JPH0792329B2 - Air liquefaction separation method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air liquefaction separation method and apparatus for compressing, purifying and cooling air, and liquefying and separating at low temperature, and particularly to air liquefaction for producing low-purity oxygen. The present invention relates to a separation method and its device.

[Conventional technology]

FIG. 7 is a system diagram of a conventional typical low-purity oxygen production apparatus, in which the raw material air A removed by the filter 1 is used.
Is compressed by the raw material air compressor 2, cooled by the preheater 3 and the aftercooler 4, further cooled by the fluorocarbon cooling device 5, and then enters the adsorber 6, where water and carbon dioxide are removed, and the main heat exchanger It is cooled to the vicinity of the dew point by the low temperature gas at 7 and introduced into the lower part of the lower tower 8.

The raw material air A is rectified in the lower tower 8 and separated into a medium pressure nitrogen gas GN at the top of the tower and an oxygen-enriched liquefied air LA at the bottom of the tower. The liquefied air LA is supercooled by the liquefied air subcooler 10, expanded by the valve 11 and introduced into the middle stage of the upper tower 12 to obtain high-purity nitrogen gas HGN at the top of the tower, low-purity nitrogen gas WN in the middle of the tower, and It is separated into low-purity liquefied oxygen LO at the bottom of the column.

On the other hand, part of the medium pressure nitrogen gas GN at the top of the lower tower 8 is
It is introduced into the main condenser evaporator 13 arranged at the bottom of 12, and heat-exchanges with the above-mentioned low-purity liquefied oxygen LO to be liquefied to become liquefied nitrogen LN. A part of the liquefied nitrogen LN is returned to the top of the lower tower 8 to become a reflux liquid, and the rest is supercooled by the liquefied nitrogen subcooler 14 and then expanded by a valve 15 to be a top part of the upper tower 12. Is introduced as a reflux liquid.

The low-purity liquefied oxygen LO exchanges heat with the medium-pressure nitrogen gas GN and is vaporized to become the low-purity oxygen gas GO, a part of which is taken out from the upper tower, and the rest is the rising gas of the upper tower 12. Also, part of the low-purity liquefied oxygen LO is derived from the bottom of the upper tower 12,
It is circulated in a route that returns to the bottom of the upper tower 12 through the thermosiphon reboiler 16 and the circulation adsorber 17, and a part of it is circulated so-called safe liquid acid SO to prevent the accumulation of hydrocarbons.
Has been extracted as.

The rest of the medium-pressure nitrogen gas GN withdrawn from the top of the lower tower 8 is partially heated in the main heat exchanger 7 to a predetermined temperature, and then expanded in the expansion turbine 18 to about atmospheric pressure to cool it. The generated air is introduced into the main heat exchanger 7 again to cool the raw material air A, heated to room temperature and discharged to the atmosphere. The rest of the medium pressure nitrogen gas GN is heated by the main heat exchanger 7 while being kept at the medium pressure and is taken out to the outside to become the product medium pressure nitrogen gas MGN.

The high-purity nitrogen gas HGN and the low-purity nitrogen gas WN extracted from the upper tower 12 are heated to room temperature in the liquefied nitrogen subcooler 14, the liquefied air subcooler 10 and the main heat exchanger 7 to obtain high purity. The nitrogen gas HGN is collected as a product, and a part of the low-purity nitrogen gas WN is released from the valve 19 to the atmosphere. Low-purity nitrogen gas WN
The remaining part of is heated to a temperature (about 100 to 150 ° C.) necessary for regenerating the adsorber 6 by the preheater 3 and the electric heater 20 and sent to the adsorber 6. Also, during the cooling process of the adsorber 6,
The low-purity nitrogen gas was introduced into the adsorber 6 through the valve 21, and the adsorber 6
To cool.

Then, the low-purity oxygen gas GO extracted from the bottom of the upper tower 12
Is heated to room temperature in the main heat exchanger 7, and is a liquefied oxygen evaporator.
It is mixed with the safe liquid acid SO heated to 22 and brought to room temperature, compressed in the oxygen compressor 23, and delivered to the customer equipment as product low-purity oxygen gas PO.

