Note: Descriptions are shown in the official language in which they were submitted.
TITLE
[0001] Ocean Powered Rankine Cycle Turbine
FIELD
[0002] There is described turbine that uses the ocean to create a Rankine
cycle to turn a
turbine.
BACKGROUND
[0003] Makai
Ocean Engineering Inc (Makai) has developed Ocean Thermal Energy
Conversion (OTEC) technology to generate electricity using the thermal
properties of the
ocean water off Hawaii.
[0004]
Referring to FIG. 3, labelled as PRIOR ART, and generally identified by
reference
numeral 10, the Ocean Thermal Energy Conversion (OTEC) technology developed by
Makai. An ocean heat source is provided by pump 12 which pumps warm ocean
water draw
from a shallow water intake 14 through a warm water supply line 16 through a
heat
exchanger 18 where the warm ocean water is used to heat a working fluid to
effect a phase
change from liquid to gas. The working fluid exiting first heat exchanger 18,
passes along a
gaseous phase working fluid supply line 20 which supplies working fluid in the
form of a gas
to power a turbine 22. Working fluid exits turbine 22 and passes along working
fluid recycle
line 32 to a heat exchanger 30.
[0005] An
ocean cold source is provided by a pump 24 which pumps cold ocean water
drawn from a deep water intake 26 through a cold water supply line 28 to the
heat exchanger
30 where the cold ocean water is used to cool the working fluid from turbine
22, until the
working fluid undergoes a phase change from gas back to liquid. The working
fluid exiting
heat exchanger 30 in the form of a liquid passes along liquid phase working
fluid supply line
34 and is pumped by a pump 36 back through first heat exchanger 18 to complete
a loop.
The warm ocean water passing through first heat exchanger 18 and the cold
ocean water
passing through second heat exchanger 30 are directed to an ocean water return
line 38,
where the two streams are mixed prior to be discharged into the ocean through
mixed
temperature water outlet 40.
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[0006] The conversion of thermal energy into usable mechanical power is
in accordance
with Carnot heat engine theory in which an amount of heat Oh flows from a high
temperature reservoir Th through a working body that does mechanical work, W
and results
in a remaining heat flow Qc to a cold sink with temperature Tc.
[0007] A standard Rankine cycle represents an application of the Carnot
engine theory,
where a phase change working fluid, such as water, is used to transfer the
heat energy to do
mechanical work. When the phase change working fluid is water, the water is
boiled to
steam, the steam drives a turbine and then condenses back to water for pumping
through the
system.
[0008] The four processes associated with a Rankine cycle are as follows:
[0009] Working fluid is pumped from low to high pressure as a liquid. The
energy
required to raise the pressure of the working fluid by the pump is represented
by Wpump.
[0010] High pressure working fluid (as a liquid) enters a boiler where it
is heated by an
external heating source to dry saturated vapour. The input energy required to
heat the
working fluid to this state is quantified as Qin.
[0011] The working fluid as a dry saturated vapour expands through a
turbine. As the
working fluid drives the turbine to do work W, the working fluid cools (lowers
temperature)
and lowers pressure.
[0012] The working fluid enters a condenser as a wet vapour to become a
saturated
liquid. Any exhaust heat that is not contained within the Rankine closed loop
cycle is
represented by Qout.
[0013] The efficiency of the cycle is measured in two ways:
[0014] Actual efficiency - = ¨
qft1
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[0015] Carnot cycle efficiency - ?-7 =
[0016] The difference between the two efficiency measures is that the
Carnot cycle
efficiency assumes that no entropy is added to the system by the pump or the
turbine (i.e. the
pump and the turbine are isentropic). In other words, the Carnot cycle
efficiency is a good
measure of the efficiency of the Carnot heat engine cycle, or the heating and
cooling
elements of the Rankine cycle. The actual efficiency considers the impact of
the pump and
the turbine on the efficiency of the system. The type of working fluid is not
critical.
