U.S. patent application number 10/943639 was filed with the patent office on 2005-12-22 for methods and systems for heating thermal storage units.
Invention is credited to Bunton, Richard L., Hudson, Robert S., Logan, Scott D., Weaver, Matthew D..
Application Number | 20050279292 10/943639 |
Document ID | / |
Family ID | 34527197 |
Filed Date | 2005-12-22 |
United States Patent
Application |
20050279292 |
Kind Code |
A1 |
Hudson, Robert S. ; et
al. |
December 22, 2005 |
Methods and systems for heating thermal storage units
Abstract
Methods and systems for heating a thermal storage unit (TSU) are
provided. A thermal storage system is provided that includes a
system of heaters removably disposed at least partially within the
TSU, a control system for adjusting power provided to the heaters,
and a removal tool for removing one or more of the heaters from the
TSU when the TSU is still hot. The thermal storage system may be
used in a thermal and compressed air storage system for backup
power applications.
Inventors: |
Hudson, Robert S.; (Austin,
TX) ; Logan, Scott D.; (Cedar Park, TX) ;
Weaver, Matthew D.; (Austin, TX) ; Bunton, Richard
L.; (Sammamish, WA) |
Correspondence
Address: |
FISH & NEAVE IP GROUP
ROPES & GRAY LLP
1251 AVENUE OF THE AMERICAS FL C3
NEW YORK
NY
10020-1105
US
|
Family ID: |
34527197 |
Appl. No.: |
10/943639 |
Filed: |
September 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10943639 |
Sep 17, 2004 |
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10738825 |
Dec 16, 2003 |
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6955050 |
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Current U.S.
Class: |
122/32 |
Current CPC
Class: |
F24H 9/2078 20130101;
F24H 7/0416 20130101 |
Class at
Publication: |
122/032 |
International
Class: |
F22B 001/02 |
Claims
What is claimed is:
1. A thermal storage system for heating fluid flowing therethrough,
the system comprising: a thermal storage unit (TSU) having a first
longitudinal axis; insulation at least partially surrounding the
TSU; at least one flow channel disposed within the TSU; an inlet in
fluidic communication with the at least one flow channel, the inlet
accepting the fluid to be heated; an outlet in fluidic
communication with the at least one flow channel; a plurality of
heaters, each of the plurality of heaters having a longitudinal
centerline and a length, wherein the plurality of heaters are
disposed at least partially within the TSU and each of the
plurality of heaters are independently removable from the TSU; and
a controller for controlling electric power provided to the
plurality of heaters.
2. The system of claim 1, wherein the plurality of heaters
comprises a plurality of resistive cartridge heaters.
3. The system of claim 1, wherein the longitudinal centerline of
each of the plurality of heaters is not parallel to the first
longitudinal axis.
4. The system of claim 3, wherein the longitudinal centerline of
each of the plurality of heaters is orthogonal to the first
longitudinal axis.
5. The system of claim 3, wherein the longitudinal centerlines of
the plurality of heaters form a single plane that is parallel to
the first longitudinal axis.
6. The system of claim 1, wherein the at least one flow channel
comprises at least two flow channels each having a channel
centerline parallel to the first longitudinal axis, wherein the at
least two flow channels are disposed next to each other and the
plurality of heaters are disposed in between the at least two flow
channels.
7. The system of claim 1, wherein the plurality of heaters are
disposed to protrude externally out of the insulation.
8. The system of claim 1, wherein the plurality of heaters
comprises one or more redundant heaters.
9. The system of claim 1, wherein at least two of the plurality of
heaters are coupled in parallel to form a heater network, wherein
the heater network is coupled to an electric power source.
10. The system of claim 1, further comprising a plurality of
heater-fuse assemblies each having a fuse coupled in series with
one of the plurality of heaters, wherein at least two of the
plurality of heater-fuse assemblies are coupled in parallel to form
a heater network.
11. The system of claim 9, further comprising a current sensor,
wherein: the current sensor is coupled to the heater network such
that the current sensor detects current drawn by the heater
network, and the controller is programmed to adjust the electric
power provided to the plurality of heaters responsive to signals
from the current sensor.
12. The system of claim 1, further comprising a plurality of
temperature sensors disposed to sense the temperature of the TSU at
a plurality of locations, wherein the controller is programmed to
require no more than a single temperature input signal to control
the electric power provided to the plurality of heaters, wherein
the single temperature input signal is equal to the average value
of two or more of the temperatures sensed by the plurality of
temperature sensors.
13. The system of claim 12, wherein the plurality of locations are
a plurality of thermally equivalent locations.
14. The system of claim 12, further comprising a current sensor,
wherein: the current sensor is coupled to the plurality of heaters
such that the current sensor detects current drawn by the plurality
of heaters, and the controller is programmed to adjust the electric
power provided to the plurality of heaters responsive to signals
from the current sensor.
15. The system of claim 1, further comprising: a heater puller
having proximal and distal ends, a coupler disposed on the distal
end and an actuator disposed on the proximal end, wherein: the
coupler is configured to engage at least one of the plurality of
heaters, and the actuation of the actuator engages the coupler to
at least one of the plurality of heaters.
16. The system of claim 15, further comprising a locking mechanism
that prevents the coupler from disengaging from the at least one of
the plurality of heaters.
17. The system of claim 15, wherein: the coupler comprises a
plurality of gripping surfaces to engage at least one of the
plurality of heaters, and the actuator comprises a plurality of
handles and a pivot about which each one of the plurality of
handles rotates, each one of the plurality of gripping surfaces
coupled to one of the plurality of handles.
18. The system of claim 15, wherein: the actuator comprises a
sliding sleeve and a center rod slidably disposed within the
sliding sleeve, the sliding sleeve having a distal sleeve end and
the center rod having a distal rod end, and the coupler comprises a
ferrule disposed on the distal sleeve end, a plurality of compliant
extensions disposed on the distal rod end, and grips mounted on the
plurality of compliant extensions, the ferrule engaging the
plurality of compliant extensions when the sliding sleeve is
actuated in a distal direction with respect to the center rod.
19. The system of claim 15, wherein: at least one of the plurality
of heaters comprises at least one pin, and the coupler comprises at
least one L-shaped slot, the L-shaped slot configured to engage the
at least one pin.
20. The system of claim 15, wherein: at least one of the plurality
of heaters comprises a loop, and the coupler comprises a hook
configured to engage the loop.
21. The system of claim 15, further comprising a protective housing
having insulation, the protective housing having a longitudinal
length equal to at least the length of each of the plurality of
heaters.
22. A backup energy system comprising: the thermal storage system
of claim 1 for heating fluid; a turbine coupled to the thermal
storage system for receiving the heated fluid from the outlet, the
heated fluid driving the turbine; and an electrical generator for
providing electric power when the turbine is driven by the heated
fluid.
23. The backup energy system of claim 22, wherein the fluid is
compressed gas, the backup energy system further comprising a
compressed gas system to provide the compressed gas to the thermal
storage system.
24. The backup energy system of claim 22, further comprising at
least one temperature sensor to sense the temperature of at least
one component of the thermal storage system, wherein the controller
is configured to reduce the electric power provided to the
plurality of heaters when the temperature of the at least one
component of the thermal storage system deviates from at least one
acceptable temperature parameter that is related to parameters
measured during a previous discharge event.
