KR102163161B1 - Method and apparatus for purifying argon - Google Patents

Abstract

An object of the present invention is to provide a method and apparatus suitable for purifying argon using a pressure swing adsorption method, reducing the pressure to a lower pressure even if there is a fluctuation in the amount of off-gas, and obtaining high-purity argon in a high yield.
In order to solve the above problem, the present method is a pressure swing adsorption method performed using adsorption towers 20A to 20C filled with an adsorbent, while the adsorption tower is at a relatively high pressure, and the mixed gas is introduced into the adsorption tower. Adsorption step of adsorbing impurities in the mixed gas to the adsorbent to derive argon-enriched gas from the adsorption tower, and counter-current decompression step of depressurizing the adsorption tower to desorb impurities from the adsorbent to extract gas from the adsorption tower Repeatedly performing a cycle including, and introducing the gas derived from the adsorption tower in the countercurrent decompression process into the gas holder 3 whose capacity is changed, while maintaining a substantially constant pressure in the gas holder 3 The gas in the gas holder 3 is extracted.

Description

Argon purification method and argon purification apparatus TECHNICAL FIELD [METHOD AND APPARATUS FOR PURIFYING ARGON}

The present invention relates to a method and apparatus for purifying argon using a pressure swing adsorption method.

As the atmosphere gas in the furnace in a silicon single crystal pulling up furnace, ceramic sintering furnace, vacuum degassing furnace for steelmaking, silicon plasma melting furnace for solar cells, polycrystalline silicon casting furnace, etc., a deep cooling device from air Argon obtained by is used. Since argon exists only 0.9% in air, its manufacturing cost is several times higher than that of oxygen or nitrogen. Therefore, it is useful to recover and reuse argon once used as the atmospheric gas, but argon used as the atmospheric gas in the furnace contains impurities such as carbon monoxide, carbon dioxide, hydrogen, and air, and the purity is lowered. So, in order to increase the purity of the recovered argon and to promote reuse in the furnace, oxygen is converted into water or carbon dioxide by catalytic reaction with hydrogen or carbon monoxide, and then by pressure swing adsorption (PSA method). Purification by removing impurities has been proposed. Purification of argon by the PSA method is, for example, a process of introducing a mixed gas containing argon under high pressure into an adsorption tower filled with an adsorbent to adsorb impurities to the adsorbent, and to derive the gas enriched with argon. And, the cycle including the step of decompressing the inside of the adsorption tower to desorb impurities from the adsorbent and extracting gas (off gas) from the adsorption tower is repeated. About the technique of purifying argon using the PSA method, it is described in patent document 1, for example.

In Patent Document 1, as a method of purifying argon, a storage tank is prepared in a gas line supplied with a source gas, and off-gas derived from a PSA (pressure swing adsorption method) adsorption tower and a TSA (thermal swing adsorption method: Thermal Swing Adsorption) adsorption tower is A part is introduced into the storage tank and off-gas to be discarded is recycled to increase the recovery rate of argon. In the pressure swing adsorption method, in order to obtain high purity argon at a higher recovery rate, it is known that it is effective to make the pressure at the time of desorption faster and at a lower pressure. When the pressure in the adsorption tower is lowered during the desorption operation, the gas desorbed from the adsorbent is released as off-gas from the adsorption tower, but the amount of gas discharged from the adsorption tower is large at the beginning of the desorption operation and decreases as it approaches the end. . However, in the prior art, since the gas line through which the off-gas flows is fixed, the flow resistance of the gas increases as the amount of gas from the adsorption tower increases, and the pressure in the space through which the off-gas flows is once increased during the desorption operation. . Such a pressure increase due to fluctuations in the amount of off-gas lowers the desorption and regeneration effect of the adsorbent and becomes an impediment factor in increasing the recovery rate and purity of argon, but in the above conventional technique, the recovery rate of argon due to fluctuations in the amount of off-gas The effect of deterioration or purity deterioration was not considered.

JP 2010-285317 A

The present invention was devised under such circumstances, and in the purification of argon performed using a pressure swing adsorption method, a method and apparatus suitable for obtaining high purity argon in a high yield by lowering the pressure to a lower pressure even if there is a fluctuation in the amount of off-gas. It is a task to provide.

The argon purification method provided by the first aspect of the present invention is a method for purifying argon from a mixed gas containing argon, and by a pressure swing adsorption method performed using an adsorption tower filled with an adsorbent, the adsorption tower is relatively Under high pressure, an adsorption process of introducing the mixed gas into the adsorption tower to adsorb impurities in the mixed gas to the adsorbent to extract the argon-enriched gas from the adsorption tower, and decompressing the adsorption tower to reduce impurities from the adsorbent. By desorption and repeatedly performing a cycle including a countercurrent decompression step of desorbing gas from the adsorption tower, introducing the gas derived from the adsorption tower in the countercurrent decompression step into a gas holder whose capacity is changed, in the gas holder It is characterized in that the gas in the gas holder is extracted while maintaining the pressure substantially constant.

Preferably, the gas holder accommodates gas to block contact with the atmosphere, and includes a blocking portion that is displaced according to the amount of the gas, and the capacity of the gas holder acts from the outside of the blocking portion toward the inside. The force acting from the inside to the outside of the blocking part is changed while maintaining a balance by the load and the pressure of the gas inside.

Preferably, the blocking portion includes a membrane-shaped member or a cover-shaped metal member.

Preferably, the gas holder has a weight supported or included in the blocking portion.

Preferably, the pressure swing adsorption method is performed by using a plurality of adsorption towers filled with an adsorbent, and the cycle decompresses the inside of one adsorption tower that has finished the adsorption process to bring gas from the one adsorption tower in parallel. At the same time as the derivation, further comprising a washing step of washing the other adsorption tower by introducing the derived gas as a cleaning gas into another adsorption tower in which the countercurrent depressurization process has been completed, and the cleaning process includes: A first washing step of deriving a first gas from the other adsorption tower until halfway, and a second washing step after the first washing step of deriving a second gas from the other adsorption tower, wherein the first gas is The gas is introduced into the gas holder, the second gas is discharged out of the system, and the gas drawn out from the gas holder is added to the mixed gas before being introduced into the adsorption tower.

Preferably, prior to introducing the mixed gas into the adsorption tower in the adsorption process, pretreatment is performed on the mixed gas to remove or denature at least a part of the impurities contained in the mixed gas, and lead out from the gas holder. The resulting gas is added to the gas that has undergone the pretreatment.

In the pressure swing adsorption method (PSA method), in order to obtain high-purity argon from an argon-based mixed gas containing carbon monoxide, carbon dioxide, hydrogen, oxygen, nitrogen, methane, etc. as impurities, in general, oxygen is Pretreatment is carried out to convert into water or carbon dioxide by reacting with hydrogen or carbon monoxide catalytically. After performing the pretreatment, impurities such as carbon dioxide, carbon monoxide, water and nitrogen are adsorbed and removed in the adsorption tower by a pressure swing adsorption method (PSA method) to purify argon. In order to obtain purified argon at a higher recovery rate, for example, a part of the gas (off gas) discharged from the adsorption tower is added to the mixed gas before being introduced into the adsorption tower and recycled. In the PSA method, when depressurizing the inside of the adsorption tower by desorption, if a vacuum pump is used, since the pressure is reduced over the flow path of the off gas in the adsorption tower, there is a possibility that air may penetrate.If air penetrates, the impurity concentration of the gas to be recycled decreases. It rises. In order to avoid such a situation, it is preferable to remove and desorb using a discharge pressure without using a vacuum pump, and in that means, increasing the pressure in the flow path through which the off-gas flows is faster and lower pressure increases the recovery rate. It was known, but no specific countermeasures were taken.

In order to solve this problem, the present inventor made the following analysis.

Regarding the gas pressure and the amount of gas during the desorption operation, if the pressure in the adsorption tower is lowered during the desorption operation, the amount of gas (off gas) extracted from the adsorption tower is large at the beginning of the desorption operation and decreases as the end approaches. It becomes. Therefore, if the space for the off-gas to flow is fixed, the resistance of the gas flow increases as the amount of gas from the adsorption tower increases, and the pressure of the space through which the off-gas flows increases once during the desorption operation. On the other hand, when the desorption operation proceeds and the amount of gas from the adsorption tower decreases, the gas flow resistance decreases, and the pressure in the space decreases.

