(115x) Dissolved Gas Studies for Areation Turbines

Stratification of reservoir water is a common occurrence during hydroelectric production, resulting in low dissolved oxygen (DO) values at lower depths, where turbine intakes are often located. This results in low tailwater DO concentrations, posing an environmental threat. Recent government regulations on minimum tailwater DO levels have affected several plants that cannot meet this requirement.

The most cost effective methods to improve DO levels have involved turbine venting. Air is introduced to flowing water in the turbine by making use of the natural pressure gradient between the inner turbine chamber and the atmosphere. The consequent concentration gradient between the two phases causes oxygen and nitrogen to dissolve into flowing water. It is important to have control of the flow and diffusion of these gases, the accompanying increase in Total dissolved gas can harm water quality. Cavitation, which damages turbine quality, is also a threat.

In order to completely understand this process, the Discrete Bubble Model is used (DBM). The DBM is based on the initial bubble size of incoming gases and is dependent on turbine geometry, local pressure at various sections, air and water flow rates. It is used to predict diffusion and pressure trends at experimental discharge rates, which are compared to those at peak efficiency. This poster will provide an overview of the calculations and trends used for dissolved oxygen predictions for three particular aeration systems, The peripheral, distribution and central venting aeration systems. These trends are used to compare the effectiveness of these three methods, at different experimental conditions. I was guided and mentored by Jason Foust, of Voith Siemens Hydropower, York, PA. He was instrumental in my understanding of the DBM and helped me work on some of the trends that he had developed.