Abstract:
A method and apparatus for continuously producing charcoal and graphite of selectable varying degrees of volatile content from all types of waste wood, bark and vegetable matter are disclosed. The method uses horizontal force fed retorts arranged in tiers of rows across the width of a refractory oven. Because it can use various organic material, including wood waste, mixed up with bark in any ratio, the invention provides a solution to the forest industry waste proliferation problem. Organic material is carried through the retort by a screw which has its flights interrupted in gas collection areas. Loose plugs of organic material form in the gas collection areas and prevent the escape of gases by way of the ends of the retort. Gases are collected by gas vents which connect to the retort in the gas collection areas.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of international application No. PCT/CA99/00321 entitled Continuous Production Closed Retort Charcoal Reactor filed Apr. 14, 1999 which is incorporated herein by reference.  
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to apparatus and methods for producing charcoal in a continuous manner. In particular, the invention relates to apparatus and methods in which organic material is advanced by a screw through one or more substantially horizontal retort tubes. The organic material is heated anaerobically in the retort tubes and is converted to charcoal.  
         BACKGROUND OF THE INVENTION  
         [0003]    In the 1950&#39;s and 1960&#39;s charcoal was mass produced from wood or agricultural refuse in large machines having vertical retorts. Virtually all of these machines were shut down and dismantled about 40 years ago. Primitive though they were, and elementary as the control instruments were at that time, continuous charcoal production was achieved. It was possible to intentionally produce charcoal with few contaminants and, for example, high or low ash content, volatility or carbon content. It was possible to control the approximate final chemical and physical properties of the charcoal using the machines.  
           [0004]    At a certain stage during the production of charcoal, organic material typically adopts a sticky plastic state. In this state, the material is very susceptible to compression. When a vertical retort is being used, a plug of compressed organic material can sometimes block the venting of gases and the steady feed-through of material. Dangerously high pressures can build up in the retort as a result. The reliance on gravity to move materials through a vertical retort makes it impossible to prevent the material from being compressed. When the operators were able to bring the pressure back down to normal in such vertical retorts, all quality control in the charcoal produced was lost until conditions were stabilized.  
           [0005]    Some vertical reactors had one or more vertical retorts approximately fifty feet high. Such reactors relied solely on gravity to feed sawdust through the retort. The retorts were inside a heated chamber. This configuration permitted the sawdust to hang up within the retort creating super hot spots and extremely perilous conditions when the sawdust was finally freed and fell into these spots. The first sawdust batches to hit the hot spots were literally vaporized on contact and all quality control would be temporarily lost.  
           [0006]    With previous retorts, to exercise what little control could be had over the finished product; the temperature of the chamber surrounding the retorts had to be varied between such extremes that the continued expansion and contraction of the equipment induced unnecessary fatigue in the metals and shortened the service life of the retorts.  
           [0007]    Furthermore, servicing the retorts of previous reactors proved difficult and time-consuming. In order to replace or service retorts, the entire roof of the reactor had to be torn off. Retorts would have to be removed one half at a time. While the upper half of the reactor was lowered to the ground, the lower half of the retort would have to hang suspended in the retort.  
           [0008]    It is known that charcoal may be produced by moving organic material through horizontal tubes. For example, Canadian Patent No. 1,226,840 discloses a method of low temperature carbonization of coal hydrogenation residue by subjecting the residue to reduced pressure distillation. The residue is carried through a tubular apparatus by a screw that runs the entire length of the tubular apparatus  
           [0009]    Canadian Patent No. 1,062,192 discloses a method of destructive distillation of organic waste material by subjecting the waste material to pulverization, drying, and alternating heating and cooling.  
           [0010]    Canadian Patent Application No. 2,009,666 discloses a method of producing sawdust charcoal from cylindrical Ogalite. Ogalite is carried through a heated tubular apparatus by means of a screw that runs the entire length of the apparatus.  
           [0011]    Canadian Patent Application No. 2,110,282 relates to a method of treating biomass material wherein the material is carried through a heated casing by an auger which runs the entire length of the heated casing.  
           [0012]    Canadian Patent Application No. 2,140,898 discloses an apparatus that allows thermal dimensional changes of metal parts in a retort mechanism which incorporates heating and cooling stages and comprises a retort auger that extends the entire length of the retort.  
