U.S. patent application number 14/802474 was filed with the patent office on 2015-11-12 for ocean thermal energy conversion cold water pipe.
The applicant listed for this patent is The Abell Foundation, Inc.. Invention is credited to Andrew Rekret, William Schulz, Henry Sibenaller.
Application Number | 20150322928 14/802474 |
Document ID | / |
Family ID | 44276504 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150322928 |
Kind Code |
A1 |
Rekret; Andrew ; et
al. |
November 12, 2015 |
Ocean Thermal Energy Conversion Cold Water Pipe
Abstract
An offshore power generation structure comprising a submerged
portion having heat exchange sections, power generation sections, a
cold water pipe and a cold water pipe connection. The cold water
pipe comprises a plurality of offset first and second staved
portions.
Inventors: |
Rekret; Andrew; (Toronto,
CA) ; Sibenaller; Henry; (Greensburg, PA) ;
Schulz; William; (Manassas, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Abell Foundation, Inc. |
Baltimore |
MD |
US |
|
|
Family ID: |
44276504 |
Appl. No.: |
14/802474 |
Filed: |
July 17, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12691655 |
Jan 21, 2010 |
9086057 |
|
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14802474 |
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Current U.S.
Class: |
60/641.7 ;
138/172; 139/177 |
Current CPC
Class: |
Y10T 29/49826 20150115;
F16L 1/15 20130101; Y02E 10/34 20130101; Y02E 10/30 20130101; F16L
9/22 20130101; F03G 7/05 20130101 |
International
Class: |
F03G 7/05 20060101
F03G007/05; F16L 9/22 20060101 F16L009/22 |
Claims
1. A pipe comprising: an elongated tubular structure having an
outer surface, a top end and a bottom end, the tubular structure
comprising: a plurality of first and second stave segments, each
stave segment having a top portion and a bottom portion, wherein
the top portion of the second stave segment is offset from the top
portion of the first staved segment.
2. The pipe of claim 1 further comprising a strake at least
partially wound around the pipe on the outside surface of the
tubular structure.
3. The pipe of claim 2 wherein the strake extends from the bottom
end to the top end of the tubular structure and at least partially
covers the outer surface thereof.
4. The pipe of claim 2 wherein the strake comprises the same
material as the first and second stave segments.
5. The pipe of claim 1 wherein each stave segment further comprises
a tongue on a first side and a groove on a second side for mating
engagement with an adjacent stave segment.
6. The pipe of claim 1 wherein each stave segment is between 30
feet and 90 feet between the bottom portion and the top
portion.
7. The pipe of claim 5 wherein each stave segment is between 10
inches and 120 inches between the first side and the second
side.
8. The pipe of claim 1 wherein each stave segment is pulltruded,
extruded, or molded.
9. The pipe of claim 1 wherein each stave segment comprises
polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC),
fiber reinforced plastic (FRP), reinforced polymer mortar (RPMP),
polypropylene (PP), polyethylene (PE), cross-linked high-density
polyethylene (PEX), polybutylene (PB), acrylonitrile butadiene
styrene (ABS); polyester, fiber reinforced polyester, nylon
reinforced polyester, vinyl ester, fiber reinforced vinyl ester,
nylon reinforced vinyl ester, concrete, ceramic, or a composite of
one or more thereof.
10. The pipe of claim 1 wherein each stave segment comprises at
least one internal void.
11. The pipe of claim 10 wherein the at least one void is filled
with water, polycarbonate foam, or syntactic foam.
12. The pipe of claim 10 wherein the plurality of first and second
stave segments are adhesively bonded.
13. The pipe of claim 10 wherein the pipe forms a cold water pipe
for an OTEC power plant.
14. An offshore power generation structure comprising a submerged
portion, the submerged portion further comprising: a heat exchange
portion; a power generation portion; and a cold water pipe
comprising a plurality of offset first and second stave
segments.
15. The offshore power generation structure of claim 14 wherein
each stave segment comprises polyvinyl chloride (PVC), chlorinated
polyvinyl chloride (CPVC), fiber reinforced plastic (FRP),
reinforced polymer mortar (RPMP), polypropylene (PP), polyethylene
(PE), cross-linked high-density polyethylene (PEX), polybutylene
(PB), acrylonitrile butadiene styrene (ABS); polyester, fiber
reinforced polyester, vinyl ester, reinforced vinyl ester,
concrete, ceramic, or a composite of one or more thereof.
16. The offshore power generation structure of claim 14 wherein the
first and second stave segments are adhesively bonded.
17. The offshore power generation structure of claim 14 wherein the
cold water pipe further comprises a ribbon at least partially
rapping the cold water pipe.
18. A method of forming a cold water pipe for use in an OTEC power
plant, the method comprising: forming a plurality of first and
second stave segments; and adhesively bonding alternating first and
second stave segments such that the second stave segments are
offset from the first stave segments to form a continuous elongated
tube.
19. The method of claim 18 wherein each of the stave segments
comprises polyvinyl chloride (PVC), chlorinated polyvinyl chloride
(CPVC), fiber reinforced plastic (FRP), reinforced polymer mortar
(RPMP), polypropylene (PP), polyethylene (PE), cross-linked
high-density polyethylene (PEX), polybutylene (PB), acrylonitrile
butadiene styrene (ABS); polyester, fiber reinforced polyester,
vinyl ester, reinforced vinyl ester, concrete, ceramic, or a
composite of one or more thereof.
20. The method of claim 18 wherein comprises a tongue on a first
side and a groove on a second side for mating engagement with an
adjacent stave segment.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of and claims
priority to U.S. application Ser. No. 12/691,655, filed on Jan. 21,
2010. The entire contents of the related application is hereby
incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to ocean thermal energy conversion
power plants and more specifically to floating, minimum heave
platform, multi-stage heat engine, ocean thermal energy conversion
power plants.
BACKGROUND
[0003] Energy consumption and demand throughout the world has grown
at an exponential rate. This demand is expected to continue to
rise, particularly in developing countries in Asia and Latin
America. At the same time, traditional sources of energy, namely
fossil fuels, are being depleted at an accelerating rate and the
cost of exploiting fossil fuels continues to rise. Environmental
and regulatory concerns are exacerbating that problem.
[0004] Solar-related renewable energy is one alternative energy
source that may provide a portion of the solution to the growing
demand for energy. Solar-related renewable energy is appealing
because, unlike fossil fuels, uranium, or even thermal "green"
energy, there are few or no climatic risks associated with its use.
In addition, solar related energy is free and vastly abundant.
[0005] Ocean Thermal Energy Conversion ("OTEC") is a manner of
producing renewable energy using solar energy stored as heat in the
oceans' tropical regions. Tropical oceans and seas around the world
offer a unique renewable energy resource. In many tropical areas
(between approximately 20.degree. north and 20.degree. south
latitude) the temperature of the surface sea water remains nearly
constant. To depths of approximately 100 ft the average surface
temperature of the sea water varies seasonally between 75.degree.
F. and 85.degree. F. or more. In the same regions, deep ocean water
(between 2500 ft and 4200 ft or more) remains a fairly constant
40.degree. F. Thus, the tropical ocean structure offers a large
warm water reservoir at the surface and a large cold water
reservoir at depth, with a temperature difference between the warm
and cold reservoirs of between 35.degree. F. to 45.degree. F. This
temperature difference remains fairly constant throughout the day
and night, with small seasonal changes.
[0006] The OTEC process uses the temperature difference between
surface and deep sea tropical waters to drive a heat engine to
produce electrical energy. OTEC power generation was identified in
the late 1970's as a possible renewable energy source having a low
to zero carbon footprint for the energy produced. An OTEC power
plant, however, has a low thermodynamic efficiency compared to more
traditional, high pressure, high temperature power generation
plants. For example, using the average ocean surface temperatures
between 80.degree. F. and 85.degree. F. and a constant deep water
temperature of 40.degree. F., the maximum ideal Carnot efficiency
of an OTEC power plant will be 7.5 to 8%. In practical operation,
the gross power efficiency of an OTEC power system has been
estimated to be about half the Carnot limit, or approximately 3.5
to 4.0%. Additionally, analysis performed by leading investigators
in the 1970's and 1980's, and documented in "Renewable Energy from
the Ocean, a Guide to OTEC" William Avery and Chih Wu, Oxford
University Press, 1994 (incorporated herein by reference),
indicates that between one quarter to one half (or more) of the
gross electrical power generated by an OTEC plant operating with a
AT of 40.degree. F. would be required to run the water and working
fluid pumps and to supply power to other auxiliary needs of the
plant. On this basis, the low overall net efficiency of an OTEC
power plant converting the thermal energy stored in the ocean
surface waters to net electric energy has not been a commercially
viable energy production option.
