Abstract:
A method for torrefaction of lignocellulosic biomass comprising: continuously feeding the biomass to an upper inlet to the torrefaction reactor vessel such that the biomass material is deposited on an upper tray assembly of tray assemblies stacked vertically within the reactor; as the biomass moves over each tray assembly, heating and drying the biomass material with a non-oxidizing gas under a pressure of at least 3 bar gauge and at a temperature of at least 200° C.; cascading the biomass down through the trays by passing the biomass through an opening in each of the trays to deposit the biomass on the tray of the next lower tray assembly; discharging torrefied biomass from a lower outlet of the torrefaction reactor, and circulating gas extracted from the reactor vessel back to the reactor.

Description:
CROSS RELATED APPLICATION 
       [0001]    This applications claims priority to U.S. Provisional Patent Application Ser. No. 61/501,900 filed Jun. 28, 2011 and is related to U.S. Provisional Patent Application Ser. No. 61/502,116 filed Jun. 28, 2011. The entirety of these applications are incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention generally relates to methods for torrefaction of biomass material such as lignocellulosic material including wood and other biomass, and more particularly relates to a pressurized reactor vessel for the torrefaction of such material. 
         [0003]    Torrefaction can be used to convert biomass, e.g., wood, to an efficient fuel having increased energy density relative to the input biomass. For example, wood generally contains hemicellulose, cellulose and lignin. Torrefaction removes organic volatile components from wood. Torrefaction may also depolymerize the long polysaccharide chains of the hemicellulose portion of biomass and produce a hydrophobic solid combustible fuel product with an increased energy density (on a mass basis) and improved grindability. Because torrefaction changes the chemical structure of the biomass, torrefied biomass may be burned in coal fired facilities (torrefied wood or biomass has the characteristics that resemble those of low rank coals) and can be compacted to high grade fuel pellets. 
         [0004]    Torrefaction refers to the thermal treatment of biomass, usually in an oxygen deprived atmosphere at relatively low temperatures of 200 degrees Celsius (° C.) to 400° C., or 200° C. to 350° C., or temperatures outside the range used for the process known as pyrolysis. An oxygen deprived atmosphere may have a low percentage of oxygen as compared to the percentage of oxygen in atmospheric air. A torrefaction process is described in related U.S. Provisional Patent Application Ser. No. 61/235,114. 
         [0005]    Unpressurized reactor vessels with multiple trays have been used for torrefaction, as is described in U.S. Patent Application Publication 2010/0083530 (the &#39;530 application). The &#39;530 application states that torrefaction should be performed in a reactor vessel operating at atmospheric pressure. By stating that it is advantageous to operate the vessel at atmospheric pressure, the &#39;530 application teaches that vessels should not be operated at above-atmospheric pressures. See &#39;530 application, para. 0061. 
         [0006]    Pressurized reactor vessels with multiple trays have been used in pulp mills to delignify pulp by oxidation. Examples of a pulping reactor vessel with multiple trays are disclosed in U.S. Pat. Nos. 3,742,735 (&#39;735 patent) and 3,660,225 (&#39;225 patent). Multiple tray vessels allow pulp to cascade through the vertical arrangement trays in the reactor. The trays allow the pulp to cascade in discrete batches down through the vessel. An oxygen rich environment in the pulping reactor promotes delignification and bleaching of the pulp. The &#39;735 patent and &#39;225 patent do not suggest using a pulping reactor vessel having an oxygen deprived environment for torrefaction of wood or other biomass material. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0007]    A difficulty with unpressurized reaction vessels is their large size needed to handle the large volume of gas required to transfer a given amount of heat to the material to be torrefied. The mass of a gas per unit volume at atmospheric pressure is substantially less than the mass of gas per unit volume at a substantial pressure, such as above 20 bar gauge (290 psig). The volumetric flow rate of the gas impacts the pressure drop in the bed of material, piping, heat exchangers, and thus requires larger equipment and higher energy consumption to perform the same heating duty. 
         [0008]    Pressurizing the gas increases the mass of the gas for a given volumetric flow rate. As compared to an unpressurized vessel, a pressurized reaction vessel may have a smaller volume due to the use of compressed gas. The ability of a gas to transfer heat to a biomass is proportional to the mass of the gas. The greater its mass, the faster a gas can heat the biomass. 
         [0009]    As is well known in the art, pressurized reaction vessels require seals and other devices to keep the gas and materials in the vessel under pressure. Similarly, pressure transfer devices are required at the input to or in the feed systems for a pressurized vessel to pressurize the material being fed to the vessel. Further, pressurized reaction vessels require pressurized gases and conduits for the pressurized gases. 
         [0010]    A novel reaction vessel has been conceived for torrefaction of biomass material having vertically stacked trays for drying and heating biomass using an oxygen deprived hot gas under substantial pressure. The stacked trays provide what amounts to as a moving bed for the biomass, in a relatively compact vertical reactor vessel. In addition, the vessel may be substantially smaller than a reaction vessel for torrefaction performed at atmospheric pressure. The oxygen deprived pressurized gas may be circulated through the vessel and through pressurized conduits that reheat the gas. 
         [0011]    The vessel uniformly heats through each tray such that the material being torrefied is uniformly heated at each elevation in the vessel. To achieve uniform heating of the material on each tray the flow of oxygen deprived gas through the bed of material on each tray is regulated in a range of 1 to 6 kilograms (kg) of gas per kilogram of dry material being treated on the tray. The ratio of flowing oxygen deprived gas to dry material through the bed of material on each tray may be in another range, such as a range of 1 to 3. 
         [0012]    The flow of the oxygen deprived gas through each of the trays may be continuous. The oxygen deprived gas is need not be totally devoid of oxygen. The gas is a heat transfer media that may add or remove heat from the material undergoing torrefaction. The gas flows through the material and the trays. The continuous flow of oxygen deprived gas through the material in the tray heats the material, provided that the gas is at a higher temperature than the material. The constant flow of gas may also cool the material where the torrefaction reaction, which is exothermic, causes the material to become hotter than the gas. If the material overheats, the torrefaction reaction may over-react. Accordingly, the continuous flow of gas regulates the temperature of the material in each tray to be about the same temperature as the gas. 
         [0013]    The biomass material may have a total retention period for all of the trays in the reactor vessel of 15 to 60 minutes. This retention period may include trays in which the material undergoes torrefaction and lower trays in which the material is cooled after the reaction. The retention period in the reaction vessel may be selected based on the material processed in the vessel. For example, the total retention period in the vessel may be to 25 minutes for lignocellulose material, such as wood. 
