A method and device for removing liquid from a mixture of liquid and solid matter

Abstract: The invention relates to a method for removing liquid from a mixture of liquid and solid matter. Said mixture is led over one or more casings by means of a conveyor belt which is pervious to liquid. In use a sub-atmospheric pressure is generated in the casings during a first period, in which said casing(s) and said conveyor belt are stationary with respect to each other, whilst at the same time a pressure is exerted on the mixture by means of rollers. During a period following on said first period a relative movement takes place between the conveyor belt and the casing(s), whilst during this period no sub-atmospheric pressure is exerted in the casings and no compressive force is exerted on the mixture by means of the rollers.

Description: The invention relates to a method for removing liquid from a mixture of liquid and solid matter, whereby the mixture is led over one or more casings by means of a conveyor belt which is pervious to liquid, whereby during operation first periods, in which said casing(s) and said conveyor belt are stationary with respect to each other and in which a sub-atmospheric pressure is maintained in said casing(s), are alternated with second periods in which a relative movement between the conveyor belt and the casing(s) is effected and the pressure in the casing(s) is kept at that of the surrounding atmosphere. Such a method can be derived from FR-A-2,194,466. Said known device is satisfactory by itself, but in a number of cases it may be desirable to effect an even better removal of liquid from a mixture of liquid and solid matter. According to the invention the method is performed as described in the characterising part of claim 1. By using the method according to the invention a particularly effective removal of liquid from the mixture can be obtained during the periods when the casing(s) and the belt are stationary with respect to each other, as a result of the sub-atmospheric pressure in the casing(s) and the simultaneous compression of the mixture by means of the pressure rollers. By not exerting a force in the direction of the conveyor belt by means of the pressure rollers during said second periods, the casing(s) and the belt can move with respect to each other, without undesirably large forces being exerted on the parts formed by the casing(s) and the conveyor belt which are moving with respect to each other, which forces might lead to excess wear and/or rupture of the parts in question. It is noted that from FR-A-2,168,154 a device is known which is provided with a filter belt which moves over a trough . Near said trough a few pressure rollers are disposed above the filter belt, said rollers only being supported on the belt under the influence of their own weight. It is not possible hereby to release the pressure exerted on the material by the rollers, nor is it possible to control the pressure exerted by the rollers independently. Consequently such a construction will not be suitable for use in a device wherein the belt moves over casings in which a sub-atmospheric pressure can be generated. A similar device is known from US-A-3,531,404. This publication does not relate to a device in which the extraction of liquid from a mixture is promoted by means of a vacuum either. Also with this known device the rollers occupy a fixed position with respect to the conveyor belt, by means of which the material to be de-watered is moved. Said publication does mention, however, that the rollers are mounted in such a manner that it is possible to adjust the pressure exerted by the rollers, but no means are provided for moving the rollers, once they are arranged in a certain position, to and fro between a position in which they exert an effective pressure on the mixture to be de-watered and a position, in which no substantial pressure is exerted on said mixture. US-A-4 101 400 discloses a device having a filter belt supported by rollers. Above said filter belt there has been arranged a further belt which is passed over further rollers. Said further rollers cannot be displaced independently of each other. Further there is known from FR-A-2 416 043 a device having a filter belt which is continuously driven during operation of the device. The filter belt is vibrated by a vibrating device and downstream of said vibrating device there are arranged pressure rolls continuously pressing the mixture on the filter belt. A device according to the invention, which is particularly suited for carrying out a method according to the invention is described in claim 3, 8 and 