U.S. patent application number 14/974880 was filed with the patent office on 2017-06-22 for cold start helium compressor.
This patent application is currently assigned to Sumitomo (SHI) Cryogenics of America, Inc.. The applicant listed for this patent is Sumitomo (SHI) Cryogenics of America, Inc.. Invention is credited to Stephen Dunn, Ralph C. Longsworth.
Application Number | 20170175743 14/974880 |
Document ID | / |
Family ID | 59066059 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170175743 |
Kind Code |
A1 |
Dunn; Stephen ; et
al. |
June 22, 2017 |
COLD START HELIUM COMPRESSOR
Abstract
This invention provides a means to start an oil lubricated air
cooled helium compressor at ambient air temperatures in the range
from -30.degree. C. to 0.degree. C. by heating the oil in the sump
and opening one or more by-pass valves that allows oil to flow to
the oil injection port of the compressor without passing through
all of the after-cooler.
Inventors: |
Dunn; Stephen; (Bethlehem,
PA) ; Longsworth; Ralph C.; (Allentown, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo (SHI) Cryogenics of America, Inc. |
Allentown |
PA |
US |
|
|
Assignee: |
Sumitomo (SHI) Cryogenics of
America, Inc.
Allentown
PA
|
Family ID: |
59066059 |
Appl. No.: |
14/974880 |
Filed: |
December 18, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04C 23/008 20130101;
F04C 29/021 20130101; F25B 9/14 20130101; F04C 28/28 20130101; F25B
43/02 20130101; F04C 18/0215 20130101; F04C 2270/701 20130101; F04C
2210/105 20130101; F25B 31/004 20130101 |
International
Class: |
F04C 29/00 20060101
F04C029/00; F04C 28/06 20060101 F04C028/06; F25B 9/14 20060101
F25B009/14; F04C 29/02 20060101 F04C029/02; F25B 31/00 20060101
F25B031/00; F25B 43/02 20060101 F25B043/02; F04C 18/02 20060101
F04C018/02; F04C 29/04 20060101 F04C029/04 |
Claims
1. An oil lubricated air cooled compressor which supplies helium to
a cryogenic expander when the ambient temperature is in the range
of -30.degree. C. to 45.degree. C., said system comprising; a
compressor having a port in which oil is injected and mixed with
the helium during compression, a volume in which the discharge
mixture of helium and oil separate such that most of the oil
collects in a sump, a heater in the sump, an air cooled
after-cooler having separate channels for helium and oil, piping
that directs all of the oil to flow from the sump through the
after-cooler to the injection port in the compressor when the
ambient temperature is greater than 0.degree. C., at least one
by-pass valve that connects a point in the oil piping between the
sump and an intermediate point in the after-cooler to the oil
injection port when the ambient temperature is less than 0.degree.
C., an oil management system that maintains a discharge temperature
of less than 100.degree. C. when the ambient air temperature is
between -30.degree. C. to 45.degree. C.
2. An oil lubricated helium compressor system in accordance with
claim 1 in which a by-pass valve connects the oil piping between
the sump and the after-cooler to the oil injection port.
3. An oil lubricated helium compressor system in accordance with
claim 1 in which a by-pass valve connects the oil piping between
the entrance to the after-cooler and an intermediate point in the
after-cooler to the oil injection port.
4. An oil lubricated helium compressor system in accordance with
claim 1 in which a by-pass valve is one of an active and a passive
valve.
5. A method to start an oil lubricated air cooled compressor which
supplies helium to a cryogenic expander when the ambient
temperature is in the range of -30.degree. C. to 0.degree. C., said
system comprising; a compressor having a port in which oil is
injected and mixed with the helium during compression, a volume in
which the discharge mixture of helium and oil separate such that
most of the oil collects in a sump, a heater in the sump, an air
cooled after-cooler having separate channels for helium and oil,
piping that directs all of the oil to flow from the sump through
the after-cooler to the injection port in the compressor when the
ambient temperature is greater than 0.degree. C., a by-pass valve
that connects a point in the oil piping between the sump and an
intermediate point in the after-cooler to the oil injection port
the method comprising; 1. heating the oil in the sump to a
temperature greater than 0.degree. C., 2. starting the compressor,
3. opening the oil by-pass valve when the compressor is
started.
