U.S. patent application number 12/743545 was filed with the patent office on 2010-11-04 for cryogenic refrigerator and control method therefor.
This patent application is currently assigned to IHI CORPORATION. Invention is credited to Nobuyoshi Saji, Toshio Takahashi, Hirohisa Wakisaka, Seiichiro Yoshinaga.
Application Number | 20100275616 12/743545 |
Document ID | / |
Family ID | 40667390 |
Filed Date | 2010-11-04 |
United States Patent
Application |
20100275616 |
Kind Code |
A1 |
Saji; Nobuyoshi ; et
al. |
November 4, 2010 |
CRYOGENIC REFRIGERATOR AND CONTROL METHOD THEREFOR
Abstract
A cryogenic refrigerator (10) which generates a cryogenic
temperature by compressing and expanding a working gas in a closed
loop (11). The cryogenic refrigerator comprises a bypass line (22)
allowing a high-pressure portion and a low-pressure portion to
communicate with each other, a gas storage tank (24) located midway
in the bypass line and having pressure regulation valves (23a, 23b)
on the high-pressure side and the low-pressure side, respectively,
and a pressure control unit (26) controlling the pressure
regulation valves. The pressure control unit (26) controls the
pressure regulation valves (23a, 23b) so that the pressure in the
gas storage tank (24) is equal to the pressure in the closed loop
at room temperature and in a stopped state and so that the pressure
in the gas storage tank (24) is between the pressures in the
high-pressure portion and in the low-pressure portion and is close
to the pressure in the low-pressure portion in an operating
state.
Inventors: |
Saji; Nobuyoshi; (Tokyo,
JP) ; Takahashi; Toshio; (Tokyo, JP) ;
Yoshinaga; Seiichiro; (Tokyo, JP) ; Wakisaka;
Hirohisa; (Tokyo, JP) |
Correspondence
Address: |
GRIFFIN & SZIPL, PC
SUITE PH-1, 2300 NINTH STREET, SOUTH
ARLINGTON
VA
22204
US
|
Assignee: |
IHI CORPORATION
Tokyo
JP
|
Family ID: |
40667390 |
Appl. No.: |
12/743545 |
Filed: |
November 5, 2008 |
PCT Filed: |
November 5, 2008 |
PCT NO: |
PCT/JP2008/070108 |
371 Date: |
May 18, 2010 |
Current U.S.
Class: |
62/6 |
Current CPC
Class: |
F25B 9/14 20130101; F25J
1/0062 20130101; F25J 2270/16 20130101; F25J 2270/912 20130101;
F25B 2400/16 20130101; F25B 2600/2519 20130101; F25J 1/005
20130101; F25B 2500/27 20130101; F25J 1/0276 20130101; F25J 1/0248
20130101; F25J 2245/02 20130101; F25B 9/06 20130101; F25B 45/00
20130101; F25B 2309/1401 20130101; F25J 1/0065 20130101 |
Class at
Publication: |
62/6 |
International
Class: |
F25B 9/00 20060101
F25B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2007 |
JP |
2007-298812 |
Claims
1. A cryogenic refrigerator which generates a cryogenic temperature
by compressing a working gas in a closed loop and expanding the
compressed working gas, the cryogenic refrigerator comprising: a
bypass line which allows a high-pressure portion and a low-pressure
portion in the closed loop to communicate with each other; a gas
storage tank which is located midway in the bypass line and has
pressure regulation valves on the high-pressure side and the
low-pressure side, respectively; and a pressure control unit which
controls the pressure regulation valves, wherein the pressure
control unit controls the pressure regulation valves so that the
pressure in the gas storage tank is equal to the pressure in the
closed loop at room temperature and in a stopped state and controls
the pressure regulation valves so that the pressure in the
high-pressure portion is equal to a predetermined pressure in an
operating state in which a cryogenic temperature is generated.
2. The cryogenic refrigerator according to claim 1, wherein the
capacity of the gas storage tank is set so as to enable the
pressure in the gas storage tank to be maintained at a
predetermined reference pressure or lower at room temperature and
in the stopped state and so as to enable the pressure in the
high-pressure portion to be maintained at a predetermined operating
pressure in the operating state in which the cryogenic temperature
is generated.
3. The cryogenic refrigerator according to claim 1, wherein the
pressure control unit: maintains the pressure regulation valves to
be fully opened in the stopped state of the cryogenic refrigerator;
and opens the pressure regulation valve connected to the
high-pressure side in the case where the pressure in the
high-pressure portion exceeds a predetermined maximum pressure and
opens the pressure regulation valve connected to the low-pressure
side in the case where the pressure in the high-pressure portion is
equal to or lower than a predetermined minimum pressure.
