Comparison of SO₂ capture capacities of limestones and dolomites under pressure

The sulfur capture capacities of 11 limestones and six dolomites were determined by means of a pressurized thermogravimetric analyser. The determinations were made under conditions relevant to pressurized fluidized bed combustion. The actual experiments were performed at two different temperatures (850 and 950°C) and at a pressure of 1.5 MPa. Additionally, some experiments were performed at atmospheric pressure for comparison. The particle size of the samples was screened to 200-400 μm. By using a thin (1 mm) sample layer diluted with an inert material (quartz sand), the external mass transfer and the interparticle diffusion problems were excluded. For each experiment the conversion versus time curve was determined. The results showed great variations between different sorbent qualities. Conversions between 7 and 83% were measured. The sulfur absorption capacity order was approximately the same under both atmospheric and pressurized conditions. Higher temperature resulted in considerably higher conversion. The temperature effect differed between the absorbents and was clearly more pronounced for the dolomites than for the limestones. This resulted in one absorbent being more efficient at 850°C, while the other absorbent was more efficient at 950°C.