JP2781983B2 - Air liquefaction separation method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air liquefaction separation method and apparatus, and more particularly to an air liquefaction separation apparatus capable of co-producing oxygen and argon in air. The present invention relates to an air liquefaction separation method and an apparatus thereof that can be preferentially collected.

[Conventional technology]

After compressing and refining the raw air, it is cooled to near the liquefaction point,
There is known an air liquefaction separation method in which liquefaction rectification is carried out by introducing into a rectification column to obtain nitrogen, oxygen, argon and the like.

FIG. 5 shows an example of a conventional air liquefaction / separation apparatus which co-produces oxygen and argon.
Is the main heat exchanger 2 for cooling the compressed and purified raw air A
A double rectification tower 3 for rectifying the raw material air A cooled to the vicinity of the liquefaction point in the main heat exchanger 2, a booster 4 for branching and pressurizing a part At of the raw air A, and a booster The raw material air At, which has been pressurized at 4 and cooled to the intermediate temperature in the main heat exchanger 2, is expanded,
An expansion turbine 5 to be reduced in pressure, a feed line 7 for introducing the raw material air At expanded and reduced in pressure by the expansion turbine 5 into an upper column 6 of the double rectification column 3, and connected to the upper column 6. An argon column 8 is provided.

The compressed and purified raw material air A is divided into two parts before introduction into the main heat exchanger 2, and one of them is cooled to near the liquefaction point by the product gas or exhaust gas (not shown) separated in the main heat exchanger 2. Then, it is introduced into the lower tower 9 of the double rectification tower 3. The feed air A is rectified in the lower tower 9 and separated into nitrogen N at the top of the lower tower 9 and oxygen-enriched liquefied air LA at the bottom of the lower tower 9. The oxygen-enriched liquefied air LA is led out from the bottom of the lower tower 9 and passed through a subcooler 10 to be divided into two parts. One of the divided oxygen-enriched liquefied air LA is depressurized to the upper column pressure and introduced into the middle stage of the upper column 6, and the other oxygen-enriched liquefied air LA is similarly depressurized and condensed in the argon column 8. The refrigerant is introduced into the condenser 11 as a refrigerant, most of which is vaporized and vaporized, and is introduced from the condenser 11 into the upper tower 6. The nitrogen N at the top of the lower tower 9 is condensed and liquefied in the main condensing evaporator 12 and then partly led out of the lower tower 9.
After passing through the subcooler 10, the pressure is further reduced to the upper tower pressure and introduced into the upper part of the upper tower 6.

On the other hand, a part At of the raw air divided into two before the introduction of the main heat exchanger 2 is introduced into the main heat exchanger 2 after the pressure is increased by the booster 4, and reaches the intermediate temperature in the main heat exchanger 2. After being cooled, it is introduced into the expansion turbine 5. The raw material air At is expanded to the upper tower pressure by the expansion turbine 5 and reduced in pressure, and then introduced into the middle stage of the upper tower 6 through the introduction path 7.

As described above, in the upper tower 6 where each gas and liquid are introduced, each gas and liquid is rectified and the liquefied oxygen at the bottom of the upper tower 6 is removed.
It is separated into LO and nitrogen gas PN at the top of the upper tower 6, and argon is concentrated in the middle.

Nitrogen gas PN is introduced from the top of the upper tower 6 and is supplied to the subcooler 10.
And after the temperature is recovered through the main heat exchanger 2.
The liquefied oxygen LO at the bottom of the upper tower 6 is partially liquefied oxygen.
It is led out as LO, and a part is evaporated and vaporized in the condensing evaporator 12 to become a rising gas in the upper tower 6 and is collected as a product oxygen gas GO.

In the argon column 8, the argon-enriched gas in the middle stage of the upper column 6 is introduced into the bottom of the column to become an ascending gas, and the condensed liquid cooled and condensed by the oxygen-enriched liquefied air LA in the condenser 11 is refluxed. The rectification is performed as a liquid, and crude argon Ar is collected from the top of the argon column 8, and the condensate is refluxed to the upper column 6 from the bottom of the argon column 8.

As described above, in the air liquefaction / separation apparatus 1 that produces oxygen gas GO and argon Ar simultaneously, it is desired that argon can be preferentially collected or oxygen can be preferentially collected according to fluctuations in product demand. .