4. The cryogenic refrigerator according to claim 1, further
comprising: a room-temperature compressor which is installed in a
room temperature portion in the closed loop to compress the working
gas from a predetermined low pressure to a predetermined
high-pressure; a first intermediate heat exchanger which is located
between a cryogenic temperature portion in the closed loop and the
room temperature portion to perform a heat exchange between the
working gases; and an expander which is installed on the cryogenic
temperature portion side from the first intermediate heat exchanger
to isentropically expand the working gas.
5. The cryogenic refrigerator according to claim 4, wherein: the
room-temperature compressor includes a plurality of turbo
compressors which compress the working gas in multiple stages from
the predetermined low pressure to the high pressure; the expander
includes a plurality of expansion turbines which expand the working
gas in multiple stages from the high pressure to the low pressure;
and a plurality of intermediate heat exchangers which perform a
heat exchange between the working gases are disposed in the middle
of the plurality of expansion turbines.
6. A control method for a cryogenic refrigerator which generates a
cryogenic temperature by compressing a working gas in a closed loop
and expanding the compressed working gas, the control method
comprising: providing the cryogenic refrigerator with a bypass line
which allows a high-pressure portion and a low-pressure portion in
the closed loop to communicate with each other and a gas storage
tank which is located midway in the bypass line and has pressure
regulation valves on the high-pressure side and the low-pressure
side, respectively; and controlling the pressure regulation valves
so that the pressure in the gas storage tank is equal to the
pressure in the closed loop at room temperature and in a stopped
state and controlling the pressure regulation valves so that the
pressure in the high-pressure portion is equal to a predetermined
pressure in an operating state in which a cryogenic temperature is
generated.
7. The control method for the cryogenic refrigerator according to
claim 6, wherein the capacity of the gas storage tank is set so as
to enable the pressure in the gas storage tank to be maintained at
a predetermined reference pressure or lower at room temperature in
the stopped state and so as to enable the pressure in the
high-pressure portion to be maintained at a predetermined operating
pressure in the operating state in which the cryogenic temperature
is generated.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field of the Invention
[0002] The present invention relates to a cryogenic refrigerator
having a cooling capacity of cooling a cooled object up to
cryogenic temperatures and a control method therefor.
[0003] 2. Description of the Related Art
[0004] A cryogenic refrigerator (for example, a Brayton cycle
refrigerator or an Ericsson cycle refrigerator) is used to cool
down high temperature superconducting (HTS) equipment (for example,
a superconducting transmission cable, a superconducting
transformer, a superconducting motor, a superconducting coil for
storing superconducting power, a large accelerator, a nuclear
fusion test facility, MHD power generation, a superconducting coil,
or the like).
[0005] For example, in the case of using the cryogenic refrigerator
for cooling the high temperature superconducting equipment, the
lowest temperature is 65K, 40K, 30K, 20K, or the like, though it
depends on the type and application of a superconducting wire.
Moreover, cooling output is 1 to 10 kW or so at each temperature,
and helium (the boiling point is approx. 4K), neon (the boiling
point is approx. 27K), or a mixture gas of helium and neon is used
as a refrigerant gas.
[0006] This type of cryogenic refrigerator is disclosed in, for
example, Patent Documents 1 and 2 and Non-patent Document 1.
[0007] As shown in FIG. 1, the cascade-turbo helium refrigerating
liquefier in Patent Document 1 includes a neon refrigeration cycle,
which has a turbo type compressor 51, heat exchangers 52a to 52e,
and a turbo type expander 53, and a helium refrigeration cycle,
which has a turbo type compressor 54, heat exchangers 55a to 55c,
an expansion turbine 56, and a Joule-Thomson valve 57. It is
characterized that the neon refrigeration cycle previously cools
helium.
[0008] The refrigerator disclosed in Patent Document 2 is intended
to prevent a cooling medium from being solidified, to extend the
maintenance period, to enable a large output, and to eliminate
vibration. As shown in FIG. 2, the refrigerator 61 includes a
centrifugal compressor 62 and a turbine 63 with a one-stage wing 64
of the compressor 62 and converts a gas 65, which is compressed by
the compressor 62 and introduced to the turbine 63, to, for
example, a gas mixture of helium and argon or of helium and
nitrogen or the like.
[0009] Non-patent Document 1 discloses a cryogenic refrigerator for
cooling liquid nitrogen (the boiling point is approx. 77K) up to
65K in order to cool a high temperature superconducting cable as
shown in FIG. 3.
[0010] [Patent Document 1]
[0011] Japanese Patent Application Laid-Open No. S59-122868
[0012] [Patent Document 2]
[0013] Japanese Patent Application Laid-Open No. H11-159898.
