Note: Descriptions are shown in the official language in which they were submitted.
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CASCADING CLOSED LOOP CYCLE POWER GENERATION
FIE~,D OF THE INVENTION
The present invention relates to apparatus and methods for generating energy.
More
specifically, the present invention relates to the use of a Cascading Closed
Loop Cycle
employing particular devices and fluids that may be used in combination with
conventional
power generation systems to extract a useful amount of additional energy from
the
conventional power generation process.
BACKGROUND OF THE INVENTION
The primary process used to generate electricity is the combustion of a fossil
fuel to
heat air. This high temperature air, or thermal energy, is then. used to heat
a liquid power
generation medium (typically water) in a boiler to create a gas (steam) that
is expanded
across a steam turbine that drives an electrical generator. The measure of the
thermal energy
is the British Thermal Unit (BTU). Other sources of energy used to heat air
and/or water to
generate electricity in this mariner include: heat from nuclear reactions;
heat from the exhaust
of gas turbines; heat from the combustion of refuse or other combustible
materials in
incinerators; and others.
Steam turbine systems used to generate power are generally closed loop systems
in
which pressurized water is vaporized in a boiler or heat exchanger; expanded
in the steam
turbine where the pressure levels are reduced as power is generated; condensed
back to water
in a condenser or cooler; and pumped back to pressure and returned to the
boiler to repeat the
cycle. In the process of making steam in this closed loop system, there are
two major sources
of wasted energy. The first is the waste heat exiting the boiler in the form
of high
temperature flue gas (typically heated air) due to the inherent design and
thermodynamic
characteristics of the water to steam conversion process that prevents using
all the useful
thermal energy (heat) in the flue gas. The second is the latent heat of
vaporization or the
amount of energy required to convert water to steam that is dissipated to the
atmosphere
during the process of condensing the steam back to water.
In the first instance of wasted heat, the boiler heat source must provide
thermal energy
(in the form of high temperature flue gas) not only to deliver 1000 BTU/LB to
convert water
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to steam but also sufficient thermal energy to superheat the steam to high
enough energy
levels to provide sufficient excess energy to drive a steam turbine to
generate power. The
thermodynamic requirements of the steam cycle limit the temperature
differential available to
produce superheated steam to the difference between the original heat source
temperature and
approximately 400 to 500 °F. This results in wasted heated flue gas
exiting the boiler at
temperatures of about 400 to 500 °F. Although a portion of the energy
in the flue gas exhaust
may be recaptured by, for example, using it to heat the power plant, using it
to pre-heat the
boiler water, or by other known means, the amount of useful energy recovered
is limited.
In the second instance of wasted heat, the energy in the form of heat required
to
change the state of a liquid to a gas is controlled by the thermodynamic
characteristics of the
liquid. The pressure and associated temperature at which a fluid begins to
become a vapor is
defined as the vapor pressure of the fluid. For a given liquid there is a
specific range of
pressures and temperatures at which the liquid becomes a vapor. The BTUs
required to
change a liquid to a gas at the vapor pressure is defined as the "heat of
vaporization". The
heat of vaporization for water is approximately 1000 BTU/LB. At the vapor
pressure at
which water turns to steam, the amount of energy resident in the vapor is only
that amount
required to maintain a vaporous state and is defined as the "latent heat of
vaporization". At
the vapor pressure point, if the vapor is cooled in a condenser or the
pressure is reduced
through an expansion process, the vapor will change states back to a liquid by
discharging the
latent heat of vaporization, or 1000 BTU/LB to the environment as an increase
in thermal
energy or temperature of the cooling medium. As such, little, if any, useful
energy can be
extracted from a vapor that only contains the latent heat of vaporization
because such vapor
will immediately condense upon expansion in a turbine, causing dramatic
inefficiencies and
possibly damaging the turbine. The physical phenomenon of the heat of
vaporization causes
waste heat in conventional power generation cycles because this amount of heat
must be
imparted into the liquid water before it changes into a useful gaseous state
but this heat can
not be extracted as useful energy. Upon cooling the medium back to a liquid so
that it can be
pumped to the desired pressure, this latent heat is discharged without being
recaptured in the
form of useful energy. Thus, the thermal energy discharged to the atmosphere
through the
cooling medium that returns the water to the liquid state is waste heat.
Converting heat to useful power and developing power in a more efficient
manner
from the combustion of fossil fuels are of paramount importance as fuel costs
rise and energy
sources are depleted. In addition, the negative effects on the environment
caused by pollution
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generated from the combustion of fossil fuels dictates that power plants be
designed to reduce
the pollutants generated per unit of energy produced. These factors create a
need to improve
power plant efficiency and recover energy from waste heat generated by power
plants, waste
heat from various manufacturing processes, and thermal energy from renewable
energy
sources.
Various methods and processes are used to improve the efficiency of power
systems
that convert fossil fuels to usable energy. These efficiency-enhancing systems
include gas
turbine combined cycle plants, cogeneration plants and waste heat recovery
systems.
Cogeneration and combined cycle systems generate useful energy from the waste
heat of gas
turbine exhausts or other fossil fuel heat sources, including low grade
heating value fuel
sources, by using the heat of combustion to generate steam. In systems that
use water as the
primary power generation medium, the temperature of the heat source (typically
flue gas
heated by combusting fossil fuels) must be high enough to vaporize the water
to create steam
in a heat exchanger (boiler). The resulting steam is expanded in a steam
turbine to produce
power. Steam boilers are generally limited to recovering the thermal energy
associated with
the differential temperature between the initial temperature of the heat
source and about 500
°F or higher because this is the temperature required to achieve
efficient thermal energy
transfer to water to produce steam. Further, the available heat for
transferring energy to the
steam is limited by the temperature differential restrictions imposed by the
vapor pressure
versus temperature characteristics of steam, and using a heat source with a
temperature close
to about 500 °F can lead to inefficient and minimal steam production.
In a typical steam
power generation system, the low temperature 0500 °F) exhaust of the
heat source exiting
the boiler can be used to pre-heat the boiler feed water using a separate heat
exchanger.
However, only a limited amount of the heat in the discharge air is
recoverable, and this heat
is generally restricted to the temperature differential between the 500
°F discharge
temperature of the heat source exhaust and about 300 °F or above due to
the vapor pressure
and temperature characteristics of water. Using the exhaust heat to pre-heat
the boiler feed
water in this manner increases the overall efficiency of the system, and may
provide about a
10% increase in efficiency in some cases.
Some cogeneration and combined cycle systems also envision incorporating an
Organic Rankine Cycle (ORC) system in combination with the steam turbine
system to
capture additional power output from the low temperature exhaust stream of the
heat source
as it exits the boiler. Methods are known in the prior art that utilize an ORC
cycle to generate
useful power. Typical methods are disclosed, for example, in U.S. Patent Nos.
5,570,579 and
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5,664,414, which are incorporated herein by reference. These prior art systems
use a
conventional ORC medium such as normal pentane, iso-pentane, toluene,
fluorinated
hydrocarbons and other refrigerants. These conventional ORC media have
pressure and
temperature limitations and can not sustain high temperatures due to their
respective auto
ignition temperatures and vapor pressure versus temperature characteristics.
For example,
prior art ORC systems that utilize refrigerants or toluene are restricted to
operation with
heated water since the ORC medium can not absorb energy at elevated
temperatures. Other
prior art ORC methods require an ORC medium with a vapor pressure near
atmospheric
pressure to be efficient. Other prior art systems are restricted to a specific
power output
range while others require spraying a fluid ORC medium into the heat exchanger
for efficient
operation. These limitations reduce their effectiveness and efficiency thereby
restricting the
circumstances under which they can be employed, and limiting the useful energy
output that
may be obtained from them.
In addition, although the majority of energy is generated using closed loop
systems
(i.e., systems in which the power generation medium, such as water/steam is
constantly
recirculated) such as those described above, other methods of generating power
have been
created to take advantage of open loop power sources that require constant
replenishment of
the power generation medium. For example, where the pressure of light
hydrocarbon
supplies in petrochemical plants or on gas pipelines must be reduced before
being sent to
consumers, it is known to generate useful power by expanding the high pressure
gas in an
expansion turbine that operates an electrical generator, pump or compressor,
rather then
reducing the gas pressure in a valve where no energy is recovered. Examples of
this type of
technology are provided in U.S. Patent Nos. 4,711,093 and 4,677,827, which are
incorporated
herein by reference. These systems are open loop systems that require constant
replenishment of the power generation medium, and depend on the pressure level
of the
process design.
BRIEF DESCRIPTION OF THE INVENTION
In a first embodiment, the present invention provides a method for generating
energy.
