JP5005708B2 - Air separation method and apparatus - Google Patents

Description

  The present invention relates to an air separation method and apparatus, and more particularly to an air separation method and apparatus for collecting oxygen as a product by low-temperature distillation of compressed, purified, and cooled raw material air.

As a method for producing product oxygen gas by cryogenic separation of air, a double rectification process as shown in FIG. 5 is the most common method (see Non-Patent Document 1).
The conventional double rectification process air separation apparatus 121 shown in FIG. 5 includes a high-pressure column 109 that separates compressed, purified, and cooled raw material air into low-pressure distilled and medium-pressure nitrogen gas and an oxygen-enriched liquid, and the reduced pressure The low pressure column 108 that separates the oxygen-enriched liquid into low-pressure nitrogen gas and high-pure liquefied oxygen by low-temperature distillation, and the medium-pressure nitrogen gas and the high-pure liquefied oxygen are indirectly heat-exchanged to condense and liquefy the medium-pressure nitrogen gas. To obtain medium pressure liquefied nitrogen and at the same time evaporate gas of high pure liquefied oxygen to obtain high pure oxygen gas, and a product that collects a part of the high pure oxygen gas as product oxygen gas after heat recovery The recovery path L124 is a main component.
Usually, the product oxygen gas is collected from the bottom of the low pressure column 108, and the product nitrogen gas is collected from the top of the low pressure column 108.

  One method for reducing power consumption in the double rectification process shown in FIG. 5 is to collect medium-pressure nitrogen gas from the top of the high-pressure column 109. When high-pressure nitrogen is required as a product, the power of the nitrogen compressor can be reduced by compressing the collected medium-pressure nitrogen gas, or the pressure of the product nitrogen is equal to or higher than the pressure of the medium-pressure nitrogen gas. If it is low, the nitrogen compressor can be omitted. Further, even when nitrogen is unnecessary, the collected medium pressure nitrogen gas can be expanded by an expansion turbine to recover power.

In the double rectification process shown in FIG. 5, the sampling rate of the medium pressure nitrogen gas is about 5 to 10% of the amount of raw material air. As a method of increasing this, the oxygen concentration of the liquid introduced into the low pressure column 108 is increased. A method is conceivable. By introducing a liquid having a relatively high oxygen concentration into the low-pressure column 108, the L / V of the recovery unit of the low-pressure column 108 can be increased. It is possible to reduce the amount of heat exchanged by the main condenser 106.
Therefore, the flow rate ratio of the medium pressure nitrogen gas introduced into the main condenser 106 out of the medium pressure nitrogen gas derived from the top of the high pressure column 109 can be reduced, and the flow rate of the medium pressure nitrogen gas that can be collected is increased. Can do.

  Further, as described above, when the oxygen concentration of the liquid introduced into the low pressure column 108 is increased to improve the L / V of the recovery unit of the low pressure column 108, it is supplied to the expansion turbine instead of collecting the intermediate pressure nitrogen gas. By increasing the gas flow rate, it is possible to increase the amount of cold generated and increase the amount of liquefied product collected.

Further, when the oxygen concentration of the liquid introduced into the low pressure column 108 is increased as described above to improve the L / V of the recovery unit of the low pressure column 108, it is introduced into the high pressure column 109 instead of collecting the medium pressure nitrogen gas. It is possible to reduce the amount of high-pressure raw material air to be supplied and supply a part of the raw material air to the low-pressure tower 108 at a low pressure, thereby reducing the power consumption of the air compressor.
A process for realizing these is shown in FIG.

The reference process shown in FIG. 6 is an improvement of the conventional process shown in FIG. 5. This air separation device 221 is a medium-pressure nitrogen gas and oxygen-enriched liquid obtained by low-temperature distillation of compressed, purified, and cooled raw material air. A high pressure column 209 that separates into a low pressure, a first low pressure column 281 that separates the decompressed oxygen-enriched liquid into low-pressure nitrogen gas and low-pure liquefied oxygen, and a low-pressure distillation of the pressurized low-pure liquefied oxygen. The second low pressure column 282 that separates into low pure nitrogen gas and high pure liquefied oxygen, and the intermediate pressure nitrogen gas and the high pure liquefied oxygen are indirectly heat-exchanged to condense and liquefy the intermediate pressure nitrogen gas. At the same time as obtaining nitrogen, high purity liquefied oxygen is vaporized to obtain high purity oxygen gas, and the low purity nitrogen gas and the low purity liquefied oxygen are indirectly heat exchanged to condense the low purity nitrogen gas. Liquefied to obtain low pure liquefied nitrogen and at the same time low pure liquefied oxygen An intermediate condenser 216 for generating low purity oxygen gas by generating gas, a product recovery path L224 for collecting a part of the high purity oxygen gas as a product oxygen gas GO after heat recovery, and a part of the medium pressure oxygen gas A product recovery path L207, which is collected as product intermediate pressure nitrogen gas MGN after heat recovery, is a main component.
The product oxygen gas is collected from the bottom of the second low pressure column 282, and the product nitrogen gas is collected from the top of the first low pressure column 281 and the top of the high pressure column 209, respectively.

In the conventional process shown in FIG. 5, an oxygen-enriched liquid having an oxygen concentration of about 40% is introduced into the middle portion of the low-pressure column. On the other hand, in the reference process shown in FIG. Low-pure liquefied oxygen distilled and separated in one low-pressure column and concentrated to an oxygen concentration of 90% or more is introduced into the middle of the second low-pressure column.
Thereby, since the L / V can be increased by improving the distillation efficiency of the second low-pressure column recovery section, the flow rate of the high purity oxygen gas which is evaporated and gasified in the main condenser can be reduced, and the intermediate pressure It is possible to increase the amount of nitrogen gas collected, increase the amount of liquefied product collected, or supply a part of the raw material air at a low pressure.

