Abstract:
A tubular reactor useful for converting biomass to char has walls projecting into its interior. The walls are hollow. Cavities in the walls are in fluid connection with the outside of the reactor by way of openings. The reactor may be deployed in a furnace chamber. Hot gases from the furnace chamber may enter the cavities through the openings to heat the walls from within. Biomass may be pyrolized as it passes along the reactor.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Application No. 61/715,796 filed 18 Oct. 2012. For purposes of the United States, this application claims the benefit under 35 U.S.C. §119 of U.S. Application No. 61/715,796 filed 18 Oct. 2012 and entitled BIOMASS CONVERTER AND METHODS which is hereby incorporated herein by reference for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to the reduction of biomass to char. Embodiments of the invention provide methods and apparatus for reducing biomass to char. 
       BACKGROUND 
       [0003]    Biomass such as straw, other crop residues, wood chips, and the like are readily available. It is often a problem to dispose of biomass. Various agricultural operations can produce significant amounts of biomass as byproducts. Biomass can be reduced to char by heating the biomass in a reduced-oxygen atmosphere. Char is a useful material that may, for example, be mixed into soil to improve the quality of the soil. 
         [0004]    Various systems for processing biomass are known. Some of those systems are described in the following patents and patent applications: 
         [0000]    
       
         
               
               
             
           
               
                   
               
               
                 Pat. No./ 
                   
               
               
                 Publication No. 
                 Title 
               
               
                   
               
             
             
               
                 U.S. Pat. No. 7,497,392 
                 PROCESS AND APPARATUS FOR TRANSFORMING 
               
               
                   
                 WASTE MATERIALS INTO FUEL 
               
               
                 U.S. Pat. No. 8,034,132 
                 PROCESS AND APPARATUS FOR TRANSFORMING 
               
               
                   
                 WASTE MATERIALS INTO FUEL 
               
               
                 U.S. Pat. No. 7,625,532 
                 ABLATIVE THERMOLYSIS REACTOR 
               
               
                 U.S. Pat. No. 7,780,750 
                 INTEGRATED BIOMASS CONVERTER SYSTEM 
               
               
                 U.S. Pat. No. 7,914,750 
                 CONTINUOUS REACTOR SYSTEM FOR ANOXIC 
               
               
                   
                 PURIFICATION 
               
               
                 U.S. Pat. No. 7,998,226 
                 APPLIANCE FOR CONVERTING HOUSEHOLD WASTE 
               
               
                   
                 INTO ENERGY 
               
               
                 U.S. Pat. No. 3,841,851 
                 PROCESS AND APPARATUS FOR THE GASIFICATION 
               
               
                   
                 OF ORGANIC MATTER 
               
               
                 U.S. Pat. No. 5,047,217 
                 REACTOR WITH INTERNAL HEAT CONTROL BY 
               
               
                   
                 HOLLOW HEAT EXCHANGER PLATES 
               
               
                 U.S. Pat. No. 5,666,890 
                 BIOMASS GASIFICATION SYSTEM AND METHOD 
               
               
                 U.S. Pat. No. 6,328,234 
                 APPARATUS AND METHOD FOR RECYCLING SOLID 
               
               
                   
                 WASTE 
               
               
                 U.S. Pat. No. 7,347,391 
                 WASTE PROCESSING APPARATUS AND METHOD 
               
               
                 US 2007/0190643 
                 ANGLED REACTION VESSEL 
               
               
                 US 2011/0265373 
                 ROTARY TORREFACTION REACTOR 
               
               
                 US 2011/0278150 
                 METHOD AND APPARATUS FOR CONTINUOUS 
               
               
                   
                 PRODUCTION OF CARBONACEOUS PYROLYSIS 
               
               
                   
                 BY-PRODUCTS 
               
               
                 US 2012/0017499 
                 TORREFACTION SYSTEMS AND METHODS 
               
               
                   
                 INCLUDING CATALYTIC OXIDATION AND/OR 
               
               
                   
                 REUSE OF COMBUSTION GASES DIRECTLY IN A 
               
               
                   
                 TORREFACTION REACTOR, COOLER, AND/OR 
               
               
                   
                 DRYER/PREHEATER 
               
               
                 EP0891799 
                 PROCESS AND APPARATUS FOR DE-OILING OIL 
               
               
                   
                 AND GREASE CONTAINING MATERIALS 
               
               
                 EP1405895 
                 APPARATUS AND PROCESS FOR THE TREATMENT 
               
               
                   
