Effect of horizontal baffles on the performance of mechanically agitated gas-liquid contactors

Abstract

The objective of this investigation was to study the effect of horizontal baffles on the performance of a mechanically agitated gas-liquid contactor in comparison to its performance with vertical baffles. The performance criteria were: the overall average volumetric mass-transfer coefficient, k^a, and the agitation power.

The investigation was conducted on a lab-scale tank 1 f t . in diameter and 2 f t . height agitated with a 3" Rushton Turbine. Air was injected into a 0.25M Sodium Sulfite solution, and the oxygen consumption rate was determined. The primary independent variables were the impeller speed (changed from 500 to 1450 rpm.) and the rate of air injection (changed from zero to 0.67 l./sec).

The horizontal baffles improved the contactor performance over that when vertical baffles were used. The values of kjâ were 80% tol30% higher, while the agitation power required was as much as 33% lower at certain operating conditions. The improvement was more pronounced at impeller speeds of 800-1450 rpm.

The experimental data indicated that the improvement in kjâ was identical to the increase of the gas holdup in the liquid. It was seen that the horizontal baffles induce entrainment from the upper surface of the liquid (surface aeration) and the increase of k^a is due to a higher entrainment of gas in the liquid and not due to smaller size bubbles.

The results of this investigation suggested that there is a potential for using horizontal baffles on an industrial scale.