Method and apparatus for regeneration water
Ice condensed in a portion in a case in which a cryogenic refrigerator is installed, which is cooled by the cryogenic refrigerator, is melted by increasing a temperature of the ice to a melting point of the ice or higher. Then, while the temperature of the melted ice and a pressure thereof are kept to be equal to or higher than a freezing point of water, the pressure is reduced by rough evacuation so as to vaporize water. At a time at which the water is discharged, the pressure is further reduced so as to discharge water vapor. In this manner, regeneration of water is performed in accordance with a state of the water (i.e., a solid state, a liquid state, and a gas state), thereby shortening a regeneration time.
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This application is a continuation of U.S. patent application Ser. No. 10/580,688 filed on May 26, 2006, which is the U.S. National Phase Application of International Application No. PCT/JP2004/17502, filed on Nov. 25, 2004 and claims priority from Japanese Patent Application Serial No. 2003-399206 filed on Nov. 28, 2003, the contents of which are incorporated herein by reference in their entirety.
TECHNICAL FIELDThe present invention relates to a water regeneration method and a water regeneration apparatus. In particular, the present invention relates to a water regeneration method and a water regeneration apparatus for discharging ice condensed in a portion cooled by a cryogenic refrigerator installed in a case to the outside of the case, which are suitably used for discharging water that is condensed as ice on a cryopanel in a cryopump out.
BACKGROUND ARTA cryopump is conventionally used for evacuation of a vacuum chamber (that may be called as a process chamber) of a semiconductor manufacturing apparatus or the like in order to keep the inside of the vacuum chamber vacuum.
An exemplary use of the cryopump described in Japanese Patent Laid-Open Publication No. 2000-274356 is shown in
The cryopump 20 includes a two-stage GM (Gifford-McMahon) expansion type refrigerator 24 that works by receiving supply of compressed helium gas from a compressor 22, for example. The refrigerator 24 includes a first (cooling) stage 26 and a second (cooling) stage 28 having a lower temperature than the first stage 26. A heat shield 30 is connected to the first stage 26, thereby preventing a radiation heat from entering the second stage 28 and a cryopanel 34. A louver 32 is provided in a vacuum-chamber side opening of the heat shield 30. To the second stage 28 is connected the cryopanel 34 (that may be called as a second-stage panel because it is connected to the second stage 28) including activated charcoal 36.
In
The cryopump 20 having the above structure is connected to a vacuum chamber 10 via a gate valve 12. The louver 32 and the heat shield 30 that are cooled to about 40 K to about 120 K cool a gas having a relatively high freezing point such as water vapor so as to condense that gas. Moreover, the cryopanel 34 cooled to 10 K to 20 K cools a gas having a low freezing point such as nitrogen gas or argon gas so as to condense that gas. A gas that is not condensed by the above cooling, such as hydrogen gas, is absorbed by the activated charcoal 36. In this manner, gases inside the vacuum chamber 10 are discharged.
As described above, the cryopump 20 is an accumulation type pump and therefore requires a regeneration process for discharging accumulated gases to the outside of the cryopump 20 when the amount of the accumulated gases reaches a certain amount.
Examples of conventional regeneration methods include (1) a method in which temperatures of the louver 32, the heat shield 30, and the cryopanel 34 are increased by using a heater or the like at the same time as start regeneration and thereafter a purge gas (e.g., nitrogen gas) is kept flowing, as described in Japanese Patent Laid-Open Publications Nos. Hei 8-61232 and Hei 6-346848, and (2) a method in which roughing and purging are repeated (hereinafter, referred to as rough-and-purge), as described in Japanese Patent Laid-Open Publication No. Hei 9-14133.
In
In regeneration of the cryopump described above, regeneration of water becomes a problem. Ice that has resulted from water vapor evacuated and condensed by and in the cryopump cannot be melted, unless its temperature is increased to its melting point, 273 K or higher, at an atmospheric pressure. The boiling point of water is 373 K at the atmospheric pressure. However, it is difficult to increase the temperature to 373 K because of structures of the cryopump and the refrigerator. This means that ice cannot be discharged from the inside of the cryopump only by increasing the temperature, unlike other gases that can be placed in a gas state during the temperature increase of the cryopump and can be discharged to the outside of the cryopump. Insufficient regeneration of water affects an evacuating performance of the cryopump.
In the conventional regeneration method (1) in which a purge gas is kept flowing so that water is saturated in the purge gas and is discharged from the inside of the cryopump, it is difficult to determine whether or not regeneration is completed. Moreover, the purge gas is made to flow only for a time determined in accordance with an assumed amount of the water. Thus, it is necessary to make the gas flow for a long period of time so as to finish discharging of the water under a worst condition and therefore wasteful time is very long.
