Note: Descriptions are shown in the official language in which they were submitted.
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SUPPLEMENTARY THERMAL ENERGY TRANSFER IN THERMAL
ENERGY RECOVERY SYSTEMS
FIELD OF THE INVENTION
The present invention relates generally to thermal energy recovery systems.
More particularly,
the present invention relates to the efficient, controlled operation of an
Organic Rankine Cycle
(ORC) system in which waste heat is recovered from a reciprocating engine
and/or a natural gas
compressor coupled to a reciprocating engine.
BACKGROUND OF THE INVENTION
Methods for implementing a Rankine cycle within a system to recover thermal
energy from a heat
source are well known. Although most waste heat recovery systems were
initially developed to
produce steam that could be used to drive a steam turbine, the basic
principles of the Rankine
cycle have since been extended to lower temperature applications by the use of
organic
propellants within the system. Such ORC systems are typically used within
thermal energy
recovery systems or geothermal applications, in which heat is converted into
mechanical energy
that can be used to generate electrical energy. As such, these systems have
become particularly
useful in heat recovery and power generation - collecting heat from turbine
engine exhaust,
combustion processes, geothermal sources, solar thermal energy collectors, and
thermal energy
from other industrial sources.
Generally, a Rankine-based heat recovery system includes a propellant pump for
circulating
propellant throughout the system, an evaporator for evaporating propellant
that has become
heated by collection of waste heat, an expander (typically a turbo-expander)
through which
evaporated propellant is allowed to expand and create power or perform work,
and a condenser
for cooling the propellant back to liquid state so it may be pumped to again
collect heat and
repeat the cycle. The basic Rankine cycle has been adapted for collection of
heat from various
sources, with conversion of the heat energy to other energy outputs.
For example, US 5,440,882 describes a method for using geothermal energy to
drive a modified
ORC based system that uses an ammonia and water mixture as the propellant. The
evaporated
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working fluid is used to operate a second turbine, generating additional
power. Heat is conserved
within the Rankine cycle portion of the system through the use of a
recuperator heat exchanger at
the working fluid condensation stage.
US 6,986,251 describes an ORC system for extracting waste heat from several
sources in a
reciprocating engine system A primary propellant pump drives the Rankine cycle
with assistance
from the auxiliary booster pump, to limit pump speeds and avoid cavitation
When the Rankine
cycle is inactive (e.g. due to reciprocating engine failure or maintenance),
the auxiliary pump
continues to operate alone, circulating propellant until the propellant and
system components
have cooled sufficiently for complete shut down. Diversions are present to
prevent circulation of
propellant through the evaporator and through the turbine during this cooling
cycle.
US 4,228,657 describes the use of a screw expander within a Rankine cycle
system. The screw
expander is used to expand a propellant, and waste heat is further extracted
from the expander in
order to improve system efficiency. A geothermal well supplies pressurized hot
water or brine as
the heat source.
When using organic propellants within a Rankine cycle, care must be taken to
avoid exposure of
the propellants to flame. Although specialized organic propellants having high
flash temperatures
(for example Genetron R-245fa, which is 1,1,1,3,3-pentafluoropropane) have
been developed,
the danger of combustibility still exists, as engine exhaust may reach
temperatures up to 1200
degrees F. Further, the purchase of proprietary propellants adds a significant
cost to these
systems and requires the ORC system to be in close proximity to the heat
source.
A common problem particularly relevant to recovery of thermal energy is that
when using air-
cooled condensers, ambient air temperatures significantly impact the ORC
system efficiency and
total power generated. Applicant's co-pending application, WO 2008/106774,
describes a robust
configuration and associated operation of an ORC system, with heat collection
from various
waste heat sources driving evaporation of propellant to provide secondary
energy output. This
secondary power may be used to directly power parasitic loads within the
system, enabling
independent control and operation of these loads, improving system efficiency.
One notable
application of this system lies in the compression of natural gas at both on-
grid and off-grid sites
for pipeline transport, with the reciprocating engine driving the natural gas
compressor.
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Published application WO 2006/138459 describes an ORC system in which an
organic propellant
is used to remove heat from the engine.
Retrofitted systems for recovering heat from a reciprocating engine are
generally limited by pre-
existing space constraints and site conditions, particularly when used in
remote locations.
Generally, heat recovery systems of the prior art require close proximity to
the engine, liquid
condensing, expensive components, do not incorporate a recuperator
(economizer) and are not
sufficiently adaptable to recover and utilize thermal energy from other
sources, if present.
SUMMARY
It is an object of the present invention to obviate or mitigate at least one
disadvantage of previous
Rankine-based heat recovery systems.
In a first aspect, there is provided a system for collection and conversion of
thermal energy to
mechanical energy, the system comprising:
- a reciprocating engine operable to provide a primary power source and a
first source of
thermal energy;
- a circulating pump, at least one propellant heat exchanger, an expander, and
a
condenser, arranged to operate an Organic Rankine Cycle (ORC) in which thermal
energy from
said first source of thermal energy is transferred to a liquid organic
propellant in the propellant
heat exchanger to evaporate the propellant, which expansion of gaseous
propellant then drives
the expander in production of mechanical energy to create secondary power,
with spent
propellant from the expander condensed back into liquid form by the condenser
for recirculation
to the heat exchanger;
- a cooler comprising a cooling fluid circulating through a supplementary heat
exchanger,
the supplementary heat exchanger operatively located within the ORC system
between the
expander and the condenser to provide supplementary propellant cooling
capacity; and
- a control module for regulating operation of the Rankine cycle and
supplementary
cooler to maximize secondary power generation.
In an embodiment, the first source of thermal energy comprises engine cooling
fluid. For
example, the engine cooling fluid may be engine jacket fluid or auxiliary
cooling fluid.
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In an embodiment, when the first source of thermal energy is engine jacket
fluid, the cooling fluid
circulating through the supplementary heat exchanger may also be engine jacket
fluid. Further, in
such embodiment, the engine jacket fluid may be overcooled at the propellant
heat exchanger to
transfer an excess of thermal energy to propellant, and the engine jacket
fluid may then be
reheated at the cooler prior to circulation back to the engine jacket.
In another embodiment, the first source of thermal energy comprises a
combination of engine
cooling fluid and engine exhaust.
In another embodiment, the system further comprises an engine radiator,
wherein cooling fluid
from the cooler is circulated to the radiator to dissipate thermal energy
transferred to the cooling
fluid from propellant at the supplementary heat exchanger.
In an additional embodiment, the cooler further comprises a ground source heat
exchange
conduit, whereby heat transferred from the propellant to the cooling fluid at
the supplementary
heat exchanger is dissipated by circulation of the cooling fluid through the
ground source heat
exchange conduit.
Further, the system may further comprising a second source of thermal energy,
and a second
source heat exchanger for transferring thermal energy from the second source
of thermal energy
directly or indirectly to the propellant. The second source of thermal energy
may be, for example,
engine exhaust, or a natural gas compressor operatively associated with the
engine. When the
second source of thermal energy is a natural gas compressor, thermal energy
may be collected,
for example, from lubricating fluid circulating within the compressor, and/or
from compressed
natural gas conduits associated with the compressor.
In any embodiment, thermal energy may be transferred directly or indirectly to
propellant within
the ORC. For example, thermal energy from a second source of thermal energy
may be first
transferred to an intermediate fluid, which transfers thermal energy to the
propellant. When the
first source of thermal energy is engine jacket fluid, thermal energy from the
second source may
be transferred to the engine jacket fluid to further increase the thermal
energy content of the
jacket fluid prior to the engine jacket fluid circulating to the propellant
heat exchanger.
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In further embodiments, the system comprises additional sources of thermal
energy, and
corresponding heat exchangers for transferring thermal energy directly or
indirectly to the
propellant. Some examples of appropriate sources of thermal energy include:
engine jacket fluid,
engine auxiliary cooling fluid, engine exhaust, natural gas compressor
lubricating fluid, and
natural gas conduits.
In another embodiment, a system parasitic load is powered with secondary power
during
operation of the ORC. For example, the parasitic load may be a cooling fan for
cooling one or
more system components selected from the group consisting of: propellant
conduits, engine fluid
conduits, and natural gas conduits. Further, two or more system may be co-
located in proximity
to the cooling fan so as to be simultaneously cooled by the fan using
secondary power.
In accordance with a further aspect, there is provided a system for collection
and conversion of
thermal energy to mechanical energy, the system comprising:
- a reciprocating engine operable to provide a primary power source;
- an engine cooling system comprising engine jacket fluid circulating about
the engine,
and an engine auxiliary cooling system comprising auxiliary cooling system
fluid circulating about
the engine;
- a circulating pump, at least one propellant heat exchanger, an expander, and
a
condenser, arranged to operate an Organic Rankine Cycle (ORC) in which an
excess of thermal
energy from the engine jacket fluid is transferred to a liquid organic
propellant at the propellant
heat exchanger to evaporate the propellant, which gaseous propellant then
drives the expander in
production of mechanical energy to create secondary power, with spent
propellant from the
expander condensed back into liquid form by the condenser for recirculation to
the heat
exchanger;
- a supplementary heat exchanger for transferring thermal energy from the
auxiliary
cooling system fluid to the engine jacket fluid to reheat the engine jacket
fluid prior to circulation
of the engine jacket fluid to the reciprocating engine; and
- a control module for regulating operation of the Rankine cycle and
supplementary heat
exchanger.
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In a further aspect, there is provided a system for collection and conversion
of thermal energy to
mechanical energy, the system comprising:
- a natural gas compressor operable to compress natural gas within natural gas
conduits,
the natural gas compressor providing a first source of thermal energy;
- a circulating pump, one or more heat exchangers, an expander, and a
condenser,
arranged to operate an ORC in which thermal energy is transferred directly or
indirectly to a
liquid organic propellant using the one or more heat exchangers to evaporate
the propellant,
which gaseous propellant then drives the expander in production of mechanical
energy to create
secondary power, with spent propellant from the expander condensed back into
liquid form by
the condenser for recirculation to the heat exchanger; and
- a control module for regulating operation of the Rankine cycle to maximize
secondary
power generation.
In an embodiment, the condenser comprises cooling fluid circulating through a
supplementary
heat exchanger. For example, the cooling fluid may be continuous with a ground
source heat
exchange conduit, whereby heat transferred from the propellant to the cooling
fluid at the
condenser is dissipated by circulation of the cooling fluid through the ground
source heat
exchange conduit.
In an embodiment, a system parasitic load is powered with secondary power
during operation of
the ORC. The parasitic load may be a cooling fan for cooling one or more
system components
selected from the group consisting of. propellant conduits, compressor
lubricating fluid, and
natural gas conduits. Two or more system components may be co-located in
proximity to the
cooling fan so as to be simultaneously cooled by the fan using secondary
power.
