The Science Behind Our Kraft Pulp Process
The essential elements for making kraft pulp are wood fibre, water, chemicals and heat. We make kraft pulp by mixing wood fibres with a solution of caustic soda and sodium sulphide, and cooking them inside a digester. This separates the fibres from the lignin, which is a natural glue-like substance that binds them together. Our production facilities are designed to recover and reuse much of the water, chemicals and steam used in the process.
Kraft pulp (a type of chemical pulp) is made using raw wood (both soft wood and hard wood) chips which are pre-steamed in steaming vessel. Steamed chips are then cooked inside a pressurized digester with a combination of chemicals and heat to dissolve the lignin glue which holds the wood fibres together.
The digester’s pressure is relieved into a blow tank which separates the chips into unbleached pulp fibre.
Residual chemicals are removed and recycled in the brown stock washing stage.
The pulp is then bleached to its recognized bright white color in the bleach plant.
The bleached pulp is then diluted to a slurry where it is sprayed across a pulp machine screen to form the pulp mat and begin the dewatering process of pressing and drying in the dryer section.
The dried pulp is then cut and baled into 400 kg bales on the baling line in preparation for transport around the world.
THERMO-MECHANICAL PULP
Paper Excellence sells its kraft pulp externally to customers around the world. Some of Paper Excellence’s Canadian mills also produce a type of mechanical pulp, referred to as thermo-mechanical pulp or TMP, for use in making their own paper products (see How We Make Paper). Our Meadow Lake mill makes Bleached Chemi Thermal Mechanical Pulp (BCTMP) which is a hybrid of kraft and TMP.
ENVIRONMENTAL ASSURANCE
The fibre we use to make kraft pulp is mainly made up of leftovers from lumber mills. These wood chips and shavings were once considered waste and sent to landfills or burned. We match tree species and other pulp characteristics with customers’ end-use requirements, and control blending and bleaching to exacting specifications.
PUTTING SAWMILL LEFTOVERS TO USE
As with all products from our Canadian mills, our kraft pulp is made from responsibly sourced fibre and in facilities that have achieved sector-leading greenhouse gas reductions. We use a lower-impact elemental chlorine-free bleaching process. With our chain-of-custody systems using globally recognized standards, we can provide pulp and paper products that are certified as originating from sustainably managed forests for those customers wishing additional assurance.