Patent Publication Number: US-2023149875-A1

Title: Fluidized bed reactor systems and methods for torrefaction and catalytic pyrolysis of biomass

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of PCT International Patent Application No. PCT/CA2020/050546 filed 24 Apr. 2020 entitled FLUIDIZED BED REACTOR SYSTEMS AND METHODS FOR TORREFACTION AND CATALYTIC PYROLYSIS OF BIOMASS which is hereby incorporated herein by reference for all purposes. 
    
    
     TECHNICAL FIELD 
     This application relates to fluidized bed reactors for processing biomass and to methods and systems for biomass processing. Some embodiments are operative to perform torrefaction or pyrolysis of biomass. 
     BACKGROUND 
     Biomass is a promising source of renewable energy. However, the energy density of raw biomass may be undesirably low. Processes such as pyrolysis or torrefaction may be employed to increase the energy density of biomass and/or to convert biomass into other forms that may be useful for specific purposes. ‘Pyrolysis’ of biomass refers to chemical decomposition of biomass under limited oxygen levels or in total absence of oxygen under elevated temperatures. Reaction temperatures for pyrolysis are typically in the range of about 300° C. to about 650° C. A milder process, often referred as ‘torrefaction’, typically involves subjecting biomass to temperatures in the range of about 200° C. to about 300° C. 
     Products of biomass pyrolysis may include liquids (e.g. bio-oil), gases (e.g. bio-oil vapour and/or non-condensable gases) and/or solids (e.g. bio-char). Bio-oil is sometimes referred to as tar or bio-crude. Bio-oil typically has higher energy density than its parent biomass material, which facilitates storage and transportation. 
     One of the major challenges in developing processes for treating biomass (e.g. by torrefaction or pyrolysis) is providing a cost-effective reactor that matches the capacity of available equipment for drying, grinding and pelleting biomass. Previously proposed torrefaction reactors include fixed beds, moving beds or screw types. These reactors commonly employ wood chips as feedstock. These reactors require large footprints due to the at least 40 to 60 minutes of residence time required by these reactors to perform torrefaction and/or pyrolysis. 
     Employing fluidized beds for processing biomass has also been proposed. However, fluidization of biomass is complicated by the fact that biomass particles tend to clump together. The poor flowability and high cohesiveness of biomass particles can cause undesirable phenomena such as channeling, bypassing and defluidization in biomass fluidized beds. One can add inert solid bed particles such as sand or calcite to mix with biomass in a fluidized bed such that gas-solid flow is stabilized. However, a disadvantage of such a strategy is that fine powders of the bed particles are produced during fluidization. These fine particles may undesirably adhere to the biomass particles and be included in subsequent biomass products. In the case of torrefaction and pyrolysis where thermal-treated biomass solids will later be utilized as a biofuel or feedstock, the increased ash content can reduce product quality and/or harm downstream equipment. 
     The quality of torrefied or pyrolyzed biomass product is also determined by the uniformity of the processing. In conventional fluidized beds of the type where particles are fed continuously into a reactor and discharged continuously from the reactor, particles are vigorously mixed, resulting in a broad distribution of residence time for different particles. This variation in residence times yields non-uniform product in which some particles are over-reacted and some particles are under-reacted. 
     There is a general need for apparatus and methods for processing biomass which are efficient in operation and cost effective. 
     The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. 
     SUMMARY 
     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
     One aspect of the invention provides a fluidized bed reactor for treatment of particles. The reactor comprises a vessel extending in a first direction from a first end to a second end, an inlet at the first end of the vessel for feeding particles into the vessel, an outlet at the second end of the vessel for outputting processed particles, a first fluid inlet independently activatable to deliver a first volume of a gas in a second direction into a first region of the vessel, a second fluid inlet spaced apart from the first fluid inlet in the first direction and independently activatable to deliver a second volume of the gas in the second direction into a second region of the vessel, the second region adjacent the first region. 
     In some embodiments, the particles comprise biomass particles. In some embodiments, the particles comprise polymer particles. In some embodiments, the particles comprise a mixture of biomass and polymer particles. 
     In some embodiments, the first direction is non-parallel to the second direction. In some embodiments, the first direction is orthogonal to the second direction. 
     In some embodiments, the first volume of the gas is heated and the second volume of the gas is heated. In some embodiments, the first volume of the gas is heated to a temperature, T1, and the second volume of the gas is heated to a temperature, T2, and T2 is greater than T1. In some embodiments, the first volume of the gas is heated to a temperature, T1, and the second volume of the gas is heated to a temperature, T2, and T2 is approximately equal to T1. 
     In some embodiments, the first volume of the gas is delivered into the vessel through a first plenum chamber and the second volume of the gas is delivered into the vessel through a second plenum chamber and the first and second plenum chambers are spaced apart and separated. In some embodiments, the first volume of the gas and the second volume of the gas are provided from a single fluid source. 
     In some embodiments, the vessel is divided into a first zone and a second zone and wherein one or more magnetrons produce microwaves in the second zone. 
     In some embodiments, first and second sidewalls of the vessel extend in the first direction and are each sloped downward toward one another. 
     In some embodiments, a bottom wall of the vessel is perforated to allow gas delivered by the first fluid inlet and the second fluid inlet to pass through perforations in the bottom wall into the vessel. 
     In some embodiments, the reactor comprises a third fluid inlet spaced apart from the second fluid inlet in the first direction and independently activatable to deliver a third volume of the gas in the second direction into a third region of the vessel, the third region adjacent the second region. In some embodiments, the reactor comprises a fourth fluid inlet spaced apart from the third fluid inlet in the first direction and independently activatable to deliver a fourth volume of the gas in the second direction into a fourth region of the vessel, the fourth region adjacent the third region. In some embodiments, the reactor comprises a fifth fluid inlet spaced apart from the fourth fluid inlet in the first direction and independently activatable to deliver a fifth volume of the gas in the second direction into a fifth region of the vessel, the fifth region adjacent the fourth region. 
     In some embodiments, the reactor comprises a pressurized fluid source. In some embodiments, the first fluid inlet comprises a first piston selectively operable to open a first seal between the pressurized fluid source and the vessel to thereby deliver the first volume of the gas in the second direction into first region of the vessel. In some embodiments, the second fluid inlet comprises a second piston selectively operable to open a second seal between the pressurized fluid source and the vessel to thereby deliver the second volume of the gas in the second direction into the second region of the vessel. 
     In some embodiments, the reactor comprises a vibrating apparatus for vibrating the vessel. 
     In some embodiments, the reactor comprises one or more direct heaters for heating the particles. 
     In some embodiments, the polymer particles comprise one or more of polyethylene, polypropylene and rubber. 
     In some embodiments, the particles comprises greater than 90% biomass particles by weight. In some embodiments, the composition of the particles comprises between 20% and 90% biomass particles by weight and between 10% and 80% polymer particles by weight. In some embodiments, the composition of the particles comprises between 70% and 90% biomass particles by weight and between 10% and 30% polymer particles by weight. In some embodiments, the composition of the particles comprises less than 10% biomass particles by weight. 
     Another aspect of the invention provides a method of processing particles in a fluidized bed reactor. The method comprises feeding particles through a vessel of the reactor in a first direction, propagating fluidization waves in the first direction inside the vessel and heating the particles. 
     In some embodiments, the particles comprise biomass particles. In some embodiments, the particles comprise polymer particles. In some embodiments, the particles comprise a mixture of biomass and polymer particles. 
     In some embodiments, propagating the fluidization waves in the first direction inside the vessel comprises delivering gas into the vessel in a second direction. 
     In some embodiments, the first direction is non-parallel to the second direction. In some embodiments, the first direction is orthogonal to the second direction. 
     In some embodiments, propagating the fluidization waves comprises repeatedly delivering a first volume of the gas into a first region of the vessel in the second direction to fluidize particles in the first region of the vessel and delivering a second volume of the gas into a second region of the vessel in the second direction to fluidize particles in the second region of the vessel, the second region of the vessel adjacent to the first region of the vessel. 
     In some embodiments, propagating the fluidization waves comprises repeatedly delivering a first volume of the gas into a first region of the vessel in the second direction to fluidize particles in the first region of the vessel, delivering a second volume of the gas into a second region of the vessel in the second direction to fluidize particles in the second region of the vessel, the second region of the vessel adjacent to the first region of the vessel and delivering a third volume of the gas into a third region of the vessel in the second direction to fluidize particles in the third region of the vessel, the third region of the vessel adjacent to the second region of the vessel. 