FIG. 8 shows an example in which a sub-condensing evaporator 24 is provided in the system above in addition to the main condensing evaporator 13. Low-purity liquefied oxygen LO is led out from the bottom of the upper tower 12 and a valve 25 is used. After being expanded, it is introduced into the sub-condensing evaporator 24, and is heat-exchanged with the medium pressure nitrogen gas GN at the top of the lower tower 8 to be vaporized to obtain the product low-purity oxygen gas PO.

In this way, the low-purity liquefied oxygen LO is extracted from the bottom of the upper tower 12 and introduced into the sub-condensation evaporator 24, where it is vaporized, so that the composition of the low-purity liquefied oxygen LO at the bottom of the upper tower 12 is the product of low purity. It can have the same composition as the oxygen gas PO. At this time, the purity of the liquefied oxygen in the sub-condensation evaporator 24 becomes higher than the purity of the product low-purity oxygen gas PO, so the evaporation temperature of the liquefied oxygen is mainly condensed by lowering the pressure in the sub-condenser evaporation 24. It can be the same as the evaporation temperature of the liquefied oxygen in the vessel 13. As a result, the boiling point of the low-purity liquefied oxygen LO in the main condensation evaporator 13 and the sub-condensation evaporator 24 can be lowered, and the intermediate pressure introduced from the top of the lower tower 8 to the main condensation evaporator 13 and the sub-condensation evaporator 24 can be reduced. The temperature of nitrogen gas GN can be lowered. Therefore, the pressure of the lower tower 8, that is, the compression pressure of the raw material air A is lowered to reduce the power consumption.

For example, when the product low-purity oxygen gas PO is 1.45ata, 90% O ₂ , the composition of the low-purity liquefied oxygen LO at the bottom of the upper tower 12 is about 95.7% O _{2 in} the method shown in FIG. (Boiling point -180.2
° C.) and is, in the method shown in FIG. 8, is about 90.0% O ₂ (boiling point -181.5 ℃). In this way, the boiling point of low-purity liquefied oxygen LO drops by 1.3 ° C, so the medium pressure nitrogen gas G from the lower column 12
The temperature of N can also be reduced by 1.3 ° C. That is, since the dew point of the medium pressure nitrogen gas GN can be lowered, its pressure, that is, the compression pressure of the raw material air A can be lowered by about 0.5 kg / cm ² A.
According to this method, in the case of producing oxygen with a purity of 90%, the power consumption is reduced by about 4% as compared with the method of FIG. 7 (see FIG. 3).

[Problems to be solved by the invention]

However, in the above-mentioned one, the product low-purity oxygen gas, the upper tower rising gas, and the production of liquefied nitrogen introduced into the upper tower as a reflux liquid are used as low-purity liquefied oxygen in equilibrium with the product low-purity oxygen gas or product low-purity oxygen gas. Since it depends only on the heat exchange between the low-purity liquefied oxygen having the same concentration as the above and the medium pressure nitrogen gas at the top of the lower column, a high feed air pressure is required. In the rectification of the upper column, as shown in Fig. 9, the operating line OL and the equilibrium line GL are observed especially in the region where the oxygen concentration is high (lower left part of the diagram).
Are far apart, causing a significant loss of useful energy in the upper tower. This loss accounts for a large proportion of the effective energy loss of the entire air separation device.

Moreover, the effect of reducing the power cost by the method shown in FIG.
Compared to the method shown in the figure, it is about 4% when the product oxygen gas is 90% O ₂ , and about 1% when the product oxygen gas is 95% O ₂ . In this method, since the product low-purity oxygen gas is collected from the sub-condensing evaporator having a lower pressure than the upper tower, the load of the oxygen compressor is increased as compared with the method shown in FIG. The cost is a comparative value including this amount).

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an air liquefaction separation method and an apparatus therefor capable of improving these problems and significantly reducing power consumption.