                 OF A MATERIAL UNDER PYROLYTICAL 
               
               
                   
                 CONDITIONS, AND USE THEREOF 
               
               
                   
               
             
          
         
       
     
         [0005]    There remains a need for cost effective and efficient systems for processing biomass to yield char. There is a particular need for such systems that are easily transportable to locations where biomass is available and/or locations where char may be useful. For example, there is a need for such systems that are transportable to farms which yield biomass byproducts so that biomass can be converted to char at the farm and the char can be used on the farm, thereby eliminating transportation of the biomass and char. There also remains a need for new cost effective and efficient systems for producing syngas or producer gas. 
       SUMMARY 
       [0006]    This invention has a number of aspects. These aspects may be applied to advantage in combination. However, these aspects may also have application individually and/or in combination with other existing apparatus and/or methods. 
         [0007]    One aspect provides apparatus for thermal decomposition of biomass. The apparatus comprises a tubular reactor vessel that extends through a furnace. Hollow walls or paddles project inwardly from an outside wall of the tubular reactor. Openings in an outer wall of the tubular reactor vessel provide fluid communication between the interior of the furnace and spaces interior to the hollow walls or paddles. The openings are slit-shaped in some embodiments. Hot gases in the furnace can enter the interior spaces in the hollow walls or paddles by way of the openings. The hot gases heat the paddles from inside and the heat from the paddles may be transferred to biomass being processed. 
         [0008]    In some embodiments the hollow walls or paddles extend transversely to a longitudinal centerline of the reactor vessel. The hollow walls or paddles may be spaced apart from one another along the reactor. In an example embodiment, the hollow walls or paddles alternate—with one hollow wall or paddle projecting inwardly from a first side of the reactor vessel, a next hollow wall or paddle projecting inwardly from a second side of the reactor vessel opposed to the first side of the reactor vessel, a next next hollow wall or paddle projecting inwardly from the first side of the reactor vessel, and so on. In other embodiments successive hollow walls or paddles project into the interior of the reactor vessel from different directions. 
         [0009]    The hollow walls of paddles in some embodiments project inwardly past the longitudinal centerline of the reactor vessel such that, when the reactor vessel is viewed end-on, the hollow walls or paddles overlap with one another. 
         [0010]    In some embodiments the hollow walls or paddles have arcuate inward edges. In some embodiments the hollow walls or paddles are at least generally planar. In some embodiments the hollow walls or paddles are substantially perpendicular to the longitudinal centerline of the reactor vessel. 
         [0011]    The tubular reactor vessel may be supported for rotation in the furnace and the apparatus may comprise a drive coupled to rotate the reactor vessel about its longitudinal axis. In some embodiments the reactor vessel is inclined such that an input end of the reactor vessel is higher than an output end of the reactor vessel. 
         [0012]    Another aspect provides apparatus for thermal decomposition of biomass which includes an airlock upstream from a heated reactor vessel. A supply of syngas or producer gas is connected to supply syngas or producer gas into the airlock. In some embodiments the airlock includes a reciprocating piston that pushes the biomass along a channel into the reactor. The syngas or producer gas may be introduced into a chamber behind the piston. 
         [0013]    Introduction of syngas or producer gas may be coordinated with operation of the piston such that syngas is fed into the airlock when the piston is advancing. The coordination may be facilitated, for example, by an electronic controller (which may, for example comprise a programmable controller) controlling an electrically-controlled valve or by a mechanical system. 
         [0014]    In some embodiments the airlock comprises a pair of gate or flap valves that can be closed to define a chamber between them and syngas is introduced into the chamber. Introduction of the syngas may be coordinated with operation of the airlock such that the syngas is admitted into the chamber while the chamber is closed. In some embodiments a vacuum pump is connected to extract gases from the chamber. By a combination of applying vacuum and/or introducing syngas or producer gas into the chamber the air content of the chamber may be significantly reduced. The vacuum pump may deliver gases withdrawn from the chamber to a burner. 
