Abstract:
A gasification system having a combustor vessel, an optional scrubber vessel, an optional fixer vessel, an optional cyclone vessel and an optional demister vessel. A wide variety of possibly moist solid or semi-solid carbonaceous fuels may be partially combusted in the combustor to generate a combustible gas and a mineral ash. An improved ash support and removal subsystem reduces clogging and other problems. The combustible gas is conveyed by optional heavy-duty blowers through the optional vessels to remove liquids and particulates and to undergo catalytic chemical reactions to provide a relatively clean, dry, highly-combustible hydrocarbon gas that captures a relatively high fraction of the potential heating value of the fuel. Internal gases, liquids and particulates from the vessels may be recycled inside the system to improve efficiency and prevent liquid waste. A portion of the internal liquids may also be extracted for other uses.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 11/196,977, filed Aug. 4, 2005, which is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/911,386, filed Aug. 4, 2004, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/492,363, filed Aug. 4, 2003. Each of the aforementioned related patent applications is herein incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gasification apparatus that produces combustible fuel gases from a wide variety of carbonaceous fuel sources or combinations of fuel sources. 
     2. Brief Description of the Related Art 
     Gasification has generally been known for years. In gasification, a carbonaceous fuel source is partially combusted to produce a combustible gas, synthesis gas, or syngas. The combustible gas is then combusted to produce work. The combustible gases produced by gasification may find a variety of uses, including, but not limited to, supplying heat, powering a motor, or producing electricity. Gasification provides many advantages, such as allowing fuels having relatively low heating values to be used, allowing waste products to be used to produce work and, similarly, reducing the amount of waste material sent to landfills. Despite these obvious advantages, gasification has met with only limited success, because gasification systems have typically been plagued by a number of disadvantages or difficulties. For example, the heating values of gases produced using prior art systems have tended to fluctuate to an undesirable degree, particularly when a variety of fuel sources or fuel sources of varying compositions have been used. Similarly, it has also proven difficult to consistently produce gases having sufficiently high heating values. Separating particulate matter from the produced gas has proven problematic. Similarly, it has proven difficult to produce sufficiently clean gases having sufficiently low amounts of particulate matter as well as sufficiently low amounts of pollutants such as such as sulfur dioxide (SO 2 ), nitrogen oxides (NO x ), carbon monoxide (CO), volatile organic compounds (VOC), ammonia (NH 3 ), hydrogen chloride (HCl) and other chlorides. Environmentally sound disposal of wastewater generated by such systems has also presented difficulties. Further still, the presence of water or other liquids in the combustible gas has made it difficult or impossible to use blowers for moving the combustible gases without creating undesirable levels of wear and tear on the blowers. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a flexible gasification apparatus that provides combustible gases having high heating values while avoiding pitfalls of prior attempts at gasification. 
     It is a further object of the present invention to provide an apparatus of the above type that can easily handle a wide variety of carbonaceous fuel sources or combinations of fuel sources. 
     It is a further object of the present invention to provide an apparatus of the above type that produces a high value heating gas having low amounts of particulate matter and other pollutants. 
     It is a further object of the present invention to provide an apparatus of the above type that requires little or no wastewater disposal. 
     It is a still further object of the present invention to provide an apparatus of the above type that captures a relatively high fraction of the potential heating value of the fuel sources. 
     It is a still further object of the present invention to provide an apparatus of the above type that safely and cleanly consumes a wide variety of agricultural and industrial byproducts, including, but not limited to, animal waste and wood pulp sludge. 
     It is a still further object of the present invention to provide an apparatus of the above type that is less prone to clogging problems typically associated with ash removal. 
     It is a still further object of the present invention to provide an apparatus of the above type that may easily process a wide variety of combinations of solid, semi-solid and liquid fuels. 
     It is a still further object of the present invention to provide an apparatus of the above type that can safely and efficiently handle and dry relatively wet combustible gases. 
     It is a still further object of the present invention to provide an apparatus of the above type that uses one or more rugged blowers that can safely and efficiently handle both dry and relatively wet combustible gases. 
