Critical flow atomizer in SO2 spray scrubbing

Owing to its various deleterious effects, abatement of SO2 from point sources assumes significant importance over the years. Spray towers offer great advantages over other gas cleaning devices. The performance of a counter-current spray tower for SO2 scrubbing using water and dilute NaOH deploying an energy efficient critical flow atomizer is reported. The atomizer is capable of generating finer drops at very high velocity with high degree of spray uniformity. Preliminary hydrodynamic studies indicated that droplet diameter and velocity were strongly dependent on atomizing air pressure and liquid flow rate. Experimentation revealed that SO2 removal efficiency increased with the increase in liquid flow rate, liquid-to-gas flow rate ratio, atomizing air pressure, droplet velocity and pH of the scrubbing liquor while it decreased with the increase in droplet diameter and gas flow rate. Inlet SO2 concentration, however, has no noticeable effect on the removal efficiency. Very encouraging results were obtained for removal efficiency (∼100%) and critical design parameters. Results also indicated that the present system is energy wise and efficiency wise much better than the existing systems. Empirical and semi-empirical correlations were developed for predicting the scrubbing performances as a function of pertinent variables studied in water and alkali, respectively. The water scrubbing efficiency and the mass transfer enhancement factor were combined while predicting the performance in alkaline scrubbing. The predicted values fitted excellently well with the experimental values. That the enhancement factor of mass transfer in alkaline scrubbing could never be expected to increase indefinitely with the concentration ratio of alkali to SO2 at the interface is a striking feature of this study verified by experimentation. This finding does not seem to be detailed in the available literature of gas–liquid mass transfer as well as gas scrubbing. Determination of sizing parameters is also described for the purpose of designing.