U.S. patent number 3,585,807 [Application Number 04/850,755] was granted by the patent office on 1971-06-22 for method of and apparatus for pumping gas under cryogenic conditions.
This patent grant is currently assigned to Balzers Patent-und Beteiligungs-Aktiengesellschaft. Invention is credited to Jurgen Hengevoss, Hermann Wossner.
United States Patent |
3,585,807 |
Hengevoss , et al. |
June 22, 1971 |
METHOD OF AND APPARATUS FOR PUMPING GAS UNDER CRYOGENIC
CONDITIONS
Abstract
In pumping a gas under cryogenic conditions, condensation
surfaces disposed within a receiver containing the gas to be pumped
are cooled to a predetermined temperature while the surfaces are
thermally insulated from any heat within the receiver. During
initial cooling the gas is not permitted to flow over the
condensation surfaces. When the predetermined temperature is
reached, the gas within the receiver, which is under vacuum
conditions, is circulated over the condensation surfaces. The
amount of gas flowing over the condensation surfaces is regulated
in accordance with the temperature, vacuum and other conditions
within the receiver.
Inventors: |
Hengevoss; Jurgen (Balzers,
FL), Wossner; Hermann (Balzers, FL) |
Assignee: |
Balzers Patent-und
Beteiligungs-Aktiengesellschaft (Balzers, FL)
|
Family
ID: |
4385104 |
Appl.
No.: |
04/850,755 |
Filed: |
August 18, 1969 |
Foreign Application Priority Data
Current U.S.
Class: |
62/55.5 |
Current CPC
Class: |
F04B
37/08 (20130101); F25B 23/00 (20130101) |
Current International
Class: |
F04B
37/08 (20060101); F25B 23/00 (20060101); F04B
37/00 (20060101); B01d 005/00 () |
Field of
Search: |
;62/55.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wye; William J.
Claims
What we claim is:
1. A method of pumping a gas under cryogenic conditions comprising
the steps of providing an enclosed space for the gas to be pumped,
positioning deep cooled condensation surfaces within the enclosed
space, thermally insulating the condensation surfaces from the heat
supply within the enclosed space while cooling the condensation
surfaces to a predetermined low temperature and while colling the
condensation surfaces preventing the flow of the gas to be pumped
over the surfaces, and regulating the flow of gas to the
condensation surfaces after the predetermined temperature is
reached.
2. A method, as set forth in claim 1, wherein establishing vacuum
conditions within the enclosed space for pumping the gas under
cryogenic conditions.
3. A method, as set forth in claim 2, wherein cooling the
condensation surfaces to a temperature of about 20.degree. Kelvin
and regulating the gas flow over the condensation surfaces for
maintaining the vacuum conditions at about 10.sup.-.sup.4 mm.
Hg.
4. Apparatus for pumping gas under cryogenic conditions comprising
walls forming a closed chamber containing the gas to be pumped,
means for forming condensation surfaces within the chamber for
cooling the gas to the requisite low temperature, means for
enclosing said condensation surfaces within said chamber for
preventing the gas within said chamber from flowing over the
condensation surfaces, means for thermally insulating said
enclosing means for preventing heat within said chamber from
affecting said condensation surfaces, and means for throttling the
flow of gas within said chamber over said condensation
surfaces.
5. Apparatus, as set forth in claim 4, wherein said enclosing means
for said condensation surfaces comprising wall means surrounding
said condensation surfaces and including a hood member, and said
thermal insulating means comprising thermal insulation material
covering said wall means including said hood for preventing heat
from within said chamber from contacting said condensation
surfaces.
6. Apparatus, as set forth in claim 5, wherein said means for
throttling the flow of gas comprising a shaft extending into said
chamber and being secured to said hood, and means for engaging said
shaft exteriorly of said chamber for displacing said hood member
from its position enclosing said condensation surfaces for variably
admitting flow of gas to said condensation surfaces.
