US3668881A

US3668881A - Adsorptive cryopumping method and apparatus

Info

Publication number: US3668881A
Application number: US55482A
Authority: US
Inventors: Jean-Jacques Thibault; Jacques Carle
Original assignee: Air Liquide SA
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 1969-12-01
Filing date: 1970-07-16
Publication date: 1972-06-13
Anticipated expiration: 1989-06-13
Also published as: DE2024991A1; CA926639A; FR2048253A5; GB1292489A; JPS5027205B1

Abstract

Cryopumping method and apparatus in which two cryopump chambers containing adsorbent are successively cooled and used to evacuate a third chamber by cryopumping. The first chamber to be cooled is used to evacuate the second chamber when both of the pump chambers are out of communication with the third chamber and before the second chamber is cooled. Then the first chamber is put into communication with the third chamber after the first and third chambers are sealed from each other.

Description

e States ae Thibault et al. [45] June 13, 1972 [54] ADSORPTIVE CRYOPUMPING [56] References Cited METHOD AND APPARATUS UNITED STATES PATENTS [721 Invent: i -J i 3,490,247 1/1970 Wing ..62/555 5 25'" ggf f f D 3,335,550 8/1967 Stern ..ss/2os 3,371,499 3/1968 Hagenbad ..62/55.5 [73] Assignee: L'Alr Liquide Societe Anonyme pour 3,387,767 6/1968 Hecht ..4l7/48 LEtude et L'Exploitatlon des Pr Georges Claude, Paris, France primary wm y Wye 221 Filed: July 16, 1970 Attorneyg & Thompson [21] Appl. No.: 55,482 [57] ABSTRACT Cryopumping method and apparatus in which two cryopump [30] Foreign Apphcauon Priority Data chambers containing adsorbent are successively cooled and Dec. 1, 1969 France ..6941309 u ed to evacuate a third chamber by cryopumping. The first chamber to be cooled is used to evacuate the second chamber [52] US. Cl. ..62/55.5, 417/48, 417/901, when both f the pump chambers are out f communication 51 I CI 55/208 62/ with the third chamber and before the second chamber is cooled. T-hen the chamber is put into communication the third chamber after the first and third chambers are sealed ADSORPTIVE CRYOPUMPING METHOD AND APPARATUS The present invention concerns a method and apparatus for pumping by adsorption, more particularly of the type in which a vacuum is produced in a chamber by placing the chamber in communication with a body of adsorbent that has been cooled to a very low temperature, e.g., cryopumping."

It is an object of the present invention to provide cryopumping methods and apparatus that conserve the cryogenic liquid used for cooling.

Another object of the present invention is the provision of such methods and apparatus that have reduced risk of contamination.

Still a further object of the present invention is the provision of cryopumping methods and apparatus in which the apparatus can be stationary and relatively free from vibration.

Still another object of the present invention is the provision of cryopumping methods and apparatus characterized by high thermal efficiency, high adsorptive capacity and improved heat transfer while maintaining a relatively small volume of the apparatus.

Still another object of the present invention is the provision of cryopumping apparatus which will be relatively simple and inexpensive to manufacture, easy to install, operate, maintain and repair, and rugged and durable in use.

Finally, it is an object of the present invention to provide cryopumping methods which will be simple and reliable to produce relatively high vacuum for a given cost of operation.

Briefly, the objects of the present invention are achieved by providing two chambers containing adsorbent, by cooling a first of these chambers, by putting the chambers in communication with each other so that the cold first chamber adsorbs gases from the relatively warm second chamber, by then cooling the second chamber by immersion in a cryogenic liquid while using the first chamber to cryopump gas from a third chamber which is the chamber to be evacuated, and finally by thereafter placing the cooled second chamber in communication with the third chamber to further evacuate the third chamber while sealing the first and third chambers from each other.

Other objects, features and advantages of the present invention will become apparent from a consideration of the following description, taken in connection with the accompanying drawings, in which:

FIG, 1 is aside cross-sectional view, somewhat schematic in nature, of apparatus according to the present invention; and

FIG. 2 is a section taken on the line 2-2 of FIG. 1 and looking in the direction of the arrows.

Referring now to the drawings in greater detail, there is shown cryopumping apparatus according to the present invention, comprising a vessel 40 having a bottom 41 and side walls 42 that are insulated and an insulated cover 43 which may be releasably clamped on to close the vessel.

Disposed inside vessel 40 are several chambers. Chamber 44 is in the form of a bell and has an insulated top wall 45 and a cylindrical side wall 46, which is also the radially inner side wall of a pumping chamber 51 that is annular and that surrounds chamber 44. Chamber 51 also has a cylindrical outer side wall 52, a bottom wall 53 and a top wall 54. Chamber 51 comprises a first cryopumping chamber.

