Paper production involves the combination of cellulose fibers (from wood), water and additives. The mixture is spread across a screen table and the water is vacuumed out of the fiber mesh. The fiber mesh is then passed to a felt press and then to driers, where the final moisture is removed.
The screen table and felt require constant cleaning. Commonly used for this purpose are a series of spray nozzles, called “showers”. For economic reasons, it is undesirable to obtain a clean external source of water for use with these showers, so an alternate internal source is required.
The water that is obtained from the screen table is one solution. The water, called white water due to its appearance, is typically highly laden with fibers, usually up to 3000 ppm. As such, it is undesirable to use untreated white water for the showers.
The first step in treating white water is to remove the majority of the fibers. The first stage of filtration produces two streams, one of which is highly laden with fibers and is returned to the mixing tank for reuse. The other stream is nearly suitable for use, but requires some polishing. This water can usually be treated using Ruickly filters to produce a stream suitable for use on showers, gland seal protection and vacuum pumps.