JP2002115965A - Method of recovering rare gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the quantity of consumed energy of the reboiler heat source of the first condensing column of rare gas, by enabling xenon to be separated and recovered efficiently. SOLUTION: A method of recovering rare gas from liquefied oxygen containing the rare gas consisting of krypton and xenon taken out of the lower part of the upper column of an air liquefying separator 1, comprises a process of introducing the liquefied oxygen into the first condensing column 6, taking out condensed liquefied oxygen 9 where the rare gas is condensed from the bottom of the column, returning its one part to the first condensing column via a reboiler 11, taking out oxygen gas 8 from the column head, and returning its one part to the first condensing column; and a process of introducing a part of the above condensed liquefied oxygen into the second condensing column 14 via a decarbonized hydrogen processor 13, and taking out rare gas from the column bottom. Besides, the heat source of the above reboiler 11 is made nitrogen gas or dry air, and the inner pressure of the first condensing column 6 is decompressed to or under atmospheric pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a rare gas composed of krypton and xenon, particularly xenon, which is enriched in liquefied oxygen at the lower part of the upper part of a rectification column of an air liquefaction separation apparatus.

[0002]

2. Description of the Related Art Rare gases such as krypton and xenon are:
Since it is concentrated in the liquefied oxygen of the air liquefaction separation unit,
This is further concentrated and recovered as a rare gas of 95% or more. Further, rare gas containing 95% or more of krypton and xenon is further distilled and separated and recovered.

[0003] The rare gas recovery apparatus repeats the steps of rectification, adsorption, catalytic reaction and the like to obtain a rare gas liquid of 90 to 95% of krypton and 5 to 10% of xenon, and then separates krypton and xenon if necessary. I am trying to do it. Generally, liquefied oxygen extracted from the upper and lower towers of an air liquefaction separator, for example, from the vicinity of a reboiler condenser called a main condenser, a first concentration tower, a hydrocarbon adsorber, a catalytic reactor for oxidizing hydrocarbons A rare gas is recovered through a recovery step including an adsorber for adsorbing and removing water and carbon dioxide generated in the catalytic reactor and a second concentration tower, and the rare gas is further rectified to obtain krypton and xenon.

The main purpose of the air liquefaction / separation apparatus is to separate it into oxygen and nitrogen, but the secondary purpose may be to recover rare gases. When recovering rare gas, krypton has a problem that it is easily entrained by oxygen because it has a boiling point close to that of oxygen.To reduce this, the lower part of the upper tower of the air liquefaction and separation unit is used. A tray is provided at the top to increase the rare gas separation efficiency. In this case, the rare gas concentration in the liquefied oxygen near the reboiler condenser also increases,
The concentration of hydrocarbons such as methane, which has a higher boiling point than oxygen, also increases. Hydrocarbons in liquefied oxygen are known to increase the risk of explosion as their concentration increases, which increases as the rare gas recovery rate is increased.
However, since krypton and xenon contained in the atmosphere are extremely small at 1.14 ppm and 0.086 ppm, respectively, it is necessary to increase the concentration rate in order to recover them at a high level. Concentration of hydrocarbons contained in the air in the vicinity is inevitable. In the past, in order to prevent a decrease in the capacity utilization rate of the rare gas recovery process, the emphasis was on increasing the recovery rate of krypton, which accounts for the majority of the rare gas, but the demand for xenon, which is much less abundant than krypton, was It is increasing. Therefore, at the expense of krypton recovery, xenon has a boiling point sufficiently higher than that of oxygen, and not only does not require a tray to increase the separation efficiency, but also the concentration of hydrocarbons, especially methane, in liquefied oxygen is so low. It has been found that it has the advantage of not increasing.

As a method for recovering rare gas, Japanese Patent Application Laid-Open No. 7-2
Japanese Patent No. 70067 proposes a method in which a part of the top gas from the second concentration tower is purified and then circulated.
Japanese Patent Application Laid-Open No. 79756/1999 proposes a method in which hydrocarbons are removed from concentrated liquefied oxygen from the first concentration tower and a part of the liquefied oxygen is circulated at the bottom of the first concentration tower. In addition, Japanese Patent Application Laid-Open No. 7-9
No. 1826 proposes a method for temporarily storing a rare gas liquid from the bottom of the second concentration tower.
No. 81 proposes a method in which a part of the catalytic reaction and the adsorption step can be omitted. However,
It does not teach suppressing hydrocarbon enrichment in an air liquefaction separator or reducing the energy consumption of the reboiler heat source in the first enrichment tower.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a purification method capable of efficiently separating and recovering xenon, in particular, and suppressing the concentration of hydrocarbons in an air liquefaction separator. . It is another object of the present invention to reduce the energy consumption of the reboiler heat source of the first concentration tower.

