GB1423916A - Process for purifying gases - Google Patents

Abstract

1423916 Purifying gases OSAKA GAS CO Ltd 8 March 1973 [14 March 1972] 11252/73 Heading C1A [Also in Division C5] H 2 S and/or HCN are removed from gases by treating them with an aqueous alkaline absorbent, e.g. an ammonia solution of a desulphurizing catalyst or an ammoniacal suspension of solid sulphur so as to form with the contaminant a compound containing nitrogen and sulphur, e.g. ammonium thiosulphate, ammonium thiocyanate, discharging the treated gas and combusting the absorbent medium containing the fixed contaminant at a temperature from 800- 1300‹ C. to produce a gaseous combustion product containing SO 2 , removing the SO 2 from the gaseous product and discharging the residual gas. The fixed contaminant may have a concentration of 5 to 80% by weight in the absorbent medium, preferably 50-70% by weight and the combustion temperature may be 1100-1200‹ C. In the apparatus of Fig. 1 gas is washed in absorption tower 1 with an ammoniacal suspension of S which is recycled by way of tank 3, so as to fix HCN as ammonium thiocyanate and H 2 S as ammonium thiosulphate. Fresh S suspension may be supplied from tank 4. Partially spent suspension may pass via pump 5 to filter press 6 from where solid S is returned to tank 4 and filtrate passed to tank 8. Alternatively partially spent suspension may pass directly to tank 8 from which liquid is sent to steam heater 11 via pump 9 and thereafter to concentration tower 12. Concentrated liquid is pumped into tank 16 by pump 13. Vapour from tower 12 is condensed by cooler 17 and separated in vapour liquid separator 18. Separated gas returns to absorption tower 1 and separated liquid to tank 3. Concentrated liquid from tank 16 is sprayed into furnace 22 by pump 21. At concentrations of nitrogen containing S above 70%, air is blown into furnace 22 at an initial temperature of at least 800‹ C. by blowers 23, 24 to decompose the N-containing S compound. At concentrations below 70% fuel is also supplied. Heat is recovered from the combustion products in boiler 26 and dust is removed in filter 27. Gas from filter 27 passes to reactor 28 where SO 2 is oxidized to H 2 SO 4 in condenser 30 and collected in tank 33. The acid is sent to heat exchanger 32 by pump 31 for cooling. Gases from condenser 30 may be discharged to the atmosphere or passed through washing tower 34 and Cottrell precipitator 35 before discharge through chimney 36.