Bleach Kraft Pulp Process
Northern Pulp manufactures northern bleached softwood kraft (NBSK), more commonly referred to as kraft pulp. Our product is derived from wood fibre from sustainably managed Nova Scotia forests and is used in all types of paper products. We supply our customers around the world with pulp to manufacture common household products such as tissue, towel and toilet paper, along with writing and photocopy paper.
About Bleach Kraft Pulp Processing
There are two major categories of pulping processes: mechanical and chemical. Mechanical pulp mills use high electrical energy instead of chemicals to produce pulp. The kraft process is a chemical process. There are approximately 30 kraft pulp mills in Canada.
The kraft process involves the conversion of wood chips into wood pulp and the separation of lignin from cellulose. This is a seven-step process to treat wood chips and to produce the pulp bales that are shipped to customers worldwide.
Step 1: Chip delivery and screening
We produce and purchase about 3000 tonnes of chips daily from our suppliers. These are screened to remove over-sized chips and fines (sawdust).
Step 2: Digester
We ‘cook’ the chips with steam in a mixture of sodium hydroxide and sodium sulphide to soften wood and remove lignin to form a dark brown pulp, like what would be used to make a cardboard box or brown paper bag.
Step 3: Washing and processing
Pulp is washed and screened to remove uncooked wood material, debris and chemical solution. The spent chemical solution is recovered and reused. Also, during this recovery process, the combustion of the organics in the spent cooking chemicals converts water to steam in the boiler, which is used in a turbine generator to produce green energy for the Mill.
Step 4: Bleaching
Washed pulp is bleached to transform the brown pulp into a white product. This is a five-stage process using chlorine dioxide, sodium hydroxide, hydrogen peroxide and oxygen. Our Mill has used an elemental chlorine free (ECF) bleaching process since 1997.
Step 5: Sheet formation
Bleached pulp is formed into a continuous sheet on the pulp machine.
Step 6: Sheet drying
The pulp sheet is dried in the air borne pulp drier.
Step 7: Bale cutting
The continuous pulp sheet is cut, formed into bales and wrapped for shipment.