JP2015114083A - Air separation method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air separation method and apparatus capable of further improving air separation efficiency in AB processing and reducing more power cost.SOLUTION: An air separation method for collecting product oxygen through cryogenic liquefaction/separation of compressed, refined and cooled raw material air includes: a first distillation step of separating into first nitrogen gas and oxygen enriched liquid; a second distillation step of separating into second nitrogen gas and liquefied oxygen; a first indirect heat exchange step of indirect heat exchanging the first nitrogen gas and part of the liquefied oxygen; a second indirect heat exchange step of indirect heat exchanging low-temperature compressed second raw material air and the remaining of the liquefied oxygen; and a third indirect heat exchange step of decompressing third liquefied air to an intermediate pressure followed by indirect heat exchanging for third nitrogen gas.

Description

  The present invention relates to an air separation method and apparatus, and more particularly to an air separation method and apparatus for collecting product oxygen by cryogenic liquefaction separation of raw material air.

  When collecting product oxygen by cryogenic liquefaction separation of raw material air, an air separation device equipped with a double rectification column is generally used. FIG. 7 is a system diagram showing a basic configuration example of an air separation device equipped with a double rectification column for collecting product oxygen. In FIG. 7, the raw material air compressed by the air compressor 101 is cooled to room temperature by an aftercooler 101a and then introduced into a purification facility 102 filled with molecular sieves and the like, and impurities such as carbon dioxide and moisture are removed by adsorption. Is done. The raw material air purified by the purification facility 102 passes through the path 121 and is cooled to the dew point temperature by indirect heat exchange with a low-temperature return gas such as product oxygen gas in the main heat exchanger 103. It passes through the path 122 in a partially liquefied state and is introduced into the lower part of the first distillation column (medium pressure column) 104 of the double rectification column.

  In the first distillation column 104, the raw air introduced from the bottom of the column becomes the rising gas in the column, and low-temperature distillation is performed by gas-liquid contact with the reflux liquid from the top of the column, with nitrogen gas at the top and oxygen at the bottom. Each enrichment separates. The nitrogen gas separated at the top of the column is introduced into the main condenser 106 installed at the bottom of the second distillation column (low pressure column) 105 through the path 123 and separated into the liquefied oxygen separated at the bottom of the second distillation column 105. Indirect heat exchange is performed to vaporize liquefied oxygen into oxygen gas, and nitrogen gas is liquefied to become liquefied nitrogen. The liquefied nitrogen is led to the path 124, and a part of the liquefied nitrogen is returned as a reflux liquid to the top of the first distillation column 104 through the path 125 and descends in the first distillation column 104. The remaining liquefied nitrogen passes through the path 126, is cooled by the supercooler 107, is reduced to the top pressure of the second distillation column 105 by the pressure reducing valve 108, and is then introduced into the top of the second distillation column 105 as a reflux liquid. The

  Further, the oxygen-enriched liquid separated at the bottom of the first distillation column 104 is extracted into the path 127, cooled by the supercooler 107, and depressurized by the pressure reducing valve 109 to the middle pressure of the second distillation column 105. After that, it is introduced into the middle stage of the second distillation column 105 as a reflux liquid.

  The second distillation column 105 is vaporized by the reflux liquid (liquefied nitrogen and oxygen-enriched liquid) introduced from the paths 126 and 127 and the main condenser 106 at the bottom of the column at an operating pressure close to the atmospheric pressure. Low temperature distillation is performed by gas-liquid contact with oxygen gas rising inside, and nitrogen gas is separated at the top of the column and liquefied oxygen is separated at the bottom of the column.

  The nitrogen gas separated at the top of the second distillation column 105 is withdrawn into the path 128, recovered by the supercooler 107 and the main heat exchanger 103 and heated up to near room temperature, and then discharged as waste gas from the path 129. Derived. A part of the waste gas is used as a regeneration gas for the purification facility 102.

  Also, part of the oxygen gas vaporized by heat exchange in the main condenser 106 is extracted to the path 130 and introduced into the main heat exchanger 103, where heat is recovered by exchanging heat with the raw material air, and the room temperature. The temperature is raised to the vicinity and collected as product oxygen gas from the path 131. A part of the liquefied oxygen is extracted from the bottom of the second distillation column 105 to the path 132 as a safety liquid acid.