         [0014]    Each tray may have a pie-segment shaped opening through which biomass material falls to the tray at the next lower elevation in the vessel. The biomass material falls through the opening after traveling around the vessel and on the tray. A scraper may slide the material over the tray toward the opening. The rotational speed of the scraper is selected to provide the desired retention period on each tray. The retention period may be uniform for each of the trays in the vessel. The retention period may be selected based on the number of trays performing each of drying, torrefaction and cooling (optionally) of the biomass, and the period required to perform each of these processes. 
         [0015]    A method has been conceived for torrefaction of biomass using a torrefaction reactor vessel having stacked trays including: feeding the biomass to an upper inlet of the vessel such that the biomass material is deposited on an upper tray of a vertical stack of trays in the reactor; as the biomass moves around the vessel on each of the stacked trays, heating and drying the biomass material with an oxygen deprived gas injected into the vessel under a pressure of 3 to 20 bar; cascading the biomass down through the trays by passing the biomass through an opening in each of the trays to deposit the biomass on a lower tray; discharging torrefied biomass from a lower outlet of the torrefaction reactor vessel, and circulating extracted gas from a lower elevation of the reactor and feeding the gas to an upper region of the vessel. 
         [0016]    The oxygen deprived gas may include superheated steam, nitrogen and other non-oxygen gases, or oxygen lean gases suitable for the purpose of this invention. The biomass may be pressurized before being fed to the vessel with a pressure transfer device. The trays may be a mesh, screen or have perforations or slots and the heating and drying of the biomass includes passing the gas through the biomass and the trays. A scraper device may rotate to move the biomass material across the tray in an arch-shaped path. Alternatively, the trays may rotate while the scraper device and biomass do not rotate about the vessel. The opening in each tray may be a triangular shaped section extending from the shaft in the vessel to the wall of the vessel. 
         [0017]    The gas may be injected into the vessel at multiple elevations wherein the gas is hotter when injected at a lower elevation than the gas injected at an upper elevation. At an elevation of the vessel below from which the gas is extracted, the biomass may continue to cascade down through the trays. 
         [0018]    A method for torrefaction of lignocellulosic biomass using a torrefaction reactor vessel having stacked tray assemblies has been conceived comprising: continuously feeding the biomass to an upper inlet to the torrefaction reactor vessel such that the biomass material is deposited on an upper tray assembly of a plurality of tray assemblies stacked vertically within the reactor; as the biomass moves in the vessel while supported by a tray of each tray assembly, heating and drying the biomass material with a gas injected into the vessel, wherein the gas is substantially non-oxidizing of the biomass and is under a pressure of at least 3 bar gauge and at least a temperature in a range of 200° C. to 250° C., and cascading the biomass down through the trays by passing the biomass through an opening in each of the trays to deposit the biomass on the tray of the next lower tray assembly; discharging torrefied biomass from a lower outlet of the torrefaction reactor, and circulating gas extracted from the reactor vessel back to the reactor. 
         [0019]    The trays of each of the tray assemblies have a mesh, screen or have perforations, and the heating and drying of the biomass includes passing the gas through the biomass and the trays. Any holes or openings in the tray assemblies may be cover by a finer mesh or screen material than the material used to form the tray assemblies. The gas entering each tray assembly may pass through a pipe at substantially a similar elevation as an extraction pipe which extracts gases from an immediately above tray assembly. In addition, each tray assembly may include a rotating scraper device above the tray and an extraction gas chamber below the tray. 
         [0020]    The gas injected into tray assemblies for torrefaction may be hotter, e.g., by 5 to 60° C., than the gas injected to the tray assemblies for drying or cooling. Further, a void space, below all of the tray assemblies, in the bottom of the vessel may be a zone in which the biomass forms a pile. The void space may be used to complete the torrefaction of the biomass and cool the torrefied biomass before it is discharged from the vessel. The cooling gas injected into the cooling zone may be cooler than the gas injected to the cooling tray assemblies, wherein the cooling zone cools the torrefied biomass to below a temperature at which the biomass auto-combusts when exposed to the atmosphere and the cooling tray assemblies cool the torrefied biomass to stop or suppress the torrefaction reaction. It is possible for gas flows in the void to flow concurrent or countercurrent to the flow of the biomass material. 
         [0021]    Gases extracted from the tray assemblies and the cooing zone may be circulated back to the vessel by blowers or compressors. The gases to be circulated may pass through a cyclone, condenser or filter to separate particles and condensable byproducts before the gas flows to the compressor or blower. The gases circulated back to the torrefaction tray assemblies may be heated before being injected to the torrefaction tray assemblies. A portion of the gases extracted from the tray assemblies may be directed to a combustor to generate heat energy to be added to the gases circulated back to the torrefaction tray assemblies, or for other process steps. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a perspective view of the front and top of a pressurized reactor treatment vessel in which the front wall of the vessel has been removed to allow for illustration of the interior components of the vessel. 
           [0023]      FIG. 2  is a perspective view of the front and bottom of a pressurized reactor treatment vessel in which the front wall of the vessel has been removed to allow for illustration of the interior components of the vessel. 
           [0024]      FIG. 3  is a perspective view of a lower region of the pressurized reactor treatment vessel which illustrates the support legs and bottom discharge outlet of the vessel, and shows the convergence section in the interior of the vessel. 
           [0025]      FIG. 4  is a bottom-up view of the pressurized reactor treatment vessel. 
           [0026]      FIG. 5  is a side view of the pressurized reactor treatment vessel, with a quarter section of the vessel removed for purposes of illustration. 
           [0027]      FIG. 6  is a perspective view of the top and side of the pressurized reactor treatment vessel with a quarter-section of the vessel removed for purposes of illustration. 
           [0028]      FIG. 7  is a close-up view of a cross-section of a portion of the pressurized reactor treatment vessel that illustrates a portion of tray assemblies. 
           [0029]      FIG. 8  perspective view of an open top of the pressurized treatment vessel wherein the outer wall of the vessel is removed to illustrate the components of the tray assemblies. 
           [0030]      FIG. 9  is a top down view of an open top of the pressurized treatment vessel. 
           [0031]      FIG. 10  is a cross-sectional view of a portion of the pressurized treatment vessel which illustrates the vertical shaft and the lower support for the shaft. 
           [0032]      FIG. 11  is a perspective view of a spoke wheel scraper component of a tray assembly. 
           [0033]      FIG. 11A  is a schematic diagram of an enlarged portion of the lower edge of one of the spokes or blades  60  of the scraper device. 
           [0034]      FIG. 12  is a perspective view of a tray and bottom plate of a tray assembly. 
