Dewatering Disc Filter And Screw Press - Process Info

The disc filter is the first stage in a dewatering process that also includes the dewatering screw press. The dewatering has two functions, to give the right pulp consistency for dispersing and to split up the deinking process in two white water loops. The split reduces the amount of chemicals and collodial materials that follows the pulp to the paper machine. This is beneficial both for quality and for economy (chemical consumption).

The pulp from the fine screening is dewatered to about 14 % consistency on the disc filter discs.
In the disc filter screw conveyor the pulp is diluted to 6 – 7 % with water from the white water loop 2 before it falls down in the dilution chest. When pumping the pulp to the screw press the pulp is further diluted to 5 %, with press filtrate and white water from loop 2. This dilution has two effects, the white water supply through counter current washing and an extra pulp washing in the dilution chest. Two or three filtrates (cloudy, clear and super clear filtrat) are taken out from the filter vacuum valve. The filtrates are led to one or more white water tanks to be used in white water
loop 1. The filter cloth on the discs are cleaned with clear or super clear filtrate through oscillating cleaning showers.

From the dilution chest the pulp is pumped at 5 % consistency, to the screw press prior to the disperger. The screw press dewaters the pulp to 30 % consistency. Prior to the disperger, in the screw press outlet chute, talcum may be added. Its function is to adsorb on the sticky particles in the pulp, to reduce the agglomeration of stickies. Filtrate from the screw press flows to a press filtrate tank and is partly used as dilution water in the dilution chest.

The other part of the press filtrate may be led to the microflotation to be cleaned before it is
reused in the first white water loop.