  Furthermore, a cold generation circuit 140 is provided to compensate for heat loss during operation. This cold generation circuit 140 divides a part of the compressed and refined raw material air into a path 141, pressurizes it with a blower (expansion turbine braking blower) 142, cools it to room temperature with an aftercooler 142a, and further heats the main heat exchanger. After cooling to the intermediate temperature at 103, the refrigerant is introduced into the expansion turbine 144 from the path 143 to adiabatically expand to the middle stage pressure of the second distillation tower 105, and after generating cold, the second distillation tower 105 from the path 145 is cooled. It is introduced in the middle part of

  Many various configurations for reducing the power consumption have been proposed for such a basic configuration. One of them is a so-called air-evaporation process (AB process). (For example, refer to Patent Documents 1 to 5.)

  FIG. 8 is a system diagram showing an example of a basic configuration of an air separation apparatus employing this AB process. In the description of FIG. 8, the same components as those of the air separation device shown in FIG. 7 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In FIG. 8, this air separation device is provided with a second indirect heat via a partition plate 105a below a main condenser (hereinafter referred to as a first indirect heat exchanger) 106 provided at the bottom of the second distillation column 105. An exchanger 151 is provided so that a part of the liquefied oxygen separated into the bottom of the second distillation column 105 by the second indirect heat exchanger 151 and a part of the raw air are indirectly heat-exchanged.

  That is, a part of the liquefied oxygen separated at the bottom of the second distillation column 105 is introduced into the second indirect heat exchanger 151 through the path 152, and a part of the raw air flowing through the path 122 is converted into the path 153. And is introduced into the second indirect heat exchanger 151. In the second indirect heat exchanger 151, the liquefied oxygen is vaporized to become oxygen gas and the raw material air is liquefied to become liquefied air. The liquefied air is introduced as a reflux liquid into the middle stage of the first distillation column 104 through the path 154.

  Further, a part of the oxygen gas vaporized by the second indirect heat exchanger 151 is extracted to the path 130, recovered by the main heat exchanger 103, and collected as product oxygen gas from the path 131. The remaining oxygen gas is introduced as a rising gas into the lower part of the second distillation column 105 through the path 155.

  Further, from the middle stage of the first distillation column 104, a part of the nitrogen-enriched liquid flowing down in the column is extracted to the path 156, passes through the supercooler 107, and is depressurized by the pressure reducing valve 157, and then the second stage. A reflux liquid is introduced into the upper middle part of the distillation column 105.

JP-A-6-117753 JP-A-6-101963 JP-A-10-185425 Japanese Patent Laid-Open No. 11-257845 JP 2011-518307 A

  However, in the AB process described in each patent document, there is a problem in the apparatus configuration and operability although a certain degree of effect can be expected by reducing the raw material air pressure.

  Accordingly, an object of the present invention is to provide an air separation method and apparatus capable of further improving the air separation efficiency in the AB process and further reducing the power cost.

  In order to achieve the above object, the air separation method of the present invention includes a first raw material air, a first liquefied air, and a first raw material air, a first liquefied air. A first distillation step in which the first liquefied nitrogen and the third liquefied nitrogen are subjected to low-temperature distillation at a preset first pressure to be separated into a first nitrogen gas and an oxygen-enriched liquid; a second liquefied nitrogen and a second liquefied liquid A second distillation step in which air, oxygen-enriched liquid, third raw material air and oxygen gas are subjected to low-temperature distillation at a second pressure lower than the first pressure to separate into second nitrogen gas and liquefied oxygen, and are set in advance A step of diverting the raw material air compressed to pressure, purified and cooled into a first raw material air and a second raw material air, a step of introducing the first raw material air into the first distillation step, and the second raw material air The first pressure higher than the third pressure to low temperature A step of compressing, a step of reducing the oxygen-enriched liquid to the second pressure and introducing it into the second distillation step, and a step of diverting a part of the first nitrogen gas as a third nitrogen gas; Indirect heat exchange between the first nitrogen gas and a part of the liquefied oxygen, the first nitrogen gas is liquefied to form first liquefied nitrogen and the liquefied oxygen is vaporized to form oxygen gas. Indirect heat exchange between the heat exchange step and the low-temperature compressed second raw material air and the remainder of the liquefied oxygen, liquefying the second raw material air into liquefied air and vaporizing the liquefied oxygen into oxygen gas A second indirect heat exchanging step, a step of diverting the liquefied air into a first liquefied air, a second liquefied air, and a third liquefied air, and reducing the first liquefied air to a first pressure to reduce the first distillation. Introducing the second liquefied air to the second pressure; And introducing the second liquefied air into the second distillation step, reducing the third liquefied air to an intermediate pressure, and then indirectly exchanging with the third nitrogen gas, liquefying the third nitrogen gas, and liquefying the second liquefied nitrogen And a third indirect heat exchange step to vaporize the third liquefied air to form third raw material air, a step of diverting a part of the second liquefied nitrogen as third liquefied nitrogen, and the third liquefied Introducing nitrogen and the first liquefied nitrogen into the first distillation step, reducing the remaining pressure of the second liquefied nitrogen to a second pressure and introducing the second liquefied nitrogen into the second distillation step; and the third raw material. A step of adiabatic expansion of air to reduce the pressure to the second pressure and then introducing the second distillation step; a step of collecting a part of the oxygen gas as a product oxygen gas after heat recovery; and a balance of the oxygen gas. Introducing into the second distillation step, and the second nitrogen. And a step of deriving the raw gas after heat recovery.