     Toward the fulfillment of these and other objects and advantages, the system of the present invention comprises a combustor vessel, an optional scrubber vessel, an optional fixer vessel, an optional cyclone vessel, an optional demister vessel and one or more optional blowers. A carbonaceous fuel is partially combusted in the combustor to generate a combustible gas. An improved ash support and removal subsystem reduces clogging and other problems in the combustor. The combustible gas passes through one or more optional blowers to the scrubber. The combustible gas passes through the scrubber to remove matter such as tar and oil and to undergo preliminary catalytic chemical reactions. The scrubbed gas passes through one or more optional blowers to the fixer. Additional catalytic chemical reactions occur in the fixer and wood chips or other filters may also be used in the fixer to provide a relatively clean, dry, combustible gas. The combustible gas passes through one or more optional blowers to the cyclone, which helps separate additional liquids from the gas. The combustible gas then passes through one or more optional blowers to the demister, which allows additional catalytic reactions to occur and separates additional liquids from the gas. Wastewater, condensate, and other waste products from the scrubber, fixer, cyclone and demister may be captured and returned to the combustor or extracted. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The above brief description, as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a flow diagram of an embodiment of the present invention; 
         FIG. 2  is a side elevation, schematic view of a combustor for practicing the present invention; 
         FIG. 3  is an overhead plan cross sectional view of a blower for practicing the present invention; 
         FIG. 4  is a side elevation cross section view showing the impeller blades of the blower of  FIG. 3 ; and 
         FIG. 5  is a flow diagram of an alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 and 5 , the reference numerals  10  and  200  refer in general to a gasification system for practicing the present invention. The system  10 ,  200  typically comprises a combustor  12 , an optional scrubber  14 , an optional fixer  16 , an optional cyclone  203  and an optional demister  204 , with one or more optional blowers between these vessels. One or more optional blowers may also be disposed before the first vessel in the system  10 ,  200  sequence. One or more optional blowers may also be disposed after the last vessel in the system  10 ,  200  sequence. The system  10 ,  200  principally consists of preferably the combustor  12  and the fixer  16 , more preferably the combustor  12 , the scrubber  14  and the fixer  16 , more preferably the combustor  12 , the scrubber  14 , the fixer  16  and the cyclone  203 , and most preferably the combustor  12 , the scrubber  14 , the fixer  16 , the cyclone  203  and the demister  204 . The combustor  12 , the scrubber  14 , the fixer  16 , the cyclone  203  and the demister  204  may comprise any type of reaction vessel. In the system  10 ,  200 , after the combustor  12 , the typical and preferable sequence of vessels, the scrubber  14 , the fixer  16 , the cyclone  203  and the demister  204 , may also be arranged in different sequences. 
     Referring to  FIG. 1 , the fuel conduit  24  is disposed to provide a carbonaceous fuel source into an upper portion of combustor  12 . The fuel conduit  24  comprises preferably a conveyor, more preferably an auger drive, suitable for the transfer of solid and semi-solid material. The fuel conduit  24  transfers the solid or semi-solid carbonaceous fuel into an upper portion of combustor  12 . 
     Referring to  FIG. 2 , the combustor  12  has an upper outer wall portion  20  and a lower base portion  22 . The combustor  12  is preferably open, more preferably closed at the top and is preferably configured as a downdraft combustor, more preferably as an updraft combustor. The fuel conduit  24  transfers the solid or semi-solid carbonaceous fuel into an upper portion of combustor  12 , preferably into an upper portion of the inner chamber  30 , more preferably into an upper portion of the inner chamber  30  above the fuel level sensor  68 . Another feed conduit  26  may also be provided to recycle material into the combustor  12  from other portions of the system  10 ,  200  as discussed in more detail below. Additional feed conduits may also be used, for example, to provide different types of solid, semi-solid and liquid fuel sources. The inner wall  28  is disposed within the combustor  12  and is connected to the combustor  12  to form the inner chamber  30  and the outer chamber  32 . A lower portion of the inner wall  28  defines the opening  34 . The ash support member  36  is affixed below the inner wall  28 , preferably by support members  38 , more preferably by affixing portions of the outer periphery of the ash support member  36  to the upper outer wall portion  20 , so that the ash support member  36  is disposed a distance below the opening  34 . The outer periphery of the ash support member  36  is relatively free from obstructions about the vast majority of the outer periphery, providing relatively open side passageways between the inner wall  28  and the ash support member  36 . This allows ash to spill from the ash support member  36  preferably over at least approximately 80 percent of the outer periphery of the ash support member  36 , more preferably over at least approximately 90 percent of the outer periphery of the ash support member  36  and most preferably over at least approximately 95 percent of the outer periphery of the ash support member  36 . 
     A conduit or gas manifold  46  extends preferably through the upper outer wall portion  20 , more preferably through the lower outer wall portion  22 , of the combustor  12 , below the ash support member  36 . The conduit or gas manifold  46  is connected to an air source and is preferably connected to an auxiliary fuel source, such as a source of natural gas, liquefied petroleum gas (LPG or LP gas), or propane (C 3 H 8 ). As seen in  FIGS. 1 and 5 , a recycle conduit  48  may also be provided to return a portion of the combustible gas generated by the system  10 ,  200 . The igniter  50 , such as a spark plug igniter, is preferably disposed in the conduit or gas manifold  46  adjacent to the combustor  12 . As depicted in  FIG. 5 , the most preferably sequence of attachments along the external portion of the conduit or gas manifold  46  is to have the recycle conduit  48  attachment disposed closest to the combustor  12 , the igniter  50  disposed further from the combustor  12 , the auxiliary fuel conduit  126  disposed an additional further distance from the combustor  12  and the auxiliary air conduit  124  disposed the furthest distance from the combustor  12 . 
