Note: Descriptions are shown in the official language in which they were submitted.
CA 02692188 2009-12-21
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
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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
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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.
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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.
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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,
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- 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;
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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
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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
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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.
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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.