9. When using such a device it is possible, if required, to exert additionally and independently pressures on the mixture present on the conveyor belt, by means of the various pressure rollers, during those periods in which a vacuum is generated in the casing(s), as a result of which a very effective de-watering adapted to the material to be processed can be achieved. The invention will be explained in more detail hereafter, with reference to a few possible embodiments of a device according to the invention diagrammatically illustrated in the accompanying Figures. Figure 1 is a diagrammatic side elevational view of a first embodiment of a device according to the invention. Figure 2 is a larger-scale view of a part of the device shown in Figure 1. Figure 3 is a cross-sectional view of Figure 2. Figure 4 is a diagrammatic, larger-scale view of a part of the device shown in Figure 1, illustrating a modified embodiment. Figure 5 is a diagrammatic side elevational view of a second embodiment of a device according to the invention. Figure 6 is a larger-scale cross-sectional view of a part of Figure 5, wherein for easy reference certain parts have been left out. Figure 7 is a side elevational view of a third possible embodiment of a device according to the invention. The device shown in Figure 1 comprises a endless conveyor belt 1 which is pervious to liquid, said conveyor belt being passed over guide rollers 2 and a drive pulley 3. The upper part of the conveyor belt 1, on which the mixture of liquid and solid matter is present during operation, and which thus forms the mixture-moving conveying portion of the conveyor belt, is led over one or more casings 4 which are coupled together, said casings being connected, by means of pipes 5, to vessels 6 in which a sub-atmospheric pressure can be generated by means of a vacuum pump 7 connected to said vessels. Liquid collected in said vessels 6 can be discharged via the pipes 8. The casings 4 can be moved to and fro in the direction indicated by the arrow A by driving means (not shown). The construction of such a device, as far as described above, is generally known per se. According to the invention a plurality of rollers 9, three in the illustrated embodiment, are provided near the downstream end of the upper conveying portion of the conveyor belt 1. Said rollers 9 are resting on a part of a pressure belt 11 supported by guide rollers 10, said part extending parallel to the upper part of the conveyor belt 1. As is illustrated in more detail in Figures 2 and 3, each of the rollers 9 is freely rotatably supported by a shaft 12. The ends of each shaft 12 are coupled to setting cylinders 13, by means of which the shaft 12, and with it the roller 9 supported by the shaft 12 in question, can be moved in vertical direction. Three supporting rollers 14 extending parallel to the rollers 9 are disposed under the casing(s) 4, near the pressure rollers 9. Each supporting roller 14 is mounted on a shaft 15. Each shaft 15 has a sprocket wheel 16 mounted on one of its ends. An endless driving chain 18 is passed over said sprocket wheels and over a sprocket wheel 17 coupled to the driving drum 3, as is diagrammatically indicated in Figure 2. Near the supporting rollers 14 a reinforcing place 18' is provided between the supporting rollers and the bottom side of the casing(s) 4. During operation the conveyor belt 1 will generally be driven continuously by means of the driving drum 3, in such a manner that the upper part of said conveyor belt 1 is moved in the direction according to the arrow B. As already said before the casing(s) 4 are moved to and fro during operation by driving means (not shown). When the casings move in the same direction as the upper part of the conveyor belt 1 a sub-atmospheric pressure will be generated in at least some of the casing(s) 4, so as to suck liquid from the mixture of liquid and solid matter present on the belt 1. During the movement of the casing(s) 4, in a direction opposite the direction of movement of the conveyor belt, generally no vacuum will be maintained in the casing(s) 4, in order to prevent the conveyor belt from adhereing to the casings during the return movement. Whilst the casings 4 are moved in the same direction as the upper part of the conveyor belt 1, the rollers 9 will be pushed downwards by means of the setting cylinders 13, so as to exert pressure, via the pressure belt 11, on the material present on the conveyor belt 1, in order to squeeze moisture from said material. The compressive force exerted on the casing(s) 4 is thereby transmitted, via the plate 18', to the supporting rollers 14. The drive