In the latter method (2), as shown in
However, in the latter method (2), water is frozen during roughing by means of the dry pump. Thus, water is not sufficiently discharged and the pressure is not reduced to the set value. Therefore, a time required for regeneration becomes longer in some cases. Moreover, it is necessary to perform the rough-and-purge step again in some cases.
It is therefore an object of the present invention to efficiently discharge water and shorten a regeneration time, thereby overcoming the aforementioned conventional problems.
According to the present invention, a water regeneration method for discharging ice condensed in a portion cooled by a cryogenic refrigerator installed in a case to an outside of the case, includes: a temperature increasing step for melting the ice; a vaporizing step for vaporizing water; and a discharging step for discharging water vapor, wherein the ice, the water, and the water vapor are regenerated in stages, thereby achieving the above object.
Moreover, each of the vaporizing step and the discharging step may include buildup determination.
The temperature increasing step may be a warm-up step for increasing a temperature of the portion of the case in which the ice is condensed to a melting point of the ice or higher to melt the ice.
Moreover, the temperature increasing step may be performed by one or more of temperature increase by a reverse rotation in which a motor of the refrigerator is rotated in an opposite direction to a rotation direction during cooling, temperature increase by purge in which a purge gas having a higher temperature than the melting point of the ice is made to flow in the case to return a pressure in the case that is kept vacuum to an atmospheric pressure and improve thermal conductivity with the outside of the case, and temperature increase by a heater.
In the vaporizing step, water is vaporized by performing rough evacuation to reduce a pressure of the portion in which the water generated from melting of the ice by the temperature increasing step is accumulated within a range in which the temperature and the pressure of the portion are prevented from reaching a freezing point of the water, the buildup determination for determining pressure increase by discharged moisture or a gas when the evacuation is stopped is performed, and the water vaporization and the buildup determination are repeated until the water vanishes away.
The pressure during the rough evacuation may be set to 100 Pa to 200 Pa to prevent the water from being frozen.
The discharging step may be an evacuation step for discharging the water vapor by further reducing the pressure by the rough evacuation at a time when the water is vaporized by the vaporizing step, performing the buildup determination to determine the pressure increase by a gas when the evacuation is stopped, and repeating the discharge of the water vapor and the buildup determination until the pressure increase is smaller than a value used for the determination.
The temperature increasing step may be switched to the vaporizing step at a time when the temperature of the portion of the case in which the ice is condensed reaches the melting point of the ice.
The vaporizing step may be switched to the evacuation step based on the buildup determination using the discharged moisture or gas when the evacuation is stopped.
According to the present invention, a water regeneration apparatus for discharging ice condensed in a portion cooled by a cryogenic refrigerator installed in a case to an outside of the case, includes: temperature increasing means for increasing a temperature of the portion in the case in which the ice is condensed to a melting point of the ice or higher to melt the ice; vaporizing means for vaporizing water generated by melting of the ice by performing rough evacuation to reduce a pressure of the portion in which the water is accumulated within a range in which the temperature and the pressure of the portion are prevented from reaching a freezing point of the water, performing buildup determination based on discharged moisture or gas when the evacuation is stopped, and repeating the water vaporization and the buildup determination until the water vanishes away; and evacuation means for discharging water vapor by further reducing the pressure at a time when the water is vaporized, thereby achieving the above object.
The temperature increasing means may be achieved by one or more of a reverse rotation of a motor of the refrigerator, a purge gas, and a heater.
The present invention also provides a cryopump or a water trap that is characterized by including the aforementioned water regeneration apparatus.
According to the present invention, regeneration of water, which is the problematic issue during regeneration, is divided into three steps, i.e., melting ice, vaporizing water, and discharging water vapor. In each of the three steps, a regeneration condition (pressure, temperature) that is appropriate for a corresponding state (i.e., a solid state, a liquid state, a gas state) is used, so that ice is melted by increasing a temperature of the ice itself, water generated from melting of the ice is vaporized by self-evaporation by performing rough evacuation to a pressure at which the water is not frozen, and water vapor distributed on a surface of a structure is completely discharged at a further reduced pressure. In this manner, regeneration of the water is performed in stages, namely, in an ice state, in a water state, and in a water-vapor state in that order in accordance with the state of the water. Thus, it is possible to efficiently reprocess the water and shorten a regenerate time.
An exemplary embodiment of the present invention is now described in detail with reference to the drawings.
