Air separation device and air separation method

Abstract

Provided is an air separation device and an air separation method capable of reducing power consumption. Provided is an air separation device comprising: a high-pressure column (50); a low-pressure column (60); an argon column (70); a main condenser (150) for producing a reflux liquid; and an argon condenser (170) for liquefying argon gas, supplied from the top of the argon column (70), by using liquid oxygen supplied from the bottom of the low-pressure column (60), thereby generating liquid oxygen, which is a reflux liquid of the argon column (70). In the argon condenser (170), the difference between the temperature of the argon gas supplied from the argon column (70) and the temperature of oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column (60) is at most 2K.

Description

Air separation unit and air separation method

[0001] The present invention relates to an air separation unit and an air separation method for separating and extracting nitrogen, argon, and oxygen from air as a raw material by cryogenic distillation.

[0002] Patent Document 1 discloses an air separation unit having a high-pressure column that separates supplied feed air into nitrogen gas and oxygen-enriched liquid air, a low-pressure column that separates the oxygen-enriched liquid air separated in the high-pressure column into low-pressure nitrogen gas, low-pressure liquid oxygen, and low-pressure argon-enriched liquid oxygen, an argon column that separates the low-pressure argon-enriched liquid oxygen withdrawn from the low-pressure column into argon gas and medium-pressure liquid oxygen, a main condenser that liquefies nitrogen gas from the top of the high-pressure column with medium-pressure liquid oxygen from the bottom of the argon column to produce reflux liquid for the high-pressure and low-pressure columns, and an argon condenser that liquefies argon gas from the top of the argon column with liquid oxygen from the bottom of the low-pressure column to produce reflux liquid for the argon column.

[0003] JP 2016-008778 A

[0004] In the air separation unit disclosed in Patent Document 1, the argon column has a higher pressure than a typical double-column rectification air separation unit in which the argon column is not directly thermally coupled to the high-pressure column, and the power consumption of the feed air compressor is greater, but since a larger amount of high-pressure nitrogen gas can be recovered from the high-pressure column, the total power consumption, including the power to compress the nitrogen, is small. However, the power consumption of the feed air compressor cannot be ignored, and reducing the pressure of the high-pressure column has been an issue.

[0005] The present invention provides an air separation apparatus and method that can reduce power consumption and that separates and extracts nitrogen, argon, and oxygen from air as a raw material by cryogenic distillation.

[0006] In order to solve the above problems, research was conducted on the effect of the argon condenser on the pressure of the high-pressure column in the air separation unit of Patent Document 1, and it was found that, unlike a typical double-column rectification air separation unit, the pressure of the high-pressure column decreases when the temperature difference between the argon gas flowing into the argon condenser and the oxygen gas generated from liquid oxygen supplied from the bottom of the low-pressure column decreases. This is because the pressure of the argon gas condensed in the argon condenser determines the pressure of the bottom of the argon column, and the pressure of the high-pressure column is determined by the temperature difference between the pressure of the argon column bottom and the temperature of the fluid undergoing heat exchange in the main condenser.

[0007] However, in a typical double-column air separation unit, the argon column is not directly thermally coupled to the high-pressure column, and in the argon condenser, argon gas at the top of the argon column is liquefied with oxygen-enriched air extracted from the bottom of the high-pressure column and depressurized. Therefore, the pressure of the argon gas affects the pressure of the oxygen-enriched air extracted from the bottom of the high-pressure column after depressurization, but does not affect the pressure of the high-pressure column. Therefore, in order to achieve compactness in the unit, it is important to maximize the temperature difference above 2 K and minimize the heat transfer area of ​​the argon condenser.

[0008] The present inventors have found that the above-mentioned problem can be solved by setting the difference between the temperature of the argon gas supplied from the argon column and the temperature of the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column to 2 K or less. In the present invention, in the case of an argon condenser, the "temperature difference" means the difference between the temperature of the argon gas flowing into the argon condenser and the temperature of the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column. The present inventors have also found that the above-mentioned problem can be solved by employing a multi-stage bath condenser as the argon condenser.