  Furthermore, the air separation method of the present invention is characterized in that the second raw material air is boosted to the second pressure with energy generated when the nitrogen-enriched gas is adiabatically expanded.

  The air separation device of the present invention is an air separation device that collects product oxygen by subjecting compressed, refined, and cooled raw material air to cryogenic liquefaction separation. The first raw material air, the first liquefied air, and the first liquefied nitrogen And a first distillation column for low-temperature distillation of the third liquefied nitrogen at a preset first pressure to separate it into a first nitrogen gas and an oxygen-enriched liquid, a second liquefied nitrogen, a second liquefied air, and an oxygen-enriched liquid Liquid, third raw material air and oxygen gas are subjected to low-temperature distillation at a second pressure lower than the first pressure and separated into second nitrogen gas and liquefied oxygen, and compressed to a preset pressure, A path for diverting the purified and cooled source air into the first source air and the second source air, a path for introducing the first source air into the first distillation column, and the second source air as the first pressure. A cold compressor that cold compresses to a higher third pressure, and before A path for reducing the oxygen-enriched liquid to the second pressure and introducing it into the second distillation column; a path for diverting a part of the first nitrogen gas as a third nitrogen gas; the first nitrogen gas; A portion of the liquefied oxygen is indirectly heat-exchanged, and the first nitrogen gas is liquefied to be the first liquefied nitrogen and the liquefied oxygen is vaporized to be oxygen gas, and is compressed at a low temperature. A second indirect heat exchanger that indirectly heat exchanges the second raw material air and the remainder of the liquefied oxygen, liquefies the second raw material air into liquefied air, and vaporizes the liquefied oxygen into oxygen gas. A path for dividing the liquefied air into a first liquefied air, a second liquefied air, and a third liquefied air; a path for reducing the first liquefied air to a first pressure and introducing it into the first distillation column; The second liquefied air is reduced to the second pressure and introduced into the second distillation column. The third liquefied air is reduced to an intermediate pressure, and then indirectly heat exchanged with the third nitrogen gas to liquefy the third nitrogen gas into second liquefied nitrogen and to evaporate the third liquefied air. A third indirect heat exchanger that converts the second liquefied nitrogen into a third raw material air, a path for diverting a part of the second liquefied nitrogen as the third liquefied nitrogen, and the third liquefied nitrogen and the first liquefied nitrogen as the first liquefied nitrogen. A path for introducing each into the distillation tower, a path for reducing the remainder of the second liquefied nitrogen to a second pressure and introducing it into the second distillation tower, and adiabatically expanding the third source air with an expansion turbine to A path for reducing the pressure to two pressures and introducing it into the second distillation column, a path for collecting a part of the oxygen gas as product oxygen gas after heat recovery, and introducing the remainder of the oxygen gas into the second distillation column And a route for deriving the second nitrogen gas after heat recovery It is characterized by having.

  Furthermore, the air separation device of the present invention is characterized in that the third indirect heat exchanger is a dry type or a thermosiphon type.

  According to the present invention, since the warm fluid that exchanges heat with liquefied oxygen in the third indirect heat exchanger that performs the third indirect heat exchange step is the second raw material air that is cold-compressed by the low-temperature compressor, the third indirect The heat exchange efficiency in the heat exchange process can be improved, and the power required for boosting the second raw material air can be reduced and the equipment can be downsized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram showing a first embodiment of an air separation device capable of implementing an air separation method of the present invention. It is a systematic diagram which shows the 2nd example of an air separation apparatus which can implement the air separation method of this invention. It is a systematic diagram which shows the 3rd example of an air separation apparatus which can implement the air separation method of this invention. It is a systematic diagram which shows the 4th example of an air separation apparatus which can implement the air separation method of this invention. It is a systematic diagram which shows the 5th example of an air separation apparatus which can implement the air separation method of this invention. It is a systematic diagram which shows the 6th form example of the air separation apparatus which can implement the air separation method of this invention. It is a systematic diagram which shows the basic structural example of the air separation apparatus provided with the double rectification column for extract | collecting product oxygen. It is a systematic diagram which shows the basic structural example of the air separation apparatus which employ | adopted AB process.