     As seen in  FIG. 2 , one or more fuel agitators such as the fuel stirring member  52  are preferably provided in the inner chamber  30 , preferably disposed above the opening  34 . Similarly, one or more combustion bed agitators such as the combustion bed stirrer  54  are preferably provided inside the combustor  12 , preferably below the opening  34  and above the ash support member  36 . One or more ash agitators such as ash stirring member  55  are preferably provided inside the combustor  12 , preferably below the ash support member  36 , more preferably below both the ash support member  36  and the conduit or gas manifold  46 . Coaxial shafts  56  and  58  extend upward from the stirring members  52 ,  54  and  55  to or above an upper portion of the combustor  12 . Motors  60  and  62  are operably connected to the shafts  56  and  58  for rotating the shafts and stirring members  52 ,  54  and  55 . 
     Hollow shaft  58  is rotated by motor  60  and is preferably connected to both stirring members  52  and  54 , more preferably connected to stirring member  52  but not to stirring member  54 . Solid shaft  56  is rotated by motor  62  and is preferably connected to stirring member  55  but not to stirring member  54 , more preferably connected to both stirring member  54  and stirring member  55 . Most preferably, motor  60  is disposed near the top of combustor  12  and rotates a solid shaft replacement for hollow shaft  58  which is operably connected to one or more stirring members  52 , while motor  62  is disposed near the bottom of combustor  12  and rotates a separate solid shaft that is operably connected to stirring members  54  and  55 . 
     The preferably frustoconical, more preferably cylindrical, lower base portion  22  of the combustor  12  extends below the ash support member  36 . An opening is provided at or near the bottom of the lower base portion  22  to allow ash to pass from the combustor  12  to the ash removal conduit  64 . The ash removal conduit  64  preferably comprises an auger drive suitable for solids transfer. A conduit  66  is disposed through the outer wall of the combustor  12  in an upper portion of preferably the outer chamber  32 , more preferably the inner chamber  30 , to provide a path for combustible gases generated within the combustor  12  to pass from the combustor  12 . 
     A fuel level sensor  68  is provided in the inner chamber  30 , preferably above the opening  34 , more preferably above both the opening  34  and the fuel agitator  52 . The fuel level sensor  68  is operably coupled with the fuel conduit  24  to automate the process of maintaining fuel at a desired level within the inner chamber  30 . Additionally, an optional screen is preferably disposed inside an upper portion of the inner chamber  30 , between the fuel conduit  24  and the conduit  66 . The optional ash level sensor  70  is disposed within the combustor  12 , preferably below the ash support member  36 , more preferably below both the ash support member  36  and the conduit or gas manifold  46 . The optional ash level sensor  70  is operably coupled with the ash removal conduit  64  to automate the process of maintaining ash at a desired level within the combustor  12 . Additional optional conduits are preferably provided for extracting gas from combustor  12  for testing and other uses. Additional optional conduits are also preferably provided for extracting liquids from the combustor  12  for testing and other uses. It is understood that the combustor  12  may take any number of sizes, shapes and configurations. It is also understood that the combustor  12  need not be closed at the top and need not be an updraft combustor. 
     Referring to  FIGS. 1 and 5 , the conduit  66  operably couples the combustor  12  with the scrubber  14 , providing a flow path through preferably one or more of the optional blowers  90  into preferably an upper portion, more preferably a lower portion of the scrubber  14 . As seen in  FIG. 3 , the blowers  90  are heavy duty hybrids that combine desirable features of blowers designed for moving gases and pumps designed for moving liquids. The blowers  90  move gases and/or liquids from an inlet  209  to an outlet  210 . Walls forming the impeller housing  92  have a wall thickness of preferably approximately ¾ inch (2 centimeters), more preferably approximately ⅝ inch (1.6 centimeters). A sealing member  94 , such as a gasket, is used to create an airtight and watertight seal between the walls forming the impeller housing  92 . Referring to  FIG. 4 , the impeller blades  96  are preferably straight, more preferably curved, and are thicker than impeller blades of common blowers designed for moving gases, preferably approximately 50 percent thicker. Referring back to  FIG. 3 , the mechanical seal  98 , similar to a mechanical seal used in a typical centrifugal compressor, is used to provide the impeller shaft  100  seal. Although not preferred, one or more packing glands similar to those found in a typical water pump may be used as substitutes for the mechanical seal  98 . Additional sets of the bearings  102  are also preferably used in connection with the impeller shaft  100 . It is preferable to use at least two sets of the bearings  102 . It is understood that the blowers  90  may be disposed at any number of locations in the system  10 ,  200  and that the blowers  90  may take any number of different sizes, shapes and configurations. It is also understood that, although not preferred, conventional blowers, pumps, centrifugal compressors or similar devices may be used as substitutes for the blowers  90 . 