     In some embodiments, delivering the second volume of the gas occurs concurrently with delivering the first volume of the gas. In some embodiments, delivering the second volume of the gas occurs after delivering the first volume of the gas. In some embodiments, delivering the second volume of the gas at least partially overlaps temporally with delivering the first volume of the gas. In some embodiments, delivering the third volume of the gas occurs concurrently with delivering the first volume of the gas. 
     In some embodiments, each of the fluidization waves comprises a wave region of particles at least temporarily having a relatively lower packing density than a rest of a bed of particles within the reactor and wherein each wave region travels in the first direction. 
     In some embodiments, heating the biomass comprises directly heating the biomass. In some embodiments, heating the biomass comprises indirectly heating the biomass. In some embodiments, heating the biomass comprises convectively transferring heat from the gas to the biomass. 
     In some embodiments, the method comprises heating the gas to 500° C. or higher. 
     In some embodiments, heating the biomass comprises convectively transferring heat from the gas to the biomass in a first zone of the vessel and microwaving the biomass in a second zone of the vessel. 
     In some embodiments, delivering the first volume of the gas in the second direction into the first region comprises operating a first piston to open a first seal between a pressurized fluid source and the first region of the vessel to allow the gas into the first region of the vessel. In some embodiments, delivering the second volume of the gas in the second direction into the second region of the vessel comprises operating a second piston to open a second seal between the pressurized fluid source and the second region of the vessel to allow the gas into the second region of the vessel. 
     In some embodiments, the particles comprises greater than 90% biomass particles by weight. In some embodiments, the composition of the particles comprises between 20% and 90% biomass particles by weight and between 10% and 80% polymer particles by weight. In some embodiments, the composition of the particles comprises between 70% and 90% biomass particles by weight and between 10% and 30% polymer particles by weight. In some embodiments, the composition of the particles comprises less than 10% biomass particles by weight. 
     Another aspect of the invention provides a system for processing biomass. The system comprises a dryer for drying raw biomass, a grinder for making biomass particles from dried biomass, a fluidized bed reactor as described herein for processing the biomass particles, a conditioner for adjusting a humidity of processed biomass received from the fluidized bed reactor, a pelletizer for fabricating biomass pellets out of processed biomass received from the conditioner and a cooler for reducing the temperature of the biomass pellets. 
     In some embodiments, off-gasses from the fluidized bed reactor are combusted to heat the raw biomass in the dryer. In some embodiments, off-gasses from the fluidized bed reactor are combusted to heat the biomass particles in the fluidized bed reactor. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
         FIG.  1    is a schematic side view cross-section of a reactor according to an exemplary embodiment of the invention. 
         FIG.  2    is a schematic front view cross-section of the reactor of  FIG.  1   . 
         FIG.  3 A  is a schematic perspective view of a plurality of fluid inlets for a reactor according to an exemplary embodiment of the invention.  FIG.  3 B  is a schematic front view cross-section of one of the fluid inlets of  FIG.  3 A .  FIG.  3 C  is a schematic front view cross-section of a reactor according to an exemplary embodiment of the invention.  FIG.  3 D  is a schematic partial side view cross-section of a bottom wall of the reactor according to an exemplary embodiment of the invention.  FIG.  3 E  is a schematic bottom view of the bottom wall of  FIG.  3 D . 
         FIG.  4 A  is a schematic top plan view of the reactor of  FIG.  1   .  FIG.  4 B  is a schematic top plan view of an orientation of fluid inlets of a reactor according to an exemplary embodiment of the invention.  FIG.  4 C  is a schematic top plan view of an orientation of fluid inlets of a reactor according to an exemplary embodiment of the invention.  FIG.  4 D  is a schematic top plan view of an orientation of fluid inlets of a reactor according to an exemplary embodiment of the invention. 
         FIG.  5 A  is a block diagram of a method for processing biomass according to an exemplary embodiment of the invention.  FIG.  5 B  is a block diagram of a method for fluidizing biomass according to an exemplary embodiment of the invention. 
         FIGS.  6 A to  6 F  are schematic side view cross-sections of a reactor at various steps of the method of  FIG.  5 A  according to an exemplary embodiment of the invention. 
         FIG.  7    is a schematic perspective view of a fluidization wave according to an exemplary embodiment of the invention. 
         FIG.  8 A  is a chart representing the temperature of a biomass particle as it travels in a reactor according to an exemplary embodiment of the invention.  FIG.  8 B  is a chart representing the temperature of a biomass particle as it travels in another reactor according to an exemplary embodiment of the invention. 
         FIG.  9    is a schematic diagram of a system for processing biomass according to an exemplary embodiment of the invention. 
     
    
    
     DESCRIPTION 
     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. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
     One aspect of the invention provides fluidized bed reactors useful for biomass treatment (e.g. torrefaction and/or pyrolysis), polymer treatment (e.g. pyrolysis) and/or treatment of mixtures of biomass and polymers (e.g. pyrolysis). An example reactor comprises a vessel extending in a first direction from a first end to a second end. An inlet for feeding particles into the vessel is provided at the first end of the vessel. One or more outlets for outputting products is provided at the second end of the vessel. 
     In operation, a fluidized bed of particles is created in the vessel by introducing an upwardly-flowing gas into the vessel. The particles are heated to a temperature sufficient for torrefaction or pyrolysis. 
     A controlled atmosphere is maintained in the vessel. For example, the atmosphere may have an oxygen content that is significantly reduced as compared to air. The pressure in the vessel may be at or near atmospheric pressure. For example, in some embodiments, the pressure inside the vessel is approximately 1 atm or a slight vacuum. The pressure within the vessel may be controlled by, for example, an induction fan (or similar apparatuses). 
     The heated particles migrate in the first direction along the vessel. Solids resulting from the treatment of the particles in the vessel (e.g. torrefied biomass, bio-char, char, etc.) exit the vessel at the outlet. Volatile material(s) released from the particles can be collected at one or more vents. In some embodiments some of the volatile materials are reacted (e.g. oxidized) in-situ or ex-situ to generate heat for heating the particles in the vessel. 
     In some embodiments, the flow of gas is separately controlled in plural regions spaced apart in a direction between the first and second ends of the reactor. For example, the reactor may include a first fluid inlet activatable to control delivery of a first flow of the gas in a second direction into a first region of the vessel, and a second fluid inlet spaced apart from the first fluid inlet in the first direction and activatable to deliver a second flow of the gas in the second direction into a second region of the vessel that is adjacent to the first region. 
     Separate control over the flow of gas in different regions may be applied in ways that help to maintain a flow of the particles in the first direction and/or help to break up clumps of the particles as described herein. 
       FIG.  1    is a schematic cross-section of an example fluidized bed reactor  20  which may be employed for biomass treatment. For example, reactor  20  may be employed for torrefaction and/or pyrolysis of particles  5 , as desired. 
     Particles  5  may comprise biomass particles derived from any non-fossilized and biodegradable organic material originating from plants, animals and/or micro-organisms. Biomass particles may include, but are not limited to, products, by-products, residues and waste from agriculture, forestry and related industries as well as the non-fossilized and biodegradable organic fractions of industrial and municipal wastes. Specific non-limiting examples of particles  5  are particles of trees (tree particles may include particles of wood, bark, leaves, needles, cones, etc. from trees such as but not limited to Douglas fir, pine, etc.), particles of grasses (e.g. switchgrass), particles of crop residue (e.g. wheat straw, corn stover, etc.). Particles  5  may comprise particles derived from polymers. Such polymers may include, but are not limited to, products, by-products, residues and waste including municipal waste and recycling. Specific non-limiting examples of polymers include polyethylene, polypropylene, polyethylene terephthalate, polyvinyl chloride, polystyrene, rubbers, etc. Particles  5  may comprise a mixture of biomass particles and polymer particles. 
     In some embodiments, a composition of particles  5  comprises greater than 90% biomass particles by weight. In some embodiments, a composition of particles  5  comprises greater than 95% biomass particles by weight. In some embodiments, a composition of particles  5  comprises between about 20% and 90% biomass particles by weight and between about 10% and 80% polymer particles by weight. In some embodiments, a composition of particles  5  comprises between about 70% and 90% biomass particles by weight and between about 10% and 30% polymer particles by weight. In some embodiments, a composition of particles  5  comprises greater than 90% polymer particles by weight. In some embodiments, a composition of particles  5  comprises greater than 95% polymer particles by weight. 
