U.S. patent number 3,901,766 [Application Number 05/366,785] was granted by the patent office on 1975-08-26 for method and apparatus for producing charcoal.
Invention is credited to David E. Smith.
United States Patent |
3,901,766 |
Smith |
August 26, 1975 |
Method and apparatus for producing charcoal
Abstract
A method for producing charcoal consisting of introducing the
material to be carbonized into, through, and out of a single
chamber in which it is heated to a carbonizing temperature by the
combustion of gases emitted by the carbonizing of previously
inserted material, the gases being intermixed for combustion with
air also injected into the chamber, but the air and gas being
directed and controlled in the chamber in such a manner that the
carbonizing material is never exposed to sufficient oxygen to
support free combustion thereof, and an apparatus capable of
carrying out this method.
Inventors: |
Smith; David E. (Rolla,
MO) |
Family
ID: |
23444486 |
Appl.
No.: |
05/366,785 |
Filed: |
June 4, 1973 |
Current U.S.
Class: |
201/32; 201/37;
202/216; 202/131 |
Current CPC
Class: |
C10B
49/04 (20130101); C10B 1/10 (20130101) |
Current International
Class: |
C10B
49/04 (20060101); C10B 1/10 (20060101); C10B
1/00 (20060101); C10B 49/00 (20060101); C10B
047/20 (); C10B 049/06 (); C10B 049/18 (); C10B
001/10 () |
Field of
Search: |
;201/32,33,36,37,27,29,15 ;202/216,218,131,136 ;110/14 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yudkoff; Norman
Assistant Examiner: Sanders; D.
Attorney, Agent or Firm: Hamilton; John A.
Claims
What I claim as new and desire to protect by Letters Patent is:
1. A method of producing charcoal from wood or the like in small
pieces consisting of the following steps:
a. continuously introducing said wood into the higher end of an
elongated, slightly inclined retort which is inclined downwardly
toward its opposite or exit end,
b. rotating the retort about its longitudinal axis, whereby the
wood pieces are constantly tumbled and advanced toward the lower
end of the retort along the length thereof, in the form of a bed
only partially filling said retort,
c. heating said wood by combustion of an external fuel long enough
only to dry and initiate carbonization of a portion of said wood,
whereby a combustible wood gas is driven from said wood, and
d. introducing air tangentially into a peripheral portion of the
retort not occupied by the wood bed, in a direction opposite to the
rotation of the retort and at a point angularly remote from the
bed, considered in the direction of circulation of the air, whereby
wood gas driven off is entrained in the circulation, mixed with the
air, and burned to the extent permitted by the available oxygen of
the admitted air, before the circulating gases again engage said
bed, the heat of said combustion serving to dry subsequently added
wood and bring it to carbonization temperature, and the tumbling of
the wood pieces in the bed serving to expose the entire mass of
said bed to the heat of said combustion, and
e. removing the resulting charcoal from the lower end of said
retort.
2. An apparatus for producing charcoal from wood or the like in
small pieces comprising:
a. an elongated retort the axis of which is inclined slightly from
horizontal whereby to have upper and lower ends,
b. means operable to introduce said wood into the upper end of said
retort at a regulated rate,
c. means operable to rotate said retort about its longitudinal axis
at a rate sufficiently slow that said wood gathers in a bed in the
lower portion of said retort, said bed tending to rise along the
ascending side of the retort until gravity causes the wood pieces
to tumble, said bed also being moved along the length of said
retort as a result of said tumbling and the inclination of said
retort,
d. means operable to burn an external fuel in or adjacent said
retort long enough only to dry and bring to carbonization
temperature a portion of said wood, whereby carbonization is
initiated and a combustible wood gas emanates from said wood,
and
e. means operable to inject air in regulated amounts tangentially
into a lower peripheral portion of said retort not normally
occupied by said wood bed, and to direct said air peripherally of
said retort in a direction opposite to the rotation of said retort,
whereby said wood gas is intermixed with said air and burned to the
extent permitted by the available oxygen of said air, as it flows
peripherally around said retort, before the hot, oxygen-deficient
gaseous products of its combustion again flow over said wood bed to
entrain additional wood gas, and
f. means operable to remove the resulting charcoal from the lower
end of said retort.
Description
This invention relates to new and useful improvements in methods
and apparatus for producing charcoal. The invention has been
conceived and developed particularly for the production of charcoal
from wood chips, but it will be readily apparent that the
principles thereof are readily applicable to other materials.