[0007]

According to the present invention, there is provided a method for recovering rare gas from liquefied oxygen containing a rare gas consisting of krypton and xenon taken out from the upper and lower portions of an air liquefaction / separation apparatus. Introduced into the column, take out concentrated liquefied oxygen in which the rare gas is concentrated from the bottom of the tower, return at least a part of this to the first concentration tower via a reboiler, take out oxygen gas from the top of the tower, and remove at least a part of this. Returning the first concentrated tower via a condenser, dehydrocarbonizing a part of the concentrated liquefied oxygen, introducing the dehydrocarbonated concentrated liquefied oxygen into the second concentrated tower, Removing the oxygen gas from the top and removing the rare gas liquid from the bottom of the tower, and using a nitrogen gas as the heat source of the reboiler, and reducing the internal pressure of the first concentration tower to a pressure lower than the atmospheric pressure. It is a method of recovering rare gas. Here, it is advantageous to increase the ratio of xenon / krypton in the liquefied oxygen taken out from the air liquefaction / separation device to at least twice the abundance ratio in the atmosphere without concentrating hydrocarbons,
It is also advantageous that the rare gas to be recovered is mainly xenon. The liquefied oxygen in each step may be partially gasified by heat intrusion.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a flow sheet showing one embodiment of the present invention. Since this flow sheet is for explaining the characteristic parts of the present invention, parts not directly related to the present invention are omitted or greatly simplified. The air liquefaction separation device 1
It has an upper tower 1a and a lower tower 1b, and a reboiler condenser 2 is provided below the upper tower. Air 3 is supplied from the lower tower 1b, separated by cryogenic cooling, and nitrogen gas N ₂ , oxygen gas O ₂ , and argon, which are products, are respectively removed from the upper tower 1a. The component having a boiling point or higher of the oxygen gas including the rare gas is condensed and accumulated in the liquefied oxygen phase 4, and is supplied to the first concentration tower 6 through the pipe 5. Further, the air liquefaction / separation apparatus 1 may have a tray above the reboiler condenser 2 in order to increase the recovery rate of the rare gas, but it is preferable that the air liquefaction / separation apparatus 1 be substantially free from the problem that the hydrocarbon concentration increases. .
In addition, a tank may be provided between the pipe 5 and the first enrichment tower 6, which makes it possible to adjust the extraction amount in accordance with the fluctuation of the air liquefaction / separation apparatus, and to stabilize the operation of the air liquefaction / separation apparatus. To contribute. When there are a plurality of air liquefaction / separation devices, it is preferable to connect the plurality of air liquefaction / separation devices and the tank to stabilize the operation of the rare gas recovery equipment and the air liquefaction / separation device. Further, a switchable hydrocarbon adsorber or a heat exchanger may be provided between the pipe 5 and the first concentration tower 6.

[0009] The liquefied oxygen 4 supplied from the pipe 5 is separated in the first condensing column 6 and oxygen-free oxygen 8 is supplied from the top of the column.
However, concentrated liquefied oxygen 9 in which the rare gas is concentrated is taken out from the bottom of the column. The impurity-free oxygen 8 taken out from the top of the column is liquefied in the condenser 10, and at least a part thereof is returned to the first concentration column 6. In addition, if necessary, a part may be returned to the liquefied oxygen phase 4 near the reboiler condenser 2 of the air liquefaction / separation apparatus 1 to reduce the hydrocarbon concentration. There is an advantage that this is not required because the hydrocarbon concentration is low.

On the other hand, at least a part of the concentrated liquefied oxygen 9 from which the rare gas extracted from the bottom of the first concentration tower 6 is concentrated is returned to the lower part of the first concentration tower 6 via the reboiler 11. Here, nitrogen gas or dry air is used as a heat source of the reboiler 11, but nitrogen gas is preferable.
Hereinafter, a case where nitrogen gas is used as a heat source of the reboiler 11 will be described, but the present invention can be applied to dry air accordingly. The temperature of this nitrogen gas needs to be higher than the temperature by several degrees or more because it is necessary to increase the efficiency of heat transfer to the concentrated liquefied oxygen 9 passing through the reboiler 11. For example, when the boiling point of oxygen is −183 ° C. (atmospheric pressure), the temperature of the nitrogen gas needs to be −181 ° C. or higher, for example. Here, due to the heat balance between the condenser 10 and the reboiler 11 using nitrogen as a medium (cooling heat source), it is preferable that the nitrogen gas used as the heat source of the reboiler 11 becomes liquefied nitrogen by the latent heat of vaporization of the concentrated liquefied oxygen. . That is, the temperature of the nitrogen gas is higher than the boiling point of the concentrated liquefied oxygen 9, and the pressure of the nitrogen gas is desirably a pressure at which the liquid is liquefied at the boiling point of the concentrated liquefied oxygen 9. Therefore, in order to liquefy nitrogen gas having a boiling point of -196 ° C (atmospheric pressure) at -183 ° C, a pressure of 3 kg / cm ² · G or more is required. If the operating pressure of the first concentrating tower is equal to or higher than the atmospheric pressure, the required pressure further increases.

