U.S. patent application number 11/000112 was filed with the patent office on 2006-06-01 for method and apparatus for power generation using waste heat.
Invention is credited to Timothy Neil Sundel.
Application Number | 20060112693 11/000112 |
Document ID | / |
Family ID | 36565361 |
Filed Date | 2006-06-01 |
United States Patent
Application |
20060112693 |
Kind Code |
A1 |
Sundel; Timothy Neil |
June 1, 2006 |
Method and apparatus for power generation using waste heat
Abstract
According to the present invention, a method and apparatus for
generating power aboard a marine vessel is provided. The method
comprises the steps of: (a) providing a Rankine Cycle device that
includes at least one of each of an evaporator, a turbo-generator
that includes a turbine coupled with an electrical generator, a
condenser, and a refrigerant feed pump; (b) disposing the one or
more evaporators within an exhaust duct of a power plant of the
marine vessel; (c) operating the power plant; and (d) selectively
pumping refrigerant through the Rankine Cycle device, wherein
refrigerant exiting the evaporator powers the turbine, which in
turn powers the generator to produce power.
Inventors: |
Sundel; Timothy Neil; (West
Hartford, CT) |
Correspondence
Address: |
MCCORMICK, PAULDING & HUBER LLP
CITY PLACE II
185 ASYLUM STREET
HARTFORD
CT
06103
US
|
Family ID: |
36565361 |
Appl. No.: |
11/000112 |
Filed: |
November 30, 2004 |
Current U.S.
Class: |
60/670 |
Current CPC
Class: |
F01K 25/10 20130101;
Y02E 20/363 20130101; F01K 15/00 20130101; Y02E 20/16 20130101;
Y02E 20/30 20130101; F22B 1/1807 20130101; F28B 1/02 20130101 |
Class at
Publication: |
060/670 |
International
Class: |
F01K 23/06 20060101
F01K023/06 |
Claims
1. An apparatus for generating power using exhaust from a marine
power plant, the apparatus comprising: an evaporator operable to be
disposed within the exhaust from the marine power plant; a
turbo-generator that includes a turbine coupled with an electrical
generator; a condenser having a plurality of tubes disposed within
a housing, wherein the tubes form a closed circuit within the
housing that is sized to permit a flow of coolant into and out of
the condenser; and a refrigerant feed pump operable to pump
refrigerant.
2. The apparatus of claim 1, further comprising a coolant source
that provides the coolant flow into and out of the condenser.
3. The apparatus of claim 2, wherein the coolant source is
environmental water.
4. The apparatus of claim 2, further comprising a selectively
operable bypass valve disposed within the apparatus and positioned
to provide a path between the evaporator and the condenser, so that
refrigerant may be selectively bypassed around the
turbo-generator.
5. The apparatus of claim 1, further comprising a recuperator
disposed within the condenser, and the recuperator is positioned
within the apparatus such that refrigerant from the refrigerant
feed pump enters the recuperator and refrigerant exiting the
recuperator passes into the evaporator.
6. The apparatus of claim 1, further comprising a pair of the
refrigerant feed pumps operable to pump refrigerant, wherein one of
the feed pumps is connected to the condenser adjacent a first
lengthwise end of the condenser, and the other of the feed pumps is
connected to the condenser adjacent a second lengthwise end of the
condenser, opposite the first lengthwise end.
7. The apparatus of claim 1, wherein the condenser has a
selectively removable access panel attached to a first lengthwise
end of the housing, wherein removal of the access panel permits
access to the plurality of tubes.
8. A method for generating power aboard a marine vessel, comprising
the steps of: providing a Rankine Cycle device that includes at
least one of each of an evaporator, a turbo-generator that includes
a turbine coupled with an electrical generator, a condenser, and a
refrigerant feed pump; disposing the one or more evaporators within
an exhaust duct of a power plant of the marine vessel; operating
the power plant; and selectively pumping refrigerant through the
Rankine Cycle device.
9. The method of claim 8, further comprising the steps of:
disposing a selectively operable bypass valve disposed within the
device, positioned to provide a path between the evaporator and the
condenser; and selectively operating the bypass valve to bypass at
least a portion of the refrigerant flow around the
turbo-generator.
10. The method of claim 9, wherein the bypass valve is selectively
operated to bypass refrigerant around the turbo-generator during
start-up of the Rankine Cycle device and during shut-down of the
Rankine Cycle device.
11. The method of claim 9, wherein the bypass valve is selectively
operated to bypass refrigerant around the turbo-generator when the
turbo-generator is inoperable.