The control of the priority of the extracted product is described in, for example,
In the method described in Japanese Patent No. 44587, a branch pipe 13 is provided in the introduction path 7 for introducing the raw material air At expanded and reduced in pressure by the expansion turbine 5 into the upper tower 6, and a valve is provided in the introduction path 7 and the branch pipe 13. 14 and 15 are provided, and the opening degree of the valves 14 and 15 is controlled to adjust the amount of the raw material air At introduced into the upper tower 6.

[Problems to be solved by the invention]

However, in the above-described method, the L / V value (the ratio of the amount of liquid and the amount of gas in countercurrent contact in the column) in the upper column 6 is increased (to approach 1) to improve the argon yield. However, in order to improve the recovery rate of argon, most of the raw material air At which has been purified by compressing with a raw material air compressor, cooled, and introduced into the expansion turbine 5 is discharged without being subjected to rectification. Must. That is, oxygen and argon contained in a part of the raw material air At are not rectified and separated, and only the cold generated by the expansion turbine is collected and discharged. Therefore, for example, when the argon yield is improved by 10%, the oxygen yield is reduced by about 2 to 3%. In addition, the pretreatment equipment such as a raw material air compressor and an adsorber is operating wastefully for the discharged raw material air, resulting in waste of power costs and the like, which deteriorates the power consumption unit of the product. Had become.

Therefore, the present invention makes it possible to easily switch the preferential collection of oxygen or argon, and does not wastefully discharge the compressed, purified, and cooled raw material air, but effectively rectifies the entire amount thereof to separate each product. It is an object of the present invention to provide an air liquefaction / separation method and an apparatus which can be obtained.

[Means for solving the problem]

In order to achieve the above object, the air liquefaction separation method of the present invention comprises compressing and purifying raw air, cooling it with a main heat exchanger, introducing it into double rectification, liquefaction rectification and separating oxygen and argon. In a method capable of co-production, the raw material air before being introduced into the double rectification column is branched, and one of the branched raw material airs,
Alternatively, at least one of the air derived from the lower tower of the double rectification tower is cooled or heated to an intermediate temperature, and then introduced into an expansion turbine to correspond to the pressure of the upper tower of the double rectification tower. After the pressure is expanded and reduced, the raw material expanded and reduced by the expansion turbine and / or the air derived from the lower column is collected with priority on oxygen, and the gas phase composition in the column of the upper column is determined. When introduced into a rectification stage having substantially the same composition as the air composition, and argon is preferentially collected, the column gas phase composition of the upper column is introduced into the rectification stage with a nitrogen-enriched composition from the air composition, and When oxygen and argon are equally collected, they are simultaneously introduced into both rectification stages of the upper column.

Further, the air liquefaction and separation apparatus of the present invention comprises a main heat exchanger for cooling the compressed and purified raw air, a double rectification column for rectifying the raw air cooled to near the liquefaction point in the main heat exchanger, An expansion stage for expanding and reducing the pressure of at least one of the raw air and / or the air derived from the lower column of the double rectification column.
An air liquefaction / separation apparatus comprising: a bottle; an introduction circuit for introducing air derived from the expansion turbine into an upper column of the double rectification column; and an argon column connected to the upper portion of the double rectification column. The introduction circuit that introduces the air from the bin into the upper tower is connected to a rectification stage in which the gas phase composition in the upper tower is substantially the same as the air composition. An introduction path connected to a rectification stage of the chemical composition, and an introduction amount adjusting means for adjusting an introduction amount of the air derived from the expansion turbine into both introduction paths. Features.

(Operation)

As described above, the air expanded and reduced in pressure by the expansion turbine is introduced into a rectification stage having substantially the same composition as that of the air in the upper column, so that oxygen is preferentially collected in the column with priority given to oxygen. The staying condition can be set. In addition, by introducing the air derived from the expansion turbine into the rectification stage of the upper column, which has a nitrogen-enriched gas phase composition, a large amount of argon concentrated in the vicinity of the stage leading out to the argon column is concentrated. Since dilution with air or the like can be prevented, the argon yield can be improved, and all the raw material air can be used for rectification, a decrease in oxygen yield can be suppressed. In addition, by introducing air into both rectification stages simultaneously at an appropriate ratio, oxygen and argon can be collected with a desired priority.

Further, as in the apparatus of the present invention, an introduction path for connecting the air derived from the expansion turbine to a rectification stage having a gas phase composition substantially the same as the air composition, such as the upper portion, and a nitrogen-enriched gas phase composition. By providing the introduction path connected to the rectification stage and the introduction amount adjusting means for adjusting the introduction amount to both introduction paths, it is possible to easily switch the introduction position by operating the adjusting means, The sampling priority operation or the argon sampling priority operation can be easily switched.