7. Apparatus, as set forth in claim 4, wherein said enclosing means
comprising a housing enclosing a portion of said condensation
surfaces, a cover for cooperation with said housing for completely
enclosing said condensation surfaces, a cooling coil mounted on
said housing for circulating a cooling medium therethrough for
removing heat from said housing and preventing the heat from
reaching said condensation surfaces, and said cover comprising a
frame, a plurality of metallic plates mounted within said frame and
arranged to prevent heat from within said chamber from contacting
said condensation surfaces, and a second coil encircling said frame
for removing heat therefrom.
8. Apparatus, as set forth in claim 7, wherein a rotatable shaft
extending through said wall means into the interior of said chamber
and being secured at its inner end to said cover, and means located
exteriorly of said chamber for rotating said shaft and displacing
said cover from said housing and thereby admitting gas within said
chamber to flow over said condensation surfaces within said
housing.
9. Apparatus, as set forth in claim 4, wherein said enclosing means
comprising a pair of spaced plates located on opposite sides of
said condensation surfaces, a plurality of rotatable plate sections
extending between said plates and being arranged in combination
with said plates to completely enclose said condensation
surfaces.
10. Apparatus, as set forth in claim 4, wherein said means for
throttling the flow of gas comprising a shaft member centrally
located within said plate sections and extending into said chamber
from the exterior of said wall means, a drive gear mounted on said
shaft, a plurality of individual gears each mounted on one of said
plate sections and in meshed engagement with said drive gear, and
means for rotating said shaft whereby said drive gear is rotated
and in turn individually rotates said plate sections for
selectively admitting gas for flow over said condensation
surfaces.
11. Apparatus, as set forth in claim 4, wherein said condensation
surfaces comprising a cooling coil located within said chamber, and
conduit means connected to said cooling coil for circulating a
refrigerant therethrough.
12. Apparatus, as set forth in claim 4, wherein means being
connected to said chamber for establishing a vacuum therein.
13. Apparatus, as set forth in claim 4, wherein a temperature
sensor positioned within said chamber adjacent said condensation
surfaces, a control device operatively connected to said
temperature sensor, and drive means for opening and closing said
throttle means being in communication with said control device
which regulates the extent of the opening of said throttle means by
said drive means.
Description
SUMMARY OF THE INVENTION
The present invention is directed cryogenic a method of and
apparatus for pumping gases under cryogenic conditions wherein the
gas being pumped flows over deep-cooled condensation surfaces, and,
more particularly, it is concerned with the enclosure for the
condensation surfaces within the receiver and with the means for
admitting gas for passage over the condensation surfaces.
In the past, it has been known to use a refrigerator to establish
the cryogenic pumping conditions for the starting operation and
then to maintain these conditions at the operating temperature
during pumping. The output of the refrigerator is established so
that the required low temperature cooling is possible in a
sufficiently short time. Experience has shown that the
refrigeration output required to establish the low temperature
conditions is much greater then is required for the continuous
pumping operation at pressures below 10.sup.-.sup.4 mm. Hg for
maintaining the operating temperature. During normal operating
conditions, the heat directed to the condensation surfaces is
predominantly by heat radiation whereas the heat of condensation
liberated by the condensation of the gases being pumped is not of
any decisive importance. In bringing the operating temperature to
the desired level under cryogenic operating conditions, the
refrigeration output has to be rated in accordance with the desired
short cooling period, as a result, if the working speed demanded
for a modern industrial pumping station is to be attained, the
initial refrigeration output is required to be several times higher
than that necessary for actual pumping operation. In cryogenic
pumping operations conducted by the supply of liquefied gases from
a storage tank, there is no problem in obtaining the greater
refrigeration output required for the initial cooling phase since
it can be supplied by a correspondingly larger refrigerant supply
from the storage tank.
Therefore, it is the primary object of the present invention to
improve the economic efficiency of a cryogenic pumping operation
which employs refrigeration apparatus.
In the prior art where the given output of the refrigerator was
employed for cooling to the desired operating temperature, a
radiation protection was employed around the condensation surfaces.
