Thermal decomposition apparatus

An apparatus is disclosed for the continuous non-oxidative thermal decomposition of heat-dissociable organic matter to a solid carbon residue, particularly activated carbon, and a mixture of gaseous products, without substantial coking or tar formation. The apparatus involve a cylindrical rotating drum in a substantially horizontal position, into which feed material is introduced at one end and products recovered at the other end. An axial temperature gradient, increasing in the direction of flow, is maintained within the drum, enabling the exercise of a high degree of control over the reaction to fully convert the feed into the desired products.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the processing of organic waste materials for the 
recovery of useful products therefrom by non-oxidative thermal 
decomposition. 
High molecular weight organic wastes from both industry and the consumer 
have long presented a disposal problem. Some materials, such as hard nut 
shells and certain fruit seeds, by-products of the agricultural industry, 
have a high oil content which discourages the industry from using common 
means of disposal. Other materials, such as used rubber tires, liberate 
large amounts of soot and other atmospheric pollutants when burned. A 
further problem is the high energy consumption inherent in many disposal 
processes and the loss of useful organic values. 
A need therefore exists for an energy efficient and environmentally sound 
process and apparatus for recovering organic values in a useful form from 
organic waste materials. 
2. Description of the Prior Art 
Reaction vessels and processes for the carbonization or destructive 
distillation of organic material are widely disclosed. Examples of 
disclosures most pertinent to the present invention are the rotating 
vessels of Frank, U.S. Pat. No. 1,677,757, issued July 17, 1928; Goodell, 
U.S. Pat. No. 2,265,158, issued Dec. 9., 1941; and Taciuk, U.S. Pat. No. 
4,285,773. 
The present invention is of particular interest in the processing of scrap 
rubber, typically in the form of used automobile tires. A variety of 
methods for processing scrap rubber are known. 
One such method is the "digester" process, in which ground scrap rubber is 
heated under pressure in a solution of a cellulose-destroying chemical 
such as caustic soda, calcium chloride and zinc chloride. This treatment 
destroys the fiber present in the rubber and plasticizes the rubber. 
Swelling oils are usually added to enhance the process. Such processes are 
described in Carr, et al., U.S. Pat. No. 2,567,802, issued Sept. 11, 1951; 
Elgin, U.S. Pat. No. 2,593,279, issued Apr. 15, 1952; Brown, et al., U.S. 
Pat. No. 2,640,035, issued May 26, 1953; Green, U.S. Pat. No. 2,879,245, 
issued Mar. 24, 1959; and Soott, U.S. Pat. No. 3,700,615, issued Oct. 24, 
1972. 
In another method, known as the "heater" process, ground scrap rubber is 
heated with live steam under pressure, usually with the addition of 
softening agents, until the rubber becomes plasticized. Descriptions of 
such processes are found in Mankowich, et al., U.S. Pat. No. 2,871,206, 
issued Jan. 27, 1959, and Glenn, et al., U.S. Pat. No. 3,272,761, issued 
Sept. 13, 1966. 
Mechanical processes, which involve mechanical working of the rubber at 
elevated temperature, are described in Sverdrup, U.S. Pat. No. 2,809,944, 
issued Oct. 15, 1977; Sverdrup, U.S. Pat. No. 2,845,395, issued July 29, 
1958; Dasher, U.S. Pat. No. 2,853,742, issued Sept. 30, 1958; Dasher, U.S. 
Pat. No. 2,966,468, issued Dec. 27, 1960; Lee, et al., U.S. Pat. No. 
4,049,588, issued Sept. 20, 1977; and Maxell, U.S. Pat. No. 4,146,508, 
issued Mar. 27, 1979. 
Dissolving processes, using a hydrocarbon solvent at elevated temperatures, 
are also known. An example is that described by Wakefield, et al., in U.S. 
Pat. No. 3,896,059, issued July 22, 1975. 
