Abstract:
An apparatus to convert carbonaceous materials, particularly biomass and those biomass resources which are remotely located, into a solid material, which may be a high performance solid fuel, are presented. The apparatus provides a continuous process which can be completely powered by the energy contained in the biomass. The heat, mechanical power and electrical power are provided from the energy in the biomass, through the methods described. In this way, the apparatus is free to operate in remote locations, where no power or auxiliary fuel sources are available.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/105,801, filed Oct. 15, 2008, and U.S. Provisional Application No. 61/248,660, filed Oct. 5, 2009. The entire contents of the above-listed provisional applications are hereby incorporated by reference herein and made part of this specification. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention generally relates to the processing of biomass, and more particularly to a self-contained method and system for generating solids from biomass. 
     Discussion of the Background 
     The use of solid fuels is the world&#39;s largest energy market. In the United States, solid fuels are used primarily for generating electric power and in metallurgic and cement manufacturing processes. This market is dominated by non-renewable resources, principally coal, and to a lesser extent petroleum coke. Biomass sources, which are generally considered to be renewable, form less than 5% of the U.S. Market. 
     There is an urgency to switch to energy sources that will have less of an environmental impact, especially with regards to the emission of greenhouse gases. Biomass sources are an attractive alternative to conventional solid fuels, but high transportation costs and low energy density of the biomass materials have hindered their widespread use. 
     Prior art techniques that have been used improve the fuel value and physical properties of biomass range include, for example, drying the biomass to remove moisture contained therein without chemically altering the biomass, and producing charcoal from the biomass, where the biomass is chemically altered into fixed carbon. Drying is accomplished at temperatures below 120 C, while charcoal production requires temperatures above 500 C. Both drying and producing charcoal are incomplete solutions, and do not enable the access to remote biomass resources. Dry biomass has low energy volumetric density, and its transportability is not improved over wet biomass. The energy per truckload, and hence the transportation cost, does not improve significantly when compared to wet biomass. Producing charcoal is inefficient, with only 20% to 30% of the energy in the original biomass preserved in the charcoal. So much energy is lost that producing charcoal for fuel is discouraged except for use in metallurgical processes, where it is mandatory and thus unavoidable. 
     Drying the biomass combined with grinding and pelletizing the resultant fuel produces a fuel with energy density of between 7,000 and 8,000 Btu per pound, and a density of 0.6-1 g/cm 3 , and is something of an improvement. However the pellets are intolerant to water, are capable of spontaneous combustion, and are thus difficult to store. In addition, densifying charcoal requires a binder, a severe limitation when operating remotely. In either case, the resultant fuel is unsatisfactory for widespread application to industrial combustion processes. 
     Thus there is a need in the art for a method and apparatus that permits for the widespread use of biomass as a solid fuel. Such a method and apparatus should be inexpensive to implement and should produce a fuel that is compatible with apparatus that use conventional solid fuels. 
     BRIEF SUMMARY OF THE INVENTION 
     Certain embodiments described herein overcome the disadvantages of the prior art by torrefaction (driving off of volatile ingredients) and pelletization of the resultant biomass. The biofuel thus produced may have an energy density superior to lower grade fossil coals, and physical properties (density, grindability, water tolerance) compatible with industry needs. 
     Certain other embodiments described herein overcome the disadvantages of the prior art by utilize the energy content in gasses driven off during torrefaction to operate the biomass-to-biofuel process, resulting in a self contained fuel production facility, requiring only biomass for steady state operation. Specifically, torrefaction typically produces low energy value gas products, i. e. ascetic acid and methanol, which contain energy which has been lost to the solids. Certain embodiments recover the thermal energy in the gas and/or convert the gas to mechanical and/or electrical energy in a heat engine or fuel cell. 
     Embodiments presented herein overcome the disadvantages of prior art by remotely converting biomass to a biofuel. For example, one embodiment is an apparatus that may be place near a source of biomass and processes the biomass into a biofuel, which is then transported to market. Such apparatus has several advantages. First, the biomass can be converted to a biofuel that is more generally usable than the raw biomass. Second, biofuels have a higher energy density than biomass, thus reducing the transportation cost per energy stored within the fuel. Third, previously uneconomic biomass resources, particularly remote resources, can be economically brought to market. 
     Certain embodiments provide a method for converting a biomass into a biofuel within an apparatus. The method includes heating the biomass to produce a gas and the biofuel, reforming at least a portion of the gas to form a fuel, recovering thermal energy from the reforming, and providing at least a portion of the recovered thermal energy for the heating. 
     Certain other embodiments provide a method of processing biomass to form a biofuel in an apparatus. The method includes heating the biomass to produce torrefied biomass and torrefaction gases evolved from torrefaction of the biomass, and gasification of the biomass to produce gasified biomass. The amount of torrefaction gases and the amount of gasified biomass are adjusted to vary characteristics of the biofuel. 
     Certain embodiments provide an apparatus for converting a biomass into a biofuel. The apparatus includes a reactor, a reformer, and a heat exchanger. The reformer includes a first portion and a second portion. The first portion is for transporting and thermally treating biomass and the second portion is for transporting a heat transfer medium. At least part of the second portion is in thermal contact with at least part of the second portion. The first portion includes an inlet to accept the biomass, a first outlet to provide treated biomass, and a second outlet to provide gases evolved from the biomass at the second outlet. The second portion includes an inlet to accept a heat transfer medium and an outlet to provide the heat transfer medium. The reformer has an inlet in fluid communication with the second outlet of the first portion, and an outlet, where the reformer is adapted to chemically react gas accepted at the inlet and provide a fuel at the outlet. The heat exchanger is adapted to provide thermal contact between the heat transfer medium and the fuel, where the heat exchanger has an inlet in fluid communication with the second portion outlet, an outlet in fluid communication with the second portion inlet, a fuel inlet in fluid communication with the reformer outlet, and a fuel outlet to provide fuel. In the embodiment, when the apparatus is provided with biomass, the reactor thermally treats the biomass to form the biofuel and the heat exchanger recovers thermal energy for the reactor. 
     In certain embodiments the apparatus and method includes the steps of drying the biomass, torrefying the biomass, and pelletizing the resulting biofuel. In another embodiment, the gases resulting from torrefaction of the biomass have a significant energy content, which is utilized in operating the process. In yet another embodiment, the apparatus and method are self-contained—the input of energy when starting up the process can be provided from the biomass itself. 
     In certain embodiments, the apparatus and method converts carbonaceous materials, such as biomass which may be remotely located, into a high performance solid fuel for use in industrial combustion processes. The apparatus and method may provide a continuous process which can be completely powered by the energy contained in the biomass. Thus the heat, mechanical power and electrical power may be provided from the energy in the biomass. The apparatus is thus free to operate in remote locations, where no power or auxiliary fuel sources are available. In certain embodiments, utility services may be available and may be utilized to simplify the apparatus. 
     In certain other embodiments, the apparatus and method converts biomass into a biofuel and a gas having energy value. This gas may be converted into thermal, mechanical, and or electrical power for the process. In many embodiments, the gas generated has sufficient energy content to power the process. Thus only the energy contained in the biomass is utilized in the production of biofuel. 
     In certain embodiments, it is possible to operate only from the biomass and generate a biomass having between 70% and 90% of the energy of the biomass, on a dry basis. 
     In one embodiment, one or more reactors heat and/or cool the biomass operates using the phase change of a heat transfer medium. The phase change occurs on a surface of the reactor that is in thermal contact with the biomass. 
     In another embodiment, at least a portion of the steam that is used to dry a biomass is obtained by compressing steam from previously dried biomass—that is, drying causes steam to leave the biomass, is compressed to a higher temperature and pressure, and is provided for thermal contact with fresh, incoming biomass. 
     In yet another embodiment, gasses evolved from the torrefaction of biomass are used to provide heat for biomass processing and/or are used directly or after further processing to operate a heat engine or fuel cell to generate power of operating the process. 
     In one embodiment, heat generated in a heat engine is used to provide heat for a portion of the torrefaction of biomass. The fuel for operating the heat engine may be gas from previously torrefied biomass, from an external source, or from a separate biomass gasification unit. 
     In another embodiment, at least a portion of reformed or unreformed gases evolved during torrefaction are used to reform torrefaction gases to form a fuel. 
     In yet another embodiment, reformed torrefaction gases are cooled to remove water and increase the energy value of the gases. 
     These features together with the various ancillary provisions and features which will become apparent to those skilled in the art from the following detailed description, are attained by the apparatus and method of the present invention, preferred embodiments thereof being shown with reference to the accompanying drawings, by way of example only, wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general schematic of an apparatus for converting biomass to biofuel; 
         FIG. 2  is a first embodiment of a biomass-to-biofuel apparatus; 
         FIG. 3  is a schematic of a solid processing module of the embodiment of  FIG. 2 ; 
         FIG. 4  is a schematic of a heat transfer module of the embodiment of  FIG. 2 ; 
         FIG. 5  is a schematic of a gas processing module of the embodiment of  FIG. 2 ; 
         FIG. 6  is a schematic of a power generation module of the embodiment of  FIG. 2 ; and 
         FIG. 7  is an alternative embodiment of the drying, torrefaction, and cooling reactors. 
     
