CA2242279C - Continuous production closed retort charcoal reactor - Google Patents

Abstract

This is a process, with the entailing equipment arrangement and machinery, designed to produce charcoal and graphite of selectable varying degrees of volatile content from all types of waste wood, bark, and vegetable matter. The procedures used in the past, or those current or planned for the future are obsolete, time consuming, inefficient, and dangerous, and require vast amounts of investment capital to bring into production. The process I have outline is continuous, 24 hrs. per day seven days a week, safe, non-pollutant, profitable, and requires the minimum capital expenditure necessary to produce a commodity of the highest quality. Instead of the huge vertical, gravity feed retorts, and the attendant costs and dangers they generate, this process is not reliant on gravity in vertical retorts but uses horizontal force fed, oxygen negligent tubes arranged in tiers of rows across the width of the refractoried oven, each tube independently controlled, vented, and monitored and small enough to prohibit massive volumes of exhaust gases at extreme temperatures thus eliminating dangerous conditions. With the requirement of only two people per shift to operate it, the machine is extremely cost efficient. Because it can use any and all wood waste, mixed up with bark in any ratio it is also a complete solution to the forest industry waste proliferation problem in any region with forest based industries. It can use the waste from the harvesting in the bush, to the manufacturing of finished products. It can use various other types of vegetable waste with minor modifications to the raw material handling procedures.

Description

CONTINUOUS PRODUCTION CLOSED RETORT CHARCOAL REACTOR
Field of the Invention 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 through a substantially horizontal retort tube with a screw. The design of the screw, the exhaust venting system, and the handling of the finished charcoal just prior to exiting the retort, avoid certain disadvantages and dangers of prior charcoal making equipment and offer new advantages for the manufacture of charcoal.
Supplementary to this is the exhaust gas collection system and the precise location of its components so as to prevent any atmospheric pollution as well as the accumulation of gases to a point of dangerous explosions. Without the provision for pollution prevention, no region of the world will allow the implementation of any production system. Furthermore, without the provision to prevent explosive disintegration of the equipment, the system will not survive long.
Background of the Invention The original machines to successfully achieve the continuous production of charcoal from wood or agricultural refuse, as is further described later, were shut down and dismantled almost 40 years ago. Primitive though they were, and elementary as the control instruments were at that time, production of charcoal was achieved. As well, a certain amount of pre-determination as far as the final chemical and physical properties of the charcoal was also achieved. It was possible to intentionally produce high volatile, high ash content, low carbon material or material with very low contaminant and very high carbon.
During that time, it was learned that in continuous closed retort operations for the distillation of wood there is a certain stage where the raw material adopts a sticky plastic state and is very susceptible to compression, which must be avoided at all cost.
However, with a vertical retort relying on gravity to move material through the retort, it was impossible to avoid compressing the material. In such machines when the inevitable compression takes place, venting of gases through the compressed raw material is prevented, the material plugs the retort, pressure builds up, and dangerous conditions are reached. Where the operators could succeed in bringing the pressure back to normal all quality control was lost. This invention addresses these problems.
Summary of the Invention The production of charcoal today is a stop and start "batch" procedure which involves cooling down periods and time consuming renewed start up. This new process eliminates that, since once it is started it can be run continuously, twenty four hours a day and seven days a week. The only other continuous charcoal production process that the inventor is aware of involved at least ten times the invested capital, emitted exhaust gases steadily, was difficult to service and maintain, and at times was very dangerous to operate. Rather than developing improvements for it, it was abandoned thirty-eight years ago.
The reactor, as it was called then, comprised a vertical retort machine reaching fifty feet into the air and relying solely on gravity to feed sawdust through retorts inside a heated chamber. This caused the sawdust to hang up within, creating super hot spots, and extremely perilous conditions when it was finally freed and fell into the hot empty