[0007] An additional factor resulting in further reductions in
overall thermodynamic efficiency is the loss associated with
providing necessary controls on the turbine for precise frequency
regulation. This introduces pressure losses in the turbine cycle
that limit the work that can be extracted from the warm sea water.
The resulting net plant efficiency would then be between 1.5% and
2.0%.
[0008] This low OTEC net efficiency compared with efficiencies
typical of heat engines that operate at high temperatures and
pressures has led to the widely held assumption by energy planners
that OTEC power is too costly to compete with more traditional
methods of power production.
[0009] Indeed, the parasitic electrical power requirements are
particularly important in an OTEC power plant because of the
relatively small temperature difference between the hot and cold
water. To achieve maximum heat transfer between the warm sea water
and the working fluid, and between the cold sea water and the
working fluid large heat exchange surface areas are required, along
with high fluid velocities. Increasing any one of these factors can
significantly increases the parasitic load on the OTEC plant,
thereby decreasing net efficiency. An efficient heat transfer
system that maximizes the energy transfer in the limited
temperature differential between the sea water and the working
fluid would increase the commercial viability of an OTEC power
plant.
[0010] In addition to the relatively low efficiencies with
seemingly inherent large parasitic loads, the operating environment
of OTEC plants presents design and operating challenges that also
decrease the commercial viability of such operations. As previously
mentioned, the warm water needed for the OTEC heat engine is found
at the surface of the ocean, to a depth of 100 ft or less. The
constant source of cold water for cooling the OTEC engine is found
at a depth of between 2700 ft and 4200 ft or more. Such depths are
not typically found in close proximity to population centers or
even land masses. An offshore power plant is required.
[0011] Whether the plant is floating or fixed to an underwater
feature, a long cold water intake pipe of 2000 ft or longer is
required. Moreover, because of the large volume of water required
in commercially viable OTEC operations, the cold water intake pipe
requires a large diameter (typically between 6 and 35 feet or
more). Suspending a large diameter pipe from an offshore structure
presents stability, connection and construction challenges which
have previously driven OTEC costs beyond commercial viability.
[0012] Additionally, a pipe having significant length to diameter
ratio that is suspended in a dynamic ocean environment can be
subjected to temperature differences and varying ocean currents
along the length of the pipe. Stresses from bending and vortex
shedding along the pipe also present challenges. And surface
influences such as wave action present further challenges with the
connection between the pipe and floating platform.
[0013] An enormous challenge of OTEC operations has been the need
to fully assemble a pipe having a length of 2000 ft to 4000 ft or
more and transporting such a pipe to the operational site.
Furthermore, a greater challenge has been upending such a pipe for
installation to a floating platform and ultimately making a
connection to the platform.
[0014] Previous OTEC cold water pipe construction has used
segmented pipes. A segmented pipe is a pipe constructed of
cylindrical segments joined together in series to the obtain the
desired length. Segmented pipes are disclosed in "Ocean Thermal
Energy Conversion Cold Water Pipe Preliminary Design Project," TRW
Energy Systems Group, Final Report, Nov. 20, 1979 (incorporated by
reference herein in its entirety). Segmented pipes can be heavier
and less flexible than continuously constructed pipes. Moreover,
various connection methods can interfere with the flow of the fluid
through the pipe.
[0015] A cold water pipe intake system having desirable
construction, installation and performance criteria would increase
the viability of an OTEC power plant.
SUMMARY
[0016] Aspects of the present invention are directed to a power
generation plant utilizing ocean thermal energy conversion
processes.
[0017] Further Aspects of the invention relate to an offshore OTEC
power plant having improved overall efficiencies with reduced
parasitic loads, greater stability, lower construction and
operating costs, and improved environmental footprint. Other
aspects include large volume water conduits that are integral with
the floating structure. Modularity and compartmentation of the
multi-stage OTEC heat engine reduces construction and maintenance
costs, limits off-grid operation and improves operating
performance. Still further aspects provide for a floating platform
having integrated heat exchange compartments and provides for
minimal movement of the platform due to wave action. The integrated
floating platform may also provide for efficient flow of the warm
water or cool water through the multi-stage heat exchanger,
increasing efficiency and reducing the parasitic power demand.
Aspects of the invention can promote an environmentally neutral
thermal footprint by discharging warm and cold water at appropriate
depth/temperature ranges. Energy extracted in the form of
electricity reduces the bulk temperature to the ocean.
[0018] Still further aspects of the invention relate to a cold
water pipe for use with an offshore OTEC facility, the cold water
pipe being an offset staved, continuous pipe.
[0019] An aspect relates to a pipe that comprises an elongate
tubular structure having an outer surface, a top end and a bottom
end. The tubular structure comprises a plurality of first and
second staved segments, each stave segment has a top portion and a
bottom portion, wherein the top portion of the second stave segment
is offset from the top portion of the first staved segment.
[0020] A further aspect relates to a pipe comprising a ribbon or a
strake at least partially wound around the pipe on the outside
surface of the tubular structure. The ribbon or strake can be
circumferentially wound around the outer surface of the top portion
of the pipe, the middle portion of the pipe, or the lower portion
of the pipe. The ribbon or strake can be circumferentially wound
around the entire length of the pipe. The ribbon or strake can be a
be attached so as to lay substantially flat against the outer
surface of the pipe. The ribbon or strake can be attached so as to
protrude outwardly from the outer surface of the pipe. The ribbon
or strake can be made of the same or different material as the
pipe. The ribbon or strake can be adhesively bonded to the outer
surface of the pipe, mechanically bounded to the outer surface of
the pipe, or use a combination of mechanical and adhesive bonds to
attach to the outer surface of the pipe.
[0021] Further aspects of the invention relate to an offset staved
pipe wherein each stave segment further comprises a tongue on a
first side and a groove on a second side for mating engagement with
an adjacent stave segment. The offset stave pipe can include a
positive locking system to mechanically couple a first side of one
stave to the second side of a second stave. Stave can be joined
vertically from the top portion of one stave to the bottom portion
of an adjacent stave using biscuit joinery. In an alternative
embodiment, the top portion of a stave and the bottom portion of a
stave can each include a joining void, such that when the top
portion of a first stave is joined with the bottom portion of a
second stave, the joining voids align. A flexible resign can be
injected into the aligned joining voids. The flexible resign can be
used to fill gaps in any joined surfaces. In aspects of the
invention the flexible resign is a methacrylate adhesive.
[0022] Individual staves of the current invention can be of any
length. In aspects each stave segment is between 20 feet and 90
feet measured from the bottom portion to the top portion of the
stave. Stave segments can be sized to be shipped by standard
inter-modal container. Individual stave segments can be between 10
inches and 120 inches wide. Each stave segment can be between 1
inch and 24 inches thick.
[0023] In aspects of the invention stave segments can be pultruded,
extruded, or molded. Stave segments can comprise polyvinyl chloride
(PVC), chlorinated polyvinyl chloride (CPVC), fiber reinforced
plastic (FRP), reinforced polymer mortar (RPMP), polypropylene
(PP), polyethylene (PE), cross-linked high-density polyethylene
(PEX), polybutylene (PB), acrylonitrile butadiene styrene (ABS);
polyester, fiber reinforced polyester, nylon reinforced polyester,
vinyl ester, fiber reinforced vinyl ester, nylon reinforced vinyl
ester, concrete, ceramic, or a composite of one or more
thereof.
[0024] In further aspects of the invention the materials selected
can provide neutral buoyancy of the fully assembled pipe.
[0025] In further aspects of the invention, a stave segment can
comprise at least one internal void. At least one void can be
filled with water, resin, adhesive, polycarbonate foam, or
syntactic foam.
[0026] In aspects of the invention, the pipe is a cold water intake
pipe for an OTEC power plant.
[0027] A still further aspect of the invention relates to an
offshore power generation structure comprising a submerged portion,
the submerged portion further comprises: a heat exchange portion; a
power generation portion; and a cold water pipe comprising a
plurality of offset first and second stave segments.
[0028] Yet another aspect of the invention relates to a method of
forming a cold water pipe for use in an OTEC power plant, the
method comprises: forming a plurality of first and second stave
segments joining alternating first and second stave segments such
that the second stave segments are offset from the first stave
segments to form a continuous elongated tube.
[0029] A further aspect of the invention relates to a submerged
vertical pipe connection comprising: a floating structure having a
vertical pipe receiving bay, wherein the receiving bay has a first
diameter; a vertical pipe for insertion into the pipe receiving
bay, the vertical pipe having a second diameter smaller than the
first diameter of the pipe receiving bay; a partially spherical or
arcuate bearing surface; and one or more movable detents, pinions
or lugs operable with the bearing surface, wherein the detents
define a diameter that is different than the first or second
diameter when in contact with the bearing surface.