           [0013]    Japanese Patent Document 58-501912 discloses a method for manufacturing carbonised briquettes by introducing vegetable matter into a heated retort. The heated retort incorporates a screw to advance material through the retort.  
           [0014]    Australian Patent Document 90 50613 discloses an apparatus for use in the production of charcoal comprising a hollow retort shell containing an auger for advancing material through the shell.  
           [0015]    The prior methods and apparatus for producing charcoal by passing organic material from a heated horizontal retort suffer from the disadvantage that gases tend to leak from the ends of the vessels in which the organic material is heated. There is a need for apparatus and methods for safely producing high quality charcoal on a continuous basis.  
         SUMMARY OF THE INVENTION  
         [0016]    This invention provides apparatus and methods for the continuous production of charcoal which avoids safety problems of prior vertical retort charcoal making machines and prior horizontal retort reactors.  
           [0017]    Accordingly, one aspect of this invention provides apparatus and methods for producing charcoal by means of a heated retort which comprises a screw with an interrupted flight. The retorts of the reactor are horizontal. Material is carried through the retort by the screw element. The interrupted flight permits loose plugs of organic materials to form at locations along the screw. These loose plugs prevent gases from blowing out the ends of the retort.  
           [0018]    Preferred embodiments feature an exhaust gas collection system which collects and circulates accumulated gases for subsequent combustion or extraction. The exhaust gas collection system prevents gases from escaping uncontrolled and polluting the surrounding atmosphere. Gas is preferably collected at locations near interruptions in the screw flight.  
           [0019]    Another aspect of this invention provides an apparatus for producing charcoal. The apparatus comprises a furnace, a retort tube extending substantially horizontally through the furnace, and a screw element extending through the retort tube. The screw element has a generally helical flight. The flight of the screw comprises two or more sections separated by one or more longitudinally extending gaps wherein the flight is removed. The gaps in the flight are coincident with one or more gas vents which penetrate the retort tube. In use, loose plugs of material form in the gaps and prevent exhaust gases from exiting through the ends of the retort tube.  
           [0020]    When organic material is introduced into a retort, the material is carried by the flight of the screw and advanced through the retort. When the material is carried to a gas vent within the retort, the material accumulates below the vent and forms a loose plug of material. This plug causes any gases produced during the carbonization process to exit the retort through pipes connected to the gas vent. As more material is fed into the retort, this material builds up behind the loose plug of material formed within the retort and pushes the plug of material through the region below the gas vent to the next section of the retort which is again occupied by a portion of the screw which has flights. In this next section of the retort, the material is again carried by the flight of the screw until it again reaches a section having a gas vent. Again material accumulates to form a loose plug in the region below the gas vent. The material in the loose plug remains below the gas vent until further material being advanced along the retort pushes it into the next section of the retort. In this manner raw material is advanced along to the end of the retort where it eventually exits as charcoal product.  
           [0021]    In apparatus of currently preferred embodiments of this invention, the retort is maintained at a constant temperature of at least 600° C., (obviating the need for cooling down and heating up stages). One or more gas vents are connected to an exhaust gas collection system. Distillate gases are collected from the gas vents and circulated via the exhaust gas collection system to a combustion chamber through burner draft ports. The distillate gases may be used as supplementary fuel.  
           [0022]    In other preferred embodiments of this invention, the gas vents are connected to a precipitation recovery system, and by-products such as alcohol, turpentine, creosote and tar are removed before circulation to a combustion chamber.  
           [0023]    In reactors according to preferred embodiments of this invention, a retort can be exposed for service by removing split slip plates from the front and rear of the particular retort needing service. The retort can then be pulled out on roller jacks. The reactor can then be easily re-started after covering the holes with solid dummy plates. This reduces the shut-down time of the facility.  
           [0024]    An advantage of this invention lies in the provision of retort screws in horizontal retorts which are used to force feed the material through the retort. Since the speed of the screws can be precisely controlled by means of a motor, so can the quality and the chemical composition of the charcoal produced. Increasing the speed at which the screw turns results in the material being moved faster through the retort and will give a higher composition of volatiles in the finished product. Slowing the speed at which the screw turns results in materials remaining in the heated retort longer and will result in finished products with higher carbon composition, such as graphite. With this invention, the quality of the finished product can be controlled by adjusting the operation of screw, without changing the operating temperature.  
