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Disposal process for sulfide-free black liquors

Inactive Publication Date: 2010-05-06
NIHON CELLULOSE CO LTD +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0039](1) As the pH of the black liquor is controlled to neutrality or acidity in removal of lignin from the black liquor, it allows the dissolved lignin to turn easily into a suspendible substance for flocculation and separation so that the removal rate of lignin can be improved, facilitating black liquor disposal.
[0040](2) Lignin, water, acids and caustic soda can be recovered from black liquor discharged out of a pulp digestion step and free of sulfide.
[0041](3) Even black liquor having a high concentration of silica can be disposed so that for pulp raw materials use may be made of woody or non-woody raw materials that are not used with the kraft method thanks to an increased content of silica.

Problems solved by technology

Such corrosion takes place mainly at a black liquor concentrator in a pulp-making plant, doing damage to evaporating and heating pipes, etc.

Method used

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  • Disposal process for sulfide-free black liquors
  • Disposal process for sulfide-free black liquors
  • Disposal process for sulfide-free black liquors

Examples

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example 1

[0063]The present invention is now explained with reference to the flowchart of FIG. 1.

[0064]As the black liquor, a sulfides-free black liquor discharged out of the pulp digestion step is used.

[0065]The black liquor suited for the inventive disposal is a black liquor discharged out of the process set forth in Japanese Patent Application No. 2007-006159-Patent Publication 1, i.e., the pulp-making process in which chips are partially oxidized with dilute nitric acid, and then digested with dilute caustic soda. More specifically, that black liquor is free of sulfides, and contains lignin in a concentration of a few % by weight or less.

[0066]Note here that a black liquor occurring with the kraft method where the incorporation of sulfides is unavoidable cannot be applied to the invention, because the sulfides are oxidized into sulfur that in turn clings and sticks to disposal equipment, rendering it difficult to run.

[0067]In the pH control step the mineral acid and, if necessary, dilutin...

example 2

[0088]Another example of the invention is now explained with reference to the flowchart of the invention of FIG. 2.

[0089]Example 2 is the same as Example 1 in that the sulfide-free black liquor discharged out of the pulp digestion step is used.

[0090]In the neutralizing step a mineral acid and, if necessary, diluting water is added to the black liquor to control its pH to 6 to 9. The mineral acid used here may include hydrochloric acid, and sulfuric acid. Note here that nitric acid is not preferable because it tends to give rise to NOx in the later steps. As the concentration of solid matters (total remnants after evaporation) is lower, the rate of collection of organic matters during flocculation grows high, but as that concentration is all too low, disposal efficiency goes worse because the liquor amount grows large. Dilution should thus be carried out such that the solid matters are kept at 1 to 8% by weight in the later pH control step.

[0091]In the first flocculation step, stirri...

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Abstract

Lignin is flocculated and batched off from a sulfide-free black liquor discharged out of a pulp digestion step by water disposal techniques, and organic matters remaining in the filtrate are removed to recover water, acids and caustic soda.A mineral acid and, if necessary, diluting water is added to the black liquor to control its pH to 1 to 7, and a flocculant is added to the black liquor to filtrate out flocculating lignin. Further, ozone is brought into contact with the filtrate to oxidize and break down organic matters in the filtrate and remaining organic matters are adsorbed onto activate charcoal for removal.

Description

TECHNICAL FIELD[0001]The present invention relates to the disposal of a sulfide-free black liquor discharged out of a pulp digesting step for the purpose of recovering lignin from the black liquor by water disposal techniques.BACKGROUND ART[0002]Generally in pulp production by the kraft method, black liquor discharged from a digesting step is concentrated to bring the proportion of solid matters (total evaporative remnants) up to 70% by weight or higher, and the solid matters are incinerated to recover thermal energy and chemicals (soda and sodium sulfide) from incinerated ashes.[0003]Now then, the raw woody material for pulp contains silica (silicon dioxide) although varying in proportion depending wood types. Non-woody raw materials, especially bagasse, bamboo and palm contain it in large amounts. Silica is insoluble in water and acids, but it dissolves in alkalis such as caustic soda into alkali silicates. The alkali silicates include sodium silicate (Na2SiO3) that sticks and cli...

Claims

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Application Information

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IPC IPC(8): D21C11/00C07G1/00
CPCB01D61/025B01D61/04B01D2311/04B01D2311/08C02F1/283C02F1/32C02F1/441C02F1/461C02F1/4618C02F1/56C02F1/66C02F1/78C02F9/00C02F2103/28B01D2311/18B01D2311/2626B01D2311/2642B01D2311/26B01D2311/2684
Inventor AKO, AKIRAKOIKE, KAZUMASA
Owner NIHON CELLULOSE CO LTD
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