Predictive Numerical Analysis to Optimize Ventilation Performance in a Hydropower Surge Chamber for H2S Removal

Abstract

The role of a hydropower plant surge chamber as a pressure buffer to compensate excessive pressure fluctuations as a result of load demand variations contributes to the degassing phenomenon of hydrogen sulfide (H2S). Recent data collected from the surge chamber of a hydropower plant reveals that the H2S extraction designs are not effective in controlling the H2S concentration levels especially during surge events. To manage a safe working environment in the presence of H2S requires a systematic evaluation and prediction of the influence of critical flow control conditions in relation to suction optimization and exhaust ducting location. A numerical study was carried out to analyze the flow dynamics and the subsequent response of H2S concentrations to cases involving the following flow mixing and suction scenarios: C1 - absence of suction fans, C2 - absence of fresh air supply, C3 - enhanced suction capability, C4 - reduction in the amount of fresh air supply and C5 - presence of additional ducting. The CFD model was able to provide a reliable assessment of the case scenarios as justified by the validation carried out with in-situ measurements (within 10 % of the actual measured data). The cases where the H2S presence was found to be acceptable with concentrations less than 5 ppm at the upper region of the surge chamber, are C3, C4 and C5. A major finding from the flow studies in the surge chamber is that a combination of negative pressure at the suction locations and the absence of the forced fresh air resulted in significant amount of air drawn in from the outdoors. It was also found that the existing forced fresh air inlet locations are inappropriate as they generate vortex flows which displaces the H2S adjacent to the water level upwards and would later fill the entire chamber. All in all, the validated CFD model of the hydropower plant surge chamber was helpful in providing an understanding of the flow conditions in relation to the management of H2S concentrations.