GB750347A - Improvements in and relating to the treatment of waste sulphite pulp liquors - Google Patents

Abstract

<PICT:0750347/III/1> Waste sodium sulphite pulp liquor is evaporated and burnt to remove organic constituents and leave a sulphide/carbonate residue which is dissolved in water and the solution treated at 70-100 DEG C. with sulphur dioxide, either the sulphuric dioxide passing upwardly through a coherent downwardly flowing body of liquid, or the liquid passing in divided form through an upwardly flowing body of sulphur dioxide, the hydrogen sulphide thus formed being removed continuously. In the Figure accompanying the Provisional Specification, waste sodium sulphite liquor enters an evaporator 2, passes to a furnace 3, and thence passes in molten state to a dissolver 4, where it is preferred to use sufficient water to give the required sodium concentration in the final liquor. The solution is sprayed into a tower 11 into which sulphur dioxide is being passed, and the solution of sodium bisulphite collected in the storage tank 15. Hot gases from the furnace are utilized in evaporator 2 and sulphur dioxide separated therefrom by means of water in scrubbing tower 6. The sulphur dioxide solution passes to a stripper 9 and the gas is then passed into the lower part of the tower 11. Hydrogen sulphide produced is conducted to a burner 13 and the products added to the main sulphur dioxide supply. In the example a mixture of 20 per cent of sulphur dioxide and 80 per cent of nitrogen by volume was passed through a downwardly moving body of solution in a glass tower, both reactants being preheated to 100 DEG C.; the minimum of sulphur dioxide for complete reaction to form sodium bisulphite was used. Specification 376,654 is referred to.