12. A method for generating power, comprising the steps of:
providing a Rankine Cycle device that includes at least one of each
of an evaporator, a turbo-generator that includes a turbine coupled
with an electrical generator, a condenser, and a refrigerant feed
pump; disposing the one or more evaporators within an exhaust duct
of a power plant of a marine vessel; operating the power plant; and
selectively pumping refrigerant through the Rankine Cycle device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to methods and apparatus for
power generation using waste heat from a power plant in general,
and to those methods and apparatus that utilize an organic Rankine
cycle in particular.
[0003] 2. Background Information
[0004] Marine and land based power plants can produce exhaust
products in a temperature range of 350-1850.degree. F. In most
applications, the exhaust products are released to the environment
and the thermal energy is lost. In some instances, however, the
thermal energy is further utilized. For example, the thermal energy
from the exhaust of an industrial gas turbine engine (IGT) has been
used as the energy source to drive a Rankine cycle system.
[0005] Rankine cycle systems can include a turbine coupled to an
electrical generator, a condenser, a pump, and a vapor generator.
The vapor generator is subjected to a heat source (e.g., geothermal
energy source). The energy from the heat source is transferred to a
fluid passing through the vapor generator. The energized fluid
subsequently powers the turbine. After exiting the turbine, the
fluid passes through the condenser and is subsequently pumped back
into the vapor generator. In land-based applications, the condenser
typically includes a plurality of airflow heat exchangers that
transfer the thermal energy from the water to the ambient air.
[0006] In the 1970's and 1980's the United States Navy investigated
a marine application of a Rankine cycle system, referred to as the
Rankine Cycle Energy Recovery (RACER) System. The RACER system,
which utilized high-pressure steam as the working medium, was
coupled to the drive system to augment propulsion horsepower. RACER
could not be used to power any accessories because it as coupled to
the drive system; i.e., if the drive system was not engaged,
neither was the RACER system. The RACER system was never fully
implemented and the program was cancelled because of problems
associated with using high-pressure steam in a marine
application.
[0007] What is needed is a method and apparatus for power
generation using waste heat from a power plant that can be used in
a marine environment, and one that overcomes the problems
associated with the prior art systems.
SUMMARY OF THE INVENTION
[0008] According to the present invention, a method and apparatus
for generating power aboard a marine vessel is provided. The method
comprises the steps of: (a) providing a Rankine Cycle device that
includes at least one of each of an evaporator, a turbo-generator
that includes a turbine coupled with an electrical generator, a
condenser, and a refrigerant feed pump; (b) disposing the one or
more evaporators within an exhaust duct of a power plant of the
marine vessel; (c) operating the power plant; and (d) selectively
pumping refrigerant through the Rankine Cycle device, wherein
refrigerant exiting the evaporator powers the turbine, which in
turn powers the generator to produce electric power.
[0009] The present method and apparatus provides significant
advantages. For example, the range of a marine vessel that burns
liquid fossil fuel within its power plant is typically dictated by
the fuel reserve it can carry. In most modern marine vessels, a
portion of the fuel reserve is devoted to running a power plant
that generates electrical energy. Hence, both the propulsion needs
and the electrical energy needs draw on the fuel reserve. The
present method and apparatus decreases the fuel reserve
requirements by generating electricity using waste heat generated
by the power plant of the vessel rather than fossil fuel. Hence,
the vessel is able to carry less fuel and have the same range, or
carry the same amount of fuel and have a greater range. In
addition, less fuel equates to lower weight, and lower weight
enables increased vessel speed.
[0010] If one considers the amount of fossil fuel that would be
required to produce the electrical energy that can be created by
the present method and apparatus via waste heat, it is clear that
several other advantages are provided by the present invention. For
example, the weight of the fuel required to produce "N" units of
electrical power using the vessel's existing main or auxiliary
power plants far exceeds the weight of a present ORC device capable
of producing the same "N" units of electrical power via waste heat.
In addition, consumption of liquid fuel changes the buoyancy
characteristics of the vessel. The weight of the present ORC device
remains constant, thereby facilitating buoyancy control of the
vessel.
[0011] For those embodiments that utilize a recuperator disposed
within the condenser, the present inventor provides the additional
benefits of an ORC device with increase efficiency disposed within
a relatively compact unit.
