Abstract
The potential energy of the water in Water Distribution Networks (WDNs) usually exceeds the amount needed for delivery and consumption and, at the present time, it is mainly dissipated through Pressure Reducing Valves (PRVs) or Open Water Tanks. The present study suggests the use of a new energy-producing device, a Cross-flow turbine with positive outlet pressure named PRS (Power Recovery System), which can provide the same service as PRVs and water tanks, with additional significant hydropower production. After a short presentation of the PRS, the management rules of the proposed device are laid out, according to two possible modes. In the ‘passive’ mode, the piezometric level downstream of the turbine is fixed at the sought after value, in the ‘active’ mode, the discharge is regulated according to the required value. The design criterion is then presented, based on a simple relationship linking dimensionless numbers. A PRS is finally designed for a typical water distribution network, serving the city of Palermo (Italy). The resulting cost-benefit analysis is compared with a similar one carried out in previous work for a regulation system based on the use of a Pump As Turbine (PAT). The comparison shows the improvement obtained by the use of the PRS, consisting of higher energy production, as well as lower construction and installation costs.
Highlights
The water loss per unit time in a Water Distribution Network (WDN) is strictly related to the pressure around the leaks [1,2]
Pressure Reducing Valves (PRVs) are used in transport conduits to dissipate the surplus energy head resulting from lower head losses in smoother new pipes during the earlier stage of their life cycle or from low discharge transportation and, in WDNs, to create different pressure zones inside the water networks
Recovery System (PRS), is proposed, which fits all the requirements needed to provide a strong benefit from the replacement of water tanks or PRVs
Summary
The water loss per unit time in a Water Distribution Network (WDN) is strictly related to the pressure around the leaks [1,2]. The only device largely used inside pipes, far from open water tanks and for relatively small discharge values, is the PAT, because traditional Cross-flow turbines have atmospheric pressure outflow [15,16,17,18]. Recovery System (PRS), is proposed, which fits all the requirements needed to provide a strong benefit from the replacement of water tanks or PRVs. The new device 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%. When the device is set in the ‘active’ mode this provides discharge regulation by fixing the outlet piezometric level corresponding to the required discharge in the accomplishment of function (1), replacing function (3) with pressure metering. The open water tanks set the piezometric level a few meters above the ground level and this is not always the best choice in water transport conduits and WDN design, according to the actual elevations occurring in downstream conduits
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