[0030] An additional aspect of the invention relates to a method of
connecting a submerged vertical pipe to a floating platform
comprising: providing a floating structure having a vertical pipe
receiving bay, wherein the pipe receiving bay has a first diameter,
providing a vertical pipe having a top end portion that has a
second diameter that is less than the first diameter; inserting the
top end portion of the vertical pipe into the receiving bay;
providing a bearing surface for supporting the vertical pipe;
extending one or more detents such that the one or more detents
have a diameter that is different from the first or second
diameters; contacting the one or more detents with the bearing
surface to suspend the vertical pipe from the floating
structure.
[0031] Aspects of the invention may have one or more of the
following advantages: a continuous offset staved cold water pipe is
lighter than segmented pipe construction; a continuous offset
staved cold water pipe has less frictional losses than a segmented
pipe;
[0032] individual staves can be sized to for easy transportation to
the OTEC plant operational site; staves can be constructed to
desired buoyancy characteristics; mass produced uniform parts
(i.e., staves) are ultimately cheaper and provide quality control
assurance than single unitary pipe (i.e. spiral wound pipes); OTEC
power production requires little to no fuel costs for energy
production; the low pressures and low temperatures involved in the
OTEC heat engine reduce component costs and require ordinary
materials compared to the high-cost, exotic materials used in high
pressure, high temperature power generation plants; plant
reliability is comparable to commercial refrigeration systems,
operating continuously for several years without significant
maintenance; reduced construction times compared to high pressure,
high temperature plants; and safe, environmentally benign operation
and power production. Additional advantages may include, increased
net efficiency compared to traditional OTEC systems, lower
sacrificial electrical loads; reduced pressure loss in warm and
cold water passages; modular components; less frequent off-grid
production time; minimal heave and reduced susceptibility to wave
action; discharge of cooling water below surface levels, intake of
warm water free from interference from cold water discharge.
[0033] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
DESCRIPTION OF DRAWINGS
[0034] FIG. 1 illustrates an exemplary prior-art OTEC heat
engine.
[0035] FIG. 2 illustrates an exemplary prior-art OTEC power
plant.
[0036] FIG. 3 illustrates OTEC structure of the present
invention.
[0037] FIG. 4 illustrates an offset staved pipe of an OTEC
structure of the present invention.
[0038] FIG. 5 illustrates a detailed image of an offset stave
pattern of the present invention.
[0039] FIG. 6 illustrates a cross sectional view of an offset
staved cold water pipe of the present invention.
[0040] FIGS. 7A-C illustrate various views of individuals staves of
the present invention.
[0041] FIG. 8 illustrates a tongue and groove arrangement of an
individual stave of the present invention.
[0042] FIG. 9 illustrates a positive snap lock between two staves
of the present invention.
[0043] FIG. 10 illustrates an offset staved cold water pipe
incorporating a reinforcing strake of the present invention.
[0044] FIG. 11 illustrates a method of cold water pipe construction
of the present invention.
[0045] FIGS. 12A and 12B illustrate an exemplary OTEC heat engine
of the present invention.
[0046] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0047] This invention relates to electrical power generation using
Ocean Thermal Energy Conversion (OTEC) technology. Aspects of the
invention relate to a floating OTEC power plant having improved
overall efficiencies with reduced parasitic loads, greater
stability, lower construction and operating costs, and improved
environmental footprint over convention OTEC power plants. Other
aspects include large volume water conduits that are integral with
the floating structure. Modularity and compartmentation of the
multi-stage OTEC heat engine reduces construction and maintenance
costs, limits off-grid operation and improves operating
performance. Still further aspects provide for a floating platform
having integrated heat exchange compartments and provides for
minimal movement of the platform due to wave action. The integrated
floating platform may also provide for efficient flow of the warm
water or cool water through the multi-stage heat exchanger,
increasing efficiency and reducing the parasitic power demand.
Aspects of the invention promote a neutral thermal footprint by
discharging warm and cold water at appropriate depth/temperature
ranges. Energy extracted in the form of electricity reduces the
bulk temperature to the ocean.
[0048] OTEC is a process that uses heat energy from the sun that is
stored in the Earth's oceans to generate electricity. OTEC utilizes
the temperature difference between the warmer, top layer of the
ocean and the colder, deep ocean water. Typically this difference
is at least 36.degree. F. (20 C). These conditions exist in
tropical areas, roughly between the Tropic of Capricorn and the
Tropic of Cancer, or even 20.degree. north and south latitude. The
OTEC process uses the temperature difference to power a Rankine
cycle, with the warm surface water serving as the heat source and
the cold deep water serving as the heat sink. Rankine cycle
turbines drive generators which produce electrical power.
[0049] FIG. 1 illustrates a typical OTEC Rankine cycle heat engine
10 which includes warm sea water inlet 12, evaporator 14, warm sea
water outlet 15, turbine 16, cold sea water inlet 18, condenser 20,
cold sea water outlet 21, working fluid conduit 22 and working
fluid pump 24.
[0050] In operation, heat engine 10 can use any one of a number of
working fluids, for example commercial refrigerants such as
ammonia. Other working fluids can include propylene, butane, R-22
and R-134a. Other commercial refrigerants can be used. Warm sea
water between approximately 75.degree. F. and 85.degree. F., or
more, is drawn from the ocean surface or just below the ocean
surface through warm sea water inlet 12 and in turn warms the
ammonia working fluid passing through evaporator 14. The ammonia
boils to a vapor pressure of approximately 9.3 atm. The vapor is
carried along working fluid conduit 22 to turbine 16. The ammonia
vapor expands as it passes through the turbine 16, producing power
to drive an electric generator 25. The ammonia vapor then enters
condenser 20 where it is cooled to a liquid by cold sea water drawn
from a deep ocean depth of approximately 3000 ft. The cold sea
water enters the condenser at a temperature of approximately
40.degree. F. The vapor pressure of the ammonia working fluid at
the temperature in the condenser 20, approximately 51.degree. F.,
is 6.1 atm. Thus, a significant pressure difference is available to
drive the turbine 16 and generate electric power. As the ammonia
working fluid condenses, the liquid working fluid is pumped back
into the evaporator 14 by working fluid pump 24 via working fluid
conduit 22.
[0051] The heat engine 10 of FIG. 1 is essentially the same as the
Rankine cycle of most steam turbines, except that OTEC differs by
using different working fluids and lower temperatures and
pressures. The heat engine 10 of the FIG. 1 is also similar to
commercial refrigeration plants, except that the OTEC cycle is run
in the opposite direction so that a heat source (e.g., warm ocean
water) and a cold heat sink (e.g., deep ocean water) are used to
produce electric power.
[0052] FIG. 2 illustrates the typical components of a floating OTEC
facility 200, which include: the vessel or platform 210, warm sea
water inlet 212, warm water pump 213, evaporator 214, warm sea
water outlet 215, turbine-generator 216, cold water pipe 217, cold
sea water inlet 218, cold water pump 219, condenser 220, cold sea
water outlet 221, working fluid conduit 22, working fluid pump 224,
and pipe connections 230. OTEC facility 200 can also include
electrical generation, transformation and transmission systems,
position control systems such as propulsion, thrusters, or mooring
systems, as well as various auxiliary and support systems (for
example, personnel accommodations, emergency power, potable water,
black and grey water, fire fighting, damage control, reserve
buoyancy, and other common shipboard or marine systems.).
[0053] Implementations of OTEC power plants utilizing the basic
heat engine and system of FIGS. 1 and 2 have a relatively low
overall efficiency of 3% or below. Because of this low thermal
efficiency, OTEC operations require the flow of large amounts of
water through the power system per kilowatt of power generated.
This in turn requires large heat exchangers having large heat
exchange surface areas in the evaporator and condensers.
[0054] Such large volumes of water and large surface areas require
considerable pumping capacity in the warm water pump 213 and cold
water pump 219, reducing the net electrical power available for
distribution to a shore-based facility or on board industrial
purposes. Moreover, the limited space of most surface vessels, does
not easily facilitate large volumes of water directed to and
flowing through the evaporator or condenser. Indeed, large volumes
of water require large diameter pipes and conduits. Putting such
structures in limited space requires multiple bends to accommodate
other machinery. And the limited space of typical surface vessels
or structures does not easily facilitate the large heat exchange
surface area required for maximum efficiency in an OTEC plant. Thus
the OTEC systems and vessel or platform have traditional been large
and costly. This has lead to an industry conclusion that OTEC
operations are a high cost, low yield energy production option when
compared to other energy production options using higher
temperatures and pressures.
[0055] Aspects of the invention address technical challenges in
order to improve the efficiency of OTEC operations and reduce the
cost of construction and operation.
