GB837027A - A process for the production of sulphur dioxide from sulphates - Google Patents

Abstract

<PICT:0837027/III/1> Sulphur dioxide is produced by conveying granulated material, comprising a metal sulphate and optionally a solid reducing agent, e.g. sulphur or carbon, in an amount insufficient to effect complete reduction to sulphite or sulphur dioxide, on a moving grate in the form of an endless conveyer through a three-stage heating and reduction system at each stage of which hot combustion gas is passed through the solid, exhaust gas from the second and third stages being passed to the first stage and exhaust gas from the first stage being passed for recovery of sulphur dioxide, the conditions being such that the exhaust gas from the first stage contains free oxygen, the sulphate is partially reduced in the second stage to produce sulphur dioxide, and the sulphate is substantially completely reduced in the third stage to produce sulphur dioxide by reaction with the hot combustion gas passing therethrough. Inert gas may pass through the solid in the second stage. The exhaust gas from the third stage may pass to the first stage via the second stage. Air may be added to exhaust gas before passing to the first stage. The combustion gas may be produced by burning coal dust, coal gas, oil, or sulphur. Sulphates which may be used are ferrous, magnesium, calcium and aluminium sulphate. A mixture of calcium sulphate and clay, in which case cement may also be produced, and a mixture of sodium sulphate and aluminium sulphate or alumina, in which case sodium aluminate may also be produced, may also be used. The temperature in the first stage may be 500-800 DEG C., that in the second 900-1200 DEG C., and that in the third up to sintering temperature. As shown, sulphate-containing material is passed from a granulating device a via a hopper b on to a conveyer belt d which conveys the material through three separate heating zones I, II and III, each surmounted by a hood into which fuel is passed from pipe c and air for combustion from pipe p. The air for combustion is preheated before passing into the hoods by being drawn through the hot residue on belt d by pump l. The exhaust gas from zone III is withdrawn at k and is partly recycled to zone III at g and is partly passed to zone II at f. The exhaust gas from zone II is withdrawn at h and is passed to zone I at e. The exhaust gas from zone I is withdrawn at i and is passed through hopper b. In a modification (Fig. 2, not shown), the lower halves of zones II and III are combined and exhaust gas from both zones is withdrawn through a single outlet and is partly recycled separately to zones II and III at f and g respectively and is partly passed to zone I at e.