Abstract:
Systems and methods are provided for generating energy from biomass. A gasifier is provided for generating syngas from the biomass. The gasifier comprises a housing for providing a first, oxygen starved environment in which the biomass is sub-stoichiometrically combusted to generate syngas—an effluent comprising gaseous combustibles. An oxidizer is connected to receive the syngas from the gasifier and configured to oxidize the syngas in a second environment distinct from the first, oxygen starved environment and to thereby generate heat energy. An oxidative agent supply mechanism introduces an oxidative agent to the first, oxygen starved environment in the gasifier housing, the oxidative agent comprising a mixture of flue gas and air.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 12/860,759, filed on 20 Aug. 2010, entitled BIOMASS GASIFICATION IN ATMOSPHERES MODIFIED BY FLUE GAS, which is a continuation of U.S. application Ser. No. 11/801,030, filed on 8 May 2007, entitled METHOD FOR GASIFYING SOLID ORGANIC MATERIALS AND APPARATUS THEREFOR, which claims the benefit under 35 USC §119(e) of U.S. provisional patent application No. 60/801,574 filed 18 May 2006. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to the gasification of, and generating of energy from, solid organic materials and to the production of syngas. Particular embodiments provide methods, apparatus and systems for gasifying, and generating energy from, solid organic materials and generating syngas. 
       BACKGROUND 
       [0003]    It has been recognized that many industrial and agricultural solid organic by-products, such as forestry and agricultural residue, and the like, are a potential source of chemical energy. Substantial increases in the cost of traditional fuels, such as fuel, oil and natural gas, have provided corresponding economic incentive to try to develop effective and efficient techniques for recovering the energy in these organic by-products, energy that traditionally was not recovered to any substantial extent. Such organic materials, frequently referred to as “biomass” materials, are now successfully utilized to some extent as fuel in some large industrial systems, for example, in firing the power boiler and the recovery boiler in a pulp or paper mill. However, the high capital cost that has heretofore been associated with biomass energy recovery systems has precluded their successful use in small or even medium-sized energy recovery systems. 
         [0004]    Medium-sized energy recovery systems are used in community centers, schools, nursing homes, and small industrial and commercial establishments and, to date, biomass fuels have not been satisfactorily utilized as fuels in heating systems for such facilities. U.S. patents disclosing technology relating to the recovery of energy from wood chips or similar organic materials include, for example: U.S. Pat. No. 5,138,957 that issued to Morey, et al. on Aug. 18, 1992; U.S. Pat. No. 4,184,436 that issued to Palm, et al. Jan. 22, 1980; U.S. Pat. No. 4,312,278 that issued to Smith, et al. on Jan. 26, 1982; U.S. Pat. No. 4,366,802 that issued to Goodine on Jan. 4, 1983; U.S. Pat. No. 4,321,877 that issued to Schmidt, et al on Mar. 30, 1982; U.S. Pat. No. 4,430,948 that issued to Schafer, et al. on Feb. 14, 1984; U.S. Pat. No. 4,593,629 that issued to Pedersen, et al. on Jun. 10, 1986; U.S. Pat. No. 4,691,846 that issued to Cordell, et al. on Sep. 8, 1987, U.S. Pat. No. 4,971,599 that issued to Cordell et al. on Nov. 20, 1990, U.S. Pat. No. 6,120,567 that issued to Cordell et al. on Sep. 19, 2000 and Canadian Patent No. 2,058,103 that issued to Morey et al. on 14 Oct. 1997. 
         [0005]    However, it is not known that any of the inventions described in these patents have been successfully adapted to recover biomass energy on a cost-effective basis in small and medium-sized energy recovery systems. 
       SUMMARY 
       [0006]    Particular embodiments of the invention provide methods, apparatus and systems for gasifying solid organic materials and generating syngas which may be burned to create energy. Particular embodiments provide methods and apparatus that produce high energy, low temperature, and low particulate-laden syngas by controlling the oxygen content in combustion air used for “starved air” combustion of biomass in a gasifier. Recirculated flue gas mixed with an amount of fresh air is utilized for providing the oxygen content therein and for controlling the method. 
         [0007]    Particular embodiments provide methods for gasifying biomass materials, such as forestry and agricultural residues, industrial waste materials such as saw mill pulp, paper products, fowl litter, such as chicken litter and turkey litter, and hydrocarbon based plastics and the like. 
         [0008]    Particular embodiments provide apparatus used to convert the chemical energy of biomass materials into thermal energy or gaseous products, and specifically, syngas, that is also called production gas. Syngas is a compressible synthetic combustible gas containing very little particulate material. Thus, aspects of this invention can also be viewed as providing methods for producing syngas. 
         [0009]    Aspects of the invention provide a method for gasifying solid organic materials, apparatus used in such methods, and systems incorporating such methods and apparatus. One aspect of the invention provides a gasifier for gasifying solid organic materials comprising in combination a housing, wherein the housing has a lower portion and an upper portion and a cylindrical side wall supported by the lower portion and attached to the upper portion. 
         [0010]    In particular embodiments, the gasifier comprises a roof for the housing, the roof being supported by and integral with the cylindrical side wall. In some embodiments, there is at least one opening through the roof for exiting syngas effluent and at least one opening for a sensing device. In particular embodiments, the gasifier includes a device for removing the syngas from the gasifier which is located at, and connected to, the roof opening. In some embodiments, the gasifier includes, at the sensing device opening, one or more devices for sensing the elevation of any mass of any solid organic material contained in the housing. In some embodiments, the sensing device is a radar device that is mounted over the sensing device opening and surmounts a non-metallic plate that covers the opening. 
         [0011]    Located in the lower housing, particular embodiments of the gasifier comprise one or more openings for supporting a device for determining the amount of non-combustible material (e.g. ash) remaining within the gasifier. In some embodiments, the device is located at, and connected to, the lower portion of the housing, and within the opening for determining the amount of non-combustible material (e.g. ash) remaining within the gasifier. 