[0056] The vessel or platform 210 requires low motions to minimize
dynamic forces between the cold water pipe 217 and the vessel or
platform 210 and to provide a benign operating environment for the
OTEC equipment in the platform or vessel. The vessel or platform
210 should also support cold and warm water inlet (218 and 212)
volume flows, bringing in sufficient cold and warm water at
appropriate levels to ensure OTEC process efficiency. The vessel or
platform 210 should also enable cold and warm water discharge via
cold and warm water outlets (221 and 215) well below the waterline
of vessel or platform 210 to avoid thermal recirculation into the
ocean surface layer. Additionally, the vessel or platform 210
should survive heavy weather without disrupting power generating
operations.
[0057] The OTEC heat engine 10 should utilize a highly efficient
thermal cycle for maximum efficiency and power production. Heat
transfer in boiling and condensing processes, as well as the heat
exchanger materials and design, limit the amount of energy that can
be extracted from each pound of warm seawater. The heat exchangers
used in the evaporator 214 and the condenser 220 require high
volumes of warm and cold water flow with low head loss to minimize
parasitic loads. The heat exchangers also require high coefficients
of heat transfer to enhance efficiency The heat exchangers can
incorporate material and design that may be tailored to the warm
and cold water inlet temperatures to enhance efficiency. The heat
exchanger design should use a simple construction method with
minimal amounts of material to reduce cost and volume.
[0058] Turbo generators 216 should be highly efficient with minimal
internal losses and may also be tailored to the working fluid to
enhance efficiency
[0059] FIG. 3 illustrates an implementation of the present
invention that enhances the efficiency of previous OTEC power
plants and overcomes many of the technical challenges associated
therewith. This implementation comprises a spar for the vessel or
platform, with heat exchangers and associated warm and cold water
piping integral to the spar.
[0060] OTEC Spar 310 houses an integral multi-stage heat exchange
system for use with an OTEC power generation plant. Spar 310
includes a submerged portion 311 below waterline 305. Submerged
portion 311 comprises warm water intake portion 340, evaporator
portion 344, warm water discharge portion 346, condenser portion
348, cold water intake portion 350, cold water pipe 351, cold water
discharge portion 352, machinery deck portion 354, and deck house
360.
[0061] In operation, warm sea water of between 75.degree. F. and
85.degree. F. is drawn through warm water intake portion 340 and
flows down the spar though structurally integral warm water
conduits not shown. Due to the high volume water flow requirements
of OTEC heat engines, the warm water conduits direct flow to the
evaporator portion 344 of between 500,000 gpm and 6,000,000 gpm.
Such warm water conduits have a diameter of between 6ft and 35 ft,
or more. Due to this size, the warm water conduits are vertical
structural members of spar 310. Warm water conduits can be large
diameter pipes of sufficient strength to vertically support spar
310. Alternatively, the warm water conduits can be passages
integral to the construction of the spar 310.
[0062] Warm water then flows through the evaporator portion 344
which houses one or more stacked, multi-stage heat exchangers for
warming a working fluid to a vapor. The warm sea water is then
discharged from spar 310 via warm water discharge 346. Warm water
discharge can be located or directed via a warm water discharge
pipe to a depth at or close to an ocean thermal layer that is
approximately the same temperature as the warm water discharge
temperature to minimize environmental impacts. The warm water
discharge can be directed to a sufficient depth to ensure no
thermal recirculation with either the warm water intake or cold
water intake.
[0063] Cold sea water is drawn from a depth of between 2500 and
4200 ft, or more, at a temperature of approximately 40.degree. F.,
via cold water pipe 351. The cold sea water enters spar 310 via
cold water intake portion 350. Due to the high volume water flow
requirements of OTEC heat engines, the cold sea water conduits
direct flow to the condenser portion 348 of between 500,000 gpm and
3,500,000 gpm. Such cold sea water conduits have a diameter of
between 6ft and 35 ft, or more. Due to this size, the cold sea
water conduits are vertical structural members of spar 310. Cold
water conduits can be large diameter pipes of sufficient strength
to vertically support spar 310. Alternatively, the cold water
conduits can be passages integral to the construction of the spar
310.
[0064] Cold sea water then flows upward to stacked multi-stage
condenser portion 348, where the cold sea water cools a working
fluid to a liquid. The cold sea water is then discharged from spar
310 via cold sea water discharge 352. Cold water discharge can be
located or directed via a cold sea water discharge pipe to depth at
or close to an ocean thermal layer that is approximately the same
temperature as the cold sea water discharge temperature. The cold
water discharge can be directed to a sufficient depth to ensure no
thermal recirculation with either the warm water intake or cold
water intake.
[0065] Machinery deck portion 354 can be positioned vertically
between the evaporator portion 344 and the condenser portion 348.
Positioning machinery deck portion 354 beneath evaporator portion
344 allows nearly straight line warm water flow from intake,
through the multi-stage evaporators, and to discharge. Positioning
machinery deck portion 354 above condenser portion 348 allows
nearly straight line cold water flow from intake, through the
multi-stage condensers, and to discharge. Machinery deck portion
354 includes turbo-generators 356. In operation warm working fluid
heated to a vapor from evaporator portion 344 flows to one or more
turbo generators 356. The working fluid expands in turbo generator
356 thereby driving a turbine for the production of electrical
power. The working fluid then flows to condenser portion 348 where
it is cooled to a liquid and pumped to evaporator portion 344.
[0066] The performance of heat exchangers is affected by the
available temperature difference between the fluids as well as the
heat transfer coefficient at the surfaces of the heat exchanger.
The heat transfer coefficient generally varies with the velocity of
the fluid across the heat transfer surfaces. Higher fluid
velocities require higher pumping power, thereby reducing the net
efficiency of the plant. A hybrid cascading multi-stage heat
exchange system facilitates lower fluid velocities and greater
plant efficiencies. The stacked hybrid cascade heat exchange design
also facilitates lower pressure drops through the heat exchanger.
And the vertical plant design facilitates lower pressure drop
across the whole system. A hybrid cascading multi-stage heat
exchange system is described in U.S. patent application Ser. No.
12/691,663, (Attorney Docket No. 2556-0004001), entitled "Ocean
Thermal Energy Conversion Plant," filed on Jan. 21, 2010 and
concurrently with the present application, the entire contents of
which are incorporated herein by reference.
[0067] As described above, OTEC operations require a source of cold
water at a constant temperature. Variations in the cooling water
can greatly influence the overall efficiency of the OTEC power
plant. As such, water at approximately 40.degree. F. is drawn from
depths of between 2000 ft and 4200 ft or more. A long intake pipe
is needed to draw this cold water toward the surface and into the
OTEC power plant.
[0068] Such cold water pipes have been an obstacle to commercially
viable OTEC operations because of the cost in constructing a pipe
of suitable performance and durability. OTEC requires large volumes
of water at desired temperatures in order to ensure maximum
efficiency in generating electrical power. Previous cold water pipe
designs specific to OTEC operations have included a sectional
construction. Cylindrical pipe sections were bolted or mechanically
joined together in series until a sufficient length was achieved.
Pipe sections were assembled near the plant facility and the fully
constructed pipe was then upended and installed. This approach had
significant drawbacks including stress and fatigue at the
connection points between pipe sections. Moreover, the connection
hardware added to the overall pipe weight, further complicating the
stress and fatigue considerations at the pipe section connections
and the connection between the fully assembled CWP and the OTEC
platform or vessel.
[0069] The cold water pipe ("CWP") is used to draw water from the
cold water reservoir at an ocean depth of between 2000 ft and 4200
ft or more. The cold water is used to cool and condense to a liquid
the vaporous working fluid emerging from the power plant turbine.
The CWP and its connection to the vessel or platform are configured
to withstand the static and dynamic loads imposed by the pipe
weight, the relative motions of the pipe and platform when
subjected to wave and current loads of up to 100-year-storm
severity, and the collapsing load induced by the water pump
suction. The CWP is sized to handle the required water flow with
low drag loss, and is made of a material that is durable and
corrosion resistant in sea water. The material and physical
construction of the CWP can at least partially thermally insulate
the cold water as it moves from depth to the OTEC plant.
[0070] The cold water pipe length is defined by the need to draw
water from a depth where the temperature is approximately
40.degree. F. The CWP length can be between 2000 feet and 4000 ft
or more. In aspects of the present invention the cold water pipe
can be approximately 3000 feet in length.
[0071] The CWP diameter is determined by the power plant size and
water flow requirements. The water flow rate through the pipe is
determined by the desired power output and OTEC power plant
efficiency. The CWP can carry cold water to the cold water conduit
of the vessel or platform at a rate of between 500,000 gpm and
3,500,000 gpm, or more. Cold water pipe diameters can be between 6
feet and 35 feet or more. In aspects of the present invention, the
CWP diameter is approximately 31 feet in diameter.
