Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02366043 2001-12-20
METHOD AND APPARATUS FOR CONVERTING TIDAL POWER INTO
ELECTRICAL ENERGY
The present invention relates to a method and apparatus for converting tidal
power into electrical energy and more particularly, the present invention
relates to
caisson type device having a paddle wheel which may be variably positioned
within a
tidal stream.
As the moon orbits around the earth, the gravitational force of the moon and
sun pull the oceans creating the tides. It is undoubtedly the most powerful
active force
on earth. An immense amount of energy is inherent in these large bodies of
moving
water. To harness a small fraction of this energy and convert it into
electricity, many
innovative methods have been conceived.
The net energy in a tidal stream is very large. When a tidal stream is
restricted
by two points of land, the velocity is increased considerably, condensing the
net energy
through the constricting points of land. To extract a significant amount of
energy from
this relatively slow moving body of water, a large cross-section of the tidal
stream
needs to be harnessed. The simplest way to achieve this goal is through the
use of a
large paddle wheel or underwater sail. The energy extracted is directly
proportional to
the size of the paddle wheel.
For a paddle wheel to operate efficiently, only the lower half of the wheel
should
be submerged below the surface of the water, leaving the upper half of the
wheel
exposed to surface elements such as wind and waves. The paddle wheel structure
need also contend with surface conditions such as slab ice and floating
debris.
A housing may be constructed to protect the paddle wheel(s) but this would add
considerable height, cost and complexity to a potential structure. A housing
would also
elevate the centre of gravity, a characteristic not conducive to stability
during tow-out
and transportation operations. As well, to protect the paddle wheel from
floating debris,
the housing would have to protrude below the surface of the water, restricting
the flow
of water to the paddles.
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The most restrictive characteristic of a large structure protruding through
the
surface of the water is that it creates a barrier against surface ice flow.
This can be
disastrous, as the force behind a restricted ice flow can be fatal. With river
ice,
restricting the flow can mean serious flooding upstream. Marine structures
that
encounter ice are generally designed to minimize resistance. With the type of
structure
noted above, this would not be possible.
In numerous cases, the fastest (higher energy) tidal streams are found where
large bodies of water are fully or partially endosed by land except for one or
more
openings to the sea. In a lot of these cases, it would be desirable to link
the two or
more points of land adjacent to the openings. Often, the depth of water or
span at the
opening does not make a conventional bridge feasible. The preferred embodiment
is
intended to generate electricity at these tidal stream openings as well as
potentially
provide the base foundations for such a bridge.
The original and simplest method of hamessing tidal power was a barrage and
paddle wheel. Subsequently, many intricate methods using a differential of
water
elevations have been devised. In recent years, barrage of coastal waters has
elicited
considerable public opposition. Barrage restricts recreational activities and
commercial
traffic. Due to the growing opposition, the focus of harnessing tidal power
has shifted to
tidal streams and non-coastal barrage systems. This shift has introduced new
challenges and obstacles, as tidal streams are generally found in deeper and
more
treacherous waters. Structures built at such locations are susceptible to
ocean storms,
slab ice and icebergs. There have been systems developed to hamess tidal
streams in
ice-free locations that are relatively sheltered. Unfortunately, no
arrangement capable
of withstanding the environmental forces of icebergs, slab ice and severe
ocean storm
waves has become available.
In the prior art a wide variety of devices have been proposed. Typical of the
arrangements is referenced in United States Patent No. 4,717,831, issued
January 5,
1988, to Kikuchi. In the document a power generator is disclosed. The
generator
provides a plurality of paddle wheels fixed in place essentially immovable and
exposed
without any coverage from debris. It would therefore appear that the Kikuchi
system
would be vulnerable to damage if used in more extreme environments.
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Mayo, Jr., in United States Patent No. 6,208,037, issued March 27,2001,
provides a power generating system which is also a permanent structure and is
designed for fixture within a waterway. Generally speaking, these systems are
cumbersome, expensive and require the use of one or more operators.
United States Patent No.5,440,175, issued to Mayo, Jr. et al., August 8,1995,
discloses a river bridge electrical generator unit. This unit is, similar to
those discussed
above, for barrage and thus does not overcome the limitations outlined in the
discussion herein previously.
Other references in the realm of the present invention include United States
Patent Nos. 5,430,332, 4,511,808, and 4,001,596.
In view of the state of the art in this niche of civil engineering, there
exists a
distinct need for a versatile, durable and relocatable tidal power system
which is
absent the disadvantages connected with the current devices. The present
invention
addresses the requirements for a high-performance system for efficient
extraction of
the energy inherent in tides.
