TREATMENT OF SCRAP

TRAITEMENT DE RUBUTS

English Abstract

ABSTRACT OF INVENTION

A process for treating scrap comprising the steps of wetting
the scrap, passing the wetted scrap through a freezing tunnel,
the wetted scrap being contacted with a gaseous fluid in a
first region of the tunnel so as to precool the scrap, the
scrap being cooled in a second region of the tunnel to a
level at which at least a portion of the scrap becomes brittle,
said cooling being effected by the introduction of cryogenic
material into the second region of the tunnel, removing the
scrap from the tunnel, and subjecting the scrap to mechanical
fragmentation while it is at least partially brittle.

Claims

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:

1. A process for treating scrap comprising the steps of
wetting the scrap, passing the wetted scrap through a freezing
tunnel, the wetted scrap being contacted with a gaseous fluid
in a first region of the tunnel so as to precool the scrap,
the scrap being cooled in a second region of the tunnel to a
level at which at least a portion of the scrap becomes
brittle, said cooling being effected by the introduction of
cryogenic material into the second region of the tunnel,
removing the scrap from the tunnel, and subjecting the scrap
to mechanical fragmentation while it is at least partially
brittle.

2. A process for treating scrap as claimed in claim 1
wherein the scrap is reduced into a plurality of portions
before being passed through the freezing tunnel.

3. A process for treating scrap as claimed in claim 2
wherein said reduction of the scrap is effected in a primary
breaker, liquid being sprayed into the primary breaker for
effecting said wetting of the scrap.

4. A process for treating scrap as claimed in claim 1,
2 or 3 wherein said mechanical fragmentation causes the scrap
to break into separate fragments of each of the constituents
of the scrap.

5. A process for treating scrap as claimed in claim 1,
2 or 3 wherein said mechanical framentation causes the scrap
to break into separate fragments of each of the constituents
of the scrap and the fragments resulting from said mechanical
fragmentation are subjected to a separation process which
results in the constituents being removed separately.

6. A process for treating scrap as claimed in claim 1,
2 or 3 wherein said mechanical framentation causes the scrap
to break into separate fragments of each of the constituents

11

of the scrap and the cryogenic material comprises liquid
nitrogen.

7. A process for treating scrap as claimed in claim 1,
2 or 3 wherein said mechanical framentation causes the scrap
to break into separate fragments of each of the constituents
of the scrap and the fragments resulting from said mechanical
fragmentation are subjected to a separation process which
results in the constituents being removed separately and the
cryogenic material comprises liquid nitrogen.

8. A process for the treating scrap as claimed in claim
1, 2 or 3 wherein the cryogenic material comprises cryogenic
carbon dioxide.

9. A process for the treating scrap as claimed in claim
1, 2 or 3 wherein the cryogenic material comprises cryogenic
carbon dioxide said mechanical fragmentation causes the scrap
to break into separate fragments of each of the constituents
of the scrap.

10. A process for the treating scrap as claimed in claim
1, 2 or 3 wherein the cryogenic material comprises cryogenic
carbon dioxide and the fragments resulting from said
mechanical fragmentation are subjected to a separation process
which results in the constituents being removed separately.

11. A process for the treating scrap as claimed in claim
1, 2 or 3 wherein the cryogenic material comprises cryogenic
carbon dioxide and liquid nitrogen.

12. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises rubber-based articles.

13. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises rubber-based articles said
mechanical fragmentation causes the scrap to break into
separate fragments of each of the constituents of the scrap.

14. A process for treating scrap as claimed in claim 1,


12

2 or 3 wherein the scrap comprises rubber-based articles and
the fragments resulting from said mechanical fragmentation are
subjected to a separation process which results in the
constituents being removed separately.

15. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises rubber-based articles and
the cryogenic material comprised liquid nitrogen.

16. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises reinforced rubber tyres.

17. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises reinforced rubber tyres
said mechanical fragmentation causes the scrap to break into
separate fragments of each of the constituents of the scrap.

18. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises reinforced rubber tyres and
the fragments resulting from said mechanical fragmentation are
subjected to a separation process which results in the
constituents being removed separately.

19. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises reinforced rubber tyres and
the cryogenic material comprised liquid nitrogen.

20. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises plastics-based articles.

21. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises plastics-based articles
said mechanical fragmentation causes the scrap to break into
separate fragments of each of the constituents of the scrap.

22. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises plastics-based articles and
the fragments resulting from said mechanical fragmentation are
subjected to a separation process which results in the
constituents being removed separately.