           [0035]      FIG. 13  is a perspective view of the convergence section of the pressurized reactor vessel. 
           [0036]      FIG. 14  is an enlarged view of the convergence section to show the screen allowing gas to be extracted from the section. 
           [0037]      FIG. 15  is a schematic diagram of a tray assembly to illustrate the gas flowing in and gas flowing out of the biomass on the tray. 
           [0038]      FIG. 15A  is an enlarged view of a cross-section of a tray to illustrate an exemplary slot, hole or opening in the tray. 
           [0039]      FIGS. 16 to 18  are process flow diagrams showing exemplary torrefaction processes using the pressurized reactor treatment vessel. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]      FIGS. 1 and 2  illustrate a pressurized treatment vessel  10  for receiving, treating, drying and cooling biomass material from a supply of biomass  12  through an upper inlet  14 . The biomass may be wood chips, wood pulp or other comminuted cellulosic material. While moving over an upper series of drying tray assemblies  16  in the vessel, the biomass is dried. In addition or alternatively, the biomass may be dried prior to being introduced into the vessel  10 . 
         [0041]    The upper inlet  14  to the pressurized vessel may be coupled to a continuous feed, pressure isolation device, such as a conventional rotary valve or plug screw feeder, to feed the biomass into the pressurized vessel from a source of biomass at atmospheric pressure. The vessel  10  operates in a gas phase in which the dried biomass remains dry in the vessel. 
         [0042]    The biomass may be fed to the inlet  14  to the vessel at a temperature of ambient temperature or, if a dryer  21  preheats the biomass, at 80° C. to 120° C., or higher, before entering the vessel. The biomass is heated in the vessel by a pressurized, hot and oxygen starved or deprived gas. The gases entering the vessel may be at a temperature in a range of 200° C. to 600° C. and may particularly be in any of the ranges of 250° C. to 400° C., 250° C. to 300° C., and 300° C. to 380° C. 
         [0043]    The biomass enters the pressure treatment vessel through the upper inlet  14 , which may be a single inlet orifice or an array of inlet orifices in the top or upper portion of the vessel. The biomass may have been previously dried before entering the vessel or the biomass may be dried in an optional drying zone (trays)  15  in an upper region of the vessel. Below the drying zone, the biomass enters a torrefaction zone  41  (trays and optionally a chamber below the trays). 
         [0044]    Immediately below the upper inlet in the vessel  10  may be a chute that receives the biomass from the inlet and directs the biomass to a trailing section portion of the upper tray of a drying tray assembly  16 . The trailing section is adjacent a discharge opening  64  ( FIG. 12 ) in the upper tray. The biomass falls on the trailing section of the tray and is moved in an arc path across the tray until the biomass passes over leading edge of the opening to the tray and falls to the trailing section of the next lower tray. The trailing section is a region of the tray furthermost from the opening in the tray with respect to the path of the biomass on the tray. Depositing the biomass on the trailing section of the tray ensures that biomass entering the vessel is retained on the upper tray for nearly a full rotational period of the tray. 
         [0045]    The open sections  64  (also referred to as “openings”) of each tray preferably are not vertically aligned with the openings  64  in the trays immediately above and below the tray. If the openings were vertically aligned, the biomass may fall from one open section and immediately through the open section in the underlying tray without resting on the support surface of the underlying tray. 
         [0046]    The opening sections  64  may be vertically staggered such that each opening is over a trailing region of the upper section of the tray immediately below the opening. The trailing region of a tray is adjacent and behind the open section in the direction of rotation of the scraper device  56 . By aligning an open section  64  above a trailing region on a lower tray, the biomass falls through the open section and onto the trailing region. As the scraper turns, the biomass slides across the entire upper surface of the tray in an arc-shaped path from the trailing region to the opening section. Maintaining the biomass on the upper surface of each tray maximizes the retention period of the biomass on tray and, thus, allows the biomass to be heated and dried (in an upper tray and undergo torrefaction (in a lower tray). 
         [0047]    Immediately below the optional drying tray assembly(ies)  16  are arranged one or more torrefaction tray assemblies  18  on which the dried biomass material is subjected to conditions which cause the torrefaction reaction. Below the torrefaction tray assemblies are arranged optional cooling tray assembly(ies)  20 . The structure of each of the tray assemblies  16 ,  18  and  20  may be substantially similar. Each tray assembly is effectively a moving bed on which the biomass is exposed to a flow of the oxygen deprived gas. 
         [0048]    The flow of heated gas into, through and from the pressure reaction vessel may be configured to promote the flow of hot, pressurized gases through the tray assemblies in the upper elevations of the vessel where the biomass is being heated to the desired temperature for torrefaction. As shown in  FIG. 1 , the hot oxygen deprived gas may be injected into the upper section of the vessel  10  through a top input manifold  86  and gas injection nozzles  34  arranged at the various elevations of the tray assemblies  16 ,  18  and  20  in the upper portion of the vessel. 
         [0049]    The oxygen deprived gases flowing to multiple elevations in the vessel may be at temperatures and compositions that vary for each of the tray assemblies. For example, the hot gas  86  introduced to the uppermost elevation of the vessel may be at a temperature slightly, e.g., 10° C. to 40° C., hotter than the temperature, e.g., 100° C., of the dried biomass  12  being fed to the vessel. The hot gases introduced at succeeding lower elevations of the vessel may be increasingly hotter to be slightly above the temperature of the biomass in the vessel that is proximate to the injected hot gas. By injecting the gas at temperatures slightly above the biomass being heated by the gas, the efficiency of heating can be increased as compared to injecting gas at a single temperature which may be substantially hotter than the incoming biomass to the vessel. Alternatively, the gases injected for drying and torrefaction may be at substantially similar temperatures and compositions, and the gases for cooling the biomass may be recirculated gases extracted from other cooler elevations in the vessel. For example the exhaust gas from the drying trays will be cooler than that from the torrefaction levels and will be below temperatures required for torrefaction. 
         [0050]    The number of tray assemblies for drying, torrefaction and cooling may depend on various factors, including whether an optional drying device  21  is used to dry the biomass before the material enters the vessel  10 , and the extent to which the torrefaction and cooling zones  22 ,  24  or cooling screw  68  ( FIG. 16 ) are able to cool the biomass from a temperature at which the torrefaction reaction occurs to a lower temperature at which torrefaction is quenched. 
         [0051]    By way of example, the total number of tray assemblies may be a number (N) and in a range of 5 to 15. The number of drying tray assemblies  16  (DTA) may be zero, one (such as shown in  FIG. 16 ) or determined based on the following algorithm: 
         [0000]      DTA= N*L , where  L  is in a range of 0.2 to 0.3. 
