A system and a method for facilitating maintenance of an underwater power plant

Abstract

A system (1) and a method for facilitating maintenance of an underwater power plant (3) for converting kinetic energy from flowing water into electricity, the system (1) compris-ing at least two turbi

Description

[0001] A SYSTEM AND A METHOD FOR FACILITATING MAINTENANCE OF AN UNDERWATER

[0002] POWER PLANT

[0003] The present disclosure is related to a system for facilitating maintenance of an underwa- ter power plant. More particularly, the present disclosure is related to a system and a method for facilitating maintenance of an underwater power plant for converting kinetic energy from flowing water into electricity, wherein the system comprises at least two turbine houses arranged side by side in a row, each of the turbine houses comprising a slot housing a turbine apparatus removable through a top portion of the housing.

[0004] The world's population has dramatically increased over the last decades. This increase in population, together with a strong increase in living standards in many regions, have con- tributed to a growth in energy consumption. Due to the climate crises, the emission of climate gasses must be reduced.

[0005] There is therefore an increasing demand for renewable energy, for example energy from a source that is not depleted when used, such as wind, water, or solar power. However, energy harvested from wind requires major windfarms or wind parks on land or offshore. Such windfarms may comprise several hundred individual wind turbines and may cover an extended area of tens of square kilometers. As such, at least for some people, a wind- farm may represent a visible and / or audible pollution. Further, a windfarm may represent a hazard for birds. Solar power plants designed for generating electrical energy to the community suffer from some of the same disadvantages, although solar panels for self- supply of electrical energy may be incorporated in existing buildings. A major disadvantage of wind farms and solar power plants is that they depend on wind and sun (radiation from the sun), respectively, to produce energy.

[0006] Harvesting energy from water, such as for example marine currents, has several ad- vantages over harvesting energy from other renewable energy sources such as wind and sun. Marine currents may be relatively constant and thus provide a reliable energy source being independent of changing weather conditions. Energy may be harvested by means of underwater power plants that will not represent any visible or audible pollution. An- other major advantage of harvesting energy from water versus wind is the density of wa- ter being about 832 times that of air, resulting in reduced turbine blade diameters for similar power output.

[0007] Publication KR 10-1290920 discloses a turbine structure for a tidal power plant configured for preventing turbine vibration and cavitation due to aeration by easily maintaining the altitude of hydraulic turbine generation. The tidal power plant is arranged between a lake and the sea. A major challenge of prior art underwater power plants is related to maintenance. An underwater power plant is subject to harsh conditions. An underwater turbine apparatus may therefore require maintenance or replacement on a regular basis. In most cases, any maintenance will require bringing the turbine apparatus out of the water. The turbine house, i.e., the duct housing the turbine apparatus, is typically made of solid material, and designed for an operating time in the water exceeding the operating time of the turbine apparatus. Further, the turbine house may be heavy. Any lifting of the turbine house and the turbine apparatus may require a heavy-duty surface vessel. In some areas, for exam- ple in a stream, canal or a tidal bay, an available space for such a vessel may be limited. Further, a heavy-duty surface vessel is more expensive to operate than an underwater tidal power plant maintenance crane.

[0008] Another major challenge of prior art underwater power plant is significant limited work time due to the harsh conditions for the heavy-duty surface vessel compared to the un- derwater tidal power maintenance crane. Publication US 2010 / 0014920 discloses turbine structures and gate structures for tidal power plants which are integrated with management facilities and access roads as two units of one block so that the blocks of turbine structures and gate structures can be in- creased or decreased according to the site scale and generation capacity of the tidal pow- er plant and to cope with the site situation. The structures comprise at least two turbine houses arranged side by side in a row, each of the turbine houses comprising a housing and a turbine apparatus that is movable.

[0009] Publication WO 2017 / 196183 to the applicant discloses an underwater power plant, a method and a system for converting kinetic energy of flowing water into electricity. The power plant comprises at least one turbine house defining a duct for housing a turbine apparatus, and a connecting means for attaching the turbine apparatus in the duct wherein the connecting means comprises at least one member slidably connected to the turbine house for allowing sliding of the turbine apparatus out of, into or within the tur- bine house in parallel with a longitudinal axis of the flow through the apparatus. In a slid- out position, the turbine apparatus itself may be hoisted onboard a surface vessel, while the turbine housing is left in place on a seabed. Thus, a heavy-duty surface vessel may not be needed.

