Kraft mill recycle process

Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...

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162 30K, 162DIG8, 423207, 423232, 423DIG3, D21C 1104

Patent

active

042882869

ABSTRACT:
A cellulosic pulp and bleaching process is described. The process integrates two cycles, one is a digestor liquor cycle and the other is a sulfur cycle.
The digestor liquor cycle comprises the steps of digesting a fibrous cellulosic feed to form a pulp, separating the pulp and bleaching it in at least one stage with chlorine dioxide, evaporating and burning the remaining waste liquor to form a smelt, dissolving the smelt to form a green liquor and utilizing the green liquor, after recausticizing, as at least a portion of the feed stock for the digestor step.
The sulfur cycle of the present invention utilizes a portion of the green liquor of the digestor liquor cycle. The green liquor is carbonated to form a bicarbonate which is then stripped of H.sub.2 S. The H.sub.2 S is converted into H.sub.2 SO.sub.4 and utilized as a feed stock to a chlorine dioxide generator. The chlorine dioxide generator utilizes H.sub.2 SO.sub.4 as feed stock and produces Na.sub.2 SO.sub.4 as a by-product. The Na.sub.2 SO.sub.4 by-product from the chlorine dioxide generator is furnaced in common with the evaporated waste pulping liquor from the digestor liquor cycle to form a common smelt, which is dissolved to form a green liquor, a portion of which is used in the sulfur cycle and a portion of which is used in the digestor cycle.

REFERENCES:
patent: 3210235 (1965-10-01), Ferrigan et al.
patent: 3366534 (1968-01-01), Rapson
patent: 3508863 (1970-04-01), Kiminki et al.
patent: 3542511 (1970-11-01), Shah
patent: 3841961 (1974-10-01), Saiha
patent: 3954552 (1976-05-01), Lukes et al.

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