[0072] Referring to FIG. 4 a continuous offset staved cold water
pipe is shown. The cold water pipe 451 is free of sectional joints
as in previous CWP designs, instead utilizing an offset stave
construction. CWP 451 includes a top end portion 452 for connection
to the submerged portion of the floating OTEC platform 411.
Opposite top end portion 452 is bottom portion 454, which can
include a ballast system, an anchoring system, and/or an intake
screen.
[0073] CWP 451 comprises a plurality of offset staves constructed
to form a cylinder. In an aspect the plurality of offset staves can
include alternating multiple first staves 465 and multiple second
staves 467. Each first stave includes a top edge 471 and a bottom
edge 472. Each second stave includes a top edge 473 and a bottom
edge 474. In an aspect, second stave 467 is vertically offset from
an adjacent first stave portion 465 such that top edge 473 (of
second stave portion 467) is between 3% and 97% vertically
displaced from the top edge 471 (of first stave portion 465). In
further aspects, the offset between adjacent staves can be
approximately, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or
more.
[0074] FIG. 5 illustrates a detail view of an offsetting stave
pattern of an aspect of the present invention. The pattern includes
multiple first staves 465, each having a top edge portion 471,
bottom edge portion 472, connected edge 480 and offset edge 478.
The pattern also includes multiple second staves 467, each having a
top edge portion 473, a bottom edge portion 474, connected edge
480, and offset edge 479. In forming the cold water pipe, first
stave section 465 is joined to second stave section 467 such that
connected edge 480 is approximately 3% to 97% of the length of
first stave section 465 when measured from the top edge 471 to the
bottom edge 472. In an aspect, connected edge 480 is approximately
50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90% of the length of the
stave.
[0075] It will be appreciated that in a fully constructed pipe,
first stave 465 can be joined to second stave 467 along connected
edge 480. First stave 465 can also be connected to additional
staves along offset edge 478, including an additional first stave
portion, an additional second stave portion, or any other stave
portion. Similarly, second stave 467 can be joined to first stave
portion along connected edge 480. And second stave 467 can be
joined to another stave along offset edge 479, including an
additional first stave portion, an additional second stave portion,
or any other stave portion.
[0076] In aspects, the connected edge 480 between the multiple
first staves 465 and the multiple second staves 467 can be a
consistent length or percentage of the stave length for each stave
about the circumference of the pipe. The connected edge 480 between
the multiple first staves 465 and the multiple second staves 465
can be a consistent length or percentage of the stave length for
each stave along the longitudinal axis of the cold water pipe 451.
In further aspects the connected edge 480 can vary in length
between alternating first staves 465 and second staves 467.
[0077] As illustrated in FIG. 5, first stave 465 and second stave
467 have the same dimensions. In aspects, first stave 465 can be
between 30 and 130 inches wide or more, 30 to 60 feet long, and
between 1 and 24 inches thick. In an aspect the stave dimensions
can be approximately 80 inches wide, 40 feet long, and 4 to 12
inches thick. Alternatively, first stave 465 can have a different
length or width from second stave 467.
[0078] FIG. 6 illustrates a cross sectional view of cold water pipe
451 showing alternating first staves 465 and second staves 467.
Each stave includes an inner surface 485 and an outer surface 486.
Adjacent staves are joined along connected surface 480. Any two
connected surfaces on opposite sides of a single stave define an
angle .alpha.. The angle .alpha. is determined by dividing
360.degree. by the total number of staves. In an aspect, .alpha.
can be between 1.degree. and 36.degree.. In an aspect .alpha. can
be 22.5.degree. for a 16 stave pipe or 11.25.degree. for a 32 stave
pipe.
[0079] Individual staves of cold water pipe 451 can be made from
polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC),
fiber reinforced plastic (FRP), reinforced polymer mortar (RPMP),
polypropylene (PP), polyethylene (PE), cross-linked high-density
polyethylene (PEX), polybutylene (PB), acrylonitrile butadiene
styrene (ABS); polyurethane, polyester, fiber reinforced polyester,
nylon reinforce polyester, vinyl ester, fiber reinforced vinyl
ester, nylon reinforced vinyl ester, concrete, ceramic, or a
composite of one or more thereof. Individual staves can be molded,
extruded, or pulltruded using standard manufacturing techniques. In
one aspect, individual staves are pulltruded to the desired shape
and form and comprise a fiber or nylon reinforced vinyl ester.
Vinyl esters are available from Ashland Chemical of Covington,
Kentucky.
[0080] In an aspect, staves are bonded to adjacent staves using a
suitable adhesive. A flexible resin can be used to provide a
flexible joint and uniform pipe performance. In aspects of the
invention, staves comprising a reinforced vinyl ester are bonded to
adjacent staves using a vinyl ester resin. Methacrylate adhesives
can also be used, such as MA560-1 manufactured by Plexis Structural
Adhesives of Danvers, Mass.
[0081] Referring to FIGS. 7A-7C, various stave constructions are
shown wherein an individual stave 465 includes a top edge 471, a
bottom edge 472 and one or more voids 475. Void 475 can be hollow,
filled with water, filled with a resin, filled with an adhesive, or
filled with a foam material, such as syntactic foam. Syntactic foam
is a matrix of resin and small glass beads. The beads can either be
hollow or solid. Void 475 can be filled to influence the buoyancy
of the stave and/or the cold water pipe 451. FIG. 7A illustrates a
single void 475. In an aspect multiple voids 475 can be equally
spaced along the length of the stave, as illustrated in FIGS. 7B.
In an aspect, one or more voids 475 can be placed toward one end of
the stave, for example toward the bottom edge 472, as illustrated
in FIG. 7C.
[0082] Referring to FIG. 8, each individual stave 465 can include a
top edge 471, a bottom edge 472, a first longitudinal side 491 and
a second longitudinal side 492. In an aspect, longitudinal side 491
includes a joinery member, such as tongue 493. The joinery member
can alternatively include, biscuits, half-lap joints, or other
joinery structures. Second longitudinal side 492 includes a mating
joinery surface, such as groove 494. In use, the first longitudinal
side 491 of a first stave mates or joins with the second
longitudinal side 492 of a second stave. Though not shown, joining
structures, such as tongue and groove, or other structures can be
used at the top edge 471 and the bottom edge 472 to join a stave to
a longitudinally adjacent stave.
[0083] In aspects of the invention, first longitudinal side can
include a positive snap lock connection 497 for mating engagement
with second longitudinal side 492. Positive snap lock connections
or snap lock connections are generally described in U.S. Pat. No.
7,131,242, incorporated herein by reference in its entirety. The
entire length of tongue 493 can incorporate a positive snap lock or
portions of tongue 493 can include a positive snap lock. Tongue 493
can include snap rivets. It will be appreciated that where tongue
493 includes a snap locking structure, an appropriate receiving
structure is provided on the second longitudinal side having groove
494.
[0084] FIG. 9 illustrates an exemplary positive snap lock system,
wherein male portion 970 includes collar 972. Male portion 970
mechanically engages with receiving portion 975 with include
recessed collar mount 977. In use, male portion 970 is inserted
into receiving portion 975 such that collar portion 972 engages
recessed collar mount 977, there by allowing insertion of the male
portion 970 but preventing its release or withdrawal.
[0085] Positive snap locking joints between staved portions of the
offset staved pipe can be used to mechanically lock two staved
portion together. The positive snap lock joints can be used alone
or in combination with a resin or adhesive. In an aspect, a
flexible resin is used in combination with the positive snap lock
joint.
[0086] FIG. 10 illustrates a cold water pipe 451 having an offset
stave construction comprising multiple alternating first staves 465
and second staves 467 and further comprising a spirally wound
ribbon 497 covering at least a portion of the outer surface of cold
water pipe 451. In aspects the ribbon is continuous from the bottom
portion 454 of cold water pipe 451 to the top portion 452 of the
cold water pipe 451. In other aspects the ribbon 497 is provided
only in those portions of pipe 451 that experience vortex shedding
due to movement of water past the cold water pipe 451. Ribbon 497
provides radial and longitudinal support to cold water pipe 451.
Ribbon 497 also prevents vibration along the cold water pipe and
reduces vortex shedding due to ocean current action.
[0087] Ribbon 491 can be the same thickness and width as an
individual stave of cold water pipe 451 or can be two, three, four
or more time the thickness and up to 10 times (e.g, 2, 3, 4, 5, 6,
7 8, 9 or 10 times) the width of an individual stave.
[0088] Ribbon 491 can be mounted on the outside surface of the cold
water pipe so as to lay substantially flat along the outside
surface. In an embodiment, ribbon 491 can protrude outwardly from
the outside surface of cold water pipe 451 so as to form a spirally
wound strake.