SUMMARY OF THE INVENTION 
A process and apparatus are provided for the continuous non-oxidative 
thermal decomposition of non-gaseous heat-dissociable organic matter to a 
solid carbon residue and a mixture of gaseous products, without 
substantial coking or tar formation. Also provided are a process and 
apparatus for the direct conversion of carbonaceous material into 
activated carbon and a mixture of gaseous products. 
Both the structural features of the apparatus and the steps of the process 
are more fully understood by reference to the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention resides in an apparatus and process for the thermal 
decomposition of any non-gaseous heat-dissociable organic matter. Such 
matter generally includes industrial, municipal and agricultural waste 
products which contain organic matter susceptible to molecular breakdown 
by exposure to heat. The organic matter will generally contain a 
substantial quantity of high molecular weight substances, such as polymers 
and other long-chain molecules, and is preferably in liquid, slurry or 
particulate form. Examples include comminuted rubber tires and rubber 
products in general, plastics, paper, sawdust, wood chips, hard fruit 
seeds, sewage sludge, waste automotive oil, coal dust, peat, food scraps, 
fatty meat waste, ground bones, lawn trimmings, hard nut shells, rice 
hulls, straw and general agricultural wastes. 
The invention is particularly useful for the processing of waste rubber, 
such as discarded vehicle tires, inner tubes, rubber hoses, belts and the 
like. Typical materials include both natural and synthetic rubbers, such 
as thiokols, neoprenes, nitrile rubbers, styrene rubbers, butyl rubbers, 
polybutadiene, silicone rubbers, acrylate rubbers, polyurethanes and 
fluoro rubbers. 
Solid feed materials are preferably comminuted to a size which is conducive 
to a controllable flow rate and which has sufficient surface exposure to 
permit complete reaction within an economically convenient length of time. 
Subject to such considerations, however, the particle size is not critical 
and can vary over a wide range. Preferably, the particles in the feed will 
be about one inch or less in their largest linear dimension. Comminution 
is achieved by any conventional means, such as shredding, grinding or 
chopping. 
Referring to FIG. 1, an air-tight apparatus 1 is shown for the continuous 
non-oxidative conversion of heat-dissociable organic feed material to a 
solid carbon residue and a mixture of gaseous products. The term "gaseous 
products" is intended herein to include both condensible vapors and 
noncondensible gases, and denotes any substance which is in the gaseous 
phase under the conditions prevailing at the designated location. The 
substances which fit this description, of course, may vary from point to 
point in the overall system. 
The apparatus comprises a cylindrical rotating drum 2 mounted inside a 
stationary furnace 3. The drum is mounted either horizontally or at a 
slight angle pointing downward in the direction of flow (shown as right to 
left), depending on the flowable nature of the feed material and the 
desired residence time. With most feeds, forward flow in the axial 
direction is sufficiently induced by the rotation of the drum in 
conjunction with the feed of raw material in one end and the removal of 
product through the other end. A horizontal configuration is thus 
preferred. 
Rotation of the drum about its axis is provided by any conventional means, 
the example shown here being a chain gear 4 driven by a hydraulic pump 5. 
The rotation rate is one of several factors which can be varied to 
accommodate a wide range of feeds differing in physical form, chemical 
nature and throughput rate, since it affects both the residence time and 
the degree of mixing and tumbling of the reaction mixture. A maximum 
amount of tumbling within the drum is desirable since collisions among 
particles and between particles and the drum wall promote further particle 
breakage. This increases the surface area of the particles and thus 
promotes the separation and escape of gaseous matter from the solids. With 
liquid and slurry feeds, the rotation rate can be appropriately adjusted 
to provide mixing throughout the bulk of the fluid for increased surface 
area as well as improved heat transfer from the drum walls to the fluid. 