     In some embodiments, particles  5  have a largest dimension in the range of about 0.1 mm to about 4 mm. In some embodiments, particles  5  have a largest dimension of less than 3 mm. In some embodiments, particles  5  have a largest dimension of less than 1.5 mm. Ideally particles  5  are similar in size. For example, in some embodiments, particles  5  have a Sauter mean diameter of between 0.5 mm and 1 mm. In some embodiments, particles  5  are size sorted (e.g. by screening) before they are introduced into reactor  20  to remove particles having dimensions greater than a threshold size (e.g. 3 mm). 
     In some embodiments, particles  5  are roundish in shape (i.e. dimensions of the particles are similar in three orthogonal directions where one of the dimensions is the longest dimension of the particle). In some embodiments, it is preferred for particles  5  to not have one dimension significantly longer than others (e.g. as in a particle having a needle-like shape). 
     In some embodiments, particles  5  are pre-treated before being fed into reactor  20 , as discussed further herein. Pre-treatment may include, for example, steps for one or more of drying, grinding, sizing, sorting, etc. For example, pre-treatment may be employed to remove undesirable particles or fragments such as, for example, metal particles or fragments. 
     Reactor  20  comprises a vessel  22  defined by a bottom wall  22 A, a first sidewall  22 B, a second sidewall  22 C, a first endwall  22 D, a second endwall  22 E and a top wall  22 F (see  FIGS.  1  and  2   ). An interior chamber  23  of vessel  22  extends in a first direction  12 . 
     A particle inlet  24  is provided for feeding particles  5  into vessel  22 . Particles  5  may progress from inlet  24  through vessel  22  along a path extending in first direction  12 . Particle inlet  24  is located at or near first endwall  22 D and provides a route for introducing particles  5  into vessel  22 . Particles  5  may be fed into biomass inlet  24  by, for example, a screw feeder. 
     Outlet  26  is located at or near second endwall  22 E and provides a route by way of solid and/or liquid output  6  (e.g. torrefied biomass, pyrolyzed biomass, biochar, char, etc.) may be outputted from reactor  20 . In some embodiments, solid and or liquid output  6  may accumulate at second end  46  until solid and or liquid output  6  overflows through outlet  26 . In some embodiments, such as, for example, where substantially all of particles  5  may be expected to be vapourized upon pyrolysis, outlet  26  may be omitted and output  6  may be removed through fluid outlet(s)  32 . 
     Fluid outlet(s)  32  may be provided to withdraw gases from an upper part of vessel  22  (e.g. outlet(s)  32  may extend through top wall  22 F and/or an upper portion of a side or end wall). Outlets  32  are connected to provide a route for removing fluid output  6  from vessel  22 . While outlet  32  is depicted in  FIG.  1    as being near first end  44 , this is not mandatory and one or more outlets could additional or alternatively be provided near second end  46 . 
     As particles  5  progress through reactor  20 , particles  5  are fluidized by the introduction of a fluidization medium  7  into chamber  23 . In the illustrated embodiment, a plurality of fluid inlets  28  are arranged to deliver fluidization medium  7  into chamber  23  in a generally upward direction. In general, fluidization medium  7  may be delivered into vessel  22  in a second direction  14 . Second direction  14  may be non-parallel to first direction  12 . Second direction  14  may be orthogonal to first direction  12 . 
     Advantageously chamber  23  is elongated in direction  12 . In some embodiments, a length of chamber  23  along direction  12  is at least 3 or at least 5 times greater than a width of chamber  23 . In some embodiments, the length of chamber  23  in first direction  12  is in the range of about 25 cm to 10 m. In some embodiments the width of bed  25  (e.g. the width of a lower portion of chamber  23  in third direction  16 ) is in the range of about 8 cm to 2 m. 
     To increase capacity of reactor  20 , the width (in third direction  16 ) of chamber  23  and/or the length (in first direction  12 ) can be increased. To increase residence time or increase a severity of the reaction, the length (in first direction  12 ) of chamber  23  may be increased or the rate at which particles  5  are fed into reactor  20  may be decreased. In some embodiments, the height of bed  25  is independent of the length and/or width of bed  25 . In some embodiments, it is desirable to maintain the height of bed  25  generally below 10 cm (except for fluctuations in height due to bubbles and/or waves). 
     In one non-limiting embodiment, reactor  20  has a capacity to process about 20 kg/h of particles  5 , the width (in third direction  16 ) of chamber  23  is approximately 15 cm, the length (in first direction  12 ) of chamber  23  is approximately 100 cm and the height (in second direction  14 ) of bed  25  (bed  25  described in more detail herein) is approximately 10 cm or less. In another non-limiting embodiment, reactor  20  has a capacity to process about 2 kg/h of particles  5 , the width (in third direction  16 ) of chamber  23  is approximately 10 cm, the length (in first direction  12 ) of chamber  23  is approximately 25 cm and the height (in second direction  14 ) of bed  25  is approximately 10 cm or less. 
     In some embodiments, chamber  23  may be tapered along first direction  12 . For example, a third direction  16  width of chamber  23  at first end  44  may be greater than a third direction  16  width of chamber  23  at second end  46 . Such a tapering may be beneficial in maintaining a uniform horizontal flow rate of particles  5  in first direction  12  despite the volume and/or mass of biomass  5  decreasing as it travels in first direction  12  toward second end  46 . 
     In some embodiments, bottom wall  22 A may be sloped. For example, first end  44  or bottom wall  22 A may be arranged to be higher than second end  46  of bottom wall  22 A to encourage movement of particles  5  from first end  44  to second end  46  due to gravity. In other embodiments, first end  44  or bottom wall  22 A may be arranged to be lower than second end  46  of bottom wall  22 A to achieve a desired residence time of particles  5 . 
     First and second sidewalls  22 B,  22 C of vessel  22  may be formed to diverge. This can advantageously limit the depth of bed  25  in chamber  23 . As fluidization medium  7  streams upward in chamber  23 , the cross-sectional area available for the flow of fluidization medium  7  increases and consequently the flow velocity of fluidization medium  7  decreases. When the flow velocity of fluidization medium  7  is low enough, the force of gravity on particles  5  exceeds the lift provided by the flow of fluidization medium  7  thereby causing particles  5  to fall which in turn limits the depth of bed  25  and prevents particles from being entrained out of chamber  23  by fluidization medium  7 . 
     In some embodiments, as illustrated schematically in  FIG.  3 C , first and second sidewalls  22 B,  22 C are formed so that they are generally vertical up to a first elevation  27  above bottom wall  22 A and then diverge from one another above the first elevation. With this construction and suitable choice of flow of fluidization medium  7 , the top of bed  25  can be maintained to be near first elevation  27 . 
     First and second sidewalls  22 B,  22 C may be formed to diverge so that particles  5  that alight on non-vertical parts of sidewalls  22 B,  22 C fall back toward bottom wall  22 A and not accrete on first or second sidewalls  22 B,  22 C. For example, first and second sidewalls  22 B,  22 C may be sloped such that when reactor  20  is installed, first and second sidewalls are arranged at angles, α, β with respect to the horizontal, where α and β are each in the range of about 30° to about 80°, as shown, for example, in  FIG.  2   . 
     Providing first and second sidewalls  22 B,  22 C that diverge can advantageously allow a higher velocity of fluidization medium  7  within bed  25  as compared to in a vessel having parallel vertical side walls. The higher velocity of fluidization medium may in turn improve heat transfer to particles  5  and mass transfer of particles  5  in first direction  12 . 
     Inside chamber  23 , particles  5  may form a bed  25 . Bed  25  is a volume within vessel  22  defined in shape and size by the presence of particles  5 . Preferably bed  25  is located in a lower portion of chamber  23  (i.e. there is an elevation within chamber  23  above which, in normal operation, there are few or no particles  5 . 
     The volume and shape of bed  25  may change as more particles  5  are fed into vessel  22  or as the packing density of particles  5  changes. For example, the size of bed  25  may increase as the packing density of particles  5  within all or a portion of vessel  22  decreases. A decrease in packing density of particles  5  may, for example, be caused by increasing a flow of fluidization medium  7 , thereby raising an elevation of the top of bed  25 . Conversely, an increase in packing density of particles  5  may be caused by reducing a flow of fluidization medium  7 , thereby causing an elevation of the top of bed  25  to be lowered. The volume of bed  25  may also be affected by adjusting a rate at which particles  5  are fed into reactor  22 . 
     The elevation of the top of bed  25  may be relatively constant or may change along the length of vessel  22 . For example, bed  25  height may change as one gets closer to second end  46  due to a reduction in size of individual particles  5  and/or a reduction of density of particles  5  due to drying and/or torrefaction and/or pyrolysis. Bubbles and/or waves which result from delivery of fluidization medium  7  may cause localized variations in the height of bed  25  by between approximately 10% and 30%. 
