Abstract: The SO.sub.2 content of gases is catalytically reacted to form SO.sub.3. The SO.sub.3 -containing gases are cooled in a plurality of stages with a cooling fluid (A) before the SO.sub.3 is absorbed. The absorbing acid is cooled by a cooling fluid (B) which delivers heat to a consumer. To increase the temperature of the cooling fluid (B) or to reduce the expenditue and to prevent a temperature drop in the SO.sub.3 -containing gases below the dew point temperature, the SO.sub.3 -containing gases are cooled first by and indirect heat exchange and then by a second indirect heat exchange with a cooling fluid (A) to a temperature slightly above the dew point temperature of the SO.sub.3 -containing gases. The cooling fluid (A) is conducted in a closed cycle. The sulfuric acid circulated through the absorber is cooled by an indirect heat exchange with a liquid cooling fluid (B), which is conducted in a closed cycle.

Abstract: A process for the thermal decomposition and conversion of metal chlorides to metal oxides in a fluidized bed wherein the fluidizing gas contains oxygen and the reaction temperature is maintained above the thermal decomposition temperature of the metal chloride but below the sintering temperature of the metal oxide thus produced. The gas velocity is determined by the critical relationship 0.34.rho..sup.0.9 .ltoreq. W.sub.G .ltoreq. 0.56.rho..sup.0.9 where W.sub.G is the approximate gas velocity through the fluidized bed chamber in the absence of the bed and .rho. is the density of the pure fluidized-bedmaterial (metal oxide). The height of the bed is also critical and should be that at which a critical pressure drop of 1200 to 2400 mm (water column) is obtained but at least 350 mm, measuring with the static or settled bed (nonfluidized).