U.S. patent number 3,864,926 [Application Number 05/372,106] was granted by the patent office on 1975-02-11 for apparatus for liquefying a cryogen by isentropic expansion.
This patent grant is currently assigned to Cryogenic Technology, Inc.. Invention is credited to Samuel C. Collins.
United States Patent |
3,864,926 |
Collins |
February 11, 1975 |
APPARATUS FOR LIQUEFYING A CRYOGEN BY ISENTROPIC EXPANSION
Abstract
Method and apparatus for liquefying relatively large quantities
of a cryogen, helium in particular. After the high-pressure fluid
has been cooled through indirect heat exchange with a cold
low-pressure stream it is isentropically expanded in an expansion
engine. The rate of liquefaction may be increased by as much as 30
percent by substituting isentropic expansion for the conventional
isenthalpic expansion.
Inventors: |
Collins; Samuel C. (Oxon Hill,
MD) |
Assignee: |
Cryogenic Technology, Inc.
(Waltham, MA)
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Family
ID: |
22167358 |
Appl.
No.: |
05/372,106 |
Filed: |
June 21, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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81937 |
Oct 19, 1970 |
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Current U.S.
Class: |
62/608; 505/888;
505/899 |
Current CPC
Class: |
F25J
1/0065 (20130101); F25J 1/0072 (20130101); F25J
1/0017 (20130101); F25J 1/004 (20130101); F25J
1/005 (20130101); F25J 1/0037 (20130101); F25J
1/0075 (20130101); F25J 1/0224 (20130101); F25J
1/0236 (20130101); F25J 1/0042 (20130101); F25J
1/0221 (20130101); F25J 1/0276 (20130101); F25J
1/001 (20130101); F25J 1/0015 (20130101); F25J
1/0007 (20130101); Y02E 60/32 (20130101); F25J
2270/912 (20130101); F25J 2210/42 (20130101); F25J
2270/06 (20130101); Y10S 505/899 (20130101); F25J
2270/16 (20130101); Y10S 505/888 (20130101) |
Current International
Class: |
F17C
13/00 (20060101); F25J 1/00 (20060101); F25J
1/02 (20060101); F25j 003/00 () |
Field of
Search: |
;62/9,11,22,38,40 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Scott, R. B.; Cryogenic Engineering, 6/60, pgs. 62-72..
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Primary Examiner: Bascomb, Jr.; Wilbur L.
Assistant Examiner: Sever; Frank
Attorney, Agent or Firm: Lepper; Bessie A.
Parent Case Text
This application is a continuation of my application Ser. No.
81,937 filed Oct. 19, 1970 and now abandoned.
Claims
I claim:
1. An apparatus for liquefying helium, comprising in
combination
a. high-pressure fluid flow path means;
b. low-pressure fluid flow path means;
c. heat exchange means arranged to provide heat exchange between
high-pressure helium flowing in said high-pressure fluid flow path
means and low-pressure helium flowing in said low-pressure fluid
flow path means;
d. means to divert a portion of said high-pressure helium from said
high-pressure fluid flow path means, to expand the helium so
diverted and to introduce the resulting cooled low-pressure helium
into said low-pressure fluid flow path means at at least one
temperature level within said heat exchange means;
e. liquefied fluid receptacle means;
f. a slow-speed intermittent expansion engine arranged to
periodically receive high-pressure cold helium and to
isentropically expand said helium with the production of mechanical
energy thereby to liquefy at least one portion of said
high-pressure helium and discharge the at least partially liquefied
helium into said receptacle means;
g. surge chamber means in said high-pressure fluid flow path means
between said heat exchange means and said expansion engine and
arranged to receive and store high-pressure cold helium discharged
at the cold end of said heat exchange means and to deliver said
high-pressure cold helium periodically to said expansion engine;
and
h. means to return nonliquefied low-pressure helium from said
receptacle means through said low-pressure fluid flow path
means.
2. An apparatus in accordance with claim 1 including precooling
heat exchange means adapted to precool at least a portion of said
high-pressure helium in said high-pressure fluid flow path
means.
3. An apparatus in accordance with claim 2 including means to
expand high-pressure helium precooled in said precooling heat
exchange means thereby to provide further cooled low-pressure
helium, and means to introduce said further cooled low-pressure
helium into said low-pressure fluid flow path means.