[0012] Yet another advantage of the present invention results from
the thermal energy removed from the exhaust gases of the marine
vessel power plant. The mass flow of the exhaust is a function of
the volumetric flow and density of the exhaust. The present method
and apparatus enables the exhaust gases to be significantly cooled
and consequently the density of the exhaust gases increased. As a
result, the mass flow is substantially decreased, and the required
size of the marine power plant exhaust duct is substantially
less.
[0013] These and other objects, features and advantages of the
present invention will become apparent in light of the detailed
description of the best mode embodiment thereof, as illustrated in
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a diagrammatic perspective view of an embodiment
of the present invention ORC device, having a single
turbo-generator.
[0015] FIG. 2 is a diagrammatic perspective view of an embodiment
of the present invention ORC device, having a pair of
turbo-generators.
[0016] FIG. 3 is a diagrammatic perspective view of an embodiment
of the present invention ORC device, having three turbo-generators
and a single condenser.
[0017] FIG. 4 is a diagrammatic perspective view of an embodiment
of the present invention ORC device, having three turbo-generators
and a pair of condensers.
[0018] FIG. 5 is a sectional planar view of a condenser.
[0019] FIG. 6 is a diagrammatic perspective view of an
evaporator.
[0020] FIG. 7 is a schematic diagram of an ORC device that includes
a single turbo-generator.
[0021] FIG. 8 is a schematic diagram of an ORC device that includes
a pair of turbo-generators.
[0022] FIG. 9 is a schematic diagram of an ORC device that includes
three turbo-generators.
[0023] FIG. 10 is a schematic diagram of an ORC device that
includes three turbo-generators and a pair of condensers.
[0024] FIG. 11 is a diagrammatic pressure and enthalpy curve
illustrating the Rankine Cycle.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Referring to FIGS. 1-6, the present method for utilizing
waste heat includes an organic Rankine cycle (ORC) device 20 for
waste heat utilization. The ORC device 20 includes at least one of
each of the following: 1) a turbine coupled with an electrical
generator (together hereinafter referred to as the "turbo-generator
22"); 2) a condenser 24; 3) a refrigerant feed pump 26; 4) an
evaporator 28; and 5) a control system. The ORC device 20 is
preferably a closed "hermetic" system with no fluid makeup. In the
event of leaks, either non-condensables are automatically purged
from the device 20 or charge is manually replenished from
refrigerant gas cylinders.
[0026] The ORC device 20 uses a commercially available refrigerant
as the working medium. An example of an acceptable working medium
is R-245fa (1,1,1,3,3, pentafluoropropane). R-245fa is a
non-flammable, non-ozone depleting fluid. R-245fa has a saturation
temperature near 300.degree. F. and 300 PSIG that allows capture of
waste heat over a wide range of IGT exhaust temperatures.
[0027] Now referring to FIGS. 1-4, the turbo-generator includes a
single-stage radial inflow turbine 30 that typically operates at
about 18000 rpm, a gearbox 32 with integral lubrication system, and
an induction generator 34 operating at 3600 rpm. The gearbox 32
includes a lubrication system. In some instances, the gearbox
lubrication system is integral with the gearbox 32.
[0028] In one embodiment, the turbo-generator 22 is derived from a
commercially available refrigerant compressor-motor unit; e.g., a
Carrier Corporation model 19XR compressor-motor. As a turbine, the
compressor is operated with a rotational direction that is opposite
the direction it rotates when functioning as a compressor.
Modifications performed to convert the compressor into a turbine
include: 1) replacing the impeller with a rotor having rotor blades
shaped for use in a turbine application; 2) changing the shroud to
reflect the geometry of the rotor blades; 3) altering the flow area
of the diffuser to enable it to perform as a nozzle under a given
set of operating conditions; and 4) eliminating the inlet guide
vanes which modulate refrigerant flow in the compressor mode. To
the extent that there are elements within the 19XR compressor that
have a maximum operating temperature below the operating
temperature of the turbine 30, those elements are replaced or
modified to accommodate the higher operating temperature of the
turbine 30.
[0029] In some embodiments, the turbo-generator 22 includes
peripheral components such as an oil cooler 36 (shown schematically
in FIGS. 7-10) and oil reclaim eductor (not shown). Both the oil
cooler 36 and the eductor and their associated plumbing are
attached to the turbo-generator 22.