6. A method to start an oil lubricated air cooled compressor which
supplies helium to a cryogenic expander when the lubricating oil
has a pour point higher than -45.degree. C. and the ambient
temperature is more than 10.degree. C. warmer than the pour point,
said system comprising; a compressor having a port in which oil is
injected and mixed with the helium during compression, a volume in
which the discharge mixture of helium and oil separate such that
most of the oil collects in a sump, a heater in the sump, an air
cooled after-cooler having separate channels for helium and oil,
piping that directs all of the oil to flow from the sump through
the after-cooler to the injection port in the compressor when the
ambient temperature is greater than 0.degree. C., a by-pass valve
that connects a point in the oil piping between the sump and an
intermediate point in the after-cooler to the oil injection port
the method comprising; 4. heating the oil in the sump to a
temperature greater than 0.degree. C., 5. starting the compressor,
6. opening the oil by-pass valve when the compressor is started.
Description
[0001] This invention relates generally to oil lubricated helium
compressor units for use in cryogenic refrigeration systems. More
particularly, the invention relates to an oil management system
that enables an air cooled compressor to start when the ambient air
temperature is low, e.g. -30.degree. C.
BACKGROUND OF THE INVENTION
[0002] The GM cycle has become the dominant means of producing
cryogenic temperatures, temperatures below 120K, in small
commercial refrigerators primarily because it can utilize mass
produced oil-lubricated air-conditioning compressors to build
reliable, long life, refrigerators at minimal cost. The basic
principal of operation of a GM cycle refrigerator is described in
U.S. Pat. No. 2,906,101. GM cycle refrigerators operate well at
pressures and power inputs within the design limits of
air-conditioning compressors, even though helium is substituted for
the design refrigerants. Typically, GM refrigerators operate at a
high pressure of about 2 MPa, and a low pressure of about 0.8 MPa.
The cold expander in a GM refrigerator is typically separated from
the compressor by 5 m to 20 m long gas lines. Cryogenic expanders
that operate on the Brayton cycle, and valved pulse tube expanders,
have also used these same compressors. It is preferred to mount the
expander and compressor indoors where the air temperature is kept
in the range of 15.degree. C. to 30.degree. C. Air cooled and water
cooled compressors are available for these applications. Some
applications however require mounting compressors outdoors where
the temperature of the air can be in the range of -30.degree. C. to
40.degree. C.
[0003] Compressors designed for air-conditioning service require
additional cooling when compressing helium because monatomic gases
including helium get a lot hotter when compressed than standard
refrigerants. For example when helium at 20.degree. C. is
compressed isentropically from 0.8 MPa to 2.0 MPA the temperature
increases 129.degree. C., while nitrogen, a diatomic molecule,
increases 88.degree. C., and Refrigerant 22 increases 61.degree. C.
U.S. Pat. No. 7,674,099 describes a means of adapting a scroll
compressor manufactured by Copeland Corp. to compressing helium by
injecting oil along with helium into the scroll such that about 2%
of the displacement is used to pump oil when the air temperature is
approximately 20.degree. C. The oil injection rate increases as the
temperature increases because the viscosity of the oil decreases as
it gets hotter and flows through the orifice that controls the oil
flow rate at a higher rate. For oil and helium entering at the same
temperature, compressing the mixture from 0.8 to 2 MPa, and an oil
injection rate of 2% of the displacement, the mixture leaves
19.degree. C. warmer than it entered. For an oil injection rate of
2% approximately 70% of the heat of compression leaves the
compressor in the hot oil and the balance in the hot helium. The
objective is to keep the temperature of the helium/oil mixture
leaving the compressor at a temperature of less than 100.degree. C.
The primary claim of the '099 patent is to divert most of the oil
from returning to an end port of the compressor, where it
lubricates a bearing, to return through a port near the entrance to
the scroll. This turns out to be beneficial in adapting the
compressor to start at low ambients for reasons to be described
later.
