Influence of CO₂ and O₂ on the Reaction of Ca(OH)₂ under Spray-Drying Flue Gas Desulfurization Conditions

Abstract

The influence of CO2 and O2 in the flue gas on the reaction of hydrated lime sorbent with SO2 was studied using a fixed-bed differential reactor under conditions prevailing in the spray-drying flue gas desulfurization process. With the presence of CO2, the sulfation and carbonation reactions of Ca(OH)2 took place simultaneously until Ca(OH)2 ceased to react. The CaCO3 produced reacted further to form CaSO3·1/2H2O. The apparent sulfation rate, total reaction rate, and final total conversion of Ca(OH)2 were greater than those for the case without CO2. The final total conversion was about 1.45 times that for the latter case at the conditions of 1000 ppm SO2, 60 °C, and 70% relative humidity. The same effect was observed whether CO2 was present with O2 or not. Kinetic expressions obtained by assuming chemical reaction control and considering the surface coverage by product crystals best represented the kinetic data.

Sulfation and Carbonation Competition in the Treatment of Flue Gas from a Coal-Based Power Plant by Calcium Hydroxide

“…Breakthrough curves of CO 2 and SO 2 were discussed in a previous work [17], showing that both gases react simultaneously with the calcium hydroxide according to Ho et al [14]. Furthermore, the CO 2 breakthrough curve shows at about 600 s, a gas concentration higher than the initial one due to the reaction of SO 2 with CaCO 3 that releases CO 2 .…”

“…Guang et al [13], working with Ca(OH) 2 , injected in the flue gas, at temperatures about 500°C, SO 2 concentrations of 3,000 or 1,500 ppm and CO 2 concentrations of 14% found that the carbonation of the sorbent hinders the SO 2 capture even though slight alterations in CO 2 concentrations did not have significant effects on the SO 2 removal. Ho et al [14] proved that when O 2 , CO 2 and SO 2 were present in the flue gas, the sulfation and carbonation reactions took place simultaneously and the carbonate formed further reacted with SO 2 to form sulfite. Liu et al [15], working at the conditions similar to those in the bag filters of dry or semi-dry flue gas desulfurization (FGD) systems, found when CO 2 and SO 2 are present that the final carbonate amount was lower than when only CO 2 is present because the CaCO 3 reacts with SO 2 .…”

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

“…7 Ca(OH) 2 is also reactive toward CO 2 . 8,15 Table 1 shows that X C was 0.34 when CO 2 alone was present. However, when both SO 2 and CO 2 were present, X C was small (about 0.06), and X S1 was almost the same as that obtained when SO 2 alone was present.…”

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

“…The experimental conditions are shown in Table 1. No CO 2 was included in these experiments to avoid the interference between the sulfation and carbonation reactions [9].…”

“…In Eqs. (9) and (10), the reaction rate is proportional to the conversion. Similar equations have been used in the surface coverage model that describes the reaction between Ca(OH) 2 or Ca(OH) 2 /fly ash sorbent and SO 2 at low temperatures [7,8].…”