         [0012]    In particular embodiments, the gasifier comprises one or more openings in the cylindrical wall for supporting one or more devices for providing oxidative gas to the solid organic materials. In some embodiments, the oxidative gas comprises recirculated flue gas containing a predetermined portion of fresh air. In some embodiments, a device for providing the oxidative gas to the solid organic materials is located in, and connected to the oxidative gas opening. 
         [0013]    In particular embodiments, a floor is located in the lower portion of the gasifier, the floor having a top surface and a bottom surface, and at least one opening therethrough to allow for the passage of solid organic material into the interior of the gasifier. In some embodiments, the top surface of the floor comprises a retaining wall on the outside of each of the floor openings to form a retention basin to retain the solid organic materials in the lower portion of the gasifier to form a floorless hearth. 
         [0014]    Particular embodiments of the gasifier include a device for moving solid organic materials through the floor opening and into the gasifier in an upward motion and a device for providing and retaining a cone structure to the underside of the solid organic materials. 
         [0015]    In some embodiments, the gasifier comprises a device for containing the solid organic materials while above the retention basin and one or more openings in the lower portion of the gasifier to allow movement of non-combustibles out of the gasifier, along with a device in the retention basin for removing noncombustible materials from the gasifier. 
         [0016]    In particular embodiments, the gasifier comprises a control and monitor for the amount of mass of solid organic material within the gasifier and a control and monitor for the amount of non-combustibles in the gasifier. 
         [0017]    Another aspect of the invention provides a square or rectangular “loaf” gasifier for gasifying solid organic materials. In particular embodiments, the loaf gasifier comprises a housing incorporating a lower portion and an upper portion and four side walls supported by the lower portion and attached to the upper portion. 
         [0018]    The loaf gasifier has a roof supported by, and integral with, the four side walls. In some embodiments, the loaf gasifier comprises one or more openings through a side wall for exiting syngas effluent and one or more openings through the roof for a sensing device. In some embodiments, the loaf gasifier comprises a device for removing the gaseous effluent from the gasifier which is located at, and connected to, the side wall opening. In particular embodiments, the loaf gasifier comprises a device for sensing the elevation of any mass of any solid organic material contained in the housing which is located at, and associated with the sensing device opening. In some embodiments, the sensing device comprises a radar device that is mounted over any sensing device opening and that surmounts a non-metallic plate that covers the opening. 
         [0019]    Located in the lower housing, particular embodiments of the loaf gasifier comprise one or more openings for supporting a device for determining the amount of non-combustible material (e.g. ash) remaining within the gasifier. In some embodiments, the device is located at, and connected to, the lower portion of the housing, and within the opening for determining the amount of non-combustible material (e.g. ash) remaining within the gasifier. 
         [0020]    In some embodiments, the loaf gasifier comprises one or more openings in its side walls for supporting one or more devices for providing oxidative gas to the solid organic materials. In some embodiments, the oxidative gas comprises recirculated flue gas containing fresh air. In particular embodiments, a device for providing the oxidative gas to the solid organic materials is located in, and connected to the oxidative gas opening. 
         [0021]    The gasifier of particular embodiments comprises a floor located in the lower portion of the loaf gasifier, the floor having a top surface and a bottom surface, and at least one opening therethrough to allow for the passage of solid organic material into the interior of the gasifier. In some embodiments, the top surface of the floor comprises a retaining wall on the outside of each of the floor openings to form a retention basin to retain the solid organic materials in the lower portion of the gasifier to form a floorless hearth. 
         [0022]    In particular embodiments, the loaf gasifier includes a device for moving solid organic materials through the floor opening and into the gasifier and a device for providing and retaining a cone structure to the underside of the solid organic materials. 
         [0023]    In some embodiments, the loaf gasifier comprises a device for heating the solid organic materials while above the retention basin and one or more openings in the lower portion of the gasifier to allow movement of non-combustibles out of the gasifier, along with a device in the retention basin for removing noncombustible materials from the gasifier. 
         [0024]    In particular embodiments, the loaf gasifier comprises a control and monitor for the amount of mass of solid organic material within the gasifier and a control and monitor for the amount of non-combustibles in the gasifier. 
         [0025]    In another embodiment, the circular gasifier described above is modified to alter the flow of effluent by providing a constriction in the midsection of the gasifier. This embodiment provides a gasifier for gasifying solid organic materials comprising a housing wherein the housing has a lower portion having a top part and an upper portion having a bottom part. The housing has a cylindrical side wall supported by the lower portion and attached to the upper portion. The cylindrical side wall has a constricted section where the top part of the lower portion and the bottom part of the upper portion meet and join. 
         [0026]    In yet another embodiment of this invention, the loaf gasifier described above is also modified to provide a constriction in its side walls. This embodiment provides a loaf gasifier for gasifying solid organic materials comprising a housing wherein the housing has a lower portion with a top part and an upper portion with a bottom part. The housing has four side walls supported by the lower portion and attached to the upper portion. The side walls have a constricted section where the top part of the lower portion and the bottom part of the upper portion meet and join. 
         [0027]    Another aspect of the invention provides a method for gasifying solid organic materials to produce a gaseous effluent and a solid residue. The method comprises providing a supply of solid organic material and providing a circular gasifier as set forth in this disclosure. Thereafter, the solid organic materials are introduced into the gasifier upwardly from a lower portion of the gasifier to provide a mass of solid organic materials in the gasifier. The solid organic materials are ignited and then heated in the gasifier while providing an oxidative gas to the gasifier. In particular embodiments, the oxidative gas comprises recirculated flue gas from a flue stack located in a system in which the gasifier is operating. In some embodiments, the oxidative gas comprises a combination of the flue gas and a predetermined portion of fresh air. 
         [0028]    In particular embodiments, there is provided an effluent flow path in the gasifier for a portion of the gaseous effluent to migrate, mix, and react through the heated solid organic materials and the syngas formed thereby is transferred outwardly from the gasifier. Non-combustible solids are also transferred out of the gasifier. 