    
    
     Reference symbols are used in the Figures to indicate certain components, aspects or features shown therein, with reference symbols common to more than one Figure indicating like components, aspects or features shown therein. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a general schematic of an apparatus  100  for converting biomass to biofuel. The term “biomass” is a general term that refers to living matter or formerly living matter. It may include, for example and without limitation, material specifically grown or gathered for conversion to biofuel, or waste products from the use or maintenance of plants. Examples of biomass include, but are not limited to, woody biomass, agricultural byproducts, and municipal green waste. A “biofuel” is a fuel composed of or produced from biological raw materials. One type of preferred biofuel is a solid that is compatible with existing power plants, allowing for the reduction or elimination of conventional hydrocarbon fuels. Other types of biofuels are gaseous, liquid, or some combination of gaseous, liquid, and/or solid biofuel. The term “torrefied biomass” as used herein refers to a biomass that is heated to a moderate temperature, such as above approximately 100 C and below approximately 500 C, for example and without limitation. The resultant torrefied biomass has volatile gases that are driven off are sometimes referred to herein as “torrefaction gases.” In certain embodiments, the biomass is heated to a first temperature of approximately 100 C, driving off gases that are very volatile, including steam, and then is heated to a higher temperature, resulting in gases having a low steam contents. 
     It is a general feature that apparatus  100  converts a biomass to a biofuel efficiently, both from an energy and cost perspective. In certain embodiments apparatus  100  is a system that includes physical and/or chemical processes to accept a biomass at an input  101  and produce a biofuel at an output  111 . Certain embodiments of apparatus  100  may also include the generation of electrical power which is generally, but not necessarily exclusively, used within the apparatus. 
     Apparatus  100  may further include other inputs that accept other materials that may be used in the conversion of biomass to biofuel and other outputs that are used to reject products that are not included in the biofuel. Thus for example, and without limitation, apparatus  100  may have an input  103  for accepting ambient air and an output  113  for rejecting humid air, an output  115  for rejecting gases that are either inappropriate for, or not easily included in, the biofuel, or that contain excess heat from the apparatus, an output  117  that rejects water, and an output  119  that rejects ash. 
     In certain other embodiments, an input  105  is provided for an auxiliary fuel. The auxiliary fuel, which may, for example be diesel fuel, methane, or some other liquid or gaseous fuel, is an optional input that may be used in the conversion of biomass to biofuel. The auxiliary fuel may thus be used to generate electric, thermal or mechanical energy. In certain embodiments, apparatus  100  operates as a self-sustained process, not requiring auxiliary fuel. In these embodiments, an auxiliary fuel may be used during the start-up of the process, either as needed energy to start the process or to allow components obtained therein to more quickly reach temperatures that allow for the efficient operation of the apparatus. In certain other embodiments, the auxiliary fuel may include, or be replaced by, an input of electrical power, or the fuel may be the biomass or a stored portion of the torrefied product, or gasified biomass. 
     In addition, apparatus  100  includes a control system  110 , such as programmable computer, that collects information from sensors within the apparatus, which may include but are not limited to, contact or non-contact temperature sensors, pressure sensors, gas analyzers, humidity sensors, liquid level sensors, solid level sensors, and flow sensors and/or controllers. Control system  110  may also provides signals to operate and/or control valves, motors, pumps and the like within apparatus  100 . Control system  110  may, for example and without limitation, control valves or flow rates to optimize the performance of apparatus  100  by, for example, ensuring that various components are operating at predetermined temperatures or pressure that allow catalysts, heat engines or heat exchanger to operate at certain conditions. 
       FIG. 2  is a first embodiment of a biomass-to-biofuel apparatus  200 . Apparatus  200  may be generally similar to apparatus  100 , except as further detailed below. 
     Apparatus  200  is shown, schematically, as including a solids processing module  210 , a heat transfer module  220 , a gas processing module  230 , and a power generation module  240 . The names given to modules  210 ,  220 ,  230 , and  240  (“solids processing,” “heat transfer,” “gas processing,” and “power generation”) are not limiting—they are meant to aid in the discussion of apparatus  200  and are invocative of their general function. Thus for example and without limitation, while heat transfer module  220  includes several boilers, which may include heat exchangers, other modules may also include heat exchanges. Also, for example, while gas processing module  210  converts volatiles into gaseous fuels, some gas processing may also occur at the conditions of solids processing module  210 . 
     As discussed subsequently in greater detail with respect to a specific embodiment, solids processing module  210  is generally configured to have a steady-state operating condition to a) accept biomass including, but not limited to, wood, plant residues, forest trimmings, or paper residue, b) dry the biomass; c) torrefy the biomass, and d) pelletize the torrefied biomass to form a biofuel. The gases evolved from torrified gases are processed in gas processing module  230  to form fuel gases which exchange heat in heat transfer module  220  and are utilized to generate electricity within power generation module  240 . Heat transfer module  220  is integrated into apparatus  200  to efficiently utilize the fuel gases and any heat in the combustion products in solids processing module  210 . 
     In one embodiment, solids processing module  210  accepts biomass at input  101 , provides biofuel at output  111 . Solids processing module  210  also rejects humid air at output  113 . 
     Solids processing module  210  exchanges material with gas processing module  230 . Thus, for example, gases (labeled “Torrefaction Gases”) are provided from solids processing module  210  to gas processing module  230  via a line  201  and other material (labeled “Particulates”) are accepted from the gas processing module via a line  203 . 
     Solids processing module  210  also exchanges several working fluids with heat transfer module  220 . The working fluids, which are heated or cooled in heat transfer module  220  may be used to thermally process the biomass in solids processing module  210 .  FIG. 2  illustrates that apparatus  100  may include a high, medium, and low temperature heat transfer fluid. In one embodiment, a high temperature fluid is transferred between module  210  and  220  as a high temperature heat transfer medium liquid (HTL) via a line  213  and a high temperature heat transfer medium vapor (HTV) via line  225 ; a medium temperature heat transfer medium is transferred as water via a line  211  and steam via a line  223 ; a low temperature heat transfer medium is transferred as a low temperature vapor (LTV) via a line  215 , and a low temperature heat transfer medium liquid (LTL) via a line  227 ; and hot air is transferred via a line  221 . 
     In addition to the heat transfer fluids discussed in the previous paragraph, heat transfer module  220  accepts ambient air at input  103 - 1  and an optional auxiliary fuel at input  105 - 1 , and rejects exhaust gases at output  115  and water at output  117 . Heat transfer module  220  also accepts fuel gases at a line  233  from gas processing module  230  and provides fuel gases at a line  229  to power generation module  240 , and accepts combustion products at line  231  from gas processing module  230  and a line  241  from power generation module  240 . 