In order to solve the above problems, the present inventors have studied intensively in order to reduce the desorption pressure at once without using a vacuum pump, or to quickly bring this pressure to the atmospheric pressure level. It was found that the desorption pressure can be reduced at once by varying the capacity without being fixed, and this pressure can be reduced to the atmospheric pressure level. Specifically, it has been found that this effect is achieved by installing a variable-capacity gas holder capable of changing the capacity of the gas at a position close to the adsorption tower, and introducing off-gas from the adsorption tower into the gas holder.

It has also been found that when the flow path of the off-gas from the adsorption tower is in a stable state at a low pressure, the gas pressure in the adsorption tower decreases at a faster rate, and impurities adsorbed from the adsorbent are desorbed more rapidly, thereby enhancing the effect of reduced pressure regeneration. That is, if the space (gas holder) in which the off-gas flows is increased or decreased according to the amount of off-gas while maintaining the balance with the atmospheric pressure, the flow path of the off-gas can be infinitely fixed to a pressure close to atmospheric pressure, and separation performance by the pressure swing adsorption method Can improve.

The argon purification apparatus provided by the second aspect of the present invention is an apparatus for purifying argon from a mixed gas containing argon, and the mixing in the adsorption tower by a pressure swing adsorption method performed using an adsorption tower filled with an adsorbent. A pressure for introducing a gas to adsorb impurities in the mixed gas to the adsorbent, to derive argon from the adsorption tower, and depressurizing the adsorption tower to desorb impurities from the adsorbent, and to extract off-gas from the adsorption tower. A fluctuating adsorption type gas separation device, a first gas line for supplying the mixed gas to the adsorption tower, a capacity variable gas holder for introducing and deducting the off-gas derived from the adsorption tower, and the And a second gas line for supplying the off-gas discharged from the adsorption tower to the gas holder.

Preferably, a body portion configured in the shape of a container, and a blocking portion accommodated in the body portion and displaceable while maintaining a gas-sealed state between the body portion, and according to the displacement of the blocking portion, the body portion And the amount of gas accommodated in the gas receiving portion partitioned by the blocking portion is changed.

Preferably, the blocking portion includes a membrane-shaped member or a cover-shaped metal member.

Preferably, the gas holder includes a weight portion supported or included in the blocking portion.

Preferably, a third gas line connecting between the gas holder and the first gas line so that gas derived from the gas holder can be added and supplied to the first gas line, and the second gas It is connected to the line and includes a fourth gas line for discharging the gas discharged from the adsorption tower to the outside of the system.

Preferably, a pretreatment unit for performing pretreatment for removing or modifying at least a part of impurities contained in the mixed gas is provided in the first gas line, and the third gas line comprises the first It is connected to the rear end of the pretreatment unit in the gas line of.

Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

In purifying argon using a pressure swing adsorption method from a mixed gas containing argon, a space (gas holder) for storing and discharging off-gas derived from the adsorption tower is changed in capacity according to fluctuations in the amount of off-gas. As a result, pressure fluctuations in the entire space through which the off-gas flows are eliminated and the pressure is maintained at a constant low pressure, so that the reduced pressure regeneration effect is enhanced and the argon recovery rate is improved. In addition, as a result, the amount of off-gas to be recycled does not fluctuate and is stable, so that it can be recycled and mixed with the raw material system, thereby improving the argon recovery rate of the entire system.

1 is a diagram showing a schematic configuration of an argon purification apparatus according to the present invention;
2 is a diagram showing a schematic configuration of an example of a pressure swing adsorption type gas separation device;
3 is a longitudinal sectional view showing a schematic configuration of an example of a gas holder;
4 is a view showing a gas flow state in steps 1 to 6 of the argon purification method according to the present invention;
5 is a view showing a gas flow state in steps 7 to 12 of the argon purification method according to the present invention;
Fig. 6 is a graph showing changes in internal pressure of a desorption pressure and capacity variable gas holder and a fixed capacity gas tank in a pressure swing adsorption method;
7 is a longitudinal sectional view showing a schematic configuration of another example of a gas holder;
Fig. 8 is a longitudinal sectional view showing a schematic configuration of another example of a gas holder.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

1 shows a schematic configuration of an argon purifying apparatus according to the present invention. The argon purifying apparatus X includes a pretreatment unit 1, a pressure swing adsorption type gas separation apparatus 2 (hereinafter referred to as "PSA apparatus 2"), a gas holder 3, and contains argon. It is configured to continuously purify argon while recovering the raw material gas.

The raw material gas contains argon as a main component and contains, for example, hydrogen, nitrogen, carbon monoxide, oxygen, and the like as impurities. The main impurity is, for example, hydrogen. Such a raw material gas is a mixture of impurities generated by processing in the furnace into argon used as an atmosphere gas in the furnace in a silicon crystal pulling furnace, a ceramic sintering furnace, a silicon plasma melting furnace for solar cells, and the like. , Discharged continuously or intermittently using a vacuum pump. The source gas is introduced into a gas line 41 for supplying gas to the adsorption towers 20A, 20B, and 20C described later.

The pretreatment unit 1 removes impurities that are difficult to remove from the source gas according to the pressure swing adsorption method (PSA method) performed in the PSA apparatus 2 at the rear stage. As impurities that are difficult to remove by the PSA method, oxygen and hydrogen are mentioned, for example. Among these, oxygen becomes an obstacle when the purified argon is reused as an atmosphere gas in the furnace, and thus the need for removal is high. The pretreatment unit 1 is a filter 11, a blower 12, a heater 13, a reactor 14A, 14B, an oxygen supply 15, a carbon monoxide supply 16 and a cooler, as shown in FIG. 1. Includes (17, 18). The filter 11, the blower 12, the heater 13, the reactors 14A and 14B, and the coolers 17 and 18 are provided in a gas line 41 and are connected in series on a gas path.

The filter 11 removes solid components such as dust and metal powder, which are often contained in the raw material gas that is the exhaust gas from the furnace, from the raw material gas. The raw material gas discharged from the furnace (not shown) and introduced into the gas line 41 is vibration-absorbed by the filter 11 and then boosted by the blower 12 and introduced into the heater 13. In the heater 13, the gas is heated to around 250° C. so that the oxidation reaction between hydrogen and carbon monoxide tends to occur.

Next, the source gas is introduced into the reactor 14A. The reactor 14A substantially removes hydrogen or carbon monoxide in the raw material gas by denaturing it by a catalytic reaction. Here, about 1.1 times of the reaction equivalent of hydrogen or carbon monoxide is added to the inlet of the reactor 14A via the oxygen supply device 15. That is, oxygen is excessively added to the reactor 14A. The reactor 14A is filled with a catalyst for accelerating the oxidation reaction of hydrogen or carbon monoxide. As such a catalyst, for example, a palladium catalyst or a ruthenium catalyst can be employed. In the reactor 14A, hydrogen and carbon monoxide are combusted to become water vapor and carbon dioxide.

The gas that has passed through the reactor 14A is cooled to about 150°C or less in the cooler 17, and is introduced into the reactor 14B. The reactor 14B denatures oxygen in the gas introduced into the reactor 14B by a catalytic reaction to substantially remove it. Here, in order to remove excess oxygen added in the reactor 14A, the inlet of the reactor 14B, through the carbon monoxide supply unit 16, for example, about 1.05 times the equivalent of the reaction with oxygen carbon monoxide. Is added. That is, carbon monoxide is added in excess to the reactor 14B. The reactor 14B is filled with a catalyst for accelerating the reaction of oxygen and carbon monoxide. As such a catalyst, a noble metal catalyst, for example, a palladium catalyst supported on alumina or a ruthenium catalyst can be employed. In the reactor 14B, oxygen and carbon monoxide react to form carbon dioxide. As a result, excess oxygen becomes carbon dioxide, and the gas passing through the reactor 14B is easily removed by a pressure swing adsorption method carried out using an adsorption tower filled with, for example, zeolite to be described later together with carbon monoxide or nitrogen. Then, the gas that has passed through the reactor 14B is cooled to room temperature in the cooler 18. Then, a part of the off-gas (to be described later) from the PSA device 2 is recycled and mixed with the gas that has passed through the cooler 18 through a gas line 46 to be described later.