         [0029]    Another aspect of the invention provides a method for gasifying solid organic material to produce a gaseous effluent and a solid residue. The method comprises providing a supply of solid organic material and providing a loaf gasifier as set forth in this disclosure. The method also involves introducing the solid organic materials into the gasifier upwardly from a lower portion of the gasifier to provide a mass of solid organic materials in the gasifier. The solid organic materials are ignited and then heated in the gasifier while providing an oxidative gas to the gasifier to provide a gaseous effluent. In some embodiments, the oxidative gas comprises recirculated flue gas from a flue stack located in a system in which the gasifier is operating. In particular embodiments, the oxidative gas comprises a combination of the flue gas and a predetermined portion of fresh air. 
         [0030]    In particular embodiments, there is provided an effluent flow path in the gasifier for a portion of the gaseous effluent to migrate, mix, and react through the heated solid organic materials and the syngas formed thereby is transferred outwardly from the gasifier. Non-combustible solids are also transferred out of the gasifier. 
         [0031]    Aspects of the invention provide systems that utilize each of the various gasifiers disclosed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0032]      FIGS. 1A and 1B  are schematic drawings showing gasifiers, apparatus and methods for gasification of biomass and producing syngas and corresponding portions of systems incorporating such gasifiers according to an example embodiment. 
           [0033]      FIG. 2  is a front view of a circular gasifier according to a particular example embodiment. 
           [0034]      FIG. 3  is a cross sectional front view of the  FIG. 2  gasifier through line A-A. 
           [0035]      FIG. 4  is an enlarged front view of a radar sensing device. 
           [0036]      FIG. 5  is a perspective view of a segmented, round feed cone which may be used in gasifiers according to particular embodiments of the invention. 
           [0037]      FIG. 5A  is a perspective view of a unitary, round feed cone feed which may be used in gasifiers according to particular embodiments of the invention. 
           [0038]      FIG. 6  is a perspective view of a segmented, square feed cone which may be used in gasifiers according to particular embodiments of the invention. 
           [0039]      FIG. 6A  is a perspective view of a unitary, square feed cone which may be used in gasifiers according to particular embodiments of the invention. 
           [0040]      FIG. 7  is a cross sectional view of the area designated  28  of  FIG. 3 , showing an example of the detail of the moveable cone feed and the bottom tuyeres according to a particular embodiment. 
           [0041]      FIG. 8  is a front view of a square or rectangular, loaf gasifier, according to a particular embodiment. 
           [0042]      FIG. 9  is a cross sectional view of the  FIG. 8  loaf gasifier through line B-B. 
           [0043]      FIG. 10A  is a cross sectional view of an example construction of walls having an insulation layer which may be used with particular gasifier embodiments. 
           [0044]      FIG. 10B  is a cross sectional view of another example construction of walls using air as insulation which may be used with particular gasifier embodiments. 
           [0045]      FIG. 11  is an enlarged side view of the roof the  FIG. 8  loaf gasifier according to a particular embodiment. 
           [0046]      FIG. 12  is a cross sectional view of the  FIG. 11  roof according to a particular embodiment. 
           [0047]      FIG. 13  is a top view of an ash collection system suitable for use with particular embodiments of the  FIG. 8  gasifier. 
           [0048]      FIG. 14  is an angled side view of a gasifier according to a particular embodiment, with the sides open to show its ash-removal grate system. 
           [0049]      FIG. 15  is a side cross sectional view of the  FIG. 14  grate system through the line C-C. 
       
    
    
     DETAILED DESCRIPTION 
       [0050]      FIGS. 1A and 1B  (together,  FIG. 1 ) are schematic representations of portions of an apparatus, method and system for gasification of, and generation of energy from, biomass according to an example embodiment.  FIG. 2  is a front view of a circular gasifier  1  suitable for use as the gasifier of  FIG. 1A .  FIG. 3  is a cross sectional front view of the  FIG. 2  gasifier through line A-A. 
         [0051]      FIG. 1  shows a circular gasifier  1  according to a particular embodiment having an ash removal system  4  and a solid mass feeder  2  comprising a collection bin  5 , connected by auger feed  3  to gasifier  1 . In the illustrated embodiment, a portion of solid mass feeder  2  runs essentially horizontally  7  beneath gasifier  1  and then turns essentially ninety degrees vertically  8  and thus feeds gasifier  1  from the center of floor  9  of gasifier  1  (as shown in  FIGS. 2 and 3 ). In horizontal run  7 , solid mass feeder  2  may be shrouded or may comprise an open trough. In the illustrated embodiment, solid mass feeder  2  is covered by a shroud  6  enclosing auger feed  3  (as shown in  FIG. 3 ). 
         [0052]    In some embodiments, the solid mass materials are first comminuted or chopped, if it is forestry product, so that it will flow and be ignited readily. Generally this chopped material is best handled if the pieces are 3 inches or less in any dimension. If the solid mass material is chicken litter or turkey litter, then chopping is not required. 
         [0053]      FIG. 2  is an enlarged front view of a circular gasifier, according to a particular example embodiment, showing gasifier  1 , auger feed  3 , shroud  6 , horizontal run  7  and vertical run  8  of solid mass feeder  2 . Gasifier  1  comprises a housing  10  that has a cylindrical side wall  11  supported by the lower portion, generally shown as  12 , of housing  10 . Cylindrical side wall  11  is attached to the upper portion of housing  10 , indicated generally as  13 . Housing  10  is surmounted by a roof  14 , which is supported by, and integral with, cylindrical side wall  11 . 
         [0054]    In particular embodiments, gasifier  1  is modified to alter the flow of effluent by providing a constriction (not shown) in the mid-section of gasifier  1  (e.g. between the upper part of lower portion  12  and the lower part of upper portion  13 ). In some embodiments, the constriction is provided in cylindrical side wall  11  and is located where the upper part of lower portion  12  joins the lower part of upper portion  13 . Constriction of the gasifier is shown in  FIG. 9  with respect to the loaf gasifier  60  described below. 