25. A thermal storage system for heating fluid flowing
therethrough, the system comprising: a thermal storage unit (TSU)
having a first longitudinal axis; insulation at least partially
surrounding the TSU; at least one flow channel disposed within the
TSU; an inlet in fluidic communication with the at least one flow
channel, the inlet accepting the fluid to be heated; an outlet in
fluidic communication with the at least one flow channel; a
plurality of heaters; a controller for controlling electric power
provided to the plurality of heaters; and a plurality of
heater-fuse assemblies each having a fuse coupled in series with
one of the plurality of heaters, wherein at least two of the
plurality of heater-fuse assemblies are coupled in parallel to form
a heater network.
26. The system of claim 25, further comprising a current sensor,
wherein: the current sensor is coupled to the heater network such
that the current sensor detects current drawn by the heater
network, and the controller is programmed to adjust the electric
power provided to the plurality of heaters responsive to signals
from the current sensor.
27. A thermal storage system for heating fluid flowing
therethrough, the system comprising: a thermal storage unit (TSU)
having a first longitudinal axis; insulation at least partially
surrounding the TSU; at least one flow channel disposed within the
TSU; an inlet in fluidic communication with the at least one flow
channel, the inlet accepting the fluid to be heated; an outlet in
fluidic communication with the at least one flow channel; a
plurality of heaters; and a controller for controlling electric
power provided to the plurality of heaters, wherein the controller
is programmed to require no more than a single temperature input
signal to control the electric power provided to the plurality of
heaters.
28. The system of claim 27, further comprising a plurality of
temperature sensors disposed to sense the temperature of the TSU at
a plurality of thermally equivalent locations, wherein the single
temperature input signal is equal to the average value of two or
more of the temperatures sensed by the plurality of temperature
sensors.
29. The system of claim 27, further comprising a current sensor,
wherein: the current sensor is coupled to the plurality of heaters
such that the current sensor detects current drawn by the plurality
of heaters, and the controller is programmed to adjust the electric
power provided to the plurality of heaters responsive to signals
from the current sensor.
30. A thermal storage system for heating fluid flowing
therethrough, the system comprising: a thermal storage unit (TSU)
having a first longitudinal axis; insulation at least partially
surrounding the TSU; at least one flow channel disposed within the
TSU; an inlet in fluidic communication with the at least one flow
channel, the inlet accepting the fluid to be heated; an outlet in
fluidic communication with the at least one flow channel; a
plurality of heaters including at least one redundant heater; and a
controller for controlling electric power provided to the plurality
of heaters.
31. A method for heating fluid flowing through a thermal storage
system, the method comprising: providing a thermal storage unit
(TSU) having at least one flow channel disposed therein; providing
a plurality of heaters disposed at least partially within the TSU;
controlling electric power provided to the plurality of heaters;
transferring heat from the plurality of heaters to the TSU from a
plurality of locations within the TSU; heating the TSU to a steady
state temperature within a predetermined amount of time;
maintaining the TSU at the steady state temperature; transferring
heat from the TSU to the fluid flowing in the at least one flow
channel; and removing at least one of the plurality of heaters from
the TSU without removing the remaining ones of the plurality of
heaters from the TSU.
32. The method of claim 31, wherein providing a plurality of
heaters comprises providing a plurality of resistive cartridge
heaters.
33. The method of claim 31, wherein heating the TSU comprises
heating the TSU to the steady state temperature within the
predetermined amount of time even when one of the plurality of
heaters fails.
34. The method of claim 31, wherein controlling electric power
further comprises requiring no more than a single temperature input
signal to control the electric power provided to the plurality of
heaters.
35. The method of claim 34, further comprising sensing current
drawn by the plurality of heaters, wherein controlling electric
power further comprises controlling electric power provided to the
plurality of heaters responsive to the sensed current.
36. The method of claim 31, further comprising removing at least
one of the plurality of heaters from the TSU while the temperature
of the TSU is substantially equal to the steady state
temperature.
37. The method of claim 31, wherein controlling electric power
comprises controlling electric power provided to the plurality of
heaters using a DC voltage control algorithm.
38. The method of claim 31, wherein controlling electric power
comprises controlling electric power provided to the plurality of
heaters using a variable time-base zero-crossing control algorithm.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/738,825 (hereinafter "the '825 patent
application"), (Attorney Docket No. AP-46), filed Dec. 16, 2003,
entitled "Thermal Storage Unit and Methods for Using the Same to
Heat a Fluid," the entirety of which is incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to methods and systems for
heating thermal storage units (TSUs) and managing a system of
heaters in a manner that increases the operational life of the
heaters and maintains the TSUs at desired operating conditions with
less interruption.
BACKGROUND OF THE INVENTION
[0003] TSUs are well-known and often used in power delivery
systems, such as compressed air storage (CAS) systems and thermal
and compressed air storage (TACAS) systems. Such systems, often
used to provide an available source of electrical power, often use
compressed air to drive a turbine that powers an electrical
generator.
[0004] In TACAS systems, it is desirable to heat the compressed air
prior to reaching the inlet port of the turbine. It is known that
heated air, as opposed to ambient or cool air, enables the turbine
to operate more efficiently. Therefore, a mechanism or system is
needed to heat the air before providing it to the turbine. One
approach is to use a TSU.
[0005] TSUs provide thermal mass for energy storage. Once a TSU is
heated to a desired temperature, fluid, such as compressed air, may
be heated by routing the fluid through the TSU. Convection
transfers heat from the TSU's thermal mass to the fluid, raising
the temperature of the fluid as it passes through the TSU.
Illustrative TSUs are described, e.g., in the '825 patent
application.
[0006] A TSU in a TACAS system for backup power applications, such
as that described in the '825 patent application and in U.S. patent
application Ser. No. 10/361,728, (Attorney Docket No. AP-44), filed
Feb. 5, 2003, entitled "Systems and Methods for Providing Backup
Energy to a Load," the entirety of which is incorporated herein by
reference, preferably is maintained at its operating temperature
continuously during a standby mode of operation for the system to
deliver the rated power. The criteria for selecting a heating
system, including the heater controller, is based on reliability
and cost over the product life, which typically is 20 years. The
following considerations are taken into account:
[0007] (1) operational life of the heater;
[0008] (2) the nature of heater failure and the impact on the
operation of the heating system;
[0009] (3) difficulty of heater replacement and the impact of
replacement on the ability of the backup power system to protect
the load;
[0010] (4) integration and packaging of the heaters with the
insulation system and the impact on the overall size of the TSU
assembly;
[0011] (5) impact on standby losses the TSU assembly experiences
when it is not delivering backup energy; and
[0012] (6) product availability--that is, whether the heating
system is standard or custom.
[0013] In the past, TSUs largely have been heated with radiant
heaters, which are disposed external to the TSUs.
Disadvantageously, radiant heaters may waste a lot of energy by
emanating heat to the ambient environment outside the TSUs,
resulting in high standby losses. To reduce this type of standby
loss, the radiant heater may be encased in thick insulation. This,
however, occupies valuable space in a TACAS system, in which space
is at a premium. Radiant heaters also are difficult to repair,
requiring removal of the thick insulation surrounding the radiant
heater and requiring additional personnel and/or special tools to
maneuver the nearly half ton TSU out of the TACAS cabinet. When a
radiant heater malfunctions, there often is significant loss in the
overall uniformity of the temperature in the TSU, thereby requiring
the TACAS system to be shutdown immediately for repair. This
typically requires several days for a well-insulated TSU system to
cool down to a safe handling temperature. During this time period,
the TACAS system is offline and unable to provide backup power.
