LAB REPORT

Oxygen Transfer in Aerated Tanks

Oxygen Transfer in Aerated Tanks

Introduction

The study is related to the oxygen transfer in aerated tanks which focuses on estimation of oxygen transfer coefficients as a function of air flow rate and location of the sparging device in the tank. Moreover, the objective of the study is to correlate mass transfer coefficients and air flow rates. In addition, the study also focuses in determining the best practical locations of air sparging devices in the tank by estimating the KLa values for each case considered that is flow rate 25 m/min, flow rate 50 m/ min, flow rate 75 m/ min and flow rate 100 m/ min.

Discussion

The overall objective of the work is to develop a tool for analysis and simulation of flow and oxygen transfer in aeration tanks to correlate mass transfer coefficients and air flow rates and also to determine the best practical locations of air sparging devices in the tank by estimating the KLa values for each case considered that is flow rate 25 m / min, flow rate 50 m / min, flow rate 75 m / min and flow rate 100 m / min. Ultimately, this tool will simulate and interpret the impact of design parameters, design and management of technical installations on the capacity of oxygen aeration systems and the location of the sparging device in the tank. Initially, the measurement methods were developed to measure the local parameters and flow characteristics of oxygen transfer in clean water on a real site. The weak influence of the circulation of water on the size of air bubbles was highlighted. The increase in oxygen transfer by imposing a horizontal velocity of water is mainly due to an increase in overall gas holdup, for neutralization of spiral flow. The second objective was to determine the best practical locations of air sparging devices in the tank. This tool, validated experimentally on a pilot basin and a real site, can accurately reproduce the oxygen transfer. In a third step, this numerical tool was used to analyze the phenomena of local oxygen transfer. The evolution of the oxygen saturation instant CL and its influence on the determination of the coefficient of oxygen transfer have been identified. An adaptation of the method for determining the oxygen transfer coefficient taking into account the real evolution was proposed. The impact of the provision of ramps diffusers, air flow rates and surface velocity of water on oxygen transfer were analyzed globally and locally.

Three parameters that govern the amount of oxygen transfer to the aerated tank are:

- The specific interfacial area which is an increase in specific interfacial area can be induced by a decrease in bubble size or increasing the gas retention;

- The transfer coefficient overall liquid side; its value increases when the thickness of the boundary layer (EL) decreases that is when the turbulence increases. It also depends on the physicochemical properties of the liquid;

- The concentration gradient (C* - C), the concentration gradient can intensified by increasing the partial ...