         [0055]    Located in cylindrical side wall  11 , particular embodiments may include one or more openings for providing oxidative gas  121  to the solid organic materials. In some embodiments, the oxidative gas comprises recirculated flue gas and fresh air. In some embodiments a device is located in, and connected to, the oxidative gas opening for providing an oxidative gas to the solid organic materials. 
         [0056]    In the illustrated embodiment, solid organic materials are introduced upwardly into gasifier  1  from a lower portion (e.g. lower portion  12 ) of gasifier  1  to provide a mass of solid organic materials in gasifier  1 . The solid organic materials are ignited and then heated in gasifier  1 , while providing an oxidative gas to gasifier  1 , to provide a gaseous effluent. In particular embodiments, the oxidative gas comprises recirculated flue gas from a flue stack located in a system in which gasifier  1  is operating. In particular embodiments, the oxidative gas comprises a combination of recirculated flue gas from a flue stack (e.g.  117  in  FIG. 1B ) located in a system in which gasifier  1  is operating and fresh air. 
         [0057]    An effluent flow path is provided within gasifier  1  for a portion of the gaseous effluent to migrate, mix, and react through the heated solid organic materials. The syngas formed thereby is transferred outwardly from gasifier  1  and any noncombustible solids are transferred out of gasifier  1 . 
         [0058]      FIG. 3  is a cross sectional front view of gasifier  1  (shown also in  FIG. 2 ). In the illustrated embodiment, syngas exits inner chamber  62  of gasifier  1  through exit port  15  in roof  14 . Also shown in  FIG. 3  is a sensing device  16  that is positioned over an opening  17 . Sensing device  16  is a radar that is used to monitor the top of the solid mass pile  18  shown in  FIG. 3 . For purposes of illustration, only one such device  16  is shown, but more than one such device  16  may be used. Gasifiers according to particular embodiments use at least three such sensing devices  16 . Gasifiers according to other embodiments use at least five such sensing devices  16 . As described herein, sensing devices are used to monitor the height of solid mass pile  18 . It is generally desirable to maintain an appropriate height of solid mass pile  18  to produce syngas with lower amounts of particulate. 
         [0059]      FIG. 4  is an enlarged front view of sensing device  16  shown in  FIG. 3 . In the illustrated embodiment of  FIG. 4 , sensing device  16  comprises a radar.  FIG. 4  shows details of the construction of sensing device  16  while  FIG. 3  shows how sensing device  16  may be positioned on gasifier  1 . 
         [0060]      FIG. 4  shows a radar sensing device  16  mounted on roof  14  of circular gasifier  1 . Sensing device  16  is housed in an open housing  21  and supported by adjustable fasteners  19  and has the capacity to be adjusted angularly on swivelled fasteners  20  so that sensing device  16  can sense the contour of solid mass pile  18  in the interior of gasifier  1 . In the illustrated embodiment, sensing device  16 , in its housing  21 , is mounted over a non-metallic plate  22 . Plate  22  is generally non-metallic so that sensing device  16  can direct a radar beam into the interior of gasifier  1  and sense the top of solid mass pile  18 . It should be noted that the opening  17  in gasifier  1  is only an opening in the metal cladding of housing  10 , and not an opening through the firebrick contained in the interior of housing  10 . 
         [0061]    Maintaining control of the height of solid mass pile  18  is desirable for combustion control and the release of gaseous combustibles, i.e., the “product gas”. The location of feed cone(s)  25  and vertical auger(s) in vertical run  8  (see  FIG. 3 ) are designed to provide a solid mass pile  18  having a generous depth, and a generally flat upper periphery. In some embodiments, this flat, mesa-like upper surface extends over 60 to 70 percent of the floor area, generally filling the lower portion (e.g. lower portion  12 ) of gasifier  1 , and sharply tapers downward adjacent side wall  11 . This downward taper, referred to as the angle of repose, is dependent upon the type of fuel used. A flat fuel pile  18  may help to achieve uniform combustion without bridging. This flat configuration results in an approximately uniform pile depth, which in turn may result in uniform air pressure within pile  18 , thus minimizing channeling of pile  18 . In addition to the flat shape of fuel pile  18 , it may be desirable to maintain a depth of pile  18 . Ash may be maintained below the actively burning portion of pile  18  to prevent heat damage to feed cone  25  and ash removal system  4 . In an example embodiment, about 6 inches or more of ash is maintained below the actively burning portion of pile  18 . 
         [0062]    As the solid organic feed material in gasifier  1  moves from feed cone  25  to the center and top of pile  18 , it gets hotter and hotter, and volatile components in such material and combustion products begin to dissipate from the surface of pile  18 , partly being assisted by the gases that are rising through such material. As the feed material in pile  18  loses more and more of the volatile and pyrolytic ingredients, it will begin to form high molecular weight carbonaceous derivatives and char until, eventually, it is exposed to the full operating temperature inside gasifier  1 . This material moves generally horizontally outward and then downward toward the outer wall and lower floor  9  where it is exposed to further oxidation agents via tuyere arrays  32  and  33  for a more complete reaction, at which time further organic constituents of such feed material will gasify, and will pass from gasifier  1  as an incompletely oxidized gaseous effluent of combustibles (syngas). In the illustrated embodiment, the effluent is carried away from gasifier  1  through an insulated exit duct. The velocity of the effluent above fuel pile  18  and through exit port  15  is kept low, reducing particulate carryover. 
         [0063]    In various embodiments, air-modified flue gas (oxidative gas), steam-modified ambient air or steam-modified pure oxygen is provided to burning piles  18  and  71  through the respective tuyeres fitted on gasifiers  1  and  60 . Loaf gasifier  60  and pile  71  are described in more detail below with reference to  FIG. 9 . 
         [0064]    In some embodiments, the feed rate into gasifier  1  is monitored and controlled by monitoring and controlling the height of fuel pile  18  within gasifier  1 . Suitable instrumentation, not shown, is provided to control the rate of the delivery of the feed material into gasifier  1  by the feed assembly (e.g. solid mass feeder  2 ) as a function of the elevation of the top of the feed material in the height of pile  18 . The shape and height of feed material pile  18  may thereby be maintained substantially constant. 