[0014] In view of the foregoing, it would be desirable to be able
to provide methods and systems for heating a TSU with compact size
and reduced standby losses.
[0015] It further would be desirable to be able to provide methods
and systems for easily replacing and repairing the heating system
of a TSU assembly without requiring additional personnel and/or
special tools.
[0016] It even further would be desirable to be able to provide
methods and systems for continuously heating a TSU without
significant loss in the overall uniformity of the temperature of
the TSU even when the heating system malfunctions.
[0017] It also would be desirable to be able to provide methods and
systems for reducing the amount of time that the TACAS system is
offline when repairing and/or replacing the heating system.
SUMMARY OF THE INVENTION
[0018] In view of the foregoing, it is an object of the present
invention to provide methods and systems for heating a TSU with
compact size and reduced standby losses.
[0019] It further is an object of the present invention to provide
methods and systems for easily replacing and repairing the heating
system of a TSU assembly without requiring additional personnel
and/or special tools.
[0020] It even further is an object of the present invention to
provide methods and systems for continuously heating a TSU without
significant loss in the overall uniformity of the temperature of
the TSU even when the heating system malfunctions.
[0021] It also is an object of the present invention to provide
methods and systems for reducing the amount of time that the TACAS
system is offline when repairing and/or replacing the heating
system.
[0022] These and other objects of the present invention are
accomplished by a TSU heating system preferably comprising a
plurality of resistive cartridge heaters removably disposed in
bores that are uniformly distributed throughout the thermal storage
mass of the TSU. This reduces standby losses since the heat from
the resistive cartridge heaters flows directly into and through the
thermal storage mass of the TSU before passing through the
insulation of the TSU and into the ambient environment.
[0023] In one embodiment, the heating system of the present
invention comprises one or more redundant heaters, which are
heaters in excess of a minimum number of heaters needed to
heat/reheat the TSU within specification. More specifically, the
minimum number of heaters is that quantity needed to raise a
characteristic temperature of the TSU to a predetermined value in a
predetermined amount of time when the minimum number of heaters are
operated at the maximum power permitted by a heater control
program. The redundant heaters shortens the time needed to reheat
the TSU after a discharge event in which the temperature of the TSU
is reduced and enables the heating system to operate within
specification even with the failure of one or more heaters. That
is, the redundant heaters allow the system to operate continuously
without significant loss in the overall uniformity of the
temperature of the TSU, even when one or more of the heaters have
failed. Furthermore, when more than the minimum number of heaters
are operational, the load on each individual heater is reduced,
thereby extending its operational life. The use of redundant
heaters also permits replacement of failed heaters to be deferred
to routine TACAS maintenance intervals, rather than requiring
immediate repair or replacement when an individual heater
malfunctions.
[0024] The heaters may be configured so that a heater that
experiences failure automatically disconnects from the heater
network without affecting the other individual heaters, thereby
permitting uninterrupted operation of the TSU system. A sensor
coupled to the heaters detects when failure of any individual
heater or heaters occur, thereby permitting a controller to adjust
control parameters for uninterrupted operation and to generate
warnings and alarms for maintenance.
[0025] In one embodiment, the present invention also utilizes a
control system that requires no more than a single temperature
input signal to reliably control the operation of the heater
system. Preferably, the single temperature input signal to the
heater control system comprises an average temperature signal
derived from a plurality of temperature sensors positioned at
numerous thermally equivalent locations over the TSU.
[0026] In one embodiment, the TSU assembly is disposed in the TACAS
cabinet for easy access to the cartridge heaters. Systems and
methods are provided to remove one or more cartridge heaters from
the TSU assembly while the TSU assembly is still hot. This reduces
the amount of time the TACAS unit is offline and the backup power
system is unable to provide backup power.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Further features of the present invention, its nature and
various advantages will be more apparent from the accompanying
drawings and the following detailed description, in which:
[0028] FIG. 1 illustrates one embodiment of a TSU assembly of the
present invention comprising a plurality of heaters removably
disposed within a TSU;
[0029] FIG. 2 illustrates a typical construction of an electrical
resistance cartridge heater;
[0030] FIG. 3 illustrates the TSU system of the present invention
comprising the TSU assembly of FIG. 1 coupled to a controller;
[0031] FIG. 4A is a simplified block diagram of a backup power
system, which is one application that can use the TSU system of the
present invention;
[0032] FIG. 4B illustrates a system cabinet having the TSU system
of the present invention;
[0033] FIG. 5A illustrates an example of characteristic heating
curves of a TSU assembly of the present invention;
[0034] FIG. 5B illustrates the power provided to a heating system
of the present invention to heat a TSU assembly in accordance with
the characteristic heating curves of FIG. 5A;
[0035] FIG. 6 illustrates a removal tool and storage/transport
container for removing and storing/transporting cartridge heaters;
and
[0036] FIGS. 7A-G illustrates various embodiments of couplers
incorporated in the removal tool of FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
[0037] Referring to FIG. 1, an illustrative TSU assembly of the
present invention is described. TSU assembly 10 comprises TSU 12
within which are disposed flow channels 14a-d and a plurality of
heaters 16, e.g., a plurality of cartridge heaters. Insulation (not
shown) can be disposed around TSU 12 to increase the efficiency of
TSU assembly 10. In one embodiment, flow channels 14a-d are coupled
together in fluidic communication. Fluid, such as compressed air,
enters TSU 12 via inlet port 18, flows through flow channels 14a-d,
and exits TSU 12 via outlet port 20. Fluid may flow sequentially
through each flow channel, in parallel through two or more flow
channels, or any other combination of flow channels. Alternatively,
fluid may enter TSU 12 via port 20 and exit via port 18.
Alternatively, TSU 12 may comprise one or more independent flow
channels that are not coupled in fluidic communication--e.g., fluid
entering each flow channel 14a-d exits that flow channel without
flowing through any of the other flow channels. A more detailed
description of TSU 12 may be found in commonly-assigned U.S. patent
application No. ______ (Attorney Docket No. AP-46 CIP), entitled
"Thermal Storage Unit and Methods for Using the Same to Heat a
Fluid," filed on Sep. 17, 2004, the entirety of which is
incorporated herein by reference.
[0038] TSU 12 may be constructed from solid material(s) that have
adequate thermal conductivity and other desirable thermal
properties such as high volumetric heat capacity to provide thermal
mass for energy storage. TSU 12 also may be constructed from
material(s) capable of withstanding high pressure, in addition to
possessing desirable thermal properties. For example, TSU 12 may be
constructed from iron, steel, aluminum, any alloys thereof,
ceramic, fluid-filled rigid structure, or any other suitable
material(s). TSU 12 also may be constructed of a material from
which energy may be extracted as the material transitions from a
liquid to a solid. For example, TSU 12 may be filled with molten
aluminum that is normally maintained at approximately 670.degree.
C., e.g., by heaters 16. When power is needed to be extracted from,
e.g., a TACAS system employing TSU assembly 10, the molten aluminum
cools and starts to solidify, thus releasing heat at a
substantially constant temperature that is then used to heat fluid
flowing through flow channels 14a-d.