4. An apparatus in accordance with claim 1 wherein said means to
divert said portion of said high-pressure helium and to expand said
helium so diverted is arranged to introduce said resulting cooled
low-pressure helium into said low-pressure fluid flow path means at
two different temperature levels.
5. An apparatus in accordance with claim 1 including separate,
distinct surge chamber means in said low-pressure fluid flow path
means between said fluid receptacle means and cold end of said heat
exchange means.
Description
This invention relates to the liquefaction of gases and more
particularly to the liquefaction of cryogens such as oxygen,
nitrogen, hydrogen and helium.
The liquefaction of cryogens, and particularly of helium, is now
performed on a large scale to provide refrigeration for a wide
range of equipment such as superconducting magnets, superconducting
cavities and the like.
Although there are several known cycles for liquefying helium and a
number of apparatus capable of performing these cycles, the most
widely used cycle and apparatus are those embodied in the Collins
helium crysotat described in U.S. Pat. No. 2,458,894. Improvements
in this cryostat are disclosed in U.S. Pat. Nos. 3,250,079 and
3,438,220, the latter being directed in part to the use of a unique
type of expander.
In the basic Collins liquefaction cycle a stream of high-pressure
helium is precooled, by indirect heat exchange with a
counterflowing stream of cold low-pressure helium, to a temperature
below the inversion temperature of helium. Liquefaction is then
accomplished by one or more isenthalpic expansions through one or
more Joule-Thomson valves. The cold low-pressure stream is provided
in part from high-pressure fluid which is withdrawn at two
appropriate temperature levels from the high-pressure stream for
isentropic expansion and return in the low-pressure stream.
Liquefaction of helium by the method and in the apparatus of U.S.
Pat. No. 2,458,894 requires a highly efficient heat exchange system
in order to precool the high-pressure helium to below its inversion
temperature (30.degree.K). It is, moreover, difficult to effect
complete liquefaction of the helium through isenthalpic expansion
in the Joule-Thomson expansion valve. I have now discovered that by
substituting a relatively slow-speed expansion engine for the
Joule-Thomson expansion valve or valves in a helium liquefier of
the general character described it is possible to increase the
amount of helium liquefied by as much as 30 percent.
It is therefore a primary object of this invention to provide an
improved apparatus for liquefying helium through the use of
expansion engines. It is another object of this invention to
provide apparatus of the character described which makes it
possible to liquefy a greater percentage of a stream of precooled
high-pressure helium.
Another primary object of this invention is to provide an improved
cycle for liquefying high-pressure precooled helium by substituting
isentropic expansion for isenthalpic expansion. Other objects of
the invention will in part be obvious and will in part be apparent
hereinafter.
The invention accordingly comprises the several steps and the
relation of one or more of such steps with respect to each of the
others, and the apparatus embodying features of construction,
combination of elements and arrangement of parts which are adpated
to effect such steps, all as exemplified in the following detailed
disclosure, and the scope of the invention will be indicated in the
claims.
For a fuller understanding of the nature and objects of the
invention, reference should be had to the following detailed
description taken in connection with the accompanying drawings in
which.
FIG. 1 is a diagram of one embodiment of the cycle and apparatus of
this invention; and
FIGS. 2-6 are simplified diagrams of four additional embodiments of
this invention.
In the following detailed presentation the cycle and apparatus of
this invention will be described in terms of liquefying helium. It
is, however, to be understood that the cycle and apparatus are also
suitable for liquefying other cryogens, particularly hydrogen. The
drawings are diagrammatic inasmuch as several different types of
heat exchangers, expansions engines and work-absorbing means may be
used. These will be identified in the following description.