     As compared to traditional fluidized bed reactors, bed  25  may be relatively shallow. For example, bed  25  may be maintained with a height (in second direction  14 ) of 30 cm or less, 17 cm or less, or even 10 cm or less. Such a shallow design may improve the efficacy of fluidization medium  7  to fluidize particles  5  in bed  25  and/or may reduce undesirable rearward travel (e.g. back mixing) of particles  5 . 
     The contents of reactor  20  may be heated by heating fluidization medium  7 . Additional mechanisms for heating reactor  20  may optionally be provided. Additional heating mechanisms may be particularly useful for bringing particles  5  to temperatures required for pyrolysis. 
     For example, in some embodiments, reactor  20  comprises one or more direct heaters (not depicted). Such direct heaters may be provided on or within the walls of vessel  22 . Such direct heaters may also or alternatively be provided to heat the walls of vessel  22 . Such direct heaters could comprise heat exchange tubes or the like. In some embodiments, heat exchange tubes or the like may be immersed in bed  25 . 
     As another example of an additional heating mechanism, reactor  20  may comprise a mechanism for microwave heating of contents of reactor  20 . For example, one or more magnetrons  34  may be provided to heat particles  5  as they travel through vessel  22 . For example, in some embodiments, magnetrons  34  are employed for microwave-assisted pyrolysis. Magnetrons  34  may comprise any suitable type of magnetrons such as, for example, negative resistance magnetrons, cyclotron frequency magnetrons and travelling wave or cavity magnetrons. In some embodiments magnetrons  34  may be concentrated toward second end  46  of reactor  20  where particles  5  have reached higher temperatures and pyrolysis reactions are taking place and not relatively closer to first end  44  where particles  5  may not yet have reached temperatures where pyrolysis reactions are occurring. 
     In some embodiments, one or more windows  34 A (as shown, for example, in  FIG.  1   ) may be provided to allow microwaves from magnetrons  34  to pass into chamber  23 . Windows  34 A may comprise glass or quartz. In some embodiments, at least a portion of top wall  22 F may comprise a material that allows microwaves to pass from magnetrons  34  into chamber  23 . 
     In cases where microwave heating is used, particles of a suitable microwave catalyst (also referred to herein as absorbent) may be mixed with particles  5 . The microwave catalyst may be a material that absorbs microwave energy and becomes hot. In the fluidized bed heat is transferred from the particles of microwave catalyst to particles  5 . The catalyst may decompose organic vapours generated from biomass cracking. As described elsewhere herein, appropriate selection of a microwave catalyst material may enhance the value of products output by reactor  20 . 
     Bottom wall  22 A may include openings such as slits, perforations or the like to allow fluidization medium  7  to be delivered into vessel  22  from beneath particles  5 .  FIG.  3 A  shows an example in which perforations in bottom wall  22 A allow the flow of fluidization medium  7  from fluid inlets  28  into chamber  23 . In some embodiments, the perforations of bottom wall  22 A cover in the range of about 1% to about 10% of the surface area of bottom wall  22 A. Bottom wall  22 A may also serve to prevent or hinder particles  5  from leaving vessel  22  undesirably. Bottom wall  22 A may comprise a perforated sandwiched distributor, one or more nozzles, bubble caps and/or the like to distribute fluidization medium  7  into chamber  23 . 
       FIGS.  3 D and  3 E  are schematic depictions of a portion of a bottom wall  22 A comprising an exemplary perforated sandwiched distributor according to one embodiment of the invention. In the illustrated embodiment, bottom wall  22 A comprises three layers: a mesh screen  21 A, a first perforated support sheet  21 B and a second perforated support sheet  21 C. 
     Apertures of mesh screen  21 A may be sufficiently small to prevent particles  5  from passing through. Mesh screen  21 A may be a metal mesh screen. First and second perforated support sheets  21 B,  21 C may provide structural support to mesh screen  21 A. First and second perforated support sheets  21 B,  21 C may reduce damage to mesh screen  21 A. First and second perforated support sheets  21 B,  21 C may channel fluidization medium  7  through mesh screen  21 A. 
     As can be seen from  FIGS.  3 D and  3 E , the perforations in second support sheet  21 C may be larger than the perforations in first support sheet  21 B. This may facilitate alignment of first and second perforated support sheets  21 B,  21 C. The size and number of perforations in first and second perforated support sheets  21 B,  21 C may be chosen to facilitate fluidization of the selected particles  5 . For example, for larger or heavier particles  5 , the perforations may be smaller to thereby increase the velocity of fluidization medium  7 . However, the pressure drop across bottom wall  22 A should not be so great as to prevent or impede the pulsation of gas flow. 
     A plurality of fluid inlets  28  may be arranged to deliver fluidization medium  7  into chamber  23  of vessel  22  and bed  25 . In some embodiments, fluid inlets  28  are arranged to deliver fluidization medium  7  into vessel  22  and bed  25  substantially (e.g. within +/- 20°) of vertical in second direction  14  as shown, for example, in  FIG.  1   . 
     Fluidization medium  7  may comprise a gas. The gas may be selected to not cause undesired reactions with particles  5 . For example, fluidization medium  7  may have an oxygen gas content of about 8% or less (by volume) which is significantly lower than that of atmospheric air which generally has an oxygen content of about 21%. Fluidization medium  7  may comprise, for example, air that has been depleted in oxygen, nitrogen gas, steam, exhaust gas from a combustion process, flue gas, mixtures of these or the like. In some embodiments, fluidization medium  7  is recirculated flue gas. In some embodiments, fluidization medium  7  is an inert gas. Fluidization medium  7  may be pressurized (e.g. fluidization medium  7  may be at a pressure greater than 1 atm). 
     As discussed further herein, reactor  20  may have a plurality of fluid inlets  28  which can carry fluidization medium  7  into corresponding regions in reactor  20 . In the embodiments illustrated in  FIGS.  3 A and  6 A to  6 E , reactor  20  comprises five fluid inlets  28  (e.g. fluid inlets  28 A,  28 B,  28 C,  28 D,  28 E) for delivering fluidization medium  7  into five regions  23 A,  23 B,  23 C,  23 D,  23 E respectively. The number of fluid inlets  28  and regions may be varied. Reactor  20  may comprise more than or less than five fluid inlets  28 . 
     Fluid inlets  28  are spaced apart along vessel  22  in first direction  12 . In some embodiments, fluid inlets  28  are spaced apart evenly in the first direction  12 . This is not mandatory. In some embodiments, fluid inlets  28  are spaced apart in the first direction  12  by between about 20 cm and 60 cm. In some embodiments, fluid inlets  28  may be aligned with one another (e.g. as shown, for example, in  FIG.  4 B ). This is not mandatory. In some embodiments, fluid inlets  28  are staggered (as shown, for example, in  FIG.  4 C ). In some embodiments, fluid inlets  28  are centered on bottom wall  22 A in the third direction  16 . 
     In some embodiments, fluid inlets  28  may be paired as shown in Figured 4D. For example, two fluid inlets  28 A- 1  and  28 A- 2  may be aligned in third direction  16  and additional pairs of fluid inlets (e.g. fluid inlets  28 B- 1  and  28 B- 2 ,  28 C- 1  and  28 C- 2 ,  28 D- 1  and  28 D- 2 , and  28 E- 1  and  28 E- 2 ) may be spaced apart in first direction  12  to effectively create  10  regions  23 A- 1 ,  23 A- 2 ,  23 B- 1  ,  23 B- 2 ,  23 C- 1 ,  23 C- 2 ,  23 D- 1  ,  23 D- 2 ,  23 E- 1   23 E- 2 . Such a configuration, with pairs (or triplets or quadruplets etc.) of fluid inlets  28  aligned in third direction  16  may allow for a chamber  23  with an increased width in third direction and/or may reduce undesired piling of particles  5  (particularly near the third direction  16  edges of chamber  23 ). 
     Fluid inlets  28  may comprise any suitable apparatus for delivering fluidization medium  7  into vessel  22  in second direction  14 . In some embodiments, fluid inlets  28  are operable to vary the flow of fluidization medium  7  for example by ‘pulsing’ or switching the flow of fluidization medium  7  on and off. 
     Fluid inlets  28  may be controlled by a suitable mechanical and/or electronic control mechanism to vary the flow of fluidization medium  7  into different regions of chamber  23  in coordination with one another. For example, fluid inlets  28  may be independently controllable or controlled by a mechanism which adjusts fluid inlets  28  to vary flows of fluidization medium  7  into different regions in a desired sequence. 
