Note: Descriptions are shown in the official language in which they were submitted.
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Installation and Method for Separating
Substance Mixtures having Different Densities
Description
The quantity of waste materials of all kinds is becoming constantly greater
with the
increase in population. The disposal of the waste material in landfills and
the like brings
with it a great demand for land area. A location of a disposal depot near to a
residential
area is a source of nuisance due to ammonia vapors and endangers the health of
the
populace from the dissemination of fungus and spores. Incineration for the
destruction of
waste materials evolves COz as an ofd gas, besides producing slag, which in
turn, must
again be transported to a landfill. Insofar as waste materials of plastic are
concerned,
besides COz other gases of toxic effect are produced, which pollute the
atmosphere.
Where waste materials are sorted and taken to landfills, the assorted volume
of waste
forms an environmental burden, or the said materials are chemically unstable
and over long
periods deteriorate. This is especially true in the cases of wastes of packing
materials of
plastic with adhering foodstuffs.
In the state of the technology, numerous attempts have been undertaken in
separating plastic waste mixtures for the purpose of recycling.
DE 28 27 335 A1 makes known, for instance, a fimnel shaped separation
apparatus
with a central mixing mechanism for the separation of plastic particles, which
are heated to
a temperature of up to 200 °C. Problems seem to lie with this
apparatus, in that a
turbulent flow is generated against baffle plates in the midsection of the
fiznnel and that
heating by fuel leads to changes in the density of the plastic materials.
Especially, in the
case of multilayered plastics, the degree of separation is scarcely
satisfactory.
DD 256 049 A3 discloses a process for the treatment of "Plastic-waste". In
this
process, likewise, a funnel shaped apparatus is employed, which, in its upper
part,
possesses diversion plates to treat the materials to be separated. As before,
in this
apparatus the degree of valuable content of the separated fraction is not
sufficient.
FR 25 73 340 brings forth a process for the conditioning of waste plastic
material
after paper has been removed which is marked by an intensive mixer. The intent
is, that in
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a cylindrical tube, which has a narrowing section underneath the entry port,
by the
fashioning of a zone with reduced flow velocity, plastic particulate will
divide itself into a
light, floating fraction and into a heavy fraction which will sink. In the
case of another
design of construction, it is given that a separation will be performed at the
wide upper
sides of funnels, which are stacked one on the other. This to be brought
about, in that the
separation space possesses vertically disposed, parallel, dividing walls,
which present tube-
shaped separation surfaces. On the circularly shaped separation line of two
funnels, a
small volume of calm liquid is generated. This calm zone has a through-flow in
a
horizontal direction from the entering and leaving separating medium. This
apparatus
permits only the separation of plastics, which, because of their chemical
composition
exhibit greater density differences. The achievable precision of assorting is
scarcely
satisfactory. Also, the through-flow capacity of this apparatus is small.
The publication "Plastics" (Kunststoffe) 74/1984, page 189, right hand column,
lines
9 to 13 fundamentally confirms that such separation devices, based on the
"swim and sink"
process, in the state of the technology for practical long term usage, have
shown
themselves to be too subject to disturbance.
DE 42 09 277 teaches of a separation aggregate with an eccentrically placed
mixer
placed in a cylindrical tube. By means of a baffle plate with channeled exit
openings
placed vertically to the said tube, a sudden drop in the velocity of the
liquid flow velocity
should take place. However, even with this arrangement of the swim and sink
process, a
satisfactory separation with concurrent sufficient capacity can scarcely be
achieved.
In Ullmann's Encyclopedia of Technology (Llllmanns Enzyklopadie der Technik),
4th edition, volume 2, Process Technology I, 1972 page 77, a flow classifier
is made
known which is equipped with a movable gooseneck for the purpose of changing
the
height of the bed. The classifier is so designed, that the free inflow flows
out through an
inverted funnel and upon flowing out of this container, which is closed at the
top, the
direction of flow changes upward and downward. The classifier serves for the
separation
of a sludge of kaolin. In this case, the intent is to separate a fraction of
fines from a
fraction of large particulate, i.e. not, however, the fractionation of
particulates of different
densities. Only the height of the bed, not the quantity of outflow is
controlled by said
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L
gooseneck.
In a design based on EP 0 557 816 A2, in accord with the concepts of the
subordinate claims thereof, equipment is made known, wherein the separation of
material
mixtures of different densities is carried out by means of a liquid separating
medium. This
occurs by the ascending of lighter fractions and the sinking of heavier
fractions. The
equipment comprises: a tank with mixer for producing a mixture of the material
with the
separating medium; at least one separating tank; a separation element
comprised of two
cones, mutually confronting one another, in the center zone of said separating
tank,
whereby the mixture is fed into the said separating tank, and the separation
element being
constructed of two mutually confronting cones, namely an upper and a lower
cone,
wherein the mixture enters centrally through one of the cones; outlet lines
located on the
separation tank above and below; and at least one apparatus for the freeing of
the fractions
which have been separated by the separating medium.
In a technical scale, this proposal has not yet advanced beyond pilot plant
operation.