     Referring to  FIGS. 1 and 5 , the scrubber  14  preferably contains one or more filters (including, but not limited to, ferrous or non-ferrous metals, precious metals, ceramics, minerals, liquids, plastics, fibrous or non-fibrous materials, wood chips, organic or inorganic materials, porous or non-porous materials, natural or artificial materials, absorbents or adsorbents, diatomaceous earth, mixtures or combinations of these and other materials, or any other filter known to those skilled in the art). The scrubber  14  more preferably contains one or more filters and one or more catalysts (including, but not limited to, ferrous or non-ferrous metals, precious metals, ceramics, minerals, liquids, plastics, fibrous or non-fibrous materials, wood chips, organic or inorganic materials, porous or non-porous materials, natural or artificial materials, absorbents or adsorbents, diatomaceous earth, mixtures or combinations of these and other materials, or any other catalyst known to those skilled in the art). Most preferably, the scrubber  14  contains catalyst material whose surface has properties of stainless steel. Without limiting the present invention thereto, 304, 304H and 316 types of stainless steel have been found to be effective in the practice of the invention. It is hypothesized that the presence of manganese (Mn) in the stainless steel may be significant in promoting the formation of C 4  and higher hydrocarbons and other high heating value compounds. Non-stainless steel, such as mild steel, cold-rolled steel, hot-rolled steel and chrome steel have been found to have poor performance as compared to stainless steel catalysts. Aluminum has been found to be less effective than non-stainless steel and brass to be less effective than aluminum. The catalysts used in the present invention may be of various shapes and sizes and could include other materials, such as ceramic beads, plated with stainless steel. 
     Referring to  FIG. 1 , an optional pump  72  is preferably provided to pass liquid, for example water with impurities therein, through a feed conduit  74  into a preferably lower portion, more preferably upper portion, of the scrubber  14  and preferably through sprayers. A liquid return conduit  76  is preferably connected to a lower portion of the scrubber  14  for returning liquid to the optional pump  72  for reuse within the scrubber  14 . A feed conduit  78  may also be provided for providing preferably gas from combustor  12 , more preferably gas and liquids from combustor  12 , most preferably gas and liquids from combustor  12  and recirculated liquid to scrubber  14 . Optional wash conduit  80  may be provided for intermittent use to transfer liquid through conduits  66 ,  82  and  104  for cleaning. Scrubbed gas exits through conduit  82  that is disposed at a preferably lower, more preferably upper portion of the scrubber  14 . Additional optional conduits are preferably provided for passing the scrubbed combustible gas to flare, to recycle, for testing and for further uses. Additional optional conduits are also preferably provided for extracting liquids from the scrubber  14  or returning liquids from the scrubber  14  to the combustor  12  for recycling. An optional skim conduit  84  is preferably provided at a lower portion of the scrubber  14  and a drain conduit  86  is provided at the bottom of the scrubber  14 . An optional level sensor  88 , such as a float switch, is preferably disposed in the scrubber  14  for maintaining liquid levels within the scrubber  14  at desired levels. It is understood that the scrubber  14  may take any number of shapes, sizes and configurations and that any number of different filter media or catalysts or different combinations of filter media and catalysts may be used in the scrubber  14 . 
     Referring to  FIG. 1 , the conduit  104  connects the scrubber  14  with the fixer  16 , providing a flow path through one or more optional blowers  90  into preferably an upper portion, more preferably a lower portion of the fixer  16 . The fixer  16  preferably contains one or more filters (including, but not limited to, ferrous or non-ferrous metals, precious metals, ceramics, minerals, liquids, plastics, fibrous or non-fibrous materials, wood chips, organic or inorganic materials, porous or non-porous materials, natural or artificial materials, absorbents or adsorbents, diatomaceous earth, mixtures or combinations of these and other materials, or any other filter known to those skilled in the art). The fixer  16  more preferably contains one or more filters and one or more catalysts (including, but not limited to, ferrous or non-ferrous metals, precious metals, ceramics, minerals, liquids, plastics, fibrous or non-fibrous materials, wood chips, organic or inorganic materials, porous or non-porous materials, natural or artificial materials, absorbents or adsorbents, diatomaceous earth, mixtures or combinations of these and other materials, or any other catalyst known to those skilled in the art). Most preferably, the fixer  16  contains catalyst material whose surface has properties of stainless steel as described above. The conduit  106  passes from preferably a lower portion, more preferably an upper portion, of the fixer  16  to provide a flow path for the scrubbed and fixed combustible gas. The conduits  108 ,  48  and  110  are preferably provided for passing the scrubbed and fixed combustible gas to flare, to recycle, for testing and for further uses. Additional optional conduits are also preferably provided for extracting liquids from the fixer  16  and returning liquids from the fixer  16  to the combustor  12  for recycling. An optional skim conduit is preferably provided at a lower portion of the fixer  16 . The drain conduit  112  passes from a lower portion of the fixer  16  for removing wastewater and other matter that condenses or is removed from the gas as it passes through the fixer  16 . An optional level sensor, such as a float switch, is preferably disposed in the fixer  16  for maintaining liquid levels within the fixer  16  at desired levels. It is understood that the fixer  16  may take any number of shapes, sizes and configurations and that any number of different filter media or catalysts or different combinations of filter media and catalysts may be used in fixer  16 . 
