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Technical University of Civil engineering Bucharest, Blvd. Lacul Tei, 124, sect .... SRp Petricani: Qmax =560 mc/h and overflow discharge pressure pref = 4,9 bar.
Operation optimization of several pumping stations interconnected to a complex water distribution network - case study Sorin Perju*, Andrei Georgescu**, Anton Anton***, Lucian Sandu**** * Technical University of Civil engineering Bucharest, Blvd. Lacul Tei, 124, sect. 2, 020396 Bucharest Romania, E-Mail: [email protected]; ** Technical University of Civil engineering Bucharest, Blvd. Lacul Tei, 124, sect. 2, 020396 Bucharest Romania, E-Mail: [email protected]; *** Technical University of Civil engineering Bucharest, Blvd. Lacul Tei, 124, sect. 2, 020396 Bucharest Romania, E-Mail: [email protected]; **** Technical University of Civil engineering Bucharest, Blvd. Lacul Tei, 124, sect. 2, 020396 Bucharest Romania, E-Mail: [email protected]; Abstract The following study presents the complex water distribution network numerical model of the high-pressure zone of “Lacul Tei” and “Colentina” quarters. We aimed at the impact it has, by functioning connected / interconnected with respect to the exploitation optimization of drinkable water distribution networks. The present study refers to the assurance of the highpressure supply and distribution network quality services delivered to the consumers (water demands, minimum necessary pressure and the maximum pressures in order to avoid network failure) and also to the optimization of the exploitation expense. Keywords pumping stations, booster stations, water distribution network.

INTRODUCTION Within the water supply systems for populated centers or industries, the water distribution network occupies a very important place from the operational point of view and has an important weight, both regarding the length of conduit routes and the value of the necessary investment for its execution. Worldwide as well as in our country, the technology for the development of water supply has imposed the reconsideration of water catchment methods, treatment threads, transport and storage capabilities, operation of pumping installations, as well as tracking along time the behaviour of the entire hydraulic system for the distribution of potable water. An essential role within the complex water supply systems is played by the distribution networks and the appropriate pumping stations that have the role of achieving the desired parameters for the consumers, under complete safety conditions. Under these conditions, the rehabilitation of the water distribution networks and the modernisation of the pumping stations, is the fundamental preoccupation of water producers and distributors, as the social and environmental impact depends on the operational, energetic, and economic performances of the operational hydraulic complexes, i.e. distribution networkspumping stations. With respect to the technical aspects, the optimization of the distribution networks and of the pumping stations is conditioned by several factors such as:  the quality of the technical solutions adopted.  the quality of the materials and equipments used.  the quality of the work execution.  the logistic of exploitation and maintenance. The operation optimization of water distribution networks and of the appropriate pumping stations, is done by employing a modern and well suited mathematical instrument (calculation

software), with which numerical calculation models may be created that will form the basis for the analysis of operation scenarios in various operational configurations. The results of the analysis and the reports will constitute a foundation for the final decision taking required for the rehabilitation and modernisation of distribution networks and pumping stations. In this context, the paper presents the complex model of the water distribution networks in the high pressure area from the Colentina district, and in general, the impact of the interconnected/independent operation of several drinking water distribution networks on the optimization of the operation. It refers to both the insurance of the consumer service parameters (consumption discharge, minimal necessary pressure, maximum pressure to the limit of avoiding damage to the network and the reduction of water loss) and to the optimization of the operation costs. DESCRIPTION OF WATER SUPPLY SYSTEM The analysed network consists of four high pressure sub-networks that ensure the drinking water supply for buildings with a P+8 ... P +10 height regime. The delimitation of the four areas has been imposed by the urban development stages of the neighbourhood from the 1960 – 1990 period. Corresponding to these stages, in each of the four zones, residential blocks were built that were serviced by independent water distribution networks supplied by re-pumping stations, for three of these areas, and by three booster stations for the fourth area. In time, interconnections were made among several of these distribution networks. The main water supply system of Bucharest is presented in figure1, where we emphasized the studied area in a magenta circle.

