Available energy assessment in water supply systems

Transcription

1 Avalable energy assessment n water supply systems Helena Ramos, Dída Covas 2, Luz Araujo 3, Mara Mello 4 Professor, Cvl Eng. Dept., Insttuto Superor Técnco, Av. Rovsco Pas, 49- Lsbon, Portugal (Tel: , Fax: , e-mal: hr@cvl.st.utl.pt ) 2 Assstant Professor, Cvl Eng.Dept., Insttuto Superor Técnco, Av. Rovsco Pas, 49- Lsbon, Portugal (Tel: , Fax: , e-mal: dda@cvl.st.utl.pt ) 3 PhD student, Cvl Eng. Dept., Insttuto Superor Técnco, Av. Rovsco Pas, 49- Lsbon, Portugal (Tel, Fax: , e-mal: araujols@cvl.st.utl.pt ) 4 Manager of Hdropower Company, Lsboa, m.mello@hdropower.pt Abstract Wthn European Unon prortes, the problematc of avalable water sources have pad attenton through the development of an ntegrated polcy to reduce and control pressures and consequently leakage. In drnkng ppe systems Pressure Reducng Valves () are used as dsspatve devces for pressure control through a localzed pressure drop. The use of mcroturbnes or pumps operatng as turbnes (PT) seem to be an alternatve and sustanable soluton to ether control the pressure as well to produce energy. Ths type of soluton generally well accepted wthn renewable energy sources can be adopted as a mtgaton method to control the systems loss, n partcular the excess avalable energy whch would be dsspated and the rupture occurrence. The exstence of hgh topographc gradents are favorable to adopt these solutons, avodng the use of hgh pressure ppe classes wth the consequent mnmzaton of costs and the beneft assocated to energy yeldng, whch although depends on the daly consumptons s always a guaranteed energy. Expermental research s carred out n the Hydraulc Lab of the Department of Cvl Engneerng at IST, to analyze the hydraulc system response under steady and transent state condtons, as well as the development of comparatve analyss between real and PT. The problematc of waste avalable energy must pad attenton through the mplementaton of contnuous montorng systems, n partcular n drnkng and rrgaton systems. Furthermore, an ntegrated polcy of water and energy systems management must be developed by usng optmzaton analyses, as well as to encourage water companes to mplement t. Keywords: drnkng systems, pressure reducng valves, pressure control, energy producton, pump as turbne.

2 . INTRODUCTION The use of pressure reducng valves n water dstrbuton systems s to unform and control the pressure by separatng water ppe systems n dstrct meter areas (DMA) dentfed by pressure classes accordngly to the topographc development of the zone where the system s mplanted. Generally speakng, each DMA s suppled for a guaranteed pressure range or by nterconnected reservors or even by usng pressure reducng valves n each actve DMA entrance. Snce water supply and dstrbuton systems have serous problems of leakage, the pressure control s fundamental for an optmsed and sustanable system management. The use of renewable energy sources wthn drnkng system seem to be a valuable alternatve soluton to proft excess avalable energy nstead of the use of dsspatve devces. Ths s a clean project of energy producton wthout sgnfcant envronmental mpacts, wth a guaranteed dscharge, whch can be used n multpurpose systems, wthout constrants for consumers, or other water uses. 2. BRIEF BACKGROUND REVIEW The use of pressure reducng valves () am at lmtng the downstream pressure by regulaton of valve openng whch nduces a local head loss n the hydraulc grade lne. There are several types of (Fgure ), n partcular wth sprng, pston and daphragm control (COVAS and RAMOS, 99). The man operatng prncple of a conssts n actng the lock devce whenever the downstream pressure s too hgh, n order to ncrease the local head loss reducng the downstream pressure tll the requred value (.e. LR- load reference of each pressure reducng valve); or on the contrary, the downstream pressure decreases above the load reference value, the valve opens dmnshng the local head loss, ncreasng the downstream pressure to the requred value. Hence t can be dstngushed three types of operaton: () the valve provokes a local head loss to reduce the downstream pressure ths s the actve state of the valve (Fgure 2 ); () when the upstream pressure s lower than the load reference value, then the valve opens completely mantanng at upstream and downstream the same pressure ths s the passve state of the valve (Fgure 2 ); () If the downstream pressure s hgher than the upstream pressure the valve closes totally operatng as a check valve avodng the flow nverson ths s the passve state of the closed valve. Ths type of valves can operate for dfferent pressure ranges by electrcal or mechancal control n order to obtan a better effcent system management and a hgher hydraulc performance. Bascally, regardng the load, there are the followng actve operaton status (Fgure 3): () wth constant load the valve reduces and stablses the downstream pressure, mantanng the pressure constant and equal to the load reference value for each (HLR-) for any upstream pressure and flow n the system Fgure 3-(); () wth constant head loss the valve reduces the downstream pressure by a constant local head loss ndependent of the upstream pressure so the downstream pressure vares wth the upstream pressure - Fgure 3-(); () wth constant load but varable n tme s analogous to a wth constant load however the pressure s mantaned constant n pre-defned ntervals varyng along the tme Fgure 3-(), beng the more common stuaton the use of only two tme ranges of pressures one for daly and other for nghtly perod; (v) wth constant load ftted to the demand the valve reduces the downstream pressure as a functon of dscharge or pressure n crtcal sectons of the network Fgure 3-(v). 2