[0004] The Copeland compressor is oriented horizontally and
requires an external bulk oil separator to remove most of the oil
from the helium. Another scroll compressor that is widely used for
compressing helium is manufactured by Hitachi Inc. The Hitachi
compressor is oriented vertically and brings the helium and oil
directly into the scroll through separate ports at the top of the
compressor and discharges it inside the shell of the compressor.
Most of the oil separates from the helium inside the shell and
flows out of the shell near the bottom while the helium flows out
near the top. Helium compressor systems that use the Copeland and
Hitachi scroll compressors have separate channels in an
after-cooler for the helium and oil. The power input to these
compressors is typically in the range of 2 to 15 kW.
[0005] A problem arises when starting these oil lubricated
compressors after they have cooled to low ambient temperatures. The
lubricating oil can become so viscous that the thick oil in the
lines moves so slowly that an insufficient amount flows into the
compression chamber along with the helium to cool the helium enough
to keep the discharge temperature below 100.degree. C., the cut-out
temperature of the switch that shuts down the compressor to prevent
the helium from getting to hot.
[0006] UCON.TM. oils, manufactured by Dow Chemicals, are commonly
used in helium compressors for cryogenic applications because they
have very low vapor pressures and residual oil vapors are easily
removed in an adsorber to prevent oil from freezing in the cold
piping. UCON.TM. LB-300 has a pour point of -40.degree. C. and
UCON.TM. LB-170 which is less viscous has a pour point of
-46.degree. C. The test for determining the pour point is defined
in ASTM D97-12. Some helium compressors use the lower viscosity oil
because they can be designed to start at low ambient temperatures
without having to make as many accommodations as are needed to
overcome the problems of the more viscous LB-300 oil. At high
ambient temperatures however the less viscous oil does not have as
good lubricating properties thus resulting in higher compressor
failure rates.
SUMMARY OF THE INVENTION
[0007] The objective of this invention is to provide an oil
management system to start an oil lubricated air cooled helium
compressor, which has oil that has a pour point within -10.degree.
C. of the minimum starting temperature, by heating the oil in the
sump and opening one or more by-pass valves that allow oil to flow
to the oil injection port of the compressor without passing through
all of the air cooled after-cooler. A preferred system uses an oil
with a pour point of -40.degree. C. to start at ambient air
temperatures in the range from -30.degree. C. to 0.degree. C. and
has four by-pass valves, the first by-passes the entire
after-cooler and the other three by-pass sections of the
after-cooler.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic diagram of an oil-lubricated air
cooled helium compressor system that uses an Hitachi scroll
compressor which has a vertical orientation.
[0009] FIG. 2 is a schematic diagram of an oil-lubricated air
cooled helium compressor system that uses a Copeland scroll
compressor which has a horizontal orientation.
[0010] FIG. 3 shows the temperature vs. time at key points in the
compressor system of FIG. 2 from a test when it was started in an
ambient of -30.degree. C.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] FIG. 1 is a schematic diagram of oil-lubricated air cooled
helium compressor system 100 which has a vertically oriented
Hitachi compressor and FIG. 2 is a schematic diagram of
oil-lubricated air cooled helium compressor system 200 which has a
horizontally mounted Copeland compressor.
[0012] Compressor system components that are common to both of the
figures and are used in compressors operating in an indoor
environment are: compressor shell 2, compressor scroll 13, drive
shaft 14, motor 15, oil pump 18, after-cooler 6, fan 5, oil return
line 16, helium return line 17, helium/oil mixture discharge from
the scroll 19, oil separator 7, adsorber 8, main oil flow control
orifice 22, orifice 23 which controls the flow rate of oil from the
oil separator, gas line 33 from oil separator 7 to adsorber 8,
internal relief valve 35 and pressure equalization solenoid valve
39, gas line 34 from internal relief valve 35 and pressure
equalization solenoid valve 39 to helium return line 17, pressure
relief valve 32, adsorber inlet gas coupling 36, adsorber outlet
gas coupling 37 which supplies high pressure helium to the expander
1 through gas line 46 and returns it through line 47 to coupling 38
which receives low pressure helium from the expander, and discharge
temperature sensor Td, 50.