[0014] [Non-patent Document 1]
[0015] N. Saji, et. al, "DESIGN OF OIL-FREE SIMPLE TURBO TYPE 65K/6
KW HELIUM AND NEON MIXTURE GAS REFRIGERATOR FOR HIGH TEMPERATURE
SUPERCONDUCTING POWER CABLE COOLING," CP613, Advances in Cryogenic
Engineering: Proceedings of the Cryogenic Engineering Conference,
Vol. 47, 2002
[0016] While the working gases (helium, neon, and the like) for use
in the foregoing cryogenic refrigerator have extremely low
liquefaction temperatures and therefore are excellent in preventing
liquefaction in the inside of an expander, there is a problem that
the working gases are very expensive.
[0017] The cryogenic refrigerator using the expensive working gases
is required to minimize a gas charging weight and to stabilize the
internal pressure from the start of the refrigerator to the steady
operation.
[0018] If, however, a low-pressure low-temperature portion of the
running cryogenic refrigerator is cooled from, for example, a room
temperature (for example, 300 K) to a cryogenic temperature (for
example, 60 K) along with a decrease in temperature of the inside
of the refrigerator, the gas volume of the low-pressure
low-temperature portion is reduced to one fifth (1/5). Therefore,
in order to maintain a predetermined pressure (for example, one
half (1/2) of the pressure on start-up), the low-pressure
low-temperature portion is required to be supplied with a working
gas so that the working gas is five halves (5/2) of the working gas
on start-up.
[0019] Contrarily, the pressure rises after the stop of the
operation and therefore it is necessary to discharge the working
gas to the outside or to bleed the working gas to a pressure
vessel, which is provided separately. In this case, discharging the
working gas to the outside causes a great loss of the expensive
working gas, and bleeding the working gas to the pressure vessel
causes excess pressure resistance of the pressure vessel.
[0020] Moreover, if the entire refrigerator is stopped directly
without using the pressure vessel, it is necessary to increase the
pressure resistance of the entire refrigerator in advance. In this
case, there is a problem that an excess load is applied to the
compressor on start-up.
[0021] Furthermore, if the refrigerator is suddenly stopped in an
emergency stop or the like, the working gas on the high-pressure
side flows backward passing through the compressor and the
compressor turns in reverse, which adversely affects a drive system
or the like in some cases.
SUMMARY OF THE INVENTION
[0022] The present invention has been devised in order to solve the
above problems. Specifically, it is an object of the present
invention to provide a cryogenic refrigerator and a control method
therefor, the cryogenic refrigerator having a cooling capacity of
cooling a cooled object up to a predetermined cryogenic
temperature, capable of maintaining the pressure in a high-pressure
portion at a substantially constant level from a room temperature
in a stopped state to a cryogenic temperature in an operating state
without using a pressure vessel whose pressure resistance exceeds a
predetermined pressure (for example, 1 MPa) and without discharging
or supplying a working gas, and capable of preventing a reverse
rotation of a compressor even in the case of an emergency stop.
[0023] According to the present invention, there is provided a
cryogenic refrigerator which generates a cryogenic temperature by
compressing a working gas in a closed loop and expanding the
compressed working gas, the cryogenic refrigerator comprising: a
bypass line which allows a high-pressure portion and a low-pressure
portion in the closed loop to communicate with each other; a gas
storage tank which is located midway in the bypass line and has
pressure regulation valves on the high-pressure side and the
low-pressure side, respectively; and a pressure control unit which
controls the pressure regulation valves, wherein the pressure
control unit controls the pressure regulation valves so that the
pressure in the gas storage tank is equal to the pressure in the
closed loop at room temperature and in a stopped state and controls
the pressure regulation valves so that the pressure in the
high-pressure portion is equal to a predetermined pressure in an
operating state in which the cryogenic temperature is
generated.
[0024] According to a preferred embodiment of the present
invention, the capacity of the gas storage tank is set so as to
enable the pressure in the gas storage tank to be maintained at a
predetermined reference pressure or lower at room temperature and
in the stopped state and so as to enable the pressure in the
high-pressure portion to be maintained at a predetermined operating
pressure in the operating state in which the cryogenic temperature
is generated.
[0025] Preferably, the pressure control unit maintains the pressure
regulation valves to be fully opened in the stopped state of the
cryogenic refrigerator and opens the pressure regulation valve
connected to the high-pressure side in the case where the pressure
in the high-pressure portion exceeds a predetermined maximum
pressure and opens the pressure regulation valve connected to the
low-pressure side in the case where the pressure in the
high-pressure portion is equal to or lower than a predetermined
minimum pressure.