[0009] In order to solve the above problems based on these findings, the present invention provides the following air separation unit and air separation method: [1] An air separation unit for separating and extracting nitrogen, argon, and oxygen from air as a feedstock by cryogenic distillation, comprising: a high-pressure column for separating supplied feed air into nitrogen gas and oxygen-enriched liquid air using a reflux liquid; a low-pressure column for separating the oxygen-enriched liquid air into nitrogen gas, liquid oxygen, and argon-enriched liquid oxygen using the reflux liquid; an argon column for separating the argon-enriched liquid oxygen into argon gas and medium-pressure liquid oxygen; a main condenser for liquefying nitrogen gas supplied from the top of the high-pressure column using the medium-pressure liquid oxygen supplied from the bottom of the argon column to produce the reflux liquids for the high-pressure column and the low-pressure column; and an argon condenser for liquefying argon gas supplied from the top of the argon column using the liquid oxygen supplied from the bottom of the low-pressure column to produce the reflux liquid for the argon column. an air separation unit, wherein in the argon condenser, the difference between the temperature of the argon gas supplied from the argon column and the temperature of the oxygen gas produced from the liquid oxygen supplied from the bottom of the low-pressure column is 2 K or less. [2] The air separation unit according to [1], wherein the argon condenser is a multistage bath condenser-reboiler comprising: condensation passages formed by stacking fins and plates, through which argon gas flows and condenses; evaporation passages formed by stacking fins and plates, and partitioned into multiple stages, through which liquid oxygen and a gas-liquid two-phase fluid of oxygen flow, which exchange heat with the argon gas and evaporate; a plurality of liquid reservoir sections provided for each of the multiple stages, which collect liquid supplied to the evaporation passages partitioned into multiple stages and flow out of the evaporation passages; and a liquid communication passage for flowing liquid in the liquid reservoir section from an upper liquid reservoir section to a lower liquid reservoir section, the condensation passages and the evaporation passages being stacked to form a heat exchange section, and the liquid reservoir section is provided for each of the multiple stages of the evaporation passages partitioned into multiple stages, excluding the lowest evaporation passage, on at least one side surface of the heat exchange section, perpendicular to the stacking direction of the heat exchange section, which is the direction in which the condensation passages and the evaporation passages are stacked. [3] The air separation unit according to [2], wherein the liquid communication passage is provided on at least one side of the heat exchange units in the stacking direction of the heat exchange units.[4] The air separation unit according to any one of [1] to [3], wherein the difference between the temperature of the argon gas supplied from the argon column and the temperature of the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column is 0.5 K to 2 K. [5] The air separation unit according to any one of [1] to [3], wherein the difference between the temperature of the argon gas supplied from the argon column and the temperature of the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column is 1.0 K to 1.5 K. [6] An air separation method for separating nitrogen, argon, and oxygen by cryogenic distillation of air, comprising: a high-pressure column step for separating supplied feed air into nitrogen gas and oxygen-enriched liquid air using a reflux liquid; a low-pressure column step for separating the oxygen-enriched liquid air into nitrogen gas, liquid oxygen, and argon-enriched liquid oxygen using a reflux liquid; an argon column step for separating the argon-enriched liquid oxygen into argon gas and medium-pressure liquid oxygen; a main condenser step for liquefying nitrogen gas supplied from the top of the high-pressure column using the medium-pressure liquid oxygen supplied from the bottom of the argon column, thereby producing the reflux liquids for the high-pressure column and the low-pressure column; and an argon condenser step for liquefying argon gas supplied from the top of the argon column using the liquid oxygen supplied from the bottom of the low-pressure column, thereby producing the reflux liquid for the argon column. 1. An air separation method comprising the steps of: (a) supplying argon gas from the argon column to the low-pressure column; (b) supplying oxygen gas from the liquid oxygen column to the low-pressure column;[7] In the argon condenser step, an argon condenser is used, the argon condenser comprising: condensation passages formed by stacking fins and plates, through which argon gas flows and condenses; evaporation passages formed by stacking fins and plates, partitioned into multiple stages, through which liquid oxygen and a gas-liquid two-phase fluid of oxygen flow and evaporate by heat exchange with the argon gas; a plurality of liquid reservoirs provided for each of the multiple stages, which store liquid supplied to the evaporation passages partitioned into multiple stages and flowing out of the evaporation passages; and liquid communication passages for flowing the liquid in the liquid reservoirs from an upper liquid reservoir to a lower liquid reservoir, the condensation passages and the evaporation passages being stacked to form a heat exchange section, [6] The air separation method according to [6], wherein the multistage bath condenser-reboiler is provided with the liquid reservoir section for each of the evaporation passages partitioned into multiple stages, excluding the lowest evaporation passage, on at least one side of the heat exchange section perpendicular to the stacking direction of the heat exchange section, which is the direction in which the condensation passages and the evaporation passages are stacked. [8] The air separation method according to [6] or [7], wherein, in the argon column step, the difference in temperature between the argon gas supplied from the argon column and the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column is 0.5 K to 2 K. [9] The air separation method according to [6] or [7], wherein, in the argon column step, the difference in temperature between the argon gas supplied from the argon column and the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column is 1.0 K to 1.5 K.

[0010] According to the air separation unit and air separation method of the present invention, the power consumption of the air separation unit can be reduced.

[0011] 1 is a diagram showing an embodiment of an air separation unit of the present invention. It is a diagram showing an embodiment of an argon condenser provided in the air separation unit of the present invention. It is a graph showing an example of temperature distribution when a general immersion-type condenser is used as the argon condenser provided in the air separation unit of FIG. 1. It is a graph showing the relationship between the temperature difference (Twi-Tco in FIG. 3) and the temperature difference taking into account the liquid head (Two-Tb in FIG. 3) when a general immersion-type condenser is used as the argon condenser provided in the air separation unit of FIG. 1. It is a graph showing the relationship between the temperature difference of the argon condenser provided in an air separation unit of one embodiment of the present invention and the bottom pressure of the high-pressure column. It is a graph showing the difference in temperature between the supplied argon gas and the outflowing oxygen gas, measured by changing the argon gas flow rate, in the argon condenser provided in the air separation unit of one embodiment of the present invention.

