CA2692188A1 - Apparatus for converting ocean wave energy into mechanical energy - Google Patents

Abstract

The apparatus for converting sea wave energy into mechanical energy is a device that uses sea wave energy to rotate a wind turbine. The system consists of an arrangement of interconnected underwater air chambers and, through the action of the sea waves and the assistance of a pair of throttle valves, via each air chamber, the air contained in the inside thereof is circulated in one direction through a central turbine. Its simple design, with no moving parts in contact with the water, and the fact that it is underwater reduce its impact on marine life and shipping routes. Its modular nature makes it easier to handle in general during manufacture and installation, which makes it attractive in terms of cost. Applications include: generation of electricity, generation of hydrogen and oxygen and desalination of sea water.

Description

Apparatus for Converting Ocean Wave Energy into Mechanical Energy Description , BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a system able to use the potential energy of the ocean waves to make rotate a wind turbine, which can be further used to generate electricity, water pumping, produce Hydrogen-Oxygen by electrolysis, water desalination, or a combination of the formers.

2. State of the Art Wave Energy Converters are a relatively new renewable source technology.
Over the last decade, there has been significant amount of research and development in Ocean Wave Energy technology. The application for Ocean Wave Energy technologies are limited dUe to their high production cost comparing to other forms of electricity generation. There are many different forms of renewable energy, such as sunlight, wind, rain, geothermal heat and Ocean wave. Ocean wave has many different approaches to harvest the renewable resource more than any other form of renewable sources. In the field of ocean wave technology there are literally hundreds of inventions working under different principles.

The fol(owing inventions are some of the most relevant and developed devices:
a) Limpet, Azores, Mighty Whale, Energetech, b) Pelamis, c) Wave Dragon, d) Wave Swing.

The first group uses a principle called Oscillating Water Column (OWC). OWC
uses an air chamber at the surface of the ocean with typically two openings:
one on the bottom part that makes contact with the ocean surface and the second at the top part where an air turbine is located. The rise and fall of the water level at the bottom of the chamber creates an oscillating airflow, which rotates a special turbine that accepts an oscillating flow to further generate electricity.

Oscillating Water Column devices can be either near shore, such as the plants Limpet in the U.K. and the Azores in Portugal; or offshore, such as Mighty Whale in Japan and Energetech in Australia.

Although OWC devices are the most promising approaches to efficiently harvesting ocean wave energy, there are many challenging issues yet to be resolved. One of the main challenges with onshore devices is finding suitable locations to situate a large power plant. In most cases, suitable locations are located in remote areas, which lack the necessary infrastructure required for setting up a large power plant. It is not cost effective to create the necessary infrastructure to support the development of a large power plant. Another challenge with OWC devices is the efficiency. OWC devices typically use a Wells turbine to account for the oscillating airflow. The Wells turbine is less efficient than its equivalent unidirectional turbine.

Another promising approach and developed technology is Pelamis. Pelamis consists of several articulated cylindrical sections floating off shore. These sections are moved relative to each other while the wave passes. Such relative movement actuates pumps that drive pressurized oil through motors to generate electricity. It has excellent survivability characteristics; however, its efficiency still needs to be improved. Sections of Pelamis are fixed in size resulting in different efficiencies for different wavelengths. The ocean generates waves of all sizes, which affect and diminish the overall efficiency of Pelamis..

Another device is the Wave Dragon (European Patent 95923202.6-2315, Munich, Germany). Wave Dragon is an overtopping device that concentrates waves in order to further capture them as they spill into a reservoir. The elevated water is then bled through low head turbines, which generate electricity. This device is relatively large having a width of about 300 m. One of the main disadvantages of the Wave Dragon is the scalability. The device lacks the ability to easily down-size for small scale operations.

Another device is the Wave Swing. Wave Swing is a submerged device that consists of two concentric vertical cylinders. The external cylinder has a volume of air trapped in its interior. When waves pass, they alter the ambient water pressure resulting in a change of air pressure inside. Then it forces the external cylinder to oscillate upward and downward. A linear generator converts the motion into electricity. As an underwater device, it addresses one of the most important concerns in the wave industry, which is the survivability of the devices.
Under water devices are safer since the susceptibility to storms decrease exponentially with the depth of the water. In addition, Wave Swing has only one moving part which led to its wide acceptance. However, as a relatively large submerged device, servicing and maintenance can be problematic. Regular servicing and maintenance of the device may require floating the device, which can be challenging due its dimensions and weight.