The principal objects of the present invention are the provision of
a method and apparatus which provides a continuous operation, with
fresh wood chips being continuously added and completed charcoal
being continuously removed, as distinguished from "batch" methods
in which a quantity of material to be carbonized is sealed in a
kiln or the like, heated to carbonizing temperature by external
fuel, allowed to carbonize and then cool, and finally removed to
permit recharging of the kiln with a fresh batch; which permits the
use of heat provided by combustion of combustible hydrocarbon gases
emitted from carbonizing wood to elevate freshly added wood chips
to carbonizing temperature, thereby eliminating any requirement for
external fuel once the process has been initiated; and which
permits the entire process to be carried out in a single chamber or
retort, with the air introduced for combustion of the wood gases
being restrained from contact with the carbonizing wood by
controlled movement of the wood, gas and air within the
chamber.
Another object is the provision of a method and apparatus of the
character described which is "clean" in operation, that is, it
discharges so little smoke or other objectionable fumes to the
atmosphere as to be acceptable under present strict environmental
regulations. Such regulations are particularly strict in cities or
other densely populated areas, and have in the past often
necessitated location of charcoalling operations in remote
areas.
A further object is the provision of a method and apparatus of the
character described which is capable of producing large quantities
of useful heat as a by-product, which may be utilized in many
different ways.
Other objects are simplicity and economy of both the method and the
apparatus, and efficiency and dependability of operation.
With these objects in view, as well as other objects which will
appear in the course of the specification, reference will be had to
the accompanying drawing, wherein:
FIG. 1 is a side elevational view, partially broken away, of an
apparatus embodying the present invention, and capable of carrying
out the method of the invention,
FIG. 2 is an enlarged sectional view taken on line II--II of FIG.
1,
FIG. 3 is a fragmentary sectional view taken on line III--III of
FIG. 2,
FIG. 4 is an enlarged sectional view taken on line IV--IV of FIG.
1, and
FIG. 5 is a fragmentary sectional view taken on line V--V of FIG.
4.
The process of producing charcoal from wood constitutes the
destructive distallation of said wood, and is performed by heating
the wood to drive therefrom first the free moisture and then the
volatile hydrocarbon constituent elements of the wood, reducing it
ideally to carbon, plus the small proportion of incombustible
ingredients thereof. The disposition of the volatile hydrocarbons
is called carbonization. The carbonization proceeds spontaneously
once it is initiated, initiation requiring that its temperature be
elevated to about 550.degree. Fahr. It is an exothermic chemical
reaction, releasing heat equal to about 6% of that obtainable by
complete combustion of the wood, and elevates the temperature of
the wood to about 850.degree. Fahr. It is also accompanied by the
release of large quantities of hydrocarbon wood gas, which is
combustible if intermixed with air to supply the necessary oxygen.
However, since the wood temperature during carbonization is well
above its ignition temperature, the process must be carried out in
the absence of sufficient oxygen to support combustion, in order to
avoid burning of the wood to ash. In older charcoalling methods,
the heat necessary to dry and heat the wood to carbonization
temperature was supplied entirely by an external commercial fuel
such as oil or gas, which made such processes relatively expensive.
Also, the heat produced by the carbonization reaction was
ordinarily eventually dissipated to the atmosphere as a waste
product. Also, the wood gases were ordinarily burned off as a waste
product, but this produced large quantities of smoke and noxious
fumes, which were always objectionable, and which are now more and
more strictly prohibited by environmental regulations. Such gases
could be processed to produce by-products such as ascetic acid,
methanol, oils and tars, etc., but such products are presently more
cheaply available from other sources, and the commercial value of
wood gases for these purposes is negligible.
The method contemplated by the present invention comprises the
following steps:
1. Introducing wood in the form of chips or the like into one end
of an elongated chamber or retort, conveying it through said
retort, and removing it from the opposite end of said retort, in a
continuous movement.
2. Burning an external fuel in the entry end of the retort for a
time sufficient to dry and elevate a portion of the wood chips to
carbonization temperature, whereby production of heat and wood gas
by the carbonization reaction is commenced, after which the fuel
supply is terminated.
3. Introducing air in a controlled amount into the retort to cause
combustion of the wood gases produced to generate additional heat,
the carbonization heat and heat produced by the combustion of the
gas being utilized to dry and heat freshly introduced wood to
carbonization temperature.
4. Controlling and directing movement of the wood, gas and air in
such a manner that while the wood is thoroughly exposed to the
available heat, it is not exposed to sufficient oxygen to support
combustion thereof.
Other steps performed by the apparatus to be described, such as the
cooling and storage of the charcoal produced, and the disposition
of any unburned combustible material emerging from the retort, are
considered merely ancillary to the process performed in the retort,
and are not here listed.
The process as just described provides continuous, high speed
production of high quality charcoal in a single chamber or retort.