           [0025]    The design of the interrupted screw which has gaps in its flight in a region near each gas vent permits quality to be adjusted while the retort temperature is kept virtually constant.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    In drawings which illustrate non-limiting specific embodiments of the invention:  
         [0027]    [0027]FIG. 1 is a front view of apparatus according to the invention;  
         [0028]    [0028]FIG. 2 is a right side view thereof;  
         [0029]    [0029]FIG. 3 is a rear view thereof;  
         [0030]    [0030]FIG. 4 is left side view thereof;  
         [0031]    [0031]FIG. 5 is a detailed top view of a dryer heat exchanger which may be used in the invention;  
         [0032]    [0032]FIG. 6 is a top view of the inside of a reactor according to the invention with the roof and dryer exchanger taken off;  
         [0033]    [0033]FIG. 7 is a cutaway detail of a closed retort;  
         [0034]    [0034]FIG. 8 is an end view of a closed retort from its sawdust intake end;  
         [0035]    [0035]FIG. 9 is an end view of a closed retort from its charcoal exhaust end, (less flange);  
         [0036]    [0036]FIG. 10 is an elevational view of a dryer cone showing sawdust feed conveyor, front on c/w blower and intake and exhaust pipes;  
         [0037]    [0037]FIG. 11A is a front view of a split slip plate; and,  
         [0038]    [0038]FIG. 11B is a partially cut away side view of split slip plate c/w asbestos seals against reactor wall and around retort tube.  
     
    
     LIST OF REFERENCE SYMBOLS USED IN THE DRAWINGS  
       [0039]    [0039] 1 : Blower Motor  
         [0040]    [0040] 2 : Blower Impeller Shaft  
         [0041]    [0041] 3 : Blower  
         [0042]    [0042] 4 : Sawdust Feed Conveyor from Bin  
         [0043]    [0043] 5 : Hot Air Intake Pipe  
         [0044]    [0044] 6 : Dryer Cone  
         [0045]    [0045] 7 : Exhaust Air and Sawdust Pipe  
         [0046]    [0046] 8 : Air Shut-Off Gate and Handle  
         [0047]    [0047] 9 : Pillars of Reactor Frame  
         [0048]    [0048] 10 : Collection Conveyor Motor  
         [0049]    [0049] 11 : Storage Conveyor Motor  
         [0050]    [0050] 12 : Sawdust Over-flow Pipe  
         [0051]    [0051] 13 : Sawdust Feed Pipe  
         [0052]    [0052] 14 : Split Slip Plates  
         [0053]    [0053] 15 : High Temperature Resistant Seal (on slip plate)  
         [0054]    [0054] 17 : Concrete Pad  
         [0055]    [0055] 18 : Bin  
         [0056]    [0056] 19 : Reactor  
         [0057]    [0057] 20 : Reactor Housing &amp; Stack  
         [0058]    [0058] 22 : Burners  
         [0059]    [0059] 24 : Sawdust Receiving Cyclone  
         [0060]    [0060] 26 : Retort  
         [0061]    [0061] 27 : Inlet End of Retort  
         [0062]    [0062] 28 : First section of retort  26  occupied by a screw comprising flights  
         [0063]    [0063] 30 : First Gas venting section of retort  26   
         [0064]    [0064] 32 : Second section of retort  26  occupied by a screw comprising flights  
         [0065]    [0065] 34 : Second gas venting section of retort  26   
         [0066]    [0066] 36 : Third section of retort  26  occupied by a screw comprising flights  
         [0067]    [0067] 37 : Sawdust Feed System  
         [0068]    [0068] 38 : Sawdust Feed Conveyors  
         [0069]    [0069] 40 : Charcoal Chutes  
         [0070]    [0070] 42 : Charcoal Collection Conveyor  
         [0071]    [0071] 44 : Sawdust Return Blower  
         [0072]    [0072] 46 : Inspection Window  
         [0073]    [0073] 48 : Service Doors  
         [0074]    [0074] 50 : Gas Monitoring Vents  
         [0075]    [0075] 52 : Exhaust Gas Collection System  
         [0076]    [0076] 53 : Exhaust Gas Collection pipes  
         [0077]    [0077] 54 : Storage Bin Conveyor  
         [0078]    [0078] 56 : Product Sampling Holes  
         [0079]    [0079] 58  Concrete Foundation  
         [0080]    [0080] 60 : Finished Grade Level  
         [0081]    [0081] 62 : Hot Air Manifold  