[0039] Cartridge heaters 16 preferably are disposed in bores
uniformly distributed throughout TSU 12 such that the heaters
provide uniform heating and allow for loss of an individual heater
without significant loss in overall uniformity of temperature in
TSU 12. This configuration also reduces standby losses since most
of the heat emanating from the cartridge heaters flows directly
into and through the thermal storage mass of TSU 12 before passing
through the insulation to the ambient environment.
[0040] The bores are sized such that there is a small air gap
(preferably, less than 1 mm) between each heater and the perimeter
of the bore. Because the air gap is so small, the primary modes of
heat transfer between the heaters and the TSU are conduction and
radiation. Advantageously, the air gap permits the heaters to be
easily removed from the bores. If the nominal dimensions of the
bores were approximately equal to that of the heaters, it may be
difficult to remove the heaters from the bores for replacement or
repair if oxidation of the heater and bore surfaces causes the two
structures to oxidize together. A small percentage of the heat
emanating from the heaters may be lost to the ambient environment
without flowing through the thermal storage mass of TSU 12 by (1)
escaping through the gap between the heaters and TSU 12 and/or (2)
being conducted down the sheath of heater 16 and lost through the
end of heater 16 that is adjacent to the insulation.
[0041] Preferably, heaters 16 are disposed within TSU 12 so that
(1) the proximal ends of the heaters protrude out of the TSU and
the insulation (not shown) surrounding the TSU and (2) the heater
wiring may be connected to a control system (e.g., control system
40 shown in FIG. 3) located external to the TSU. Preferably,
heaters 16 are disposed in TSU 12 so that each heater is
independently removable from the TSU. That is, each heater may be
physically detached from the TSU without having to detach any of
the remaining heaters. Advantageously, this facilitates repair and
replacement of failed heaters. Preferably, each cartridge heater 16
is releasably coupled to a metal skin that covers the insulation
surrounding TSU 12 using fasteners 22, e.g., clips that screw into
studs that are affixed to the metal skin. In the embodiment of FIG.
1, cartridge heaters 16 are disposed between flow channels 14a,c
and 14b,d and have longitudinal centerlines disposed orthogonal to
the longitudinal axis of TSU 12 such that the longitudinal
centerlines of the heaters form a plane. Alternatively, cartridge
heaters 16 may be distributed throughout TSU 12 in an alternative
configuration.
[0042] FIG. 2 illustrates a typical construction of an electric
resistance cartridge heater 16 (as described in Integrating
Electrical Heating Elements in Appliance Design; Hegbom, Thor, 1997
(page 306)). Cartridge heater 16 comprises outer tube 24 made from
a good thermal conductor such as metal. Inside outer tube 24 are
two layers of insulators: cylindrical insulator 26 made from, e.g.,
ceramic, and insulation powder 28 made from, e.g., magnesium oxide
powder, disposed between ceramic insulator 26 and outer tube 24.
Insulators 26 and 28 may be made from any electrically
non-conducting materials having good heat transfer properties.
Helically wound around the outer perimeter of insulator 26 is
resistive wire 30, which provides heat from cartridge heater 16 to
the TSU when current is run through the wire. The proximal end of
resistive wire 30 is coupled to terminal 32a, which may be disposed
through the longitudinal length of insulator 26. The distal end of
resistive wire 30 is coupled to terminal 32b, which is disposed in
electrical isolation from terminal 32a. Terminals 32a-b protrude
from the distal end of cartridge heater 16 through end plug 34. End
plug 34 prevents contaminants and moisture from entering outer tube
24. End plug 34 may be made from any electrically non-conducting
material. Electrical cartridge heaters are readily available from a
number of manufacturers. Examples include the CIR Cartridge Heaters
marketed by Chromalox.RTM., Inc. of Pittsburgh, Pa., the Mighty
Watt Cartridge Heaters marketed by Ogden Manufacturing Co. of
Arlington Heights, Ill., and the FIREROD.RTM. Cartridge Heaters
marketed by Watlow Electric Manufacturing Company of St. Louis,
Mo.
[0043] Advantageously, cartridge heaters are low cost, readily
available, and well characterized for performance and reliability.
Cartridge heaters are available in a variety of lengths, diameters,
powers and voltages. As opposed to radiant heaters, the use of
cartridge heaters reduces the cost of the TSU assembly because it
allows a manufacturer to take advantage of volume discounts. That
is, a TSU system uses more cartridge heaters per system than
radiant heaters. This allows a manufacturer to qualify for volume
discounts even when manufacturing fewer TSU systems. Furthermore,
because cartridge heaters are compact heaters, the cartridge
heaters may be installed through the insulation surrounding the TSU
so that the heaters substantially share the same volume occupied by
the TSU. This reduces the overall size of the TSU assembly, as
compared to radiant heaters that are installed external to the TSU
and requires additional insulation to reduce flow of energy to the
ambient environment. The compact size of cartridge heaters also
allows an operator to easily remove and replace a heater without
requiring additional manpower and/or special tools.
[0044] Pursuant to one aspect of the present invention, TSU
assembly 10 comprises one or more redundant heaters, which are
heaters in excess of a minimum number of heaters needed to
heat/reheat TSU 12 within specification. More specifically, the
minimum number of heaters is that quantity needed to raise a
characteristic temperature of TSU 12 (e.g., the average temperature
of TSU 12) to a predetermined value in a predetermined amount of
time when the minimum number of heaters are operated at the maximum
power permitted by a heater control program, e.g., controller 40 of
FIG. 3. The redundant heaters shorten the time needed to reheat the
TSU after a discharge event in which the temperature of the TSU is
reduced and enables the heating system to operate within
specification even with failure of one or more heaters. That is,
the redundant heaters allow the system to operate continuously
without significant loss in the overall uniformity of the
temperature of the TSU, even when one or more of the redundant
heaters have failed. Furthermore, when more than the minimum number
of heaters are operational, the load on each individual heater is
reduced, extending its operational life.
[0045] The use of redundant heaters also permits replacement or
repair of failed heaters to be deferred to routine TACAS
maintenance intervals, rather than requiring immediate repair or
replacement when an individual heater malfunctions. For example, if
the TSU assembly incorporates five redundant heaters in addition to
the minimum number of heaters needed to heat/reheat the TSU, the
TSU system operates within specification until more than five of
the total number of cartridge heaters fail. Accordingly, even when
one or more of the heaters fail, TSU assembly 10 continues to heat
TSU 12 within specification, e.g., by heating TSU 12 to and
maintaining TSU 12 at a steady state temperature. Replacement of
failed heaters during routine maintenance permits continuous
operation between maintenance intervals and potentially extends the
operational life of the remaining heaters.
[0046] Heaters 16 may fail in one of two modes. First, heater 16
may experience a short-to-ground type of failure, e.g., a failure
that occurs when the insulation within the heater fails. In a
short-to-ground type of failure, the failed heater draws excessive
amounts of current. Second, heater 16 may experience element
failure by one of several causes, including fracture/breakage of
resistive wire 30 at one or more locations along its length. This
may result from oxidation of the wire surface and the associated
loss of material as the wire elongates and contracts during thermal
cycling. Additionally, element failure can occur when wire 30
breaks at a junction (weld joints, etc.) used to connect adjacent
sections of wire or when solder connections connecting terminals
32a and/or 32b to resistive wire 30 fail. In element failure, the
failed heater acts as an open-circuit and stops drawing
current.