Regeneration of water according to the present invention is performed in a procedure shown in
In the present exemplary embodiment, the heaters 52 and 54 are provided. Thus, all of temperature increase by a reverse rotation, temperature increase by a heater, and temperature increase by purge can be used. Therefore, it is possible to rapidly increase the temperature. Moreover, any one of the above temperature increase methods or a combination of given two of those methods may be used for increasing the temperature. Furthermore, the heater may be omitted.
In the exemplary embodiment, the present invention is applied to the cryopump. However, an application of the present invention is not limited thereto. As shown in
The present invention can be also applied to apparatuses other than a cryopanel and a water trap, in which it is necessary to discharge ice (water, water vapor) that is accumulated because of cooling by a refrigerator or the like, e.g., a professional-use refrigerator, in general.
Claims
1. A water regeneration method for discharging ice condensed in a portion cooled by a cryogenic refrigerator comprising:
- a temperature increasing step for melting the ice into water at approximately atmospheric pressure and at a melting temperature of at least 273 K;
- a first roughing step performed between the approximate atmospheric pressure and a first reduced pressure being less than the atmospheric pressure but higher than and yet close to a water-freezing pressure that causes the water to freeze;
- and
- a second roughing step performed between a second reduced pressure and a third reduced pressure, the second and third reduced pressures being less than the first reduced pressure and the second reduced pressure being greater than the third reduced pressure,
- wherein each one of the first roughing step and the second roughing step occurs at the melting temperature of at least 273 K.
2. The water regeneration method according to claim 1, comprising a reducing step of reducing a pressure and a temperature in the portion after the second roughing step.
3. The water regeneration method according to claim 2, wherein the reducing step is performed when the pressure increase does not occur within a predetermined time during the second roughing step.
4. The water regeneration method according to claim 2, comprising a step of starting a cryopump after the reducing step.
5. The water regeneration method according to claim 4, a dry pump is operated during the reducing step to reduce the pressure, and the dry pump is stopped before the cryopump is started.
6. The water regeneration method according to claim 1, wherein the second roughing step includes a buildup determination.
7. The water regeneration method according to claim 6, wherein the buildup determination is performed by measuring a pressure increase while an evacuation is stopped, and is determined when the pressure increase is smaller than a predetermined value.
8. The water regeneration method according to claim 1, wherein the first reduced pressure is set to approximately 100 Pa.
9. The water regeneration method according to claim 1, wherein the third reduced pressure is set to approximately 10 Pa.
10. A water regeneration apparatus for discharging ice condensed in a portion cooled by a cryogenic refrigerator comprising:
- temperature increasing means for melting the ice into water at approximately atmospheric pressure and at a melting temperature of at least 273 K;
- vaporizing means for vaporizing the water by performing a first roughing step between the approximate atmospheric pressure and a first reduced pressure being less than the atmospheric pressure but higher than and yet close to a water-freezing pressure that causes the water to freeze;
- and
- water vapor discharging means for discharging water vapor by performing a second roughing step between a second reduced pressure and a third reduced pressure, the second and third reduced pressures being less than the first reduced pressure and the second reduced pressure being greater than the third reduced pressure,
- wherein each one of the roughing steps occurs at the melting temperature of at least 273 K.
11. The water regeneration apparatus according to claim 10, wherein pressure and temperature in the portion are reduced to less than the second reduced pressure and less than 273 K respectively, after the second roughing step.
12. The water regeneration apparatus according to claim 11, wherein the pressure and temperature in the portion are reduced when a pressure increase does not occur within a predetermined time during the second roughing step.
13. The water regeneration apparatus according to claim 11, wherein a cryopump is operated when the pressure or the temperature in the portion is a predetermined pressure or a predetermined temperature.
14. The water regeneration apparatus according to claim 13, a dry pump is operated during the pressure in the portion is reduced, and the dry pump is stopped before the cryopump is started.
15. The water regeneration apparatus according to claim 10, the first or second roughing step is performed by a dry pump.
16. The water regeneration apparatus according to claim 10, the apparatus further comprising means for buildup determination.
17. The water regeneration apparatus according to claim 16, wherein the means for buildup determination comprising means for measuring a pressure increase while an evacuation is stopped, the means for buildup determination determines when the pressure increase is smaller than a predetermined value.
18. The water regeneration apparatus according to claim 16, wherein the means for buildup determination determines during the second roughing step that pressure and temperature in the portion are to be reduced to less than the third reduced pressure and less than 273 K respectively.
Type: Application
Filed: Aug 4, 2011
Publication Date: Feb 9, 2012
Applicant: SUMITOMO HEAVY INDUSTRIES, LTD. (Tokyo)
Inventor: Ryosuke Tsuyuki (Saitama)
Application Number: 13/137,296
International Classification: F25C 5/02 (20060101);