[Means for solving problems]

In order to achieve the above object, the present invention firstly provides, as an air liquefaction separation method, an air liquefaction separation method in which raw material air is compressed, purified, and cooled, and then introduced into a double rectification column consisting of a lower tower and an upper tower, and liquefied In the method, the lower column is divided into a high-pressure lower column and a medium-pressure lower column, and the upper column is divided into a lower pressure first and second upper columns than the medium-pressure lower column, and high-pressure and medium-pressure raw materials. Air is supplied by two different supply systems, introduced into the high-pressure lower column and the medium-pressure lower column, respectively, for rectification separation, and the separated oxygen-enriched liquid air is extracted and expanded at the bottoms of both lower columns. After that, it is fed to the middle portion of the second upper column for further rectification, and the bottom liquid separated at the bottom of the second upper column is fed to the top of the first upper column as a reflux liquid. After rectifying and collecting product oxygen from the bottom of the first upper column, The nitrogen gas separated at the top of the partial column is used as the warm fluid of the main condenser evaporator which performs heat exchange with the bottom liquid of the first upper column, and the separated nitrogen gas at the top of the intermediate pressure lower column is As a warm fluid of the intermediate condenser evaporator that performs heat exchange with the bottom liquid of the second upper column, the oxygen-enriched gas separated at the top of the first upper column rises to the lower part of the second upper column. As the apparatus, the lower column is divided into a high-pressure lower column and an intermediate-pressure lower column, and the upper column is divided into a lower pressure first and second upper column than an intermediate-pressure lower column. Splitting, the bottoms of both lower towers and the middle part of the second upper tower are connected via an expansion valve, the bottom of the second upper tower and the top of the first upper tower are connected, and the first Connect the product oxygen sampling tube to the bottom of the upper tower, connect the top of the first upper tower and the bottom of the second upper tower, A main condenser evaporator for heat exchange between the gas at the top of the high-pressure lower column and the liquid at the bottom of the first upper column is provided, and the gas at the top of the medium-pressure lower column and the bottom of the second upper column are further arranged. A high pressure air supply system for supplying raw material air to the high pressure lower column, and an intermediate pressure air supply system for supplying raw material air to the medium pressure lower column. It is characterized by having.

[Work]

By configuring as described above, the pressure and temperature inside each tower can be optimized according to the composition of the rectified and separated gas or liquid, and the raw material air is divided into a high pressure air supply system and an intermediate pressure air supply system. By supplying as a whole, the compression pressure of the raw material air in the entire apparatus can be lowered, and the power consumption rate can be reduced.

〔Example〕

Hereinafter, the present invention will be described with reference to the drawings. It should be noted that the same elements as those in the conventional example have the same reference numerals or the same reference numerals a, b.
Will be attached and will not be described in detail. Further, in the following description, the composition and pressure of each gas-liquid, or the comparison of power costs, etc. shows the case where the pressure of the upper tower is 1.4 ~ 1.5ata, the pressure of the upper tower is more than this, For example, even when it is set to about 2ata, similarly good results can be obtained.

First, FIG. 1 shows a first embodiment of the present invention, in which the lower tower is divided into a high-pressure lower tower 30a and an intermediate-pressure lower tower 30b, and the upper towers are first and second It is divided into upper towers 31a and 31b.

The bottoms of the both lower towers 30a, 30b and the intermediate portion of the second upper tower 31b are connected via expansion valves 32a, 32b, and oxygen enrichment is rectified and separated into the bottoms of the both lower towers 30a, 30b. Liquefied air LA
Is introduced into the second upper tower 31b.

The bottom of the second upper tower 31b has a valve at the top of the first upper tower 31a.
Connected by conduit 34 with 33, second upper tower 31
b Low-purity liquefied oxygen LOb that is rectified and separated at the bottom is the first upper column
It is introduced into 31a as a reflux liquid.

A product oxygen sampling pipe 35 is connected to the bottom of the first upper tower 31a to collect the product low-purity oxygen gas PO. Further, the top of the first upper tower 31a is connected to the lower portion of the second upper tower 31b by a conduit 36 different from the conduit 34, and the first upper tower 31a.
Low-purity oxygen gas GO, which is rectified and separated at the top, is passed through the second upper column 31
Introduced as rising gas of b.

