JPH04170309A - Method for recovering argon - Google Patents

Abstract

PURPOSE:To miniaturize equipment, to reduce power and to efficiently recover argon by introducing the waste gas from a specified oxygen aeration stage into an adsorptive separation means using zeolite through an adsorptive separation means using moleculer-sieve carbon. CONSTITUTION:The waste gas from the oxygen aeration stage of a water treating plant using an oxygen-enriched gas obtained by a first adsorptive separation means using zeolite as an adsorbent is introduced into a second adsorptive separation means using molecular-sieve carbon as the adsorbent, and then introduced into a second adsorptive separation means using zeolite as the adsorbent. The waste gas is then introduced into a third adsorptive separation means using zeolite as the adsorbent to remove the oxygen, carbon dioxide, nitrogen, etc., contained in the gas, and argon is recovered. Since this recovery method effectively utilizes the waste gas from an oxygen aeration tank which has been discharged as such, a water treating plant having this oxygen aeration tank is efficiently operated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for recovering argon, and particularly to a method for separating and recovering argon contained in exhaust gas discharged from an oxygen aeration process of water treatment equipment.

[Conventional technology]

Conventionally, in sewage treatment and the like, oxygen is blown into wastewater to decompose and remove organic substances that are pollutants in the wastewater by aerobic microorganisms. In this so-called oxygen aeration, the oxygen blown into the water is
Oxygen gas obtained by cryogenic separation or liquid oxygen can be vaporized and used, but due to cost considerations, PSA (Pr
Oxygen-enriched gas obtained by treating air with essureSwing Adsorption (pressure swing adsorption separation method) is generally used.

By the way, the oxygen-enriched gas obtained by PSA using such synthetic zeolite as an adsorbent is enriched with argon, which has similar adsorption characteristics to oxygen to synthetic zeolite. For example, by treating raw air to create an oxygen concentration of 90%
When obtaining an oxygen-enriched gas, argon in the air is also concentrated in substantially the same way as oxygen, so the argon concentration in the oxygen-enriched gas is about 4%, which is about four times the argon concentration in the air.

Furthermore, when oxygen aeration is performed by blowing oxygen-enriched gas with such a composition into wastewater, only the oxygen in the oxygen-enriched gas is consumed by microorganisms, so there is no oxygen in the exhaust gas released from the oxygen warming tank. Argon will be concentrated. In particular, in recent oxygen aeration tanks, the oxygen usage efficiency has reached approximately 90%, so the argon concentration in the exhaust gas is more than 10 times the argon concentration in the air.

[Problem to be solved by the invention]

However, in conventional water treatment facilities, the above exhaust gas is
The reality is that the argon is released into the atmosphere after post-processing such as deodorization, but it is possible to collect and recycle argon in the exhaust gas emitted from processes such as steel manufacturing that use argon-based gases. While it is being used
Alcon in the gas discharged from the wastewater oxygen aeration process has been overlooked as an argon source.

Therefore, the present invention focuses on the argon that is concentrated in the gas discharged from the oxygen warming process of the wastewater, and aims to provide a method that can economically recover the argon.

[Means to solve the problem]

In order to achieve the above object, the argon recovery method of the present invention includes, as a first configuration, water treatment using an oxygen-enriched gas obtained by a first adsorption separation means using zeolite as an adsorbent. The exhaust gas discharged from the oxygen aeration process of the equipment is introduced into a second adsorption/separation means using molecular sieve carbon as an adsorbent, and then introduced into a third adsorption/separation means using zeolite as an adsorbent, It is characterized by removing oxygen, carbon dioxide, nitrogen, etc. contained in the exhaust gas.

Furthermore, a second configuration of the present invention is to introduce the exhaust gas into a second adsorption/separation means using zeolite as an adsorbent,
The exhaust gas is then introduced into a third adsorption/separation means using molecular sieve carbon as an adsorbent to remove oxygen, carbon dioxide, nitrogen, etc. contained in the exhaust gas.