[0012] An air separation unit according to one embodiment of the present invention will be described in detail below with reference to the drawings. The drawings used in the following description may show characteristic portions enlarged for ease of understanding, and the dimensional ratios of the components may not be the same as in reality. In this specification, a numerical range expressed as "to" means a range of values ​​with the numbers before and after "to" as the lower and upper limits, respectively.

[0013] (Air Separation Unit) First, the air separation unit of this embodiment will be described using Figure 1. Figure 1 shows an example of an air separation unit of this embodiment. The air separation unit 100 includes a high-pressure column 50, a low-pressure column 60, an argon column 70, a main condenser 150, and an argon condenser 170, which is a multi-stage bath condenser.

[0014] The air separation unit 100 will be described in detail below. In Figure 1, AIR means feed air, CAr means low-purity crude argon, LPGO2 means product low-pressure oxygen gas, MPGO2 means product medium-pressure oxygen gas, HPGO2 means product high-pressure oxygen gas, WG means exhaust gas, LPGN2 means product low-pressure nitrogen gas, MPGN2 means product medium-pressure nitrogen gas, GN2 means nitrogen gas, LN2 means liquid nitrogen, and LO2 means product liquid oxygen.

[0015] Feed air (AIR) is compressed and purified by air compressor 1 and an air purifier and supplied to the bottom of high-pressure column 50 via line 21. The compressed and purified feed air thus supplied rises through gas-liquid contact with the reflux liquid flowing down through high-pressure column 50, concentrating nitrogen, a low-boiling component, and producing nitrogen gas at the top of the column. Meanwhile, the reflux liquid flowing down through high-pressure column 50 is enriched in oxygen, a high-boiling component, as it descends, producing oxygen-enriched liquid air at the bottom of the column. Oxygen-enriched liquid air withdrawn from the bottom of high-pressure column 50 is supplied to evaporator 250 via line 3. A portion of the oxygen-enriched liquid air supplied to evaporator 250 is evaporated and sent to main heat exchanger 10, booster 30, and expansion turbine 40 via line 4, becoming low-temperature oxygen-enriched air, which compensates for any lack of refrigeration throughout the entire system. The oxygen-enriched liquid air that is not evaporated in the evaporator 250 is further enriched in oxygen and is supplied to the low-pressure column 60 via line 5 .

[0016] The oxygen-enriched liquid air supplied to the low-pressure column 60 flows downward through gas-liquid contact with the ascending gas within the column, concentrating oxygen, a high-boiling component, and producing liquid oxygen at the column bottom. Furthermore, nitrogen, a low-boiling component, is concentrated in the ascending gas within the column as it rises, producing nitrogen gas at the column top. This gas passes through line 6 and main heat exchanger 10, and is recovered as product low-pressure nitrogen gas (LPGN2). Furthermore, argon-enriched liquid oxygen, which is enriched with argon, is extracted from the bottom of the low-pressure column 60 via line 7 and supplied to the argon column 70. The supplied argon-enriched liquid oxygen comes into gas-liquid contact with the ascending gas within the argon column 70. The high-boiling component oxygen contained in the argon-enriched liquid oxygen is concentrated, producing liquid oxygen at the column bottom. Furthermore, argon, a low-boiling component, is concentrated in the ascending gas within the column as it rises, producing argon gas at the column top.

[0017] A portion of the nitrogen gas produced at the top of the high-pressure column 50 is recovered as product medium-pressure nitrogen gas (MPGN2) via line 8 and main heat exchanger 10. Another portion is supplied to evaporator 250 via line 9, which branches off from line 8, and heat exchanges with oxygen-enriched liquid air from the bottom of the high-pressure column 50 to form liquid nitrogen. The resulting liquid nitrogen is supplied to the low-pressure column 60 via line 13 to form reflux. Still another portion is supplied to main condenser 150 via line 11, which branches off from line 9, and heat exchanges with medium-pressure liquid oxygen from the bottom of the argon column 70 to form liquid nitrogen. A portion of the resulting liquid nitrogen is returned to the high-pressure column 50 via line 12 to form reflux. Another portion is supplied to the low-pressure column 60 via line 12 and line 13, which branches off from line 12, to form reflux. Meanwhile, a portion of the oxygen gas produced from the liquid oxygen by heat exchange in the main condenser 150 is recovered as product low-pressure oxygen gas (LPGO2) via pipe 14 and main heat exchanger 10. The remaining oxygen gas becomes an ascending gas in the argon column 70 via pipe 15. The liquid oxygen that did not evaporate in the main condenser 150 is extracted via pipe 16 and pressurized by pump 500. After being pressurized by pump 500, a portion of the liquid oxygen has its pressure adjusted by a pressure regulating valve, evaporates in the main heat exchanger 10, and is recovered as product high-pressure oxygen gas (HPGO2). The remainder of the liquid oxygen pressurized by pump 500 has its pressure adjusted by a pressure regulating valve provided in pipe 23 branching off from pipe 16, evaporates in the main heat exchanger 10, and is recovered as product medium-pressure oxygen gas (MPGO2).

