The absorption rate of lean SO
2 and/or NO
2 into aqueous slurries of fine Ca(OH)
2 or Mg(OH)
2 particles was measured using a stirred vessel with a plain gas-liquid interface at 25°C and 1 atm. The absorption process of lean SO
2 into Ca(OH)
2 slurries was found to be almost gas-film controlled under the partial pressures considered here. On the other hand, for SO
2-Mg(OH)
2 slurry system, the diffusion of the reactant across the liquid film was significant and the absorption rate was increased with solid concentration. The observed enhancement factors were compared with the theoretical prediction according to the previously proposed model to estimate the dimensionless parameter concerning solid dissolution. For NO
2-slurry system, the reaction between NO
2 and the aqueous slurry may satisfactorily be considered the reaction between NO
2 and water. The hydrolysis was found to be second-order in NO
2 and the secondorder rate constant was derived as 5.0×10
7 l/mol•sec. The absorption rate of NO
2 with coexistence of SO
2 into aqueous slurries of Mg(OH)
2 greatly exceeded that of NO
2 alone into clear solutions with the same sulfite concentrations, which may be due to the solid-surface reaction in a region from the interface to the reaction plane.
View full abstract