US3536420A

US3536420A - Condensate purifier for diffusion pump

Info

Publication number: US3536420A
Application number: US811904A
Authority: US
Inventors: Claire E Miner
Original assignee: US Atomic Energy Commission (AEC)
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1969-04-01
Filing date: 1969-04-01
Publication date: 1970-10-27
Anticipated expiration: 1987-10-27

Description

Oct. 27, 1970 c. E. MINER CONDENSATE PURIFIER FOR DIFFUSION PUMP- 2 Sheets-sheaf 1 Filed April 1, 1969 VACUUM PUMPING MECHANISM CLAIRE E. MINER ATTORNEY Oct. 27, 1970 c, m 3,536,420

CONDENSATE PURIFIER FOR DIFFUSION PUMP Filed April 1, 1969 2 Sheets-Sheet 2 INVENTOR.

CLAIRE E. MINER BY ATTORNEY United States Patent Office 3,536,420 Patented Oct. 27, 1970 3,536,420 CONDENSATE PURIFIER FOR DIFFUSION PUMP Claire E. Miner, Lafayette, Califi, assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Apr. 1, 1969, Ser. No. 811,904 Int. Cl. F04!) 23/ F04f 9/00, 9/06 US. Cl. 41777 10 Claims ABSTRACT OF THE DISCLOSURE A condensate purifier for a high vacuum diffusion pump in which the pumping fluid condensate is purified before returning to the boiler of the pump for recirculation, thereby increasing the efliciency of the pump. The purifier receives the condensed vapor together with adsorbed gases from the pump and wherein it is heated to drive off the gases. These gases and some vapor from the pump fluid rise into a refrigerated baffle where the vapor is condensed and drops back into the lower part of the purifier. The gas liberated in this manner may be removed by a vacuum pump of the type used in forevac systems, such as a mechanical pump, or other vacuum arrangement. The purified fluid is returned to the boiler for continuous use in the diffusion pump.

BACKGROUND OF THE INVENTION The invention described herein was made in the course of, or under, Contract No. W7405ENG48 with the United States Atomic Energy Commission.

The present invention relates to condensate purifiers, and more particularly to a condensate purifier for a high vacuum diffusion pump which functions to remove gasabsorbed in the pumping fluid thereby increasing the efliciency of the pump.

In the operation of non-fractionating diffusion pumps, gas molecules absorbed in the pumping fluid condensate have been a constant problem. When the condensate is returned from the vapor jets in the pump body to the pump boiler the absorbed gas is boiled off with the vapor and reenters the vapor jets. This gas in the vapor jets apparently decreases the efiiciency of the diffusion pump by deforming the jet profile because of increased scattering. This action also directly increases the amount of backstreaming since deformation of the jet causes some jet particles to move toward the space being evacuated.

SUMMARY OF THE INVENTION of the liquid, for example, to about 35 C. for mercury.

A tube from the baffled section to a forevac line, or other vacuum arrangement, removes the gas driven off by heating the condensate. The purified pumping fluid is then returned to the pump boiler for recirculation.

Accordingly it is an object of the present invention to provide a condensate purifier to improve the efficiency of operation of a diffusion pump.

It is another object of this invention to increase the ultimate degree of vacuum that is attainable with a diffusion pump by maintaining the pumping fluid in a purified state.

It is still another object of the present invention to remove absorbed gases from the condensed pumping fluid of a diffusion pump prior to returning the pump fluid to the boiler for recirculation.

The invention together with further objects and advantages thereof will be best understood by reference to the following specification in conjunction with the accompanying drawings of which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view of the inventive purifier and associated diffusion pump, each shown partly cutaway, and

FIG. 2 is a plan view of the pump and purifier with the connecting tubing.

DESCRIPTION OF THE INVENTION Referring now to the drawing and particularly to FIG. 1 there is shown a diffusion pump generally indicated at 11 and of the non-fractionating type and similar to the pump disclosed in US. Pat. No. 3,391,857 issued July 9, 1968 to L. R. Lucas et al., and assigned to the same assignee. The pump 11 is comprised of an upright cylindrical casing 12 having the upper end adapted for connection to a vessel (not shown) to be evacuated, and a tubular jet forming stack 13 extending upwardly within the casing. The jet stack 13 has a series of annular jet openings 14 for directing streams of mercury vapor outwardly and downwardly whereby gas molecules are entrained and carried away from the vessel being evacuated. A boiler generally indicated at 22 is coupled to the stack 13 for supplying heated mercury vapor thereto. Since the details of the diffusion pump 11 and boiler 22 therefor do not constitute part of this invention, a more detailed description thereof is deemed unnecessary.