     Referring to  FIG. 1 , the conduits  84 ,  86  and  112  preferably provide a flow path from the scrubber  14  and fixer  16  into the conduit  114 , which leads into the pump  118 . Referring to  FIG. 5 , the conduits  86 ,  112 ,  205 ,  207  and  208  provide a flow path from the scrubber  14 , the fixer  16 , the cyclone  203  and the demister  204  into the conduit  114  which leads to pump  118 . Referring to  FIGS. 1 and 5 , conduit  26  preferably operably couples the pump  118  with the combustor  12 . It is understood that the pump  118  may be disposed at any number of locations in the system  10 ,  200  and that the pump  118  may take any number of different sizes, shapes and configurations. Liquids may be extracted from conduit  114 , conduit  26  and other conduits for testing or use in petrochemical, chemical or other applications. 
     Referring to  FIG. 5 , the conduit  110  operably couples the fixer  16  with the cyclone  203 , providing a flow path through preferably one or more of the optional blowers  90  into preferably a lower portion, more preferably a tangential upper portion of the cyclone  203 . The cyclone  203  preferably contains no filters and no catalysts so as to facilitate rotary gas motion for additional liquid separation. Additional optional conduits are preferably provided for passing combustible gas from the cyclone  203  to flare, to recycle, for testing and for further uses. Additional drain conduit  205  is also preferably provided for extracting liquids from the cyclone  203  and returning liquids from the cyclone  203  to the combustor  12  for recycling. Operably connected from a lower portion of the cyclone  203  to the drain conduit  205  is an optional skim conduit. An optional level sensor, such as a float switch, is preferably disposed in a lower portion of the cyclone  203  for maintaining liquid levels within the cyclone  203  at desired levels. It is understood that the cyclone  203  may take any number of different sizes, shapes and configurations and that any number of different filter media or catalysts or different combinations of filter media and catalysts may be used in the cyclone  203 . 
     Referring to  FIG. 5 , the conduit  206  is preferably disposed vertically along the center axis of the cyclone  203 , opening inside a lower portion of the cyclone  203 , exiting the cyclone  203  at the top center of the cyclone  203  and operably coupling the cyclone  203  with the demister  204 , providing a flow path through preferably one or more of the optional blowers  90  into preferably an upper portion, more preferably a lower portion of the demister  204 . The demister  204  preferably contains one or more filters (including, but not limited to, ferrous or non-ferrous metals, precious metals, ceramics, minerals, liquids, plastics, fibrous or non-fibrous materials, wood chips, organic or inorganic materials, porous or non-porous materials, natural or artificial materials, absorbents or adsorbents, diatomaceous earth, mixtures or combinations of these and other materials, or any other filter known to those skilled in the art). The demister  204  more preferably contains one or more filters and one or more catalysts (including, but not limited to, ferrous or non-ferrous metals, precious metals, ceramics, minerals, liquids, plastics, fibrous or non-fibrous materials, wood chips, organic or inorganic materials, porous or non-porous materials, natural or artificial materials, absorbents or adsorbents, diatomaceous earth, mixtures or combinations of these and other materials, or any other catalyst known to those skilled in the art). Most preferably, the demister  204  contains catalyst material whose surface has properties of stainless steel as described above. Additional optional conduits are preferably provided for passing the demisted combustible gas to flare, to recycle, for testing and for further uses. The drain conduit  208  is also preferably provided for extracting liquids from the demister  204  and returning liquids from the demister  204  to the combustor  12  for recycling. An optional skim conduit is also preferably provided at a lower portion of the demister  204 . An optional level sensor, such as a float switch, is preferably disposed in a lower portion of the demister  204  for maintaining liquid levels within the demister  204  at desired levels. It is understood that the demister  204  may take any number of shapes, sizes and configurations and that any number of different filter media or catalysts or different combinations of filter media and catalysts may be used in the demister  204 . It is also understood that the sequence of scrubber  14 , fixer  16 , cyclone  203  and demister  204  may be rearranged to adjust characteristics of the gas and liquids. 
     In operation, referring to  FIG. 1 , the fuel conduit  24  provides solid or semi-solid carbonaceous fuel to the combustor  12 . Referring to  FIG. 2 , the solid or semi-solid carbonaceous fuel from the fuel conduit  24  enters an upper portion of the combustor  12 , drops through the inner chamber  30 , is at least partially combusted, accumulates on the ash support member  36  and builds up within the inner chamber  30  to a level above the fuel stirring member  52 . Fuel stirring member  52  agitates and preferably partially levels the carbonaceous fuel. Fuel stirring member  52  also reduces and preferably prevents carbonaceous fuel channeling, bridging, clumping, voids, and similar problems. As seen in  FIGS. 1 and 5 , an oxygen source, such as air, is provided preferably via auxiliary air conduit  124  and an auxiliary fuel source is provided preferably via auxiliary fuel conduit  126 . Referring to  FIG. 2 , the air and auxiliary fuel are mixed inside conduit or gas manifold  46 , ignited by igniter  50  and transferred into the combustor  12  through openings  42 . The burning mixture of air and auxiliary fuel heats the carbonaceous fuel within the inner chamber  30 . Once measured temperatures within the lower portion of inner chamber  30  exceed preferably at least 120 degrees Celsius (248 degrees Fahrenheit) and preferably no more than 260 degrees Celsius (500 degrees Fahrenheit), it is preferable for the overall efficiency of the system  10 ,  200  that auxiliary fuel sources be at least partially shut off, the igniter  50  be at least partially shut off and recycled material from other portions of the system  10 ,  200  entering the combustor  12  be sufficient to continue normal operation. As the carbonaceous fuel passes downward within the inner chamber  30 , the carbonaceous fuel sources are at least partially combusted to produce, among other materials, ash and a combustible gas. 
