Abstract:
Embodiments presented herein describe an apparatus and method to convert carbonaceous materials, particularly biomass and those biomass resources which are remotely located, into a high performance solid fuel. This method, and the apparatus described as the means to accomplish this method, 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 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/311,696 filed Mar. 8, 2010. The entire contents of the above-listed provisional application are hereby incorporated by reference herein and made part of this specification. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to the production of fuels from biomass, and more particularly to a self-contained method and system for generating biofuels from biomass. 
         [0004]    2. Discussion of the Background 
         [0005]    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. 
         [0006]    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. 
         [0007]    Methods to improve the fuel value and physical properties of biomass range include drying the biomass to remove moisture 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. 
         [0008]    Drying the biomass combined with grinding and pelletizing the resultant fuel produces a fuel with energy density of between 7,000 Btu per pound (16,000 kJ/kg) and 8,000 Btu per pound (19,000 kJ/kg), and a density of 0.6 g/cm 3  (600 kg/m 3 ) and 1 g/cm 3  (1,000 kg/m 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. 
         [0009]    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. 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. 
         [0010]    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 
       [0011]    Certain embodiments described herein overcome the disadvantages of the prior art by torrefaction, and pellitization of the resulting biomass. The biofuel thus produced may have an energy density superior to lower grade fossil coals, and physical properties, such as density, grindability, or water tolerance, that are compatible with industry needs. 
         [0012]    Certain other embodiments described herein overcome the disadvantages of the prior art by utilizing 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. acetic 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 electrical energy in a heat engine. 
         [0013]    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 placed 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. 
         [0014]    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 and/or auxiliary fuel may be available and may be utilized to simplify the apparatus. 
         [0015]    In certain embodiments, it is possible to operate only from the biomass and generate a biofuel having between 70% and 90% of the original energy of the biomass, on a dry basis. 
         [0016]    In one embodiment, one or more heat exchangers heat and/or cool the biomass using the phase change of a heat transfer medium. The phase change occurs on a surface of the heat exchanger that is in thermal contact with the biomass. 
         [0017]    Certain embodiments provide a method for converting a biomass into a coal-like biofuel within an apparatus comprising a heat transfer fluid in a closed-loop heat transfer circuit. The method includes torrefying the biomass utilizing heat by extracting heat from the heat transfer fluid, where the torrefying produces a torrefaction gas and the biofuel; exothermically reacting the torrefaction gas; and heating the heat transfer fluid from the reacted torrefaction gas. 
         [0018]    Certain other embodiments provide an apparatus for converting a biomass into a coal-like biofuel. The apparatus includes: a closed-loop heat transfer circuit having a heat transfer fluid; a heat exchanger having an input for accepting biomass, a first output for providing torrefied biomass, a second output for providing torrefaction gases, and a surface in contact with condensing heat transfer fluid of the heat transfer circuit for condensing the heat transfer fluid; and a chemical reactor for extracting chemical energy from the torrefaction gases and boiling the heat transfer fluid. 
         [0019]    Yet certain other embodiments provide a method for converting a biomass into a coal-like biofuel. The method includes drying the biomass to form steam; and providing heat from the steam to a heat engine. 
         [0020]    Certain embodiments provide an apparatus for converting a biomass into a coal-like biofuel. The apparatus includes: a heat exchanger having an input for accepting biomass, a first output for providing at least partially dried biomass, a second output for providing steam obtained from the biomass; and a heat engine to generate electricity from heat extracted from the steam. 
         [0021]    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 SEVERAL VIEWS OF THE DRAWING 
         [0022]      FIG. 1  is a general schematic of an apparatus for converting biomass to biofuel; 
           [0023]      FIG. 2  is a first embodiment of a biomass-to-biofuel apparatus; 
           [0024]      FIGS. 3A and 3B  are schematics of a biomass processor of the embodiment of  FIG. 2 ; 
           [0025]      FIG. 3C  is a schematic of a heat recovery unit of the embodiment of  FIG. 2 ; 
           [0026]      FIG. 3D  is a schematic of a power generator of the embodiment of  FIG. 2 ; 
           [0027]      FIG. 4  is a schematic of an alternative biomass processor; 
           [0028]      FIG. 5  shows the flow of mass and chemical energy at various points in the system of  FIG. 2 ; 
           [0029]      FIG. 6  shows the flow of mass and chemical energy in a power generator; and 
           [0030]      FIG. 7  is a schematic of a proof-of-principle heat exchanger. 
       
    
    
