Narrow Dispersed Fractions of High-Calcium Fly Ash Produced from the Pulverized Combustion of Irsha-Borodinsky Coal

By means of airflow aerodynamic classification, high-calcium fly ash (with a bulk density of 1.14 g/cm³ and size distribution parameters of d_av = 5 µm and d₉₀ = 14 µm) produced from the combustion of Irsha-Borodinsky coal and sampled from the fourth field of the electrostatic precipitator at the Krasnoyarsk TPP-2 has been separated. The obtained morphologically homogeneous fractions of spherical particles with a narrow distribution are characterized by d_av = 1, 2, 3, 4, and 10 μm and d₉₀ = 3, 4, 5, 9, and 16 μm. It has been established that the main chemical component of the obtained narrow fractions is represented by CaO with a content of 34–43 wt %; the content of the other components is as follows: 15–34 wt % of SiO₂, 13–16 wt % of Fe₂O₃, 9–10 wt % of MgO, 8–10 wt % of Al₂O₃, 2–10 wt % of SO₃. The phase composition has 35–49 wt % of crystalline calcium-containing compounds, including 11–15 wt % of aluminum substituted calcium ferrite and 8–11 wt % of tricalcium aluminate, which are the main phases of Portland cement. The content of crystalline quartz amounts to 2–7 wt %, and that of the amorphous glass phase is 41–51 wt %. It has been established that, as the average fraction size d_av obtained after the aerodynamic separation of ash increases from 1 to 10 μm, the bulk ash density exhibits an increase from 0.89 to 1.50 g/cm³ and the content of the magnetic component also increases, amounting up to 4 wt %. At the same time, the chemical composition of the fractions exhibits an increase in the content of SiO₂ as well as a decrease in the content of Al₂O₃ and SO₃. The content of СаО and Fe₂O₃ in the fractions having d_av = 1–3 μm increases, then it exhibits an abrupt decrease with increasing particle size. As far as the phase composition is concerned, an increase in the content of crystalline quartz is observed, and the total fraction of calcium-containing phases gradually decreases. At the same time, the percentage of calcium sulfate decreases and the percentage of free calcium oxide exhibits a considerable increase. The content of calcium hydroxide increases in the fractions having d_av = 1–2 μm and then decreases with increasing particle size.