Operation in practice has shown, that with this system, no satisfactory
material separation
with an acceptable through-put can been achieved.
Thus the invention has the purpose of making available equipment and a process
for
the separation of material mixtures of different densities, by means of which,
at low cost,
improvements can be achieved in regard to the purity of the sorted materials
and in regard
to the through-put. This purpose is achieved, in accord with the first aspect
of the
invention, by means of equipment conforming to the concept of Claim 1, which
is
characterized by a separation tank, within which first and second guide plates
are
provided, which are horizontally disposed, fixing cones between them and
forming therein
a side liquid flow space for the outflowing mixture. Surprisingly, it has been
demonstrated, that this characterizing measure permits a substantial
improvement in
regard to the purity of the sorting achieved by the separation.
Following another aspect of the invention, a purpose of the present invention
is
achieved by equipment in keeping with the concept of Claim 2. This equipment
is
characterized by an apparatus for selective control of the quantity of the
mixture of heavy
fraction and a separating medium which is removed through the lower outlet
opening per
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unit of time. By the term "selective control" is to be understood a control
which directly
influences the material removed from below and also effects a controlled
change of the
ratios of the quantities removed from the upper and lower discharge means.
In the equipment disclosed in the EP 0 557 816, no control of this sort is
provided.
It is true, however, that, in accord with EP 0 557 816 a change in the
quantity fed into the
separation tank also has an effect on the quantity taken out from below.
However, a
selective control in accord with the present invention, which permits a change
in the ratio
of this quantity to the charged quantity - and thus the quantity removed from
above - is,
however, in the case of EP 0 557 816, not provided. Such a type of selective
control acts
advantageously in regard to the running of the process and permits, on this
account, an
increase in the precision of the sorting while allowing greater through-flows.
It has been mentioned, that the lower outlet lines need in no way be set at
the
deepest part of the separation tank. These lines can much more be placed at a
somewhat
higher level, for example to the side of the separation tank.
In the latter case, exceptionally heavy portions need not be removed through
the
outlet line, but these sink to the deepest part of the separation tank. At
this point, a
removal apparatus for these especially heavy particles can be provided.
Advantageously, the apparatus for selective control is an active transport
apparatus,
namely one with a pump activated by a drive. To this, along with other
possibilities, may
also be joined a power driven screw conveyor. (See Claim 3).
Advantageously, this active transport apparatus can be so designed, that it
can bring
out the selective control of the removed quantities without cross-sectional
variation of the
exit line and do this solely through a variation of the volume of material
transported per
unit time. In this matter, a pressure piston pump may be involved, or
especially a rotary
piston pump, such as is used for pumping concrete. Such a rotary piston pump
can, for
instance, be so designed, that the rotor is a one-way screw, which, in a two
lane screw
pump housing carries out an eccentric rotary motion. A pump of this kind can
be
designed so that valves are not needed. Also a helical screw pump is
applicable. The
control of the removed quantity is executed by a variation of the volume
transported per
unit time or, through the corresponding change of the speed of rotation of the
pump or the
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screw conveyor. (See Claim 4).
Alternatively, the apparatus for selective control of the removed quantity can
also be
designed passively by means of putting gravity to use, since, for example, the
bottom exit
line can be made as a flexible hose, which, for the control of the quantity of
output, is
lifted or lowered, without any variation in cross-section. (See Claim 5).
On the upper end of the separation tank, advantageously, is located an
overflow
apparatus, onto which the upper removal line connects (See Claim 6). By means
of the
selective control of the quantity removed at the bottom the height of the
liquid level in the
separation tank - and therewith also, indirectly, the quantity of the liquid
escaping through
the overflow apparatus is also controlled.
Fundamentally, the overflow opening can show a constant cross-sectional area.
Advantageously however, the said opening is equipped with an apparatus for an
adjustment of the cross-section. (See Claim 7).
In the case of finer plastic granulate, it is possible that a relatively small
overflow
opening is desired, in order, in the upper zone of the separating tank, to
encourage a
relatively large flow. Such a large flow, acts favorably in consideration of
an avoidance of
material adherence on the inner separation tank wall. In case particulate
comprised of
large parts, such as foil pieces. In case however, larger particles are
present in the
mixture, for instance foil pieces, to avoid plugging, it will be found of
advantage to
operate the equipment with a greater overflow cross-sectional area.
For the control of the process, at least one apparatus is provided for the
determination of the quantity introduced into the separator tank on a pro time
unit basis as
well as an apparatus for the determination of the quantity removed per unit of
time from
the bottom of the separation tank. (See Claim 8). In the case of these
measurement
apparatuses independent flow meters or through-put sensors can be considered,
which
detect partial or full blockages in the connecting lines to the separation
tank, for example
in the bottom outlet. It is also possible, to make conclusions as to the
through-flow by the
speed of rotation of the respective liquid transport pump. The latter type of
determination
can be sufficient if, in the case of a plugging, the speed of rotation of the
serving pump is
correspondingly reduced. The determined quantities serve the control of the
material
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removal from the bottom - and thereby indirectly also control of the
determined value of
the upper removed quantities. Moreover, the determined value of the quantity
introduced
into the separating tank can also serve for the control of the transport pump,
which is
responsible for the transfer of the mixture from the mixing tank into the
separating tank.
