Process and apparatus for the production of gases containing sulfur trioxide

In the production of sulphur trioxide by catalytic oxidation of sulphur dioxide in several stages with intermediate cooling by p direct admixture of colder gases, the admixture takes place in restricted passages arranged within the reaction chamber and connecting each stage with the next, the velocity of flow in said passages being considerably greater than in the reaction stages themselves. As shown in Fig. 2 the gases entering at 10 pass successively through catalyst layers 12, 16, 19, 21, 23 and 26, undergoing heat exchange at 11 before and after the first layer. Colder gas is admitted at 18a, 20a and 22a into the passages 18, 20 and 22 preceding the 3rd, 4th and 5th stages. A heater 25 controls the temperature of the 6th stage. In another embodiment the stages and passages are arranged as concentric annuli round a central inlet. In a third embodiment, Figs. 4 and 5, the reaction stages are separated by hollow plates 57, 60, 63, 66 containing nozzles 71, Fig. 5, through which the reaction gas passes. The cold additional gas is admitted at 72 to the interior of the plates and passes through holes 73 in the walls of the nozzles. The plates may be divided into sectors into each of which the cold gas is separately fed at a number of points. The addition of cold gas particularly to the last stage may be thermostatically controlled.