Method for treating refined mechanical pulp and thermo mechanical pulp with ozone
AssigneeMyrens Verksted A/S
InventorsBjorn H. Fritzvold, Nicolai Soteland
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Abstract
When treating refined mechanical pulp and thermo mechanical pulp with ozone, it is of great importance that the process be carried out at the most favorable conditions and with a minimum consumption of energy. According to the present invention the pulp is refined to a freeness value of at least 200 csf in a first stage refiner from which the pulp is passed to a high consistency ozonizer and maturation reactor for a time limited to maximum 30 minutes. From the reactor the pulp is passed direct to a second stage refiner, the pulp then having a solids content of approximately 8-10% and an alkaline value in the range of 7-10.
Claims5
In a method for continuously treating refined mechanical pulp and thermo-mechanical pulp in which the pulp is subjected to a first stage refining process, treated with ozone and subsequently treated in a second stage refining process, wherein the improvement comprises:
- (a) refining the pulp in said first stage refining process, by means of a single grinding step to a freeness value of at least 200 csf, and a dry substance consistency of 20-60%,
- (b) cooling the refined pulp to a temperature below approximately 70.degree. C.,
- (c) treating the cooled pulp with ozone,
- (d) treating the ozonized pulp in a high-consistency maturation reactor in which a material selected from the group consisting of alkali and bleaching chemicals is added for not more than 30 minutes to produce a high-consistency pulp having a solids content of between 10-40% and a pH in the range of 7-10,
- (e) passing the matured, high consistency pulp directly and continuously to a second stage refiner,
- (f) grinding the pulp in said second stage refiner by means of a single grinding step to a desired freeness value.
Dependencies are inferred from the claim text.