As an additional measure for avoiding, or eliminating, any plugging,
advantageously, an
apparatus for the introduction of pressure pulsations into the lower outlet
opening can be
provided. (See Claim 9). In particular, this concerns an air impulse.
In order to get rid of heavy, contaminating materials (such as metallic
pieces)
upstream of the separating tank, the mixture leaves the mixing tank
advantageously
through a fitting on the side. (See Claim 10). Metal parts, because of their
relatively great
weight, sink to the bottom of the mixing tank and with the side outlet being
elevated, are
not forwarded to the separating tank.
In order to assure uniform relations in the production of the mixture, the
mixing
equipment possesses, advantageously a level controller for the determination
of the
mixture level in the mixing tank and for maintaining this at a constant level.
(See Clairn
11). Further, it is of advantage if the mixing tank possesses such a mixing
device, wherein
the rate of rotation thereof can be controlled. (See Claim 12). In order to
avoid
turbulence in the separator tank, the separation element between the
horizontal baffle
plates can be equipped with vertical straightening vanes (See Claim 13).
A corresponding function can, however, be achieved by horizontal ribs, which
are
arrayed on the inside walls of the separation tank. In the case of metal foil
contamination,
it would be better to refrain from the use of vertical straightening vanes, in
order to
prevent plugging at the outlet thereof.
In regard to the process claims (Claims 14 to 26), reference should be made to
the
above descriptions and explanations concerning the various aspects and
formulations of
the equipment.
The invention is now more closely described with the aid of the drawing. The
drawing figures show:
Fig. 1 a separating tank in cross section,
Fig. 2 a side view of the separation tank of Fig. 1 with a flexible hose for
the
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control of the quantity of material taken from the bottom connection
thereof,
Fig. 3 a mixing tank in cross section,
Fig. 4 a schematic flow-diagram of equipment for the separation of material
mixtures, and
Fig. 5 a view of another embodiment with mixer andseparating tanks, in which
the removal of mixture from the separating tank is accomplished by a
pump.
The separating tank l, as shown in Figs. l and 2, is constructed of a middle
portion
9, this being a cylinder of circular cross-section, surmounted with a conical
top part 10
and possessing a corresponding conical bottom part 11. The transition location
between
the cylindrical to the conical parts of the separating tank 1, exhibits an
angle of 30 - 45°.
The cylindrical midsection 9 has, advantageously, a diameter in the range of
1.9 to
2.4 m. The separator 1 extends, in its entirety over a height ranging from 4
to 6 m.
Centrally located within the separating tank 1, is found the separation
element 3. This
assembly 3 is comprised of two cones disposed apex to apex, thus being an
upper cone 6
and a lower cone 7. Serving as the bases of these two cones are an upper guide
plate 4
and a lower guide plate 5. To be precise, the apex of one of the cones is
lacking, since at
that point a piping connection 2 is made. Thus, when as was stated above,
"apex to apex",
what is meant is that in the case of one of the cones 6, 7 an "imaginary" apex
is referred
to. These cones 6, 7, are placed at a small distance from one another. For
example, the
distance between the apex of one cone and the piping connection 2 is between l
and 10
cm, preferably between 3 and 5 cm. A preferred arrangement is that, in which
the apexes
(of which one is "imaginary") would touch each other.
The cones 6, 7 have a (measured at the cone apexes) a conical angle 8 between
110' to 150', preferably about 120°. The parallel arranged guide plates
4, 5 are circular
and exhibit a diameter of, for instance, 0.7 m to 1.1 m, preferably 0.8 m to
1.0 m thus
providing a space of about 0.3 m - 0.7 m, preferably 0.4 m - 06 m to the
inside wall of the
separation tank 1. The distance between the guide plates 4, S runs between 0.2
m to 0.4
m, preferably about 0.3 m. The diameter of these guide plates comprises about
40% to
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60% of the inside diameter of the separation tank. The input line for the
mixture into the
separation tank 1 is introduced either below or above and through one of the
said cones 6,
7. The introductory means is the piping line 2. The corresponding cone 6 or 7,
connected
thereto, lacks the conical apex because of the pipe connection formed at that
plane of the
frustum of one of the cones and axially opposite to the apex of the other of
the cones 6 or
7.
The location at which the (imaginary) point lies on the axis which binds the
apexes
of the two cones (6, 7) together, is advantageously at the geometric center
point of the
separation tank 1.
This axial point is thus at half the height of the separation tank 1 on its
centerline.
The guide plates 4, 5 form a defined, geometric space, which provides a
calming zone in
accord with fluid flow technical principles. Only upon leaving this space at
the outer
circumference of the guide plates 4, 5, does the mixture separate itself
finally into the
ascending light fraction and the descending heavy fraction. This action is
supported by
partial flows of the separating medium which guide upward and downward. In the
zone
between the guide plates 4, 5 there is engendered a laminated flow to the
outside. At the
circumferential rim of the space formed between the guide plates 4, 5, can be
found
vertical directing vanes 29 which are circumferentially symmetrically
distributed.