         [0082]    [0082] 64 : Reactor Lining  
         [0083]    [0083] 66 : High Temperature Resistant Gaskets  
         [0084]    [0084] 68 : Retort Screw Motors  
         [0085]    [0085] 70 : Graphite Bushings on all Retort Screws exhaust ends  
         [0086]    [0086] 72 : Dryer Heat Exchanger Tube  
         [0087]    [0087] 74 : Feed Conveyor Motors  
         [0088]    [0088] 76 : Distillate Gas Vent  
         [0089]    [0089] 78 : Retort Screw  
         [0090]    [0090] 79 : Screw Flights  
         [0091]    [0091] 80 : Reactor Thermocouples  
         [0092]    [0092] 82 : Dryer Thermocouples  
       DETAILED DESCRIPTION  
       [0093]    The apparatus and methods of this invention concern the continuous production of charcoal from a closed retort charcoal reactor. A feed system  37  supplies organic material to one or more retorts  26  for carbonization. A screw  78  which passes through each retort  26  draws organic material into retort  26  and moves the organic material along retort  26 . Excess organic material not drawn into a retort  26  is recycled by feed system  37 .  
         [0094]    Screw  78  has a central shaft to which is attached a helical flight  79 . Screw  78  has one or more gap sections where the flight  79  has been removed. As the organic material is advanced through retort  26  by screw  78 , it is heated and alternatingly compressed and decompressed. While advancing through retort  26  the organic material forms a loose plug in a first gap venting section  30  which corresponds to the first gap section in screw  78 . The central portion of screw  78  in second section  32  draws material from the downstream side of this loose plug and carries the material to a second gap venting section  34 . The material forms a loose plug in second gap section  34 . The loose plugs block the easy passage of gases formed during the charcoal production process from occupying empty areas of the retort and creating super hot spots. These plugs help to direct gases produced during the carbonization process out of retort  26  via exhaust gas collection system  52  which comprises a system of exhaust gas collection pipes  53 . Exhaust gas collection system  52  collects and circulates these gases for eventual combustion in a chamber. Finished charcoal products exit retorts  26  via a charcoal collector system  29  which includes charcoal chutes  40 , charcoal collection conveyor  42  and storage bin conveyor  54 .  
         [0095]    Primary components of sawdust feed system  37 , as shown in FIG. 10 include a blower  3 , a feed conveyor  4 , a dryer cone  6 , and an exhaust air and sawdust pipe  7 . These components may be mounted to a reinforced concrete pad  17  along with appropriate conduits  5  for supply and control wiring. Organic material, such as sawdust, is stored in a bin  18 . Feed conveyor  4  carries the organic material from bin  18  to blower  3 . Blower  3  creates an air flow which carries the organic material through hot air intake pipe  5  into dryer cone  6 . In dryer cone  6  the material undergoes drying.  
         [0096]    Material exiting dryer cone  6  travels along exhaust air and sawdust pipe  7  to reactor  19 . The material is transferred from sawdust and air exhaust pipe  7  to sawdust receiving cyclone  24 . From sawdust receiving cyclone  24  the material is carried down sawdust feed pipe  13  to a sawdust feed conveyor  38 . At certain intervals, sawdust feed conveyors  38  connect to the inlet end  27  of a retort  26 . Material can drop from sawdust feed conveyor  38  into retorts  26  through apertures in the bottom of sawdust feed conveyor  38 . Material carried in sawdust feed conveyor  38  may be drawn by screw  78  into retort  26  at inlet end  27 . Material which does not get fed into inlet end  27  of retort  26  continues along sawdust feed conveyor  38  to sawdust return blower  44 . From sawdust return blower  44 , the material passes to sawdust over-flow pipe  12  which returns the material to bin  18 .  
