SEAPLACE-501: TLP TURBINE FOR HARNESSING MARINE CURRENTS

Transcription

1 Seaplace contribution to Ocean Líder A CENIT-E Project SEAPLACE-501: TLP TURBINE FOR HARNESSING MARINE CURRENTS Jaime Moreu

2 INDEX Introduction Marine turbines Seaplace-501 Marine turbine General ideas about the design Experimental tests

3 Marine turbines versus wind turbines Water is about 830 times denser than air, but wind is, generally speaking, an order of magnitude faster than water currents Thus the kinetic power per unit area is very similar: P P wind current air water AV AV 3 wind 3 current For similar power characteristics of the turbine, drag and lift forces will be an order of magnitude higher for the water solution: air V air V 3 current 3 current 1.2 F F water air water air V V 2 current 2 wind 830 V air air 10V 2 current 2 current 8.3 Therefore marine turbines generally require somewhat sturdier structures

4 Marine turbines versus wind turbines The Capital expenditure required to install water turbines is higher than for wind turbines mainly because: Electric equipment shall be specially protected from water, increasing the cost Operation and maintenance are harder Mechanical components, specially the shaft sealing, gets very expensive with increasing depth. So how can water turbines compete against wind turbines? Because the capacity factors can be up to 3 times those of wind turbines!

5 Types of Marine Currents Tidal currents Driven by gravitational forces Bidirectional flows with high peak speeds on shallow waters and/or narrow areas Ocean currents They are mainly due to: Rotation of the earth Wind Density differences caused by salinity and temperature gradients (thermohaline currents) Unidirectional and relatively constant in time, although they only get fast enough on very specific locations Current type TIDAL OCEAN Capacity factor * ** (*) Jones et al. IIEE PESGM 05. June 2005 (**)

6 Ocean currents Ocean currents are predictable and stable, not depending significantly on the weather Some ocean currents are very constant in time, with high mean speeds (Gulf stream, Kuroshio) There are few possible locations with high speeds in relatively deep waters, such as the Strait of Gibraltar (3 kn at 300 m) and the Strait of Florida (4 kn at 400 m) Source: From

7 State of the art of marine turbines Most of them are axial flow turbines First and second generation designs Fixed structures: Monopile and gravity based Nominal velocities are frequently above 2 m/s The rated power for the already installed devices is about 1 MW Efficiencies being achieved nowadays are about 30% of the kinetic power Shallow waters: limited draft to about 50 m Mostly harnessing tidal currents (bidirectional flows)

8 Some examples of fixed turbines Turbine: Openhydro Company: Openhydro Power: 1 MW Rotor: 6 m Foundation: gravity base Openhydro turbine (Openhydro) Turbine: SeaGen Company: SeaGen Ltd. Power: 1.2 MW Rotor: 2 x 16 m Foundation: monopile SeaGen project (Sea Generation Ltd.) Turbine: RTT Company: Lunar Energy Power: 1.5 MW Rotor: 21 m Foundation: gravity base Lunar Energy s Rotech Tidal Turbine (RTT). Turbine: HS-1000 Company: Andritz Hydro Hammerfest Power: 1 MW Rotor: 23 m Foundation: gravity base HS-1000 turbine (Andritz Hydro Hammerfest) rom.com

9 A fixed turbine at the Gulf stream? The mass transport of this current is more than 30 times the total flow of the fresh water rivers of the entire world The annual power density is about 1,95 kw/m 2 at some points (corresponding to a current of about 3kn mean speed). The current speed ranged between 1 and 2 m/s in the top 100 m, 85% of the time A device at m should be optimal (for less than 40 m it can interfere with navigation). Since depths are about 200 to 500 m in the best regions A MOORED SOLUTION SEEMS BEST From Tomczak et al. Regional Oceanography: an Introduction 2nd ed (2003) Source: Driscoll et al, 2008

10 Characteristics of Moored turbines The device can be located at the optimal depth without significant economic repercussion The turbine requires buoyancy, increasing the structure cost, and shall be moored to the seabed A ballast system is frequently used to control the emersion / immersion of the turbine for installation and maintenance Stability in most designs is achieved using a kite concept

11 Possible disadvantages of moored turbines using the kite concept A change of thrust (e.g. if the turbine is not working) could mean: A significant vertical displacement of the turbine, modifying substantially the pressure on the watertight tanks and probably requiring active control of the tanks. This could be solved using passive floaters, but they make the installation process more difficult A significant axial and lateral displacement, requiring more space with respect to other turbines, and probably leading to a smaller exploitation of a specific field If forward and aft mooring lines are required the footprint on the seabed is high, and the device cannot look into the stream direction If only a forward mooring line is required, a big space shall be left between adjacent turbines