[0047] In one embodiment of the present invention shown in FIG. 3,
the network of cartridge heaters 16 are configured to allow any
individual heater 16 to be removed automatically from the
electrical circuit after the heater fails, either by a
short-to-ground or element failure, without affecting operation of
the remaining heaters, thereby permitting uninterrupted operation
of the TSU system. In one embodiment, each cartridge heater 16 is
coupled in series to fuse 36 that is sized to rapidly disconnect
its associated cartridge heater in the event of a short-to-ground
type of failure. All heater-fuse assemblies are connected in
parallel to form a heater network, which is coupled to single
electrical supply line 38 that is controlled by heater controller
40. When an element failure occurs, the failed heater automatically
is removed from the heater network because the failed heater stops
drawing current from electrical supply line 38, acting as an open
circuit. Similarly, when a short-to-ground failure occurs, the fuse
coupled in series to the failed heater blows, rapidly disconnecting
the failed cartridge heater from the heater network.
[0048] This configuration allows any individual heater 16 to be
removed automatically from the electrical circuit after the heater
fails without affecting operation of the remaining heaters, thereby
permitting uninterrupted operation of the TSU system. That is, this
permits continued operation of the system within specification,
e.g., heating TSU 12 to and maintaining TSU 12 at a steady state
temperature. The ability to disconnect failed heaters automatically
is particularly effective when used in conjunction with redundant
heaters to provide uninterrupted operation of the TSU to both
reheat TSU 12 to and maintain the temperature of TSU 12 at steady
state conditions.
[0049] Current sensor 42, which is disposed in series with
electrical power supply line 38 and coupled to controller 40,
senses the current drawn by cartridge heaters 16. When a heater
fails and automatically disconnects from the heater network, the
current flowing through power supply line 38 reduces by a
proportional amount. Current sensor 42 senses this current
reduction, thereby detecting when a cartridge heater has failed.
Controller 40, which may comprise a computer or
application-specific integrated circuit (ASIC), responds to the
signals output by current sensor 42 by adjusting control
parameters, adjusting the power provided to the heaters, and
generating warnings and/or alarms for maintenance. Advantageously,
this allows controller 40 to limit the maximum temperature to which
heaters 16 are heated, extending the operational life of the
heaters, reducing maintenance costs and improving reliability.
Current sensor 42 may comprise an open loop Hall effect transducer,
e.g., the HAL 50-S current transducer marketed by LEM Components of
Switzerland, or another type of current sensor known to one of
skill in the art or otherwise.
[0050] The present invention may be used in many applications. FIG.
4A illustrates one such application. More specifically, FIG. 4A
shows a TACAS system 21 for providing output power utilizing TSU
assembly 10 of FIGS. 1 and 3, described above. For example, FIG. 4A
may represent a backup energy system that provides backup power to
a load in the event of a disturbance in the supply of power from
another power source (e.g., utility power failure.)
[0051] The following discussion of TACAS system 21 is not intended
to be a thorough explanation of the components of a TACAS, but
rather an illustration of how TSU assembly 10 can enhance the
performance of a TACAS system. For a detailed description of a
TACAS system, see commonly-assigned, co-pending U.S. patent
application Ser. No. assembly 10/361,728, filed Feb. 5, 2003, which
is hereby incorporated by reference herein in its entirety.
[0052] As shown in FIG. 4A, TACAS system 21 includes storage or
pressure tank 23, valve 25, TSU assembly 10, electrical input 27,
turbine 29, generator 31 and electrical output 33. When electric
power is needed from system 21, compressed air from pressure tank
23 may be routed through valve 25 to TSU assembly 10. TSU assembly
10 may heat the compressed air before it is provided to turbine
29.
[0053] The hot air emerging from TSU assembly 10 may flow against
the turbine rotor (not shown) of turbine 29 and drive turbine 29,
which may be any suitable type of turbine system (e.g., a
radial-flow turbine). In turn, turbine 29 may drive electrical
generator 31, which produces electric power and provides it to
electrical output 33.
[0054] Also shown in FIG. 4A is turbine exhaust 35 (e.g., the
exhaust gases emerging from turbine 29). Turbine exhaust 35 may be
vented through an exhaust pipe (not shown), or simply released to
recombine with atmospheric air.
[0055] Not only is system 21 advantageous because it uses a
relatively inexpensive and efficient TSU, it is also non-polluting.
That is because, unlike conventional systems that use
fuel-combustion systems to provide hot air to the turbine, it does
not require a fuel supply to heat the air that is being supplied to
turbine 29. Instead, TSU assembly 10 may be powered by electrical
input 27 during standby operation, which provides the energy needed
to heat the compressed air, while providing effective pressure
containment. System 21 therefore provides the benefits of heating
compressed air from pressure tank 23 before it is supplied to
turbine 29, without producing the harmful emissions associated with
combustion systems.
[0056] TACAS system 21 may also include control circuitry 37 which
may be coupled to both TSU assembly 10 and electrical input 27.
Control circuitry 37 may include controller 40 of FIG. 3. Control
circuitry 37, along with electrical input 27, may therefore be used
to monitor and control the temperature of TSU assembly 10. As a
result, the TSU assembly 10 may be heated to and maintained at a
desired steady state temperature.
[0057] Moreover, valve 25 may be coupled to piping (not shown) that
bypasses TSU assembly 10 and feeds into turbine 29 along with the
output from TSU assembly 10. By controlling the portion of the
total compressed air flow through the TSU, the ratio of heated to
non-heated air provided to turbine 29 may be modified, thereby
providing another means for controlling the temperature of the air
being supplied to the turbine. A more detailed discussion of
systems and methods for controlling the temperature and pressure of
fluid being provided to turbine 29 can be found, for example, in
U.S. patent application Ser. No. ______, filed Sep. 17, 2004
(Attorney Docket No. AP-48), entitled "Systems and Methods for
Controlling Temperature and Pressure of Fluids" and U.S. patent
application Ser. No. ______, filed Sep. 17, 2004 (Attorney Docket
No. AP-50), entitled "Systems and Methods for Controlling Pressure
of Fluids", both of which are hereby incorporated by reference in
their entireties.
[0058] Another advantage of utilizing TSU assembly 10 is that
larger pressure tanks are not required as is the case with
compressed air storage systems that do not utilize thermal storage
units or combustion systems.
[0059] The present invention is presented in the context of
industrial backup utility power. Alternatively, the present
invention may be used in any application associated with generating
power, such as in thermal and solar electric plants or continuously
operating TACAS systems. Furthermore, the present invention may be
used in any other application where thermal storage, fluid heating
or heated fluid delivery may be desirable.
[0060] FIG. 4B illustrates TSU assembly 10 (absent insulation)
disposed within system cabinet 46 for a backup generator 44. In a
preferred embodiment, TSU assembly 10 is oriented for access to
cartridge heaters 16 from the front of system cabinet 46. In the
embodiment of FIG. 4B, backup generator 44 includes compressor 48
disposed between TSU assembly 10 and cabinet door 50. To permit
ease of access to TSU assembly 10 and cartridge heaters 16,
compressor 48 is designed to be easily detachable from backup
generator 44.