By means of the designed construction of the separation element 3, the liquid
flow is
non-turbulent or a laminar streamline flow. The space between the guide plates
4, 5
present a calming zone wherein an optimal laminar flow for the entry of the
mixture into
the separation tank may be formed. This laminar flow allows, following the
exit from
between the said plates, a sharp separation of the fractions of different
density. If the
space between the guide plates 4, 5 is chosen to be too narrow, a turbulent
flow can be
developed. If the said separating space is too wide, then no satisfactory
guidance of the
flow into a laminar state would result.
The diameter of the inlet pipe 2 is selected to be relatively large, in order
to favor the
laminar flow in the separation element 3. A diameter which is too small, leads
to a
relatively high flow velocity, which can be contrary to interests of building
a laminar flow.
Also, the distance between the cones 6, 7 has a bearing on the lamellar nature
of the flow.
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In the case of a separation distance which is two small or too great, the
laminar effect and
concurrently the separation effects deteriorate.
At the lowest end of the separation tank is located a bottom outlet line 12,
through
which the heavy fraction which has sunk downward is removed along with a
partial flow
of the separating medium.
The quantity so removed can be selectively controlled. In the embodiment as
shown
in Fig. 2, this control is accomplished by the construction of the bottom
removal line 12 as
a flexible hose. This hose can be lifted up to the height of the liquid level
in the separation
tank and from there, brought downward.
With a hoist mechanism 13 located at the highest point of the flexible hose,
the level
of the highest position can be varied. In this way, in accord with the
principle of
communicating liquid channels, the liquid level in the separating tank 1 can
be raised or
lowered. This has the result that the intake rate - in a manner described more
fully below
- of the separating tank 1, and indirectly the rate of the material removed
from above, can
be regulated. With the aid of selective control of the bottom removal of heavy
material,
also under control are the partial streams of the mixture being introduced
into the
separating tank which flow upward and downward.
In the embodiment in accord with Fig. 5 the control of quantity removed from
the
bottom is effected by a pump 44. The pump concerned is a rotary piston pump,
Type PL-
300 of the firm Borger GmbH in D-16325 Borken. The control of the removed
quantity is
done by the regulation of the pump speed of rotation. By the increasing or
decreasing of
the flow of the pump 44 - as in the case of the first mentioned type of
construction, where
the lifting and lowering of the flexible hose was the means of control - the
liquid level in
the separating tank is likewise raised or lowered, whereby, indirectly, the
quantity
removed from the upper part of the separation tank was also controlled.
Common to both embodiments, is that the control of the quantity removed at the
bottom is carried out without any restricting of the cross section of the
bottom outlet line
12. In the case of the first mentioned embodiment, this is assured, in that
the flexible hose
is only displaced as to height, however, its diameter remains unchanged. Where
the
second named embodiment is concerned, the said assurance is provided through
the use of
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a pump 44, which, for instance, transports in "compartment-wise" fashion,
whereby the
cross-section of the "compartment" is not smaller than the cross section of
the bottom
outlet line 12.
A valve 14 at the bottom of the tank does not serve to control the quantity
being
removed from the separator tank by means of cross-section changing, but makes
possible
a shutoff of the separating tank 1. The valve itself is a shut off slide, for
example.
If the light fraction and the heavy fraction are present in the mixture in
equal
proportions, then the removal through the bottom outlet line 12 can be
electronically
controlled in such a manner, that, above and below, approximately equal outlet
quantities
are removed from the separation tank 1. If the portion of the light fraction
is clearly
greater, then by means of the top overflow, more material will be removed than
from the
bottom. This can be accomplished by lifting of the flexible hose higher or by
a diminishing
of the quantity transported through the pump 44. In the case of a greater
proportion of
the heavy fraction, conversely to the above, the flexible hose would be
lowered, or, where
the pump is employed, then the delivery of the pump 44 is increased, so that
the bottom
removed quantity is correspondingly greater than that removed through the top.
In all
cases, this control is without any diminishing of a cross section, so that the
occurrence of
plugging is avoided.
At the upper end of the separating tank 1, there is to be found an overflow
opening
which is placed in an overflow box 16 in which the removal line 15 begins. The
upper
outlet line of the separating tank 1 has an opening cross-section, which, in
the range of
145 mm and 300 mm can be adjusted by a positioning device. This opening is so
controlled, that, when foil material is being separated, it lies in the upper
zone and when
the concern is the separation of granulate, then the opening lies in the lower
zone.
Thereby, the greatest possible flow velocity is reached in the overflow, so
that the removal
can be carried out without material clinging to the equipment or the
occurrence of
plugging.
In accord with Fig. 3, an open top mixing tank 17 with an opening cross
section of
140 mm - 300 mm has a mixing assembly 18. This mixing assembly 18 is found
axially
centered in the said mixing tank 17 and is connected by a mixing shaft with at
least one
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mixer blade 19 which is located in the middle or lower part of the tank 17.