[0018] The argon gas produced at the top of the argon column 70 is supplied to an argon condenser 170 via a line 17 .

[0019] The argon condenser 170 is a plate-fin type heat exchanger made up of plates and fins, and is housed inside a container 174. The argon condenser 170 is a multi-stage bath condenser-reboiler comprising: condensation passages formed by stacking fins and plates, through which argon gas flows and condenses; evaporation passages formed by stacking fins and plates, which are partitioned into multiple stages, through which liquid oxygen and a gas-liquid two-phase fluid of oxygen flow, which exchange heat with the argon gas and evaporate; a plurality of liquid reservoir sections provided for each of the multiple stages, which collect liquid supplied to the evaporation passages partitioned into multiple stages and flowing out of the evaporation passages; and a liquid communication passage for allowing the liquid in the liquid reservoir sections to flow from an upper liquid reservoir section to a lower liquid reservoir section; the condensation passages and the evaporation passages are stacked to form a heat exchange section, and the liquid reservoir section is provided for each of the multiple stages of the evaporation passages partitioned into multiple stages, excluding the lowest evaporation passage, on at least one side surface of the heat exchange section, which is perpendicular to the stacking direction of the heat exchange section, which is the direction in which the condensation passages and the evaporation passages are stacked.

[0020] The argon condenser 170 of the air separation unit 100 of this embodiment will be described in detail below with reference to Figure 2. As shown in Figure 2, the argon condenser 170 is a multi-stage bath condenser that has condensation passages 1701 and evaporation passages 1702, the evaporation passages 1702 are divided into four evaporation zones, first to fourth, and each zone (except the lowest evaporation zone, which in this embodiment excludes the fourth evaporation zone) is provided with a liquid reservoir section 172. More specifically, the argon condenser 170 of the air separation unit 100 of this embodiment comprises a condensation passage 1701 through which argon gas flows and is condensed, an evaporation passage 1702 partitioned into first to fourth evaporation zones, each partitioned into multiple stages (four stages in FIG. 2 ), through which medium-pressure liquid oxygen and a gas-liquid two-phase fluid of oxygen flow and vaporize by heat exchange with the argon gas, liquid reservoirs 172 provided in the first to third evaporation zones for supplying liquid to the evaporation passages 1702 and for storing liquid flowing out of the evaporation passages 1702, and a liquid communication passage 1703 for flowing liquid in the liquid reservoir 172 to the liquid reservoir 172 in the next lower stage. A container 174 functions as the liquid reservoir of the fourth evaporation zone.

[0021] The condensation passages 1701, the evaporation passages 1702, and the liquid communication passages 1703 are made up of plates and fins. The condensation passages 1701 and the evaporation passages 1702 are stacked to form the heat exchanger 1704. The direction in which the condensation passages 1701 and the evaporation passages 1702 are stacked is the stacking direction of the heat exchanger 1704. Liquid communication passages 1703 are provided on both ends of the heat exchanger 1704 in the stacking direction. The liquid communication passages 1703 are provided integrally with the heat exchanger 1704, but this is not essential and may be formed separately from the heat exchanger 1704, for example, by pipes connecting the liquid reservoirs.

[0022] An upper header 171 is provided at the upper end of the heat exchange unit 1704 along the stacking direction. The upper header 171 is provided with an argon gas inlet 171a. A lower header 173 is provided at the bottom of the fourth evaporation zone. The lower header 173 is provided with an outlet 1731 for extracting two-phase gas-liquid argon. Liquid reservoirs 172 are provided on both side surfaces of the first to third evaporation zones where the upper headers 171 are not provided, in a direction perpendicular to the stacking direction of the heat exchange unit 1704.

[0023] Argon gas generated at the top of the argon column 70 is introduced into the upper header 171 of the argon condenser 170 having the above-described configuration through an argon gas inlet 171a provided in the upper header 171 and then flows into the condensation passage 1701. The argon gas flowing through the condensation passage 1701 imparts heat to liquid oxygen (described in detail below) flowing through the evaporation passage 1702. The argon gas itself absorbs heat and condenses as it flows downward. It is then discharged in a two-phase gas-liquid state through the lower header 173 and the outlet 1731 provided in the lower header 173. The discharged two-phase gas-liquid argon is separated into gas and liquid through the gas-liquid separation tube 90. The separated gas is recovered as crude argon gas (CAr). The separated liquid is returned to the argon column as reflux via pipe 18. The recovered crude argon gas (CAr) contains oxygen and nitrogen as impurities. Therefore, hydrogen is first added to remove oxygen. The nitrogen is then removed by distillation in a high purity argon column operated at low temperature, and product liquid argon (LAr) is recovered from the bottom of the column (not shown).