[0026] Further, according to a preferred embodiment of the present
invention, the cryogenic refrigerator further comprises: a
room-temperature compressor which is installed in a room
temperature portion in the closed loop to compress the working gas
from a predetermined low pressure to a predetermined high-pressure;
a first intermediate heat exchanger which is located between a
cryogenic temperature portion in the closed loop and the room
temperature portion to perform a heat exchange between the working
gases; and an expander which is installed on the cryogenic
temperature portion side from the first intermediate heat exchanger
to isentropically expand the working gas.
[0027] Moreover, the room-temperature compressor includes a
plurality of turbo compressors which compress the working gas in
multiple stages from the predetermined low pressure to the high
pressure; the expander includes a plurality of expansion turbines
which expand the working gas in multiple stages from the high
pressure to the low pressure; and a plurality of intermediate heat
exchangers which perform a heat exchange between working gases are
disposed in the middle of the plurality of expansion turbines.
[0028] Moreover, according to the present invention, there is
provided a control method for a cryogenic refrigerator which
generates a cryogenic temperature by compressing a working gas in a
closed loop and expanding the compressed working gas, the control
method comprising: providing the cryogenic refrigerator with a
bypass line which allows a high-pressure portion and a low-pressure
portion in the closed loop to communicate with each other and a gas
storage tank which is located midway in the bypass line and has
pressure regulation valves on the high-pressure side and the
low-pressure side, respectively; and controlling the pressure
regulation valves so that the pressure in the gas storage tank is
equal to the pressure in the closed loop at room temperature and in
a stopped state and controlling the pressure regulation valves so
that the pressure in the high-pressure portion is equal to a
predetermined pressure in an operating state in which a cryogenic
temperature is generated.
[0029] Furthermore, according to a preferred embodiment of the
present invention, the capacity of the gas storage tank is set so
as to enable the pressure in the gas storage tank to be maintained
at a predetermined reference pressure or lower at room temperature
in the stopped state and so as to enable the pressure in the
high-pressure portion to be maintained at a predetermined operating
pressure in the operating state in which the cryogenic temperature
is generated.
[0030] According to the cryogenic refrigerator and the method of
the present invention, the cryogenic refrigerator comprises a
bypass line which allows a high-pressure portion and a low-pressure
portion in the closed loop, which constitutes the cryogenic
refrigerator, to communicate with each other and a gas storage tank
which is located midway in the bypass line and has pressure
regulation valves on the high-pressure side and the low-pressure
side, respectively, and therefore it is possible to set the
pressure of the entire system, which includes the closed loop, the
bypass line, and the gas storage tank, to a predetermined reference
pressure or lower by controlling the pressure regulation valves
(for example, maintaining the pressure regulation valves to be
fully opened in the stopped state) so that the pressure in the gas
storage tank is equal to the pressure in the closed loop at room
temperature and in a stopped state. Moreover, this enables the
pressures on the inlet side and outlet side of the compressor to be
equalized in the stopped state of the refrigerator, and therefore
it is possible to prevent a reverse rotation of the compressor
caused by a pressure difference between the inlet side and the
outlet side of the compressor after the stop.
[0031] Moreover, even if the low-pressure low-temperature portion
of the cryogenic refrigerator in the operating state requires, for
example, five halves of the working gas on start-up due to a
decrease in temperature and in pressure, it is possible to supply
the required working gas from the gas storage tank by controlling
the pressure regulation valves so that the pressure in the
high-pressure portion is equal to a predetermined pressure in the
operating state where the cryogenic temperature is generated.
[0032] Therefore, the capacity of the gas storage tank is set so
that the pressure in the gas storage tank is able to be maintained
at a predetermined reference pressure or lower level at room
temperature in the stopped state and so that the pressure in the
high-pressure portion is able to be maintained at a predetermined
operating pressure level in the operating state in which the
cryogenic temperature is generated, thereby enabling the cryogenic
refrigerator to have a cooling capacity of cooling an cooled object
up to a predetermined cryogenic temperature and to maintain the
pressure in the high-pressure portion at a substantially constant
level from the room temperature in the stopped state to the
cryogenic temperature in the operating state without using a
pressure vessel whose pressure resistance exceeds a predetermined
pressure (for example, 1 MPa) and without discharging or supplying
the working gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a schematic diagram of an apparatus in Patent
Document 1.
[0034] FIG. 2 is a block diagram of a refrigerator in Patent
Document 2.
[0035] FIG. 3 is a schematic diagram of an apparatus in Non-patent
Document 1.
[0036] FIG. 4 is a diagram illustrating a first embodiment of a
cryogenic refrigerator according to the present invention.
[0037] FIG. 5 is a diagram illustrating a second embodiment of the
cryogenic refrigerator according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] Preferred embodiments of the present invention will be
described hereinafter with reference to the accompanying drawings.
In the drawings, the same reference numerals are used for the same
parts and the overlapped description thereof is omitted.
