Washing And Thickening

Question 1

Explain the purpose and characteristics of thickening vs washing

Answer 1

Purpose of washing is to separate solids from the suspension whereas thickening is to separate solids from water. Washing is used to remove small contaminants like filler, inks, colloidal material. Purpose of thickening is to separate process loops and store pulp at higher consistencies

Question 2

Name 4 basic parameters which affect disk filter performance

Answer 2

Feed consistency
Feed flow
Outlet consistency
Vacuum

Question 3

How would you calculate this:
Disk filter has an inflow volume of 1000 l/min at 1.8%. How many litres of water per min need to be removed to get a stock consistency of 6%

Answer 3

Remember the equation MASS OF SOLIDS = consistency x flow
You can rearrange this,
Think of the thickener like a black box

Question 4

Explain dewatering principle of a screw press and what is the influence on capacity and outlet consistency of 5 parameters

Answer 4

Speed increases capacity decreases consistency because not as much time
Temperature slight increase in capacity, increase in consistency because water is less viscous
Freeness increase because water is not so tightly held
Fines fraction decreases capacity and consistency
Ash/filler Decrease capacity and consistency

Question 5

What are the objectives of washing
Compare ash removal and ink removal of following products tissue, newsprint, sc papers, lwc papers

Answer 5

Principle is to remove small contaminants such as filler fines and inks
Newsprint does not require removal of ash and fines but does need ink removal
Sc paper partially need to remove ash and fines, need to remove both ink s
LWC needs removal of all
Tissue yes to all