[0001] This invention covers the implementation of a system, preferentially but not exclusively
devised for discrimination of solid fractions having differentiated density in heterogeneous
mixtures using water as a fluid and in particular for descrimination of putrescible
organic fractions of solid urban waste to be converted into compost or used for biogas
production.
[0002] This invention will make it possible almost completely to separate the heavy components
in the raw organic fraction (glass, fragments of pottery, stones, metal, rigid plastic
material, cells and heavy inert matter of any kind) from the lighter fractions (paper,
organic matter etc.)
[0003] To separate a heterogeneous mixture of solids having different density values into
two (or even more than two) fractions, known - so called "sink-float" systems - may
be used based upon usually dense liquids in which some solids may float while others
will sink to the bottom.
[0004] Water too may permit - within well defined limits - sink-float operations to separate
materials having a higher than 1 density from those whose density is less than 1,
i.e. having a lower density than water.
[0005] There is, however, a large quantity of solid waste components , such as vegetables,
some legumes, fruit, paper, organic tissue , just to list a few and many others which
may either float or sink with some difficulty (as for instance a leaf of lattuce or
onion or paper); they often remain floating midway in the water. A slight current
is enough to keep them floating or entrain them without remaining at the surface or
sinking down to the bottom.
[0006] This means that the systems hitherto known for gravitational "sink-float" separation
in water have yielded no practical results, especially for solid urban waste discrimination
and can therefore not be used.
[0007] This invention has the aim to make it possible to take advantage of gravitational
separation in water since this method is most economic because of its low operating
cost.
[0008] This aim is achieved by combining two effects: i.e. gravitational separation and
the generation of water streams having differentiated entrainment capacity thus inviting
irresolute fractions to follow given routes and hence promoting the desired discrimination.
[0009] For this purpose, the invention provides for a cylindrical discrimination chamber
having a truncated cone shaped bottom, placed inside an external settling basin filled
with water.
[0010] Furthermore, an also cylinder-shaped dispersion chamber with truncated-cone bottom
fed with the mixture to be treated, is coaxially placed in the discrimination tank
. These two settling and discrimination tanks have an open bottom.
[0011] The system is completed by a screw distributor located in the lower part of the discrimination
tank and a propelling impeller mounted below the dispersion tank just above the distributor,
in order to generate adequate current flows to complete the required sorting.
[0012] The invention in question is illustrated in its preferable implementation in the
enclosed drawings in which:
fig.1 shows a lengthwise vertical section of the separator in question;
Fig.2 shows a top view of the separator illustrated in fig.1;
Fig.3 shows the central vertical section of the propelling unit.
Fig.4 shows a top view of the propeller illustrated in fig.3.
[0013] With reference to these figures, the separator is essentially consisting of four
assemblies which will be described hereinafter.
[0014] The first assembly is consisting of a cyclin- drical discrimination tank 1 with truncated
cone-shaped bottom which is kept constantly filled with water, surrounding and supporting
- by means of four tie rods 32 - the coaxial dispersion chamber 2 which is completely
immersed in the liquid and in which the mixture to be processed is fed through the
channel 3 together with most of the process water . The discrimination tank 1 has
an overflow 4 through which excess water is discharged together with any supernatant
fractions of the mixture which are collected in the ring-shaped effluent channel 5
and are drained through the outlet 6 connected to the channel 5. The lower orifice
7 of the discrimination tank is hydraulically closed.
[0015] The heavy inert fractions such as glass, stones, metals, cells etc. are discharged
through this orifice and are then mechanically removed as will be explained hereinafter.
[0016] A "spiral chamber" for distribution of the make-up water 8 is located outside the
terminal cone of the discrimination tank, immediately above the orifice 7; this spiral
chamber lets the water into the tank 1 by means of the guide vanes 9 conveying the
water entering the tube 10, in the correct flow direction of the fluid .
[0017] The second assembly is consisting of a propelling unit located inside the discrimination
tank 1 along its central vertical axis XX; this propeller is essentially consisting
of a geared motor 11, a shaft coinciding with the XX axis and an impeller 13 forged
into the shape of an upside-down "chinese hat" fitted with upper and lower radial
vanes (fig.3). The "propeller" assembly is completed by a base supporting the geared
motor unit and a flexible coupling 15 connecting the driving unit to the impeller
shaft. The latter is supported by two water lubricated bushes 16 and 17 mounted at
the upper and lower end of the casing 18 resting on the flange 19 with the fitting
20 through which pressurized clean water can be let into the casing 18 for lubrication
of the bushes 16 and 17. The impeller is located below the lower orifice of the dispersion
chamber 2 and above the row of guide vanes 9 of the spiral chamber 8 as illustrated
in fig.1.