The wood gas, which is an inherent by-product of the carbonization
reaction, is utilized to produce the heat necessary to make the
process continuous after the initial starter flame is shut off.
Moreover, although the wood gas is mixed with air and burned within
the carbonization retort, the air does not reach the wood to cause
burning and reduction thereof to ash. A pilot plant constructed to
perform this method has consistently produced charcoal with less
than 3% ash, the amount permitted in high-grade industrial
charcoal. In other usages, a much higher ash content is permitted.
It should be noted that while carbonizing wood does release heat,
such heat is not sufficient to dry and heat the freshly added wood
to carbonization temperature, and that the reaction would be
"snuffed out" were it not for the additional heat supplied by
combustion of the wood gas. The initial drying of the wood, for
example, often requires several times the heat required to raise
the sensible temperature of the wood from atmospheric to
carbonization temperature.
In the drawing, which illustrates an apparatus capable of carrying
out the method described above, like reference numerals apply to
similar parts throughout the several views, and the numeral 2
applies generally to a retort which constitutes a large cylindrical
vessel with its axis inclined slightly from horizontal, about which
a pair of track members 4 are concentrically affixed as by spoke
members 6. Each track member is supported by a pair of rollers 8
disposed respectively at opposite sides of the midline of the
retort, each roller being carried rotatably by a ground-supported
pillow block 10. At least one pair of said rollers is driven
rotatably in the same direction by an electric motor 12 also
mounted on a ground-supported pillow block 14. As best shown in
FIG. 4, sprockets 16 fixed on the rotor of said motor are
operatively connected by sprocket chains 18 to sprockets 20 fixed
respectively on the axles of two of rollers 8. Thus the retort is
turned slowly (about 2 or 3 rpm) about its axis in the direction of
arrow 22 in FIGS. 2 and 4.
At the wood-entry end of the retort, which is its higher end, the
retort is provided with an end wall 24 having formed therein a
central circular aperture 26 into which extends a stationary,
horizontal flue pipe 28 which is interconnected at its opposite end
into a vertical, ground-supported stack 30 which may be of any
necessary or desired height. Below the level of flue pipe 28, stack
30 is provided with a plurality of air-admitting apertures 32 (see
FIG. 3) spaced angularly thereabout, each aperture being provided
with a hinged closure door 34 operable to regulate the amount of
air introduced by its associated aperture. Disposed above flue pipe
28 is a hopper 36, or other storage or conveying means, operable to
deposit wood chips or the like at a pre-determined rate, regulated
for example by a "damper" valve 39, into a chute 38 which extends
in sealed relation through the top wall of the flue pipe, then into
retort 2 through the inner end of said flue pipe, and deposits said
chips in the lower portion of the retort, at the "descending" side
of the midline thereof. The entire inner surface of the retort,
including its end walls, is provided with a thick lining 40 of
ceramic insulating material. Also extending through a wall of flue
pipe 28 is a fuel pipe 42 for gas or the like, controlled by valve
44, and terminating in a burner nozzle 46 (see FIG. 3) directed
into the retort through the inner end of the flue pipe.
At the opposite or lower end of the retort, said retort is provided
with an end wall 48 provided with a central circular aperture 50
through which extends an air pipe 52. Externally of the retort,
said air pipe is interconnected to an air blower 54 driven by an
electric motor 56, and operable to draw a pre-determined amount of
atmospheric air, regulated for example by a damper 58, through an
intake pipe 60, and to deliver said air to the interior of the
retort. It will be understood that the blower and air pipe are
rigidly supported exteriorly of the retort by any suitable means,
not shown. Interiorly of the retort, air pipe 52, has a first
section 52A extending downwardly adjacent end wall 48, a second
section 52B extending parallel to the retort axis but adjacent the
bottom of the retort, a third section 52C extending upwardly
adjacent end wall 24, and an open spout 52D opening into flue pipe
28, as best shown in FIG. 3. Spaced along section 52B, a series of
holes 62 are formed in the air pipe, all of said holes being
directed identically, slightly above horizontal, to cause
circulation of air and gas in the retort in a direction opposite to
the rotation of the retort itself, as indicated by arrows 64 in
FIG. 2. While the air pipe is provided with a coating 66 of
insulating material, it is located in a very hot zone, and might
become overheated were it not for the terminal spout 52D thereof,
which permits a larger quantity of air to be delivered by the
blower to the pipe than is actually required at holes 62 thereof.
This larger air volume has a cooling effect, and prevents
overheating of the air pipe.