This method includes the steps of providing a working fluid, increasing the
pressure of the
working fluid, dividing the working fluid into multiple streams, including at
least a first
stream and a second stream, transferring a first amount of heat energy from an
energy source
to the first stream and subsequently transferring a second amount of heat
energy from the first
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steam to the second stream, extracting a first amount of useful energy from
the first stream,
extracting a second amount of useful energy from the second stream, merging
the first stream
with the second stream, and reducing the first stream and the second stream to
a minimum
pressure. The minimum pressure is approximately equal to or below the vapor
pressure of
the working fluid at an ambient temperature.
In this embodiment, the step of transferring a second amount of heat energy
from the
first stream to the second stream may comprise the steps of transferring a
first portion of the
second amount of heat energy from the first stream to the second stream before
the step of
merging the first stream with the second stream; and transferring a second
portion of the
second amount of heat energy from the first stream to the second stream after
the step of
merging the first stream with the second stream. Also in this embodiment the
step of
transferring a first portion of the second amount of heat energy from the
first stream to the
second stream may be performed after the step of extracting a first amount of
useful energy
from the first stream. Still further in this embodiment, the sum of the first
amount of useful
energy and the second amount of useful energy may be equal to at least about
20% of the first
amount of heat energy.
In this and other embodiments of the invention, the working fluid may be
selected
from the group consisting of propane, propylene, light hydrocarbons and
combinations
thereof; the minimum pressure may be about 25 psia to about 300 Asia; the
ambient
temperature may be about -50 degrees Fahrenheit to about 160 degrees
Fahrenheit; the
energy source may be selected from the group consisting of fossil fuel energy,
nuclear
energy, solar energy, geothermal energy, waste heat, hydrogen and combinations
thereof.
Also in this and other embodiments, the working fluid may be pumped to a
pressure of about
300 psia to about 1000 psia.
In another embodiment, the present invention provides an apparatus for
generating
energy. The apparatus has: multiple fluid conduits, including at least a first
fluid conduit, a
second fluid conduit, and a combined fluid conduit, the multiple fluid
conduits being adapted
to contain a working fluid; a pump operatively attached to the multiple fluid
conduits and
adapted to pressurize the working fluid; an energy source; a first heat
exchanger operatively
attached to the first fluid conduit and adapted to allow a first amount of
heat energy to
transfer from the energy source to the working fluid in the first fluid
conduit; a second heat
exchanger operatively attached to the first fluid conduit and the second fluid
conduit and
adapted to allow a second amount of heat energy to transfer from the working
fluid in the
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first fluid conduit to the working fluid in the second fluid conduit, the
second heat exchanger
being positioned, with respect to the first fluid conduit, downstream of the
first heat
exchanger; a first fluid expander operatively attached to the first fluid
conduit and adapted to
extract a first amount of useful energy from the working fluid in the first
fluid conduit; a
second fluid expander operatively attached to the second fluid conduit and
adapted to extract
a second amount of useful energy from the working fluid in the second fluid
conduit; and a
cooling device operatively attached to at least one of the multiple fluid
conduits and adapted
to reduce the working fluid to a minimum pressure, the minimum pressure being
approximately equal to or below the vapor pressure of the fluid at an ambient
temperature.
The first fluid conduit and the second fluid conduit join at a merge point to
form the
combined fluid conduit.
In this second embodiment, the second heat exchanger may have a primary second
heat exchanger operatively attached to the primary fluid conduit and the
secondary fluid
conduit, and being located, with respect to the first fluid conduit, between
the first fluid
expander and the merge point, and being adapted to transfer a first portion of
the second
amount of heat energy from the working fluid in the first fluid conduit to the
working fluid in
the second fluid conduit; and a secondary second heat exchanger operatively
attached to the
second fluid conduit and the combined fluid conduit, and being positioned,
with respect to the
combined fluid conduit, between the merge point and the pump, and being
adapted to transfer
a second portion of the second amount of heat energy from the working fluid in
the combined
fluid conduit to the working fluid in the second fluid conduit. The second
heat exchanger
may be positioned, with respect to the first fluid conduit, after the first
fluid expander. Also
in this embodiment, the sum of the first amount of useful energy and the
second amount of
useful energy may be equal to at least about 20% of the first amount of heat
energy.
In still another embodiment, the present invention provides a method for
converting
heat to useful energy that includes the steps of providing a combined fluid
stream in a liquid
state; pressurizing the combined fluid stream; dividing the combined fluid
stream into a
primary fluid stream and a secondary fluid stream; applying thermal energy
from a heat
source to vaporize the primary fluid stream; expanding the vaporized primary
fluid stream to
produce a first amount of useful energy; transferring heat from the vaporized
and expanded
primary fluid stream to superheat the vaporized secondary fluid stream;
expanding the
vaporized second fluid stream to produce a second amount of useful energy;
mixing the
vaporized and expanded primary fluid stream with the vaporized and expanded
secondary
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fluid stream to form a combined fluid stream; transferring heat from the
combined fluid
stream to vaporize the secondary fluid stream; and condensing the combined
fluid stream to a
liquid state.
In this embodiment, the step of transferring heat from the combined fluid
stream to
vaporize the secondary fluid stream may also include the step of maintaining
the pressure of
the combined fluid stream above the vapor pressure of the fluid.
In still another embodiment, the present invention provides an apparatus for
converting heat to useful energy. The apparatus includes a combined fluid
conduit adapted to
convey a fluid stream; a pump operatively attached to the combined fluid
conduit; a stream
separator operatively attached to the combined fluid conduit downstream of the
pump, the
stream separator further being operatively attached to a primary fluid conduit
and a secondary
fluid conduit; a first heat exchanger operatively attached to the primary
fluid conduit
downstream of the stream separator, the first heat exchanger further being
operatively
attached to a heat source; a first expander operatively attached to the
primary fluid conduit
downstream of the first heat exchanger; a second heat exchanger operatively
attached to the
primary fluid conduit downstream of the first expander, the second heat
exchanger further
being operatively attached to the secondary fluid conduit; a third heat
exchanger operatively
attached to the secondary fluid conduit downstream of the fluid separator; the
third heat
exchanger further being operatively attached to the combined fluid conduit; a
second
expander operatively attached to the secondary fluid conduit downstream of the
second heat
exchanger; a stream mixer operatively attached to the combined fluid conduit,
to the primary
fluid conduit downstream of the second heat exchanger, and to the secondary
fluid conduit
downstream of the second expander; and a cooler operatively attached to the
combined fluid
conduit between the stream mixer and the pump. The third heat exchanger is
positioned, with
respect to the combined fluid conduit, between the stream mixer and the
cooler, and the
second heat exchanger is positioned, with respect to the secondary fluid
conduit, between the
third heat exchanger and the second expander.
In yet another embodiment, the present invention provides a method for
improving
the efficiency of a power system having an energy source and a cooling system.
The method
includes the steps of transferring a first amount of heat energy from the
cooling system to a
first loop of a cascading closed loop cycle system; extracting a first amount
of useful energy
from the first loop; transferring a second amount of heat energy from the
energy source to a
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second loop of a cascading closed loop cycle system; and extracting a second
amount of
useful energy from the second loop.
In this embodiment, the method may include the steps of transferring a third
amount
of heat energy from the second loop to a third loop of a cascading closed loop
cycle system
and extracting a third amount of useful energy from the third loop. Also in
this embodiment,
the power system may receive a fourth amount of heat energy from the energy
source and
may generate a fourth amount of useful energy. The sum of the first amount of
useful
energy, the second amount of useful energy, the third amount of useful energy
and the fourth
amount of useful energy may be equal to at least about 30% of the fourth
amount of heat
energy.
W another embodiment, the present invention provides a method for improving
the
efficiency of a power system having an energy source and a cooling system. The
method has
the steps of providing a working fluid; increasing the pressure of the working
fluid; dividing
the working fluid into multiple streams, including at least a first stream and
a second stream;
transferring a first amount of heat energy from the cooling system to the
first stream;
extracting a first amount of useful energy from the first stream; transferring
a second amount
of heat energy from the energy source to the second stream; extracting a
second amount of
useful energy from the second stream; and cooling the working fluid to a
minimum pressure,
the minimum pressure being approximately equal to or below the vapor pressure
of the
working fluid at an ambient air temperature.
In this embodiment, the second stream may comprise a primary second stream and
a
secondary second stream, and the step of transferring a second amount of heat
energy from
the energy source to the second stream may include transferring the second
amount of heat
energy from the energy source to the primary second stream, and transferring a
portion of the
second amount of heat energy from the primary second stream to the secondary
second
stream. Also in this embodiment, the step of extracting a second amount of
useful energy
from the second stream may include extracting a first portion of the second
amount of useful
energy from the primary second stream, and extracting a second portion of the
second
amount of useful energy from the secondary second stream. In this embodiment,
the power
system may be a steam power generation system.