-2-space. The first batch to hit literally vaporized on contact and all control was temporarily lost. The reactor of this invention has horizontal retorts (D), and is force fed by an injection screw (Z) cancelling any possibility of an empty retort over heating, and the subsequent violent potential.
Distillate gases from prior continuous reactors were simply released into the open air, where they burned freely, when hot enough. In apparatus of the preferred embodiments of this invention distillate gases are collected, confined in recovery pipes (L) and circulated into the combustion chamber through the burner (B) draft ports as a supplementary fuel; or if a precipitation recovery assembly is installed, by products such as alcohol, turpentine, creosote and tar can be removed first.
With the previous reactors the entire roof had to be tom off to replace or service one retort, removing it one half at a time, the lower half hanging suspended in the reactor while the upper was lowered to the ground, and then the lower pulled out and lowered also. In reactors according to preferred embodiments of this invention, a retort can be exposed for service by removing split slip plates (14), FIG. 7, (shown in the backed away position), 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 hole with a solid dummy plate. This reduces the shut-down time of the facility. Previous reactors were crippled until the missing retort was replaced.
An advantage of this invention lies in the provision of retort screws in horizontal retorts. Since their speed can be precisely controlled, so can the quality and the chemical composition of the charcoal produced. All this can be done while maintaining a constant temperature within the enclosure. Pushing raw material faster through the retort will give a higher composition of volatiles in the finished product;
slowing them

-3-down will increase the carbon composition of the finished product, allowing the production of graphite, or a product very near it.
Previously, to exercise what little control could be had over the finished product; the temperature around the retorts had to be varied between such extremes that the continued expansion and contraction of the equipment inducted unnecessary fatigue in the metals and shortened the service life throughout. Here, control can be provided by adjusting operation of screw (Z).
The design of the screw (Z) shown in FIG. 7 which has a flight removed before and after each gas vent (Y) vastly improves the capacity to control quality, making this innovation in conjunction with the horizontal arrangement of and forced progression in the retorts, the mainstay of the entire process. It is due to this fact that once the temperature is reached to reduce the raw material to charcoal, it need not be altered, thus improving the efficiency of the combustion fuel and the life of the machine.
Brief Description of the Drawings In drawings which illustrate specific embodiments of the invention:
FIG. 1 is a front view (From control room) of apparatus according to the invention;
FIG. 2 is a right side view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is left side view thereof;
FIG. 5 is a detailed top view of a dryer heat exchanger which may be used in the invention;
FIG. 6 is a top view of the inside of a reactor according to the invention with

-4-the roof and dryer exchanger taken off; and front on elevation showing exhaust gas collection system in detail with screws removed and flanges left off for clarity;
FIG. 7 is a cutaway detail of a closed retort (One of up to 24 that can be installed in the reactor's heated enclosure.) FIG. 8 is an end view of closed retort from its sawdust intake end;
FIG. 9 is an end view of a closed retort from its charcoal exhaust end, (less flange);
FIG. 10 is an elevational view of a dryer cone showing sawdust feed conveyer, front on clw blower and intake and exhaust pipes; and, FIG. 11 is a detailed view of a split slip plate clw asbestos seals against reactor wall and around retort tube. (Front on and top views).
List of Reference Symbols Used in the Drawings A: Reactor Housing & Stack B: Burners C: Sawdust Receiving Cyclone D: Closed Retorts (see Fig. 7 detailed cutaway) 18 Total E: Sawdust Feed Conveyers F: Charcoal Chutes G: Charcoal Collection Conveyer (water jacket) H: Sawdust Return Blower I: Inspection Window J: Service Doors K: Gas Monitoring Vents (open daily when needed) L: Exhaust Gas Collection System M: Charcoal to Storage Bin Conveyer (water jacket)

-5-N: Product Sampling Holes O Concrete Foundation (4 feet thick reinforced) P: Finished Grade Level Q: Hot Air Manifold for Dryer R: Four Inch Lining of 1400F Refractory Inside S: Asbestos Gaskets '/2" thick min. all Retorts, both ends T: Retort Screw Motors (6 driving 3 screws each) U: Graphite Bushings on all Retort Screws exhaust end V : Dryer Heat Exchanger Tube (8" diameter) X: Feed Conveyers Motor Y: Distillate Gas Vent Z: Retort Screw (flight cut away over gas vents) Thermocouples, Reactor a Thermocouples, Dryer 1: Blower Motor 60-90HP 650 RPM