[0010] Publication US 2010 / 0148513 discloses a system having a plurality of underwater turbine units. Turbine modules are installed in housings placed underwater. To achieve accurate installation of the turbine modules, a docking device is used to guide the turbine module into the housing.

[0011] Publications KR 20110043169 and KR 101290898 disclose use of a crane for handling a water turbine.

[0012] There is a need for a simple and reliable system for facilitating maintenance of an under- water power plant, wherein the maintenance may be performed without the use of a surface vessel, and wherein maintenance may be performed substantially independent of weather conditions. The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art.

[0013] The object is achieved through features, which are specified in the description below and in the claims that follow. The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

[0014] In a first aspect of the invention there is provided a system for facilitating maintenance of an underwater power plant for converting kinetic energy from flowing water into electric- ity, the system comprising at least two turbine houses arranged side by side in a row, each of the turbine houses comprising a slot housing a turbine apparatus removable through a top portion of the housing. The system comprises a guide track arranged on a top portion of the row of at least two turbine houses, and a crane supported by and mov- able along the guide track, the crane configured for bringing the turbine apparatus inde- pendently out of and into the slot of each of the turbine houses. The effect of arranging a crane movable along a guide track on a top portion of the tur- bine houses, is that the crane is supported by the turbine houses. Thus, the crane can be operated substantially independently of weather conditions. Further, the crane is station- ary at the power plant and may be operable on short notice.

[0015] Arranging the turbine houses in a row, for example directly or indirectly on a seabed, has the effect that the power plant may be upscaled substantially without influencing the operation of an existing part of the power plant.

[0016] In one embodiment is a first turbine house in the row of turbine houses arranged adja- cent to a land, the guide track has a length exceeding a length of the row of the at least two turbine houses, and a first end portion of the guide track extends onto the land, so that the crane is movable between a passive position on said land, and an active position on top of the turbine houses. In one embodiment is the portion of the guide track extend- ing onto the land, substantially at the same elevation as the portion of the guide track being on top of the turbine houses. In an alternative embodiment is the portion of the guide track extending onto the land, at a higher elevation than the portion of the guide track being on top of the turbine houses. Providing a crane movable between a passive position on said land, and an active position on top of the turbine houses has the effect that the crane in a passive position does not represent any obstructions for surface ves- sels that may pass over the power plant. This effect is of particular importance for a pow- er plant arranged for example in a river or in a narrow strait.

[0017] The first end portion of the guide track may be within a workshop hall for housing the crane when in the passive position.

[0018] In one embodiment is a first turbine house in the row of turbine houses arranged adja- cent a workshop hall, the guide track has a length exceeding a length of the row of the at least two turbine houses, and a first end portion of the guide track extends into the work- shop hall, so that the crane is movable between a passive position within said workshop hall, and an active position on top of the turbine houses. The workshop hall may be sup- ported by a floating installation. This has the effect that the system comprising a work- shop hall may be arranged offshore.

[0019] The crane may be a gantry crane comprising a traverse elevator provided with a gripping device configured for engaging a top portion of the turbine apparatus. A gantry crane comprising a traverse elevator is a very stable hoisting device. A stable hoisting device is operable substantially independently of any weather conditions. Each end portion of the traverse elevator may be operatively connected to an elevator guiding means provided with a driving device for moving the traverse elevator along the elevator guiding means. Preferably, the traverse elevator is provided with guideposts for engaging or mating aper- tures in a periphery portion of a turbine apparatus being carried by the traverse elevator, so that the turbine apparatus is aligned with respect to the slot of the turbine house. A risk of any rotation of the turbine apparatus prior to entering the slot of the turbine house is thereby substantially eliminated.

