High yield semichemical wood pulping process
AssigneeWestvaco Corporation
InventorsJack A. Hammond, Elias M. Karter
Life of this patent
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Abstract
70 To 85% yield semichemical wood pulping may be prepared for mechanical defibration by cooking comminuted hardwood in a continuous digestion vessel with an alkaline cooking solution wherein 50 to 100% as sodium oxide thereof is sodium carbonate. The solution may be formulated from unmodified kraft recovery process green liquor or, if a sulfur free cooking process is desired, the solution may be formulated from soda ash.
Claims8
A method of operating a continuous digester having respective charging and discharging ends for the production of semichemical pulp of greater than 70% yeild, said method comprising steps of:
- A. formulating a green liquor pulping solution having 50 to 150 grams per liter total alkali concentration measured as sodium oxide wherein at least 50% of said total alkali is derived from sodium carbonate, said solution further including an effective presence of sodium sulfide;
- B. continuously charging said digester at said charging end with said solution and wood chips at a combined flow rate providing 5 to 10 grams of titratable sodium compounds expressed as sodium oxide per 100 grams of O.D. chips but no more than 2.4 grams of sodium sulfide measured as sodium sulfide per 100 grams of O.D. chips;
- C. continuously combining steam with said solution and chip charge flow at a steam flow rate sufficient to provide a liquor-to-wood ratio of up to 2.5:1 and a combined charge temperature of 170.degree. to 185.degree. C;
- D. continuously transporting said combined charge flow between said digester charging and discharging ends over an interim of approximately 5 to 20 minutes;
- and
- E. continuously withdrawing said combined charges from said digester at said discharge end.
Dependencies are inferred from the claim text.