One object of the present invention is to provide a caisson for creating
electrical
power from a tidal stream, comprising:
a body having an inlet and an outlet to allow the passage of water there
through;
a compartment extending between the inlet and the outlet;
at least one paddle wheel rotatably mounted within the compartment for contact
with incoming water;
means for pressurizing the compartment to reduce the volume of water present
in the compartment when the caisson is submerged in the stream;
pump means connected with the at least one paddle wheel; and
generator means connected to the pump means for generating electrical power.
A further object of the present invention is to provide a method of converting
mechanical energy from tidal motion to electrical energy, comprising:
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CA 02366043 2001-12-20
providing a movable paddle wheel within an enclosure, the enclosure having an
inlet and an outlet for facilitating contact of the paddle wheel with a tidal
stream;
connecting the paddle wheel to means for converting energy created during
rotation of the paddle wheel to electrical energy;
positioning the paddle wheel into contact with the stream;
selectively pressurizing the enclosure to alter the level of submersion of the
paddle wheel in the water within the enclosure; and
collecting energy created from the tidal motion of the paddle wheel.
Having thus described the invention, reference will now be made to the
accompanying drawings illustrating preferred embodiments and in which:
Figure 1 is a perspective view of the apparatus according to one embodiment in
the present invention;
Figure 2 is a plan view of the arrangement as positioned with a bridge deck;
Figure 3 is a front elevation view of the arrangement shown in Figure 1;
Figure 4 is a cross-section of the apparatus;
Figure 5 is a plan view of the access support and hydraulic drive system; and
Figure 6 is a side elevation view of the access support hydraulic drive
system.
Similar numerals used in the specification denote similar elements.
Referring now to the drawings, and in particular Figures 1 through 4, shown is
one embodiment of the present invention where numeral 10 denotes the overall
structure. In Figure 1, the body includes a base 12, spaced apart side walls
14 and 16
and front wall 18 and rear wall 20. A top wall 22 is provided with bridge
truss members
24 and 26. As illustrated in the drawings, the arrangement effectively
provides a base
portion, intermediate portion and a top portion.
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In greater detail, the structure 10 provides an internal volume or compartment
28 which is shown best in Figure 4. Intermediate of the structure 10 is a
series of
portals 30 which permit a tidal stream to pass through the compartment 28 from
one
side to the other. The portals 30 are defined by a plurality of spaced apart
fins 32
which act as means for directing the tidal stream into the internal volume 28
of the
structure 10 and also additionally provide structural support for the opening
within
which they are positioned. The top wall 22 includes a downwardly directed wall
34.
Wall 34 is oriented about the perimeter of the structure and, when the
structure 10 is
positioned in the water according to one embodiment, the downwardly directed
wall 34
contacts the water line, generally denoted by W. In this manner, when the
arrangement is positioned in situ within the water, packed ice flow and slabs
of ice (not
shown) are pushed onto and across top wall 22. Accordingly, packed slab ice is
not
restricted by the relatively large structure. This significantly reduces the
lateral force
applied the structure 10 by ice flows.
Wall segment 34 cooperates with the individual fins 32 to prevent large debris
from entering into the compartment 28 which would otherwise damage or impair
the
function of the paddle wheel 36.
Paddle wheel 36 rotates about a transverse access relative to the vertical
orientation of the device about axis 38 and includes a plurality of radially
spaced apart
support members 40. A flexible material 42 extends between the supports 40.
As water flows through the structure 10, the force slowly rotates paddle wheel
36 and therefore creates a torque on axis 38. In order to convert the axial
torque into
electricity, hydraulic pumps 44 are connected to the axis 38 through a
transfer case 46
on both sides of the axis 38. The axis 38 of the paddle wheel 36 and the
hydraulic
pumps 44 are supported on a frame 50 (shown in Figure 6), which frame 50 is
secured
internally of compartment 28 and in particular to one of walls 14 or 16. This
fixes the
elevation of the paddle wheel 36. Adjustment of the elevation of the wheel in
the sea
water is achieved by alternate means discussed hereinafter.
The hydraulic pressure from each of the hydraulic pumps 44 is combined to
drive at least one electric generator 52 through a hydraulic drive motor 54.
The drive
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motors 54 and the generators 52 are positioned above water level, W, for
purposes of
safety. It is well known by those skilled in the art as to the mechanism of
conversion of
axial torque to electricity.
In view of the altemating flow pattern of a tidal stream, the hydraulic pumps
44
are constructed such that positive hydraulic pressure is created independent
of paddle
wheel 36 direction. The crankshaft of the pump (not shown) typically would
drive one
or more pistons whereby a spring loaded supply valve (not shown) typically
controls
hydraulic fluids supplied to each piston. When the piston is extracted, the
negative
pressure opens the supply valve (not shown) and the hydraulic fluid is drawn
into the
cylinder (not shown). During compression, the spring loaded valve (in the
other
direction) allows the pressurized fluid to flow into the pressure manifold
(not shown).