         [0052]    The number of cooling tray assemblies  20  (CTA), if any, may be two, such as is shown in  FIG. 16 , or determined based on the following algorithm: 
         [0000]      CTA= N −( N*M ), where  M  is in a range of 0.7 to 0.8.
 
         [0053]    The number of torrefaction tray assemblies  16  (TTA) may be greater than each of DTA and CTA, such as the four TTAs shown in  FIG. 16 , or determined based on the following algorithm: 
         [0000]      TTA=(( N*L )+1)−(( N*M )−1)
 
         [0054]    The number of tray assemblies in a vessel and the proportions of drying, torrefaction and cooling tray assemblies will depend on the design requirements for the vessel. For example, the total number of tray assemblies in the vessel  10  may be in any of the ranges of 4 to 20 and 6 to 15. The proportion of drying tray assemblies and of cooling tray assemblies may each be in a range of 15 to 30 percent (%) of the total number of tray assemblies. The proportion of tray assemblies for torrefaction may be in a range of 70 to 40% of the total number of tray assemblies. These ranges are exemplary and do not define limits on the numbers of tray assemblies. For example, the vessel may have no drying tray assemblies and no cooling tray assemblies, and have all tray assemblies for torrefaction. 
         [0055]    The torrefaction reaction may occur in the middle tray assemblies. The ranges of the middle tray assemblies where torrefaction occurs may be any of 15 to 85%, 30 to 60% and 15 to 100% of the total number of tray assemblies. Where torrefaction occurs is most or all of the tray assemblies, the drying of the biomass may occur fully or partially in a dryer external to and upstream of the vessel, and the optional cooling may occur in the pile of the torrefied biomass in a lower region of the vessel or in a cooling screw near the discharge of the vessel. 
         [0056]    The inlet nozzles and extraction nozzles are numbered in  FIG. 16  according to their corresponding tray assemblies. The top tray assembly  16  receives hot oxygen deprived gas from the top inlet  86  that receives gas from a heat exchanger  84  or from gases extracted from the cooling tray assembly or zone of the vessel  10 . 
         [0057]    The supply of biomass  12  may provide, such as lignocellulose material that has been chipped or cut to have chip dimensions of a length between 10 to 50 millimeters (mm), a width of 10 to 50 mm, and a thickness of 5 to 20 mm. The chip thickness may be in other ranges, such as 20 to 30 mm, 15 to 25 mm, and 3 to 10 mm. These chip dimensions may be most suitable for wood. Other chip dimensions may be suitable depending on the type of wood or the non-wood material being used for the biomass. 
         [0058]    Below the stack of tray assemblies  16 ,  18  and  20 , the vessel  10  may have a torrefaction zone  22  and an optional lower cooling zone  24 . The torrefaction zone  22  and lower cooling zone  24  may be hollow regions of the pressure reactor vessel below the lowest tray  20  and may span the lower one-half or lower two-thirds of the height of the pressure vessel. The pressure vessel may have dimensions, such as diameter and height, based on the desired operational conditions, such as the composition of the biomass material and the volumetric rate of biomass to flow through the vessel. In general, for industrial scale units, the pressure vessel may have a height of over 100 feet (33 meters) and a diameter of over 9 feet (3 meters). 
         [0059]    The lower cooling zone  24  of the pressure reactor vessel may include a convergence section, such as one-dimensional convergence, to provide uniform movement of the biomass through the bottom of the vessel and to a bottom discharge port  26 . The convergence section may be a DIAMONDBACK® convergence section sold by the Andritz Group and described in U.S. Pat. Nos. 5,500,083; 5,617,975 and 5,628,873. 
         [0060]    The lower zone  24  of the pressure reactor vessel may be maintained at a cooler temperature than the tray assemblies used for torrefaction. The lower zone  24  may contain a pile of torrefied biomass material which has been treated in the tray assemblies and drop down into the lower zone. 
         [0061]    The temperature in the lower zone  24  may be below 265° C., 240° C. or 200° C., in addition or alternatively, the temperature in the lower zone  24  may be at least 15° C. to 40° C. lower than the maximum temperature of the hot gases entering the torrefaction tray assemblies. To control and maintain the temperature in the lower zone cooling gas may be inject to the upper section of the lower zone such as into the injection nozzle  92  ( FIG. 16 ) to provide cooling gas the flows concurrently with the downward flow of biomass through the reactor vessel. It may also be desirable for these gases to flow counter-currently to the flow of the biomass, displacing the hot contaminated gas entering with the biomass toward the top of the pile. Alternatively, cooling gas may be injected in to a bottom portion of the lower region through nozzles  94 , which nozzles may be part of a center pipe extending upwardly and axially through the vessel. The cooling gas entering through nozzles  94  flows cross-currently to the biomass flow. Further, cooling gas nozzles  94  may be arranged to provide a cross-current gas flow through the vessel such that gas is injected at one side of the vessel and extracted at an opposite side of the vessel. The injection and extraction of cooling gases may occur at several elevations of the lower zone  24 . The temperature of the cooling gases injected into the cooling tray assemblies and cooling zone may be controlled such that the cooler cooling gasses enter lower elevations of the vessel. The torrefied biomass material should be at a temperature below that which the material with auto-combusted at the bottom of the vessel or at least when passed through a pressure transition device after which the biomass is exposed to the atmosphere. 
         [0062]    As shown in  FIGS. 3 and 4 , the pressure reactor vessel may be supported by support legs  28  extending vertically between the vessel and the ground. The support legs elevate the bottom of the vessel to allow for discharge devices to be mounted to the discharge port  26  and below the vessel. Alternative support structures may include a skirt arrangement or use of a support ring located at some mid-point on the vessel above the DIAMONDBACK® convergence section. Such as support ring would then be attached to the building structure in some appropriate fashion. 
         [0063]    The pressure vessel  10  may have an access and observation port  30  which, when open, provides access to the cooling and convergence zones of the vessel. The access and observation port is generally closed during operation of the vessel. The observation port may include a clear window to provide for viewing of the interior of the vessel. Other observation ports, with clear windows or sight glasses, may be located in the vessel at locations other than at the access and observation port  30 . 
         [0064]      FIG. 5  is a cross-sectional diagram of the pressurized treatment vessel  10 . A vertical shaft  32  is coaxial with the vessel and extends at least up through the tray assemblies  16 ,  18  and  20  in the vessel. An upper portion of the shaft  32  extends from the top of the vessel and is rotationally driven by a motor and gear assembly  33 , which is fixed to the top of the vessel for torsion support. The lower end of the shaft  32  may be supported by a bearing and bracket assembly  35  that is below the lowermost tray in the vessel. Similarly the upper end of the shaft is supported by a bearing at the top of the vessel and associated with the gear and motor assembly. A spadone journal  37  may rotatably couple the shaft  32  to the bearing and bracket assembly  35 . 