In still another embodiment, the present invention provides a method for
generating
energy. In this embodiment, the method includes the steps of: providing a
first working fluid;
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increasing the pressure of the first working fluid; transferring a first
amount of heat energy
from an energy source to the first working fluid; extracting a first amount of
useful energy
from the first working fluid; providing a second working fluid; increasing the
pressure of the
second worlting fluid; dividing the second worlcing fluid into multiple
streams, including at
least a first stream and a second stream; transferring a second amount of heat
energy from the
first working fluid to the first stream; extracting a second amount of useful
energy from the
first stream; transferring a third amount of heat energy from the energy
source to the second
stream; extracting a third amount of useful energy from the second stream; and
cooling the
second working fluid to a minimum pressure, the minimum pressure being
approximately
equal to or below the vapor pressure of the second working fluid at an ambient
air
temperature.
In this embodiment, the second stream may have a primary second stream and a
secondary second stream, and the step of transferring a third amount of heat
energy from the
energy source to the second stream may include the steps of transferring the
third amount of
heat energy from the energy source to the primary second stream, and
transferring a portion
of the third amount of heat energy from the primary second stream to the
secondary second
stream. Still further, in this embodiment, the step of extracting a third
amount of useful
energy from the second stream may include the steps of extracting a first
portion of the third
amount of useful energy from the primary second stream, and extracting a
second portion of
the third amount of useful energy from the secondary second stream. In this
embodiment, the
first working fluid may be water.
In yet another embodiment, the present invention provides a method for
improving
the efficiency of a power system having an energy source and a cooling system.
The method
of this embodiment includes: providing a working fluid; increasing the
pressure of the
working fluid; dividing the working fluid into a first stream a second stream
and a third
stream; transferring a first amount of heat energy from the cooling system to
the first stream;
extracting a first amount of useful energy from the first stream; transferring
a second amount
of heat energy from the energy source to the second stream; extracting a
second amount of
useful energy from the second stream; transferring a third amount of heat
energy from the
second stream to the third stream; extracting a third amount of useful energy
from the third
stream; and cooling the working fluid to a minimum pressure, the minimum
pressure being
approximately equal to or below the vapor pressure of the working fluid at an
ambient air
temperature.
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In this embodiment, the step of transferring a second amount of heat energy
from the
energy source to the second stream may include transferring a first portion of
the second
amount of heat energy from the energy source to the second stream in a first
heat exchanger,
and transferring a second portion of the second amount of heat energy from the
energy source
to the second stream in a second heat exchanger. Also in this embodiment, the
step of
extracting a first amount of useful energy from the first stream may include
expanding the
first stream in a first expander, the step of extracting a second amount of
useful energy from
the second stream may include expanding the second stream in a second
expander, and the
step of extracting a third amount of useful energy from the third stream may
include
expanding the third stream in a third expander. In this embodiment, the power
system may
be a steam power generation system.
In still another embodiment, the present invention provides an apparatus for
generating supplemental energy from a power system having an energy source and
a cooling
system. The apparatus of this embodiment has the features of: multiple fluid
conduits,
including at least a first fluid conduit, a second fluid conduit, and a
combined fluid conduit,
the multiple fluid conduits being adapted to contain a working fluid; one or
more pumps
operatively attached to the multiple fluid conduits and adapted to pressurize
the working
fluid; a first heat exchanger operatively attached to the first fluid conduit
and adapted to
allow a first amount of heat energy to transfer from the cooling system to the
working fluid in
the first fluid conduit; a first fluid expander operatively attached to the
first fluid conduit and
adapted to extract a first amount of useful energy from the working fluid in
the first fluid
conduit; a second heat exchanger operatively attached to the second fluid
conduit and adapted
to allow a second amount of heat energy to transfer from the energy source to
the working
fluid in the second fluid conduit; a second fluid expander operatively
attached to the second
fluid conduit and adapted to extract a second amount of useful energy from the
working fluid
in the second fluid conduit; and a cooling device operatively attached to at
least one of the
multiple fluid conduits and adapted to reduce the working fluid to a minimum
pressure, the
minimum pressure being approximately equal to or below the vapor pressure of
the fluid at
an ambient temperature. The first fluid conduit and the second fluid conduit
join at one or
more merge points to form the combined fluid conduit.
In this embodiment, the multiple fluid conduits may further include a third
fluid
conduit, and the apparatus may further have a third heat exchanger operatively
attached to the
second fluid conduit and the third fluid conduit and adapted to transfer a
third amount of heat
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energy from the working fluid in the second fluid conduit to the working fluid
in the third
fluid conduit and a third fluid expander operatively attached to the third
fluid conduit and
adapted to extract a third amount of useful energy from the worlcing fluid in
the third fluid
conduit. In this embodiment, the third heat exchanger may be located, relative
the second
fluid conduit, after the second fluid expander. Also in this embodiment, the
second heat
exchanger may be two heat exchangers. Still further, in this embodiment the
power system
may receive a fourth amount of heat energy from the energy source and may
generate a
fourth amount of useful energy. The sum of the first amount of useful energy,
the second
amount of useful energy, the third amount of useful energy and the fourth
amount of useful
energy may be equal to at least about 30% of the fourth amount of heat energy.
In still another embodiment, the present invention provides an apparatus for
converting heat energy to useful energy. The apparatus includes a primary
power system and
a secondary power system. The primary power system has: an energy source; a
primary fluid
conduit adapted to contain a primary working fluid; a primary fluid pump
operatively
attached to the primary fluid conduit and adapted to pressurize the primary
working fluid; a
primary fluid heat exchanger operatively attached to the primary fluid conduit
and adapted to
allow a first amount of heat energy to transfer from the energy source to the
primary fluid
contained in the primary fluid conduit; and a primary fluid expander
operatively attached to
the primary fluid conduit and adapted to extract a first amount of useful
energy from the
primary working fluid in the primary fluid conduit. The secondary power system
has: a
secondary fluid conduit system comprising a first fluid loop, a second fluid
loop, and a third
fluid loop, the secondary fluid conduit system being adapted to contain a
secondary working
fluid; one or more secondary fluid pumps operatively attached to the secondary
fluid conduit
system and adapted to pressurize the secondary working fluid; a first heat
exchanger
operatively attached to the first fluid loop and the primary fluid conduit and
being positioned,
relative to the primary fluid conduit, between the primary fluid expander and
the primary
fluid pump, the first heat exchanger being adapted to allow a second amount of
heat energy to
transfer from the primary fluid in the primary working fluid conduit to the
secondary working
fluid in the first fluid loop; a first fluid expander operatively attached to
the first fluid loop
and adapted to extract a second amount of useful energy from the secondary
working fluid in
the first fluid loop; a second heat exchanger operatively attached to the
second fluid loop and
adapted to allow a third amount of heat energy to transfer from the energy
source to the
secondary working fluid in the second fluid loop; a second fluid expander
operatively
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attached to the second fluid loop and adapted to extract a third amount of
useful energy from
the secondary working fluid in the second fluid loop; a third heat exchanger
operatively
attached to the second fluid loop and the third fluid loop and being located,
relative the
second fluid loop, after the second fluid expander, the third heat exchanger
being adapted to
allow a fourth amount of heat energy to transfer from the secondary working
fluid in the
second fluid loop to the secondary working fluid in the third fluid loop; a
third fluid expander
operatively attached to the third fluid loop and adapted to extract a fourth
amount of useful
energy from the secondary working fluid in the second fluid loop; and a
cooling device
operatively attached to the secondary fluid conduit system and adapted to
reduce the
secondary working fluid to a minimum pressure, the minimum pressure being
approximately
equal to or below the vapor pressure of the secondary working fluid at an
ambient
temperature.
In this embodiment, the primary working fluid may be water. Also in this
embodiment, the sum of the first amount of useful energy, the second amount of
useful
energy, the third amount of useful energy and the fourth amount of useful
energy may be
equal to at least about 30% of the first amount of heat energy.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention may be more readily understood by reference to the
accompanying drawings, which are briefly described as follows.
Figure 1 is schematic diagram of an embodiment of a cascading closed loop
cycle
(CCLC) power generation system of the present invention.
Figure 2 is a Mollier diagram of the power cycle of the CCLC of Figure 1.
Figure 3 is a schematic of a typical prior art steam power generating system.
Figure 4 is schematic diagram of an embodiment of a super cascading closed
loop
cycle (Super-CCLC) power generation system of the present invention.
Figure 5 is a Mollier diagram of the power cycle of the steam portion of the
Super-
CCLC of Figure 4.