       [0031]    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 
       [0032]      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. Such biofuels are coal-like, and are referred to herein as “biocoal.” 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 torrefied—that is, heated to drive off volatile components without significantly affecting the remaining material. Torrefaction of biomass is achieved at moderate temperatures, such as above approximately 200° C. and below approximately 350° C., for example and without limitation. The volatile gases thus driven off are sometimes referred to herein as “torrefaction gases,” or “torr 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 more combustible components. 
         [0033]    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. 
         [0034]    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  102  for accepting water, 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 solids that do not form part of the biofuel. 
         [0035]    In certain other embodiments, an input  105  is provided for an auxiliary fuel. The auxiliary fuel, which may, for example be diesel fuel, propane, natural gas, 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. Alternatively, an auxiliary electric power source may be used for start-up or for stead-state operation under certain conditions. 
         [0036]    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, chemical analyzers, solids 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, blowers 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. Control system  110  may be physically included in apparatus  100 , or may include wireless connections to computers or other electronic components that are physically removed from the apparatus. 
         [0037]      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. Where possible, similar elements are identified with identical reference numerals in the depiction of the embodiments of  FIGS. 1 and 2 . 
         [0038]    Apparatus  200  is shown as including a biomass processor  210 , a heat recovery unit  220 , and a power generator  230 . The names given to biomass processor  210 , heat recovery unit  220 , and power generator  230  are not limiting—they are meant to aid in the discussion of apparatus  200  and are invocative of possible functions. Thus, for example, one or more of processor  210 , heat recovery units  220 , and/or power generator  230  may include gas processing and/or heat transfer elements. 
         [0039]    As discussed subsequently in greater detail with respect to a specific embodiment, biomass processor  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 torrefaction are provided to heat recovery unit  220 , and then to power generator  230  to generate electricity that is used in biomass processor  210  and heat recovery unit  220 , and by control system  110 . 
         [0040]    In one embodiment, biomass processor  210  accepts biomass at input  101 , water at input  102 , and ambient air at input  103 - 1 , and provides biofuel at output  111 , moist air at output  113 , water at output  117 , waste solids at output  119 , and torrefaction gases at line  213 . As discussed subsequently, biomass processor  210  also exchanges a heat transfer fluid  202  via lines  211  to heat recovery unit  220  and a heat transfer fluid  204  via lines  215  to power generator  230 . 
         [0041]    Alternatively, biomass processor  210  may also provide for the cleaning, washing, hydrating, and/or sizing of the biomass as appropriate for further processing. 
         [0042]    In certain embodiments, apparatus  200  utilizes a heat transfer fluid  202  that boils in the temperature range torrefaction, such as from 200° C. to 350° C. Thus, for example, the heat transfer fluid may be mixture of biphenyl (C 12 H 10 ), diphenyl oxide (C 12 H 10 O), poly-phenyls, and halogenated derivatives thereof. One such particularly useful heat transfer fluid is a mixture of biphenyl and diphenyl oxide (C 12 H 10 O) marketed as DOWTHERM™ A, (Dow Chemical Company, Midland, Mich.). DOWTHERM™ A has a boiling point of 257° C. at ambient pressure (0.1 MPa), increasing to a 355° C. at 0.58 MPa. Another heat transfer fluid  202  is a mixture of isomers of an alkylated aromatic. One such heat transfer fluid is DOWTHERM™ J, which is also manufactured by Dow Chemical Company. 
         [0043]    This temperature range includes the temperature range of torrefaction of biomass. In the present invention, torrefaction occurs within a heat exchanger providing indirect heat transfer to boil such a heat transfer fluid, thus ensuring that the biomass temperature is controllable, via the heat transfer fluid pressure, and within the temperature range for torrefaction. 
         [0044]    Heat recovery unit  220  accepts torrefaction gases from line  213 , ambient air at input  103 - 2 , and auxiliary fuel, when needed, at input  105 - 2 . As discussed subsequently in certain embodiments, heat recovery unit  220  chemically reacts air from input  103 - 2  and torrefaction gases from line  213  to produce exhaust gases at line  223 . The reaction of air and torrefaction gases is exothermic, with the heat provided to biomass processor  210  via an exchange of fluids through heat transfer lines  211  and to power generator  230  via fluid in heat transfer lines  221 . 
         [0045]    Power generator  230  accepts the processed torr gases from line  223  and produces an exhaust that is ejected at exhaust output  115 . Water or other liquids may also condense from biomass processor  210  and be ejected at water output  117 . Power generator  230  generates electricity which is provided, via line  231  to power input  225  of heat recovery unit  220 , to control system  110  at power input  207 , and to biomass processor  210  at power input  217 . 
         [0046]    Apparatus  200  includes sensors, motors, and valves that are in communication with control system  110 . The sensors collect information, which may include, for example and without limitation, temperatures, pressures, material levels and flow rates, moisture content, and oxygen content. The control elements, which may include, for example and without limitation, valves, motors, pumps and blowers, may be actuated according to commands from control system  110  to enable apparatus  200  to produce biofuel from biomass. Control system  110  may collect data and/or provide control signals via lines  201 ,  203 , and  205  to biomass processor  210 , heat recovery unit  220 , and power generator  230 . Apparatus  200  may also include check valves and/or pressure relief valves that automatically operate to maintain pressures within the apparatus. 
         [0047]    One embodiment of apparatus  200  is provided in  FIGS. 3A ,  3 B,  3 C, and  3 D. Specifically,  FIGS. 3A and 3B  illustrate one embodiment of biomass processor  210 ,  FIG. 3C  illustrates one embodiment of heat recover unit  220 , and  FIG. 3D  illustrates one embodiment of power generator  230 . Apparatus  200  of  FIGS. 3A ,  3 B,  3 C, and  3 D may be generally similar to the apparatus of  FIGS. 1  and/or  2 , except as further detailed below. Where possible, similar elements are identified with identical reference numerals in the depiction of the embodiments of  FIGS. 1 ,  2 ,  3 A,  3 B,  3 C, and  3 D. 
         [0048]    In the discussion that follows, it is understood that all sensors may provide signals to control system  110 , and that apparatus control elements may obtain control signals from control system  110 . It is understood that embodiments may have more or fewer sensors, and more or fewer control elements. In addition, there may be more than one control system, the one or more control systems may communicate or operate separately. Further, one or more sensors may provide information for information purposes and not affect the control of apparatus  200 , and one or more process control elements may be under manual operation, or manual override of an automatic control system. 
         [0049]    Biomass processor  210  includes a biomass preparation portion  301  (as shown in  FIG. 3A ) a biomass metering portion  303  (as shown in  FIG. 3A ), and a biomass thermal processing portion  305  (as shown in  FIG. 3B ). 