In an embodiment, the first source of thermal energy comprises compressor
lubricating fluid. The
first source of thermal energy may further comprise a heat transfer fluid
circulating about the
natural gas conduits.
In an embodiment, the first source of thermal energy comprises a heat transfer
fluid circulating
about the natural gas conduits.
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In an embodiment, the compressor is powered by a reciprocating engine, the
reciprocating engine
providing a second source of thermal energy, which may be engine cooling
fluid. For example,
the engine cooling fluid may be engine jacket fluid or engine auxiliary
cooling fluid.
In an embodiment, the second source of thermal energy comprises engine
exhaust.
In an embodiment, thermal energy from the first or second source of thermal
energy is transferred
to an intermediate fluid, which transfers thermal energy to the propellant.
For example, the
intermediate fluid may be engine jacket fluid or engine auxiliary cooling
fluid.
In an embodiment, the second source of thermal energy is engine cooling fluid,
and thermal
energy from the first source of thermal energy is transferred to the engine
cooling fluid to further
increase the thermal energy content of the engine cooling fluid prior to the
engine cooling fluid
circulating to the propellant heat exchanger. In certain embodiments, the
engine cooling fluid may
be engine jacket fluid or engine auxiliary cooling fluid.
In an embodiment, the second source of thermal energy is compressor
lubricating fluid.
In another embodiment, the system further comprises a cooler, the cooler
comprising a cooling
fluid circulating through a supplementary heat exchanger, the supplementary
heat exchanger
operatively located within the ORC between the expander and the condenser to
provide
supplementary propellant cooling capacity. Further, the system may further
comprise a
reciprocating engine for powering the natural gas compressor, wherein the
cooling fluid is cooled
engine jacket fluid from which an excess of engine heat has been transferred
at the propellant heat
exchanger.
In an embodiment, the engine comprises a radiator, and propellant heat
transferred to the jacket
fluid is dissipated by circulation of the jacket fluid through the radiator.
The cooler may further comprises a ground source heat exchange conduit,
whereby heat
transferred from the propellant to the cooling fluid at the supplementary heat
exchanger is
dissipated by circulation of the cooling fluid through the ground source heat
exchange conduit.
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In another aspect, there is provided a method for heating propellant within an
ORC system, the
ORC system associated with a natural gas compressor powered by a reciprocating
engine, the
method comprising the steps of
- collecting waste thermal energy from the reciprocating engine within a heat
transfer
fluid;
- collecting waste thermal energy from the natural gas compressor by
circulation of
compressor lubricating fluid about the compressor;
- circulating each of the heat transfer fluid and compressor lubricating fluid
to one or
more heat exchangers to facilitate direct or indirect transfer of engine and
compressor thermal
energy to propellant circulating within the ORC.
In an embodiment, the method further comprises the steps of: collecting a
further amount of
thermal energy from compressed natural gas conduits associated with the
natural gas compressor;
and transferring the further amount of thermal energy directly or indirectly
to the propellant.
In another embodiment, thermal energy from the compressor lubricating fluid is
transferred to the
heat transfer fluid at a first heat exchanger to increase the thermal energy
content of the heat
transfer fluid; and then the heat transfer fluid is circulated to a second
heat exchanger to transfer
thermal energy to the propellant.
In an embodiment, the heat transfer fluid is engine jacket fluid. In another
embodiment, the heat
transfer fluid is engine auxiliary cooling fluid.
The method may further comprise the step of reheating the heat transfer fluid
following heat
exchange with propellant.
In an embodiment, the step of reheating the heat transfer fluid comprises heat
exchange with
propellant in the ORC at a location between the expander and the condenser.
In an embodiment, the step of reheating the heat transfer fluid comprises heat
exchange with
heated auxiliary cooling fluid.
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In an embodiment, the step of reheating the heat transfer fluid comprises heat
exchange with
engine exhaust.
In another aspect, there is provided a method for providing supplementary
propellant cooling
capacity in an ORC system, the method comprising the steps of
- providing a cooler comprising a cooling fluid circulating through a
supplementary heat
exchanger located downstream of an ORC expander;
- circulating heated propellant to the supplementary heat exchanger to
transfer propellant
heat to the cooling fluid, for assisting in condensation of propellant within
the ORC system
- dissipating transferred heat from the cooling fluid; and
- recirculating the cooling fluid to the supplementary heat exchanger.
In an embodiment, the cooling fluid is engine jacket fluid, and wherein the
step of dissipating heat
from the cooling fluid comprises transferring an excess of thermal energy from
the engine jacket
fluid to the propellant at the propellant heat exchanger to reduce the thermal
energy of the jacket
water below that which is acceptable for return to the engine.
In another embodiment, the engine comprises a radiator, and wherein the step
of dissipating heat
from the cooling fluid comprises circulation of the cooling fluid through the
engine radiator.
In another embodiment, the step of dissipating heat from the cooling fluid
comprises circulation
of the cooling fluid through a ground source heat exchange conduit.
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In another aspect, there is provided a system for collection and conversion of
thermal
energy to mechanical energy, the system comprising: a reciprocating engine,
configured
to provide primary power and to provide thermal energy comprising engine
exhaust and
one or more non-exhaust sources of energy; and an Organic Rankine Cycle (ORC)
comprising a propellant heat exchanger comprising an evaporator configured to
collect
heat from one or more non-exhaust sources of thermal energy, a superheater
heat
exchanger configured to collect heat directly or indirectly from the engine
exhaust source
of thermal energy, an expander and a condenser, wherein the ORC is configured
to
collect and use (i) at least a portion of the one or more non-exhaust sources
of thermal
energy to heat and evaporate an organic propellant in the propellant heat
exchanger and
(ii) superheat the evaporated organic propellant using exhaust heat to drive
the expander
in generating secondary power, and wherein the condenser is configured to
condense
spent propellant from the expander into liquid form for recirculation to the
propellant
heat exchanger.
In another aspect, there is provided a system for collection and conversion of
thermal
energy to mechanical energy, the system comprising: a reciprocating engine,
configured
to provide primary power and to provide thermal energy comprising engine
exhaust and
one or more non-exhaust engine sources of energy; and; a natural gas
compressor
operable to compress natural gas within natural gas conduits, wherein the
natural gas
compressor is configured to provide a source of thermal energy; and an Organic
Rankine
Cycle (ORC) comprising a propellant heat exchanger, comprising an evaporator
configured to collect thermal energy from at least one the natural gas
compressor and
thermal energy other than the engine exhaust from the reciprocating engine, a
superheater
heat exchanger configured to collect heat directly or indirectly from the
engine exhaust
source of thermal energy, an expander and a condenser, wherein the ORC is
configured
to collect and use at least one of (i) the one or more non-exhaust sources of
thermal
energy to heat and evaporate an organic propellant in the propellant heat
exchanger, and
(ii) the thermal energy from the natural gas compressor to heat and evaporate
an organic
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propellant in the propellant heat exchanger, wherein the ORC is configured to
superheat
the evaporated organic propellant using exhaust heat to drive the expander in
generating
secondary power, and wherein the condenser is configured to condense spent
propellant
from the expander into liquid form for recirculation to the propellant heat
exchanger.
In another aspect, there is provided a method for collecting and converting
thermal
energy in a system, the method comprising: providing primary power and thermal
energy
via a reciprocating engine, the thermal energy comprising engine exhaust and
one or
more non-exhaust sources of energy; collecting heat in an Organic Rankine
Cycle (ORC)
from one or more non-exhaust sources of thermal energy via a propellant heat
exchanger
comprising an evaporator; collecting heat in the ORC directly or indirectly
from the
engine exhaust source of thermal energy via a superheater heat exchanger;
collecting, in
the ORC, at least a portion of the one or more non-exhaust sources of thermal
energy to
heat and evaporate an organic propellant in the propellant heat exchanger; and
superheating the evaporated organic propellant using engine exhaust thermal
energy to
drive an expander in the ORC to generate secondary power; and condensing, via
a
condenser in the ORC, spent propellant from the expander into liquid form for
recirculation to the propellant heat exchanger.
In another aspect, there is provided a method for collecting and converting
thermal
energy to mechanical energy in a system, the method comprising: providing
primary
power and thermal energy via a reciprocating engine, the thermal energy
comprising
engine exhaust and one or more non-exhaust sources of energy; compressing
natural gas
within natural gas conduits via a natural gas compressor configured to provide
a source of
thermal energy; collecting thermal energy, via a propellant heat exchanger
comprising an
evaporator of an Organic Rankine Cycle (ORC), from at least one of the natural
gas
compressor and thermal energy other than the engine exhaust from the
reciprocating
engine, collecting, via a superheater heat exchanger of the ORC, thermal
energy directly
or indirectly from the engine exhaust source of thermal energy; collecting and
using, via
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the ORC, at least one of (i) the one or more non-exhaust sources of thermal
energy to heat
and evaporate an organic propellant in the propellant heat exchanger, and (ii)
the thermal
energy from the natural gas compressor to heat and evaporate an organic
propellant in the
propellant heat exchanger; superheating, via the ORC, the evaporated organic
propellant
using exhaust heat to drive an expander of the ORC in generating secondary
power; and
condensing, via a condenser of the ORC, spent propellant from the expander
into liquid
form for recirculation to the propellant heat exchanger.
In another aspect, there is provided a system for collection and conversion of
thermal
energy to mechanical energy, the system comprising: a reciprocating engine,
configured to
provide primary power and to provide thermal energy comprising engine exhaust
and one
or more non-exhaust sources of energy; and an Organic Rankine Cycle (ORC)
comprising
a propellant heat exchanger comprising an evaporator for collecting heat from
one or more
non-exhaust sources of thermal energy to evaporate an organic propellant, a
superheater
heat exchanger for collecting heat directly or indirectly from the engine
exhaust source of
thermal energy to superheat evaporated organic propellant, an expander and a
condenser,
wherein the ORC is operable to collect and use (i) at least a portion of the
one or more
non-exhaust sources of thermal energy to heat and evaporate an organic
propellant in the
propellant heat exchanger, and (ii) the evaporated organic propellant to
superheat the
evaporated organic propellant using exhaust heat of the superheater to drive
the expander
in generating secondary power, and wherein the ORC comprises a processor-based
control
module configured to actively control a flow of the organic propellant to the
propellant
heat exchanger to match the flow of the organic propellant to a rate of
evaporation in the
propellant heat exchanger to provide only vapor from an outlet of the
propellant heat
exchanger to drive the expander, and wherein the condenser is configured to
condense
spent propellant from the expander into liquid form for recirculation to the
propellant heat
exchanger.