Such radiation protection usually consisted of an arrangement of
sheetlike members shielding against heat radiation. However, while
these sheets permitted the gas being pumped to pass over the
condensation surface, they constituted a flow obstacle which caused
a disadvantageous reduction in the pumping rate. Accordingly, the
present invention is directed to overcoming this disadvantageous
construction of the prior art.
In accordance with the present invention, in the method of pumping
a gas under cryogenic conditions and employing a refrigerator to
obtain the desired low temperature conditions the novel
characteristic involves the thermal insulation of the condensation
surfaces from the heat within the receiver while the surfaces are
being cooled to a predetermined temperature.
In carrying out the cryogenic pumping operation under high vacuum
conditions the surfaces for reducing the gas to the necessary low
temperatures are disposed within a space containing the gases to be
pumped and an adjustably movable device, operable from the exterior
of the enclosed space, is arranged to admit the flow of gas over
the cryogenically cooled surfaces, and the movable device is
arranged to provide a thermal shield for the surfaces while the
operating temperature is being established. In a known high vacuum
cryogenic pumping system, in which the cryogenically cooled
surfaces over which the gases pass are arranged in a space
communicating with the space to be evacuated, an enclosure device
has been used for temporarily separating the cooled surfaces from
the space to be evacuated. This prior device overcame the problem
of previous cryogenic pumping systems wherein the water vapor which
precipitated on the condensation surfaces had to be retained until
the process being carried out under a vacuum was completed. This
system was not only time consuming and required a considerable
amount of refrigerant, but it also posed the danger that a sudden
rise in the temperature within the receiver, which could easily
occur in the course of such a process, could lead to the release of
the water vapor from the condensation surfaces and result in an
undesired increase in pressure. By employing the above mentioned
enclosure for the condensation surfaces, it was possible to seal
the surfaces from the space containing the gas to be evacuated and
to thaw the water condensed thereon discharging it through a
separate pumping line without interfering with the vacuum within
the space containing the gas and otherwise interrupting the
process. Such operation required that the closure device was
designed to afford a high vacuum seal between the space containing
the condensation surfaces and the space containing the gases to be
pumped. The arrangement which served only to thaw the condensate
during operation is not an element of the present invention.
To attain the objectives of the present invention, as set forth
above, the closure device for the cryogenically cooled condensation
surfaces of the prior art is not sufficient. Under the present
invention, it is necessary during the initial cooling phase to
provide a temporary thermal separation between the condensation
surfaces and the gas to be pumped. The thermal separation can be
effected by providing a thermal shield to enclose the condensation
surfaces. Such a thermal shield can be provided by cooling the
surfaces of the shield or by the application of a thermal
insulating material. A simple covering about the condensation
surfaces, as disclosed in the prior art, is not sufficient because
the surface of the covering facing toward the condensation surfaces
acts as a heat radiation source of the same intensity as the
receiver, which forms the space containing the gas without the
covering, and the condensation surfaces would be exposed to the
same temperatures. On the other hand, as compared to the prior art
arrangement, it is not necessary, in accordance with the present
invention, to provide a gas-proof seal between the space containing
the gas and the space containing the condensation surfaces.
The various features of novelty which characterize the invention
are pointed out with particularity in the claims annexed to and
forming a part of this specification. For a better understanding of
the invention its operating advantages and specific objects
attained by its use, reference should be had to the accompanying
drawings and descriptive matter in which there are illustrated and
described preferred embodiments of the invention .
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a somewhat schematic vertical sectional view of an
apparatus constructed in accordance with the present invention;
FIGS. 2a and 2b show another arrangement of apparatus in accordance
with the present invention; and
FIGS. 3a and 3b show still another embodiment of apparatus in
accordance with the present invention for pumping gas under
cryogenic conditions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 a receiver 2 encloses a chamber 1 which is to be
evacuated in effecting the cryogenic pumping operation.