These devices are some of the most developed yet they are not cost effective to compete with electricity generated from fossil fuels. In addition, most of these devices have moving parts, which makes contact with the water posing a potential risk of damaging the marine ecosystem.

The following are other devices, similar to the present invention, yet to be fully developed. These devices elevate the pressure of fluid and use it to further drive a turbine or a motor. The fluid is pumped by using an array.of reservoirs, with at least one of the reservoirs' walls being flexible. In this manner, the reservoir is able to pump the fluid and decrease and increase its volume.

An. example of such a device is Lesster, et al. U.S. Pat. No. 3,989,951. The device consists of a series of adjacent underwater pneumatic cells with a flexible upper wall. It uses the pressure changes created from the passing waves to inflate and deflate the pneumatic cells. The volume change created is use to pump air through a turbine. Cells use an external concrete cover to protect the flexible material from damage. With. the help of a couple of check valves per cell it directs the air uni-directionally. One disadvantage of this device is the necessity of an extra wall to protect the cell. This feature increases the cost of the device.
Furthermore, in order to avoid an intermittent airflow, it is necessary that the individual cells pump air sequentially without interruption. Such an effect can only be achieved by having an array of sufficient size, typically more than one and a half wavelengths. A typical wavelength is on the order of 120 metres and the array proposed by Lesster uses adjacent cells. Considering these specifications the system proposed by Lesster will be very large. The present invention uses a spaced array of air chambers that allows the system to exceed the size of a typical wavelength, achieving a more uniform airflow.

Another example is the Meyerand U.S. Pat. No. 4,630,440. It describes an apparatus for power generation that consists of an array of chambers comprising of two housings; one inside the other, and having water in between. The outer housing has at least one opening to the water with a turbine located on it.
The inner housing is filled with a gas with a flexible bladder that compresses and decompresses the gas in the interior while the waves pass. The volume within the two housings changes, while the flexible bladder changes its volume. The water is forced to go inside and outside of the outer housing; this flow drives the turbine. The major disadvantage of this invention is that it requires one turbine for each chamber. This could make the cost prohibitive. Furthermore, finding a material that can meet large expansion-contraction cycles for a very long period of time is a real challenge.

Semo in his U.S. Pat. No. 3,353,787 uses a submerged system of elongated tubes with a flexible upper wall that is moved by the action of the waves.
When the upper wall is compressed, it pushes an incompressible fluid that dives a motor located offshore. The displacement of the incompressible fluid by wave in practical operation is questionable.
The three previously mentioned devices use a flexible wall. They are subject to failure due to fatigue as the flexible material is under continuous flexion.
Nevertheless, flexible walls are not the only way to pump a fluid using ocean waves. The most common examples of pumping devices are the OWC's previously explained above. Other devices, that pump air, use a piston-like mechanism. Graff U.S. Pat. No. 4,001,597 discloses a device that consists of a plurality of compression cylinders. These cylinders are activated by the downward movement of a rigid hinged pressure plate, which oscillates as the waves pass. Meano U.S. Pat. No. 6,800,954 discloses a device that uses a piston. The rise and fall of the pistons are precipitated by the action of the waves, which pump air from the atmosphere to a pressurized chamber. In contrast to these technologies, the present invention uses an underwater mechanism with no moving parts to pump the air.

The advantages of the present invention are:
- it is unobtrusive - it has no moving parts in contact with the water; therefore, the system will have minimum impact on the marine life - it does not negatively affect navigation or seascapes - it has excellent survivability characteristics to account for the unpredictable ocean environment - it has the capability to operate for long periods of time without any supervision - it requires little or no maintenance since there are no moving components - the system uses only one complex part, the turbine, and only two moving parts, the turbine and the valves, - The system is cost effective due to the diminutive size of its parts;
therefore, parts can be easily manufactured on-site, transported and assembled on-site.