As shown in Figs. 1 and 2, the PSA device 2 includes, for example, adsorption towers 20A, 20B, and 20C, a gas compressor 21, a cooler 22, and a drain tank 23. And, argon contained as a main component in the gas from the pretreatment unit 1 including lines 41 to 47 constituting a gas flow path is continuously concentrated and purified by a pressure swing adsorption method (PSA method).

The gas compressor 21 is installed in the gas line 41. The gas compressor 21 sends the gas that has passed through the pretreatment unit 1 toward the adsorption towers 20A, 20B, and 20C. The gas that has passed through the pretreatment unit 1 is compressed by the gas compressor 21 to, for example, about 850 kPaG, and the heat of compression is cooled and removed by the cooler 22. Subsequently, water is discharged from the drainage tank 23, and the gas is brought to room temperature.

In this way, the gas (mixed gas) provided to the PSA method via the drainage tank 23 contains carbon dioxide, carbon monoxide, nitrogen, and the like as impurities in addition to argon as a main component. An example of the composition of the gas mixture is 99.5 mol% of argon, 0.3 mol% of carbon dioxide, 0.02 mol% of carbon monoxide, and 0.18 mol% of nitrogen.

Each of the adsorption towers 20A, 20B, and 20C has gas passage ports 201 and 202 at both ends, and between the gas passage ports 201 and 202, impurities contained in the mixed gas (carbon dioxide, carbon monoxide, It is filled with an adsorbent for selectively adsorbing nitrogen). Examples of such an adsorbent include zeolite, carbon molecular sieve, alumina, and the like, and these may be used alone or in combination of multiple types. The type and number of adsorbents to be filled in the adsorption towers 20A, 20B, and 20C are determined according to the type and amount of impurities to be removed in the adsorption towers 20A, 20B, and 20C.

The gas line 41 is connected to each of the gas passage openings 201 of the main path 41' and the adsorption towers 20A to 20C in order to supply the mixed gas to the adsorption towers 20A, 20B, and 20C. It has branch paths 41A, 41B, and 41C. In the branch paths 41A to 41C, automatic valves 41a, 4lb, and 41c for switching between an open state and a closed state are provided.

The gas line 42 is a flow path for a product gas (a gas enriched with argon) drawn from each of the adsorption towers 20A to 20C, and each gas passage port 202 of the main path 42' and the adsorption towers 20A to 20C. It has branch paths 42A, 42B, and 42C each connected to the) side. In the branch passages 42A to 42C, automatic valves 42a, 42b, and 42c for switching between an open state and a closed state are provided.

The gas line 43 supplies a part of the product gas flowing through the gas line 42 (main path 42 ′) to the adsorption towers 20A to 20C, so that the main path 42 ′ of the gas line 42 ), and branch furnaces 43A, 43B and 43C each connected to each of the gas passage ports 202 of the adsorption towers 20A to 20C. In the main passage 43', a flow rate adjustment valve 431 is provided. In the branch passages 43A to 43C, automatic valves 43a, 43b, and 43c for switching between an open state and a closed state are provided.

The gas line 44 is a main passage 44' connected to the main passage 43' of the gas line 43 in order to connect either two of the adsorption towers 20A to 20C to each other, and the adsorption tower ( 20A to 20C) have branch paths 44A, 44B, and 44C each connected to each gas passage port 202 side. In the main path 44', a flow rate adjustment valve 441 is provided. The branch paths 44A to 44C are provided with automatic valves 44a, 44b, 44c for switching between an open state and a closed state.

The gas line 45 is a main path connected to the gas holder 3 in order to introduce gas (off gas) derived from the gas passage port 201 of each adsorption tower 20A to 20C into the gas holder 3. (45') and branch paths 45A, 45B, and 45C each connected to each of the gas passage ports 201 of the adsorption towers 20A to 20C. In the branch paths 45A to 45C, automatic valves 45a, 45b, and 45c for switching between an open state and a closed state are provided. In the main path 45', an automatic valve 451 for switching between an open state and a closed state is provided.

The gas line 46 is a flow path for off-gas drawn out from the gas holder 3, and one end is connected to the gas holder 3. The other end of the gas line 46 is connected between the cooler 18 and the gas compressor 21 in the middle of the gas line 41. That is, the gas line 46 is connected to the rear end of the pretreatment unit 1 in the gas line 41.

The gas line 47 is provided for discharging the gas (off gas) that is drawn out from the gas passage port 201 of each of the adsorption towers 20A to 20C. The gas line 47 is provided with an automatic valve 471 for switching between an open state and a closed state.

The gas holder 3 is for receiving gas (off gas) from the adsorption towers 20A to 20C, and its capacity is variable. In this embodiment, as shown in FIG. 3, the gas holder 3 is a piston type, and includes a main body 31, a diaphragm 32, and a piston 33.

The body part 31 is a metal cylindrical container, such as iron or stainless steel, for example. The main body 31 has a lower body 311 and an upper body 312, and can be separated up and down, and flanges of the lower body 311 and the upper body 312 are connected to the bolt 313 By joining together, they are integrated together. A gas inlet 314 and a gas outlet 315 are provided in appropriate places of the lower body 311. A main path 45' of the gas line 45 is connected to the gas inlet 314, and a gas line 46 is connected to the gas outlet 315.

The diaphragm 32 is a series of membrane bodies molded from synthetic rubber reinforced with fibers. The diaphragm 32 has an annular blade bottom 321, a cylindrical portion 322 extending by connecting one end side to an inner peripheral edge of the blade bottom 321, and the other end of the cylindrical portion 322 It has a bottom portion 323 that blocks the side. The diaphragm 32 is accommodated inside the main body 31 in a state in which the blade bottom 321 is fitted between the flanges of the lower body 311 and the upper body 312 in a sealed state. The diaphragm 32 has a function as a blocking portion, and is capable of being displaced vertically while maintaining a gas-sealed state between the lower body 311 (the main body 31). And, the area divided by the diaphragm 32 and the lower body 311 (the main body 31) becomes a gas receiving part 34 for receiving gas (off gas) from the adsorption towers 20A to 20C. .

The piston 33 is made of metal, such as iron or stainless steel, and is disposed inside the cylindrical portion 322 of the diaphragm 32. The piston 33 has a cylindrical piston cylinder portion 331 extending in the vertical direction, and a piston bottom portion 332 connected to a lower end of the piston cylinder portion 331. The piston 33 is supported by the diaphragm 32 in a state in which the piston bottom portion 332 is aligned with the bottom portion 323 of the diaphragm 32.

In the vicinity of the upper end of the piston cylinder 331, a guide roller 335 is provided through an installation tool 334. At least three guide rollers 335 are provided, and these guide rollers 335 are disposed at different positions in the circumferential direction in the piston cylinder portion 331. The guide rollers 335 are preferably arranged in the circumferential direction of the piston cylinder portion 331 via a predetermined interval. Each guide roller 335 contacts the inner peripheral surface of the upper body 312 and is rotatable around a horizontal axis. The outer diameter dimension of the piston cylinder part 331 is about 1000 mm, for example. The gap between the outer peripheral surface of the piston cylinder portion 331 and the inner peripheral surface of the upper body 312 is, for example, 50 to 200 mm, and preferably 60 to 150 mm. Although described in detail later, the diaphragm 32 and the piston 33 supported by the diaphragm 32 move up and down while maintaining a substantially constant posture by the guide roller 335.