At the lower end of the retort, adjacent end wall 48 thereof, a
plurality of scoops 68, each being elongated and of U-shaped
cross-sectional contour, are fixed to the inner surface of the
cylindrical retort wall at regular angular intervals, and project
through and inwardly from the refractory lining 40 of the retort.
They are so arranged as to open upwardly when on the upwardly
moving side of the retort, and at the bottom of the retort they
pass between end wall 48 and section 52A of the air pipe (see FIG.
5). As will be described, these scoops transport finished charcoal
upwardly from a bed of charcoal in the lower portion of the retort,
each scoop, as it approaches the top of the retort, depositing its
contents in a hopper 70 disposed above air pipe 52 adjacent the
inner surface of retort end wall 48. Said hopper directs the
charcoal through a downwardly inclined tubular chute 72 which is
inclined and passes downwardly through the top wall of air pipe 52
inside of the retort, through the bottom wall of the air pipe
externally of the retort, and is connected in sealed relation to a
horizontal auger tube assembly 74, at one end of the latter. Said
assembly includes an inner tube 76 into which chute 72 is sealed,
and in which an auger 78 is operatively mounted, and driven by an
electric motor 80, and an outer tube 82 spaced outwardly from tube
76 to form a chamber 84 through which cooling water is circulated
by any suitable means through hose connections 86. At the end of
the assembly opposite from chute 72, auger tube 76 is connected, as
at 88, to a storage container 90 for the charcoal. As best shown in
FIG. 5, a flexible sealing strip 92 encircles air pipe 52 adjacent
the external surface of retort end wall 48, being affixed to said
air pipe as by rivets 94, and having a wiping contact with end wall
48, whereby to prevent air from entering the retort through
aperture 50 around the air pipe, for a reason to be described.
In operation, wood chips or the like are allowed to enter the
retort through chute 38 from hopper 36, at a rate regulated by
damper 39, with the hopper being rotated in the direction of arrow
22 by operation of motor 12. Due to this retort rotation, the wood
chips collect in a bed 96 at the bottom of the retort, and the bed
tends to ride up the ascending side of the retort, as indicated in
FIGS. 2 and 4. It of course can rise in this manner only until its
exposed surface reaches the normal "angle of repose" of the chip
material, which is about 45 degrees, whereupon the chips begin to
tumble and slide in a circulatory path within the bed, said path
being indicated by arrows 98 in FIG. 2. Due to this tumbling
action, the chips throughout the mass of the bed are repeatedly
exposed both to the hot gases which as will appear are present in
the retort, and to the liner 40 of the retort. Due to the
inclination of the retort, the tumbling action of the chips causes
them to advance slowly toward the opposite or lower end of the
retort, until eventually the bed 96 will be of substantially
uniform depth along the entire length of said retort. The feed rate
of the chips from hopper 36 is so regulated, in relation to the
degree of tilt of the retort, that the chip bed 96 will be of such
depth that it engages the retort wall only substantially over the
lower quadrant thereof, at the ascending side thereof, as shown in
FIGS. 2 and 4.
After insertion of the wood chips into the retort, an external fuel
such as gas is injected through nozzle 46 and burned to provide
drying, heating, and the commencement of either carbonization or
actual combustion of some of the chips. Carbonization rather than
combustion can be encouraged by leaving blower 54 shut off at this
time, so that there will be relatively little air within the retort
to support actual combustion. In any event, at least some of the
chips will be started into a carbonization reaction even though
others may be in full combustion. The fuel supply to nozzle 46 may
be shut off at valve 44, and the process will thereafter be
self-sustaining. The retort could also be heated externally to
initiate carbonization. Blower 54 is then set in operation.
Operation of blower 54 introduces air into the retort through holes
62 of air pipe section 52B, which are spaced along substantially
the entire length of the retort, in a direction indicated by arrow
100 in FIG. 2, setting up a clockwise circulation of air and gases
in the retort as indicated by arrows 64, opposite to the
counter-clockwise rotation of the retort itself. In passing over
the chip bed 96, this circulation entrains the combustible wood
gases being produced by the carbonization reaction occurring within
the bed, and these wood gases are then intermixed with fresh air
emerging from holes 62, principally in the lower quadrant of the
retort at the descending side thereof. The wood gas and spent gases
in which it is entrained are of course extremely hot, and the air
in pipe 52B is pre-heated by the presence of the pipe in the
circulating zone of the hot gases, and therefore the wood gases
burn freely when intermixed with the air. The principal zone of
combustion or "fireball," is indicated at 102 in FIG. 2. The
quantity of air introduced is much less than that required for full
combustion of the wood gas, since full combustion would produce
much more heat than is required to dry and heat freshly inserted
wood chips to carbonization temperature. Nearly all of the
available oxygen of the air introduced will be consumed in the
fireball zone, and virtually none will remain by the time the hot
gases again circulate around the retort and flow over the chip bed.