2: Blower Impeller Shaft 3: Blower 4: Sawdust Feed Conveyer from bin 5: Hot Air Intake Pipe 22

6: Dryer Cone

7: Exhaust Air and Sawdust Pipe

8: Air Shut-Off gate and Handle

9: Main Corner Pillars of Reactor Frame

10: Collection Conveyor Motor

11: Storage Conveyor Motor

12: Sawdust Over-flow Pipe

13: Sawdust Feed Pipe

14: Split Slip Plates c/w asbestos backing seal

15: Asbestos Seal {on slip plate) Detailed Description APPARATUS
A specific example of apparatus according to the invention will now be described. The following dimensions, conveyor and blower sizes, speeds, and motor HP and RPM
are the values currently preferred where the organic matter being used as raw material is sawdust with a particle size of about '/a inch cube, and initial moisture content of 40-60 % by weight.
A sawdust-dryer assembly (Fig. 10) has a feed conveyer (4), a four foot diameter blower (3), a twenty foot high, six foot diameter drying cone (6), and a 75HP
motor ( 1 ) . These components are all bolted to a reinforced concrete pad at least ten feet square and one foot thick, along with an appropriate conduit for supply and control wiring.
The circuits for the thermocouples, (e) located at the top of the cone, the bottom of the cone and directly in front of the air intake shut-off gate (8), are run in wire having a high temperature rating, such as asbestos coated wire. Intake hot air pipe (5) and sawdust and air exhaust pipe (7) are both twenty-four inches in diameter made from ten or eight gauge mild steel, the former should be insulated with two inches of fiber-glass wool wrapped over with flexible heavy aluminum foil. A blower housing and driver cone may be made of mild steel, three sixteenths of an inch thick, but the drive shaft and impeller (2) is preferably 316 stainless steel.
A reactor shown in FIGS. 1-4 is constructed on a heavily reinforced concrete pad, two _7_ feet thick, measuring twenty-four feet square. All conduits are installed before pouring as are the mounting bolts and steel bases for the reactor pillars, (9) and the sawdust return blower (H).
Four corner pillars (9) are eight inch steel H beams measuring twelve feet from each other at ninety degree angles and are twenty feet high. These are tied together every four feet in height with three by three inch angle members (not shown) and to these the three Bights inch thick steel sheathing is penetration welded. On the inside, the reactor is coated with castable refractory four inches thick, from the floor to the stack. The reactor lining must be able to withstand the expected operating temperatures which may reach 1200°C.
All thermocouples (~) should be installed before the reactor lining is applied. The stack shown is for the use of hog fuel burners. If bunker fuel burners are used the stack construction may differ. Burner manufacturers typically provide stack specifications for use with their burners.
Reactor components may be made from mild steel, but preferably retorts (D) and that part of the gas venting system (L) which is inside the heated enclosure are fabricated of 316 stainless steel. Retort screws (Z) FIG. 7, may be made of mild steel for cost efficiency. (Mild steel subjected to the conditions inside the reactor would not likely survive beyond six months). Retort tubes (D) are twelve inches in external diameter with a wall thickness of 318 inch. Flanges on both sides '/2 inch thick drilled with six '/2 inch holes each are provided to bolt the end sections on with '/2 inch thick ring gaskets (S) between the tube and end assembly portion of the retort.
A heat exchanger for the sawdust dryer FIG. 5, comprises items (V) and (Q) which are _g_ preferably made of mild steel since the steady flow of air through them will prevent heat build-up and prolong their lives. The manifold (Q) is 24 inches in diameter, with 1/8 inch wall pipe. The five inside tubes (V) are ten inches diameter and 3/32 wall thickness.
A top receiving cyclone (C) is 4 feet in diameter, and six feet high. A
discharge pipe (13) bottom is of 12 inch diameter and 16 AWG wall.
Electric motors which can be three phase, 550-600 Volt. Those adjacent to the reactor must be of the totally enclosed dust-proof type, and those mounted on the metal components of the reactor, such as the retort screw motors (T), the sawdust feed cross-conveyer motor (X), and the collection conveyer motor (10), should be rated for hazardous locations and be explosion proof. This is not in anticipation of any explosions but to protect the motors from heat conducted through the metal mountings from the reactor, and from the incessant abrasion they may be subjected to internally from any charcoal dust that may drift around. It is my experience that these ultra fine, particles are next to impossible to contain or eliminate during the course of production.
Supply circuits, controls, and monitoring wiring attached to the reactor housing should be insulated with asbestos or equivalent type and enclosed in rigid conduit.
All other wiring should be to C.S.A. and regional code standards or better.
Bearings for the retort screw shafts are: on the input end, S.K.F'~", or similar, sealed ball bearings with lubricating fittings as per their specifications. On the output end they should be oilite casings lined with 'h inch graphite bushings. These may be available commercially or may be made up.