[0020] It is an advantage if the crane comprises maintenance and control facilities. By providing the crane itself with maintenance and control facilities, a turbine apparatus that has been lifted out of the turbine house, may be inspected, serviced, and even repaired. In one embodiment the guide track arranged on the top portion of the at least two tur- bine houses, is submerged. Thereby, a top portion of the turbine houses is also sub- merged. This has the effect that a surface vessel having a certain maximum deep-draught, or any extraneous matter, may pass over the top portion of the housings. In one embodiment a bottom portion of the at least two housings is resting on a level seabed, alternatively on a supporting frame carried by pillars protruding from the seabed. In still another embodiment is the at least two turbine houses provided by a buoyancy means having an adjustable weight. In a preferred embodiment a bottom portion of the housings is carried by a hollow supporting structure configured for being filled with a gas, typically air and / or a liquid, typically water, or any other matter that increases the weight of the buoyance means, such as sand or gravel. The buoyancy means is preferably de- signed so that when it is filled with a gas, the buoyancy means is capable of carrying at least the housings at a surface of the sea, and when the buoyance means is filled with a liquid or any other weight increasing matter, the buoyancy means abuts against the sea- bed, thereby providing a support for the housings. In one embodiment is the buoyance means provided by means of a barge.

[0021] In a second aspect of the invention, there is provided a method of operating the system according to the first aspect of the invention. The method comprises:

[0022] - moving the crane along the guide track and aligning the crane with respect to the slot of a turbine house; and

[0023] - activating the crane to insert the turbine apparatus into the house or retract the turbine apparatus out of the house.

[0024] In an underwater power plant comprising at least two, preferably a plurality of turbine apparatuses, the power plant may be in operation while for example maintenance or re- placement of the relevant turbine apparatus(es) takes place, thereby providing a power plant being reliable with respect to producing electrical energy. Preferably, at least one of the turbines is controlled independently of the other turbines. In one embodiment, each turbine is controlled independently of the other turbines. The turbine apparatus itself may typically be an "off-the-shelf product" being commercial- ly available on the market, this allows for replacement of any outdated turbine apparatus while keeping the turbine houses in place.

[0025] The turbine may be bidirectional or unidirectional. A bidirectional turbine is particularly advantageous when the underwater power plant is a tidal power plant. Electrical energy will then be produced for both directions of the tidal current. In a preferred embodiment, the turbine rotor discs may have an elliptic profile mirrored about a centerline of the blades of the discs. The generator of the turbine apparatus may be a permanent magnet generator. A unidirectional turbine is particularly advantageous when the underwater power plant is an ocean current power plant.

[0026] The turbine house comprises wall portions having an outer surface and an inner surface, the wall portions being interconnected for forming the duct having an inlet and an outlet. A longitudinal axis of the duct is preferably substantially in parallel with a flow of the wa- ter.

[0027] The slot in the turbine house is preferably arranged in a center portion of the turbine house. The slot may be unlined, especially if the slot is provided in a portion of the tur- bine house made from metal. However, in one embodiment the housing may be made from for example concrete. In such an embodiment, the slot may be lined, i.e., provided with a suitable lining material, for example metal, to prevent wear of the concrete.

[0028] In order to increase the efficiency of an underwater power plant, a flow area at an inlet and an outlet of the turbine house may be larger than a flow area at a section between said inlet and outlet in the direction of flow, thereby providing a constricted section creat- ing a Venturi effect. The section between said inlet and outlet may typically be a center portion surrounding the turbine apparatus.

[0029] An object flowing in the water may flow into the duct of the turbine house. Such an ob- ject hitting the turbine apparatus, especially the blades of the turbine, may cause serious damage to the turbine apparatus. An object flowing into the duct may also get stuck and cause blockage of the duct and malfunction of the turbine apparatus. In order to at least reduce the risk of objects damaging the turbine apparatus and / or fully or partially block- ing the duct of the turbine house, the end portions of the turbine house may be provided with a lattice. In one embodiment, the lattice has a conical form for diverting objects ex- ceeding a predetermined size towards the wall portions of the turbine house.

[0030] In one embodiment, at least one of the lattices is releasably connected to a portion of the turbine house.

