Hydrodynamic Capacity Study of the Wave-Energized Baltic Aeration Pump
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Hydrodynamic Capacity Study of the Wave-Energized Baltic Aeration Pump General Applicability to the Baltic Sea and Location Study for a Pilot Project in Kanholmsfjarden¨ Christoffer Carstens March 2008 TRITA-LWR Master Thesis ISSN 1651-064X LWR-EX-08-05 c Christoffer Carstens 2008 Master of Science thesis KTH-Water Resources Engineering Department of Land and Water Resources Engineering Royal Institute of Technology (KTH) SE-100 44 STOCKHOLM, Sweden ii Abstract To counteract one of the most urgent environmental issues in the Baltic Sea; eutrophication, excessive algal blooms and hypoxia, a proposal to use wave energy to pump oxygen-rich surface water towards the sea bottom is investigated. Proposals have suggested that 100 kg of oxygen per second is needed to oxygenate bottom water and enhance binding of phosphorus to bottom sediments. This corresponds to 10 000 m3/s of oxygen-rich surface water. This thesis investigates a wave-powered device to facilitate this oxygen flux. Results give expected water flow rates between 0.15{0.40 m3/s and meter breakwater. The mean specific wave power for the analyzed wave data is calculated to be between 3{4 kW/m wave crest and the median to 1 kW/m. This study indicate, however, that the energy fluxes in the Baltic Proper are significantly higher. The study gives that the wave climate of the Baltic Sea is sufficiently intense to facilitate vertical pumping with a feasible number of breakwaters. A full-scale implementation in the Baltic Sea would require some 300 to 1 200 floating breakwaters of a length of 50 m each. The total cost is roughly estimated to 170{680 million EURO. The study also concludes that the interleaving of surface water should be constrained to a relatively small vertical distance from the outlet depth (20{30 m) and not stir up deep water to the surface. Wave modelling for the proposed pilot location Kanholmsfj¨ardenindicate that this bay is not large enough to permanently produce a favorable wave climate. It is, however, still an interesting location consistently to its vicinity to Stockholm and relatively long measurement series. Key words: Baltic Sea, Oxygenation, Wave power, Breakwater, Halocline ventilation iii Hydrodynamic Capacity Study of the Wave-Energized Baltic Aeration Pump iv Sammanfattning I syfte att syres¨attaanoxiskt djupvatten och anoxiska bottnar i Ostersj¨onhar¨ ett f¨orslagatt utnyt- tja v˚agkraft f¨or¨andam˚aletunders¨okts. Den grundl¨aggandeprincipen ¨aratt leda v˚agorin i flytande v˚agbrytareoch skapa en h¨ogrevattenyta i utrymmen bakom sj¨alva brytaren. Med r¨ors¨attsdetta vatten i kontakt med subhaloklint vatten p˚a60{100 m djup och genom det h¨ogretrycket inuti brytaren induceras en transport av vatten, som leder syresatt ytvatten till de anoxiska niv˚aerna. Tidigare studier av Stigebrandt and Gustafsson (2007) och en sammanfattning av Zill´enand Conley (2007) har visat att 63{190 kg syre per sekund skulle beh¨ova tillf¨oras Ostersj¨onf¨oratt¨ uppn˚aen kontin- uerlig syres¨attningoch goda f¨orh˚allandenvilket motsvarar 6 300{19 000 m3 vatten per sekund. Eftersom detta m˚astep˚ag˚aunder en l˚angtidsperiod blir f¨ornybar energi ett krav f¨oren liknande operation. Syftet och omf˚anget av detta examensarbete har varit att utreda kapaciteter f¨orovan beskrivna syrepump och att s¨attadet i ett ¨ostersj¨operspektiv genom att unders¨oka det regionala v˚agklimatet f¨oratt utreda den totala m¨angdv˚agbrytaresom skulle beh¨ovas f¨oren fullskalig implementering i Ostersj¨on.