However, the reference process shown in FIG. 6 has a problem that the operating pressure of the high-pressure tower is significantly higher than that of the conventional process of FIG. 5, and the power consumption of the air compressor is greatly increased.
The reason for this is that, in the intermediate condenser 216, low pure liquefied oxygen at the bottom of the first low-pressure column 281 is vaporized with low pure nitrogen gas at the top of the second low-pressure column 282, for example, due to a process restriction. It is necessary to increase the operating pressure of the second low-pressure column 282 to about 0.47 MPaA when the operating pressure of the first low-pressure column 281 is 0.13 MPaA. Similarly, in the main condenser 206, the bottom of the second low-pressure column 282 This is because the operating pressure of the high-pressure column needs to be increased to about 1.43 MPaA due to process restrictions that require evaporative gasification of the high-pure liquefied oxygen with medium-pressure nitrogen gas at the top of the high-pressure column 209.

Takashi Tsuji, Hideyuki Hashimoto “Refrigeration and Air Conditioning Handbook” Volume 2, 6th edition, pages 402-406, Japan Society of Refrigerating and Air Conditioning Engineers

  The object of the present invention is to improve the second low-pressure column recovery unit in the above reference process to increase the amount of medium-pressure nitrogen gas collected, increase the amount of liquefied product collected, or supply one part of raw air at a low pressure It is an object of the present invention to provide an air separation method and apparatus capable of reducing power consumption by lowering the operating pressure of the second low-pressure column and lowering the operating pressure of the high-pressure column and the raw material air pressure. .

  In order to achieve the above object, the air separation method of the present invention is an air separation method for collecting product oxygen by cryogenic liquefaction separation of raw material air. A first separation step for separating the gas into a first oxygen-enriched liquid; and a second process for separating the first oxygen-enriched liquid into a first low-pressure nitrogen gas and a second oxygen-enriched liquid by low-temperature distillation after decompression. The second oxygen-enriched liquid is heated by indirect heat exchange with the condensation distillation passage in the separation step and the evaporation distillation passage of a heat exchange type distiller having an evaporative distillation passage and a condensation distillation passage that can exchange heat indirectly with each other. A third separation step in which a part of the second oxygen-enriched liquid is distilled while evaporating and separating it into a first oxygen-enriched gas and low-pure liquefied oxygen; and the low-pure liquefied oxygen is distilled at a low temperature To separate the second oxygen-enriched gas and the highly pure liquefied oxygen The second oxygen-enriched gas is cooled by indirect heat exchange with the evaporative distillation passage in the condensation distillation passage of the heat exchange-type distiller, and a part of the second oxygen-enriched gas is distilled while being condensed and liquefied. A fifth separation step for separating the second low-pressure nitrogen gas and the third oxygen-enriched liquid, and the intermediate-pressure nitrogen gas and the highly pure liquefied oxygen are indirectly heat exchanged to condense and liquefy the intermediate-pressure nitrogen gas. An indirect heat exchange step for obtaining high-pure oxygen gas by evaporating gas of high-pure liquefied oxygen at the same time as obtaining pressurized liquefied nitrogen; and a product recovery step for collecting a part of the high-pure oxygen gas as product oxygen gas after heat recovery; It is characterized by including.

  Furthermore, in the air separation method of the present invention, in the air separation method of the above-described configuration, in order to obtain coldness necessary for operation of the apparatus, a cold generation step of introducing a part of the raw material air into an expansion turbine to expand, or the above A cold generating step of introducing a part of the medium-pressure nitrogen gas into the expansion turbine to expand, or a cold generating step of introducing a part or all of the first low-pressure nitrogen gas into the expansion turbine to expand, or the second low pressure It is characterized in that it includes any one of the cold generation steps in which a part or all of the nitrogen gas is introduced into the expansion turbine and expanded.

  Further, the air separation device of the present invention is an air separation device that collects product oxygen by cryogenic liquefaction separation of raw material air. The compressed, purified, and cooled raw material air is subjected to low-temperature distillation to obtain medium pressure nitrogen gas and primary oxygen. A high-pressure column that separates into an enriched liquid; a first low-pressure column that separates the first oxygen-enriched liquid into a first low-pressure nitrogen gas and a second oxygen-enriched liquid by low-temperature distillation after decompression; A condensable distillation passage and an evaporative distillation passage that are exchangeable, and the condensing distillation passage heats a part of the second oxygen-enriched liquid by indirect heat exchange with the evaporative distillation passage and distills while evaporating and gasifying it. 1 Oxygen-enriched gas and low-pure liquefied oxygen are separated, and the evaporative distillation passage cools a part of the second oxygen-enriched gas described later by indirect heat exchange with the condensation distillation passage and distills while condensing into liquid. Into a second low-pressure nitrogen gas and a third oxygen-enriched liquid. A heat-exchange distiller, a second low-pressure column that separates the low-pure liquefied oxygen into a second oxygen-enriched gas and high-pure liquefied oxygen by low-temperature distillation, and the medium-pressure nitrogen gas and high-pure liquefaction A main condenser for indirect heat exchange with oxygen to condense and liquefy medium pressure nitrogen gas to obtain medium pressure liquefied nitrogen and at the same time evaporate gas of high pure liquefied oxygen to obtain high pure oxygen gas; and the high pure oxygen gas A product recovery path for collecting a part of the product as product oxygen gas after heat recovery is provided.

  According to the present invention, a heat exchange type distiller configured by a condensing distillation passage and an evaporative distillation passage, and capable of distilling in each passage at the same time while exchanging heat between both passages, is efficiently used. The low-pressure column and the second low-pressure column can be thermally coupled, and the amount of medium-pressure nitrogen gas collected, the amount of liquid collected can be increased, The supply power of the entire apparatus can be reduced by suppressing the increase of the raw material air pressure while supplying the part at a low pressure.

It is a schematic block diagram which shows 1st Embodiment of the air separation apparatus of this invention. It is a schematic block diagram which shows 2nd Embodiment of the air separation apparatus of this invention. It is a schematic block diagram which shows 3rd Embodiment of the air separation apparatus of this invention. It is a schematic block diagram which shows 4th Embodiment of the air separation apparatus of this invention. It is a schematic block diagram which shows the air separation apparatus of the conventional process. It is a schematic block diagram which shows the air separation apparatus of a reference process. It is a schematic block diagram which shows the air separation apparatus of another conventional process. It is a schematic block diagram which shows the air separation apparatus of another reference process.

