GB742052A - Improvements relating to the washing and cooling of gases containing sulphur dioxide - Google Patents

Abstract

Roasting and combustion gases containing sulphur dioxide are washed and cooled in two or more successive towers by spraying with dilute sulphuric acid continuously circulated in a separate closed circuit for each tower in which the acid fed to the first tower is at about the temperature to which the gases are to be cooled in that tower, said acid being maintained at a concentration such that the desired cooling occurs due to the evaporation of water therefrom without substantial rise in temperature of the acid, there by utilising the sensible heat of the gases to supply the latent heat of vaporisation of the wash liquid which latent heat is reconverted to sensible heat on condensation in the second tower and which sensible heat is removed from the wash liquid in the second tower by passing it during circulation thereof, in contact with cooling surfaces. According to an example a gas at 400 DEG C. containing 6 vols. per cent. of SO2 is cooled to 117 DEG C. by washing in a first tower with 70 per cent strength sulphuric acid. The arsenic trioxide content of the gas is removed by the acid in the first tower and can be recovered therefrom as a sludge. Preferably, however, the hot acid is cooled and diluted to deposit the arsenic trioxide before recirculation. In a subsequent tower or towers the water evaporated in the first tower condenses in the circulating wash liquid of that tower and the heat is removed from the combined condensate and wash liquid at cooling surfaces. The temperature of the final gas is reduced to 30 DEG C. by the washing liquid in the second or subsequent towers.