[0039] Referring to FIG. 4, there is shown a diagram illustrating a
first embodiment of a cryogenic refrigerator according to the
present invention.
[0040] The cryogenic refrigerator 10 according to the present
invention is a cryogenic refrigerator which generates a cryogenic
temperature by compressing a working gas in a closed loop 11 and
expanding the compressed working gas. The expansion by an expansion
turbine is preferably an isentropic expansion.
[0041] In this figure, the cryogenic refrigerator 10 according to
the present invention has the closed loop 11 in which a working gas
circulates, and the closed loop 11 is provided with a cryogenic
heat exchanger 12, a room-temperature compressor 14, a first
intermediate heat exchanger 16, and an expander 18. The working gas
used to circulate in the closed loop 11 is helium (the boiling
point is approx. 4K), neon (the boiling point is approx. 27K), or a
mixture gas of helium and neon.
[0042] The cryogenic heat exchanger 12 is installed in a cryogenic
temperature portion of the closed loop 11 and indirectly cools down
a cooled object with the working gas. The cooled object is high
temperature superconducting (HTS) equipment (for example, a
superconducting transmission cable, a superconducting transformer,
a superconducting motor, a superconducting coil for storing
superconducting power, a large accelerator, a nuclear fusion test
facility, MHD power generation, a superconducting coil, or the
like), and the outlet temperature of the cryogenic heat exchanger
12 in the cryogenic temperature portion is, for example, 65K.
[0043] The room-temperature compressor 14 is, for example, a turbo
compressor, which is installed in a room temperature portion (for
example, in a room at a temperature around 300 K) of the closed
loop 11 to compress the working gas from a predetermined low
pressure to a predetermined high pressure. Preferably the
predetermined low pressure is, for example, 0.5 to 0.6 MPa, the
predetermined high pressure is, for example, 1.0 to 1.2 MPa, and
the compression ratio of the compressor is around 2.
[0044] A water-cooled gas cooler 15 is installed on the downstream
side (high-pressure side) of the room-temperature compressor 14 to
cool the working gas, which has increased in temperature as a
result of the compression, preferably up to around 300 K by using
cooling water supplied from an external cooling water circulation
unit 9.
[0045] The first intermediate heat exchanger 16 is located between
the cryogenic temperature portion and the room temperature portion
to perform a heat exchange between the working gas in the
high-pressure side and the working gas in the low pressure side.
The heat exchange cools the working gas on the high-pressure side
preferably up to 65 to 70 K.
[0046] The expander 18 is, for example, an expansion turbine and is
installed on the cryogenic temperature portion side from the first
intermediate heat exchanger 16 to isentropically expand the working
gas, which has been cooled by the first intermediate heat exchanger
16. The expansion by the expansion turbine causes the working gas
to generate a predetermined cryogenic temperature (for example, 56
K). The expansion turbine is coaxial with the turbo compressor, and
preferably the same electric motor drives the expansion turbine and
the turbo compressor.
[0047] The working gas at the cryogenic temperature is supplied to
the cryogenic heat exchanger 12 to cool the cooled object
indirectly with the working gas, and cools the working gas on the
high-pressure side indirectly in the first intermediate heat
exchanger 16. Subsequently, the working gas is supplied to the
room-temperature compressor 14 and is compressed again.
[0048] The foregoing structure allows the cooled object up to the
predetermined cryogenic temperature by compressing the working gas
in the closed loop 11 and expanding the compressed working gas
using the expander 18 to generate a cryogenic temperature.
[0049] In FIG. 4, the cryogenic refrigerator 10 according to the
present invention further includes a bypass line 22, a gas storage
tank 24, and a pressure control unit 26.
[0050] The bypass line 22 allows a high-pressure portion and a
low-pressure portion of the closed loop 11 to communicate with each
other directly. The above high-pressure portion is on the
downstream side from the compressor 14 in this example, and more
specifically, has the volume of the high-pressure side of the gas
cooler 15 and the first intermediate heat exchanger 16, and a
connecting pipe located from the outlet of the compressor 14 to the
inlet of the expander 18. The above low-pressure portion is on the
upstream side from the room-temperature compressor 14 in this
example, and more specifically, has the volume of the low-pressure
side of the cryogenic heat exchanger 12 and the first intermediate
heat exchanger 16, and a connecting pipe from the outlet of the
expander 18 to the inlet of the room-temperature compressor 14.
[0051] The gas storage tank 24 is located midway in the bypass line
22, having pressure regulation valves 23a and 23b on the
high-pressure side and the low-pressure side, respectively.