In another aspect, there is provided a system for collection and conversion of
thermal
energy to mechanical energy, the system comprising: a reciprocating engine,
configured to
provide primary power and to provide thermal energy comprising engine exhaust
and one
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or more non-exhaust engine sources of energy; a natural gas compressor
operable to
compress natural gas within natural gas conduits, wherein the natural gas
compressor is
configured to provide a source of thermal energy; an Organic Rankine Cycle
(ORC)
comprising a propellant heat exchanger, comprising an evaporator for
collecting thermal
energy from at least one of the natural gas compressor and the non-exhaust
engine sources
of energy, a superheater heat exchanger for collecting heat directly or
indirectly from the
engine exhaust source of thermal energy to superheat organic propellant an
expander, and a
condenser, wherein the ORC is operable to collect and use at least one of (i)
the one or
more non-exhaust sources of thermal energy to heat and evaporate an organic
propellant in
the propellant heat exchanger, and (ii) the thermal energy from the natural
gas compressor
to heat and evaporate an organic propellant in the propellant heat exchanger,
and wherein
the ORC is operable to superheat the evaporated organic propellant using
exhaust heat of
the superheater to drive the expander in generating secondary power, and
wherein the ORC
comprises a processor-based control module for actively controlling a flow of
the organic
propellant to the propellant heat exchanger to match the flow of the organic
propellant to a
rate of evaporation in the propellant heat exchanger to provide only vapor
from an outlet of
the propellant heat exchanger to drive the expander, and wherein the condenser
is
configured to condense spent propellant from the expander into liquid form for
recirculation to the propellant heat exchanger.
In another aspect, there is provided a method for collecting and converting
thermal energy
in a system, the method comprising: providing primary power and thermal energy
via a
reciprocating engine, the thermal energy comprising engine exhaust and one or
more non-
exhaust sources of energy; collecting heat in an Organic Rankine Cycle (ORC)
from one or
more non-exhaust sources of thermal energy via a propellant heat exchanger
comprising an
evaporator; collecting heat in the ORC directly or indirectly from the engine
exhaust
source of thermal energy via a superheater heat exchanger; collecting, in the
ORC, at least
a portion of the one or more non-exhaust sources of thermal energy to heat and
evaporate
an organic propellant in the propellant heat exchanger; superheating, via the
superheater
heat exchanger, the evaporated organic propellant using engine exhaust thermal
energy to
drive an expander in the ORC to generate secondary power; actively
controlling, via a
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processor-based control module, a flow of the organic propellant to the
propellant heat
exchanger to match the flow of the organic propellant to a rate of evaporation
in the
propellant heat exchanger to provide only vapor from an outlet of the
propellant heat
exchanger; and condensing, via a condenser in the ORC, spent propellant from
the
expander into liquid form for recirculation to the propellant heat exchanger.
In another aspect, there is provided a method for collecting and converting
thermal energy
to mechanical energy in a system, the method comprising: providing primary
power and
thermal energy via a reciprocating engine, the thermal energy comprising
engine exhaust
and one or more non-exhaust sources of energy; compressing natural gas within
natural gas
conduits via a natural gas compressor configured to provide a source of
thermal energy;
collecting thermal energy, via a propellant heat exchanger comprising an
evaporator of an
Organic Rankine Cycle (ORC), from at least one of the natural gas compressor
and thermal
energy other than the engine exhaust from the reciprocating engine,
collecting, via a
superheater heat exchanger of the ORC, thermal energy directly or indirectly
from the
engine exhaust source of thermal energy; collecting and using, via the ORC, at
least one of
(i) the one or more non-exhaust sources of thermal energy to heat and
evaporate an organic
propellant in the propellant heat exchanger, and (ii) the thermal energy from
the natural gas
compressor to heat and evaporate an organic propellant in the propellant heat
exchanger;
superheating, via the superheater heat exchanger, the evaporated organic
propellant using
exhaust heat to drive an expander of the ORC in generating secondary power;
actively
controlling, via a processor-based control module, a flow of the organic
propellant to the
propellant heat exchanger to match the flow of the organic propellant to a
rate of
evaporation in the propellant heat exchanger to provide only vapor from an
outlet of the
propellant heat exchanger; and condensing, via a condenser of the ORC, spent
propellant
from the expander into liquid form for recirculation to the propellant heat
exchanger.
Other aspects and features of the present invention will become apparent to
those
ordinarily skilled in the art upon review of the following description of
specific
embodiments of the invention in conjunction with the accompanying figures.
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BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of example
only, with
reference to the attached Figures, wherein:
Fig. 1 is a schematic diagram of an ORC system coupled to a reciprocating
engine;
Fig. 2 is a schematic diagram of an ORC system coupled to a reciprocating
engine,
the ORC system including a supplementary cooling fluid continuous with an
engine
radiator;
Fig. 3 is a schematic diagram of an ORC system coupled to a reciprocating
engine,
the ORC system including a supplementary cooler containing engine cooling
fluid;
Fig. 4 is a schematic diagram of an ORC system coupled to a reciprocating
engine,
the ORC system including a ground source heat exchange condenser;
Fig. 5 is a schematic diagram of an ORC system coupled to a reciprocating
engine,
in which engine jacket fluid passes from the first heat exchanger, at which
propellant is
heated, to a supplementary heat exchanger continuous with engine auxiliary
cooling fluid.
Fig. 6 is a schematic diagram of a prior art system for dissipating heat
during
natural gas compression;
Fig. 7 is a schematic diagram of an ORC system for heat recovery during
natural
gas compression;
Fig. 8 is a schematic diagram of a prior art method of dissipating heat from
the
lubricating oil of a natural gas compressor;
Fig. 9 is a schematic diagram of an ORC system coupled to a reciprocating
engine
and natural gas compressor, in which waste heat from the lubricating oil of a
natural gas
compressor is transferred indirectly to ORC propellant;
Fig. 10 is a schematic diagram of an ORC system for recovering waste heat from
a
reciprocating engine and natural gas compressor, in which waste heat from the
lubrication
oil of the natural gas compressor is transferred directly to the ORC
propellant;
Fig. 11 is a schematic diagram of an ORC system for recovering waste heat from
a
reciprocating engine and natural gas compressor, in which waste heat from the
lubrication
oil of the natural gas compressor is transferred directly to the ORC
propellant;
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Fig. 12 is a schematic diagram of an ORC system for recovering waste heat from
a
reciprocating engine and natural gas compressor, in which waste heat from the
lubrication
oil of the natural gas compressor is transferred directly to the ORC
propellant; and
Fig. 13 is a schematic diagram of an ORC system for recovering waste heat from
a
reciprocating engine and natural gas compressor, in which waste heat from the
lubrication
oil of the natural gas compressor is transferred directly to the ORC
propellant, and
including a supplementary cooler.
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DETAILED DESCRIPTION
Generally, the present invention provides a method and system to recover and
dissipate thermal
energy from a reciprocating engine and/or a natural gas compressor, through
controlled operation
of an ORC system to produce secondary power. Various configurations are
provided to
maximize efficiency of the Rankine cycle and secondary energy output in
various applications.
With improvements in efficiency and increased generation of secondary power,
system resources
may be further allocated to heating and/or cooling the organic propellant,
allowing for more
efficient operation of the ORC system and/or increased secondary power
generation.
Generally, an ORC system is provided in which thermal energy is collected from
a reciprocating
engine and/or a natural gas compressor, and used to produce secondary power.
Accordingly,
thermal energy may be collected from one or more of the following sources and
transferred to
propellant: engine jacket fluid, engine auxiliary cooling fluid, engine
exhaust, natural gas
compressor lubricating fluid, and natural gas conduits.
Similarly, supplementary cooling may be provided to the ORC system to assist
in condensation of
propellant exiting the expander. For example, cooling may be provided by heat
transfer from
propellant to one of the following cooling fluids: overcooled engine jacket
fluid, overcooled
auxiliary cooling fluid, a ground source heat transfer fluid, or a further
amount of engine jacket or
auxiliary fluid that is cooled at an otherwise underutilized corresponding
radiator.
Overview
With reference to Figure 1, a reciprocating engine 10 provides a primary power
source, releasing
thermal energy through engine exhaust 12 and as radiant energy. The radiant
energy is typically
dissipated from the engine block by heat transfer within the engine jacket
(housing) to an engine
cooling fluid circulating within the engine jacket 11. In the present system,
the thermal energy
collected by the circulating jacket fluid 11 (typically a glycol and water
mixture) is transferred to
organic propellant within the Rankine cycle through a first heat exchanger 20
to either preheat or
evaporate the propellant, depending on the type of propellant used and the
degree of heat
exchange permitted. Circulation of jacket fluid may be assisted using a
booster pump 52, as
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required. Thermal energy collection from the engine jacket fluid may be
supplemented or replaced
by heat collection and exchange from the engine auxiliary cooling fluid
system.
The preheated or evaporated organic propellant 86 may collect additional
thermal energy from
engine exhaust 12 through circulation (by pump 51) of a thermal fluid 14
between an exhaust
thermal fluid heater 13 and propellant heat exchanger 60. This circulation
will result in
evaporation or superheating of propellant 86 prior to delivery to the expander
30. Propellant 86 is
then condensed back to liquid state by condenser 40 and stored in tank 45 such
that the
propellant is available to feed the circulating pump 50 to circulate the
propellant 86 back to heat
exchangers 20 and/or 60.
With reference to Figures 2 through to Figure 4, additional cooling capacity
is provided to the
ORC system through:
1) leveraging underutilized engine radiator capacity to cool a supplementary
amount of engine
cooling fluid (for example engine jacket water 11 or engine auxiliary cooling
fluid 16) for heat
exchange with propellant at liquid cooler 42 (see Figure 2),
2) increasing heat transfer from an engine cooling fluid at the first heat
exchanger 20 and using
this overcooled engine cooling fluid for heat exchange with propellant at
liquid cooler 42, thereby
cooling the propellant to assist condensation, and reheating the overcooled
engine cooling fluid
.. (either engine jacket water 11 or engine auxiliary cooling fluid 16)(see
Figure 3),
3) a ground source heat exchange system for use in condensing or otherwise
cooling propellant
(see Figure 4).
With reference to Figures 5 through to Figure 13, additional heating capacity
may be provided to
the system through:
1) increasing heat transfer from the engine jacket fluid 11 at heat exchanger
20, and then
reheating the overcooled fluid with heat collected from the engine auxiliary
cooling fluid system
at a further heat exchanger 47 (see Figure 5);
2) when the reciprocating engine is coupled to a natural gas compressor 68,
collecting thermal
energy from any combination of engine exhaust 12; radiant energy from the
engine collected in
engines jacket cooling fluid 11 or the engine auxiliary cooling fluid system
16; radiant energy
collected in the compressed natural gas 55 (Figure 6 and 7) and, radiant
energy collected in the
lubricating oil 17 of the compressor (Figures 8 through to Figure 13).