Furthermore, at the bottom of the first upper column 31a, a main condensing evaporator 37 for heat exchange between the nitrogen gas GNa at the top of the high-pressure lower column 30a and the low-purity liquefied oxygen LOa at the bottom of the first upper column 31a is provided. In addition, at the bottom of the second upper column 31b, nitrogen gas GNb at the top of the medium pressure lower column 30b and low-purity liquefied oxygen LO at the bottom of the second upper column 31b.
An intermediate condenser evaporator 38 for heat exchange with b is provided.

The raw material air supply system is composed of a high pressure air supply system 39 for supplying the raw material air Aa to the high pressure lower tower 30a and an intermediate pressure air supply system 40 for supplying the raw material air Ab to the medium pressure lower tower 30b. There is.

The apparatus of this embodiment will be described below according to the flow of air flow.

First, the raw material air Aa, Ab is dust-removed by the filters 1a, 1b in both the high-pressure air supply system 39 and the medium-pressure air supply system 40, compressed by the raw air compressors 2a, 2b to predetermined pressures, respectively, and the preheater 3 ( High pressure air supply system only) and after cooler 4
After being cooled by a, 4b and further cooled by CFC cooling devices 5a, 5b, they enter the adsorbers 6a, 6b to remove water and carbon dioxide gas, and the main heat exchangers 7a, 7b are brought to near the dew point by low temperature gas. To be cooled.

The raw material air Aa of the high pressure air supply system 39 is the high pressure lower tower.
Introduced at the bottom of 30a, raw air A of medium pressure air supply system 40
b is introduced at the bottom of the medium pressure lower column 30b.

The raw material air Aa, Ab is rectified in both lower columns 30a, 30b, and becomes high pressure and medium pressure nitrogen gas GNa, GNb at the top of the column and oxygen enriched liquefied air LA, LA at the bottom of the column. The liquefied air LA is subcooled by the liquefied air subcoolers 10a and 10b, respectively, expanded by the expansion valves 32a and 32b, introduced into the middle stage of the second upper column 31b and rectified, and high-purity nitrogen at the top of the column. Gas HGN, low-purity nitrogen gas WN in the middle of the tower, and low-purity liquefied oxygen LOb at the bottom of the tower are separated. This low-purity liquefied oxygen LOb has an oxygen concentration of 60 to 85% and has a first upper column 31a.
The concentration is lower than the oxygen concentration of the bottom liquid, and a part of it undergoes heat exchange with the intermediate pressure nitrogen gas GNb in the intermediate condenser evaporator 38 to be vaporized to become low-purity oxygen gas and rise in the second upper column 31b. It becomes gas.

The remaining low-purity peroxygen LOb having an oxygen concentration of 60 to 85% is introduced by the conduit 34 and introduced into the top of the first upper column 31 as a reflux liquid, and rectified to produce oxygen having an oxygen concentration of 32 to 65%. Separated into enriched gas GO and low-purity liquefied oxygen LOa having an oxygen concentration of 92 to 99%. This low-purity liquefied oxygen LOa has a higher oxygen concentration than the low-purified oxygen LOb at the bottom of the second upper column 31b by being rectified in the first upper column 31a.

And the low-purity liquefied oxygen LOa at the bottom of the first upper column 31a performs heat exchange with the high-pressure nitrogen gas GNa in the main condenser evaporator 37,
Evaporated into 80-98% low-purity oxygen gas, which is an equilibrium composition, and part of it is used as product low-purity oxygen gas PO.
It is taken out from 35, and the rest becomes the rising gas of the first upper tower 31a. Further, a part of the low-purity liquefied oxygen LOa is circulated through the circulation adsorber 17 by the thermosiphon reboiler 16 as in the conventional example, and a part thereof is extracted as a safe liquid acid SO.