         [0050]    As shown in  FIG. 3A , biomass preparation portion  301  includes a biomass washing tank  601  that can accept an input biomass  609  from inlet  101 , and water  603  from spray nozzle  605 , according to the action of a water selection valve V 1  and one or more pumps (not shown). Specifically, valve V 1  may accept water from biomass preparation portion  301  at locations labeled “A” or “C,” or from power generator  230  at the location labeled “B.” 
         [0051]    A liquid level sensor LL 1  may determine the liquid level  607  in tank  601 . Water may be recirculated by drawing liquid (at position “C”) from near the top of tank  601  to valve V 1  using a pump (not shown). The bottom of tank  601  includes a funnel  625  connected to output  119  through a load lock  629  operated by a motor  631 . A solid level sensor SL 2  may determine a solid level  627  in funnel  625 . Liquid level sensor LL 1  may be, for example and without limitation, a float switch. 
         [0052]    In general, any of the load locks described herein may be rotary valves, such as star valves, or may be formed from pairs of pinch valves. Thus a rotary transfer lock may be, for example and without limitation, a PN #12rvccma1b000, manufactured by Rotolok Valves, Inc (Monroe N.C.). The pinch valves may be pneumatic RF Valves, type be4 p15-543s, manufactured by RF Valves, Inc (Columbia Md.). 
         [0053]    Biomass preparation portion  301  also includes devices to move biomass through the portion. Thus, for example and without limitation, portion  301  is shown as having a first conveyor  615 , a second conveyor  619 , and a third conveyor  635  that are powered, respectively, by a motor  617 , a motor  621 , and a motor  637 . 
         [0054]    Biomass metering portion  303  includes a hopper  641  adjacent to third conveyor  635  for accepting washed biomass  639 , and a load lock  651  operated by a motor  653  that provides washed biomass  657  to chute  655 . The level of material in hopper  641  may be monitored by a solid level sensor SL 3 . Solid level sensor SL 3  may be, for example and without limitation, an ultrasound or optical detector. Hopper  641  has a surrounding hot air plenum  645  that can accept hot air  647  from heat recovery unit  220  at “D,” and inject the air into hopper  641 , indicated by arrows, resulting in moist air  649  which may be provided to output  113 . The pressure of plenum  645  may be monitored by a pressure sensor P 4 . 
         [0055]    In certain embodiments, load lock  651  is air-tight. In certain other embodiments, load lock  651  permits gas to flow, even when no solids are being transferred through the lock. Thus, for example,  FIG. 3A  illustrates a flow of gas  644  back through chute  655 , load lock  651 , and into hopper  641 . In yet other certain embodiments, load lock  651  may be located between conveyor  635  and hopper  641 , effectively isolating the contents of the hopper  641  from air. 
         [0056]    Alternatively, if the biomass is sufficiently clean, it may be provided directly into hopper  641  without going through biomass preparation portion  301 . 
         [0057]    Biomass processing portion  305  heats the biomass to dry and torrefy the biomass, and may optionally cool the torrefied biomass (the biofuel, or biocoal) to recover heat. As shown in  FIG. 3B , biomass thermal processing portion  305  includes a heat exchanger  306 . Heat exchanger  306  has a biomass transfer portion  308  that provides for transport of the biomass from an inlet  703  to an outlet  770 . In addition, biomass transfer portion  308  may also provide for gases or liquids to be removed from contact with the biomass. Thus  FIG. 3B  shows extraction lines connected to locations “A,” “F”, and “G.” As discussed subsequently, these lines may also include valves and, depending on the temperature and/or location in heat exchanger  306  may include liquid water, steam, or torrefaction gases. 
         [0058]    In certain embodiments, the flow of biomass from inlet  703  to outlet  770  may reverse direction for short periods of time to agitate the biomass to facilitate heating, cooling, or aiding in providing a uniform biofuel mixture. 
         [0059]    Heat exchanger  306  also includes one or more heat transfer fluid portions  307 , illustrated without limitation as heat transfer fluid portions  307   a  and  307   b,  for providing indirect heat transfer between the biomass in biomass transfer portion  308  and a heat transfer fluid, which may be water/steam or a commercially obtainable heat transfer fluid, flowing through portion  307 . Fluid in portions  307  may thus heats and/or cools the biomass at different locations in the heat exchanger by indirect contact with one or more heat transfer fluids. 
         [0060]    In an illustrative example,  FIG. 3B  shows heat exchanger  306  as consisting of three heat exchanger portions: a biomass dryer  310 , a biomass torrefier  320 , and a biomass cooler  330 . The names of heat exchanger portions  310 ,  320 , and  330  are not limiting—they are meant to aid in the discussion of apparatus  200  and are invocative of possible functions. Thus, for example, biomass dryer  310  may not completely dry the biomass, or may at times partially torrefy the biomass. Biomass dryer  310  and biomass torrefier  320  are shown as corresponding to heat transfer fluid portion  307   a,  which accepts a heat transfer fluid from location “J” and provides the fluid to location “H.” Biomass cooler  330  is shown as corresponding to heat transfer fluid portion  307   a,  accepting water from location “A,” “B,” or inlet  102  and providing steam at location “F.” 
         [0061]    Heat exchanger  306  collects washed biomass  657  in inlet  703  from the location labeled “E” in  FIG. 3A . Heat transfer fluids are provided to heat the biomass and biomass derived material within heat exchanger sections  310  and  320 , and to cool the biomass derived material within biomass cooler  330 . In biomass dryer  310 , the biomass is heated to remove a substantial amount of the water and any of the more volatile gases, and is provided as a dried biomass  735  to biomass torrefier  320 . In biomass torrefier  320 , the biomass is further heated to form torrefied biomass  736 , and to collect the remaining volatile gases. In cooling biomass cooler  330 , heat is recovered from the torrefied biomass. Cooled, torrified biomass  658  is delivered from outlet  770  is then provided to biomass compression portion  340 , which provides the biomass as a biocoal product to output  111 . 
         [0062]    More specifically, heat exchanger  306  is shown illustratively as comprising a biomass transport portion  308  and one or more heat transfer fluid portions  307   a  and  307   b.  Biomass transport portion  308  accepts washed biomass  657  and moves the biomass material sequentially through biomass dryer  310 , biomass torrefier  320 , and cooling biomass cooler  330 , while providing heat transfer fluids to maintain the reactors or heat exchangers at specified or controlled temperatures. Torrefied biomass  658  is provided at outlet  770  into a biomass compression portion  340 . Biomass dryer  310 , biomass torrefier  320 , and cooling biomass cooler  330  thus includes one transport device or several transport devices in serial or parallel to move biomass through each heat exchanger portion  310 ,  320 , and  330 . Biomass transport portion  308  may include, but is not limited to, augers, rotary kilns, vibratory devices, or conveyors. 
         [0063]    Heat exchanger portions  310  and  320  correspond to heat transfer fluid portion  307   a,  which accepts a heat transfer fluid  202  from the location labeled “J” in heat recover unit  220 , provides a flow of the heat transfer fluid along those parts of biomass transport portion  308  associated with heat exchanger portions  310  and  320 , and provides the heat transfer fluid to the location labeled “H” in heat recovery unit  220 . 
         [0064]    Water from the biomass in biomass dryer  310  is collected at the location labeled “A,” or may be discharged through output  117 . Steam from the biomass in biomass dryer  310  is collected in line  215  and provided to the location labeled “F,” which is provided to the power generator  230 . 