In most prior diffusion pumps, including the pump disclosed in the above cited US. patent, the mercury vapor which condenses following impact of the vapor jets against the inner wall of the pump 11, merely drains back into a boiler pool at the base of the pump. Here it is reheated and returned as vapor to the jets 14 through stack 13. However as previously discussed, absorbed gases in the condensed mercury vapor which is recirculated causes backstreaming and otherwise reduces efliciency and the ultimate degree of vacuum that may be attained. Accordingly the present invention provides a condensate purifier generally indicated at 16 which is connected to the base of the pump 11 and to the boiler 22 for removing the condensate from the pump and returning purified fluid to the boiler for recirculation.

The condensate purifier 16 has a long, upright, cylindrical outer shell or housing 17. A heavy bottom plate 18 at the bottom of shell 17 holds a cartridge type heater unit 19. The shell or housing 17 is mounted adjacent to the diffusion pump 11 by means of a bracket 21 in such manner that the bottoms of boiler 22 and shell 17 are at the same level. A tube or conduit 23 connects the bottom or base of pump 11 to bottom plate 18 of purifier 16 to carry condensate from the pump to the purifier. A second tube or conduit 24 connects the bottom plate 18 of purifier 16 to the bottom of boiler 22 for returning purified pump fluid 20 to the boiler 22. Thus the pump fluid 20 will seek a common level in the boiler 22 and the shell 17. The tubes or

conduits

23 and 24 are provided with normally

open valves

26 and 27, respectively, to isolate the boiler 22 from the purifier 16 when this is desired.

The shell or housing 17 has a flange 28 at the top edge thereof and a cover 29 secured to this flange closes the top of the shell. Two

tubes

31 and 32 which pass through the cover 29 support a short cylindrical enclosed container 33 inside the shell 17. Container 33 holds a refrigerant 34, which may be Freon for example, for which the

tubes

31 and 32 serve as input and outlet to provide for a continuous flow of the refrigerant. Depending upon the bottom of container 33 is a cylindrical bafiie 36 which is cooled by contact with the refrigerant container 33. The baffle 36, which is a hollow cylinder, extends downwardly inside shell 17 spaced only a small distance from the inner walls thereof to somewhat above the surface of pump fluid 20. The baflle 36 is open at the bottom to permit the rise of gas and some small amount of vapor driven from the pump fluid 20 which is heated in the bottom of shell 17 by cartridge heater 19. This gas and vapor rises principally inside the baflie 36 but a small amount also rises outside the baflie. A bore 37 in the wall of bafile 36 near the top edge thereof lines up with a tube 38, one end of which penetrates the shell 17 in sealed relationship thereto. A flange 39 at the opposite end of tube 38 provides means for connecting the interior of shell 17 to a trapped forevac line or trapped mechanical vacuum pump indicated by line 40 and vacuum mechanism 41 to remove any gas that collects in the shell.

In operation the condensed pumping vapor of diffusion pump 11 together with the absorbed gas which the condensate carries enters shell 17 through tube 23 and is heated by heater 19 to a temperature about half of that required for boiling the pump fluid 20. This, in the case of mercury which boils at about 180 C. in vacuum, would be about 90 C. This temperature is suflicient to drive off the gas which is absorbed in the condensate. The gas thus driven off rises inside baflle 36 and in lesser amounts outside the baffle and is withdrawn from the shell 17 through tube 38 to a forevac system or other system 41. Some vapor will also be driven off from the condensate although the liquid does not boil. This vapor is condensed on the baflle 36 and drips back into the liquid 20 in the lower part of shell 17. By this operation the pump fluid 20 in the lower part of shell 17 is maintained in a gas free condition so that fluid returned to the boiler 22 through tube 24 is free of gas.

It has thus been shown that the present invention functions to improve the efliciency of diffusion pumps by removing the absorbed gas from the pumping fluid thereby overcoming the problems of the non-fractionating diffusion pumps.