Figure 6 is a Mollier diagram of the power cycle of the CCLC portion of the
Super-
CCLC of Figure 4
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Developing electricity in a more efficient manner is of paramount importance
as
energy sources are depleted and the pollution generated from the combustion of
fossil fuels
continues to harm the environment. The Cascading Closed Loop Cycle of the
present
invention provides a closed loop power generation system that may be used as a
primary
power source. With the CCLC, improved efficiency is provided by reducing the
amount of
energy lost to overcome the latent heat of vaporization of the power
generation medium and
more effectively capturing heat from available heat sources and converting
this heat to useful
energy. The Super Cascading Closed Loop Cycle (Super-CCLC) of the present
invention
offers a secondary power source that can be used in conjunction with
conventional power
systems to increase power generation efficiency by generating useful energy
from the heat
lost in the process of generating power using steam turbines or other
conventional power
systems. In the Super-CCLC, improved efficiency comes from recovering energy
from the
two sources of waste heat noted in the Background of the Invention. The first
source is the
recovery of the waste heat exiting the boiler and the second source is
recovery of the waste
heat discharged during the condensing process.
It can be shown thermodynamically that converting thermal energy to mechanical
energy is performed particularly well with the Organic Rankine Cycle (ORC).
The Super
CCLC system is an ORC designed to convert the heat lost in the process of
developing steam
turbine power. U.S. Patent Application No. 10/199,257, filed on July 22, 2002,
which is
incorporated herein by reference, describes a method to utilize an ORC cycle
to generate
useful power using propane, propylene, or an equivalent or similar light
hydrocarbon
medium, as the fluid medium in a Cascading Closed Loop Cycle (CCLC). As used
herein,
the term "fluid" means any material in a liquid, gaseous and/or vaporous
state. Generally, the
materials described herein as "fluids" will remain in a liquid, gaseous andlor
vaporous state at
all times, but it will be appreciated that such fluids may solidify under some
circumstances,
but typically not during the operation of the inventions described herein. The
present
invention further envisions using multiple integrated CCLC systems to
simultaneously
recover the waste heat exiting a steam boiler (or other heat source) and the
waste heat from
the steam condensing process (or similar process).
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Various preferred embodiments of the present invention are now described in
more
detail with reference to the attached Figures.
In one embodiment, the present invention utilizes a unique arrangement and
method
for operating a Cascading Closed Loop Cycle (CCLC) to extract additional
efficiency from
energy sources. The Cascading Closed Loop Cycle (CCLC) is a hermitically
sealed closed
loop process. As shown in Figure 1, the CCLC 100 has a primary fluid stream,
which is
generally designated by the letter A, a secondary fluid stream, B, and a
combined fluid stream
C. The combined fluid stream C comprises essentially the entire supply of the
power
generation medium, which preferably comprises a light hydrocarbon material,
and more
preferably comprises propylene, propane or a combination of these materials.
Primary fluid
stream A and secondary fluid stream B comprise portions of the combined fluid
stream C that
have been divided by a stream separator 104.
The CCLC 100 begins at a high pressure pump 102 that pumps the combined fluid
stream C, in a liquid state, to the desired initial pressure. (Because this is
a closed loop
system in which the cycle continually recirculates, there is technically no
point at which the
system "begins," so the selection of this point as the beginning point is
arbitrary and made
solely for clarity of explanation.) At this point, the combined fluid stream C
has certain
physical properties (pressure, temperature and mass flow rate), defined herein
as state CI.
State C1 and other states of the fluid streams at various points in the
process are described in
more detail elsewhere herein. The combined fluid stream C is then divided to
become the
primary fluid stream A, having state Al, and the secondary fluid stream B,
having state B1, by
a stream separator 104. The various states described herein are
approximations, and although
a portion of the apparatus is designated as having a single state, that state
may have variations
in temperature, pressure and so on caused by friction, local heating or
cooling, fluid
dynamics, and so on.
The primary fluid stream A is routed to a primary indirect heat exchanger 106,
where
the primary fluid stream A is vaporized by exposure to a heat or energy
source. The heat or
energy source can be any available source of heat, such as combustion of
fossil fuels or
hydrogen, nuclear reactions, solar heat, fuel cells, geothermal energy, waste
heat, and so on.
In addition, the heat source can be excess heat from other industrial
operations. Non-limiting
examples of such heat sources are: heat from smelters, chemical processing and
refining
systems, drying systems, kilns and ovens, boilers, heaters and furnaces, gas
turbines, and so
on. The amount of heat transferred to the primary fluid stream is identified
as Qlo6. In Figure
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1, the heat source is a flow of air (flue gas) heated by burning fossil fuel,
and is generally
designated by the letter H. Flue gas H enters the primary indirect heat
exchanger 106 at state
Hl, and exits at state H2. Flue gas H leaving the primary indirect heat
exchanger 106 may be
released to the atmosphere through a smoke stack or the like. Of course, any
type of heat
exchanging device may be used for primary indirect heat exchanger 106, or any
other heat
exchanger, cooler, condenser, etc. described herein. The selection of the
particular heat
exchanging device may depend on the type of heat source being used. For
example, in
various embodiments the heat exchanging device may be an air-to-liquid heat
exchanger, a
water tube boiler, a shell (fire tube boiler), or the like. The selection and
use of such devices
is known in the art.
Once vaporized, the primary fluid stream A is at state A2. The primary fluid
stream is
then expanded in a primary expansion turbine 108 (preferably a turbo-expander)
until it
reaches state A3, thereby creating a first supply of useful energy WloB. Once
expanded, the
primary fluid stream A is routed to a secondary indirect heat exchanger 110,
where the
primary fluid stream A adds heat to the secondary fluid stream B, and exits at
state A4. The
heat transfer between the primary and secondary fluid streams is identified as
Qlo. Finally,
the primary fluid stream A is discharged into a stream mixer 112, where it is
combined with
the secondary fluid stream B. The combined primary and secondary fluid streams
become
the combined fluid stream C, which is at state C2.
The secondary indirect heat exchanger 110 superheats the secondary fluid
stream B
by using heat remaining in the vaporized fluid of primary fluid stream A after
it exits the
primary expansion turbine 108. The secondary fluid stream B enters the
secondary indirect
heat exchanger 110 at state B2, and exits at state B3. The secondary fluid
stream B having
state B3 is then directed to a secondary expansion turbine 116 for generating
a second supply
of useful energy W ~ 16. The secondary fluid stream changes to state B4 as it
passes through
the secondary expansion turbine 116. The secondary fluid stream B is then
combined with
the primary fluid stream A in the stream mixer 112 to form the combined fluid
stream C, as
previously explained. The combined fluid stream C is then directed to a
tertiary indirect heat
exchanger 114 where heat in the combined fluid stream C is transferred to the
secondary fluid
stream B, causing the secondary fluid stream B to change from state B~ to
state B2, and
causing the combined fluid stream to change from state C2 to state C3. The
amount of heat
transferred from the combined fluid stream to the secondary fluid stream is
identified as Qn4.
After exiting the tertiary indirect heat exchanger 114, the combined fluid
stream C is directed
to a condenser 118 where the combined fluid stream C is condensed to a liquid
having state
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C4. Heat, in the amount of Q11$ is extracted from the combined fluid stream C
by the
condenser 118 and absorbed by any suitable cooling medium, such as water or
air. Once the
fluid of the combined fluid stream C is condensed back to a liquid state, it
is directed to the
high pressure pump 102 to begin the cycle anew. Pump 102 requires a certain
amount of
power Ploz to pressurize the combined fluid stream C to the desired state C1.
The primary expansion turbine 108 and secondary expansion turbine 116 may be
connected in series or parallel to an energy generation device using any speed
changing
means to produce mechanical or electrical energy. Alternatively, one or both
of the
expansion turbines may be attached to compressors, pumps, electrical
generators or other
devices that may be used to provide additional useful energy or work.
Furthermore, the
CCLC of Figure 1 may be modified within the basic idea to include additional
heat
exchangers, condensers, pumps or expansion turbines. Pumps, stream separators,
heat
exchangers, expansion turbines, turbo-expanders, condensers and equivalent and
alternative
devices are well known in the art. Furthermore, techniques and devices for
attaching these
various devices are also known in the art.
The Cascading Closed Loop Cycle of the present invention is now further
explained
with reference to Figure 2, which is a Mollier (i.e., pressure vs. enthalpy)
diagram for the
CCLC power generation cycle. In Figure 2, pressure is represented by the
vertical axis 250,
enthalpy (i.e., BTU per pound) is represented by the horizontal axis 252, and
numerous
isotherms 254 are depicted, along with the saturation curve 256 of the working
fluid. The
working fluid in the embodiment of Figure 2 preferably is propane. Also in
Figure 2, the
combined fluid stream C of Figure 1 is depicted as double line C, the primary
fluid stream A
is depicted as single line A, and the secondary fluid stream B is depicted as
dashed line B.