SUMARY OF THE INVENTION

The present invention consists of a submerged array of spaced vertical air chambers wherein the air trapped in their interior is constantly pumped in and out of the chamber by the action of the water level that increases and decreases in the interior of the chamber. Each said air chamber has two conduits, one wherefrom the air is taken out and other wherefrom the air is taken into the chamber. The earlier conduits are called a supply conduits because they feed the turbine while the former are called the return conduits because take the air from the outlet of the turbine back to the chambers. Check valves are disposed in the supply and return conduits in opposite directions to make sure a unidirectional flow is kept.

Since the system is composed of a plurality of air chambers, the supply conduits are collected in a component called the supply manifold, which leads the air toward the central conduit where the turbine is located. Once the air has passed through the turbine, it is passed to the return manifold which distributes the air to the return conduits for its return into.the air chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic which depicts a possible configuration of the invention having 6 air chamber;

Fig. 2 is a schematic of an exploded view of the assembly including the main parts of the apparatus referred in the present invention;

Figs. 3 and 4 show a section view of the submerged air chamber and explain the principle that the present invention uses to create the airflow that drives the turbine;

Fig. 5 is a top view of a simplified array of 6 air chambers divided in different zones regarding the waves in a given instant of time, and is intended to explain the principle that the present invention uses to have a more uniform flow;

Fig. 6 is a complement of fig. 5 and shows an array, a few waves, and its direction of propagation, and also shows what part of the wave is used to create the supply airflow, and what part is used to create the return airflow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus to use the ocean wave energy, object of the present invention, is a device which uses the ocean wave's energy to rotate a wind turbine (7). It comprises an array of submarine air chambers (1) connected to a wind turbine (7). Said air chambers (1) are fixed to the ocean floor through the mooring supports (2) and are partially filled with water and partially filled with air. Each air chamber (1) has an opening in the bottom which allows the ocean water pressure from the near surroundings to be transmitted to the interior of the air chamber (1). Said opening, allows the water to freely enter and exit the air chamber (1) in accordance with the relative pressures in the exterior and interior of the air chamber (1) in a given instant of time.

Since air and water share the space in the interior of the air chamber (1) and are .in direct contact, pressure variations in the exterior do impact air and water in the interior of the air chamber (1). Such a pressure depends almost exclusively from the water height and such a height varies with regards of the wave height.
Therefore, the pressure around a given air chamber (1) depends on its position relative to the wave. Being an array of air chambers (1), and being each of them in different positions relative to the waves, a pressure difference exists between the different air chambers (1), and then an airflow is induced. The airflow moves from an air chamber (1) at a higher pressure toward another at a lower pressure.
This is the basic mechanism used in the present invention to create the airflow which rotates the wind turbine (7).

Each air chamber (1) has two conduits, one supply conduit (3) to conduct air from the interior of the air chamber (1) toward the supply manifold (5), and one return conduit (10) to conduct air from the return manifold toward the interior of the air chamber (1).

The air chamber (1) is kept approximately in vertical position by the action of the buoyant force of the air (13) in its interior and fixed to the ground by the mooring means (2). While the crest (12) is approximating above the air chamber (1), the ambient pressure gradually increases and forces the air (13) to go to another place at lower pressure. The displacement of the air (13) outward the air chamber can be seen in the change of the water level from the position (14b) to the position (14a). Since the return check valve (11) is closed in the direction outward the air chamber (1), the only via available for the air is the supply conduit means (3). The supply check valve (4) is open at that instant since it allows flow in the direction toward the supply manifold (5).
Check valves (4 & 11) are mounted in opposite direction in such a way which keep the flow unidirectional along all the components which conduct air, being those the supply conduit (3), return conduit (10), supply manifold (5), return manifold (9) and central conduit (6).
Whenever the wave height is excessively high with regards the air chamber's (1) dimensions, the water level (14a) raises and action the floating valve (8) which closes to prevent the water intrusion toward the conduits during large waves.

The opposite process comes when the wave trough (15) is approximating to the air chamber (1) and it is explained in Figure 3. In this case, the ambient pressure gradually decreases and forces the air to go inward the air chamber for being in there at lower pressure. The displacement of the air (13) inward the air chamber can be seen in the change of the water level from the position (14a) to the position (14b). Since supply check valve (4) is closed in the direction toward the air chamber (1), then, the air is coming only from the return means (10).
Return check valve (11) is open at that instant of time.

