Micro-hydro potential of the supply networks in the Territorial Area of Murcia. A. Cortés Marco(1)(2), J. Pérez-García(1), S. Nevado Santos(2), J.A. Imbernón Manresa(3) (1) Universidad Politécnica de Cartagena, ETSII Campus Muralla del Mar, C/Dr. Fleming s/n 30202 Cartagena (España) Tlf: +34 968325986
[email protected] (2) Empresa Municipal de Aguas y Saneamiento de Murcia, S.A. (3) Aqualogy Aqua Ambiente Servicios Integrales, S.A. 1. Introduction – Hydropower represents about 16.2% of global electricity supply, covering most of the production of clean energy which is about 19.5% of the total energy production (Figure 1). Although in recent years, electricity generation from renewable energy sources has grown significantly, also the CO2 emissions derived from the energy generated with fossil fuels it has been increased until a total of 28.999x106 CO2 Ton/year [1].
Figure 1. Global energy production.
Currently, the concept of hydraulic exploitation is far from conventional large hydroelectric plants configuration, with their important associated environmental impact. These are now usually mini-hydro facilities (power below 10 MW) and micro-hydro (up to 1 MW) [2], with a featured positive environmental impact of energy production by 100% clean and renewable. Due to the technological evolution of turbo machinery, as well as, to the new fields of application of these equipments, exploitations in the range of 10 ≤ N ≤ 100 (kW) are becoming special interest. In Spain the group of companies AGBAR (Aguas de Barcelona), in which are embedded a large number of private or mixed capital companies that manage a large number of water supply and sewerage networks, is strongly committed to exploit these micro-hydro systems. In this work, we present a summary of the study about the micro-hydro potential in the supply networks of the territorial area of Murcia, managed by the companies of the AGBAR Group. The objective is to determine the technical and economic feasibility of different technologies in solutions that are currently commercially available. 2. Methodology – The methodology consists in studying the information about operating pressures and available flow rates, and identify static pressure regulation elements and intermediate tanks in the network, in which an energy dissipation take place. These elements may be replaced by hydropower systems that allow us to recovery energy. 2.1 Identification of suitable sites for energy recovery. We performed a detailed study of several supply networks in the territorial area of Murcia managed by AGBAR group to identify sites where the excess of static pressure must be dissipate to adjust the pressure level to the demand pattern curve system (Figure 2). Figure 2. Micro-hydro potential in the territorial area of Murcia (Spain).
Two types of sites, based on their hydraulic conditions, downstream from the point of regulation, can be distinguished. In each case, the strategy followed to energy production will be different: a)
Discharge to atmospheric pressure (intermediate deposit breaking charge or distribution chest). These sites are especially suited to use turbo machinery operating at constant ambient pressure. b) Discharge backpressure (pressure control valves). In this type of sites, we can use conventional reaction turbines or pumps operating as turbines (PaTs). 2.2 Study of the technological solutions commercially available. The available commercial technologies suitables in our case are summarized in the following scheme (Figure 3).
Hydraulic turbomachinery
Conventional turbines
Constant ambient pressure turbines (Banki-Mitchel, Pelton)
Francis Turbine type PaTs
Centrifugal pumps operating as turbines Axial or mixed pumps Volumetric pumps
Figure 3. Available commercial technologies.
a) Constant ambient pressure cross-flow turbine (Banki-Michell). Banki-Michell turbines are radial, partial admission turbo machines with horizontal axis and low specific speed. This type of turbo machinery is suitable for high head and variable flow rate. The impeller can be fed at three operation stages allowing a more effective exploitation when fluctuating flow rates are available, such as case of supply networks. Cross-flow turbines provide constant high efficiency, above 85%, for a wide range of flow rates. However, its use is limited to locations where discharge is at atmospheric pressure. b) Pumps operating as Turbines, PaTs (centrifugal, mixed or axial pumps running in reverse mode). The use of PaTs constitutes a technical and economically viable solution for micro-hydro power [3]. The flow through a PaT occurs in reverse, ie in the opposite direction to that of conventional pump operation. The head and flow rate must be sufficient to overcome the initial torque of the turbine-generator group, although conventional asynchronous electric motor can be used as generator. PaTs can operate with backpressure discharge or discharging to the ambient pressure, so this solution it is well positioned as generalized solution for all of the sites with hydraulic potential. The main advantage of this solution lies in its reduced investment costs and low maintenance. 2.3 Two cases in study In this section, two cases of application, representative of both types of sites in water distribution networks according to their hydraulic properties, are described. Both energy recovery plants are currently being implemented in the city of Murcia. The operation of both facilities will be coordinated with the aim to optimize the existing supply network system. 2.3.1 Micro-hydro recovery plant "El Quiebre" "El Quiebre" is an intermediate tank located in one of the main pipelines of water distribution in the city
of Murcia. Is fed from the main reserve tanks through a pipe of 900 mm of diameter and 650 m of length. The available head and flow rate are summarized in Table 1. Flow rate 277.8 l/s
Production interval 18 h/day 76%
56 kW
3
1000 m /h Head 27 m
Power averaged 1,007 kWh/day
Table 1. Available head and flow rate in “El Quiebre” energy recovery plant
This micro-hydropower plant is based on the use of a cross-flow Banki-Mitchell conventional turbine coupled to an electric generator. The turbo machinery proposal allows us to profit variable flow rate due to fluctuations in the supply network associated with the demand pattern. A schematic layout is shown in Figure 4.