     Gas processing module  230  also accepts ambient air at an input  103 - 2 , rejects gases at exhaust line  115 , and has an optional auxiliary fuel at input  105 - 2 ; provides gases to heat transfer module  220  including combustion gases via a line  223  and fuel gases via a line  231 ; and exchanges material with solids processing module  210 , including accepting torrefaction gases via line  201  and providing particulates via line  203 . 
     Power generation module  240  accepts ambient air at an input  103 - 2 , rejects gases at exhaust line  115 , has an optional auxiliary fuel at input  105 - 3 , and exchanges material with heat transfer module  220  including providing exhaust gases via line  241  and accepting fuel gases via line  229 . Power generation module  240  optionally accepts biomass via a line  101   a  that may be gasified for producing power. 
     Power generation module  240  produces electric power, which may be provided to more or more of the other modules  210 ,  220 , or  230 , or for the control of the entire Apparatus  200 . 
       FIG. 3  is a schematic of one embodiment of solids processing module  210 . Solids processing module  210  may be generally similar to the similarly labeled module of  FIG. 2 , except as further detailed below. 
     Module  210  includes an input unit  310 , a dryer reactor  320 , a torrefaction reactor  330 , a cooling reactor  340 , a pelletizer  350 , an output hopper  360 , and a compressor  370 . 
     Input unit  310  includes a hopper  311  and an input metering load lock  313  powered by a motor  315 . In one embodiment, load lock  313  provides for metering of material and can allow for a pressure differential across the load lock. Thus load lock  313  may be, for example and without limitation a star valve, and be operated using pressure sensors (not shown), which may be, without limitation, a Hastings HPM-2002-OBE (Teledyne Hastings Instruments, Hampton Va.). 
     Gases present in hopper  311  are collected and provided as humid air to line  113 , which removes water from apparatus  100 . Hopper  311  accepts biomass from input  101  and accepts solid material, such as particulates, from gas processing module  230  via a line  201 . 
       FIG. 3  illustrates reactors  320 ,  330 , and  340  schematically as augers, which have cylindrical inner cavities with a helical screw. Solid material may be pushed through the auger by rotating the screw. 
     Thus, for example, the dryer reactor  320  of  FIG. 3  includes a drying auger  321  having a biomass input  322  to accept the output of load lock  313 , a heated biomass output  323  to discharge non-gaseous biomass derived material from the reactor, and a gas output  301  through which gases that evolve from the biomass are captured. Output  323  provides material to an output metering load lock  328  powered by a motor  329 . Gas output  301  is connected by line  303  to compressor  370  driven by a motor  371 . In one embodiment, compressor  370  is of the type commonly used in automotive applications, which may be, for example and without limitation, a Lysholm supercharger LYS 1200 AX (Lysholm Technologies AB, Saltsjo-Boo, Sweeden). Compressor  370  also has an associated valve  373  that allows gas to be diverted from the compressor to humid air line  113 . Thus, for example, the amount of gas provided to compressor  370  may be controlled by opening valve  373 , which redirects some or all of the flow in line  303  to line  113 . 
     In one embodiment, drying auger  321  has a hollow drive shaft  324  driven by a motor  327 , where a medium temperature heat transfer medium is provided to flow from a high temperature input  325  to a low temperature output  326 . The medium temperature heat transfer medium flowing from input  325  to output  326  is thermal contact with biomass within auger  321 . In one embodiment, the medium temperature heat transfer medium undergoes a phase change within drying auger  321 , resulting in a uniform temperature within the drying auger that may be controlled by the pressure of the medium temperature heat transfer medium. 
     Input  325  combines the compressed output from line  303  and steam from line  223 . Output  326  is separated in to humid air, provided to line  113 , and condensate, which is provided to line  211 . 
     In an alternative embodiment, the heat transfer medium flows from an input  325  to an output  326  on the outside of auger  321 , providing heating of the biomass through the outer walls of the auger. 
     In one embodiment, drying auger  321  provides for movement and heating of biomass there through. Auger  321  is preferably sized to transport and provide sufficient heating for the biomass passing there through. Thus drying auger  321  may be, for example and without limitation, of the type manufactured by Augers Unlimited (Coatsville Pa.) fabricated of stainless steel. Thus, for example and without limitation, a throughput of 500 kg/hr may require that auger  321  has a diameter of 24 inches, a length of 32 feet long, and capable operating at of 4 bars pressure. 
     In one embodiment, load lock  328  provides for metering of material and can allow for a pressure differential across the load lock. Load lock  328  may be generally similar to load lock  313 . 
     In one embodiment, torrefaction reactor  330  provides for movement and heating of biomass there through. Thus torrefaction reactor  330  may be generally similar to drying reactor  320 . 
     The torrefaction reactor  330  of  FIG. 3  includes a torrefaction auger  331  having a heated biomass input  332  to accept the output of load lock  328 , a torrefied biomass output  333  to provide non-gaseous material from the reactor, and a gas output  305  through which gases that evolve from biomass are collected. Gas output  305  is connected to line  203 . 
     In one embodiment, torrefaction auger  331  has a hollow drive shaft  334  driven by a motor  337 , where a high temperature heat transfer medium is provided to flow from a high temperature input  335  that is connected to line  225 , to a low temperature heat transfer medium output  336  that is connected to line  213 . The heat transfer medium flowing from input  335  to output  336  is thermal contact with biomass within auger  331 . In one embodiment, the high temperature heat transfer medium undergoes a phase change within torrefaction auger  331 , resulting in a uniform temperature within the torrefaction auger that may be controlled by the pressure of the high temperature heat transfer medium. 
     In an alternative embodiment, the heat transfer medium flows from an input  325  to an output  326  on the outside of auger  331 , providing heating of the biomass through the outer walls of the auger. 
     In one embodiment, cooling reactor  340  provides for movement and heating of biomass there through. Thus cooling reactor  340  may be generally similar to drying reactor  320  and/or torrefaction reactor  330 . 
     The cooling reactor  340  of  FIG. 3  includes a cooling auger  341  having a torrified biomass input  342  to accept the output of output  333 , a cooled biomass output  343 , and a common gas output  305  with torrefaction reactor  330 . 
     In one embodiment, cooling auger  341  has a hollow drive shaft  344  driven by a motor  347 , where a medium temperature heat transfer medium is provided to flow from a low temperature input  346  to a high temperature output  345 . The heated medium temperature heat transfer medium then flows into high temperature input  325  of drying reactor  320 . In one embodiment, the medium temperature heat transfer medium undergoes a phase change within cooling auger  341 , resulting in a uniform temperature within the cooling auger that may be controlled by the pressure of the medium temperature heat transfer medium. 