[0030] Referring to FIG. 6, a number of different evaporators 28
can be used with the ORC device 20. A single pressure once-through
evaporator 28 with vertical hot gas flow and horizontal flow of
refrigerant through fin-tube parallel circuits serviced by vertical
headers is an acceptable type of evaporator 28. Examples of
acceptable evaporator tube materials include carbon steel tubes
with carbon steel fins, and stainless steel tubes with carbon steel
fins, both of which have been successfully demonstrated in exhaust
gas flows at up to 900.degree. F. Other evaporator tube materials
may be used alternatively. Inlet header flow orifices are used to
facilitate refrigerant flow distribution. Different refrigerant
flow configurations through the evaporator 28 can be utilized;
e.g., co-flow, co-counterflow, co-flow boiler/superheater and a
counterflow preheater, etc. The present evaporator 28 is not
limited to any particular flow configuration.
[0031] In all the evaporator 28 embodiments, the number of
preheater tubes and the crossover point are selected in view of the
desired hot gas exit temperature as well as the boiler section
inlet subcooling. A pair of vertical tube sheets 38, each disposed
on an opposite end of the evaporator 28, supports evaporator coils.
Insulated casings 40 surround the entire evaporator 28 with
removable panels for accessible cleaning.
[0032] The number of evaporators 28 can be tailored to the
application. For example, if there is more than one exhaust duct,
an evaporator 28 can be disposed in each exhaust duct. More than
one evaporator 28 disposed in a particular duct also offers the
advantages of redundancy and the ability to handle a greater range
of exhaust mass flow rates. At lower exhaust flow rates a single
evaporator 28 may provide sufficient cooling, while still providing
the energy necessary to power the turbo-generators 22. At higher
exhaust flow rates, a plurality of evaporators 28 may be used to
provide sufficient cooling and the energy necessary to power the
turbo-generators 22.
[0033] Referring to FIGS. 1-5, the condenser 24 is a shell-and-tube
type unit that is sized to satisfy the requirements of the ORC
device. The condenser 24 includes a housing 42 and a plurality of
tubes 44 (hereinafter referred to as a "bank of tubes") disposed
within the housing 42. The housing 42 includes a working medium
inlet port 46, a working medium exit port 48, a coolant inlet port
50, and a coolant exit port 52. The coolant inlet and exit ports
50,52 are connected to the bank of tubes 44 to enable cooling fluid
to enter the condenser 24 housing, pass through the bank of tubes
44, and subsequently exit the condenser housing 42. Likewise, the
working medium inlet and exit ports 46,48 are connected to the
condenser housing 42 to enable working medium to enter the housing
42, pass around the bank of tubes 44, and subsequently exit the
housing 42. In some embodiments, one or more diffuser plates 54
(see FIG. 5) are positioned adjacent the working medium inlet 46 to
facilitate distribution of the working medium within the condenser
24. In the embodiment shown in FIGS. 1-4, the housing 42 includes a
removable access panel 56 at each axial end of the housing 42. In a
preferred embodiment, one of the access panels 56 is pivotally
attached to one circumferential side of the housing 42 and
attachable to the opposite circumferential side via a selectively
operable latch (not shown) so that the access panel 56 may be
readily pivoted to provide access to the bank of tubes 44.
[0034] In some embodiments, a non-condensable purge unit 58 (shown
schematically in FIGS. 7-9) is attached to the condenser 24. The
purge unit 58 is operable to extract air and water vapor that may
accumulate in the vapor region of a condenser housing 42 to
minimize or eliminate their contribution to oil hydrolysis or
component corrosion. The purge unit 58 is actuated only when the
system controller thermodynamically identifies the presence of
non-condensable gas.
[0035] Referring to FIG. 5, in some embodiments, the ORC device 20
includes a recuperator 60 for preheating the working medium prior
to its entry into the evaporator 28. The recuperator 60 is operable
to receive thermal energy from at least a portion of the working
medium exiting the turbo-generator 22 and use it to preheat working
medium entering the evaporator 28. In the embodiment shown in FIG.
5, the recuperator 60 includes a plurality of ducts 62 disposed
within the housing 42 of the condenser 24. The ducts 62 are
connected inline downstream of the working medium exit port 48 of
the condenser 24 and upstream of the evaporator 28. A partition 64
partially surrounds the recuperator ducts 62 to separate them from
the remainder of the condenser 24. Working medium enters the
condenser 24 through the working medium inlet port 46 and passes
through the recuperator 60 prior to entering the remainder of the
condenser 24. One or more diffusers 54 can be disposed within the
recuperator to facilitate distribution of the working medium within
the recuperator 60. Placing the recuperator 60 within the condenser
24 advantageously minimizes the size of the ORC device 20. A
recuperator 60 disposed outside of the condenser 24 can be used
alternatively, however.