SUMMARY
[0017] There is provided an ocean powered Rankine cycle turbine which
includes a
primary Rankine cycle loop in which is circulated a working fluid which
changes phase from
a liquid to a gas when heated. A liquid phase working fluid supply line feeds
working fluid
in liquid form to a first heat exchanger which effects a phase change from
liquid to gas. The
first heat exchanger is connected by a gaseous phase working fluid supply line
which
supplies working fluid in gas form to a turbine. A working fluid recycle line
feeds working
fluid in gas form to a second heat exchanger to effect a phase change from gas
to liquid. The
second heat exchanger is connected to the liquid phase working fluid supply
line which
supplies working fluid in the form of liquid to the first heat exchanger. A
first pump is
positioned on the liquid phase working fluid supply line to pump the working
fluid in the
form of liquid. One or more piston assemblies are provided for compressing
air. Each piston
assembly includes a piston that is reciprocally movable within an interior of
a piston housing
between an extended position extending farther out of the piston housing and a
retracted
position retracted farther into the piston housing. Ocean powered input is
provided in the
form of a wave energy converter that uses ocean wave energy to reciprocally
move each
piston between the extended position and the retracted position. As each wave
goes down,
each piston is moved to the extended position drawing air into the interior of
the piston
housing. As each wave goes up, the piston is moved to the retracted position
compressing
air within the interior of the piston housing. A heat source is provided in
the form of a
hollow structure forming part of the piston housing that defines the first
heat exchanger of
the closed working fluid loop. Heat generated within the interior of the
piston housing, as
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the piston compresses air, is used to effect a phase change of the working
fluid from a liquid
to a gas. A cold source is provided in the form of cold compressed air
expelled from the
interior of the piston housing. The cold compressed air is directed through
the second heat
exchanger to effect a phase change of the working fluid from gas to liquid.
[0018] In the
manner described above, the piston assemblies provide both a heat source
and a cold source, powered by the endless energy supplied by the wave action
of the ocean. It
has been found that there is a surplus supply of compressed air. This surplus
supply of
compressed air can be used for other purposes. For example, the surplus supply
of
compressed air can be used to power one or more air driven motor. The energy
from the one
or more air driven motors can be used within the primary Rankine cycle loop to
drive the
pump. The energy from the one or more air driven motors can be used for other
purposes
outside of the Rankine cycle loop. The surplus supply of compressed air can
also be used
pressurize sequential piston assemblies, as will hereafter be further
described.
[0019] The
ocean powered Rankine cycle turbine that uses wave action, as described,
above, can also be used to increase the actual efficiency of an ocean powered
Rankine cycle
turbine that uses differential ocean temperatures, as disclosed by Makai Ocean
Engineering.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] These
and other features will become more apparent from the following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to be in any way limiting,
wherein:
[0021] FIG. 1
is a schematic diagram of an ocean powered Rankine cycle turbine that
uses wave energy.
[0022] FIG. 2
is a diagram of a wave energy converter with sequential piston assemblies.
[0023] FIG. 3
labelled as PRIOR ART, is a schematic diagram of an ocean powered
Rankine cycle turbine that uses differential ocean temperatures.
[0024] FIG. 4
is a diagram of an ocean powered Rankine cycle turbine that uses a
combination of wave energy and differential ocean temperatures.
[0025] FIG. 5
is a side elevation view, in section, of a heat exchanger built into a piston
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housing.
[0026] FIG. 6 is a top plan view, in section, of the heat exchanger built
into the piston
housing of FIG. 5.
DETAILED DESCRIPTION
[0027] An ocean powered Rankine cycle turbine generally identified by
reference
numeral 100, will now be described with reference to FIG. 1 and 2.
Structure and Relationship of Parts:
[0028] Referring to FIG. 1, ocean powered Rankine cycle turbine 100,
includes a primary
Rankine cycle loop 102 in which is circulated a working fluid which changes
phase from a
liquid to a gas when heated. A liquid phase working fluid supply line 104
feeds working
fluid in liquid form to a first heat exchanger 106 to effect a phase change
from liquid to gas.
