SO₃ Removal from Flue Gas with Ca(OH)₂ in Entrained Flow Reactors

Abstract

Experiments were carried out in a pilot-scale entrained flow reactor (EFR) to investigate the reaction of SO3 with Ca­(OH)2 as a method of dry sorbent injection (DSI) for SO3 removal from flue gas. The results indicate that SO3 can be removed by Ca­(OH)2 with an efficiency that can reach 80%, and it was found that the molar ratio of Ca­(OH)2 to SO3 ([Ca]/[S]) and reaction temperature have a significant effect on SO3 removal efficiency. The experimental data measured inside the EFR were analyzed with a computing fluid dynamic (CFD) simulation, in which the Euler–Lagrangian frames were used for gas- and discrete-phase modeling. The CFD models were validated and applied to analyze the effects of certain parameters on SO3 removal efficiency, such as particle velocity, [Ca]/[S], temperature and residence time. It was found that the sorbent diameter has a significant influence on SO3 removal efficiency, with an obvious decrease in efficiency if the Ca­(OH)2 particle diameter increases. For example, if the sorbent diameter increases from 3 to 10 μm, the SO3 removal efficiency at the reactor outlet will decrease from 99% to 55%. A detailed comparison and theoretical analysis indicated that external diffusion of SO3 from the gas phase to the particle surface is the rate controlling step for larger Ca­(OH)2 particles, and more attention should be paid to the competition between external diffusion and surface reaction when applying the DSI method for removing SO3 from flue gas.

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Influence of SO2 in the Medium to High Temperature Range of SO3 Removal by CaO

“…Chen [11] compared the absorption performance of Ca(OH)2, Mg(OH)2, MgO and CaO on SO3, and found that the SO3 efficiency all above 60% in 400℃. And more researchers focused on the calcium-based sorbents taking into account the cost and the reactivity [12][13][14][15]. Wang [12] discovered that SO3 removal efficiency by Ca(OH)2 was approximately 92% with entrained flow reactors.…”

“…And more researchers focused on the calcium-based sorbents taking into account the cost and the reactivity [12][13][14][15]. Wang [12] discovered that SO3 removal efficiency by Ca(OH)2 was approximately 92% with entrained flow reactors. But He [13] found that SO2 has a competitive absorption against SO3 when studied the SO3 absorption of Ca(OH)2 on at 200-350℃, and the SO3 selectivity at the initial moment is only 0.16 at 350℃.…”