         [0097]    Referring to FIG. 7, material intercepted and fed by screw  78  into inlet end  27  of retort  26  enters first section  28  of heated retort  26 . Section  28  is occupied by a portion of screw  78  comprising a flight  79 . As motors  68  cause screw  78  to turn, material is carried by the flight of screw  78  through section  28  to first gas venting section  30 . In first gas venting section  30 , the flight of screw  78  is interrupted. Material entering first gas venting section  30  is not advanced through first gas venting section  30  by the rotation of screw  78 . Instead, material in first gas venting section  30  accumulates within section  30  to form a loose plug. As shown in the drawings, the gas venting sections have cross sectional areas substantially the same as the cross sectional area of the portions of retort  26  in which screw  78  has flights. The gas venting sections are substantially unobstructed. Only the narrow central shaft of screw  78  passes through the gas venting section. Substantially the entire volume of the gas venting section is available to contain the loose plug of material. While in first gas venting section  30 , the loose plug of material undergoes venting in a state of low compression until such time as additional material carried by the flight of screw  78  of first section  28  accumulates behind it and pushes it through first venting section  30  into second section  32  of retort  26 .  
         [0098]    Section  32 , similar to section  28 , is occupied by a portion of screw  78  which has a flight. Material entering second section  32  is carried by the flight of screw  78  to second gas venting section  34 . In second gas venting section  34 , material forms another loose plug and undergoes further venting. The material remains in second gas venting section  34  until further material being introduced from second section  32  pushes the material through second gas venting section  34  into section  36 . Material in second gas venting section  34  advances to section  36  in a manner similar to the manner in which material is advanced from first gas venting section  30  to section  32 .  
         [0099]    As the material accumulates in both gas venting sections  30  and  34 , the loose plugs of material direct gases produced during the carbonization process to exit retort  26  through distillate gas vents  76  of exhaust gas collection system  52 . The plugs block the gases from exiting at the ends of retort  26 . Material is advanced through retort  26  in this manner until the charcoal product exits retort  26  via charcoal chutes  40 . A gas monitoring vent  50  and product sampling hole  56  permit an operator to sample gases and test ejected material to confirm the status of the reaction taking place.  
         [0100]    Upon exit from retort  26 , the charcoal product enters the charcoal collection system. The primary components of charcoal collection system  29  include charcoal collection conveyor  42  and storage bin conveyor  54 , both which are preferably water jacketed. Charcoal exiting retort  26  is carried along charcoal collection conveyor  42  and storage bin conveyor  54  for final deposit and collection in a storage bin.  
         [0101]    As mentioned above, gases produced during the carbonization of the raw material exit retort  26  via distillate gas vents  76  and enter exhaust gas collection system  52  (see FIG. 6) The primary components of exhaust gas collection system  52  include distillate gas vents  76 , exhaust gas collection pipes  53  and burner  22 . Gases exiting retort  26  via distillate gas vents  76  are carried by exhaust gas collection pipes  53  which circulate collected gases to burner  22 . A low volume fan or draft suction of burner  22  combined with the pressure in retort  26 , may be used to feed the collected gases to burner  22  as a supplemental fuel. Alternatively, gases exiting retort  26  may be first condensed into liquid before being fed to burner  22  as supplementary fuel.  
         [0102]    Apparatus according to a specific embodiment of the invention will now be described. The following dimensions, conveyor and blower sizes, speeds, and motor HP and RPM are values which are currently preferred where the organic matter being used as raw material is sawdust with a particle size of about 1¼ inch cube, and initial moisture content of 40-60% by weight These values are included here for illustrative purposes.  
         [0103]    In sawdust feed system  37 , intake hot air pipe  5  and exhaust air and sawdust pipe  7  are preferably both of the same cross sectional area. Both of these pipes are typically round. Both may be, for example, made from 8 or 10 gauge mild steel. Intake hot air pipe  5  is preferably insulated, for example, with fiber-glass wool wrapped over with flexible heavy aluminum foil. Dryer cone  6  is preferably made of mild steel and may be, for example, twenty feet high with a six foot diameter. Blower motor  1  may be a 75 HP, blower four feet in diameter. Sawdust feed conveyors  38  may have a 10-12 inch trough, and be driven at variable RPM with a 3-5 HP motor. Dryer blower  3  could have a 48 inch diameter housing, 24 inch intake and outlet, and be powered by 90 HP motor at 650 RPM.  