         [0015]    Another aspect provides apparatus for thermal decomposition of biomass which includes an airlock upstream from a heated reactor vessel and a vacuum pump for removing air or other gases from the airlock. An outlet of the vacuum pump may communicate with a burner so that flammable gasses that pass through the vacuum pump are combusted before being released. A valve may be provided to control application of the vacuum to the airlock. In some embodiments, application of the vacuum is coordinated with operation of the airlock. For example, the airlock may comprise a chamber between a pair of valves for passing biomass. A controller, mechanical linkage or the like may cause application of the vacuum to the chamber while at least an inlet one of the valves is closed. For example, the vacuum may be applied for a few seconds after the inlet valve is closed. 
         [0016]    Other aspects of the invention provide methods for reducing biomass to char. Some such methods comprise passing biomass into a tubular reactor vessel that is heated by contact with hot gases surrounding the reactor. The method involves heating paddles or walls that project into the reactor by permitting the hot gases to enter chambers within the paddles or walls through openings. Some embodiments comprise rotating the tubular reactor and allowing the biomass to be moved through the tubular reactor at least in part by the force of gravity. In such embodiments the biomass may take a zig-zag path along the reactor as it spills over the puddles or walls. 
         [0017]    The example aspects described above may be combined with one another in any combinations to yield further aspects. The disclosure describes a large number of additional features. Further embodiments may be arrived at by combining such aspect with any one or any combination of the additional features described in this disclosure. Other aspects provide methods and apparatus which include novel combinations and sub-combinations of the features described in this disclosure. 
         [0018]    Further aspects and example embodiments are illustrated in the accompanying drawings and/or described in the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The accompanying drawings illustrate non-limiting example embodiments. 
           [0020]      FIG. 1  is a schematic drawing showing a biomass converter. 
           [0021]      FIG. 2  illustrates an example biomass dryer. 
           [0022]      FIGS. 3 and 4  show details of an exemplary airlock. 
           [0023]      FIG. 5  illustrates an example method admitting biomass into a reactor using an airlock. 
           [0024]      FIG. 6  shows a furnace having a reactor passing through the furnace. 
           [0025]      FIG. 7  illustrates a flow of biomass around the hollow walls of a reactor according to an example embodiment. 
           [0026]      FIG. 8  illustrates one possible cross-section of a reactor tube. 
           [0027]      FIGS. 9A and 9B  show example configurations for hollow walls in a reactor. 
           [0028]      FIG. 9A  illustrates a configuration where hollow walls are flat-topped.  FIG. 9B  illustrates a configuration where hollow walls have arcuate edges. 
           [0029]      FIG. 10  is a plan view of a trailer illustrating a possible arrangement of components of a biomass converter on the trailer. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. The following description of examples of the technology is not intended to be exhaustive or to limit the system to the precise forms of any example embodiment. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
         [0031]      FIG. 1  illustrates an example biomass processing system  10 . System  10  has a biomass supply  12  such as a hopper, chute, intake or the like which can supply into system  10  biomass of any suitable type. For example, biomass supply  12  may comprise a hopper or the like equipped with a conveyor or other feed mechanism for feeding biomass from biomass supply  12  into subsequent parts of apparatus  10 . Details of the feed mechanism may be varied to accommodate different types of biomass. Before feeding biomass into subsequent parts of the apparatus  10 , feedstock may be classified to eliminate stones, metal, glass and other material that do not thermally break down. In some embodiments, biomass is chopped, shredded, mulched, macerated or otherwise broken down into small pieces before entering system  10  or by a suitable apparatus provided as part of system  10 . 
         [0032]    In some embodiments, biomass supply  12  comprises a charge bin from which biomass is delivered by a conveyor, such as a screw auger. The conveyor may have a variable-speed control to permit the speed with which biomass is introduced into the rest of apparatus  10  to be adjusted and/or to permit the operation of the conveyor to be timed to coordinate with other aspects of the operation of apparatus  10 . 
         [0033]    Biomass from biomass supply  12  is fed into a dryer  14 . Dryer  14  reduces the moisture content of the biomass. The biomass is then fed through an airlock  16  into a reactor  18 . Reactor  18  heats the biomass in an oxygen-reduced atmosphere to reduce the biomass to char and volatile gases (sometimes called ‘producer gas’). The producer gas is given off as the biomass decomposes under the conditions within reactor  18 . The pressure within the reactor  18  is controlled in a manner that produces a positive pressure pushing the producer gas out of reactor  18 . Material exits reactor  18  into a separator  20  which separates solids (e.g. char) from the gases exiting reactor  18 . 