[0061] Referring now to FIGS. 5A-B, a preferred control algorithm
for controlling cartridge heaters 16 is described. The control
algorithm preferably requires no more than a single temperature
input signal to control the electric power provided to heaters 16.
Such a control algorithm is based, in part, on a single temperature
input from the TSU and a characteristic heating curve. Preferably,
the control algorithm accepts TSU sensor temperature of FIG. SA and
not the average heater temperature of FIG. 5A because temperature
sensors for the heater may be more prone to failure than
temperature sensors for the TSU due to the higher heater
temperatures. Instead, the control algorithm preferably is
programmed to infer the average heater temperature based on the TSU
sensor temperature and a model that provides a relationship, which
may be empirically determined or derived from thermal modeling,
among the TSU sensor temperature, the average heater temperature,
and optionally the average temperature of the TSU (i.e., the TSU
average block temperature in FIG. 5A). Using the model,
characteristic heating curve H of heaters 16, illustratively
depicted in FIG. 5A, may be determined given the behavior of the
TSU sensor temperature. The temperature of each cartridge heater 16
theoretically equals the average heater temperature shown in FIG.
5A.
[0062] As used herein, when controller 40 is programmed to require
no more than a single temperature input to control the power
provided to heaters 16, the controller is capable of controlling
the heater power with one or more input data signals, only one of
which represents temperature. Accordingly, the controller still may
accept one or more input data signals in addition to a single input
data signal that represents temperature. The controller may still
receive input signals that are functions of other parameters, such
as a signal indicative of the current from current sensor 42 of
FIG. 3. Indeed, controller 40 also may accept additional input
signals that represent temperature so long as the controller is
capable of controlling the power delivered to the heaters using one
or more data input signals, only one of which represents
temperature. For example, the controller may accept additional data
signals representing temperature to implement a backup algorithm to
detect fault conditions (as described in greater detail
hereinbelow).
[0063] In an alternative embodiment, the heater system of the
present invention may be programmed to use a two temperature input
control system that accesses both the heater temperature and the
temperature of the TSU for proper operation. Such a two temperature
input control system may be more complex to implement than a single
temperature control system, such as that described below with
respect to FIGS. 5A and 5B. That is, in a two temperature control
system, the heater controller operates properly when both
temperature signal inputs are accurate (within predetermined
tolerance levels). If one malfunctioned, then the control system
may become non-operational. Since a TSU assembly requires a high
degree of reliability to service the TACAS system properly, the
control system may be programmed so that redundant temperature
readings and algorithms for checking the redundancies are
implemented for each of the two temperature inputs. Thus, the
complexity of a reliable control system increases with the number
of inputs. Furthermore, since sensors fail more rapidly at higher
temperatures and thus temperature sensors for the heater may be
more prone to failure than temperature sensors for the TSU, the
control algorithm may be programmed with additional control
measures for the heater temperature sensors to provide an accurate
control signal.
[0064] Accordingly, while there may be advantages to using a
control system that requires no more than a single temperature
input signal to reliably control the operation of the heater
system, the heater system of the present invention alternatively
may comprise a control algorithm that requires more than a single
temperature input signal to reliably control the operation of the
heater system. For example, two temperature input signals may be
used with the variable time-base zero-crossing control algorithm
discussed below with respect to CHART 1.
[0065] The TSU sensor temperature may be determined from a
plurality of temperature sensors, e.g., thermocouples 51 of FIG. 3,
that are distributed about the TSU preferably in thermally
equivalent locations. The term "thermally equivalent locations"
refers to isothermal locations in the TSU in which all the sensors
report the same temperature within a specified tolerance.
Preferably, controller 40 is programmed to use an average sensor
temperature (which is designated as the TSU sensor temperature of
FIG. 5A) to control the heating system of the present invention.
This may be accomplished, for example, by coupling thermocouples in
parallel so that the TSU sensor temperature represents the average
of the individual temperature data collected from the temperature
sensors. Indeed, when thermocouples disposed in thermally
equivalent locations are coupled in parallel, the average of the
temperature signals theoretically is equal to the temperature
sensed by each thermocouple (not accounting for tolerances). This
average sensor temperature may not, however, be the same value as
the average temperature of the TSU (as discussed in greater detail
below). Alternatively, controller 40 may be programmed to accept
all the temperature sensor signals and use the average of two or
more of the temperature sensor signals to control the heating
system of the present invention. For example, the control algorithm
may be programmed with a polling algorithm that determines and
rejects data outliers. If a temperature sensor fails and
disconnects from the sensor network, the system continues to
operate normally.
[0066] The control algorithm illustrated in FIGS. 5A-B comprises
several stages. Immediately following a discharge event, in which
the TSU is reheated after a discharge of power from the TACAS, the
control algorithm enters an equilibrate stage. In the equilibrate
stage, cartridge heaters 16 are idle for a predetermined period of
time to protect the heaters by permitting temperature gradients in
the TSU and heaters to level out.
[0067] Thereafter, the control algorithm enters a ramp stage, in
which power is provided to cartridge heaters 16. During the ramp
stage, the level of power provided to cartridge heaters 16 ramps up
to full power (that is, the maximum power permitted by the control
algorithm) over a predetermined period of time to soft-start the
heaters. The maximum power permitted by the control algorithm is
selected, in part, based on a goal to heat the TSU to the TSU set
point within a predetermined amount of time. Note that, depending
on the locations in which the temperature sensors are disposed
within the TSU, the actual average temperature of the TSU may lag
the TSU sensor temperature when the TSU is being reheated. This is
due to the fact that the temperature sensors may not be distributed
at, and therefore not account for, the colder extremities of the
TSU. However, as shown in FIG. 5A, the TSU sensor temperature and
the average temperature of the TSU converges to the same TSU set
point temperature at steady-state standby operation.
[0068] Once the cartridge heaters are ramped up to the maximum
power permitted by the control algorithm, the heaters are
maintained at full power until the average heater temperature
reaches a maximum heater temperature, the selection of which is
based, in part, on the following considerations: a desire for
heaters that have long operational life, a desire for cheaper and
smaller heaters, and metallurgical and other thermal instabilities
that occur at higher temperatures. Because controller 40 preferably
is programmed to control the power provided to the heaters based on
the TSU sensor temperature, and not the average heater temperature,
the control algorithm infers that the average heater temperature
has reached the maximum heater temperature based on the TSU sensor
temperature and the model described above. Accordingly, the heaters
are maintained at full power until the TSU sensor temperature
reaches a value corresponding to the maximum heater temperature.
Advantageously, by limiting the TSU sensor and heater temperatures,
controller 40 reduces the likelihood that the TSU may be damaged by
excessive stress during pressurized operation.
[0069] If redundant heaters are used, the full power period is
shorter than that experienced when only the minimum number of
heaters is used to heat TSU 12. Advantageously, this reduces load
on each heater and lengthens the operational life of all the
heaters.
[0070] If the previous discharge event only partially discharged
the energy stored in the TSU, the TSU sensor temperature may reach
the value corresponding to the maximum heater temperature before
the cartridge heaters are ramped up to the maximum power permitted
by the control algorithm. In this situation, control algorithm
begins to reduce the rate at which power is delivered to the
cartridge heaters without ever maintaining the heaters at full
power.
[0071] Once the TSU sensor temperature has reached the value
corresponding to the maximum heater temperature, the power to the
cartridge heaters is reduced at a rate that maintains the average
heater temperature at the maximum heater temperature. The control
algorithm calculates this rate based on the model described
above.
