Effect of ultrasonic vibration on the mass transfer coefficient in a sieve plate scrubber

The air pollution technique of wet scrubbers for fumes, mists and suspended dusts as part of a polluted gas stream has been study as well as used for industries for many decades. The sieve tray is the simplest type of these scrubbers. A laboratory-scale single-stage, sieve tray countercurrent wet scrubber has been designed to study the effect of ultrasonic vibrations on the rate of mass transfer. A 20 kHz ultrasound frequency was chosen for a high performance cavitation to enhance the mass transport between the gas and liquid phases. Various perforation diameters and weir heights were employed in order to permit a different foam level and foam density. The mass transfer of dissolved oxygen was measured across the system as the main parameter followed to quantify the absorption and to calculate the mass transfer coefficient KLa for the system. The sieve tray was operated at the same conditions with and without ultrasound to determine the effect on KLa, oxygen was chosen because it is not likely that any chemical reactions between O2 and H2O would enhance the rate of mass transfer due to the use of ultrasound and because KLa for oxygen is dominated by liquid-phase mass transfer. The overall liquid mass transfer coefficient with and without the use of ultrasonic vibrations was on the order of 10-4 mg/s&dotcm3. The shorter weir of 1 inch height influence a higher dissolved oxygen concentration of a difference about 1.5x10-4 mg/s&dotcm3 with respect to the 1.5 and 2.0 inch weirs. The overall results also indicate that there is no difference on the mass transfer coefficient between different sieve-tray materials, in comparison with the perforations hole size diameter.