         [0034]    Solids may be received from separator  20  into a solids receptacle  21 . The solids may then be taken off to use for soil remediation or any other purpose to which they are suited. 
         [0035]    Gaseous materials exiting reactor  18  (e.g. producer gas) are taken off and may be used for various purposes. For example, the gaseous materials may be taken off by a gas handling system  22  which may generate a supply of syngas. The syngas may be used for a range of purposes including, for example, running motors to drive apparatus  10  or other apparatus, generating electrical power (for example by running an engine to drive a generator or generating steam to drive a turbine or other steam engine), feeding a burner to generate heat or the like. 
         [0036]    In the illustrated embodiment, gas handling system  22  provides syngas to an engine  24  that runs on the syngas and drives a generator  25  to generate electrical power. The electrical power may be used to power apparatus  10  and/or used for other applications. 
         [0037]    In some embodiments, as described more particularly below, some syngas from handling system  22  is directed into airlock  16  as indicated by line  22 A. The syngas helps to maintain an appropriate oxygen level within reactor  18  by one or a combination of steps assisting in purging air from incoming biomass and consuming oxygen within reactor  18 . 
         [0038]      FIG. 2  illustrates an example dryer  14 . Dryer  14  has an intake  32  which receives biomass from biomass supply  12 . Dryer  14  comprises an elongated cylindrical tube  33  containing paddles  35 . Paddles  35  are rotated about an axis of dryer tube  33  on a shaft  37  driven by a motor 38. Paddles  35  are angled so that, as they rotate they drive biomass along dryer tube  33  in direction  36 . In an example embodiment, dryer tube  33  is approximately 1½ to 2 meters long. Paddles  35  may, for example, be spaced apart by approximately 3 inches (7½ cm). Paddles  35  may, for example, be approximately 2 inches (5 cm) by 3 inches (7½ cm) in size. 
         [0039]    Hot gases from elsewhere in apparatus  10  flow along dryer tube  33 . The hot gases preferably flow in a direction  39  countercurrent to the direction  36  in which biomass is moved along dryer tube  33 . The hot gases may comprise, for example, one or more of: flue gas from a furnace (such as furnace  72  described below, for example); gas heated directly or indirectly from cooling products of reactor  18 ; exhaust gas from an engine or burner fueled by syngas or gas heated directly or indirectly from such exhaust gases; or the like. Exhaust stack  31  carries the heated mixture of gases that has passed through dryer tube  33  away. 
         [0040]    Dryer tube  33  exits into a conveyor  40  which carries the biomass to airlock  16  for delivery into reactor  18  downstream from the airlock. In the illustrated embodiment, biomass is gravity-assisted in passing through airlock  16  and conveyor  40  is an elevator that lifts the biomass to a height sufficient that the biomass can be fed into the top of airlock  16 . In the illustrated embodiment, conveyor  40  is made up of an endless chain  42  carrying paddles  43 . 
         [0041]      FIGS. 3 and 4  show details of an exemplary airlock  16 . Airlock  16  comprises dump valves  45 A and  45 B. Biomass can be allowed to enter a chamber  46  between dump valves  45 A and  45 B by opening dump valve  45 A while dump valve  45 B is closed. Dump valve  45 A may then be closed. One of dump valves  45 A and  45 B may be kept closed at all times such that there is never an open path for gases and heat to escape from the inlet end of reactor  18  to the atmosphere and also so that there is never an open path for air to flow unobstructed into the inlet end of reactor  18 . 
         [0042]    After biomass has been received into chamber  46  and dump valve  45 A has been closed, the biomass can be allowed to fall from chamber  46  into an injection chamber  47  by opening dump valve  45 B. A reciprocating piston  48  moving in a channel  49  delivers biomass from injection chamber  47  into reactor  18  by way of a valve  50  such as a flap valve. 
         [0043]    Biomass falls from injection chamber  47  into channel  49  which may, for example, comprise a cylinder that opens into injection chamber  47  through opening  51 . The biomass is then delivered along channel  49  and through flap valve  50  into reactor  18  by reciprocation of piston  48 . In a prototype embodiment, a feed tube which provides channel  49  has a diameter of approximately 3½ inches. 
         [0044]    Piston  48  is driven by a piston rod  53  which passes through a seal  54  in the end of channel  49 . Piston  48  may be driven in any suitable way, for example by a hydraulic actuator, an electric actuator, a pneumatic actuator, a crank, or the like. Where piston  48  is driven by an actuator, apparatus  10  may comprise a suitable controller to cause piston  48  to operate in a manner coordinated with the operation of the valves of airlock  16 . The controller may, for example, comprise a programmable controller that may also be connected to control other aspects of the operation of apparatus  10 . 