A first embodiment of the air separation device of the present invention is shown in FIG.
The air separation device 21 in this example includes an air compressor 1 that compresses raw material air, an air precooler 2 that removes the compression heat of the compressed raw material air, and impurities (moisture, moisture) in the raw material air that has passed through the air precooler 2. Carbon dioxide and the like, a main heat exchanger 4 that cools the raw air that has passed through the purifier 3, and medium-pressure nitrogen gas at the top of the tower by low-temperature distillation of the raw air that has passed through the main heat exchanger 4 A high-pressure column 9 that separates into a first oxygen-enriched liquid at the bottom of the column, and low-temperature distillation of the first oxygen-enriched liquid after depressurization, and a first low-pressure nitrogen gas at the top of the column and a second oxygen-enriched liquid at the bottom of the column And a condensing distillation passage 51 and an evaporative distillation passage 52 that are capable of indirect heat exchange with each other, and the condensing distillation passage 51 performs the second oxygen by indirect heat exchange with the evaporative distillation passage 52. Distilling while heating a part of the enriched liquid to evaporate gas 1 The oxygen-enriched gas and the low-pure liquefied oxygen are separated, and the evaporative distillation passage 52 cools a part of the second oxygen-enriched gas described later by indirect heat exchange with the condensation distillation passage 51 to condense and liquefy. While distilling and separating into a second low-pressure nitrogen gas and a third oxygen-enriched liquid, and the low-pure liquid oxygen is subjected to low-temperature distillation to produce a second oxygen-enriched gas and a high-pure gas. At the same time as obtaining the intermediate pressure liquefied nitrogen by condensing and liquefying a part of the intermediate pressure nitrogen gas by indirect heat exchange between the second low pressure column 82 separated into liquefied oxygen and the intermediate pressure nitrogen gas and the high purity liquefied oxygen. A main condenser 6 that evaporates high-pure liquefied oxygen to obtain high-pure oxygen gas, an expansion turbine 10 that introduces a part or all of the medium-pressure nitrogen gas to obtain the cooling required for the apparatus, and the high-pure oxygen A product recovery path L24 for collecting a part of oxygen gas as product oxygen gas after heat recovery; Some of the serial in-pressure nitrogen gas product recovery path L7 harvesting as a product during pressure nitrogen gas after heat recovery, a blower 11, to a subcooler 7 and the main components.

Next, a first embodiment of an air separation method using the air separation device 21 will be described.
After the raw material air is compressed by the air compressor 1 and cooled to near normal temperature by the air precooler 2, impurities such as moisture and carbon dioxide in the raw material air are adsorbed and removed in the purifier 3. The raw material air that has passed through the purifier 3 is introduced into the cold insulation outer tank 15, is cooled to near the dew point in the main heat exchanger 4, and is introduced into the high-pressure tower 9 through the path L <b> 5.

  The raw material air introduced into the high-pressure tower 9 is distilled by gas-liquid contact with medium pressure liquefied nitrogen described later, and the nitrogen component is concentrated toward the top of the tower. Part of the medium-pressure nitrogen gas led out from the top of the high-pressure tower 9 is branched to a path L6, recovered by the main heat exchanger 4 and then led out from the cold storage outer tank 15, and as product medium-pressure nitrogen gas MGN Collected.

The remainder of the medium-pressure nitrogen gas is introduced into the main condenser 6 via the path L8, and the high-pure liquefied oxygen is evaporated by indirect heat exchange with the high-pure liquefied oxygen at the bottom of the second low-pressure column 82, which will be described later. Is condensed to medium pressure liquefied nitrogen. Part of the condensed medium pressure liquefied nitrogen is introduced into the top of the high pressure column 9 via the path L9 as the reflux liquid of the high pressure column 9.
The remainder of the medium pressure liquefied nitrogen is cooled through the supercooler 7, and after being decompressed by the pressure reducing valve V <b> 1, is introduced into the top of the first low pressure column 81.
In addition, the first oxygen-enriched liquid led out from the bottom of the high-pressure column 9 is cooled through the supercooler 7, depressurized by the pressure reducing valve V <b> 2, and then introduced into the lower portion of the first low-pressure column 81.

  In the first low-pressure column 81, the medium-pressure liquefied nitrogen decompressed by the decompression valve V1, the first oxygen-enriched liquid decompressed by the decompression valve V2, and a first oxygen-enriched gas described later are distilled, The nitrogen component concentrates in the upper part of the first low-pressure column 81 and the oxygen component concentrates in the lower part. The first low-pressure nitrogen gas is led out from the top of the first low-pressure tower 81 to the path L14, is recovered from the heat through the supercooler 7 and the main heat exchanger 4, and is led out from the cold insulation outer tank 15 to produce the product low-pressure nitrogen. Collected as gas GN. Part or all of the product low-pressure nitrogen gas GN can be used for regeneration of the purifier 3.

From the bottom of the first low-pressure column 81, the second oxygen-enriched liquid is led out to the path L16 and introduced into the upper part of the evaporative distillation passage 52 of the heat exchange-type distiller 5.
In the evaporative distillation passage 52 of the heat exchange type distiller 5, the second oxygen-enriched liquid introduced from above is partly exchanged with the fluid in the condensation distillation passage 51 in the process of descending the evaporative distillation passage 52. While evaporating, the nitrogen component is concentrated in the upper portion of the evaporative distillation passage 52 and the oxygen component is concentrated in the lower portion.

  The first oxygen-enriched gas led to the path L17 from the upper part of the evaporative distillation passage 52 of the heat exchange-type distiller 5 is introduced to the lower part of the first low-pressure column 81 and led to the path L18 from the lower part of the evaporative distillation path 52. The low purity liquefied oxygen thus introduced is introduced into the middle or upper part of the second low pressure column 82. Usually, the operating pressure of the evaporative distillation passage 52 is lower than the operating pressure of the second low-pressure column 82, but since the pressure difference is relatively small, the liquid can be fed by the liquid head of low pure liquefied oxygen in the path L18. However, if necessary, a liquid pump can be provided in the path L18 to send the liquid.