[0031] The underwater power plant may comprise a plurality of turbine houses, where the hous- es of the turbine row may be constructed as one solid piece or wherein an outer surface of the houses being complementary adapted to each other for allowing adjacent place- ment of the houses side by side. This has the effect that more water has to pass through the ducts and thereby the turbines. The turbine houses may in such an embodiment be provided with engagement means for interlocking neighbouring turbine houses. The ef- fects of such interlocking means are increased stability of the houses in that relative movement between the houses is prevented, and that they may facilitate correct ar- rangement of the houses during installation.

[0032] Base beams for supporting the at least two turbine houses may be connectable to a plu- rality of supports extending into a seabed.

[0033] In another embodiment, the at least two turbine houses in a row may comprise a solid construction resting on the seabed by means of gravity.

[0034] In the following is described an example of a preferred embodiment illustrated in the ac- companying drawings, wherein:

[0035] Fig. 1 shows a principle view of an embodiment of the system according to the present invention, wherein a crane is in a passive position within a work- shop hall adjacent several submerged turbine houses;

[0036] Fig. 2 shows a top plan view of fig. 1; Fig. 3a shows in a larger scale a front view of the system wherein a crane is in a moving position on the top of a turbine house wherein a hoisting beam is in an uppermost position;

[0037] Fig. 3b shows a sideview of the system in fig. 3a; Fig. 4a shows the system in fig. 3a after the hoisting beam has been lowered for gripping the turbine apparatus;

[0038] Fig. 4b shows a sideview of the system in fig. 4a;

[0039] Fig. 5a shows the system in fig. 3a and 4a after the turbine apparatus has been hoisted out of the turbine house. Fig. 5b shows a sideview of the system in fig. 5a;

[0040] Fig. 6a shows in a larger scale detail A in fig. 3a, and illustrates a driving and clamping means of the hoisting beam; and

[0041] Fig. 6b shows in a larger scale detail B in fig. 5a and illustrates a device for gripping a portion of the turbine apparatus.

[0042] Any positional indications refer to the position shown in the figures.

[0043] In the figures, same or corresponding elements are indicated by same reference numer- als. For clarity reasons some elements may in some of the figures be without reference numerals. A person skilled in the art will understand that the figures are just principle drawings. The relative proportions of individual elements may also be strongly distorted.

[0044] In the figures reference numeral 1 denotes a system according to the present invention. The system 1 comprises an underwater power plant 3 comprising a turbine house 5 pro- vided with a slot 7 for receiving a turbine apparatus 9. The slot 7 is arranged in a top por- tion of the turbine house 5, as best seen in fig. 2. A guide track 20 for supporting a crane 30 forming part of the system 1 according to the invention, comprises two parallel and spaced apart guides arranged at a periphery of the top portion of the turbine house 5.

[0045] Fig. 1 shows an embodiment of a system 1 wherein the underwater power plant 3 com- prises a plurality of turbine houses 5 (five shown). The turbine houses 5 are supported by a supporting structure comprising beams B carried on pillars P extending into a seabed S. A top portion of the turbine houses 5 is in the embodiment shown arranged below a wa- ter level W, so that a surface vessel (not shown) may pass over the turbine houses 5.

[0046] The guide track 20 arranged on the top portion of the turbine houses 5, extends into a workshop hall 40 configured inter alia for housing the crane 30. The workshop hall 40 may also be a workshop for service and maintenance of the turbine apparatus 9, the crane 30 itself, and any appurtenant equipment.

[0047] In the embodiment shown, the portion of the guide track 20 being located inside the workshop hall 40 is substantially at the same elevation as the portion of the guide track 20 being on top of the turbine houses 5. Thus, the guide track 20 being located inside the workshop hall 40 may be arranged in recesses in a floor in the workshop hall 40.

[0048] In fig. 2, a power station 45 is arranged next to the workshop hall 40. The power station 45 is operatively connected to the turbine apparatuses 9.

[0049] Fig. 3a shows in a larger scale a front view of one embodiment of the system 1 according to the invention. The crane 30 is on the top of a turbine house 5 comprising a turbine ap- paratus 9. A hoisting device, here in the form of a traverse elevator 31 is in fig. 3a in an uppermost position.

