Study on the Gas Holdup of Triangular Pitch and Square Pitch Sparger Geometry in Bubble Column

摘要

Gas holdup in a bubble column has been studied for triangular and square geometries of a pitch sparger. The investigation was carried out in a bubble column characterized by an aspect ratio equal to four. The column was made up of plexiglas, equipped with sparger. The top of the column was open to atmosphere. The column was also equipped with appropriate rotameters for gas phase flow measurement and control. The liquids used in experiments were: deionised water, glycerin (50%) and butanol (1.5%) with atmospheric air representing the gas phase. A high-speed digital video camera was employed for the measuring of bubble rise velocity. The recorded images are also used to obtain an insight into the coalescence/breakage mechanisms occurring during bubble formation at the vicinity of the sparger. Using the appropriate software, rise velocity of the bubbles after their detachment from the triangular and square pitch spargers can be obtained from recorded images for examined liquid and flow conditions. The effect of sparger's geometry on the rise velocity of the bubbles was studied. An average gas holdup was estimated by bed expansion. The uncertainty of measurements is estimated to be less than 10%. For two tested spargers, the transition point was determined to be independent from the pore size. It is also evident that the increase of liquid phase viscosity shifts the transition point to lower velocities. The only exception is a water whose transition velocity is lower than that of butanol solutions, despite of its higher viscosity. This behavior can be attributed to simultaneous effect of relatively low viscosity and high surface tension.