of said supporting rollers by means of the chain 18 and the sprocket wheels 16 and 17 is thereby chosen such that the peripheral velocity of the parts of the supporting rollers 14 making contact with the plate 18' is at least substantially equal to the rate of displacement of the conveyor belt 1 in the direction indicated by the arrow B. During the return movement of the casings the pressure rollers 9 will be moved upwards, so as to prevent the occurrence of undesirable forces in the system. Preferably the forces exerted on the pressure rollers 9 by means of the setting cylinders 13 can be independently adjusted for each pressure roller, so as to be able to squeeze out the material present on the conveyor belt 1 in the most optimal manner. Thus it is e.g. conceivable, as is also the case with similar known devices, to drag along the casings 4 in the direction according to the arrow B by means of the conveyor belt 1, by the forces which are generated as a result of the conveyor belt being sucked against the casing(s) 4. Since large forces are exerted by the pressure rollers, however, it is preferred to provide a positive drive for the casings 4. Furthermore a casing 20 may be provided beside the pressure rollers 9, as is diagrammatically shown in Figure 4, via which pressurized air or a suitable gas can be blown through the layer of mixture present on the conveyor belt 1, so as to blow off moisture present in said layer of mixture in this manner. The casing 20 may occupy a fixed position thereby, or be reciprocatingly movable by means of setting cylinders, in a similar manner as the pressure rollers 9. Also it will be possible to provide the pressure rollers 9 and/or the casing 20 without using the pressure belt 11. With the embodiment according to Figure 5 use is made of a number of casings 21 which are pivotally coupled together so as to form an endless chain, said casings being passed over guide rollers 22, whereby at least one of said guide rollers is driven. Said device is furthermore provided with an endless conveyor belt or filter belt 23 whose path, guided by guide rollers 24, is such that the upper part of said conveyor belt 23 is supported on the upper part of the endless chain formed by the casings 21. The bottoms of the casings 21 are provided with perforations, which move, in the upper part of the chain formed by the casings 21, over casings 25 disposed under said upper part, in which casings a sub-atmospheric pressure can be generated by means similar to those described with reference to the first embodiment. Near the downstream end of the upper part of the conveyor belt 23 pressure rollers 9 and a pressure belt 11 are provided again, in a similar manner as explained with reference to the first embodiment. Near said pressure rollers 9 the casings 21 are supported by supporting rollers 26 provided under the casings 21 and on both sides of the casings 25, which supporting rollers 26 can again be rotated via a chain 27. With this device the endless chain formed by the casings 21 and the conveyor belt 23 moves continuously in the direction according to the arrow C, whilst a sub-atmospheric pressure is being generated in the casings 25. By means of the rollers 9 a pressure may be exerted again, in a similar manner as described above, on the layer of mixture present on the upper part of the conveyor belt 23. Said pressure may be exerted continuously or intermittently and/or different for each roller, as required. Figure 7 shows an embodiment wherein an endless conveyor belt 28 is moved over a number of stationary casings 29, in which a sub-atmospheric pressure can be generated in a manner similar to the one described above. The belt 28 will thereby be driven in steps in the direction indicated by the arrow D. In this embodiment the pressure rollers 9 and the pressure belt 11, if provided, are accommodated in a frame part which is reciprocatingly movable, by means of a setting mechanism 30, in the direction according to the arrow E. During the movement of the conveyor belt 28 in the direction according to the arrow D the rollers 9 will be pressed down, in the manner described above, on the layer of mixture which is present on the conveyor belt 28 and which is simultaneously moved, by means of the setting mechanism 30, in the same direction as the upper part of the conveyor belt 28. During the standstill period of the intermittently moving belt 28 the pressure rollers 9 will be moved upwards and the frame part supporting the pressure rollers will be returned to its initial position in a direction opposite the direction of movement of the upper part of the belt 28.