  FIG. 1 is a system diagram showing a first embodiment of an air separation device capable of implementing the air separation method of the present invention. The air separation apparatus shown in the present embodiment includes, as main equipment, a first distillation column 11 that performs a first distillation step at a preset first pressure, and a second distillation step at a second pressure lower than the first pressure. The second distillation column 12 that performs the first indirect heat exchanger 13 that performs the first indirect heat exchange step provided at the bottom of the second distillation column 12, and the partition plate 12a below the second distillation column 12 A second indirect heat exchanger 14 for performing the second indirect heat exchange step disposed in the second position, and a third indirect heat exchanger 15 for performing the third indirect heat exchange step disposed at the lower side of the second distillation column 12; And an expansion turbine 16 that performs the adiabatic expansion process, a low-temperature compressor 17 that performs a low-temperature compression process driven by the expansion turbine 16, and a cold generation circuit 18 for replenishing the cold.

  The raw material air is compressed to a first intermediate pressure (intermediate pressure) set in advance by the air compressor 20, cooled to room temperature by an aftercooler 20 a, and then introduced into a purification facility 21 filled with molecular sieves and the like. Impurities such as carbon dioxide and moisture are removed by adsorption. The raw material air purified by the refining equipment 21 is introduced into the main heat exchanger 22 through the path 31, and is cooled to near the dew point temperature by exchanging heat with a low-temperature return gas such as product oxygen gas. , Route 32.

  The raw material air flowing through the path 32 is divided into the first raw material air of the path 33 and the second raw material air of the path 34, and the first raw material air of the path 33 is introduced into the lower part of the first distillation column 11. Further, the second raw material air in the path 34 is compressed to a third pressure higher than the first pressure by the low-temperature compressor 17, and then introduced into the second indirect heat exchanger 14 through the path 35.

  In the first distillation column 11, a first distillation step is performed, and the first raw material air and first liquefied air, first liquefied nitrogen, and third liquefied nitrogen, which will be described later, are subjected to low temperature distillation, so that One nitrogen gas is separated and the oxygen-enriched liquid is separated at the bottom of the column. The oxygen-enriched liquid is extracted from the bottom of the first distillation column 11 to the path 36, passes through the supercooler 23, is depressurized by the pressure reducing valve 24, and is then introduced as a reflux liquid into the middle stage of the second distillation column 12. Is done.

  After the first nitrogen gas at the top of the first distillation column 11 is extracted to the path 37, a part of the first nitrogen gas is diverted to the path 38 as the third nitrogen gas, and the divided third nitrogen gas is obtained. Is introduced into the third indirect heat exchanger 15, and the remaining first nitrogen gas is introduced into the first indirect heat exchanger 13 through the path 39. In the first indirect heat exchanger 13, a part of the liquefied oxygen (first liquefied oxygen) separated at the bottom of the second distillation column 12 and the first nitrogen gas perform the first indirect heat exchange step, and the first nitrogen gas Is liquefied to become first liquefied nitrogen, and first liquefied oxygen is vaporized to become first oxygen gas. The liquefied first liquefied nitrogen is returned as a reflux liquid to the top of the first distillation column 11 through the path 40.

  Further, the remaining portion of the liquefied oxygen separated at the bottom of the second distillation column 12 passes through the gas-liquid contact portion 14a as the reflux liquid from the path 41 as the second liquefied oxygen, and is then introduced into the second indirect heat exchanger 14. . Most of the second liquefied oxygen is subjected to a second indirect heat exchange step with the second raw material air compressed to the third pressure, and the second raw material air is liquefied to liquefied air. The liquefied oxygen is vaporized into a second oxygen gas. A part of the second oxygen gas is extracted into the passage 42 and is recovered as heat by heating the raw air in the main heat exchanger 22 and then collected as product oxygen gas from the passage 43. The remaining portion of the second oxygen gas passes through the gas-liquid contact portion 14a as an ascending gas, and then is introduced into the lower portion of the second distillation column 12 through the path 44 having the valve 25, and merges with the first oxygen gas. It becomes the rising gas of the second distillation column 12. A small amount of the second liquefied oxygen is withdrawn from the passage 45 as a protective liquid acid for preventing the concentration of hydrocarbons.

