Effects of SO3 formation on high temperature flue gas desulphurization performance

Abstract

The removal of SO2 from a synthetic flue gas using limestone sorbent was investigated. The formation of SO3 in situ was quantified and its effect on the desulphurization performance of the sorbent was determined. The transient response was measured in a bench-scale fixed-bed reactor at 700 °C, 800 °C and 900 °C, and under inert and catalytic wall conditions. Under the homogeneous gas-phase reaction conditions (inert wall effects), it was found that the breakthrough times increased as the temperature increased, indicating an increasing sorbent capacity. The SO3 molar yields under these conditions were found to remain constant at 0.24% at all temperatures. It was found that after the pickling and cleaning of the reactor vessel, the iron oxide on the exposed stainless steel reactor walls had catalytically accelerated the conversion of SO2 to SO3 as the temperature increased. Longer breakthrough times were thus obtained for SO2 removal and increased SO3 molar yields of 1.62%, 2.8% and 4.65% were obtained at each of the temperatures, respectively. The increasing SO3 molar yield had an adverse effect on the desulphurization performance of the sorbent as indicated by decreasing desulphurization ratios (0.95, 0.91 and 0.864), where the desulphurization ratio is the ratio of the actual degree of desulphurization to the apparent degree of desulphurization. It was determined that under these mild desulphurization conditions, the conversion of SO2 to SO3 influences the overall desulphurization performance of the hot-gas system, with increased effects at higher temperatures and a catalytically active reactor wall.

Keywords

• Flue gas desulphurization
• Limestone sorbent
• SO2
• SO3
• High temperature