Microstructure contradistinction for indirect/direct desulfurization product layer of limestone particle in coal-fired flue gas

The micro morphology of limestone sorbent is a key for improving the SO2 removal efficiency in the coal-fired power plant. The tube furnace system was built for imitating the indirect desulfurization reaction in traditional boiler atmosphere (65%N2, 15%CO2, 4.7%O2, 15%H2O, 0.3%SO2) and the direct desulfurization reaction in oxygen-fired atmosphere (80%CO2, 4.7%O2, 15%H2O, 0.3%SO2). The reacted limestone particle samples were observed by SEM and are analyzed by Fourier transformation 3-D reconstruction technique. It is shown that the sizes of internal pore within sorbent particle in two kind atmospheres differ by an order of magnitude, one is about 200 nm for indirect desulfurization, and the other is about 20 nm for direct desulfurization. The CaSO4 products of indirect desulfurization are chaotic derivatives with serious blockage, and the direct desulfurization product layer belongs to uniform honeycombed micro-structure without blockage. Those numerous micro-porous passages can guarantee continuous reactive substance transmission. Key words: Limestone powder, SO2 removal, particle surface, 3-D reconstruction, product layer.