by the continuous or intermittent transport of the charcoal bed toward combustion zone II. In practice a very high rate of combustible gas production may be maintained by this method with a suction of less than 2.5″ water column (0.1 psi).  
         [0028]     Actively transporting the char downward also helps ensure that channels do not develop through which oxygen or noncombustible gases can travel to the gas collector surface. Channeling is the formation of passages through the char bed by erosion, which allow unreacted combustion gas, such as carbon dioxide, water vapor and hydrocarbons, to bypass the char bed and pass directly into the gas collector. Channeling occurs in conventional fixed bed gasifiers when the openings in the gas collector or grate are large enough to allow the passage of both intermediate size and small char particles out of the charcoal bed. When the charcoal bed is vibrated or otherwise disturbed, these particles may discharge from a portion of the char bed especially when the gas suction is strong. The present invention prevents channeling by utilizing very small gasflow passages in the gas collector surface, these being the gaps between adjacent rings. In addition gas suction across the char bed is very weak because of the continuous renewal of the char bed due to its downward displacement. Newly produced char from combustion zone I, containing relatively large particles, presents relatively little resistance to the flow of gas, and continuously or intermittently replaces the partially densified bed as it is moved toward combustion zone II.  
         [0029]     Since the area surrounding the gas collector contains mostly carbonized fuel, it reacts with the hot gases, such as carbon dioxide and water vapor, that are produced in combustion zone I, located above the gas collector, and combustion zone II, located below the gas collector. This endothermic reaction yields carbon monoxide and hydrogen gas. The region of chamber  12  below Combustion Zone I and above Combustion Zone II (which is described below) comprises the reduction zone, which is also a region wherein the temperatures are lower than in either of the combustion zones surrounding it.  
         [0030]     Because the zone of the gasifier surrounding the gas collector is not fed with air and is involved in endothermic reactions, its temperature is lower than that of combustion zone I, or combustion zone II, which is located in the lower portion of the chamber  12 . To protect the gas collector from the extreme temperatures both above and below it, ceramic materials are used in the production of the hearth  30  and the heat shield  66 . The gas collector itself may be made from relatively less temperature resistant material, such as high temperature corrosion resistant alloy steel. The gas temperature exiting the gasifier typically has a temperature of 800 to 1000 degrees Fahrenheit.  
         [0031]     As the carbonized fuel passes below the gas collector, it enters combustion zone II, where air or oxygen is injected, using blower  38 , into chamber  12  through nozzles  32 . As in the case of combustion zone I, the flow of air or oxygen can be controlled by damper or valve  42 , and can be completely stopped when the gasifier is inactive. This injection of air allows for the complete combustion of the char particles that have been transported down by the auger  60 . This process will typically yield carbon dioxide and completely consumed fuel, in the form of ash. The second combustion zone produces much of the energy required for the conversion of noncombustible carbon dioxide gas to combustible carbon monoxide gas as the gas travels upward through the charcoal bed and is captured by the gas collector. The reduction of carbon dioxide to carbon monoxide is accompanied by the oxidation of carbon in the charcoal to carbon monoxide, which consumes a portion of the charcoal before it reaches combustion zone II.  
         [0032]     The nozzles  32  are configured to consume charcoal as completely as possible, allowing only noncombustible ash to reach the ash auger  36 . Auger  36  is rotated intermittently or continuously in response to excess air pressure encountered by air blower  38 . Excess air pressure indicates a buildup of ash interfering with the injection of air into combustion zone II.  
         [0033]     Summarizing the operation of the gasifier, combustion zone I uses air to convert fresh biomass into carbon dioxide, water vapor and carbonized fuel. This partially burned fuel is moved downward through the chamber by the rotation of the auger  60 . As the hot carbon dioxide and water vapor move away from combustion zone I, they continue to react with the partially burned fuel, yielding carbon monoxide and hydrogen gas, which are captured by the gas collector  14 . The rotation of the auger  60  also continues to push this carbonized fuel downward. The unique configuration of the gas collector, in conjunction with the rotary action of the auger, serve to continuously clean the surface of the gas collector to prevent aggregation. As the remaining carbonized fuel reaches the lower portion of the chamber  12 , it enters combustion zone II. In this zone, air is injected into the chamber and the carbonized fuel is completely combusted to yield hot carbon dioxide and ash. Hot carbon dioxide travels through the carbonized fuel up toward the gas collector. While traveling, it reacts with the fuel to create carbon monoxide, which is captured by the gas collector. Thus, the gas collector is capable of capturing gases produced in both Combustion Zone I and Combustion Zone II after reaction with the reduction zone.  