For clarity, the lines representing the fluid streams have been separated in
some locations to
be clearly distinguishable from one another. Also for clarity, each of the
points on Figure 2
symbolically represents the temperature and pressure of one or more of the
states (e.g., state
C1, state C2, state A1, state B1, etc.) described above with reference to
Figure 1. For clarity,
single points are used, however one of ordinary skill will readily recognize
that the various
states represented by each point may be located apart from one another in
actual practice.
The CCLC of Figure 2 begins, for the purposes of this discussion, at point 201
(corresponding to states Al, B1 and C1), at which point the combined fluid
stream C has been
pressurized by the high pressure pump 102 and divided into separate streams.
States C1, Al
and B1 are approximately the same, with some differences being attributable to
pumping
losses, friction, and the like. Beginning from point 201, the first fluid
stream A and second
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fluid stream B are processed along separate paths. The first fluid stream A is
heated at an
approximately constant pressure to point 202 (state AZ) by absorbing heat from
the flue gas H
in the primary indirect heat exchanger 106. The first fluid stream A is then
expanded,
essentially along a line of constant entropy (not shown), in the primary
expansion turbine 108
until it reaches point 203 (state A3). Next, the first fluid stream A is
cooled at an
approximately constant pressure to point 204 (state A4) by releasing heat to
the secondary
fluid stream B in the secondary indirect heat exchanger 110. At this point,
the primary fluid
stream A is mixed with the secondary fluid stream B to once again become the
combined
fluid stream C.
The secondary fluid stream B also begins at point 201 (representing state B1),
and is
heated at an approximately constant pressure to point 205 (state BZ) by
absorbing heat from
the combined fluid stream C in the tertiary indirect heat exchanger 114. Next,
the secondary
fluid stream B is heated at an approximately constant pressure to point 206
(state B3) by
absorbing heat from the primary fluid stream A in the secondary indirect heat
exchanger 110.
The secondary fluid stream B is then expanded, essentially along a line of
constant entropy
(not shown), in the secondary expansion turbine 116 until it reaches point 204
(state B4),
where it is mixed with the primary fluid stream A to form the combined fluid
stream C.
Once combined, the combined fluid stream C is cooled at an approximately
constant
pressure to point 207 (state C3) by releasing heat to the secondary fluid
stream B in the
tertiary indirect heat exchanger 114, as noted above. The combined fluid
stream C is then
cooled even further by the condenser 118 until it reaches point 208 (state
C4). Again, the
cooling from point 207 to point 208 occurs at a relatively constant pressure.
After the
combined fluid stream is cooled to a liquid state, the high pressure pump 102
pumps it, at a
relatively constant temperature, to point 201 (state C1) to begin the cycle
anew.
By carefully selecting and controlling the various states of the fluid
streams, the
present invention may be used to provide extremely efficient power generation
when
compared to conventional steam power generation systems. Table 1 provides
approximate
values for a preferred embodiment of the various states identified in Figure
1, as well as other
data related to the operation of the preferred embodiment. The working fluid
in Table 1 is
propane. While the data provided in Table 1 and elsewhere herein represents
certain
preferred embodiments of the invention, it will be understood that these
values may be
changed significantly or adapted to particular operating systems or operating
requirements
without leaving the scope and spirit of the invention.
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Fluid Heat Transfer
States Rates
(Properties) BTU/hr
132,
Temperature
Pressure
Flow
Rate
(F) Qio6 146,300,000
(psia)
(lb/hr)
Hl 750 24.7 833,300 Qiio 29,040,000
Hz 132 14.7 833,300 Qlia 122,700,000
C~ 110 770 706,800 Q11$ 114,300,000
Cz 464 204 706,800
C3 156 199 706,800 Power
C4 100 189 706,800
AI 110 770 304,400 BTU/hr
Az 700 765 304,400 Wlo$ 17,013,000
A3 608 209 304,400 W1s 19,291,000
A4 464 204 304,400 Pioz - 4,301,000
B1 110 770 402,400 NET 32,003,000
Bz 454 765 402,400
B3 558 760 402,400
B4 464 204 402,400 ~ Efficiency:21.9%
Table l: CCLC (Figure 1)
The efficiency of the embodiment of the CCLC provided in Table 1 is calculated
as
the net power (WloB + Wlis - Pioz) divided by the amount of heat entering the
system from the
heat source (Qlo6). It has been discovered that the efficiency of the present
invention greatly
exceeds the efficiency of conventional power systems. This greater efficiency
can be used to
increase power output or reduce resource consumption, and can be readily used
to provide
significant environmental benefits in the form of reduced emissions (both in
the amount of
pollutants and the thermal pollution caused by high-temperature exhausts) and
increased
resource conservation. Other benefits of this improved efficiency are too
numerous to list,
but will be readily grasped by those of ordinary skill in the art. W a
preferred embodiment,
the efficiency of the CCLC is at least about 17%, and more preferably at least
about 20%.
Furthermore, as can be seen in Table 1, it has been found that the efficiency
of one preferred
embodiment of the present invention is nearly 22%. This efficiency is
significantly greater
than the efficiency obtained by prior art steam power generation systems of
comparable cost
and complexity. An example of such a steam power generation system is provided
in Figure
3.
In the prior art steam system 300 of Figure 3, a water fluid flow, generally
designated
by the letter S, is circulated through the system 300. A pump 202 pressurizes
the water fluid
flow to state S 1. The pump 202 requires a certain amount of power Pzoz to
pressurize the
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water. The pressurized water is then heated and vaporized into steam having
state SZ in an
indirect heat exchanger 204 by flue gas 220 or any other conventional heat
source. The flue
gas 220 enters the indirect heat exchanger 204 at state HI, and exits at Hz,
imparting heat in
the amount of Q2od to the water fluid flow S. The steam is then directed to an
expansion
turbine 206, where it is expanded to state S3, thereby creating a supply of
useful energy WZOS.
The steam is cooled in a condenser 208 or other type of cooler until it
becomes a liquid
having state S4. During this cooling process, heat in the amount of Q2o8 must
be removed
from the steam in order to condense it into a liquid. Table 2 shows typical
optimized
approximate values for the various states and other variables of the prior art
steam system
300 of Figure 3.
Fluid Heat Transfer
States Rates
(Properties) BTU/hr
132,
Temperature
Pressure
Flow
Rate
(F) (psia) (lb/hr) QZO4 80,210,000
Hl 750 24.7 833,300 QZOB 67,410,000
HZ 409 14.7 833,300
S1 104 770 62,258 Power
SZ 730 765 62,258
S3 209 11 62,258 BTU/hr
S4 100 1 62,258 Wzos 13,038,000
Plot - 237,100
NET 12,800,900
Efficiency: 16.0%
Table 2: Steam Cycle (Figure 3) (Prior Art)
As shown in Table 2, the conventional steam cycle receives the same heat input
as the
CCLC demonstrated in Figures 1 and 2 and Table 1 -both systems receive an
833,300 lb/hr
supply of flue gas at 750 F and 24.7 psia as the heat source. However, the
conventional
steam cycle has an efficiency ((WZO6 - Pioz) / Qzo4) of 16.0%, as compared to
an efficiency of
21.9% for the CCLC. Thus, the CCLC provides about a 33% efficiency increase
over
conventional steam systems. This higher efficiency is provided despite the
additional
pumping energy required by the CCLC system due to the slightly compressible
nature of
liquid propane or equivalent light hydrocarbons.
The present invention is able to provide this remarkable increase in
efficiency in part
because it operates using propane or other light hydrocarbons as the operating
fluid, rather
than water. It has been discovered that propane has certain properties that
provide numerous
advantages over water when being used in a power generation cycle. In any
power
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generation cycle, the working fluid (typically water) must be pumped while in
a liquid state,
heated to change it into a gas, further heated to impart greater energy to the
gas, expanded
(decompressed) to obtain useful energy, and cooled into a liquid to be pumped
back into the
cycle. As noted elsewhere herein, the amount of energy that is required to
change the fluid
from a liquid to a gas is essentially lost without being converted to useful
energy.
Advantageously, propane has a relatively low latent heat of vaporization
(about 1/7th that of
water), so that it takes less energy to change the liquid propane into gaseous
propane. This
provides a substantial energy savings over conventional steam-based power
systems.
The present invention also has other features that contribute to obtaining a
relatively
high efficiency. For example, it has been discovered that propane can be
practically
employed in a high-temperature power generation system by maintaining the
propane at a
minimum pressure of about 200 psia. This is the approximate pressure at which
the propane
condenses at room temperature (i.e., the vapor pressure of propane). By
keeping the
minimum pressure at or below the vapor pressure of the working fluid, the
system may be
operated in typical climactic conditions without requiring active cooling
(i.e., refrigeration) to
condense the working fluid into a liquid. In practice, it will be sufficient
to establish the
minimum pressure at approximately the vapor pressure of the working fluid for
the given
ambient temperature. Some variation in this pressure may be allowed to
accommodate
expected or unexpected fluctuations in the ambient temperature, to maximize
the overall
efficiency of the system, or for other reasons as will be apparent to those of
ordinary skill in
the art. The maximum pressure of the propane preferably can also be regulated.