     As discussed further herein, in some embodiments, fluid inlets  28  may be operable in series (e.g. fluid inlets  28  may be operable such that second fluid inlet  28 B delivers fluidization medium  7  into chamber  23  after first fluid inlet  28 A delivers fluid into chamber  23  and third fluid inlet  28 C delivers fluidization medium  7  into chamber  23  after second fluid inlet  28 B delivers fluidization medium  7  into chamber  23 , and so on). 
     In some embodiments each fluid inlet  28  is controlled to vary the flow of fluidization medium  7  into a corresponding region according to a cycle and fluid inlets  28  are collectively controlled so that the relative phases of their cycles are delayed more and more as one progresses along chamber  23  in direction  12 . For example, in each cycle a fluid inlet  28  may deliver fluidization medium  7  at a first rate in a first portion of the cycle and may deliver fluidization medium  7  at a second rate lower than the first rate in a second portion of the cycle. In some embodiments the first rate is at least twice the second rate. In some embodiments a fluid outlet  28  may be controlled to deliver no or very little fluidization medium  7  for the second portion of each cycle. 
     In some embodiments, fluidization medium  7  is delivered into vessel  22  at a rate such that a superficial velocity of the fluidization medium  7  entering chamber  23  is in the range of about 1 to about 1.5 times the minimum fluidization velocity of particles  5 . In some embodiments, fluidization medium  7  is delivered into vessel  22  at a rate such that a superficial velocity of the fluidization medium  7  entering chamber  23  is in the range of about 1 to about 1.2 times the minimum fluidization velocity of particles  5 . “Minimum fluidization velocity” is the superficial velocity of fluidization medium  7  at which the drag force of the upward moving fluidization medium  7  on particles  5  becomes equal to the weight of particles  5  in vessel  22 . When the superficial velocity of fluidization medium  7  is greater than the minimum fluidization velocity, the drag force of the upward moving fluidization medium  7  on particles  5  is greater than the weight of particles  5  in vessel  22  and particles  5  may be described as being “fluidized”. 
     In some embodiments, a rate at which fluidization medium  7  is delivered into vessel  22  is higher near first end  44  where particles  5  may be larger and/or heavier than near second end  46  where particles  5  may be smaller and/or lighter. 
     In some embodiments, each of fluid inlets  28  comprises flow control means for regulating the flow of fluidization medium  7  into chamber  23  via inlets  28 . The flow control means may comprise, for example, a distributed plate, valves (e.g. butterfly valves), a rotating air distributor or other available intermittently activatable apparatus for delivering fluidization medium  7 . In some embodiments, each fluid inlet  28  is connected to a common fluid source. In other embodiments, one or more of fluid inlets  28  have their own fluid source. 
     Where valves are provided to regulate the flow of fluidization medium  7  via fluid inlets  28  the valves may be electronically operated (e.g. using solenoids or other electrically operable valve actuators) and/or mechanically operated (e.g. by cams, pneumatic actuators, hydraulic actuators or the like). In some embodiments, the duration and interval of valves being opened may be controlled by a suitable controller. 
     In some embodiments, the flow of fluidization medium  7  via fluid inlets  28  may be regulated by employing different length manifolds to provide fluidization medium  7  from a single source (e.g. a combustor such as a pulse jet). Due to the different length manifolds, the fluidization medium  7  can be caused to arrive at each fluid inlet  28  as desired without employing valves. 
       FIG.  3 B  depicts an exemplary, non-limiting, fluid inlet  28 A as may be applied in some embodiments of the invention. In the  FIG.  3 B  embodiment, fluid inlet  28 A comprises a fluid chamber  36  containing pressurized fluidization medium  7 . A seal  40  is moveable between an open position and a closed position. If seal  40  is in the open position (as shown, for example, in  FIG.  3 B ), fluidization medium  7  may be caused to travel from fluid chamber  36  into chamber  23  due to the pressure gradient between fluid chamber  36  and chamber  23 . When in the closed position (as shown, for example, in  FIG.  3 A ), seal  40  prevents or substantially prevents fluidization medium  7  from travelling from fluid chamber  36  into chamber  23  or reduces the flow of fluidization medium  7  into vessel  22 . By selectively operating a piston  38 , seal  40  may be opened or closed. 
     Piston  38  may be a cam-actuated piston, a hydraulic piston, a pneumatic piston or any other suitable piston. As compared to, for example, a distributing plate, a piston does not require revolving parts and is less likely to fail. Pistons of different drive force, frequency and size are widely available. As compared to solenoid valves, pistons tend to be more reliable and are more suited to continuous operation at frequencies in the range of about 1 Hz to 2 Hz. 
     In some embodiments, fluid chamber  36  is common to one or more of fluid inlets  28 . For example, fluid chamber  36  may comprise a plenum that is common to two or more or all of fluid inlets  28 A,  28 B,  28 C,  28 D,  28 E. Each fluid inlet  28  may comprise a flow control means (e.g. a piston-activated seal  40 ) operable to allow fluidization medium  7  to be selectively delivered from common fluid chamber  36 , through the respective fluid inlet  28  and into to chamber  23  as desired. 
     In some embodiments, fluidization medium  7  is delivered into vessel  22  through one or more plenum chambers  30 A,  30 B,  30 C,  30 D,  30 E. In the  FIG.  1    embodiment, fluidization medium  7  delivered from first fluid inlet  28 A is delivered through first plenum chamber  30 A, fluidization medium  7  delivered from second fluid inlet  28 B is delivered through second plenum chamber  30 B, fluidization medium  7  delivered from third fluid inlet  28 C is delivered through third plenum chamber  30 C, fluidization medium  7  delivered from fourth fluid inlet  28 D is delivered through fourth plenum chamber  30 D and fluidization medium  7  delivered from fifth fluid inlet  28 E is delivered through fifth plenum chamber  30 E. 
     By delivering fluidization medium  7  through separated plenum chambers, the instantaneous gas flow rate may be relatively higher when any one seal  40  is open (as compared to if all seals  40  were open concurrently), thereby facilitating particles  5  to overcome their cohesive forces and improving gas-solid contact and heat/mass transfer. By delivering fluidization medium  7  through a plurality of separated plenum chambers, fluidization medium  7  may be more precisely distributed along vessel  22 . This facilitates independently delivering fluidization medium  7  to individual regions (e.g. to deliver fluidization medium  7  from first fluid inlet  28 A into first region  23 A or to deliver fluidization medium  7  from second fluid inlet  28 B into second region  23 B, etc.) as desired. 
       FIG.  4 A  is a top plan view of reactor  20  according to one embodiment of the invention which provides microwave boost heating. In the  FIG.  4 A  embodiment, vessel  22  of reactor  20  may nominally be separated into a first zone  48 A and a second zone  48 B. First zone  48 A is located toward inlet  24  and second zone  48 B is located toward outlet  26 . In first zone  48 A, particles  5  are heated by fluidization medium  7  while in second zone  48 B, particles  5  are heated by fluidization medium  7  and by energy from microwaves emitted by magnetrons  34 . Any suitable number of magnetrons  34  may be provided to heat particles  5  in second zone  48 B. For example, in the illustrated embodiment, eight magnetrons  34  are provided to heat particles  5  in second zone  48 B. In other embodiments, more than or fewer than eight magnetrons may be provided. The number of magnetrons may be dependent on the length of vessel  22 . In some embodiments, magnetrons  34  may be arranged to heat particles  5  along an entire first direction  12  dimension of vessel  22  (e.g. there is no first zone  48 A). In some embodiments, magnetrons  34  may be arranged to heat particles  5  along less than 80%, less than 60% or less than 50% of the first direction  12  dimension of vessel  22 . 
     In some embodiments, reactor  20  comprises one or more vibrators to cause vessel  22  to vibrate. For example, reactor  20  may comprise a vibration motor such as an eccentric rotating mass vibration motor, a linear resonant actuator, or the like to cause vessel  22  and/or particles  5  to vibrate as desired. 
     Although the embodiments depicted and described herein may show a reactor  20  that provides a linear travel path for particles  5 , this is not mandatory. For example, a reactor could provide a travel path for particles  5  that is curved in one or more of first direction  12 , second direction  14  and third direction  16 . 
     Although the embodiments of reactor  20  depicted and described herein may show a reactor that provides a travel path for particles  5  from one end of a vessel to the other, it should be understood that the travel path for particles  5  could extend from a central region of a vessel to a more distal region of the vessel. For example, particles  5  could be fed to a middle of a vessel and directed in opposite directions toward opposite ends of the vessel. Alternatively or additionally, reactor  20  could be split across multiple vessels. 