[0036] Referring to FIGS. 1-4, the ORC device 20 includes one or
more variable speed refrigerant feed pumps 26 to supply liquid
refrigerant to the evaporator 28. In one embodiment, the
refrigerant feed pump 26 is a turbine regenerative pump that
supplies liquid refrigerant to the evaporator 28 with relatively
low net pump suction head (NPSH). This design, combined with the
relatively low system pressure difference, allows the feed pump 26
and condenser 24 to be mounted at the same elevation and obviates
the need for separate condensate and feed pumps. In alternative
embodiments, the refrigerant feed pump 26 may be a side channel
centrifugal pump or an axial inlet centrifugal pump. The
refrigerant feed pump 26 is equipped with an inverter to allow
fully proportional variable speed operation across the full range
of exhaust conditions. Other pump controls may be used
alternatively. Applications using two or more refrigerant feed
pumps 26 offer the advantage of redundancy. In some embodiments,
the piping 74 disposed immediately aft of each of the feed pumps 26
are connected to one another by a cross-over piping segment 76.
Multiple refrigerant feed pumps 26 and the cross-over segment 76
enhance the ability of the ORC device 20 to accommodate a marine
environment having significant pitch and roll by collecting working
medium at different locations in the condenser 24. ORC
configurations having more than one turbo-generator 22 and more
than one refrigerant feed pump 26 are provided with valves 66 (see
FIGS. 7-10) that enable each turbo-generator 22 or feed pump 26 to
be selectively removed from the working medium flow pattern.
Alternatively, a feed pump 26 may be associated with each
turbo-generator 22, and selective actuation of the associated feed
pump 26 can be used to engage/disengage the associated
turbo-generator 22.
[0037] The ORC device 20 configurations shown in FIGS. 7-10 each
includes a cooling circuit 68 used in marine applications, wherein
a cooling medium (e.g., seawater) is accessed from a cooling medium
source 70 (e.g., the body of water in the environment surrounding
the marine vessel) and circuitously passed through the condenser 24
(via the coolant inlet and exit ports 50,52) and returned to the
cooling medium source 70. In alternative embodiments, the cooling
circuit 68 includes a heat exchanger (e.g., a cooling tower) to
remove thermal energy from the cooling medium.
[0038] ORC device 20 configurations are shown schematically in
FIGS. 7-10. These configurations represent examples of ORC device
20 configurations and should not be interpreted as the only
configurations possible within the present invention. Arrows
indicate the working medium flow pattern within each
configuration.
[0039] Referring to a first configuration shown in FIG. 7,
beginning at a pair of refrigerant feed pumps 26, working medium is
pumped toward an evaporator 28. In the embodiment shown in FIG. 7,
prior to entering the evaporator 28, the working medium passes
through a recuperator 60, wherein the working medium is preheated.
In a marine application, the evaporator 28 is disposed within an
exhaust duct that receives exhaust products from the vessel's power
plant. Working medium exiting the evaporator 28 subsequently
travels toward the turbo-generator 22. A bypass valve 72, disposed
between the evaporator 28 and the turbo-generator 22, enables the
selective diversion of working medium around the turbo-generator 22
and toward the condenser 24. An orifice 73 is disposed downstream
of the bypass valve 72 to produce a flow-restriction. As will be
discussed below, the bypass valve 72 is operable to fully bypass
working medium around the turbo-generator 22. Alternatively, the
bypass valve 72 can operate to selectively vary the amount of
working medium that is introduced into the turbo-generator 22.
Assuming some, or all, of the working medium has not been diverted
around the turbo-generator 22, the working medium enters the
turbine 30 portion of the turbo-generator 22 and provides the
energy necessary to power the turbo-generator 22. Once through the
turbo-generator 22, the working medium travels toward the condenser
24. Working medium that is diverted around the turbo-generator 22
also travels toward the condenser 24. A perspective view of this
configuration of the ORC device 20 is shown in FIG. 1, less the
evaporator 28.
[0040] A second ORC device 20 configuration is schematically shown
in FIG. 8 that includes a pair of turbo-generators 22. The turbine
inlets are connected to a feed conduit from the evaporator 28. A
turbine inlet valve 66a is disposed immediately upstream of each
turbo-generator 22. In some embodiments, a turbine exit valve 66b
is disposed immediately downstream of each turbo-generator 22. In
those embodiments, a safety pressure bleed is provided connected to
the low pressure side of the ORC device. The second ORC device 20
configuration also includes a plurality of evaporators 28. An
evaporator inlet valve 78 is disposed immediately upstream of each
evaporator 28. In some embodiments, an evaporator exit valve 80 is
disposed immediately downstream of each evaporator 28. A
perspective view of this configuration of the ORC device 20 is
shown in FIG. 2, less the evaporator 28.