¨ Vidare har Kanholmsfj¨ardenoch S¨oderM¨ojafj¨ardi Stockholms sk¨arg˚ardunders¨oktsmed avseende p˚av˚agklimati syfte att utreda deras l¨amplighet som lokaler f¨orett pilotprojekt. Vidare gjordes en grundl¨aggandesammanst¨allning av sv˚arigheter,kunskapsluckor och risker g¨allandesyres¨attningav anoxiska bottnar, i synnerhet vid br¨ackvattenf¨orh˚allanden. F¨orkapacitetsuppskattningar anv¨andesdels erfarenheter och fl¨odesber¨akningar fr˚anliknande pro- jekt f¨orutnyttjande av v˚agenergi,exempelvis Wave Dragon (www.wavedragon.net). Dessutom gjordes en energifl¨odesbetraktelse utifr˚anlinj¨arv˚agteori. V˚agdatafr˚anSMHI analyserades med avseende p˚a v˚agh¨ojd,period och distribution f¨oratt ber¨aknakapaciteter f¨orv˚agpumpari Ostersj¨on.J¨amf¨orelsermed¨ v˚agmodellering har ocks˚agenomf¨orts.Inlagringsdjupet har studerats f¨orgivna data fr˚anSMHI:s SHARK- databas f¨oratt bed¨ommavar den l¨attareytvattenplymen lagrar in sig och vilka skikt som potentiellt r¨ors om. Resultaten visar att ett f¨orv¨antat fl¨odei Ostersj¨onkan¨ vara 0.15{0.40 m3/s och det genomsnittliga specifika v˚agenergifl¨odet¨ar3{4 kW per breddmeter v˚ag,medianen ¨ar1 kW/m. B˚adadessa resultat pekar p˚aatt en total l¨angdav 15{60 km v˚agbrytareskulle beh¨ovas f¨oren fullskalig syres¨attningav Ostersj¨on.¨ Detta skulle d˚amotsvara ett antal 300{1 200 stycken `a50 meter. De v˚agdatasom anv¨andes ¨arn¨astan alla tagna ralativt n¨araden svenska kusten och modellering visar att v˚agenergidensiteten¨arsignifikant h¨ogrei Egentliga Ostersj¨on,vilket¨ skulle g¨oradetta arbetes uppskattningar relativt konservativa. En prelimin¨arkostnadsbed¨omningger att den totala kostnaden f¨oren fullskalig implementering i Ostersj¨on¨ skulle kosta 170{680 millioner EURO. Inlagringsdjupet har ber¨aknatsoch faller inom 60{80 meters djup vid ett utsl¨appsdjupp˚a100 meter, vilket g¨oratt metoden blandar om runt haloklinen men ej h¨ogre¨ans˚a,vilket ¨arett ¨onskv¨artresultat. Resultaten f¨orKanholmsfj¨ardenoch S¨oderM¨ojafj¨ardvisar att de generellt ¨arf¨orsm˚af¨oratt tillr¨ackligt h¨ogav˚agorskall f¨orv¨antas existera under s˚al˚angtid att de kan vara effektiva lokaler f¨orprovpumpning med enbart v˚agkraft. D˚adet ¨and˚afinns l˚angam¨atserierd¨arifr˚anoch det faktum att de angr¨ansande sunden g¨orm¨atningav in- och utfl¨odenrelativt enkel, ¨arslutsatsen att de fj¨ardarna skulle fungera som pilotlokaler men att pumpningen d˚abeh¨over intensifieras av en elektrisk pump. Slutligen sammanfattas kunskapsl¨agetf¨orsyresituationen i Ostersj¨onoch¨ m¨ojlighetertill tekniska ˚atg¨arder. Slutsatserna ¨aratt haloklin omr¨orninganses vara det enda nuvarande f¨orslagetsom skulle kunna ge ¨onskv¨ardeffekt utan f¨orstor negativ p˚averkan. Kunskaperna om n¨arsaltsdynamiken och sedimentens reaktion vid skiftande oxiska f¨orh˚allanden ¨arl˚agaoch beh¨over ut¨okas. Dessa fr˚agorkommer att hamna i fokus vid framtida provanl¨aggningar,b˚adef¨oratt uppn˚a¨onskat resultat med syres¨attning men ocks˚af¨oratt tidigt uppt¨acka eventuella negativa effekter. Nyckelord: Ostersj¨on,Syres¨attning,¨ V˚agkraft,V˚agbrytare,Haloklin omr¨orning v Hydrodynamic Capacity Study of the Wave-Energized Baltic Aeration