In the second low-pressure column 82, low pure liquefied oxygen introduced from the evaporative distillation passage 52 via the path L18, a third oxygen-enriched liquid described later, and a part of the high pure oxygen gas evaporated by the main condenser 6 And the nitrogen component concentrates in the upper part of the second low-pressure column 82 and the oxygen component concentrates in the lower part.
The second oxygen-enriched gas led out from the top of the second low-pressure column 82 to the path L19 is introduced into the lower part of the condensation distillation passage 51 of the heat-exchange distiller 5, and is routed from the bottom of the second low-pressure column 82 to the path L19. A part of the high-purity oxygen gas led out to L23 is led out from the cold insulation outer tank 15 after being recovered by the main heat exchanger 4, and collected as product oxygen gas GO.

  In the condensation distillation passage 51 of the heat exchange type distiller 5, the second oxygen-enriched gas introduced from the lower part exchanges heat with the fluid in the evaporation distillation passage 52 in the process of rising in the condensation distillation passage 51, and is partially condensed. While being distilled, the nitrogen component concentrates in the upper part of the condensation distillation passage 51 and the oxygen component concentrates in the lower part.

  The second low-pressure nitrogen gas led out from the upper part of the condensing distillation passage 51 of the heat exchange type distiller 5 to the path L21 is recovered from the heat through the supercooler 7 and the main heat exchanger 4, and then from the cold insulation outer tank 15. Derived and collected as product low-pressure nitrogen gas GN. The third oxygen-enriched liquid led out from the lower part of the condensation distillation passage 51 to the path L20 is introduced into the upper part of the second low-pressure column 82.

  When collecting the product liquefied oxygen LO, the high-pure liquefied oxygen at the bottom of the second low-pressure column 82 can be led to the path L25 and collected. When collecting the product liquefied nitrogen LN, the medium-pressure liquefied nitrogen A part can be branched to the path L26 and collected.

  The cold necessary for the operation of the apparatus is led out from the top of the high-pressure column 9, branched, and part or all of the intermediate-pressure nitrogen gas recovered by heat is branched into the path L <b> 2. Can be introduced and expanded. When the pressure of the intermediate pressure nitrogen gas is increased by the blower 11, it is preferable that the blower 11 is driven coaxially with the expansion turbine 10 and using power obtained when the expansion air is adiabatically expanded by the expansion turbine 10.

  As indicated by a broken line in FIG. 1, the second low-pressure nitrogen gas can be introduced into the intermediate portion of the first low-pressure column 81 after being led to the path L21.

  Further, as in the air separation device 22 of the second embodiment shown in FIG. 2, a part of the raw material air that has been compressed and purified for the operation of the device is branched into a path L31 and pressurized by the blower 31. It can also be obtained later by being introduced into the expansion turbine 30 and expanded. The expanded raw material air is introduced into the first low-pressure column 81 via the path L32.

  Further, as in the air separation device 23 of the third embodiment shown in FIG. 3, a part of the product low-pressure nitrogen gas GN is branched into a path L41 for the cooling necessary for the operation of the device, and the pressure is increased by the blower 41 and then expanded. It can also be obtained by being introduced into the turbine 40 and expanded. In this case, it is necessary to increase the pressure of the product low-pressure nitrogen gas GN so that the expansion ratio required by the expansion turbine 40 can be obtained, and the operation is performed by increasing the pressure of the entire apparatus.

  In the air separation device configured in this way, compared with the case where a conventional process is used, the amount of medium-pressure nitrogen gas collected is increased and the increase in the raw material air pressure is suppressed to reduce the power consumption of the entire device. Will be able to.

Next, the effects of the first embodiment shown in FIG. 1 will be described in comparison with the conventional process shown in FIG. 5 and the reference process shown in FIG.
The component of the conventional process that can be regarded as substantially the same as the component of the first embodiment is given a symbol consisting of a number added with 100, and the component of the reference process is assigned a symbol consisting of a number added with 200. It is.

  As described above, the air separation device 121 of the conventional process shown in FIG. 5 is a high pressure column 109 that separates compressed, purified, and cooled raw material air into low-pressure nitrogen gas and oxygen-enriched liquid by low-temperature distillation, The low-pressure column 108 for separating the decompressed oxygen-enriched liquid at low temperature and separating it into low-pressure nitrogen gas and high-pure liquefied oxygen; and the intermediate-pressure nitrogen gas and the high-pure liquefied oxygen are indirectly heat-exchanged to obtain medium-pressure nitrogen gas. To obtain medium pressure liquefied nitrogen and at the same time, main condenser 106 to obtain high pure oxygen gas by evaporating gas of high pure liquefied oxygen, and a part of the high pure oxygen gas as product oxygen gas after heat recovery The product collection path L124 to be collected is a main component.

In the conventional process shown in FIG. 5, when medium pressure nitrogen gas is collected, a part of medium pressure nitrogen gas derived from the top of the high pressure column 109 can be collected as product medium pressure nitrogen gas MGN after heat recovery.
When producing higher-pressure nitrogen gas, the product intermediate pressure nitrogen gas MGN is boosted with a nitrogen compressor, or even when nitrogen is not required, the product intermediate pressure nitrogen gas MGN is expanded with an expansion turbine to recover power. By doing so, the power consumption of the entire apparatus can be reduced.

However, as the amount of collected intermediate-pressure nitrogen gas is increased, the intermediate-pressure nitrogen gas introduced into the main condenser 106 decreases, the amount of exchange heat of the main condenser 106 decreases, and evaporative gasification occurs at the bottom of the low-pressure column 108. The amount of high pure oxygen gas to be reduced is reduced.
The rising gas in the recovery unit of the low-pressure column 108 contributes to distillation in the recovery unit of the low-pressure column 108, and the low-pressure column 108 has a low pressure due to the oxygen concentration at the bottom of the low-pressure column 108, the oxygen concentration of the liquid introduced into the middle of the low-pressure column 108, the pressure, and the like. The amount of rising gas required for the tower 108 recovery section is determined.
Therefore, when the amount of high pure oxygen gas that evaporates at the bottom of the low pressure column 108 decreases, the product oxygen gas is reduced and the rising gas in the recovery unit of the low pressure column 108 is maintained in order to maintain the oxygen concentration at the bottom of the low pressure column 108. The amount must be maintained and the oxygen recovery rate is reduced.
Due to this restriction, the extraction rate of medium pressure nitrogen gas in the conventional process with respect to the amount of raw material air is optimally about 5 to 10%.