         [0065]    Biomass cooler  330  corresponds to heat transfer fluid portion  307   b,  in which a heat transfer fluid  204  is water. Liquid water may be provided input  102  and/or the locations labeled as “A” or “B” in from apparatus  200  and as selected by a valve V 2 . After cooling the biomass, the water may be removed as steam is collected in line  215  and provided to the location labeled “F,” which is provided to the power generator  230 . 
         [0066]    Torrefaction gases are collected from the biomass in biomass torrefier  320  and provided in line  213  to the location labeled “G” in heat recovery unit  220 . 
         [0067]    In certain embodiments, the biomass is processed to remove water from the biomass in biomass dryer  310  without evolving a substantial amount of combustible volatile compounds. The biomass is further processed in biomass torrefier  320  to collect combustible torrefaction gases at “G,” which will then be reacted in heat recovery unit  220 . In general, the volume and composition of the torrefaction gas is a function of the solid transit time through the biomass torrefier  320  and the temperature of heat transfer fluid  202 . Bound oxygen is driven off (reduced) from the biomass in biomass torrefier  320  producing torrefaction gases composed of CO 2 , H 2 O and C x H y O z  volatiles. As the temperature of biomass torrefier  320  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 biomass 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 power generator  230  can be met. 
         [0068]    In one embodiment, heat exchanger portions  310  and  320  are operated at the same temperature, and the feed rates of biomass is adjusted so that dried biomass  735  contains some amount of water, such as less than 15% by weight. In one embodiment, fluid  202  is provided to heat exchanger portions  310  and  320  in the temperature range of 200° C. to 350° C. 
         [0069]      FIG. 4  is a second embodiment biomass thermal processing portion  305  and biomass compression portion  340 , which are generally similar to the embodiment of  FIG. 3B .  FIG. 4  also shows the placement of sensors, which are particular to the specific heat exchangers. 
         [0070]    In the embodiment of  FIG. 4 , biomass dryer  310 , biomass torrefier  320 , and biomass cooler  330  include augers that permit indirect contact of the biomass with heat transfer surfaces. Biomass dryer  310  collects biomass material from the location labeled “E” in biomass dryer  310  in inlet  703 , and may include a moisture content sensor MC 5  to determine the moisture content of material  657 . Biomass dryer  310  moves the material to an outlet  729  by rotating auger blades  707  that are located within an auger housing  705 . Blades  707  are mounted on a hollow auger shaft  709  controlled by a motor  711 . Rotary couplings  727  and  723  are provided near inlet  703  and outlet  729 , respectively, to allow a heat transfer fluid to flow through the center of hollow auger shaft  709 . An auger housing jacket  713  extends along housing  705  to allow a heat transfer fluid to flow on the outside of the housing. 
         [0071]    The output  729  of biomass dryer  310  is provided to a load lock  731  controlled by a motor  733  and provides dried biomass  735  through chute  737  to an input  739  of biomass torrefier  320 . The moisture content of dried biomass  735  may be monitored in chute  737  with moisture content sensor MC 7 . Biomass torrefier  320  provides the torrefied biomass to an outlet  757  with auger blades  743  that are located within an auger housing  741 . Blades  743  are mounted on a hollow auger shaft  745  controlled by a motor  747 . Rotary couplings  755  and  753  are provided near inlet  739  and outlet  757 , respectively, to allow a heat transfer fluid to flow through the center of hollow auger shaft  745 . An auger housing jacket  749  extends along housing  741  to allow a heat transfer fluid to flow on the outside of the housing. 
         [0072]    The output  757  of biomass torrefier  320  includes a temperature sensor T 9  that may measure the temperature of biomass  736  from the biomass torrefier. The biomass  736  is provided to an inlet  759  of cooling biomass cooler  330 , which transports the material to an outlet  770  with auger blades  763  that are located within an auger housing  761 . Blades  763  are mounted on an auger shaft  765  controlled by a motor  766 . A housing inlet  764  is provided near inlet  736  to allow a heat transfer fluid to mix with biomass  736 . An auger housing jacket  767  extends along housing  761  to allow a heat transfer fluid to flow on the outside of the housing. 
         [0073]    The cooled, torrified biomass material from outlet  770  is then provided to a chute  771 , where a temperature sensor T 11  may measure the biomass temperature. Chute  771  is an input for a grinder  772  that is operated by a motor  773 , and then to a briquetter  774  operated by a motor  775 , which provides the biomass as a biocoal product  776  to output  111 . Grinders and briquetters are well known in the field of wood pelletization for fuel production. 
         [0074]    Auger housings  705 ,  741 , and  761  correspond to biomass transfer portion  308 . The center of hollow auger shafts  709  and  745 , and auger housing jackets  713  and  749  correspond to heat transfer fluid portion  307   a,  and auger housing jacket  767  corresponds to heat transfer fluid portion  307   b.    
         [0075]    Heat transfer fluids are provided to heat the biomass and biomass derived material within heat exchanger portions  310  and  320 , and to cool the biomass derived material within biomass cooler  330 . In heat exchanger portions  310  and  320 , a heat transfer line  721  provides fluid, whose pressure may be monitored by a pressure sensor P 12 , and which is obtained from the location labeled “J” the heat recovery unit  220 . Heat transfer line  721  provides the fluid to auger jacket housing  713  (which is the exterior of biomass dryer  310 ), rotary coupling  723  (which provides flow into the interior of the biomass dryer), auger jacket  749  (which is the exterior of biomass torrefier  320 ), and rotary coupling  753  (which provides flow to the interior of the biomass torrefier). Heat transfer fluid is recovered in line  725  from auger jacket housing  713 , rotary coupling  727 , auger jacket  749 , and rotary coupling  755 . 
         [0076]    Water from the drying biomass is collected at auger output  719 , and may be provided back to valve V 1  (as indicated by the label “A”), or may be discharged through output  117 . Steam from the dried biomass is collected in line  717 , where the temperature may be measured by temperature sensor T 7 , the non-water components are measured with a volatile organic compound (VOC) sensor VOC 6 , and mass flow may be measured by mass flow sensor MF 6 . 
         [0077]    Liquid water is used as a heat transfer fluid to cool biomass in cooling biomass cooler  330 . Liquid water  768  may be provided to auger housing jacket  767  and inlet  764 , where the water may be provided from input  102  and/or the locations labeled as “A” or “B” in biomass processor  210  and power generator  230 , as selected by a valve V 2 . After cooling the biomass, the water may be removed as steam  769 , where the pressure may be measured by pressure sensor P 10 . Liquid level sensor LL 2  is used to ensure that the auger is filled with water to maintain the temperature of cooling biomass cooler  330 . 
         [0078]    As shown in  FIG. 3C , heat recovery unit  220  includes a combustion mixer  779 , a pressure vessel  784  that contains a catalytic combustor  781 , a heat transfer augmenter  785 , and a heat transfer tube  783 , a recuperator  787 , a blower  790 , and valve V 4 . 
         [0079]    Biomass gases obtained from biomass torrefier  320  at “G,” and hot air  647 , obtained from recuperator  787  via valve V 4  are mixed in combustion mixer  779 . In addition, auxiliary fuel may be provided to mixer  779  via input  105 - 2 . 
         [0080]    The output of combustion mixer  779  is a combustible gas mixture  780  whose temperature, pressure, and oxygen content may be measured by temperature sensor T 15 , pressure sensor P 15 , and oxygen sensor O 15 , respectively. The mixture is then provided to catalytic combustor  781 , and combusted gases  782  flow through heat transfer augmenter and a heat exchange tube  783 , where the gases exit as medium temperature exhaust gases  786 . The temperature, pressure, and oxygen content may be measured by temperature sensor T 18 , pressure sensor P 18 , and oxygen sensor O 18 , respectively, before entering recuperator  787 . 