Further, the oxygen-enriched gas GO at the top of the first upper tower 31a is led from the tower top by the conduit 36 and introduced into the lower part of the second upper tower 31b, and becomes the rising gas of the second upper tower 31b.

And the product low-purity oxygen gas PO extracted from the lower part of the first upper tower 31a is branched and warmed to room temperature in the main heat exchangers 7a and 7b, respectively, and then joined again, and further in the liquefied oxygen evaporator 22. The safe liquid acid SO, which has been warmed to normal temperature, joins and is compressed by the oxygen compressor 23 and sent to the customer facility.

On the other hand, a part of the high-pressure nitrogen gas GNa separated at the top of the high-pressure lower column 30a is introduced into the main condenser evaporator 37 arranged in the first upper column 31a, and exchanges heat with the low-purity liquefied oxygen LOa. To liquefy and condense into liquefied nitrogen to become liquefied nitrogen LNa. This liquefied nitrogen LNa is partially returned to the top of the high-pressure lower column 30a to become a reflux liquid, and the rest is expanded by the expansion valve 41 and then the intermediate-pressure lower column 30a.
It is introduced at the top of b and becomes the reflux liquid for the intermediate pressure lower column 30b.

Further, part of the medium pressure nitrogen gas GNb at the top of the medium pressure lower column 30b is introduced into the intermediate condenser evaporator 38 arranged in the second upper column 31b, and exchanges heat with the low-purity liquefied oxygen LOb. Liquefy,
It becomes liquefied nitrogen LNb, part of it becomes the reflux liquid of the intermediate pressure lower column 30b, and the rest is supercooled by the liquefied nitrogen subcooler 14 and then the expansion valve
It expands at 15 and is introduced at the top of the second upper tower 31b, and becomes the reflux liquid for the second upper tower 31b.

A part of the rest of the medium pressure nitrogen gas GNb is the main heat exchangers 7a, 7b.
After being heated to a predetermined temperature in the
At 18 it expands to about atmospheric pressure, produces cold, is again introduced into the main heat exchanger 7b, cools the medium pressure raw material air Ab, is heated to room temperature and is released to the atmosphere. Remaining medium pressure nitrogen gas GNb
Is heated in the main heat exchanger 7b at medium pressure and is heated to medium pressure nitrogen gas.
It is taken out as MGN.

Further, the high-purity nitrogen gas HGN at the top of the second upper tower 31b and the low-purity nitrogen gas WN at the middle of the tower are respectively discharged from the second upper tower 31b and are liquefied nitrogen supercooler 14, liquefied air subcooler 10a, 10b. After passing through the high-purity nitrogen gas HGN, the main heat exchanger 7a exchanges heat with the raw material air Aa to reach room temperature and is collected.

Further, the low-purity nitrogen gas WN exchanges heat with the raw material air Ab in the main heat exchanger 7b to reach room temperature, and part of it is released from the valve 19 to the atmosphere. The remaining part is heated to a temperature necessary for regenerating the adsorbers 6a and 6b by the preheater 3 and the electric heater 20, and both systems 3
It is sent to the respective adsorbers 6a and 6b of 9,40. Also adsorber 6
During the cooling process of a and 6b, the low-purity nitrogen gas WN is supplied to the valve 21a,
It is introduced from 21b into the adsorbers 6a and 6b, and the adsorbers 6a and 6b are cooled.

By thus forming the air liquefaction / separation device and setting the flow of each gas / liquid as described above, it is possible to set the optimum pressure and temperature in each column according to the composition of the gas or liquid that has been rectified and separated.

For example, when the composition of the product low-purity oxygen gas PO is 80 to 98% O ₂ , since the product low-purity oxygen gas PO derived from the lower part of the first upper tower 31a has this composition, the bottom of the first upper tower 31a The composition of the liquefied oxygen LOa is 92 to 99% O ₂ . At this time,
The composition of the liquefied oxygen LOb introduced as the reflux liquid of the first upper tower 31a from the second upper tower 31b may be lower than the composition of the liquefied oxygen LOa at the bottom of the first upper tower 31a due to the rectification action of the first upper tower 31a. , 60 to 85% O ₂ is good enough.