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As described above, radiant energy from the engine is typically dissipated
from the engine block
by heat transfer within the engine jacket (housing) to a cooling fluid
circulating within the engine
jacket. The fluid being circulated within the engine jacket is typically
referred to as engine jacket
water/fluid. This thermal energy from engine jacket fluid may instead be
transferred directly or
indirectly to the organic propellant of the ORC system. Similarly, in the
compressor 68, the
thermal energy available in the compressed natural gas 55 is typically
dissipated to the
atmosphere through air exchangers 89 (see Figure 6) and the lubricating oil 17
is typically
dissipated via heat transfer to either the engines jacket cooling fluid 11 and
then dissipated
through radiator 81 or transferred to the engine auxiliary cooling fluid
system 16 on the
reciprocating engine and then dissipated through the radiator 64 (see Figure
8), but may instead
by transferred directly (Figures 10, 11, 12 and 13) or transferred indirectly
(Figure 9 ¨ lubricating
oil to engine jacket water or engine auxiliary cooling fluid system) to the
organic propellant of the
ORC system, Notably, the thermal energy from compressed natural gas 55,
lubricating oil 17, the
engines exhaust 12, the engine jacket fluid 11, and/or the engines auxiliary
cooling fluid 16, or
any combination thereof, can be used to preheat, evaporate, and in some cases
superheating the
propellant 86, depending on the type of propellant used and the degree of heat
exchange
available.
Thermal energy may also be collected from the engine auxiliary cooling fluid
system (typically
used to cool the turbo after-cooler) with or without the additional waste heat
from the natural gas
compressor, for direct or indirect transfer to organic propellant at any
appropriate point in the
ORC system prior to delivery of propellant to the expander 30.
Controlled circulation of evaporated or superheated propellant 86 through the
expander 30 drives
generation of secondary power, which may be converted to electric power and
used on site as
required, or may be used as shaft power to drive other devices such as on-site
compressors or
pumps. The spent propellant exiting the expander 30 is condensed at condenser
40, passes
through storage tank 45, and then to pump 50 prior to returning to the heat
exchanger 20 to
.. repeat the cycle. A control module 100, although not shown in all Figures,
is included in each
system described herein to control various components and regulate functions,
as described.
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Generally, flow of propellant 86 within the Rankine cycle is driven by pump
50, which may be
controlled directly by controlling the pump motor, or indirectly by placing a
flow control valve
downstream of the pump outlet (not shown). The flow of gaseous organic
propellant through
expander 30 may also be controlled via by-passing flow around the expander,
regulating
generation of secondary power. Propellant exiting the expander 30 may be
passed through a
recuperator 70 prior to circulation to the condenser 40 (for example, see
Figures 4, 9, 11, 12, and
13).
The recuperator 70 (when present) reabsorbs thermal energy not dissipated at
the expander 30,
and simultaneously pre-heats the cooled propellant discharged from the pump 50
prior to heat
transfer at the first heat exchanger 20. The recuperator thereby improves
efficiency of the system,
increasing secondary power generation.
Suitable organic propellants for use within Rankine cycle systems are known in
the art, and
generally include branched, substituted, or aromatic hydrocarbons, and organic
halides. Suitable
propellants may include refrigerants, CFCs, and hydrocarbons (propanes,
butanes, or pentanes).
Preferably, the propellant is butane, pentane, isobutane, R-134, or R-245fa.
Secondary Power
Secondary power is produced by the expander as mechanical shaft power, which
may be
converted to electricity or used to drive other equipment such as pumps or
compressors.
Secondary electric power may be used to power other site equipment, may feed
into a motor
control centre to be used on site, or may directly supplement primary power
generated, for
example by powering an electric motor coupled to a boost compressor, a cooling
fan, or a pump.
The ability to control and independently power various engine, compressor and
ORC system
components will improve energy efficiency of the system, as parasitic loads
may be set to use
power only when necessary. Further, when these system components are sources
of parasitic load
of the reciprocating engine, natural gas compressor, or within the balance of
the ORC system,
decoupling these loads from their current power source and instead using
secondary power
.. (generated using waste heat) will increase the amount of capacity available
by the reciprocating
engine to produce primary power and thus improve overall efficiency of the
reciprocating engine.
This additional engine capacity may be used to generate more primary power or
reduce fuel
consumption. Notably, the reduced load on the reciprocating engine will reduce
engine reject
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heat, thereby reducing the amount of gross secondary power generated. The
parasitic loads will
adjust accordingly until a new equilibrium is reached.
Parasitic Loads
In a typical ORC system for collection of waste heat from an engine, net
secondary power is the
result of gross secondary power, less the system parasitic loads (for example,
the condenser
fan(s), propellant pump, thermal fluid circulating pump and jacket water pump
(if present)). That
is, the power required to blow adequate ambient air across propellant
condenser conduits when
the condenser is an air-cooled condenser, or pump operation to drive liquid-
cooled condensers
(which use cooling water to condense the propellant), detract from the gross
secondary power
generated by the ORC.
In the system shown in Figure 1, fans 72 on the air-cooled condensers 40 are
controlled by
controller 100 to establish the level of cooling (sub-cool if necessary) that
is required in the
propellant. When ORC secondary power is used to power an electric motor
driving the fan 83 on
the reciprocating engine radiator 81, that motor can also be controlled by the
control system 100
on an as needs basis. Further, should the reciprocating engine 10 be coupled
to a natural gas
compressor 68, electric power from the ORC may be used to power the motor
driving the fan 77
on the aerial cooler, which can also be controlled by the control system 100
on an as needs basis
to prevent the compressed gas from freezing in cold ambient conditions. Fan(s)
on the condensers
40, radiator 81 and aerial cooler fan 77 (shown in figure 11) can be similarly
controlled and/or
combined (simultaneously cooling any combination of engine jacket water,
engine auxiliary
cooling fluid, compressed natural gas, compressor lubricating fluid) to reduce
the parasitic loads
on the reciprocating engine and the ORC system.
Typically, the aerial cooler fan 77 would be driven by the output shaft of the
reciprocating engine
10 via direct shaft and pulley combination from the reciprocating engine. De-
coupling this fan
from the reciprocating engine and using a controlled electric motor powered by
the secondary
power output from the ORC, improves the overall system efficiency. It is
estimated that this
change alone will reduce the power requirement of the reciprocating engine by
6%, thereby
reducing fuel consumption by approximately 6%.
Similarly, the engine radiator 81 is cooled by a fan 83 that is typically
powered by a rotating shaft
extending from the engine. As the fan operation would therefore be coupled to
the engine, the fan
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would run constantly during engine operation, even under cool ambient
conditions or other
conditions not requiring active cooling of radiator fluid. Decoupling engine
parasitic loads from
the reciprocating engine power, and independent control of each system
parasitic load will
maximize energy efficiency. The controlled use of secondary power, generated
by the expander,
to power parasitic loads will control the parasitic loads of the reciprocating
engine and natural
gas compressor, and thus provide greater overall system energy efficiency.
Computer modelling
indicates that during controlled system operation in accordance with the
present disclosure,
secondary power generated solely by reject heat collected from the engine
jacket fluid is suitable
to provide power to the parasitic loads required to run an ORC system on the
jacket water reject
heat. That is, the heat collected from the engine jacket water, in the
appropriate ambient air
temperatures, can provide enough secondary power to drive all ORC parasitic
loads (e.g.
propellant circulating pump, jacket water booster pump (if required),
condenser fans and aerial
cooler fan) that may be required.
Supplementary Cooling Capacity
With reference to Figure 1, an ORC system is shown in which heat from the
reciprocating engine
10 jacket fluid 11 is collected at a first heat exchanger 20, and heat from
engine exhaust 12 is
collected within a thermal fluid 14, and transferred to the propellant 86 at a
second heat
exchanger 60. Organic propellant is heated to evaporation at heat exchangers
20 and/or 60, and
the evaporated propellant passes through expander 30, to generate secondary
power. Spent
propellant exiting the expander 30 flows through a recuperator (when present),
a condenser, a
surge tank, a pump and then is returned to collect further heat from the heat
exchangers
collecting waste heat from the reciprocating engine 10.
With reference to Figure 2, condensation of propellant may be aided by the
addition of a
supplementary cooler 42 as needed. Cooler 42 permits heat exchange between
spent propellant
exiting the expander and engine cooling fluid 11 or 16 which has been isolated
from the
reciprocating engine by control valves. This engine cooling fluid may be
cooled in the engine
radiator (see below) as required through appropriate operation of fan 83 (or
fan 77 if the radiator
has been stacked in an aerial cooler). The control will be through altering
air flow across the
radiator 81, speed of pump 87 and opening/closing of valves 80, 82, 84 and 85.
Secondary power
may be used to drive the circulating fluid pump 87, condenser fans 72, and
radiator fan 83 (or
aerial cooler fan 77, if applicable). The cooler 42 may be placed at any
suitable location within the
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ORC system. For example, as shown in Figure 2, the cooler may be used to
transfer propellant
heat (to the isolated engine cooling fluid which may be from either jacket
water cooling system
11 or the auxiliary cooling fluid system 16, with heat then dumped to
atmosphere through the
radiators 81 or 64 respectively) at any location between the expander and
condenser. When the
ORC system includes a recuperator, the cooler 42 may be placed between the
recuperator and
condenser or between the expander and recuperator.
With reference again to Figure 1, the radiator (not shown) associated with the
reciprocating
engine is not required for jacket water cooling during normal operation of the
ORC, as waste
heat collected by the engine jacket water 11 is instead transferred to
propellant at the first heat
exchanger 20, thereby also cooling the jacket water 11 sufficiently for safe
return to the engine
10. Accordingly, the engine radiator 81 may be under-utilized, except when the
ORC system is
not capable of taking all of the jacket water reject heat, and/or during a
shutdown of the ORC
system when propellant flow is not available to cool the jacket water. As seen
in Figure 2, the
radiator 81 remains present adjacent the engine, but may be isolated from the
engine jacket 11
loop by opening or closing valves 80, 82, 84 and 85. Therefore, under most
operating conditions,
the radiator would be available to provide cooling of jacket fluid 11 as
necessary, for example as
cooling fluid circulating to and from cooler 42. This additional cooling
capacity logic may also be
applied to the auxiliary cooling fluid system 16 of the reciprocating engine.
This radiator-based additional cooling capacity may further be combined with
condenser cooling
capacity by coupling or sharing of fans. That is, co-location of the condenser
with the radiator, as
shown in Figure 9 and 12, may allow simultaneous air cooling with reduced
parasitic load.
Further, co-location of the condenser 40, engines auxiliary cooling fluid
system radiator 64 and
the engine jacket water radiator 81, will permit sharing of fan capacity,
blowing ambient air
across multiple cooling lines (of condenser 40, and/or radiator 64 and/or
radiator 81)
simultaneously with fan 72. Further still, co-location of the condenser 40,
radiator 64, radiator 81
and natural gas cooling conduits 89 (not shown) will permit sharing of fan
capacity, blowing
ambient air across multiple fin-tube sets, simultaneously. When these fans are
driven by secondary
power rather than as a direct load on the engine, further efficiency is
realized.