         [0081]    Heat transfer fluid  202  from liquid heat transfer fluid from line  725  in biomass dryer  310  is provided to catalytic combustor  781 , and heat transfer tube  783 , to raise the temperature of the heat transfer fluid and return it as a vapor to line  721  (“J” in heat recovery unit  220 ). A liquid level sensor LL 17  may measure the level of the heat transfer fluid  202  in heat recovery unit  220 . Liquid heat transfer fluid is also obtained from power generator  230  (at “K”), and vapor heat transfer fluid may also be provided to the power generation unit (at “L”). 
         [0082]    Auxiliary air from inlet  103 - 2 , and whose temperature may be measured with temperature sensor T 20 , is provided, via blower  790 , as pressurized air  788 . Heat from gases  786  are provided to pressurized air  788  to form hot air  647 , which is then provided to valve V 4 . Cooled combusted gases  789 , whose temperature may be measured with a temperature sensor T 19 , leave heat recovery unit  220  in line  223 . 
         [0083]    The augers of heat exchanger portions  310 ,  320 , and  330  of  FIG. 4  are preferably sized to transport and provide sufficient heating for the biomass passing there through. Thus auger 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 has a diameter of 12 inches (0.3 m) to 24 inches (0.6 m), a length of 10 feet (3 m) to 30 feet (10 m), and capable of operating an external pressure of 4 bars (0.4 MPa) absolute. 
         [0084]    As shown in  FIG. 3D , power generator  230  includes a heat receiver  801 , a heat engine  813 , a waste heat rejection system  819 , a closed water loop  811  between the heat receiver and heat engine, and a closed water loop  817  between heat engine and heat rejection system. Power generator  230  utilizes the exhaust gases to generate power, as for example and without limitation, in a Rankine cycle engine, such as an organic Rankine cycle (OCR) engine model UTC 2800, manufactured by UTC Power (United Technologies Corporation, South Windsor, Conn.), or a turbine. In heat receiver  801 , heat from exhaust gas  789  is accepted from “M” from heat recovery unit  220  and rejected as a colder exhaust  115 , heat from vapor heat transfer fluid  721  is accepted from heat recovery unit  220  at “L” and provided back to heat recovery unit  220  at “K,” and heat from steam  717  and  769  from two locations labeled “F” in  FIG. 3B , and is returned as liquid water  803 , to wash the biomass (“B” in biomass processing unit  210 ) or to output  117 . In an alternative embodiment, heat receiver  801  includes a boiler to provide pre heat the steam  717  or  769  as it enters the receiver. In yet another alternative embodiment, heat from steam is obtained from only one of either steam  717  or steam  769 . Closed water loop  811  transfers the heat from heat receiver  801  to heat engine  813 , which generate electric power provided to line  231 . Closed water loop  817  transfers heat through waste heat rejection system  819  to the environment. 
         [0085]    The temperature of water in loops  811  and  817  may be measured with temperature sensors T 21  and T 22 , respectively. 
         [0086]    The measurement 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. The sensors noted herein are well known in the field. 
       Operation of the Apparatus 
       [0087]    The material flow rates and temperature of the components of system  200  are preferably operated to: 1) minimize the amount of volatile components (with the exception of water) recovered from biomass dryer  310 ; 2) minimize the amount of water recovered from biomass torrefier  320 ; and 3) generate enough electric power in the power generation unit to operate the system. 
         [0088]    Minimizing volatile components recovered from biomass dryer  310  and minimizing the amount of water recovered from biomass torrefier  320  may be accomplished in a number of ways. Thus, for example and without limitation, load locks positioned at different stages in system  200  may isolate the drying, torrefaction, and cooling portion from the biomass inlet and biofuel outlet. Gases extracted from these stages may thus be substantially partitioned between steam and torr gases. Additionally, or in place of the load locks, steam and torr gas extraction locations may include valves to control the exit of steam and torr gas from system  200 . 
         [0089]    Thus for example, steam generated by the biomass in transport portion  703  prevents torr gas from flowing upstream from torrefier  320 , and providing the torr gas to line  213 . In addition, the steam thus generated may flow further upstream, essentially purging air from the biomass, and providing a “self-purging” system. Further, water added to biomass cooler  330  may also generate steam, further isolating the torr gases to torrefier  320  for extraction at line  213 . 
         [0090]    As an example of the operation of apparatus  200  of  FIGS. 3A ,  3 B (or  4 ),  3 C and  4 D, raw biomass may be loaded into input  101  of biomass preparation portion  301 , and provided to tank  601 . Preferably, the biomass is provided at a nearly constant rate. A spray of water is provided through nozzle  605 , where the water is either obtained from biomass dryer  310  (“A”), power generator  230  (“B”), or by recirculation from tank  601  (“C”) according to the selection of valve V 1 , where the water is provided to maintain a constant level as indicated by sensor LL 1 . 
         [0091]    As solid material settles in tank  601 , sensor SL 2  indicates when motor  631  needs to be operated to discharge the solids to output  119 . 
         [0092]    Motors  617 ,  621 ,  631 , and  637  and valve V 1  are thus operated by control system  110  utilizing the output of sensors LL 1  and SL 2  to provide the correct water level, to move biomass and solids through tank  601 , and to provide biomass into biomass metering portion  303 . 
         [0093]    In biomass metering portion  303  the biomass is partially dried using a stream of hot air provided to hopper  641 . In the embodiment of  FIG. 3A , the pressure of hot air is monitored by sensor P 4 , and is controlled by blower  790  and valve V 4 , which directs hot air into hopper  641 . If the pressure at sensor P 4  is insufficient to flow through the biomass, then valve V 4  may direct more flow towards hopper  641 , and/or the blower may be operated to provide a higher pressure. 
         [0094]    In general, the moisture content of biomass  657  varies with feedstock location, age and weather. System  200  may be controlled to accommodate these changes. 
         [0095]    Since the torrefaction of biomass is best done in the absence of oxygen, biomass  657  leaves biomass metering portion  303  through lock  651  operated to prevent air from entering heat exchanger portions  310  and  320 . Thus, for example, the biomass within heat exchanger portions  310 ,  320 , and  330  may be at an elevated pressure, such as from 0.11 MPa absolute to 0.3 MPa absolute. Water evolving from biomass dryer  310  and torrefaction gases evolving from biomass torrefier  320  will pressurize the heat exchangers. Load locks at the ends of heat exchanger portions  310 ,  320 , and/or  330 , coupled with valves on outgas lines from the heat exchanger, will permit the separation of the various gases. 
         [0096]    In one embodiment, steam  644  that leaves the drying biomass flows back into hopper  641 , purging any air contained in the biomass before it leaves the hopper. 
         [0097]    In certain embodiments, heat exchanger portions  310  and  320  are operated to obtain torrefaction gases, which are then used to generate electricity for operating system  200 . It is thus important that the quality and quantity of torrefaction gas obtain from biomass torrefier have sufficient chemical energy. In one embodiment, heat exchanger portions  310  and  320  are operated at the same temperature, as provided by the saturation temperature of the heat transfer fluid in lines  721  and  725  at the pressure measured at sensor P 12 . This fluid is provided to both the inside and outside of heat exchanger portions  310  and  320 , and may be at a temperature of between 200° C. and 350° C. The temperature of fluid provided to heat exchanger portions  310  and  320  may thus, for example, be approximately 200° C., approximately 225° C., approximately 250° C., approximately 275° C., or approximately 300° C., or approximately 325° C., or approximately 350° C. 