First heat exchanger 106 is connected by a gaseous phase working fluid supply
line 110
which supplies working fluid in gas form to a turbine 112 which has a work
output 117. A
working fluid recycle line 114 feeds working fluid in gas form to a second
heat exchanger
116 to effect a phase change from gas to liquid. The second heat exchanger
being 116 is
connected by the liquid phase working fluid supply line 104 which supplies
working fluid in
the form of liquid to first heat exchanger 106. A first pump 118 is positioned
on liquid
phase working fluid supply line 104 to pump the working fluid in the form of
liquid.
[0029] A piston assembly 120 is provided for compressing air. Piston
assembly 120 has
a piston 122 that is reciprocally movable within an interior 124 of a piston
housing 126
between an extended position extending farther out of piston housing 126 and a
retracted
position retracted farther into piston housing 126. An ocean powered input, in
the form of a
wave energy converter 128, uses ocean wave energy to reciprocally move piston
122
between the extended position and the retracted position, such that as each
wave goes down
the piston 122 is moved to the extended position drawing air into interior 124
of piston
housing 126 and as each wave goes up and piston 122 is moved to the retracted
position
compressing air within interior 124 of piston housing 126.
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[0030] A heat source for the Rankine Cycle is provided in the form of a
hollow structure
within piston housing 126 that defines first heat exchanger 106 of the closed
working fluid
loop. Heat generated within interior 124 of piston housing 126 as piston 122
compresses air
is used to effect a phase change of the working fluid from a liquid to a gas.
[0031] A cold source for the Rankine Cycle is provided in the form of
cold compressed
air expelled from interior 124 of piston housing 126. This cold compressed air
is directed
through the second heat exchanger 116 to effect a phase change of the working
fluid from
gas to liquid.
[0032] It is preferred that some of the compressed air generated be used
to power an air
driven motor 130 prior to being circulated through second heat exchanger 116.
Air driven
motor 130 can be used for various purposes, such as driving first pump 118.
Compressed air
exiting second heat exchanger 116 is vented to atmosphere 119.
[0033] Referring to FIG. 2, a portion of the compressed air 129 exiting
piston assembly
120 can be used to pressurize sequential piston assemblies in a series of
stages. Piston
assembly 120 draws air in through an atmospheric air intake. However, there is
excess
compressed air 129 that can be used to supply subsequent stages with air that
has already
been compressed and, consequently, the compression cycle for the subsequent
stage starts at
a higher pressure. This has been illustrated by a stage 2 identified as piston
assembly 120A,
stage 3 identified as piston assembly 120B and stage 4 identified as piston
assembly 120C. It
should be noted that with each sequential stage the pressure of the incoming
compressed air
has been increased by the prior stage. As a consequence the operating
pressures of piston
assembly 120A are higher than those in piston assembly 120; the operating
pressures of
piston assembly 120B are higher than those in piston assembly 120A; and the
operating
pressures of piston assembly 120C are higher than those in piston assembly
120B. This
sequential pressurization allows pressures to be achieved that would not be
possible with a
single piston assembly 120. It is to be noted that at each stage heat is
generated during
compression and that heat energy is captured and stored, in storage units
121A, 121B, 121C
respectively, for either heat exchange or other useful purposes.
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[0034] Referring to FIG. 5 and FIG. 6, further information is provided
regarding the
structure of heat exchanger 106 associated with piston assembly 120. In order
to capture
heat from piston assembly 120, piston housing 126 is dual walled, with a heat
capture space
127 positioned between the dual walls. In order to effect a heat exchange a
network of pipes
131 traverses heat capture space 127. Network of pipes 131 has an inlet 133
which connects
to liquid phase working fluid supply line 104 and an outlet 135 which connects
to gaseous
phase working fluid supply line 110.
