CA1058445A - Refuse pelletizer - Google Patents

Abstract

REFUSE PELLETIZER

ABSTRACT

Apparatus capable of producing pellets of com-pacted refuse having a density of at least 20 lbs./ft.3 com-prising:
(1) a cylindrical tube having a compacted chamber whose length is shorter than the shortest critical length for the refuse to be pelletized, with a feed port in the side wall of the tube and a discharge port at the end of the tube, (2) a feed hopper communicating with the inlet port of the tube, (3) a reciprocating ram in the inlet end of the tube capable of exerting a pressure of at least 200 psi on each forward stroke, and (4) a refuse flow restrictor in the tube in which the degree of restriction is controlled in response to changes in the ram pressure required to advance the compacted refuse down the tube.

Description

~058~5 This invention relates in general, to apparatus for pelletizing solid waste, and more specifically to a device which is capable of compacting shredded refuse and the like to such an extent as to form a coherent pellet which remains intact as it is pyrolyzed in a vertical shaft furnace.
During the past several years considerable effort has gone into developing new technology for disposing of solid refuse in an environmentally acceptable manner and at the same time recovering, insofar as possible, the useful resources contained therein. One such process is described in U.S.P.~ No. 3,729,298 wherein solid refuse is fed directly into a vertical shaft furnace in which the combustible por-tion of the refuse is pyrolized - principally to a fuel gas consisting of carbon monoxide and hydrogen - and in which the uncombustible portion of the refuse is fluidized to molten metal and slag.
An improvement on the process described in the above men~ioned U.S. patent is described and claimed by J. E. Anderson in U.S. Patent No. 4,042,345, issued August 20 16, 1977. This process requires that the refuse be compacted into pellets that are sufficiently strong to remain intact as they move down through the drying and pyrolysis zones of the furnace. Anderson has found that in order to have a refuse pellet which is sufficiently strong to remain coherent, i.e. intact, his process

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requires that it have a density greater than that given by the equation:

(100-0.8A) where:
D = the density of the pellet (lbs./ft.3) A = percent inorganics in the refuse pellet.
Anderson has also discovered that if the refuse pellets are sufficiently dense to have the necessary struc-tural strength, then the drying and pyrolysi~ reactions become limited by the rate of heat transfer and diffusion within the pellets, and that in order to obtain a satis-factory process, the ratio of the surface area to the volume of the pellets should be greater than that given by the equation:
\0.625 R = 15 H ) where:
R = the surface to volume ratio (ft.2/ft.3) H = the height of the refuse bed in the furnace (ft.) -~ G = the refuse feed rate (tons/day/ft.2 of furnace cross-sectional area).
OBJECTS
- It is an object of the present invention to provide -- apparatus capable of compacting refuse into individual pellets which have sufficient strength to remain intact while being consumed in a shaft furnace or similar device.

It is another object of this invention to provide a compacting pelletizer which is capable of feeding coherent refuse pellets into a furance at a controllable rate and in such manner as to prevent the escape of flammable and toxic gases from the furnace through its feed inlet port.
It is still another object of this invention to provide a device for compacting shredded refuse into coherent pellets of a suitable size and with such density and strength as to remain substantially intact while being converted in-a shaft furnace to a useful fuel gas and a fluid inorganic slag or residue.
: SUMMARY OF THE INVENTION
The above and other objects which will become apparent to those skilled in the art from the detailed dis-closure and claims to follow are achieved by the present invention which comprises:
apparatus ~capable of producing pellets of compacted refuse having a density of at least 20 lbs./ft.3 comprising:
(1) a cylindrical tube, having a compacted chamber whose length is shorter than the shortest critical length for th~e refuse to be pelletized, said tube being pro-vided near the inlet end thereof with a feed port in the side wall of the tube, the opposite open end of said tube con-stituting the discharge port, (2) a feed hopper for the refuse to be compacted having an outlet port communicating with the inlet port of said tube, 4.