         [0098]    Thus, for example, if there is some amount of moisture in the biomass as it leaves biomass dryer  310 , one may be assured that evaporation of liquids less volatile than water has not occurred within the biomass dryer. An initial drying of the biomass takes place in dryer  310  through the phase change fluid of heat transfer fluid  202  at a constant temperature, for instance 300 C. Biomass  657  with a moisture content of up to 60% on a wet basis leaves dryer  310  as biomass  735 , with a moisture content of 10% to 20% on a wet basis. The moisture leaves as steam  717  or liquid water  719 . 
         [0099]    The biomass within dryer  310  may be, for example and without limitation, near at ambient pressure, with the steam nearly saturated at 100 C. In one embodiment, the output of sensor MC 7  is monitored, and the speed of motor  711 , and thus the flow of biomass through the biomass dryer, is adjusted to maintain a moisture content of from 10% to 25%. from 15% to 20%, or to be approximately 10%, 15%, 20% or 25%. If the moisture content is too high, then control system  110  may slow down motor  711  to provide more drying, while if the moisture content is too low, then control system  110  may speed up motor  711  to provide less drying. 
         [0100]    In certain embodiments, electric power from power generation unit  230  may be maximized or controlled by adding water directly to the biomass in the dryer  310  (not shown) or by washing the biomass in the biomass preparation portion  301  to provide a steady supply of steam  717 , to hydrate the biomass to operate the dryer at a high effective moisture content, for example 50% moisture content on a wet basis. It may also be desirable to move biomass  657  through dryer  310  at a rate where biomass  735  has a constant moisture content, as determined by MC 7  of, for example and without limitation, of 10% to 20%. This control provides for a more uniform feed to torrefier  320 , and prevents steam  717  from becoming superheated. An additional benefit is that less torrefaction will occur in dryer  310 . A small flow of steam from dryer  310  into torrefier  320  can also serve to limit the backward flow of torr gases from the torrefier to the dryer. 
         [0101]    In addition to the control of biomass through system  200 , control system  110  may operate heat recovery unit  220  to change the pressure in line  721 , and thus the temperature of heat exchanger portions  310  and  320 . 
         [0102]    Control system  110  may also control the speed of motors  653 ,  747 ,  766 ,  773 , and/or  775  to match the flow rate of biomass through the other components and prevent the build up or total removal of biomass in the various components. 
         [0103]    The time that the biomass is in biomass torrefier  320  may be, for example and without limitation, between approximately 5 minutes and approximately 60 minutes. 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. 
         [0104]    The material evolved from the biomass in biomass dryer  310  is primarily water, which exits the biomass dryer as liquid water  719  and as steam  717 . The liquid water  719  may be provides at “A” to wash the incoming biomass, or provided to output  117 . The steam is provided to power generator  230 , where energy is extracted for power generation. The condensed water may then be returned at “B” to wash the incoming biomass, or provided to output  117 . 
         [0105]    The material evolved from the biomass in biomass torrefier  320  is a torrefaction gas  751 , which is provided to heat recover unit  220  for recovery of the heat of combustion of the torrefaction gases. 
         [0106]    Next, the torrefied biomass in cooled in biomass cooler  330 . The outside of cooling biomass cooler  330  is provided with liquid water selected by valve V 2  as coming from biomass evolved water from biomass dryer  310  (at “A”), from power generator  230  (at “B”) or from water input  102 . Liquid level LL 2  is used to sense the water level and operate water pumps to ensure that the heat exchanger is filled, or nearly filled, with liquid water. The cooling water leaves biomass cooler  330  as steam, which is provided, along with steam  717  from biomass dryer  310 , to power generator  230 . Biomass cooler  330  is maintained at a temperature of 120° C. to 200° C. 
         [0107]    Liquid water is also provided at inlet  764  into the biomass portion of cooling biomass cooler  330 . This water evaporates when contacting the biomass in biomass cooler  330 . The flow of water at inlet  764  is provided to prevent or greatly inhibit torrefaction gases from flowing out of biomass torrefier  320 , and thus facilitate the removal of torrefaction gases in line  213 . 
         [0108]    The biofuel leaving cooling biomass cooler  330  is then ground, in grinder  772 , and compressed in briquetter  774  to produce biocoal at output  111 . Briquetter  774  preferably acts as a load lock, preventing or reducing the flow of gases from biomass cooler  330 . Optionally, an additional load lock may be provided at or near biomass compression portion  340 . 
         [0109]    Heat recovery unit  220  pressurizes ambient air in blower  790 , heats it in recuperator  787 , and then, according to the operation of valve V 4  mixes the heated air with torr gases  751  and, alternatively, with auxiliary fuel from input  105 - 2 . The resulting combustible mixture  780  is then reacted in catalytic combustor  781 , which includes heat transfer augmenter  785  and heat transfer tube  783  for heating the heat transfer fluid (from “K” and “H,” and supplied to “J” and “L”). The output of the combustor is provided to recuperator  787  for preheating the air, and then to power generator  230  for electric energy production. The heat recovered from the torr gas can is divided between the biomass processor  210  and power generator  230 . 
         [0110]    In certain embodiments, it is desired to maintain catalytic combustion at some optimal temperature, for example and without limitation, from between 250° C. and 800° C. Thus, for example, higher temperatures may cause the catalyst to deactivate and possible structurally collapse and a lower temperature will be unable to initiate or support combustion. Additionally, high temperatures will tend to degrade the phase change fluid. Thus, it may be of advantage to provide a means to moderate the temperature of the catalytic reaction. 
         [0111]    In certain embodiments, combustible gas mixture  780  is run lean—and may have, for example a stoichiometry of 0.50. In addition to the previously mentioned advantages, running combustor  781  lean provides for complete combustion of the torrefaction gases and keeps the temperature of the combustor low, and prevents fouling of the system due to incomplete combustion of the volatiles. 
         [0112]    Power generator  230  recovers heat from steam generated in biomass dryer  310  and heat recovered in the heat transfer fluid in heat recovery unit  220  into output of the combusted torr gases  789 , uses the recovered energy to operate a heat engine to generate electricity at power output  231 , and then discharge the exhaust at output  115 . 
         [0113]    In another embodiment, an optional pressure regulator V 3  is provided between steam obtained from drying the biomass in dryer  310  and the power generation unit  230 . Pressure regulator V 3 , which provides saturated steam at elevated pressure, such as 0.1 MPa and 120° C. 
       System Simulation 
       [0114]    An analysis was performed to analyze how various parameters (such as feedstock moisture content) affect the overall heat and mass balances. These calculations were conducted for the nominally 1 ton/hr (1,000 kg/hr) device, utilizing the apparatus of  FIGS. 3A ,  4 ,  3 C and  3 D, where Table 1 lists the input parameters. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
             