[0013] Additional compressor system components that are common to
both of the figures and are used in compressors operating in an
outdoor environment are: orifice 24 that limits the flow through
first oil by-pass valve 40, second oil by-pass valve 41 that allows
oil to exit after-cooler 6 after flowing through a first section,
third oil by-pass valve 42 that allows oil to exit after-cooler 6
after flowing through a first and second section, fourth oil
by-pass valve 43 that allows oil to exit after-cooler 6 after
flowing through a first, second, and third section, temperature
sensor To1, 51, which is used to control oil heaters 10 and 11, and
temperature sensor To2, 52, which is used to control the speed of
fan 5.
[0014] The components that are unique to system 100, FIG. 1, are
volume 4 at high pressure internal to the Hitachi compressor,
heater 10 that heats oil 26 in the compressor sump, and temperature
sensor To3, 53, which is used to control by-pass valve 40.
[0015] The components that are unique to system 200, FIG. 2, are
volume 3 at low pressure internal to the Copeland compressor,
heater 11 that heats oil in the sump of bulk oil separator 9,
temperature sensor To4, 54, which is used to control by-pass valve
40, oil by-pass valve 44 which on startup takes heated oil through
lines 31 and 30 to orifice 28 which controls the flow of oil into
the bearing on the end of shaft 14, and line 45 which takes oil
from orifice 23 directly to volume 3 in the compressor.
[0016] It is noted that the Hitachi compressor of system 100 has an
oil injection port from line 16 that is separate from the suction
port for helium from line 17. The Copeland compressor of system 200
has a common pickup point into the scroll for oil and helium and
the rate of flow of oil into the scroll depends on the oil level.
For this reason the oil return port is near the pickup point and
heated oil preferentially flows into the scroll while some mixes
with and heats the rest of the oil in the sump. Temperature sensor
To4, 54 is thus located near the point where the oil is entering
the scroll and is measuring a temperature comparable to To3, 53 in
system 100. It is also noted that most of the oil, more than 99%,
separates from the helium after compression in volumes at high
pressure in which oil collects in a sump. For the Hitachi
compressor this is volume 4 inside the compressor and for the
Copeland compressor it is in bulk oil separator 9. Prior to
starting the compressor in cold ambients the oil in the sump is
heated by heaters 10 and 11 respectively which are turned off when
sensor To1, 51 reaches a preset temperature, e.g. 20.degree. C.
[0017] According to the present invention, when system 100 or 200
is off and cools to a temperature below about 10.degree. C.,
by-pass valves 40, 41, 42, 43, and 44, open. Valves 41, 42, 43, and
44 are controlled by their temperature if they are thermally
actuated valves or by the temperature of a line near them if they
are actively controlled. Thermally actuated valves have a member in
them that changes shape as its temperature changes and causes a
port to open or close. Valves 41, 42, 43, and 44 close when they
warm to about 10.degree. C. Valve 40 is an active valve, e.g. a
solenoid valve, which is controlled by sensor To3, 53 on the oil
injection line, after oil from lines 16 and 21 have mixed, in
system 100, and by sensor To4, 54 on the compressor shell in system
200.
[0018] The oil management system results in the following sequence
of events for starting system 100 when the ambient temperature is
less than about 0.degree. C. Heater 10 is turned on until oil 26 in
the sump of the compressor reaches a temperature of about
20.degree. C. before starting the compressor. When the compressor
is turned on the pressures within a few seconds come to the normal
operating pressures and the gas in discharge line 30 heats within a
minute or two towards a cutout temperature of less than 100.degree.
C. During the first minute cold thick oil in line 21 is being
pushed through valve 40 and orifice 24 at a low rate until heated
oil reaches orifice 24 and an oil flow rate into the injection port
is sufficient to bring the discharge temperature down to an
acceptable operating temperature. During the next few minutes cold
thick oil is slowly being pushed through the after-cooler but the
discharge temperature continues to rise as oil 27 in the sump warms
while it absorbs most of the heat of compression. Cool oil flows
slowly through orifice 22 and line 16 to the injection port but it
is followed by heated oil leaving after-cooler 6 which then
establishes a normal oil injection flow rate. An acceptable flow
rate is typically established at a temperature greater than
0.degree. C. as measured by To2 at main orifice 22. By-pass valve
40 is closed when the injection temperature as measured by sensor
To3, 53 reaches about 20.degree. C.
