GB484714A - Improvements in processes of recovering sulphur dioxide from waste gases - Google Patents

Abstract

In recovering sulphur dioxide from gases by cyclicly contacting the gases with a cold aqueous solution containing a sulphite and a bisulphite and thereafter heating the said solution, the heating is effected in the presence of a liquid organic acid which is only slightly soluble in the cold solution but whose solubility increases rapidly with increase in temperature, the liquid acid not being substantially present as a second liquid phase with the cold aqueous solution when it contacts with the gases. Suitable acids are n-butyric, n-valeric or n-caproic acids, or their isomers, or mixtures thereof. Waste gases containing sulphur dioxide are introduced into a scrubber 5 through a pipe 6, the sulphur dioxide being absorbed by a solution of ammonium sulphite and bisulphite introduced through a distributer 9. The sulphur dioxide-free gas passes <PICT:0484714/III/1> through baffles 10 to an exit pipe 12. The scrubber is provided with a cooling coil 7. The charged solution passes through a pipe 13, a heat exchanger 14 and a pre-heater 15 to a regenerator chamber 18, being mixed on its way with liquid organic acid supplied through a pipe 30 to the connection 32. The regenerator is provided with a heater 20. The regenerated solution passes through the heat-exchanger 14 and a cooler 24 to a trap 28. The liquid acid separates from the solution owing to cooling and is removed by means of the trap 28 for recirculation into the pipe 30 while the aqueous phase is returned through a pipe 29 to the scrubber 5. The sulphur dioxide evolved in the regenerator 18 is washed free from ammonia in a scrubber 33, is cooled in a cooler 38 and is freed from condensed water in a separating chamber 36. The condensed water is returned by a pipe 19 in part to the bottom of the regenerator and in part to the scrubber 33. The ammonia containing liquor from the scrubber passes through a pipe 40 to the bottom of the regenerator. U.S.A. Specification 1,908,731 and German Specification 553,910 are referred to. The Specification as open to inspection under Sect. 91 comprises also the application of the process to the recovery of other acidic gases such as carbon dioxide and hydrogen sulphide. This subject-matter does not appear in the Specification as accepted.