Details will be described later, but when gas (off gas) from the adsorption towers 20A to 20C is introduced into the gas receiving portion 34 (in the gas holder 3) through the gas inlet 314, the gas receiving portion ( The gas amount of 34) changes (increases), and according to the change of the gas amount, the piston 33 rises while being supported by the diaphragm 32. The pressure (internal pressure) of the gas receiving portion 34 is determined according to the weight of the piston 33, and at the lowest pressure, it can be set to 1 kPaG or less (G means a gauge pressure, hereinafter the same). Further, on the surface side of the diaphragm 32, an air introduction hole (not shown) is formed in, for example, the upper body 312 of the main body 31 so that atmospheric pressure other than the weight of the piston 33 acts.

In this embodiment, the argon purification method according to the present invention can be carried out using the argon purification apparatus X having the above configuration. In the pretreatment unit 1, the blower 12 is operated and gas is boosted. Then, the mixed gas is supplied to the PSA apparatus 2 (adsorption towers 20A, 20B, 20C) through the reactors 14A and 14B in sequence.

When the PSA device 2 is operated, automatic valves 41a to 41c, 42a to 42c, 43a to 43c, 44a to 44c, 45a to 45c, 451, 471 And by appropriately switching the flow rate control valves 431 and 441, a desired gas flow state in the device is realized, and one cycle consisting of the following steps 1 to 12 can be repeated. In one cycle of this method, in each of the adsorption towers 20A, 20B, and 20C, an adsorption process, a co-current decompression process, a pressure equalization (reduction) process, a countercurrent decompression process, a washing (first washing) process, and a washing (second washing) ) Process, a pressure equalization (pressure increase) process, and a pressure increase process are performed. In the present embodiment, in the interior of each of the adsorption towers 20A to 20C, alumina as an adsorbent is stacked and filled with alumina as an adsorbent in the lower part and LiX zeolite as an adsorbent in the upper part. 4 and 5 schematically show a gas flow state in the PSA device 2 in steps 1 to 12.

In step 1, the gas flow state as shown in Fig. 4(a) is achieved, so that the adsorption process in the adsorption tower 20A, the washing (first cleaning) process in the adsorption tower 20B, and the adsorption tower 20C flow together. A decompression process is performed. The operation time of each step of Step 1 is, for example, 60 seconds.

As can be understood by referring to Figs. 2 and 4(a) together, in Step 1, the gas (mixed gas) passes through the gas line 41 to the gas passage port 201 of the adsorption tower 20A. Is introduced on the side. The inside of the adsorption tower 20A in the adsorption process is maintained at a predetermined high pressure, and impurities (carbon dioxide, carbon monoxide, nitrogen, etc.) in the mixed gas are adsorbed by the adsorbent in the adsorption tower 20A, and the gas passes through the adsorption tower 20A. The product gas (argon enriched gas) having a high argon gas concentration is derived from the sphere 202 side. This product gas is recovered outside the apparatus via the gas line 42. The internal pressure (adsorption pressure) of the adsorption tower 20A is, for example, about 800 kPaG.

Along with this, the gas (cleaning gas) in the adsorption tower 20C led out from the gas passage port 202 of the adsorption tower 20C passes through the gas line 44 to the gas passage port 202 side of the adsorption tower 20B. After being introduced, the gas remaining in the tower while washing the inside of the adsorption tower 20B is led out as off-gas from the gas passage port 201 side. On the other hand, in the co-current decompression step, as understood from Figs. 2 and 4 (a), the gas in the adsorption tower 20C is extracted from the gas passage port 202, and the gas in the adsorption tower 20A in the adsorption step Gas is drawn out in the same direction as the gas is drawn out (cocurrent).

Here, the gas (off gas) drawn out from the gas passage port 201 side of the adsorption tower 20B has a relatively low impurity concentration compared to the cleaning (second cleaning) step of the later step 2, and thus the gas line It is introduced into the gas holder 3 via 45.

In step 1, further, in the gas holder 3, as the gas amount increases, the diaphragm 32 rises, and the off-gas inside is led out to the gas line 46. Then, the gas flowing through the gas line 46 flows into the gas line 41 connected to the gas line 46, joins the mixed gas, and is recycled.

In step 2, the gas flow state as shown in Fig. 4(b) is achieved, so that the adsorption process continues in the adsorption tower 20A, the cleaning (second cleaning) process in the adsorption tower 20B, and the adsorption tower 20C. Subsequently, a co-current decompression step is performed. The operation time of each step of Step 2 is, for example, 55 seconds.

As can be understood by referring to Figs. 2 and 4(b) together, in Step 2, continuing from Step 1, the mixed gas is passed through the gas line 41 and the gas passage port of the adsorption tower 20A ( It is introduced to the 201) side, and product gas is extracted from the adsorption tower 20A. Product gas is recovered in the same manner as in Step 1. Along with this, in Step 2, from Step 1, the gas (cleaning gas) in the adsorption tower 20C drawn out from the gas passage port 202 of the adsorption tower 20C passes through the gas line 44 to the adsorption tower 20B. ) Is introduced into the gas passage port 202 side, and the gas remaining in the tower while cleaning the inside of the adsorption tower 20B is led out as off-gas from the gas passage port 201 side.

Here, the gas (off-gas) derived from the adsorption tower 20B in step 2 has a relatively high impurity concentration compared to the gas (off-gas) derived from the adsorption tower 20B in step 1, so the gas line It is discharged out of the system through (47).

In step 2, further, in the gas holder 3, the derivation to the internal off-gas gas line 46 is continued. Then, the gas flowing through the gas line 46 flows into the gas line 41, joins the mixed gas, and is recycled. In addition, in step 2, since gas is not introduced toward the gas holder 3, the amount of gas in the gas holder 3 decreases.

In step 3, the gas flow state as shown in Fig. 4(c) is achieved, and the adsorption process continues in the adsorption tower 20A, the pressure equalization (boost) process in the adsorption tower 20B, and the pressure equalization in the adsorption tower 20C. The (pressure reduction) process is performed. The operation time of each step of Step 3 is, for example, 15 seconds.

As can be understood by referring to Figs. 2 and 4(c) together, in Step 3, from Step 2, the mixed gas is passed through the gas line 41 and the gas passage port of the adsorption tower 20A ( It is introduced to the 201) side, and product gas is extracted from the adsorption tower 20A. Product gas is recovered in the same manner as in Step 1. Along with this, in step 3, a gas having a relatively low impurity concentration in the adsorption tower 20C, which is extracted from the gas passage port 202 of the adsorption tower 20C, passes through the gas line 44 through the adsorption tower 20B. It is introduced on the sphere 202 side.

In step 3, in the gas holder 3, the internal off-gas is led out to the gas line 46. Then, the gas flowing through the gas line 46 flows into the gas line 41, joins the mixed gas, and is recycled. In addition, in step 3, since gas is not introduced toward the gas holder 3, the amount of gas in the gas holder 3 continues to decrease.

In step 4, the gas flow state as shown in Fig. 4(d) is achieved, so that the adsorption process continues in the adsorption tower 20A, the pressure increase process in the adsorption tower 20B, and the countercurrent decompression process in the adsorption tower 10C is performed. Done. The operation time of each step of Step 4 is, for example, 70 seconds.

As can be understood by referring to Figs. 2 and 4(d) together, in Step 4, continuing from Step 3, the mixed gas passes through the gas line 41 and the gas passage port of the adsorption tower 20A ( It is introduced to the 201) side, and product gas is extracted from the adsorption tower 20A. The product gas is recovered in the same manner as in Steps 1 to 3, but a part thereof is introduced into the adsorption tower 20B via the gas line 43, and the pressure of the adsorption tower 20B is increased. In the adsorption tower 20C, impurities are desorbed from the adsorbent by decompressing in the countercurrent direction, and gas (off gas) in the tower is drawn out from the gas passage port 201 side of the adsorption tower 20C. In the countercurrent decompression process, as understood from Figs. 2 and 4(d), the gas in the adsorption tower 20C is extracted from the gas passage port 201, and the gas in the adsorption tower 20A in the adsorption process is The gas is released in a gas flow (counter-current) in the opposite direction to that that is drawn.

