Oxygen pulping with recycled liquor
AssigneeThe Black Clawson Company
InventorScott A. Wallick
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Abstract
Fibrous material is pre-steamed, impregnated with alkali liquor, refined, and then oxygen pulped at a low consistency (about 3 to 8 percent solids) using an alkali liquor which contains boron compounds. The pulping step of the process is carried out in stages with recycle of liquor to preceding stages after it has been reoxygenated. By recycling a major portion of the pulping liquor, the actual liquor to fibrous material ratio at each stage of the pulping step is maintained at a relatively high level (12/1 to 30/1) while the effective liquor to fibrous material ratio for the overall process is much lower (4/1 to 8/1). This results in a bright pulp of acceptable strength as well as a high solids content spent liquor which is economically recoverable.
Claims10
A process for the oxygen delignification of wood chips comprising the steps of:
- subjecting the wood chips to steam for a time sufficient to form a softened fibrous material,
- refining said softened fibrous material to form a refined material,
- delignifying said refined material at a consistency of about 3 to about 8% solids content in the presence of oxygen and an alkali liquor containing sodium tetraborate in a plurality of stages in which a major portion of partially spent alkali liquor from each stage is recycled to the next preceding deliqnification stage.
Dependencies are inferred from the claim text.