         [0065]      FIG. 6  is a perspective view of the top and side of the vessel  10  with a quarter-section of the vessel removed for purposes of illustration. The shaft  32  extends up beyond the top of the vessel. A spline on the top end of the shaft fits into the motor and gear assembly. A top plate  38  ( FIG. 5 ) seals the top of the vessel and provides a support for the shaft bearing and the motor and gear assembly  33 . 
         [0066]      FIGS. 6 to 12  illustrate the structure and operation of the tray assemblies  16 ,  18  and  20 . The tray assemblies  16 ,  18  and  20  each include a horizontal tray  40  which may be perforated, screened, meshed or otherwise structured to allow gases to pass through the tray and block the passage of the biomass materials, such as fibers. The tray  40  may be annular and extend radially from the shaft  32  to the inside surface of the cylindrical wall  42  of the vessel  10 . The tray may also be horizontal and generally level. The tray may be fixed to the vessel and not rotate with the shaft. For example, the tray may be a perforated steel mesh arranged horizontally and substantially covering the open area in the vessel between the shaft  32  and the wall  42  of the vessel. Other materials that may be used to form the tray  40  included steel plates perforated by drilled or laser cut openings, slots or holes. 
         [0067]      FIG. 15A  is an enlarged view of a cross-section of a tray to illustrate an exemplary slot, hole or opening  100  in the tray. As the biomass moves over the surface of the tray in the direction of flow arrow  102 , gas flows down through the biomass and through the opening to the gas passage  52  below the tray. The slot, hole or opening may have a generally uniform cross section through the tray. Alternatively and as shown in  FIG. 15A , it  100  may have an upper portion  104  that is generally uniform in cross section and a lower portion  106  that expands in cross-sectional area in a downward direction. The upper portion of the slot, hole or opening  100  may be 30 to 50 percent the thickness of the tray. Further, the upper rim of the slot, hole or opening may be beveled  108 , such as at the trailing edge as shown in  FIG. 15A . The bevel  108  assists in avoiding fibers from the biomass being caught on the upper rim of the slot, hole or opening, and especially on the trailing edge of the rim. The slot, hole or opening may be covered with finer mesh or screen material. 
         [0068]    Immediately below the tray  40  is a solid annular bottom plate  44  that forms a bottom to a gas passage  52  between the tray  40  and the plate  44 . The gas passage is for gases drawn through the biomass and tray to be exhausted to the extraction nozzles  36  that are mounted to the wall  42  of the vessel at elevations corresponding to the gas passage between the tray and bottom plate  44 . Baffle plates  46 ,  48  and  50  may be mounted on the bottom plate  44  and extend upward through the gas passage to the tray  40 . The baffle plates direct gases towards the inlets to the extraction nozzles  36 . The baffle plates may include short  46  and long  48  radially extending plates, and a circular wall plate  50  that forms and end wall for the gas passage. The long  48  radial plates divide the gas passage into triangular shaped screen segments. By way of example, each tray may have four to eight screen segments. In addition to the tray  40  being formed of pie-shaped segments, the plate  44  may also be pie-shaped segments and the long radial plates  48  may form sidewalls to each of these segments. 
         [0069]    The baffle plates also provide support for the screen or grating of the tray  40 . The circular wall plate may have open slots to allow gases to flow to the inlet to the extraction nozzle  36  and to allow the pipe for the injection nozzle  34  to pass from the wall of the vessel through the bottom plate  44  and open to the next lower tray assembly. 
         [0070]    The trays  40  may be supported by the inner surface of the wall  42  of the pressurized treatment vessel  10 . The wall  42  may include hangers, ridges or other support surfaces on which rest the outer rim of each tray. The trays may be removed, replaced and repositioned in the vessel by opening the vessel and sliding the trays in and out of the vessel. 
         [0071]    Alternatively, the trays, rotating scrapers and shaft may be constructed as a cartridge assembly and primarily supported from the top head plate of the vessel. A cartridge assembly could be inserted and removed from the vessel as a whole. Anti-rotation clips or pieces may be affixed to the vessel walls for the purpose of preventing the cartridge assembly from rotating within the vessel. 
         [0072]    The biomass flowing through the chute  116  drops into an optional lower portion  80  of the vessel. The biomass may form a pile in the lower portion which temporarily retains the biomass in the lower portion. While in the pile, the biomass continues to undergo the torrefaction reaction. The torrefied biomass is discharged from an outlet  116 . 
         [0073]    As an alternative to a rotating scraper device, the trays may rotate with the shaft. A stationary scraper device may be in a fixed position and may include radial arms extending over the tray. 
         [0074]    The injection nozzles  34  may extend through the gas passage and have an outlet  53  that extends through the bottom plate  44 . The outlet  53  discharges gas into the biomass passage  54  formed between a bottom plate  44  of one tray assembly and the tray  40  of tray assembly immediately below the bottom plate. The biomass passage is a volume in the vessel  10  which receives the biomass. The number of injection nozzles  34  for each tray may be uniform and selected based on operational requirements of the vessel. The selection of the number of the nozzles may be sufficient to provide uniform gas flow, at a uniform flow distribution and gas temperature, through the biomass material on the tray. For example, six to eight injection nozzles may be used to provide uniform gas flow to each tray. 
         [0075]    The injection nozzles  34  may be configured to supply 1 to 4 kilograms (kg) of gas per kilogram of biomass on the tray. The volume of gas supplied by the injection nozzles may also be in ranges of 1 to 6 kg, 1 to 12 kg or 1 to 24 kg of gas to kg of biomass. 
         [0076]    The injection nozzle may be fabricated with the tray  40 , bottom plate  44  and baffle plates  46 ,  48  and  50 . For example, each pie shaped segment of tray, bottom plate, baffle plates and injection nozzle may be prefabricated and installed on a support structure, e.g., radial spokes, in the vessel. Further, these prefabricated tray assembly segments or prefabricated tray assemblies may be installed in the vessel by removing the top plate  38  and lowering the prefabricated assemblies down into the vessel to the appropriate elevations, wherein the assemblies are to be positioned. Once positioned, the injection nozzle is coupled to a nozzle opening in the sidewall  42  of the vessel  10 . Similarly, once the tray assembly has been positioned in the vessel, an opening in the outer baffle plate  50  is aligned with an extraction nozzle  36  mounted to the sidewall  42  of the vessel. 