               
               
             
               
               
               
             
               
               
             
               
               
               
             
               
               
             
               
               
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Input parameters for mass and energy 
               
               
                 balances - 1 ton/hour (1,000 kg/hr) scale. 
               
             
          
           
               
                 Parameter 
                 Value 
               
               
                   
               
             
          
           
               
                 Feedstock feed rate 
                 2.8 
                 tons/hr 
               
             
          
           
               
                   
                 (2,500 kg/hr) 
               
               
                 Feedstock moisture mass fraction, wet basis (at 609) 
                 50% 
               
               
                 Moisture mass fraction of partially dried wood 735 
                 0%-60% 
               
               
                 entering torrefier 
               
             
          
           
               
                 Heat of combustion of dry feedstock 
                 20 
                 MJ/kg 
               
               
                 Heat of combustion of torrefied wood 
                 25 
                 MJ/kg 
               
             
          
           
               
                 Yield of torrefied wood - dry wood basis 
                 68% 
               
             
          
           
               
                 Air specific heat capacity 
                 1 
                 kJ/kg-K 
               
             
          
           
               
                 Air/fuel mass ratio in combustor (at 780) 
                 3.29 
               
             
          
           
               
                 Wood specific heat capacity 
                 1.5 
                 kJ/kg-K 
               
               
                 Liquid water specific heat capacity 
                 4.2 
                 kJ/kg-K 
               
               
                 Torrefied wood specific heat capacity 
                 1.5 
                 kJ/kg-K 
               
               
                 Water heat of vaporization 
                 2260 
                 kJ/kg 
               
               
                 Steam specific heat capacity 
                 1.9 
                 kJ/kg-K 
               
               
                 Heat of torrefaction 
                 0 
                 kJ/kg 
               
               
                 Exhaust gas specific heat capacity 
                 1.5 
                 kJ/kg-K 
               
             
          
           
               
                 ORC efficiency 
                 10% 
               
               
                   
               
             
          
         
       
     
         [0115]    The moisture content (MC %) is a very significant feedstock variable. Using experimental measurements, discussed subsequently, the analysis provided a calibrated model for estimating system performance. Specifically, Table 2 shows the effect of moisture content on the operation of the system. The first column is the moisture content of the biomass being provided to the biomass dryer, on a percent wet basis. The second column is the amount of time spent in biomass dryer  310  at a temperature of 300° C., the third column is the amount of time spent in biomass torrefier  320  at a temperature of 300° C., the fourth column is the sum of the time spent in heat exchanger portions  310  and  320 , the fifth column is the amount of water evolved, per ton of wet biomass, and the sixth column is the amount of wet biomass processed, per day. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 The effect of moisture content on the operation of the system 
               
             
          
           
               
                   
                   
                   
                 Total 
                 Mass Water 
                   
               
               
                 % MC 
                 Dry Time 
                 Torr Time 
                 Time 
                 ton/ton 
                 ton/day 
               
               
                 Wet Basis 
                 sec 
                 sec 
                 sec 
                 (kg/kg) 
                 (kg/day) 
               
               
                   
               
             
          
           
               
                 0% 
                 0.0 
                 12.6 
                 12.6 
                 0.00 
                 30.10 (27310) 
               
               
                 10% 
                 2.5 
                 12.5 
                 15.0 
                 0.11 
                 25.28 (22930) 
               
               
                 20% 
                 5.6 
                 12.6 
                 18.2 
                 0.25 
                 20.81 (18880) 
               
               
                 30% 
                 9.6 
                 12.6 
                 22.2 
                 0.43 
                 17.05 (15470) 
               
               
                 40% 
                 15.0 
                 12.6 
                 27.6 
                 0.67 
                 13.74 (12460) 
               
               
                 50% 
                 22.5 
                 12.6 
                 35.1 
                 1.00 
                 10.80 (9797)  
               
               
                 60% 
                 33.8 
                 12.6 
                 46.4 
                 1.50 
                 8.18 (7420) 
               
               
                   
               
             
          
         
       
     
