Simultaneous Removal of SO₂ and Trace SeO₂ from Flue Gas:  Effect of Product Layer on Mass Transfer

Abstract

Sulfur dioxide (SO2) and trace elements are all pollutants derived from coal combustion. This study relates to the simultaneous removal of sulfur and trace selenium dioxide (SeO2) by calcium oxide (CaO) adsorption in the medium temperature range, especially the mass transfer effect of sulfate product layer on trace elements. Through experiments on CaO adsorbing different concentrations of SO2 gases, conclusions can be drawn that although the product layer introduces extra mass transfer resistance into the sorbent-gas reaction process, the extent of CaO adsorption ability loss due to this factor decreases with decreasing SO2 concentration. When the gas concentration is at trace level, the loss of CaO adsorption ability can be neglected. Subsequent experiments on CaO adsorbing trace SeO2 gas suggest that the sulfate product layer, whether it is thick or thin, has no obvious effect on the CaO ability to adsorb trace SeO2 gas.

The selenium oxygen clusters SeOn (n=1–5) and their anions: Structures and electron affinities

“…It can also protect against some kinds of cancer, and in particular, selenium deficiency causes Keshan disease (a disease of the heart muscle) [3]. However, at high levels it can be toxic causing hair and nail loss and disorders of the nervous system [4][5][6], and mainly existing under the form of selenate [7][8][9].…”

Sulfation diffusion model for SO2 capture on the T-T sorbent at moderate temperatures

“…In this case, the product layer diffusion may be related to the ionic outward diffusion where the solid reactant migrates outward through the product layer by Ca 2+ and O 2− ionic diffusion to react with the SO 2 and O 2 on the surface [13][14][15]. If the number of ions diffusing to the gas/CaSO 4 interface is less than the number of SO 2 molecules there, increases of the SO 2 concentration will not contribute much to the reaction rate.…”

Density Functional Theory Study of Steam Effect on SeO2 Capture by CaO Adsorbents

“…CaO, a widely used adsorbent, has been proven to be highly effective in SeO 2 capture in flue gas . According to previous research studies, water vapor is an important component in flue gas, which has been fully confirmed to be able to promote the adsorption of CO 2 or SO 2 by CaO. − Based on experiments and kinetic study, Li proposed that H 2 O would decompose on the CaO surface to form superficial OH, which could greatly increase the adsorption capacity.…”