No abstract

A model has been developed to predict the dissolution rate of a limestone slurry as a function of particle size distribution and limestone conversion. The model is based on basic mass-transfer theory and includes a factor allowing the flux of calcium ions from the limestone surface to vary with the fraction dissolved. Changes in the flux with the fraction dissolved have been reported to be caused by the presence of sulfite but can also be caused by accumulation of inerts at the liquid−solid interface and/or by changes in the effective mass-transfer area. Calculations show that the decrease in flux reported for sulfites can have a significant impact on the slurry conditions within the reaction tank, i.e., impact on the limestone conversion and the relationship between liquid and solid alkalinity. In the absence of sulfites, the flux from limestone particles has been assumed to be constant with respect to the degree of dissolution. The modeling results have been found to be in good agreement with the measured values of a continuous stirred tank reactor. The model was able to accurately predict the impact of both the particle size distribution and reaction tank residence time on limestone conversion and dissolution rate.

A packed column has been used to study the absorption of nitrogen oxide in an alkaline solution of sodium chlorite. The reactions taking place during the absorption have been examined and a lumped reaction model has been used to estimate rate constants from experimental data. Several parallel and consecutive reactions were found to take place during the absorption. NO was found to be oxidized to NO 2 and/or to NO 2 ± , and ClO 2 ± was reduced to Cl ± and/or to ClO ± . The pH value of the absorbing liquid was found to have a great impact both on the absorption rate and on the extent of the different redox reactions within the liquid. Experimental results indicate that sodium chlorite mainly works as an agent to oxidize NO to NO 2 and that the major part of the nitrogen oxides are absorbed via the hydrolysis of N 2 O 3 and N 2 O 4 .

A packed column has been used to study the absorption of nitrogen oxide in an alkaline solution of potassium permanganate. The reactions taking place during the absorption have been examined and the rate constants have been estimated from experimental data. The experiments show that potassium permanganate is an excellent absorbent for nitrogen oxide. However, to avoid formation of Mn02, the hydroxide concentration has to be very high, i.e. > 3 mol/l. It was found that the reaction could be expressed as first-order with respect to NO and with respect to KMn04. The rate constant may be expressed in terms of the hydroxide concentration as follows: k, , , , = 6114.9CNaoH m3 mol-' s-'.

A packed column has been used to study the absorption of nitrogen oxide in an alkaline solution of potassium permanganate. The reactions taking place during the absorption have been examined and the rate constants have been estimated from experimental data. The experiments show that potassium permanganate is an excellent absorbent for nitrogen oxide. However, to avoid formation of Mn02, the hydroxide concentration has to be very high, i.e. > 3 mol/l. It was found that the reaction could be expressed as first-order with respect to NO and with respect to KMn04. The rate constant may be expressed in terms of the hydroxide concentration as follows: k, , , , = 6114.9CNaoH m3 mol-' s-'.