         [0077]    Below each tray may one or more gas extraction nozzles  36  arranged at substantially the same elevation on the outer wall of the vessel and separated by uniform angles around the vessel. The number of gas extraction nozzles may be the same as or different from the gas injection nozzles. For example, one, two or three gas extraction nozzles may be below each tray or alternatively one for each tray segment. The gas injection nozzles  34  may be of a smaller diameter than the gas extraction nozzles, especially if the oxygen deprived gas expands as it enters the vessel. The gas inlet manifolds for the nozzles  34 ,  36  may be thick walled pipes or fabricated from steel. With respect to each tray, gas enters the vessel through the gas injection nozzles  34 , passes through the biomass material on the tray, the tray and is discharged from the vessel through the extraction nozzles  36 . 
         [0078]      FIG. 11  shows a scraper device  56  that moves the biomass through the biomass passage of each tray assembly. The scraper device  56  may have radial scraper spokes or blades  60 , a center collar  58  and an outer annular ring  56 . The ring  56  is proximate to the wall  42  of the vessel  10 , such as within 3 to 5 millimeters (mm) of the wall  42 . The lower edges of the blades  60  are proximate to the upper surface of the tray, e.g., within 3 to 10 mm of the tray. The upper edges of the blades may be proximate to, e.g., within 10 to 25 mm, the bottom plate  44  of the next higher tray assembly. The spokes or blades  60  of the scraper device may straight and aligned with radial lines extending between the collar and ring. Alternatively, the spokes or blades  60  may be inclined with respect to radial lines at angles of 15 to 20 degrees towards the angle of rotation (as is shown in  FIG. 11 ), and the blades may be curved or swept towards the angle of rotation. 
         [0079]      FIG. 11A  is a schematic diagram of an enlarged portion of the lower edge of one of the spokes or blades of the scraper device. A slot, pipe or other gas passage  112  is provided on the lower edge, and has openings or nozzles  114  arranged along the radial length of the passage  112 . A source of high pressure gas  114  is coupled to the passage  112  through the shaft  32  of the vessel. The high pressure gas source  114  may be external to the vessel and is shown in the shaft solely for illustrative purposes in  FIG. 11A . The high pressure gas flowing through the passage  112  and the nozzles  114  is applied to clean the openings  100  in the tray to ensure that gas is free to pass through the openings. Alternatively, the high pressure gas source  114  may be a source of suction such as an air pump or blower. The suction applied to the passage  112  and nozzles  114  removes fibers and debris from the openings. As the blade with the passage  112  rotates over the tray, the openings  100  in the tray are cleaned. The cleaning of the openings in the tray may be concurrent with the treatment of biomass in the vessel  10 . 
         [0080]    The scraper device  56  may be prefabricated and installed by sliding the device down into the vessel. The center collar may be welded or otherwise affixed to the shaft. The diameter of the scraper bar may conform to the inner diameter of the vessel with a small clearance. The center collar may be fixed to the shaft  32 , such that the scraper device rotates with the shaft. The height of the scraper device  56  may be nearly the same as the height of the biomass space  54 , or may be about the desired thickness of the biomass  66  on the tray, as shown in  FIG. 15 . 
         [0081]    The rotation of the shaft  32  rotates a scraper device  56  immediately above each of the trays  40 . The biomass fills or partially fills the volume between the spokes  60  of the scraper device. The rotation of the scraper device over its respective the tray moves the biomass material across the tray. As the biomass material moves across the tray, the material is exposed to a constant flow of the oxygen deprived gas at a uniform temperature. The gas enters the vessel through gas injection nozzles  34  that has an opening at the outer wall of the vessel or an opening  53  in the bottom plate  44  above the tray and biomass space  54 . The opening  53  in the bottom plate may be a single discharge port, or a gas distribution manifold  55  with an array of gas discharge ports arranged above the biomass on the tray. The opening may also be flared to assist with disbursing the oxygen deprived gas over the biomass on the tray. The gas distribution manifold  53  may be an arrangement of pipes and pipe fittings with nozzles, and fabricated with the tray assembly. The opening or gas distribution manifold may be arranged to uniformly distribute gas over the biomass on the entire tray. To achieve uniform gas distribution, multiple injection nozzles may be arranged around the wall of the vessel, such as at least one nozzle for each tray segment. 
         [0082]    As the gas moves through the biomass and the tray, the scraper device rotates to move the biomass in an arc shaped path through the tray assembly. The biomass moves through the tray assembly and is discharged through an opening  64 , shown in  FIG. 12 . The opening may include a chute, duct, pivoting door or other discharge device in the tray. The biomass drops through the opening  64  to into the scraper device and onto the tray of the next lower tray assembly. The opening  64  may be vertically aligned with the opening  64  in the next lower tray assembly, such that the biomass falls into the triangular shaped section of the scraper device that has just rotated over the chute in the next lower tray assembly. This alignment of the chutes ensures that the biomass moves in an arc over the entire tray and provides maximum retention time of the biomass in each of the tray assemblies. The lowermost tray may be an inverted cone with a center discharge chute to allow biomass to flow to a vertical center of the cooling zone. 
         [0083]      FIGS. 13 and 14  show the convergence zone  24  in the bottom section of the vessel  10 . The convergence section may include regions which converge in one-dimension only, such as having flat sidewalls that converge and curved walls joining these sidewalls that do not converge. One-dimensional convergence sections reduce the tendency of biomass material to become stuck in the vessel while flowing to the outlet  26 . One-dimensional convergence sections are marketed by the Andritz Group under the Diamondback™. One dimensional convergence sections generally avoid the need to have a rotating scraper or other mechanical device to prevent biomass blockages in the bottom of the vessel. Although one dimensional convergence sections are disclosed here, other means of bringing the material to a discharge point at the bottom of the vessel such as motor driven moving bottom units, e.g., scrapers, and outlet device assemblies may be used. 
         [0084]      FIG. 15  is a schematic illustration of the gas flow through a tray assembly. The gas flow through the injection nozzle  34  which is aligned with and passes through the gas passage  52  of the immediately above tray assembly. The injected oxygen deprived gas flows through outlet  53  and into the biomass space  54  in the tray assembly. There may be several injection nozzles  34  with outlets  53  arranged radially around the biomass space for each tray assembly. The gas flow is distributed uniformly over the upper surface of the bed of biomass  66  by entering a gas space in the biomass space  54  that is above the bed. The thickness of the bed may be, by way of example, one meter (1 m) or some other thickness which achieves the desired biomass throughput and allows heating gases to flow uniformly through the bed. For example, the bed thickness may be in ranges of 150 millimeters to one meter, or greater than one meter. The bed sits on the tray  40 . 
