| An experimental program including a kinetic study and a parametric study was conducted to study the reaction mechanisms and to develop models of the spray dry SO(,2) absorption process by solutions of sodium carbonate. A single-droplet technique was employed in these studies. For various time intervals, the rate of SO(,2) absorption, the temperature and the general appearance of the droplet were recorded.; The data of the temperature history showed that the reaction in the first drying period occurred nearly isothermally at a temperature equivalent to the wet-bulb temperature of the flue gas. This indicated that the heats of absorption and reaction had a negligible effect on the rate of SO(,2) absorption. The data also showed that the time of the solid layer formation was proportional to the droplet area, and inversely proportional to the evaporation rate and the initial sorbent concentration.; The results of the kinetic study indicated that the overall reaction between SO(,2) and Na(,2)CO(,3) in the spray dry process can be considered to be instantaneous and irreversible. The rate of SO(,2) absorption in the first drying period was controlled by either the gas-film resistance or the liquid-phase resistance depending on the SO(,2) concentration. In the second drying period, the SO(,2) absorption was inhibited due to the formation of the solid layer.; The data from the parametric tests indicated that the SO(,2) concentration is an important factor in a design calculation. For low SO(,2) cases, the absorption rate was a function of gas velocity, but it was independent of the sorbent concentration. On the other hand, the rate of absorption in high SO(,2) experiments increased with sorbent concentration but was not a function of SO(,2) concentration. For an intermediate SO(,2) concentration, the rate of absorption was dependent on both SO(,2) and sorbent concentrations. The results also showed that the rate was not affected by the CO(,2) and water vapor contents in the flue gas. However, for the high humidity case, the total absorption increased due to the longer first drying period.; An unsteady-state, analytical model was developed to predict the SO(,2) absorption in the spray dry system. This model coupled the gas-film control model and the liquid-phase control model, and also accounted for the effect of the solid layer formation in the second drying period. This model gave a reasonably good prediction of the SO(,2) absorption. |