With reference now to Figure 3, heat is transferred from spent propellant 86
exiting the expander
30, to the engine jacket fluid 11 (and/or to the engine auxiliary cooling
fluid system 16, not
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shown in Figure 3) flowing through supplementary cooler 42. The heated jacket
fluid 11 may be
appropriately circulated through the engine housing, or the engine auxiliary
cooling fluid system.
Accordingly, the engines jacket fluid or engine auxiliary cooling fluid system
can initially be
overcooled (for example, at the first heat exchanger 20) to a greater degree
than that
recommended by the engine manufacturer. The overcooled fluid is then reheated
to appropriate
temperature by passage through the cooler 42, by transfer of thermal energy
from the spent
propellant. The heat exchangers 20 and 42 are to be designed to provide
sufficient heat duty
/exchange such that the jacket fluid/auxiliary cooling fluid returning to the
engine is consistent
with the engine operating specifications.
With reference now to Figure 4, condensation of propellant (or other liquid-
cooling functions)
may be supplemented or wholly provided by circulation of a cooling fluid to
and from an
underground location, where temperature is relatively constant throughout the
year. Unlike air-
cooled condensing in which significant temperature swings between seasons
causes
corresponding operational variations in equipment utilization from summer to
winter seasons,
ground source heat transfer is much more stable, as seasonal variations
generally cease below
approximately seven meters (thermal inertia) and therefore the equipment
utilization will be more
consistent than with an air cooled system. The desired temperature of the
cooling fluid and
geographic location will determine the length of condensing tubing required,
and the depth to
which fluid must be circulated prior to return to the condenser/heat
exchanger. Accordingly, this
method will be most practical in climates where ground temperatures are cool
and wet and where
land conditions are favorable to excavation for installation of fluid lines to
appropriate depth. For
example this cooling method may be suitable in Northern locations below the
frost line where
appropriate subsurface temperatures of 4 degrees Celsius to 12 degrees Celsius
may be achieved
at depths of approximately 2 to 6 meters. These temperatures and depths will
vary with the
geologic conditions of sub-surface conditions and vary with changing surface
conditions
depending on global location. In appropriate conditions, the operational
energy required to
condense in this manner is limited to the energy required to operate the
circulation pump driving
the subsurface circulation of cooling fluid. Geo heat exchange is more energy
efficient than any
other type of heat exchange as the parasitic load required to circulate the
cooling fluid is
significantly (3 to 5 tines) less than the amount of thermal energy
transferred, resulting in net
thermal efficiencies greater than 100% (combustion is always below 100%), as
high as 200%
depending on the conditions. Accordingly, in favorable conditions, this ground
source
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condensing/cooling will minimize parasitic load to the system by reducing or
eliminating the need
for cooling fans, thereby increasing the ORC system energy output.
Typirnlly, a water/glycol mixture would be used as the heat transfer medium in
the ground source
condenser piping 99 and exchanged with the propellant at a heat exchanger 93.
The water/glycol
mixture would be pumped by pump 94 through the sub-surface tubing 99 to
exchange heat with
the relatively stable ground temperature. This relatively stable temperature
would lend some
predictability to the system. That is, with a stable ambient temperature
(ground temperature), the
power output curve when comparing ground source condensing to air cooled
condensing would
be flatter when plotting power versus ambient temperature such that the system
components
could be sized to appropriate capacity and better utilized throughout the
year. By contrast, with
air cooled condensing, much of the component capacity is under-utilized in
cold weather due to
limited requirement for cooling capacity and run at maximum capacity in warm
weather.
As with any heat exchanger, if sufficient surface area is provided for
consistent heat exchange, the
only parasitic load associated with this heat sink would be the fluid
circulating pump 94.
The water table will also impact heat exchange. Should the ground source
condenser pipes be
submerged below the level of the water table, the moisture within the soil
will facilitate this heat
exchange.
Increasing the recovery of additional energy from the reciprocating
engine/compressor
combination or increasing the cooling capacity of the system directly
correlates with the ability to
produce more net secondary power when the parasitic loads of the system are
controlled
independently of reciprocating engine and/or natural gas compressor operation.
That is, if
parasitic load on the reciprocating engine is reduced, the engine will not
produce as much waste
thermal energy, which will reduce waste heat collected by the ORC system, with
reductions in the
overall ORC output. Accordingly, adding further cooling capacity to the system
without adding
parasitic load directly to the engine, will increase available secondary
power.
With reference now to Figure 5, an excess of heat is transferred from the
jacket fluid to the
propellant. That is, in this example, the jacket fluid is cooled beyond the
engine manufacturers
specification to provide supplementary heat to the propellant, and then the
jacket fluid is
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subsequently reheated to appropriate temperature for return to the engine by
thermal energy
collected within the engine auxiliary cooling fluid at heat exchanger 47. The
jacket fluid can also
be reheated by the other heat sources available such as the engine exhaust, or
the compressor
lubricating oil or gas conduits. Other modifications may also be made to the
ORC portion of the
system, as described herein.
Figure 6 demonstrates how the thermal energy in compressed natural gas is
typically dissipated.
Figure 7 demonstrates generally how this thermal energy might be harnessed in
an ORC system.
Figure 8 shows how a natural gas compressor package (reciprocating engine 10
and compressor
68) typically dissipates excess heat energy from the compressors lubricating
oil 17 to atmosphere
through heat exchanger 69 (a lube oil to engine cooling fluid heat exchanger)
transfer from the
lubricating oil 17 to either the engines auxiliary cooling fluid system 16 (or
the engines jacket
water 11) which then has ambient air blown across a radiator 64 (or 81 if
jacket water) with fan
77 located on the aerial cooler.
Figure 9 shows how the lube oil energy can be transferred to either the
engines auxiliary cooling
fluid system 16 (or to the engines jacket water system 11, not shown) through
heat exchanger 69,
where that cooling fluid with the additional thermal energy is then circulated
to heat exchanger
20, thereby increasing the amount of thermal energy delivered to the
propellant.
Figure 10 through 13 shows various configurations of how the thermal energy
from the
lubricating oil can be directly transferred via heat exchanger 66 to the
propellant. Heat exchanger
66 can be located in various locations of the ORC system. Also shown is the
various
configurations of condenser 40 configurations, and aerial cooler
configurations.
Safety precautions
With respect to the collection of thermal energy from engine exhaust, thermal
energy is
transferred from the engines exhaust 12 to a thermal fluid 14 at heat
exchanger 13, which then
transfers the thermal energy to the propellant 86 at heat exchanger 60. Use of
thermal fluid in this
loop is preferable due to its stability even in the presence of high
temperatures and sparks that
may be present within the engine exhaust system. That is, if thermal fluid
were to leak into the
exhaust piping, it would likely bum-off within the exhaust stack (at worst,
causing a fffe within
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the stack). By contrast, a propellant leak within the exhaust piping may cause
a fire or even an
explosion, as exhaust gases may reach temperatures in excess of the propellant
flash temperature.
Suitable thermal fluids for use within the thermal fluid loop are typically
mineral oils or synthetic
oils (for higher temperature applications). These oils are generally
formulated from alkaline
.. organic or inorganic compounds.
Further, the thermal fluid loop allows the ORC system to be located a
reasonable distance from
the reciprocating engine, as thermal fluid may easily be pumped through a
piping system
(insulated pipes in cold climates) with little risk if energy losses are
experienced, compared to
energy loss from propellant over the same distance could cause the propellant
to condense before
reaching the expander 30. That is, using propellant within such pipes would
risk a phase change
in the propellant over the distance. Accordingly, the use of thermal oil to
collect thermal energy
from engine exhaust allows site space constraints (and potentially hazardous
area classification
inconsistencies) to be overcome. Accordingly, the reciprocating engine 10 can
be housed
separately from the ORC system, as there is no need to house the ORC
components (heat
exchangers, pumps, tanks, expander, etc.) within the reciprocating engine
building. Separation of
these components within different classification areas (hazardous area
classification versus non-
hazardous areas) or buildings provides further opportunities to improve
efficiency, for example
through use of propellant and equipment that is available at lower cost.
Gas Compression
The above improvements are particularly notable when the reciprocating engine
primary power is
used to drive natural gas compression, due to the above-described ability to
physically separate
components and for additional reject heat that can be utili7ed by the ORC
system. For example,
with natural gas compressors operating on a continuous basis, retrofitting an
ORC system to the
natural gas compressor package would require physical separation between the
two systems due
to the hazardous area classification of compressed explosive hydrocarbons
would require the
ORC system controller 100 and electric generator to be located at a safe
distance (as per the
hazardous area classification requirements) away from any piping. Further, it
is typical that an
existing compressor skid (some with a building surrounding them) would not
physically
accommodate a reciprocating engine and an ORC system.
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In addition to waste heat from the reciprocating engine, thermal energy may be
recovered from
two sources of a natural gas compressor 68. As shown in Figure 7, the first
source is the
temperature rise of the natural gas after each stage of gas compression, which
can be used to
directly (or indirectly) heat propellant within the ORC system. As shown in
Figure 10 to Figure
13, the second source is the temperature rise of the lubricating oil of the
natural gas compressor
that can be used to heat propellant directly or indirectly within the ORC
system
The compressor lubricating oil is normally cooled using reciprocating engine
jacket water 11 or
auxiliary cooling fluid system 16 (see Figure 8) which is then cooled in a
radiator with a fan
blowing air across it. The engine auxiliary cooling fluid system is typically
used to cool engine
intake air after the air has been compressed by the turbo charger(s). In the
present system, as
shown in Figure 9 through to Figure 13, thermal energy from the compressor
lubricating oil may
be collected directly or indirectly within the propellant 86.
With reference to Figure 9, thermal energy from the compressor lubricating oil
17 is transferred
to the engine auxiliary cooling fluid system fluid 16 (or jacket fluid 11) at
heat exchanger 69,
increasing the thermal energy of the transfer fluid. The lubricating oil 17
then returns to the
compressor, and the heated auxiliary cooling fluid is directed to heat
exchanger 20 where thermal
energy is transferred to propellant.