[0052] The capacity of the gas storage tank is set so that the
pressure in the gas storage tank 24 is able to be maintained at a
predetermined reference pressure (for example, 1 MPa) or lower
level at room temperature in a stopped state and so that the
pressure in the high-pressure portion is able to be maintained at a
predetermined operating pressure level (for example, 1.0 to 1.2
MPa) in an operating state in which a cryogenic temperature is
generated.
[0053] The capacity of the gas storage tank 24 requires a volume of
the gas storage tank, which satisfies the condition that a
difference between the total mass of a gas exclusive of the gas
storage tank 24 in the closed loop 11 calculated from the
temperature and pressure in the operating state and the mass of a
gas loaded at the pressure (for example, 1 MPa) in the
high-pressure portion (on the downstream side from the gas cooler
15 in FIG. 4) in the operating state for the volume of the closed
loop 11 exclusive of the gas storage tank 24 in the stopped state
and at room temperature is equal to a difference between the mass
of a gas obtained in the case where the gas storage tank 24 is
filled with the pressure in the high-pressure portion in the
operating state and the mass of a gas obtained in the case where
the gas storage tank 24 is filled with the pressure in the
low-pressure portion (the upstream side from the room-temperature
compressor 14 in FIG. 4) in the operating state.
[0054] The temperature of the gas storage tank is always constant.
The pressure in the gas storage tank is maximum when it is equal to
the pressure on the high-pressure side in the operating state and
is minimum when it is equal to the pressure on the low-pressure
side in the operating state. The mass of the gas which the gas
storage tank is able to absorb is obtained from the pressure
difference at the constant temperature and the volume.
[0055] Therefore, the capacity of the gas storage tank 24 is
preferably set so as to be 3 or more times, preferably 4 or 5
times, the volume of the low-temperature low-pressure portion at
cryogenic temperature and low pressure.
[0056] Moreover, a pressure sensor 25 is installed in the
high-pressure portion in the closed loop 11, and detected pressure
data is input to the pressure control unit 26.
[0057] The pressure control unit 26 controls the pressure
regulation valves 23a and 23b so that the pressure in the gas
storage tank 24 is equal to the pressure in the closed loop 11 at
room temperature and in a stopped state on the basis of the
detected pressure data and controls the pressure regulation valves
23a and 23b so that the pressure in the gas storage tank 24 is
between the pressures in the high-pressure portion and in the
low-pressure portion and close to the pressure in the low-pressure
portion (a pressure slightly higher than the pressure in the
low-pressure portion) in the operating state in which the cryogenic
temperature is generated.
[0058] In the control method for the cryogenic refrigerator
according to the present invention, the pressure control unit 26
performs the following controls by using the cryogenic refrigerator
10 having the above configuration:
(A) The pressure regulation valves 23a and 23b are maintained to be
fully opened in the stopped state of the cryogenic refrigerator 10.
This operation enables the pressure on the inlet side of the
compressor 14 to be equalized with the pressure on the outlet side
of the compressor 14 in the stopped state of the refrigerator, and
therefore it is possible to prevent a reverse rotation of the
compressor caused by pressure after the stop of the refrigerator.
(B) The pressure regulation valves 23a and 23b are fully closed
before the start-up of the cryogenic refrigerator 10. This
operation enables the gas storage tank 24 to be isolated from
pressure fluctuations on the high-pressure side and on the
low-pressure side caused immediately after the start-up, by which
the cryogenic refrigerator 10 is able to be started only in the
closed loop 11. (C) During the start-up of the cryogenic
refrigerator 10, the pressure regulation valve 23a on the
high-pressure side is opened if the pressure in the high-pressure
portion exceeds a predetermined maximum pressure (for example, 1.1
MPa). This operation prevents the pressure in the high-pressure
portion from exceeding the predetermined maximum pressure and
enables excess working gas to be collected into the gas storage
tank 24. (D) During the start-up of the cryogenic refrigerator 10,
the pressure regulation valve 23b on the low-pressure side is
opened if the pressure in the high-pressure portion is equal to or
lower than a predetermined minimum pressure (for example, 0.9 MPa).
This operation enables the low-pressure portion in the closed loop
11 to be supplied with working gas from the gas storage tank 24,
thereby inhibiting the pressure in the high-pressure portion from
decreasing.
[0059] Through the operations of (B) to (D), it is possible to
complete the start-up of the cryogenic refrigerator 10 and to
perform the steady operation which generates the cryogenic
temperature.
[0060] Moreover, the same controls are performed to stop the
cryogenic refrigerator 10 from the steady operation which generates
the cryogenic temperature. More specifically, the pressure on the
high-pressure side rises up along with an increase in the
temperature and pressure of the low-temperature low-pressure
portion at cryogenic temperature and low pressure in the operating
state, and therefore it is possible to collect excess working gas
into the gas storage tank 24 by the above operation (C).
