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

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

Hydraulic Design of a USBR Type II Stilling Basin

The present paper deals with a United States Bureau of Reclamation (USBR) Type II stilling basin, which is characterized by blocks at the end of the chute and a dentated sill at the end of the basin. For this basin, USBR only gives overall design criteria concerning basin length and block dimensions on the basis of the assumption that the hydraulic jump remains confined within the sill. No considerations are provided concerning possible different jump types, pressure regimes, and forces acting on the sill. To comply with such a lack, an experimental campaign was undertaken that focuses on the differences among hydraulic jump types that can occur in a USBR Type II stilling basin. Jump types can range between submerged and spray jump types; accordingly, dimensionless relations are provided to predict jump type and position for assigned boundary conditions, with particular concern about the submerged/nonsubmerged distinction. Considerations about the drag force and drag coefficients are provided, along with estimates of pressure extreme fluctuations. Finally, an evaluation of the dissipation efficiency is presented for both submerged and nonsubmerged jumps, enabling comparisons among different jump types and with classical hydraulic jump. - See more at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)IR.1943-4774.0001150#sthash.ajmk3TuB.dpu

Optimal pump scheduling for urban drainage under variable flow conditions

The paper is focused on the optimal scheduling of a drainage pumping station, complying with variations in the pump rotational speed and a recurrent pattern for the inflow discharge. The paper is structured in several consecutive steps. In the first step, the experimental set-up is described and results of calibration tests on different pumping machines are presented to obtain equations linking significant variables (discharge, head, power, efficiency). Then, those equations are utilized to build a mixed-integer optimization model able to find the scheduling solution that minimizes required pumping energy. The model is solved with respect to a case study referred to a urban drainage system in Naples (Italy) and optimization results are analysed to provide insights on the algorithm computational performance and on the influence of pumping machine characteristics on the overall efficiency savings. With reference to the simulated scenarios, an average value of 32% energy can be saved with an optimized control. Its actual value depends on the hydraulic characteristics of the system

A Comparison of Energy Recovery by PATs against Direct Variable Speed Pumping in Water Distribution Networks

Water systems are usually considered low efficiency systems, due to the large amount of energy that is lost by water leakage and dissipated by pressure reducing valves to control the leakage itself. In water distribution networks, water is often pumped from the source to an elevated tank or reservoir and then supplied to the users. A large energy recovery can be realized by the installation of energy production devices (EPDs) to exploit the excess of pressure that would be dissipated by regulation valves. The feasibility of such a sustainable strategy depends on the potential of energy savings and the amount of energy embedded in water streams, assessed by means of efficiency measures. Alternatively, energy savings can be pursued if the water is directly pumped to the network, bypassing the elevated reservoir. This study focuses on the comparison of two solutions to supply a real network, assessed as a case study. The first solution consists of water pumping to a reservoir, located upstream of the network; the excess of energy is saved by the employment of a pump as turbine (PAT). The second scenario is characterized by a smaller pressure head since a direct variable speed pumping is performed, bypassing the reservoir. The comparison has been carried out in terms of required energy, assessed by means of a new energy index and two literature efficiency indices. Furthermore, differing design conditions have been analyzed by varying the pumping head of both the scenarios, corresponding to different distances and elevation of the water source

Hydropower Potential inWater Distribution Networks: Pressure Control by PATs

Pressure control is one of the main techniques to control leakages in Water Distribution Networks (WDNs) and to prevent pipe damage, improving the delivery standards of a water supply systems. Pressure reducing stations (PRSs) equipped by either pressure reducing valves or motor driven regulating valves are commonly used to dissipate excess hydraulic head in WDNs. An integrated new technical solution with economic and system flexibility benefits is presented which replaces PRSs with pumps used as turbines (PATs). Optimal PAT performance is obtained by a Variable Operating Strategy (VOS), recently developed for the design of small hydropower plants on the basis of valve time operation, and net return determined by both energy production and savings through minimizing leakage. The literature values of both leakages costs and energy tariffs are used to develop a buisness plan model and evaluate the economic benefit of small hydropower plants equipped with PATs. The study shows that the hydropower installation produces interesting economic benefits, even in presence of small available power, that could encourage the leakage reduction even if water savings are not economically relevant, with consequent environmental benefits

Monitoring planning for urban drainage networks

Urban drainage network (UDN) monitoring is an important task whose planning can be related to various purposes, as for example contaminant detection and epidemiological studies. This paper proposes two different strategies for the identification of a monitoring system for UDNs. The optimal solution, in terms of location and number of sensors, is firstly addressed using a deterministic approach. A new mathematical model is developed and a global optimization solver is employed to perform the optimization procedure. Secondly, the position of devices is also investigated using a new strategy based on the complex network theory (CNT) tools. The comparison between the results achieved by both the strategies is finally presented with reference to a benchmark network

Experimental results on the physical model of an USBR type II stilling basin

The present paper describes the experimental campaign carried on the physical model of the spillway of Lower Diamphwe Dam (Malawi), which is provided with a USBR type II stilling basin. Stilling basins are used in order to reduce the excessive kinetic energy of flowing water downstream of spillways. Specifically, a USBR type II basin is provided with blocks at the end of the chute and with a confining dentated sill; these appurtenances allow to dissipate excess energy with high efficiency. The study focuses on the hydraulic behavior of the stilling basin; tests were carried on for different values of incoming discharge and downstream water depth. Results show the dissipation efficiency of the stilling basin in terms of pressure fluctuation and the variability of the jump type with the hydraulic characteristics of the incoming and the downstream flow depths

IMPIEGO DI POMPE COME TURBINE: calcolo fluidodinamico per l'analisi prestazionale e l'inserimento in rete

L’inserimento delle PAT nelle idrica con il duplice scopo di regolare il livello delle pressione e di riconvertire le dissipazioni funzionali in potenza elettrica può risultare molto vantaggioso, ma la scarsa conoscenza relativa al loro funzionamento in condizioni sia stazionarie che dinamiche ha fatto sorgere la necessità di uno studio più approfondito. Uno studio sulla numerosità della griglia fluidodinamica e sull’influenza dei rasamenti ha permesso di ridurre notevolmente i tempi e le risorse richiesti per i calcoli CFD, garantendo risultati affidabili in termini di prestazioni idrauliche della PAT in regime stazionario. Lo studio CFD del comportamento della PAT in condizioni transitorie ha mostrato che la risposta dinamica della turbomacchina non è trascurabile. Il nuovo modello proposto, che accoppia lo studio CFD della PAT con le equazioni delle linee caratteristiche, mostra come, in condizioni di colpo d’ariete, si generino sovrapressioni maggiori rispetto alla modellazione classica quasi steady. Di tali sovrapresssioni si deve necessariamente tener conto in fase di progettazione, onde evitare disservizi e malfunzionamenti della rete idrica. La forte variabilità delle condizioni idrauliche all’interno di una rete idrica esclude la possibilità di poter progettare un impianto di riconversione energetica sulla base di un unico punto di funzionamento. Un semplice schema idraulico permette di inserire la PAT nella rete senza alterarne le condizioni di funzionamento. Inoltre è stato elaborato un criterio di progettazione che permette la scelta ottimale della macchina in assenza di un unico rated point