         [0065]    As solid mass pile  18  burns, it creates ash, which in particular embodiments is removed from gasifier  1 . Gasifier  1  of the illustrated embodiment comprises one or more trenches  24  provided in the gasifier floor and one or more devices for removal of ash and combustion residues and for control of the elevation of the “moving bed of ash” hearth described in more detail below. In the illustrated embodiment of  FIG. 3 , the ash removal system  4  comprises an auger  26 .  FIGS. 2 and 3  show two trench sections  24 , one on either side of a centrally located feed cone  25 . Feed cone  25  is described in more detail below. Ash augers  26  in trench sections  24  move the ash toward points of discharge  27  suitably located at the ends or bottoms of trench sections  24 . In the illustrated embodiment, trench sections  24  are connected to a bin or a conveyor of suitable design for further disposal of the ash (see ash removal system  4  of  FIG. 1A ). 
         [0066]    Formation of ash creates a floorless hearth  30  in gasifier  1  on which burning solid mass pile  18  is situated. This ash build up, together with intermittent or continuous ash removal, creates a “moving bed of ash”, which provides floorless hearth  30 . 
         [0067]    In other embodiments, control of the level of the “moving bed of ash” that creates hearth  30  and removal of ash can be accomplished by a conveyor or conveyors moving across the entire floor, or section thereof, from side to side, or end to end of gasifier  1 . In other embodiments, a set, or sets, of dump grates can be inserted under “moving bed of ash” hearth  30  to facilitate and control removal of the ash. 
         [0068]    In some particular embodiments of the invention, for example, when forestry products are used as the feed, ash removal system  4  comprises a peppermill grate  40  (see  FIG. 7  which is a cutaway portion of  FIG. 3 , section  28 ). In the illustrated embodiment, peppermill grate  40  comprises a flat metal plate  39  that is perforated with a multiplicity of holes  41  for allowing ash to fall therethrough. Over top of flat plate  39  is a moveable grate  42  that is also perforated with holes  43 . Moveable grate  42  may be moved such that it covers part of holes  41  part of the time and can allow holes  43  to be aligned with holes  41 , such that ash may fall through aligned holes  43 ,  41 . Grate  42  may be moved in a generally oscillating motion. Ash may then fall through aligned holes  41 ,  43  and into retention basins  29  below (see  FIG. 2 ). Augers  26  move the ash to discharge point(s)  27  where it is moved out of retention bins  29  into a conveyor portion of ash removal system  4  (see  FIG. 1A ) for transfer away from gasifier  1 . 
         [0069]      FIG. 7  further shows a portion of a segment of feed cone  25  surmounting grate  42 . Grate  42  is surmounting flat plate  39 . At one edge  44  of grate  42  of the illustrated embodiment, there is a pin  45  that attaches grate  42  to flat plate  39 . Grate  42  may partially swing around pin  45  such that grate  42  moves in an oscillating motion. The swinging motion of grate  42  moves the ash that piles on grate  42  and flat table  39  and the ash falls through holes  41  and  43  into basin  29  below. Also shown in  FIG. 7  are bottom tuyeres  34 , which are described in more detail below. 
         [0070]      FIG. 14  is an angled side view of a gasifier  1  according to another embodiment with its sides open to show another type of grate system  84 , which is similar to peppermill grate  40  of  FIG. 7 .  FIG. 15  is a side cross sectional view of grate system  84  through the line C-C. Grate system  84  comprises two grates  85  and  86  (see  FIG. 15 ) at the bottom of gasifier  1 . In the illustrated embodiment, bottom grate  85  is stationary and has openings  87 . In particular embodiments, openings  87  are approximately 8 inches wide by 20 inches long. Top grate  86 , which also has openings  88 , is moveable relative to bottom grate  85 . In the illustrated embodiment, top grate  86  is moved by two hydraulic cylinders (not shown). In particular embodiments, the hydraulic cylinders have a stroke maximum of about 8 inches. Because grate ring  86  is round, this stroke rotates grate ring  86 . The hydraulic cylinders stroke top grate  86  such that it aligns openings  87 ,  88  and, on the back stroke, misaligns openings  87 ,  88 . 
         [0071]    In the illustrated embodiment of  FIG. 15 , top grate  86  has wedge plates  89  mounted on top of it. These plates  89  are installed in such a way that when the top grate  86  is rotating, wedge plates  89  push the ash in front of them towards the openings  87  in the bottom grate  85 . The movement and height of wedge plates  89  ensure measurable ash removal from the bottom of pile  18 , and can prevent the ash bridging above the ash grate openings. 
         [0072]    As the bottom layer of ash is discharged, the mixture of ash and unburned carbon from above drops down lower. As the carbon burns, the process temperature in the vicinity of the ash discharge thermocouples (for example, temperature probes  53  described below) becomes higher indicating that the system has to wait for the next ash dump. As the carbon is more and more combusted and disintegrates, the bottom of gasifier  1  becomes colder and colder indicating that only ash is left at the bottom of gasifier  1  and it is time for a new ash dump. 
         [0073]    Where the feed material into gasifier  1  is soft, easily combustible material, such as chicken litter, turkey litter, or plastics, and the like, a peppermill grate system (e.g. peppermill grate system  40  of  FIG. 7  or grate system  84  of  FIG. 14 ) may not be used. 
         [0074]    For circular gasifier  1  of  FIGS. 2 and 3 , feed cone  25  is also circular—see  FIGS. 5 and 5A . As shown in  FIG. 3 , feed cone  25  is centrally located and arranged along the centerline of the chamber of gasifier  1  and protrudes above the general elevation of the “moving bed of ash” hearth  30 . In the illustrated embodiment, feed cone  25  is serviced by a single, or twin set, of vertical fuel feed augers  31  to move feed material through vertical run  8 . For the loaf type gasifier  60  of  FIGS. 8-9  (described below), which has a rectangular profile, feed cone  25  is also square or rectangular—see  FIGS. 6 and 6A . Feed cones  25  may move solid organic material upwardly into gasifier  1  and may provide a cone-like structure to the underside of solid organic material pile  18  or  71 . 
