Patent US4073678A successfully refreshed from Google Patents.
US4073678A
Expired / Lapsed
US
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High yield semichemical wood pulping process
Assignee: Westvaco Corp
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Filing: 1977-01-14
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Granted: 1978-02-14
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Expires: 1997-01-14
Abstract
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.
Inventors
- 👤 Jack A. Hammond
- 👤 Elias M. Karter
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 21:28
CPC Classifications
D; D21; D21C; D21C11/00; D21C11/0014; D21C11/04; D21C3/00; D21C3/02
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
204 words
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° to 185° 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.
Claim 2
Independent Claim
204 words
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° to 185° 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.
Claim 3
Dependent Claim
36 words
A method as described by claim 1 wherein the alkalinity of said pulping solution at said discharge end is regulated by the combination of washer filtrate from a pulp washer system at said digester discharging end.
Claim 4
Dependent Claim
25 words
A method as described by claim 2 wherein the alkalinity of pulping solution withdrawn from said digester discharge end is approximately 9.4 to 10 pH.
Claim 5
Dependent Claim
36 words
A method as described by claim 3 wherein a portion of pulping solution withdrawn from said digester is separated from said chips and residual chemical values therein are recovered in combination with kraft process spent liquor.
Claim 6
Dependent Claim
29 words
A method as described by claim 4 wherein a portion of pulping solution withdrawn from said digester is directly combined with kraft process fresh pulping liquor for alkalinity adjustment.
Claim 7
Dependent Claim
74 words
A method as described by claim 1 wherein said pulping solution is formulated from green liquor comprising approximately 80% sodium carbonate and 12% sodium sulfide which is concentrated to approximately 140 grams of equivalent sodium oxide per liter and combined with said chips to provide approximately 5.25 grams of equivalent sodium oxide per 100 grams of O.D. chips and retained between said digester charging and discharging ends approximately 8 minutes at approximately 185° C.
Claim 8
Dependent Claim
69 words
A method as described by claim 1 wherein said pulping solution is formulated from green liquor comprising approximately 98% sodium carbonate which is concentrated to approximately 100 grams of equivalent sodium oxide per liter and combined with said chips to provide approximately 6.25 grams of equivalent sodium oxide per 100 grams of O.D. chips and retained between said digester charging and discharging ends approximately 14 minutes at 174° C.
Claim 9
Dependent Claim
72 words
A method as described by claim 1 wherein said pulping solution is formulated from green liquor comprising approximately 80% sodium carbonate and 15% sodium sulfide which is concentrated to approximately 100 grams of equivalent sodium oxide per liter and combined with chips to provide approximately 6.55 grams of equivalent sodium oxide per 100 grams of O.D. chips and retained between said charging and discharging ends approximately 8 minutes at approximately 183° C.
References Cited (Backward Citations)
CA709600A
Cited
US1921539A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1981-02-13 | 1981-08-15 | 1982-02-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-02-13 | 1985-08-15 | 1986-02-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-02-13 | 1989-08-15 | 1990-02-14 | $7700.00 | Window Closed / Lapsed |