Continuous prodn. of oleum and sulphuric acid by contact process - using added sulphur di:oxide with low nitrogen oxide content to minimise nitrous gas formation

摘要

Continuous prodn. of oleum contg. 10-45 wt% SO3 and/or 94-100 wt% H2SO4 involves super- or sub-stoichiometric combustion of S with atmos. O2, cooling the resultant gas contg. SO2 to 390-480 deg C, catalytic reaction of the cooled gas to gas contg. SO3 by simple or double contact catalysis on a catalyst contg. V, absorption of the SO3 gas after cooling, opt. sepn. of liquid from the gas by absorption and energy recovery. The novelty is that dry gas (I) contg. SO2 and up to 5000, pref. under 2000 ppm (NO)x (calculated as NO) is added in the combustion of S with atmos. O2. Pref. (I) is obtd. by thermal decompsn. of waste H2SO4 and pref. contains 5-10 vol% O2, 5-8 vol% SO2, under 200 ppm CO, under 1000 ppm (NO)x, under 50 ppm hydrocarbon cpds. and 82-90 vol% H2O, N2 and CO2. Alternatively, (I) is obtd. by combustion of materials contg. S. The ratio of the amt. of SO2 added in (I) to the amt. of SO2 formed by combustion of S is 1:5 to 3:1. -