         [0075]    In particular embodiments, feed cones  25  comprise a single piece, that is a unitary article, for example as shown in  FIGS. 5A and 6A , respectively. In other embodiments, feed cones  25  are segmented as shown in  FIGS. 5 and 6  so that they can more easily be moved into and out of gasifier  1  or  60  respectively, for servicing, maintenance and repair. The individual segments of segmented feed cones  25  can be simply set in place adjacent each other, or they can be mortared together, or glued together to hold them in place. The segmented feed cones  25  shown in  FIGS. 5 and 6  may be used to implement the moveable feed cones  25  described below. 
         [0076]    Feed cones  25  may be moveable or non-moveable. In particular embodiments, feed cones  25  may be moved such that they oscillate in a partial circular motion within gasifier  1 . A moveable feed cone  25  provides relatively even introduction of oxidative gases through burning solid mass pile  18 , which may in turn minimize creation of gas channels. Periodic movement of feed cone  25  also prevents oxidative gas from burning holes between the gas sources and the surface of pile  18 . 
         [0077]    Within gasifier  1 , combustion is carried out sub-stoichiometrically with the application of an oxidizing agent. In particular embodiments, the oxidizing agent comprises flue gas mixed with fresh air. Solid organic materials are transferred continuously or intermittently to gasifier  1  at a rate to maintain a mass of solid organic materials in gasifier  1 . The oxidizing agent is continuously added to gasifier  1  to continuously gasify the solid organic materials in solid mass pile  18 , and the solid residue (non-combustibles) are transferred out of gasifier  1 , for example, as described above. In particular embodiments, the oxidizing agent is administered through a set or sets of suitable ducts connected to nozzles, for example, tuyeres and injection points located within, around and between feed cones  25 , and to a row, or line of nozzles and/or tuyeres in the surrounding walls of gasifier  1 . 
         [0078]      FIG. 3  shows upper tuyeres  32  and lower tuyeres  33  in side walls  11  of gasifier  1  and bottom tuyeres  34  in feed cone  25 . Tuyeres  32 ,  33 ,  34  are used to facilitate the movement of the oxidizing agent (e.g. air-modified flue gas) to gasifier  1  and into burning solid mass  18 . In the illustrated embodiment, upper tuyeres  32  are fed through a common manifold  35  and lower tuyeres  33  are also be fed through a common manifold  36 . Tuyeres  32  are linked to manifold  35  by feed tubes  37  and tuyeres  33  are linked to the manifold  36  by feed tubes  38  (see  FIG. 2 ). 
         [0079]    In the embodiment shown in  FIGS. 2 and 3 , manifolds  35  and  36  are fed from a flue gas return system  48  that includes a duct  49  and an air motor  50 . Inlet  51  of air motor  50  is attached to system  200  ( FIG. 1B ) for supplying air-modified flue gas to flue gas return system  48 . 
         [0080]    Gasifier  1  is equipped with an exit port  15  for the movement of syngas produced therein. In the illustrated embodiment, a fixture  52  is surmounted on exit port  15  for allowing the attachment of components (described below) which may be used to handle the syngas. 
         [0081]    In the illustrated embodiment, the lower portion (e.g. lower portion  12 ) of housing  10  of gasifier  1  includes one or more devices (e.g. probes  53 ) for determining the amount of non-combustibles (e.g. ash) within gasifier  1 . Probes  53  can be used to monitor the level of a moving ash bed defined by the upper elevation of the accumulated ash. As an example, probes  53  may comprise a pair or pairs of thermo elements located one above the other, distanced such that the level of the moving ash bed is in between them, and capable of characterizing the temperature of, and the difference in temperatures between, the material above and below the moving ash bed in operation. This temperature difference can then be used to dictate the degree of movement of ash removal auger(s)  26  and to thereby control the level of the moving ash bed. In particular embodiments, gasifier  1  is equipped with several sets of probes  53 , inserted through openings  55 , around the perimeter of the gasifier chamber. In such embodiments, an average of probe  53  input data is used determine the desired movement of ash removal auger(s)  26 . 
         [0082]    Lower portion  12  of gasifier  1  includes a floor having a top surface and a bottom surface. The gasifier floor may have one or more openings through it to allow for the passage of the solid organic material into the interior of gasifier  1 . In the illustrated embodiment, the top surface of the floor is provided with a retaining wall on the outside of the floor openings to form a retention basin to retain the solid organic materials in lower portion  12  and to thereby form floorless hearth  30 . 
         [0083]    To bring gasifier  1  to an operational condition on start up, solid mass feeder  3  is activated to form pile  18  of feed material in gasifier  1  in preparation of development of a “moving ash bed” above gasifier floor  9 . Pile  18  of feed material is ignited. To bring pile  18  of feed material up to its normal operating temperature, fuel oil or other readily combustible supplemental fuel may be added to it. As an example, this may be done manually through an opening  54  provided in the wall of gasifier  1 . 
         [0084]    As the oxidation proceeds and the temperatures elevate, the solid mass in pile  18  pyrolyzes and gasifies. Combustion of the solid mass may take place below the top of pile  18 . Gas produced in the starved combustion sifts through burning pile  18  and into the upper portion of burning pile  18 , pile  18  acting as a filter for particulate material. The products of combustion rise through pile  18  and cool because the latent heat of water absorbs the energy. As fuel is delivered, it gets pyrolyzed and the fuel moisture and volatile hydrocarbons are separated from the non-volatile components. These processes are driven by the hot gases that result from the combustion of the fixed carbon, which takes place below the top of pile  18 . 