In an another embodiment, as shown in Figure 5, the jacket fluid 11 may
transfer supplementary
heat to propellant (overcooling the jacket fluid) in heat exchanger 20. The
amount of
supplementary heat (i.e. amount of overcooling) can be matched to the expected
reject thermal
energy from the engine auxiliary cooling fluid system That is, additional heat
(beyond the engine
manufacturers recommended heat rejection) can be extracted from the jacket
fluid and provided
to propellant in the ORC system (at heat exchanger 20), provided that an
appropriate amount of
heat is available from another source (for example the auxiliary cooling
fluid) to reheat the jacket
fluid at the engine after-cooler or heat exchanger 47. Appropriate sizing of
the heat exchangers
20 and 47 will provide the appropriate heat balance of the system In order to
allow the
reciprocating engine to operate with or without the ORC system operating, the
engine auxiliary
cooling fluid system may be interfaced with a heat exchanger 47 and
appropriate valving to the
jacket water's return line to the engine. That way, if the ORC is not
operational, the engine can
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continue to send the jacket water 11 and the auxiliary cooling fluid system 16
to their respective
radiators.
With reference to Figure 10, thermal energy from the compressor lubricating
oil 17 is transferred
directly to propellant 86 within the ORC system at supplementary heat
exchanger 66, which may
be placed at any suitable location within the ORC system. In the embodiment
shown, cooled
compressor lubricating oil 17 is returned to the compressor 68, and heated
propellant is directed
to either heat exchanger 20 or 60, depending where heat exchanger 66 is
inserted into the ORC
system. In Figures 11, 12 and 13, similar embodiments are shown, wherein
thermal energy from
the compressor lubricating oil is transferred directly to propellant in heat
exchanger 66. The
propellant is thereby preheated prior to exposure to the jacket fluid heat
exchanger 20 and the
thermal fluid heat exchanger 60.
Addition of Capacity to Existing Systems
It is expected that the teaching of the present description will provide
significant advantages when
used with existing reciprocating engine operations, in particular when coupled
to a natural gas
compressor. For example, an existing reciprocating engine used at a remote
work site (for
example, to power natural gas compression for pipeline transport) may be
exploited to produce
further site power by adding an ORC system, supplementary cooling capacity,
and decoupling of
engine, compressor and/or aerial cooler parasitic loads.
Collection of engine waste heat within exhaust based thermal fluid prior to
transfer to organic
propellant may overcome space constraints within close proximity to the
reciprocating engine.
Notably, the present teaching takes advantage of the existing engine radiator
capacity to provide
additional ORC cooling, and increasing heat recovery and conversion to useful
power. Further,
decoupling of the parasitic loads from the engine provides further efficiency
in permitting careful
control of the power supplied to these loads. Still further, the use of a
thermal fluid loop to
recover heat from the engine exhaust, and potentially other on-site heat
sources, and transfer this
heat to propellant enables heat to be transferred a reasonably significant
distance from the engine,
providing further opportunities for generation and use of secondary power.
Moreover, the
present system may be used to power parasitic loads of the reciprocating
engine, power gas
compressors, pumps, or electric generators, and the reciprocating engine ORC
system may be
further exploited by collection of reject heat from the compressed natural gas
in compression
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conduits, and natural gas compressor lubricating oil for the purpose of
generating additional
secondary power. Such heat collection configurations and combinations are not
contemplated in
prior art systems.
A preferred system in accordance with the invention is intended for use with a
reciprocating
engine of the type commonly used to power electric generators or natural gas
compressors, but is
also useful with reciprocating engines that supply motive power to a vehicle,
heavy equipment, or
otherwise provide power to do useful work.
Generally, the reciprocating engine is used to provide power in stationary
applications for
generating electricity and for compressing natural gas for pipeline transport,
and the secondary
power source is produced in the form of mechanical shaft horsepower by the
expander. This
mechanical shaft power may be used to: 1) couple to a compressor to boost the
inlet pressure of a
primary compressor or to generically move gases; 2) couple to a pump to pump
liquids; or 3)
couple to an electric generator to produce electricity at grid-connected or
remote sites where the
electricity is then used to reverse feed the grid, supplement electrical
demand on-site or power
parasitic loads of the reciprocating engine or the ORC system. More
specifically, the mechanical
shaft power may be used to compress gas as a boost compressor for the primary
compressor, to
supplement the mechanical shaft power of the primary reciprocating engine, to
pump liquids, or
to generate electricity for any other local energy need. Thermal energy may be
collected from one
or more such engines and processes, with the system collecting thermal energy
from all sources
to provide further efficiencies in the operation of the Rankine cycle to
produce secondary power.
System Operation
With reference to Figure 1, flow of propellant through the Rankine cycle may
be adjusted by a
control module 100, which may include a motor controller (variable frequency
drive - VFD) to
vary the operation of the pump 50. Alternatively, the pump 50 may be a multi-
stage centrifugal
pump or a positive displacement pump that is adjustable directly by the
control module 100. In
the former case, should the control module receive data from the monitoring
module that
indicates the pump speed or torque should be increased/decreased, the control
module sends a
signal to the VFD that controls the electric motor at the propellant pump,
thereby adjusting the
flow rate or pressure of the propellant. Temperature and pressure of the
propellant may therefore
be monitored at one or more locations within the cycle to determine
appropriate propellant flow
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CA 02676502 2009-08-24
and pressure for current operating conditions. A liquid level switch may be
present on either the
first heat exchanger 20 or on the second heat exchanger 60, which would be
monitored by the
monitoring system and provide feedback to the control module 100. When the
level is low, the
control module will increase the flow rate to send more propellant to the heat
exchangers.
Notably, with respect to Figures 9 through 13, thermal energy sources may be
evaluated based on
the need to dissipate engine heat and where that heat could be utilized in the
ORC system
operation. That is, in any system, the engine jacket fluid or the engine
auxiliary cooling fluid
system will collect waste thermal energy from the engine that must be
dissipated. Similarly, when
a natural gas compression module is present, the compressor lubricating oil
will also collect waste
thermal energy, and further thermal energy from the gas compression conduits
must be
dissipated. Therefore, these heat sources should be prioritized for heat
collection by their relative
temperatures so that heat is being added to the propellant with each added
waste heat source.
Conversely, the engine exhaust need not be dissipated for proper system
operation, as it may
simply be vented to atmosphere. Therefore, heat collection from engine exhaust
may be of a
different priority, and utilized to increase the secondary power output of the
ORC and to obtain
suitable gaseous propellant temperature/pressure for delivery to the expander.
In other words,
once the ORC system is extracting heat from the sources that require heat
dissipation, the exhaust
can be trimmed to extract the amount of heat that the ORC system requires to
function properly
and most efficiently without affecting the reciprocating engines or
compressors ability to operate.
In other words, the various sources of waste heat within a particular system
configuration should
be ordered/prioritized for heat transfer to propellant based on the ability to
add heat to the
propellant and thereby offset the parasitic load that would otherwise be
required to dissipate that
source of waste heat.
As an example, in cold weather conditions, propellant passing through an air-
cooled condenser
40 may require only minimal forced air flow across the condenser, as the
surface area of the
condenser fm tubes permits a significant degree of thermal energy transfer
with the cool ambient
air. Similarly, in cold weather, less thermal energy may be available for
collection from the engine
10 jacket fluid and compressor lubricating fluid (if present). Therefore, in
cold temperatures,
additional thermal energy may be collected from engine exhaust (and other
lower priority heat
sources) as needed, and the control module may additionally adjust the flow of
propellant through
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the Rankine cycle by adjusting the speed of pump 50 to permit sufficient time
to heat and cool
propellant within the cycle. Supplementary cooling sources may also be
adjusted or terminated.
The rotational speed of the expander 30 is controlled by operation of throttle
valve 31 and or 32
(opening and closing to adjust propellant flow through the expander),
regulated by a speed
control module (not shown), which interfaces and communicates with controller
100. Cooling
fans (if present) at the condenser may also be subject to the control module
100 such that fans are
slowed, sped-up, or shut-down, depending on the cooling requirements, and the
outside ambient
temperature.
Further, the control module 100 may control/regulate exhaust bypass valves 15
and/or valve 80
and 82 to divert engine jacket water thermal energy to/from the organic
Rankine cycle system.
Propellant valve 90, in combination with propellant valve 31 and/or 32 (if
present) may divert
propellant (in fluid state or gaseous state) around the expander 30 during
start-up and shutdown
of the Rankine cycle and/or engine. When de-activated, bypass 15 diverts
engine exhaust gases to
atmosphere rather than to the heat exchanger 13 and diverter valve(s) 80 and
82 divert jacket
water to the radiator 81. If required, thermal fluid circulating pump 51 (and
jacket water pump 52
if utilized) may be sped-up or slowed-down by the control module 100 or shut
down entirely.
Similarly, as shown in Figure 2, valves 80 and 82 may be activated by the
control module 100 to
fully or partially divert jacket fluid to the engine radiator 81 (which is
preferably under utilized
during operation of the Rankine cycle) rather than to the heat exchanger 20,
and if required
and/or present, jacket fluid booster pump 52 (shown in Figure 1) may be
simultaneously adjusted
to meet the required flow. Similarly, the thermal fluid loop collecting engine
exhaust 12 heat may
be shut down by de-actuating valve 15 such that it diverts engine exhaust to
atmosphere and if
required, deactivating thermal fluid pump 51 so that propellant does not
receive thermal energy
from the thermal fluid loop, nor extract heat from heat exchanger 60, if the
propellant is
circulating in the ORC while the exhaust thermal fluid system is not
functioning. Therefore,
propellant within the Rankine cycle will adapt quickly to the thermal energy
added or removed
from the system.
As illustrated in Figure 1, bypass line 91 directs propellant from heat
exchanger 60 directly to the
recuperator 70 (if present) and directly to the condenser 40 bypassing
expander 30. Similarly, the
recuperator 70 (not shown) may also be bypassed such that the propellant flows
directly from the
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CA 02676502 2009-08-24
heat exchanger 20 or 60 to the condenser. Bypass of the expander 30 prevents
propellant from
entering expander 30. This may be desirable when the propellant is in liquid
state, as entry of
liquid propellant at high flow rates and pressures into the expander 30 may
damage the internal
components of the expander.
On system start-up, the expander may be bypassed by controlling valve 90 and
31 or 32 (if
present) such that propellant is diverted to flow through bypass 91. It is
generally desirable to
maintain flow through the recuperator and prevent circulation of propellant
through the expander
30 and of cooling fluid through cooler 42 (Figure 2 and Figure 3), to speed
heating of the organic
propellant within the Rankine cycle system. In certain embodiments, such as
use of a screw
expander, such bypass may not be necessary, as a screw expander has robust
internal components
and can handle limited liquids flow at low pressure. In a start-up situation,
propellant pump 50
may not be activated by the control module 100 to operate until the heat at
the heat exchangers
and/or 60 are sufficient to evaporate (and possibly superheat) any propellant
that is in the
15 ORC system between the pump and the expander at start-up. Either heat
exchanger 20 or 60 may
have a level switch installed to send a signal to the monitoring module, which
then sends a signal
to the control module, which then controls the speed of the propellant pump.