[0024] Meanwhile, liquid oxygen accumulated at the bottom of the low-pressure column 60 is supplied via line 19, argon column 70, line 20, and line 1720 to liquid reservoir 172 at the top of argon condenser 170, and then to evaporation passage 1702. A portion of the supplied liquid oxygen flows into evaporation passage 1702 from lower opening 1705 of evaporation passage 1702 in each evaporation zone due to the thermosiphon effect, rises while evaporating, and flows out from upper opening 1706 into liquid reservoir 172. The evaporated gas is discharged from the top of liquid reservoir 172 into container 174, and the unevaporated liquid is returned to liquid reservoir 172, repeating evaporation and circulation. The remainder of the supplied liquid oxygen is supplied to liquid reservoir 172 below via communication passage 1703, repeats evaporation and circulation, and is supplied downward. The fourth evaporation zone, which is the lowest part, is not provided with the liquid reservoir 172 provided in the first to third evaporation zones. Liquid oxygen stored in a container flows into the fourth evaporation zone from the bottom, rises while evaporating, and is returned to the container 174 in a gas-liquid two-phase state from the top opening 1706 provided at the top of the passage. Product liquid oxygen (LO) is then released from the bottom of the container 174 through the pipe 22. ２The gas evaporated in each evaporation zone is collected in a vessel 174 and then supplied to the low-pressure column 60 as an ascending gas. In other words, the vessel 174 functions as a liquid reservoir for the fourth evaporation zone.

[0025] The temperature of the argon gas supplied from the argon column is the dew point at the pressure at the top of the argon column, and the temperature of the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column 60 is the dew point at the pressure at the bottom of the low-pressure column. Therefore, the pressure difference between the two corresponds to the temperature difference in the argon condenser 170.

[0026] In this multistage bath condenser-reboiler, the liquid oxygen flowing from the liquid reservoir 172 provided in each evaporation zone into the evaporation passage 1702 has a small liquid head and is suppressed from rising in boiling point because the evaporation zones are partitioned into multiple upper and lower zones. This makes it possible to reduce the temperature difference between the condensing argon and the evaporating oxygen.

[0027] Figure 3 shows an example of the temperature distribution when a typical immersion-type condenser is used as the argon condenser in the air separation unit of Figure 1. Argon gas flows into the argon condenser at temperature Twi and flows out of the argon condenser at temperature Two, which is approximately the same as temperature Twi. Due to the influence of liquid head, liquid oxygen flows into the argon condenser at temperature Tci, which is lower than the boiling point Tb, and its temperature rises as it flows upward due to heat generated by the argon gas. After boiling, the temperature (saturation) decreases as the pressure drops, and the argon gas flows out of the condenser at temperature Tco. Figure 3 shows that the heat exchange between argon gas and liquid oxygen in the argon condenser has a pinch point at the boiling point of the liquid oxygen due to the influence of liquid head, and the temperature difference at the pinch point significantly affects the temperature difference in the argon condenser.

[0028] Figure 4 plots the temperature difference (Twi - Tco) versus the temperature difference (Two - Tb) taking into account the boiling point rise when an immersion-type condenser (core height: 2 m, liquid surface height: top of core) is used for the argon condenser in Figure 1. It can be seen that when the temperature difference is reduced by lowering the argon gas pressure, the temperature difference taking into account the liquid head also decreases, and the temperature difference at which it becomes zero is 2 K. In other words, with a commonly used immersion-type condenser, it is not possible to reduce the temperature difference below 2 K.

[0029] Figure 5 shows the relationship between the temperature difference of the argon condenser and the pressure at the bottom of the high-pressure column. When the temperature difference of the argon condenser is 2 K, the pressure at the bottom of the high-pressure column is approximately 780 kPaA, but at 1 K this drops to 730 kPaA, indicating that the power consumption of the feed air compressor can be reduced. This shows that by using a condenser that can achieve a temperature difference smaller than the minimum temperature difference of 2 K for an immersed condenser, it is possible to reduce the power consumption of the air separation unit described in Patent Document 1.

[0030] In the multistage bath condenser-reboiler used in the air separation unit of this embodiment, liquid oxygen flows into evaporation passages 1702 from liquid reservoirs 172 provided in each of the evaporation zones, which are partitioned vertically. As a result, the effect of liquid head on the liquid oxygen in the passages is small and the rise in boiling point is suppressed, so the temperature difference between the condensing argon and the evaporating oxygen can be reduced, achieving a temperature difference of less than 2 K.

[0031] Furthermore, by adopting the vertical stack type condenser-evaporator disclosed in Japanese Patent No. 6,871,962, a temperature difference of 2 K or less can be achieved. A vertical stack type condenser-evaporator has one or more partition plates that vertically divide the inner space of a cylindrical container into upper and lower chambers, and a heat exchange core is placed in each of the multiple chambers that are arranged vertically above and below the partition plates. Similar to an immersion type condenser, the heat exchange core placed in each chamber has condensation passages and evaporation passages and operates while immersed in the evaporating fluid. As a result, by disposing the heat exchange cores in multiple chambers, the height of each heat exchanger core can be reduced, and the corresponding liquid head can be made smaller, making it possible to achieve a temperature difference of less than 2 K.