         [0085]    The moderately slow burning lower portion of pile  18  serves to establish a quiet oxidation zone whereby entrainment of particulate matter and fly ash is minimized or reduced. In particular embodiments, gasifier  1  produces syngas with a maximum of combustible gaseous components and a minimum of particulate matter. 
         [0086]      FIG. 8  is a front view of a loaf type gasifier  60 , according to another embodiment.  FIG. 9  is a cross sectional view of the  FIG. 8  gasifier  60 , through line B-B. Gasifier  60  is defined by four vertical side walls  61 , giving the chamber of gasifier  60  a square or rectangular cross section and forming an enclosure  62  ( FIG. 9 ) which has an irregularly shaped bottom  63 . Gasifier  60  includes a roof  64 , which in cross section may be vaulted, tapered or flat or any combination thereof. 
         [0087]    In particular embodiments, walls  61  are made up of a multiplicity of layers.  FIGS. 10A and 10B  show cross-sections of walls  61  according to particular embodiments. In the embodiment of  FIG. 10A , the innermost layer  65  is an insulating layer of a high-temperature resistant type refractory that is capable of withstanding the elevated temperatures that develop within gasifier  60 , for example, temperatures in the range of approximately 2300° F. to approximately 2500° F. Such high-temperature resistant type refractory is capable of withstanding operational temperature variations as well as the corrosive, erosive effects of the gaseous materials produced by the oxidation of biomass feed material that is delivered into gasifier  60 . Walls  61  may also include an insulating layer  66  on the outside of wall layer  65  to further prevent loss of heat through walls  61  of gasifier  60 . As an example, insulating layer  66  may comprise a single layer of insulating firebrick, block insulation, or blanket insulation. In the illustrated embodiment, the outer casing of the wall  61  is a structural layer or shell  67  comprising sheet metal, for example, plate steel, which is airtight and provides the necessary strength and rigidity for walls  61 . 
         [0088]      FIG. 10B  shows second embodiment of wall  61 , wherein insulating layer  66  is not used, and a vacant layer or space  68  is provided between refractory innermost layer  65  and shell  67 . The air which fills vacant layer  68  acts as an insulator between refractory layer  65  and shell  67 . This warmed air in vacant layer  68  can also be used as a source of preheated air for injection into gasifier  60  and recovery and regeneration equipment  96  and  98  (see  FIG. 1 ) which are described in more detail below. 
         [0089]    Referring to  FIGS. 8 and 9 , the biomass feed material from the storage hopper assembly (not shown) is introduced into gasifier  60  from below gasifier  60  through at least one feed cone  59 . In the illustrated embodiment, feed cone  59  is located along the centerline of bottom  63  of gasifier  60 . During normal operating conditions, the feed material rises over the top of feed cone(s)  59  and rests on hearth  70  until it forms a pile  71  of such material, which is the normal or equilibrium condition of gasifier  60 . Hearth  70  is made up of ash and other solid combustion residues. This self-generated hearth  70  is similar to the “moving ash bed” configuration that was described above in connection with gasifier  1 . As primary oxidation progresses, this bed continues to elevate and the ash is removed at essentially the same rate it is formed to maintain the appropriate height of fuel pile  71 . 
         [0090]    As described above for gasifier  1 , the height of pile  71  may be controlled to control combustion and the release of gaseous combustibles. The principles discussed above for the control of pile height in gasifier  1  apply for gasifier  60  and will not be repeated herein. 
         [0091]    In the illustrated embodiment (see  FIGS. 9 ,  11  and  12 ), exit ports  69  are positioned so as to vent gasifier  60  through roof  64 . It should be noted that prior art loaf gasifiers required that the exit for the gases produced therein must be through the side wall to minimize the flow of particulate materials along with the gas. In particular embodiments, side walls  61  are provided in a height which allows any air-borne particulate to fall back to pile  71  rather that exit via ports  69 . The positioning of exit ports  69  within gasifier  60  can be as shown in  FIGS. 9 ,  11  and  12 , may be sloped or vertical, and is selected to be practical and suitable for the specific application. 
         [0092]    As in gasifier  1  described above, an oxidizing agent is administered through a set or sets of suitable ducts connected to nozzles, for example tuyeres, and injection points located within, around and between feed cones  59 , and to a row, or line of nozzles and/or tuyeres in the surrounding walls  61  of gasifier  60 . 
         [0093]      FIG. 9  shows upper tuyeres  73  and lower tuyeres  74  in side walls  61  and bottom tuyeres  75  in feed cone  59 ; all of which, in particular embodiments, are used to facilitate the movement of the oxidizing agent (e.g. air-modified flue gas) to gasifier  60  and into burning solid mass pile  71 . In the illustrated embodiment, upper tuyeres  73  are fed through a common manifold  76  and lower tuyeres  74  are also fed through a common manifold  77 . In the illustrated embodiment, tuyeres  73  are linked to manifold  76  by feed tubes  78  and tuyeres  74  are linked to manifold  77  by feed tubes  79 . 
         [0094]    System  200  ( FIG. 1 ) for supplying fresh air-modified flue gas may also be used in conjunction with gasifier  60 . Manifolds  76  and  77  of gasifier  60  are fed from a flue gas return system, generally  48  (see  FIG. 8 ), which comprises a duct  49  and an air motor  50 . In the illustrated embodiment, the inlet  51  of air motor  50  is attached to system  200  ( FIG. 1 ) for supplying fresh air-modified flue gas to flue gas return system  48 . The details of the movement of the fresh air-modified flue gas from flue stack back to gasifier  60  are set forth in detail below. 
         [0095]    In the illustrated embodiment of gasifier  60 , the upper part of lower portion  12  and the lower part of upper portion  13  (see  FIG. 3  for reference to lower portion  12  and upper portion  13 ) provide a constriction  80  in the interior chamber  62  of gasifier  60 . In the illustrated embodiment, constriction  80  is built into layer  65 , or it can be formed from a plate that is set at an angle into layer  65 . Constriction  80  slows down the upward flow of product gas and thereby assists in reducing the amount of particulate material that tends to reach exit ports  69 . 
