GB443452A - Production of sulphur dioxide from acid sludge - Google Patents

Abstract

<PICT:0443452/III/1> Sulphur dioxide is obtained by contacting sludge from the sulphuric acid purification of carbonaceous material (e.g. petroleum or coal tar fractions) with a stream of highly heated non-gaseous heating medium, continuously removing the sulphur dioxide evolved from the reaction zone and removing the carbonaceous residue and the heating medium. Suitable heating media are molten metals or salts, solids such as iron or steel balls and finely divided solids such as sand. Hot sand at about 1500 DEG F. is fed into a revolving kiln 1 by means of a screw 2 while sludge is pumped in by a pump 4. A mixture of sand and coke is discharged at 6 while the evolved gases pass out through a gas outlet 5. The mixture of coke and sand is transferred by a conveyer 7 and elevator 8 to a heating kiln 9 where the coke, ignited by a pilot flame 21, burns to reheat the sand for further use. The gases pass through a baffled air condenser 12 and a cooled condenser coil 13 to a water-irrigated scrubbing tower 15 which removes the hydrocarbons present. The scrubbed gas passes to an absorption tower 23 which absorbs the sulphur dioxide in water. The resulting sulphur dioxide solution is contacted with air in a stripping tower 28, the resulting sulphur dioxide-air mixture being dried by contact with strong sulphuric acid in a drier 34. The dried gases are forced by a blower 38 through a converter which consists of a catalyst containing portion 40 and a heat-exchanger 41. The sulphur trioxide containing gases are absorbed in strong sulphuric acid in an absorber 43. By means of connecting pipes 48 and 49, water needed to combine with sulphur trioxide in the absorber 43 is obtained from the drier 34 and strong sulphuric acid needed in the drier is obtained from the absorber 43. Alternatively, the hydrocarbon content of the gases may be burnt out. According to a modification, the sludge is decomposed by hot metal balls. The resulting mixture of coke and balls is discharged on to a screen through which the coke passes, the balls, freed from coke, being heated by travel in countercurrent to combustion gases in a vertical shaft. The separated coke may be used as a fuel. Specifications 398,023 and 443,800 are referred to.