How Does Pre-coating Vacuum Drum Filter Process?

A pre-coating vacuum drum filter operates by first applying a layer of filter aid material, typically diatomaceous earth or similar, onto the surface of the drum to create a porous filter cake. Here's how the process works:

1. Pre-Coating:

   • The drum is submerged in a slurry of the filter aid material. As the drum rotates, a vacuum is applied from inside the drum.
   • The vacuum draws liquid through the drum's surface, causing the filter aid material to build up as a uniform layer (pre-coat) on the drum's outer surface.

2. Filtration:

   • After the pre-coat layer is established, the drum rotates through the slurry of the actual material to be filtered.
   • The vacuum continues to draw the liquid through the pre-coat layer, filtering out suspended solids and leaving them on the surface of the pre-coat.

3. Cake Formation:

   • As the drum rotates, more solids accumulate on the pre-coat layer, forming a cake on the drum surface. The thickness of the cake increases as more slurry is processed.

4. Discharge:

   • When the drum reaches a certain point in its rotation, a knife or blade scrapes off the top layer of the cake (which includes the trapped solids) from the drum surface.
   • The scraped solids are collected, and the pre-coat layer remains on the drum for continued filtration.

5. Continuous Operation:

   • The drum continues to rotate, continuously filtering and removing solids until the pre-coat layer needs to be renewed, which is done by another application of filter aid.

This process is particularly useful in applications where very fine filtration is required, and the solids are difficult to filter through a traditional filter medium.

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