         [0096]    In the illustrated embodiment, feed rate into gasifier  60  is monitored and controlled by monitoring and controlling the height of fuel pile  71  within gasifier  60  using the same sensing devices  16  (e.g. radar sensing devices  16 ) as described above. Suitable instrumentation, not shown, is provided to control the rate of the delivery of the feed material into gasifier  60  by the feed assembly as a function of the elevation of the top of the feed material in the height of pile  71 , in some embodiments to maintain such elevation at a substantially constant value, and thereby to contain the pile  71  of feed material at a substantially constant size. 
         [0097]      FIG. 11  is an enlarged front view of roof  64  of loaf gasifier  60 .  FIG. 12  is a cross sectional view of roof  64 , showing the construction of the walls of roof  64 . In the illustrated embodiment, roof  64  comprises two exit ports  69  for syngas. Also shown in  FIG. 11  is a placement of radar sensing device  16  on roof  64 , between exit ports  69 . Dotted lines  184  (shown in  FIG. 9 ) illustrate the beam of radar sensing device  16  penetrating into the interior  62  of gasifier  60 . In the illustrated embodiment, roof  64  comprises an outer steel wall  67 , insulating layer  66  and interior refractory layer  65 . In the illustrated embodiment, component  82  is a flange useful for fitting the roof  64  to the side walls  61  of gasifier  60 . 
         [0098]      FIG. 13  is a cross sectional view showing a number of components of the ash handling system  81  of loaf gasifier  60 . Ash handling system  81  of the illustrated embodiment comprises removable grates  42 , increasing flight ash removal augers  26  in collection bin and retention bin  29 , and castable tuyere panels  83 .  FIG. 13  also shows the exit of centered feed cone  59 . 
         [0099]      FIGS. 1  A and  1  B schematically depict gasifier  1  in use with a system  200  for generating energy from biomass materials. System  200  incorporates one or more methods according to a particular embodiment of the invention. 
         [0100]    As discussed above, gasifier  1  is fed a solid mass material using solid mass feeder  2  comprising auger feed  3 , and ash is removed from gasifier  1  by ash removal system  4 . Syngas  90  that is produced by the pyrolysis and gasification of the solid mass material exits gasifier  1  through exit port  15  into syngas burner  91 . Syngas  90  is controlled by draft controls  93 . In the illustrated embodiment, syngas burner  91  is aided in combustion using a combustion air blower  94  that provides air  95  to syngas burner  91 . 
         [0101]    In particular embodiments, syngas  90  is provided to syngas burner  91  at a temperature of about 500° F. to about 600° F. and is in a starved air condition. This contrasts with prior art systems in that the normal temperature of the syngas from prior art devices is in the range of 1200 F to 1400 F, and in prior art systems, this syngas is not “starved air” and before the prior art syngas can be used, it has to be cooled and compressed, requiring additional and expensive equipment. Syngas burner  91  heats and combusts syngas  90 , for example, up to a temperature in the range of 1200° F. to 1400° F. before the syngas is provided to a low NO x  oxidizer  96 . 
         [0102]    Syngas  90  may be provided to a kiln  98  using syngas blower  99  that moves syngas  90  to a nozzle mix syngas burner  100 . Thereafter, syngas  90  is moved through nozzle mix syngas burner  100  into kiln  98 . Hot gas stream  107  (about 2200° F.) output from kiln  98  is moved to low NO x  oxidizer  96  and combined with the oxidation product  97  coming from syngas burner  91 . 
         [0103]    In the illustrated embodiment, the heating and movement of the gases in kiln  98  is aided by mixing heated air  101  from a heat exchanger  102  (see  FIG. 1B ) with heated ambient air  105  to form heated air stream  103  which is bled into nozzle mix syngas burner  100  using a preheated combustion air blower  104 . A portion  106  of heated air  101  from heat exchanger  102  ( FIG. 1B ) is also bled directly into kiln  98 . 
         [0104]    Hot gas stream  107  output from kiln  98  is fed into low NO x  oxidizer  96  and mixed therein with the oxidation product  97  from syngas burner  91  being fed into the top portion of the low NO x  oxidizer  96 . Low NO x  oxidizer  96  is fed ambient air  108  using a combustion/tempering air fan  109 , through manifolds  110  and tuyeres (not shown) and the flue gas  111  that exits low NO x  oxidizer  96  does so at about 2000° F. and passes to heat exchanger  102  shown in  FIG. 1B . 
         [0105]      FIG. 1B  shows heat exchanger  102  into which flue gas  111  from low NO x  oxidizer  96  has been passed. Exchanged (cooled) flue gas  112  is then passed to a metal heat exchanger  113 , for example, at about 1400° F. Metal heat exchanger  113  is useable because of the relatively lower temperature of cooled flue gas  112  as compared to flue gas  111  input into heat exchanger  102  which is at about 2000° F. Air  114  output from metal heat exchanger  113  becomes the input air to heat exchanger  102 . In the illustrated embodiment, the movement of air  114  is aided by the introduction of fresh air  124  using an air blower  125 . 
         [0106]    Air  101  is the exchanged air output from heat exchanger  102  and has a temperature, for example, in the range of about 400° F. to 1200° F. Air  101  is passed back to kiln  98  ( FIG. 1A ). In the illustrated embodiment, air  101  is occasionally vented (as shown at  116 ) to control the temperature and pressure thereof. 
         [0107]    Heat-exchanged flue gas  127  from metal heat exchanger  113  ( FIG. 1B ) is moved to an induction draft fan  115  before it enters stack  117 . Prior to exhaust flue gas  122  exiting flue stack  117 , a portion of flue gas  120  is withdrawn from stack  117  and moved to a flue gas eductor  118 , which is aided by an induced draft fan  119 . At this point, fresh air  128  is inducted and mixed with flue gas  120  and it is this flue gas modified with fresh air  121  that is moved back to gasifier  1  as the oxidative gas for use in gasifier  1 . Also shown in  FIG. 1B  is sampling port  129 .