Here, the adsorption tower 20C is continuously depressurized in Steps 1 to 3, and the pressure in the adsorption tower 20C at the start of Step 4 is considerably lowered, but the pressure in the adsorption tower 20C is further reduced to near atmospheric pressure, The off-gas derived from the 201 side is introduced into the gas holder 3 via the gas line 45.

In step 4, further, in the gas holder 3, as the gas amount increases, the diaphragm 32 rises, and the internal off-gas is led out to the gas line 46. Then, the gas flowing through the gas line 46 flows into the gas line 41, joins the mixed gas, and is recycled.

Steps 1 to 4 correspond to 1/3 of one cycle constituted by Steps 1 to 12, and the process time of Steps 1 to 4 is 200 seconds in total.

In steps 5 to 8, as shown in Figs. 4(e) and (f) and Figs. 5(g) and (h), in the adsorption tower 20A, the adsorption tower 20C and the adsorption tower in steps 1 to 4 Similarly, a co-current pressure reduction step, a pressure equalization (pressure reduction) step, and a countercurrent pressure reduction step are performed. In the adsorption tower 20B, the adsorption process is performed in the same manner as in the adsorption tower 20A in steps 1 to 4. In the adsorption tower 20C, a washing (first washing) step, a washing (second washing) step, a pressure equalization (boost) step, and a pressure boosting step are performed in the same manner as in the adsorption tower 20B in steps 1 to 4.

In steps 9 to 12, as shown in Figs. 5(i) to (l), in the adsorption tower 20A, in the same manner as the adsorption tower 20B in steps 1 to 4, a washing (first washing) process, Washing (second cleaning) step, pressure equalization (pressure increase) step, and pressure increase step are performed, and in the adsorption tower 20B, in the same manner as the adsorption tower 20C in steps 1 to 4, a co-current decompression step, a pressure equalization (depressurization) step, and counter flow A decompression process is performed. In the adsorption tower 20C, the adsorption process is performed in the same manner as the adsorption tower 20A in steps 1 to 4.

And, by repeatedly performing steps 1 to 12 described above in each of the adsorption towers 20A to 20C, the mixed gas is continuously introduced into any of the adsorption towers 20A to 20C, and the argon gas concentration is high. Product gas is continuously acquired.

In this embodiment, the adsorption tower 20A (20B, 20C) in either the washing (first washing) step or the countercurrent decompression step by the operation steps (steps 1 to 12) shown in FIGS. 4 and 5 When a gas (off gas) is derived from ), the off gas is introduced into the gas holder 3 through the gas line 45 and the gas inlet 314 and is led out from the gas outlet 315. Here, since the gas holder 3 is of a variable capacity type, the capacity of the space through which the gas flows (gas holder 3) increases or decreases according to the amount of off-gas gas drawn out from the adsorption towers 20A to 20C.

For example, as will be understood with reference to FIG. 3, when the amount of gas introduced into the gas holder 3 increases, the diaphragm 32 and the lower body 311 (main body 31) The internal pressure of the area surrounded by) (gas receiving portion 34) is about to rise. Then, in response to the weight (load) of the piston 33, the diaphragm 32 and the piston 33 supported by the diaphragm 32 are pushed up, and gas is accumulated. In Fig. 3, the state in which the piston 33 is raised is indicated by a virtual line. On the other hand, when the amount of gas introduced into the gas holder 3 decreases or disappears, the piston 33 descends by the gas being discharged from the gas outlet 315. In Fig. 3, the volume of the gas receiving portion 34 in the state where the piston 33 is indicated by the solid line at the lowest and the volume in the state where the piston 33 is indicated by the virtual line at the highest position. The difference in the volume of the gas receiving portion 34 becomes a capacity that can be increased or decreased in the gas holder 3 (gas receiving portion 34).

As is understood from this, in the gas holder 3, the diaphragm 32 is caused by the load of the piston 33 acting downward on the diaphragm 32 and the pressure of the gas in the gas receiving portion 34. The capacity of the gas holder 3 (gas receiving portion 34) is changed while maintaining the balance of the force acting upwardly against the. Accordingly, even if the gas amount of the gas (off gas) drawn out from the adsorption towers 20A to 20C fluctuates, the capacity of the gas holder 3 increases or decreases according to the amount of the off gas, and the pressure in the gas holder 3 does not change. Without and remains substantially constant.

Unlike the present embodiment, when off-gas is accumulated in a fixed-capacity gas tank, the pressure in the gas tank fluctuates due to fluctuations in the amount of off-gas gas from the adsorption tower. In this case, when the amount of off-gas gas from the adsorption tower is increased by depressurizing the inside of the adsorption tower during the desorption operation, the pressure in the gas tank increases, so it is difficult to lower the gas pressure (desorption pressure) in the adsorption tower during the desorption operation. On the other hand, in the present embodiment, as described above, even when the amount of off-gas from the adsorption towers 20A to 20C increases, the pressure in the gas holder 3 is maintained substantially constant. Therefore, the adsorption tower in the desorption operation The effect of increasing the speed of decompression of (20A to 20C) can be obtained. As a result, the vacuum regeneration effect of the adsorption towers 20A to 20C increases, the amount of product gas obtained increases, and the argon recovery rate increases.

Further, unlike the present embodiment, when off-gas is accumulated in a fixed-capacity gas tank, the internal space capacity is fixed. For this reason, fluctuations in the amount of off-gas gas from the adsorption tower are absorbed by accompanying pressure changes in the gas tank. Therefore, in the fixed-capacity gas tank, in order to adequately absorb fluctuations in the amount of gas, a relatively large space capacity is required, and, for example, a space capacity of about 8.6 times the capacity of the adsorption tower is required. On the other hand, when off-gas is accumulated in the variable-capacity gas holder 3 as in the present embodiment, the diaphragm 32 (blocking portion) is displaced according to the fluctuating gas amount without a pressure change, It is possible to increase or decrease the capacity of the space accommodating the off-gas. Thereby, in the gas holder 3, it is sufficient to secure about 2.2 times the capacity of the adsorption towers 20A to 20C as the maximum space capacity, thereby eliminating wasted gas storage space.

Further, as described above, when the pressure in the gas holder 3 is kept substantially constant, the amount of off-gas that is led out through the gas outlet 315 is also substantially constant. And in the present embodiment, the off gas drawn out from the gas holder 3 is added to the mixed gas in the gas line 41 via the gas line 46 and recycled. Therefore, such a method enables the off gas to be stably recycled at a constant flow rate and increases the argon recovery rate.

In the gas separation by the PSA method, among the off gases derived from the adsorption towers 20A, 20B, and 20C in the cleaning process, the gas derived in the first cleaning process from the start to the middle of the cleaning process (first gas) The gas derived in the countercurrent decompression step is introduced into the gas holder 3 and recycled, while the gas (second gas) derived in the second washing step after the first washing step is discharged out of the system. According to this method, the off-gas having a relatively low impurity concentration is recycled and recovered as described above, and the off-gas having a relatively high impurity concentration is discharged to the outside of the system, which is suitable for increasing the recovery rate of argon.

In this embodiment, the off gas drawn out from the gas holder 3 is added to the mixed gas before being supplied to the adsorption towers 20A, 20B, and 20C via the pretreatment unit 1. This is because the off gas drawn out from the gas holder 3 does not contain oxygen and hydrogen substantially, and therefore there is no need to perform pretreatment when the off gas is added to the mixed gas and recycled. And, according to the method of adding the off gas to the mixed gas that has undergone pretreatment as described above, the composition of the gas subjected to pretreatment does not change compared to the case where the off gas is added to the gas (raw material gas) before the pretreatment is performed. Therefore, the pretreatment itself is stable.

6 shows a case where a variable capacity gas holder is attached to a gas line for off-gas and a fixed capacity gas tank is attached in a pressure fluctuation adsorption operation for purifying argon from a mixed gas using a three-tower adsorption tower. The pressure profile in one case is shown. The variable-capacity gas holder uses the piston-type gas holder 3 shown in Fig. 3, and the capacity of the gas holder 3 (gas receiving portion 34) is approximately 2.2 times the capacity of the adsorption tower. On the other hand, the capacity of the fixed capacity gas tank was about 8.6 times the capacity of the adsorption tower. As the mixed gas, a composition of 99.5 mol% of argon, 0.3 mol% of carbon dioxide, 0.02 mol% of carbon monoxide, and 0.18 mol% of nitrogen was used. The adsorption pressure was set to 800 kPaG, and the desorption pressure was set to 1 kPaG.