[0032] The smaller the temperature difference, the more power consumption can be reduced, but since the heat transfer area of ​​the argon condenser increases, the temperature difference is more preferably 0.5K to 2K, and particularly preferably 1.0K to 1.5K.

[0033] (Air Separation Method) The air separation method of this embodiment will be described below. The air separation method of the present invention is an air separation method for separating and collecting nitrogen, argon, and oxygen from air as a feedstock by cryogenic distillation, comprising: a high-pressure column step for separating supplied feed air into nitrogen gas and oxygen-enriched liquid air using a reflux liquid; a low-pressure column step for separating the oxygen-enriched liquid air into nitrogen gas, liquid oxygen, and argon-enriched liquid oxygen using a reflux liquid; an argon column step for separating the argon-enriched liquid oxygen into argon gas and medium-pressure liquid oxygen; a main condenser step for liquefying nitrogen gas supplied from the top of the high-pressure column using the medium-pressure liquid oxygen supplied from the bottom of the argon column to produce the reflux liquids for the high-pressure column and the low-pressure column; and an argon condenser step for liquefying argon gas supplied from the top of the argon column using the liquid oxygen supplied from the bottom of the low-pressure column to produce the reflux liquid for the argon column. In the argon condenser step, the difference between the temperature of the argon gas supplied from the argon column and the temperature of the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column is set to 2 K or less.

[0034] Each step of the air separation method using the air separation unit shown in Figure 1 will be described below. First, feed air (AIR) compressed and purified by the air compressor 1 and air purifier is supplied to the bottom of the high-pressure column 50. (High-pressure column step) In the high-pressure column step, the supplied compressed and purified feed air is brought into gas-liquid contact with reflux liquid flowing down through the high-pressure column 50, concentrating nitrogen, a low-boiling component, as the feed air rises, producing nitrogen gas at the top of the column. In addition, the reflux liquid flowing down through the high-pressure column 50 is brought into gas-liquid contact with the feed air, enriching it with oxygen, a high-boiling component, to produce oxygen-enriched liquid air at the bottom of the column.

[0035] (Low-Pressure Column Step) In the low-pressure column step, the oxygen-enriched liquid air obtained in the high-pressure column step is brought into gas-liquid contact with the ascending gas obtained in the argon condenser step, together with the reflux liquid obtained in the main condenser step described below. As a result, the ascending gas concentrates nitrogen, a low-boiling point component, and nitrogen gas is produced at the top of the column. In addition, argon-enriched liquid oxygen is produced at the bottom of the low-pressure column 60. Furthermore, liquid oxygen is produced at the bottom of the column.

[0036] (Argon Column Step) In the argon column step, the argon-enriched liquid oxygen obtained in the low-pressure column step, together with the reflux liquid from the argon condenser 170, is brought into gas-liquid contact with the ascending gas obtained in the main condenser step. As a result, argon, a low-boiling point component, is produced at the top of the argon column 70, and medium-pressure liquid oxygen, a high-boiling point component, is produced at the bottom of the column.

[0037] (Main Condenser Step) In the main condenser step, the nitrogen gas obtained in the high-pressure column step is liquefied using the medium-pressure liquid oxygen obtained in the argon column step. The liquid nitrogen obtained by liquefaction is used as reflux liquid for the high-pressure column 50 and the low-pressure column 60. In addition, the oxygen gas generated from the medium-pressure liquid oxygen is used as ascending gas for the argon column.

[0038] (Argon Condenser Step) In the argon condenser step, the argon gas obtained in the argon tower step is liquefied using the liquid oxygen obtained in the low-pressure column step to produce reflux liquid for use in the argon tower step. Furthermore, oxygen gas to be used as ascending gas in the low-pressure column step is produced from the liquid oxygen. In the argon condenser step, the temperature difference between the argon gas flowing in from the argon tower and the temperature of the oxygen gas produced from the liquid oxygen supplied from the bottom of the low-pressure column is set to 2 K or less. To adjust the temperature difference to 2 K or less, it is preferable to use the multistage bath evaporator described above as the argon condenser 170. In the multistage bath evaporator described above, the liquid oxygen flowing from each liquid reservoir 172 into the evaporation passage 1702 has a small liquid head because the evaporation zones are partitioned into multiple upper and lower sections, thereby suppressing the rise in boiling point. Therefore, the temperature difference can be easily adjusted to 2 K or less. By setting the temperature difference in the argon condenser to 2 K or less, the pressure in the high-pressure column step can be set low. This makes it possible to reduce the power consumption required to compress the feed air used in the high-pressure column process. Note that, although the smaller the temperature difference, the more power consumption can be reduced, the heat transfer area of ​​the argon condenser increases, so the temperature difference is more preferably 0.5 K to 2 K, and particularly preferably 1.0 K to 1.5 K.