13

23. A process for treating scrap as claimed in claim 1,
2 or 3 wherein the scrap comprises plastics-based articles and
the cryogenic material comprised liquid nitrogen.

24. A process for treating a reinforced rubber tyre
comprising the steps of reducing the tyre into a plurality of
tyre portions, wetting said tyre protions, passing the wetted
tyre portions through a freezing tunnel, the wetted tyre
portions being contacted with a gaseous fluid in a first
region of the tunnel so as to precool said tyre portions, the
tyre portions being cooled in a second region of the tunnel to
a level at which at least the rubber constituent of the tyre
becomes brittle, said cooling being effected by the
introduction of cryogenic material in the second region of the
tunnel, removing the tyre portions from the freezing tunnel,
subjecting the tyre portions to mechanical fragmentation while
said rubber constituent is brittle, the mechanical
fragmentation process causing the scrap to break into separate
fragments of each of the constituents of the tyre, and
subjecting the fragments to a separation process which effects
separation of said constituents.

25. A process for treating a reinforced rubber tyre as
claimed in claim 24 wherein the tyre portions are subjected to
a magnetic separation process before being passed through the
freezing tunnel, said magnetic separation process being
intended to remove any exposed relatively large metallic
constituents of the tyre.

26. A process for treating a reinforced rubber tyre as
claimed in claim 24 wherein said separation process comprises
the steps of passing the tyre fragments through a first screen
for separating relatively large fragments of metallic
constituent and relatively large fragments of fabric
constituent from the tyre fragments, subjecting the fragments
which passed through said screen to a magnetic separation
process for removing all remaining fragments of metallic
constituent form the fragments, passing the fragments
remaining after said magnetic separation process through a
gravity separation stage for separating said fragments into


14


two grades one being a relatively fine grade and the other
being a relatively coarse grade, the coarse grade containing
only fragments of rubber constituent, passing the coarse grade
of fragments through a sizing stage at which oversize coarse
fragments are returned for reprocessing, the remaining coarse
fragments being divided into a plurality of fractions, the
fragments contained in the fine grade being passed through a
second screen for separating fragments of rubber constituent
and fragments of fabric constituent, and subsequently passing
the fine rubber constituents through said sizing stage for
dividing the fine rubber constituent into a plurality of
fractions.

27. A process for treating a reinforced rubber tyre as
claimed in claim 25 wherein said separation process comprises
the steps of passing the tyre fragments through a first screen
for separating relatively large fragments of metallic
constituent and relatively large fragments of fabric
constituent from the tyre fragments subjecting the fragments
which passed through said screen to a magnetic separation
process for removing all remaining fragments of
metallic constituent from the fragments, passing the fragments
remaining after said magnetic separation process through a
gravity separation stage for separating said fragments into
two grades one being a relatively fine grade and the other
being a relatively coarse grade, the coarse grade containing
only fragments of rubber constituent, passing the coarse grade
of fragments through a sizing stage at which oversize coarse
fragments are returned for reprocessing, the remaining coarse
fragments being divided into a plurality of fractions, the
fragments contained in the fine grade being passed through a
second screen for separating fragments of rubber constituent
and fragments of fabric constituent, and subsequently passing
the fine rubber constituents through said sizing stage for
dividing the fine rubber constituent into a plurality of
fractions.

Description

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TI~IS lNVENTION relatcs to tllc trcatmcnt of scrap.

The inyention is particularly applicable for the recovcry
of rubber from rubber-based scrap articles such as r~in-
forced rubber tyres and the recovery of plastics from
plastics-based scrap articlcs such as insulated wire and
the like.

It is known to treat scrap by cooling the scrap to below
the embrittlement temperature of at least a portion of
the scrap and then subjecting the scrap to mechanical
fragmentation whilst it is at least partially brittle.
The scrap is generally cooled by means of a cryogenic
material such as liquid nitrogen, the cryogenic material being
sprayed Into a freezing tunnel through which the scrap
is passed on a conveyor. Because of the cost of cryogenic
material used in such treatment processes, even marginal
savings in the quantity of cryogenic material consumed
per unit weight of scrap being processed results in a
significant decrease in the costs of processing said scrap.

It has now been found that the consumption of cryogenic
material per unit weight of scrap being processed may be
reduced by wetting the scrap and subjecting the wetted
scrap to a gaseous fluid stream as it passes through the
tunnel. This has the effect of precooling the scrap
before it is cooled to below the embrittlement temperature
of at least a portion thereof, thus allowing more
efficient use of the cryogenic material.