Conveyers carrying charcoal from where it exits the reactor, (C) and (M) must be water jacketed. For the delivery to bin conveyer (M) it is recommended that split shell graphite bushings be installed at 10 foot intervals if the distance goes beyond 15 feet.
A sawdust return blower (H) 36 inches in diameter is powered by a 30 H.P.
motor at 600- 700 RPM with intake and outlet pipes 16-18 inches diameter and standard blowpipe thickness.
CONVEYOR AND BLOWER:
Sawdust Feed Conveyer (E): 12 in total inch trough; screw one turn in 10 inches driven at variable RPM with 3 HP motor.
Dryer Blower (3): 48 inch diameter housing, 24 inch intake and outlet, powered by 90 HP motor at 650 RPM, fixed.
Sawdust Cross Feed Conveyers (E) three in all: these have the 12 inch troughs, screw, one turn in 10 inches, and all are driven with one 5 HP motor at variable RPM.
Closed Retorts (D): 18 in total are 12 inch diameter, O.D., wall thickness of .373 inches and made preferably of 316 stainless steel with 1/2 inch thick flanges on both ends, drilled to accept six I/2 inch bolts used to secure the feed and exhaust portions to them with 'h inch gaskets in place. These retorts are installed in the reactor with slip plates (14) FIG. 7, on either end in holes with allowance for radial expansion. The slip plates cover the allowance cracks but must be free to slide on the retort tube at all times. These plates are made in two pieces, backed with 1/2" thick asbestos on the reactor side, and put on once the retorts are in place. Neither the retorts nor their drive machinery are secured to anything that will prevent free expansion in both linear and radial directions.
The sawdust receiving slots in the retort tubes are larger than the delivery on in the cross conveyer for expansion, as is the charcoal out-put smaller than the one in the collection conveyer for the same reason. The chutes (F) are made from thin sheet metal and are flexible enough to allow for what small difference in the length may occur between one layer of retorts and another.
Retort Screws (Z): Eighteen in Total, see Fig. 7 have a diameter of 10 '/a inches with a twist of one in 6-8 inches. The flight is cut out for 24 inches centered on the first vent hole, to slow progress through the tube and allow gas venting as well as compensate for the shrinking of the sawdust due to the same. This is done again at the second vent but only for 18 inches for the same reasons. This is one of the designs critical to a steadier, more efficient operation of the closed retort production principle. The retort screws are powered in sets of 3 by a 5 HP motor for each set, at RPMs that will have to be set by the operators according to the inside temperature, the moisture content of the wood, delivered to the retorts, and the degree of volatiles they wish to achieve in the final product. Suggest for startup 30 RPM.
Charcoal Collection Conveyer (G): 8 inch water jacketed trough with a screw of one, twist in 10 inches powered by 2 HP at 120 RPM.
Charcoal to bin conveyer (M) 10 inch trough, (added cap. for future second reactor running in tandem), water jacketed, screw twist of one in 10 inches, powered by 3 HP, depending on distance to bin, at 60 RPM . All conveyers will be tightly covered, drive mechanisms guarded safely.