Claims: A method for removing liquid from a mixture of liquid and solid matter, whereby the mixture is led over one or more casings (4) by means of a conveyor belt (1) which is pervious to liquid, whereby during operation first periods, in which said casing(s) (4) and said conveyor belt (1) are stationary with respect to each other and in which a sub-atmospheric pressure is maintained in said casing(s) (4), are alternated with second periods in which a relative movement between the conveyor belt (1) and the casing(s) (4) is effected and the pressure in the casing(s) (4) is kept at that of the surrounding atmosphere, characterized in that in order to promote the discharge of liquid during said first period the mixture is compressed by means of pressure rollers (9) arranged above the casing(s) (4) above the part of the conveyor belt supporting the mixture and opposite supporting rollers (14) supporting the casing(s) and being driven in such a manner that the peripheral velocity of the parts of the supporting rollers (14) making contact with the casing(s) (4) is at least substantially equal to the velocity of displacement of the part of the conveyor belt supporting the mixture, whereby said pressure rollers are independently pressed down on the mixture with an adjustable force, whilst during said second periods the pressure rollers (9) do not exert a force in the direction of the conveyor belt (1) on the mixture. A method according to claim 1, characterized in that downstream of the location where the pressure rollers (9) are pressed down on the mixture pressurized air or gas is blown through the mixture. A device for removing liquid from a mixture of liquid and solid matter, provided with an endless conveyor belt (1) which is pervious to liquid and with one or more casings (4) over which a conveying portion of the conveyor belt (1) moving the mixture during operation is led, whereby means are provided for intermittently effecting a relative movement between the casings (4) and the conveyor belt (1) and a relative standstill between the casings (4) and the conveyor belt (1), as well as means (5-7) for generating a sub-atmospheric pressure in said casing(s) (4) during the periods when the conveyor belt (1) and the casing(s) (4) do not move with respect to each other, characterized in that a plurality of pressure rollers (9) extending transversely to the direction of movement are disposed above a conveying portion of the conveyor belt extending over a casing(s) (4) whilst means are provided by which said pressure rollers can be independently pressed down in the direction of the conveyor portion and be moved in a direction away from the conveying portion and means (16-18) are provided for driving the supporting rollers (14, 26) arranged below the casing(s) opposite the pressure rollers (9) in such a manner that the peripheral velocity of the parts of the supporting rollers (14, 26) making contact with the casing(s) (4) is at least substantially equal to the velocity of displacement of the part of the conveyor belt supporting the mixture. A device according to claim 3, characterized in that the construction of said means for pushing the rollers (9) in the direction of the conveyor belt (1) is such that the pressure exerted by a roller (9) can be adjusted independently of the pressure exerted by another roller. A device according to claim 3 or 4, characterized in that a pressure roller (9) is provided freely rotatably about a shaft (12), whose ends are supported by means of setting cylinders (13). A device according to any one of the claims 3-5, characterized in that an endless pressure cloth (11) is passed over the pressure rollers (9). A device according to any one of the claims 3-6, characterized in that downstream of the pressure rollers (9) means (20) are provided for blowing air or gas through the mixture. A device for removing liquid from a mixture of liquid and solid matter, provided with an endless conveyor belt (28) which is pervious to liquid and with one or more casings (29) over which a conveying portion of the conveyor belt (28) moving the mixture during operation is led, whereby means are provided for intermittently effecting a relative movement between the casings (29) and the conveyor belt (28) and a relative standstill between the casings (29) and the conveyor belt (28), as well as means (5-7) for generating a sub-atmospheric pressure in said casings (29) during the periods when the conveyor belt (28) and the casing(s) (29) do not move with respect to each other, characterized in that a plurality of pressure rollers (9) extending transversely to the direction of movement are disposed above a conveying portion of the conveyor belt extending over a casing (29) having a fixed position, whilst means are provided by which said pressure rollers (9) can be independently pressed down in the direction of the conveying portion and be moved in a direction away from the conveying portion. A device for removing liquid from a mixture of liquid and solid matter provided with an endless conveyor belt (23) which is pervious to liquid and with an endless chain of casings (22) and means for guiding the casings (22) and she conveyor belt (23) so that an upper run of the conveyor belt moving the mixture during operation will be supported by the casings which move together with the conveyor belt during operation and whereby there are provided means (5-7) for generating a sub-atmospheric pressure in said casings, characterized in that a plurality of pressure rollers (9) extending transversely to the direction of movement of the conveyor belt (23) are disposed above the upper run of the conveyor belt opposite supporting rollers (26) supporting casings (22), whilst means are provided by which said pressure rollers can be indepedently pressed down in the direction of the upper run of the conveyor belt and be moved in a direction away from the upper run.

Inventors: PRINSSEN ALPHONS ARNOLDUS JOHA, PRINSSEN, ALPHONS ARNOLDUS JOHANNES ANTONIUS
Applicants: PANNEVIS BV, PANNEVIS B.V.
Application year: 1991
Main classification: B01D33
IPC codes: B01D33, B01D29