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US 6,143,130 AGranted
Polysulfide pulping process
AssigneeKvaerner Pulping AB
InventorsLars Stigsson, Mikael Linstrom
Life of this patent
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Abstract
A method for impregnation and chemical digestion of lignocellulosic material and recovery of pulping liquors. A spent impregnating or cooking liquor is withdrawn and sulphurous compounds are recovered therefrom in a partial oxidation reactor. These sulphurous compounds are converted into hot liquid elemental sulphur which thereafter is mixed with a hot sulphide containing liquor to provide a polysulphide liquor with a concentration greater than 10 g/l and which is essentially free from thiosulphate. This polysulphide liquor is used for carbohydrate stabilising impregnation and/or for cooking at a relatively low temperature.
Claims23
A process for producing pulp from cellulosic fiber material comprising the steps of:
- (a) impregnating a cellulosic fiber material with a first cooking liquor comprising polysulfide, wherein said first cooking liquor provides about 60% or less of a total effective alkali utilized for cooking said cellulosic fiber material;
- (b) cooking said cellulosic fiber material with a second cooking liquor in one or more cooking stages, wherein said second cooking liquor provides at least about 40% of the total effective alkali utilized for cooking said cellulosic fiber material;
- (c) extracting a spent cooking liquor comprising sulfide compounds from at least one of said impregnating step (a) or said cooking step (b);
- (d) gasifying at least a portion of said spent cooking liquor from step (c) in a gasification reactor to form a first gas stream comprising hydrogen sulfide;
- (e) treating said first gas stream to form an acidic gas stream comprising hydrogen sulfide and carbon dioxide;
- (f) reacting said acidic gas stream under conditions to provide a hot liquid stream of elemental sulfur;
- (g) admixing at least a portion of said hot liquid, elemental sulfur stream with an alkaline liquor containing sulfide under conditions that the elemental sulfur reacts with the sulfide to form polysulfide, whereby an alkaline liquor containing at least about 10 grams/liter of polysulfide and which is substantially free of thiosulfate is formed;
- and
- (h) adding at least a portion of said alkaline polysulfide liquor to said first cooking liquor or directly to said impregnation step (a) to stabilize carbohydrates in the cellulosic fiber material.
6 more elements
A process for producing pulp from cellulosic fiber material comprising the steps of:
- (a) impregnating a cellulosic fiber material with a first cooking liquor comprising polysulfide, wherein the first cooking liquor provides about 60% or less of a total effective alkali utilized for cooking the cellulosic fiber material;
- (b) cooking the cellulosic fiber material with a second cooking liquor in one or more cooking stages under conditions such that at least about 30% of the polysulfide supplied to said cooking step (b) remains intact in a spent liquor following completion of cooking, wherein the second cooking liquor provides at least about 40% of the total effective alkali utilized for cooking the cellulosic fiber material;
- (c) extracting a spent cooking liquor comprising said intact polysulfide and sulfide compounds from said cooking step (b);
- (d) gasifying at least a portion of the spent cooking liquor extracted from step (c) or at least a portion of a spent liquor extracted after said impregnation step (a) in a gasification reactor to form a first gas stream comprising hydrogen sulfide;
- (e) treating the first gas stream to form an acidic gas stream comprising hydrogen sulfide and carbon dioxide;
- (f) reacting the acidic gas stream under conditions to provide a hot liquid stream of elemental sulfur;
- (h) utilizing at least a portion of a spent liquor containing intact polysulfide from step (c) as the first cooking liquor, (g) admixing at least a portion of the hot liquid, elemental sulfur stream with an alkaline liquor containing sulfide under conditions that the elemental sulfur reacts with the sulfide to form polysulfide, whereby an alkaline polysulfide liquor containing at least about 10 grams/liter of polysulfide and which is substantially free of thiosulfate is formed;
- (i) adding at least a portion of said alkaline polysulfide liquor from step (g) to said second cooking liquor or directly to said one or more cooking stages in step (b);
- and
- (j) adding a portion of said polysulfide liquor to said first cooking liquor or directly to said impregnation step (a) to provide a desired polysulfide concentration in said impregnation stage when an amount of polysulfide supplied by said spent cooking liquor in step (h) is below an amount sufficient to provide the desired polysulfide concentration in said impregnation stage.
7 more elements
Dependencies are inferred from the claim text.