[0050] The traverse elevator 31 is operatively connected to an elevator guiding means provided with a driving device which in the embodiment shown in a larger scale in fig. 6a showing detail A in fig. 3a, are in the form of rack guides 32 and rack motors 32'. The rack guides 32 are supported by a frame structure 33. Similar rack guides 32 and rack motors 32' are also provided on the right side of the transverse elevator 31 shown in fig. 3a. As best seen in figures 3b and 4b, a lower end portion of each of the four vertical frame structures 33 (only two shown in figures 3b and 4b) are provided with sets of wheels 36 for rolling on the guide track 20. At least one set of wheels is provided with a motor for rotating the wheel. A mid-portion of the traverse elevator 31 is provided with a downwardly extending grip- ping device 34 configured for engaging a connector 9' protruding from a top portion of the turbine apparatus 9. The gripping device 34 and the connector 9' are shown in greater detail in fig. 6b showing detail B in fig. 5a. The gripping device 34 comprises hydraulically operated locking members 34' configured for engaging the connector 9' of the turbine apparatus 9. In the embodiment shown, the connector 9' has the form of a mushroom.

[0051] In the embodiment shown, the traverse elevator 31 is further provided with downwardly extending guideposts 35 (see figures 3a, 4a, and 5a) for engaging apertures 35' in a pe- riphery portion of a turbine apparatus 9 being connected to the traverse elevator 31 as illustrated in figures 4a and 5a, so that the turbine apparatus 9 is aligned with respect to the slot 7 of the turbine house 5, as illustrated in figures 4a and 4b.

[0052] Within the frame structure 33 of the crane 30, there is in the embodiment shown herein, provided maintenance and control facilities 50 such as a workshop for at least an initial control and simple in situ service of the turbine apparatus 9, and a control room for oper- ating the crane 30. However, it should be noted that in an embodiment wherein the sys- tern 1 comprises a workshop hall 40, inspection, service, and maintenance of turbine ap- paratus 9 are preferably performed inside said workshop hall 40.

[0053] It may be necessary to access submerged parts of the system 1, for example for inspec- tion, maintenance, or removal of any objects at an entrance of the duct of the turbine house 5. The maintenance may also comprise in situ removal of marine growth on the turbine apparatus 9, and / or within the duct of the turbine house 5. Due to tidal currents and / or flowing water of a river, an ROV (remotely operated vehicle) is for safety reasons preferred over a diver for performing underwater activities. Therefore, in a preferred em- bodiment of the system 1, the facilities 50 further comprise an ROV hangar and a hoisting device for bringing the ROV into and out of the water. The ROV and appurtenant equip- merit including the hoisting device may be inspected and maintained within the facilities 50 of the crane 30.

[0054] In figures 4a and 4b, the traverse elevator 31 is in its lowermost position wherein the gripping device 34 is in engagement with the connector 9' of the turbine apparatus 9. In fig. 4a is the traverse elevator 31, the gripping device 34, and the guideposts 35 of the crane 30, and a periphery and the connector 9' of the turbine apparatus 9, are indicated by dotted lines. The guideposts 35 have been inserted into the apertures 35' indicated in figures 3b and 4b. In fig. 4a is the left guidepost 35 shown shorter than the right guide- post 35. The purpose of the different lengths is to facilitate entering of the guideposts 35 into the apertures 35'.

[0055] In figures 5a and 5b, the traverse elevator 31 is in its uppermost position holding the tur- bine apparatus 9 outside the slot 7 of the turbine house 5. In this position, the turbine apparatus 9 may be inspected and serviced in situ, i.e., at the maintenance and control facilities 50. Alternatively, the turbine apparatus 9 may be brought into the workshop hall 40 shown in figures 1 and 2.