Cooling systems of the type wherein scrap is passed
through a freezing tunnel on a conveyor have an inherent
disadvantage in that the conveyor is cooled on each pass
30 through the tunnel. This leads to a greater consumption
of cryogenic material than otherwise would be required as a
portion of the refrigerant value of the cryogenic material
is wasted on cooling of the conveyor.

It is an object of this invention to provide a process
for treating scrap which provides for a more efficient

-3-
utili~ation of cryogcnic matcrial uscd in the coolin~ of thc
sc nap .

In one form the invention residcs in a process for trcating
scrap comprising the stcps of wetting the scrap, passing
the wetted scrap through a freezing tunnel, the wetted
scrap being contacted with a gaseous fluid in a first
region of the tunnel so as to precool the scrap, the
scrap being cooled in a second region of the tunnel to
a level at which at least a portion of the scrap becomes
brittle, said cooling being effected by the introduction
of cryogenic material into the second region of the tunnel,
removing the scrap from the tunnel, and subjecting the
scrap to mechanical fragmentation while it is at least
partially brittle.

It is preferred that said freezing tunnel comprises a
delivery passage defining said first region of the tunnel
and a freezing passage defining said second region of the
tunnel; the delivery passage being in communication with
one end of the freezing passage, said one end being the
20 scrap inlet end of the freezing passage, the other end of
the freezing passage being the scrap outlet end; the
freezing passage being defined by a rotatable casing dis-
posed such that on rotation thereof scrap is conveyed
along the freezing passage from the scrap inlet end to
the scrap outlet end; means for introducing cryogenic
material into the freezing passage at or near the scrap
outlet end thereof, and extraction means for extracting
the material from the freezing passage at or near the scrap
inlet end thereof, said extraction means being adapted to
30 induce a flow of gaseous fluid along the delivery passage
in a direction corresponding to that of incoming scrap.

It is preferred that the scrap is subjected to mechanical
fragmentation by means of a rotary hammer mill.

A preferred form of rotary hammer mill comprises a casing
defining a substantially cylindrical fragmentation
chamber, a roughened surface being provided on at least

1~3~
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a portion of tl~e peripl-cry of the ch.~ er, a rotor mou~ltcd
for rotation about the ccntral axis oi the fra6m~ntation
chamber, one or more hammer members mounted on the rotor,
inlet means for introdueing scrap into the fragmentation
ehamber, outlet means for removing fragmented scrap from
the fragmentation chamber, and an extraetion vacuum inten-
ded to be associated with said outlet means for at least
assisting in the removal of fragmented serap through said
outlet means.
The term "eryogenie material" is taken to include cryogenic
liquid, eryogenie gas, cryogenie solids and any combination
thereof.

The invention will be better understood by reference to
the following description of one specific embodiment.
The embodiment will be described in relation to the
treating of reinforced rubber tyres, but it should be
appreeiated that the invention is not limited to that
partieular applieation. The description will be made with
referenee to the aeeompanying drawings wherein:
-




Fig. 1 is a sehematie elevation of the layout of a
plant for tPeating scrap by the process according to
the invention;
Fig. 2 is a sehematic plan of the plant of Fig. 1;
Fig. 3 is a sectional elevation of one form of
freezing tunnel of the plant;
~ig. 4 is a eross-seetional elevation along the line
4-4 of Fig. 3; and
Fig. ~ is a sectional elevation of a preferred form
of rotary hammer mill for fragmenting the serap.

3 In the embodiment shown in the drawings scrap tyres awaiting
processing are stoekpiled in a eircular stockpile area 11.
When required for treatment the tyres are manually loaded
without regard to tyre size or form of construction onto
a mobile eonveyor 13 whieh delivers the tyres to a primary
breaker 15 eentrally loeated within the stockpile area 11.
The mobile conveyor 13 is capable of pivotal movement
about the primary breaker in a substantially hozizontal

113fi5~4
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planc; thlls thc position of thc mobilc cor.vcyol is ~ .Ible
of bcing selectively adjusted within the stockpilc area 11
in accordance with the loca'ion of tyrcs stocked within said
area.