Condensation surfaces which are deep-cooled during the cryogenic
pumping operations are formed with the chamber 1 by means of a
cooling coil 4 through which a refrigerant is passed. The
refrigerant is circulated in a closed cycle flowing into the
cooling coil 4 through and inlet line 5 and passing out through an
outlet line 6 for flow through a refrigerator 7. In accordance with
the invention, the condensation surfaces provided by the coil 4 are
enclosed during the period in which the surfaces are brought to a
predetermined low temperature. The closure for the condensation
surfaces is provided by a vertically movable hood member 8 which
covers the sides and upper surface of the coil protecting it from
any heat supply within the chamber 1 of the receiver 2. A column 9
extends into the receiver 2 through its base and is secured to the
hood member. A vacuum-proof seal is provided by a packing member 10
for the opening through which the column 9 enters the receiver.
Exteriorly of the receiver, the column 9 is connected to a threaded
spindle 11 and by means of gear wheels 12 mounted on the spindle
and a servomotor 13, the column 9 and the hood 8 can be lifted or
lowered within the receiver. As indicated in dot-dash lines in FIG.
1, the hood 8 can be lifted from the position enclosing the
condensation surfaces to a position designated by the reference
character 8' fully exposing the condensation surfaces to the gas
within the chamber 1, or the hood can be positioned in any location
intermediate the fully closed and fully opened positions in
accordance with the operating conditions of the pumping system.
The exterior surface of the hood 8 is covered with a thermal
insulating material 14 which prevents the condensation surfaces
from being exposed to any heat within the receiver during the time
when the surfaces are being cooled to the operating
temperature.
The servomotor for positioning the hood is controlled by a control
device which is connected to a temperature sensor 15 located
adjacent the coil 4 for providing a continuous measurement of the
temperature of the condensation surfaces and thereby regulating the
servomotor.
Before the pumping operation is commenced in the apparatus
disclosed in FIG. 1, the protective hood is closed separating the
cooling coil 4 from the remainder of the chamber 1. The
condensation surfaces provided by the coil 4 are reduced to a
predetermined temperature and the chamber 1 is evacuated by a
forepump 16 through a line 17 containing a valve 18 which is in the
opened position. When starting vacuum for the pumping operation,
for example 10.sup.-.sup.4 mm. Hg and the predetermined temperature
of the condensation surfaces, for example, 20.degree. Kelvin, have
been reached, the protective hood 8 is opened and the pumping
operation commences under full suction capacity. The establishment
of the vacuum conditions within the receiver can be observed on the
gauge 19 mounted on the receiver.
FIGS. 2a and 2b, a receiver 21 provides a complete enclosure for a
chamber 22 arranged to contain a gas to be pumped under cryogenic
conditions. In the lower portion of the chamber 22 a cooling coil
24 forms the condensation surfaces for reducing the gas to the
desired low temperature. An inlet line 25 and and outlet line 26
circulate a refrigerant through the cooling coil 24. A heat
radiation shield 23 surrounds the coil 24 and is formed along the
sides and lower surfaces of the coiling coil 24 by a housing member
27 and the lower surface of this housing member is cooled by
another cooling coil 28 soldered to it and through which another
refrigerant flows at a higher temperature than that in the cooling
coil 24 forming the condensation surfaces. The heat shield is
completed by a radiation shield 29 which covers the upper surface
of the cooling coil. The radiation shield 29 is constructed of a
number of chevron-shaped sheets 30 arranged to prevent heat
radiation within the receiver from being directed against the
cooling coil 24. Encircling the angle sheets 30 is another cooling
pipe 31 having an inlet line 32 and an outlet line 33 for flowing
refrigerant through the pipe. The sheets 30 are supported by a
frame 34 and, in turn, the frame is supported on a shaft 36 which
extends through the wall of the receiver at 35 through a device
effecting a vacuum seal. In addition, the inlet and outlet lines 32
and 33 for the cooling pipe 31 enter and leave the chamber 22
through the shaft 36. The upper part 29 of the heat shield 23
enclosing the condensation surfaces can be pivoted by means of a
shaft 36 between a position, as shown in FIG. 2b, where it covers
the condensation surfaces to a position, shown in FIG. 2a, where
the gases within the receiver can flow over the condensation
surfaces. By selectively positioning the upper cover of the
condensation surfaces the flow of gas over the cooling coil 24 can
be regulated. The shaft supporting the upper cover can be pivoted
by hand or by a motor drive, such as shown in FIG. 2b comprising a
gear transmission means 37 and a servomotor 38. A control device 39
is connected to the servomotor for positioning the upper cover of
the heat shield. The servomotor is connected to a pressure gauge 40
in such a manner, that after the predetermined temperature, for
example 20.degree. Kelvin, has been reached the condensation
surfaces remain available for pumping as long as the pressure in
the receiver does not exceed a predetermined value. In addition, a
forepump 41 is connected to the receiver through a preevacuation
line 42 which contains a valve 43 for establishing the desired
vacuum conditions.