     Referring to  FIG. 2 , ash passes through opening  34  and collects on ash support member  36 . The combustion bed stirrer  54  prevents excessive ash accumulation by moving the collecting ash preferably outward so that the ash spills or passes from the outer periphery of the ash support member  36 , more preferably moving the collecting ash downward so that the ash spills or passes through perforations in ash support member  36 , most preferably moving the collecting ash both outward over the outer periphery of ash support member  36  and downward through perforations in ash support member  36  so that the ash falls down to the lower base portion  22  of the combustor  12 . Other than the combustion bed stirrer  54  and support members  38 , the area between the opening  34  of the inner wall  28  and the top surface of ash support member  36  is substantially unobstructed to provide a ready path for ash removal. The ash support member  36  is affixed below the inner wall  28 , preferably by support members  38 , more preferably by affixing portions of the outer edge of ash support member  36  to the upper outer wall portion  20  or the lower outer wall portion  22 . The ash support member  36  is affixed in a manner that allows ash to spill from the ash support member  36  preferably over at least approximately 70 percent of the outer periphery of the ash support member  36 , more preferably over at least approximately 80 percent of the outer periphery of the ash support member  36 , and most preferably over at least approximately 90 percent of the outer periphery of the ash support member  36 . 
     Referring to  FIG. 2 , ash that accumulates in the lower base portion  22  of the combustor  12  passes through an opening in the bottom of the combustor  12  and is removed by the ash removal conduit  64 . The ash removal conduit  64  is operably coupled with the optional ash level sensor  70  to maintain the level of ash in the combustor  12  below a desired amount. The ash removed from the combustor  12  is typically a salable product. For example, the ash may be suitable for sale as fertilizer, soil stabilizer, filter material and as an extender for mortar, concrete, or road material, among other uses. 
     Referring to  FIG. 2 , the fuel level sensor  68  is operably coupled with the fuel conduit  24  to maintain the level of solid or semi-solid fuel within a desired height range within the inner chamber  30 . The desired height range may vary depending upon a number of factors, including, but not limited to, the properties of the solid or semi-solid fuel. It is typically desirable to maintain the solid or semi-solid fuel level within the inner chamber  30  at a level that maintains an adequate partial seal, preferably to help regulate the flow of products of combustion from the combustor  12  through the conduit  66 , preferably to facilitate heating of the carbonaceous fuel and preferably to help control the degree of partial combustion within the inner chamber  30 . The preferable level may vary with factors such as the density and moisture content of the solid or semi-solid fuel. For example, the preferable level for a solid or semi-solid fuel comprised primarily of chicken litter (including, but not limited to, chicken waste products, absorbents such as rice hulls or wood chips, or any combination of these and similar or related materials), wood pulp or paper mill sludge, or sanding dust or wood dust is approximately 25 inches (approximately 64 centimeters) above the ash support member  36 . 
     Referring to  FIG. 1 , the optional blowers  90  draw products of combustion preferably downward, more preferably upward, through the combustor  12  so that they pass through the opening  34  in the inner wall  28  and upwardly through preferably the outer chamber  32 , more preferably the inner chamber  30  before passing through conduit  66 . Material from the combustor  12  travels through conduit  66  and enters preferably an upper portion, more preferably a lower portion, of the scrubber  14 . The optional pump  72  preferably circulates liquid, for example water with impurities therein, through the scrubber  14 . The circulated liquid cools and scrubs the combustible gas, removing matter from the combustible gas including, but not limited to, tar, oil and particulates. The liquid level in the scrubber  14  is preferably maintained at a level so that tar, oil and similar matter may be removed from the scrubber  14 , preferably via the skim conduit  84 . Particulates, water and preferably other components that settle to the bottom of the scrubber  14  are removed via the drain conduit  86 . The optional valves  128  are also opened preferably intermittently so that the optional pump  72  may circulate liquid through the optional wash conduit  80  and through the conduits  66 ,  82  and  104  for cleaning. The optional valve  130  may also be opened preferably periodically so that the liquid in the scrubber  14  may be drained through the conduit  86  into conduit  114 . Optional filters in the scrubber  14  preferably help remove liquids and particulates from the gas. Catalysts in the scrubber  14  primarily improve the chemical composition of the gas and preferably also help remove liquids and particulates from the gas. 
     Referring to  FIG. 1 , the scrubbed combustible gas exits the scrubber  14  through conduit  82  and passes through one or more of the optional blowers  90  into fixer  16 . Wastewater and other matter that are removed from the combustible gas and that are not absorbed by the wood chips or other filters fall to the bottom of the fixer  16  and are removed via conduit  112 . Optional filters in the fixer  16  preferably help remove liquids and particulates from the gas. Catalysts in the fixer  16  primarily improve the chemical composition of the gas and preferably also help remove liquids and particulates from the gas. Scrubbed, fixed combustible gas exits the fixer  16  via conduit  106 . From there the combustible gas is flared via optional conduit  108 , returned to the combustor  12  via optional conduit  48 , or sent to other uses via optional conduit  110 , for example, as shown in  FIG. 5 , to cyclone  203  and demister  204 . 