Regarding the
mixer blade 19, this can be, for instance, a mixing propeller with stirring
blades, which can
be designed to be movable.
The mixing tank 17 is designed to have a conical bottom part. Approximately in
the
midsection of the mixing tank 17, on a wall of the cylindrical portion, is
connected an
outlet fitting 20, which connects the mixing tank with the separating tank 1.
At the deepest point of the conical part of the mixing tank 17, is located a
shutoff
valve 22 of the sliding type, through which the settled out heavy material can
be removed.
The feeding of the material mixture to be separated into the mixing tank 17 is
carried out
by means of a pipe line 32. The input of the separating medium (this, as will
be later
explained, is returned separating medium) in the mixing tank 17 is made by a
medium
return line 28. The material mixture to be separated is first fed into the
mixing tank which
is, at the beginning, already four fifths filled with separating medium. In
the running
process, the feed of material mixture is carried out with a constant flow, so
that in the
mixing tank, it is found in a concentration of from 5 wt % to 20 wt %,
preferably 10 wt
- 15 wt %, the weight percent being relative to the liquid phase.
By means of the mixing assembly 18, a homogenous mixture is obtained, wherein
the
rotary speed of the mixing elements is so adjusted, that heavy contamination,
such as
metal parts and foreign materials, sink into the conical underpart and the
homogenous
mixture flows continually in laminar flow, through the wall outlet 20, while
heavy
materials are periodically removed through the exit slider 22. For example
these heavier
contaminations are removed at periods within the range of 0.1 to 1 hour by
electronic
control. The mixing assembly 18 possesses an electronic control of its speed
of rotation,
by means of which, the speed of rotation remains constant, independently of
the solids
content of the mixture. The speed of rotation of the mixing assembly is so
chosen, that
turbulence in the liquid phase of the mixture is avoided. Further, by means of
an
electronic control of liquid level, the height of the mixture in the tank is
monitored and
held constant. For this purpose a level sensor 21 (see Fig. 5) is provided. In
accord with
Fig 5, in the outlet connection line 20 is found a shutoff valve 35, a flow
meter 36 and a
pump 37. In the flow direction, a heavy particulate cyclone 38 follows, from
which, by
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means of a sluice, the heavy particulate is withdrawn. This would be such
heavy material
as had not deposited itself on the bottom of the mixing tank 17.
Another flow meter 40 follows this in the flow direction until finally, the
connecting
line 20 transitions into the intake line 2 which opens into the separation
arrangement 3.
In the lower part of the separator 1 is provided, as may be seen in Fig. 5, a
valve 41
for the blowdown of the separator tank content. The lower outlet connection
line 12 of
the separator tank 1 is equipped, shortly after the outlet, with a compressed
air impulse
connection 42, with which the compressed air impulse in introduced into the
outlet
opening line 12. In the case of other embodiments, instead of compressed air
impulses,
for instance pressure pulses in the separating medium can be applied. Further
downstream
in the outlet line 12, is a through-flow meter 43 and the pump 44, which
requires no
changes of cross-section.
The pumps 37 and 44 are so interconnected by flow meters and through-flow
meters
36, 40 and 43, that a constant material flow from the mixing tank 17 into the
separating
tank 1 as well as through the two outlet lines 12, 15 is maintained.
Especially, by means of
the through-flow measurement in the connection line 20 and in the bottom
outlet line 12, it
becomes known which quantity per time unit flows through the upper overflow
15. By
this means, the apportionment of the flows between the upper and bottom
outlets of the
separating tank 1 is held at a constant value, which is chosen with
consideration given to
the ratio of the light fraction to the heavy fraction. If, fox example, in the
connection line
20 a flow of 50 m3/h was held constant, and in the bottom outlet connection
line 12 a flow
of 26 m3/h was maintained then, obviously, by indirect control, a flow of 24
m3lh was
being held constant in the upper overflow line 15. A typical quantity of flow
runs in the
range of 10 to 25 m3/h in the bottom outlet line 12. With the aid of the flow
meter 43, it
becomes possible to detect partial or complete obstruction in the said outlet
line 12. In
case of plugging, the control directs the apparatus, by means of which the
compressed air
impulse is introduced through the pressure connection 42, to remove the said
obstruction.
Pressure impulses of this kind can helpfully be administered in a constant
succession, for
instance, 5 to 7 pressure impulses per minute. The chosen flow velocity is so
controlled
electronically, that this velocity is so high, that the removal of the
separated fraction from
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the separation tank 1 can be accomplished without adherence or deposition on
the conical
walls of the separating tank 1.
The shutoff valves, i.e. the sliding plates 22, 35, 42 can be pneumatically
activated
by an electronic control. In the case that the equipment is taken off line,
these are
automatically closed by said control and conversely, upon a restart of the
process, these
are automatically opened.
A complete, operating installation and the entire process will now be more
closely
described and explained by the following example and with the aid of Fig. 4.
