Pump as turbine for throttling energy recovery in water distribution networks

Abstract

Nowadays, a great effort is increasingly put by the scientific community into a more sustainable energy management, which requires a higher harvesting of renewable energy sources with respect to conventional ones. In the framework of distributed electricity production, Pumps as Turbines (PaTs), i.e. pumps operated in reverse mode, are becoming more and more tempting, being very cost effective with respect to customized hydro turbines. For instance, Water Distribution Networks (WDNs) are equipped by pressure relief valves (PRVs) in order to regulate flow rates and to reduce leakages. The replacement of PRVs with PaTs could be a feasible practice to achieve both an effective pressure control and a throttling energy recovery. The preliminary identification of specific speed of a pump to be used as a turbine is fundamental in order to find the best suitable solution. However, the insertion of a PaT must consider the variability of water demand and pressure patterns. The hydraulic variability in a water distribution network does not permit to define a unique operating point for a PaT and this aspect is a further obstacle for the functional planning of such a system. In this framework, the present work aims at proposing a methodology to find the more suitable PaT for a specific WDN, starting from the analysis of the pressure and flow rate patterns. The methodology is based on the selection of an existing machine from a pump catalogue. Then, knowing its geometrical information, it is possible to predict the characteristic curve of the pump operating as turbine by using a 1-D performance prediction model. The WDN of a town in the Apulia region (Southern Italy) has been used as a case study, in order to select a PaT useful for throttling energy recovery. Finally, a techno-economic evaluation has been carried out.