Figure 1. Location of the studied area within the main water supply system of Bucharest

Estimated initially to work as a classical pumping installation for which the aspiration of the pumps is done from tanks with constant levels and discharge is done into its own distribution network, in time, due to the rise in the arterial network pressure, the respective stations are now operating as interconnected with the role to ensure the service pressure necessary for drinking water supply of the consumers connected to these networks. The modifications made to the aspiration of the pumps, through the elimination of the tanks and the introduction of aspiration directly from the low pressure artery network, as well as the interconnection of the high pressure networks, have forced the pumping equipments to act inadequately with respect to the requirements of the distribution networks they serve. For the rehabilitation choice of the distribution system exploitation, a hydraulic analysis has been considered necessary, regarding the operation of the distribution networks serviced by the three repumping stations and the three booster stations. As a result, it was necessary to model the entire water distribution system, so that based upon several operation scenarios, a final solution could be adopted, with the aim of diminishing the energy consumption at the pumping stations. NUMERICAL MODELING OF WATER DISTRIBUTION NETWORKS For the creation of the distribution network model and the analysis of its operation, based on the hypothesis of various operation scenarios, the RET&LOB&DES programme package has been used. It was developed within the Department for Hydraulics and Environmental Protection which is part of TUCB. The package has a classical structure: pre-processing (the DAT module), calculation (RET modules for permanent movement and LOB for non-permanent movement), and graphical post-processing (DES module). By employing the RET module for permanent movement within the conduit networks the following calculations can be performed: classical flow and pressure calculations for a given network; distribution optimization of the pumping capacity for the pumping station within the same network, optimization of the driving rotation of the pumps, optimization of the diameters of the pipes within the network, and the calculation of the safety indicators of the network. The stages of the model creation were:  The proper definition of the configurations of the networks corresponding to the six areas, regarding the physical elements (nodes, arteries, diameters, geodesic elevations, links, etc.).  Determination of the real consumptions.  Creation of the calculation model for each of the four distribution networks  The creation of the distribution network model for the entire studied area by identifying the links between sub-networks and coupling them according to the existent situation.  The calibration of the resulted network based on the measured values for flow and pressures within the network.  The hydraulic calculations for the optimization of the water supply system for the hypothesis of shutting down one SRP and the SH-s. For the hydraulic calculations, the consumption values in the nodes were allocated while considering statistical data for 2003. The data file also contains the coordinates of the nodes so that the graphical representation of the network, with the visualization of the areas in which the service pressures are achieved or not, is possible while employing a color code.

For the hydraulic calculations regarding the optimization of the water distribution networks, three initial numerical calculation models have been made, each one corresponding to each re-pumping station and a numerical calculation model for the house water supply plants. Furthermore, because the networks proper to the three pumping stations were operating as interconnected, we simulated this operation mode by employing the network coupling module within the calculation programme, thus resulting only two numerical calculation models, as follows:  a numerical model composed of 335 arteries and 286 nodes served by the re-pumping stations  a numerical model composed of 121 arteries and 104 nodes served by the house water supply plants

Figure 2. Numerical calculation models, with the configurations of the high pressure networks and the influence area of each station

The numerical calculation models, in which the configurations of the high pressure networks and the influence area of each station are shown, is presented in figure 2. The calibration of the numerical calculation models has been done while relying on discharge and pressure measurements done in the re-pumping plants. Thus for the numeric model of the distribution networks serviced by the re-pumping stations the calibration parameters of the model have been:  SRp Colentina: Qmax =400 mc/h and overflow discharge pressure pref = 4,6 bar.  SRp Petricani: Qmax =560 mc/h and overflow discharge pressure pref = 4,9 bar.  SRp Teiul Doamnei:Qmax=1650 mc/h and overflow discharge pressure pref=5,5 bar.

RESULTS OF HYDRAULIC CALCULATIONS FOR NETWORK OPERATION OPTIMIZATION The first stage in performing the hydraulic calculations has been the determination of the pressures in the nodes of the distribution network, considering, as an operation sequence, the parameters measured at the re-pumping stations and certain maximum flows measured as well as the pressures recorded at the pumping stations exit. The results of the calculations for this variant have shown that the values for pressures in the nodes of the network are between 42,6 mCA and 55 mCA, values that are sufficient for providing the water supply service for the consumers.

