GB712906A - Improvements in the production of gases containing sulphur dioxide - Google Patents

Abstract

In the roasting of sulphidic materials, especially iron pyrites in a bed consisting predominantly of substantially roasted particles of a grain size up to 10 mm. fluidized by the upward passage of a free-oxygen containing gas (see Specification 712,899) the hourly loading per square metre of bed area corresponds to more than 250 kilograms of sulphur content of the material to be roasted. The roasting temperature is kept below the softening point of the roasted materials by some or all of the following measures: employing excess oxygen containing gas (which must in any case be sufficient to complete the roasting to form oxidic roasted material), returning cooled roaster gas or cooled roaster material to the bed, carrying out heat consuming processes simultaneously in the bed, e.g. by spraying in water or dilute sulphuric acid (see Specification 712,907), the inclusion of heat withdrawing members. The oxygen containing gas, particularly when the solid materials have a high content of fine grained constituents, may be blown in part, tangentially or radially into the upper part of the bed to ensure complete condensation. An example relates to the roasting of iron pyrites (sulphur content 48 per cent.) of which 1,350 kilograms (corresponding to 650 kilograms of sulphur) are introduced per hour per square metre of bed cross sectional area into a fluidized bed 50 centimetres deep. 2,900 cubic metres of air are passed upwardly and the temperature is maintained at 850 DEG C. by spraying in water. Entrainment is avoided by providing above the bed a quiescent zone preferably widening conically in the direction of gas flow. An overflow pipe maintains the bed level constant and the sulphur content of the roasted material and the flue dust is reduced to below 1.5 per cent. A gas containing 15 per cent. sulphur dioxide is produced. Reference is also made to roasting copper pyrites, zinc blende, bismuth glance and lead glance alone or in association with iron pyrites. Specification 688,983 also is referred to.