GB2085750A

GB2085750A - Vacuum apparatus for liquid extraction of solids

Info

Publication number: GB2085750A
Application number: GB8022699A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-07-24
Filing date: 1980-07-24
Publication date: 1982-05-06
Also published as: DE3128576A1

Abstract

An intermittently operating device for extracting or washing components from solids lying on a pervious band 24 contained within a chamber 28, 2 that is sealed by means of a hinged cover 1 that can be moved vertically by means 21. A batch of solids in slurry form is introduced from agitation tank 17 into the chamber where the slurry is dewatered by means of a vacuum pump 20 connected through vacuum receivers 29, 30 via line 34 to the bottom sealed chamber 2 that supports the pervious band. A number of charges of liquid with various concentrations of solute which have been obtained from the extraction of the previous batch of solids are consecutively drawn under vacuum into the chamber containing the solids and sucked through the solids and the pervious band. The liquids with differing concentrations of solute are then removed as described to separate vacuum chambers 29, 30, the liquid with the strongest solute concentration being first pumped from the system via line 37 to a storage tank. The cover 1 is then raised and the solids are then discharged from the chamber by means of pervious band 24 driven by a motor 5. The sequence of opening and closing the various valves indicated is described in detail. <IMAGE>

Description

SPECIFICATION A device for the extraction and washing of solids by means of vacuum Many devices are employed in a wide variety of industries for facilitating the separation of two or more components which are in intimate contact with one another whereby at least one component is in the solid phase.

In many cases the high affinity of a solvent for one particular component in a solid is employed for leaching or extracting the component out of the solid thereby achieving the required separation. These operations are commonly referred to as extraction.

In some cases the surfaces of solids in granular or crystalline form are covered by a layer of liquid containing a component in solution that has to be separated from the solid phase. These liquids often fill the interstices between and within the grains of solids. These liquids containing dissolved substances are often displaced by the same liquid in a pure state. This type of operation is often called washing but the actual removal or separation mechanism is in part similar to the mechanism involved with extraction operations.

The mechanism common to both operations is one of diffusion whereby a solute migrates from an area of higher concentration to one of lower concentration.

In order to minimize the usage of solvent or wash ing liquid for separation countercurrnnt extraction or washing techniques are mostly employed.

The conventional devices for these operations normally take the form of a moving endless band with or without a number of containers open at the top. Another variation takes the form of a rotating horizontal circular disc.

These devices rely on gravity for forcing the solvent through the layer of solids and can only handle materials with a relatively coarse particle size. Finer particles are often more desirable because the necessary diffusion can take place more rapidly and thoroughly thus increasing the yield of the component being extracted. The conventional devices for extraction cannot handle very fine particulate matter because the capacity of the device is too low and the finer particles either tend to escape through the medium supporting the bed of solids or the medium supporting the bed of solids blinds within a short time. A further disadvantage of these conventional devices is that a large number of pumps are required to recirculate the solvent after it has passed through the beds or individual containers.

The conventional devices used for washing solids normally take the form of a moving endless band where the liquid used for washing is sprayed onto the top of the layer of solids lying on the surface of a porous band. Mixing of the streams of washing liquid in counter-current washing takes place on the surface of the solids reducing the washing efficiency Gas tends to be drawn through the bed of solids together with the liquid causing cracks in the structure of the bed of solids. This leads to by-passing of the wash liquid and further inefficiency. Atrue displacement washing of the solids cannot take place because a layer of washing liquid cannot be held on the surface of the bed of solids. Each washing section requires a separate pump for recirculating the washing liquid.

The present invention which can be described as a vacuum extractor solves these problems and consists essentially of an endless porous band 24 mounted on rollers 4. 27. Roller 27 is driven by motor 5. The top section of the endless band lies on a perforated support plate 23 which forms the top surface of a lower chamber 2. A lid 1 hinged at one end is movable in a vertical direction and in the lowered position seals the section of the band lying on chamber 2 thus forming a top chamber 28. The lower chamber 2 is connected by pipe 34 to tanks 29,30.

