Apparatus for the recovery of liquid from a liquid medium containing solids

An apparatus for the recovery of liquid from a liquid medium containing solids includes a rotatable outer drum having a liquid-permeable drum wall and containing liquid-absorbing material, a rotatable inner wall having a liquid impervious drum wall and being mounted for rotation within and eccentrically relative to the outer drum, the drums being rotatable in the same direction into the liquid medium so as to transport the material through a compression zone in which the material is compressed so as to remove absorbed liquid therefrom and subsequently through a pressure-relief zone in which the liquid-absorbing material is allowed to expand and to absorb liquid from the liquid medium, a device or devices contacting the exterior surface of the outer drum to remove solids deposited thereon, such devices being located between the zones, and a device for collecting liquid removed from the liquid-absorbing material in the compression zone.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus for the recovery of a liquid from a 
liquid medium containing solids, said apparatus comprising means for 
contacting said liquid medium with a resilient absorbing material to 
absorb the liquid therein, means for removing the absorbed liquid from 
said resilient absorbing material by pressing and means for collecting the 
liquid thus removed. 
U.S. Pat. No. 1,958,279 discloses an apparatus comprising a hopper for 
feeding sludge onto the top surface of an endless band and means for 
passing said band along a perforated support at which it is compressed by 
one or more rollers to remove liquid therefrom, said liquid being 
collected below said porous support. This prior art apparatus also 
comprises means for removing a layer of solids formed on the top surface 
of said endless band by doctors, and means for subsequently passing the 
endless band through a set of rollers in which additional amounts of 
liquids are removed by pressing. 
A serious drawback of said prior art apparatus is that it is difficult to 
obtain a strong absorbing band having a mechanical strength sufficiently 
high to permit the band to be used over long periods of time under the 
severe influences to which it is subjected during its continuous movement 
and the squeezing operations. 
The object of the invention is to provide an improved apparatus which does 
not suffer from the drawbacks of the prior art apparatus. 
SUMMARY OF THE INVENTION 
The apparatus of the invention is characterized in that it comprises an 
outer rotatable drum having a liquidpermeable drum wall and containing a 
loose liquid-absorbing material, an inner rotatable drum having a 
liquid-impervious drum wall and being mounted within and eccentrically 
relative to said outer drum, driving means for rotating the outer and the 
inner drums in the same direction and at least one device contacting the 
exterior surface of the outer drum and being adapted for removing solids 
therefrom, said device being mounted between the zone in which the liquid 
medium is contacted with the loose liquid-absorbing material and the zone 
in which liquid is squeezed out of the liquid-absorbing material. 
The operation of the apparatus of the invention is as follows: 
During the rotation of the two drums which rotation may be at the same or 
different speeds, the loose liquid-absorbing material is carried along 
with the outer drum and is compressed when it reaches the zone at which 
the distance between the inner surface of the outer drum and the exterior 
surface of the inner drum starts decreasing. During the passage through 
said zone, liquid which previously has been absorbed in the 
liquid-absorbing material, is squeezed out of said material and flows 
towards the exterior surface of the outer drum from which it may be 
collected. 
The apparatus of the invention clearly differs from the above mentioned 
prior art apparatus in which the liquid medium to be treated is introduced 
directly onto the absorbing material because in the apparatus of the 
invention the liquid is extracted from said liquid medium while leaving 
back the solids contained therein. 
This difference not only results in an improved absorption of liquids but 
also extends the time periods in which the absorbing material can be 
efficiently utilized. Thus, the absorbing material becomes less 
contaminated by solids than in the prior art apparatus in which solids 
tend to be deposited in the pores and interstices of the absorbing 
material. 
The outer drum preferably extends into a container for a bath of liquid 
medium to be treated. This embodiment allows the absorption of liquid to 
take place over a relatively long period of time and simultaneously with 
the release of pressure exerted on the absorbing material. Therefore, the 
absorption becomes particularly effective. 
In a further preferred embodiment of the invention a screw conveyor 
extending through a hole in the side wall of said container is mounted for 
rotation at the bottom of said container. This screw conveyor serves to 
remove precipitated solids from the container. By using such a screw 
conveyor, the precipitated solids can be removed from the container 
without stopping the operation of the apparatus. 
The device for removing solids from the exterior surface of the outer drum 
preferably comprises a roller extending parallel to the axis of rotation 
of the outer drum and rolling on and together with said outer drum. By 
using such a roller, the major portion of the solids deposited on the 
exterior surface of the outer roller can be removed in one operation. The 
roller preferably has a coating of a plastics material, such as polyvinyl 
chloride and neoprene rubber, to which the solids deposited on the 
exterior surface of the outer drum adhere. This embodiment of the 
apparatus of the invention preferably also comprises a scraper contacting 
the surface of the roller in a zone opposite to the zone in which the 
roller contacts the outer drum. 
The device for removing solids from the exterior surface of the outer drum 
is preferably located shortly above the surface of the bath of liquid 
medium to be treated. 