Instead, the gases circulating over the bed will consist virtually
entirely of spent air, unburned or only partially burned wood
gases, and of course smoke. These gases will be amply hot to dry
and heat the chips to carbonization temperature as and after they
are inserted, while the heat produced by the exothermic character
of the carbonization reaction already occurring in previously
inserted chips would not, but contain virtually no free oxygen,
which would cause combustion of the chips. Of course, fireball 102
also heats the retort liner 40 to a very high temperature, and the
liner is also an important factor in supplying heat to the chip
bed. The previously described tumbling circulation of the chips
within the bed insures that all of the chips will be thoroughly and
intimately exposed both to the circulating gases and also to the
liner.
If the length of the retort has been properly selected relative to
its degree of inclination, carbonization of the chips to charcoal
will be completed by the time they reach the lower end of the
retort. At this point, as shown in FIG. 4, scoops 68 pass upwardly
through the bed in succession, each scoop trapping a portion of the
finished charcoal, elevating it, and dropping it into hopper 70 for
conveyance through chute 72 and auger tube 76, in which it is water
cooled, to storage container 90. The current of cool air in air
pipe 52, which chute 72 traverses, also assists in the cooling of
the finished charcoal. As previously mentioned, it is preferable
that storage container 90 be sealed, since unless auger-tube 76 is
impractically long, there might still be "hot spots" in the
charcoal, which could cause combustion if the charcoal were
immediately exposed to air. Scoops 68 must of course be of
sufficient number and capacity to remove charcoal from the retort
as fast as wood chips are added, despite the slow rotational speed
of the retort. They may in fact be provided with a still greater
removal capacity, since this would not adversely affect operation,
and would permit adjustment of the rate of introduction of chips
with no possibility of pile-up of charcoal at the lower end.
Adjustment to a greater rate of introduction of chips may be
possible, for example, when the chips are relatively dry, and hence
require less time, and a smaller proportion of the retort length,
for the drying phase of the operation. The desirability of air seal
92 may now be appreciated. While the mere admission of air to the
retort is not in itself objectionable, since air is being
introduced by blower 54 at all times, the admission of air at this
point could provide oxygen for combustion of the hot charcoal which
might reach the coal as it is elevated and dropped by the
scoops.
The spent air, unburned or partially burned hydrocarbon wood gases,
and smoke, emerge from the retort through flue pipe 28 to stack 30,
where their high temperature creates a strong updraft. In passing
through the flue pipe, which chute 38 traverses, they also assist
in pre-heating the chips as they pass through the chute. If allowed
to escape to the atmosphere in the condition they leave the retort,
they would constitute an objectionable environmental threat, with
heavy smoke representing unburned particulate matter, and noxious
fumes. The present apparatus overcomes this difficulty by admitting
air to the stack below flue pipe 28, through door apertures 32, as
regulated by doors 34. The smoke and gases in the flue contain much
matter still combustible and still hot enough to burn, but unburned
due to lack of oxygen. Air admitted by doors 34 therefore causes
ignition of the stack gases, creating a very hot flame which
consumes virtually all combustible material still remaining.
Preferably all of doors 34 are hinged at the same side, so that if
they are opened slightly, the air is admitted with a swirling
motion into the stack. This creates a "vortex" action in the stack,
which promotes a fuller degree of combustion by retaining the gases
in the stack for a longer time period. The "afterburner" provided
by admission of air to the stack provides a "clean" emission from
the stack, which is virtually free of all smoke or other
objectionable fumes or gases. While not considered to be properly a
portion of the present invention, it is of interest that heat
released by the stack combustion is quite large in amount, about
2,000 B.t.u. per pound of wood chips carbonized. With a retort of
the size contemplated and tested, (about 71/2 ft. in diameter and
16 ft. long), which is designed to process about 5,000 lbs. of
chips per hour, the heat released in the stack thus amounts to
about 10,000,000 B.t.u./hr. and this heat could be utilized in many
valuable applications.
It will of course be apparent that when operation is first started,
and until the heat and flow conditions of wood chips, air and gas
throughout the retort have become stabilized, a quantity of
completely or only partially carbonized chips, and charcoal of low
quality, may be produced. This initial output may be discarded as
waste, or preferably recycled to hopper 36 for reprocessing.
While I have shown and described a specific embodiment of my method
and apparatus, it will be readily apparent that many minor changes
of both the method, and also of the structure and operation of the
apparatus, may be made without departing from the spirit of the
invention.
* * * * *