The
pressure of the propane exiting the pump may be varied to optimize the turbo-
expander
expansion ratios with the energy available from the heat source and the work
required to
pump the fluid to a particular pressure. In a preferred embodiment, the
maximum pressure of
the propane is about 300 psia to about 1000 psia, although other pressures may
be used
depending on the circumstances. One of ordinary skill in the art will be able
to optimize the
propane pressure to obtain this or other objectives.
Another advantageous property of propane, provided by its lower heat of
vaporization
than water, is that it can be superheated (i.e., can recover more heat) to
produce more excess
energy for expanding in a turbine at temperature ranges between 100 °F
to 1000 °F. Indeed,
propane can recover available heat at temperatures approaching normal ambient
temperatures, allowing the CCLC to be used to generate power from low-
temperature heat
sources. As such, a CCLC of the present invention can be used in place of
steam systems or
other high-temperature systems, or in place of low-temperature ORC systems.
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The high efficiency of the present invention is also provided in part by the
unique
cascading turbine arrangement in which successive turbines are operated by
"cascading" the
energy obtained from the heat source from one fluid stream to the next. Still
further, the high
efficiency of the present invention is also provided, in part, by a unique
tertiary indirect heat
exchanger arrangement to preheat the secondary fluid stream, providing still
greater increases
in efficiency.
In addition to increased efficiency, the CCLC provides additional performance
advantages over conventional steam systems. For instance, the efficiency of
the CCLC is not
adversely affected by altitude changes or variations in the pressure of the
heat source
(provided the heat source is of sufficient temperature to vaporize the
propane) because the
working fluid is hermetically sealed in its own enviromnent. Of course, the
heat source that
powers the CCLC may be adversely affected by the altitude, leading to a
corresponding
reduction in power output - however the efficiency of the CCLC will remain
substantially
the same.
In addition, the power output of the CCLC increases as the ambient temperature
decreases because as the ambient temperature decreases, the pressure at which
the
condensing begins also decreases. As such, when operating in a colder
enviromnent, the
lower limit of the propane pressure can be reduced, while maintaining the
remaining
pressures of the propane at the same levels. As this is done, the pressure
differential of the
propane increases, and the expansion ratio of the turbo-expander can be
increased to take
advantage of the additional amount of energy available across this broader
pressure range.
This advantage may also be realized by using a colder condensing medium than
ambient air.
For example, if cold water (e.g., 40 degrees Fahrenheit) is used as the
cooling medium to
condense the propane into a liquid, the system may be modified to operate the
turbo-expander
at a lower baclcpressure to take advantage of the fact that the propane will
condense at a
correspondingly lower pressure. In contrast, conventional steam systems are
largely
temperature independent. This feature makes the CCLC system even more
desirable for use
in colder climates. Although it is anticipated that the present invention will
be efficient when
used without substantial modification at a wide range of ambient temperatures,
it may be
desirable to modify the minimum pressure of the propane (or other medium) to
be
approximately equal to or below vapor pressure of the propane at the
particular ambient
temperature of the power generation facility. Preferably, the ambient
temperature is between
about -50 degrees Fahrenheit to about 160 degrees Fahrenheit, and the minimum
pressure is
adjustable from about 25 psia to about 300 psia. Of course, these range
limitations are not
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limiting, and the present invention may be readily modified to have pressures
below or above
these ranges to take advantage of the particular operating conditions expected
for the system.
The CCLC of the present invention provides still other advantages. For
example, a
CCLC system of the present invention can be built at or below the cost of a
conventional
steam power generation system. This is because propane can be expanded using
relatively
inexpensive turbo-expanders, rather than expensive steam turbines. However,
even if the
construction cost of the CCLC exceeds that of a conventional power system, the
higher
efficiency of the CCLC also allows any excess manufacturing costs to be
recaptured by lower
operating costs and/or higher power output. Typical turbo-expanders that may
be used with
the present invention include those commercially available from GE Power
Systems, ABB
Alstom, Atlas Copco, Mafi Trench and GHH-Borsig. The turbo-expanders may be of
any
design, and in one embodiment, the turbo-expanders are centrifugal-type
expanders.
The CCLC also offers numerous service benefits. Conventional steam systems
require periodic cleaning and chemical treatment to prevent or reduce scale
buildup caused
by minerals in the water. Steam systems also may be run so that the steam
obtains a negative
vacuum relative to the atmosphere, which allows air and other contaminants to
enter the
system, reducing its efficiency. In typical steam systems, the water must be
bled off to
remove contaminants and replaced at regular intervals to maintain the system.
This results in
a large consumption of valuable water resources. In contrast a propane CCLC
system can be
hermetically sealed with relatively pure propane, requiring little cleaning or
maintenance.
Still further, the CCLC operates at lower waste heat discharge temperatures
(i.e., the
temperature at state C3) than steam systems (i.e., the temperature at state
S3), which allows
the CCLC to be cooled by natural water resources such as lakes and rivers
while minimizing
the amount of heat pollution created. The CCLC also operates entirely above
atmospheric
pressure, eliminating the possibility of contaminants leaking into the system,
and eliminating
the need to consume water resources to maintain the system. The CCLC also
operates at the
same pressure range as conventional systems, and therefore may be fabricated
using
conventional construction techniques and plumbing technology.
W another embodiment, the present invention may be used in conjunction with a
conventional steam system or any other source of heat. In this embodiment, the
present
invention comprises a Super Cascading Closed Loop Cycle (Super-CCLC) for
converting
waste heat into usable power. In one embodiment, the Super-CCLC system
develops power
in a cascading expansion turbine arrangement using propane, or an equivalent
light
hydrocarbon medium, by converting the waste heat from the boiler exhaust and
the waste
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heat from the condensing process into useful output as long as the temperature
of these heat
sources are high enough to vaporize propane. The present invention consists of
one or more
indirect heat exchangers, expansion turbines, stream mixers; condensing units;
pumps; and
stream separators operating in conjunction with a steam boiler and steam
turbine. In the
event the steam turbine is a vacuum design, the steam turbine preferably is
modified to
operate as a back pressure steam turbine with the back pressure controlled at
about 25 psia
with the vacuum condensing system being modified, eliminated or bypassed. A
propane-to-
steam heat exchanger would be installed in place of the vacuum condenser to
absorb the
latent heat of vaporization in the steam as the steam is condensed to water.
The air exhaust from the steam boiler is directed to an air-to-propane heat
exchanger and the
exhaust from the steam turbine to a steam-to-propane condenser. The waste heat
exiting the
steam boiler vaporizes propane that has been pressurized using one or more
pumps. The heat
from the steam turbine exhaust vaporizes a liquid propane stream that has been
pressurized
using one or more pumps. The pressurized liquid propane streams are vaporized
in multiple
indirect heat exchangers and expanded in multiple turbo-expanders. The exhaust
heat from
the turbo-expanders can be used to recover additional heat using propane-to-
propane heat
exchangers. The turbo-expanders can be connected in series or in parallel to
multiple power
generation devices such as a generator, pump or compressor using any speed
changing
means. Power generation devices, such as electrical generators, and the
equipment used to
attach them to turbo-expanders, turbines and the like are well known in the
art.
An embodiment of a Super-CCLC system is schematically depicted in Figure 4.
The
Super-CCLC system 400 of Figure 4 comprises a steam loop, shown by the double
line and
generally designated by the letter S, and a mufti-loop CCLC system, shown by
single lines
and generally designated by the letters A through E. Although the Super-CCLC
400 of
Figure 4 is shown in operation with a steam loop, the Super-CCLC arrangement
of the
present invention also may be operated with other types of power generation
systems and
heat sources. Indeed, various embodiments of the Super-CCLC may be adapted to
generate
power from waste heat generated by any number of devices or systems, including
those
sources of heat described above, or any other heat source. Furthermore, the
embodiments of
the Super-CCLC (or CCLC) of the present invention may be made having various
different
sizes, and may be large enough to provide substantial power generation for
utilities, or
compact enough to act as portable power generators or to provide motive and/or
auxiliary
power for automobiles, trucks, trains, ships, aircraft and the like.