     Pelletizer  350  includes a pelletizer screw  352  that accepts material from cooled biomass output  343  and which is driven by a motor  351 , a transfer mechanism  354  which driven by a motor  353 . Transfer mechanism  354  places the processed solid material in thermal contact with heat exchanger  355 , which accepts a low temperature fluid from line  227  and discharges a high temperature fluid into line  215 . 
     In one embodiment, pelletizer screw  352  converts the torrefied biomass into pellets having a maximum size which may be, for example and without limitation, from 1 cm to 10 cm in diameter. In one embodiment, transfer mechanism  354  is a conveyer belt. In one embodiment, heat exchanger  355  is an evaporator coil. 
     Output hopper  360  includes a material holding bin  361  that includes a heat exchanger  365  that is in series with heat exchanger  355 , and has an output  363  that provides processed material, which may be a liquid or a solid, as biofuel to line  111 . 
     Solids processing module  210  may include one or more sensors which may provide sensor output to control system  110 . Thus, for example and without limitation, solids processing module  210  is shown as having sensors SHA to sense the humid air within line  113 , sensors SD 1  to sense the steam exiting drying reactor  320  at output  301 , sensors SD 2  to sense the gas in the output of compressor  370 , sensors SD 3  to sense the solids being processed at the exit of the drying reactor, sensors ST 1  to sense the solids exiting torrefaction reactor  340 . sensors ST 2  to sense the torrefaction gases exiting torrefaction reactor  340  and cooling reactor  350 , sensors SC 1  to sense the solids exiting the cooling reactor, sensors SF 1  to sense the solids in holding bin  363 , and sensors SF 2  to sense the biofuel. 
     In an alternative embodiment, the heating of one or more of reactors  320 ,  330 , and  340  is accomplished heat transfer to the external casing of the auger  321 ,  331 , or  341 , respectively. External heating via heat transfer medium may take place in place of, or in addition to, heating of the auger of the respective reactors, as described here. In another alternative embodiment, two or more of reactors may have a common auger.  FIG. 7  is an alternative embodiment of the drying, torrefaction, and cooling reactors, and includes both of these alternative embodiments. 
     As shown in  FIG. 7 , a single dryer assembly  700  has a single auger  701  and a motor  709  driving the auger. As the biomass flows though the auger, a first portion of auger  701  forms drying reactor portion  320 , a second portion of the auger forms torrefaction reactor portion  330 , and a third portion of the auger forms cooling reactor portion  340 . Specifically, a medium temperature heat transfer jacket  703  surrounds the drying reactor portion  320  of auger  701 , a high temperature heat transfer jacket  705  surrounds the torrefaction reactor portion  330  of the auger, and a medium temperature jacket  707  surrounds the cooling reactor portion  340  of the auger. Connections to the high temperature medium and medium temperature medium loops, gas outflows, and sensors and control mechanisms are generally similar to those of reactors  320 ,  330 , and  340 , and are not shown in  FIG. 7   
     In one embodiment, sensors SHA include a temperature, humidity, gas composition, and flow rate of humid air; sensors SD 1  include a temperature, and pressure sensor for steam; sensors SD 2  sense the temperature and pressure of the compressor output; sensors SD 3  sense the temperature of the solids; sensors ST 1  sense the temperature of solids; sensors ST 2  sense the temperature, pressure, and gas composition of gases; sensors SC 1  sense temperature of solids; sensors SF 1  sense level of solids within holding bin  363 ; and sensors SF 2  sense the temperature of the biofuel. The measure of temperature, pressure, gas composition, humidity, liquid and solid levels, and flow rates are well known in the field, and may include, but are not limited to, contact and non-contact measurements, optical measurements (i.e. Omega OS100E infrared thermometer to measure temperature or a NIR optical analyzer to determine gas composition), and may include measurements nearby the intended material to be measured, such as measuring a liquid temperature by measuring the wall temperature of a liquid container. 
     It is understood that the sensors enumerated herein are not meant to be limiting or exclusive, and there may only some of the sensors listed, or there may be other sensors within apparatus  100  that provide output to controller  110 . 
       FIG. 4  is a schematic of one embodiment of heat transfer module  220 , which may be generally similar to the similarly labeled module of  FIG. 2 , except as further detailed below. 
     Module  220  includes blowers  401  and  417 , boiler/heat exchangers  405 ,  407 , and  409 , heat exchanger  403 , a pump  411 , separators  413  and  415 , a burner  419 , and a valves  421  and  425 . 
     Blower  401  accepts ambient air from input  103 - 1   a , where it passes through heat exchanger  403  and is provided to line  221  as hot air. Optionally, blower  417  accepts ambient air from input  103 - 1   b , where it is combined with auxiliary fuel from line  105 - 1  in burner  419 . 
     Boiler  405  is part of a closed, high temperature heat transfer loop that provides heat to torrefy the biomass. Boiler  405  that accepts high temperature heat transfer medium liquid (HTL) from line  213  and provides high temperature heat transfer medium vapor (HTV) to line  225 . Apparatus  100  thus has a high temperature heat transfer loop that transfers heat in boiler  405  from the fuel line  233  and exhaust lines  231  and  241  to a high temperature heat transfer medium, which flows via line  225  as a HTV to torrefaction reactor  330 , then returning as a HTL via line  213  to boiler  405 . 
     Boiler  407  is part of a medium temperature heat transfer loop that is used for drying the biomass. Boiler  407  is shown, for illustrative purposes, as a water/steam mixture that accepts a low temperature heat transfer medium (such as water) from line  211  and provides high temperature heat transfer medium (such as steam) line  223 . 
     Apparatus  100  thus has a medium temperature heat transfer loop that transfers heat in boiler  407  from the fuel line  233  and exhaust lines  231  and  241  to a medium temperature heat transfer medium, which flows as steam via line  223 , joining steam leaving cooling reactor  340  and optionally compressed steam from the biomass before flowing through drying reactor  320 . Water leaving drying reactor  320 , is provided to cooling reactor  340  and to boiler  407 . Since water may be added to the medium temperature heat transfer loop, provisions are provided for excess water to exit by the action of valve  425 . 
     Boiler  409  is part of a closed, low heat transfer loop for recovering energy from the torrefied biomass. Boiler  409  accepts the low temperature heat transfer medium vapor (LTV) from line  215 , and provides the output to a pump  411  to provide the low temperature heat transfer medium liquid to line  227 . Boiler  409  also has a line  423  that carries vapor away from the boiler and combines it with the vapor of line  215 . Line  423  permits excess heat from building up in the system by providing cooling by air in boiler  403 . A parallel set of lines run from high-to-low boilers  405 ,  407 ,  409 , including the combination of line  231  from gas processing module  230 , line  241  from power generation module  240  and optional gases from burner  419  in a first line, and line  233  from gas processing module  230  in a second line. In one embodiment, boilers  405 ,  407 ,  409  transfer heat from their respective heat transfer medium across tubes containing fuel and exhaust gases, as shown in  FIG. 4 . 
     Boilers  405 ,  407 ,  409  are generally similar, have decreasing temperatures, and exchange heat between working fluids and combustion and fuel gases, as described subsequently. 
