Laboratory and Field Testing of PRS Turbines for Energy Recovery in Pipeline Systems

Pressure Reducing Valves (PRV) are used in water pipes to control the pressure in the conduit, for given demand, or to control the discharge for given fixed outlet pressure. Micro-turbines are used to produce electric energy and are often installed in the conduit immediately before open water tanks to allow a free outflow discharge. A new turbine has been recently proposed to perform simultaneously the two mentioned tasks. The new device, named Power Recovery System (PRS) has the simplicity of Banki turbines for free outflow, but can be installed in pipes with positive outflow pressure and has high hydraulic efficiency, almost always larger than 75%.

A first prototype of about 10kW has been designed, constructed and tested in the Hydraulic Lab of the Engineering Department of the University of Palermo. A second prototype of about 70 kW has been installed in the pumping station of “Fontes Episcopi” (Aragona (RA), Italy), which is run by the Sicilacqua S.p.a. water manager. In the paper the experimental results of the two turbines are compared with the numerical results obtained by a 2D and a 3D model. The efficiencies computed by the 3D model are lower than the efficiencies computed by the 2D, but provide an accurate prediction of the efficiencies measured in the lab, for different positions of the control flap which regulates the characteristic curve of the turbine.

A detailed analysis of the energy dissipation occurring inside the turbine case according to the 3D model is carried out. It is shown that, for given geometry of the impeller, it is possible to get an important increment of the hydraulic efficiency by simple changes of the inner geometry of the hosting case. These changes are aimed to limit the energy dissipation inside the diffusor linking the turbine case with the outlet pipe, as well as to obtain a direction of the relative velocities, inside the impeller, close to the ideal radial one.