METHOD OF PROCESSING SPENT AQUEOUS SULFURIC ACID LIQUOR

1443878 H 2 SO 4 processing METALLGESELLSCHAFT AG 5 July 1974 [7 Aug 1973] 30035/74 Heading C1A Spent aqueous sulphuric acid liquor which contains substantially inorganic impurities and up to 40% by weight of H 2 SO 4 , is processed by treating with hot H 2 SO 4 -decomposition gases so that water is evaporated from the liquor by direct heat exchange to give an H 2 SO 4 content of not more than 65% by weight, and forming water-vapour laden exhaust gases of temperature 80-100‹ C.; the hot H 2 SO 4 -decomposition gases are generated by heating the concentrated H 2 SO 4 liquor to 800-1100‹ C. in a fluidized bed using oxygen-enriched air and a fuel. In the Figure, spent H 2 SO 4 liquor is introduced via 5 into a spray evaporator 3 where it is contacted countercurrently with H 2 SO 4 -decomposition gases introduced via 6. The pre-concentrated liquor formed flows via 7 to a pump receiver 8, and from there via 9 to a second spray-evaporator 4, where it is conducted co-currently with H 2 SO 4 -decomposition gases introduced via 10 from hot cyclone 2. From 4, the spent H 2 SO 4 liquor (now containing up to 65% by weight of H 2 SO 4 ) is passed via 11 to a second pump receiver 12, and from thence via 13 to charging lances by which it is introduced into the fluidized bed of reactor 1. O 2 -enriched air is introduced into 1 via conduit 14, while fuel (e.g. fuel oil, fuel gas, FeS 2 , sulphur) is introduced via lance 15. Dust from the H 2 SO 4 -decomposition gases from 1 is collected in the hot cyclone 2, while the gases enter the spray evaporator 4 via conduit 10. The hot, moist exhaust gases from the process leave the spray evaporator B via conduit 17.