Abstract: A method of modifying the course of combustion when evaporated black liquor is burnt in the furnace cavity of a recovery boiler is described. The method implies that lime sludge is supplied to the furnace cavity whereby the course of combustion is modified so that the temperature in the furnace cavity is raised. Also use of a recovery boiler for simultaneous combustion of black liquor and processing of lime sludge is described. In one embodiment of this use is disclosed that the processing of lime sludge is performed so that increased formation of calcium sulphide in the smelt of inorganic chemicals, which is formed in the recovery boiler, is obtained and/or so that the lime sludge is calcined.

Abstract: A method of producing white liquor having enhanced and/or reduced sulphidity in the recovery of chemicals in a sulphate pulp process is described. In the method one starts from a calcium sulphide rich smelt of inorganic chemicals, which has been obtained by simultaneous combustion of black liquor and processing of lime sludge. This smelt is treated with an aqueous solution, whereupon the calcium sulphide in the smelt is present in a solid form and the rest of the chemicals are in solution. Thereupon the solid calcium sulphide is separated and the obtained solution is processed as a green liquor in per se known manner to a white liquor having reduced sulphidity, whereupon optionally the separated solid calcium sulphide is mixed with the required amount of white liquor to a white liquor having enhanced sulphidity.