  By the way, the amount of ascending gas necessary for the low pressure column recovery section can be reduced by increasing the oxygen concentration of the liquid introduced into the middle section of the low pressure column. Therefore, while maintaining the oxygen recovery rate, In order to increase the amount to be collected, the oxygen concentration of the liquid introduced into the middle part of the low-pressure column may be increased. The process for realizing this is shown in FIG.

  As described above, the air separation device 221 of the reference process shown in FIG. 6 is a high-pressure column 209 that separates compressed, purified, and cooled raw material air into low pressure nitrogen gas and oxygen-enriched liquid by low-temperature distillation. A first low-pressure column 281 that separates the decompressed oxygen-enriched liquid at low temperature to separate it into low-pressure nitrogen gas and low-pure liquefied oxygen; and low-pressure nitrogen gas and high-pure water that are low-pressure distilled from the pressurized low-pure liquid oxygen. The second low-pressure column 282 that separates into liquefied oxygen and the intermediate-pressure nitrogen gas and the high-pure liquefied oxygen are indirectly heat-exchanged to condense and liquefy the medium-pressure nitrogen gas to obtain medium-pressure liquefied nitrogen and at the same time high-pure liquefaction. The main condenser 206 for evaporating oxygen to obtain high pure oxygen gas, and the low pure nitrogen gas and the low pure liquefied oxygen are indirectly heat exchanged to condense and liquefy the low pure nitrogen gas to produce low pure liquefied nitrogen. At the same time, low pure oxygen gas is obtained by evaporating low pure liquid oxygen. Intermediate condenser 216, product recovery path L224 for collecting a part of the high purity oxygen gas as product oxygen gas GO after heat recovery, and a part of the intermediate pressure oxygen gas as product intermediate pressure nitrogen gas MGN after heat recovery The product collection path L207 to be collected is a main component.

  In the conventional process of FIG. 5, the oxygen concentration of the oxygen-enriched liquid introduced into the low-pressure column 108 is about 40%. However, in the reference process of FIG. Distillation and separation into low-pure liquefied oxygen having an oxygen concentration of 90% or more and introducing this low-pure liquefied oxygen into the middle part of the second low-pressure column 282 may reduce the amount of ascending gas required for the second low-pressure column 282 recovery unit. Therefore, the amount of collected medium-pressure nitrogen gas MGN can be increased while maintaining the oxygen recovery rate.

However, in the reference process of FIG. 6, in the intermediate condenser 216, the low pure liquefied oxygen at the bottom of the first low pressure column 281 must be evaporated and gasified with the low pure nitrogen gas at the top of the second low pressure column 282. Due to the above restrictions, for example, when the operating pressure of the first low pressure column 281 is 0.13 MPaA, the operating pressure of the second low pressure column 282 needs to be increased to about 0.47 MPaA.
Similarly, in the main condenser 206, the operating pressure of the high pressure column 209 is reduced to about 1.43 MPaA in order to evaporate and gasify the highly pure liquefied oxygen at the bottom of the second low pressure column 282 with the medium pressure nitrogen gas at the top of the high pressure column 209. Since it is necessary to raise, the raw material air pressure becomes about 1.47 MPaA, and there is a problem that the power consumption of the air compressor 201 is significantly increased.

  On the other hand, in the first embodiment of the present invention, a device similar to the reference process for increasing the amount of collected intermediate-pressure nitrogen gas MGN by reducing the amount of ascending gas required in the second low-pressure column recovery unit is used. Even in this case, it is possible to suppress an increase in the operating pressure of the second low-pressure column 82 by efficiently heat-integrating the first low-pressure column and the second low-pressure column using the heat exchange-type distiller 5.

In the reference process of FIG. 6, while the low pure liquefied oxygen and the low pure nitrogen gas are subjected to heat exchange in the intermediate condenser 216, the low pure liquefied oxygen is evaporated and simultaneously the low pure nitrogen gas is condensed and liquefied. In the process of the present invention, in the heat exchange-type distiller 5, the evaporative distillation passage 52 and the condensation distillation passage 51 are subjected to heat exchange, and the liquid descending the evaporative distillation passage 52 is evaporated and gasified, and at the same time, the condensation distillation passage 51 is The rising gas is condensed and liquefied. In the heat exchange-type distiller 5, heat exchange and distillation are performed at the same time. Therefore, in each passage, the nitrogen component is concentrated in the upper part and the oxygen component is concentrated in the lower part by distillation.
Therefore, heat exchange between the nitrogen-enriched fluids is performed at the upper part of the heat exchange-type distiller 5, and heat exchange between the oxygen-enriched fluids is performed at the lower part, so that the passages can be operated at close pressures. Therefore, since the pressure rise in the second low-pressure column 82 can be suppressed and the raw material air pressure can be made to be approximately the same as that in the conventional process of FIG. 1, the product intermediate-pressure nitrogen gas MGN is efficiently collected to reduce the power consumption. be able to.

  Further, instead of collecting the product intermediate pressure nitrogen gas MGN, it is possible to increase the amount of medium pressure nitrogen gas introduced into the expansion turbine and increase the amount of cold generation to collect the liquefied product. The product liquefied oxygen LO is extracted from the bottom of the second low-pressure column 82 to the path L25 and collected, and the product liquefied nitrogen LN is condensed and liquefied by the main condenser 6 and is supplied to the first low-pressure column. The part is derived to the path L26 and collected.

  In the case of the process of the second embodiment shown in FIG. 2, by increasing the ratio of the raw air supplied to the blower 31 and the expansion turbine 30 by branching to the path L31, the generated cold amount is increased and the product liquefied oxygen LO or the product is increased. Liquefied nitrogen LN can be collected. When the raw material air amount of the expansion turbine 30 is increased and the raw material air amount supplied to the high pressure tower 9 is decreased, the medium-pressure nitrogen gas introduced into the main condenser 6 is reduced and the exchange heat amount of the main condenser 6 is reduced. Therefore, the amount of rising gas in the second low-pressure column 82 recovery section tends to decrease, but by reducing the product intermediate-pressure nitrogen gas MGN, the exchange heat amount of the main condenser 6 is made constant so that the expansion turbine 30 It is possible to cope with an increase in the amount of liquefied product due to an increase in the amount of cold generated.