When the propellant
level in the heat exchanger with the level indicator is high, the propellant
pump slows down and
when the level is low, the propellant pump 50 speeds up to send more
propellant to the heat
20 exchangers. In a start-up situation where a by-pass around the expander
does not exist, the level
switch in the heat exchanger will read that the level is high and the pump
will be inactive. Once
the thermal energy from the engine heats up the propellant, the propellant
will expand and flow
towards the expander (because the propellant pump 50 is off and the valve 90
and/or 31 and/or
32 (if present) will be open). Once the level in the level controlled heat
exchanger gets low, the
propellant pump will start pumping fluid through the ORC such that the rate of
pumping will
match the rate of evaporation, thereby insuring that any propellant entering
the expander is in a
gaseous or semi-gaseous/saturated state. Therefore, on start-up, the only
liquid propellant that
shall pass through the expander will be the propellant that was between the
evaporator 60 and the
expander 30, which condensed to liquid when the system was not operating. That
fluid will be
slowly moved through the expander in liquid state at a low pressure and low
speed, thereby
minimizing the liquid exposure to the expander.
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Rather than using level control on the heat exchangers to control pump
operation, temperature
and pressure sensors at the expander 30 and the condenser 40 can be used to
determine the state
of the propellant. Should the temperature and pressure of the propellant
indicate that the
propellant is near a phase change towards liquid state, the pump will be
slowed down by the
controller 100 to allow the heat exchangers 20 and/or 60 to deliver adequate
heat to the system
to evaporate propellant, such that only vapour reaches the expander.
If a secondary cooler 42 is present, for example as shown in Figure 2 and
Figure 3, this
configuration can be considered with or without a recuperator in the ORC
system. When a
recuperator is present, the cooler 42 would be located either between the
recuperator and the
condenser or the recuperator and the expander. As shown in Figure 2, whether a
recuperator is
present or not, the cooler 42 would reduce the thermal energy reject load
(duty) on the condenser
40 by offloading some of this heat dissipation in the engine radiator under
operating conditions
when the radiator is not being utilized.
If a secondary cooler 42 is present, whether a recuperator is present or not,
the cooler may be
used to reheat the engine jacket water 11 (or the engine auxiliary cooling
fluid 16) such that the
cooling fluid may be returned to the engine at the appropriate temperature.
When a recuperator is present, the cooler 42 could be located either between
the recuperator and
the expander or between the recuperator and the condenser. In either case,
whether a recuperator
is present or not, the cooler 42 would reheat the jacket water 11 leaving heat
exchanger 20
before the jacket water 11 is returned to the reciprocating engine 10. In
other words, heat
exchanger 20 will extract more heat energy from the jacket water 11 than
recommended by the
engine manufacturer and then that jacket water 11 will be re-heated by the
spent propellant off
the back of the expander such that the reciprocating engine will not
experience thermal shock and
keep the engine thermostatic control valve flowing all of the jacket water to
heat exchanger 20.
To prevent surging in the ORC system, it is important to remove the
appropriate amount of heat
from the jacket water (per the manufacturer's specifications) so as to prevent
jacket water flow
from entering the engines internal re-circulation loop that maintains the
jacket fluid at the
appropriate temperature. In short, the system is designed to extract more
energy than
recommended from the jacket fluid in front of the expander in the ORC system
and then add back
some of that heat back to the jacket fluid before it returns to the engine,
thereby utilizing the
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CA 02676502 2009-08-24
energy to extract secondary power but not affecting the reciprocating engines
jacket cooling
system. As an example, an engine manufacturer may suggest removing 10 degrees
Fahrenheit
between the engines discharge and the engine inlet. In the above example, the
heat exchanger 20
could remove 25 degrees Fahrenheit from the engines jacket water discharge and
then reheat that
jacket water 15 degrees Fahrenheit by utilizing the heat in the spent
propellant in cooler 42. The
heat exchangers would have to be designed for the appropriate flow and
temperature deltas to
have a heat balance in the system so that flow of jacket water within the
engine will not affect the
engines thermostatic valve and the jacket flow will remain steady (no
surging).
Likewise, if a geo-cooling loop is present as shown in Figure 4, the cooling
system consisting of
the sub-surface geo heat exchanger 99, the circulating pump 94 and the
propellant heat exchanger
93 may replace the air-cooled or liquid-cooled condenser operation, reducing
the operating
energy load by reducing the parasitic load for condensing propellant. The geo-
cooling loop would
have a heat transfer liquid (more than likely a water/glycol mixture)
circulated between heat
exchanger 93 and 99 by the use of circulating pump 94, all controlled by the
control module 100.
Control Examples
Thermal energy is collected from the engine jacket fluid 11 and compressor
lubricating oil 17 (if
present), as these heat sources must be cooled appropriately for safe
operation of the engine and
compressor (if present). The rate of thermal energy exchange may be controlled
to some extent
by controlling pump 51, (pump 52 if present, using a motor controller -
variable frequency drive),
and using diverter valves 15 to vent exhaust gas or valve 80 and 82 to divert
jacket water to the
radiator 81, as necessary. For example, the amount of jacket water flow to the
radiator may be
proportioned to establish the amount of cooling required. When the ORC system
is operational,
diverter valves 80 and 82 direct jacket cooling fluid to the radiator 81 in
conditions when thermal
energy exchange with organic propellant is not desirable, or is not effective
to sufficiently cool
the cooling fluid of the reciprocating engine 10.
In the system depicted in Figure 2, the control system 100 would utilize the
capacity of the engine
radiator by addition of the supplementary cooler 42. That is, when the engine
radiator is not being
utilized for engine cooling, its duty can be utilized to extract heat from the
spent propellant of the
ORC system, thereby reducing the load on the condenser 40. This would be
accomplished by
opening valve 80, opening valve 85, closing valves 82 and 84, turning on the
circulating pump 87,
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CA 02676502 2009-08-24
turning on the cooling fan for the radiator and circulating the cooling fluid
that is in the pipes and
heat exchangers to extract heat from the spent propellant via the radiator.
When the engine
radiator 81 is required to cool engine jacket fluid 11, the supply of fluid
from the supplementary
cooler to the radiator will not be circulated through the cooling radiator and
the engines jacket
water will be pumped directly to the radiator. This would be accomplished by
opening valves 82
and 84, while closing valves 80 and 85. When the radiator is not required to
cool engine jacket
water returning to the engine, radiator capacity may be leveraged by cooler 42
to provide
additional propellant or compressor cooling capacity.
In the system depicted in Figure 3, the control system 100 would utilize the
capacity of cooler 42
to extract heat from the spent propellant to reheat the jacket water that was
enroute from heat
exchanger 20. This will be accomplished by control system 100 controlling
booster pump 87 and
valves 80 and 82, which will control the flow of jacket water between the
radiator 81 and
propellant heat exchanger 20. The duty of cooler 42 is sized with heat
exchanger 20 and the
amount of reject heat available from the engine so that regardless of the flow
experienced, the
energy transferred will be proportionate in both heat exchangers, which in
turn will be calibrated
to remove a pre-determined amount of thermal energy (duty) from the jacket
water such that the
jacket water temperature delta is commensurate with the amount of heat
rejection the
reciprocating engine manufacturer recommends.
In the system depicted in Figure 5, the control system 100 would control
valves 80, 82 on the
jacket water 11 lines and valves 62 and 63 on the auxiliary cooling fluid
system 16 lines such that
the propellant at heat exchanger 20 could extract more heat energy from the
jacket water than
recommended by the engine manufacturer. To prevent the engines thermostatic
valve from
altering the jacket water flow to reject heat, the heat exchangers would be
sized accordingly and
controller 100 would sense the temperature of the jacket water before
returning to the engine to
determine the actions that are required of the jacket flow. That is, if enough
heat has been
extracted, then no flow will be directed to the radiators 81 and 64. Should it
be determined that
the jacket water is too warm to return to the engine, then flow will be
directed to radiators 81
and 64 and the fan 83 speed will be adjusted accordingly.
The engine exhaust can be directed to the thermal fluid heater 13, or diverted
past the thermal
fluid heater (the organic Rankine cycle system) and vented to atmosphere. The
diverter valve can
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CA 02676502 2009-08-24
be two valves working in unison, or a single integral valve that diverts flow
from one path to the
other. When the thermal energy from the engine exhaust 12 is required,
diverter valve 15 will: 1)
simultaneously start closing flow to atmosphere and start opening flow to the
thermal oil heater
13 or 2) start opening flow to the thermal oil heater 13 and then start
closing the flow to
atmosphere, as regulated by the control module 100.
The exhaust thermal fluid cycle pump 51 driving the thermal fluid loop may
also be controlled by
the control module 100 using a motor controller as needed. In situations when
the organic
Rankine cycle is inoperative due to shutdown or failure of the ORC, the
exhaust diverter valve 15
will divert the hot engine exhaust 12 to atmosphere and the thermal fluid
circulating pump 51
turned off Another option is to shut down the entire thermal fluid system to
avoid supplying any
residual thermal energy already present in the thermal fluid to heat exchanger
60. A thermal fluid
storage tank (not shown) may be located in series with the heat exchangers or
in parallel
configuration.
Similarly, as shown in Figure 4, with the ground source condensing
application, heat exchangers
93 and 99, and pump 94 may be controlled to increase or decrease flow of a
cooling medium
which then will exchange heat with the propellant in heat exchanger 93 to
increase or decrease
cooling capacity of the propellant as desired.
As it is desirable that the propellant should enter and exit the expander in
gaseous form,
appropriate temperature and pressure sensors (and controls) are present at the
expander 30 to
allow the control module 100 to monitor and adjust the rate of thermal energy
entering the ORC
system, air flow across the condenser, propellant flow and back pressure by
valves 31, 32 (if
present) and 90 through the expander. Information from these sensors may also
be used in the
control of propellant flow within the Rankine cycle by adjusting pump 50 or
the pressure across
valves 31, 32 (if present) and 90. If necessary, valves 31, 32 (if present)
and 90 may be activated
to direct propellant through bypass loop 91 when secondary power generation is
not necessary,
or to divert liquid propellant from entering the expander 30. In addition to
diverting the
propellant within the ORC, engine thermal energy may be diverted to
atmosphere, by directing
jacket fluid to the radiator 81, and by diverting engine exhaust to
atmosphere.
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The expander 30 may be a screw expander. A screw expander typically has 65% to
85%
efficiency, is easily controlled, is robust, and may be used with a variety of
temperatures,
pressures and flow rates. Moreover, although typical turbine blades may
sustain damage upon
contact with condensed/saturated droplets of propellant, the large diameter
steel helical screws of
a screw expander provide a robust mass and surface capable of withstanding
temporary exposure
to liquids. Therefore, use of a screw expander will improve the overall
efficiency and integrity of
the system.