3 3. MODELLING AND ENERGY RECOVER The proft of excess avalable energy n water supply systems, namely water drnkng and rrgaton systems can be a valorous alternatve for energy producton wthn the renewable energy sources, wth low cost, clean energy source and wth no sgnfcant envronmental mpacts (RAMOS e BORGA, 2a, 2b; VALADAS, 2; VALADAS e RAMOS, 23). For ths propose can be used small or mcro-turbnes or even pumps as turbnes (PT) whenever the power or dscharge are reduced that would be economcally not vable to nstall turbnes. Whenever the ppe system presents excess avalable hydraulc energy n some ppe sectons, specal favourable condtons are created to nstall turbo-machnes for energy recover, whch would be dsspated by pressure reducng valves n order to control the maxmum admssble servce pressure and avod eventual leakage or rupture occurrence. In drnkng or rrgaton system, the pressure vares along the day and along the ppe profle. The hydraulc grade lne prncple assocated to the effect of a turbne operaton s qute smlar to a, snce the net head proft by a turbne allows also the downstream pressure control. Accordng wth some researchers (JOWITT e XU (99); REIS et al. (997); KALANITHY e LUMBERT (99); TUCCIARELLI et al. (999); REIS e CHAUDHRY (999); ULANICKA et al. (2); ARAUJO et al. (a, b, 23); RAMOS et al. (24)) the best soluton for pressure control corresponds the use of head losses devces, namely pressure reducng valves or other hydraulcally equvalent equpment. Fgure 4-b and c show the effect of pressure reducng valves (.e. one and fve, respectvely) for pressure control proposes when compared wth the system wthout any control system (Fgure 4-a). The smulaton of these systems s developed for a perod of 24-hour, wth ntervals of hour. The objectve conssts to mnmse the pressure, but to not let t be lower than Pmn value predefned, n any node of the system. The hydraulc smulator needs, for each tme nterval, to know the values of varables n the modellng process, namely values of roughness n each branch ppe and head loss coeffcents for each valve. A Genetc Algorthm (GA) s used to generate these values and runs the optmsaton process as a whole. The hydraulc smulaton of the system s developed by usng routnes based on EPANET 2,. The choce of ths tool s due to be a wdely tested robust model and, wth a large communty of users n all the world (e.g., MARTÍNEZ et al. (999), HERNÁNDEZ et al. (999); SAKARYA & MAYS, (2); PRESCOTT & ULANICKI, (2); ARAUJO et al. (, a,b). Darwnan theory of the natural selecton and the paradgm of the survval of the most apt had nspred the development of these relatvely recent computatonal technques, as artfcal ntellgence and the evaluatve computaton. Among these technques, the developed by Holland (975) s dstngushed and s the well known technque of Genetc Algorthms. Ths technque s robust and effcent n rregular, multdmensonal and complex spaces of search and, accordng to GOLDEBERG (99, 994), t does not requre dervatves, operates n a populaton of ponts, works on representatve form of parameters (normally bnary representaton), uses non-determnstc rules or, probablstc, and, for each element of a populaton, t requres nformaton only on the value of an apttude-functon. These technques have been commonly used, wth suffcent success, n several felds of scences, nclusvely n the resoluton of optmsaton problems of water dstrbuton systems. The mathematcal formulaton, for ths component of the optmzaton, s based on the followng apttude-functon to mnmse the pressure and the number of to be consdered: 3

