Numerical design and optimization of a hydraulic micro-turbine adapted to a wastewater treatment plant

Abstract

Wastewater Treatment Plants (WWTPs) are considered as an Ultra Low Head (ULH) hydraulic resource. This has provoked an inadequate extraction of its potential energy by Micro Hydroelectric Plants (MHP) due to the improper relationship between the size and performance of the turbine. Thus, this work proposes the optimized design of a turbine composed of an intake-runner-diffuser, which looks for the maximum energy extraction from this kind of hydraulic resource. The annual Flow Duration Curve (FDC) of a WWTP effluent was examined to determine the flow rate with which the maximal available energy could be extracted through an adequate runner design. A 3D computational model of the intake-runner-diffuser was optimized by coupling a Computational Fluid Dynamics (CFD) software with a Multi Island Genetic Algorithm, while the pressure and flow field of the selected cases were qualitative and quantitatively analyzed. It was found that with the lowest Reaction Degree (RD), a propeller turbine reached its highest efficiency and pressure ratio coefficient, extracting 76% of the annual available energy of the hydraulic resource. In this way, the maximal exploitation of a ULH resource through the turbine design of the MHP system instead of adapting turbines from Large Hydropower Plants (LHP) could help to establish an actual and attractive project cost-benefit ratio.