     Another aspect of the invention provides methods for processing particles  5 . Processing particles  5  may comprise torrefying particles  5  or pyrolyzing particles  5 , as desired. In some embodiments, if particles  5  comprise a mixture of biomass particles and polymer particles having, for example, a composition with greater than 10% polymer particles by weight, it may be desirable to pyrolyze particles  5 . The methods may be implemented using one or more of the reactors described herein, although this is not mandatory. 
       FIG.  5 A  shows a block diagram of an exemplary non-limiting method  100  for processing biomass. Method  100  may be described herein in relation to reactor  20  for convenience. However, it should be understood that method  100  could be carried out with reactors other than reactor  20  or the reactors described herein. 
     In some embodiments, method  100  comprises a first step  110  of feeding particles  5  through chamber  23  of reactor  20 . In some embodiments, particles  5  may be fed through chamber  23  in first direction  12 . Step  110  may comprise feeding particles  5  into first region  23 A of chamber  23  through a biomass inlet  24  as described herein. 
     Particles  5  may travel in first direction  12  through vessel  22  due to the feeding of particles  5  into vessel  22 . In some embodiments, the feeding of new particles  5  into vessel  22  at step  110  may increase a density of particles  5  near inlet  24 . This in turn may create a density gradient that pushes particles  5  already in vessel  22  in first direction  12 . For example, particles  5  being fed into first region  23 A may cause at least some particles  5  previously in first region  23 A to move into second region  23 B. Such first direction  12  movement of particles  5  may be aided by the fluidization of particles  5  which facilitates or promotes movement of particles  5  in first direction  12  in chamber  23  and/or by gravity if reactor  20  is sloped downward. 
     The rate at which particles  5  are fed into vessel  22  may be dependent on the desired residence time of particles  5  in reactor  20 . For a longer desired residence time (e.g. for torrefaction), the feed rate may be reduced. For shorter residence times (e.g. for pyrolysis), the feed rate may be increased. In some embodiments, the desired residence time of particles  5  in reactor  20  is in the range of about 5 minutes to about 40 minutes (e.g. for torrefaction). In some embodiments, the desired residence time of particles  5  in reactor  20  is in the range of about 10 minutes to about 30 minutes (e.g. for torrefaction or pyrolysis). In some embodiments, the desired residence time of particles  5  in reactor  20  is in the range of about 1 minute to about 10 minutes (e.g. for pyrolysis). By adjusting the residence time of the reactor, the severity of pyrolysis, yield and conversion of bio-oil and biochar may be controlled. By shortening the residence time of reactor  20 , the reactor footprint can be reduced for a given level of throughput of biomass. 
     Method  100  comprises a step  120  of fluidizing particles  5 . Step  120  may occur concurrently with step  110 . Fluidizing particles  5  may comprise propagating one or more fluidization waves in first direction  12  inside chamber  23 . Second step  120  may comprise a number of sub-steps as shown, for example, in  FIG.  5 B . 
     In some embodiments, second step  120  includes a sub-step  120 A. Sub-step  120 A comprises delivering a first volume  7 A of fluidization medium  7  into a first region  23 A of vessel  22  in second direction  14  to fluidize particles  5  in first region  23 A of vessel  22 , as shown, for example, in  FIG.  6 A . First volume of fluidization medium  7 A may be delivered by first fluid inlet  28 A. First volume of fluidization medium  7 A may be a discrete volume  7 A of fluidization medium  7  delivered as a burst. Delivery of fluidization medium  7  into first region  23 A may, at least temporarily, cause the particles  5  located in first region  23 A to fluidize (e.g. convert from a solid-like state to a dynamic fluid-like state) and/or may reduce the packing density of particles  5  located in first region  23 A. 
     After the delivery of first volume  7 A of fluidization medium  7 , particles  5  located in first region  23 A may begin to settle (e.g. due to the force of gravity). In some embodiments, particles  5  located in first region  23 A may settle completely (e.g. on bottom wall  22 A) before additional fluidization medium  7  is delivered to first region  23 A. In other embodiments, an additional burst of fluidization medium  7  into first region  23 A (e.g. when sub-step  120 A is repeated) may cause the particles  5  located in first region  23 A to fluidize and/or may reduce the packing density of particles  5  located in first region  23 A before particles located in first region  23 A have settled completely (e.g. on bottom wall  22 A). 
     In some embodiments, second step  120  includes a sub-step  120 B as shown, for example, in  FIG.  6 B . Sub-step  120 B may occur, after, with a delay after or concurrently with sub-step  120 A. Sub-step  120 B may be substantially similar to sub-step  120 A except that sub-step  120 B comprises delivering a second volume  7 B of fluidization medium  7  into a second region  23 B of vessel  22  in second direction  14  to fluidize particles  5  in second region  23 B of vessel  22 . Second volume  7 B of fluidization medium may be delivered by second fluid inlet  28 B. 
     In some embodiments, second step  120  includes a sub-step  120 C as shown, for example, in  FIG.  6 C . Sub-step  120 C may occur, after, with a delay after or concurrently with sub-step  120 B. Sub-step  120 C may be substantially similar to sub-step  120 B except that sub-step  120 C comprises delivering a third volume  7 C of fluidization medium  7  into third region  23 C of vessel  22  in second direction  14  to fluidize particles  5  in third region  23 C of vessel  22 . Third volume  7 C of fluidization medium  7  may be delivered by third fluid inlet  28 C. 
     In some embodiments, second step  120  includes a sub-step  120 D as shown, for example, in  FIG.  6 D . Sub-step  120 D may occur, after, with a delay after or concurrently with sub-step  120 C. Sub-step  120 D may be substantially similar to sub-step  120 C except that sub-step  120 D comprises delivering a fourth volume  7 D of fluidization medium  7  into fourth region  23 D of vessel  22  in second direction  14  to fluidize particles  5  in fourth region  23 D of vessel  22 . Fourth volume  7 D of fluidization medium  7  may be delivered by fourth fluid inlet  28 D. 
     In some embodiments, second step  120  includes a sub-step  120 E as shown, for example, in  FIG.  6 E . Sub-step  120 E may occur, after, with a delay after or concurrently with sub-step  120 D. Sub-step  120 E may be substantially similar to sub-step  120 D except that sub-step  120 E comprises delivering a fifth volume  7 E of fluidization medium  7  into fifth region  23 E of vessel  22  in second direction  14  to fluidize particles  5  in fifth region  23 E of vessel  22 . Fifth volume  7 E of fluidization medium  7  may be delivered by fifth fluid inlet  28 E. 
     Sub-steps  120 A to  120 E may repeat until method  100  is completed. In some embodiments, each sub-step of step  120  occurs in sequence without any overlap. This is not mandatory. In some embodiments, one or more sub-steps may occur concurrently or may partially overlap. 
     Each repetition of step  120  may cause a fluidization wave  42  (or fluidization wave  42 ) to travel through bed  25  in first direction  12  as illustrated in  FIG.  7   . Fluidization wave  42  may comprise a region of bed  25  where a packing density of particles  5  is relatively lower than a packing density of particles  5  in the rest of bed  25  due to the delivery of fluidization medium  7  into that region. As fluidization medium  7  is delivered sequentially at spaced apart locations in first direction  12  during step  120 , fluidization wave  42  is caused to travel in first direction  12 . This phenomenon can be seen in  FIGS.  6 A to  6 E  where a first fluidization wave  42  travels from first end  44  to second end  46  and in  FIG.  6 F  where a second fluidization wave  42  is started in first region  23 A. While the illustrated embodiments only show a single fluidization wave  42  travelling through bed  25  at any given time, this is not mandatory. Instead, multiple fluidization waves  42  could travel through bed  25  at any given time (e.g. by allowing multiple sub-steps of step  120  to occur concurrently). 
     Fluidization waves  42  may facilitate and/or cause particles  5  to travel in first direction  12 . Fluidization waves  42  may facilitate in transforming random bubble behaviour typically seen in fluidized bed reactors into regular and ordered patterns, thereby achieving a relatively uniform and even bed  25 . particles suspended in bed  25  are therefore more likely to experience uniform and consistent residence times. 
     The periodic supply of fluidization medium  7  (as opposed to maintaining a constant flow rate) in each of regions  23 A,  23 B,  23 C,  23 D,  23 E imparts additional acceleration on particles  5  that may help to break down cohesion and/or bridging between particles  5  and/or to increase the flowability of particles  5  in bed  25  (e.g. in first direction  12 ). Consequently, better gas-solid contact is present between particles  5  and fluidization medium  7  in reactor  20  which allows for higher heat and mass transfer rates between fluidization medium  7  and particles  5 . 
