The CTMP process
Our Star products are manufactured from sawmill chips from spruce and birch wood, which is delivered from SCA’s own sawmills and forests. The majority of the sawmill wood is delivered chipped; and the rest is debarked and chopped into wood chips in the wood room.
To achieve the correct quality, the chips are screened before being moved into the facility. The chips are carefully washed prior to steaming. During steaming, the chips are impregnated in a pressurised impregnator, in which the active chemicals are sodium sulphite and sodium hydroxide. Both the impregnator and the subsequent refining stages are conducted at varying pressures and temperatures to manufacture CTMP or HT CTMP. HT denotes “high temperature” and is a patented technique in which refining takes place at a high pressure and temperature. During the manufacturing of HT pulps, the temperature is increased over lignin’s softening temperature. This results in a more gentle exposure of the fibres without any shortening of the fibre length. Accordingly, we reduce the proportion of fines in the pulp. After refining the pulp is screened and the reject is processed separately in a rejects refiner. The screened pulp is washed and dewatered in a wash filter before being moved to the dewatering press. The pulp is bleached with peroxide before it is washed twice more in dewatering presses.
The dewatered pulp is defibrated and flash dried. The bales are wrapped and bound with wire. One of the advantages with CTMP from Östrand is that it can also be delivered without bale wire. In this case, the bale wires are replaced with water-soluble glue that facilitates handling of pulp bales prior to pulping.