[For production]

Oxygen, carbon dioxide, and nitrogen present in the exhaust gas are separated from argon by either adsorption separation means using molecular sieve carbon as an adsorbent or adsorption separation means using zeolite as an adsorption agent.

Therefore, by sequentially performing both of the adsorption and separation means described above, argon in the exhaust gas can be separated and recovered.

〔Example〕

Hereinafter, the present invention will be explained in more detail based on embodiments shown in the drawings.

First, FIG. 1 shows a first embodiment of the present invention, and shows an embodiment corresponding to the first configuration described above.

First, the raw air to obtain the oxygen necessary for oxygen aeration is
The oxygen is introduced into a first adsorption separation means (hereinafter referred to as oxygen PSA) 1. This oxygen PSAI uses zeolite as the main adsorbent to separate oxygen and nitrogen in the raw air, and produces oxygen-enriched gas with an oxygen concentration of about 90% for oxygen aeration. In this way, the above-mentioned zeolite-based adsorbent is filled into a plurality of adsorption towers, and the plurality of adsorption towers are sequentially switched to an adsorption process, a regeneration process, and a repressurization process to continuously supply the oxygen-enriched gas. This is what you get.

The oxygen-enriched gas obtained by the oxygen PSAI is introduced into an oxygen aeration tank 2 of a sewage treatment facility, etc., contacts water in the oxygen warming tank 2, supplies oxygen to microorganisms for decomposing organic matter,
Most of the oxygen is consumed.

This oxygen aeration I! 2 consists of one or more tanks of various capacities depending on the amount of water to be treated, and is a closed type in order to increase the utilization efficiency of oxygen blown into the water and to recover exhaust gas. It is formed so that oxygen can be brought into contact with water repeatedly by providing wings or the like or by providing a circulation system. By forming oxygen aeration e12 in this way, the oxygen usage efficiency can be increased to 90%.
It can be raised to a certain extent.

The exhaust gas discharged from the oxygen aeration tank 2 is recovered through an exhaust gas recovery system, and is temporarily stored in a buffer tank 3 in order to equalize fluctuations in the composition and flow rate of the exhaust gas. A predetermined flow rate of the exhaust gas in the buffer tank 3 is extracted, the pressure is increased by a compressor as necessary, and the exhaust gas is introduced into a second adsorption/separation means (hereinafter referred to as carbon PSA) 4. This carbon PSA4 uses molecular sieve carbon as the main adsorbent and alumina gel, silica gel, etc. as the secondary adsorbent to separate and remove oxygen, carbon dioxide, and moisture from exhaust gas. A plurality of adsorption towers are filled with the agent, and the plurality of adsorption towers are sequentially switched to an adsorption step, a pressure equalization step, a regeneration step, and a pressure equalization step to separate and remove oxygen, carbon dioxide, and water in the exhaust gas. Therefore, in the adsorption tower in this carbon PSA4,
By using the molecular sieve carbon in the upper part and a desiccant such as alumina gel, silica gel, etc. in the lower part, that is, the inlet side, the moisture in the exhaust gas can be removed at the same time, but if a cooling type dehumidifier is installed separately, The adsorption tower may be filled only with molecular sieve carbon.

Furthermore, the waste gas derived from the adsorption tower in the regeneration process of the adsorption tower in this carbon PSA4 contains not only the oxygen and carbon dioxide gas after the separation, but also nitrogen and argon, and the argon concentration is usually is still significantly higher than atmospheric argon concentrations. Therefore, by circulating and merging the waste gas derived from the carbon PSA 4 with the raw material air introduced into the oxygen PSAI without directly releasing it into the atmosphere, the argon in the waste gas discharged from the oxygen aeration tank 2 can be efficiently removed. Argon can be recovered without waste, and the efficiency of recovering argon can be improved. In addition, the waste gas derived from the carbon PSA4 also contains a high concentration of oxygen separated by the carbon PSA4, so oxygen can also be used effectively by circulating and combining the waste gas with the raw air. I can do it.