[0089] Ribbon 491 can be of any suitable material compatible with
the material of the multiple staves forming cold water pipe 451,
including: polyvinyl chloride (PVC), chlorinated polyvinyl chloride
(CPVC), fiber reinforced plastic (FRP), reinforced polymer mortar
(RPMP), polypropylene (PP), polyethylene (PE), cross-linked
high-density polyethylene (PEX), polybutylene (PB), acrylonitrile
butadiene styrene (ABS); polyurethane, polyester, fiber reinforced
polyester, vinyl ester, reinforced vinyl ester, concrete, ceramic,
or a composite of one or more thereof. Ribbon 491 can be molded,
extruded, or pulltruded using standard manufacturing techniques. In
one aspect, ribbon 491 is pulltruded to the desired shape and form
and comprises a fiber or nylon reinforced vinyl ester similar to
that used with the staves of cold water pipe 451. Ribbon 491 can be
joined to cold water pipe 451 using a suitable adhesive or resin
including the resins of any of the materials above.
[0090] In some aspects, ribbon 491 is not continuous along the
length of cold water pipe 451. In some aspects, ribbon 491 is not
continuous about the circumference of cold water pipe 451. In some
aspects, ribbon 491 comprises vertical strips adhered to the
outside surface of the cold water pipe 451. In some aspects, where
radial or other structural support is required, ribbon 491 can be a
circumferential support member around the outside surface of the
cold water pipe.
[0091] Ribbon 491 can be adhesively bonded or adhered to the
outside surface of the cold water pipe, using a suitable flexible
adhesive. In an aspect, ribbon 491 can be mechanically coupled to
the outside surface of cold water pipe 451 using multiple positive
snap locks.
[0092] With regard to FIG. 11, an exemplary method of assembling a
cold water pipe provides for the efficient transport and assembly
of the cold water pipe 451. Vertical cylindrical pipe sections are
assembled by aligning 1110 alternating first and second stave
portions to have the desired offset as described above. The first
and second stave portions are then joined 1120 to form a
cylindrical pipe section. The offset first and second staves can be
joined using any of a variety of joining methods. In an aspect the
multiple offset first and second stave portions are joined using a
tongue and groove arrangement and a flexible adhesive. In an aspect
the multiple first and second staved portions are joined using a
mechanical positive snap lock. A combination of tongue and groove,
snap lock mechanisms, and flexible adhesives can be used.
[0093] After joining 1120 the multiple first and second stave
portions to form a cylindrical pipe section having offset first and
second stave portions, a retaining band, inflatable sleeve or other
jig can be attached 1122 to the cylindrical pipe section to provide
support and stability to the pipe section. The steps of aligning
1110 and joining 1120 multiple offset first and second stave
portions can be repeated 1124 to form any number of prefabricated
cylindrical pipe sections. It will be appreciated that the
cylindrical pipe section can be prefabricated at the OTEC plant
facility or remotely and then transported to the OTEC plant
facility for additional construction to form the fully assembled
cold water pipe 451.
[0094] Having assembled at least two cylindrical pipe sections
having offset staves, an upper and lower cylindrical pipe sections
are joined 1126 and the offset staves of each pipe section are
aligned. A flexible adhesive can be applied 1130 to the butt joint
of the offset staves of the upper and lower cylindrical pipe
sections. The staves of the two pipe sections can be joined using a
variety of end butt joints including biscuit joinery. In an aspect,
the offset staves of the upper and lower cylindrical pipe portions
can be provided with aligning joining voids which in turn can be
filled with a flexible adhesive.
[0095] Gaps in and joints between pipe sections or between and
individual staves can be filled 1132 with additional flexible
resin. Once the two pipe sections have been joined and the resin
applied where need the two pipe sections are allowed to cure
1134.
[0096] The retaining band is then removed 1136 from the lower pipe
section and a spirally wound strake is attached thereto. The
spirally wound strake can be attached using adhesive bonding,
mechanical bonding, for example positive snap locks, or a
combination of the adhesive and mechanical bonding.
[0097] In an aspect of the method of assembly, after the spiral
strake is attached to the lower pipe section, the entire pipe
assembly can be shifted, for example lowered, so that the previous
upper pipe portion becomes the new lower pipe portion, 1138. Then a
new upper cylindrical pipe section is assembled 1140 in a similar
manner as described above. That is, first and second stave portions
are aligned 1142 to achieve the desired offset. The first and
second stave portions are then joined 1144 to form a new
cylindrical pipe section, e.g., new upper pipe section. As
previously mentioned, a retaining band, inflatable sleeve or other
jig can be used to provide support and stability to the cylindrical
pipe section during construction of the cold water pipe 451.
[0098] Having assembled new upper pipe section 1144, the offset
staves of the new lower pipe section and the new upper pipe section
are aligned and drawn together 1146. Adhesive or flexible resin is
applied 1148 to the end butt joints as described above, for example
in conjunction with biscuit joinery or with aligning joining voids.
Any gaps between the new lower pipe section and the new upper pipe
section or between any two stave portions can be filled 1150 with
additional flexible resin. The entire assembly can then be left to
cure 1152. The retaining jig can be removed 1154 as before and the
spiral strake can be attached to the new lower portion. And as
before the entire pipe assembly can be shifted to provide for the
next cylindrical pipe section. In this manner, the method can be
repeated until the desired pipe length is achieved.
[0099] It will be appreciated that joining cylindrical pipe
sections having offset staves can be accomplished in a number of
manners consistent with the present invention. The method of
joining offset staves provides for a continuous pipe without the
need for bulky, heavy or interfering joining hardware between the
pipe segments. As such a continuous pipe having nearly uniform
material properties, including flexibility and rigidity, is
provided.
Example
[0100] A cold water pipe assembly is provided that facilitates on
site construction of a continuous, offset staved pipe of
approximately 3000 feet. Additionally the staved design accounts
for adverse shipping and handling loads traditionally experienced
by segmented pipe construction. For example towing and upending of
traditionally constructed segmented cold water pipes imposes
hazardous loads on the pipe.
[0101] Staved construction allows offsite manufacturing of multiple
staves of 40 to 50 ft lengths. Each stave is approximately 52
inches wide and 4 to 12 inches thick. The staves can be shipped in
stacks or containers to the offshore platform and the cold water
pipe can then be constructed on the platform from the multiple
staves. This eliminates the need for a separate facility to
assemble pipe sections.
[0102] The stave portions can be constructed from a nylon
reinforced vinyl ester having a modulus of elasticity of between
about 66,000 psi and 165,000 psi. The stave portions can have an
ultimate strength of between about 15,000 psi and 45,000 psi, with
a tensile strength between about 15,000 psi to 45,000 psi. In an
aspect, the stave portions can have an modulus of elasticity of
150,000 psi, an ultimate strength of 30,000 psi and a yield
strength of 30,000 psi, such that the installed CWP behaves similar
to a hose rather than a purely rigid pipe. This is advantageous in
storm conditions as the pipe is more flexible and avoids cracking
or breaking In an aspect, the pipe can deflect approximately two
diameters from center at the unconnected lower end. Deflection at
the unconnected lower end should not be so great as to interfere
with the mooring system of the OTEC power plant or any other
underwater systems involved in plant operations. The cold water
pipe connects to the bottom portion of the OTEC power plant.
[0103] More specifically, the cold water pipe connects using a
dynamic bearing with the bottom portion of the OTEC spar of FIG. 3.
Cold water pipe connections in OTEC applications are described in
Section 4.5 of Avery & Wu, "Renewable Energy from the Ocean, a
Guide to OTEC," Oxford University Press, 1994, incorporated herein
by reference in its entirety.
[0104] One of the significant advantages of using the spar buoy as
the platform is that doing so results in relatively small rotations
between the spar itself and the CWP even in the most severe
100-year storm conditions. In addition the vertical and lateral
forces between the spar and the CWP are such that the downward
force between the spherical ball and its seat keeps the bearing
surfaces in contact at all times. Because this bearing, that also
acts as the water seal, does not come out of contact with its
mating spherical seat there is no need to install a mechanism to
hold the CWP in place vertically. This helps to simplify the
spherical bearing design and also minimizes the pressure losses
that would otherwise be caused by any additional CWP pipe
restraining structures or hardware. The lateral forces transferred
through the spherical bearing are also low enough that they can be
adequately accommodated without the need for vertical restraint of
the CWP.
[0105] Cold water is drawn through the cold water pipe via one or
more cold water pumps such and flows via one or more cold water
passages or conduits to the condenser portion of a multi-stage OTEC
power plant.
Example
[0106] Aspects of the present invention provide an integrated
multi-stage OTEC power plant that will produce electricity using
the temperature differential between the surface water and deep
ocean water in tropical and subtropical regions. Aspects eliminate
traditional piping runs for sea water by using the off-shore
vessel's or platform's structure as a conduit or flow passage.
Alternatively, the warm and cold sea water piping runs can use
conduits or pipes of sufficient size and strength to provide
vertical or other structural support to the vessel or platform.