As a result, the boiling point of the liquefied oxygen LOb in the intermediate condenser / evaporator 38 provided at the bottom of the second upper column 31b is liquefied oxygen in the main condenser / evaporator 37 provided at the bottom of the first upper column 31a. Since the boiling point of LOa is lower than the boiling point of LOa, the dew point of nitrogen gas GNb introduced into the intermediate condensation evaporator 38 as a warm fluid can be lowered.

That is, it becomes possible to reduce the pressure of the nitrogen gas GNb,
In accordance with this, the lower tower is a high-pressure (5 Kg / cm ² A to ⁶ Kg / cm ² A) high-pressure lower tower 30 a and a lower pressure (0.8 to 2.5 Kg / CM ² A lower pressure, 3.2 Kg / cm ^{2 A to} 4.8). (Kg / cm ² A) medium pressure lower tower 30b, and the raw material air is divided into a high pressure air supply system 39 and a medium pressure air supply system 40 (high pressure air: 36
~ 55%, medium pressure air: the same 64-64%), the compression pressure of the raw material air in the entire device can be reduced, and the power consumption rate can be reduced.

The following table shows examples of the amount (rate) of raw material air and its pressure in the above device. For comparison, the pressure of the raw material air in the conventional apparatus shown in FIGS. 7 and 8 is shown.

As shown in the table above, under the requirements of this example,
53-63% is 0.9-1.8Kg / cm ² ab from conventional raw material air compression pressure
s A low intermediate pressure can be achieved, and the overall air compression amount can be reduced by about 10%.

The pressure ranges of the high-pressure lower column and the intermediate-pressure lower column are not limited to the above ranges, and can be set to a wider range when a higher value of the obtained power consumption unit is allowed. Accordingly, both the first upper column and the second upper column can be set to a wider pressure range.

Fig. 2 (Maccab of the upper tower in the method of the present invention.
As shown in the seal diagram), by providing the intermediate condenser / evaporator 38, the operation line OLa of the first upper column 31a part becomes the equilibrium line GL.
Since the first upper column 31a and the second upper column 31b are combined, effective energy loss as an upper column can be reduced, and the rectification separation efficiency of the entire apparatus can be improved.

Furthermore, since the product low-purity oxygen gas PO can be derived and collected at the pressure of the first upper column 31a, the load on the oxygen compressor 23 is not increased.

FIG. 3 shows the power consumption reduction effect in this example as 100 when 95% O ₂ is sampled by the apparatus of FIG. 7, and the apparatus of FIG. 8 is also shown as a reference. In all cases, the raw material air was purified by an adsorber, and medium pressure nitrogen gas (MGN) was not collected. The power of the oxygen compressor is also taken into consideration.

As is clear from the figure, the method and apparatus of the present invention can reduce power consumption by nearly 10% as compared with the conventional method and apparatus. Therefore, the operating cost can be reduced significantly,
It is possible to achieve cost reduction that exceeds the equipment cost for having two raw air systems.

Further, in the device in this example, at the same time as the low-purity oxygen gas from the first upper column, the medium-pressure nitrogen gas from the medium-pressure lower column and the high-purity nitrogen gas from the second upper column are collected. When nitrogen gas (product) from the lower tower is not needed, it is not necessary to collect it. When not collecting high-purity nitrogen gas from the second upper tower, only low-purity nitrogen gas is collected from the top of the second upper tower. You can derive it. Incidentally, when nitrogen gas is not collected from the upper middle pressure lower column, the amount of liquefied nitrogen introduced into the second upper column is increased correspondingly, and the required number of stages of the rectification plate is increased due to the increased reflux liquid of the column. As a result, the pressure at the bottom of the tower becomes lower, and the pressure of the raw material air can be further lowered.

FIG. 4 is a system in which a power recovery system is provided in the system shown in FIG. This power recovery system 42 introduces medium-pressure nitrogen gas MGN into the preheater 3 to heat it and then introduces it into the turbine 43, recovers the pressure of the nitrogen gas MGN as power, and supplies it to a power source such as a compressor or a pump. Is used as.