         [0045]    In some embodiments syngas is delivered to airlock  16 . The syngas may be admitted on regular intervals to airlock  16  by a solenoid valve that may be on a feed system timer, where the syngas is under operating pressure of a few psig and the airlock  16  is under atmospheric or vacuum pressure. The syngas can assist in maintaining appropriate conditions within reactor  18 . One process parameter that may be controlled by addition of syngas into airlock  16  is the oxygen content within reactor  18 . The syngas may be syngas generated from the biomass in reactor  18  that has been separated downstream. The syngas may be cooled prior to injecting it into airlock  16 . 
         [0046]    Syngas is optionally introduced into chamber  52  behind piston  48 . In the illustrated embodiment, syngas is admitted into chamber  52  by way of delivery line  55 . Delivery of syngas into chamber  52  may be timed to the operation of airlock  16  such that syngas is delivered into chamber  52  prior to and/or during the operation of piston  48  to push biomass into reactor  18 . When the syngas is not being delivered into chamber  52  it may be diverted to a burner (for example, a burner used to heat reactor  18 ). In the illustrated embodiment, the syngas may be delivered either into chamber  52  or diverted to a burner by way of a two-way valve  56 . 
         [0047]    In some embodiments syngas is optionally also injected into chamber  46 . In the illustrated embodiment, syngas is delivered into chamber  46  by way of a delivery line  57 . In the illustrated embodiment, the syngas may be delivered either into chamber  46  or diverted to the burner by way of a two-way valve  58 . Delivery of syngas into chamber  46  may be timed to the operation of airlock  16 . 
         [0048]    A vacuum line  59  may be provided to assist in removing air from chamber  46 . In the illustrated embodiment, vacuum line  59  is connected to a vacuum pump  59 A by way of a valve  59 B. Valve  59 B may be operated to withdraw gases from chamber  46 . Air may be purged from chamber  46  by admitting syngas by way of syngas line  57  while withdrawing gas by way of vacuum line  59 . 
         [0049]    In some embodiments a controller, mechanical linkage or the like may cause application of the vacuum to chamber  46  while at least inlet valve  45 A is closed. For example, the vacuum may be applied for a few seconds after inlet valve  45  is closed. In some embodiments, chamber  46  is purged of oxygen by introducing one or more of: syngas, flue gas, and/or a backflow of gases from reactor  18  into chamber  46  and/or injector chamber  47  prior to and/or during application of the vacuum to chamber  46 . 
         [0050]      FIG. 5  illustrates an example method  60  for operating airlock  16  to admit biomass into reactor  18 . Method  60  begins by opening dump valve  45 A to admit biomass into chamber  46  in block  62 . In block  64  a vacuum is applied to chamber  46 . Application of the vacuum draws out air from chamber  46 . In block  63 , syngas is injected into chamber  46 . Blocks  63  and  64  may overlap so that, for a period, syngas is being injected into chamber  46  while gas is being removed from chamber  46  by a vacuum system. Gases that are removed from chamber  46  by the vacuum system may be delivered to a burner. The combined effect of applying a vacuum to chamber  46  and introducing syngas into chamber  46  purges chamber  46  of air, and thereby significantly reduces the oxygen content of chamber  46 . 
         [0051]    In block  65 , dump valve  45 B is opened to allow the biomass contained within chamber  46  to fall into injection chamber  47 . In block  66 , piston  48  is advanced to drive biomass along channel  49 . The plug of biomass travelling along channel  49  pushes flap valve  50  open to allow the biomass to exit into reactor  18 . As this is occurring, additional syngas may be introduced into chamber  52  behind piston  48 . The introduction of the additional syngas prevents air from entering the system and also mixes syngas into the biomass being fed into reactor  18 . Oxidation of syngas in reactor  18  can further reduce the oxygen content within reactor  18 . In block  67  piston  48  is retracted. Blocks  66  and  67  may be repeated multiple times to deliver most or all of the biomass from chamber  47  into reactor  18 . 
         [0052]    In an example embodiment, upper dump valve  45 A opens and allows biomass to fall into chamber  46 . Upper dump valve  45 A is then automatically closed. Vacuum valve  59 B is then opened for a period of time sufficient to withdraw a significant amount of air out of chamber  46 . For example, valve  59 B may open for 15 seconds. Piston  48  is then moved to a fully retracted position and lower dump valve  45 B is opened to allow biomass to fall from chamber  46  into injection chamber  47 . Lower dump valve  45 B is then closed. Syngas valve  56  is then opened so that syngas is delivered to chamber  52  behind piston  48 . Piston  48  is then advanced toward reactor  18 . 
         [0053]    As piston  48  completes its travel, biomass being pushed in front of piston  48  through channel  49  is pushed into reactor tube  70  via flapper valve  50 . At the end of the stroke, syngas valve  56  is closed. Upper dump valve  45 A is then opened and simultaneously piston  48  is retracted back towards its fully retracted position. The cycle then repeats. 
