Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Patent
1990-12-21
1994-01-11
Alvo, Steve
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
162 19, 162 24, 162 40, 162 52, 162 56, 162 65, D21C 302, D21C 326, D21C 916
Patent
active
052777600
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to continuous production of pulp by means of a combined chemical and mechanical method for digesting plant and wood fibers to pulp to be used as raw material for paper, board, fiberboards and other fiber-containing products. The present process is also well suited for de-inking and washing of cellulose fibers, delignification and, optionally, bleaching of secondary fibers.
THE PRIOR ART
Pulp has for several decades been produced by means of the well known sulphite or sulphate processes. Both processes today require very large plants to enable them to be carried out economically, and it is highly expensive to build new cellulose mills for the production of pulp by means of these processes. Nevertheless, in the recent years some new large cellulose mills have been built in the developed countries of the world, and after starting up, these cellulose mills have suffered heavy economic losses.
In international application PCT/NO88/00011 filed on Feb. 11, 1988 with claim to priority inter alia from Norwegian Patent Application No. 870562 filed on Feb. 12, 1987 a process for digesting plant and wood fibers and/or for delignification, optionally with preceding deinking, of secondary fibers, possibly with subsequent bleaching, with obtainment of a pulp which is suited as raw material for paper, board, fiber boards and paper products which contain plant and/or wood fibers has been disclosed and claimed. The fibrous raw material is introduced into a digesting zone and is digested therein in alkaline slurry at elevated temperature and pressure using an alkaline cooking chemical in combination with oxygen and, optionally, minor amounts of other additives, like e.g. anthraquinone. The cooking chemicals are removed from the digesting process in the form of a black liquor which is deposited or subjected to recovery of chemicals. The process according to the above-mentioned international application is characterized in that pulp and chemical substances during the digestion and the optional bleaching are transported in the form of a pumpable slurry through a closed, continuous and pressurized tube system by the use of pulp pumps which are simultaneously used as mixing aggregates for the slurry and the chemicals. While transporting the pulp slurry through the tube system the pulp slurry is repeatedly subjected to dewatering steps by pressing out liquid from the pulp slurry, and prior to each dewatering step of the process, the pulp is diluted with pressed out process liquid returned from a downstream dewatering step of the process and/or from a downstream pumping step of the process. While being transported through the tube system, the pulp is subjected to stepwise in the pumping steps, and prior to the last dewatering step the pulp is diluted and, optionally, cooled with fresh water and/or bleaching liquor supplied under pressure. After the last dewatering step of the pressurized digestion or delignification system the pulp is washed and optionally bleached in a continuation of the pressurized system or in the non-pressurized state after cold or hot blowing from the pressurized system.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a process for the production of pulp which is suited as raw material, for paper, board, fiberboard and other products which contain plant and/or wood fibers. The present process is to be carried out at stepwise increasing pressure in a closed, pressurized tube system comprising several pressure steps in succession while using several circulation circuits for the pulp suspension at the different pressure steps with the object of improving the transfer of thickened pulp from one pressure step into the next (higher) pressure step in order to secure improved pulp flow through the process system compared with the transfer of thickened pulp disclosed in said international application PCT/NO88/00011. Likewise, it is also an object of the invention to enhance the turbulence of the fiber suspension thereby promoting the spee
REFERENCES:
patent: 1679336 (1928-07-01), Dunbar
patent: 4248662 (1981-02-01), Wallick
patent: 4259150 (1981-03-01), Prough
patent: 4416727 (1983-11-01), Elton et al.
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