AMAR EQUIPMENTS PVT. LTD. -- Pressure Leaf Filter

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Pressure Leaf Filter

CONSTRUCTION & WORKING PRINCIPLE

How is the Leaf Constructed?
Each leaf is made of 5 ply of SS wire mesh of different gauge wires. Two outer filtering mesh are Hollander weaves & 3 inner are only for support. The 5-ply wire mesh are held together by a tubular frame & made leak proof by machine riveting. The quality of filtration & life of filter depends mainly on the quality of outer wire mesh & riveting. We at M/s. Amar Equipments Pvt. Ltd. Ensure the quality by inspecting quality of wire mesh and each leaf. Old worn out & torn leaves can be repaired by only replacing the outer Hollander weave.

How is Vertical Pressure Leaf Filter constructed?
It consists of a vertical MS/ SS tank with filter elements (leaves) inside. The leaves are mounted vertically on a common manifold pipe, through which the filtered liquid flows out. On the top, the leaves are held by a vibrating shaft. A mechanical vibrator driven by electric motor / pneumatic vibrator is provided for vibrating the leaf shaft for cake discharge. Optionally spray nozzles can also be provided for wet cake discharge. Jacket for hot filtration can be offered if desired over flow, vent / steam / air charging pressure gauge & safety valve are provided on the top. The top cover is provided with devit arm mechanism for raising the lid for cleaning / removing the leaves. ‘T’ bolts are provided for quick opening and closing of top lid. A mechanical jack is provided to lift the top for cleaning / removing the leaves. Lugs are provided for mounting the PLF.

How is Horizontal PLF constructed?
Horizontal PLF works on similar principle but the shell is horizontal & leaves are vertical on common manifold. The filter shell has 4 wheels & can be retractable by a hydraulic cylinder on a rail. Two hydraulic cylinders are provided one each for opening & closing the wedge lock mechanism between the shell & cover. A hydraulic power pack unit, Pressure gauge, vent / steam valves, panel board etc is provided. After the filtration & cake drying is over, the outer vessels is retracted, thus opening up the leaves for cake discharge,. During opening / cleaning no connections have to be removed as the cover with leaves remain in fixed position. Cake can either be discharged manually by rubber mallet or optionally pneumatic / mechanical vibration can be provided for dry cake discharge. Spray nozzles can be provided for wet cake discharge. Horizontal PLF is preferred for higher filtration area or when solid cake has to be removed manually in semidry condition & in short period.

WORKING PRINCIPLE

How do they work?
Leaf Filters are ideal for solid – liquid separation & work on principle of precoating & pressure. Pre-coating is done with the help of suitable filter aid about 0.5 to 1% (Bleaching earth, supercel, hyflo, superflo etc.) mixed with the liquid to be filtered. Unfiltered liquid is pumped into the filter vessel. Initially the filter aid starts forming a precoat layer on both sided of the filter leaves, until then cloudy material comes out of the filter. Once the layer is formed, pressure starts developing, restricting the impurities. Clear liquid flows from both sides in to the leaves (filter elements), flows along the tubular channel & gets discharged from bottom of the leaf. All the leaves are mounted on a common manifold. The leaves start getting choked on both the sides by impurities forming cake, which is in wet form. Once the leaves get choked completely, the pressure rises to 3-4kg./cm2 and the output flow almost stops. This means the batch size is reached. The pump is stopped & steam / air pressure is applied from the top (without dropping the filter pressure) to to filter the material around the leaves heldup in the tank & to squeeze the cake further & reduce the liquid retention in it. The hold up unfiltered liquid in the conical portion is taken back.

How is the cake discharged?
In both vertical & horizontal filters the cake can be dried by steam / hot air & then discharged from the bottom with the help of mechanical / pneumatic leaves vibrator. The whole operation of cake drying takes 3-45 min. & cake discharge takes 5-10 min. For wet cake discharge water spray nozzles are provided. In Horizontal Pressure Leaf Filter wet cake can also be discharged manually by scrapping. The shell is slided over with hydraulic mechanism keeping the leaves in fixed position.

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