         [0054]    As shown in  FIG. 6 , reactor  18  comprises a tube  70  that passes through a furnace  72 . Reactor tube  70  may, for example, have a diameter in the range of 25 to 75 cm. In the illustrated embodiment of  FIG. 6 , furnace  72  comprises two parts, a burner compartment  74  in which a fuel is burned to heat furnace  72  and an upper compartment  76  through which reactor tube  70  passes. 
         [0055]    The burner which heats the furnace  72  may burn any of a wide variety of fuels. For example, in some embodiments, the burner comprises one or more of a wood burner, a gas burner, an oil burner, or the like. The burner may burn solid fuels such as wood (in any suitable form, for example, logs, chips, shavings, sawdust, hog fuel, or pellets). In some embodiments, syngas is fed into the burner and at least some of the heat developed by the burner is developed by way of the combustion of syngas. 
         [0056]    Baffles  77  in upper compartment  76  cause hot gases from burner compartment  74  to make intimate contact with reactor tube  70  as they pass through upper chamber  76  to an outlet (not shown in  FIG. 6 ). In some preferred embodiments, the temperature in the reactor tube  70  may maintained in excess of 400° C. For example, the temperature in reactor tube  70  may be maintained in the range of 450 to 500° C. The operating pressure in reactor tube  70  may, for example, be approximately 35 to 50 kPa. The reactor temperature may be controlled by a temperature controller that is connected to a sensor monitoring the temperature of gases inside or exiting reactor tube  70 . The temperature controller may comprise, for example, a PID controller. The controller may, for example, control the temperature in reactor  70  by adjusting fuel and combustion air valves that control combustion in furnace  72  according to the deviation of temperature measured by the temperature sensor from a set point. In some embodiments, the hot gases exiting upper chamber  76  are carried from the outlet to dryer  14  where they pass countercurrent through dryer tube  33  to assist in drying the biomass passing through dryer tube  33 . 
         [0057]    Reactor tube  70  is inclined at a descending angle so that biomass which enters through flap valve  50  is carried down through reactor tube  70  by the action of gravity. Flap valve  50  acts as a check valve to prevent the backflow of gases from reactor  18  into feed channel  49 . 
         [0058]    The angle of inclination, θ, of reactor tube  70  may, for example, be on the order of 5 to 25 degrees. In a preferred embodiment, reactor tube  70  is sloped downward at a 20% (a one in five grade corresponding to an angle θ of approximately 11 degrees). Reactor tube  70  is rotated as the biomass passes through it. The rotation may be fairly slow. In one embodiment the reactor tube  70  rotates at a rate of less than 2 rpm. For example in one embodiment reactor tube  70  rotates at approximately ½ rpm. 
         [0059]    The rotation of reactor tube  70  causes the biomass to tumble as it passes through the reactor tube. In the illustrated embodiment, rotation of reactor tube  70  is driven by a drive system  78  (not shown). Drive system  78  may, for example, comprise an electric motor and a speed-reducing transmission. The transmission may comprise one or more of a chain drive, gear reducer, gear drive, roller drive or the like, for example. The length of reactor tube  70  may vary depending on the diameter of tube  70  and the resistance time of biomass inside reactor tube  70 , which in turn is dependent on the feed rate of biomass into reactor  18 . More biomass input feed per unit time would require a reactor tube  70  having a larger diameter and/or a faster turning speed to ensure the biomass feed is relatively spread evenly for efficient heating. In some preferred embodiments, the residence time of biomass inside reactor tube  70  is, at least 15 minutes. For example, the residence time may be in the range of 20 to 25 minutes. 
         [0060]    Reactor tube  70  has walls  79  that project into its interior. Each wall  79  is hollow and has at least one opening  80  which opens into the interior of furnace  72 . Hot gases from furnace  72  can enter openings  80  and heat walls  79  from the inside. Walls  79  in some embodiments are spaced a apart and are arranged in an alternating pattern while projecting into the interior of reactor tube  70 . Walls  79  may, for example, be spaced apart from one another by 6 inches (15 cm) in the direction along the longitudinal axis of reactor  70 . In some embodiments, walls  79  are unequally spaced apart along the longitudinal axis of reactor  70 . In particular, it can be advantageous for walls  79  to be spaced farther apart near the entrance of reactor  70  and to be spaced more closely toward the exit from reactor  70 . Near the entrance to reactor  70  entering biomass may have a moisture content high enough to make the biomass tend to stick together so that it flows over walls  79  with more difficulty than the drier biomass found closer to the exit from reactor  70 . Providing more widely-spaced walls  79  near to the entrance to reactor  70  facilitates passage of the biomass along the initial part of reactor  70 . 