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(3) a reciprocating driven ram located in the inlet end of said tube and axially aligned therewith, the perimeter of said ram being in sliding contact with the inner surface of said tube, and capable of exerting a pressure of at least 200 psi on each forward stroke of the ram, and

(4) means for restricting the flow of refuse through said tube, such that the degree (i.e. the amount) of restriction is variable in response to changes in the force required to advance the column of compacted refuse in the tube.
Preferably, said apparatus also comprises:

(5) means for closing the tube feed port in sequenced timing with said reciprocating ram, such that the tube feed port is open when the ram is in its retracted posi-tion and closed while the ram is moving forward past the tube feed port.
The preferred structure of said restricting means comprises a plurality of axially elongated leaves, each of which constitutes a flush section of tube wall, flexibly attached at its upstream end to the tube, movable radially inward or outward of the tube axis at its downstream end, and having edge surfaces parallel to each other.
A preferred embodiment of the invention comprises two parallel cylindrical tubes whose respective reed ports communicate with a single feed hopper, wherein the respective rams within each tube operate in tandem, such that when one is retracted the other is extended. It is also preferred that the means for closing the feed ports constitutes a power ~058445 driven rotating vane, located in the base of the hopper which is o~erable in timed sequence with each of the reciprocating rams. Means for dewatering the refuse, located in the downstream portion of the tube are also preferred, as is the provision of a gas tight housing to enclose the restrictors and the dewatering means, thereby rendering the pelletizer capable of feeding pellets directly to a refuse disposal furnace in a gas-tight manner.
THE DRAWINGS
Figure 1 is a side view in partial cross-section illustrating the preferred double barreled embodiment of the apparatus which constitutes the present invention.
Figure 2 is a top view of Figure 1.
- Figure 3 is an enlargement of the upper portion of the dewatering means used in the apparatus of Figures 1 and 2.
Figure 4 is a diagramma~ic side view illustrating the manner in which the apparatus of the present invention functions to provide a dense pellet of shredded refuse.
Figure 5 is a front view in cross-section taken along line 5-5 in Figure 1 illustrating operation of the vane.
Figure 6 is an enlarged longitudinal view in partial cross-section illustrating the restrictor assem~ly shown in Figure 1. -~
Figure 7 is a cross-section of the restrictor

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~ 058445 assembly shown in Figure 6 taken along line 7-7.
Figure 8 is a cross-section of the tube having circumferential cuts which can be made in the i~side sur-face of the tube to reduce friction.
DETAILED DESCRIPTION
Figures 1 and 2 disclose in side and top views, respectively, the double barreled pelletizing refuse feeder which constitutes the preferred embodiment of the present invention. The apparatus consists of two identical parallel cylindrical tubes 1 and 1' into which refuse is fed from a common hopper 3 through feed inlet ports 4 and 4' located in the tops of the respective tubes l and 1'. The refuse is directed into the tubes and contained therein with the aid of a rotating vane 5 (more clearly seen in Figure 5).
Tubes 1 nd 1' are most conveniently constructed from a plurality of flanged sections of steel tubing conventionally bolted together. The flanged back end of tubes 1 and 1' are bolted to hydraulic cylinders 2 and 2' which drive rams - (not shown) axially aligned within the feed ends of each tube. The perimeter of each ram is in sliding contact with the inner surface of each tube. Each ram is capable of exerting a pressure in excess of 100~ psi upon the refuse in the tube, thereby being capable of compressing the refuse to a density of at least 20 lbs.tft.3 and of pushi~g the compacted refuse through the tube and out the discharge - ports 6 and 6'. The pelletizer apparatus rests upon a base frame 7 to which the pelletizer is firmly secured through a ~.. ~
10584~5 plurality of supports 8. The rota~ing vane 5 is driven by means of a conventional ~rive means 9. Means for dewatering the refuse 10 and 11 are located near the downstream end of the tubes. The upper portion of these are shown in greater detail in Figure 3. The variable restrictor assembly 12, which constitutes a section of each of the tubes 1 and 1', is disclosed in greater detail in Figures 6 and 7. The dis-charge end of the restrictor assembly 12 communicates with the discharge conduit 13 the diameter of which is wider than that of tube 1.
In order to provide a vapor tight seal between the pelletizer and a furnace, a flexible sleeve 15 surrounds tubes 1 and 1', connecting the feed port of a furnace and the housing 16 which surrounds the forward end of the pelletizer. Re3trictor assembly 12 as well as the dewatering - means 10 and 11 are lo~ated inside of the vapor tight housing 16 in order to prevent gases from escaping to the atmosphere.
Housing 16 is provided with a drainage plug 17 through which any accumulation of liquid may be either periodically dis-charged through a suitable valve, or continuously discharged through a suitable water leg. For purposes of safety a rupture diaphragm 18 is provided in ~he top of housing 16.
Although any type of motive means, such as pneumatic pump or electric motor could be used to power the rams, both - cylinders 2 and 2' are preferably powered by a single hydraulic power unit. The two parallel tubes operate in tandem. As . . .

