Extended delignification in pressure diffusers

Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Continuous chemical treatment or continuous charging or...

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162 19, 162 52, 162 61, 162 62, 162 82, D21C 326

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active

050663623

ABSTRACT:
Extended delignification of kraft pulp in a pressure diffuser allows a pulp mill with a digester (e.g. continuous digester) to increase its production capacity without building a new line, or to decrease its demand in its bleach plant, or to increase the strength of softwood pulp it produces. Comminuted cellulosic fibrous material is kraft cooked to produce kraft pulp having a blow temperature over about 300.degree. F. The pulp is diffusion treated in the first stage of a pressure diffuser to replace the water around the pulp with delignifying liquor. The liquor has a dissolved lignin concentration of less than 12% (optimally less than about 4%), has an effective alkali concentration of at least 2 gm/l (preferably 8-55 gm/l), and a temperature of at least about 300.degree. F. Treating the pulp with the delignifying liquor significantly reduces the K-number (e.g. on the order of about 5). After extended delignification, the pulp is washed in subsequent stages of the pressure diffuser. The components of the delignifying area of the pressure diffuser are of stainless steel to avoid corrosion from the alkaline liquor.

REFERENCES:
patent: 3372087 (1968-03-01), Richter
patent: 3575795 (1971-04-01), Brinkley et al.
patent: 4436586 (1984-03-01), Elmore
patent: 4690731 (1987-09-01), Hartler et al.
Knutson et al, World Pulp and Paper Week Proc., "Pressure Diffuser--A New Versatile Pulp Washer"; 97-99; Apr. 10-13, 1984, abstract.
Southern Pulp & Paper 48, No. 6: 14-15 (Jun. 1985), abstract; "Pressure Diffuser . . . ".
Kleppe et al, TAPPI, vol. 59, No. 11, 1976, "Oxygen/Alkali Delignification . . . ".
Phillips, "Kamyr Diffusion Washing" paper presented at CPPA, Montreal, Quebec, Jan. 27, 1976, Kamyr Diffusion Washing.

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