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The operation of the steam loop of Figure 4 begins when a water pump 402
pressurizes a water stream S to state S~. The water pump 402 requires a
certain amount of
power P4oz to pressurize the water stream S. The pressurized water stream S is
heated in a
boiler 404 from state S1 to state Sz by a heat source, such as flue gas
(generally designated by
the letter H), entering the boiler at state Hl, and exiting at state Hz. The
amount of heat
absorbed by the water stream S is designated herein as Q4o4~ The water stream
S, which is a
superheated steam at state Sz, is then directed to a steam turbine 406, where
the water stream
S is expanded to state S3, generating an amount of useful energy W4os in the
process. The
water steam S is then passed through a first indirect heat exchanger 408,
where heat Q4o$ is
transferred to a first loop stream C of the CCLC portion of the Super-CCLC
system 400 (as
described below). Preferably, the heat transfer out of the water stream S in
the first indirect
heat exchanger 408 causes the water stream S to partially or completely
condense from a
gaseous state (state S3) to liquid at state S4, however lesser amounts of heat
transfer also may
be used. A supplemental condenser (not shown) may be provided after the first
indirect heat
exchanger 408 to provide additional cooling to the water stream S to more
fully condense it
to a liquid. At this point, the water stream S is directed back to the water
pump 402 to begin
the cycle anew.
W one embodiment of the invention, the steam loop may be provided with a
bypass
system that allows it to be operated as a conventional steam power system.
This may be
desirable, for example, when it is desired to update, modify or service the
CCLC portion of
the system. In such an embodiment, one or more bypass valves 434 may be
provided to
redirect the water stream through a condenser 408', rather than the first
indirect heat
exchanger 408, and then to the water pump 402 to restart the cycle. In such an
embodiment,
the condenser 408' extracts heat Q4o$' from the water to bring it to state
S4'. Of course, other
valves (not shown) may be provided to fully reroute the water stream S, as
will be understood
by those of ordinary skill in the art. This bypass route can also be used
during initial startup
of the CCLC.
The mufti-loop CCLC portion of the Super-CCLC system 400 comprises three loops
that originate from a main combined fluid stream A or multiple combined
streams. In a
preferred embodiment, the operating fluid comprising the fluid stream is
propane or another
light hydrocarbon. The main combined fluid stream A is divided into a
secondary combined
fluid stream B and a first loop stream C. The secondary combined fluid stream
B, in turn, is
divided into a second loop stream D and a third loop stream E. Useful energy
is extracted
24
CA 02493155 2005-O1-21
WO 2004/009965 PCT/US2003/022399
from each of the first, second and third loop streams (C, D and E), and then
they are
recombined to again form the main combined fluid stream A and start the
process anew.
Although it is preferred for the fluid in the loop streams to commingle when
they are
combined, it is also anticipated that the loop streams (or the various streams
of any other
embodiment of the invention) may instead be isolated from one another at all
times, in which
case separate pumps will be required for each fluid stream. The processes by
which the first,
second and third loop streams create useful energy are now described in more
detail.
The first loop stream C begins at state C1, at which point it is preferably a
liquid. The
first loop stream C is compressed to state CZ by a first high pressure pump
414. This
pumping process requires a certain amount of work input P4i4~ The first loop
stream C is then
directed to the first indirect heat exchanger 408, where it absorbs energy in
the amount of
Q4o8~ and becomes a vapor at state C3. The first loop stream C then enters a
first turbo-
expander 416 where it expands to state C4, and drives the turbo-expander 416
to produce
useful energy W4is. The expanded first loop stream C is then mixed in a stream
mixer 418
with the second and third loop streams (D and E), each of which is at the end
of its respective
cycle as described below, to form the main combined fluid stream A. As can be
seen from
Figure 4, the first loop stream C receives heat primarily from the waste heat
Q4o$ from the
steam loop S. Normally this heat is entirely lost without producing any useful
work, but with
the Super-CCLC, it is partially converted to useful energy, thereby improving
on the
efficiency of the unmodified system.
In the embodiment of Figure 4, the secondary combined fluid stream B is
pressurized
from state B1 to state BZ by a second high pressure pump 420. This process
requires an input
of a certain amount of work P~zo. After being pressurized, the secondary
combined fluid
stream B is divided into the second loop stream D and the third loop stream E
by a second
stream separator 422. Using the depicted arrangement, a single pump can be
used to
pressurize both the second and third loop streams. In other embodiments, the
second and
third loop streams may be pressurized separately, or the first, second and
third loop streams
may be pressurized by a single pump or set of pumps before being divided into
respective
loop streams. Of course, other pump configurations may be used. Ideally, the
pumping
configuration is selected to minimize the amount of work required to pump the
fluids and
reduce the overall cost of the system. The pump configuration may be based on
such factors
as: the desired flow rates of the streams, the pumping efficiency of various
capacity pumps,
and the costs of various capacity pumps. The pumping configuration also may be
influenced
CA 02493155 2005-O1-21
WO 2004/009965 PCT/US2003/022399
by the desired pressures of the various loop streams, with streams having the
same or similar
desired pressures being pumped by the same pumps or set of pumps. One of
ordinary skill in
the art will be able to perform this optimization for the various embodiments
of the present
invention without undue experimentation.
The second loop stream D begins at state D~, preferably as a pressurized
fluid, as it
emerges from the stream separator 422. As shown in Figure 4, The second loop
stream D is
heated by the flue gas H (or any other heat source) exiting the steam loop
boiler 404. As
noted previously, in prior art systems, the energy contained in the flue gas
exhaust is
normally lost without receiving any substantial benefit from it. However, in
the Super-
CCLC, one or more heat exchangers may be employed to transfer heat from the
flue gas H to
the second loop stream D. In the embodiment of Figure 4, two heat exchangers
are used.
The second loop stream D is preheated in a second indirect heat exchanger 428,
where it
changes from state D1 to state Dz as it absorbs heat in the amount of Q4z$
from the flue gas H.
This heat transfer cools the flue gas H from state H3 to state H4. The second
loop stream D is
further heated by the flue gas H in a third indirect heat exchanger 430, where
it receives heat
in the amount of Q4so and exits at state D3. This heat exchange cools the flue
gas H from
state Hz to state H3. Next, the second loop stream D is directed to a second
turbo-expander
432, where it is expanded to state D4, thereby generating useful energy W43z.
The expanded
second loop stream D then passes through a fourth indirect heat exchanger 424,
where it
transfers heat to the third loop stream E, and is thereby cooled from state D4
to state D5.
Finally, the second loop stream D is mixed in the stream mixer 418 with the
first and third
loop streams (C and E).
The third loop stream E emerges from the stream separator 422 at state El. The
third
loop stream E passes through the fourth indirect heat exchanger 424, where it
absorbs heat in
the amount Of Q4z4 from the second loop stream D. This heat exchange vaporizes
the third
loop stream E, bringing it to state Ez. Once vaporized, the third loop stream
E is directed to a
third turbo-expander 426, where it is expanded to state E3, thereby creating
useful energy
Wazs. Finally, the third loop stream E is mixed in the stream mixer 418 with
the first and
second loop streams (C and D).
As shown in Figure 4, the first, second and third loop streams (C, D and E)
are
combined at their respective states (states C4, DS and E3) to form the primary
combined fluid
stream A, which equalizes at state Al. The primary combined fluid stream A is
passed
through a condenser 410 to release heat in the amount of Q4io to any suitable
cooling
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WO 2004/009965 PCT/US2003/022399
medium, causing the primary combined fluid stream A to change to state Az.
State AZ
preferably is a liquid state to facilitate pumping. After being cooled in
condenser 410, the
primary combined fluid stream A is divided in a first stream separator 412
into the secondary
combined fluid stream B, which is at state B1, and the first loop stream C,
which is at state
CI. From here, the process begins anew. As noted before, various different
pump
configurations may be used with the present invention , and other
configurations of stream
separators may be used to feed these different pump configurations.
One or more of the turbo-expanders 416, 426, 432 and steam turbine 406 can be
connected in series or in parallel to multiple power generation devices such
as generators,
pumps or compressors using any speed changing means. Power generation devices,
such as
electrical generators, and the equipment used to attach them to turbo-
expanders, turbines and
the like are well known in the art.
Referring now to Figures 5 and 6, the Super-CCLC process is described in
further
detail. Figures 5 and 6 are Mollier diagrams for the steam and CCLC portions
of the Super-
CCLC, respectively. In Figure 5, pressure is represented by the vertical axis
550, enthalpy is
represented by the horizontal axis 552, and numerous isotherms 554 are
depicted, along with
the saturation curve 556 for water. Similarly, in Figure 6, pressure is
represented by the
vertical axis 650, enthalpy is represented by the horizontal axis 652, and
numerous isotherms
654 are depicted, along with the saturation curve 656 for propane. In Figure
5, the water
stream S of Figure 4 is depicted as line S. In Figure 6, the primary combined
fluid stream A
of Figure 4 is depicted as triple line A, the secondary combined fluid stream
B is depicted as
dashed double line B, the first loop stream C is depicted as solid line C, the
second loop
stream D is depicted as dashed line D, and the third loop stream E is depicted
as broken line
E. For clarity, the lines representing the fluid streams have been separated
in some locations
to be clearly distinguishable from one another. Also for clarity, each of the
points on Figures
5 and 6 symbolically represents the temperature and pressure of one or more of
the states
(e.g., state Al, state B1, etc.) that are described above with reference to
Figure 4. Although
single points may be used in these Figures for clarity, one of ordinary skill
will readily
recognize that the vaxious states represented by each point may be located
apart from one
another in actual practice.