The optimum rate of rotation further depends on the chemical nature of the 
feed materials, since the amount of time necessary to achieve complete 
thermal decomposition while avoiding coking and tar formation varies with 
the molecular structure. Coking and tar formation cause the accumulation 
of adherent material inside the drum. In addition to consuming otherwise 
useful organic values, coke and tar are difficult to remove and inhibit 
the free flow of gases and solids through the drum. For lighter feed 
stocks, i.e., those which are easily distilled, a relatively short 
residence time and hence higher rotation rate is appropriate. For denser 
materials, the appropriate residence time is longer and the rotation rate 
slower. Thus, while neither the rotation rate nor the residence time are 
critical, the appropriate ranges will vary with the dimensions of the drum 
and the type of material present in the feed. Appropriate operating 
conditions are readily determined by one of routine skill in the art 
through an examination of the flow characteristics and product 
composition. For most applications, a rotation rate ranging from about 0.5 
to about 10 revolutions per minute is appropriate, with the preferred 
range being from about 1 to about 6 revolutions per minute. Similarly, 
the reactor residence time for most applications will range from about one 
minute to about twenty minutes, preferably from about two minutes to about 
ten minutes. 
The drum itself consists of a cylindrical drum wall 6 and two end faces 7 
and 8 forming, respectively, the upstream and downstream ends of the drum. 
The interior space of the drum comprises two axially spaced zones, a 
reaction zone 9 at the upstream end and a removal zone 10 at the 
downstream end. Feed material is introduced into reaction zone 9 through 
an inlet port 11 in the center of the upstream end 7, while the reaction 
products, both solid and gaseous, escape through an outlet port 12 in the 
center of the downstream end 8. 
The feed material is introduced into the reaction zone by any means capable 
of a controlled rate and the substantial avoidance of air. In the 
embodiment shown in the drawing, the feed passes through a hopper 13 into 
a rotary air-lock feed valve 14, which consists of a rotary shaft with 
radial paddles housed inside a cylindrical housing to form air-tight 
chambers. The chambers receive the feed material as the shaft rotates and 
pass it through an air-tight connective port 15 into a piston valve (or 
ram) chamber 16 consisting of a piston 17 in a cylindrical housing 18. 
With appropriate coordination of the rotary valve and the piston, the 
material can be fed at a regular and controlled rate through chambers 
which remain closed to the atmosphere at all times. When feed stocks such 
as particulate matter are used, with air occupying the space between the 
particles, the feed mixture can be readily purged of air before it enters 
the reaction chamber by the maintenance of a positive pressure within the 
chamber. Purging is then accomplished by either the use of a small bleed 
of vapor from the enclosed chamber or permitting the escape of air from 
the empty chamber as it rotates back up toward the hopper. 
The furnace 3 completely encloses the rotating drum 2. The heat source, 
shown in FIG. 1 as a burner or series of burners 19, is positioned within 
the furnace to direct heat at the outer surface of the drum wall 6 toward 
the discharge end of the drum. In the preferred configuration shown, the 
burners are controlled by pilot lights 20 and positioned within a well 21 
extending downward from the end of the furnace. The burner flames are 
directed against opposing wall 22 of the well which disperses the hot 
combustion gases before they reach the outer drum wall. The combustion 
gases proceed through the furnace in the annular space 23 between the drum 
and the furnace wall, generally moving toward the opposite end of the 
furnace in the direction opposite to that in which the feed and product 
mixture inside the drum itself moves. Various design features can be 
incorporated into the furnace construction to promote the turbulent flow 
of the combustion gases around the perimeter of the rotating drum, thereby 
promoting heat transfer by avoiding the formation of a boundary layer 
adjacent to the drum. As the combustion gases reach the end of the 
furnace, they escape to the atmosphere through an exhaust stack 24. 
The counter-current nature of the flow between the combustion gases and the 
process gases is essential to the maintenance of a temperature gradient 
within the reaction chamber itself, increasing in the direction of process 
gas flow. The relatively low temperature of the feed material also 
contributes to the temperature gradient, as does the loss of heat to the 
atmosphere through the furnace walls. A further contribution to the 
temperature gradient can be made by recycling a portion of the product 
gases through the reaction chamber in the direction of flow. This is more 
fully discussed below. 
