Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Patent
1995-10-05
1998-06-02
Czaja, Donald E.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
162 3011, 162 36, D21C 1112
Patent
active
057593450
DESCRIPTION:
BRIEF SUMMARY
PROCESS FOR TREATING SULPHUR-CONTAINING SPENT LIQUOR USING MULTI-STAGE
CARBONIZATION
The present invention relates to a process for converting spent liquid containing sodium sulfite and carbonate with sulfate and thiosulfate impurities into cooking liquor containing sodium sulfite and sodium carbonate for an sodium (Na)-based cellulose pulping process or Na-based pulp digestion process, such as, for example, the ASAM process or alkaline or acidic sodium sulfite processes, in which the spent liquor is burned in a liquor burning boiler with liquid slag extraction and a multistage waste gas purification with recovery of the sodium sulfur compound. The waste gases leaving the liquor boiler are first freed of dust in a dry process and are subsequently in one stage, preferably in at least two stages, washed with different washing liquids. The separated dust, in particular the separated Na.sub.2 SO.sub.4 is mixed with the liquor to be burned and the liquid slag from the liquor burning boiler is dissolved in water. The dissolved sodium compounds, in particular the Na.sub.2 S formed, is converted by carbonation with a portion of the purified waste gas to form NaHCO.sub.3, NA.sub.2 CO, and NaHS.
The ASAM process (Alkaline Sulfite Process with Anthraquinone and Methanol addition) is a further development of the neutral or alkaline sulfite process known and used in the industry for centuries. The true innovation in the ASAM process is the addition of methanol to the pulping solution. In comparison to the sulfite and to the sulfate processes, the ASAM process has the advantage that during the digestion, gaseous sulfur compounds do not develop and that the chemical pulp can be bleached to the highest degrees of whiteness without the use of chlorine-containing bleaching agents. Since when using chlorine-free bleaching agents in the digestion as well as also in the various bleaching stages, exclusively sodium is present as the base, the resulting bleaching tower spent liquor can be processed during the pulp washing stage together with the spent liquors from the digester house. The alkali used in the various bleaching stages can be recovered and the possibility is given of largely closing the water cycle of the factory.
With reference to the prior art, several prior art processes will be described.
Austrian Patent No. AT-B 351 359 discloses the removal of NaCI from the digestion liquid without including the solid residues of the waste gas purification.
European Patent Publication No. EP-B1 223 821 discloses a pyrolysis process for the spent liquor in which a portion of the combustible components resulting in the pyrolysis is burned and the inorganic residues are present in the molten state and are quenched. In this process as well, the solid residues from the waste gas purification are not introduced into the smelt.
European Patent Publication No. EP-A1 538 576 discloses the carbonation of the green liquor with CO.sub.2 -containing gas, such as for example purified waste gas or gas or from the causticizing stage with the formation of NaHCO.sub.3 and the release of H.sub.2 S. The concentration of H.sub.2 S is decreased by the nitrogen contained in these gases leading to an increase in the gas volumes to be treated so that large quantities of gas must be supplied to the liquor boiler or must be burned in the H.sub.2 S muffle. Moreover, the conversion of the NaHCO.sub.3 formed with NaHS to form Na.sub.2 CO.sub.3 and H.sub.2 S leads to an increase of the pH-value and a decrease of the partial pressure of H.sub.2 S in the solution as well as to a high requirement of stripping gas as a result.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new and improved process for converting sodium sulfate in which the disadvantages of the prior art are avoided.
The invention is based on the task of addressing the problems and of closing the recovery of the chemicals via the cycle of conversion of spent liquor to cooking liquor. The recovery installations have two main functions: the recovery of inorganic
REFERENCES:
patent: 3366535 (1968-01-01), Cann
patent: 3826710 (1974-07-01), Anderson
patent: 4148684 (1979-04-01), Farin
patent: 4941945 (1990-07-01), Pettersson
Hauki, T., "TRP in the Kraft Proc. . . . Chemical balance", P&P Canada, 85:2 (1984), pp. 31-35.
P.E. Shick, "Development in Recov . . . Cooking Chemicals", Tappi, vol. 56, No. 8, Aug. 1973, pp. 96-98.
Bobik Michael
Chybin Dieter
Glasner Alfred
Taferner Karin
Austrian Energy & Environment SGP/Waagner-BIRO GmbH
Czaja Donald E.
Nguyen Dean T.
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