4 2 2 ( Pcal, t P ), mn T N T Optmze f ( p, nv ) t = = nv t nv t + nv t () t = = P mn wth T the total number of ntervals to smulate (normally equal to 24 ntervals of hour); N the total number of nodes; P cal,,t the pressure calculated n the node for the hour t; Pmn the mnmum pressure, pre-establshed by the user, for any node of the network and n vt the number of valves calculated for nstant t (.e., number of ppes wth roughness greater than the orgnal roughness.e., small Hazen-Wllams coeffcents) beng, therefore, a condtonng of the formulated problem, n order to have lesser possble number of ppes wth Hazen-Wllams coeffcents below to the real ones (.e., mnor number of possble locatons for the valves). The program generates results that can be used by EPANET program n order to proptate to each user the possblty to defne where and how many valves wll be used to model the network for pressure optmsaton (Fgure 5). These type of analyse are used for extended perod for a statonary flow regme (.e. an assocaton of dfferent steady state regmes for each tme nterval) and the real behavour of and PT under transent condtons requre a specfc analyss based on expermental research (RAMOS et al., 24). Fgure 5 shows two dfferent stuatons: () on the left-top pressure values along a day by the nfluence of a to fx the downstream pressure (upper curve node 2) and the pressure varaton at the more dstant ppe secton (down curve node ); () on the rght-top a pump operatng as a turbne wth small downstream pressure varaton (depends on pump characterstc curves) (at nodes 2 and ). The system typology wth pressure and dscharge dstrbuton for an nstant of a day and the characterstc curve of the selected pump operatng as a turbne (at the bottom-rght). Fgure 6 shows an equvalent effect between and PT for all nodes of the system and along the tme. Mnmum pressure values obtaned n dfferent nodes are lmted by regulaton or through the characterstc curves of the turbo machne adequately selected. 4. EXPERIMENTAL RESEARCH The expermental research s developed n the Hydraulc Lab of the Department of Cvl Engneerng, at Insttuto Superor Técnco (RAMOS et al., 24) and t s composed by a ppelne, connected at upstream to an ar vessel, wth a volume of. m3, and at downstream to an open flow reservor wth a wer whch dscharges the flow to a constant water level reservor. The ppe materal s HDPE of pressure level PN, wth a length of 2 m, wth a dameter of.43 m, thckness of.35 m, wth a roughness of.5 m and a wave speed of 2 m/s. In the mddle length of the ppe s ntally nstalled a to analyse the operatng condtons for steady state and unsteady state condtons and afterwards ths valve was replaced by a pump operatng as a turbne PT to allow comparsons of the system responses. In ths type of analyss are consdered dfferent flow condtons, namely flow energy at the ar vessel (upstream) and flow dscharge. Whenever a valve, a turbne or a pump as a turbne s nstalled n a transmsson ppe lne the hydraulc grade lne can present dfferent confguratons, dependng on the flow condtons and the head loss values whch s a characterstc of each devce (Fgure 7). In partcular n the draft tube of a turbne (or a PT) due to the runner rotaton, the pressure can drop tll the vaporsaton pressure, nducng vortex formaton. In these cases the downstream pressures at the valve (p d-valve ) are lower than the downstream pressure at the end of the system (pd-end) where s also located the dscharge control valve at downstream secton. 4