[0039] In the air separation method of this embodiment, the argon condenser step has been described using the multistage bath evaporator described above, but the present invention is not limited to this. It is sufficient to adjust the temperature difference to 2 K or less. For example, a vertical stack condenser-reboiler such as that disclosed in Japanese Patent No. 6,871,962 may also be used.

[0040] (Operation and Effect) In the argon condenser 170 of the air separation unit 100 of this embodiment, the liquid oxygen flowing from the liquid reservoir 172 provided in each evaporation zone into the evaporation passage 1702 has a small liquid head and suppresses boiling point rise because the evaporation zones are partitioned into multiple upper and lower zones. This makes it possible to reduce the temperature difference between the condensing argon and the evaporating oxygen. Furthermore, although the argon condenser 170 uses liquid oxygen as a cold source, a sufficient liquid flow rate can be ensured to prevent the concentration of hydrocarbons contained in the feed air inside the evaporation passage 1702. According to the air separation method of this embodiment, the pressure in the high-pressure column 50 can be set low by keeping the temperature difference in the argon condenser at 2 K or less. This makes it possible to reduce the power consumption required to compress the feed air to be supplied to the high-pressure column 50.

[0041] The air separation method and air separation apparatus of the present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0042] Example 1: A multi-stage bath condenser (four evaporation zones, heat transfer area of ​​evaporation passage: 220 m) shown in FIG. ２ ) was used as the argon condenser 170, and argon gas was liquefied. The relationship between the temperature difference in the argon condenser 170 and the flow rate of argon gas was measured. The results are shown in FIG. 6. The horizontal axis of FIG. 6 represents the flow rate of argon gas (mass flow rate per cross-sectional area of ​​the condensation passage), and the vertical axis represents the temperature difference in the argon condenser 170. As shown in FIG. 6, it can be seen that heat exchange is possible even when the temperature difference in the argon condenser 170 is 2 K or less, specifically, approximately 0.7 K to 1.1 K.

[0043] Examples 2 to 5 Using the air separation unit 100 shown in Figure 1, air was separated by changing the heat transfer area of ​​the argon condenser to change the temperature difference. The product specifications of the air separation unit, the flow rate and pressure of the feed air compressor 1, the flow rate of the compressed feed air supplied to the air booster 2, the pressure of the supplied feed air (suction pressure), and the pressure of the feed air after pressurization (discharge pressure) are as shown in Table 1 below. In Table 1, each flow rate is expressed as a percentage (%) with the sum of all oxygen product amounts (product high-pressure oxygen gas HPGO2 + product medium-pressure oxygen gas MPGO2 + product low-pressure oxygen gas LPGO2 + product liquid oxygen LO2) as the denominator. Table 2 also shows the power consumption of the air compressor 1 and the air booster 2 when separating air using an argon condenser with a temperature difference of 1.5 K.

[0044] Comparative Example 1 The argon condenser of the air separation unit shown in Figure 1 was replaced with a general immersion-type condenser, and air separation was carried out with a temperature difference of 2.3 K. The flow rate and pressure of feed air compressor 1, the flow rate of compressed feed air supplied to air booster 2, the pressure of the supplied feed air (suction pressure), and the pressure of the feed air after boosting (discharge pressure) are shown in Table 1 below. The power consumption of air compressor 1 and air booster 2 are also shown in Table 2.

[0045]

[0046] From Table 1 above, it can be seen that, compared to Comparative Example 1 in which the difference in temperature between the argon gas supplied from the argon column 70 in the argon condenser 170 and the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column 60 is 2.3 K, Example 4 in which the temperature difference is 1.5 K results in a lower pressure despite the same flow rate of the air compressor 1. It can also be seen that the suction pressure is lower despite the same flow rate and discharge pressure of the air booster 2.

[0047]

[0048] ​Furthermore, as can be seen from Table 2, in the air separation unit of Example 4, the power consumption of air compressor 1 is small and the suction pressure of air booster 2 is low, resulting in a large power consumption of booster 2. However, it was confirmed that the total power consumption of air compressor 1 and the air booster could be reduced by approximately 2% compared to the conventional air separation unit of Comparative Example 1.

[0049] According to the air separation unit and air separation method of the present invention, power consumption can be reduced.

[0050] REFERENCE SIGNS LIST 1 air compressor 2 air booster 3, 5 to 23 pipe 10 main heat exchanger 30 booster 40 expansion turbine 50 high pressure column 60 low pressure column 70 argon column 90 gas-liquid separation tube 100 air separation unit 150 main condenser 170 argon condenser 1701 condensation passage 1702 evaporation passage 1703 liquid communication passage 1704 heat exchange section 1705 lower opening 1706 upper opening 171 upper header 171a argon gas inlet 172 liquid reservoir section 173 lower header 1720 pipe 1731 outlet 174 container 250 evaporator 500, 600 pump