[0018] The third assembly is consisting of a settling basin 21 surrounding the discrimination
tank 1 and extending above the upper level of the fluid overflowing from the spillway
4 of the discrimination chamber 1.
[0019] The settling basin 21 has two vertical and parallel sides 22 and 23, separated by
a third polygonal traverse wall 24 at right angles to the walls 22 and 23 so as to
form the bottom of the sattling basin 21.
[0020] Fig. 1 clearly shows that the polygonal wall 24 is consisting of an initial section
a, followed by a sub-vertical section b, a horizontal section c and a final section
d gently sloping upwards and extending well beyond the free surface of the liquid.
[0021] The section d of the polygonal wall 24 has an opening with a discharge nozzle 25
at its upper end, well above the liquid surface.
[0022] The settling basin 21 is communicating with the discrimination tank 1 by means of
an orifice 7. Basin 21 and tank 1 are both filled with water and will have the same
free surface level e I according to the principle of communicating vessels.
[0023] Therefore, no water should flow through the orifice 7. Actually, there will be a
slight upward flow due to clean make-up water entering through the feed cokck 25 which,
among others, will make up for any imbibition losses caused by the heavy inert and
polluting material discharged through the outlet 25.
[0024] From fig. 1, it can be observed that the discrimination and dispersion tanks 1 and
2 have their XX axis in the maximum vertical dimension zone of the settling basin
21.
[0025] The fourth assembly is consisting of a chain scraper 27 having the task to collect
the heavy inert fractions, discharged through the lower orifice 7 of the discrimination
tank 1 into the settling basin 21 where they settle on the bottom of the basin.
[0026] The chain scraper 27 is fitted with scraper blades 28 slowly grazing the bottom and
dredging the deposited material, dragging it along the section d of the bottom wall
24 of the basin, so that it can be discharged, after a short drying length, above
the water surface, through the outlet 25.
[0027] Outside the settling basin, the chain scraper 27 is supported by a guide pulley 29
and supporting roller 30. The chain is driven by a properly recessed or toothed driving
roller 31, driven by a geared motor so that it will be possible to adjust the scraper
speed within a large range and hence to vary its transport and discharge capacity.
[0028] Based upon the foregoing, the separator subject matter of this invention is operating
as described hereinafter. To obtain acceptable results and yields it is obviously
necessary to provide for extreme dispersion of the mixture to be sorted out so that
each elementary item in the dispersed mixture has a sufficient degree of freedom.
[0029] Dispersions with a 3% to 8% content of dry solid matter are usually adopted. The
mixture to be separated is introduced through the channel 3 where a fair amount of
water is also added. The heterogenous suspension is let into the dispersion chamber
2 in which downward circulating water is whirling under the helical action of the
bladed impeller 13 having the shape of an upside-down "chinese hat".
[0030] The mixture is dispersed during its downward motion towards the impeller and even
water-repellent items which tend to float are entering the liquid whirlpool and entrained
downwards. The dispersed mixture thus obtained is hurled outwards where the lighter
and floating fractions (vegetables, paper and organic matter) will reascend in a spiral
motion along the wall of the discrimination tank 1 until they reach the water surface
where part of it will flow over the edge 4 to be discharged through the drain channel
5 whereas another part will be drawn back to the center of the dispersion chamber
2 to start another cycle together with the material coming from the channel 3.
[0031] Heavy fine solid matter will be centrifuged beyond the fluid threads which can be
ideally identified in the water flow and these fines will impinge on the fixed wall
of the discrimination tank 1. When impinging on the wall, their speed is checked or
at least greatly reduced so that the gravity action and the differential downward
thrust will prevail.
[0032] Thus, the lighter solid fractions or those having a larger wetted surface with respect
to their volume will be entrained upwards in a spiral motion toward the water surface,
whereas the heavier fractions such as inert materials, metals etc. will move downwards
following the same helical motion. The more or less fast downward movement will bring
these heavy fractions below the YY center-line of the impeller 13 where they will
be entrained by a secondary whirlpool and hurled outwards and then thrust axially
upwards under the action of the radial blades mounted on the lower surface of the
impeller 13. The discriminant action leading to complete release and separation of
inert solids from the remaining components of the mixture is thus completed in this
cone-shaped terminal section of the tank 1.
[0033] Inevitably, some fractions having a density of approximately 1 will also be entrained
during the downward spiral movement and will zeroize their centrifugal component when
impinging on the cone wall so that they will be conveyed downward together with the
heavier material.
[0034] At a given point during their sinking, the ideal trajectory will convey this mixture
of inert and organic matter in front of the blading 9 through which a certain amount
of clean (or recycled) make-up water will be let in the same direction of the spiral
flow inside the cone.
[0035] This strean will ensure that less heavy particles will be directed towards the cone
axis where they will be caught by the axial flow towards the impeller and recycled
towards the periphery of the YY section.