The primary breaker 15 is intended to rc~uce each tyre to
manegeable portions for further processing. The primary
breaker also serves to expose relatively large metallic
constituents of each tyre such that said metallic consti-
tuents may be removed from the rcmainder of the reduced
tyre by a magnetic separation process at a later stage.
During the primary breaking operation liquid such as water
is sprayed into the primary breaker for effecting initial
cooling of the reduced tyres; the liquid additionally
serves to wash the reduced tyres. The wetted tyre portions
are delivered from the primary breaker, to a freezing tunnel
17 by means of a further conveyor 19. The further conveyor
19 conveys the tyre portions through one or more magnetic
separation stations 21 prior to delivery to the freezing
tunnel 17. The magnetic separation stations 21 are intended
to remove said relatively large metallic constituents of the
tyres which have been exposed by the primary breaker. As
the wetted tyre portions pass through the freezing tunnel 17
they are contacted by a gaseous fluid such as air in a first
region of the freezing tunnel so as to cause further precoo-
ling of the tyre portions. The tyre portions are then cooled
in a second region of the tunnel to a level at which at
least the rubber constituent of the tyres becomes brittle,
said cooling being effected by the introduction of cryogenic
material into said second region of the tunnel The cryoge-
nic material is preferably liquid nitrogen but any othersuitable cryogenic material such as cryogenic carbon dioxide
may be used. The tyre portions are discharged from the
freezing tunnel through a discharge chute 25 into fragmenta-
tion means 27 for mechanically fragmenting the tyre portions
while still at least partially brittle. The fragmentation
process causes the tyre portions to break into separate
fra~ments of each of the constituents of the tyre, the
fragments being of a suitable size for recovery.

113~594
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The fragments are subjected to a separation plOCCSS which
results in the various eonstituents of the tyres bcing
removed separately. In this embodiment the fragments
emerging from said fragmentation means 27 are ~clivcrcd
to sereening means 29 having a pair of screen decks.
~elatively large fragments of metallic eonstitllents and
relatively large fragments of fabric reinforccment are
confined on the first deck of the screening means.
The fragments passing through said first screen of the
screening means 29 are not passed through the second
screen at this stage. The separated metallic and fabric
fragments are deposited on a waste discharge conveyor 31.
The remaining fragments whieh have passed through the
first screen of the screening means 29 are subjected to
a magnetie separation process at a magnetic separation
station 33 where all remaining fragments of metallic
eonstituents are removed and subsequently discharged onto
the waste diseharge eonveyor 31. The fragments remaining
20 after the magnetic separation proeess are conveyed to a
gravity separator 35 the function of which is to separate
the fragments into two grades - fine and coarse; the
fine grade being fragments of a size less than approximate-
ly 700 microns and the coarse grade being fragments of a
size greater than approximately 700 microns. The frag-
ments of fabric reinforcements are in the fine grad e of
fragments, the coarse grade being only rubber fragments.
The coarse fragments are then conveyed to a sizing
apparatus 37 where oversize coarse fragments are returned
30 to the plant for reproeessing and the remainder of the
coarse fragments are divided into a number of fractions
aceording to size and bagged accordingly at a bagging
station 39. The fine grade of fragments which eontains
the fabric eonstituent is passed to the second sereen
of the sereening means 29 where the fragments of fabrie
constituent are separated from the fragments of rubber
eonstituent. The fabrie fragments are deposited on the
waste diseharge eonveyor 31 and the fine fragments of
rubber eonstituent proceed to the sizing apparatus 31.

113~594
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The freezing tunncl 17 preferably includcs a clclivcry
passage 41 one end of which is adapted to rcccive wettcd
scrap to be cooled. In this cmbodimcnt said further
conveyor 19 discharges the wettcd reduced tyrcs directly
into said one end of the delivery passage 41. The deli-
very passage communicates with one end of a freezing
passage 43, said end being the scrap inlet end of the
freezing passage; the other end of the freezing passage
being the scrap outlet end. The freezing passage 43 is
10 defined by a rotatable casing 45 formed such that on
rotation thereof scrap is conveyed along the freezing
passage from the scrap inlet end to the scrap outlet end.
In this instance the casing 45 is mounted on a support
structure 47 for rotation about an axis inclined
downwardly from the horizontal in the direction of travel
of scrap along the passage 43 from the inlet end to the
outlet end; said axis of rotation being indicated in the
drawings by the reference numeral 49. The inclination
of the axis of rotation is preferably adjustable. The
20 casing 45 is preferably of cylindrical construction with
the central longitudinal axis thereof being coincident
with the a~is of rotation 49 of the casing. The casing
is supported on rollers (not shown) provided on the suppor-
ting structure 47 and is rotated by a driving motor
(not shown) coupled to the casing by suitable means such
as a chain and sprocket drive. The casing is of a
double wall construction with the space between outer wall
51 and inner wall 53 ~eing filled with insulating material.
A plurality of longitudinally extending ribs 55 are mounted
30 in a spaced relationship around the periphery of the
freezing passage 43 on the inner wall 53. The ribs 55
cause tumbling of the scrap on rotation of the casing and
hence assist in conveying the scrap along the freezing
passage. A fluid tight seal is fitted at the joint
~etween the delivery passage 41 and freezing passage 43.
The delivery passage is disposed such that tyre portions
introduced therein are gravity fed therealong to the
freezing passage. Tyre portions delivered to the freezing
passage 43 are conveyed therealong on rotation of the
casing. Cryogenic material is introduced into the freezing