FIG. 5 is a middle pressure lower tower 30b in the system shown in FIG.
The medium pressure nitrogen gas GN derived from the above is only introduced into the intermediate condenser evaporator 38 of the second upper column 31b, and the air Ac is derived from the lower stage of the intermediate pressure lower column 30b to raise the temperature in the main heat exchangers 7a, 7b. After being allowed to flow, the air Ac, which has been introduced into the expansion turbine 18 and expanded and cooled, is introduced into the middle stage of the second upper tower 31b.

Further, FIG. 6 shows an example in which the water washing cooling towers 44a and 44b using cooling water Ca and Cb and the reversing (reversible) heat exchangers 45a and 45b are used in the feed air supply system. At the bottoms of both the high-pressure and intermediate-pressure lower columns 30a, 30b, liquefiers 46a, 46b for liquefying the air Aa, Ab at the bottoms are respectively connected, and at the bottom of the intermediate-pressure lower column 30b, a reboiler 47 is provided. A circulating circuit 48 provided is provided.

The raw material air Aa, Ab is compressed and then pre-cooled in the washing and cooling towers 44a, 44b, the switching valves 49a, 49b are used to switch and switch the flow paths, and the reversing heat exchangers 45a, 45b are cooled respectively, and a check valve. Five
It is introduced into both lower towers 30a and 30b through 0a and 50b. In the lower towers 30a, 30b and the first and second upper towers 31a, 31b, rectification separation and gas-liquid exchange are performed as in the above-described embodiment, and the product low-purity oxygen gas PO is collected.

On the other hand, the nitrogen gas WGN at the top of the second upper tower 31b is branched through the liquefied nitrogen subcooler 14, both of which have passed through the air subcoolers 10a and 10b, and then one of them is reversing the high pressure air supply system 39a. It is introduced into the heat exchanger 45a, cools the raw material air Aa and regenerates the reversing heat exchanger 45a, and the other one of the nitrogen gas WGN is introduced into the reversing heat exchanger 45b of the medium pressure air supply system 40a. To be done.

Further, a part of the medium-pressure nitrogen gas GNb derived from the medium-pressure lower column 30b is branched in three directions, and then the two systems are heated by the reversing heat exchangers 45a and 45b, respectively. Then, it merges with the medium-pressure nitrogen gas GNb while still at low temperature, expands in the expansion turbine 18 to generate cold, and merges with a part of the nitrogen gas WGN from the second upper tower 31b to form a medium-pressure air supply system. It is introduced into the reversing heat exchanger 45b of 40a to cool the raw material air Ab and regenerate the reversing heat exchanger 45b. The gas discharged from both reversing heat exchangers 45a and 45b merges and then is discharged through a valve 51.

As described above, the present invention can be implemented by various systems, and in any system, the operating cost can be significantly reduced as compared with the conventional system of the same type.

The gas-liquid composition, pressure and temperature of each tower can be appropriately set by the composition and pressure of the low-purity oxygen gas sampled as a product, and various conventional control equipment and the like can be added. It is possible to improve the power consumption rate.

In addition, each of the towers may be vertically separated by partitioning the inside of one rectification tower without being completely separated and independent. Especially in the upper column, since the internal pressures of the first upper column and the second upper column are about the same, even if they are generally formed and an intermediate condenser / evaporator is arranged in the middle part, the same action can be obtained. it can.

〔The invention's effect〕

As described above, the present invention divides the lower tower into a high-pressure lower tower and an intermediate-pressure lower tower, and divides the upper tower into first and second upper towers, and a high-pressure lower tower and a first upper tower. Between the middle pressure lower column and the second upper column, and a high-pressure air supply system for supplying raw air to the high-pressure lower column, Since an intermediate pressure air supply system for supplying raw material air to the lower pressure column was provided to supply gas and liquid of appropriate pressure, temperature, and composition to each part, it was significantly larger than the conventional air liquefaction separation method and its apparatus. It is possible to reduce the power consumption and to supply low-cost product gas.