The temperature at the discharge end of the drum chamber and the 
temperature rise from the inlet end to the discharge end are variable over 
a wide range depending on the type of material constituting the feed and 
the degree and type of chemical transformation sought to be achieved 
within the chamber itself. If one merely seeks to decompose the feed 
material to char and gaseous products by destructive distillation, a 
relatively low temperature and short retention time will suffice. If 
further conversion is sought within the drum it will be necessary to 
substantially complete the destructive distillation at a point along the 
length of the drum sufficiently removed from the discharge end to leave 
sufficient residence time for the further transformation to take place. 
For example, if water vapor is present in the drum chamber, further 
residence time will permit the formation of activated carbon from the 
char. As a further example, the char can be converted to producer gas by 
reaction with water vapor. In a typical application, both such 
transformations occur simultaneously. These are achieved by using 
sufficient heat input and residence time to insure substantially complete 
carbonization well upstream of the discharge end. 
The axial temperature gradient (increasing in the direction of flow) is 
particularly useful in controlling the various transformations inside the 
drum chamber while substantially preventing coking and tar formation, 
since the optimum temperature for carbonization (char formation) is 
generally several hundred degrees (Fahrenheit) below that for carbon 
activation or producer gas formation. Thus, depending on whether the 
object is merely carbonization, or the combination of carbonization with 
subsequent transformations to produce activated carbon, producer gas or 
both, the temperature within the reaction zone and the gradient from the 
inlet to the discharge end can vary considerably. In most applications, 
however, the temperature difference between the inlet end and the 
discharge end will be from about 40.degree. F. (50.degree. C.) to about 
300.degree. F. (150.degree. C.) and the maximum temperature will range 
from about 700.degree. F. (370.degree. C.) to about 1,200.degree. F. 
(650.degree. C.). In preferred embodiments, the temperature increase 
ranges from about 50.degree. F. (10.degree. C.) to about 200.degree. F. 
(95.degree. C.), and the maximum ranges from about 800.degree. F. 
(430.degree. C.) to about 1,000.degree. F. (540.degree. C.). For 
comminuted scrap rubber, the preferred temperature increase is from about 
70.degree. F. to about 150.degree. F., and the preferred temperature 
maximum is from about 850.degree. F. to 950.degree. F. 
Further features affecting the position of the various transformations 
along the length of the drum, and hence the degree of formation of 
activated carbon and producer gas, include the drum dimensions, the rate 
of rotation, the feed rate and all other factors affecting the retention 
time. Carbon activation and producer gas formation can also be enhanced by 
adding water to the feed stock, either from an external source or by 
recycling water from the product stream. Reactions such as producer gas 
formation which consume water are particularly advantageous since they 
consume contaminated process water which is otherwise difficult to dispose 
of. 
The removal zone portion of the drum chamber and the means within this zone 
for moving gaseous and solid product from the chamber are shown in lateral 
sectional perspective in FIG. 1 and transverse sectional prospective in 
FIG. 2. Solids are removed from the chamber by a screw conveyor 25 
consisting of a rotating screw 26 mounted within a stationary housing 27. 
The housing contains an opening 28 at the top, forming a trough into which 
the solid carbon residue formed in the reaction chamber falls as the drum 
rotates. 
Means are provided in the drum for lifting the solids from the inner wall 
of the drum and directing substantially all of them into the open trough. 
The means shown in FIGS. 1 and 2 are baffles 29 extending radially from 
the drum walls toward the central axis of the drum. The number of baffles 
used is not critical but merely sufficient in number to provide 
satisfactory flow of the residue. One or more will suffice. Preferably, at 
least two are used. 
The gap between the longitudinal or axial edge 30 of each baffle and the 
outer wall of the screw trough is small enough to direct substantially all 
of the solids into the trough opening, yet large enough to prevent the 
wedging of large particles therein, which might interfere with the 
rotational motion of the drum. A gap of minimal size provides maximal 
control of the residence time. Preferred such gaps are approximately one 
inch or less, more preferred being approximately one-half inch or less. A 
typical gap width is approximately one-quarter inch. 