Introduced through the feed line 32 into the mixing tank 17 is a mixture of
plastic
particulate, reduced in size to some 10 mm to 30 mm. This plastic is in
granular form
and/or as film, originating from "Green Point". At the same time water is
brought in
through the return line 28 to serve as a separating medium. The resulting
mixture is
homogenized by the mixing blade 19 to form a concentration of approximately
10%
plastic per kg of separating medium. In a through-put loading of 1 to 1.2
metric tons/hr,
this homogenized mixture is continually transported to the separating tank 1
by means of
the outlet connection 20 of the mixer and the feed line 2 of the separating
tank 1. The
separating tank 1 is already prepared by a fill of separating medium. In the
separation
element 3, the local laminar flow between the guide plates 5 and 6 starts the
separation of
the heavy and light fractions. Upon exiting from the space between guide
plates 5 and 6, a
further material separation is done in a rising fraction of low density and a
sinking fraction
of greater density than that of the separating medium. After the removal from
the
separation tank 1 through the top and bottom outlet lines 15, 12, these
fractions are
separated from the liquid phase of the separating medium, (for instance,
water) on the
sieves 23, 2b and by filters 24 and 27. If necessary, a further dewatering
with a centrifi~ge
31 can be earned out. The separating medium isolated by these processes is
directed to a
surge tank 25 and from this reservoir is conducted through the return line 28
back to the
mixing tank 17.
For a further separation of the light and heavy fractions, these fractions can
subsequently be subjected to further separation steps, which, in turn, are
again constructed
of a mixing tank and a separating tank.
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The essential difference of these subsequent separation stages lies therein,
in that in
these said stages, the separating medium is either heavier or lighter than in
the preceding
stage.
With water as the separating medium, the following fractions were separated:
Fraction Designation% Density in g/cm3
Light FractionPO 60 0.96 - 0.98
Heavy FractionPS 10 1.06
Residual 30 1.10 and greater
Fraction*
* The residual fraction falls together with the heavy fraction PS
and can be separated from this in additional stages.
The residual fraction, in a corresponding manner, can be separated with a
magnesium sulfate solution as a separating medium.
Taken together, the execution of the process for continual and non-plugging
separation of material mixtures of varying densities, especially of fine
plastic material in
granular or film form, is carried out by means of a separating medium by the
introduction
of the comminuted material into a mixing tank for homogenization therein, the
pumping
into a separation tank with a separation element and the removal of the
separated fractions
and the recycling of the separating medium. In a more exact description, the
example
process possesses the following steps:
1 ) The mixture of pulverized material, which is to be separated, is
introduced in a
constant quantity per time unit through a feed line 32 into a mixing tank 17.
This mixing tank 17 has a lower conical section and initially contains
separation
liquid which is recycled through a return line 28. The said constant feed of
the
mixture allows achieving a concentration of 10 wt% - 20 wt%, preferably 10
wt% - 15 wt%, the percent being relative to the liquid phase. The said mixture
is brought to a homogenous mixture by means of the mixing assembly 18. The
mixing assembly 18 possesses one or more mixing shafts with a mixing
propeller ( 19) with adjustable mixing blades. The mixing speed of the said
shaft
is so adjusted, that contaminating materials, such as metals and foreign
materials, sink into the conical under part and the homogenized mixture moves
in laminar flow toward the sidewall and exits approximately in the midsection
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of the mixing tank. In his midsection is an outlet connection line 20 and
heavy
contamination is periodically removed through a bottom shutoff slide valve 22.
2) The next step is the entry of the homogenous material mixture into the
separation tank 1. This tank 1 is constructed of a cylindrical middle part 9
and
upper and lower conical parts 10, 11. The homogenous mixture enters
through the inlet line 2 closely above the lower conical part 10. This inlet
line
2 midway in the said center part is bent vertically upward with the homogenous
mixture freely flowing out of the inlet line 2 to enter the separation element
3.
This element 3, by an upper and a lower polygonal or circular shaped guide
plate 4, 5 bounds a geometrical space therebetween. On these plates 4, 5 an
upper and a lower cone 6, 7 are opposingly placed with an intervening space.
The said cones have an apex angle 8 of, for instance, 10 ° -
130°, preferably
120° and the cones 6, 7 closely approach one another at the apexes in
the
above described concept, in order to guide the homogenized mixture in laminar
flow into the liquid separating medium. Since the homogenized mixture now
enters the liquid separating medium without turbulence but with laminar flow
velocity, this enables a separating action of components with different
densities. Immediately at the circumferential terminations of the guide plates
4,
5, which plates are provided with optional radial straightening vanes 29, the
material particles in size range of 10 mm to 50 mm, preferably from 20 mm to
30 mm rise or fall in the conical parts 10, 11 of the separation tank 1. In
this
way, material separation into one or more heavy fractions is brought about. A
control of the liquid phase with the separated fractions can be carried out by
means of a flexible hose 12 connected to the opened slide valve 14. The hose
12 is vertically displaceable by a block and tackle or a hoist drive. The
vertical
displacement is such that the upper curve of the hose 12, following the fluid
principle of a communicating tube, adjusts its liquid level to the same height
as
that of the liquid level in the separating tank. Alternatively, instead of the
hose,
by means of a pump 44 the transport quantities of which are variable by
adjustment of the speed of rotation without cross-sectional change. The light
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fraction of the upper conical part 10 exits through top outlet line 15 with an
overflow box 16. The separated heavy fraction is freed of the liquid phase by
means of sieve-dewatering, and the liquid phase is conducted to a surge tank
25 and from this tank 25 is recycled through a return line 28 into the mixing
tank 17. The separated fractions are centrifuged and if necessary, the
residual
quantity is run through a drying process to free itself from the separating-
medium, and is then transported to silos for further applications. In the case
of
standstill of the equipment, the bottom valve 14 remains shut until the
restart
of the throughput of the material mixture, while, through the same period, the
separation tank remains full.
