Process for oxygen pulping of lignocellulosic material and recorvery of pulping chemicals
First Claim
1. A substantially sulfur-free process for the production of a chemical pulp from lignocellulosic material and the recovery of chemicals used in said process comprising the steps of:
- a) providing a feed stream of comminuted lignocellulosic material, b) subjecting said feed stream of comminuted lignocellulosic material to a pretreatment, c) reacting the pretreated lignocellulosic material from step b) with oxygen or oxygen-containing gas, in the presence of an alkaline buffer solution comprising at least one sodium or potassium compound in order to obtain a stream of at least partially delignified lignocellulosic material, d) further treating said at least partially delignified material from step c) to obtain a chemical pulp product, e) extracting spent liquor comprising dissolved lignin components and spent chemical substances from step b) or both steps b) and c), f) recovering chemical substances from the spent liquor obtained in step e) and preparing fresh alkaline buffer solution to be charged to step c) or both steps c) and b), wherein in step b) said comminuted lignocellulosic material is subjected to a mild prehydrolysis in an aqueous solution and thereafter precooked in the presence of an alkaline buffer solution, and in step b) an aromatic organic compound is added to promote selective delignification, and in step f) the recovery of chemical substances from the spent liquor obtained in step e) comprises, f1) treating at least part of said spent liquor to form a concentrated stream of cellulose spent liquor, f2) reacting said concentrated cellulose spent liquor stream with an oxygen containing gas at elevated temperature in a gas generator to form a hot gas comprising carbon dioxide and molten droplets of sodium or potassium compounds or an aerosol of sodium or potassium compounds, f3) dissolving said sodium or potassium compounds in water to form an alkaline buffer solution and f4) recycling and charging at least a portion of said alkaline buffer solution to step c) or both steps c) and b).
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Abstract
A substantially sulfur free process for the manufacturing of a chemical pulp with an integrated recovery system for recovery of pulping chemicals is carried out on in several stages involving physical and chemical treatment of lignocellulosic material in order to increase accessibility of the lignocellulosic material to reactions with an oxygen-based delignification agent. Spent cellulose liquor comprising lignin components and spent chemical reagents is fully or partially oxidized in a gas generator wherein a stream of hot raw gas and a stream of alkaline chemicals and chemical reagents is formed for subsequent recycle and reuse in the pulp manufacturing process.
124 Citations
42 Claims
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1. A substantially sulfur-free process for the production of a chemical pulp from lignocellulosic material and the recovery of chemicals used in said process comprising the steps of:
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a) providing a feed stream of comminuted lignocellulosic material, b) subjecting said feed stream of comminuted lignocellulosic material to a pretreatment, c) reacting the pretreated lignocellulosic material from step b) with oxygen or oxygen-containing gas, in the presence of an alkaline buffer solution comprising at least one sodium or potassium compound in order to obtain a stream of at least partially delignified lignocellulosic material, d) further treating said at least partially delignified material from step c) to obtain a chemical pulp product, e) extracting spent liquor comprising dissolved lignin components and spent chemical substances from step b) or both steps b) and c), f) recovering chemical substances from the spent liquor obtained in step e) and preparing fresh alkaline buffer solution to be charged to step c) or both steps c) and b), wherein in step b) said comminuted lignocellulosic material is subjected to a mild prehydrolysis in an aqueous solution and thereafter precooked in the presence of an alkaline buffer solution, and in step b) an aromatic organic compound is added to promote selective delignification, and in step f) the recovery of chemical substances from the spent liquor obtained in step e) comprises, f1) treating at least part of said spent liquor to form a concentrated stream of cellulose spent liquor, f2) reacting said concentrated cellulose spent liquor stream with an oxygen containing gas at elevated temperature in a gas generator to form a hot gas comprising carbon dioxide and molten droplets of sodium or potassium compounds or an aerosol of sodium or potassium compounds, f3) dissolving said sodium or potassium compounds in water to form an alkaline buffer solution and f4) recycling and charging at least a portion of said alkaline buffer solution to step c) or both steps c) and b). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42)
in step b) anthraquinone, 2-naphtol or xylenol or derivatives thereof is added to be present during the pretreatment, and in step c) said alkaline buffer substantially is made up of an alkali carbonate or an alkali borate or combinations thereof, and in step f2) said concentrated spent cellulose liquor from step f1) is reacted with an oxygen containing gas in a reaction zone of a gas generator at a temperature in the range of 700-1300°
C. to produce a hot raw gas comprising carbon dioxide and at least one of H2, CO, H2O, and NH3, said raw gas containing entrained molten particulate matter and an aerosol of alkaline compounds, andat least a major portion of said entrained particulate molten matter being separated from the raw gas stream and dissolved in an aqueous solution to form an alkaline solution comprising sodium or potassium compounds, and wherein at least a portion of said alkaline solution is recycled to the oxygen delignification step c), without having been subjected to causticizing.
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34. Process according to claim 33, wherein said hot raw gas is cooled and cleaned to produce a clean gas stream substantially free from particulate matter and alkali metal compounds.
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35. Process according to claim 33, wherein a major portion of the entrained particulate molten matter is separated from the raw gas by gravity in a gas diversion and smelt separation zone arranged in or adjacent to the gas generator, said separation being effected without substantially reducing the temperature of the hot gas stream.
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36. Process according to claim 33, wherein a gas generator is an updraft gasifier with smelt removal in a lower section of the gas generator and wherein the hot raw fuel gas is discharged from an upper section of the gas generator.
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37. Process according to claim 33, wherein the addition of oxygen containing gas to the gas generator corresponds to 30-65% of stoichiometric complete combustion of the cellulose spent liquor.
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38. Process according to claim 33, wherein the pressure in the gas generator ranges from about 0.1 MPa to 10 MPa.
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39. Process according to claim 34, wherein cellulose spent liquor is completely oxidized in the gas generator or reactor and wherein hot raw gas comprising carbon dioxide and steam, after separation of alkaline compounds, cooling and optional removal of trace contaminants and particulates, is discharged to the atmosphere.
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40. Process according to claim 1, wherein an alkaline buffer solution comprising sodium or potassium compounds is subjected to an oxidative treatment with an oxygen containing gas in order to activate chemical reagents, catalysts or carbohydrate protectors and/or to eliminate any traces of sulfide before the alkaline buffer solution is recycled as desired to a pretreatment, precooking or an oxygen delignification stage.
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41. Process according to claim 1, wherein:
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a portion of the lignin and other organic material in a cellulose spent liquor stream from step b) or c) or a digester circulation stream is extracted and separated from the spent liquor stream or digester circulation stream before it is discharged to concentration or combustion in order to recover substantially sulfur chemicals free lignin and other organic material, a spent liquor stream recovered after extraction of lignin another organic material is discharged and withdrawn to be further processed in a recovery system according to steps f1) to f4) to recover inorganic chemicals, chemical reagents or chemical reagent precursors and energy values.
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42. Process according to claim 1, wherein lignocellulosic material is subjected to mechanical defiberization before step c), said mechanical defiberization being effected by an energy input ranging from about 50 to 300 kWh/ton of dry cellulosic material.
Specification