[0056] Thus, as will be appreciated from the disclosure above, the crane forming part of the sys- tem according to the invention may be utilized for inspection operations, maintenance operations and repair operations of the power plant throughout its lifetime. When a tur- bine apparatus 9 is to be pulled out from the turbine house 5, the crane 30 is aligned with the slot 7 of the turbine house 5. Thereafter, the traverse elevator 31 is lowered and the guideposts 35 connected to the traverse elevator 31 fully align the gripping device 34 of the traverse elevator 31 with respect to the connector 9' of the turbine apparatus 9, whereupon the gripping device 34 lockingly engages the connector 9'. By raising the trav- erse elevator 31, the turbine apparatus 9 is pulled out from the turbine house 5. The tur- bine apparatus 9 may thereafter be inspected, serviced, or repaired either at the work- shop 50 on the crane 30, or the crane 30 can bring the turbine apparatus to the workshop hall 40 on land for inspection, service, repair or even replacement, as required. To insert a turbine apparatus 9 into the turbine house 5, the above process is reversed. When the turbine apparatus 9 is pushed down into the slot 7 of the turbine house 5, it will self-lock by gravity and friction. When the turbine apparatus 9 has been fully inserted in the slot 7 of the turbine house 5, the gripping device 34 is released before the traverse elevator 31 is raised with respect to the turbine house 5.

[0057] The system according to the present invention is particularly suitable for use in relatively shallow water, such as in a river, in an entrance of a sill fjord subject to tidal water, or in a tidal current. Especially when the top portion of the turbine houses 5 is submerged to allow surface vessels to pass above the turbine houses 5, and if the crane 30 is configured for moving to a passive position on land, the power plant does not represent any obstruc- tions to surface traffic. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embod- iments without departing from the scope of the appended claims. In the claims, any ref- erence signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

C l a i m s1. A system (1) for facilitating maintenance of an underwater power plant (3) for converting kinetic energy from flowing water into electricity, the system (1) comprising at least two turbine houses (5) arranged side by side in a row, each of the turbine houses (5) comprising a slot (7) housing a turbine apparatus (9) re- movable through a top portion of the housing, c h a r a c t e r i s e d i n that the system (1) comprises a guide track (20) arranged on a top portion of the row of at least two turbine houses (5); and a crane (30) supported by and movable along the guide track (20), the crane (30) being configured for bringing the turbine apparatus (9) independently out of and into the slot (7) of each of the turbine houses (5).

2. The system (1) according to claim 1, wherein a first turbine house (5) in the row of turbine houses is arranged adjacent to a land, the guide track (20) has a length exceeding a length of the row of the at least two turbine houses (5), and wherein a first end portion of the guide track (20) extends onto the land, so that the crane (30) is movable between a passive position on said land, and an active po- sition on top of the turbine houses (5).

3. The system (1) according to claim 2, wherein the first end portion of the guide track (20) is within a workshop hall (40) for housing the crane (30) when in the passive position.

4. The system (1) according to claim 1, wherein a first turbine house (5) in the row of turbine houses is arranged adjacent a workshop hall (40), the guide track (20) has a length exceeding a length of the row of the at least two turbine houses (5), and a first end portion of the guide track (20) extends into the workshop hall (40), so that the crane (30) is movable between a passive position within said workshop hall (40), and an active position on top of the turbine houses (5).

5. The system (1) according to claim 4, wherein the workshop hall (40) is supported by a floating installation.

6. The system (1) according to any one of the previous claims, wherein the crane comprises a traverse elevator (31) provided with a gripping device (34) config- ured for engaging a top portion of the turbine apparatus (9).

7. The system (1) according to claim 6, wherein each end portion of the traverse el- evator (31) is operatively connected to an elevator guiding means (32) provided with a driving device (32') for moving the traverse elevator (31) along the eleva- tor guiding means (32).

8. The system (1) according to claims 6 or 7, wherein the traverse elevator (31) is provided with guideposts (35) for engaging apertures (35') in a periphery portion of a turbine apparatus (9).

9. The system (1) according to any one of the preceding claims, wherein the crane (30) comprises maintenance and control facilities (50).

10. The system (1) according to any one of the preceding claims, wherein the guide track (20) arranged on the top portion of the at least two turbine houses (5), is submerged.

11. The system (1) according to any one of the preceding claims 1-10, wherein the at least two turbine houses (5) are provided by a buoyancy means having an ad- justable weight.

12. A method of operating the system (1) according to any one of claims 1-11, c h a r a c t e r i s e d i n that the method comprises:- moving the crane (30) along the guide track (20) and aligning the crane (30) with respect to the slot (7) of a turbine house (5); and- activating the crane (30) to insert the turbine apparatus (9) into the house (5) or retract the turbine apparatus (9) out of the house (5).

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