- The exhaust gas from which oxygen and carbon dioxide gas have been separated by the carbon PSA 4 is then introduced into a third adsorption separation means (hereinafter referred to as zeolite PSA) 5. This zeolite PSA
No. 5 uses zeolite as the main adsorbent to separate and remove nitrogen from exhaust gas, and a plurality of adsorption towers are each filled with the above-mentioned zeolite-based adsorbent, and the plurality of adsorption towers are sequentially loaded. The nitrogen in the exhaust gas is separated and removed by switching to the pressure adsorption process, regeneration process, and repressurization process. The pressure during the pressurized adsorption step and the regeneration step can be appropriately set depending on the composition of the exhaust gas and the target composition of the recovered gas to be derived. Either of these may be used, and if necessary, purging with a non-adsorptive gas may be performed.

In this way, the exhaust gas discharged from the oxygen aeration tank 2 of a sewage treatment facility etc. is treated with carbon PSA4 and zeolite P-,
By sequentially introducing the gas into S A 5, oxygen and carbon dioxide in the exhaust gas containing a high concentration of argon are
In step 4, nitrogen in the exhaust gas is removed by the zeolite PSA5, and argon with a purity of 90% or more can be recovered from the zeolite PSA5. The purity of the recovered argon varies depending on the operating conditions of the carbon PSA4 and the zeolite PSA5, and it is possible to recover argon of appropriate purity depending on the purpose for which the recovered argon is used.

In addition, the exhaust gas is
By treating with both adsorption and separation means of sA5, the malodorous components in the exhaust gas are also adsorbed by the respective adsorbents, so that the treatment of the malodorous components is also facilitated.

Here, an example of the argon recovery operation in the process of the above embodiment will be explained. First, raw air 900ONn1'/h
is introduced into the oxygen PSAI and subjected to adsorption separation treatment to separate nitrogen from the air and produce 90% oxygen.

Oxygen enriched gas 120O with 4% argon and 6% other nitrogen
It becomes Nr111/h. This oxygen-enriched gas is introduced into the oxygen aeration tank 2, and oxygen is consumed through oxygen aeration treatment.
50% oxygen, 15% argon, 27% nitrogen, 8% carbon dioxide
% exhaust gas 100Nr//h is discharged. This exhaust gas is temporarily stored in the buffer tank 3, and then pressurized to an operating pressure of 5 kg/c G by a compressor and introduced into the carbon PSA 4. In carbon PSA4, a plurality of adsorption towers are each filled with 250 kg of molecular sieve carbon with a pore diameter of 3A to 4A and 50 kg of alumina gel as adsorbents, and water is adsorbed and separated along with oxygen and carbon dioxide gas by the adsorbents. Note that the alumina gel is filled at the entrance of the adsorption tower, and water is removed there. Non-adsorbent argon and nitrogen pass through the adsorbent;
15Nry of argon-enriched gas with 35% argon, 64% nitrogen, and 1% oxygen! '/h is derived from carbon PSA4. This argon Th gas is then introduced into a zeolite PSA5 in which an adsorption tower consisting of a plurality of 10 kg of molecular sieves 5A with a pore diameter of 5A is packed, and the nitrogen contained therein is adsorbed by the adsorbent and separated, resulting in 97% argon,
3Nrrr/h of crude concentrated argon containing 1% nitrogen and 2% oxygen is obtained. On the other hand, the waste gas 85 Nrrl'/h derived in the carbon PSA 4 regeneration process has a composition of 58.6% oxygen, 11.5% argon, and 20% nitrogen.
5%, carbon dioxide gas 9.4%, and contains a large amount of argon and oxygen. This allows effective use of argon and oxygen.

Furthermore, since the waste gas derived from the regeneration process of the zeolite PSA5 still contains a considerable concentration of argon, this waste gas is also circulated into the raw material air of the rII element PSAI to recover the argon it contains. can do.