While the description has been directed to mercury as the pumping fluid, other fluids such as appropriately high molecular weight organic compounds, silicones, or other metals, such as cesium, having sufl'lciently high vapor pressures may be utilized.

Although the invention has been disclosed with respect to a single exemplary embodiment it will be evident to those skilled in the art that many variations are possible within the spirit and scope of the invention. Therefore it is not intended to limit the invention except as defined by the following claims.

What is claimed is:

1. A condensate purifier for a high vacuum pumping system of the type employing at least one vapor diflusion pump and a pumping fluid boiler comprising: a housing means adapted to conduct condensed pumping fluid of an associated diffusion pump to said housing, means adapted to conduct purified pumping fluid from said housing to an associated pumping fluid boiler, heating means located in the lower portion of said housing for heating condensate from such an associated diffusion pump to drive off entrained gas therefrom, cooling means disposed in said housing above said heating means for condensing any pumping fluid vapor which is driven ofl? with entrained gas, and means for withdrawing gas driven oft" from said housing.

2. The condensate purifier defined in claim 1, wherein said housing defines an upright cylindrical vessel hav ing top and bottom members sealingly connected thereto, said heating means being supported by said bottom member, said cooling means being supported by said top member.

3. The condensate purifier defined in claim 1, wherein said means adapted to conduct condensed pumping fluid to said housing consists of a tube having one end thereof penetrating the bottom of said housing and adapted to penetrate the bottom of an associated diffusion pump at the location where condensate collects therein, said tube having a valve means located therein whereby an associated diffusion pump may be isolated from said housing.

4. The condensate purifier defined in claim 1, wherein said means adapted to conduct purified pump fluid from said housing to an associated pumping fluid boiler consists of a tube having one end which penetrates the bottom of said housing and the other end of which is adapted to penetrate the bottom of an associated pumping fluid boiler, said tube having a valve means located therein whereby an associated pumping fluid boiler may be isolated from said housing.

5. The condensate purifier defined in claim 1, wherein said heating means is a cartridge type heater unit.

6. The condensate purifier defined in claim 1, wherein said cooling means includes a container, means for main taining refrigerant in said container, and baflle means suspended from said container and cooled by refrigerant in said container, said baffle means extending toward but in spaced relation with respect to said heating means.

7. The condensate purifier defined in claim 1, wherein said housing consists of a hollow upright cylindrical shell, a plate member secured to and sealing the lower end of said shell, a flange-like member secured to the upper end of said shell and a cover member secured to said flange-like member and sealing the upper end of said shell.

8. The condensate purifier defined in claim 7, wherein said heating means is operatively mounted in said plate member, said heating means consisting of a cartridge type heater unit.

9. The condensate purifier defined in claim 7, wherein said cooling means is supported by and suspended from said cover member; said cooling means including a container of coolant, means for conducting coolant to and from said container extending through said cover member and a hollow baffle member suspended from and cooled by said coolant container extending toward plate member and in spaced relationship within said shell interior wall surface, said batfle member being provided with an opening in a wall thereof, whereby vapor driven ofif from condensate in the lower portion of said shell by said heating means condenses on said bafiie means and drops back into the lower portion of said shell, while gas driven off from condensate in the lower portion of said shell by said heating means rises inside and outside of said baffle member for removal therefrom by said gas withdrawing means, said opening in said baffle member wall allowing gas to be withdrawn therethrough from within said baffle member.

-10. The condensate purifier defined in claim 7, wherein said means adapted to conduct condensed pumping fluid to said housing comprises conduit means operatively connected at one end to said plate member and adapted to be connected at the other end to a condensate collection area of an associated diffusion pump; wherein said means adapted to conduct purified pump fluid from said housing to an associated pumping fluid boiler comprises conduit means operatively connected at one end to said plate member and adapted to be connected at the other end thereof to a bottom area of an associated pumping fluid boiler, each of said conduit means being provided with valve means for controlling flow therethrough; and wherein said gas withdrawing means is operatively connected to the upper portion of said shell adjacent said cooling means.

References Cited UNITED STATES PATENTS MARK M. NEWMAN, Primary Examiner 15 W. J. KRAUSS, Assistant Examiner U.S. Cl. X.R.