〔Example〕

Hereinafter, the present invention will be described in more detail based on embodiments shown in the drawings. In the following description, the same elements as those of the conventional example shown in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

First, FIG. 1 shows a first embodiment of the air liquefaction / separation apparatus of the present invention.

In the air liquefaction / separation apparatus 20, a branch pipe 21 is provided in the middle of the main heat exchanger 2 for cooling the compressed and purified raw air A, and a part At of the raw air is branched by the branch pipe 21 and expanded. A lower introduction passage 23 connected to a middle stage of the upper tower 6, a lower introduction path 23 connected to a middle circuit of the upper tower 6, and an introduction circuit 22 for introducing the raw material air At derived from the expansion turbine 5 to the upper tower 6 while introducing the expanded turbine 5. An upper introduction path 24 connected to the upper stage is provided, and both introduction paths 23 and 24 are provided.
And the two introduction paths of the raw material air At from which the expansion turbine 5 is derived.
Valve 2 as introduction amount adjustment means for adjusting the introduction amount to 23, 24
5, 26 are provided.

The lower introduction passage 23 is connected to the oxygen-enriched liquefied air LA of the upper tower 6.
Is connected to a rectification stage whose gas phase composition is substantially the same as that of the air below the introduction stage of the column.
Is connected to a rectification stage in which the gas phase composition in the upper tower 6 is more nitrogen-rich than air. As the rectification stage having this nitrogen-enriched composition, any rectification stage having a composition having a nitrogen content larger than 15 vol% of oxygen and 85 vol% of nitrogen may be used. It is appropriately selected and determined according to conditions such as the flow rate (depending on the sampling ratio of the gas product and the liquid product). A plurality of introduction paths to the nitrogen-rich composition rectification stage may be provided in advance.

In order to carry out the method of the present invention using the apparatus of the present embodiment,
By controlling the opening degree of the valves 25, 26 provided in the two introduction paths 23, 24,
It can be carried out by adjusting the ratio of the raw material air At introduced into the upper tower 6 from both the introduction paths 2324. For example, when preferentially collecting oxygen gas GO, the valve 25 of the lower introduction passage 23 is opened and the valve 26 of the upper introduction passage 24 is closed,
The raw material air At expanded and reduced in pressure by the expansion turbine 5 is introduced into the rectification stage in which the gas phase composition in the upper tower 6 is substantially the same as the air composition. Thereby, a composition distribution suitable for separating nitrogen and oxygen in the upper tower 6 can be obtained, and the yield of oxygen gas GO can be improved. Argon in this state
Is approximately the same as the amount of argon collected by a conventional general air liquefaction / separation apparatus for collecting argon.

When argon Ar is to be collected preferentially, the valve 26 of the upper inlet channel 24 is opened and the valve 25 of the lower inlet channel 23 is closed, and the raw material air At expanded and reduced in pressure by the expansion turbine 5 is transferred to the upper portion. The gas phase in the column 6 is introduced above the rectification stage having a nitrogen-enriched composition over the air composition, that is, above the rectification stage introduced when the oxygen collection is prioritized. Thereby, it is possible to prevent the argon concentrated in the vicinity of the lead-out stage to the argon column 8 from being diluted with a large amount of the raw material air At, and to improve the argon Ar yield.

Further, the valves 25 and 26 of both the introduction paths 23 and 24 are adjusted to an appropriate opening degree, and the gas phase composition in the upper tower 6 is substantially equal to the air fractionation stage (the middle stage of the upper column). At the same time, the feed air At which has passed through the expansion turbine 5 is introduced at an appropriate ratio into both the rectification stages (the upper column in the upper column) and the rectification stage having the enriched composition, so that oxygen gas GO and argon Ar can be collected.

In addition, even during the argon collection priority operation, since all the raw material air is used for rectification, a decrease in the oxygen yield can be suppressed, and equipment such as a raw material air compressor and an adsorber can be effectively used. be able to.

FIG. 2 shows the effect of controlling the improvement of the argon yield and the decrease of the oxygen yield in the argon collection priority operation. In the apparatus configuration in which the oxygen yield and the argon yield in the oxygen collection priority operation are the same, the present invention is applied. This is a comparison between the case where the method is applied and the case where the conventional method of discharging a part of the raw material air. That is, in the oxygen collection priority operation, both methods have the same oxygen yield as indicated by point A in the figure.
89% and an argon yield of 54.1% were obtained.
%, That is, when the oxygen yield is 87%, the argon yield becomes 60.5% as shown by the point B in the figure in the method of the present invention.
The argon yield is 12 compared to 54.1% in the oxygen sampling priority operation.
In contrast, in the conventional method, the argon yield is 59.4% as shown by the point C in the drawing, and the argon yield is only improved by 10% compared to 54.1% in the oxygen collection priority operation. In the case where the improvement of the argon yield by the method of the present invention is 10%, which is the same as the conventional case, that is, the argon yield is 59.4%, the oxygen yield is 87.4% as shown by the point D in the figure, and the oxygen yield is 87% when priority is given to argon collection. And a decrease in oxygen yield can be suppressed.