  In the case of the process of the third embodiment shown in FIG. 3, by increasing the operating pressure of the entire apparatus and increasing the pressure of the waste gas supplied to the expansion turbine 40, the amount of generated cold is increased and the product liquefied oxygen LO or Product liquefied nitrogen LN can be collected. When the operating pressure of the apparatus is increased, the distillation efficiency in the rectification column decreases, and the amount of ascending gas required in the second low pressure column 82 recovery section tends to increase, but by reducing the product intermediate pressure nitrogen gas MGN, Increasing the amount of heat exchanged in the main condenser 6 can cope with an increase in operating pressure.

Next, a fourth embodiment of the present invention is shown in FIG. The air separation device 24 includes a low-pressure air compressor 91 that compresses a part of the raw material air, a low-pressure air precooler 92, and a low-pressure purifier 93 in addition to the air separation device 21 of the first embodiment. Have been added.
An embodiment using the air separation device 24 will be described focusing on the difference from the first embodiment.
Part of the raw material air necessary for the apparatus is compressed by the air compressor 1, purified in the same manner as in the first embodiment, and then supplied to the high-pressure column 9 via the main heat exchanger 4. On the other hand, the remaining raw material air necessary for the apparatus is compressed by the low-pressure air compressor 91, introduced into the cold insulation outer tank 15, cooled by the main heat exchanger 4, and then supplied to the first low-pressure column 81.
Inside the cold insulation outer tank 15, as in the first embodiment, the high pressure column 9, the first low pressure column 81, the second low pressure column 82, the heat exchange distillation unit 5, the main condenser 6, the supercooler 7, etc. Distillation and heat exchange are performed, and product oxygen gas GO, product low-pressure nitrogen gas GN, product medium-pressure nitrogen gas MGN, product liquefied oxygen LO, and product liquefied nitrogen LN are collected.

  In the air separation apparatus configured as described above, by reducing the product intermediate pressure nitrogen gas MGN, as described above, the amount of raw material air supplied to the high pressure column 9 is reduced as compared with the case where the conventional process is used. Therefore, part of the raw material air necessary for the apparatus can be supplied at a low pressure, so that the power consumption of the entire apparatus can be reduced.

Example 1
Using the air separation device 21 of the first embodiment shown in FIG. 1, product oxygen gas having an oxygen concentration of 99.6% or more and product intermediate-pressure nitrogen gas having an allowable oxygen concentration of 1 ppm are sampled from the raw air having a flow rate of 1000. An example of the case will be described.
The compressed and refined raw material air having a flow rate of 1000, 0.55 MPaA and 40 ° C. is introduced into the cold insulation outer tank 15, cooled to the vicinity of the dew point in the main heat exchanger 4, and operated at 0.53 MPaA. To be introduced. The raw air introduced into the high-pressure column 9 is separated into medium-pressure nitrogen gas having an oxygen concentration of 1 ppm and a first oxygen-enriched liquid having an oxygen concentration of 39.7%, and the medium-pressure led out from the top of the high-pressure column 9 The flow rate 280 of the nitrogen gas is derived from the cold insulation outer tank 15 after being recovered by the main heat exchanger 4.

Of this medium pressure nitrogen gas, a flow rate 200 is taken as the product medium pressure nitrogen gas, and the remaining flow rate 80 is branched into the path L 2, boosted by the blower 11, introduced into the cold insulation outer tub 15, and cooled by the main heat exchanger 4. And introduced into the expansion turbine 10. The medium-pressure nitrogen gas introduced into the expansion turbine 10 expands to generate cold necessary for operation of the apparatus, and then merges with a first low-pressure nitrogen gas, which will be described later, via a path L3. It is recovered and collected as product low-pressure nitrogen gas GN.
The remainder of the medium-pressure nitrogen gas derived from the top of the high-pressure column 9 is introduced into the main condenser 6 via the path L8, and the indirect heat exchange with the high-purity liquefied oxygen at the bottom of the second low-pressure column 82 is high. Pure liquefied oxygen is evaporated, and the entire amount is condensed to medium pressure liquefied nitrogen.

A part of the condensed medium pressure liquefied nitrogen is introduced into the top of the high pressure column 9 as a reflux liquid of the high pressure column 9. The remainder of the medium-pressure liquefied nitrogen is cooled through the supercooler 7, and after being reduced in pressure by the pressure reducing valve V1, is introduced into the top of the first low-pressure column 81 operated at 0.13 MPaA. In addition, the first oxygen-enriched liquid led out from the bottom of the high-pressure column 9 is cooled through the supercooler 7, depressurized by the pressure reducing valve V <b> 2, and then introduced into the lower portion of the first low-pressure column 81.
In the first low-pressure column 81 and the evaporative distillation passage 52 of the heat exchange-type distiller 5, the first oxygen-enriched liquid is distilled, and the first low-pressure nitrogen gas having an oxygen concentration of 1.7% and the oxygen concentration of 89.8% are obtained. Separated into low pure liquefied oxygen. The first low-pressure nitrogen gas derived from the top of the first low-pressure column 81 is recovered from the heat and then derived from the cold insulation outer tank 15 and collected as product low-pressure nitrogen gas.

Further, the low purity liquefied oxygen led out from the lower portion of the evaporative distillation passage 52 is introduced into the middle of the second low pressure column 82 operated at 0.13 MPaA. In the second low-pressure column 82 and the condensation distillation passage 51 of the heat exchange-type distiller 5, low-pure liquefied oxygen is distilled, and second low-pressure nitrogen gas having an oxygen concentration of 6.1% and high-pure having an oxygen concentration of 99.6%. Separated into liquefied nitrogen.
Of the high-purity oxygen gas evaporated and gasified by the main condenser 6 at the bottom of the second low-pressure column 82, the flow rate 200 is derived from the bottom of the second low-pressure column 82 and is recovered by the main heat exchanger 4. Later, it is led out from the cold insulation outer tank 15 and collected as product oxygen gas GO.