Supply manifold (5) receives air from a plurality of supply conduit means (3) coming from several individual air chambers (1) from the array and discharges it into the central conduit (6) entrance. The air flows unidirectionally and rotates the wind turbine (7) which is located inside the central conduit (6). The airflow pass toward the return manifold (9) which distributes the air to a plurality of return conduit means (10). Finally air is returned to the individual air chambers (1).

Once the energy from the ocean waves is transformed into mechanical energy, this can be used for different applications as needed. Examples of such applications are: electricity generation, Hydrogen and Oxygen generation by electrolysis, water pumping, and sea water desalination.

Intermittency of the airflow, affects negative and directly the performance of the wind turbine (7). Then, the more uniform the airflow can be, the better the performance is. Nevertheless, the airflow produced by a single air chamber (1) is completely intermittent by its own nature, since it follows the sinusoidal form of the wave. Figure 5 and 6 assume the wave propagates in the direction of the arrow showed in Figure 6, and divide the wave into 3 different zones regarding the action a given region produce in the air chamber (1). All air chambers (1) within zone A, are supplying air toward the turbine, those which are within zone B, are returning air toward the air chambers (1), and those which are within zone T, are in a transition zone ant then, pumping no air. All the former assuming a given instant of time when the wave is as showed.

The present invention is modular by nature due to two main reasons: i) to minimize the costs, since manufacturing, and handling modules or parts, is cheaper and simpler rather than handling a huge device, and ii) to minimize the intermittency of the flow which feed the wind turbine (7). Intermittency is minimized by superposing a plurality of sinusoidal flows at a different wave phases. In such a way, the net flow is a collective flow much more uniform than the single source flow coming from each air chamber (1). Figure 5 shows a simplified array with only a few air chambers (1) where each of them is under a different wave phase. Parameters such as spacing, number of air chambers (1), and shape of the array, play an important role to minimize intermittency.

An additional feature of the present invention is that it is able to operate with a flow other than air, as long as it is less dense than salt water.

It is also possible to locate the central conduit (6) and the wind turbine (7) either submerged and moored to the ocean floor, or floating over the water surface, or moored on-shore, out of the water. The former is possible since the fluid in its interior is less dense than salt water, and because the conduits net is a closed system.

Current wave energy technology is not competitive in applications such as electricity generation due to the high cost while compared to fossil fuel technologies. In order to take wave technology to the commercial stage, it is necessary that such technology be, not only ambient friendly but also, competitive in terms of cost. This is probably the only way to spread out the use of the renewable energies and slow down the emissions of the green house gases.

Claims (6)

1. An apparatus for utilizing the ocean wave energy comprising-a) an array of at least ten submerged air chambers containing air and water inside it, which proportion varies according to the surrounding pressure imposed by the waves to the apparatus, and having each air chamber an opening in wherever the bottom area that permits the exterior pressure from the water to impact in the interior of the air chamber;
b) a mooring means to keep every air chamber submerged and moored to the ocean floor;
c) supply conduit means that air will be led from the said individual air chambers to the supply manifold means;
d) supply check valve means that for each supply conduit only air flow in the direction toward the turbine entrance is permitted;

e) a supply manifold means that collects the air coming from said supply conduits into a central flow which supply the turbine;
f) a central conduit means wherein the air flows unidirectionally and wherein the wind turbine is mounted;
g) a turbine which rotates whenever an airflow is present, h) a return manifold means that takes the air coming from said wind turbine toward the return conduit means;
i) return conduit means that lead the air from said return manifold means to said air chambers;
j) return check valve means for each return conduit means permitting airflow only in the direction toward the air chamber.

2. The apparatus according to claim 1, wherein the check valve means make the airflow inside the supply conduit means, return conduit means and central conduit means is unidirectional.

3. The system according to claim 1, wherein a fluid less dense than water is used to drive the turbine.

4. The system according to claim 1, wherein the supply and return conduit means inside the chamber have a buoyant valve means that secure the conduit means against water intrusion whenever the water level inside the air chamber is very high.

5. The system according to claim 1, wherein the turbine is placed on shore.

6. The system according to claim 1, wherein the turbine is submerged.