Conventionally, since the first enrichment tower 6 is operated at a pressure higher than the atmospheric pressure, nitrogen gas used as a reboiler heat source has required a high pressure. Has been found to be more energetically favorable. In order to reduce the operating pressure of the first concentrating tower 6, it is necessary to reduce the pressure with the vacuum device 12, but when comparing the operating energy of the vacuum device 12 with the operating energy for increasing the pressure of the nitrogen gas, It has been found that reducing the operating pressure of the first enrichment tower 6 to a reduced pressure from normal pressure to about 300 Torr is advantageous in terms of energy saving. For example,
If the operating pressure of the first concentrating tower 6 is about 500 Torr, the boiling point of the concentrated liquefied oxygen 9 will be lowered to about -187 ° C., and the temperature of the nitrogen gas supplied as the heat source of the reboiler 11 will be -18.
The temperature may be about 5 ° C., and at this temperature, the liquid is liquefied at about 2-3 kg / cm ² · G. From such a viewpoint, the operating pressure of the first concentration tower 6 is equal to or lower than normal pressure, preferably lower than or equal to about 700 Torr, and more preferably lower than or equal to about 700 Torr, more preferably 600 to 400 Torr.
Has been found to be advantageous. The nitrogen gas supplied as a heat source for the reboiler 11 is 2 to 4 kg.
It can be liquefied by the reboiler 11 at about / cm ² · G. It is advantageous that the liquefied nitrogen liquefied here is used as a cold source for the condenser 10. In addition, in the vacuum device,
A vacuum pump or an ejector may be used. Further, when the liquid oxygen of the first concentration tower is used for other equipment by a pump, if the pressure in the tower is reduced, it is necessary to increase the height of the first concentration tower to prevent cavitation. In some cases, it is preferable to maintain the pressure as low as possible at atmospheric pressure.

On the other hand, the concentrated liquefied oxygen 9 taken out from the first enrichment tower 6 contains not only rare gases but also hydrocarbons. Therefore, after being dehydrocarbonated, it is sent to the second enrichment tower. preferable. At least a portion is sent to the dehydrocarbon treatment device 13, and after being subjected to the dehydrocarbon treatment, is sent to the second concentration column 14. The configuration of the dehydrocarbonation device 13 can be a known configuration. As an example, the concentrated liquefied oxygen 9 is stored in a tank if necessary, then heated and vaporized in a heat exchanger, and then sent to a catalytic reactor to oxidize hydrocarbons, mainly methane, into water and carbon dioxide. I do. The gas removed from the catalytic reactor is sent to the adsorber,
After adsorbing water and carbon dioxide gas, it is cooled by a heat exchanger to be liquefied oxygen, and then supplied to the second concentration tower 14. Second concentration tower 1
An oxygen gas 15 is taken out from the top of column 4 and a rare gas liquid 16 in which rare gas is concentrated to about 95% is taken out from the bottom of the column. The rare gas liquid 16 is further sent to a rectification column if necessary, and separated into krypton and xenon.

The air liquefaction / separation apparatus 1 is operated so that the hydrocarbon concentration in the liquefied oxygen phase 4 is not excessively increased. For this purpose, a part of the hydrocarbon having a boiling point lower than that of xenon is extracted therefrom. Advantageously, it is entrained by oxygen. Although hydrocarbons mainly composed of methane have a lower boiling point than xenon, they also have low krypton, so that the recovery of krypton naturally decreases. Therefore, it is preferable to operate the air liquefaction / separation apparatus 1 under conditions where the abundance ratio of xenon / krypton in the atmosphere is twice or more, preferably five times or more.

By the way, the operating conditions of the method of the present invention described with reference to the flow sheet of FIG. 1 can employ known conditions, and a part of the process can be omitted or added, or modified by referring to the known method. It is possible. The hydrocarbon content at the outlet of the dehydrocarbon treatment device 13 is 0.05 pp.
m or less.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments. First, 150 liters of air 3 is supplied to the air liquefaction separation device 1.
Liquefied oxygen phase 4 concentrated at 10 000 Nm ³ / hr and concentrated to 10 to 50 ppm of krypton and 5 to 50 ppm of xenon, and 5 to 50 ppm of hydrocarbon (mainly methane).
To 450 Nm ³ / hr into the middle stage of the first concentration column 6. At the bottom of the first concentration tower 6, a reboiler 11 using -182 ° C. and a nitrogen gas of 3 kg / cm ² · G as a heating source is provided, and a condenser 10 using liquefied nitrogen as a cold source is provided at the top. Is provided. Liquefied nitrogen condensed by the reboiler 11 was used as at least a part of the liquefied nitrogen used as a cold source of the condenser 10. In the first concentration tower 6, the descending liquid and the rising gas from the top make gas-liquid contact, and rectification is performed. Condensed liquefied oxygen obtained by concentrating krypton and xenon 10- to 100-fold is obtained at the bottom of the first concentrating column 6, and impurities are greatly reduced from the top of the column, and oxygen gas 8 having a hydrocarbon concentration of about 5 ppm is obtained. At this time, a part of the oxygen gas 8 was drawn by the vacuum device 12 to maintain the pressure in the first concentration column 6 at 550 Torr.