Flow rate ratio 100% 90% 60% 30% 17% 12% Power output (kW) 59 54 36 18 10 6.5 Flow rate (l/s) 278 250 167 83 47 34 Efficiency (%) 83 83 83 82 80 75
Figure 4. Schematic layout of “El Quiebre” energy recovery plant.
2.3.2 Micro-hydro recovery plant "C2BIS" The regulation chest “C2Bis", also located in another one of the main pipelines of water distribution in the city of Murcia, receives flow rates of other main reserve tank through a pipe of 800 mm of diameter and 9,250 m of length, and feeds directly the urban network. The available head and flow rate are summarized in Table 2. Flow rate configuration Flow rate (m3/h) Head (m) Interval (h/day) Power output (kW) Minimum PaT1 400 40 8 32.09 Medium PaT2 800 35 8 56.16 Maximum PaT1+PaT2 1200 30 8 72.2 Efficiency 73% Power averaged 1,283.58 kWh/day Table 2. Available head and flow rate in “C2BIS” energy recovery plant
This micro-hydropower plant is based on the use of a system composed of two pumps operating as turbines (PaTs) coupled in parallel. Energy recovery is carried out from the replacement of pressure reducing valves by PaTs. The system allows us to adapt the configuration of single PaT, or coupled according to the consumption of supply network. A schematic layout is shown in Figure 5.
Figure 5. Schematic layout of “C2BIS” energy recovery plant.
3. Results and discussion – Sites with great micro-hydro potential it has been identified. In those sites where a backpressure discharge exists, the most suitable pump operating as turbine will be selected and their turbine characteristics will be predicted using the proper prediction model [4][5][6]. According to these prediction models, the available power output will be obtained and the commercial pump and control equipment will be implemented. On the other hand, in those sites in which the discharge is at atmospheric pressure, conventional cross-flow Banki-Mitchel turbine will be installed. With this program the company will acquire an important know-how to expand this type of energy recovery plant to the rest of the supply networks under their control in other zones in Spain or in Europe. 4. Conclusions – The exploitation of sites with micro-hydro potential in water supply networks is technical and economically feasible, but is necessary to define a global strategy management system that takes into account the entire supply network coordinating the operation of different micro-hydro facilities while the reliability and efficiency of the system is maintained. Early estimations in terms of potential hydro-power, economic and environmental profits of the territorial area of Murcia are summarized in Table 3.
Production potential Economic benefits Environmental benefits
2,875 248,745 776 Ton
MWh/year €/year CO2/year
Table 3. Potential hydro-power production and economic and environmental benefits.
5. Referencias bibliográficas [1] IEA International Energy Agency (Key World Energy Statistics 2011) [2] B.O.E. Real Decreto 661/2007. Actividad de producción de energía eléctrica en régimen especial. [3] J. Pérez-García, A. Cortés Marco, S. Nevado Santos, Use of centrifugal pumps operating as turbines for energy recovery in water distribution networks. Two case study. 3rd Int. Congress of Energy and Environment Eng. and Management, Portalegre (Portugal) 2009 [4] P. Singh, F. Nestmann, A Consolidated Model for the Turbine Operation of Centrifugal Pumps, Journal of Engineering for Gas Turbines and Power, Vol 133 063002 pp: 1-9 (2011) [5] A. Cortés Marco, J. Pérez-García, S. Nevado Santos, Optimization of the micro-hydro energy recovery plant “La Contraparada” using Pumps as Turbines (PATs). 4th Int. Congress of Energy and Environment Eng. and Management, Mérida (Spain) 2011 [6] S. Derakhsham, A. Nourbakhsh, Experimental study of characteristic curves of centrifugal pumps working as turbines in different specific speeds, Exp.Thermal and Fluid Science 32 (2008) 800-807
