SU387062A1 - A method of producing white liquor - Google Patents

Description

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This invention relates to methods for regenerating waste (black) liquors from sulphate pulping to produce white liquor for pulping.

A known method for producing white liquor by regenerating black liquor by pre-evaporation, drying it in the presence of sodium sulfate and concentrated sulfuric acid as an additional additive is sulfur-containing reagent, dissolving the resulting melt to produce green liquor and causticadia of the latter.

In the known method, concentrated sulfuric acid is used, which, on the one hand, requires the use of corrosion-resistant equipment, and, on the other hand, leads to the precipitation of lignin flakes, resulting in clogged pipelines.

With an improvement in the process, it is proposed to use calcium sulfate as an additional additive to the sulfur-containing reagent.

For this purpose, both natural calcium sulphate and its various modifications in the form of chemical production wastes can be used.

When burning black liquor in the reduction zone of the soda recovery boiler, calcium sulphate is the same as sulphate.

sodium is converted to sulphide. When the melt dissolves, the calcium sulfide reacts with sodium hydroxide, which is always present in green liquor, to form sodium sulfide, which increases the sulfidity of white liquor. Calcium hydroxide, which also forms in the process of melting, causticizing soda of green liquor, simultaneously intensifies the removal of sludge, which is a mixture of compounds of iron, chromium, silicon, etc. The amount of calcium sulfate added to black liquor before it is burned is relatively small. For example, to increase the content of sodium sulphide in green liquor by 1%, it is necessary to add 10–12 kg of calcium sulphate per ton of pulp during cooking to black liquor simultaneously with sodium sulphate. The latter relates to the case of slisi one stripped off black liquor in a modern recovery unit, the degree of sulfate reduction in which is 90-92%.

For laboratory experience, one stripped off industrial black liquor containing 55% solids (34% mineral and 66% organic) is used. 100 g of this liquor will be placed in a beaker and 2 g of finely divided chemically pure calcium sulphate is added to it. The contents of the glass carefully moved.

In one of the two prepared crucibles placed 50 g of the original one stripped off black liquor, and in the other 51 g of liquor with the addition of gypsum. The crucibles are placed in a drying cabinet, their contents are dried at 80 ° C and then kept to a constant weight at 105 ° C. The crucibles with dried lye are covered with porcelain lids and placed in an MV-2 muffle furnace approximately 1.5 hours after it starts warming up. The temperature in the furnace is raised to 900 ° C. The crucibles are kept at this temperature for about 1 hour, after which they are removed and cooled in a vacuum desiccator. The contents of the crucible are dissolved in hot water. The solutions obtained are filtered from the coal, and the coal is washed again with water. The filtrates and washings are combined in volumetric flasks. The analysis of the two solutions obtained (green liquor) was carried out according to the procedures described in the special reference literature. The residues in the crucibles that are not soluble in water are dissolved in hydrochloric acid, the amount of liquid is measured and analyzed.

The compositions of liquids obtained by dissolving residues from burning samples of sulphate liquor in a reducing medium are listed in the table.

The subject of the invention. A method for the production of white liquor by the regeneration of black liquor by its preliminary evaporation, sshgapi in the presence of sodium sulfate and an additional additive of sulfur-containing reagent, dissolving the resulting melt in order to obtain green 100

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Thus, the use of calcium sulphate as an additional sulfur-containing additive to the evaporated black liquor prior to its combustion provides the required increase in the sulfidity of the white liquor. At the same time, an improvement in the clarification of green liquor and a reduction in lime consumption for causticization are achieved. The proposed method also makes it possible to use cheap, widespread calcium sulfate instead of the scarce and expensive concentrated sulfuric acid.

acid, elemental sulfur and sulfur-rich sodium compounds; to intensify the purification of green liquor from compounds of iron, chromium, silicon and other elements. caustisation of the latter, characterized in that, ic, to improve the process, calcium sulphate is used as an additional additive to the sulfur-containing reagent.