Single and simultaneous absorptions of lean SO2 and NO2 into aqueous slurries of Ca(OH)2 or Mg(OH)2 particles.

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The absorption rate of lean SO2 and/or NO2 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 SO2 into Ca(OH)2 slurries was found to be almost gas-film controlled under the partial pressures considered here. On the other hand, for SO2-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 NO2-slurry system, the reaction between NO2 and the aqueous slurry may satisfactorily be considered the reaction between NO2 and water. The hydrolysis was found to be second-order in NO2 and the secondorder rate constant was derived as 5.0×107 l/mol•sec. The absorption rate of NO2 with coexistence of SO2 into aqueous slurries of Mg(OH)2 greatly exceeded that of NO2 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.
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