One of the earliest processes used to make sulphuric acid, an ore containing iron(FeS2: Iron pyrite) is roasted (burned) with air. The following reactions take place in the furnace (s denotes a solid species, and g a gaseous species):
2FeS2 (s)+ 15/2 O2 Fe2O3 (s) +4 SO3 (g)
2FeS2 (s)+ 11/2 O2 Fe2O3 (s) +4 SO2 (g)
(In later stages of the process, not to be considered here, the SO2 is further oxidized to SO3, which is then absorbed in water to produce the H2SO4 product.)
A solid ore containing 82 wt% FeS2 AND 18 wt% inerts is fed to the furnace. Dry air is fed in 40% excess of the amount theoretically required to oxidize all of the sulphur in the ore to SO3. A pyrite conversion of 85% is obtained, with 40% of the FeS2 converted to form sulphur dioxide, and the rest forming sulphur trioxide. Two streams leave the roaster: a gas stream containing SO3, SO2, O2 and N2, and a solid stream containing unconverted pyrite, ferric oxide (Fe2O3), and inerts.
a) Draw and completely label a flowsheet of the process (use 100 kg/min of ore as a basis).
b) Calculate the rate of Fe2O3 production (kg/min) in the outlet stream, and the total molar flow and composition of the outlet gas stream.