Method for recovery of pulping chemicals in an alkaline sulphite pulping process and for production of steam

摘要

A method of recovery of alkaline sulphite pulping chemicals and for production of steam is disclosed. The method comprises gasification of evaporated spent cooking liquor at conditions resulting in a hydrogen sulphide containing gas and a solid residue. The gas is combusted in a steam boiler, where the hydrogen sulphide is converted into sulphur dioxide and steam is produced. The solid residue is recovered in a leaching process, preferably a two-stage leaching process, where process-foreign substances are removed and the rest of the contents is divided into substantially pure sodium carbonate and a mixture of sodium carbonate, sodium sulphate and sodium sulphide. The substantially pure sodium carbonate is used for absorption of sulphur dioxide from the steam boiler. The mixture of sodium carbonate, sodium sulphate and sodium sulphide is causticized and the resulting sodium hydroxide containing solution can optionally be mixed with the substantially pure sodium carbonate after the absorption of sulphur dioxide in order to produce a fresh cooking liquor.