[Brief description of drawings]

FIG. 1 is a system diagram showing one embodiment of the present invention, FIG. 2 is a McCabe seal diagram in the upper tower of the present invention, FIG. 3 is an explanatory diagram showing the effect of reducing power consumption, and FIGS. FIG. 6 is a system diagram showing another embodiment of the present invention, FIGS. 7 and 8 are system diagrams showing conventional examples, and FIG. 9 is a McCabe seal diagram in a conventional upper tower. . 2a, 2b ... Raw air compressor, 6a, 6b ... Adsorber, 7a, 7b ...
… Main heat exchanger, 18 …… Expansion turbine, 30a …… High pressure lower tower, 30b …… Medium pressure lower tower, 31a …… First upper tower, 31b ……
2nd upper tower, 32a, 32b …… expansion valve, 34 …… conduit, 35 ……
Product oxygen sampling tube, 36 ... Conduit, 37 ... Main condenser evaporator, 38
...... Intermediate condenser evaporator, 39 ...... High pressure air supply system, 40 ......
Medium pressure air supply system, 41 …… Expansion valve, Aa, Ab …… Material air, GNa, GNb …… Medium pressure nitrogen gas, GO …… Low purity oxygen gas, HGN …… High purity nitrogen gas, LA …… Liquefaction Air, LNa, LNb
...... Liquefied nitrogen, LOa, LOb …… Low-purity liquefied oxygen, MGN …… Product medium-pressure nitrogen gas, PO …… Product low-purity oxygen gas, WN …… Low-purity nitrogen gas

Claims (2)

[Claims] 1. An air liquefaction separation method in which raw material air is compressed, purified, cooled and introduced into a double rectification column composed of a lower tower and an upper tower, and liquefied and separated, wherein the lower tower is a high pressure lower tower and an intermediate pressure lower tower. And the upper tower is divided into a low pressure first and second upper tower from a medium pressure lower tower, and high pressure and medium pressure raw material air are supplied by two different supply systems,
Introduced into the high-pressure lower column and the medium-pressure lower column respectively for rectification separation, after the oxygen-enriched liquid air separated at the bottoms of both lower columns is expanded and expanded, then in the middle part of the second upper column. It is supplied and further rectified, and the bottom liquid separated at the bottom of the second upper column is supplied to the top of the first upper column as a reflux liquid to be rectified and the product is obtained from the bottom of the first upper column. While collecting oxygen, the nitrogen gas separated at the top of the high-pressure lower column is used as the warm fluid of the main condenser evaporator for heat exchange with the bottom liquid of the first upper column, and the column of the medium-pressure lower column is also used. The nitrogen gas separated at the top is used as a warm fluid of an intermediate condenser evaporator which performs heat exchange with the bottom liquid of the second upper column, and the oxygen-enriched gas separated at the top of the first upper column is the second gas. An air liquefaction separation method, characterized in that the gas is introduced as a rising gas into the lower part of the upper tower. 2. An air liquefaction separation apparatus for compressing, purifying and cooling raw material air and introducing the air into a double rectification column consisting of a lower tower and an upper tower, and liquefying and separating the lower tower, wherein the lower tower is a high pressure lower tower and an intermediate pressure lower tower. And the upper tower is divided into first and second upper towers of lower pressure than the middle-pressure lower tower, and the bottoms of both lower towers and the intermediate portion of the second upper tower through an expansion valve. Connecting, connecting the bottom of the second upper tower and the top of the first upper tower, connecting the product oxygen collection tube to the bottom of the first upper tower,
A top condenser of the first upper column and a bottom of the second upper column are connected, and a main condenser evaporator for heat-exchanging the gas at the top of the high-pressure lower column and the liquid at the bottom of the first upper column is provided. A high pressure air supply system for further providing an intermediate condenser evaporator for heat exchange between the gas at the top of the medium pressure lower column and the liquid at the bottom of the second upper column, and supplying raw material air to the high pressure lower column And an intermediate pressure air supply system for supplying raw material air to the intermediate pressure lower column.