The Super-CCLC process of Figure 4 begins, for the purposes of this
discussion, at
point 501, (corresponding to states AI, B1 and C1), at which point the water
stream S has been
pressurized by the water pump 402 to state S1. The water stream S is then
heated at an
27
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approximately constant pressure to point 502 (state SZ) by absorbing heat Q4oa
from the flue
gas H in the boiler 404. From here, the water stream S is expanded in the
steam turbine 406
essentially along a line of constant entropy (not shown) to point 503 (state
S3) to generate
useful energy W4o6. The water stream S is then cooled at a relatively constant
pressure to
point 504 (state S4), during which time the water stream condenses from a
gaseous state to a
liquid state. During this cooling step, the enthalpy of the water stream S is
reduced by
transferring enthalpy (heat) from the water stream S to the first loop stream
of the CCLC
portion of the system, as shown in Figure 4. Once cooled, the water pump 402
pumps the
water stream S at a relatively constant temperature to point 501 (state S1) to
begin the cycle
anew. The steam cycle shown in Figure 5 is similar to steam cycles for
conventional steam
power systems, with the primary exception being the medium to which the heat
Q4o8 is
extracted from the water stream S during cooling from point 503 to point 504.
The CCLC portion of the Super-CCLC begins, for purposes of this discussion, at
point 601 (corresponding to states Aa, B1 and C1), where the primary combined
fluid stream
A is initially divided into the secondary combined fluid stream B and the
first loop stream C,
and the fluid streams are all in a liquid state. The first high pressure pump
414 compresses
the first loop stream C at a relatively constant temperature to point 602
(state CZ). The first
loop stream C is then heated and vaporized, at an approximately constant
pressure, to point
603 (state C3) by absorbing heat Q4o8 from the first indirect heat exchanger
408. Once
vaporized, the first loop stream C is expanded in turbo-expander 416 along a
line of constant
entropy (not shown) to point 604 (state C4), thereby generating useful energy
W4~6. From
point 604, the first loop stream C is mixed with the other loop streams to
form the primary
combined fluid stream A, at point 605 (state Al).
Meanwhile, the second high pressure pump 420 compresses the secondary combined
fluid stream B at a relatively constant temperature to point 606
(corresponding to states Bz,
D1 and El). At point 606, the secondary combined fluid stream B divides into
the second
loop stream D and third loop stream E, at states D1 and El, respectively. From
here, the
second and third loop streams (D and E) are processed along separate paths.
The second loop
stream D is first heated to point 607 (state Dz) at an approximately constant
pressure by flue
gas H in the second indirect heat exchanger 428. The second loop stream D is
then further
heated to a vapor at point 608 (state D3), again at an approximately constant
pressure, by flue
gas H in the third indirect heat exchanger 430. Next, the second loop stream D
is expanded
essentially along a line of constant entropy (not shown) in the second turbo-
expander 432
until it reaches point 609 (state D4), thereby creating useful energy W43z. As
can be seen in
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WO 2004/009965 PCT/US2003/022399
Figure 6, at point 609 the second loop stream D still contains a relatively
large amount of
internal energy, as shown by its relatively high enthalpy value. This energy
is released to the
third loop stream E in the fourth indirect heat exchanger 424, thereby cooling
the second loop
stream D, at a relatively constant pressure, to point 610 (state DS). From
here, the second
loop stream D is mixed with the other loop streams to form the primary
combined fluid
stream A, at point 605 (state Al).
Beginning from point 606, the third loop stream E is heated, at an
approximately
constant pressure, by the second loop stream D in the fourth indirect heat
exchanger 424 until
the third loop stream E reaches point 611 (state EZ), at which point it is a
vapor. From here,
the third loop stream E is expanded essentially along a line of constant
entropy (not shown) in
the third turbo-expander 426 to create useful energy W4z6. The third loop
stream E exits the
third turbo-expander 426 at point 612 (state E3), and is then mixed with the
other loop
streams to form the primary combined fluid stream A, at point 605 (state AI).
After the three loop streams are combined to form the primary fluid stream A
at point
605 (state AI), the primary fluid stream is cooled in the condenser 410 at a
relatively constant
pressure until it is fully liquefied at point 601 (state AZ), where the
process begins anew.
By carefully selecting and controlling the various states of the fluid
streams, the
present invention may be used to increase the efficiency of any conventional
power system
(including nuclear, steam or other power systems) or variations thereof. Table
3 provides
approximate values for a preferred embodiment of the various states identified
in Figures 4-6,
as well as other data related to the operation of the preferred embodiment.
The working fluid
in this embodiment is propane. As with the data provided in Table 1, these
values may be
varied substantially depending on the particular operating circumstances or
requirements or
for other reasons, and any such variations are within the scope of the present
invention.
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WO 2004/009965 PCT/US2003/022399
Fluid States(Properties)132, Heat Transfer
TemperaturePressureFlow Rates
Rate BTU/hr
(F) (psia) (lb/hr) Q4oa 79,100,000
Hl 750 34.7 833,300 Q4o$ 68,310,000
Hz 414 24.7 833,300 Q4io 114,900,000
H3 241 19.7 833,300 Q424 21,350,000
H4 138 14.7 833,300 Qz$ 22,860,000
A1 110 199 832,800 Q430 39,440,000
Az 100 189 832,800
B1 100 189 372,700 Power
Bz 110 770 372,700
C1 100 189 460,100 BTU/hr
Cz 108 682 460,100 W4os 11,035,000
C3 231 677 460,100 W4i6 8,836,000
C4 104 199 460,100 W4zs 2,970,000
DI 110 770 229,500 W43z 8,574,000
Dz 221 765 229,500 Paoz - 234,000
D3 404 760 229,500 P4i4 - 2,377,000
D4 303 204 229,500 P4zo - 2,270,000
DS 128 199 229,500 NET 26,534,000
El 110 770 143,200
Ez 245 760 143,200
E3 104 199 143,200 Efficiency:33.5%
~
Table 3: Super-CCLC (Figure 4)
The efficiency of the embodiment of the Super-CCLC provided in Table 3 is
calculated as the net power (W4o6 + W416 + W426 + W432 - P402 - P414 - Pazo)
divided by the
amount of heat entering the steam system from the heat source (Q4oa). In a
preferred
embodiment, the efficiency of the Super-CCLC is at least about 25%, and more
preferably
about 30%. Furthermore, as shown in Table 3, the efficiency of one preferred
embodiment is
about 33.5%, which is an increase of about 100% over the system if it were
operated as a
regular steam power generation system. The addition of the CCLC portion to the
steam
system may, in some cases, reduce the power generated by the steam turbine
406, but this
loss in power is overcome by the additional power generated by the turbo-
expanders 416, 426
and 432. Also, when modifying or designing a steam system to be a Super-CCLC
system of
the present invention, the steam portion of the system preferably is be
operated as a
backpressure system (i. e., wherein the water stream has a positive pressure
at the exit of the
steam turbine), and preferably is operated with at least about 25 psia of
backpressure. This
backpressure helps improve the overall efficiency by ensuring that sufficient
heat is
CA 02493155 2005-O1-21
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transferred to the first loop cycle C of the CCLC portion of the system to
provide significant
power generation by the first turbo-expander 416.
The present invention is not restricted to the embodiments presented above.
The
present invention can be modified within the scope and spirit of the invention
to include
additional heat exchangers, condensers, pumps, turbo-expanders, mixers or
stream separators.
Alternate arrangements and configurations can also be used to connect to and
drive pumps,
compressors, electrical generators and the like. Those of ordinary sleill in
the art will
understand that the various devices described herein may be modified or
replaced with
equivalent devices or increased or decreased in number without leaving the
scope and spirit
of the invention. The data provided with reference to the preferred
embodiments is also not
intended to limit the invention, and the values provided for these variables
in the attached
tables and their relative relationships as shown in the attached Figures may
be altered for any
number of reasons to accommodate various operating conditions, operating
requirements, and
so on, as will be readily understood by those of ordinary skill in the art.
The preferred
embodiments described herein are exemplary only and are not intended to limit
the scope of
the invention in any way, which is limited only by the following claims.
31