The baffles extend inward from end face 8 for a sufficient distance (thus 
forming the removal zone) to provide solids removal, leaving the remainder 
of the drum interior (the reaction zone) for the desired amount of 
tumbling action. It will be apparent to those skilled in the art that the 
optimum baffle configuration and hence the relative sizes of these zones 
are dictated by the operating conditions as well as the physical and 
chemical characteristics of the feed material. The dimensions are thus not 
critical but will be selected together with other factors such as the drum 
dimensions, rotation rate, temperatures and feed rate to regulate the 
residence time and operating conditions in order to achieve the type and 
extent of feed material transformation desired. 
The length of the conveyor trough is subject to similar considerations and 
further enhances control of residence time. Like the baffles, the trough 
will be short enough to permit sufficient residence time for complete 
carbonization to occur, plus activation and producer gas formation if 
these are also intended, yet long enough to collect solids and to remove 
them before coking or tar formation occur and to provide a sufficient 
opening for gases to enter the discharge conduit and thereby exit the 
reaction zone. In most applications, the length of both the discharge 
screw and the baffles fall within the range of about one-tenth to about 
one-half of the length of the reaction drum, preferably from about 
one-sixth to about one-half the length. Preferably, the discharge screw 
and the baffles are coterminous. 
The discharge screw conveyor consists of a spiral flight 32 mounted on a 
shaft 33 which is rotatably mounted within the trough 27. The trough is 
mounted to remain stationary while the drum rotates. The flight is 
designed and mounted such that its outer edge comes sufficiently close to 
the bottom of the trough to convey substantially all the solid residue 
falling within the trough. The cross section of the flight, however, 
occupies only a portion of the cross-sectional areas of the trough 27 and 
the exit conduit 31, leaving sufficient passage for the process gases to 
escape from the reaction zone. This can be accomplished for example by the 
use of a conveyor screw with a ribbon flight and a central shaft coaxial 
with the trough axis, permitting gases to flow through the space between 
the shaft and the flight. Alternatively, a closed flight on an eccentric 
shaft can be used, permitting the flow of gases above the flight. The 
latter configuration is shown in the drawings and is preferred due to its 
ability to avoid plugging of the exit conduit in the event of coking, tar 
formation or condensation around the screw shaft. 
The screw 26 extends through the exit conduit 31 to the exterior of the 
furnace housing 3. The rotation of the screw is achieved by any 
conventional means, shown in FIG. 1 as a right angle worm drive 34. As the 
solids and gases leave the reaction zone, they are separated by any 
conventional means, shown in FIG. 1 as a T-shaped conduit 35 in which the 
solids fall to a hopper 36 and the vapors pass through an overhead conduit 
37. 
The chemical transformations inside the reaction zone are conducted in the 
substantial absence of air. This can be accomplished by any conventional 
means known to those skilled in the art. One convenient means is to 
maintain a positive pressure inside the drum chamber, i.e., a pressure in 
excess of that of the surrounding atmosphere. In addition to preventing 
the entry of air into the chamber in general, the positive pressure is 
useful in purging comminuted feed particles in the feed valve chambers 
before the particles enter the reaction zone. Air is thus prevented from 
entering with the feed mixture. 
The actual pressure in the drum chamber is not critical and can vary over a 
wide range. For most applications, a pressure within the range of about 
0.1 to about 20.0 pounds per square inch gauge (1.007 to 2.4 atmospheres), 
preferably about 0.5 to about 10.0 (1.03 to 1.7 atmospheres) will be 
appropriate. Pressure control is achieved by the use of suitable control 
valves and pressure regulating devices. The optimal use and positioning of 
such equipment will be readily apparent to one skilled in the art. 
For system start-up, the drum chamber, feed valves and connecting conduits 
are purged with an inert gas and the drum is pre-heated to the desired 
temperature. Suitable adjustments are made once the feed has been 
initiated and steady state has been achieved. 
A wide variety of operations external to the reaction zone can be used for 
the treatment, separation and purification of product materials. An 
illustrative flow sheet is shown in FIG. 3. 