1~ 58 44 5 the ram in one pelletizing tube moves back, the other moves forward, so that they are always about 180 out of phase.
This relationship permits sharing of a common feed hopper, rotating vane and hydraulic power system, which considerably reduce~ the complexity and cost of the apparatus.
While the pelletizer shown in Figures 1 and 2 is in the horizontal position, it cou~ be operated in an inclined or vertical position if this were found to be desirable or convenient. Thus, while hopper 3 as shown in the drawings communicates with tubes 1 and 1' through feed ports 4 and 4' located in the top sides of the tubes' side walls, the hopper could be made so as to communicate with the tubes in the vertical position by placing the dis-charge ports from the hopper in its side walls. In such case the feed ports to the tubes would be located in the sides of the side walls of the tubes. Under these circum-stances, the rotating vane 5 could either be mounted in the base of the hopper, with the axis of its drive shaft placed vertically, or a different directing mechanism could be used to precompact and feed the refuse into the tubes. A side-to-side push type of feede~ which would alternately feed one tube and then the other could be used for this purpose.
It should also be noted that while the pelletizer of this invention is preferably used in direct communication with a furnace refuse feed opening, it does not have to be used in such manner. That is, the pellets do not have to be fed directly from the pelletizer into the furnace. It would, for example, be possible to mount the pelletizer on the ground, to transport the pellets either immediately or some time later to the top of a shaft furnace, and then feed the pellets into the furnace through a gas tight feeding mechanism. One of the advantages of the pelletiæer of the present invention, however, is that it avoids the need for additional feeding mechanism, since the pelletizer is capable of feeding the compacted refuse pellets directly into the furnace without permitting any gases to escape into the atmosphere from the furnace through the pelletizer.
Figure 3 is an enlarged view in cross-section of the upper part of a preferred dewatering means 10 and 11.
This consists of three plates 19 located between the flanged ~ ends of two tube sections 20 and 21 bolted together. Plates ; 19 are each formed on one side only with outwardly flared grooves 22 so that when placed with the grooved side of one plate opposite the flat side of another plate Yith small spacers 23 between them, a plurality of outwardly flared spaces 24 are farmed permitting water to drain through. Drainage means may be provided by any other suitable structure which permits the liquid to escape from inside the tube. However, it is important that there be a sufficient number of ports to permit most of the liquid and air compressed within the refuse by the compaction to be expelled and drained out. In addi-tion, the drainage ports must be constructed in such manner as to flare outward, since this will prevent the ports from becoming plugged by the refuse. A suitable port opening 25 ' 10.

is l/32 wide and flared out to a 3/32" width.
Figure 4 shows diagrammatically how the present apparatus functions to produce the pellets P of shredded refuse. When some loose refuse R is in front of the ram 41 and above the portion swept by the forward stroke of the ram, the vane 5 (shown in Figure 5) pushes the refuse down into the space 42 swept by the ram. The vane holds the shredded refuse within the tube space 42 during the time the ram travels through the portion between points 0 and A
of the tube beneath hopper 3. ~s the ram continues moving to the right, all of the material in the volume between points A and B becomes confined, and the further the ram travels to the right the more the refuse in the tube becomes compressed. When the newly compacted refuse is pressed hard enough against an existing slug S of compacted refuse to the right of it, the entire column of compacted refuse will move to the right. The force required to move this material is determined by wall friction and by the action of the restric-tors 12 in the tube section between points C and D. The sum of the fric~ion produced by the wall and the restrictors determine the compaction pressure the ram will exert on the refuse newly added into the tube.
~ The column of refuse that moves to the right con-- - sists of the above mentioned confined material in the tube between points ~ and D, as well as the material fitting loosely in the discharge conduit 13 between points D and E.
The dense pellet P which comes out the end of the conduit at point E will fall into the furnace. Although the compaction process produces considerable cohesion within the mass of refuse that constitutes one single stroke of the ram, i.e.
one slug, there is very little bonding between successive slugs or the resultant pellets. Thus, as t'ne material is dis-charged from conduit 13 at point E, it rëadily breaks off at the interface boundaries between each pellet. Hence, once steady state operation is reached, each stroke of the ram will pro-duce on the average one pellet of compacted refuse discharged 10 from the tube. It is to be understood that the term "slug" ;~
as used herein is intended to mean the mass of refuse squeezed together by one stroke of the ram. As the slugs are moved down the tube over a finite period of time under sustained ;~
pressure and dewatered they become more coherent, emerging at the end of the tube as strong "p~eIIets'r.~
As noted before, compaction of each new slug of refuse is achieved by squeezing it between the ram and the previously compacted slug downstream. The compaction pressure is the pressure required to move the column of compacted refuse (slugs and pellets) down the tube. In order to control this pressure it becomes necessary to maintain the amount of resistance to motion within a desired range. It has been found that for a given compaction pressure, increasing the length of the column of compacted refuse increases the pres-sure required to push the refuse down the tube. It has also been found that for a given length of the column of compacted refuse, increasing the compaction pressure increases the 12.