Pump vi Acknowlegdements First I would like to thank Anders Engqvist for his inspired and accurate supervision of my work. Thoughts and ideas have generally come out clearer after our discussions. I am also very grateful to Vladimir Cvetkovic who has contributed substantially to the final form of the thesis aswell as with in- spiration. Further thanks goes to Ida Engqvist for careful reading of the manuscript and Peter Kjaerboe for providing me with the original idea of the wave pump and good discussions. Thanks also to Marcus Flarup at SMHI who generously provided me with data. vii Hydrodynamic Capacity Study of the Wave-Energized Baltic Aeration Pump viii Table of Contents Abstract iii Sammanfattning v Acknowlegdements vii Table of Contents ix List of Figures xi List of Tables xiii Introduction 1 Short description of the Baltic Sea . .1 Oxygen balance of the Baltic Sea . .2 Excess nutrient loading and eutrophication . .2 Nutrient dynamics in the Baltic Sea . .2 The state of the Baltic Sea today . .2 General objectives and formulation of solution 5 Previous investigations and proposals . .5 Description of the pump and the physical principle . .6 Description of possible test pilot location: Kanholmsfj¨ardenand S¨oderM¨ojafj¨ard . .6 Current Status of similar projects . .6 Theory and methods 8 Linear wave theory . .8 Wave generation and energy transfer . .9 Energy Considerations . 10 Wave climate in the Baltic Sea . 10 Wave climate in Kanholmsfj¨ardenand S¨oder M¨ojafj¨ard. 11 Wave modelling . 11 Wave measurements . 12 Overtopping capacities . 12 Pipe flow and density plume interleaving . 13 Assessment of the pump and possible effects of enhanced vertical mixing . 14 Results 15 Wave height estimations for the Baltic Sea . 15 Wave heights in Kanholmsfj¨ardenand S¨oderM¨ojafj¨ard. 15 Wave measurements in S¨oderM¨ojafj¨ard . 18 Overtopping modeling . 19 Flow in the pump and dimension of pipes and diffusors . 20 Interleaving and vertical mixing . 20 Wave energy in the Baltic Sea . 21 Energy considerations of the Baltic Sea . 22 ix Hydrodynamic Capacity Study of the Wave-Energized Baltic Aeration Pump Discussion 24 Capacities and energy resources . 24 Capacities in the Baltic Sea . 24 Capacities in Kanholmsfj¨ardenand S¨oderM¨ojafj¨ard . 24 Uncertainties in wave data from SMHI . 24 Expected outcome . 24 Possible risks and uncertainties . 26 Discussion on proposed mitigation measures for the Baltic Sea . 26 Model experiments for different physical measures . 26 Other mitigation measures . 26 Uncertainties in the behavior of sediments in different redox environments . 27 Improvements and alternative design . 27 Future perspectives . 27 Conclusions 28 Bibliography 29 List of symbols 31 Terms and expressions 33 Fetches in Kanholmsfj¨arden 34 Cost Calculation 36 x List of Figures The Baltic sea drainage basin . .1 Baltic population density . .1 Example of algal blooms in the Baltic Sea . .3 Hypoxia in the Baltic sea . .4 An artist's conception of a wave pump. .5 A general sketch of the pump and the pumping principles. .6 Possible test locations . .6 Kanholmsfj¨ardendensity and oxygen profiles . .7 Example of Wave spectra . .9 Draft efficiency curves . 10 Wave measurement stations . 11 Kanholmsfj¨ardenand S¨oderM¨ojafj¨ardgrid . 11 The pressure decay factor for some different wave periods. 12 The principles of the pump under density stratification.