5 Dfferent values of dscharge and upstream load at the ar vessel are consdered and a smlar system response s obtaned for both and PT (Fgure ). New tests are runnng wth other type of wth a more sophstcated pressure control and regulaton. However, dfferent tests are carred out for dfferent operatng ntal condtons (.e. upstream hydraulc load and dscharge values). In the faclty former descrbed the valve located at downstream corresponds to the valve manoeuvre whch orgnates transent regmes. Ths complete valve closure allows one to compare the dynamc response of a PT wth a, on the pont of vew of pressure varaton. For an ntal openng adjustment (n ths case corresponds to the adjustment of the sprng) the response to the dscharge varaton can present dfferent pressure confguraton (Fgure 9 b, d and e) dependng on the ntal system condtons, n partcular the upstream load and flow dscharge. However, the turbne (or pump as turbne - PT) has a smlar response ndependent on the ntal system characterstcs (Fgure 9 a and c). The transent pass through the runner of the PT presentng an equvalent response for all three measurement ppe sectons (mddle, upstream, and downstream) wth the same wave perod. Expermentally was verfed the response of the whch depends on several factors. Accordng wth Fgure 2 ths type of valve can operate as a check valve and can solate the flow between downstream to upstream whch s qute vsble n Fgure -b, snce the wave perod s half of the total length of the ppe (.e. between ar vessel and - sectons and 2; and valve manoeuvre at downstream of the system mddle and downstream sectons). For equvalent ntal condtons wth hgh values (.e. n lab condtons) of upstream head, the reacts n dfferent way under transent condtons not always favourable n terms of extreme pressure values for the ppe located at upstream the (Fgure 9 b). Wth the decreasng of the upstream load the response fts much better the PT behavour (Fgure 9 e). In lab condtons there are several scale effects whch can nfluence the comparsons. It was not possble to test PT for the smaller dscharge of.5 l/s due to the hgh frcton n the runner rotaton. 4. CONCLUSIONS The pressure control n drnkng ppe systems has enabled ths type of analyss based on the proft of excess avalable energy that would be dsspated n specal head loss devces, such has pressure reducng valves. The use of mcro-turbnes or pumps as turbnes (PT) are alternatve solutons to be consdered ndvdually, replacng totally a or placed n parallel to a, whenever t s not necessary to fx the downstream pressure constant or when there s a reservor or a treatment plant at downstream. In alternatve a PT can be located n seres wth a n the mddle of ppe systems, when the downstream head must be mantaned always constant. A mathematcal model was developed based on EPANET program and n Genetc Algorthm technque to optmse the system performance and to analyse the best soluton regardng the valve openng adjustment and the selecton of the best characterstc curve of the turbo-machne to be used to control the pressure and to proft excess avalable energy. Innovatve solutons are requred wthn renewable energy sources for energy producton by usng water ppe systems wth guaranteed daly dscharge, wthout envronmental polluton and low cost. Expermental analyse have shown an equvalent behavour between PT and for steady state regmes and some expected dfferences under transent condtons that n some cases 5