[0072] When the TSU sensor temperature increases to a steady state
temperature called the TSU set point in FIG. 5A, the control
algorithm switches to steady state temperature control to power the
heaters sufficiently to maintain the TSU sensor temperature
approximately at the steady state TSU set point. This results in a
reduction in the rate at which power is provided to the cartridge
heaters as the heaters continue to deliver heat to the extremities
of the TSU and to offset thermal losses to the ambient environment.
The heater temperature is allowed to reduce towards the TSU set
point. After a period of time determinable from the model, the TSU
is fully charged and the TSU sensor temperature and the TSU average
block temperature have converged to the steady-state TSU set point.
Thereafter, the controller provides sufficient standby power to the
heaters to maintain the heater and TSU sensor temperatures at the
steady state TSU set point temperature. Advantageously, when
redundant heaters are used, each heater is heated to a lower
temperature than that required when only a minimum number of
heaters are used to maintain TSU 12 in standby mode. This lengthens
the operational life of all the heaters.
[0073] In preferred embodiments, the heater controller uses a
control algorithm that reduces temperature excursions within the
thermal storage mass of the TSU by adjusting the power provided to
the heaters at a high frequency, e.g., 60 Hz. Such control
algorithms may include a variable time-base zero-crossing algorithm
for AC power or a DC voltage control algorithm for DC power. For
example, in a variable time-base zero-crossing control algorithm, a
silicon controlled rectifier (SCR) may be switched on to permit
conduction of power to the heaters when the AC voltage signal
crosses zero volts. The variable time base controls the proportion
of time in which conduction is permitted to the time in which
conduction is not permitted. In variable-time based control, the
controller changes the time base according to the power
requirement. CHART 1 below provides an example of variable time
based control over a variable period:
1 CHART 1 No 0 cycles conducting for a 1 cycle period conduction
25% power 1 cycle conducting, 3 cycles non- conducting for the 4
cycle period 50% power 1 cycle conducting, 1 cycle non-conducting
for the 2 cycle period 75% power 3 cycles conducting, 1 cycle non-
conducting for the 4 cycle period Continuous 1 cycle conducting for
the 1 cycle period conduction
[0074] Advantageously, in variable time base control, the heaters
are switched on and off much more frequently than in fixed time
based control. Because the heaters are switched on and off more
frequently, the heaters experience less temperature variations,
thereby increasing operational life.
[0075] In a DC voltage control algorithm, the controller provides
predetermined DC voltage levels depending on the percent power
required. For example, with a 100V power supply, the controller may
provide 86.6V for 75% power and 70.7V for 50% power. The heater
controller of the present invention also may use other control
algorithms known to persons of skill in the art or otherwise.
[0076] Heater controller 40 also may be programmed with an optional
backup algorithm to detect fault conditions, in addition to its
main control algorithm described above. The backup algorithm may be
programmed to calculate acceptable power and temperature parameters
based on measurements of the energy delivered from the TSU during a
previous discharge event and an associated state temperature, such
as the TSU sensor temperature at the end of the discharge state.
For example, the energy delivered from the TSU during a discharge
event may be estimated based on the mass of the thermal storage
material of the TSU, the specific heat of the thermal storage
material, and the TSU's change in temperature. Based on this
estimation of the energy delivered during the last discharge event,
the backup algorithm may be programmed to determine the desired
state of the heating system from the model of the heating system,
e.g., illustrated in FIGS. 5A and 5B. From the desired state of the
heating system, the backup algorithm can determine acceptable
temperature and power parameters, incorporating tolerance levels
suitable for the application for which the system is used. If the
real-time TSU sensor temperature or a secondary temperature input
obtained from the TSU and/or the heaters deviates from the
acceptable temperature parameters, and/or the real-time power
deviates from the acceptable power parameters, controller 40 may
activate a safe operation mode in which the controller reduces the
amount of power delivered to the heaters to a predetermined level.
The controller then may direct the TSU system to operate at the
reduced level until maintenance can be performed to correct the
fault condition. Similar to the main control algorithm described
above, the backup algorithm also may employ variable time-base
zero-crossing control for AC power, DC voltage control for DC
power, or another control algorithm known to one of skill in the
art or otherwise.
[0077] Pursuant to another aspect of the present invention, methods
and systems are provided for retrieving cartridge heaters from the
TSU assembly when the TSU assembly is still hot, e.g., at the TSU
set point temperature. FIG. 6 illustrates one embodiment of a
removal tool comprising heater puller 52 and protective housing 54.
Protective housing 54 includes an insulated cylinder or other
appropriate shape having sufficient length to completely surround
cartridge heater 16. This reduces the chances that an operator
accidentally contacts any of the hot surfaces of the cartridge
heater when the heater is removed from the TSU assembly and
transferred to storage and transport container 56.
[0078] Container 56 includes protective case 58 lined with
insulation, plate 60 having one or more holes through which a
plurality of cartridge heaters 16 may be stored, cover 62 and
carrying handle 64. Preferably, protective housing 54 and container
56 are designed to handle heaters that have been heated to their
operating temperature, e.g., approximately 760.degree. C. If the
protective housing and container are designed to handle heaters
heated to a temperature less than their operating temperature,
additional time is needed to cool down the TSU before removing the
heaters therefrom. The holes in plate 60 are spaced apart
sufficiently to permit placement of cartridge heaters 16 therein
using heater puller 52 and protective housing 54. Preferably, plate
60 has a sufficient number of holes to accept a complete set of
heaters 16. Plate 60 is mounted at a distance from the bottom of
protective case 58 to allow cartridge heaters 16 to rest on the
bottom. Alternatively, each cartridge heater 16 may incorporate a
flange (see FIG. 7A) that is disposed on the heater such that the
distal end of cartridge heater 16 clears the insulation liner on
the bottom of protective case 58 when the flange is resting on
plate 60.
[0079] Heater puller 52 includes a coupler (illustrative
embodiments of which are described with respect to FIGS. 7A-G)
disposed on the distal end of puller 52 and actuator 70 disposed on
the proximal end of puller 52. The coupler is a mechanism for
releasably engaging heater puller 52 to the proximal ends of heater
cartridges 16. Actuator 70 may be mechanically coupled to coupler
68 and actuated to engage heater puller 52 to and disengage heater
puller 52 from cartridge heater 16. The coupler also may comprise
locking pliers, a locking ferrule, or a notched sleeve that rotates
and locks to a complementary feature on the proximal end of
cartridge heater 16. The coupler also may comprise other coupling
mechanisms known to one of ordinary skill in the art or
otherwise.
[0080] FIGS. 7A-G illustrate numerous embodiments of the heater
puller of FIG. 6. FIG. 7A illustrates a first embodiment of a
heater puller. Plier-type heater puller 80 comprises coupler 82 and
actuator 83. Coupler 82 includes two gripping surfaces 84 that
conform to the shape of the proximal end of heater 16. Actuator 83
includes two handles 86a and 86b, each having a distal end that is
coupled rigidly to one of the gripping surfaces, and pivot 88 about
which the handles rotate. When the proximal ends of handles 86 are
urged apart, handles 86 pivot about pivot 88 so that gripping
surfaces 84 also move away from each other. Similarly, when the
proximal ends of the handles are urged together, so too are the
gripping surfaces. Thus, when a heater is placed between the
gripping surfaces, heater puller 80 may be engaged securely to the
heater by squeezing the handles together. While the heater puller
is engaged to a heater, an operator can pull the heater from or
push a heater into a TSU.