12 A solution for the problems related to kites: a TLP mooring A TLP mooring significantly reduces the vertical displacements, reducing the pressure variation at the air tanks A TLP mooring allows a better use of a specific field since the footprint is much smaller A TLP mooring can be arranged so that the turbine can turn into the current direction, increasing easily the capacity factor of the turbine. This is possible as long as the center of gravity, buoyancy center and the hydrodynamic center are appropriately located The required buoyancy is given by a nozzle and/or diffuser. This structure can also help us to reduce the size of the screw

13 Our case: A turbine for harnessing marine currents with a TLP solution We were given the chance to design a turbine to harness currents such as those of the Strait of Florida, and we opted for a TLP arrangement In the preferred embodiment, the diffuser is first installed by controlling the air pressure Then a much smaller structure, the nozzle, which includes the electric equipment and the screw, is connected to the diffuser. If maintenance of the turbine is needed, we do not need to uninstall the TLP mooring, just uncouple the nozzle from the diffuser

14 Seaplace-501 Marine Turbine Rated Power: 1 MW Flow speed: 4 knots Diffuser In-line screw Nozzle TLP mooring tendon

15 Seaplace-501 Marine Turbine A TLP mooring system is used (Patent pending, PCT/ES2013/070328) The buoyancy is provided by the nozzle and/or diffuser bodies, which also increase the efficiency of the turbine by 4 (compared to a well-designed screw without nozzle) The turbine is a 6-blade in-line solution (shaftless turbine) Optimized via simulations and experimental tests The turbine is capable of turning into the current direction

16 Actuator disc theory including nozzles The turbine and duct interaction can be decoupled (as shown in the paper presented at the fifth Conference on Computational Methods in Marine Engineering held in Hamburg in 2013) The maximum efficiency is: 16 opt 1 CS Betz 1 C 27 p 0 V A d2 R u R u R u 0 F Domain 2 St R p T 0 V A -u * p a Domain 1 0 V A V -u p 0 V A S Domain 4 Domain 3 F Sd Domain 5 R w p 0 V A R d2 w p 0 V A R w A w

17 Power [MW] Power curve for a 4-knot current for the real-scale case Rotational Speed (RPM) Seaplace-501 Screw Design Results for the real-scale case

18 Seaplace-501: Screw Design Results for the real-scale case C P -λ curve for the real-scale case C P Tip Speed Ratio (λ) C P 1 2 P R V 2 3 h A

19 Seaplace-501 Screw Design Results for the modelscale case C P -λ curve for the model-scale case C P C P h A Tip Speed Ratio () P R V

20 Seaplace-501: Screw Design CFD simulations have been done including nozzle and diffuser, both with OpenProp and a Finite Volume Method The Seaplace-501 turbine has 6 slender blades and no shaft A scale model has been tested in CEHIPAR towing tank. This model has a shaft due to instrumentation needs Scale model In-line solution Experimental tests scale model Shaft solution

21 Seaplace-501 Marine Turbine Experimental Tests

22 Seaplace-501: Mooring arrangements There are several available configurations for the tendons depending on the specific needs for each case. Some are shown in the attached figure

23 Seaplace-501 Marine Turbine: summary Vertical tethers constrain the vertical displacement It requires a minimum footprint due to the short distance between the tendons at the seabed The stability of the system is very good, showing very soft responses against unexpected changes of the current direction because: The response against yaw for a TLP arrangement is much softer than against heave Its weight distribution allows a small distance between the center of gravity, the center of flotation and the hydrodynamic center. The appropriate arrangement of these centers ensures the good behavior of the solution The added mass against sway and yaw motions of the nozzle and diffuser is incredibly high (about an order of magnitude higher than the weight of the device)

24 Other advantages of the Seaplace-501 Marine Turbine Several devices can be fitted to the same anchoring system with minimum footprint The nozzle protects the tips of the blades from damaging the fauna It can be fully submerged, allowing navigation and fishing if needed

25 Next steps We are presenting the results of the CFD simulations at the next ASME International Conference on Ocean, Offshore and Arctic Engineering (OMAE), which will be held in San Francisco in June We are working with Professor Yeung and David Fernandez from Berkeley University A prototype that produces 50 to 100 kw should be designed and tested before going for the 1 MW device

26 Ocean Líder A CENIT-E Project SEAPLACE-501: A TLP TURBINE FOR HARNESSING MARINE CURRENTS