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force required to push said column down the tube. These two factors lead to the existence of what may be designated as a "critical length" of compacted refuse. That is, the length of compacted refuse slugs in the compacted chamber (section B-D) of the tube, for which the pressure required to move said compacted refuse is just equal to the pressure used to form the slugs. The "critical length", however, is not constant, since it is a function of the refuse character-istics; for example, it is generally shorter for dry refuse than for wet refuse. It is also shorter for tubes with a smaller diameter than for tubes with a large diameter.
The effect of the phenomenon referred to above may be illustrated by considering a pelletizer operating at the desired compaction pressure with a column of compacted refuse which is at its critical length. As long as conditions remain constant, the refuse will continue to be compressed to the desired pressure; that is, the pressure required to just move the column of compacted refuse down the tube. However, this condition is unstable since it will be upset by very slight variations in operating conditions. For example, if the refuse becomes drier, increasing the wall friction, it will increase the compaction pressure on the next slug formed. This will, in turn, further increase the force required to move the column, because higher compaction pressure causes higher wall friction, and hence further increase the compaction pressure on the following slug formed. This chain reaction of increasing 13.

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10584~5 compaction pressure will continue until the compaction capacity of the apparatus is reached, when it will become jammed. The increased wall friction noted above has the effect of decreas-ing the critical length. The actual length was then greater than the critical length. The reverse situation will occur if the refuse being fed becomes slightly wetter, resulting in progressively dropping compaction pressure until coherent pellets cease to be formed.
The prior art has attempted to solve these problems by providing additional resistance to motion, over and above that provided by wall friction by placing fixed restrictors in the tube at or near its discharge end. Such restrictors have consisted of one or more objects protruding into the ., tube, or of a reduction in tube diameter at the discharge end. However, from a control point of view, such restrictors are simply equivalent to additional tube length, and conse-quently do not solve the problem, since the same unstable compacting condition as described above still exists.
It has been discovered that in order to provide apparatus which will operate stably on material which varies almost constantly in composition or moi~ture content, it is necessary, if operating with a constant ram stroke, to make the length of the compacted chamber of the tube (B-D in Figure 4 if the restrictors open only to the size of the tube and B-C in case the restrictors can open suficiently wider than the tube diameter so that they offer very little resistance to pellet motion) shorter than the shortest "critical length"

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10 5~ 4~ 5 for the material to be pelletized, and to provide variable resistance to the flow through the tube with adjustable restrictors which are responsive to changing condi~ions, so as to remain within the desired range of compaction pressure.
The "critical length" must be determined experimentally for the particular material being compacted.
The term "tube" is used throughout the present specification and claims in a generic sense to include the entire cylindrical barrel, i.e., the length X-E in Figure 4.
However, it should be noted that the tube has six distinct functional sections. These are best seen in Figure 4. Sec-tion X-0 is the ram housing, section 0-A is the feed section, section A-B is the compacting section, B-C is the compacted section~ C-D is the restrictor section, and D-E is the (wider) conduit section. Sections B-C plus C-D, i.e. B-D constitutes the compacted chamber of the tube. It is this chamber or section (B-D) which has the "critical length" discussed above.
The practical effect of the "critical length" is that if the compacted chamber is made longer than the shortest "critical length" for the refuse being compacted, it will become jammed.
In such case, the refuse will not come out the discharge end of the tube regardless of the pressure ~pplied, since increas-ing the pressure will only jam the refuse into the tube harder.
The apparatus described above has been designed especially for pelletizing shredded municipal refuse. It has been found that in such material the shortest "critical length"
for a tube with an inside diameter of 13" is about 5 1/2 ft.