         [0061]    Some or all of walls  79  in some embodiments each project slightly more than half of the diameter of reactor tube  70  into reactor tube  70  and, in some embodiments extend at least 20% of their overall height past the centerline of reactor tube  70  (see e.g.  FIGS. 9A and 9B ). Thus, as viewed, looking along the length of reactor tube  70  from one end, walls  79  overlap with one another along the longitudinal centerline of reactor tube  70 . In some embodiments, walls  79  may be perpendicular to the centerline of reactor tube  70  or tilted on an angle. 
         [0062]    In some embodiments, walls  79  may be on opposite sides of reactor tube  70  or may have a more offset arrangement. In some embodiments, walls  79  are non-planar. For example, walls  79  may be curved about axes of curvature that extend transverse to reactor tube  70 . In such embodiments the curvature may be such that center portions of walls  79  project toward the upstream or downstream end of reactor tube  70 . 
         [0063]    Heated walls  79  both transfer heat into biomass passing through reactor tube  70  and act as mechanical lifts which mix and separate the biomass as it passes through the rotating reactor tube  70 . Heated walls  79  may be, for example, approximately 1½ to 3 centimeters in thickness. 
         [0064]      FIG. 7  illustrates how walls  79 , in one embodiment, cause biomass within reactor tube  70  to follow a sinuous path  71  as reactor tube  70  rotates and the biomass spills over one wall  79  to be caught by the next wall  79  as the biomass makes its way downward along reactor tube  70 . 
         [0065]      FIG. 8  shows a possible cross-section of a reactor tube  70  and illustrates how walls  79  projecting inwardly from opposing sides of reactor tube  70  may overlap with one another. 
         [0066]    As illustrated in  FIGS. 9A and 9B , hollow walls  79  may have various configurations.  FIG. 9A  illustrates a configuration where hollow walls  79  are flat-topped. In some embodiments, the cross section of the top edge of hollow walls  79  may be rounded, square, or may take other shapes. In some preferred embodiments, the edges of hollow walls  79  are arcuate.  FIG. 9B  illustrates a configuration where hollow walls  79  have arcuate edges projecting into the interior of reactor tube  70 . In the embodiment of  FIG. 9B , arcuate edges  82  have a radius of curvature similar to that of reactor tube  70 . In this example embodiment, the areas of overlap between hollow walls  79  projecting from opposing sides of reactor tube  70  are lenticular-shaped when viewed end-on (i.e. along the longitudinal center line of reactor tube  70 ). 
         [0067]    Reactor tube  70  may be sealed at its ends to prevent the ingress of air. In an example embodiment, the upper end of reactor tube  70  is sealed by an annular packing attached to a tube through which channel  49  extends. The packing seals against the inside of reactor tube  70  while allowing rotation of reactor tube  70 . Tube support rollers may be attached to the packing or to a separate support to permit smooth rotation of reactor tube  70 . The lower end of reactor tube  70  may be sealed to a non-rotating reactor receiver by a packing gland which bears against the external surface of reactor tube  70 . In some embodiments, reactor tube  70  may be tapered so it becomes larger towards the outlet of reactor tube  70 . 
         [0068]    In some embodiments, a grinder is provided at the output of reactor tube  70 . The grinder may grind chunks of charcoal produced by the pyrolisis of biomass in reactor tube  70  into smaller granular particles. In some embodiments the particles are smaller than about 0.5 cm. The particles may, for example, have diameters in the range of 0.1 to 0.3 cm. The particles are then separated from the gases exiting reactor  18  in separator  20 . 
         [0069]    In some embodiments, separator  20  comprises a cyclone separator. Superheated steam may be injected at a base of a riser in the separator to assist in lifting and spinning particles within the separator such that solids are separated from gases exiting reactor  18 . 
         [0070]    An airlock, such as a rotary airlock, may be provided to receive and pass solid particles separated by the cyclone separator without providing an opening through which significant amounts of gases can escape. The particles may optionally be cooled by a fine water mist or the like as they pass through the exit of the airlock on their way into solids receptacle  21 . 
         [0071]    Gas handling system  22  may treat the gases passed by separator  20  in any of a wide range of ways. In some embodiments, the gases are treated to crack heavy fractions (e.g. tars), cooled and filtered. For example, gas handling system  22  may comprise catalytic decomposition stages in which fractions of the producer gas from reactor  18  are decomposed catalytically. In such embodiments, a reheater may reheat the producer gas from approximately 400° C. to approximately 700° C. prior to passing the heated producer gas into a catalyst vessel. 