Operation:
[0035] Referring to FIG. 1, wave energy converter 128, uses ocean wave
energy to
reciprocally move piston 122 between the extended position and the retracted
position. As
the wave goes down, piston 122 is moved to the extended position drawing air
into interior
124 of piston housing 126. As the wave goes up, piston 122 is moved to the
retracted
position compressing air within interior 124 of piston housing 126. Heat is
generated within
interior 124 of piston housing 126 as piston 122 compresses air. This heat is
captured and
transferred to the working fluid by first heat exchanger 106, causing a phase
change in the
working fluid from liquid to gas. First heat exchanger 106 then supplies
working fluid in gas
form to a turbine 112 through gaseous phase working fluid supply line 110. The
expansion
of the working fluid in gas form, causes turbine 112 to rotate producing work
output 117.
Working fluid in the form of gas exiting turbine 112 passes to second heat
exchanger 116
through working fluid recycle line 114.
[0036] The stream of cold compressed air exiting piston assembly 120 is
very cold.
This cold is captured and transferred to the working fluid by second heat
exchanger 116,
causing a phase change of the working fluid from gas back to liquid. The
compressed air
generated is used to power air driven motor 130 prior to being circulated
through second heat
exchanger 116. Air driven motor 130 is used to drive first pump 118. First
pump 118 pumps
working fluid in the form of liquid back through first heat exchanger 106 via
liquid phase
working fluid supply line 104. After passing through second heat exchanger
116, the
compressed air is vented to atmosphere 119.
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Variations:
[0037] A variation of ocean powered Rankine cycle turbine 100, will now
be described
with reference to FIG. 4. All of the elements of ocean powered Rankine cycle
turbine 100,
described above with reference to FIG. 1 are present and will be identified by
the reference
numerals with which they were identified in FIG. 1. However, this variation
incorporates
and intermeshes with Ocean Thermal Energy Conversion (OTEC) technology. So
that the
reader can understand how the elements of the OTEC technology were
incorporated, the
same reference numerals will be used as were used with FIG. 3. Totally new
elements that
are introduced to integrate the two technologies will be identified by 200
series reference
numerals.
[0038] The OTEC technology is used as a secondary Rankine cycle loop 10
in which is
circulated a working fluid which changes phase from a liquid to a gas when
heated. A liquid
phase working fluid supply line 34 feeds working fluid in liquid form to a
(third) heat
exchanger 18 to effect a phase change from liquid to gas. Gaseous phase
working fluid
exiting (third) heat exchanger 18 is directed to a gaseous phase working fluid
supply line 20
which supplies working fluid in gaseous form to a (second) turbine 22 which
produces work
output 29. A working fluid recycle line 32 feeds working fluid in gas form to
a (fourth) heat
exchanger 30 to effect a phase change from gas to liquid. (Fourth) heat
exchanger 30 is
connected by a liquid phase working fluid supply line 34 which supplies
working fluid in the
form of liquid to the (third) heat exchanger 18. A (second) pump 36 being
positioned on
liquid phase working fluid supply line 34 to pump the working fluid in the
form of liquid.
[0039] A heat scavenging heat exchanger 202 is placed on working fluid
recycle line 114
feeding working fluid in gas form to second heat exchanger 116 of primary
Rankine cycle
loop 102. A cold scavenging heat exchanger 204 is placed on working fluid
recycle line 114
feeding working fluid in gas form to second heat exchanger 116 of primary
Rankine cycle
loop 102.
[0040] An ocean heat source is provided by a (third) 12 pump which pumps
warm ocean
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water draw from a shallow water intake 14 through a warm water supply line 16
through heat
scavenging heat exchanger 202 of primary Rankine cycle loop 102 where the
working fluid
of primary Rankine cycle loop 102 is used to increase the temperature of the
warm ocean
water prior to passing into (third) heat exchanger 18 that is used to heat the
working fluid for
secondary Rankine cycle loop 10. The warm ocean water exiting the (third) heat
exchanger
18 is discharged back into the ocean through outlet 19.
