Bench-scale and modelling study of the effect of H₂O on sulphur capture by limestone in conditions of fluidized-bed air combustion and oxycombustion

Limestone is used widely in fluidized bed energy applications for sulphur capture. The conditions of the novel fluidized bed energy processes can differ from the conditions (i.e., temperature and gas concentrations) in conventional fluidized bed applications for energy production. The influence of H₂O(g) on calcination and indirect sulphation was examined with one limestone type in a bench-scale reactor. A time-dependent multilayer particle model was used for analysing the experimental results. The studied atmosphere included 0%, 10% or 20% H₂O(g) and two different CO₂ concentration levels (15% and 50%). The temperature level was the same in all tests (~1188 K). The added H₂O(g) increased the conversion degree compared to conditions without H₂O(g) in all test conditions. The model was used to explicate the observed differences between test results with and without H₂O(g) and determine the conversion curve, conversion profile and magnitude of reactions and diffusion as a function of radius and time. The results show that different sulphation patterns and conversion degrees can be explained with different limitations inside the particles in terms of time and in different conditions.