     Heat to and from the high, medium, and low temperature heat transfer media is removed from fuel gases and exhaust gases from gas processing module  230  and power generation module  240 . 
     Separator  413  separates and provides gases from the exhaust into line  115  and liquid water into line  117 . Separator  415  separates and provides gases from the fuel gases into line  229  and liquid water into line  117 . In one embodiment, separators  413  and  415  include condensing coils. 
     Heat transfer module  220  may include one or more sensors which may provide sensor output to control system  110 . Thus, for example and without limitation, heat transfer module  220  is shown as having sensors SH to sense conditions in high temperature boiler  405 ; sensors SM to sense conditions in medium temperature boiler  407 ; sensors SL to sense the conditions in low temperature boiler  409 ; sensors SHA 1  to sense conditions in heat exchanger  403 ; and sensors SHA 2  to sense the hot air in line  221 . 
     In one embodiment sensors SH sense the temperature, pressure, flow rate, and level of the high temperature heat transfer liquid; sensors SM sense the temperature, pressure, flow rate, and level of the medium temperature heat transfer liquid; sensors SL sense the temperature, pressure, flow rate, and level of the low temperature heat transfer liquid; sensors SHA 1  sense the temperature of heat exchanger  403 ; and sensors SHA 2  sense temperature and flow rate of hot air. 
       FIG. 5  is a schematic of one embodiment of gas processing module  230 , which may be generally similar to the similarly labeled module of  FIG. 2 , except as further detailed below. 
     Module  230  includes a particulate filter  501  powered by a motor  503 , a catalyst bed  517  of a reformer  515 , a valve  509 , an ambient air input at a line  103 - 2  that is drawn by a blower  505 , a burner  507  and valves  519  and  521 . Reformer  515  accepts filtered torrefaction gases in line  513  and provides contact with catalyst bed  517 , while the heat for the reformer is provided by thermal contact with exhaust from burner  507  in line  511 . An auxiliary fuel line  105 - 2  provides optional fuel to burner  507  to add energy to the system, principally during start-up. Valves  519  and  521  provide a means to remove heat from the system, and are controlled by control system  110 . 
     Gas processing module  230  may include one or more sensors which may provide sensor output to control system  110 . Thus, for example and without limitation, gas processing module  230  is shown as having sensors SR to sense conditions in catalyst bed  517 ; sensors SE 1  to sense conditions exiting burner  507 ; and sensors SF to sense conditions in the fuel gas. 
     In one embodiment, sensors SR sense the temperature of catalyst bed  517 ; sensors SE 1  sense the temperature, pressure and flow rate of gases exiting burner  507 ; and sensors SF sense the temperature, pressure, gas composition, and flow rate of fuel gas. 
       FIG. 6  is a schematic of one embodiment of power generation module  240 , which may be generally similar to the similarly labeled module of  FIG. 2 , except as further detailed below. 
     Module  240  includes a generator  610  that includes a compressor  611 , a turbine  613 , and an electric generator  615  all on a common shaft  617 . Module  240  also includes a burner  603  which combusts fuel cases, auxiliary fuel, and or gasified biomass for injection into compressor  611 , a valve  621  in the exhaust line of turbine  613  to vent some or all of the exhaust to exhaust line  115 , and an emissions control subsystem  623  in the exhaust line. 
     Power generation module  240  accepts ambient air from line  103 - 3  and compresses the air in compressor  611 . The compressed air is combined with fuel gases from line  229  of heat transfer module  220  and an optional auxiliary fuel from line  105 - 3  in burner  603 . The output of burner  605  is provided via a line  605  into turbine  613 , and then through line  241  into heat transfer module  220 . Electric generator  615  is powered from turbine  613 , and generates electricity which may be used to control the power to: motors  315 ,  327 ,  337 ,  347 ,  351 ,  353 ,  371 ,  503 ; blowers  401 ,  417 ,  505 ; pump  411 ; and valves  373 ,  421 ,  509 ,  519 ,  521 ,  621  as well as computers, communications, and additional valves and other devices which may not be shown in the Figures, and alternative equipment that is described elsewhere herein. 
     In an alternative embodiment, power generation module  240  includes a gasification unit  630 . Gasification unit  630  directly converts biomass into gaseous fuel for burning in burner. In one embodiment, gasification unit  630  receives a biomass feed via line  101   a  and air via line  103 - 3  that is provided via a blower  625 . Gasification unit  630  produces a waste stream of ash, rejected via line  119  and fuel that is fed into line  229  to burner  603 . The biomass received from line  101   a  may be either raw biomass, torrefied biomass, or pelletized torrefied biomass. The gasifier may be, for example and without limitation, of the type described in U.S. Pat. No. 4,764,185, incorporated herein by reference. Gasification unit  630  is operational during startup as an option to using and auxiliary fuel, or as an alternative source of fuel gases when the torrefaction process parameters (for example, temperature and/or time) do not provide sufficient heat to operate gas processing unit  230  at a required temperature. 
     The exhaust is cleaned up in emissions control subsystem  623  before being provided to heat transfer module  220 . The energy balance and temperature in subsystem  623  may be controlled by operating valve  621 , which vents the exhaust to line  115 . 
     In one embodiment, compressor  611  and turbine  613  may be a heat engine i.e. a microturbine as manufactured by Capstone (Chatsworth Calif.). In alternative embodiments, generator  610  is an internal combustion engine (i.e. Telefelex GFI) or a fuel cell. 
     Power generation module  240  may include one or more sensors which may provide sensor output to control system  110 . Thus, for example and without limitation, power generation module  240  is shown as having sensors SE 2  to sense conditions in line  241 ; sensors SA to sense conditions of the ambient air; sensors SCO to sense the gases exiting compressor  611 ; and sensors SE 3  to sense conditions of the gases exiting burner  603 . 
     In one embodiment, sensors SE 2  senses the temperature, pressure, gas composition, and flow rate of the exhaust gases; sensors SA sense the temperature and flow rate of the ambient air; sensors SCO sense the temperature and pressure of gases exiting compressor  611 ; and sensors SE 3  sense the temperature and pressure of gases exiting burner  603 . 
     Controller  110  include programming that utilizes the output from one or more of sensors SH 1 , SIM, SD 2 , SD 3 , ST 1 , ST 2 , SC 1 , SF 1 , SF 2 , SH, SM, SL, SC, SHA 1 , SHA 2 , SF, SR, SE 1 , SE 2 , SE 3 , SEC, SA, SE 3 , and any other sensors in apparatus  100 , and control the delivery of power to or the operation of motors  315 ,  327 ,  337 ,  347 ,  351 ,  353 ,  371 ,  503 ; blowers  401 ,  417 ,  505 ; pump  411 ; and valves  373 ,  421 ,  425 ,  509 ,  519 ,  521 ,  621 . 
     Operation of the Apparatus 
     The following illustrates methods of operating apparatus  200 . 
     The components of solids processing module  210  are sealed from atmosphere, except for hopper  311 , which is pressurized by hot air delivered by line  221 . Raw biomass is loaded into input hopper  311 , as are the particulates that are separated from the torrefaction gases in particulate filter  501  (as discussed subsequent) The rate of biomass and particulates leaving hopper  311  are controlled by a motor  315  which powers input metering load lock  313 . 