         [0072]    The catalyst vessel contains a catalyst for assisting in the catalytic decomposition of tar molecules. The catalyst may, for example, comprise a mixture containing charcoal and/or dolomite. Superheated steam may optionally be injected into the producer gas in or just upstream from the catalyst vessel. The steam assists in the catalytic decomposition of heavier molecules in the syngas. 
         [0073]    In an example embodiment a steam generator cools syngas exiting the catalyst vessel and, at the same time, produces saturated steam. The saturated steam may be heated in a steam superheater, which may be located, for example, in the burner section of furnace  72 . The superheater may, for example, heat the steam from approximately 140° C. to approximately 400° C. 
         [0074]    Syngas exiting the steam generator may be further cooled to ambient temperature or near ambient temperature by a syngas-to-air heat exchanger. The air side of the heat exchanger may be cooled by a forced air draft. The cooled syngas may be filtered to remove entrained dust or other particulates. The filtered and cooled syngas may then be supplied to drive an engine or to fuel a burner or the like. In some embodiments, an engine driven by combustion of the syngas directly drives motion of various components of apparatus  10 . In other embodiments electricity generated by a syngas-driven generator is used to drive motion of some or all components of apparatus  10 . In other embodiments steam generated in cooling syngas and/or burning syngas is used to drive motion of some or all components of apparatus  10 . 
         [0075]    Air heated by the cooling of syngas in the syngas-to-air heat exchanger may be used to provide a supply of heated air to one or more of: the main burner of furnace  72 ; biomass dryer  14 ; and a flare stack in which any surplus syngas may be burned off safely. 
         [0076]    One advantage of apparatus as described herein is that some embodiments may be dimensioned and arranged so that a biomass processing apparatus as described herein may be provided on a single trailer. This can be convenient as the trailer may be taken to a farm or other area where biomass is present and the biomass may be processed at that location. This is particularly convenient in the case where it is desired to use char produced by the apparatus at the same location. For example, straw from a field on a farm, corn husks and stalks or other vegetable matter may be processed in apparatus  10  to yield char which may then be integrated into the soil at the farm. The apparatus  10  may be then taken to another location. 
         [0077]    One possible arrangement for the components of apparatus  10  on a trailer  100  is illustrated in  FIG. 10 . Reference numbers in  FIG. 10  are the same as the reference numbers used above for components and assemblies of similar function. Details of construction of any of these components and assemblies may be but are not necessarily the same as are shown in the other drawings. 
         [0078]      FIG. 10  also shows a line  101  carrying producer gas to destinations including a flare  102 , furnace  72  and a gas heater  104 . Gas heated by gas heater  104  is carried by line  106  to a catalytic reactor  108 , a gas cooler  110 , a gas chiller  112  and a gas filter  114 . Gas filtered by filter  114  may be supplied as fuel for an engine or burner or taken off for some other use. 
         [0079]      FIG. 10  also shows an air line  120  carrying air that has been pre-heated by gas chiller  112  to furnace  72  and drier  14  and a line  122  carrying flue gas from furnace  72  to drier  14 . 
       INTERPRETATION OF TERMS 
       [0080]    Unless the context clearly requires otherwise, throughout the description and the claims:
       “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.   “connected,” “coupled,” or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof.   “herein,” “above,” “below,” and words of similar import, when used to describe this specification shall refer to this specification as a whole and not to any particular portions of this specification.   “or,” in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.   the singular forms “a”, “an” and “the” also include the meaning of any appropriate plural forms.       
 
         [0086]    Words that indicate directions such as “vertical”, “transverse”, “horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”, “outward”, “vertical”, “transverse”, “left”, “right”, “front”, “back”, “top”, “bottom”, “below”, “above”, “under”, and the like, used in this description and any accompanying claims (where present) depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly. 
         [0087]    While processes or blocks are presented in a given order, alternative examples may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified to provide alternative or subcombinations. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed simultaneously or in different sequences or at different times. 
         [0088]    Where a component (e.g. an assembly, device, member, controller, valve, tube, motor, filter etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention. 
         [0089]    Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments. 
         [0090]    It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, omissions and sub-combinations as may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.