     Referring to  FIGS. 1 and 5 , during the system  10 ,  200  start-up phase, the combustible gas is flared until it is determined that gas is being produced at a desired quantity and quality. Once the system  10 ,  200  start-up phase is complete, the combustible gas may be passed via optional conduit  110 ,  207  to produce work or for further uses elsewhere. For example, the combustible gas may be combusted to supply heat to a process or may be combusted within a motor or turbine to produce work or to generate electricity. As additional examples, the combustible gas produced by the system  10 ,  200  may be used in brooder heaters in poultry houses, in internal combustion engines, to heat boilers and to provide heat for the production of petroleum substitutes such as methanol. 
     Referring to  FIGS. 1 and 5 , depending upon the properties of the carbonaceous fuels being supplied to the combustor  12 , such as the moisture content, a portion of the combustible gas is preferably returned to the combustor  12  via conduit  48  and a portion of the liquid is preferably returned to the combustor  12  via conduit  26  to facilitate the partial combustion of the carbonaceous fuel. The returned combustible gas and recycled liquid preferably serve as a complete or partial replacement for the auxiliary fuel source supplied to the combustor  12 , particularly after the system  10 ,  200  start-up phase is complete. Returning a portion of the combustible gas and a portion of the liquid to the combustor  12  tends to reduce the need for auxiliary fuel to maintain the desired partial combustion in the combustor  12  and tends to improve the overall efficiency of typical embodiments of the system  10 ,  200 . 
     Referring to  FIGS. 1 and 5 , conduits  86 ,  84 ,  112 ,  205 ,  207  and  208  connect the scrubber  14 , the fixer  16 , the cyclone  203  and the demister  204  to the conduit  114 , which connects to the pump  118 . These conduits  86 ,  84 ,  112 ,  205 ,  207  and  208  pass wastewater, excess liquid from wet fuel components, tar, oil, particulate matter, condensate, and other removed substances to the conduit  114  which connects to the pump  118 . The output of pump  118  is preferably recycled via conduit  26  back into the combustor  12 . Returning the wastewater, liquids and other components to the combustor  12  provides a number of advantages. For example, the recycled wastewater tends to scavenge additional, residual carbon from the ash as the liquid is broken down. This recycling of liquid provides for improved recovery of the heating value from the carbonaceous fuel and eliminates or drastically reduces the need to dispose of wastewater. A portion of the liquid may also be extracted from the system  10 ,  200  for use as, for example, a partial replacement for petroleum or petrochemical products in combustion or chemical applications. 
     The system  10 ,  200  may be used to process a wide variety of carbonaceous fuels, as well as combinations thereof. The spacing between the ash support member  36  and the opening  34  of the inner wall  28 , as well as the relatively unobstructed side openings there, allow a wide assortment of solid or semi-solid fuels to be used with low risk of clogging. Carbonaceous fuels used successfully in one specific embodiment of system  10 ,  200  include, but are not limited to, materials such as chicken litter, other animal waste, some municipal solid or semi-solid waste, sanding dust from glued woods (such as plywood or pressboard), paper mill or wood pulp sludge (including, but not limited to, sludge with a moisture content of 65% or higher), wood or yard waste, agricultural waste, biomass, shredded tires and mixtures or combinations of these and other carbonaceous materials. Liquid carbonaceous fuels may also be added to the solid or semi-solid carbonaceous fuel, including, but not limited to, waste petroleum products, used motor oil, used cooking oil and carbonaceous liquids extracted from the system  10 ,  200  itself. Adding such liquid carbonaceous fuels can markedly increase the overall efficiency of typical embodiments of the system  10 ,  200 . 
     One specific embodiment of the system  10 ,  200  is approximately 6 feet (1.8 meters) wide, approximately 12 feet (3.7 meters) long and approximately 8 feet (2.4 meters) tall. This specific embodiment of system  10 ,  200  gasifies approximately eighty (80) pounds (36 kilograms) of chicken litter per hour, requires no auxiliary fuel after start-up, uses approximately ten (10) kilowatt-hours of electricity, and produces approximately ten (10) pounds (4.5 kilograms) per hour of mineral ash, generating no other solid waste, no liquid waste, and essentially no gaseous waste. 
     The emissions test results in Example 1 below illustrate that at least one specific embodiment of the system  10 ,  200  can produce combustible gas that is environmentally relatively benign, while processing solid or semi-solid carbonaceous fuels that previously posed serious landfill issues. 
     Example 1 
     An emissions test was conducted on combustible gas generated by one specific embodiment of the system  10 ,  200  while combusting chicken litter. A sample run of approximately 60 minutes in duration was performed. Testing was performed in approximate accordance with the methods detailed in 40 Code of Federal Regulations (CFR), Part 60, Appendix A. The flow, based on the lowest recordable flow, had a velocity of approximately 6 feet per second (1.8 meters per second) and the sample collected had a volume of approximately 40 dry standard cubic feet (1000 liters). The results of the emissions testing for Example 1 are summarized in Table 1 below. 
     