     The material then flows through the center of auger  321  of drying reactor  320  according to the power provided to motor  327 . In one embodiment the temperature of drying reactor  320  is chosen to drive off volatile liquids, principally water, from the biomass. As such, the temperature of drying reactor  320  is approximately 100 C. The steam, along with some air, thus driven off is collected within auger  321  and exits at gas output  301 . The steam and air flow through line  303 , where the pressure is increased according the power provided to motor  371 , and is combined with steam from line  223  at the high temperature input  325 . 
     Heat is provided to solid processing module  210  through reactors  310  and  330 , and recovered through auger  340 . Compressor  370  recovers the latent heat of evaporation of the biomass moisture through the addition of work provided by power generation module  240 . 
     In one embodiment, the conditions within shaft  324  are a pressure of approximately 2 bars and a temperature of approximately 170 C at 2 bars. Heat is supplied to the water/steam within shaft  324  in three ways: 1) water is evaporated in boiler  407 ; 2) biomass moisture, which evaporates in drying reactor  320  is compressed by compressor  370  and mixed with steam from boiler  407 ; and 3) superheated steam within cooling reactor  340 . 
     Steam is thus piped to hollow drying auger shaft  324  where it condenses at 120 C, releasing the latent heat. The liquid moves by gravity through boiler  407 . Compressor  370  maintains a pressure at 2 bars by the addition of mechanical energy. Excess water in the medium temperature heat transfer loop may be sensed by a liquid level sensor SM, and drained from by operating valve  425  to allow the water to exit via line  117 . 
     The operation of the drying reactor, and the associated heat transfer components, is dependent on the moisture content of the raw biomass. For low moisture contents, compressor  370  is under utilized. The solids can thus be processed at a constant rate, independent of moisture content. Similarly, the solids transfer rate can be varied to adjust for moisture content. The solid temperature is measured by sensor SD 3 , and if this temperature is less than some value, for example and without limitation less than 110 C, the compression will be increased to achieve this temperature, under the control of control module  110 . Sensors SD 1  and SD 2  provide information on the compressor operation. 
     After heating the biomass in drying reactor  320 , the water/steam/air mixture is separated in separator  326  into humid air, which exits at output  113 , and water, which exits at line  211 . The water is converted to steam in boiler  407 , as described subsequently, and returned as steam in line  233 . 
     The dried biomass exiting drying reactor  320  is then metered according to load lock  328  by the power provided to motor  329 . Isolating the biomass within drying reactor  320  between load locks  313  and  328  permits the pressure of the biomass to be maintained at a pressure slightly above atmospheric pressure. Thus for example, the pressure of the biomass within drying reactor  320  is from 1 to 10 psi. 
     Next, the biomass is further heated in torrefaction reactor  330 . A “high temperature” heat transfer medium flows between hollow drive shaft  334  and boiler  405  to maintain a temperature high enough to torrefy the biomass. In one embodiment, a temperature of between 200 C and 300 C is maintained. As discussed subsequently, the energy content, density, and other physical quantities of the biofuel are governed, in large part by the conditions in torrefaction reactor  330 —that is the temperature and time spent by the biomass in the torrefaction reactor. In general, increasing the temperature of torrefaction reactor  330  and decreasing the speed of drive shaft  334  (that is, increasing the processing time), result in more highly proceeded biomass. 
     In one embodiment the high temperature heat transfer medium operating between torrefaction reactor  330  and high temperature boiler  405  is Dow Therm A, (Dow Chemical Company, Midland, Mich.), an organic heat transfer fluid that evaporates at 260 C at ambient pressure. Dow Therm gas is piped to the auger  331 , where it condenses, releasing latent heat. The liquid returns by gravity to boiler  405 , where the liquid temperature is maintained at 260 C. The temperature of boiler  405  is determined by the temperature and volume of the fuel gases in line  233  and exhaust gases in line  231  and  241 . These parameters are measured by sensors SH, and controlled by the operation of valve  421 ,  521  and  519 . 
     Thus, for example and without limitation, embodiments may include a temperature of reactor  330  of approximately 200 C, approximately 225 C, approximately 250 C, approximately 275 C, or approximately 300 C. In another embodiment, embodiments of reactor  330  may, for example and without limitation, have a temperature range comprising a high temperature and a low temperature, where the low temperature is approximately 200 C, approximately 225 C, approximately 250 C, or approximately 275 C, and where the high temperature is approximately 225 C, approximately 250 C, approximately 275 C, or approximately 300 C. 
     The time that the biomass is in torrefaction reactor  330  may be, for example and without limitation, between approximately 5 minutes and approximately 60 minutes. In one embodiment, the time that the biomass is in torrefaction reactor  330  is controlled by motor  334 . The time may be, for example, approximately 5 minutes, approximately 10 minutes, approximately 15 minutes, approximately 20 minutes, approximately 25 minutes, approximately 30 minutes, approximately 35 minutes, approximately 40 minutes, approximately 45 minutes, approximately 50 minutes, approximately 55 minutes, or approximately 60 minutes. In another embodiment, the time is controllable between a minimum time and a maximum time, where the minimum time is any one of the following approximate times: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55 minutes and the maximum time is any one of the following approximate times: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 minutes. In other embodiments, the time may be less than 5 minutes or greater than 60 minutes. 
     The time that the biomass spends in reactors  320  and  340  may be approximately the same as that spent in reactor  330  or may be longer or shorter depending on the size and throughputs of the reactors, and may be controlled by their respective motors  324  and  344 . 
     Next, the torrefied biomass in cooled in cooling reactor  340 , and heat in the biomass is recovered. Cooling reactor  340  is maintained at a temperature of 120 C to 200 C, as provided by heat exchange with water/steam in parallel with drying reactor  320 . 
     The gases evolved from torrefaction reactor  330  and cooling reactor  340  are piped to gas processing module  230  at a pressure slightly above atmospheric, as provided by the sealing action of load lock  328  and pelletizer  352 . Cooling auger shaft  344  is filled with liquid water, in parallel with drying auger shaft  324 , and recovers sensible heat from the solids by the evaporation of water. 
     When the heat generated in gas processing module  230  and power generation module  240  are not adequate to maintain the desired temperature, as may occur during the start up of the processes, auxiliary heat is added through burner  507 , which combusts an auxiliary fuel (i.e. diesel) with air supplied by blower  505 . 
     Pelletizer  350  provides mechanical power to compress the solid product. The densified pellets are further cooled to 150 C in transfer mechanism  354 , and moved to output hopper  360  where they are further cooled to 60 C. Heat is removed through heat exchangers  355  and  365 , which are part of the low temperature heat transfer loop that includes boiler  409 . In one embodiment, the low temperature heat transfer medium is methanol, and is maintained at a temperature of 60 C in boiler  409 . 
