Liquid purification or separation – Processes – Separating
Patent
1997-10-22
2000-06-06
Popovics, Robert J.
Liquid purification or separation
Processes
Separating
210797, 210798, 210225, B01D 25127
Patent
active
060714255
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for washing the filter fabric of a filter press, said method comprising a filtration sequence in which the material being filtered such as a slurry is taken to a filter cell, whereby the solids suspended in the slurry remain on the surface of the filter fabric thus forming a filter cake while the liquid vehicle of the slurry is passed as the filtrate through the filter fabric.
2. Description of the Related Art
Automatic filter presses are widely employed in the mining and process industries for filtering slurries, whereby the suspended solids are separated from the liquid.
Typically, an automated filter press comprises a filter pack formed by a plurality of identical stacked filter plates performing a parallel function in the filter press. Between the filter plates is adapted in a zig-zag fashion meandering a long, endless filter fabric belt or similar filter medium on which the solids particles accumulate during filtration thus forming a filter cake. On the upper surface of the filter plate is provided a grating, a grooved pattern or similar recessed structure that supports the overlying filter fabric, however, simultaneously permitting the filtrate, which is formed in the filtration process by permeation through the fabric, to discharge from the interior of the filter plate. To the lower surface of the filter plate is arranged an almost constant-height cell with an area covering almost the entire plate and sealed at its edges, into which cell the slurry to be filtered is fed by pumping. The upper part of the cell is generally provided with an elastic compression membrane made of rubber, for instance, whereby a pressurized medium (water, air, etc.) applied above the membrane permits compression of the formed filter cake for dewatering the cake.
In the beginning of the filtration sequence performed using such a filter press, a closing device first pushes the filter plates pressure-tightly against each other to secure the plate pack between compressive end plates, whereby filter cells are formed in the stacked filter plate pack. Next, into each filter cell is pumped the slurry to be filtered, whereby the solids suspended in the slurry remain on the surface of the filter fabric thus forming a filter cake while the liquid filtrate is drained away through the filter fabric.
After the slurry infeed step, above said elastic compression membrane is applied a pressurized medium causing the membrane to exert mechanical compression on the filter cake thereby reducing its moisture content. At the completion of the compression step, the applied pressure is released and compressed air or similar gaseous medium is passed through the filter cake in order to reduce its moisture content. When required, the filter cake may further be subjected to washing using at least one washing fluid passed through the cake.
After the completion of the filtration steps, the closing device opens the filter plate pack, whereby the filter plates remain hanging by their hanging lugs at a distance from each other. The filter cakes are removed to opposite sides of the filter press when the endless filter fabric belt adapted to pass between the filter plates is actuated to move with the help of a conveyor means of the filter fabric. During the motion of the filter fabric belt, the fabric is conventionally washed with the help of washing spray nozzles placed into a stationary position.
As the filter fabric which forms a long, endless belt is moved during the filter cake discharge step, the filter cakes are dropped from both ends of the filter plate pack into cake discharge hoppers, and therefrom, further onto a belt conveyor or similar device placed under the filter frame. If such a belt conveyor can be adapted parallel to the filter plates, the arrangement based on two discharge points operates without problems. However, in some cases (e.g., when the belt conveyor cannot be adapted parallel to the filter plates) it may be advantageous to have the di
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Paavola Esa
Vartiainen Timo
Larox Oy
Popovics Robert J.
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