The ratio of the diameter of the guide plates 4, 5, to the diameter of the
cylindrical
part 9 of the separating tank 1 is 0.4 - 0.6, preferably 0.47 - 0.5. For
example, should the
diameter of the guide plates be 900 mm, then the diameter of the cylindrical
part 9 would
be 1900 mm.
The outlet direction and the quantity of the liquid separating medium at the
upper
overflow 15 and/or at the bottom outlet 14 is carried out either by the
adjustment of a
variable height of the flexible hose 12, or by a control of the transport
quantity of the
pump 44 through change in the height of the communicating liquid level in the
separating
tank 1. The diameter of the upper and the lower outlet lines 15, 12 are equal,
these
measuring preferably 100 mm. The diameter of the inlet connection line 2 is
one to two
times that of the outlet lines 12, 1 S.
Water, or aqueous solutions of inorganic salts, the salts being for instance
NaCI,
KCI, or MgSOa, adjusted to different densities between 1.1 g/cm3 and 1.4 g/cm3
can serve
as a separating medium. The separating medium can also be water and organic
liquids
miscible with water, such as isopropyl alcohol with a density of 0.80 g/cm3 -
0.98 glcm3,
whereby the density of the liquid separating medium is adjusted fall between
the densities
of the light and the heavy fractions.
After the removal of the light fraction, it is possible that in additional
separating
tanks, and in the same way, for instance, one or more heavy fractions from the
presently
lighter fraction again can be separated and be treated in the same way.
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The reduction of size of the material mixture, can be accomplished, for
example, by
grinding to small particulate. Fundamentally, it is possible to separate small
particulate
materials, such as ores, coal from gangues, or metals, for instance separating
aluminum
from iron or separating non-miscible liquids of different densities, such as
water and oils.
Advantageously, other applications are found with organic material mixes, for
instance
mixes of PE, PS PVC, PET with the densities of 0.96 g/cm3, 1.05 g/cm3, 1.30
g/cm3, 1.31
g/cm3 which are separated in several stages in separating tanks into pure
fractions. The
available plastic found in the pure fractions can be reworked to granulate
through
extrusion.
The separating tank 1 has for instance, the following dimensions: overall
height is
4 m, diameter of the cylindrical part is 1.90 m, height of the cylindrical
part, more than
2 m. With this size, and a through-put capacity of 1 metric ton/h - 2 metric
ton/h of
plastic mixture feed, a separation into practically pure sorted fractions can
be expected.
An embodiment of the equipment possesses a conical mixing tank 17 with an
inlet
line 28 for the introduction of the separating medium and has an entry fitting
32 for the
feed of a mixture of small particulate. This mixing tank 17 further possesses
a mixing
apparatus 18 with drive shaft and mixer blades 19, such as, for example,
mixing propellers
with adjustable blades for the production of a homogeneous mixture. The mixing
tank 17
of this embodiment further exhibits an outlet connection line 20 for the
removal of the
homogeneous mixture which said line is connected on the wall of the
cylindrical part of
the tank. The lower apex of the conical bottom the mixing tank is connected to
a removal
slide gate 14. The outlet line 20 leads to the separation tank 1, which said
tank comprises
a cylindrical midsection 9 and upper and lower conical parts 10, 11. In the
separation tank
1 is the separation element 3, which forms a geometrical space confined
between the guide
plates 4, 5. On the guide plates 4, 5 are respectively placed an upper cone 6
and a lower
cone 7 which are situated very close to one another, in the concept described
above, with
an intervening space of some 4 cm - 5 cm.
On the outer rim of the guide plates 4, 5, vertical straightening vanes 29 are
optionally inserted.
Through the bent pipe line 2, the homogenous mixture enters from below,
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discharging from the center of the lower cone 7 and flows out between the
guide plates 4,
at a laminar flow velocity, so that, at the top circumferential termination of
the round,
preferably circular, guide plates 4, 5, said flow enters the separating
section and the
specifically lighter fraction (or fractions) escapes through the overflow line
1 S which is
equipped with the overflow box 16, and at the lower circumferential
termination of the
guide plates 4, S, the specifically heavy fraction (or fractions) settle to be
removed through
the outlet slide gate 14 and hose 12, which can be elevated or lowered, or
said heavy
fraction is removed by the pump 44 through the bottom exit line 12. The
separation
element 3 is affixed in the cylindrical midsection 9 of the separation tank 1.