FIG. 2 shows a second embodiment of the present invention.
An example corresponding to the configuration is shown.

This example uses zeolite PSA, which is the third adsorption separation means in the first example, as the second adsorption separation means.
5, and carbon PSA4, which is the second adsorption separation means in the first embodiment, is used as the third adsorption separation means.
This is what was used.

First, the raw material air is treated by the oxygen PSAI, which is the first adsorption/separation means, to become an oxygen-enriched gas, as in the first embodiment, and is supplied to the oxygen aeration tank 2 as oxygen gas for oxygen warming. The exhaust gas discharged from the oxygen aeration tank 2 is temporarily stored in a buffer tank 3, and then introduced into zeolite PSA5, which is a second adsorption separation means that uses zeolite as the main adsorbent and alumina gel as the secondary adsorbent. be done. In this zeolite PSA5, nitrogen is an easily adsorbed component to zeolite and alumina gel.

Carbon dioxide gas and moisture are adsorbed and separated, and non-adsorbed components oxygen and argon are derived. This gas containing oxygen and argon as main components is introduced into the carbon PSA 4, and the oxygen is adsorbed on the carbon molecular sieve, thereby separating argon and oxygen. As a result, highly concentrated recovered argon can be obtained from the carbon PSA4.

In addition, the waste gas discharged from the adsorption tower in the regeneration process of the adsorption tower in the above-mentioned zeolite PSA5 contains argon and oxygen in addition to the nitrogen, carbon dioxide, and moisture after the separation. The concentration is considerably higher than that in the middle of the day. Therefore, the argon in the exhaust gas discharged from the oxygen aeration tank 2 can be efficiently recovered by circulating and combining the waste gas from the zeolite PSA5 with the raw material air introduced into the oxygen PSAI without releasing it into the atmosphere. It is possible to do so.

Here, an example of the argon recovery operation in the process of the second embodiment will be explained. In this recovery operation, conditions are set so that the purity of the recovered argon is such that it can be used as is, for example, as a seal gas for welding.

First, in the same way as above, 900 ONrri'/h of raw material air is treated with oxygen PSAI and 120ONrI? /h, and then introduced into the oxygen aeration tank 2, and during the wastewater purification process, the oxygen aeration tank 2 contains 50% oxygen, 15% argon,
Exhaust gas of 27% nitrogen and 8% carbon dioxide 100Nrrl'/
h is discharged and stored in the buffer tank 3. This exhaust gas is generated at the operating pressure 2 of the compressor Nyori Zeolite PSA5.
The pressure is increased to kg/cJ and introduced into the zeolite PSA5.

This zeolite PSA5 has a pore size of 5A as an adsorbent.
Using 100 kg of Molecular Sieves 5A and 15 kg of alumina gel, this adsorbent is packed into an adsorption tower consisting of a plurality of alumina gel on the inlet side and Molecular Sieves 5A on the outlet side, and moisture is removed together with nitrogen and carbon dioxide gas. Separate by adsorbing on adsorbent, argon 23%, 1
tHK75%.

4ONrrl'/h of argon-enriched gas with 0.1% nitrogen is introduced. This argon-enriched gas continues to contain carbon P.
Introduced in SA4. The carbon PSA4 has a pore diameter of 3
The structure is such that multiple adsorption towers are filled with molecular sieve carbon 130 A to 4A and used selectively, and the oxygen contained therein is adsorbed and separated, leaving 99% argon and 0.4% nitrogen.
%, high purity argon with 0.6% oxygen 3.7Nr111/
h is collected.