6 a PT behavour can be better than a but n other cases a mxed soluton of PT+ s certanly advsable, dependng on the system characterstcs and objectves. 5. REFERENCES ARAUJO, L. S, RAMOS, H. e COELHO, S. T. (a) Gestão Integrada de Sstemas de Dstrbução de Água para um Melhor Controlo de Perdas, 6º Congresso da Água, Porto, Portugal. ARAUJO, L.S.; RAMOS, H.M.; COELHO, S.T. (b) - Optmzação da Localzação de Válvulas numa Rede de Dstrbução para a Mnmzação de Fugas. º Encontro Naconal de Sanemamento Básco - 6 a 9 de Setembro, Braga,. ARAUJO, L.S., RAMOS, H.M., COELHO, S.T. (23) Optmsaton of the use of valves n a network water dstrbuton system for leakage mnmsaton. CCWI (Computng and Control for the Water Industry), Imperal College, UK, 23. COVAS, D.; RAMOS, H. (99) A Utlzação de válvulas redutoras de pressão no controlo e redução de fugas em sstemas de dstrbução de água. º Encontro Naconal de Saneamento Básco, Barcelos 27 a de Outubro, 99. GOLDBERG, D.E. (994) - Genetc and Evolutonary Algorthms Come of Age. Communcatons of the ACM, Vol. 37, nº 3, pp HERNÁNDEZ, V. MARTÍNEZ, F., VIDAL, A.M., ALONSO, J.M., ALVARRUIZ, F., GUERRERO, D., RUIZ, P.A.., VERCHER, J. (999) HIPERWATER: A hgh Performance Computng EPANET-Based Demonstrator for Water Network Smulaton and Leakage Mnmsaton. Water Industry Systems: Modellng and Optmzaton Applcatons, Vol., Research Studes Press Ltd., Baldock. Hertfordshre, England. pp.4-3. JOWITT, P.W. & XU, C. (99) - Optmal Valve Control n Water Dstrbuton Networks. Journal of Water Resources Plannng and Management, ASCE, July/August. pp KALANITHY, V. & LUMBERS, J. (99) - Leakage Reducton n Water Dstrbuton Systems: Optmal Valve Control. Journal of Hydraulc Engneerng, ASCE, November. pp MARTÍNEZ, F., CONEJOS, P. & VERCHER, J. (999) Developng an Integrated Model for Water Dstrbuton Systems Consderng both Dstrbuted Leakage and Pressure- Dependent Demands. Proceedngs of the 26th ASCE Water Resources Plannng and Management Dvson Conference. July. Tempe, Arzona. PRESCOTT, S.L. & ULANICKI, B. (2) - Tme Seres Analyss of Leakage n Water Dstrbuton Networks. Water Software Systems: Theory and Applcatons. Vol. 2, Research Studes Press Ltd., Baldock, Hertfordshre, England. pp RAMOS, H.; BORGA, A. (2a) Pump as Turbnes: an Unconventonal Soluton to Energy Producton. Journal URBWAT, Vol., N.º 3, pp RAMOS, H.; BORGA, A. (2b) Pumps yeldng power. Dam Engneerng, Water Power & Dam Constructon, Volume X, Issue 4, pp.97-27, UK, ISSN X, 2. RAMOS, H.; COVAS, D.; ARAUJO, L. (24) Válvulas Redutoras de Pressão e Produção de Energa. 7º Congresso da Água, LNEC, Lsboa, 24. REIS, F.R. & CHAUDHRY, F.H. (999) - Hydraulc Characterstcs of Pressure Reducng Valves for Maxmum Reducton of Leakage n Water Supply Networks. Water Industry 6