In order to evaluate the performance of the process, the power consumption of Example 1 was compared with the apparatus 121 of the conventional process and the apparatus 221 of the reference process.
The results are shown in Table 1.
The product oxygen gas had a flow rate of 200 and a pressure of 0.50 MPaA, and the product nitrogen gas had a flow rate of 200 and a pressure of 1.50 MPaA. Oxygen gas and nitrogen gas collected from the cold insulation outer tank 15 are compressed by an oxygen compressor and a nitrogen compressor, respectively. In addition to the power of the air compressor, the power of these compressors is also compared. did. The power is a value when the total value of the conventional process in FIG.

In the conventional process of FIG. 5, since the amount of product intermediate pressure nitrogen gas MGN collected is 60, this is compressed and supplied to 1.50 MPaA with a medium pressure nitrogen compressor, and the remaining 140 of the product nitrogen gas is product low pressure nitrogen. The gas GN is supplied after being compressed to 1.50 MPaA with a low-pressure nitrogen compressor.
Similarly, in the reference process of FIG. 6, since the amount of product medium pressure nitrogen gas MGN collected is 80, this is compressed and supplied to 1.50 MPaA with a medium pressure nitrogen compressor, and the remaining 120 of the product nitrogen gas is the product. The low-pressure nitrogen gas GN is supplied after being compressed to 1.50 MPaA with a low-pressure nitrogen compressor.
In the process of the present invention, since the amount of product intermediate pressure nitrogen gas MGN collected is 200, this is compressed and supplied to 1.50 MPaA with an intermediate pressure nitrogen compressor, and compression of the low pressure nitrogen gas with the low pressure nitrogen compressor is performed. It becomes unnecessary.

In the reference process of FIG. 6, the amount of medium-pressure nitrogen gas MGN collected is increased compared to the conventional process of FIG. 5, and the consumption power of the nitrogen compressor is reduced, but the consumption power of the air compressor is greatly increased. Since it is increasing, overall power consumption is 20% or more.
In contrast, in the process of the present invention, the amount of medium-pressure nitrogen gas MGN collected is increased, the power consumption of the nitrogen compressor is reduced, and the heat exchange type distiller 5 is used to reduce the pressure of the raw material air. Since it is suppressed to the same level as the conventional process, the overall power consumption is reduced by about 8% compared to the conventional process of FIG.

(Example 2)
Next, in the case where the maximum amount of product liquefied oxygen is collected in addition to the product oxygen gas having an oxygen concentration of 99.6% or more from the raw air having a flow rate of 1000 using the air separation device of the first embodiment 21 shown in FIG. Examples of
The main differences from Example 1 are shown below.
The medium-pressure nitrogen gas flow 280, which is led out from the top of the high-pressure tower 9 and branched off and recovered by the main heat exchanger 4, is introduced into the blower 11 and the expansion turbine 10 for the cooling necessary for the operation of the apparatus. generate. Part of the highly pure liquefied oxygen at the bottom of the second low-pressure column 82 is led to the path L25 and collected as product liquefied oxygen LO.

In order to evaluate the performance of the process, the power consumption and the amount of product liquefied oxygen collected in Example 2 were compared with the apparatus 121 of the conventional process and the apparatus 221 of the reference process.
The results are shown in Table 2.
The total flow rate of product oxygen gas and product liquefied oxygen was 200, and the pressure of product oxygen gas was 0.50 MPaA. Product oxygen gas was produced by compressing oxygen gas collected from the cold outer tank with an oxygen compressor, and the power of these compressors was compared with the power of the air compressor. The power is a value when the total value of the conventional process in FIG.

  In the conventional process of FIG. 5, the amount of medium-pressure nitrogen gas that can be supplied to the blower 111 and the expansion turbine 110 is 140, so the amount of product liquefied oxygen LO collected is 7, whereas in the reference process of FIG. Since the amount of raw material air branched into the blower 211 and the expansion turbine 210 can be increased to 250, the amount of product liquefied oxygen collected is 24, which is greatly increased. However, the raw material air pressure is higher than in the conventional process of FIG. 5, and the power consumption of the entire apparatus is increased by about 35%.

On the other hand, in the process of the present invention, the amount of raw material air branched into the blower 11 and the expansion turbine 10 can be increased up to 280, so the amount of product liquefied oxygen LO collected is significantly increased compared to the conventional process of FIG. In addition, since the pressure of the raw material air is suppressed to the same level as in the conventional process by using the heat exchange type distiller, the overall power consumption is the same as that in the conventional process of FIG.
As described above, even when the product intermediate pressure nitrogen gas MGN is unnecessary, it is possible to increase the amount of collected product liquefied oxygen LO while suppressing the power consumption to the same level as the conventional process by using the process of the present invention. Become. Further, when collecting the product liquefied nitrogen LN, similarly, by using the process of the present invention, it is possible to increase the amount of collected product liquefied nitrogen LN with the same power consumption as the conventional process.

(Example 3)
Next, an embodiment in which product oxygen gas having an oxygen concentration of 99.6% or more is collected from raw air having a flow rate of 1000 using the air separation device 24 of the fourth embodiment shown in FIG.
The main differences from Example 1 are shown below.
Of the raw material air necessary for the apparatus, the flow rate 800 is compressed to 0.57 MPaA by the air compressor 1, purified, cooled by the main heat exchanger 4, and supplied to the high-pressure column 9. On the other hand, 200 of the raw material air necessary for the apparatus is compressed to 0.16 MPaA by the low-pressure air compressor 91, purified and cooled, and then supplied to the first low-pressure column 81. A flow 80 of the medium-pressure nitrogen gas led out from the top of the high-pressure tower 9 is branched, recovered by the main heat exchanger 4, and introduced into the expansion turbine 10 via the blower 11 and the main heat exchanger 4, and expanded. Thus, the cold necessary to operate the device is generated.

  In order to evaluate the performance of the process, the consumption power and the amount of product liquefied oxygen collected in Example 3 were compared with the apparatus 122 of another conventional process shown in FIG. 7 and the apparatus 222 of another reference process shown in FIG. It was. The results are shown in Table 3.