The internal pressure of the variable-capacity gas holder shown in Fig. 6 is shown for Steps 1 to 4 of Steps 1 to 12 described above, and the internal pressure of the fixed-capacity gas tank is also shown for Steps 1 to 4. The pressure in the adsorption tower (desorption pressure) is shown for the adsorption tower 20C in steps 1 to 4.

As understood from FIG. 6, the internal pressure of the fixed-capacity gas tank increases accordingly when off-gas is introduced into the gas tank after the start of steps 1 and 4, and in step 1, 100 kPaG (see FIG. In step 4, it reached 94 kPaG (at the time of about 133 seconds in Fig. 6). On the other hand, the internal pressure of the variable capacity gas holder was about 1 kPaG through steps 1 to 4, and was maintained substantially constant.

In addition, as understood from Fig. 6, the pressure in the adsorption tower (desorption pressure) is gentle from the time point at which the step 3 is switched to step 4 (at the time of 130 seconds elapsed in Fig. 6) in the case of a fixed capacity gas tank. It was lowered and required about 40 seconds to lower the pressure to the lowest pressure. On the other hand, in the case of the variable-capacity gas holder, the pressure (desorption pressure) in the adsorption tower decreases at once from the time point of switching from Step 3 to Step 4, and decreases to the lowest pressure at a fairly rapid rate within 20 seconds.

7 and 8 show another example of a variable-capacity gas holder.

The gas holder 3A shown in FIG. 7 is a balloon type, and includes a body 31A, a balloon 32A accommodated in the body 31A, and a weight 33A. The body 31A is made of, for example, iron or stainless steel, and has a cylindrical shape as a whole, and has a roof plate 316 for closing an opening formed in the upper part. An inlet gas nozzle 317 and an outlet gas nozzle 318 are provided in appropriate places under the body 31A. The main path 45' of the gas line 45 is connected to the inlet gas nozzle 317, and the gas line 46 is connected to the outlet gas nozzle 318. The balloon 32A is molded from synthetic rubber reinforced with fibers, and becomes a hemispherical membrane body upon expansion. The peripheral portion of the balloon 32A is fixed to a mounting bracket 319 provided on the inner surface of the body 31A. The balloon 32A has a function as a blocking portion, and can be displaced vertically while maintaining the gas-sealed state between the body 31A. The region partitioned from the balloon 32A and the lower portion of the body 31A serves as a gas receiving portion 34 for receiving gas (off gas) from the adsorption towers 20A to 20C. The weight 33A is for adjusting the internal pressure of the gas holder 3A, and is fixed to the central surface of the balloon 32A. The pressure (internal pressure) of the gas receiving portion 34 is determined according to the weight of the weight 33A, and the lowest pressure can be set to 1 kPaG or less.

When the amount of gas introduced into the gas holder 3A through the inlet gas nozzle 317 increases, the internal pressure of the gas receiving portion 34 surrounded by the balloon 32A and the body 31A in the gas holder 3A increases. Try to rise. Then, in response to the weight (load) of the weight 33A, the balloon 32A swells upward, and gas is accumulated. In Fig. 7, a state in which the balloon 32A is enlarged is indicated by a virtual line. On the other hand, when the amount of gas introduced into the gas holder 3A decreases or disappears, the gas is drawn out from the outlet gas nozzle 318, so that the balloon 32A retracts downward. In Fig. 7, the volume of the gas receiving portion 34 in the state where the balloon 32A is shown by the most constricted solid line, and the gas receiving portion in the state where the balloon 32A is shown by the most inflated virtual line. The difference in the volume of 34 becomes the capacity that can be increased or decreased in the gas holder 3A (gas accommodating portion 34).

In the gas holder 3A of this configuration, the load of the weight 33A acting downward on the balloon 32A and the force acting upward on the balloon 32A due to the pressure of the off gas maintain a balance. While doing this, the capacity of the gas holder 3A (gas receiving portion 34) is changed. Thereby, even if the amount of off-gas gas drawn out from the adsorption towers 20A to 20C fluctuates, the capacity of the gas holder 3A increases or decreases according to the gas amount, and the pressure in the gas holder 3A does not change and is substantially constant. maintain.

The gas holder 3B shown in FIG. 8 includes a cylindrical container-shaped body 35 and a drum 36 accommodated inside the body 35. The body 35 is made of a metal such as iron or stainless steel, and the inside of the body 35 is filled with a liquid 37 such as water or an organic liquid (oil) having low activity. The liquid 37 is continuously discharged to the outside from the overflow nozzle 352 while being introduced from the water supply nozzle 351 installed in the body 35, for example, even if the water, which is the liquid 37, evaporates. The reduction is being supplemented. When the liquid 37 is contaminated, it can be discharged from the discharge nozzle 353 and replaced.

The drum 36 is made of metal such as iron or stainless steel, and has a cylindrical shape with a closed top. The drum 36 is immersed in a liquid 37, and the inner space and the outside are blocked by the liquid 37. The drum 36 is an example of a blocking portion having a cover shape. A plurality of rollers 361 and 362 are provided in the lower and upper portions of the drum 36. Each roller 361 contacts the inner peripheral surface of the body 35 and moves vertically. Each roller 362 moves up and down using a plurality of columnar support members 38 distributed and arranged on the outer circumference of the body 35 as a guide rail. Thereby, the drum 36 moves up and down while maintaining a substantially constant posture by the liquid 37.

An inlet gas nozzle 354 and an outlet gas nozzle 355 are provided in appropriate places under the body 35. The main path 45' of the gas line 45 is connected to the inlet gas nozzle 354, and the gas line 46 is connected to the outlet gas nozzle 355. The inlet gas nozzle 354 and the outlet gas nozzle 355 are raised inside the drum 36, respectively, and the upper end portion is opened above the liquid level of the liquid 37.

The drum 36 is movable up and down by the liquid 37 while maintaining the gas-sealed state of the internal space between the liquid level and the liquid 37. The space partitioned by the drum 36 and the liquid 37 is a gas accommodation space 39 for receiving gas (off gas) from the adsorption towers 20A to 20C. The drum 36 has a function of adjusting the internal pressure of the gas holder 3B. The pressure (internal pressure) of the gas accommodation space 39 is determined according to the weight of the drum 36 floating in the liquid 37, and the lowest pressure can be set to 1 kPaG or less.

When the amount of gas introduced into the gas holder 3B via the inlet gas nozzle 354 increases, the area surrounded by the drum 36 and the liquid 37 (gas accommodation space 39) in the gas holder 3B The internal pressure is about to rise. Then, in response to the weight (load) of the drum 36, the drum 36 rises and gas is accumulated. In Fig. 8, the state in which the drum 36 is raised is indicated by a virtual line. On the other hand, when the amount of gas introduced into the gas holder 3B decreases or disappears, the drum 36 descends as gas is drawn out from the outlet gas nozzle 355. In addition, in Fig. 8, the volume of the gas accommodation space 39 in a state where the drum 36 is indicated by the lowermost solid line, and in a state where the drum 36 is indicated by the uppermost virtual line. The difference in the volume of the gas accommodation space 39 becomes a capacity that can be increased or decreased in the gas holder 3B (gas accommodation space 39).

In the gas holder 3B of this configuration, the load of the drum 36 acting downward on the drum 36 and the force acting upward on the drum 36 due to the pressure of the off gas maintain a balance. While doing so, the capacity of the gas holder 3B (gas accommodation space 39) is changed. Thereby, even if the amount of off-gas gas drawn out from the adsorption towers 20A to 20C fluctuates, the capacity of the gas holder 3B increases or decreases according to the amount of the gas, so that the pressure in the gas holder 3B does not change and is substantially constant. maintain.

