Cooking cellulose material using high alkali concentrations and/or high pH near the end of the cook
US5779856A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Oct 24, 1996 |
| Grant date | Jul 14, 1998 |
| Priority date | — |
| Expiry date | Oct 24, 2016 |
Classification
- Technology area (CPC D)Textiles; Paper
- CPC primaryD21C3/266
- WIPO fieldTextile and paper machines
- WIPO sectorMechanical engineering
Abstract
Chemical (typically kraft) pulp having enhanced intrinsic fiber strength and bleachability compared to pulp produced using conventional or modified kraft cooking is produced by using high alkali and/or pH cooking, preferably by adding the vast majority of cooking liquor (such as kraft white liquor) after the first removal of liquid from the digester so that the effective alkali concentration is high near the end of the cook. That is during at least the last minute (preferably at least the last 15 minutes and most preferably at least the last 30 minutes) before the cook is terminated the effective alkali concentration is between 15-50 g/l, more preferably between about 18-40 g/l, and most preferably between about 20-35 g/l. More than 50% (in fact most preferably more than 90%) of the total alkali added to the slurry in order to produce the chemical pulp is added after the first removal of liquid from the digester, and the alkali is added at two or more different locations so that the highest effective alkali concentration is within the range set forth above. The extracted liquors having a high effective alkali concentration are reused in the earlier stages of the cooking to avoid an…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.