[0061] Further, in the stopped state of the cryogenic refrigerator
10, the operation (A) for maintaining the pressure regulation
valves 23a and 23b to be fully opened enables the pressure on the
inlet side of the compressor 14 to be equalized with the pressure
on the outlet side of the compressor 14 in the stopped state of the
refrigerator, and therefore it is possible to prevent a reverse
rotation of the compressor caused by a pressure difference between
the inlet side and outlet side of the compressor 14 after the stop
of the refrigerator.
[0062] According to the above refrigerator and method of the
present invention, the cryogenic refrigerator 10 includes the gas
storage tank 24, which is located midway in the bypass line 22
allowing the high-pressure portion and the low-pressure portion in
the closed loop 11 to communicate with each other, and which has
the pressure regulation valves 23a and 23b on the high-pressure
side and the low-pressure side, respectively. Therefore, it is
possible to set the pressure in the entire system, which includes
the closed loop 11, the bypass line 22, and the gas storage tank
24, to a predetermined reference pressure (for example, 1 MPa) or
lower by controlling the pressure regulation valves so that the
pressure in the gas storage tank 24 is equal to the pressure in the
closed loop 11 at room temperature and in the stopped state (for
example, by maintaining the pressure regulation valves 23a and 23b
to be fully opened in the stopped state).
[0063] Moreover, this enables the pressure on the inlet side of the
compressor 14 to be equalized with the pressure on the outlet side
of the compressor 14 in the stopped state of the refrigerator, and
therefore it is possible to prevent a reverse rotation of the
compressor caused by pressure after the stop of the
refrigerator.
[0064] Furthermore, the pressure regulation valves 23a and 23b are
controlled so that the pressure in the gas storage tank 24 is
between the pressures in the high-pressure portion and in the
low-pressure portion and close to the pressure in the low-pressure
portion in the operating state in which the cryogenic temperature
is generated, and therefore it is possible to supply the
corresponding working gas from the gas storage tank even if the
pressure of the working gas in the closed loop drops along with a
decrease in the temperature of the low-temperature portion in the
refrigerator after the start of the operation.
[0065] For example, if the capacity of the gas storage tank 24 is
set so as to be 3 or more times the volume V of the low-temperature
low-pressure portion at cryogenic temperature and low pressure in
the operating state, it is necessary to supply the low-temperature
low-pressure portion with working gas so that the gas volume of the
portion is five halves (2.5) of the gas volume on start-up in order
to maintain the pressure (for example, one half of the pressure on
start-up) in the low-temperature low-pressure portion due to a
decrease in temperature (for example, 300 K to 60 K) and a decrease
in pressure (for example, to one half).
[0066] Therefore, even if the working gas corresponding to the
shortfall of 1.5 V is supplied from the gas storage tank 24 to the
low-temperature low-pressure portion, it is possible to maintain
the pressure in the gas storage tank 24 at one half or more of the
pressure in the stopped state.
[0067] More specifically, the capacity of the gas storage tank 24
is set so that the pressure in the gas storage tank 24 is able to
be maintained at the predetermined reference pressure (for example,
1 MPa) or lower level at room temperature in the stopped state and
so that the pressure in the high-pressure portion is able to be
maintained at the predetermined operating pressure level in an
operating state in which the cryogenic temperature is generated,
thereby enabling the cryogenic refrigerator to have a cooling
capacity of cooling the cooled object up to the predetermined
cryogenic temperature and to maintain the pressure in the
high-pressure portion at a substantially constant level from the
room temperature in the stopped state to the cryogenic temperature
in the operating state without using a gas storage tank whose
pressure resistance exceeds the predetermined pressure (for
example, 1 MPa) and without discharging or supplying the working
gas.
Embodiment
[0068] Referring to FIG. 5, there is shown a diagram illustrating a
second embodiment of the cryogenic refrigerator according to the
present invention. The outlet temperature of the cryogenic
temperature portion is 65 K and the cooling capacity thereof is 3
kW in this example, where P, T and G in this figure represent the
pressure (bar), the temperature (K), and the mass flow rate (g/s),
respectively.
[0069] In this example, the room-temperature compressor 14 includes
a first stage compressor 14A, which compresses a working gas from a
predetermined low pressure (5.57 bar) to a first intermediate
pressure (8.03 bar) between the low pressure and the high pressure,
and a second stage compressor 14B, which compresses the working gas
from the first intermediate pressure to a high pressure (11.0 bar).
Water-cooled gas coolers 15 are installed on the downstream side
(the high-pressure side) of the first stage compressor 14A and the
second stage compressor 14B, respectively.