The separated
fractions, for the purpose of being separated from the liquid separating
medium, are
conducted to the sieve apparatus 23 (light fraction) and the sieve apparatus
26 (heavy
fraction) and thereafter conducted to filters 24 and 27. The separating medium
flows into
a surge tank 25 and from this to the return line 28 back to the mixing tank
17. The
separated fractions are, if necessary, run through a centrifuge 31 and/or are
dried in a
heated apparatus and finally conducted to silos. If necessary, further
fractions to be
separated are fed to a subsequent, second mixing tank 17 and separating tank
1.
At the circular rim of the guide vanes 4, 5 are optionally located several,
straightening vanes 29, possibly 12 to 15 in number. These are placed at
equally
apportioned spaces and extend radially as well as being perpendicular to the
guide plates
4, 5. The union of the plates and straightening vanes is preferably made by
welding. The
diameter of the separation element 3 runs approximately 900 mm, that of the
cones 6, 7 is
about 500 mm. The apex angle of the cones is about 120°. The space
between the apexes
6, 7 (in the concept explained above) is preferably 4 cm, the distance apart
of the guide
plates 4, 5 is about 300 mm, the diameter of the pipe line 2, for instance may
be 110 mm
and the width of the radial straightening vanes 29 is, as an example 100 mm
with a spacing
of about 20 mm from the rim.
The separation of fractions of different density in the liquid separating
medium is
carried out in the separation element 3, which is constructed from the
parallel, round,
circular, or polygonal shaped plates 4, S into a defined space open at the
sides, whereby,
on the said plates, and in the interior of said space, are placed the bases of
opposingly
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situated cone shaped bodies 6, 7. This opposed placement serves for the
adjustment of the
flow direction of the liquid phase. Between the said plates is affixed a
plurality of vertical,
radially and symmetrically apportioned straightening vane elements, which
serve for the
guidance of the laminar flow. At the exit at the termination of the parallel
plates the
separating section is activated, wherein the specifically lighter fraction (or
fractions) rise
and the specifically heavier fraction (or fractions) sink, and these exit the
separation tank 1
at the top and bottom outlet openings. The separating medium is isolated and
recycled,
and the fractions are freed from residual water and stored in silos.
In the process in accord with the invention, material mixtures with variances
in solids
content from approximately 5% - SO% solids relative to the homogenous mixture
can be
separated with the separating medium. The process has wide application due to
the
sharpness of its of separation in the separation of inorganic or organic
material mixtures.
The mixtures can be plastic materials in the form of granulate and films
reduced to milled
size, coming from production waste from industry, advantageously from the
chemical
industry and from waste management sources. A further application is the
separation of
carpeting, fibers, auto parts, and the like for recycling as valuable recovery
items.
Considerably econonuc advantages are due to the process. The process, because
of the
recovery of materials, possesses a high economic importance with a minimum of
investment in operational means. The process leads to a lesser detrimental
effect on the
environmental surroundings from gaseous, liquid or solid waste materials. The
liquid
separating medium is continually recirculated. Insofar as the disposal of
aqueous solutions
is concerned, these contain, generally, no toxically acting compounds, but
mainly salts.
The invention permits a lessening of the waste materials which would otherwise
go to Iand
fill or incineration.
In conclusion, a reference number and component list, as well as various
concept
definitions are provided below. In the figures the numbers refer to:
1 Separation tank 23 OverAow sieve from
1
2 Piping or tubing 24 A first filter
lines
3 Separation element 25 Surge tank
4 Upper guide plate 26 Bottom flow sieve
from 1
Lower guide plate 27 A second filter
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6 Upper cone 28 Return line, liquid
medium
7 Lower cone 29 Radial straightening
vanes
8 Apex angle of cone 30 Line to next sep.
stage
9 Cylindrical mid-part31 Centrifuge
of
3
Top conical part 32 Piping
of 3
11 Lower conical part 33 -------
of 3
12 Bottom outlet line 34 --------
(In Fig. 1, a flexible
hose)
13 Hoist for flex hose 35 Slide shutoffvalve,
for
17
14 Pneumatic, electronic36 Flow meter at outlet
from
controlled outlet mixing tank
valve
Overflow outlet line37 Pump 17 to 1
16 Overflow box 38 Cyclone for heavy
material
17 Mixing tank, cone 39 Exit sluice from
38
bottom
18 Mixing assembly 40 Thru-flow meter
38 to 1
19 Mixing blades) 41 Blowdown valve for
1
Outlet line from 42 Compressed air inlet
17 in
12
21 Level sensor for 43 Thru-flow meter
17 1 to 44
22 Valve for outlet 44 Radial piston pump
from 17 from
1
Definitions of Concepts
Liquid separating medium, or liquid phase: that liquid which has a density
between the
densities of the materials to be separated.
Fraction: this term designates the separated materials of different densities.
Pure fraction: designates separated material of the same chemical composition.
Particle: designates material pieces such as granulate or ground material.
