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BACKGROUND: Sulfur trioxide (SO 3 ) in coal combustion flue gas can adversely affect power plant equipment and the environment. In this work, the removal of SO 3 with typical sodium (Na), magnesium (Mg) and calcium (Ca)-based sorbents was investigated at a pilot-scale facility in the temperature range 400-705 ∘ C. RESULTS:The injection of sodium bicarbonate (NaHCO 3 ) showed the highest SO 3 removal efficiency, which was ∼85% at the sorbent/SO 3 molar ratio of 2 with the gas residence time of 1 s. This is much higher than that of calcium hydroxide (Ca(OH) 2 ) (∼25%) and magnesium hydroxide (Mg(OH) 2 ) (∼30%). The removal efficiency of Mg(OH) 2 and Ca(OH) 2 increased with increasing the reaction temperature from 400 to 705 ∘ C. With the addition of 800 ppm sulfur dioxide (SO 2 ), the adsorption of SO 3 on alkaline sorbents was inhibited due to the competitive adsorption, which caused SO 3 removal efficiency to decrease by 5-12.5%. When injecting the sorbents in slurry form, the removal efficiency was found to be two times higher than that in powder form. CONCLUSION: NaHCO 3 is the most effective sorbent comparing to Mg(OH) 2 and Ca(OH) 2 . To increase the SO 3 removal efficiency, the alkaline sorbents should be injected in the high temperature zone in flue gas. It is recommended to inject the sorbents in slurry form instead of injecting powders directly to achieve high removal efficiency.

Semidry desulfurization process with in situ supported sorbent preparation was studied. The effects of bed inventory, slurry sprayer height above the distributor, and slurry spray method on desulfurization efficiency were tested. The results showed that desulfurization efficiency for 28 kg of bed inventory could reach 98.84% for Ca/S molar ratio of 2.5. This result was approximately seven times higher than the result without bed material because ultrafine Ca(OH) 2 particles in the lime slurry adhered to the bed material surface and formed the supported sorbent. A lower slurry sprayer height and countercurrent slurry spray could reach an even higher desulfurization efficiency. The desulfurization efficiency of this proposed process was approximately 30−40% higher than that of the supported sorbent prepared by the original hydration and drying method at high Ca/S molar ratio due to better contact efficiency between water and sorbent particles.

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