GB390545A - Improvements in or relating to the burning of pyrites, or iron sulphide, and the production of iron oxide - Google Patents

Abstract

In burning ferrous sulphide or iron pyrites with air, the temperature of combustion is controlled by feeding to the reaction zone a relatively cool gas consisting of sulphur dioxide, nitrogen and a relatively small amount of oxygen which has been obtained by cooling a gas resulting from the combination of pyrites, or according to the Provisional Specification ferrous sulphide, with excess of air, or from the secondary combustion with excess of air of a gas containing free sulphur and resulting from the combustion of ferrous sulphide or pyrites with a restricted supply of air. The process may be carried out in any type of pyrites burner including rotary kilns, shaft kilns and mechanical furnaces. In one modification, the burner is supplied with excess of air, the pyrites being burnt directly to iron oxide and sulphur dioxide, the part of the gas leaving the top of the furnace containing free oxygen is cooled in a waste heat boiler, preferably after being freed from dust, and is returned to the burner at a point below the main combustion zone. The returned gas may be mixed with the air supply, or the gas and the air supply may be introduced at the same point; or the preheated air supply may be introduced at a point well below the point of introduction of the returned gas. In another modification, the air supply is limited and the resulting gases contain sulphur dioxide and free sulphur. Secondary air, preferably preheated, is fed to the top of the burner or to a separate combustion chamber. The resulting combustion gases containing free oxygen are returned as before. Specifications 3704/87, 817/00, [both in Class 1, Acids, alkalies, &c.], 236,256, 247,471, [both in Class 1 (iii), Oxides &c., Metallic], 273,976, and 279,693, [both in Class 82 (i), Metals, Extracting &c.], are referred to.