These integral lsea water conduit sections or passages serve as
structural members of the vessel, thereby reducing the requirements
for additional steel. As part of the integral sea water passages,
multi-stage cabinet heat exchangers provides multiple stages of
working fluid evaporation without the need for external water
nozzles or piping connections. The integrated multi-stage OTEC
power plant allows the warm and cold sea water to flow in their
natural directions The warm sea water flows downward through the
vessel as it is cooled before being discharged into a cooler zone
of the ocean. In a similar fashion, the cold sea water from deep in
the ocean flows upward through the vessel as it is warmed before
discharging into a warmer zone of the ocean. This arrangement
avoids the need for changes in sea water flow direction and
associated pressure losses. The arrangement also reduces the
pumping energy required.
[0107] Multi-stage cabinet heat exchangers allow for the use of a
hybrid cascade OTEC cycle. These stacks of heat exchangers comprise
multiple heat exchanger stages or sections that have sea water
passing through them in series to boil or condense the working
fluid as appropriate. In the evaporator section the warm sea water
passes through the first stage where it boils off some of the
working fluid as the sea water is cooled. The warm sea water then
flows down the stack into the next heat exchanger stage and boils
off additional working fluid at a slightly lower pressure and
temperature. This occurs sequentially through the entire stack.
Each stage or section of the cabinet heat exchanger supplies
working fluid vapor to a dedicated turbine that generates
electrical power. Each of the evaporator stages has a corresponding
condenser stage at the exhaust of the turbine. The cold sea water
passes through the condenser stacks in a reverse order to the
evaporators.
[0108] Referring to FIGS. 12A and 12B, an exemplary multi-stage
OTEC heat engine 710 utilizing a hybrid cascading heat exchange
cycles is provided. Warm sea water is pumped from a warm sea water
intake (not shown) via warm water pump 712, discharging from the
pump at approximately 1,360,000 gpm and at a temperature of
approximately 79.degree. F. All or parts of the warm water conduit
from the warm water intake to the warm water pump, and from the
warm water pump to the stacked heat exchanger cabinet can form
integral structural members of the vessel.
[0109] From the warm water pump 712, the warm sea water then enters
first stage evaporator 714 where it boils a first working fluid.
The warm water exits first stage evaporator 714 at a temperature of
approximately 76.8.degree. F. and flows down to the second stage
evaporator 715. The warm water enters second stage evaporator 715
at approximately 76.8.degree. F. where it boils a second working
fluid and exits the second stage evaporator 715 at a temperature of
approximately 74.5.degree..
[0110] The warm water flows down to the third stage evaporator 716
from the second stage evaporator 715, entering at a temperature of
approximately 74.5.degree. F., where it boils a third working
fluid. The warm water exits the third stage evaporator 716 at a
temperature of approximately 72.3.degree. F.
[0111] The warm water then flows from the third stage evaporator
716 down to the fourth stage evaporator 717, entering at a
temperature of approximately 72.3.degree. F., where it boils a
fourth working fluid. The warm water exits the fourth stage
evaporator 717 at a temperature of approximately 70.1.degree. F.
and then discharges from the vessel. Though not shown, the
discharge can be directed to a thermal layer at an ocean depth of
or approximately the same temperature as the discharge temperature
of the warm sea water. Alternately, the portion of the power plant
housing the multi-stage evaporator can be located at a depth within
the structure so that the warm water is discharged to an
appropriate ocean thermal layer. In aspects, the warm water conduit
from the fourth stage evaporator to the warm water discharge of the
vessel can be comprise structural members of the vessel.
[0112] Similarly, cold sea water is pumped from a cold sea water
intake (not shown) via cold sea water pump 722, discharging from
the pump at approximately 855,003 gpm and at a temperature of
approximately 40.0.degree. F. The cold sea water is drawn from
ocean depths of between approximately 2700 and 4200 ft, or more.
The cold water conduit carrying cold sea water from the cold water
intake of the vessel to the cold water pump, and from the cold
water pump to the first stage condenser can comprise in its
entirety or in part structural members of the vessel.
[0113] From cold sea water pump 722, the cold sea water enters a
first stage condenser 724, where it condenses the fourth working
fluid from the fourth stage boiler 717. The cold seawater exits the
first stage condenser at a temperature of approximately
43.5.degree. F. and flows up to the second stage condenser 725.
[0114] The cold sea water enters the second stage condenser 725 at
approximately 43.5.degree. F. where it condenses the third working
fluid from third stage evaporator 716. The cold sea water exits the
second stage condenser 725 at a temperature approximately
46.9.degree. F. and flows up to the third stage condenser.
[0115] The cold sea water enters the third stage condenser 726 at a
temperature of approximately 46.9.degree. F. where it condenses the
second working fluid from second stage evaporator 715. The cold sea
water exits the third stage condenser 726 at a temperature
approximately 50.4.degree. F.
[0116] The cold sea water then flows up from the third stage
condenser 726 to the fourth stage condenser 727, entering at a
temperature of approximately 50.4.degree. F. In the fourth stage
condenser, the cold sea water condenses the first working fluid
from first stage evaporator 714. The cold sea water then exits the
fourth stage condenser at a temperature of approximately
54.0.degree. F. and ultimately discharges from the vessel. The cold
sea water discharge can be directed to a thermal layer at an ocean
depth of or approximately the same temperature as the discharge
temperature of the cold sea water. Alternately, the portion of the
power plant housing the multi-stage condenser can be located at a
depth within the structure so that the cold sea water is discharged
to an appropriate ocean thermal layer.
[0117] The first working fluid enters the first stage evaporator
714 at a temperature of 56.7.degree. F. where it is heated to a
vapor with a temperature of 74.7.degree. F. The first working fluid
then flows to first turbine 731 and then to the fourth stage
condenser 727 where the first working fluid is condensed to a
liquid with a temperature of approximately 56.5.degree. F. The
liquid first working fluid is then pumped via first working fluid
pump 741 back to the first stage evaporator 714.
[0118] The second working fluid enters the second stage evaporator
715 at a temperature approximately 53.0.degree. F. where it is
heated to a vapor. The second working fluid exits the second stage
evaporator 715 at a temperature approximately 72.4.degree. F. The
second working fluid then flow to a second turbine 732 and then to
the third stage condenser 726. The second working fluid exits the
third stage condenser at a temperature approximately 53.0.degree.
F. and flows to working fluid pump 742, which in turn pumps the
second working fluid back to the second stage evaporator 715.
[0119] The third working fluid enters the third stage evaporator
716 at a temperature approximately 49.5.degree. F. where it will be
heated to a vapor and exit the third stage evaporator 716 at a
temperature of approximately 70.2.degree. F. The third working
fluid then flows to third turbine 733 and then to the second stage
condenser 725 where the third working fluid is condensed to a fluid
at a temperature approximately 49.5.degree. F. The third working
fluid exits the second stage condenser 725 and is pumped back to
the third stage evaporator 716 via third working fluid pump
743.
[0120] The fourth working fluid enters the fourth stage evaporator
717 at a temperature of approximately 46.0.degree. F. where it will
be heated to a vapor. The fourth working fluid exits the fourth
stage evaporator 717 at a temperature approximately 68.0.degree. F.
and flow to a fourth turbine 734. The fourth working fluid exits
fourth turbine 734 and flows to the first stage condenser 724 where
it is condensed to a liquid with a temperature approximately
46.0.degree. F. The fourth working fluid exits the first stage
condenser 724 and is pumped back to the fourth stage evaporator 717
via fourth working fluid pump 744.
[0121] The first turbine 731 and the fourth turbine 734
cooperatively drive a first generator 751 and form first
turbo-generator pair 761. First turbo-generator pair will produce
approximately 25 MW of electric power.
[0122] The second turbine 732 and the third turbine 733
cooperatively drive a second generator 752 and form second
turbo-generator pair 762. Second turbo-generator pair 762 will
produce approximately 25 MW of electric power.
[0123] The four stage hybrid cascade heat exchange cycle of FIG. 7
allows the maximum amount of energy to be extracted from the
relatively low temperature differential between the warm sea water
and the cold sea water. Moreover, all heat exchangers can directly
support turbo-generator pairs that produce electricity using the
same component turbines and generators.
[0124] It will be appreciated that multiple multi-stage hybrid
cascading heat exchangers and turbo generator pairs can be
incorporated into a vessel or platform design.
Example
[0125] An offshore OTEC spar platform includes four separate power
modules, each generating about 25 MWe Net at the rated design
condition. Each power module comprises four separate power cycles
or cascading thermodynamic stages that operate at different
pressure and temperature levels and pick up heat from the sea water
system in four different stages. The four different stages operate
in series. The approximate pressure and temperature levels of the
four stages at the rated design conditions (Full Load--Summer
Conditions) are:
TABLE-US-00001 Turbine inlet Condenser Pressure/Temp.