The apparatus of the invention may also comprise additional devices such as 
scrapers or doctors for removing remaining solids from the exterior 
surface of the outer drum. When using only one additional device for 
removing solids from the exterior surface of the outer drum, said device 
is preferably a rubber scraper of lip which lightly contacts the exterior 
surface of the outer drum and which is located in a zone in which the 
absorbing material is under a slight compression. By providing the rubber 
scraper or lip in this zone, it will be continuously rinsed by the flow of 
liquid out through the outer drum wall. Since the amount of liquid 
required for said rinsing operation is relatively small, and since such 
liquid may be returned to the bath of liquid medium to be treated, the use 
of such rinsing liquid does not significantly reduce the capacity of the 
apparatus. On the other hand the purity of the extracted material is 
considerably increased by using such a device. 
The rubber scraper or lip is preferably associated with an inclined drain 
which communicates with the bath of liquid medium to be treated and which 
allows the liquid pressed out of the absorbing material as a rinsing 
liquid to be returned to said bath. 
The apparatus of the invention also allows the use of scrapers which are 
strongly pressed against the exterior surface of the outer drum and which 
effect an almost total removal of solids therefrom because said scrapers 
are not in direct contact with the absorbing material and consequently do 
not have any adverse influence on said material. 
The drum wall of the outer drum preferably consists of a perforated metal 
plate covered by a filter cloth. By using filter cloth to cover the 
perforations of the drum wall, various types of absorbing material can be 
used in the apparatus by merely adjusting the mesh size of the filter 
cloth to the absorbing material used. Thus, the same exterior drum may be 
used in connection with different types of absorbing material. 
The filter cloth is preferably made from a plastics material and preferably 
is a nylon fabric. In practice a nylon fabric having mesh sizes of about 
200 .mu.m have been found particularly suitable. A nylon fabric is 
preferred because of its high abrasive strength which enables it to resist 
the influences of devices for removing solids and devices for collecting 
liquid removed from the absorbed material. Furthermore, the surface 
properties of nylon fabrics are such that the solids are easily released 
from said fabrics. 
The drum wall of the outer drum preferably comprises a removable section 
for use in the introduction and discharge of absorbing material from the 
outer drum. The introduction of absorbing material is preferably carried 
out by stopping the rotation of the outer drum in a position at which said 
section is at its highest point. By allowing the inner drum to rotate in a 
direction which is opposite to the normal direction of rotation and by 
dosing absorbing material through a funnel inserted in the opening in the 
outer drum, the space between the two drums are filled. The discharge of 
absorbing material may be effected by stopping the rotation of the 
exterior drum after removing the above mentioned section of the drum wall 
and in a position in which the above mentioned opening is located below 
the axis of rotation and by allowing the inner drum to continue its 
rotation. 
The exterior surface of the inner drum is preferably provided with ribs 
extending longitudinally of said drum. Such ribs improve the movement of 
absorbing material and especially in the area in which the material is 
non-compressed. 
The inner drum preferably rotates at the same speed as that of the exterior 
drum, e.g. at a speed of 10 rpm. 
The absorbing material is preferably a granular foamed plastics material 
which allows the absorption to take place by capillary effect from 
different directions. The absorbing material is e.g. polyether foam having 
a density of 20-50 kg/m.sup.3. Such a material is inexpensive because it 
can be obtained as a waste material formed in the production of foam 
mattresses. 
Another advantage of using granular foamed plastics material as absorbing 
material in the apparatus of the invention instead of using a band 
attached to the exterior surface of the drum as in the prior art apparatus 
is that by using a granular material, the liquid can be absorbed in the 
material from many sides due to the movement of the granules relative to 
one another during the rotation of the drums. Consequently, the lifetime 
of the absorption material is increased. Furthermore, supplementary 
amounts of absorbing material for replacing decomposed material can be 
introduced at short stops of the apparatus. 
The absorbing material, however, may also be present in the form of a loose 
band. 
The means for collecting liquid pressed out of the absorbing material 
preferably comprises a roller or a guide plate which is kept pressed 
against the exterior surface of the outer drum and which is connected with 
means for collecting the liquid removed.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the drawings 1 represents an outer drum having a perforated drum wall 2 
which is coated with a filter cloth (not shown). The drum 1 is by means of 
two end plates 3 attached to two hollow journals 4, of which one is 
connected to driving means (not shown). An inner drum 5 having a 
liquid-impermeable drum wall is mounted within the outer drum 1 and 
eccentrically relative thereto. The ends of the inner drum 5 are provided 
with journals 6, of which one is connected with driving means (not shown). 
At the exterior surface of the inner drum 5 there are provided ribs 7 
extending over the full length of the drum and longitudinally thereof. The 
space between the outer drum 1 and the inner drum 5 is filled with a loose 
granular foamed plastics material 8. 