       
         
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Emissions in 
               
               
                   
                 approximate 
               
               
                   
                 lbs/hr 
               
               
                 Substance 
                 (grams/hr) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Particulate Matter (based on lowest detectable flow rate) 
                 0.003 
                 (1) 
               
               
                 VOC as Propane (corrected for moisture) 
                 0.1 
                 (50) 
               
               
                 Nitrogen Oxides as NO 2   
                 0.001 
                 (0.5) 
               
               
                 Carbon Monoxide 
                 0.003 
                 (1) 
               
               
                 Sulfur Dioxide 
                 0.1 
                 (50) 
               
               
                 Ammonia 
                 0.03 
                 (10) 
               
               
                 HCl 
                 0.008 
                 (4) 
               
               
                 Chloride 
                 0.005 
                 (2) 
               
               
                   
               
             
          
         
       
     
     Example 2 
     An emissions test was conducted on combustible gas generated by one specific embodiment of the system  10 ,  200  while combusting paper mill sludge. A sample run of approximately 60 minutes in duration was performed. Testing was performed in approximate accordance with the methods detailed in 40 CFR, Part 60, Appendix A. The flow, based on the lowest recordable flow, had a velocity of approximately 6 feet per second (1.8 meters per second) and the sample collected had a volume of approximately 40 dry standard cubic feet (1000 liters). The results of the emissions testing for Example 2 are summarized in Table 2 below. 
     
       
         
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Emissions in 
               
               
                   
                 approximate 
               
               
                   
                 lbs/hr 
               
               
                 Substance 
                 (grams/hr) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Particulate Matter (based on lowest detectable flow rate) 
                 0.001 
                 (0.5) 
               
               
                 VOC as Propane (corrected for moisture) 
                 0.01 
                 (5) 
               
               
                 Nitrogen Oxides as NO 2   
                 0.01 
                 (5) 
               
               
                 Carbon Monoxide 
                 0.05 
                 (20) 
               
               
                 Sulfur Dioxide 
                 0.02 
                 (9) 
               
               
                   
               
             
          
         
       
     
     Other modifications, changes and substitutions are intended in the foregoing and, in some instances, some features of the invention may be employed without a corresponding use of other features. For example, the configuration of the ash support member  36  may be used in combination with any number of different gasification systems, regardless of whether such systems also use other features of the present invention, and may also find uses in systems other than gasification systems. Similarly, the gaseous return and liquid recycling features of the present invention may be used separately or in combination with any number of different gasification systems, regardless of whether such systems also use other features of the present invention, and may also find uses in systems other than gasification systems. Further, the wood chip filtering or other filters or catalysts of the present invention may be used in combination with any number of different gasification systems, regardless of whether such systems also use other features of the present invention, and may also find uses in systems other than gasification systems. Further still, the design of the blower  90  of the present invention may be used in combination with any number of different gasification systems, regardless of whether such systems also use other features of the present invention, and may also find uses in systems other than gasification systems. Of course, quantitative information is included by way of example only and is not intended as a limitation as to the scope of the invention. Accordingly, it is appropriate that the invention be construed broadly and in a manner consistent with the scope of the invention disclosed. 
     Although the present invention has been described in considerable detail with reference to certain preferred versions or embodiments thereof, other versions or embodiments are possible. For example, versions or embodiments having different component dimensions, different numbers and placements of blowers, different numbers and placements of vessels, different numbers and placements of stirring members, different combinations of components, different sequences of components, or subsets of these and other differences are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions or embodiments contained herein.