Initial reaction between CaO and SO₂ under carbonating and non-carbonating conditions

The initial kinetics of the CaO/SO₂ reaction have been investigated for reaction times shorter than 1s and in the temperature interval between 450 and 600°C under both carbonating and non-carbonating conditions (0-20 vol% CO₂) to clarify how recirculating CaO influences the emission of SO₂ from a modern dry kiln preheater system for cement production. Calcined Faxe Bryozo limestone with a particle size smaller than 400μm was utilized as CaO source. It was shown, both theoretically and experimentally, that the observed reaction rates were influenced by mass transport limitations. The results showed that the CaO conversion with respect to SO₂ declined when the CO₂ concentration was increased. Under all conditions, larger specific surface areas of CaO gave higher reaction rates with SO₂. Higher temperatures had a positive effect on the reaction between SO₂ and CaO under non-carbonating conditions, but no or even a negative effect under carbonating conditions. The results led to the conclusion that SO₂ released from raw meal in the upper stages of the preheater does not to any significant extent react with CaO recirculating in the preheater tower.