A study of bubble generation and hydrodynamics in dissolved air flotation

Abstract

In Dissolved Air Flotation the performance of the saturator and subsequent release of the air from the solution is important. In particular the bubble size, the degree of saturation and the hydrodynamic bubble movement are important physical parameters. In this study all these have been investigated. The factors affecting the bubble size when gas is released from a supersaturated solution and the performance of two types of absorbers a conventional packed column and a Higee Absorber were examined. The size of the bubbles generated from a nozzle have been measured in tap water at different operation conditions of liquid flowrate, gas flowrate and pressure. The bubble size was measured using a photographic technique and found to decrease with increasing the gas pressure in the conventional saturator, but it was not possible to observe the small bubbles generated using the Higee Technique. For the conventional device, the liquid flowrate had a significant role whereby the bubble diameter fell with flowrate. Bubble uniformity increased as both pressure and liquid throughput increased. The saturation performance of the two kinds of absorbers were examined. In all the cases, the Higee technique operate better as far the saturation level was concerned. The degree of saturation in the Higee systems was found to be a strong function of both gas and liquid flowrates as well as the rotational speed (which governs the gas pressure). Finally, as it may be possible to distribute the saturated solutions and (any bubbles formed) more uniformly throughout flotation tanks if Higee saturators are used, a computer package was adopted to provide enough data for the simulation of the flow patterns in flotation tanks.