Disposed within chamber 44 is a second cryopumping chamber 62 which is surrounded by but sealed from communication with and generally spaced from the side walls of chamber 44. Chamber 62 contains an upright annular space 63 that communicates through an upwardly converging coneshaped space 64 with an upright conduit 65 that is closed at its upper end by an electrically operated valve 66. Disposed within chamber 62 is a quantity of conventional cryopumping adsorbent 67 such as any of a number of zeolites well known to persons having ordinary skill in this art, which accordingly need not be further described. The adsorbent 67 is disposed between a highly heat-conductive inner wall 68 of chamber 62, which may be of copper or the like, and a screen 69 that radially outwardly confines adsorbent 67 but exposes it to space 63. Upright U-shaped fins 80 of copper or the like are secured to wall 68 and promote heat transfer between wall 68 and adsorbent 67 (see FIG. 2). A radially outer side wall 70 completes chamber 62.

The portions of chamber 44 that are inside and outside the downwardly open bell thus fomied by chamber 62 communicate with each other through an opening 48 through space 64.

Chamber 44 outside chamber 62 communicates with the outside of the apparatus through an upright conduit 72 controlled by a valve 73. The interior of chamber 44 outside chamber 62 also communicates with the interior of vessel 40 through an opening 39 at the bottom of chamber 44. When valve 73 is closed, chamber 44 is closed except for opening 39.

Chamber 51 is filled with a cryogenic adsorbent 61 such as the zeolite mentioned above, which communicates with the exterior of chamber 51 only through an upright conduit 57 that may be selectively closed by an electrically-operated valve 58.

Valves

58 and 66 thus control the communication with a conduit 59 selectively closed by valve 60 and communicating with a third chamber to be evacuated (not shown).

The interior of vessel 40 outside

chambers

51 and 44, which will hereinafter be called chamber 47, is adapted to be filled with a cryogenic liquid such as liquid nitrogen 79, up to an initial level N, through an inlet 71. The liquid nitrogen 79 initially fills chamber 47 to the level N but does not enter chamber 44 because valve 73 is closed and there is accordingly no way for the gas inside chamber 44 to escape. As initially filled, therefore, chamber 44 will contain no cryogenic liquid but chamber 47 will be filled to level N.

The first chamber 51 is traversed by a plurality of upright tubes 56 open at both ends and having radially outwardly extending heat exchange discs 38 thereon that penetrate adsor bent 61 to promote heat exchange between adsorbent 61 and tubes 56. Cryogenic liquid fills the tubes 56 and abstracts heat from the adsorbent 61 by this heat exchange.

To effect desorption after the adsorptive cryopumping is completed, the cryogenic liquid is drained from the apparatus through a drain (not shown) so that the apparatus is entirely dry, and then the

chambers

51 and 62 are heated to desorb the adsorbed material, which leaves the chambers through

conduits

57 and 65, respectively,

valves

58 and 66 being open, and is withdrawn from conduit 59 through a discharge conduit (not shown), the valve 60 being closed. To this end, an electric resistance heater 74 is provided under the bottom wall 77 of chamber 44, which also extends to some extent under chamber 51; and heater 74 is heated by electric resistance heating, the power being brought in through a cable 75 that traverses a tube 55 in one of the tubes 56 and that leaves the apparatus through conduit 71.

In operation, with

valves

60 and 73 closed, liquid nitrogen or other cryogenic liquid is supplied through conduit 71 into chamber 47 up to the level N. As valve 73 is closed, substantially none of this liquid enters chamber 44 through opening 39. Therefore, first chamber 51 is cooled but second chamber 62 remains relatively warm.

Valves

58 and 66 are open, so that adsorbent 61 in chamber 51 tends to adsorb gas from chamber 62; but of course no gas is withdrawn from the third chamber to be evacuated, because valve 60 is closed.

When chamber 62 is thus purged of gas, valve 66 is closed and with valve 58 remaining open, valve 60 is also opened. This seals off second chamber 62 and places first chamber 51 directly in communication with the third chamber to be evacuated. The relatively cold adsorbent 61 in chamber 51 adsorptively cryopumps a great deal of the gas out of the third chamber.

In the meantime, the valve 73 is opened, which permits chamber 44 to flood with cryogenic liquid, the level of this liquid in chamber 47 falling from N to N but remaining above the top of first chamber 51. The liquid never enters chamber 62, because chamber 62 is sealed except through conduit 65; but the liquid surrounding and particularly the liquid inside the confines of the annular chamber 62 quickly abstracts heat from adsorbent 67 until this adsorbent is cooled to efficient cryoadsorption temperatures.

Then the valve 58 is closed, sealing off the used adsorbent 61 in chamber 51 and valve 66 is opened, placing second chamber 62 in communication with the third chamber which is thus further evacuated by cryopumping from second chamber 62. The pressure in this third chamber is still further reduced by adsorption of most of its remaining gas onto the adsorbent 67, it being remembered that this adsorbent 67 had been previously desorbed by communication with adsorbent 61 before any cryopumping from the third chamber began.

