Purification of process gas from a partial combustion of black liquor

Process for the separation of sulphur and sodium compounds from a hot process gas generated during gasification of spent liquor from the kraft pulping industry, through contact with hydrogen sulphide ion and hydroxide ion containing alkaline wash liquids in two or more stages, characterized in that the process gas in a first stage is brought into contact with a wash liquid selected from the group consisting of water and an aqueous alkaline washing liquid by passing the process gas through a venturi throat, a liquid trap or a combination thereof, where melt droplets consisting essentially of water soluble sodium and sulfur compounds in the process gas are separated from the gas and drawn off as an aqueous solution, and where the process gas in a subsequent washing stage is brought into contact with a finely dispersed alkaline washing liquid other than green liquor containing hydroxide ions and hydrogen sulphide ions with a molar ratio of 8:1 or greater wherein said ratio of 8:1 or greater is higher than the molar ratio of hydroxide:hydrogen sulphide ions in the washing liquid used in the first stage, thereby avoiding reformation of gaseous hydrogen sulphide in the subsequent washing stage.