[0070] Moreover, the expander 18 includes a first expander 18A,
which expands the working gas from the high pressure (11.0 bar) to
a second intermediate pressure (10.29 bar) between the low pressure
and the high pressure, and a second expander 18B, which expands the
working gas from the second intermediate pressure to the low
pressure (5.57 bar).
[0071] Furthermore, there is provided a second intermediate heat
exchanger 17, which exchanges heat between the low-pressure working
gas and the high-pressure working gas, between the first expander
18A and the second expander 18B.
[0072] The first stage compressor 14A and the second stage
compressor 14B are turbo compressors, and the first expander 18A
and the second expander 18B are expansion turbines. The first stage
compressor 14A is coaxial with the second expander 18B, and the
second stage compressor 14B is coaxial with the first expander 18A.
Preferably the same electric motor drives the turbo compressors and
the expansion turbines.
[0073] Other parts of the configuration are the same as in FIG.
4.
[0074] It is confirmed that this configuration enables the
generation of a cryogenic temperature of 56 K by compressing the
working gas in the closed loop 11 and expanding the compressed
working gas by using the first expander 18A and the second expander
18B, thereby enabling an absorption of 3 kW heat from the cooled
object.
[0075] As described above, in the present invention, a room
temperature portion is provided with the gas storage tank 24 and is
connected via a pipe (the bypass line 22) having the pressure
regulation valves 23a and 23b on the high-pressure side (the outlet
side of the compressor) and the low-pressure side (the return side)
of the refrigerator, respectively.
[0076] While both of the reference pressures in the control of the
pressure regulation valves 23a and 23b are high-pressure side
pressures, the pressure regulation valve 23a with the pipe
connected to the high-pressure side is "opened" when the pressure
exceeds a specified pressure and the pressure regulation valve 23b
with the pipe connected to the return side is "opened" when the
high-pressure side pressure drops to a lower value than the
specified pressure to increase the pressure in the system.
[0077] Moreover, the volume of the gas storage tank 24 is set to a
value as small as possible within a scope that the pressure is
maintained at a slightly higher level than the return-side pressure
in the operating state and the pressure does not exceed a design
pressure even at room temperature in the system in the stopped
state.
[0078] Furthermore, the expansion turbines (the first expander 18A
and the second expander 18B) are adapted to be coaxial with the
turbo compressors (the first stage compressor 14A and the second
stage compressor 14B) and the same electric motor drives the
expansion turbines and the turbo compressors, thereby enabling the
collection of the power of the expansion turbines so as to reduce
the electric motor power and enabling the rotational speed of the
expansion turbines to be limited to that of the electric motor so
as to essentially prevent the overspeed of the expansion turbines.
Therefore, there is no need to use bypass valves for the expansion
turbines or throttle valves in the inlet and the compressors are
able to operate at a rated speed from the start-up.
[0079] Moreover, both of the pressure regulation valves 23a and 23b
are opened in the stopped state of the refrigerator to equalize the
pressures on the inlet side and outlet side of the compressor,
thereby preventing the reverse rotation of the compressors (the
first stage compressor 14A and the second stage compressor 14B)
caused by a pressure difference between the inlet side and the
outlet side of the compressors after the stop of the
refrigerator.
[0080] According to the above configuration, the room-temperature
compressor 14 increases the pressure of the working gas, the gas
cooler 15 decreases the increased temperature of the gas up to
close to a room temperature, and then the working gas passes
through the first intermediate heat exchanger 16 and the expander
18, thereby decreasing the temperature and decreasing the pressure.
A return gas, which has removed heat from the cooled object which
is a refrigeration load, increases in temperature up to close to a
room temperature while cooling the working gas on the high-pressure
side in the first intermediate heat exchanger 16 and then returns
to the room-temperature compressor 14. A pressure ratio between the
high-pressure side and the low-pressure side is around 2. The gas
storage tank 24 is connected via the pipe (the bypass line 22)
having the pressure regulation valves 23a and 23b on the
high-pressure side of the refrigerator (the outlet side from the
compressor) and the return side of the refrigerator (the inlet side
from the compressor), respectively.
[0081] While both of the reference pressures in the control of the
pressure regulation valves 23a and 23b are high-pressure side
pressures, the pressure regulation valve 23a with the pipe
connected to the high-pressure side is "opened" when the pressure
exceeds a specified pressure and the pressure regulation valve 23b
with the pipe connected to the return side is "opened" when the
high-pressure side pressure drops to a lower value than the
specified pressure to increase the pressure in the system. Due to
the functions of the two pressure regulation valves 23a and 23b,
the pressure on the high-pressure side is maintained at a constant
level in the operating state, on start-up, and in the stopped
state.
[0082] Naturally, the present invention is not limited to the
embodiments described above, but may be changed in various ways so
as not to deviate from the scope of the present invention.
* * * * *