Effects of the Limestone Particle Size on the Sulfation Reactivity at Low SO₂ Concentrations Using a LC-TGA

Limestone particle size has a crucial influence on SO₂ capture efficiency, however there are few studies on the sulfation reactivity, which covers a broad range of particle sizes at low SO₂ concentrations. In this paper, a large-capacity thermogravimetric analyzer (LC-TGA) was developed to obtain the sulfur removal reaction rate under a wide range of particle sizes (3 μm-600 μm) and SO₂ concentrations (250 ppm-2000 ppm), and then compared with the results of a traditional fixed bed reactor and a commercial TGA. The experimental results showed that the LC-TGA can well eliminate the external mass transfer and obtain a better measurement performance. Both the final conversion and the reaction rate reduced with the decreasing of SO₂ concentration, but ultrafine limestone particles still showed the good sulfation reactivity even at 250 ppm SO₂. An empirical sulfation model was established based on the experimental results, which can well predict the sulfation process of different limestone particle sizes at low SO₂ concentrations. The model parameters have a strong negative correlation against the particle size, and the fit of the reaction order of SO₂ was found to be about 0.6. The model form is very simple to incorporate it into available fluidized bed combustion models to predict SO₂ emission.