As mentioned above, although the specific embodiment of this invention was demonstrated, this invention is not limited to this, Various changes are possible within the range which does not deviate from the idea of the invention. For example, the configuration of the gas line constituting the gas flow path in the argon purifying apparatus according to the present invention may be configured differently from the above embodiment. The number of adsorption towers is not limited to only the three-column type shown in the above embodiment, and the same effect can be expected even in the case of two or less columns or four or more columns.

[Example]

Next, the usefulness of the present invention will be described with examples and comparative examples.

[Example 1]

Using the argon purifying apparatus X having the schematic configuration shown in Figs. 1 and 2, the adsorption process, the co-current decompression process, the pressure equalization (decompression) process, the countercurrent decompression process, and the washing (removal) shown in Figs. 4 and 5 are used. One cycle (steps 1 to 12) consisting of a 1 washing) process, a cleaning (second cleaning) process, a pressure equalization (pressure increase) process, and a pressure increase process is repeated in the adsorption towers 20A, 20B, and 20C to , Argon was concentrated and purified.

Each of the adsorption towers 20A, 20B, and 20C used in this example was made of stainless steel and had a cylindrical shape (inner diameter of 37 mm, inner height of 1,000 mm), and a capacity of about 1 dm ³ . In each adsorption tower, 1 dm ³ of LiX zeolite was charged as an adsorbent. As for the gas holder, the balloon type (volume variable type) gas holder 3A shown in Fig. 7 was used, and the capacity was about 2.2 dm ³ . The composition of the mixed gas supplied to the adsorption towers 20A, 20B and 20C was 99.5 mol% of argon, 0.02 mol% of carbon monoxide, 0.3 mol% of carbon dioxide, and 0.18 mol% of nitrogen. This mixed gas was continuously supplied to the PSA device 2 at a flow rate of 1,030 Ndm ³ /h (N represents a standard state, and the same applies to the following). In this embodiment, in each of the adsorption towers 20A, 20B, and 20C, steps 1, 2, 3, and 4 are 60 seconds, 55 seconds, 15 seconds, and 70 seconds, respectively, and the sum of steps 1 to 4 is 200 seconds, The cycle time of one cycle consisting of steps 1 to 12 was 600 seconds. The maximum pressure inside the adsorption towers 20A to 20C in the adsorption process is 800 kPaG, and the minimum pressure (desorption pressure) inside the adsorption towers 20A to 20C in the desorption operation is 1 kPaG. Adjusted.

The argon purity was 99.999 mol% with respect to the product gas in which argon was concentrated and purified in this Example conducted under these conditions. The content of carbon monoxide and carbon dioxide, which are impurities in the product gas, was measured using gas chromatography (GC-FID manufactured by Shimadzu Corporation) through a methanizer. As a result, carbon monoxide was less than 1 mol ppm, carbon dioxide. Was less than 1 mol ppm. The content of impurity nitrogen in the product gas was measured with a trace nitrogen analyzer manufactured by Round Science, Inc., and was 0.6 mol ppm. The obtained product gas amount was 739 Ndm ³ /h, and the argon recovery rate in the obtained gas was 72.1%. In this example, the internal pressure of the gas holder 3A was substantially constant at 1 kPaG, and did not fluctuate. In this example, the off-gas derived from the gas holder 3A was discharged out of the system at a pressure of 1 kPaG. In particular, measuring the amount of off-gas derived from the adsorption towers 20A, 20B, and 20C in the cleaning (second cleaning) process (steps 2, 6, 10) is 146 Ndm ³ /h, and the gas analysis value is 98.0 mol of argon. %, carbon monoxide was 0.10 mol%, carbon dioxide was 1.10 mol%, and nitrogen was 0.80 mol%. The results of this example are shown in Table 1.

[Example 2]

In this example, the operating conditions of the PSA device and the PSA method were the same as in Example 1, but off-gas derived from the adsorption towers 20A, 20B, and 20C in the cleaning (second cleaning) step was discharged to the outside of the system, The remaining off-gas {off gas derived from the adsorption towers 20A, 20B, 20C in the washing (first washing) process (steps 1, 5, 9) and countercurrent decompression step (steps 4, 8, 12)) All of these were added to the pretreated mixed gas before being introduced into the adsorption towers 20A, 20B, and 20C and recycled. The recycle gas gas amount at this time was 145 Ndm ³ /h, and the composition of the recycle gas was 98.47 mol% of argon, 0.05 mol% of carbon monoxide, 1.02 mol% of carbon dioxide, and 0.47 mol% of nitrogen. A mixed gas to which a recycle gas was added (a new pretreatment gas 885 Ndm ³ /h and a recycle gas 145 Ndm ³ /h) was continuously supplied to the PSA apparatus 2 at a flow rate of 1,030 Ndm ³ /h.

In this example, the argon purity of the product gas concentrated and purified with argon was 99.999 mol%. The content of impurities in the product gas was measured by the same analysis apparatus as in Example 1, and found that carbon monoxide was less than 1 mol ppm, carbon dioxide was less than 1 mol ppm, and nitrogen was 0.6 mol ppm. The obtained product gas amount was 731 Ndm ³ /h, and the argon recovery rate in the obtained gas was 71.4%. In this example, the internal pressure of the gas holder 3A was substantially constant at 1 kPaG, and did not fluctuate. In this embodiment, the flow rate of the mixed gas before the off-gas is recycled becomes 885 Ndm ³ /h by subtracting the recycled 145 Ndm ³ /h from 1,030 Ndm ³ /h. The argon recovery rate was 83.0%. The results of this example are shown in Table 1.

[Comparative Example 1]

The gas holder 3A of the argon purifying apparatus X used in Example 1 was replaced with a fixed-capacity gas tank, and an operation consisting of each step shown in Figs. 4 and 5 by a pressure adsorption variation method (step By repeating 1 to 12), argon was concentrated and purified from a predetermined mixed gas. The configuration of the purifying apparatus used in this comparative example excluding the difference in the gas tank was the same as that of the argon purifying apparatus (X).

In this comparative example, 1 dm ^{3 of} LiX zeolite was filled in each of the three adsorption towers. As a fixed-capacity gas tank, one having a capacity of about 8.6 dm ³ was used. The composition of the mixed gas and the mode of gas supply were the same as in Example 1. In this comparative example, operations (steps 1 to 12) consisting of the steps shown in Figs. 4 and 5 were repeated, and the timing of switching each step was the same as in Example 1 above. In this comparative example, the maximum pressure inside the adsorption tower in the adsorption step was 800 kPaG, and the minimum pressure (desorption pressure) inside the adsorption tower during the desorption operation was adjusted to 1 kPaG.

In this comparative example, the purity of argon was 99.999 mol% with respect to the concentrated and purified product gas. The content of impurities in the product gas was measured by the same analysis apparatus as in Example 1, whereupon carbon monoxide was less than 1 mol ppm, carbon dioxide was less than 1 mol ppm, and nitrogen was 0.8 mol ppm. The obtained product gas amount was 712 Ndm ³ /h, and the argon recovery rate in the obtained gas was 69.5%. In this comparative example, the internal pressure of the gas tank varied from the minimum value of 1 kPaG to the maximum value of 100 kPaG as shown in FIG. 6. In this comparative example, off-gas derived from the gas tank was discharged to the outside of the system. In particular, when the amount of off-gas discharged from the adsorption tower in the cleaning (second cleaning) process (steps 2, 6, 10) is measured, it is 159 Ndm ³ /h, and the gas analysis value is 98.00 mol% for argon and 0.10 mol% for carbon monoxide. , Carbon dioxide was 1.10 mol% and nitrogen was 0.80 mol%. The results of this comparative example are shown in Table 1.