Figure 3 The results obtained from the first operation sequence simulation

After that, while examining the plan arrangement of the three re-pumping stations, we have analyzed the possibility of shutting down SRp Petricani. Thus, from the initial model we eliminated the tank that was simulating the operation of this station. The hydraulic calculations have been done for optimizing the diameters of the pipes, while simulating the operation of the network as being supplied from the two re-pumping stations at the maximum discharge rate Q=2610 mc/h, and the pressure on the overflow discharge conduit pref= 50 mCA. The results obtained from this simulation of an operation sequence have shown that in order to achieve the service pressures, the pipe segments, emphasized in the network graph shown in figure 3, must be modified, and the operation parameters for the two pumping stations must be:  SRp Colentina: Q = 934 mc/h and pref = 50 mCA.



SRp Teiul Doamnei:

Q = 1676 mc/h and pref = 50 mCA.

The next sequence of operation for the networks in the optimization process has been finding a solution for shutting down the three booster stations that had very high energy consumption.

Figure 4. The results obtained from the second operation sequence simulation

In this context, a new connection pipeline has been dimensioned, between the network serviced by the Colentina pumping station and the networks serviced by the three house water supply plants. The pipeline has a diameter of Dn 300 mm, and was added to the numerical model. The new resulting numerical model has 460 nodes, 392 arteries, and two tanks that model the two repumping stations left for the simulation. With this final numerical model the hydraulic optimization calculations have been performed simulating the two operation sequences depending on the values of pressure at the overflow discharges of the stations. The results of the hydraulic calculations for the two variants analyzed are summarized in table no. 1, and the diameters of the pipes that must be modified are emphasized with red in figure 4. Table no.1. Results of the hydraulic calculations

Case A B

SRP Colentina Teiul Doamnei Colentina Teiul Doamnei

Qmax [mc/h] 1274 1685 1108 1850

Pref [bar] 5,5 5,0

Minimum gap PN-HS [mCA] -0,26 in node 173 -0,80 in node 173

CONCLUSIONS The analyses of the optimization for the distribution networks within the Colentina neighbourhood, has been done exclusively for the high pressure networks, and we have started from the hypotheses of the reduction in electrical energy consumption recorded at the re-pumping and booster stations, while also improving the hydraulic operation of the re-pumping stations – distribution network system. The analyses have been done with the purpose of creating a technical basis for the rehabilitation and modernization solution that is best suited economically. The realization of the proposed solutions, for the equipment of the two re-pumping stations and the modifications done within the networks by introducing the connecting pipe Dn 300 mm and rehabilitating several pipe sectors by increasing the diameters, has led to certain economic advantages. The reduction in the electrical energy consumption is up to one third from the one recorded through maintaining the three re-pumping stations and the three booster stations. The values are shown in table no. 2 and figure 5. Table 2. Energy consumption reduction

Year 2003 388 020 kWh 1 497 621 kWh 463 208 kWh 445 630 kWh 2 794 479 kWh

SRp Colentina SRp Teiul Doamnei SRp Petricani Booster Stations Total

Year 2004 324 602 kWh 1 272 706 kWh 435 877 kWh 294 670 kWh 2 327 855 kWh

Energy consumption [kWh] 3000000

2500000

2000000

1500000

1000000

500000

0 2003

2004

2005

Figure 5 Energy consumption reduction after the refurbishment

Year 2005 309 627 kWh 521 019 kWh 830 646 kWh

References Cioc D., Anton A., Reţele hidraulice: calcul, optimizare, siguranţă, 2001, Editura Orizonturi Universitare, Timişoara. Iamandi C., Petrescu V., Damian R., Sandu L., Anton A., Degeratu M., Hidraulica Instalaţiilor - Elemente de calcul şi aplicaţii, 1985, Bucureşti, Editura Tehnică. Anton A., Perju., S. Grecu M., Metodologia reabilitării unei staţii de pompare. Aspecte hidraulice şi alegerea agregatelor de pompare, Conferinţa “Sisteme hidraulice sub presiune”, 1999, Bucureşti. Anton A., Perju S., Functional analysis of a booster station for rehabilitation, Conferinţa “Case Studies in Hidraulic Systems-CSHS ’03”, 2003, Belgrad. Anton A., Perju S., şi colab., Măsurători parametrii hidroenergetici şi analize de reţea la 24 staţii de repompare. Studiu hidraulic, 2003, Bucureşti. Mănescu A., Sandu M., Ianculescu O., Alimentări cu apă, 1994, Editura Didactică şi Pedagogică, Bucureşti.