In the apparatus of FIG. 1, high-pressure helium from compressor 10
is cooled in aftercooler 11 and then divided into two streams, a
first main high-pressure stream 12 and a second branch
high-pressure stream 13. The first stream 12 is directed into the
high-pressure side 14a of first section 15 of the main heat
exchanger 16. The main heat exchanger 16 is constructed in any
suitable manner to effect highly efficient indirect heat exchange
between the high-pressure fluid stream forming the high pressure
side 14 and the low-pressure fluid stream forming the low-pressure
side 17. One preferred type of such a heat exchanger is illustrated
in U.S. Pat. No. 2,895,303. It comprises means to define an annular
passage in which finned tubing is helically wound, the fins of the
tubing having a diameter essentially equal to the width of the
annular passage. The first or high-pressure fluid flow path 14 is
preferably that passage within the finned tubing; while the second
or low-pressure fluid flow path 17 is the passage defined within
the annular passage around the finned tubing. The internal volume
defined within the confines of such a heat exchanger is typically
used to locate charcoal traps and the expansion engines.
Returning to FIG. 1, the second branch high-pressure stream 13 is
directed through one side of a nitrogen precooling heat exchanger
18 adapted to effect indirect heat exchange between liquid nitrogen
introduced into the other side of heat exchanger 18 through line 19
and withdrawn as gaseous nitrogen through line 20. The
liquid-nitrogen cooled high-pressure helium in stream 13 is then
mixed with the cooled high-pressure helium of stream 12 before
forming a single precooled stream 21 which is introduced into the
high-pressure side 14, which is in effect a continuation of the
high-pressure side 14a, of the first section 15 of the main heat
exchanger 16. At the temperature level at which the high-pressure
helium is introduced into the second section 22 of the main heat
exchanger 16, a portion of the precooled high-pressure helium is
diverted by way of line 23, having a charcoal trap 24, into a first
expansion engine 25 from where, after expansion and cooling, it is
conducted by conduit 26 into the low-pressure side 17 of the main
heat exchanger.
In a similar manner, a second portion of the high-pressure helium
is diverted at a second, lower temperature level at the top of the
third section 30 of the main heat exchanger and taken by line 31,
having charcoal trap 32, into a second expansion engine 33 from
where it is returned by line 34 to the low-pressure side 17 of the
heat exchanger at approximately its lowest temperature level.
Below the main heat exchanger 16 is a second heat exchanger 40
designed to effect the final precooling of the high-pressure fluid
just prior to liquefaction. The refrigeration for this is supplied
from the helium boiled off from the liquefied helium and the
unliquefied portion of the stream flowing through the engine which
is returned through the low-pressure fluid flow path 17. The heat
exchanger 40 is preferably constructed as coiled concentric tubing
in which the high-pressure stream flows within the inner tubing and
the low-pressure stream flows in the annular passage around it.
The finally precooled high-pressure helium is then passed into a
surge volume 41 and then through a liquefying expansion engine 42.
The liquefied helium is accumulated in a suitable liquid vessel 43
where it may be stored for cooling a load which is represented
diagrammatically at 44 and which is positioned within the cryostat.
Alternatively, the liquid helium may be withdrawn through drawoff
line 45.
Inasmuch as the flow of the precooled high-pressure fluid through
expansion engine 42 will be periodic it is preferable to
incorporate the surge volume 41 in the high-pressure flow path
between heat exchanger 40 and the liquefying expansion engine 42 to
achieve a balanced and efficient heat exchange between the
high-pressure and low-pressure streams in the heat exchangers. It
is also preferable to incorporate a comparable surge volume 46 in
the low-pressure side for the same reason. These surge volumes are
fluid accumulators adapted to absorb the pulsations in fluid
flow.
The expansion engines suitable for use in this apparatus are those
which are capable of removing energy from a fluid under pressure
thereby to effect isentropic expansion of the fluid and to deliver
mechanical energy to some externally located work absorbing means.
Expansion engines which are particularly suitable for the apparatus
of this invention are those of the types described in U.S. Pat.
Nos. 2,607,322 and 3,438,222. Generally, such expansion engines
will be relatively slow-speed (60 to 100 strokes per minute piston
engine). In FIG. 1 there are shown mechanical connections 50, 51
and 52 between expansion engines 25, 33 and 42, respectively, and a
suitable work absorbing means 53 which may be a crank shaft
combined with suitable driving means and valve actuating means
associated with the expansion engines as illustrated and described
in detail in U.S. Pat. No. 3,438,220.
It will, of course, be evident that it is necessary to provide
suitable thermal insulation around the heat exchangers and
expansion engines as shown by the outlet designated by the numeral
55. Such insulation will include suitably cooled radiation
shielding and evacuated volumes and is known in the art.