Claims

1. An air separation unit for separating nitrogen, argon, and oxygen by cryogenic distillation of air, comprising: a high-pressure column that uses reflux liquid to separate supplied feed air into nitrogen gas and oxygen-enriched liquid air; a low-pressure column that uses reflux liquid to separate the oxygen-enriched liquid air into nitrogen gas, liquid oxygen, and argon-enriched liquid oxygen; an argon column that separates the argon-enriched liquid oxygen into argon gas and medium-pressure liquid oxygen; a main condenser that produces reflux liquids for the high-pressure column and the low-pressure column by liquefying nitrogen gas supplied from the top of the high-pressure column using medium-pressure liquid oxygen supplied from the bottom of the argon column; and an argon condenser that liquefies argon gas supplied from the top of the argon column using liquid oxygen supplied from the bottom of the low-pressure column to produce liquid oxygen as reflux liquid for the argon column. an air separation unit, wherein in the argon condenser, the difference between the temperature of the argon gas supplied from the argon column and the temperature of the oxygen gas produced from the liquid oxygen supplied from the bottom of the low-pressure column is 2 K or less.

2. The air separation unit according to claim 1, wherein the argon condenser is a multistage bath condenser-reboiler comprising: condensation passages formed by stacking fins and plates, through which argon gas flows and condenses; evaporation passages formed by stacking fins and plates, partitioned into multiple stages, through which liquid oxygen and a gas-liquid two-phase fluid of oxygen flow, which exchange heat with the argon gas and evaporate; a plurality of liquid reservoir sections provided for each of the multiple stages, for storing liquid supplied to the evaporation passages partitioned into multiple stages and flowing out of the evaporation passages; and liquid communication passages for flowing liquid in the liquid reservoir sections from upper liquid reservoir sections to lower liquid reservoir sections, the condensation passages and the evaporation passages being stacked to form a heat exchange section, and the liquid reservoir sections are provided for each of the multiple stages of the evaporation passages partitioned into multiple stages, excluding the lowest evaporation passage, on at least one side of the heat exchange section perpendicular to the stacking direction of the heat exchange section, which is the direction in which the condensation passages and the evaporation passages are stacked.

3. An air separation unit according to claim 2, wherein said liquid communication passage is provided on at least one side of said heat exchange units in the stacking direction of said heat exchange units.

4. An air separation unit according to any one of claims 1 to 3, wherein the difference between the temperature of the argon gas supplied from the argon column and the temperature of the oxygen gas produced from the liquid oxygen supplied from the bottom of the low-pressure column is 0.5K to 2K.

5. An air separation unit according to any one of claims 1 to 3, wherein the difference between the temperature of the argon gas supplied from the argon column and the temperature of the oxygen gas produced from the liquid oxygen supplied from the bottom of the low-pressure column is 1.0K to 1.5K.

6. An air separation process for separating nitrogen, argon, and oxygen by cryogenic distillation of air, comprising: a high-pressure column step for separating supplied feed air into nitrogen gas and oxygen-enriched liquid air using a reflux liquid; a low-pressure column step for separating the oxygen-enriched liquid air into nitrogen gas, liquid oxygen, and argon-enriched liquid oxygen using a reflux liquid; an argon column step for separating the argon-enriched liquid oxygen into argon gas and medium-pressure liquid oxygen; a main condenser step for liquefying nitrogen gas supplied from the top of the high-pressure column using the medium-pressure liquid oxygen supplied from the bottom of the argon column, thereby producing the reflux liquids for the high-pressure column and the low-pressure column; and an argon condenser step for liquefying argon gas supplied from the top of the argon column using the liquid oxygen supplied from the bottom of the low-pressure column, to produce liquid oxygen as the reflux liquid for the argon column.

1. An air separation method comprising the steps of: (a) supplying argon gas from the argon column to the low-pressure column; (b) supplying oxygen gas from the liquid oxygen column to the low-pressure column; 7. The air separation method according to claim 6, wherein the argon condenser step uses an argon condenser, the argon condenser comprising: condensation passages formed by stacking fins and plates, through which argon gas flows and condenses; evaporation passages formed by stacking fins and plates, partitioned into multiple stages, through which liquid oxygen and a gas-liquid two-phase fluid of oxygen flow and evaporate by heat exchange with the argon gas; a plurality of liquid reservoir sections provided for each of the multiple stages, for storing liquid supplied to the evaporation passages partitioned into multiple stages and flowing out of the evaporation passages; and liquid communication passages for flowing liquid in the liquid reservoir sections from upper liquid reservoir sections to lower liquid reservoir sections, the condensation passages and the evaporation passages being stacked to form a heat exchange section, and the argon condenser is a multistage bath condenser-reboiler in which the liquid reservoir sections are provided on at least one side of the heat exchange section, perpendicular to the stacking direction of the heat exchange sections, which is the direction in which the condensation passages and the evaporation passages are stacked.

8. The air separation method according to claim 6 or 7, wherein in the argon column step, the difference between the temperature of the argon gas supplied from the argon column and the temperature of the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column is set to 0.5 K to 2 K.

9. The air separation method according to claim 6 or 7, wherein in the argon column step, the difference in temperature between the argon gas supplied from the argon column and the oxygen gas generated from the liquid oxygen supplied from the bottom of the low-pressure column is set to 1.0 K to 1.5 K.

Images