Pressure/Temp. (Psia)/(.degree. F.) (Psia)/(.degree. F.) 1 Stage
137.9/74.7 100.2/56.5 2'' Stage 132.5/72.4 93.7/53 3' Stage
127.3/70.2 87.6/49.5 4'' Stage 122.4/68 81.9/46
[0126] The working fluid is boiled in multiple evaporators by
picking up heat from warm sea water (WSW). Saturated vapor is
separated in a vapor separator and led to an ammonia turbine by STD
schedule, seamless carbon steel pipe. The liquid condensed in the
condenser is pumped back to the evaporator by 2.times.100% electric
motor driven constant speed feed pumps. The turbines of cycle-1 and
4 drive a common electric generator. Similarly the turbines of
cycle-2 and 3 drive another common generator. In an aspect there
are two generators in each plant module and a total of 8 in the 100
MWe plant. The feed to the evaporators is controlled by feed
control valves to maintain the level in the vapor separator. The
condenser level is controlled by cycle fluid make up control
valves. The feed pump minimum flow is ensured by recirculation
lines led to the condenser through control valves regulated by the
flow meter on the feed line.
[0127] In operation the four (4) power cycles of the modules
operate independently. Any of the cycles can be shutdown without
hampering operation of the other cycles if needed, for example in
case of a fault or for maintenance. But that will reduce the net
power generation of the power module as a whole module.
[0128] Aspects of the present invention require large volumes of
seawater. There will be separate systems for handling cold and warm
seawater, each with its pumping equipment, water ducts, piping,
valves, heat exchangers, etc. Seawater is more corrosive than fresh
water and all materials that may come in contact with it need to be
selected carefully considering this. The materials of construction
for the major components of the seawater systems will be:
[0129] Large bore piping: Fiberglass Reinforced Plastic (FRP)
[0130] Large seawater ducts & chambers: Epoxy-coated carbon
steel
[0131] Large bore valves: Rubber lined butterfly type
[0132] Pump impellers: Suitable bronze alloy
[0133] Unless controlled by suitable means, biological growths
inside the seawater systems can cause significant loss of plant
performance and can cause fouling of the heat transfer surfaces
leading to lower outputs from the plant. This internal growth can
also increase resistance to water flows causing greater pumping
power requirements, lower system flows, etc. and even complete
blockages of flow paths in more severe cases.
[0134] The Cold Sea Water ("CSW") system using water drawn in from
deep ocean should have very little or no bio-fouling problems.
Water in those depths does not receive much sunlight and lack
oxygen, and so there are fewer living organisms in it. Some types
of anaerobic bacteria may, however, be able to grow in it under
some conditions. Shock chlorination will be used to combat
bio-fouling.
[0135] The Warm Sea Water ("WSW") system handling warm seawater
from near the surface will have to be protected from bio-fouling.
It has been found that fouling rates are much lower in tropical
open ocean waters suitable for OTEC operations than in coastal
waters. As a result, chemical agents can be used to control
bio-fouling in OTEC systems at very low doses that will be
environmentally acceptable. Dosing of small amounts of chlorine has
proved to be very effective in combating bio-fouling in seawater.
Dosages of chlorine at the rate of about 70 ppb for one hour per
day, is quite effective in preventing growth of marine organisms.
This dosage rate is only 1/20th of the environmentally safe level
stipulated by EPA. Other types of treatment (thermal shock, shock
chlorination, other biocides, etc.) can be used from time to time
in-between the regimes of the low dosage treatment to get rid of
chlorine-resistant organisms.
[0136] Necessary chlorine for dosing the seawater streams is
generated on-board the plant ship by electrolysis of seawater.
Electro-chlorination plants of this type are available commercially
and have been used successfully to produce hypochlorite solution to
be used for dosing. The electro-chlorination plant can operate
continuously to fill-up storage tanks and contents of these tanks
are used for the periodic dosing described above.
[0137] All the seawater conduits avoid any dead pockets where
sediments can deposit or organisms can settle to start a colony.
Sluicing arrangements are provided from the low points of the water
ducts to blow out the deposits that may get collected there. High
points of the ducts and water chambers are vented to allow trapped
gases to escape.
[0138] The Cold Seawater (CSW) system will consist of a common deep
water intake for the plant ship, and water pumping/distribution
systems, the condensers with their associated water piping, and
discharge ducts for returning the water back to the sea. The cold
water intake pipe extends down to a depth of more than 2700 ft,
(e.g., between 2700 ft to 4200 ft), where the sea water temperature
is approximately a constant 40.degree. F. Entrance to the pipe is
protected by screens to stop large organisms from being sucked in
to it. After entering the pipe, cold water flows up towards the sea
surface and is delivered to a cold well chamber near the bottom of
the vessel or spar.
[0139] The CSW supply pumps, distribution ducts, condensers, etc.
are located on the lowest level of the plant. The pumps take
suction from the cross duct and send the cold water to the
distribution duct system. 4.times.25% CSW supply pumps are provided
for each module. Each pump is independently circuited with inlet
valves so that they can be isolated and opened up for inspection,
maintenance, etc. when required. The pumps are driven by
high-efficiency electric motors.
[0140] The cold seawater flows through the condensers of the cycles
in series and then the CSW effluent is discharged back to the sea.
CSW flows through the condenser heat exchangers of the four plant
cycles in series in the required order. The condenser installations
is arranged to allow them to be isolated and opened up for cleaning
and maintenance when needed.
[0141] The WSW system comprises underwater intake grills located
below the sea surface, an intake plenum for conveying the incoming
water to the pumps, water pumps, biocide dosing system to control
fouling of the heat transfer surfaces, water straining system to
prevent blockages by suspended materials, the evaporators with
their associated water piping, and discharge ducts for returning
the water back to the sea.
[0142] Intake grills are provided in the outside wall of the plant
modules to draw in warm water from near the sea surface. Face
velocity at the intake grills is kept to less than 0.5 ft/sec. to
minimize entrainment of marine organisms. These grills also prevent
entry of large floating debris and their clear openings are based
on the maximum size of solids that can pass through the pumps and
heat exchangers safely. After passing through these grills, water
enters the intake plenum located behind the grills and is routed to
the suctions of the WSW supply pumps.
[0143] The WSW pumps are located in two groups on opposite sides of
the pump floor. Half of the pumps are located on each side with
separate suction connections from the intake plenum for each group.
This arrangement limits the maximum flow rate through any portion
of the intake plenum to about 1/16th of the total flow and so
reduces the friction losses in the intake system. Each of the pumps
are provided with valves on inlet sides so that they can be
isolated and opened up for inspection, maintenance, etc. when
required. The pumps are driven by high-efficiency electric motors
with variable frequency drives to match pump output to load.
[0144] It is necessary to control bio-fouling of the WSW system and
particularly its heat transfer surfaces, and suitable biocides will
be dosed at the suction of the pumps for this. The warm water
stream may need to be strained to remove the larger suspended
particles that can block the narrow passages in the heat
exchangers. Large automatic filters or `Debris Filters` can be used
for this if required. Suspended materials can be retained on
screens and then removed by backwashing. The backwashing effluents
carrying the suspended solids will be routed to the discharge
stream of the plant to be returned to the ocean. The exact
requirements for this will be decided during further development of
the design after collection of more data regarding the seawater
quality.
[0145] The strained warm seawater (WSW) is distributed to the
evaporator heat exchangers. WSW flows through the evaporators of
the four plant cycles in series in the required order. WSW effluent
from the last cycle is discharged at a depth of approximately 175
feet or more below the sea surface. It then sinks slowly to a depth
where temperature (and therefore density) of the seawater will
match that of the effluent.
[0146] Though embodiments herein have described multi-stage heat
exchanger in a floating offshore vessel or platform, drawing cold
water via a continuous, offset staved cold water pipe, it will be
appreciated that other embodiments are within the scope of the
invention. For example, the cold water pipe can be connected to a
shore facility. The continuous offset staved pipe can be used for
other intake or discharge pipes having significant length to
diameter ratios. The offset staved construction can be incorporated
into pipe sections for use in traditional segmented pipe
construction. The multi-stage heat exchanger and integrated flow
passages can be incorporated into shore based facilities including
shore based OTEC facilities. Moreover, the warm water can be warm
fresh water, geo-thermally heated water, or industrial discharge
water (e.g., discharged cooling water from a nuclear power plant or
other industrial plant). The cold water can be cold fresh water.
The OTEC system and components described herein can be used for
electrical energy production or in other fields of use including:
salt water desalination: water purification; deep water
reclamation; aquaculture; the production of biomass or biofuels;
and still other industries.
[0147] All references mentioned herein are incorporated by
reference in their entirety.
[0148] Other embodiments are within the scope of the following
claims.
* * * * *