GB1559080A - Filters - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO FILTERS (71) We, ALFA - LAVAL COMPANY LIMITED, a British Company of Great West Road, Brentford, Middlesex TW8 9BT., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the art of filtering and more especially to horizontal plate or leaf filters. Filters of this type generally consist of a plurality of horizontal - filter discs positioned one above the other in a pressure vessel. The discs surround an apertured hoilow shaft or column and an annular flow channel is defined between the periphery of the discs and the vessel.

In some installations the slurry to be filtered is fed to the annular channel from the bottom of the pressure vessel. The slurry passes upwardly through this channel and flows inwardly towards the filter axis with filtration taking place at the upper surface of each of the horizontal filter discs. Solids present in the slurry are retained by the filter discs while the cleansed liquid or filtrate passes into the central shaft to be removed from the pressure vessel near its base.

The vertical velocity component of the feed slurry in the annular channel decreases in the vertical direction as more slurry flows inwardly to be filtered by the discs, and a dead space normally exists in the annular feed channel below the lowermost leaf filter.

When the slurry is made up of easily suspended solids turbulence inside the filter vessel is sufficient to ensure homogeneity of the suspension and prevent premature sedimentation of the solids. If the slurry includes dense or coarse solids, however, such as copper alloy powder, or silica or zirconium sand, having an average particle size of approximately 20 to 50 microns, the sedimentation rate of the slurry is so high that solids tend to deposit in the dead space at the base of the filter vessel. The solids also tend to be unevenly distributed over the filter discs.

The present invention aims at eliminating this drawback and accordingly provides a horizontal leaf filter for filtering solids containing liquid comprising a casing having an inlet for the liquid in a lower- portion of the casing, a first outlet for filtered liquid and a second outlet for solids, a stack of horizontal filter plates mounted on a vertical column within the casing, the column serving to conduct liquid having passed through the filter plates to said first outlet, and means for removing unfiltered liquid from an upper portion of the casing and returning it to the lower portion of the casing, thereby to increase the flow velocity of unfiltered liquid within the casing.

The invention also provides a method of filtering solids containing liquid with a horizontal leaf filter having a casing with an inlet in a lower portion thereof for feed liquid, an outlet for filtrate and an outlet for solids, and a stack of horizontal filter plates mounted in the casing on a vertical column which serves ta conduct filtrate to the filtrate outlet, the method comprising the steps of feeding liquid to be filtered through the inlet, removing unfiltered liquid from an upper portion of the casing and returning the removed liquid to the lower portion of the casing, thereby to increase the flow velocity of unfiltered liquid within the cain: or casing.

The recycling of unfiltered liquid or slurry to increase the velocity of the suspension in the casing can ensure an homogeneous suspension within the casing.

Two embodiments of the invention are described below by way of example with reference to the accompanying drawings, in which: Figure 1 schematically illustrates a first horizontal leaf filter installation; and Figure 2 is a similar view of a second horizontal leaf filter installation.

The filter shown in Figure 1 consists of a casing in the form of a pressure vessel 1 in which a plurality of horizontal filter leaves or plates 2 are housed. An annular feed channel is defined between the periphery of the filter plates and the vessel, and an axially extending passageway connected to port 3 is provided for discharge of filtrate. The filter is adapted for use when the filtered solids are to be discharged as a dry friable powder and is provided with means 4 for removing this solid.

An inlet conduit 5 for the supply of suspension is connected to the vessel near its base, a pump 6 being inserted in the conduit for generating the required filter pressure. As so far described the filter is of conventional construction.

A vent at the top of the pressure vessel is controlled by a valve 7 and communicates with the slurry feed channel. The vent is connected to a conduit 8 leading to an inlet 9 at the base of the vessel and also com- municating with the slurry feed channel.

A pump 10 is located in the conduit 8 and in use of the filter is operated to remove slurry from the top of the vessel and return it to the vessel near its base. This recycling of slurry increases the velocity of the slurry in the annular channel and keeps the dead space below the lowermost filter disc free of deposited solids. Furthermore. the resulting homogeneity of the slurrv in the vessel results in the filtered solid being evenly distributed over the filter leaves.

The horizontal leaf filter installation shown in Figure 2 is generally similar to that of Figure 1, but is adapted for use when solids are to be discharged in a suspension. The same reference numerals have been employed to designate equivalent parts in the two Figures and the description of the Figure 1 installation will also serve for that of Figure 2.