         [0085]    Gases flow down through the bed and tray, and enter the gas passage  52 . The gases exhaust from the gas passage through the extraction nozzles  36  arranged radially around the wall of the vessel and at each segment of the tray. The gas extraction nozzles  36  may be arranged to promote the uniform flow of gases through the biomass on the tray. The number of gas extraction nozzles may be fewer than the number of gas injection nozzles  34 . 
         [0086]      FIG. 15A  is an enlarged view of the cross-section of a tray to illustrate n exemplary slot, hole or opening  100  in the tray (not shown is a finer mesh or finer screen material that may be used to cover the hole, slot or opening  100 ). As the biomass moves over the surface of the tray in the direction of flow arrow  102 , gas flows down through the biomass and through the opening to the gas passage  52  below the tray. The slot, hole or opening may have a generally uniform cross section through the tray. Alternatively and as shown in  FIG. 15A , the hole, slot or opening  100  may have an upper portion  104  that is generally uniform in cross section and a lower portion  106  that expands in cross-sectional area in a downward direction. The upper portion of the slot, hole or opening  100  may be 30 to 50 percent the thickness of the tray. Further, the upper rim of the slot, hole or opening may be beveled  108 , such as at the trailing edge as shown in  FIG. 15A . The bevel  108  assists in avoiding the fibers from the biomass from being caught on the upper rim of the slot, hole or opening, and especially on the trailing edge of the rim. 
         [0087]      FIGS. 16 to 18  are process flow charts showing exemplary torrefaction processes that may be performed in the vessel  10 . A common feature of these processes is that the torrefied biomass material is cooled prior to being depressurized and exposed to the atmosphere. The cooling may occur in lower trays of the vessel, in a cooling zone  24  or in a pressurized cooling chip tube  67  and cooling screw  68  assembly, downstream of the discharge  26  of the vessel. Alternatively, cooling could occur in a fluid bed (now shown). It is also possible for zone  24  to be a combination reaction zone followed by a cooling zone. 
         [0088]    Cooling gases may be injected in the lower(s) trays, cooling zone, chip tube or chip screw to cool the torrefied biomass prior to discharge from the reactor. The cooling gases may be used to stop or slow the torrefaction reaction and to make the torrefied biomass safe and suitable for an oxygen atmosphere outside of the vessel. For example, cooling to stop or slow the torrefaction reaction may occur to make the biomass suitable for an oxygen atmosphere may occur in the cooling zone  22  or in pressurized cooling devices downstream of the vessel. The cooling to stop or slow the torrefaction reaction may require cooling gases that are 10 to 30 degrees Celsius cooler than the gases injected in the torrefaction tray assemblies to promote the torrefaction reaction. The cooling gases to make the torrefied biomass safe for an oxygen atmosphere may be cooler by an additional 10 to 30 degrees Celsius, or 10 to 50 degrees Celsius, or 10 to 80 degrees Celsius, or 10 to 100 degrees Celsius, or 20 to 120 degrees Celsius from the cooling gases added to the cooling tray assemblies. 
         [0089]    Gases from the cooling zone  24 , such as in the convergence section, may be withdrawn through a screen  65  in a sidewall of the vessel, as is shown in  FIGS. 13 and 14 . Similarly, cooling gases may be withdrawn from a lower cooling tray or from the chip tube and screw  68 . 
         [0090]    The cooled torrefied biomass passes through a pressure transfer device  70 , such as a rotary valve. The pressure of the torrefied biomass downstream of the pressure transfer device may be at atmospheric. From the pressure transfer device, the torrefied biomass is moved to other processes such as using a screw conveyor  72 . 
         [0091]    Before the torrefaction reaction occurs in the vessel, such as in the lower trays  18 , the biomass may be dried and heated in an oxygen deprived environment at a temperature of 200° C. to 400° C. The biomass may be dried and heated in a separated dryer that acts on the biomass before it reaches the vessel  10 . In addition or alternatively, the biomass may be dried in an upper drying zone of the vessel  10 , which may include one or more of the tray assemblies. The biomass may be directly heated with an oxygen deprived gas, e.g., super-heated steam, nitrogen or a mixture of both, injected into the top of the vessel or dryer. 
         [0092]    The volume of hot oxygen deprived gas needed for the vessel is dramatically reduced in a pressurized reaction vessel  10  as compared to a vessel operating at atmospheric pressure. Pressurizing the treatment vessel  10  the volume of hot gas needed to heat the biomass is decreased by a factor of two (2) to thirty-five (35) as compared to a vessel at atmospheric pressure. The reduction factor for the vessel depends on the pressure in the vessel. 
         [0093]    Because of the reduced volume of hot gas needed in the pressurized reactor, the volume and hence the size and cost of the vessel  10  may be significantly reduced as compared to a vessel operating at atmospheric pressure. A pressurized vessel in which a hot gas is injected provides effective and economical heat transfer from the gas to the biomass in the vessel. 
         [0094]    The vessel  10  may be pressurized by injecting an oxygen deprived gas, e.g., oxygen starved gas, at a pressure of up to 35 bar gauge (barg), such as in a range of 3 barg to 35 barg. The pressurized vessel  10  operates in an oxygen deprived gas environment in which a heated pressured gas circulates through the vessel to directly heat the biomass and promote a torrefaction reaction with the biomass. 
         [0095]    The hot, oxygen deprived gas may be steam, e.g., super-heated steam, nitrogen or carbon dioxide and may contain in lesser quantities gaseous byproducts from the torrefaction reaction. Further, the hot gas may be injected into the biomass in the feed system (not shown) such as in the inlet downstream of a pressure isolation device or downstream of a high pressure transfer device. If there is a high pressure transfer device, a pressure isolation device may be unnecessary at the inlet to the vessel  10 . 
         [0096]    In the drying and torrefaction tray assemblies, the hot gas flows through the biomass in the vessel  10  and directly heats the biomass to a temperature that promotes a torrefaction reaction in the material, such as a range of 240° C. to 300° C. The hot gas and any gas generated in the reactor are exhausted from the reactor at various elevations through extraction nozzles  36 . The gas may exhaust from the vessel at a temperature of about 250° C. to 280° C. The gases used for drying may be cooler than the gases used for torrefaction. The gases for drying may be gases extracted from the torrefaction tray assemblies, and using a blower are circulated to the drying tray assemblies without adding additional heat to the gases. Gases that are circulated back to the torrefaction trays may be heated in a heat exchanger before being returned to the torrefaction tray assemblies. 