[0041] A third ORC device 20 configuration is schematically shown
in FIG. 9 that includes three turbo-generators 22. A perspective
view of a portion of this configuration of the ORC device 20 is
shown in FIG. 3, less the evaporator 28.
[0042] A fourth ORC device 20 configuration is schematically shown
in FIG. 10 that includes three turbo-generators 22 and a pair of
condensers 24. A perspective view of a portion of this
configuration of the ORC device 20 is shown in FIG. 4, less the
evaporator 28.
[0043] In all of the configurations, the ORC controls maintain the
ORC device 20 along a highly predictable programmed turbine inlet
superheat/pressure curve through the use of the variable speed feed
pump 26 in a closed hermetic environment. An example of such a
curve is shown in FIG. 11.
[0044] The condenser load is regulated via the feed pump(s) 26 to
maintain condensing pressure as the system load changes. In
addition to the primary feed pump speed/superheat control loop, the
ORC controls can also be used to control: 1) net exported power
generation by controlling either hot gas blower speed or bypass
valve 72 position depending on the application; 2) selective
staging of the generator 34 and gearbox 32 oil flow; and 3)
actuation of the purge unit 58. The ORC controls can also be used
to monitor all ORC system sensors and evaluate if any system
operational set point ranges are exceeded. Alerts and alarms can be
generated and logged in a manner analogous to the operation of a
commercially available chillers, with the control system initiating
a protective shutdown sequence (and potentially a restart lockout)
in the event of an alarm. The specific details of the ORC controls
will depend upon the specific configuration involved and the
application at hand. The present invention ORC device 20 can be
designed for fully automated unattended operation with appropriate
levels of prognostics and diagnostics.
[0045] The ORC device 20 can be equipped with a system enable relay
that can be triggered from the ORC controls or can be
self-initiating using a hot gas temperature sensor. After the ORC
device 20 is activated, the system will await the enable signal to
begin the autostart sequence. Once the autostart sequence is
triggered, fluid supply to the evaporator 28 is ramped up at a
controlled rate to begin building pressure across the bypass valve
72 while the condenser load is matched to the system load. When the
control system determines that turbine superheat is under control,
the turbine oil pump is activated and the generator 34 is energized
as an induction motor. The turbine speed is thus locked to the grid
frequency with no requirement for frequency synchronization. With
the turbine at speed, the turbine inlet valve 66a opens
automatically and power inflow to the generator seamlessly
transitions into electrical power generation.
[0046] Shutdown of the ORC device 20 is equally straightforward.
When the temperature of the exhaust products passing through the
evaporator(s) 28 falls below the operational limit, or if superheat
cannot be maintained at minimum power, the ORC controls system
begins an auto-shutdown sequence. With the generator 34 still
connected to the grid, the turbine inlet valve 66a closes and the
turbine bypass valve 72 opens. The generator 34 once again becomes
a motor (as opposed to a generator) and draws power momentarily
before power is removed and the unit coasts to a stop. The
refrigerant feed pump 26 continues to run to cool the evaporator 28
while the condenser 24 continues to reject load, eventually
resulting in a continuous small liquid circulation through the
system. Once system temperature and pressure are adequate for
shutdown, the refrigerant feed pump 26, turbine oil pump, and
condenser 24 are secured and the system is ready for the next
enable signal.
[0047] When the autostart sequence is complete, the control system
begins continuous superheat control and alarm monitoring. The
control system will track all hot gas load changes within a
specified turndown ratio. Very rapid load changes can be tracked.
During load increases, significant superheat overshoot can be
accommodated until the system reaches a new equilibrium. During
load decreases, the system can briefly transition to turbine bypass
until superheat control is re-established. If the supplied heat
load becomes too high or low, superheat will move outside qualified
limits and the system will (currently) shutdown. From this state,
the ORC device 20 will again initiate the autostart sequence after
a short delay if evaporator high temperature is present.
[0048] Although this invention has been shown and described with
respect to the detailed embodiments thereof, it will be understood
by those skilled in the art that various changes in form and detail
thereof may be made without departing from the spirit and the scope
of the invention.
* * * * *