99~9 ~0584~5 This is the length of the tube containing the compacted refuse, i.e. from the point just beyond the end of the ram stroke to the discharge end of the restrictor assembly (equivalent to the distance B-D in Figure 4). For similar municipal refuse it has been found that for a tube having a 4" inside diameter, the shortest "critical length" is about 19". Hence, it appears that for shredded municipal refuse the ratio of the shortest "critical length" to the inside diameter of the tube is approximately 5:1. For the above two cases, the ratios are - 10 5.1:1 and 4.75:1, respectively.
-~ It has been ~ und that the density of shredded refuse varies depending upon the composition of the refuse, its mois-ture content, and the degree to which the refuse has been shredded. The density of the pellets depends upon the same parameters as the shredded refuse from which it is made, as well as on the compaction pressure and on the length of time for which the compaction pressure is applied to the pellet.
For ordinary municipal refuse, with most of the ferrous metal removed, the average density of shredded municipal refuse is about 4 lbs. per cu. ft. A typical pellet useful in the Anderson process has an average density of about 40 lbs. per cu. ft. as it is formed in the pelletizer. Consequently, the pelletizing apparatus must be able to produce, on the average, a ten fold densification of the refuse.
It has been found preferable to produce pellets with lengths approximating the diameter of the pellet. The useful range of pellet lengths, however, is from about 1/3 16.

" ~
~0 ~8 44 5 the pellet diameter to about 1.5 times the pellet diameter.
If shredded refuse at a density of 4#/cu.ft. is put into the tube space between points 0-A ~n Figure 4, transferred ; -at this density into the enclosed space A-B, and then com- ~
presset to a density of 40#/cu.ft to make a slug one diameter ~;
long, both lengths 0-A and A-B must be 10 diameters long, ~-. ; , .
and the ram stroke must then be 20 diameters long. Such a long ram stroke is impractical and inef~icient. It has been found tha~ these lengths can be reduced considerably by slightly pre-compressing ehe re~use into ~e volume in front of the ram and preventing it from being pushed upward and out of th~ tube as the ram moves to the right. This is -~
preferably~accomplished by a vane $ as shown an Figure 5.
Figure 5 discloses tubes 1 and 1' commu~icating ~ -;
with a common hopper 3 through feed port~ 17 and 17' located in the top of the tubes' side walls. Vane 5 is caused ~o reciprocate from left to right as indicated by the arraw through drive shaft 9. When vane 5 is in the right hand position, re~use is directed to all into tube 1. There~
af~er vane 5 swings to the left, thereby directing the refuse into tube 1' and slightly compressing or precompacting the refuse by pushing it down into the tube.~ Vane S remains in this position to keep tube 1 closed whlle the ram 41 travels forward through the portion of the tube (0-A in Figure 4) containing the feed port 17. If vane 5 were not to keep the feed port 17 closed in tube 1, the refuse would tend ~o be pushed back up into hopper 3 when the ram 41 . .. . .

l()S8445 began to move forward. Vane 5 functions in timed sequence with the reciprocating rams such that the tube feed ports remain closed by the vane as the rams move forward and are open while the ram is in its retracted position, thus per-mitting refuse to fill the space 42 in the tube in front of the ram. Vane S serves still another function, namely to precompact the refuse. Since loose refuse fills space 43 in hopper 3 above the feed ports, most of the refuse in space 43 will be pushed down into space 42 as the vane closes, thereby increasing the qu~ntity and consequently the density of the refuse in space 42. The effect of this precompacting is to increase the amount of refuse which will be compacted by each stroke of the ram, thus increasing the compacting efficiency and capacity of the pelletizer. Refuse that hangs partially in and partially out of the zone swept by the ram should be sheared when the ram passes position A of Figure 4 to keep it from being wedged between the ram and the tube. This is made easier by securing a set of cutting teeth 44 around the entire periphery of the rams 41 and 41'.
In order to provide coherent pellets, the pelletizer requires restrictors which act without breaking up the pellets.
This can be accomplished by constructing the restrictors so that they form a smocth continuation of the inner surface of the tube; for example, from a cylinder to a smooth gradually tapered truncated cone. In addition, the degree of restriction produced by the restrictors must be variable and rapidly responsive to changes in compaction pressure so as to keep the 18 .