         [0116]    This analysis illustrates that system  200  may be controlled to provide torrefied biomass for a very wide range of biomass moisture content. 
         [0117]    The torrefaction chemistry and heat exchanger design are preferably operated at an autothermal point, where the chemical energy in the torr gases is just sufficient to support production. For example, a 40% MC feedstock, with 20 MJ/kg Higher Heating Value (HHV), can produce at 35% yield a torr gas with 11 MJ/kg and a solid product at 65% yield of 25 MJ/kg, and be self sustaining, including system heat losses. The system output may be for instance 1 ton per hour, with an electrical load of 50 kW. 
         [0118]    As another example, a 30% MC feedstock, with 20 MJ/kg HHV, can produce at 25% yield a torr gas with 11 MJ/kg and a solid product at 75% yield of 23 MJ/kg. The system output in this case would be 1.5 tons per hour (1400 kg/hr), and the electrical load of 75 kW. In this case less energy is required for drying and the system runs more quickly and uses the excess energy to produce power. 
         [0119]    The simulation indicates that the torrefaction gases in line  213  include combustible gases including acetic acid, lactic acid, furfural, formic acid, hydroxyl acetone, methanol, carbon monoxide, and non-combustible gases including water and carbon dioxide. 
         [0120]      FIGS. 5 through 6  show the mass flow and energy flow in the system, and indicate that that there is sufficient energy in the torrefaction gases to operate the entire system, and thus provide “stand-alone” operation, where biomass may be converted to biocoal without the need for additional fuel or electricity. 
         [0121]      FIG. 5  shows the flow of mass and chemical energy at various points in system  200 . Importantly, the amount of energy in the biofuel (5971 kW) is a substantial fraction of the energy available in the original biomass (7056 kW) and is in a much more useful state, being compatible with coal. In addition, a significant amount of electrical power (76 kW) is available for running system  200 . 
         [0122]      FIG. 6  shows the flow of mass and sensible energy in power generator  230 . The torrefaction gases have 190 kW of chemical energy which is supplemented by the sensible energy in the steam and which provides for 76 kW of electrical energy. 
         [0123]    It is expected that apparatus  200  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 having a controlled energy content and/or density. 
         [0124]    Thus, for example, the biofuel may have a heating value of between 9,000 Btu per pound (20934 kJ/kg) and 12,000 Btu per pound (28,000 kJ/kg) on an ash free basis, and a density after densification of between 0.8 g/cm 3  (800 kg/m 3 ) and 1.4 g/cm 3  (1400 kg/m 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 significantly chemically altered, and by subsequent compression into pellets. 
         [0125]    For the simpler case of a single auger drier and torrefier, the dwell time (set by the auger speed, inch/min, controlled by  747 ), heat exchanger temperature (set by the pressure of the heat transfer fluid, 300° C./2 bar (0.2 MPa) of 721, measured at P 12 ), and load size (set by the feed auger, kg/min of  101 , controlled by  637 ) are all be independent and can be used in combination. Thus, for example, at constant temperature and load rate, low moisture content feedstock will move faster through the auger (i.e. 15 minutes) compared to a high moisture content feedstock (i.e. 30 minutes). Alternatively, at constant temperature and auger speed, a higher feed rate is appropriate for the dry material. Further, at constant auger speed and feed rate, a higher temperature is appropriate for the wet feedstock. 
         [0126]    The torrefaction gas production rate is correlated to the torrefied solid product production rate by: 
         [0000]      Feedstock HHV=Torr Gas HHV+Torr Biomass HHV 
         [0127]    At constant feedstock moisture content, temperate and feed rate, higher torr gas rates are accomplished by reducing the auger speed, with the result that the solid product has both lower total energy, and higher energy density. Similarly with temperature and feed rate. 
         [0128]    The energy in the Torr gas is needed to dry, torrefy and produce power. The energy to torrefy is constant across moisture content. The energy required to dry is linearly related to the moisture mass in the feedstock. The power required is directly related to production rate, as the major electrical loads of pressurizing air, grinding and densification are proportional to throughput. 
       EXAMPLE 
       [0129]      FIG. 7  is a schematic of a proof-of-principle heat exchanger  900  constructed to verify the ability to torrefy biomass. Biomass is provided to upper load lock  901  and transferred through pinch valve to lower load lock  903  and to an output load lock  908 . Heat exchanger  900  includes a single auger  902  having an auger motor drive  904  that moves biomass through a vapor condensing zone  905 , a vapor condensing zone  907 , and a fluid heating zone  909 . Heat exchanger  900  also includes a first boiler  910  to maintain a first heat transfer fluid level  911 , a second boiler  920  to maintain a second heat transfer fluid level  921 . Torr gases could be sampled at ports  931  and  933 . 
         [0130]    Vapor condensing zone  905  corresponds to biomass dryer  310 , vapor condensing zone  907  corresponds to biomass torrefier  320 , and fluid heating zone  909  corresponds to cooling biomass cooler  330 . 
         [0131]    The auger had a 4″ diameter auger, was 8 feet (2.5 m) long and had a screw pitch of 4 inches (0.1 m). The auger is driven by a DC motor with gear reduction head. Typical rotation speed is 4.9 rotations per minute (RPM), both forward and reverse. 
         [0132]    The process is preferably conducted in the absence of oxygen. A pinch valve load lock was constructed using 5 inches (0.13 m) pinch valves, and a CO 2  purge gas was used. The process was conducted with heat exchanger  900  at a temperature set point between approximately 250° C. and 300° C. The process auger system was divided into three equally sized zones  905 ,  907 , and  909 . The temperature of each zone can be independently controlled and the power consumed independently monitored. 
         [0133]    Heat exchanger  900  was designed to deliver 5 lbs per hour (2.3 kg/hr), and included unattended operation and delivery of biocoal grade torrefied biomass plus recovery of the torr gas for analysis. The prototype was also engineered with sensors and data logging capability to help define and understand the process, monitor energy flow and assess effect of variations on process yield. 
         [0134]    An input hopper (not shown) was designed to hold approximately 20 lbs (9 kg) of biomass. Biomass was chipped prior to loading and contained approximately 10% moisture by weight. A 2 inch (0.05 m) diameter single screw auger that moves the biomass from the input hopper to the input load lock. The amount of load placed in the load lock in each operation is regulated by run time of the hopper&#39;s auger. A run time of 8 seconds transfers approximately 0.035 kg of biomass to the load lock. This is the standard operating setting. A new sample is added approximately every 45 seconds which produces a raw biomass flow rate of approximately 6 lb/hour (2.7 kg/hr). 
         [0135]    In a typical process, all three zones are set to 300° C. and controlled by independent PID loops, with DOWTHERM™ A as the heat transfer fluid. To maintain the nominal operating temperature of 300° C., the DOWTHERM™ A boiled at a nominal pressure of between 0.20 and 0.22 MPa absolute. 
         [0136]    Heat exchanger  900  has been used to produce torrefied biomass, which has been tested by use in a commercial boiler. In one series of tests, heat exchanger  900  was operated for 2.4 hours to produce torrefied product at 4.5 lb/hr (2 kg/hr) from an input of 6.25 lb/hr (2.83 kg/hr) raw biomass. There was no evidence of coking in heat exchanger  900 . 
         [0137]    The biomass feedstock had a higher heating value energy content of 16.3 MJ/kg. The energy content of the biofuel was found to be 20.9 MJ/kg via an oxygen bomb calorimeter. The moisture content of the biofuel was 2.1% on a dry basis 
         [0138]    In addition, heat exchanger  900  was used to test the ability to process different feedstocks. Specifically: 
         [0139]    Testing showed that 50% moisture content biomass could be dried to 20% MC in 15 minutes, at a feed rate of 6 dry pounds per hour (2.7 kg/hr). This suggests that 40% moisture content could be completely dry in 15 min, which is used as a calibration point in the analysis above. 
         [0140]    Testing also showed that 6 dry lbs (2.7 kg) of 10% moisture content biomass could be dried and torrefied in 15 min. Water evaporated per hour 2.64 pounds (1.2 kg), which was used as another calibration point in the analysis above. 
         [0141]    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. 
         [0142]    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. 
         [0143]    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.