Energy Transfer from the Freshwater to the Wastewater Network Using a PAT-Equipped Turbopump

Abstract

A new strategy to increase the energy efficiency in a water network exists using turbo pumps, which are systems consisting of a pump and a turbine directly coupled on a same shaft. In a turbo pump, the pump is fed by a turbine that exploits a surplus head in a freshwater network in order to produce energy for one system (wastewater) and reduce the excess pressure in another (drinking water). A pump as turbine (PAT) may be preferred over a classic turbine here due to its lower cost. The result of such a coupling is a PAT–pump turbocharger (P&P). In this research, the theoretical performance of a P&P plant is employed using data from a real water distribution network to exploit the excess pressure of a freshwater stream and to feed a pump conveying wastewater toward a treatment plant. Therefore, the P&P plant is a mixed PAT–pump turbocharger, operating with both fresh and wastewater. A new method to perform a preliminary geometric selection of the machines constituting the P&P plant has been developed. Furthermore, the plant operation has been described by means of a new mathematical model under different boundary conditions. Moreover, the economic viability of the plant has been assessed by comparison with a conventional wastewater pumping system working in ON/OFF mode. Therefore, the net present value (NPV) of the investment has been evaluated in both situations for different time periods. According to the economical comparison, the PAT–pump turbocharger represents the most economically advantageous configuration, at least until the useful life of the plant. Such convenience amounts to 175% up to a time period equal to 20 years.

Application of Innovative Technologies for Active Control and Energy Efficiency in Water Supply Systems

“…One of the main limitations in the exploitation of PAT technology is the necessity of a local use of the recovered energy. A possibility is represented by the use of turbo-pumps, with a direct coupling of a PAT and a pump [22]. The theory was already discussed for freshwater application but has been extended to the energy transfer from the freshwater to the wastewater network (Figure 14).…”

“…Figure 14. Hydraulic scheme of a freshwater turbine-wastewater pump system [22]. According to the basics of the eco-design, a pumping group, made by a pump, motor, speed driver, and regulation devices, working with variable speed is considered the best opportunity for the reduction of energy use in water systems.…”

A Performance Prediction Model for Pumps as Turbines (PATs)

“…For these reasons, the use of reverse pumps that work as turbines (PATs) is becoming a good alternative to PRVs, which dissipate flow head without converting it into electric energy [10][11][12][13]. A distinct advantage of PATs is their operating flexibility, because the PAT operating point can be modulated in many ways [14][15][16], bypassing part of the flow and activating a PRV in parallel with the PAT to dissipate the excess of head drop, or variating the PAT's rotation speed by means of an inverter drive [17][18][19].…”

Hydropower Generation Through Pump as Turbine: Experimental Study and Potential Application to Small-Scale WDN

“…Nowadays, the need to produce energy in a sustainable way is an important issue to tackle to both improve environment quality and human life. To this effort, new energy systems, exploiting different available natural sources such as water, have been developed over time to reduce carbon emissions and produce energy in a renewable way (e.g., [1][2][3][4][5][6][7]). One of the main and first sources used to obtain clean energy is water, since the huge availability of hydraulic resources, which can be exploited in several ways through use of turbines, spanning from large facilities (order of hundreds of MW or GW) to pico-hydro stations (order of kW or less).…”