Since the concentrated liquefied oxygen 9 also concentrates hydrocarbons (methane) in addition to krypton and xenon, the hydrocarbons are dehydrocarbonated by the dehydrocarbon treatment device 13.
In the dehydrocarbon treatment device 13, the concentrated liquefied oxygen is heated and vaporized by a heater, a heat exchanger, and the like, and is introduced into a catalytic reactor. Here, a predetermined amount of a noble metal catalyst such as platinum or palladium is charged, and a small amount of methane and a large amount of oxygen are reacted to form carbon dioxide and water. Here, the carbon dioxide concentration is set to 0.05 ppm or less. The reactor outlet temperature is usually 350 to 400 ° C. The space velocity is in the range of 500 to 6000 hr ^-1 . The gas led out of the catalytic reactor is introduced into a switchable adsorber, and carbon dioxide and water generated in the catalytic reaction step are adsorbed and removed.

The gas derived from the dehydrocarbon treatment unit 13 is further cooled or liquefied and introduced into the middle stage of the second concentration column 14 at about 50 Nm ³ / hr. This second concentration tower 11
Using a sieve tray or packing tray, the total actual number of stages of the enrichment section and recovery section of the column tower is 10 or more, preferably 20
Preferably, up to 40 rectification stages are provided. An oxygen gas 15 containing a very small amount of krypton is taken out from the top of the tower. From the bottom of the tower, krypton and xenon 9
A liquefied rare gas consisting of 0 to 95% and 5 to 10% of oxygen is taken out at about 60 L / hr.

When the amount of krypton and xenon recovered is constant, in the present embodiment, the operating pressure of the first concentration tower 6 is 550 Torr, and the nitrogen gas pressure of the reboiler 11 is 3 kg / c.
With m ² · G, the operating pressure 0 of the first rectifying column 6.
5 kg / cm ² · G, nitrogen gas pressure of reboiler 11 5 kg / cm ²
・ Required electric energy is 10% compared to G
Or more.

[0019]

As described above, rare gases in liquefied oxygen derived from an air liquefaction / separation apparatus can be efficiently purified, and the production cost and energy consumption of these gases can be greatly reduced. In addition, the air liquefaction separation device and the first concentration tower are simplified, so that their production is simplified and the operating energy efficiency is improved. In particular, xenon, whose demand is rapidly increasing, can be efficiently produced.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Air liquefaction separation apparatus 2 ... Reboiler condenser 3 ... Air 4 ... Liquefied oxygen phase 6 ... First concentration tower 8 ... Oxygen gas 9 ... Condensed liquefied oxygen 10 ... Condenser 11 ... Reboiler 12 ... Vacuum apparatus 13 ... Dehydrocarbon treatment Apparatus 14: Second concentration tower 16: Rare gas liquid

Claims (3)

[Claims] 1. A method for recovering rare gas from liquefied oxygen containing a rare gas consisting of krypton and xenon taken out from the upper and lower parts of an air liquefaction / separation apparatus, wherein the liquefied oxygen is introduced into a first concentration tower, Take out concentrated liquefied oxygen from which rare gas is concentrated, return at least a part of this to the first concentration tower via a reboiler, take out oxygen gas from the top, and pass at least a part of this through a condenser. Returning to the first enrichment tower, dehydrocarbonizing a part of the enriched liquefied oxygen, introducing the dehydrocarbonated enriched liquefied oxygen to the second enrichment tower and removing oxygen gas from the top of the tower Removing the rare gas liquid from the bottom of the tower,
And a method for recovering a rare gas, wherein the heat source of the reboiler is nitrogen gas or dry air, and the internal pressure of the first concentration tower is set to an atmospheric pressure or less. 2. The xenon / krypton ratio in the liquefied oxygen is substantially eliminated from a lower portion of the upper tower of the air liquefaction / separation device, wherein a tray for increasing the efficiency of separating rare gas is provided above the main condenser. The method for recovering rare gas described in the above. 3. The method according to claim 1, wherein the rare gas to be recovered is xenon.