[0019] Having one or more valves that by-pass sections of the
after-cooler brings warm oil into line 29 sooner than if the cold
thick oil has to be pushed through the entire heat exchanger.
By-pass valve 41 is shown at a point where oil exits the
after-cooler after passing through about a quarter of it. Valve 41
closes when the oil flowing through it reaches a temperature of
about 10.degree. C. then the oil flow rate drops in line 29 until
warm oil reaches by-pass valve 42, then the process repeats for
by-pass valve 43, and sometime after by-pass valve 43 closes, warm
oil exits the after-cooler and the compressor approaches a steady
state operating condition. During startup, fan 5 is off until the
temperature at To2, 52, reaches a temperature of about 20.degree.
C. then is operated in an on/off or variable speed mode to keep
To2, 52, from dropping below about 20.degree. C. Even with the fan
off during startup the helium exiting after-cooler 6 is cooled to
temperature near that of the oil by heat transfer through the fins.
It is noted that a common plate-fin type heat exchanger with a row
of tubes for helium in front one of more rows is preferred for this
application. Not only is heat transferred from the helium to the
oil when the air is cold but the helium is cooled to a lower
temperature than the oil when the air is hot.
[0020] The number and location of oil by-pass valves that are
needed depends on a number of factors including the type of oil,
the length and diameter of the tubing in the oil circuits, the
amount of oil in the system and the temperature limits that are set
to provide long life. For example if by-pass valve 41 is a type
that adjusts the flow rate such that temperature To2 is maintained
at about 20.degree. C. then by-pass valves 42 and 43 are not
needed. The orifices shown in FIGS. 1 and 2 are typically fixed but
could be variable. Having main orifice 22 in particular be variable
is another option that can used to help start the compressor in
cold ambients.
[0021] The oil management system for starting system 200 when the
ambient temperature is less than about 0.degree. C. turns on heater
11 until oil in the sump of bulk oil separator 9 reaches a
temperature of about 20.degree. C. before starting the compressor.
FIG. 3 shows temperatures at key points during a test with the air
temperature held at -30.degree. C. When the compressor is turned on
the pressures within a few seconds come to the normal operating
pressures and the gas in discharge line 19 heats in about a minute
to a temperature of 90.degree. C. During the first minute cold
thick oil in line 21 is being pushed through valve 40 and orifice
24 at a low rate until oil that has been heated to only -20.degree.
C. reaches orifice 24 and the oil flow rate into the injection port
becomes sufficient enough to start bringing the discharge
temperature down. The discharge temperature Td continues to drop to
a temperature of about 45.degree. C. while heating the oil in bulk
oil separator 9 and the oil flowing through by-pass valve 40. Over
the next minute the discharge temperature Td increases slightly but
then drops when oil that has been warming as it flows through
by-pass valve 41 increases the flow rate of oil through orifice 22.
When by-pass valve 41 reaches 30.degree. C. it closes thus forcing
the colder oil in the next section of the after-cooler to flow
through orifice 22 and thus temperature To2 and the flow rate drop
and Td increases. As warmer oil reaches by-pass valve 42 the flow
rate increases and Td drops until by-pass valve 42 closes. This
cycle repeats one more time until by-pass valve 43 closes and the
flow rate and temperature of the oil flowing into the injection
port is sufficient to keep the discharge temperature, Td, at
favorable temperature of about 50.degree. C. The test shown in FIG.
3 shows that by-pass valve 40 closes shortly after by-pass valve 43
closes. Valve 40 drops in temperature because it no longer has warm
oil flowing through it. At this point the speed of fan 5 is
adjusted to keep To2 at about 50.degree. C.
[0022] While this invention has been described, it will be
understood that this invention can be applied to helium compressor
systems with different configurations and with different numbers
and locations of by-pass valves. It can also be applied to
compressing other monatomic gases. Also, it is to be understood
that the phraseology and terminology employed herein, as well as
the abstract, are for the purpose of description and should not be
regarded as limiting.
[0023] It is also understood that the following claims are intended
to cover all of the generic and specific features of the invention
described herein.
* * * * *