[0036] The reascending water stream, due to the water entering the blading 9, will convey
the organic particles back to the upper portion of the YY section so that they will
recirculate in the main stream towards the upper edge 4 of the tank where the water
and the floating fractions will be discharged into the ring-shaped channel 5 and drained
through the outlet 6, as already explained above.
[0037] The heavier materials, rigid plastics, sand, glass, fragments of pottery, metal and
the like will pass the threshold 7 of the discharge orifice of the cone in a slight
counter-current flow of the water entering the settling basin 21 through the feed-cock
26, then flowing upwards through the threshold 7 into the discrimination tank 1, to
be discharged into the anular channel 5 together with the purified material and drained
through the outlet 6.
[0038] Heavy and polluting fractions entering the settling tank 21 where the water is virtually
calm, will sink to the bottom 24 of the tank 21. They will be scooped by the chain
scraper 27 gently grazing the bottom wall 24 of the settling tank 21 and lifted along
the sloping wall section d until they are raised above the liquid surface "1" and,
after partial dewatering, are discharged through the outlet 25.
1. Wet separator for discrimination of two or more solid fractions of heterogeneous
mixtures having differentiated density values in water, characterized by the fact
that the system is consisting of:
- an external settling basin (21) having two parallel sides (22, 23), closed at their
lower end by a polygonal bottom (24) and provided with an outlet nozzle (25) through
which the heavy fractions are discharged and with a feed pipe (24) for water supply,
- a chain scraper (27) dredging the bottom of the tank (21), thus collecting the heavy
fractions which have sunk to the bottom and conveying them to the above mentioned
discharge opening (25),
- a discrimination tank (1) located inside the settling basin (21) at its largest
vertical section (XX), which cylinder-shaped tank (1) has an open truncated cone shaped
bottom (7), an upper recovery channel (5) with discharge nozzle for the lighter fractions
and is kept filled with water;
- a spiral chamber (8) with inward guide vanes (9), located near the bottom orifice
(7) of the discrimination tank (1) and receiving water through the duct (10) ,
- a cylindrical dispersion chamber 2 with an open truncated cone-shaped bottom, coaxially
located inside the discrimination tank (1) and supported by the latter, in which the
material to be discriminated is charged from above through the channel (3),
- a motor-driven propelling assembly consisting of an impeller (13) shaped like an
upside-down chinese hat and fitted with blades on its upper and lower surface, mounted
between the lower orifice of the dispersion chamber and the spiral chamber (8),
so that the components of the heterogeneous mixture can be separated either by gravity
or under the action of proper whirlpools generated by the impeller and by the spiral
chamber
2. Separator as described in claim 1, characterized by the fact that the polygonal
bottom (24) of the settling tank (21?) has at one end a vertical length (a) followed
by a length (b) sloping towards the center, a horizontal length (c) and a final length
(d) gently sloping upwards towards the other end of the basin fitted with the water
feed pipe (26) and the outlet (25) through which the heavy fractions are discharged.
3. Separator as described in claim 1, characterized by the fact that the upper edge
(4) of the discrimination tank (1) has an overflow level (e) in the discharge channel
(5) coinciding with the water level (1) in the settling tank (21) when the discrimination
tank (2) is completely immersed.
4. Operation of the separator as described in claim 1, characterized by the fact that
:
- the mixture to be discriminated is let into the dispersion tank (2) through the
channel (3),
- this mixture in the dispersion chamber (2) is subjected to a whirling downward flow
and is thus dispersed, so that all fractions of the mixture, even the lighter ones,
will reach the discrimination chamber (1) where they are flung outwards under the
action of the impeller (13);
- in the discrimination chamber (1) the lighter floating fractions will spiral upwards
along the walls until they reach the free water surface and are discharged over the
edge (4) into the drain channel (5) or reach the central zone of the basin to be recycled
in the dispersion chamber (2) joining the fresh incoming mixture; ;
- The heavy fractions in the discrimination chamber (1) will move downward where they
are exposed to the action of the radial vanes (9) of the spiral chamber (8) and to
the related upward flow of the water discriminating any light fractions entrained
by the heavier fractions in their downward motion, so that the lighter fractions can
be recycled by the impeller (13);
- the heavy fractions are countercurrent discharged through the lower opening of the
discrimination tank (1) together with the water let into the settling basin (21) through
the feed-cock (26); the heavy fractions will sink to the bottom (c) of the settling
tank (21) from where they are dredged by the chain scraper (27) and discharged through
the outlet (25).
5. Operation as described in claim 4, characterized by the fact that an extreme dispersion
of the substances to be discriminated is achieved in the water and that, for indicatory
purposes, the dry substance content in the mixture ranges between 3% and 8%.