     The sub-steps of step  120  may occur at any desirable rate. In some embodiments, each fluid inlet  28  is controlled to deliver fluidization medium  7  at a rate of between approximately 0.5 Hz and 5 Hz. In some embodiments, the duty cycle of each fluid inlet  28  is between approximately 30% and 70%. For example, a fluid inlet  28  could deliver fluidization medium  7  at a rate of 1 Hz with a duty cycle of 30% such that fluid inlet  28  is repetitively opened for 0.3 seconds and closed for 0.7 seconds. In some embodiments, adjacent fluid inlets (e.g. sub-steps  120 A to  120 E) are selectively delayed by between approximately 0.1 seconds and 0.9 seconds. In some embodiments, there is no delay between adjacent fluid inlets  28  and some or all fluid inlets  28  are synchronized. In some embodiments, adjacent fluid inlets  28  are paired and there is instead a delay between pairs of fluid inlets  28 . 
     For example, first fluid inlet  28 A may operate at 1 Hz with a duty cycle of 50% while second fluid inlet  28 A operates at 1 Hz with a delay of 0.5 seconds and a duty cycle of 50% such that there is no effectively overlap between delivery of fluidization medium  7  from first fluid inlet  28 A and second fluid inlet  28 B. In this case, third fluid inlet  28 C may operate at 1 Hz with a delay of 0.5 seconds (from second fluid inlet  28 B) and a duty cycle of 50% such that there is effectively no overlap between delivery of fluidization medium  7  from second fluid inlet  28 B and third fluid inlet  28 C but there is effectively complete overlap between delivery of fluidization medium  7  from third fluid inlet  28 C and first fluid inlet  28 A. 
     In another example, first fluid inlet  28 A may operate at 1 Hz with a duty cycle of 30% while second fluid inlet  28 A operates at 1 Hz with a delay of 0.2 seconds and a duty cycle of 30% such that there is some overlap between delivery of fluidization medium  7  from first fluid inlet  28 A and second fluid inlet  28 B. 
     In some embodiments, the duty cycle of each fluid inlet  28  is chosen to ensure fluidization of particles  5  in the respective region of chamber  23 . In some embodiments, the duty cycle is increased (to lower the velocity of fluidization medium  7 ) as moisture in (and consequently mass of) particles  5  is decreased. In some embodiments, the duty cycle is decreased (to increase the velocity of fluidization medium  7 ) as particles  5  become exhibit a greater tendency to stick to one another (e.g. since they are more needle-like in shape and/or less spherical and/or contain higher moisture content). 
       FIGS.  6 A to  6 F  highlight (with a darker filling) a particular grouping  50  of particles  5  as it travels (at an exaggerated rate for illustrative purposes) in first direction  12  from first end  44  of vessel  22  toward second end  46  of vessel  22 . As can be seen from  FIGS.  6 A to  6 F , fluidization wave  42  travelling in first direction  12  from first end  44  of vessel  22  to second end  46  of vessel  22  travels faster than grouping  50  of particles  5 . As such, any individual particle  5  will generally be subject to a plurality of fluidization waves  42  as it travels through vessel  22 . 
     The number of sub-steps of step  120  may be dependent on the number of fluid inlets  28 . For example, in the illustrated embodiments, reactor  20  comprises five fluid inlets  28  and there is a corresponding sub-step of step  120  for each fluid inlet  28 . However, while the illustrated embodiment depicts five fluid inlets  28 , it should be understood that a reactor employed for method  100  could comprise any number, n, of fluid inlets  28  (where n is an integer) and that there could be a corresponding number, n, of sub-steps of step  120  corresponding to delivering volumes of fluid through each of the number, n, of fluid inlets  28 . 
     Method  100  comprises a step  130  of heating particles  5 . Step  130  may occur concurrently with one or both of steps  110  and  120 . At step  130 , particles  5  may be heated in various manners. In some embodiments, particles  5  may be heated (e.g. by convective heat transfer) by fluidization medium  7  which itself may be heated before being delivered into vessel  22  at step  120 . For example, fluidization medium  7  may enter chamber  23  at a temperature of 300° C. or more (e.g. for torrefaction) or 500° C. or more (e.g. for pyrolysis). In some embodiments, fluidization medium  7  may enter chamber  23  at a temperature of up to about 800° C. (e.g. for pyrolysis). In some embodiments, the temperature of fluidization medium  7  is dependent on the type, size and/or shape of particles  5  and the desired reaction in reactor  20 . For example, as the composition of particles  5  skews toward more polymer particles and less biomass particles, it may be desirable to reduce the temperature of fluidization medium  7 . In some embodiments, where particles  5  have a composition of greater than 90% polymer particles by weight, fluidization medium  7  may enter chamber  23  at a temperature of between about 300° C. and 500° C. (e.g. for pyrolysis). By contrast, when particles  5  comprise more than 90% biomass by weight, higher temperatures of between about 500° C. and 800° C. may be used to pyrolize particles  5 . 
     In some embodiments, fluidization medium  7  is provided from a common source and thus fluidization medium  7  provided at each sub-step of step  120  is provided at a constant or substantially constant temperature. In other embodiments, fluidization medium  7  could be provided at each sub-step of step  120  at a different temperature. For example, the temperature of fluidization medium  7  delivered at each sub-step of step  120  may increase from sub-step  120 A to sub-step  120 E to attain a desired rate of heating of particles  5  as the particles  5  travel along chamber  23 . 
     As each particle  5  travels through vessel  22  in first direction  12 , it is heated by fluidization medium  7 .  FIG.  8 A  depicts an exemplary lower boundary and an exemplary upper boundary of a temperature of a particle  5  as a function of the distance it has travelled through vessel  22  in first direction  12 . Specifically,  FIG.  8 A  represents a reactor  20  without magnetrons (e.g. a reactor without a second zone  48 B) or a reactor  20  where the magnetrons are off. The  FIG.  8 A  heating rate could be employed for torrefaction of particles  5 . 
     Method  100  may comprise an optional step  140  of microwaving particles  5 . Step  140  may occur concurrently with some or all of steps  110 ,  120  and  130 . Step  140  may occur in only a portion of vessel  22  (e.g. in second zone  48 B). 
     Compared to convective heating through fluidization medium  7 , microwave heating may be significantly faster, and particles  5  may be heated from their core to their exterior. However, some types of particles  5  may not absorb microwaves effectively. Therefore, in some embodiments, as part of step  140 , microwave absorbent (also sometimes referred to as a microwave catalyst) may be mixed with particles  5  to increase the absorption of microwaves within vessel  22  and to thereby accelerate the rate of temperature increase of particles  5 . In some embodiments, the microwave absorbent is heated by the microwaves (e.g. from magnetrons  34 ) at a higher rate than are particles  5  (e.g. because the absorbent has a higher dielectric constant than particles  5 ). Heat that is subsequently generated by the microwave absorbent may then be passed on to surrounding particles  5 . 
     Various microwave absorbents may be employed such as, but not limited to, chemical solutions (NH 3 , H2SO 4  and HCl), inorganic compounds (MgCl 2 , Na 2 HPO 4 , CH 3 COOK and Al 2 O 3 ), catalysts (K 3 PO 4 , K 2 CO 3 , KOH, FeSO 4 , H 3 BO 3 , ZnCl 2  and H2SO 4 ), natural zeolites, synthetic zeolites, and char. In some embodiments, a mixture of K 3 PO 4  and clinoptilolite or bentonite is employed as a microwave absorbent. 
     Ideally, microwave absorbents have good microwave absorption capacity and good catalytic performance so as to increase the microwave heating rate and improve the quality of bio-oil and biochar produced by reactor  20 . Resultant biochar may be employed as a soil conditioner. Biochar produced from microwave catalytic pyrolysis has been demonstrated to be more effective in increasing the soil water holding capacity due to its high porosity in comparison with biochar produced from conventional pyrolysis. Furthermore, catalysts or absorbents remaining in the biochar product can provide nutrients for the growth of bioenergy and food crops. 
     In some embodiments, microwave absorbents are provided in the form of particles that are similar in size to particles  5 . In some embodiments, a composition of bed  25  is in the range of about 5% to about 30% microwave absorbent particles by weight. In some embodiments, a composition of bed  25  is in the range of about 15% to about 20% microwave absorbent particles by weight. 
     In some embodiments, microwave absorbent particles are mixed with particles  5  before entering chamber  23 . In other embodiments, microwave absorbent particles are introduced into chamber  23  separately from particles  5 . In some embodiments, microwave absorbent particles are introduced into chamber  23  continuously. In some embodiments, microwave absorbent particles are introduced into chamber  23  periodically or as needed. 