When the pressure in the third chamber has thus fallen to its desired very low level, of the order of magnitude of mm. of mercury or even less, then valve 60 is closed. It is now time to regenerate the

adsorbents

61 and 67 by desorption; and to this end, the cryogenic liquid is drained from vessel 40 until the vessel is dry and then heater 74 is energized so that the temperature of adsorbent 61 and 67 rises and gas is desorbed therefrom. This gas leaves through

conduits

57 and 65 and through

open valves

58 and 66, valve 60 remaining closed, the desorbed gas being removed from conduit 59 through an outlet opening (not shown). Of course, if the third chamber has been detached from the equipment, then the desorbed gas can be vented through open valve 60.

From a consideration of the foregoing disclosure, therefore, it will be evident that all of the initially recited objects of the present invention have been achieved.

Although the present invention has been described and illustrated in connection with a preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit of the invention, as those skilled in this art will readily understand. Such modifications and variations are considered to be within the purview and scope of the present invention as defined by the appended claims.

Having described our invention, we claim:

1. A method of cryopumping, comprising establishing first and second chambers containing adsorbent, cooling the first chamber while maintaining the second chamber at a higher temperature than the first chamber and maintaining the first and second chambers in fluid communication with each other thereby to cryopump gas from the second chamber to the first chamber, thereafter sealing off the first and second chambers from each other and cooling the second chamber, establishing fluid communication between the first chamber and a third chamber to be evacuated, thereby to cryopump gas from the third chamber to the first chamber, and thereafter sealing off the first and third chambers from each other and establishing fluid communication between the second and third chambers thereby to cryopump further gas from the third chamber to the second chamber.

2. A method as claimed in claim 1, in which said cooling of said first chamber while maintaining said second chamber at a higher temperature is effected by immersing said first chamber in a cold liquid while maintaining said second chamber out of said cold liquid, and said cooling of said second chamber is effected by immersing said second chamber in the same liquid which previously cooled the first chamber.

3. A method as claimed in claim 2, in which the second chamber is first maintained out of the liquid and then immersed in the liquid by maintaining and then releasing a body of confined gas about said second chamber which when released escapes and permits entry of the liquid about the second chamber,

4. Cryopumping apparatus comprising a vessel, a pair of chambers in said vessel, each of said chambers containing adsorbent material, means for placing said chambers in fluid communication with each other, means for selectively individually placing said chambers in fluid communication with a third chamber to be evacuated, means for admitting a cryogenic liquid into said vessel to surround said pair of chambers, and means for contacting one of said pair of chambers with said liquid while maintaining the other of said pair of chambers out of contact with said liquid, and for thereafter admitting said liquid into contact with said other ofsaid pair of chambers, thereby selectively to cool first said one and then said other of said pair of chambers.

5. Apparatus as claimed in claim 4, said admitting means comprising means for selectively maintaining and releasing a body of confined gas surrounding said other chamber.

6. Cryopumping apparatus comprising a vessel, a plurality of pumping chambers in said vessel each containing an adsorbent material, means for admitting a cryogenic liquid into said vessel, means for thermal transfer between the liquid and the adsorbent material in each said chamber, means for bringing said liquid into contact successively with said thermal transfer means associated with each said chamber, means for individually placing said chambers in fluid communication with an external chamber to be evacuated, and warming means for regenerating said adsorbent material.

7. Cryopumping apparatus comprising a vessel, means for admitting a cryogenic liquid into said vessel, a plurality of pumping chambers in said vessel, each of said pumping chambers containing adsorbent material, individual ducts extending from said chambers to the outside of said apparatus, valve means in each of said ducts, a downwardly opening bell in said vessel, one of said chambers being disposed in said bell, said bell having a duct extending from the top of the bell to the outside of the vessel, and a valve in the last-named duct for selectively maintaining and releasing a body of confined gas under said bell thereby selectively to permit or prevent contact between said one chamber and said cryogenic liquid.

8. Apparatus as claimed in claim 7, said chambers being concentrically disposed one within another.

9. Apparatus as claimed in claim 6, one of said chambers being annular and concentrically surrounding another of said chambers, said another chamber having a top wall, a cylindrical side wall adjacent said first chamber, and heater means disposed below said another chamber for thermally regenerating said adsorbent.

10. Apparatus as claimed in claim 6, said thermal transfer means comprising tubes with fins extending inside the adsorbent, said tubes being open at both ends inside said vessel for the admission of said cryogenic liquid.

Claims

3. A method as claimed in claim 2, in which the second chamber is first maintained out of the liquid and then immersed in the liquid by maintaining and then releasing a body of confined gas about said second chamber which when released escapes and permits entry of the liquid about the second chamber.

4. Cryopumping apparatus comprising a vessel, a pair of chambers in said vessel, each of said chambers containing adsorbent material, means for placing said chambers in fluid communication with each other, means for selectively individually placing said chambers in fluid communication with a third chamber to be evacuated, means for admitting a cryogenic liquid into said vessel to surround said pair of chambers, and means for contacting one of said pair of chambers with said liquid while maintaining the other of said pair of chambers out of contact with said liquid, and for thereafter admitting said liquid into contact with said other of said pair of chambers, thereby selectively to cool first said one and then said other of said pair of chambers.