     The sensible heat stored within the pelletized, torrefied biomass is recovered through heat exchangers  355  and  365  which evaporate methanol, stored in boiler  409 , and which is used to heat air in heat exchanger  403  for input hopper drying. 
     Additional heat is available for preheating air from boiler  409  which captures heat from the exhaust and fuel gases. 
     The low temperature heat transfer “loop” could be alternatively implemented as a circulating fluid or direct air heat transfer, or by pumping a condensed liquid. 
     Torrefaction reactor  320  expresses gases with low energy value via line  203 , which are upgraded in the gas processing module  230  through the operation of a reformer  515  to form a fuel. First, particulate filter  501  cleans the gas, which contacts catalyst bed  517  of reformer  515 . The temperature of reformer  515  is preferably held at a temperature of approximately 600 C to 900 C, depending on the catalyst, by the heat provided from the exhaust of burner  507 . The air required for combustion of the fuel is supplied through blower  505 , and optional auxiliary fuel may be provided from auxiliary fuel line  105 - 2 . In one embodiment, the reforming chemistry is, for example and without limitation, C 2 H 4 O 2 →2CO+2H 2 . The exhaust then exits reformer  515  into line  231 , into heat transfer module  220 , where it is combined with the exhaust from power generation module  240 . Heat from the exhaust gas is recovered in boilers  405 ,  407 , and  409 , before being provided to power generation module  240 , as described herein. 
     A gas turbine  613 , or alternatively an internal combustion engine, is fueled by the reformed gas in line  229 . This shaft power is converted to either hydraulic power or electric power in generator  615 . This power is used to operate the motors, compressors, blowers and pumps as needed. 
     The engine exhaust gases may be one heat source for heat transfer module  220 . A 20% efficient engine may cogenerate 65% heat, which is used to partially drive the torrefaction reaction through boiler  405 . 
     In addition to the steady-state operation, as described above, apparatus  100  may also be capable of achieving a steady state operating condition. Since torrefaction gases are not present at start up, some device or means of generating or providing extra fuel is required until a steady mass flow and thermal equilibrium is reached. This may be, for example several hours. A supply of auxiliary fuel, delivered through line  105  or the operation of gasification unit  620  may provide the added energy required for start-up. 
     Further Operational Considerations and Control Issues 
     In certain embodiments, apparatus  100  may be used to convert biomass to biofuel over a wide range of conditions. Thus, for example, biomass may have a water content of from approximately 5% to approximately 60%, and have varying amounts of lignin and other compounds. In addition, it may be desirable to produce a biofuel have a well characterized energy content and/or density. 
     Thus, for example, the biofuel may have a heating value of between 10,000 and 12,000 Btu per pound on an ash free basis, and a density of between 0.8 and 1.4 g/cm 3 . The heat value, which is greater that that of the biomass, is accomplished by heating the biomass in the absence of oxygen, allowing water and volatile organic compounds resulting from the breakdown the cellulose and hemi-cellulose to be created and driven off. The high density is accomplished through maintaining the temperature below the level where the lignin is chemically altered, and by subsequent compression into pellets. 
     The fuel value of the torrefied solids can be increased, by increasing the torrefaction temperature and/or exposure time. Thus, different energy value fuels can be produced from this single apparatus, by varying operating conditions. For example, the relative ratios of Hydrogen, Carbon, and Oxygen in the output solids are determined by the operating conditions, such at the temperature and time spent in torrefaction. Similarly, the mass conversion can be adjusted from 70% to 90%, increasing the amount of a lower value fuel, or reducing the amount of a higher value fuel. The ability of the apparatus to operate above, around, or below the auto-thermal condition, based on technical and economic tradeoffs is a consideration which may be subordinated to operation just above the autothermal condition. 
     In general, the volume and composition of the torrefaction gas is a function of the solid transit time through the torrefaction reactor  330 , which is set by motor  337 , and the temperature of boiler  405 . Bound oxygen is driven off (reduced) from the biomass in torrefaction reactor  330  producing torrefaction gases composed of CO 2 , H 2 O and C x H y O z  volatiles. As the temperature of torrefaction reactor  330  increases, or the transit time increases, more of the solids are converted to gases, thus decreasing the mass, and energy content, of the solids and increasing the mass of, and the energy content of the gases. In one embodiment, the carbon conversion ratio of the process may be a control mechanism which allows the apparatus to operate under conditions of varying biomass input characteristics. Thus by adjusting the parameters of the solids processing (that is, the torrefaction auger speed and temperature), the fuel value of the torrefaction gases are likewise adjusted such that the fuel requirements of generator  610  can be met. As the fuel requirements of generator  610  demand rises, so does the heat delivered to the boiler through the cooling of the fuel gases, and through the cooling of the exhaust gases. Thus the boiler naturally increases temperature as the engine load is increased, which in turn increases the expression of combustible torrefaction gases. 
     In one embodiment, control system  110  dynamically adjusts to differing biomass inputs according to the sensor input and control of valves and motors. In another embodiment and operator may select certain control parameters and/or set points based on historical knowledge gathered by experimentation with various biomass feedstocks. 
     In yet another embodiment, the reformer  515  is controlled using sensor SR to provide information to controller  110  and valves  519  and  521 , which are controlled by the controller. Thus for example, catalysts are known to operate most efficiently at certain temperatures. A temperature measured by sensor SR is compared against a range of set point temperatures. Operating valves  519  and  521 , which direct gases to exhaust line  115 . This operation of valves allows the reformer to function in a narrow range of temperatures, independent of the volume or energy content of the torrefaction gases. Burner  507  provides the heat to drive the catalytic reforming process of reformer  515 , which chemically reduces (removes oxygen) the combustible components of the torrefaction gases. The goal of the reforming is to chemically reduce the condensable gases (present in the torrefaction gases) into non-condensable gases of higher energy value. This is important, as significant water is present in the torrefaction gases, and water is a product of the reforming process. Once the fuel is reformed, a portion is used to provide the heat required for reforming, i.e. 50% of the reformed gases, in burner  507 . 
     Once the torrefaction gas has been upgrade to fuel gas, the water can be removed, using phase separation in the water trap  413 , after the fuel gas has been cooled by the boilers, but before it enters the engine. This improves the heating value of the fuel gas by limiting the water content. 
     Table I illustrates the wide range of conditions of operation of apparatus  100 . These results were obtained from a mathematical model of the steady-state operation of an ideal system, and are meant to provide some guidance as to the operation of an actual device. The energy for operating the apparatus was obtained either from the torrefaction gases or by gasifying the biomass directly in power generation module  240 . 
     