[0081] Optionally, heater puller 80 also may comprise latching
mechanism 90 disposed on the proximal end of actuator 83 (see FIG.
7B). Latching mechanism 90 comprises hook 92 pivotally coupled to
handle 86a, release lever 94 rigidly coupled to hook 92, spring 96
coupled to hook 92 (via release lever 94) and handle 86a, and
anchor 98 coupled to handle 86b. Once gripping surfaces 84 are
engaged to heater 16, latching mechanism 90 securely maintains that
engagement without additional action on the part of the
operator.
[0082] In operation, an operator squeezes handles 86a and 86b
together to engage gripping surfaces 84 to heater 16. The operator
then may engage hook 92 to anchor 98. Spring 96 imparts tension to
hook 92 to keep the hook engaged to anchor 98, thereby preventing
gripping surfaces 84 from releasing heater 16. When the operator is
ready to release heater 16 from heater puller 80, the operator may
actuate release lever 94 against the spring force of spring 94 and
disengage hook 92 from anchor 98. This permits the operator to urge
handles 86a and 86b apart, thereby urging gripping surfaces 84
apart and disengaging the gripping surfaces from heater 16.
[0083] FIGS. 7C and 7D illustrate a second embodiment of the heater
puller. Ferrule-type heater puller 100 comprises sliding sleeve
102, ferrule 104 disposed at the distal end of sliding sleeve 102,
center rod 106, and grips 108 that are mounted on compliant
extensions 109 of center rod 104. Center rod 106 and grips 108 may
be advanced into and out of center bore 110, which extends from the
proximal end of sliding sleeve 102 to the distal end of ferrule
104, to respectively close and open grips 108. To open grips 108
(as shown in FIG. 7D), center rod 106 is advanced towards the
distal end of sliding sleeve 102. The compliance of extensions 109
allows a heater to be inserted between grips 108. Sliding sleeve
102 and ferrule 104 then may be actuated in the distal direction
towards heater 16 to close grips 108. Ferrule 104 engages compliant
extensions 109, contracting the extensions (and thus grips 108)
around heater 16 and thereby securely engaging the heater to heater
puller 100. While the heater puller is engaged to the heater, an
operator can pull the heater from or push a heater into a TSU.
[0084] Optionally, heater puller 100 also may comprise locking clip
112 which is configured to engage center rod 110. Once grips 108
are engaged to heater 16 by actuating sliding sleeve 102 in the
distal direction so that ferrule 104 engages extensions 109,
locking clip 112 may be attached to the proximal end of center rod
106 protruding out of sliding sleeve 102. This prevents the center
rod from sliding back into the sliding sleeve and thereby prevents
grips 108 from disengaging heater 16.
[0085] FIGS. 7E-F illustrates a third embodiment of a heater
puller. Notch-type heater puller 120 comprises actuator 122 and
coupler 124 having one or more L-shaped slots 126. Each slot 126
incorporates detent 128 to slide past associated pin 130 disposed
on the proximal end of heater 16. This permits pin(s) 130 to engage
coupler 124 with reduced rotation. While the heater puller is
engaged to the heater, an operator can pull the heater from or push
a heater into a TSU. FIG. 7F provides an end view of heater 16 with
two pins 130.
[0086] FIG. G illustrates a fourth embodiment of a heater puller.
Hook-style heater puller 140 comprises actuator 142 and hook
coupler 144 disposed on the distal end of actuator 142. Hook
coupler 144 is designed to be engaged to loop 146 disposed on the
proximal end of heater 16. While the heater puller is engaged to
the heater, an operator can pull the heater from or push a heater
into a TSU.
[0087] Heater puller 142 also may comprise locking rod 148 that is
rotatably and slidably disposed through retainers 150, which in
turn may be coupled to handle 152 of actuator 142. In operation,
once hook 144 is engaged to loop 146, an operator can lock hook 144
to loop 146 be actuating locking rod 148. In particular, the
operator may actuate locking rod 148 in the distal direction
towards heater 16 until the distal end of locking rod 148 engages
proximal face 154 of heater 16. Alternatively, locking rod 148 also
may engage a complementary feature on proximal face 148 designed to
receive the rod. The operator then may rotate locking rod 148 so
that latch 156 integral thereto locks into receptor 158. Because
the distal end of rod 148 is engaged to the proximal face of heater
16, hook 144 cannot accidentally disengage from loop 146.
Advantageously, when the distal end of locking rod 148 is engaged
to heater 16, the looking rod also may be used to push the heater
back into the TSU.
[0088] In operation, an operator can switch the TACAS system
containing the TSU system of the present invention to a maintenance
mode, during which power to cartridge heaters 16 is turned off and
the TACAS system is offline and unavailable to provide backup
power. The operator can disconnect the electrical connections of
cartridge heaters 16 and displace any other hardware disposed in
front of cartridge heaters 16 (e.g., compressor 48 of FIG. 4). Once
the operator removes or loosens heater restraints 22, the operator
can engage heater puller 52 to the proximal end of cartridge heater
16 that protrudes out from insulation 72 of TSU assembly 10. After
a secure engagement is made, the operator can slide protective
housing 54 over the proximal end of heater puller 52 and pull
heater 16 from its bore in TSU 12 into protective housing 54.
Thereafter, heater 16 is deposited into storage and transport
container 56.
[0089] The operator then can slide a new heater 16 into the vacant
bore preferably at a predetermined rate, secure the heater to TSU
12 using the associated heater restraint, and connect the heater to
the electrical supply. After the operator completes removal and
installation of the desired number of heaters, heater controller 40
preferably is restarted in a special restart mode similar to a
reheat cycle described above with respect to FIGS. 5A-B. While the
description herein describes shaft puller 52 as being detached from
protective housing 54, it is within the scope of the invention to
have a removal tool comprising an integral shaft puller and
protective housing.
[0090] If heaters 16 and thermal storage mass 12 are designed so
that the proximal ends of heaters 16 do not protrude out of
insulation 72, heater puller 52 may be designed to engage an
engagement feature on the proximal face of heater 16.
[0091] Advantageously, the removal tool and storage/transport
container enables an operator to replace one or more heaters
without having to wait the several days it typically takes for the
TSU to cool to a temperature low enough to permit the operator to
handle the heater without protective equipment. This reduces the
duration of the maintenance interval when the TACAS unit is offline
and the backup power system is unable to provide backup power.
[0092] Although illustrative embodiments of the present invention
are described above, it will be apparent to one skilled in the art
that various changes and modifications may be made without
departing from the invention. For example, while the present
specification describe use of resistive cartridge heaters, other
electric resistance heaters suitable for insertion into a thermal
storage unit or any other types of heaters appropriate for the
present invention also may be used. Furthermore, the present
invention also may be used with three-phase power. In that case, a
set of heaters 16 may be provided for each phase or heaters 16 may
comprise a plurality of three-phase heaters. If fuses 36 also are
employed, a fuse may be provided for each heater or phase of a
heater. It is intended in the appended claims to cover all such
changes and modifications that fall within the true spirit and
scope of the invention.
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