Effects of Flue Gas Components on the Reaction of Ca(OH)₂ with SO₂

Abstract

A differential fixed-bed reactor was employed to study the effects of the flue gas components, H 2 O, CO 2 , NO X , and O 2 , on the reaction between Ca(OH) 2 and SO 2 under conditions similar to those in the bag filters of a spray-drying flue gas desulfurization (FGD) system. The presence of CO 2 with SO 2 in the gas phase enhanced the sulfation of Ca(OH) 2 only when NO X was also present. When either NO X (mainly NO) or O 2 was present with SO 2 , the enhancement effect was slight, but became great when both NO X and O 2 were present, and was even greater when CO 2 was also present. The great enhancement effect exerted by the presence of NO X /O 2 resulted from the rise in the NO 2 concentration, which enhanced the oxidation of HSO 3and SO 3 2to SO 4 2in the water layer adsorbed on Ca(OH) 2 surface and the formation of deliquescent salts of calcium nitrite and nitrate. The enhancement effect due to the presence of NO X /O 2 was more pronounced when the relative humidity was above that at which the salts deliquesced; the extent of sulfation was more than twice that obtained when SO 2 alone was present. The presence of H 2 O, CO 2 , NO X , and O 2 in the flue gas is beneficial to the SO 2 capture in the low-temperature dry and semidry FGD processes. The presence of NO X /O 2 also enhanced CO 2 removal when SO 2 was absent.

Cerium impregnated palm shell activated carbon (Ce/PSAC) sorbent for simultaneous removal of SO2 and NO—Process study

“…The sorption capacity also increased with increasing RH from 115.8 mg/g to 131.5 mg/g. A similar report was presented by [20,21] over calcium based adsorbent, with SO 2 sorption increased with the addition of water vapor into the simulated flue gas [20,21]. Moreover water accumulating on the surface and interior pore of sorbent forms a liquid film which could make the reaction gas (SO 2 ), more easily absorbed by the sorbent rather than gas-solid reaction [22].…”

“…When both O 2 and NO are present in the gas phase, the tendency of approach to the equilibrium of the O 2 /NO/NO 2 system raises the concentration of NO 2 in the gas phase to a higher value. As NO 2 is a much stronger oxidant and more soluble in water than NO and O 2 , there are more NO 2 molecules present in the water layer, and oxidation of HSO 3 − and SO 3 2− to SO 4 2− is enhanced, which induces more SO 2 molecules to be captured into the humid layer [21]. The reactions that take place in the humid layer involving NO 2 can be represented by the following equations:…”

Dynamic Modeling and Analysis of an Industrial Gas Suspension Absorber for Flue Gas Desulfurization

“…According to Liu and Shih [15], the presence of CO 2 , O 2 , and NO x with SO 2 enhances semidry desulfurization. The temperature and the relative humidity also affect the desulfurization efficiency, and competitive carbonation reaction is moderately present according to Izquierdo and co-workers [16] and Ruiz-Alsop and Rochelle [17].…”

Enhancement Mechanism of SO2 on NO2 Removal by Calcium Hydroxide at Low Temperature

“…Some researchers have reported that the presence of NO 2 in the flue gas together with SO 2 could improve the SO 2 removal capacity of calcium based sorbents. [9,10,11] On the other hand, the effect of SO 2 on the NO 2 removal was also studied by some researchers. [12] However, little work has been done to investigate the effect of flue gas components and reaction temperature on the interaction of SO 2 and NO 2 on the surface of sorbent particle.…”