The outer drum 1 is mounted partially immersed in a liquid bath contained 
in a container 9 comprising a filtration compartment 10 and a discharge 
compartment 11. These compartments are separated by a plate 12 having an 
upper edge 13 located below the normal level of the liquid in the 
container 9. In the lower portion of the compartment 10 which is 
downwardly tapered there is provided a screw conveyor 14 having a shaft 
connected to a driving means (not shown). The screw conveyor 14 extends 
through a pipe section 16 through the plate 12 and terminates a short 
distance within the compartment 11. The lower portion 17 of the 
compartment 11 is downwardly tapered and terminates in a discharge pipe 18 
comprising a valve 19. 
At one side of the container 9 there is provided a liquid collecting 
chamber 20 having a discharge pipe 21. Located above the liquid collecting 
chamber 20 there is provided a guide plate 22 extending over the full 
length of the outer drum and being attached to a longitudinally extending 
rod 23. The edge of the guide plate 22 facing the outer drum 1 is 
connected to a rubber lip 24 which at its outer edge contacts the exterior 
surface of the drum 1. At each end of the drum 1 a sealing disc 25 which 
is displaceable on the rod 23 is maintained in contact with the end plate 
3 by a spring 26 which at its outer end contacts a stop 27 mounted on the 
rod 23. 
At the diametrically opposite side of the drum 1 there is mounted a 
discharge roller 28 extending parallel with the drum 1 and rolling 
thereon. At the side of the discharge roller 28 which is diametrically 
opposite to the zone in which it is in contact with the outer drum an 
essentially vertical scraper 29 is provided. At the upper edge of the 
scraper 29 it contacts the roller and the lower edge of said scraper is 
mounted above an inclined chute 30, the lower end of which is located 
outside the container 9. 
Between the discharge roller 28 and the guide plate 22 there is mounted a 
rubber scraper 32 supported by a holder 31 and a soft rubber lip 33 which 
is attached to the upper edge of an inclined plate 34. The lower edge of 
the plate 34 is connected to an inclined drain 35 having at its lower end 
a discharge pipe 36 terminating above the compartment 11. 
The apparatus illustrated further comprises a pipe 37 for supplying liquid 
medium to the compartment 10 of the container 9. 
The apparatus illustrated operates as follows: 
While introducing liquid medium into the compartment 10 of the container 9, 
the outer drum 1, the inner drum 5 and the screw conveyor 14 are rotated 
by the driving means (not shown). Such driving means may be an electric 
motor having pinions for effecting a syncronous rotation of the drums 1 
and 5 and the screw conveyor 14. 
During the pressure release which takes place while the absorbing foamed 
material 8 through the drum wall 2 is in contact with the liquid medium in 
the compartment 10, a quick and extensive absorption of liquid in the 
material 8 takes place. At the same time solids contained in the liquid 
medium and unable to penetrate through the filter cloth are deposited 
thereon so as to form a layer. When said layer contacts the discharge 
roller 28, a major portion thereof is transferred to said roller. The 
layer transferred is removed from the discharge roller 28 by the scraper 
29 and falls down onto the chute 30 from which it is moved outside of the 
apparatus. During the continued rotation of the outer drum 1 the exterior 
surface thereof contacts the rubber lip 32 which removes additional 
amounts of solids. The solids thus removed falls down into the zone 
between the outer drum 1 and the discharge roller 28 and are introduced 
onto said roller 28. 
When the drum 1 is further rotated, an initial compression of the absorbing 
material 8 takes place. Consequently, liquid is pressed out through the 
drum wall 2. The liquid thus removed is collected by the rubber lip 33 and 
is passed down along the plate 34 to the drain 35 from which it is 
returned to the container 9 through the pipe 36 terminating above the 
compartment 11. During this movement of liquid through the drum wall 2, 
both the drum wall 2 and the filter cloth is rinsed. When the absorbing 
material 8 is further compressed in the narrow zone between the inner 
surface of the outer drum 1 and the exterior surface of the inner drum 5 
into which zone the material is transported by means of the ribs 7, the 
absorbed liquid is squeezed out of the absorbing material and passes 
through the drum wall 2 and the filter cloth. The liquid thus removed from 
the absorbing material flows against the rubber lip 24 and from this lip 
down along the guide plate 22 and into the liquid collection chamber 20 
from which the liquid is removed through the discharge pipe 21. 
After having passed the zone adjacent to the rubber lip 24, the material 8 
expands and during said expansion it is contacted with the liquid medium 
contained in the container 9. Consequently, a renewed absorption of liquid 
takes place and the process is repeated as described above. 
During the separation of liquid from the liquid medium contained in the 
container 9, solids are concentrated at the bottom of the compartment 10. 
By rotating the screw conveyor 14, the solids precipitated are moved into 
the compartment 11 in which they are collected at the bottom 17 thereof. 
The collected solids may be removed therefrom through the pipe 18 and the 
valve 19 or may be removed by using a suction pipe which is lowered into 
the compartment 11. 
By adjusting the location of the rubber lip 33, the rinsing of the drum 
wall 2 and the filter cloth and consequently the recycled amount of liquid 
may be controlled.