lOS8~5 compaction pressure within the desired preset range. To achieve these results, the present restrictors are controlled such that if the ram pressure required to push the column of compressed refuse through the tube is greater than a predeter-mined pressure, the restrictors are caused to open slightly;
while if the ram pressure is less than a lower predetermined pressure, the restrictors are caused to close down slightly.
If the ram pressure is within the preset range, no change is made in the position of the restrictors. Adjustment of the restrictors may be made automatically and by power dri~en means. The restrictors are also made such that in their fully - open position they form an outward flared cone. This is an important characteristic of the present invention, since in this position the restric~ors cause less frictional resistance to the flow of refuse than does a straight tube of equal length.
Figures 6 and 7 show the preferred structure of ~
~ the restrictor assembly of the present invention. The restric-tor assembly 12 is made up of a 2 ft. length of the tube 1, which has an inside diameter of 13 inches. The restrictor assembly 12 consists of eight movable restrictor leaives 38 ; which function together to comprise the restrictor means.
Each leaf 38 has been cut from a section 50 of tube 1 so that it forms a smooth continuation of the inside tube wall.
Hinges for the leaves 38 may be made by milling eight grooves 25 around the outside surface of tube section 50. A like number of grooves 27 are machined around the inside surface 19 .

" lOS8~5 of the steel tube opposite slots 25 so that the grooves are parallel to each other, leaving only a thin flexible section - 28 of the original tube thickness between grooves 25 and 27.
The resultant structure can be seen more clearly in Figure 7, which is a cross-section taken alo~g line 7-7 of Figure 6.
A plurality of parallel cuts 29 and 30 are made axially through tube section 50 down to the end of the flexible section 28, thereby producing the leaves 38. Since the - thin sections 28 are flexible, the leaves are free to be moved radially inward or outward by exerting a force on their downstream ends. It is important that each pair of cuts 29 and 30, and consequently each pair of edges of leaves 38, be parallel to each other. This is necessary because as the downstream end of a leaf 38 moves in or out, the clearance between each leaf and the stationary portions 31 left between each of the leaves does not change. This constant clearance avoids packing of refuse and consequent jamming which would result if radial cuts were made. It can be seen from Figure

7 that by making eight leaves 38 from the tube section 50, will leave eight truncated cone shaped sections 31 between the leaves. These sections 31 remain an integral part of the tube section 50.
- The construction described above is preferred;
however, it will be apparent to those skilled in the art that the restrictor assembly 12 could be modified either in design or method of fabrication without departing from the basic concepts of the present invention. For example, the .
20 .