         [0034]     The efficiency of the described gasifier can be further enhanced by the re-circulation of exhaust gases from combustion zone I. In this embodiment, gases are drawn from the top of chamber  12  by the action of exhaust gas blower  40  and injected into combustion zone II via nozzles  34 . These exhaust gases, including steam, carbon dioxide, tars and other hydrocarbons, are injected to reduce their presence in the product gas and to control the relative temperatures of combustion zone I and combustion zone II. The quantity of gas recirculated may be controlled by damper or valve  42  or by varying the speed of blower  38 .  
         [0035]     The re-circulation of the exhaust gases serves several purposes. Pulling a high gas flow through the recirculation loop decreases the downward flow of combustion gas from Combustion Zone I toward the reduction zone and the gas collector. Since zone I has lower temperatures than zone II, these combustion gases are less likely to be converted to combustible gas than if they originated from zone II. Recirculation also increases the upward penetration of the flame from Combustion Zone I into the raw fuel located above Combustion Zone I, thereby increasing the rate of fuel to char conversion. At very high rates of gas recirculation, much of the heat required for fuel pyrolysis or fuel to char conversion, may come from the upward flow of a portion of the hot gases from Combustion Zone II and the reduction zone. At lower rates of gas recirculation, water vapor is withdrawn from the top of gasifier chamber  12  fast enough to prevent condensation of water in the newly added biomass fuel, which would otherwise hinder combustion in zone I. Such water vapor may be partially or wholly dissociated into hydrogen gas and oxygen where the oxygen combines with carbon under high temperatures in combustion zone II.  
         [0036]     The gas that enters the gas collector travels up inner tube  56 . This tube is preferably in communication with gas cleaning equipment and a gas suction blower, where the blower delivers gas to the end use application at a rate equal to the rate of gas consumption, thereby minimizing or obviating the storage of the low caloric value gas produced. Ideally, the gas suction blower is regulated to maintain a slightly negative pressure inside the gasifier, relative to air pressure. This eliminates the possibility of combustible and lethal gas leakage into the surrounding environment.  
         [0037]      FIG. 3  illustrates a second embodiment of the gasifier of the present invention. In this embodiment, a plurality of spindle assemblies  10  is used in conjunction with a single insulated chamber.  FIG. 3  shows a top view of the chamber  12 , with several spindle assemblies  10 . These spindle assemblies are mounted to the top of the chamber, as described in reference to  FIG. 1 . In the first embodiment, the gas collector is surrounded by the walls of gasifier chamber  12 , which are square in plan or otherwise configured to inhibit rotation of the char with the spindle assembly. In the embodiment of  FIG. 3 , there is no chamber wall around many of the augers. However, the use of multiple augers having the same pitch direction and same direction of rotation such that proximate points on adjacent augers are moving in opposition yields the same result. Referring to  FIG. 3 , a configuration of nine augers is shown. Auger  300 , like all other augers rotates in a counterclockwise direction. When viewed in relation to its immediate neighboring auger  301 , it can be seen that augers  300  and  301  are moving in opposite directions at the point where these augers are the closest together. This opposite movement creates a powerful downward tractive force on the charcoal surrounding these augers. The same phenomenon exists with respect to auger  300  and its other neighboring augers  302 ,  303  and  304 . Similarly, this exists between each pair of neighboring augers. Thus, each auger is surrounded by either a chamber wall  330 , or an opposing auger. This embodiment ensures a uniform downward motion of charcoal surrounding the gas collectors, and allows the production of large amounts of combustible gas due to the large combined surface area of multiple gas collectors.  
         [0038]     The fixed gas pipes leading from the multiple spindles of such multi-spindle gasifiers may be manifolded together such that the gas may be drawn from multiple gas collectors by a single blower.  
         [0039]     The combustible gas may be then used in a number of ways; it can be burned to produce heat, it can be used to power internal combustion engines or turbines, or it can be used as feedstock for chemical production.