Tanks 29, 30 are connected at the top through pipe 35 to the inlet of vacuum pump 20.

The invention operates in the following manner: The lid 1 is lowered onto a clean section of band 24. The solids to be extracted or the scurry to be washed are introduced to tank 17 through connection 8. Tank 29 is empty. Tank 30 contains wash or extraction liquid from the previous cycle. Tank 31 contains fresh solvent or wash liquid.

When solids are to be extracted, solvent is pumped into tank 17 from a vessel which is not shown. The contents of tank 17 are mixed by means of agitator 18. The vacuum pump 20 is started up with valves 12, 9, 26 in the open position. An under- pressure is generated in chamber 28,2 and in tank 29. On reaching a preset value of underpressure the contact manometer 22 opens inlet valve 6. The slurry in tank 17 is drawn into the chamber 28. On reaching a preset value on contact manometer 22 valves 6, 26 close and valve 38 opens.

Clean liquid extract is drawn through the band into tank 29. A signal from contact rotameter 39 closes valves 9, 12,38. Valves 40, 16 open and pump 42 starts up. The contents of tank 29 are pumped through pipe 37 to a storage tank not shown. When tank 29 is empty valves 40, 16 close and pump 42 shuts down. Simultaneously valves 9, 12, 26,41 open. On a signal from contact manometer 22 valve 14 opens and the contents of extract tank 30 are drawn into the chamber 28 and are distributed over the layer of solids lying within the chamber. The underpressure in chamber 28 rises when extract tank 30 is empty and at a preset value contact manometer 22 closes valves 14,26,41 and opens valve 38. The liquid lying on the solids is drawn into extract tank 29.The contact rotameter 39 then signals the first ingress of gas through the bed of solids and valves 9, 12 and 38 are closed. The contents of tank 29 are pumped through pipeline 37 to a storage tank not shown. Simultaneously valves 10, 11,26 open.

When a preset value on contact manometer 22 is reached valve 13 opens. The underpressure in chamber 28 rises when tank 31 is empty and at a preset value contact manometer 22 closes valves 13, 26 and opens valve 38. The liquid lying on the solids is drawn evenlythroughthe bed of solids and is collected in tank 30. Contact rotameter 39 then signals the first ingress of gas through the bed of solids and after a further set time has elapsed, during which the residual liquid is removed from the solids by the gas stream, valves 10, 11 are closed and valve 26 is opened. Tank 31 is then filled with fresh wash liquid or solvent through pipeline 32.

Further tanks for further washing or extraction stages can be used as required.

The lid 1 is opened by means of pressure cylinder 21. The motor driven roller 27 rotates in a clockwise direction and the washed or extracted solids are transported out of the chamber and discharged on roller 4. The band is then passed through a wash tank 25 fitted with spray nozzles. The resulting wash liquid is returned to tank 17 by means of a pipeline that is not shown. A timer controls the length of band that passes through the tank. The motor 5 is shut down and the lid is lowered onto the stationary section of band lying on the chamber 2.

The cycle described above is then repeated.

Claims

CLAIM

1. A device for extracting or washing components from solids having an endless porous band 24; a perforated support plate 23 to support the porous band 24 thereon and forming a lower chamber 2; a hinged lid 1 which in its lowered position seals the section of porous band lying on the perforated support plate forming an upper chamber 28 which is in communication with an agitated tank 17; a liquid extract connection 34 joining the lower chamber 2 with the liquid extract tanks 29,30; a vacuum pump 20 connected to liquid extract tanks 29,30; a connection 33 for the liquid extract and the fresh wash liquid or solvent connects the liquid extract tanks 29,30 and the fresh wash liquid or solvent tank 31 with the upper chamber 28 and a transport means 4,27,5 in engagement with the porous band 24 to transport the porous band over the perforated support plate 23 and between the upper chamber 28 and the lower chamber

2.