The Dryer Air Heat Exchangers (V): are bolted to the manifold (Q) which is in turn secured to the reactor framing. The pipes (V) are left unsecured at the opposite end so that they are free to expand and contract.
Distillate Gas Collection System (L): the portion that is inside the reactor must be made of the same material as the retort tubes. The collection pipes are mounted on the vents (Y) with gaskets to prevent gases escaping into the combustion chamber at these points.
They exit the reactor through slots, equipped with slip plates similar to those on the tubes but smaller, and then are bolted, again with gaskets to the outside portions of the gas system. Then through a low volume fan or simply by the draft suction of the burners combined with the pressure in the retorts these gases are fed back into the burner chamber as a supplemental fuel. This whole contraption can be adapted to recover the gases as liquid such as they may condense by modifying the bottom end before it returns to the burners. These are 2 inch diameter inside changing to 3 inch that the vertical outside consist of.
Gas Monitoring Vents (K): are fitted with lids to prevent escape to the atmosphere of the gases unnecessarily; but can be opened for sampling and inspection of those gases to enable the operator to tell what is happening inside the retort. The color, density, and even the smell of the smoke will reveal at what stage the wood is in,~ during its transformation to charcoal. Only seconds are needed for this and then they can be closed again. The gas monitoring vents are small stubs of 1 inch diameter pipe.
Control Room & The Switch Room Below: should be one story up to give the operator a better view of the equipment meant to be controlled and have all sides in glass for the top half. It must be of convenient size to house all remote motor stop-start buttons and their control lights, read-out dials for all thermocouples, and a 4 pen, 25 hour circular polygraph for the four point burner temperature monitors.
Electrical Switch Room (below control room): with a capacity for incoming supply of 750 KW to allow for future expansion to tandem reactors. It must also be large enough for all safety switches, splitter enclosures, magnetic starters, timers, and any necessary control paraphernalia.
Wiring Note: The wiring of all in-feed equipment is interlocked, as is that handling the actual production of charcoal and delivery of charcoal to the bin. Such as:
The retort screw motors(T) cannot be started until the collection conveyer motor is going and this cannot be started until the storage conveyor is running. The starting sequence of this is from the destination to the source. The in-feed system is similarly interlocked starting with the return blower (H), then the feed conveyor motor, the dryer blower and finally the sawdust conveyor from the bin. This wiring plan protects against plugging up any portion of the system.
OPERATION:
Generally, the apparatus of the invention operates as follows:
Since all motors are interlocked they must be started from the final destination. The storage conveyer first, then the collection conveyer, then the six retort motors, then the sawdust feed cross conveyer motor then the dryer blower and finally the sawdust from the bin conveyor.
While all this is running the burners are lit and the reactor is now heating up as the retorts fill. The retort motors continue running until sawdust comes from the output end, then they are shut down until the charcoal is ready to be extracted.
Periodical inspections at the gas vent (K) will give an indication of this, and testing of ejected material at the product sampling hole (N) will confirm the status of the reaction taking place. The sawdust feed from the bin and the dryer equipment is left running, the over flow blower will return it to the bin.
When the charcoal reaches the desired state the retort screw can run steadily, until such time as the organic material comes out raw again. Then each set of retorts must rest and cook according to the condition of the product within. While the charcoal is cooking the sawdust drying and feeding apparatus is left running steady, the overflow blower sends excess sawdust back to the bin and it goes a second time through the drying cone. This will allow a more continuous operation of the retort screws, a considerable increase in production, and a general settling down of the operation into routine checks, lubrication, and monitoring.
When it becomes necessary to shut the reactor down, first trim the burners to gradually cool the inside gear and then shut them off entirely. The retorts must remain full until the reactor has cooled to surrounding temperature even if means running a little raw sawdust into the charcoal bins. The temperature of the reactor at any of the thermocouples should never be allowed to exceed 600°Celsius. The temperature in the dryer cone should never be allowed to exceed 150°Celsius.
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. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

Claims (21)

I claim:

1. A method for producing charcoal, the method comprising:
introducing organic material into a heated tubular retort at an inlet end of the retort, said heated tubular retort extending substantially horizontally;
rotating a screw element extending through the retort to carry the organic material along the retort, the screw element having a flight, the flight comprising two or more sections separated from one another by one or more gaps, each of the one or more gaps being centred on a gas vent spaced longitudinally from the inlet end of the retort;
carrying the material to the one or more gaps by rotating the screw element;
advancing the organic material through the one or more gaps by rotating the screw element to deliver more of the organic material into the gap; and, after advancing the organic material through the one or more gaps, delivering the organic material through the retort to an outlet end of the retort;
wherein the organic material is converted to charcoal before it is delivered to the outlet end of the retort.

2. The method of claim 1 wherein the retort comprises two or more gas vents at locations spaced apart along the retort, each of the one or more gaps in the flight of the screw is centred on one of the two or more vents and the method comprises carrying the organic material sequentially, through each of the gaps by rotating the screw.

3. The method of claim 1 or 2 comprising maintaining the retort at a temperature of at least 600°C.

4. The method of claim 3 wherein maintaining the retort at a temperature of at least 600°C comprises heating a furnace through which the retort extends.

5. The method of claim 4 comprising removing flammable vapours from at least one of the vents and burning the flammable vapours in the furnace.

6. The method of any one of claims 1 to 5 comprising maintaining anaerobic conditions within a heated portion of the retort while carrying the organic material through the heated portion of the retort.

7. The method of any one of claims 1 to 6 comprising maintaining a temperature of the retort constant and controlling a quality of charcoal delivered at the output end of the retort by varying a rate of feed of the organic material through the retort.

8. The method of any one of claims 1 through 7 wherein the organic material comprises sawdust.

9. The method of claim 8 comprising blowing the sawdust through an inverted conical drying chamber before introducing the sawdust into the heated tubular retort.

10. Apparatus for producing charcoal, the apparatus comprising:
a furnace;
a retort tube extending substantially horizontally through the furnace;
a screw element extending through the retort tube, the screw element comprising a helical flight; and, one or more gas vents penetrating the retort tube;
wherein the flight comprises two or more sections separated by one or more longitudinally extending gaps, the gaps being coincident with the one or more vents.

11. The apparatus of claim 10 comprising a plurality of gas vents spaced apart along the retort tube, wherein each of the one or more longitudinally extending gaps in the flight are coincident with one of the plurality of vents.

12. The apparatus of claim 10 or 11 wherein the retort tube extends through a furnace capable of heating the retort tube to a temperature of at least 600°C.

13. The apparatus of claim 12 comprising a plurality of retort tubes extending through the furnace.

14. The apparatus of any one of claims 10 through 13 wherein at least one of the one or more gas vents is connected to a by-product fluid recovery system.

15. The apparatus of any one of claims 10 through 14 wherein an internal diameter of the retort tube is 10 1/2 inches.

16. The apparatus of claim 15 wherein a diameter of the flights is 10 1/2 inches.

17. The apparatus of any one of claims 10 through 16 wherein the screw element has a pitch in the range of 6 inches to 8 inches.

18. The apparatus of any one of claims 10 through 17 wherein each of the gaps extends longitudinally along the retort tube for a distance in the range of 18 inches to 24 inches.

19. The apparatus of any one of claims 10 through 17 wherein a first longitudinally extending one of the one or more gaps adjacent an inlet end of the retort tube has a length of approximately 24 inches and a second one of the one or more longitudinally extending gaps adjacent the outlet end of the retort tube has a length of 18 inches.

20. The apparatus of any one of claims 10 through 19 comprising a sawdust feed system connected to deliver sawdust to an inlet end of the retort tube.

21. The apparatus of claim 20 wherein the sawdust feed system comprises an air blower connected to direct a stream of flowing air into a first conduit coupled to an inlet at a lower end of an inverted conical drying chamber; a sawdust feeder connected to deliver sawdust into the first conduit; and a second conduit connected between an outlet of the drying chamber and the inlet end of the retort tube.