         [0104]    Thermocouples  82  are provided to measure the temperature of feed system  37  which is heated by hot air intake pipe  5 . Circuits for thermocouples  82  are located at the top and bottom of dryer cone  6  and directly in front of air intake shut-off gate  8 . These are preferably run in wire having a high temperature rating. The temperature in dryer cone  6  should not be allowed to exceed about 150° Celsius at thermocouples  82 .  
         [0105]    Reactor  19  is preferably constructed on a heavily reinforced concrete pad  58 . Pillars  9  support reactor  19 . The interior of reactor  19  is preferably coated with a suitable lining such as a castable refractory from the floor to the stack. Reactor lining  64  should be able to withstand the expected operating temperatures of reactor  19  which may reach 1200° C. Ideally, reactor lining  64  should be at least 4 inches thick from the floor to the stack.  
         [0106]    Reactor components may be made from mild steel, but preferably retort  26  and that part of the gas venting system  52  which is inside the heated enclosure are fabricated of 316 stainless steel.  
         [0107]    Top receiving cyclone  24  may be about 6 feet high and about 4 feet in diameter. Discharge pipe  13  ideally has a bottom diameter of about 12 inches with a 16 AWG wall.  
         [0108]    Retort  26  ideally has an internal diameter of about 12 inches, a wall thickness of about 0.375 inches, and is preferably made of 316 stainless steel with ½ inch thick flanges on both ends. Retort  26  has holes to accept fasteners which attach the tube portion of retort  26  to the end assembly portion of retort  26  with high temperature-resistant gaskets  66  in place. Retort  26  is installed in reactor  19  with slip plates  14 . Slip plates  14  are installed on either end of retort  26  in holes. This construction allows for radial expansion of retort  26 . Slip plates  14  cover the allowance cracks but are free to slide along the retort tube to permit longitudinal expansion and contraction of the retort tube. Slip plates  14  are made in two pieces, and are ideally backed with ½″ thick asbestos or like material on the reactor side. Retort  26  is able to freely expand in both linear and radial directions. Ideally, reactor  19  has eighteen retorts  26 .  
         [0109]    Retort screw  78  is preferably made of mild steel and may have a diameter of 11½ inches with a twist every 6-8 inches. Retort screw  78  has flighted sections separated by areas where the flight of screw  78  is entirely or largely removed. Ideally, the flight of retort screw  78  is interrupted by a gap of about 24 inches at first gas venting section  30  and a gap of about 18 inches at second gas venting section  32 . Gas vents  76  are preferably located centrally in each of the first and second gas venting sections. The first gas venting section preferably begins 20 to 48 inches from the inlet end of retort  26  and has a length in the range of about 8 to 24 inches. The second gas venting section preferably begins at a distance of about 65 to 80 inches past the end of the first gas venting section and has a length in the range of 10 to 20 inches. For example, in one embodiment of the invention the first gas venting section is 10 inches long and begins at a distance of 48 inches from the input end of retort  26 . The second gas venting section is also 10 inches long and begins at a distance of about 132 inches from the input end of retort  26 . A gas venting tube  56  is centered in each gas venting section. In another embodiment of the invention screw  78  has its flights removed for a length of 8 inches 20 inches from the input end of retort  26 . This area allows a plug of raw material to accumulate so as to prevent the escape of gases of the input end of retort  26  and to maintain anaerobic conditions in retort tube  26 .  
         [0110]    Bearings for retort screw  78  on the inlet and outlet end of retort  26  are preferably S.K.F™ or similar sealed ball bearings with lubricating fittings and oilite casings lined with graphite bushings. Ideally, retort screws  78  are driven in sets of three by a 5 HP motor for each set at a suggested startup of 30 RPM. The startup RPM, however, will be dependent on the inside temperature of retort  26 , the moisture content of the organic material delivered to retort  26 , and the degree of volatiles desired in the final charcoal product.  