On the other hand, the composition of the waste gas 6ONn1'/h derived in the regeneration process of the zeolite PSA5 is oxygen 3
3%, argon 9%, nitrogen 45%, and carbon dioxide gas 13%, and since it contains a large amount of argon and oxygen, it is circulated in the raw material air introduced into the oxygen PSAI, and the argon and oxygen in the waste gas are We aim to make effective use of

Further, since the waste gas in the carbon PSA 4 regeneration process also contains a considerable concentration of argon, it is possible to further increase the recovery rate by similarly circulating it in the raw material air for oxygen PSAI.

In this way, oxygen PS using zeolite as an adsorbent
The exhaust gas from the oxygen aeration tank 2, which uses the oxygen-enriched gas obtained by AI as the oxygen source, is mixed with carbon PSA4 and zeolite PSA.
Argon can be easily recovered by processing in step 5. In particular, the present invention utilizes the fact that argon is concentrated due to natural oxygen consumption during the wastewater purification action of an oxygen warming tank in wastewater treatment, so argon can be directly separated from air or obtained by oxygen PSA. Compared to separating argon from oxygen-enriched gas, the oxygen concentration in the process gas is lower, so argon can be recovered extremely efficiently. Furthermore, by selecting the operating conditions for carbon PSA4 and zeolite PSA5, the purity of the recovered argon can be set appropriately. You can also get

In all of the above examples, the aeration tank in the wastewater purification process is a normal aeration tank for wastewater treatment, so by making the aeration tank have a structure for the purpose of recovering argon, the argon concentration in the exhaust gas can be further reduced. It is possible to achieve a high concentration and a high recovery rate.

Furthermore, high purity argon or liquefied argon can be obtained by mixing the recovered argon obtained in the above operation into the argon collection system of the cryogenic separation plant. It is also possible to add hydrogen to the recovered argon, convert the trace amount of remaining oxygen into water through a catalytic reaction and remove it, and then liquefy the argon using liquid oxygen, liquid nitrogen, etc. and supply it. Furthermore, low-boiling point components such as nitrogen and added hydrogen can be volatilized and removed to highly purify the argon product, and then a high-purity liquefied argon product can be obtained.

〔Effect of the invention〕

As explained above, the argon recovery method of the present invention
Exhaust gas discharged from an oxygen aeration process using oxygen-enriched gas obtained from oxygen PSA is sequentially introduced into carbon PSA and zeolite PSA to remove oxygen, carbon dioxide, nitrogen, etc. contained in the exhaust gas. Therefore, compared to the method of recovering argon through PSA operation using air as a raw material, it utilizes the natural argon concentration effect of wastewater purification in the oxygen aeration tank of water treatment, which reduces the size of equipment and power consumption. This makes it possible to obtain argon extremely efficiently. In particular, the present invention effectively utilizes the exhaust gas from the oxygen aeration tank, which was conventionally released as it is, so that it is possible to efficiently operate a water treatment facility having the oxygen aeration tank.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing a first embodiment of the invention, and FIG. 2 is a flowchart showing a second embodiment of the invention. 1...Oxygen PSA 2...Oxygen aeration tank 3...
・Buffer tank 4... Carbon PSA5... Zeolite PSA

Claims (1)

[Scope of Claims] 1. Exhaust gas discharged from the oxygen aeration process of water treatment equipment that uses oxygen-enriched gas obtained by the first adsorption separation means using zeolite as an adsorbent, is adsorbed with molecular sieve carbon. introducing it into a second adsorption separation means using zeolite as an adsorbent, and then introducing it into a third adsorption separation means using zeolite as an adsorbent to remove oxygen, carbon dioxide, nitrogen, etc. contained in the exhaust gas. An argon recovery method characterized by: 2. The exhaust gas discharged from the oxygen aeration process of water treatment equipment that uses the oxygen-enriched gas obtained by the first adsorption separation method using zeolite as an adsorbent is transferred to the second method using zeolite as an adsorbent. Argon is introduced into an adsorption separation means, and then introduced into a third adsorption separation means using molecular sieve carbon as an adsorbent to remove oxygen, carbon dioxide, nitrogen, etc. contained in the exhaust gas. Collection method.