[0041] An ocean cold source is provided by a (fourth) pump 24 which pumps
cold ocean
water drawn from a deep water intake 26 through a cold water supply line 28 to
the (fourth)
.. heat exchanger 30 that is used to cool the working fluid and then through
cold scavenging
heat exchanger 204 where the cold ocean water exiting the (fourth) heat
exchanger 30 of the
second Rankine cycle loop 10 is used to lower the temperature of the working
fluid of the
primary Rankine cycle loop 102 prior to passing into second heat exchanger 116
that is used
to cool the working fluid for primary Rankine cycle loop 102, with the cold
ocean water
exiting cold scavenging heat exchanger 204 being discharged back into the
ocean at outlet
205.
[0042] The Makai OTEC system uses ammonia as the working fluid and uses
input warm
water from the ocean surface at about 25 degree C (298 K). The cold water
intake from
deeper locations of the ocean are about 5 degrees C (278 K). This represents a
Carnot cycle
efficiency of approximately 6.7%. In a regular OTEC system, approximately 20%
of the
energy is required for the pumps and 80% is available for the turbine. Hence,
the actual
efficiency of a OTEC system akin to the Makai is approximately 5.4%.
.. Advantages:
[00431 The key benefits of Primary Rankine Cycle Loop 102 are that more
than 50% of
the energy captured is captured as heat. Without a suitable manner to use this
heat energy, it
will be lost since the mechanical systems are unable to deal with the heat
themselves. As
such, Primary Rankine Cycle Loop 102 identifies a manner in which this energy
may be
captured and used to power a load. This in turn potentially improves the
efficiency of ocean
capture wave devices of up to 50%.
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[0044] There are even greater benefits achieved through integration with
an OTEC
system:
[0045] 1. There is an increase Carnot engine efficiency ¨ by increasing
the temperature of
the intake water, the Carnot engine efficiency of the OTEC system will be
increased.
[0046] 2. There is an increase in actual efficiency. The actual
efficiency of the system will
be improved by a larger margin than the Carnot engine efficiency as the
incorporation of the
Primary Rankine Cycle Loop 102 will remove the need for pumping power to be
added.
This results in less power needed to run the system while still providing the
same output.
Any increase in the actual efficiency will improve the commercial viability of
the OTEC
system.
[0047] 3. There is a reduction of capital costs by removing or reducing
the need to source
cooler water from ocean depths with large, long intake pipelines ¨ since the
expansion of the
compressed air used to drive the working fluid pumps will aid the cooling of
the working
fluid, it will reduce the need to source cooler water from ocean depths. This
need represents
a large portion of the OTEC system capital cost, and any reduction in this
cost will result in
better system economics overall. The cost of a large diameter intake pipeline
sourcing water
from 3,300 feet (as described above) is likely be several factors more
expensive than adding
a Primary Rankine Cycle Loop 102.
[0048] 4. It will minimize environmental impacts associated with
discharge of heated
water ¨ as the working fluid of one system can be used to cool the working
fluid of the other
system so the water will be closer to the ambient temperature of the ocean.
Hence, the
environmental impacts associated with the discharge of the water will be
reduced.
[0049] 5. There will be an increase in the number of locations where
deployment of an
OTEC system are viable ¨ since the OTEC system requires an appropriate
difference in
ocean temperature, it is usually only tropical areas where this technology is
technically and
commercially feasible. However, as the addition of the Primary Rankine Cycle
Loop aids
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the heating and cooling of the intake water and working fluid respectively,
the modified
OTEC system is more likely to be feasible in less tropical areas. This expands
the market
potential for the modified OTEC system.
[0050] In this patent document, the word "comprising" is used in its non-
limiting sense
to mean that items following the word are included, but items not specifically
mentioned are
not excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires
that there be one and only one of the elements.
[0051] The scope of the claims should not be limited by the illustrated
embodiments set
forth as examples, but should be given the broadest interpretation consistent
with a purposive
construction of the claims in view of the description as a whole.
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