  The liquefied air is extracted into the path 46, and then is divided into the first liquefied air in the path 47, the second liquefied air in the path 48, and the third liquefied air in the path 49. The air is depressurized by the pressure reducing valve 26 and is introduced as a reflux liquid into the middle stage of the first distillation column 11. Further, the second liquefied oxygen in the path 48 passes through the supercooler 23, is decompressed by the pressure reducing valve 27, and is then introduced as a reflux liquid into the middle upper part of the second distillation column 12.

  The third liquefied air in the path 49 is depressurized to the inlet pressure of the expansion turbine 16 by the pressure reducing valve 28, and then gas-liquid separated by the gas-liquid separator 29, and the liquid phase is introduced into the third indirect heat exchanger 15. The In the third indirect heat exchanger 15 employing the dry heat exchanger, the third liquefied air and the third nitrogen gas introduced from the passage 38 perform the third indirect heat exchange step, and the third liquefied air is vaporized. As a result, the third raw material air is liquefied and second liquefied nitrogen is obtained.

  The third raw material air joins with the gas phase of the gas-liquid separator 29 in the path 50, is heated to an intermediate temperature in the main heat exchanger 22, and is then introduced into the expansion turbine 16 from the path 51. In the expansion turbine 16, the third raw material air is expanded to the second pressure to generate cold, and the low-temperature compressor 17 is driven by the energy during expansion. The expanded third raw material air is introduced as a rising gas into the middle stage of the second distillation column 12 through the path 52.

  On the other hand, a part of the second liquefied nitrogen liquefied by the third indirect heat exchanger 15 and led to the path 53 is diverted to the path 54 as the third liquefied nitrogen, and as a reflux liquid at the top of the first distillation column 11. The remaining second liquefied nitrogen is returned through the passage 55 through the supercooler 23, decompressed by the pressure reducing valve 30, and then introduced into the top of the second distillation column 12 as a reflux liquid. Then, the second nitrogen gas is extracted from the top of the second distillation column 12 to the path 56, recovered by the supercooler 23 and the main heat exchanger 22, and then led out as a waste gas from the path 57. .

  The cold generation circuit 18 divides a part of the compressed and purified raw material air into the path 141 as before, pressurizes it with the blower 142, cools it to the room temperature with the aftercooler 142 a, and further with the main heat exchanger 103. After cooling to the intermediate temperature, it is introduced into the expansion turbine 144 from the path 143 to adiabatically expand to the middle pressure of the second distillation column 105, and after generating a required amount of cold, the second distillation column 105 from the path 145 is generated. It is introduced in the middle part of

  FIG. 2 is a system diagram showing a second embodiment of an air separation apparatus capable of carrying out the air separation method of the present invention. The thermosiphon is connected to the top of the first distillation column 11 via a partition plate 11a. The example which has arrange | positioned the 3rd indirect heat exchanger 15 which employ | adopted the type | mold heat exchanger is shown. In the following description, the same components as those of the air separation device shown in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the third indirect heat exchanger 15 in the air separation apparatus shown in the present embodiment, a part of the nitrogen gas extracted from the top of the first distillation column 11 to the path 37 (third nitrogen gas) is divided into the path 38. In addition, a part of the liquefied air (third liquefied air) liquefied by the second indirect heat exchanger 14 and divided into the passage 49 is decompressed by the pressure reducing valve 28 and introduced. In the case of a thermosiphon heat exchanger, a gas-liquid separator is not necessary.

  The liquefied nitrogen (second liquefied nitrogen) liquefied by the indirect heat exchange in the third indirect heat exchanger 15 and led to the path 53 is liquefied by the indirect heat exchange in the first indirect heat exchanger 13 and then the path 40. And the liquefied nitrogen (first liquefied nitrogen) led out to the first distillation column 11 is partly divided into the path 54 and returned to the top of the first distillation column 11, and the remaining liquefied nitrogen is passed from the path 55 to the supercooler 23. Then, it is introduced into the top of the second distillation column 12 through the pressure reducing valve 30.

  In addition, a part of the third liquefied air that has not been vaporized in the third indirect heat exchanger 15 is extracted to the path 61, cooled in the supercooler 23, and decompressed by the pressure reducing valve 62, and then the middle stage of the first distillation column 11. Is introduced into the part as a reflux liquid. The third raw material air vaporized in the third indirect heat exchanger 15 passes through the main heat exchanger 22 from the path 50, is introduced into the expansion turbine 16 from the path 51, expands to generate cold, and then passes through the path 52. Then, it is introduced into the middle stage of the second distillation column 12.

