Banki-Michell turbine PRS for energy recovery and water leakages reduction

Over the years, most water distribution networks have been designed and sized according to the criterion of minimum construction cost, assuming increases in water demand values that have not materialized. This assumption led to the use of larger diameters than necessary, i.e., to the over-sizing of networks, leading to increasingly high pressures and levels of water loss. Over-pressurization has led to rapid deterioration of the pipes and increased operating costs for treating, transporting and pumping unused volumes of water. In addition, the considerable volume of water lost had repercussions from an economic, social and environmental point of view.

Faced with this situation, it's clear that water distribution network management strategies, especially pressure control, are today a key and indispensable element in limiting the deterioration of pipes and the total volume of losses in these systems.

Among the many technical practices aimed at controlling pressures and reducing water losses is the installation of pressure control valves (PCVs), designed to maintain a certain target pressure immediately downstream or upstream of the pipe on which they are installed, in order to reduce its pressure. These devices enable real-time control both locally and remotely. In the first case, the set pressure value does not vary over time as a function of the water flow supplied, as the controlled node is not strategic for optimum pressure control in the network. In fact, in order to maintain the fixed pressure value, the electrical regulator must control the degree of opening of the control valve. In a second case, the device regulates pressure, increasing or reducing internal leakage so as to reduce or increase pressure at the critical node, in order to achieve the set pressure value. The disadvantage of using these devices lies in the excessive energy dissipation, without recovery, that occurs in the pressure reduction phase.

To remedy this problem, several studies in recent years have looked into the possibility of using energy recovery devices (pumps as turbines (PAT), microturbines, etc.) in water distribution networks. A new device, called the Power Recovery System (PRS), inspired by Banki-Michell turbines, has been proposed.

The PRS combines optimum performance in energy production and pressure regulation. It is particularly suitable for in-line installation in existing networks, as :

• the direction of the output flow lies in the plane of the rotating wheel, thus simplifying the return of the flow in the original direction of the pipe;

• it does not require the additional control systems typical of other similar devices;

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