The gaseous products 38 leaving the exit conduit 31 of the reactor are fed 
to a fractionating column 39 which condenses the gases and separates them 
into fractions according to boiling point ranges. Separation is achieved 
by any conventional industrial equipment, a tray tower being the most 
convenient. The type of tray and the dimensions of the tower which will 
provide the optimum and most efficient separation will depend upon the 
throughput rate, the composition of the inlet mixture, and the number of 
fractions to be collected. Suitable tray types include bubble cap, sieve, 
ballast, float valve and ripple trays. In a typical operation, as shown in 
FIG. 3, tops 40 and bottoms 41 are removed, together with two intermediate 
fractions 42 and 43. Separation is further enhanced by a reflux line 44. 
The overhead line 40 is divided between an exhaust line 45 and a 
recirculation line 46 which recirculates a portion of the noncondensed 
gases through the drum chamber in the direction of flow of the process 
gases. Recirculation provides several advantages. First, it helps maintain 
a relatively low temperature at the inlet end of the reaction zone, since 
the gases in the column overhead are cooler than the process gases inside 
the drum chamber. The temperature gradient is thus stabilized and 
regulated. Second, the forced flow of gases overcomes the adverse pressure 
gradient caused by the temperature gradient along the drum axis, thereby 
promoting the forward motion of the gases toward the discharge end. This 
helps stabilize and regulate the residence time of the process material in 
the reaction zone. Third, the recirculation gas supplies excess water 
vapor to the reaction zone. This enhances both activation of the char and 
the formation of producer gas in the reaction zone. 
The producer gas formed in the reaction zone passes through the 
fractionating column and leaves through the overhead line 40. The producer 
gas can then be used to supplement the import fuel 47 by directing a 
portion 48 of recirculation line 46 into the burners 19. This is 
particularly advantageous when gaseous fuel of relatively low heat value 
is used. The high heat value of producer gas will frequently permit a 
reduction of the number of burners in use once steady state has been 
achieved. 
For added flexibility of operation, the carbon residue 49 exiting the 
reaction zone can be fed to a gasification chamber 50 where it is reacted 
with a gas stream 51 consisting of air, water vapor, carbon dioxide or a 
combination to produce a gaseous product consisting of any of the 
synthetic gases commonly known for fuel or synthesis uses, such as 
producer gas, water gas, synthesis gas, etc. This unit can be 
advantageously operated to consume substantially all of the process water 
which is not consumed within the reaction chamber itself. As mentioned 
above, the process water is frequently contaminated with soot and organic 
wastes and is not easily disposed of otherwise for environmental reasons. 
In the embodiment shown in FIG. 3, the carbon residue 49 exiting the 
reaction zone is in the form of activated carbon, and becomes further 
activated inside the optional gasification chamber 46. Further options not 
shown in the drawing include additional vessels for further product 
treatment external to either the drum chamber or gasification chamber. A 
separate carbon activation vessel is one example. 
Once activated carbon is formed, it can be size-reduced and classified on 
site. An example of a suitable apparatus is shown in FIG. 3. The solids 
are conveyed through line 53 to a cyclone dust collector 54 which 
separates and removes the fines. The solids then pass through crushing 
rolls 55 or, alternatively, a grinding operation or a crushing and 
grinding combination to further reduce the particle size. Size 
classification is then accomplished by any conventional means, an example 
of which is a multi-deck vibratory screen 56 as shown, which separates the 
particles into a plurality of size fractions 57. Since the temperature of 
the particles may be above that necessary for combustion, it is preferable 
that an inert atmosphere be maintained throughout the size reduction and 
classification system. This is readily achieved by purging the system with 
an inert gas such as nitrogen. 
The foregoing description is offered for illustrative purposes only, and 
the invention is not intended to be limited to the exact construction and 
operation shown and described. Numerous modifications and variations will 
be readily apparent to those skilled in the art, while still falling 
within the spirit and scope of the invention as claimed hereinbelow.