  FIG. 3 is a system diagram showing a third embodiment of an air separation apparatus capable of performing the air separation method of the present invention, and a thermosiphon type heat is provided between the first distillation column 11 and the second distillation column 12. The example which has arrange | positioned the 3rd indirect heat exchanger 15 which employ | adopted the exchanger is shown.

  Also in this embodiment, a part of the nitrogen gas extracted from the top of the first distillation column 11 to the path 37 (third nitrogen gas) is introduced into the third indirect heat exchanger 15 by being divided into the path 38. At the same time, a part of the liquefied air (third liquefied air) that has been liquefied by the second indirect heat exchanger 14 and divided into the path 49 is decompressed by the pressure reducing valve 28 and introduced.

  The liquefied nitrogen (second liquefied nitrogen) liquefied by the indirect heat exchange in the third indirect heat exchanger 15 and led to the path 53 is liquefied by the indirect heat exchange in the first indirect heat exchanger 13 and then the path 40. And the liquefied nitrogen (first liquefied nitrogen) led out to the first distillation column 11 is partly divided into the path 54 and returned to the top of the first distillation column 11, and the remaining liquefied nitrogen is passed from the path 55 to the supercooler 23. Then, it is introduced into the top of the second distillation column 12 through the pressure reducing valve 30.

  In addition, a part of the third liquefied air that has not been vaporized in the third indirect heat exchanger 15 is extracted to the path 61, cooled in the supercooler 23, and decompressed by the pressure reducing valve 62, and then the middle stage of the first distillation column 11. Is introduced into the part as a reflux liquid. The third raw material air vaporized in the third indirect heat exchanger 15 passes through the main heat exchanger 22 from the path 50, is introduced into the expansion turbine 16 from the path 51, expands to generate cold, and then passes through the path 52. Then, it is introduced into the middle stage of the second distillation column 12.

  FIG. 4 is a system diagram showing a fourth embodiment of an air separation device capable of performing the air separation method of the present invention, and is arranged at the bottom of the second distillation column 12 in the first to third embodiments. The example which has arrange | positioned the 2nd indirect heat exchanger 14 currently performed separately from the 2nd distillation column 12 is shown.

  In the present embodiment, the second raw material air compressed to the third pressure higher than the first pressure by the low-temperature compressor 17 is introduced into the second indirect heat exchanger 14 from the path 35 in the same manner as the first embodiment. At the same time, the second liquefied oxygen is introduced from the bottom of the second distillation column 12 through the path 41 to above the gas-liquid contact portion 14a. The liquefied air liquefied by the second indirect heat exchanger 14 is extracted into the path 46, and then into the first liquefied air in the path 47, the second liquefied air in the path 48, and the third liquefied air in the path 49. Divide. A part of the vaporized second oxygen gas is recovered from the passage 42 through the main heat exchanger 22 and then collected as product oxygen gas from the passage 43. The remainder of the second oxygen gas passes through the gas-liquid contact portion 14a as a rising gas, and then is introduced as a rising gas into the lower portion of the second distillation column 12 through the path 44 having the valve 25. In addition, a small amount of the second liquefied oxygen is withdrawn from the path 45 as a protective liquid acid.

  FIG. 5 is a system diagram showing a fifth embodiment of an air separation apparatus capable of performing the air separation method of the present invention, and shows an example in which oxygen gas and nitrogen gas are collected as products. Yes.

  In the second distillation column shown in this embodiment, high-purity nitrogen gas is led from the top of the second distillation column 12 to the path 58 and low-purity nitrogen gas is fed to the path 59 from a position several steps below the top. It is formed to derive. The high-purity nitrogen gas led out to the path 58 is recovered by the supercooler 23 and the main heat exchanger 22, then led out as a product nitrogen gas from the path 60, and low-purity nitrogen led out to the path 59. The gas is recovered as heat by the supercooler 23 and the main heat exchanger 22, and then led out as a waste gas from the path 57.

  FIG. 6 is a system diagram showing a sixth embodiment of an air separation apparatus capable of carrying out the air separation method of the present invention, and the replenishment of cold to the apparatus is replaced with the cold generation circuit 18 from the outside. An example is shown in which liquid nitrogen is injected.