Accordingly, each cycle pressurizes hydraulic fluid regardless of the crank
shaft
direction. These principals are well known to those skilled in the art.
One of the most attractive features with the instant structure 10 relates to
the
feature of lowering the resistance of the water on paddle wheel 36 above axis
38. In
order to achieve this result, and particularly, the resistance of the water on
paddle
wheel 36 above axis 38, the water level inside the compartment 28 may be
lowered to
just below axis 38. This is achieved by pressurizing compartment 28 with air.
To this
end, an air compressor 58 is provided to compress the air to the pressure
equal to that
of the water head pressure at the axis depth. Generally speaking, the air
pressure
required is approximately half that required to inflate a conventional
automobile tire. In
order to contain the pressurized air in the compartment 28, portals 30 are
positioned
together with the wall segment 34 to be just below the desired level of water,
W, in
compartment 28. Once the water level is lowered to the desired point, further
compression is only required to replace air that escapes through the roof and
wall or
into the water.
As mentioned herein previously, the fins 32 are useful to guide water into the
compartment 28 of structure 10. To this end, and in order to further assist in
guiding
water into compartment 28, each portal may include a angularly disposed wall,
broadly
denoted by numeral 60 at the upper end of the portal and a further angularly
inclined
wall 62 at the bottom end the portal and at the top end of wall 18. In this
manner, a
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narrowing of the opening of the portal is achieved and, as is well known in
the art, this
provides an increase in the velocity of the tidal stream entering the
compartment 28
and thus increases the angular velocity of paddle wheel 36.
With respect to the segment 60, this is preferably a hingedly connected wall
or
gate which, in the example, is hingedly connected above portal 30 at 64. It
will be
understood that each of the portals will include the hingedly connected
segment 60
which may be moved from the location as shown in Figure 4 to a second position
shown in chain line where the wall 60 is swung outwardly. This permits closure
of the
respective portal for maintenance of the paddle wheel 36 and compartment 28.
As discussed herein previously, the paddle wheel 36 preferably incorporates a
high strength fabric held snugly within frame members 40 to achieve a
underwater sail.
As a preferred feature, the fabric will be held tautly near the axis, but
slack at the outer
edge of the wheel. This facilitates water flow out of the fabric paddle as it
lifts out of
the water. The slack end may optionally be weighted so that on reentry, the
outer
edge of the fabric paddle enters the water first and reduces drag on the wheel
in the
first few meters.
As a further advantageous feature, in order to reduce water flow from the
sides
of the paddle wheel 36, each frame 40 may be fitted with a flexible edge 66
shown in
Figure 6. This arrangement is useful for brushing the edges of the walls.
Depending upon the final intended use of the structure 10, the same may be
fixedly secured to the bedrock sea floor (not shown) or simply be gravity
based when
installed. Once installed, a plurality of individual ballast cells 68 bounded
by the base
wall 12 and walls 70 of compartment 28 may be charged with solid ballast in
order to
increase the overturning movement of resistantce of the structure. Depending
on the
environment in which the arrangement is used.
For further support, the portals 30 may include x-braces 72 shown best in
Figure 3, for further structural stability, the side chambers 74 of the
structure can act as
buoyancy chambers. Once the structure 10 has been installed in its
environment, the
chambers may then be filled with ballast to further increase the overtuming
moment of
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resistance. The chambers 74 are designed to provide lateral sheer and thus
structural
stability to the structure. The side chambers thus transfer lateral sheer from
the upper
to the lower section of the structure and this is further supported by tubular
bracing 72
which contributes to the overall structural integrity of the device.
Remaining on the discussion of Figure 3, shown is the structure as it would
support an independent bridge truss 76. In this manner, the structure could be
used
as a bridge column foundation and allow for the transportation of vehicles. As
discussed herein previously, supports 24 and 26 extending upwardly from wall
22 act
as supports for the truss.
It will be understood that the wall 22 of the structure 10 has to be capable
of
with standing significant air pressure within compartment 28 and additionally
the force
of ice slabs (not shown) sliding over the top. In a preferred embodiment, the
construction material would comprise reinforced concrete.
It will be understood that any number of the structures may be connected
together to act as a tidal fence and further that the individual arrangements
may be
used as bridge supports.
Although embodiments of the invention have been described above, it is not
limited thereto and it will be apparent to those skilled in the art that
numerous
modifications form part of the present invention insofar as they do not depart
from the
spirit, nature and scope of the claimed and described invention.
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