1~ 58 4 4 5 leaves 38 can be fabricated from metal other than from the tube section itself, and these could be attached at the lower end to the tube by mechanical hinges instead of the flexible steel section 28.
The manner in which leaves 38 are moved in or out can best be seen by reference to Figure 6. A set of eight blocks 33 are each fixedly attached to the downstream end of each leaf 38 at the eight grooves 26 which have been cut into each leaf. A pair of links 32 (only one is seen) are lQ pivotally attached to each side of each block 33 at one end and to a ring 36, ~hrough blocks 37 fixedly a~tached to ring 36, at their other end. Ring 36 is in sliding contact with ring 39 which is fixedly attached to the stationary secti~ns 31 between the leaves. A spacer (not shown) may be used in ~etween ring 39 and the fixed member 31 in order to make it - possible for the leaves to be movable in the radially outward - direction. Ring 36 is also fixedly attached at three equally spaced locations around its outer circumference to three nuts 34 (only two are seen) which are threaded on the inside.
Threaded rods 35 engage the inside threads of each nut 34.
Rods 35 while rotatable in place by a drive means (not shown), are attached so as to be unable to mcve from left to right.
Consequently, rotation of rods 35 will cause ring 36 to be moved from left to right in Figure 6. The three rods 35 are geared together and commonly driven in order to insure that ring 36 always remains in a plane perpendicular to the axis of the tube 50. As ring 36 is caused to move toward the right, ~ oS84~S
it will exert a force through links 32 upon each of the blocks 33 and hence upon each leaf 38, causing the leaves to be moved radially inward. By reversing the direction of rotation of rods 35, ring 36 will be pulled toward the left and leaves 38 will conse~uently be pulled radially out-ward. Ring 36 is keyed (not shown) to stationary ring 39 in order to prevent it from rotating relative to tube section 50, thereby insuring that blocks 33 and 37 and hence links 32 remain in proper alignment.
l~ As pointed out above, it is desirable to have the column of compacted refuse as long as possible in order to obtain the longest possible residence time, and hence stronger pellets. Since it is not possible to increase this length arbitrarily beyond the critical length, as previously defined, because the pelletizer will then become jammed, one way of increasing the actual length of the tube without increasing friction, is to cut circumferential grooves into the inner surface of the tube. Figure 8 shows a longitudinal cross-section of a piece of tube 82 into which a plurality of slanted cuts 81 have been made on the inside surface. The arrow indicates the direction of refuse flow. Cuts 81 may be spaced about 3/8" apart, thereby leaving 3/8" long flat surfaces 83 on the inside of the tube. ~ach of the cuts 81 is about 1/8" deep at its deepest point. The refuse pellets are sufficiently solid so that they bridge most of the grooves 81 and bear mostly on the flat surfaces 83, i.e. the ungrooved surface. This reduction in bearing area per unit length of g969 10584~5 tube reduces the total Erictional force per unit length of tube. While it might be assumed that the increased unit loading on the ungrooved surface would just counteract the decreased areal experiments have shown that this does not occur, and that reduced fricti onal drag is obtained.

23.

Claims (8)

WHAT IS CLAIMED IS:

1. Apparatus capable of producing pellets of com-pacted refuse having a density of at least 20 lbs/ft.3 com-prising:
(1) a cylindrical tube of uniform diameter com-prising a ram housing section, a feed section, a compacting section, a compacted section and a restrictor section, said tube being provided in the feed section with a feed port in its side wall, (2) a feed hopper for the refuse to be compacted having an outlet port communicating with the feed port of said tube, (3) a reciprocating driven ram located in the ram housing section of said tube and axially aligned therewith, the perimeter of said ram being in sliding contact with the inner surface of said tube and capable of exerting a pressure of at least 200 psi on each forward stroke of the ram, and (4) means located in the restrictor section of said tube for variably restricting the flow of refuse comprising a plurality of axially elongated leaves, each leaf constituting a flush section of the tube wall and being flexibly attached at its upstream end to the tube, characterized by:
(a) the side edge surface of each leaf being parallel to each other, (b) each leaf being located symmetrically around the circumference of said tube and being separated from each adjacent leaf by stationary sections that are an integral part of the tube, (c) each leaf constituting a flush section of the tube wall flexibly attached at its upstream end to the tube, and (d) means for positively moving each of said leaves uniformly toward and away from the tube axis in response to changes in the force required to advance the column of compacted refuse in the tube.

2. Apparatus as in claim 1, comprising two parallel cylindrical tubes whose respective feed ports communicate with a single feed hopper, and wherein the respective rams within each tube operate in tandem such that when one is retracted the other is extended.

3. The apparatus of claim 1, wherein said means for restricting the flow of refuse is controlled on each forward stroke of the ram.

4. Apparatus as in claim 2, additionally comprising means for closing the feed ports, said means constituting a power driven rotating vane, located in the base of the hopper, and operable in timed sequence with each of said reciprocating rams.

5. Apparatus as in claim 4, which additionally com-prises means for dewatering the refuse, said means being located in the downstream portion of the tube.

6. Apparatus as in claim 5, rendered capable of feeding said pellets directly into a refuse disposal furnace in a gas tight manner, which additionally comprises a gas tight housing enclosing said means for restricting the flow of refuse said means for dewatering, said housing communicating with a furnace feed port.

7. Apparatus as in claim 4, wherein the inside sur-face of said tube is provided with a plurality of circumferential depressions to reduce friction between the refuse and the inside surface of said tube.

8. The apparatus of claim 1, wherein said restrictor leaves are capable in their fully open position of forming an outwardly flared cone.