This is shown in the table below, for example, in terms of specific numerical values in an apparatus having a raw material air amount of 53,600 Nm ³ / h (turbine flow rate of 14,000 Nm ³ / h).

Next, FIG. 3 shows a second embodiment of the air liquefaction / separation apparatus of the present invention.

In the air liquefaction / separation apparatus 30 of this embodiment, the turbine fluid Gt introduced into the expansion turbine 5 is a part At / of the raw air and / or the air Ao derived from the lower tower 9. That is, a branch pipe 33 having a valve 32 is provided in the middle of a pipe 31 for introducing the raw material air A compressed and purified and cooled in the main heat exchanger 2 to the lower tower 9. An outlet pipe 35 having a valve 34 is provided in the rectification section several steps above the bottom, and either the air of the branch pipe 33 or the air of the outlet pipe 35 is selected, or the branch pipe 33 and the outlet pipe 35 are selected. Are connected to the reheat passage 2a of the main heat exchanger 2 and the outlet of the reheat passage 2a is connected to the expansion turbine 5.
Each of the outlets of the bottles 5 is provided with a valve as in the previous embodiment.
A lower introduction path 23 having 25 and 26 and an upper introduction path 24 are provided.

The apparatus of this embodiment also controls the valves 25 and 26 of the lower introduction path 23 and the upper introduction path 24 in accordance with the priority of oxygen collection or the priority of argon collection in the same manner as the above-described apparatus, so that the argon collection priority operation is performed. In this case, the improvement in the argon yield and the decrease in the oxygen yield can be suppressed.

The position of the outlet pipe 35 to be attached to the lower tower 9 can be appropriately set according to various conditions such as the configuration of the lower tower 9, the structure of the rectification shelf, and the type of product to be collected. That is, the outlet pipe 35
Is derived from the oxygen-enriched composition, approximately air composition,
It includes any of the nitrogen-enriched compositions, and can be selected as appropriate according to the argon priority sampling and oxygen priority sampling.

FIG. 4 shows a third embodiment of the air liquefaction / separation apparatus according to the present invention, in which a part of the raw air introduced into the expansion turbine is pressurized to increase the amount of cold generated during expansion and pressure reduction. It is a thing.

The raw material air A introduced into the air liquefaction separation device 40 is
After being compressed and refined, it is branched, and a part At of the branched raw air is introduced into the expansion turbine braking blower 41 and pressurized. The pressurized raw material air At is cooled to normal temperature by the aftercooler 42, introduced into the main heat exchanger 2, and cooled to an intermediate temperature. The raw material air At at the intermediate temperature is introduced into the expansion turbine 5 in the same manner as in the previous embodiment, expanded and reduced in pressure, and introduced into the lower introduction passage 23 or the upper introduction passage 24 at an appropriate ratio according to the operation mode. Is done.

Thus, the raw material air before being introduced into the expansion turbine 5
The amount of cold generated in the expansion turbine 5 can be increased by increasing the pressure of At (also possible with air derived from the lower tower) in advance, which is suitable, for example, for collecting liquid products such as liquefied oxygen.

In the above description of each embodiment, the expansion turbine portion, which is the gist of the present invention, has been mainly described. However, other components and operation methods are the same as those of this type of conventional air liquefaction / separation apparatus. The operation method can be appropriately performed by a commonly used means. For example, an expansion tar
This also includes the case where the air introduced into the bin is low-temperature air which is branched from the raw material air before being introduced into the main heat exchanger, introduced into the main heat exchanger, cooled to an intermediate temperature and led out.

In addition, if the argon yield in the argon collection priority operation is the same as the conventional one, the oxygen yield can be improved as described above, but usually, the yield of argon, which is more expensive than oxygen gas or liquefied oxygen, is improved. It is more effective to reduce the power consumption unit of argon.