         [0111]    Charcoal chute  40  is ideally made of flexible thin sheet metal. Charcoal collection conveyor  42  is ideally run in a 8 inch water jacketed trough with a screw of 1 twist in about 10 inches. Conveyor  42  may be driven at about 120 RPM. Preferably, the screw in the storage bin conveyor  54  is installed with split shell graphite bushings at 10 foot intervals. Storage bin conveyor  54  is ideally run in a 10 inch water jacketed trough with a screw of 1 twist in 10 inches.  
         [0112]    Dryer heat exchanger tube  72  is bolted to hot air manifold  62  which is in turn secured to the reactor framing. Dryer heat exchanger tube  72  may be about 10 inches in diameter. Hot air manifold  62  may be about 24 inches in diameter. Dryer heat exchanger tube  72  is preferably unsecured at its opposite end so that it is free to expand and contract. Dryer heat exchanger tube  72  and hot air manifold  62  are both preferably made of mild steel.  
         [0113]    Sawdust return blower  44  is ideally 36 inches in diameter and powered by a 30 HP motor at 600-700 RPM. Inlet and outlet ends of sawdust return blower  44  are ideally between 16-18 inches in diameter and of standard blowpipe thickness.  
         [0114]    Thermocouples  80  are installed to measure the temperature of the reactor components. All thermocouples  80  are preferably installed before reactor lining  64  is applied. The temperature of reactor  19  at thermocouples  80  preferably will not exceed about 600° Celsius.  
         [0115]    Those portions of exhaust gas collection system  52  that are housed within reactor  19  are preferably made of the same material as retort  26 . Exhaust gas collection pipe  53  is ideally mounted on distillate gas vent  76  with gasket  66  to prevent the escape of gases. Exhaust gas collection pipe  53  may have, for example, a 2 inch diameter inside the heated enclosure and a 3 inch diameter after exiting the heated enclosure.  
         [0116]    Gas monitoring vent  50  is fitted with a lid to prevent the escape of gases to the atmosphere. Gas monitoring vent  50  may be opened for sampling and inspection of the gases produced during the carbonization process. Inspection of gases will enable the operator of the apparatus to determine which stage of the carbonization process the raw material is undergoing. Gas monitoring vent  50  is preferably a small stub of one inch diameter pipe.  
         [0117]    All electric motors adjacent to reactor  19  are preferably dust-proof and completely enclosed. Electric motors mounted on the metal components of reactor  19 , such as retort screw motor  68 , sawdust feed cross-conveyor motor  74  and collection conveyor motor  10 , should be rated for hazardous locations and are preferably explosion proof. This is preferable so as to protect the motors from internal abrasion caused by drifting charcoal dust and from heat conducted through the metal mountings of reactor  19 .  
         [0118]    Supply circuits, controls, and monitoring wiring attached to the reactor housing should ideally be insulated with appropriate high temperature insulation and enclosed in a rigid conduit.  
         [0119]    It can be appreciated that this invention provides a method for producing charcoal as well as an apparatus for producing charcoal as described above. The method is practiced whenever apparatus as described above is used to produce charcoal from organic material. As the organic material passes through the apparatus, it is converted to charcoal by a method which includes introducing the organic material into a heated tubular retort at an inlet end of the retort which has a vent in it, carrying the material to a volume in the retort adjacent the vent (the first gas venting section  30 ), advancing the organic material through the volume by introducing more of the organic material into the volume, and, after advancing the organic material through the volume, delivering the organic material through the retort to an outlet end of the retort. Preferably before the material is delivered to the outlet end of the retort it is delivered to a second volume (second gas venting section  34 ) and is advanced through the second volume by introducing more of the organic material into the second volume from behind. The second volume is also adjacent a gas vent. Preferably enough volume of organic material is passed through to the tubular retort that a loose plug of organic material substantially fills each of the first and second gas venting sections so that gasses developed in the retort between the first and second gas venting sections are preferentially directed through the gas vents associated with the first and second gas venting sections and the gases are substantially blocked from exiting at either end of the retort. The method preferably involves controlling a rate of feed of organic material into and through the retort by controlling a rate of rotation of a screw in the retort. Preferably the method involves collecting gases from the vents and burning the gases to assist in heating the retort.  
         [0120]    As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example: the dimensions of the various components of the apparatus may be varied; screw  28  may have more than two sections in which the flights have been removed. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.