The control module 100 for use in accordance with an embodiment of the
invention includes a
monitoring module that monitors the temperature and/or pressure of propellant
within the system
and the control module adjusts the parasitic loads of the system as needed to
improve efficiency
and maximize secondary power generation. Suitably, a temperature sensing
device and/or a
pressure sensing device are placed at the expander and/or condenser to enable
monitoring of the
physical state of the propellant at these locations. Preferably, such devices
are placed at each of
the expander 30 and condenser 40 to enable monitoring of the physical state of
the propellant at
both locations. The control module may adjust: the propellant pump 50 speed,
fan speed at the
condenser if air-cooled, condenser pump speed (if liquid-cooled), ground
source condensing
pump (if present), cooler 42 circulation pump (if present), diverter valve 15
at the exhaust bypass,
speed of pump 51 of the thermal fluid pump, diverter valves 80, 82, 84 (if
present) 85 (if present)
and pump 87 (if present) at the jacket water bypass, or speed of pump 52 (if
present) of the
jacket fluid pump to ensure that propellant entering the expander is gaseous,
and propellant
exiting the condenser is liquid.
The control module 100 may be manual, but is preferably automated, including a
processor for
collecting and processing information sensed by the monitoring module, and for
generating
output signals to adjust flow of propellant through the system, activate
valves, and adjust pump
and fan speeds as necessary. These adjustments may be made through use of
relays or through
use of motor controllers and variable frequency drives associated with each
component. The
processor may further collect information regarding primary and secondary
power output and
may activate a tertiary power source when more power is required.
Notably, the amount of thermal energy collected from the reciprocating engine
10 may be
adjusted by the control module by varying the flow of jacket water through the
engine jacket to
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CA 02676502 2009-08-24
heat exchanger 20 by diverting it to the engine radiator 81. Similarly, the
amount of thermal
energy collected from the exhaust system 12 can be varied by regulating the
exhaust diverter
valve 15, such that the exhaust energy can be diverted directly to atmosphere
or to the thermal
fluid 14 through heat exchanger 13. Heat collected from a natural gas
compressor would be
controlled by altering the flow of the lubricating oil and/or the flow of the
propellant. If it is the
compressed natural gas that is the source of the waste heat, the flow of the
natural gas will not be
altered nor controlled by the controller 100, as the engine - the primary
power source is used to
compress gas and the intent of the waste recovery system is intended not to
interfere with the
primary power sources operations. The flow of propellant on the other side of
the heat exchanger
will affect the amount of energy that is extracted from the natural gas. In
either case, the
objective of recovering the waste heat from the compressed natural gas
conduits is to reduce the
load on the air cooled heat exchanger (known in the industry as an aerial-
cooler).
On start-up, the control module 100 is programmed to add engine thermal energy
to the system
without circulating propellant 86 until the liquid propellant 86 in the engine-
associated heat
exchangers reaches a predetermined temperature and/or pressure. At this point,
the propellant
circulating pump 50 is started at slow speed to ensure that propellant 86 is
sufficiently heated
within the engine-associated heat exchanger 60 and/or heat exchanger 20 to
evaporate the
propellant prior to reaching the expander. In this manner, only a minimum
amount of liquid
propellant that condensed in the piping between the evaporator 60 and the
expander 30 will pass
through the expander 30 on start-up, eliminating the need for bypassing the
expander on start-up.
Thus, the Rankine cycle is quickly operational upon pump 50 start-up and
thermal energy may be
collected and used for secondary power generation in accordance with the
invention.
With reference to Figures 9 through 13, the engine may be used to power a
natural gas
compressor. In these embodiments, further thermal energy may be recovered from
the lubricating
oil and/or one or more of the gas compression stages, as each stage of gas
compression generates
a significant amount of thermal energy that must be removed from the gas
(before the gas enters
the pipeline system) and from the lubricating oil. Typically, the engine
jacket fluid is cooled in an
air-cooled radiator 81 and the natural gas is air-cooled after each stage of
compression in gas
coolers 89. The gas coolers 89, when co-located together with the radiator 81,
are referred to as
an "aerial cooler" (an air-cooled fin-tube configuration including a common
fan 77 that blows air
across both sets of the fin-tubes), and engine exhaust is separately vented to
atmosphere. Instead
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of simply dissipating this heat to atmosphere, the thermal energy generated
from the exhaust, the
jacket water, each stage of gas compression, and the lubricating oil of the
natural gas compressor
may be collected within heat exchangers 13, 20, 21, 22, 68 and 69 and used to
heat organic
propellant between the condenser and the expander. This recovered thermal
energy will result in
additional secondary power generation, which power may be used to further
improve system
efficiency. Moreover, the gas cooler 89 may be co-located with air-cooled
condenser 40 and
with radiator 81 to permit cooling by one set of fans 72 operated by the
control module 100.
Typically, the natural gas compressor lubricating oil is cooled by heat
exchange with either the
engines jacket water or the engines auxiliary cooling fluid system (typically
a water/glycol
mixture), which is then pumped to the aerial cooler for liquid to air cooling.
The heat in the
lubricating oil that needs cooling can transfer the waste heat to the
propellant either through
direct interface through a heat exchanger or indirectly by interface with
jacket fluid or auxiliary
cooling fluid system (Figures 9 to 13). The intermediate fluid (jacket fluid,
auxiliary cooling fluid)
then transfers heat to propellant.
As the condenser fan(s) 72, the radiator cooling fan 83 and the aerial cooler
fan 77 are a major
parasitic load within the system, the control module is programmed to reduce
fan speeds
whenever possible, for example in cool weather or reduced engine output. This
is accomplished
by detecting fluid temperatures in the system and providing the fan(s) with an
electric motor(s)
with controller(s) (variable frequency drive), or by providing each fan with a
multi-speed electric
motor operated directly by the control module 100. In typical natural gas
compression
configurations, the associated aerial cooler fan 77 is often powered through a
jack-shaft coupled
to the reciprocating engine's crank shaft via a series of shafts and pullies,
drawing power directly
from the reciprocating engine (not shown). Similarly, a reciprocating engine
coupled to a
generator is typically associated with a belt-driven radiator fan 83. An
opportunity exists to de-
couple the aerial cooler fan 77 from the jack-shaft (not shown) and drive fan
77 directly with an
electric motor (not shown), that is controlled by the control module 100, by
feedback from the
monitoring module which utilizes a motor controller (or as a controllable
multi-speed fan) to
control its speed. The power load of aerial cooler fan 77 is now being
supplied by the secondary
power source, thereby reducing the load on the primary engine. The
reciprocating engine may
therefore use less fuel to produce the same amount of net power, or
conversely, may consume the
same amount of fuel with more primary power output.
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Ultimately, the control module 100 in conjunction with the monitoring module
(not shown),
controls recovery of thermal energy from the primary power reciprocating
engine 10 and uses this
thermal energy to create a secondary power source. The control module is
programmed to
maximize net horsepower by reducing parasitic loads of the ORC system or the
reciprocating
engine, when available, or to increase the amount of waste heat from the
reciprocating engine 10
or compressor 68. For example, in some circumstances, more net horsepower may
be produced
by reducing parasitic loads within the system, while in other circumstances
more net horsepower
may be produced by maintaining or increasing parasitic loads and driving
secondary power
generation by recovering more waste heat. The monitoring module and control
module 100
therefore work together to reallocate thermal energy from the compressor
lubricating oil (via the
auxiliary cooling fluid system, the jacket water system, or by direct
interface with the propellant),
the jacket water and the engine exhaust, determining the optimal parasitic
loads on the ORC
system in order to further maximize secondary power generation as necessary.
In all
embodiments, the reciprocating engine 10 operates at its required capacity to
deliver the
appropriate amount of primary power, and the inherent operational requirement
for removal of
engine thermal energy is achieved by some combination of. diversion of exhaust
gases direct to
atmosphere; cooling of the engine by its radiator fluid loop; collection of
exhaust heat for use
within the ORC system, collection of natural gas compressor reject heat (from
the lubricating oil
or the heat developed from gas compression) and collection of engine jacket
radiant heat for use
in the ORC system and collection/dissipation of auxiliary cooling fluid system
energy for use in
the ORC system.
The control module is programmed based on data that has been compiled by
running simulation
software designed to optimize power output. That is, various possible readings
from the
associated monitoring module (for example ambient air temperature or
temperature/pressure of
propellant) are initially compared to the optimized data results and
corresponding adjustments are
made to the ORC system to see if these alternations improve the net horsepower
output of the
system. The complete data set of such readings and corresponding optimized
operating
conditions are loaded into the control module and then adjusted by the control
module 100 to
enable the system to quickly settle into optimal operating condition in any
situation. As the
system gathers operating data and the system performance is compared to that
of the simulated
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CA 02676502 2009-08-24
operation, adjustments to the programming of the control system may be made to
get the best
results through a closed loop system based on the iterations previously
encountered.
When the system is generating secondary power as electricity, for example, the
secondary power
generated may be sent to a motor control centre or power hub, which also
receives power from
any other sources (the reciprocating engine coupled to a generator, the grid,
tertiary power
source, etc) and allocates power on demand. When the parasitic loads of the
ORC system and
other power loads is not satisfied by the primary and secondary power sources
alone, the motor
control centre may indicate to the demand module, which then corresponds with
the control
module 100, that the tertiary power to the site should be dispatched to start
generating power.
In a specific example, the reciprocating engine may be used to compress
natural gas, with
secondary shaft power used to: 1) power a boost compressor that boosts the
inlet gas pressure of
the primary compressor 68, 2) power a pump that can be used to re-inject
produced water, 3)
power a generator, or 4) supplement the output of the primary source or its
parasitic loads.
In certain situations, particularly in remote locations, a demand for power
exists in operation of a
work site. Notably, the demand may fluctuate from time to time. As such, a
tertiary power source
may also be available, such as a generator, stored power in a battery, solar
power, wind, fuel cell,
or grid power. This tertiary source of power may be operated as the main
source of power on the
site with the reciprocating engine and the secondary power utilized as
additional power. In some
cases, the power generated by the engine and secondary power source may not be
sufficient to
meet the needs of the job site and therefore an additional fuel based tertiary
power source may be
required to be dispatched so that the site demand can be met.
Accordingly, the control module 100 may also initiate alterations in
performance which may
require tertiary power. However, in certain embodiments, tertiary power should
only be accessed
when necessary to ensure an uninterrupted supply of power to the site. Usage
of the tertiary
power source will increase the operating cost of the site, however: 1) the
overall cost of power
will be reduced as power may be supplied by the thermal energy recovery system
in place of fuel-
fired generators; and 2) in many off-grid locations the total operating cost
is less important than
providing a reliable level of power at the site.
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CA 02676502 2009-08-24
The above-described embodiments of the present invention are intended to be
examples only.
Alterations, modifications and variations may be effected to the particular
embodiments by those
of skill in the art without departing from the scope of the invention, which
is defined solely by the
claims appended hereto.
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