GB852073A - Improvements in or relating to the production of sulphuric acid - Google Patents

Abstract

<PICT:0852073/III/1> Gases containing SO2, gaseous organic compounds and moisture, before being dried by contact with strong sulphuric acid (containing 92-98% wt. H2SO4) are first treated with weaker sulphuric acid (containing 70-90% wt. H2SO4) which is maintained at 90-170 DEG C. by external heating to remove the organic compounds, any droplets of weak acid remaining in the gases after removal of the organic compounds therefrom being eliminated by a form of spray separator before the gases are dried. As shown, SO2 gases saturated with water vapour, enter the weak acid tower 52 through main 78 and pass in countercurrent to a stream of weak acid circulating from tank 53 through line 55, tower 52, and heater 85 e.g. a tubular steam heater. Residual SO2 freed of part of its moisture and all the organic compounds leaves the tower by conduit 79, passes through spray separator 80 for removal of entrained weak acid droplets, such removed acid being returned to tank 53 by line 81, and enters drying tower 56 where it flows in countercurrent to a stream of strong sulphuric acid circulating from tank 58 through line 60, tower 56 and cooler 57. SO2 gases freed from residual moisture pass through main 82 to a catalytic converter 83 from which they emerge as SO3 gases which enter the bottom of absorption tower 61. The gases ascend the tower in countercurrent to a stream of absorber acid (containing above 98 to 99% wt. H2SO4) circulating from tank 63 through line 65, tower 61 and cooler 62. Absorber acid product and weak acid contaminated with organic compounds leave the plant through lines 71 and 73 respectively. Water, and strong acid from line 60, are added to the absorber acid by lines 74 and 76 respectively, the quantities added being controlled by valves 75 and 77 so that the total amount of water i.e. water added as such plus water contained in the strong acid, is sufficient to balance that removed from the absorber acid by the SO3 gases, thus maintaining a constant concentration of H2SO4 in the circulating absorber acid. In order to maintain the concentration of H2SO4 in the weak acid and strong acid circulating in towers 52 and 56 the concentration of which is lowered by the absorption of water from the SO2 gases, controlled proportions of absorber acid are added to tanks 58 and 53 by lines 66 and 68 respectively.