Preparation of diatomite/Ca(OH)₂ sorbents and modelling their sulphation reaction

Mixtures of Ca(OH)₂ and diatomite were hydrated at different conditions to produce reactive SO₂ sorbents. Two different hydration techniques were used; namely, atmospheric and pressure hydration. The effect of the hydration temperature, time and diatomite/Ca(OH)₂ weight ratio on the physical properties of the activated sorbents were investigated. In atmospheric hydration, it was found that increasing the temperature and hydration time caused an increase in the total surface area of the sorbents. However, surface area values of the sorbents prepared from mixtures which have different diatomite/Ca(OH)₂ weight ratio were generally not changed significantly. In pressure hydration, the surface area of the activated sorbents was positively affected from the hydration temperature and pressure. Finally, Ca(OH)₂ and two diatomite/Ca(OH)₂ sorbents were sulphated at constant temperature (338 K) using a synthetic gaseous mixture consisting of 5% O₂, 10% CO₂, 5000 ppm SO₂ and the balance of nitrogen with a 55% relative humidity. The sulphation reaction of these sorbents were investigated and modelled. The unreacted shrinking core model was chosen to describe this non-catalytic solid/gas (hydrated sorbent/SO₂) reaction mechanism. The experimental results were found to be correlated successfully by this model.