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Torrefaction Temperature Matrix 
               
             
          
           
               
                   
                   
                   
                 Operating 
                   
                   
               
               
                 Torrefaction 
                 Energy 
                 Mass 
                 Energy from 
                 Operating 
                 Excess 
               
               
                 Temperature/ 
                 Yield in 
                 Yield in 
                 Torrefaction 
                 Energy from 
                 Operating 
               
               
                 C. 
                 Solids 
                 Solids 
                 Gas 
                 Gassifier 
                 Energy 
               
               
                   
               
               
                 200 
                 95% 
                 90% 
                  60% 
                 40% 
                 — 
               
               
                 225 
                 90% 
                 85% 
                  80% 
                 20% 
                 — 
               
               
                 250 
                 85% 
                 80% 
                 100% 
                 — 
                 — 
               
               
                 275 
                 80% 
                 75% 
                 120% 
                 — 
                 20% 
               
               
                 300 
                 75% 
                 70% 
                 140% 
                 — 
                 40% 
               
               
                   
               
             
          
         
       
     
     Table I illustrates several aspects of the apparatus. First, as the torrefaction temperature is increased, the energy content of the solids decreases. This energy is available in the torrefaction gases, but not in the solid material. Second, as the torrefaction temperature is increased, the mass of solids decrease, again due to water and other volatiles being driven off. Although energy and mass are driven from the biofuel, the energy density increases with torrefaction temperature. In addition, the water resistance of the biofuel also increases with torrefaction temperature. 
     The first column is the torrefaction temperature (for example, the temperature sensed by sensor SD 3 , which is indicated, without limitation, at certain temperatures from 200 C to 300 C. The second column is the energy yield in the biofuel exiting apparatus  100 . Specifically, the second column is the ratio of the energy content in the exiting biofuel to the energy content in the input biomass, based on the higher heating value. The third column is the mass yield in the biofuel exiting apparatus  100 , that is, the biofuel mass flow out divided by the biomass mass flow in, on a dry basis. The remaining columns represent an energy balance in the apparatus. The fourth column is the fraction energy used for operating the entire apparatus that is derived from torrefaction gases, the fifth column is the energy used for operating the entire apparatus that is derived from a gasifier, and the sixth column is the amount of energy consumed in excess of the energy required. 
     One aspect of certain embodiments is illustrated by the energy balance results on Table I. By having the ability to obtain energy from both torrefaction and gasification, resulting in the dumping of excess heat at higher temperatures, the rate at which this excess heat is removed from the process provides a control mechanism to maintain the system at its desired operating temperature. While it may be possible to operate the process without removing excess heat, the density, energy content, and water resistance of the final product must also be considered, and thus the operating temperature (say, above 250 C) may generate excess heat. In general, the process may be operated over in a narrow band around the desired temperature, and a variable amount of heat escapes the system to allow dynamic control. 
     One variation in the operation of apparatus  100  results from variations in the water content of the biomass. The following are some example of how apparatus  100  may be controlled to respond to variations in biomass moisture content. 
     In one embodiment, compressor  370  is operated when the biomass moisture content is sufficiently high. Thus, for example and without limitation. Compressor  370  may be operated when the biomass moisture content is greater than 25%. 
     As an example, compressor  370  may be controlled by properties of the biomass as it enters load lock  328  using a sensor SD 3  which provide a reading to controller  110 . In one embodiment, sensor SD 3  measures a temperature of the biomass or of machinery in thermal contact with the biomass, which may be used as follows to control compressor  370 . The temperature measured by temperature sensor SD 3  is an indirect measure of the moisture content. When the temperature measured by temperature sensor SD 3  is greater than some set point, which may be for example a temperature between 90 and 120 C, compressor is 370 is turned off by controller  110 . When the temperature measured by temperature sensor SD 3  is below the set point, compressor  360  may be is turned on. The control of compressor  370  by the reading of sensor SD 3  may be determined by an algorithm which uses the time history of the measured temperature, and drives this temperature to the set point. This algorithm may be a PID control, or other control methods known in the art. When compressor  370  is off, any water vapor is vented as humid air  113 , through vent valve  373  in line  303 . 
     In another embodiment, when the biomass is dry, there is a possibility of there being too much energy in the torrefaction gases, and some of the extra heat must be vented from apparatus  100  to prevent over heating of the gases, and some of the heat is vented by allowing the exhaust to be diverted through valves  421 ,  519  and  521 . Thus, for example, sensors SH, SM, and SL may be temperature sensors to measure the temperature in boilers  405 ,  407 , and  409 , respectively. The outputs of sensors SH, SM, and SL may be used to control the operation of valves  421 ,  519  and  521 . By controlling valves  421 ,  519  and  521 , and thus the percentage of diverted exhaust gases around the heat exchangers coupled to boilers  405 ,  407  and  409 , the boiler temperatures may be effectively controlled. The temperature of heat transfer fluids in boilers  405 ,  407  and  409 , in turn, establish the volume and composition of the torrefaction gas. 
     For very dry input conditions, it is possible that up to 20% of the heat value of the torrefaction gas may be vented to exhaust lines  115 . With continued operation, the system may equilibrate so that the quantity of torrefaction gas produced is reduced and less heat is dumped, which increases the carbon conversion ratio. 
     In other embodiments, when the temperature measured by sensor SD 3  is less than some set point, such as 105 C, the biomass may be considered to not be adequately dried. Controller  110  may then activate compressor  370 . This, in turn will require that power generation module  240  utilize more fuel, auxiliary fuel, or gasified fuel to produce the required power. When compressor  370  is operated at full load, apparatus  100  power increases requiring, for example, from 2-20% more fuel. Controller  110  then determines the required fuel volume, changing the flow of fuel gas is diverted to burner  507 . The valves  421 ,  519  and  521  may then be closed, increasing the temperature of boilers  405 ,  407  and  409 . This in turn increases the volume of and energy content in the torrefaction gas. Equilibrium is reached when the high temperature boiler temperature rises to a second set point, a programmable level between 250 and 350 degrees C. 
     The engine control mechanism determines the flow through tee  509 , based on having the generator  610  utilizing all the needed fuel for operation based on exhaust oxygen sensors. All of the remaining fuel gas is burned in  507 . 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. 
     Similarly, it should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention. 
     Thus, while there has been described what is believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.