  That is, in this embodiment, liquid nitrogen is introduced from the outside through the valve 61 to the top of the second distillation column 12 without providing the cold generation circuit 18 installed in the first to fifth embodiments. A path 62 is provided, and necessary cold is replenished by liquid nitrogen introduced from the path 62. Further, in the present embodiment, as in the fifth embodiment, oxygen gas and nitrogen gas are collected as products.

  As shown in the above embodiments, the raw material air introduced as the warm fluid into the second indirect heat exchanger 14 is the second raw material air compressed by the low-temperature compressor 17 after being compressed, purified and cooled. The power required for compression can be reduced, and the compression power can be reduced and the size of the compressor can be reduced as compared with the case where the pressure of the raw material air is increased to a required pressure at room temperature. Further, since the raw material air is used as the fluid to be compressed at a low temperature, for example, a gas replacement operation as in the case of compressing nitrogen gas at a low temperature is unnecessary, and the apparatus can be started up in a short time. Furthermore, by driving the low-temperature compressor 17 with the expansion turbine 16 that expands the third raw material air, energy for compressing the second raw material air at a low temperature becomes unnecessary. Moreover, the 1st indirect heat exchanger 13 and the 3rd indirect heat exchanger 15 can also be manufactured integrally, and the indirect heat exchanger manufactured integrally is installed in the inside or the exterior of a 2nd distillation tower. It is possible.

In addition, as shown in the third embodiment and the fourth embodiment, by forming the storage device for the indirect heat exchanger separately from the distillation tower, the overall height of the distillation tower can be reduced, and the outside of the cold storage The height of the tank can be lowered.
The pressure, temperature, flow rate, etc. of each part are appropriately set in accordance with various conditions such as the scale of the apparatus and the amount of product collected, and the first distillation column and the second distillation column are The indirect heat exchangers can also be integrally formed as appropriate.

The driving power of the apparatus having the configuration shown in the first embodiment of FIG. 1, the apparatus having the conventional basic configuration shown in FIG. 7, and the apparatus adopting the AB process shown in FIG. 8 were compared. The apparatus specifications were such that product oxygen gas with an oxygen purity of 95% was sampled at 15000 Nm ³ / h. The comparison results are shown in Table 1. [Nm ³ ] represents the gas volume [m ³ ] converted to the standard state. The driving power in the table is a relative value when the example of FIG.

The driving power of the apparatus having the configuration shown in the fifth embodiment of FIG. 5, the apparatus having the conventional basic configuration shown in FIG. 7, and the apparatus adopting the AB process shown in FIG. 8 were compared. The apparatus specifications were such that product oxygen gas with an oxygen purity of 95% was sampled at 15000 Nm ³ / h. The comparison results are shown in Table 2.

The driving power of the apparatus having the configuration shown in the sixth embodiment of FIG. 6, the apparatus having the conventional basic configuration shown in FIG. 7, and the apparatus adopting the AB process shown in FIG. 8 were compared. The apparatus specifications were such that product oxygen gas with an oxygen purity of 95% was sampled at 15000 Nm ³ / h. The comparison results are shown in Table 3.

DESCRIPTION OF SYMBOLS 11 ... First distillation tower, 12 ... Second distillation tower, 13 ... First indirect heat exchanger, 14 ... Second indirect heat exchanger, 15 ... Third indirect heat exchanger, 16 ... Expansion turbine, 17 ... Low temperature compression 18 ... Cold generation circuit, 20 ... Air compressor, 21 ... Purification equipment, 22 ... Main heat exchanger, 23 ... Supercooler

Claims (4)

