Process for separating sulphur in the form of hydrogen sulphide from clarified green liquor obtained from the combustion of waste liquor

摘要

The invention relates to a process for separating hydrogen sulphide from clarified green liquor, including precarbonating green liquor with a carbon dioxide rich gas, adding alkali bicarbonate to the precarbonated green liquor and stripping hydrogen sulphide therefrom forming simultaneously alkali carbonate, and preparing the alkali bicarbonate used in the process from the alkali carbonate formed. The process of the invention is carried out by performing the hydrogen sulphide stripping without crystallizing the alkali carbonate formed, preparing the alkali bicarbonate partly from alkali carbonate-alkali sulphide solution obtained in the precarbonation step and partly from the non-crystallized alkali carbonate solution, feeding at least a portion of the alkali carbonate -- alkali sulphide solution through the carbonation step, and passing the carbon dioxide rich gas first through the carbonation step and thereafter through the precarbonation step.