US 5,628,874 AGranted

Reduction of chloride in pulping chemical recovery systems

AssigneeEka Nobel AB

InventorsHans Lindberg, Birgitta Sundblad

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Abstract

The present invention relates to an environmental-friendly process for reducing the content of chloride in a liquor inventory of a chemical pulp mill. According to the invention, in a recovery system for pulping chemicals containing sulphur and an alkali metal, precipitator dust formed in a recovery boiler is collected and withdrawn, dissolved in water and electrolyzed for production of chlorine or hydrochloric acid in the anolyte. Since the dust normally contains a large amount of sodium sulphate, sulphuric acid and sodium hydroxide can also be produced in the electrolysis. To reduce the content of impurities, before the electrolysis, the pH of the aqueous solution is adjusted to above about 10 to precipitate inorganic substances which are separated-off together with flocculated or undissolved substances.

Claims10

Dependent claims

A process for reducing the content of chloride in a recovery system for pulping chemicals containing sulphur and an alkali metal, comprising the steps of:

(a) bringing a spent liquor generated from a pulping step to a recovery boiler,
(b) burning said spent liquor optionally together with make-up chemicals,
(c) collecting precipitator dust formed and withdrawing said precipitator dust from the precipitator of the recovery boiler,
(d) dissolving at least a portion of the precipitator dust in water to produce an aqueous solution of precipitator dust,
(e) adjusting the pH of said aqueous solution of precipitator dust to a pH about 10 or above to precipitate inorganic substances, wherein flocculated or undissolved inorganic and organic substances are separated from said aqueous solution, and
(f) electrolyzing said pH-adjusted aqueous solution of precipitator dust in a membrane electrochemical cell containing at least two compartments for production of chlorine or hydrochloric acid in the anode compartment and alkali metal hydroxide in the cathode compartment.

3 more elements

Dependencies are inferred from the claim text.