In the air separation method of collecting product oxygen by cryogenic liquefaction separation of compressed, purified and cooled raw material air,
A first distillation step of separating the first raw material air, the first liquefied air, the first liquefied nitrogen and the third liquefied nitrogen into a first nitrogen gas and an oxygen-enriched liquid by low-temperature distillation at a preset first pressure; ,
A second liquefied nitrogen, a second liquefied air, an oxygen-enriched liquid, a third raw material air and an oxygen gas are subjected to low-temperature distillation at a second pressure lower than the first pressure to separate into a second nitrogen gas and liquefied oxygen. A distillation process;
Dividing the source air compressed to a preset pressure, purified and cooled into a first source air and a second source air;
Introducing the first raw material air into the first distillation step;
A low-temperature compression step of low-temperature compressing the second raw material air to a third pressure higher than the first pressure;
Reducing the oxygen-enriched liquid to the second pressure and introducing it into the second distillation step;
Branching a portion of the first nitrogen gas as third nitrogen gas;
First indirect heat in which the first nitrogen gas and a part of the liquefied oxygen are indirectly heat-exchanged to liquefy the first nitrogen gas into first liquefied nitrogen and to vaporize the liquefied oxygen into oxygen gas. An exchange process;
Second indirect heat in which the second raw material air compressed at low temperature and the remainder of the liquefied oxygen are indirectly heat-exchanged to liquefy the second raw material air into liquefied air and to vaporize the liquefied oxygen into oxygen gas. An exchange process;
Diverting the liquefied air into a first liquefied air, a second liquefied air and a third liquefied air;
Reducing the first liquefied air to a first pressure and introducing it into the first distillation step;
Reducing the second liquefied air to a second pressure and introducing it into the second distillation step;
The third liquefied air is reduced to an intermediate pressure and then indirectly exchanged with the third nitrogen gas, the third nitrogen gas is liquefied into second liquefied nitrogen, and the third liquefied air is vaporized. A third indirect heat exchange step for converting the third raw material air;
Diverting a portion of the second liquefied nitrogen as third liquefied nitrogen;
Introducing the third liquefied nitrogen and the first liquefied nitrogen into the first distillation step, respectively;
Reducing the remainder of the second liquefied nitrogen to a second pressure and introducing it into the second distillation step;
A step of adiabatically expanding the third raw material air to reduce the pressure to the second pressure and then introducing it into the second distillation step;
Collecting a portion of the oxygen gas as product oxygen gas after heat recovery;
Introducing the remainder of the oxygen gas into the second distillation step;
And a step of deriving the second nitrogen gas after heat recovery.   2. The air separation method according to claim 1, wherein the second raw material air is boosted to the second pressure with energy generated when the third raw material air is adiabatically expanded. In an air separation device that collects product oxygen by cryogenic liquefaction separation of compressed, purified and cooled raw material air,
A first distillation column for separating the first raw material air, the first liquefied air, the first liquefied nitrogen and the third liquefied nitrogen into a first nitrogen gas and an oxygen-enriched liquid by low-temperature distillation at a preset first pressure; ,
A second liquefied nitrogen, a second liquefied air, an oxygen-enriched liquid, a third raw material air and an oxygen gas are subjected to low-temperature distillation at a second pressure lower than the first pressure to separate into a second nitrogen gas and liquefied oxygen. A distillation tower,
A path for diverting the refined and cooled raw material air compressed to a preset pressure into a first raw material air and a second raw material air;
A path for introducing the first raw material air into the first distillation column;
A low-temperature compressor for compressing the second raw material air to a third pressure higher than the first pressure;
A path for reducing the oxygen-enriched liquid to the second pressure and introducing it into the second distillation column;
A path for diverting a part of the first nitrogen gas as the third nitrogen gas;
First indirect heat in which the first nitrogen gas and a part of the liquefied oxygen are indirectly heat-exchanged to liquefy the first nitrogen gas into first liquefied nitrogen and to vaporize the liquefied oxygen into oxygen gas. An exchange,
Second indirect heat in which the second raw material air compressed at low temperature and the remainder of the liquefied oxygen are indirectly heat-exchanged to liquefy the second raw material air into liquefied air and to vaporize the liquefied oxygen into oxygen gas. An exchange,
A path for diverting the liquefied air into the first liquefied air, the second liquefied air, and the third liquefied air;
A path for reducing the first liquefied air to a first pressure and introducing it into the first distillation column;
A path for reducing the second liquefied air to a second pressure and introducing it into the second distillation column;
The third liquefied air is reduced to an intermediate pressure and then indirectly exchanged with the third nitrogen gas, the third nitrogen gas is liquefied into second liquefied nitrogen, and the third liquefied air is vaporized. A third indirect heat exchanger that converts the third raw material air,
A path for diverting a part of the second liquefied nitrogen as third liquefied nitrogen;
A path for introducing the third liquefied nitrogen and the first liquefied nitrogen into the first distillation column,
A path for reducing the remainder of the second liquefied nitrogen to a second pressure and introducing it into the second distillation column;
A path for adiabatically expanding the third raw material air with an expansion turbine and reducing the pressure to the second pressure, and then introducing it into the second distillation column;
A path for collecting a part of the oxygen gas as product oxygen gas after heat recovery;
A path for introducing the remainder of the oxygen gas into the second distillation column;
A path for deriving the second nitrogen gas after heat recovery;
An air separation device comprising:   The air separation device according to claim 3, wherein the third indirect heat exchanger is a dry type or a thermosiphon type.

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