WHAT WE CLAIM IS: 1. A horizontal leaf filter for filtering solids containing liquid comprising a casing having an inlet for the liquid in a lower portion of the casing,-a first outlet for filtered liquid and a second outlet for solids, a stack of horizontal filter plates mounted on a vertical column within the casing, the column serving to conduct liquid having passed through the filter plates to said first outlet, and means for removing unfiltered liquid from an upper portion of the casing and returning it to the lower portion of the casing, thereby to increase the flow velocity of unfiltered liquid within the casing.

2. A filter according to claim 1 or 2, wherein said means comprises a pipeline and a pump positioned in the pipeline for pumping liquid from and back to the casing.

3. A filter according to claim 3, wherein a valve is located in the pipeline for controlling the amount of liquid which is removed from and returned to the casting.

4. A horizontal leaf filter substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings. 5. A method of filtering solids containing liquid with a horizontal leaf filter having a casing with an inlet in a lower portion thereof for feed liquid, an outlet for filtrate and an outlet for solids, and a stack of horizontal filer plates mounted in the casing on a vertical column which serves to conduct filtrate to the filtrate outlet, the method - comprising the steps of feeding liquid to be filtered through the inlet, removing unfiltered liquid from an upper portion of the casing and returning the removed liquid to the lower portion of the casing, thereby to increase the flow velocity of unfiltered liquid within the casing.

6. A method of filtering solids containing liquid substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. which: Figure 1 schematically illustrates a first horizontal leaf filter installation; and Figure 2 is a similar view of a second horizontal leaf filter installation. The filter shown in Figure 1 consists of a casing in the form of a pressure vessel 1 in which a plurality of horizontal filter leaves or plates 2 are housed. An annular feed channel is defined between the periphery of the filter plates and the vessel, and an axially extending passageway connected to port 3 is provided for discharge of filtrate. The filter is adapted for use when the filtered solids are to be discharged as a dry friable powder and is provided with means 4 for removing this solid. An inlet conduit 5 for the supply of suspension is connected to the vessel near its base, a pump 6 being inserted in the conduit for generating the required filter pressure. As so far described the filter is of conventional construction. A vent at the top of the pressure vessel is controlled by a valve 7 and communicates with the slurry feed channel. The vent is connected to a conduit 8 leading to an inlet 9 at the base of the vessel and also com- municating with the slurry feed channel. A pump 10 is located in the conduit 8 and in use of the filter is operated to remove slurry from the top of the vessel and return it to the vessel near its base. This recycling of slurry increases the velocity of the slurry in the annular channel and keeps the dead space below the lowermost filter disc free of deposited solids. Furthermore. the resulting homogeneity of the slurrv in the vessel results in the filtered solid being evenly distributed over the filter leaves. The horizontal leaf filter installation shown in Figure 2 is generally similar to that of Figure 1, but is adapted for use when solids are to be discharged in a suspension. The same reference numerals have been employed to designate equivalent parts in the two Figures and the description of the Figure 1 installation will also serve for that of Figure 2. WHAT WE CLAIM IS:

1. A horizontal leaf filter for filtering solids containing liquid comprising a casing having an inlet for the liquid in a lower portion of the casing,-a first outlet for filtered liquid and a second outlet for solids, a stack of horizontal filter plates mounted on a vertical column within the casing, the column serving to conduct liquid having passed through the filter plates to said first outlet, and means for removing unfiltered liquid from an upper portion of the casing and returning it to the lower portion of the casing, thereby to increase the flow velocity of unfiltered liquid within the casing.

2. A filter according to claim 1 or 2, wherein said means comprises a pipeline and a pump positioned in the pipeline for pumping liquid from and back to the casing.

3. A filter according to claim 3, wherein a valve is located in the pipeline for controlling the amount of liquid which is removed from and returned to the casting.

4. A horizontal leaf filter substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.

5. A method of filtering solids containing liquid with a horizontal leaf filter having a casing with an inlet in a lower portion thereof for feed liquid, an outlet for filtrate and an outlet for solids, and a stack of horizontal filer plates mounted in the casing on a vertical column which serves to conduct filtrate to the filtrate outlet, the method - comprising the steps of feeding liquid to be filtered through the inlet, removing unfiltered liquid from an upper portion of the casing and returning the removed liquid to the lower portion of the casing, thereby to increase the flow velocity of unfiltered liquid within the casing.

6. A method of filtering solids containing liquid substantially as herein described with reference to the accompanying drawings.