Abstract: A process for the recovery of heat and chemicals from spent liquor by evaporating water out from it in order to concentrate the liquor and be feeding the concentrated liquor thereby obtained and air into the soda-ash furnace. In order to increase the dry-matter content of the liquor to a level higher than usual, without at the same time increasing the viscositty of the liquor immoderately, at least the final concentrating (5, 9) of the liquor and its feeding (16) into the soda-ash furnace (4) are carried out under pressure at a temperature higher than the atmospheric boiling point of the liquor.

Abstract: A method for regulating the feed and/or combustion conditions of concentrated waste liquors of varying chemnical and physical properties, for their burning in a soda recovery unit, by determining the maximum expansion upon heating of a dry matter particle of the liquor to be fed into the soda recovery unit, and by regulating the feed and/or combustion conditions on the basis of the expansion thus determined. The measure used for the expansion is the ratio of the lignin present in the concentrated liquor to any one or several of the acids present in the concentrated liquor, such as aliphatic acids.

Abstract: The invention relates to a method of regulating, for the purpose of burning soda-ash in a recovery boiler furnace, the feeding-in or combustion conditions of concentrated spent liquors of varying chemical and physical properties by measuring some physical property of a liquor fed into the recovery boiler furnace and by regulating the feeding-in and combustion conditions directly on the basis of the thus measured physical properties. According to the invention, the maximum swelling, upon heating, of a dry-matter particle of the liquor fed into the recovery boiler furnace is measured. On the basis of this measurement the temperature, pH value, or injection pressure of the liquor fed into the furnace, or the height of the injection point or the direction of injection, or the feeding of air into the furnace is adjusted directly on the basis of the maximum swelling measurement.