[Comparative Example 2]

In this comparative example, the operating conditions of the PSA device and the PSA method were the same as those of Comparative Example 1, but the off-gas derived from the adsorption tower in the cleaning (second cleaning) step was discharged to the outside of the system, and the remaining off-gas (washing The off-gas derived from the adsorption tower in the (first cleaning) process (steps 1, 5, 9) and countercurrent decompression process (steps 4, 8, 12) were added to the mixed gas after pretreatment before being introduced into the adsorption tower. It was recycled. The recycle gas gas amount was 159 Ndm ³ /h, and the composition of the recycle gas was 98.76 mol% of argon, 0.03 mol% of carbon monoxide, 0.84 mol% of carbon dioxide, and 0.37 mol% of nitrogen. This mixed gas (871 Ndm ³ /h of new pretreatment gas and 159 Ndm ³ /h of recycle gas) was continuously supplied to the PSA device at a flow rate of 1,030 Ndm ³ /h.

In this comparative example, the argon purity of the product gas concentrated and purified with argon was 99.999 mol%. When the content rate of impurities in the product gas was measured by the same analysis apparatus as in Example 1, carbon monoxide was less than 1 mol ppm, carbon dioxide was less than 1 mol ppm, and nitrogen was 0.8 mol ppm. The obtained product gas amount was 693 Ndm ³ /h, and the argon recovery rate in the obtained gas was 67.7%. In particular, in this comparative example, since the flow rate of the mixed gas before the off-gas is recycled becomes 871 Ndm ³ /h by subtracting the recycled 159 Ndm ³ /h from 1,030 Ndm ³ /h, the argon recovery rate in the entire system of the argon purifier is It became 79.9%. The results of this comparative example are shown in Table 1.

Tank
form mix
Gas volume
(Ndm ³ ) absorption
pressure
(㎪G) Desorption
pressure
(㎪G) product
Gas volume
(Ndm ³ ) product
Ar purity
(%) PSA
Ar
Recovery rate (%) Total
Ar recovery rate
(%) Example
One Volume
Variable expression 1030 800 One 739 99.999 72.1 72.1 Example
2 Volume
Variable expression 1030
(885
+145 800 One 731 99.999 71.4 83.0 Comparative example
One Volume
Stationary 1030 800 One 712 99.999 69.5 69.5 Comparative example
2 Volume
Stationary 1030
(871
+159 800 One 693 99.999 67.7 79.9

In Comparative Examples 1 and 2, a fixed capacity gas tank having a tank capacity of 8.6 times the capacity of the adsorption tower was used, but the desorption pressure could not be stabilized low. In contrast, in Examples 1 and 2, by using a variable-capacity gas holder with a capacity of 2.2 times that of the adsorption tower, the pressure fluctuation inside the gas holder can be eliminated, and the desorption pressure is reduced to a lower pressure (1 kPaG). Level). As a result, the argon recovery rate was improved from 69.5% in Comparative Example 1 to 72.1% in Example 1. In addition, by recycling and mixing the off-gas having a relatively low impurity concentration in the raw material system, the argon recovery rate in the entire system was improved from 72.1% to 83.0%.

X: argon purification apparatus 1: pretreatment unit
11: filter 12: blower
13: heater 14A, 14B: reactor
15: oxygen supply 16: carbon monoxide supply
17, 18: cooler
2: PSA device (pressure fluctuation adsorption gas separation device)
20A, 20B, 20C: adsorption tower 21: gas compressor
22: cooler 23: drain tank
201, 202: gas passage 3, 3A, 3B: gas holder
31: main body 31A: body
311: lower body 312: upper body
314: gas inlet 315: gas outlet
316: roof plate 317: inlet gas nozzle
318: outlet gas nozzle 32: diaphragm (blocking part)
32A: balloon (blocking part) 321: blade bottom
322: cylindrical portion 323: bottom portion
33: piston (weight) 33A: weight
331: piston cylinder portion 332: piston bottom portion
334: installation tool 335: guide roller
34: gas receiving portion 35: fuselage
354: inlet gas nozzle 355: outlet gas nozzle
36: drum (blocking part, weight part) 361, 362: roller
37: liquid 38: support member
39: gas accommodation space 41: gas line (first gas line)
42 to 44: gas line 45: gas line (second gas line)
46: gas line (third gas line) 47: gas line (fourth gas line)
41', 42', 43', 44', 45': weekly
41A-41C, 42A-42C, 43A-43C, 44A-44C, 45A-45C: branched
41a to 41c, 42a to 42c, 43a to 43c, 44a to 44c, 45a to 45c: automatic valve
431, 441: flow adjustment valve 451, 471: automatic valve

Claims (10)

As a method for purifying argon from a mixed gas containing argon,
By a pressure swing adsorption method performed using an adsorption tower filled with an adsorbent, while the adsorption tower is at a relatively high pressure, the mixed gas is introduced into the adsorption tower to adsorb impurities in the mixed gas to the adsorbent, and argon from the adsorption tower. A cycle including an adsorption step of depressing the enriched gas, and a countercurrent decompression step of depressurizing the adsorption tower to desorb impurities from the adsorbent, and decomposing gas from the adsorption tower are repeatedly performed,
Introducing the gas derived from the adsorption tower in the countercurrent decompression process into a gas holder whose capacity is changed, while maintaining a constant pressure in the gas holder, and extracting the gas in the gas holder,
Before introducing the mixed gas into the adsorption tower, a pretreatment for removing or modifying at least a part of the impurities contained in the mixed gas is performed on the mixed gas,
The argon purification method in which the gas derived from the gas holder is added to the gas before being introduced into the adsorption tower through the pretreatment. The method of claim 1, wherein the gas holder accommodates gas to block contact with the atmosphere, and includes a blocking portion that is displaced according to the amount of the gas,
The capacity of the gas holder is an argon purification method in which the load acting from the outside of the blocking part toward the inside and the force acting from the inside of the blocking part toward the outside by the pressure of the gas inside are changed while maintaining a balance . The argon purification method according to claim 2, wherein the gas holder has a weight part supported or included in the blocking part. The method according to any one of claims 1 to 3,
The pressure swing adsorption method is performed using a plurality of adsorption towers filled with an adsorbent,
In the cycle, the inside of one adsorption tower that has finished the adsorption process is decompressed and the gas is extracted from the one adsorption tower in a parallel flow, and at the same time, the extracted gas is used as a cleaning gas to the other adsorption tower that has finished the countercurrent decompression process. Introducing and cleaning the other adsorption tower further comprises a cleaning process,
The cleaning process includes: a first cleaning process in which a first gas is extracted from the other adsorption tower from the start to the middle of the cleaning process, and a second gas after the first cleaning process in which a second gas is extracted from the other adsorption tower. Including a cleaning process,
Introducing the first gas into the gas holder and discharging the second gas out of the system,
The argon purification method, wherein the gas drawn out from the gas holder is added to the mixed gas before being introduced into the adsorption tower. An apparatus for purifying argon from a mixed gas containing argon,
By a pressure swing adsorption method performed using an adsorption tower filled with an adsorbent, the mixed gas is introduced into the adsorption tower, impurities in the mixed gas are adsorbed to the adsorbent, argon is extracted from the adsorption tower, and the adsorption tower is depressurized. A pressure swing adsorption type gas separation device for desorbing impurities from the adsorbent and desorbing off-gas from the adsorption tower;
A first gas line for supplying the mixed gas to the adsorption tower;
A variable-capacity gas holder for introducing and deriving the off-gas from the adsorption tower;
A second gas line for supplying the off gas discharged from the adsorption tower to the gas holder;
A third gas line connecting the gas holder and the first gas line so that the gas derived from the gas holder can be added and supplied to the first gas line; And
A fourth gas line connected to the second gas line for discharging the gas discharged from the adsorption tower to the outside of the system,
A pretreatment unit for performing pretreatment for removing or modifying at least a part of impurities contained in the mixed gas is provided in the first gas line,
The argon purifying apparatus, wherein the third gas line is connected to a rear end of the pretreatment unit in the first gas line. The gas holder according to claim 5, wherein the gas holder comprises a body portion configured in a container shape, and a blocking portion accommodated in the body portion and displaceable while maintaining a gas sealed state between the body portion,
According to the displacement of the blocking portion, the amount of gas accommodated in the gas receiving portion partitioned by the main body and the blocking portion is changed. The argon purifying apparatus according to claim 6, wherein the gas holder includes a weight part supported or included in the blocking part.
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