         [0097]    A portion of the exhausted gas is removed from the vessel for use outside of the torrefaction system. Another portion of the exhausted gas is indirectly heated in a heat exchanger  84  (or other heat transfer device) and returned to the gas input manifold  24  at the top of the vessel  10 . The heat exchanger  34  may add heat energy to heat the exhausted gas from about 250° C. to 300° C. to 380° C., for example. Reheating and recirculating the exhausted gas reduces the amount for additional pressurized heated oxygen deprived gas required to be supplied to the gas input manifold of the vessel. 
         [0098]    The exemplary process flow in  FIG. 16  shows the pressurized vessel  10  as having a drying tray assembly  16 , four torrefaction tray assemblies  18  and two cooling tray assemblies  20 . Hot, oxygen deprived gas circulates through the vessel, blowers  74 ,  79  and heat exchanger  84  at an elevated pressure of 3 to 20 Barg ( 300  to  2 , 000  kiopascals, or in a range of 5 to 8 Barg. The hot gases for the drying tray assembly  16  and torrefaction tray assemblies  18  are provided from a heat exchanger  84 . Heat energy is added to oxygen deprived gases flowing through the heat exchanger by, for example, hot gases  88  from a combustor. The warm combustion gases discharged from the heat exchanger  84  may flow to warm air flowing to the combustor. 
         [0099]      FIGS. 17 and 18  show process flows in which the drying gas flowing to a top inlet  90  is cooler, e.g., by 10° C. to 30° C., than the oxygen deprived gases flowing to the torrefaction tray assemblies  18 . In  FIGS. 17 and 18 , the gas flowing to the top inlet  90  is also injected to the cooling tray assembly  20 . 
         [0100]    The oxygen deprived gas shown in the process flows of  FIGS. 16 to 18  are circulated through the pressurized treatment vessel  10  in a substantially closed gas loop system. 
         [0101]    A portion of the gases may be removed from the system as bleed off gases  90 . The portion may be the just gases from the lowest one or few torrefaction tray assemblies, all of the torrefaction tray assemblies, a middle set of torrefaction tray assemblies, or just gases removed from the drying tray assembly(ies). The bleed off gases may be selected to have a high concentration of torrefaction reaction byproducts to be removed and later combusted or otherwise processed. Alternatively, bleed off gases may be selected based on having a low concentration of torrefaction reaction byproducts to be used in combustion or other processes. 
         [0102]    The oxygen deprived gases are circulated through the vessel  10  and heat exchanger  84 . Blowers  74 ,  76  and  78  provide a motive force to circulate the gases. The hot gases from the torrefaction tray assemblies may flow through the high temperature blowers  76  and  74  and the heat exchanger  84 , before being returned to the torrefaction tray assemblies  18  and, optionally, to the top inlet  86  of the vessel. Multiple blowers  74 ,  76  may be used to provide the needed flow rate to circulate gases through the many torrefaction tray assemblies. Valves  80  between the blowers  74 ,  76  may remain open to allow high temperature gases to flow in parallel through these blowers. Valves  82  may be closed to prevent the hot gases flowing through the high temperature blowers  74 ,  76  from mixing with the low temperature gases flowing through the low temperature blower  78 . The valves  80 ,  82  may be set as opened or closed depending on the rate of hot gases extracted from the vessel as compared to the rate of cooler gases extracted from the vessel. 
         [0103]    Relatively cooler oxygen deprived gases are extracted from the cooling tray assemblies  20 , the cooling zone  22  of the vessel (such as through screen  65 ) and, optionally from the drying tray assembly  16 , and flow through piping separate from the piping used for the hotter oxygen deprived gases extracted from the torrefaction tray assemblies. The cooler gases are removed through extraction nozzles  36  by a low temperature blower  78  which pushes the gases back to the vessel where they enter through injection nozzles  34  to the cooling tray assemblies  20 , and optionally to the top of the cooling zone  22  through a nozzle  92  aligned with the bottom tray assembly. 
         [0104]    The bleed off gases provide a means to remove primary byproducts of the torrefaction reaction occurring in the vessel  10 . These primary byproducts may include acetic acid, carbon monoxide, carbon dioxide, formaldehyde, formic acid, water, lignin fragments, and other lesser components. The primary byproducts are generally gaseous at the temperature and pressure at which the torrefaction reaction occurs in the vessel. Some of the byproducts may be in aerosol or fine char form carried by in the bleed off gases. Similarly, fine particles of lignocellulose material from the biomass may flow with the gas as it passes through the screens in the trays and the vessel and be carried by the bleed off gases out of the system. 
         [0105]    The primary byproducts may combine and condense to form tar like substances. If allowed to condense in the vessel and downstream process components, the tar like substances can deposit on the surfaces of the vessel and components, particularly on the interior surfaces of piping and heat exchangers. 
         [0106]    The gases being circulated through the reactor vessel  10  and heat exchanger  84  may be treated to remove reaction byproducts from the circulating gases. The system for circulating the gases through the vessel  10  and heat exchanger  84  may include separation devices  96  for removing the reaction byproducts. Separation devices  96  may be a condensation device which cools the gases to cause the byproducts to be condensed to a liquid and removed, before the gases are reheated in the heat exchanger. Other examples of separation devices  96  include devices that oxidize the byproducts, catalytically convert the byproducts, filter the byproducts from the gas flow and flow separators, such as cyclones that use centrifugal forces to separate particles from the gas stream. These separation devices may be used singularly or in combination in the system. The byproducts separated by these components may be further processed by being separated, concentrated or purified into usable products. The bleed off gases  90  remove the primary byproducts from the vessel while these byproducts are in gaseous form. As shown in  FIGS. 16 and 17 , the bleed off gases may be extracted from the drying tray assembly and, particularly, from the extraction gas stream flowing from the extraction nozzle  36  for the drying tray assembly. The extracted gases from the drying tray assembly tends to be rich in moisture and below the temperature required to initiate torrefaction. As shown in  FIG. 18 , the bleed off gases may be extracted from the torrefaction tray assemblies  18 , and particularly, from the middle to lower elevations of these tray assemblies  18 . The concentration of organic byproducts in the gases extracted from the torrefaction tray assemblies may be at a maximum level as compared to the gases extracted from the vessel  10 . 
         [0107]    The bleed off gases  90  may flow to the combustor where the gases may be mixed with a natural gas, or other gaseous fuel, and combusted. Combustion would release heat energy from the byproducts which would be used to reheat the circulating gases in the heat exchanger  84 . The heat from combustion could also be used to dry and heat the biomass in the optional dryer  21 . 
         [0108]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.