FIG. 2-5, in which like reference numerals are used to refer to
like components in FIG. 1, illustrate modifications in the manner
in which the high-pressure fluid is precooled prior to its
introduction into the liquefying expansion engine. In FIGS. 2-5 the
auxiliary equipment such as the compressor, aftercooler, and work
absorbing means, as well as the charcoal traps, insulation, etc.
are omitted for the sake of simplifying the drawings. It is, of
course, to be understood that these components will be integral
parts of the apparatus in the same way as in FIG. 1.
In the apparatus of FIG. 2 the high-pressure helium supply line 12
is branched so that a portion of the incoming high-pressure helium
is directed down through the high-pressure side or the
high-pressure fluid flow path 14 while another portion of the
incoming high-pressure helium is directed into a line 60 which
leads into and is part of one side of the liquid nitrogen heat
exchanger 18. The fluid which is cooled in the liquid nitrogen heat
exchanger is then taken to an expansion engine 61 and after
expansion and cooling is taken through line 62 into the
low-pressure side 17 of the main heat exchanger at a point nearer
the room temperature end than in FIG. 1. Thus, in effect, in the
apparatus of FIG. 2 expansion engine 61 takes the place of
expansion engine 25 in FIG. 1. Otherwise the apparatus of FIG. 2 is
essentially equivalent to that of FIG. 1.
In the apparatus of FIG. 3 that portion of the high-pressure helium
stream which is cooled in the liquid nitrogen heat exchanger 18 is
mixed with the high-pressure helium in the high-pressure side of
heat exchanger 16 after it has passed through the first section 15
of the main heat exchanger. Two additional sections 65 and 66 are
added to the main heat exchanger 16.
The apparatus of FIG. 4 adds the expansion engine 61 to the
apparatus of FIG. 3 thereby providing the apparatus of FIG. 4 with
three expansion engines associated with the main heat
exchanger.
Finally, the apparatus of FIG. 5 shows a modification in the use of
liquid nitrogen as a precooler. In this apparatus the liquid
nitrogen precooling is achieved within the main heat exchanger 16
by introducing the liquid nitrogen into suitable passages so that
it may be used to augment the low-pressure helium in cooling the
incoming high-pressure helium.
Returning to FIG. 1 a typical operation of the apparatus may be
illustrated. The high-pressure helium is introduced into the system
at a pressure of about 225 psi. The temperature of the expanded
low-pressure fluid leaving expansion engine 25 will typically be
about 40.degree.K. The high-pressure helium is introduced into the
liquefying expansion engine 42 at about 7.degree.K and is, of
course, cooled to 4.2.degree.K in expansion and liquefaction. The
pressure of the helium in the low-pressure fluid flow path is
typically about 3 psi. Using a cycle such as that described above
it is possible to liquefy as much as 75 percent of the
high-pressure helium introduced into the liquefying expansion
engine 42.
In the conventional helium liquefiers, the section of the heat
exchanger between the lowest point of precooling and the
Joule-Thomson expansion valve is typically referred to as the
Joule-Thomson heat exchanger. This would be heat exchanger 40 in
FIG. 1. For any liquefaction to take place by Joule-Thomson, or
isenthalpic expansion, the temperature of the gas entering the J.T.
heat exchanger must be below the inversion temperature of helium,
or below about 30.degree.K. In the present invention in which an
expansion engine is used in place of the Joule-Thomson valve,
giving isentropic rather than isenthalpic expansion, the
temperature of the gas entering this heat exchanger can be well
above the inversion temperature, and in fact, with an ideal heat
exchanger, it can be normal room temperature. Precooling the high
pressure gas stream to liquid nitrogen temperature before entering
what might still be referred to as the Joule-Thomson heat exchanger
permits some liquefaction of helium on isentropic expansion while
using heat exchanger of practical efficiency. FIG. 6 shows such a
liquid nitrogen precooled system.
It will thus be seen that the objects set forth above, among those
made apparent from the preceeding description, are efficiently
attained and since certain changes may be made in carrying out the
above method and in the constructions set forth without departing
from the scope of the invention, it is intended that all matter
contained in the above description or shown in the accompanying
drawings shall be interpreted as illustrative and not in a limiting
sense.
* * * * *