In FIGS. 3a and 3b, another embodiment of the present invention is
shown providing individual adjustment of the various elements
forming the heat shield enclosure for the condensation surfaces
which afford a particularly advantageous gas throttling
arrangement. A receiver 45 encloses the space containing the gas to
be pumped and, as with the other embodiments disclosed, the
condensation surfaces are provided in the lower region of the
receiver by means of a cooling coil 46. A plurality of vertically
disposed heat protection sheets are provided which are rotatable
about their vertical axes as indicated by FIG. 3b. The individual
sheets 47 extend between an upper plate 48 and a lower plate 49 and
can be rotated jointly by means of a transmission device composed
of a central gear 50 and individual gears 51 each secured to the
upper end of one of the heat protection sheets 47. By means of the
transmission device the plates can be rotated selectively to any
position between the fully opened and the fully closed positions.
For actuation of the transmission device, a vertically arranged
shaft 53 is secured at its upper end to the driving gear 50 and
extends downwardly through the cooling coil 46 and out of the
receiver 45 through a packing device 52. Exteriorly of the receiver
the shaft may be driven by hand or by means of a motor and gear
transmission means as is shown in FIG. 3a.
Connected to the motor 54 is a control device 55 which is connected
to a pressure gauge 56 for measuring the pressure within the
receiver and to a temperature sensor 57 positioned adjacent the
cooling coil 46 for determining the temperature of the condensation
surfaces. During operation the condensation surfaces are completely
enclosed by the heat protection sheets 47 until the predetermined
temperature, that is about 20.degree. Kelvin, is reached and then
the gas inflow is regulated as a function of the pressure within
the receiver to maintain a certain pressure, that is, about
10.sup.-.sup.4 mm. Hg and the flow is throttled to a minimum.
However, above this pressure the throttling is increased in an
amount based on the quantity of the condensing gas in accordance
with the constant refrigeration output. The constant refrigeration
output depends on the condensation temperature and the heat of
condensation of the gas being pumped. Accordingly, the gas inflow
over the condensation surfaces must be adjusted so that at a given
refrigeration output the corresponding quantity of gas is admitted
to flow over the surfaces. The devices disclosed in FIGS. 2b and 3a
employed, in accordance with the present invention, to insulate the
condensation surfaces from the heat within the receiver at least
during that part of the cooling of the surfaces when a
predetermined temperature is being established, which temperature
corresponds essentially to the operating temperature during
pumping. Subsequently, by movably displacing the enclosure about
the cooling coil, the condensation surfaces are fully exposed to
the heat within the receiver. In accordance with this arrangement,
it has been found that a better utilization of the refrigerating
apparatus is achieved in that the operating temperature and hence
the full suction capacity of the pump, is reached in a much shorter
time after commencing the cooling operation than would be possible
with the gas supply unthrottled and the condensation surfaces
unprotected from heat during the initial cooling period despite the
unhindered gas inflow and therefore stronger pumping during that
time.
In accordance with the general concept of the invention, the
thermally insulating enclosure about the cooling coil can include
any measures which effectively prevent the heat within the receiver
from impinging on the condensation surfaces. It can be appreciated,
of course, that a complete thermal insulation of the condensation
surfaces is not possible. However, to attain the object of the
present invention, a thermal insulation easily obtained by known
measures, such as in tanks for liquefied gas, is sufficient.
* * * * *