〔The invention's effect〕

As explained above, the air liquefaction separation method of the present invention
Since the air expanded by the expansion turbine is introduced to a predetermined position in the upper tower according to the priority of oxygen or argon,
In the oxygen collection priority operation, the same oxygen yield and argon yield as before can be obtained, and in the argon collection priority operation, the argon yield is maintained in a state where the decrease in oxygen yield is maintained as before. The yield can be improved.

In addition, the apparatus of the present invention has a simple configuration because the introduction circuit extending from the expansion turbine to the upper tower is provided with an introduction path branching into the middle and upper stages of the upper tower and an introduction amount adjusting means such as a valve. The method of the present invention can be performed, the equipment cost is low, and the conventional apparatus can be modified.

[Brief description of the drawings]

FIG. 1 is a system diagram of a main part of an air liquefaction / separation apparatus showing a first embodiment of the present invention, FIG. 2 is a view showing a change in yield in each priority operation of oxygen and argon, and FIG. System diagram of a main part of an air liquefaction separation device showing a second embodiment of the invention,
FIG. 4 is a system diagram of a main part of an air liquefaction / separation apparatus showing a third embodiment of the present invention, and FIG. 5 is a system diagram of a main part of a conventional air liquefaction / separation apparatus. 2 ... main heat exchanger, 3 ... double rectification column, 5 ... expansion turbine, 6 ... upper column, 8 ... argon column, 9 ... lower column,
20,30,40 …… Air liquefaction separator, 21… Branch pipe, 22 ……
Introductory circuit, 23 …… Lower introduction path, 24 …… Upper introduction path, 25,2
6 ... Valve, 33 ... Branch pipe, 35 ... Outflow pipe, 41 ... Expansion turbine braking blower, A, At ... Raw air, Ao ... Air out from the lower tower, Ar ... Argon , GO ... oxygen gas

Claims (5)

(57) [Claims] An air liquefaction separation method capable of compressing and purifying raw air, cooling it in a main heat exchanger, introducing it into a double rectification column, and liquefying and separating to produce oxygen and argon simultaneously. The raw material air before being introduced into the rectification tower is branched, and at least one of the branched one of the raw material air and the air derived from the lower tower of the double rectification tower is cooled or heated. After being brought to the intermediate temperature, it is introduced into an expansion turbine, expanded and reduced to a pressure corresponding to the upper column pressure of the double rectification column, and then expanded and reduced in the expansion turbine by the raw air and / or lower column. When the air derived from is collected with priority on oxygen, the gas phase composition in the upper column is introduced into a rectification stage having substantially the same composition as the air composition. The gas phase composition in the upper tower is introduced into the rectification stage with a nitrogen-enriched composition rather than air composition Further cryogenic air separation method characterized by simultaneously introducing to both rectifying trays of the upper column when equally collected oxygen and argon. 2. The one of the branched raw material air is cooled to an intermediate temperature in a main heat exchanger, and is introduced into a low-temperature air branched out from the middle of the main heat exchanger or introduced into a main heat exchanger. The air liquefaction separation method according to claim 1, wherein the low temperature air is branched from the raw material air before being introduced, introduced into the main heat exchanger, and cooled to an intermediate temperature and led out. 3. One of the branched source airs is branched from the source air derived by cooling to a vicinity of a liquefaction point in a main heat exchanger, and is heated to an intermediate temperature in a reheat passage of the main heat exchanger. The air liquefaction separation method according to claim 1, wherein the low temperature air is used. 4. One of the branched raw material air is branched from the raw material air before being introduced into the main heat exchanger and introduced into a booster or an expansion turbine braking blower. The air liquefaction separation method according to claim 1, wherein the air is low-temperature air cooled to an intermediate temperature in an exchanger. 5. A main heat exchanger for cooling compressed and purified raw air, a double rectification column for rectifying raw air cooled to near a liquefaction point in the main heat exchanger, a part of raw air, An expansion turbine for expanding and reducing the pressure of at least one of the air derived from the lower column of the double rectification column, and a raw material air derived from the expansion turbine or air derived from the lower column. In the air liquefaction / separation apparatus including the introduction circuit for introducing the air into the upper tower, and the argon tower connected to the upper tower, the introduction circuit for introducing the air derived from the expansion turbine to the upper tower includes an upper tower. An introduction path connected to a rectification stage in which the gas phase composition in the tower is substantially the same as the air composition, and an introduction path connected to a rectification stage in which the gas phase composition in the column is more nitrogen-rich than the air composition, Introducing the inflating turbine to the introduction circuit Cryogenic air separation apparatus characterized by comprising the introduction amount adjusting means for adjusting the introduction amount of the road.