Patent GB-712899-A (GB)
Title: Improvements in the production of gases containing sulphur dioxide
IPC: C22B1/10
Filed: 1950-11-22
Abstract: <PICT:0712899/III/1> <PICT:0712899/III/2> In the production of sulphur dioxide by roasting sulphide ores as a fluidized bed with oxygen containing gases, a sufficiently high temperature is maintained so that the speed of roasting in the bed relative to the introduction of the material to be roasted is so increased that the bed consists predominately of substantially roasted particles, the temperature in the bed being prevented by control cooling from exceeding the softening point of the substantially roasted product. Temperature control may be effected by introducing solid or gaseous substances into the bed or by returning cooled roasted ore or flue dust, or by introducing substances such as iron sulphate, gypsum, or kieser <PICT:0712899/III/3> <PICT:0712899/III/4> ite which evolve sulphur dioxide by an endothermic reaction; excess heat may also be withdrawn by cooling devices.  In Fig. 1 an annular bed 101 of sulphide ore supported on grate 103 is fluidized by upflowing gases entering at 105; roaster gases leave at 117 and the roasted product overflows from the annular bed into central section 112 to be withdrawn at 113.  Fresh ore is supplied through containers 106 and conveyer 108 and a small quantity of air may be passed through pipe 124.  Temperature control may be effected by the heat exchange tubes 119 and 118, the latter being arranged radially over the surface of the bed. The heat exchange tubes may be employed for the production of superheated steam and a rupturable disc 123 is provided in case of injury to the steam tubes.  Alternatively, the heat exchange tubes may be arranged in that part of the furnace to which the solids rise when fluidized as shown in Fig. 2.  Here the annular bed 201 fed from container 223 is provided with exchange tubes 207.  Water is supplied to these tubes from 214, passing through coil 232 to cool the roasted product leaving at 231.  The water then passes through pipes 210 to the tubes.  Steam evolved is withdrawn at 209.  The lower part of the furnace indicated by 217 may be lowered for cleaning, a gas tight joint being provided at 222.  A further embodiment is shown in Fig. 5 where the bed 501 is supported on a grate and a layer of coarse material 505.  Pyrites is fed from container 518 and roasted products are withdrawn at 519.  Vertical heat exchange tubes 509 are provided. Alternatively the heat exchange tubes may be arranged along one or more walls of a furnace having a generally square cross section; in such a case the supply of pyrites is preferably arranged from two diagonal points of the furnace and withdrawal is effected at the bottom through points at the other two diagonals.  In Fig. 7 the bed 709 is enclosed in a circular vessel having heat exchange tubes 716 arranged as a spiral around the wall; the tubes may be coated with a ceramic lining or a cast iron layer.  Fluidizing gases comprising fresh oxygen and re-cycled gases enter at 705 to fluidize the bed. The gases leaving the bed pass through a dust separator 702 on to a heat exchanger 703, product gases are withdrawn at 726 and part of the gases are re-circulated by pump 704.  Fresh oxygen is supplied at point 727 partly to the fluidizing gases and partly at points 728 to a point above the bed level to ensure oxidation of the gases.  Bed temperatures are normally from 850 to 1050 DEG C. and the air or oxygen enriched air supplied may be controlled to give gases containing 15 to 16 per cent. of sulphur dioxide.  According to Examples (I) a sulphidic mineral containing 75 per cent. of iron sulphide and 11 per cent. of zinc sulphide having a total sulphur content of 41 per cent. and a grain size up to 4 millimetres, is supplied to a fluidized bed consisting of roasted material having a height of 50 centimetres with an hourly throughout of 0.48 metric ton of sulphide per square metre of bed cross-section.  The temperature is kept at 1000 DEG C.  Roasted ores having a sulphur content of 0.94 per cent. are obtained and the sulphur dioxide content of the gases is 15 per cent with an oxygen content of 1 per cent.; such gases after dilution with air are suitable for sulphur trioxide manufacture.  (II) 530 kilograms of iron pyrites per hour per square metre of bed area are introduced into a bed having a quiescent height of 50 centimetres consisting of substantially roasted material.  The pyrites has a sulphur content of 48 per cent. and a grain size up to 4 millimetres.  265 cubic metres of pure oxygen mixed with 1090 cubic metres of sulphur dioxide gas, recovered from the process itself having been freed from dust, is fed to fluidize the bed.  The roasting temperature is between 840 and 850 DEG C.  The roasted ore contains 1.02 per cent. of sulphur and the entrained dust contains 1.63 per cent. sulphur; the gas obtained contains 91 per cent of sulphur dioxide, 1 per cent. of oxygen and about 8 per cent. of nitrogen.  The subject-matter of Specification 645,977 is disclaimed and Specification 688,983 is referred to.