Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
2.
~,
13~
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requires that it have a density greater than that given by
the equation:
D - 2000
(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.
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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
9969
~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
6~
9969
~ 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
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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
. . .
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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
9969
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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.
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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
9969
1058445
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.
9969
0 58 ~ ~
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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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"
14.
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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.
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~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
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~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
. .. . .
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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 .
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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 .
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" 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 .
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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,
9969
~ 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.