     In some embodiments, microwave absorbent particles are removed from chamber  23  with outputs  6 . In such embodiments, it may be desirable to introduce additional microwave absorbent particles into chamber  23  at a similar rate to their removal. In other embodiments, microwave absorbent particles may remain in chamber  23 , even as outputs  6  are removed from chamber  23 . For example, in some cases polymer particles will produce a higher volume of oil vapours and a lower volume of solid materials. In such a case, since relatively less material is being removed through outlet  32 , microwave absorbent particles may tend to remain within chamber  23  for longer periods of time. In such, cases it may be desirable to introduce additional microwave absorbent particles into chamber  23  intermittently or only as needed. 
     In some embodiments, as the composition of particles  5  comprises a greater ratio of polymer particles to biomass particles, microwave absorbent particles may facilitate maintaining fluidized bed  25  as the polymer particles are reacted and form vapours. 
       FIG.  8 B  depicts an exemplary lower boundary and an exemplary upper boundary of the temperature of a particle  5  as a function of the distance it has travelled through vessel  22  in first direction  12  for the case where the reactor  20  with magnetrons (e.g. a reactor with a second zone  48 B). The  FIG.  8 B  heating rate could be employed for pyrolysis of particles  5 . In  FIG.  8 B , it can be seen that the temperature of particles  5  rises relatively quickly in a first portion of first zone  48 A before it plateaus. Similarly, the temperature of particles  5  rises relatively linearly in a first portion of second zone  48 B before plateauing. In some embodiments, the rate of heating in the first portion of second zone  48 B is higher than the rate of heating in the first portion of first zone  48 A. This may be caused by the energy added by magnetrons  34  in second zone  48 B. 
     In some embodiments, method  100  produces one or more outputs  6 . Outputs  6  may include bio char, bio oil, one or more gases or vapours comprising carbon monoxide and or hydrocarbons or bio-oil vapours, catalyst materials, microwave absorbent materials, etc.. Some of outputs  6  (e.g. solid and liquid outputs  6 ) may exit chamber  23  through outlet  26  while other outputs (e.g. gas or vapour outputs  6 ) may exit chamber through outlet  32 . 
     In some embodiments, it may be desirable to increase the ratio of polymer particles to biomass particles in the composition of particles  5  to achieve higher quality outputs  6 . For example, in some cases, it may be possible to improve the quality of bio oil and/or bio oil vapours produced through method  100  by increasing the ratio of polymer particles to biomass particles in the composition of particles  5 . 
     In some embodiments, one or more pressure sensors, such as but not limited to pressure transducers, may be provided in chamber  23  to monitor the pressure in one or more regions of chamber  23 . In some embodiments, a pressure sensor is provided for each of one or more regions (e.g. first region  23 A, second region  23 B, etc.) of chamber  23 . By monitoring the pressure in chamber  23 , it may be possible to determine whether particles  5  are sufficiently fluidized. For example, pressure sensors may be employed to monitor for “bubbling” of particles  5  in one or more regions of chamber  23 . If particles  5  are not sufficiently fluidized, the flow rate of fluidization medium  7  may be increased. Alternatively or additionally, a frequency of delivery of bursts of fluidization medium  7  may be decreased. 
     Another aspect of the invention provides systems for processing biomass. Such systems may be employed for pyrolysis or torrefaction of biomass. System  200  is a non-limiting example of a system for processing particles  5  that incorporates reactor  20 . 
     System  200  may comprise a dryer  210 , a grinder  215 , a reactor  220 , a conditioner  225 , a pelletizer  230 , a cooler  235  and a combustor/incinerator  240 . Reactor  200  may be substantially similar to reactor  20  or any other reactor described herein. 
     Raw or substantially raw biomass may be dried in dryer  210 . Dryer  210  may comprise, for example a rotary dryer, a moving bed dryer or a fluidized/spouted bed dryer. 
     After being dried in dryer  210 , the biomass may be ground into desirably sized particles in grinder  215 . Grinder  215  may comprise, for example, a hammer mill or a knife mill, depending on the types of biomass being processed by system  200 . In some embodiments, the biomass is reduced to particles  5  having particles of similar size to sawdust (e.g. in the range of about 0.1 mm to about 3 mm). In some embodiments, it may be desirable to achieve particles  5  having a relatively narrow particle size distribution to avoid having larger particles that sink to the bottom of bed  25  and move more slowly than desirable through reactor  200 . 
     After being reduced in size by grinder  215 , particles  5  may be processed by reactor  220  (e.g. pyrolyzed or torrefied) according to method  100  herein or otherwise. 
     The torrefied biomass may then be conditioned by conditioner  225  to adjust moisture content as desired (e.g. by adding water and/or water vapour) and/or to add any binders if desired. In some embodiments, conditioner  225  may be employed to achieve a moisture content of between about 10% and 20% (by weight). 
     A pelletizer  230  may be provided to compress the conditioned torrefied biomass into torrefied pellets which are then cooled in cooler  235 . 
     A combustor/incinerator  240  may be provided to burn gaseous or condensed output fluid output  6  of reactor  200  and/or additional biomass fuels to provide hot flue gases. The hot flue gases may be provided to dryer  210  and/or used as fluidization medium  7  for reactor  200 . 
     For example, bio-oil vapours outputted from reactor  200  may be combusted in combustor/incinerator  240  to provide hot flue gases for dryer  210  and/or fluidization medium  7  for reactor  200 . In some embodiments, combustor  240  comprises a catalytic combustor for burning fluid output  6  from torrefaction in reactor  200  at approximately 500° C. In some embodiments, one or more cyclones or filters are provided to remove solid particles from fluid output  6 . 
     In a non-limiting example application of the apparatus and methods, the particles treated are biomass such as wood. The wood is comminuted into small particles that are reasonable uniform in size and, if necessary, dried to have a water content of between about 10% and 20% (by weight), or less. 
     The wood particles are then fed into a reactor  20  as described herein wherein they form a shallow fluidized bed  25  as a result of upwardly directed burst of heated fluidizing medium (e.g. gas). The wood particles travel on average in a horizontal direction from inlet  24  to outlet  26  during which time their temperature rises. As they travel along the fluidized bed, the particles become torrefied, or if temperature inside chamber  23  is sufficiently high, the particles become pyrolyzed. 
     As the wood particles travel along fluidized bed  25 , the particles may pass through zones in which fluidizing medium is delivered at different times such that a top surface of the fluidized bed forms waves that travel along fluidized bed  25  (for example, in a direction from inlet  24  to outlet  26 ). 
     The heated wood particles emit volatile compounds such as bio-oil vapours and produce, for example, bio char. The bio-oil vapours may be collected at fluid outlet  32 . The collected gases and/or vapours may be condensed to yield valuable bio-oils. 
     In another example, the wood particles are mixed with polymer particles such as particles of rubber, plastic etc. In such embodiments, the polymer particles may be volatized by heat in chamber  23  to yield, for example, oil, monomers. The products may be collected with the bio char and/or bio-oil. 
     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 herein. 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. 
     Various features are described herein as being present in “some embodiments”. Such features are not mandatory and may not be present in all embodiments. Embodiments of the invention may include zero, any one or any combination of two or more of such features. This is limited only to the extent that certain ones of such features are incompatible with other ones of such features in the sense that it would be impossible for a person of ordinary skill in the art to construct a practical embodiment that combines such incompatible features. Consequently, the description that “some embodiments” possess feature A and “some embodiments” possess feature B should be interpreted as an express indication that the inventors also contemplate embodiments which combine features A and B (unless the description states otherwise or features A and B are fundamentally incompatible). 
     Where the terms “adjacent” or “spaced apart” are used herein, it should be understood that the items described as being “adjacent” to one another or “spaced apart” from one another may or may not be abutting. 
     Where any range is described herein, the description includes all sub-ranges and combinations of sub-ranges and individual values belonging to the described range. For example the description of a range from about 300° C. to about 650° C. also describes, without limitation, the sub-range of about 325° C. to about 375° C. and also describes the sub-range of 500° C. to 600° C. and also describes each of the specific temperatures in the range such as 295° C. (which is included in “about 300° C.”), 300° C., 301° C., ... 347° C., ... 650° C., ... 656° C. (which is included in “about 600° C.) . As another example, a description of a range of between 10% and 30% also describes, without limitation, the sub-ranges 10% to 17% and 14% to 30% and 21% to 27% as well as all individual values in the described range such as 22%, 29% etc. 
     While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are consistent with the broadest interpretation of the specification as a whole.