7 Systems: Modellng and Optmzaton Applcatons, Vol., Research Studes Press Ltd., England. pp REIS, F.R., PORTO, R.M. & CHAUDHRY, F.H. (997) - Optmal Locaton of Control Valves n Ppe Networks by Genetc Algorthm. Journal of Water Resources Plannng and Management, November/December. pp TUCCIARELLI, T., CRIMINISI, A. & TERMINI, D. (999) - Leak Analyss Systems by Means of Optmal Valve Regulaton. Journal of Hydraulc Engneerng, ASCE, March. pp ULANICKA, K., BOUNDS, P., ULANICKI, B. & RANCE, J. (2) - Pressure Control of a Large Scale Water Dstrbuton Network wth Interactng Water Sources: A Case Study. Water Software Systems: Theory and Applcatons, Volume 2, Research Studes Press Ltd., England, pp VALADAS, M. (2) - Uma Solução não Convenconal no Contexto das Energas Renováves para Aprovetamento de Energa em Excesso em Sstemas de Rega. Dssertação para obtenção do grau de Mestre em Hdráulca e Recursos Hídrcos. Insttuto Superor Técnco. Unversdade Técnca de Lsboa. VALADAS, M., RAMOS, H. (23) Utlzação de bombas como turbnas para o aprovetamento hdroenergétco em sstemas de rega. Revsta Recursos Hídrcos da APRH. Lsboa. Novembro, Vol. 24, nº3, 23. pp ACKNOWLEDGEMENTS The authors want to thank to FCT through the project POCTI/3779/ECM/2 and POCTI/5375/ECM/24, whch s partly supported by fundng under the European Commsson FEDER, as well as to the Hydraulc Laboratory of Department of Cvl Engneerng, at Insttuto Superor Técnco (Lsbon, Portugal) where the expermental programme s runnng. Regulator Pressure control Pressure control Daphragm Control chamber Isolated zone Sprng Pston Lock devce Upstream chamber Downstream chamber Dscharge Upstream chamber Downstream chamber Upstream chamber Downstream chamber a) b) c) Fg. - Dfferent types of : a) controlled by a sprng; b) pston control; c) daphragm control 7

8 H LR- H d Q H LR- L.E. Q H d Q= () Actve () Open passve () Closed passve (Hu HLR- Hd) (Hd Hu HLR-) (Hd Hu) Fg. 2 Typcal operaton of a conventonal type + + H LR- L.E.. + H H H d + H d + H d (t ) H + d (t + ) + +2 H d (Q ) H) + d (Q +) H +2 d (Q +2) VRP () wth const. load () wth const. head loss () wth const. load but varable n tme (v) wth const. load ftted to demand Fg. 3 - Actve operaton status for dfferent types of a) b) c) Pressure for each node (m) vs Tme (h) Pressure for each node (m) vs Tme (h) Pressure for each node (m) vs Tme (h) Id dos nós Fg. 4- Pressure control n drnkng systems: a) system wthout control; b) and c) effect of and 5, respectvely, wth hour open regulaton

9 2 Fg. 5 - Smulaton of a operaton (left-top) and a Pump/Turbne PT (remanng graphs) press. n each node (m) vs tme (h) - no control pressure n each node (m) vs tme (h) - pressure n each node (m) vs tme (h) - PT tme (h) Id nodes tme (h) Id nodes tme (h) Id nodes Fg. 6 - System response wthout and wth pressure control by usng a and a Pump/Turbne for energy recover H H p d-valve >p d-end p d-valve <p d-end Fg. 7 Schematc confguraton of the hydraulc grade lne for dfferent flow characterstcs. 9

10 H (m) Qd=2.64 l/s Qd=.5 l/s Qd=.5 l/s L (m) H (m) Qd=2.64 l/s Qd=.9 l/s Qd=.5 l/s PT L (m) Fg. Analyss of the behavour of a and a PT. Values of pressure drop dependng on the upstream head and dscharge flow.7 H (m) 6 5 a) at valve manouevre - downst. downs. PT ups. PT H (m) PT 6 H av = m; Qd = 2.64 l/s t (s) - H (m) at valve manouevre - downst. downs. PT ups. PT H (m) at valve manouevre - downst. downs. ups. 5 5 PT c) d) H av = 2.5 m; Qd = 2.25 l/s H av = 2. m; Qd = 2.7 l/s b) at valve manouevre - dow nst. dow ns. ups. H av = 3.4 m; Qd = 2.64 l/s t (s) H (m) e) at valve manouevre - downst. downs. ups. H av =.67 m; Qd=.5 l/s t (s) Fg. 9 Analyss of the dynamc behavour of a and a PT for a fast closure of a downstream valve.