1~3~5~4
-8--
passage by way of one or more injcction lanccs 57 locatcd
at the scrap discharge end of the freezing passage. Thc
cryogenic material passes along the freezing passage in a
direction opposite to the direction in which the scrap
is conveyed. The rate of flow of the cryogcnic material is
preferably regulated such that on arriving at the scrap
inlet end of the freezing passage the cryogenic material has
fully utilized its refrigerant value. The spent material
is removed from the freezing tunnel through an outlet
passage 61 under the influence of suction means 63 such
as an extraction fan; in this instance the outlet passage
61 is in fluid communication with the delivery passage
41 at the end thereof adjacent the scrap inlet end of the
freezing passage 43. The suction means assists in inducing
the cryogenic material to pass along the freezing passage.
In addition the suction means induces a draught of air
along the delivery passage in the same direction as that
of incoming scrap. The air enters the delivery passage
from atmosphere through the scrap intake end of the
delivery passage. A baffle 67 is preferably provided to
ensure that induced air flows substantially along the full
length of the delivery passage before being extracted
from the freezing tunnel; in this case the baffle is
formed integrally with the peripheral wall of the delivery
passage. The induced air draught has the effect of pre-
cooling the wetted scrap as it passes along the delivery
passage due to the principle of latent heat of vaporisation.

In this embodiment the delivery passage 41 thus defines
said first region of the freezing tunnel 17 in which wetted
scrap is contacted with a gaseous fluid; similarly the
freezing passage 43 defines said second region of the
freezing tunnel in which the scrap is cooled to a level
at which at least a portion of the scrap becomes brittle.

The means 27 for mechanically fragmenting the scrap may
comprise a rotary hammer mill. A preferred form of
rotary hammer mill is shown in Fig. S of the drawings.
The hammer mill ~omprises a substantially cylindrical
fragmentation chamber 71 defined by a hammer mill casing

113~594

73. T11e lower portion o~ the pcriphcral wall of the
fragmentation chamber 71 is provided with a roughcned
surface 75; in this instance the roughened surface is
formed from a plurality of suitably shaped teeth 77. A
rotor 79 is mounted for rotation within the fragmentation
chamber 71 about an axis substantially coincidcnt with the
central longitudinal axis of the fragmentation chamber.
The rotor is adapted to be rotated by any suitable drive
means. A plurality of hammer members 81 are each pivotally
10 mounted at one end on the rotor for rotation about an
axis substantially parallel to the axis of rotation of
the rotor. The hammer members are adapted to extend
radially from the rotor 79 on rotation thereof such that
the outer ends of the hammer members pass in close
proximity.to the roughened surface 75. An inlet 83 is
provided in the hammer mill casing 73 for introducing
scrap into the fragmentation chamber. An outlet 85
is provided for removal of fragmented scrap from the
fragmentation chamber. The outlet 85 includes an outlet
20 passage 87 the central axis of which is substantially
parallel to the axis of rotation of the rotor. An extrac-
tion vacuum is associated with the outlet 85 so as to
at least assist in the removal of the fragmented scrap
through the outlet. The scrap makes a single pass through
the fragmentation chamber between the inlet 83 and outlet
85; the extraction vacuum associated with the outlet
ensures that there is no recirculation of fragmented
scrap. The extraction vacuum eliminates the need for the
hammer mill casing to be formed having a perforated wall
30 section or screen through which fragmented scrap may
leave the fragmentation chamber, thus eliminating the
problem of fragmented scrap blocking the perforated wall
sectiGn or screen.

As there is no recirculation of the fragmented scrap,
less power is required to drive the rotor of the hammer
mill of this invention than would be required for conven-
tional hammer ~ills.

~13~i594
-- ~o
~'hen processin6 scrap rcinforccd rubbcr tyrcs, t]lC ploccss
according to the prescnt invention has bcen foulld to
consume approximately o.6 kg of liquid nitrogen per 1.0
kg. of scrap input. This represcnts a significant rcduc-
tion in the consumption of liquid nitrogen in comparison
to other known methods which may use up to 1.0 kg. of
liquid nitrogen per 1.0 kg. of scrap input.