In the air separation device 122 of another conventional process shown in FIG. 7, a part of the raw material air necessary for the device is compressed by the low-pressure air compressor 191, purified and cooled, and then supplied to the low-pressure column 108.
In the apparatus 222 of another reference process shown in FIG. 8, part of the raw material air necessary for the apparatus is compressed by the low-pressure air compressor 291, purified and cooled, and then supplied to the first low-pressure column 281.
The total flow rate of product oxygen gas and product liquefied oxygen was 200, and the pressure of product oxygen gas was 0.50 MPaA. Product oxygen gas was produced by compressing oxygen gas collected from the cold outer tank with an oxygen compressor, and the power of these compressors was compared with the power of the air compressor. The power is a value when the total value of the conventional process in FIG.

In the conventional process of FIG. 7, the flow rate 60 of the raw material air is compressed to 0.16 MPaA by the low-pressure air compressor 191, and the flow rate 940 of the raw material air is compressed to 0.56 MPaA by the air compressor 101.
In the reference process of FIG. 8, the flow rate 80 of the raw material air is compressed to 0.16 MPaA by the low-pressure air compressor 291, and the flow rate 920 of the raw material air is compressed to 1.47 MPaA by the air compressor 201.

In contrast, in the process of the present invention, the flow rate 200 of the raw material air is compressed to 0.16 MPaA by the low-pressure air compressor 91, and the flow rate 800 of the raw material air is compressed to 0.57 MPaA by the air compressor 1. .
Therefore, as shown in Table 3, even when the product intermediate pressure nitrogen gas MGN, the product liquefied oxygen LO, and the product liquefied nitrogen LN are not required, the power consumption of the entire apparatus is compared with the conventional process by using the process of the present invention. About 8%.

 1 .... Air compressor, 2 .... Air precooler, 3 .... Purifier, 4 .... Main heat exchanger, 9 .... High pressure column, 81 .... First low pressure column, 5 .... Heat exchange distiller , 51 .. Condensed distillation passage, 52 .. Evaporative distillation passage, 82 .. Second low pressure column, 6 .. Main condenser, 10 .. Expansion turbine, L24 ... Product recovery path, L7 ... Product recovery path, 11. Blower, 7 ... Supercooler

Claims (8)

In the air separation method of collecting product oxygen by cryogenic liquefaction separation of raw material air,
A first separation step of low-temperature distillation of the compressed, purified and cooled raw material air to separate it into medium-pressure nitrogen gas and a first oxygen-enriched liquid;
A second separation step of separating the first oxygen-enriched liquid into a first low-pressure nitrogen gas and a second oxygen-enriched liquid by low-temperature distillation after decompression;
The second oxygen-enriched liquid is heated by indirect heat exchange with the condensing distillation passage in the evaporative distillation passage of a heat exchange type distiller having an evaporative distillation passage and a condensing distillation passage that can exchange heat indirectly with each other. A third separation step of distilling part of the oxygen-enriched liquid while evaporating and separating it into a first oxygen-enriched gas and low-pure liquefied oxygen;
A fourth separation step in which the low-pure liquefied oxygen is distilled at a low temperature to separate it into a second oxygen-enriched gas and high-pure liquefied oxygen;
The second oxygen-enriched gas is cooled by indirect heat exchange with the evaporative distillation passage in the condensation distillation passage of the heat exchange-type distiller, and a part of the second oxygen enriched gas is distilled while being condensed and liquefied. A fifth separation step for separating the low-pressure nitrogen gas and the third oxygen-enriched liquid;
The intermediate pressure nitrogen gas and the high purity liquefied oxygen are indirectly heat-exchanged to condense and liquefy the intermediate pressure nitrogen gas to obtain intermediate pressure liquefied nitrogen, and at the same time evaporate and gasify the high purity liquefied oxygen to obtain high purity oxygen gas. An indirect heat exchange process;
A product recovery step of collecting a part of the high purity oxygen gas as product oxygen gas after heat recovery.   Instead of the second separation step, the first low-pressure nitrogen gas and the second oxygen-enriched liquid are obtained by low-temperature distillation of a part of the compressed, purified and cooled raw material air and the decompressed first oxygen-enriched liquid. The air separation method according to claim 1, further comprising a sixth separation step of separating the air.   The air separation method according to claim 1, further comprising a cold generation step in which a part of the raw material air is introduced into an expansion turbine to be expanded.   The air separation method according to claim 1, further comprising a cold generation step of introducing a part of the medium-pressure nitrogen gas into an expansion turbine after heat recovery and expanding the gas.   3. The air separation method according to claim 1, further comprising a cold generation step of introducing the first low-pressure nitrogen gas into an expansion turbine after heat recovery and expanding the first low-pressure nitrogen gas.   3. The air separation method according to claim 1, further comprising a cold generation step of introducing the second low-pressure nitrogen gas into an expansion turbine after heat recovery and expanding the second low-pressure nitrogen gas. 4. In an air separation device that collects product oxygen by cryogenic liquefaction separation of raw material air,
A high-pressure column that separates the compressed, purified, and cooled raw material air into a low-pressure distillation by separating it into medium-pressure nitrogen gas and a first oxygen-enriched liquid; A first low pressure column that separates into a gas and a second oxygen-enriched liquid, and a condensation distillation passage and an evaporative distillation passage that are capable of indirect heat exchange with each other, wherein the condensation distillation passage is indirect heat exchange with the evaporative distillation passage. A part of the second oxygen-enriched liquid is heated and evaporated to be distilled to separate it into the first oxygen-enriched gas and low-pure liquefied oxygen, and the evaporative distillation passage is indirectly heated with the condensation distillation passage. A heat exchange-type distiller which cools a part of the second oxygen-enriched gas described later by exchange and distills while condensing it into a second low-pressure nitrogen gas and a third oxygen-enriched liquid; Low-pure liquefied oxygen is distilled at low temperature and separated into second oxygen-enriched gas and high-pure liquefied oxygen. The intermediate pressure nitrogen gas is condensed and liquefied by indirect heat exchange between the second low pressure column and the intermediate pressure nitrogen gas and the high purity liquefied oxygen to obtain medium pressure liquefied nitrogen, and at the same time, the high purity liquefied oxygen is vaporized and gasified. An air separation apparatus comprising: a main condenser for obtaining high-purity oxygen gas; and a product recovery path for collecting a part of the high-purity oxygen gas as product oxygen gas after heat recovery.   8. The air separation apparatus according to claim 7, further comprising a raw air introduction path for compressing, refining and cooling a part of the raw air to supply to the first low pressure column.

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