Cryogenic air separation unit, and method for shutting down and starting up a cryogenic air separation unit

Abstract

To provide an air liquefaction separation device capable of greatly extending a low-temperature standby time, and further shortening a total heating time and an activation time.SOLUTION: An air liquefaction separation device comprises a heat exchanger 13 that cools compressed and purified raw air, and a double rectification tower that combines a high pressure tower 14 and a low pressure tower 15 that separate raw air by liquefaction rectification. A first pressure adjustment path 24 is provided so as to branch off from a path 22 connecting the low pressure tower 14 and the heat exchanger 13. The first pressure adjustment path 24 comprises a first gas release valve 23 that is controlled so that a pressure in the low pressure tower 15 does not exceed a preset pressure. A second pressure adjustment path 80 is provided so as to branch off from a path 52 connecting the high pressure tower 14 and the heat exchanger 13. The second pressure adjustment path 80 comprises a second gas release valve 81 that is controlled so that a pressure in the high pressure tower 14 does not exceed a preset pressure. A bypass path 84 is provided that connects the first pressure adjustment path 24 and the second pressure adjustment path 80.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cryogenic air separation unit, and a method for shutting down and starting up a cryogenic air separation unit. More specifically, the present invention relates to a cryogenic air separation unit equipped with a configuration for preventing a pressure rise in the system when operation of the cryogenic air separation unit is temporarily stopped for compressor inspection or the like, and a configuration for shortening the start-up time, and a method for shutting down and starting up a cryogenic air separation unit. [Background technology]

[0002] An air cryogenic separation unit is a unit that separates air into oxygen, nitrogen, etc. by low-temperature distillation. Therefore, liquefied air, liquefied oxygen gas, liquefied nitrogen gas, etc. are present inside the air cryogenic separation unit in normal operating condition. Meanwhile, the air cryogenic separation unit may be temporarily stopped for a short period of time due to maintenance or trouble of the component equipment, etc., and then restarted. Temporarily stopping the operation of the air separation unit while liquefied air, liquefied oxygen gas, liquefied nitrogen gas, etc. remain inside the air cryogenic separation unit is called low-temperature standby.

[0003] In this low-temperature standby state, the low-temperature liquefied gas remaining in the cryogenic air separation unit evaporates due to the heat intrusion, causing the pressure in the system to rise above the design pressure, so that a part of the low-temperature gas is discharged from the system to the outside. However, when gas is discharged from the normal temperature gas system, only cold fluid flows without any warm fluid entering the heat exchanger, so that, for example, the warm end of the heat exchanger is cooled, and gas piping made of carbon steel or the like, which is intended to carry normal room temperature gas, may develop low-temperature brittleness and break. Therefore, it is considered preferable to stop the low-temperature standby of the cryogenic air separation unit before the warm end temperature of the heat exchanger falls below -10°C, which is the allowable temperature for carbon steel piping, and to discharge the liquefied gas outside the system.

[0004] In view of this, a cryogenic air separation unit and a method for shutting down a cryogenic air separation unit have been proposed that are configured to prevent the low-temperature gas released when the cryogenic air separation unit is shut down from flowing into piping for product gas collection, etc., and that can also accommodate long-term shutdowns (see, for example, Patent Document 1).

[0005] On the other hand, the cryogenic air separation unit is composed of rotary machinery and the like, and these devices require maintenance. For this purpose, the operation of the cryogenic air separation unit is periodically stopped, and the inside of the unit is returned to room temperature. Then, when the maintenance is completed, an operation is performed to remove moisture and carbon dioxide from the equipment piping in the unit (full heating operation), and then an operation is performed to cool the unit from the room temperature state and start it up. Since the start-up operation requires a huge amount of energy and time, it is preferable to shorten the operation time.

[0006] In other words, when a large cryogenic air separation unit is placed on low-temperature standby and then started up, it is important to (1) prevent low-temperature fluid from flowing through piping and equipment that is designed on the assumption that normal-temperature fluid (fluid that is not low-temperature) will flow, (2) minimize the amount of refrigeration energy released from the cryogenic air separation unit to the outside (minimize the amount of low-temperature gas and liquefied gas released to the outside), and (3) shorten the startup time. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-178816 A Summary of the Invention [Problem to be solved by the invention]

[0008] Here, the air cryogenic separation apparatus using the double rectification column described in Patent Document 1 is shown in FIG. 3. When this double rectification column apparatus 16 is stopped in a low temperature state, liquefied gas (liquefied oxygen gas, liquefied nitrogen gas, liquefied air, etc.) remains in the lower part of the high-pressure column 14 and the low-pressure column 15. In this state, after the air cryogenic separation apparatus is stopped, the liquefied gas in the high-pressure column 14 and the low-pressure column 15 is vaporized due to heat intrusion from outside the cold box, etc., and the pressure in the column increases. In order to suppress the increase in pressure in the high-pressure column 14, it was necessary to introduce a part of the liquefied gas into the low-pressure column 15 through the liquefied air discharge line 53, the liquefied air introduction line 54, and the pressure reducing valve 54a, and further release the vaporized gas from the low-pressure column 15 to the atmosphere through the pressure adjustment line 24. Also disclosed is a method of introducing low-temperature high-pressure gas in the high-pressure column 14 into the low-pressure column 15 through a liquid nitrogen passage 57 and a pressure reducing valve 57a in order to reduce loss of liquefied gas stored in the lower part of the high-pressure column 14 when reducing a pressure increase in the high-pressure column 14. However, the pipe diameter, valve CV value, etc. of the liquid nitrogen passage 57 and the pressure reducing valve 57a are designed on the assumption that liquid nitrogen flows during normal operation, and the pipe diameter, valve CV value, etc. are not sufficient to allow gas to flow, and it may be difficult to ensure a sufficient gas flow rate.

[0009] On the other hand, when starting up this cryogenic air separation unit that has become room temperature due to maintenance or the like, moisture and carbon dioxide are removed during full heating operation before startup, and the heated feed air is introduced into the high-pressure column 14 via the feed air passage 51 and the low-temperature feed air passage 52, and the high-pressure column 14 is heated. Thereafter, the feed air is introduced into the low-pressure column 15 via the liquid nitrogen passage 57, the pressure reducing valve 57a, the liquefied air introduction passage 54, the pressure reducing valve 54a, or the like, and the low-pressure column 15 is heated. However, the pipe diameter, the CV value of the valve, and the like of the liquid nitrogen passage 57, the pressure reducing valve 57a, or the liquefied air introduction passage 54, the pressure reducing valve 54a are designed on the assumption that low-temperature liquefied gas flows, and the pipe diameter, the CV value of the valve, and the like are not sufficient to flow the feed air for heating, making it difficult to ensure a sufficient flow rate. In order to heat the low-pressure column 15, for example, it may be possible to install a start-up pipe for directly introducing a portion of the feed air flowing through the low-temperature feed air passage 52 into the low-pressure column 15, but this also results in an increase in the cost of the equipment.

[0010] Even in the case of the cryogenic air separation plant using a single-column rectification column described in Patent Document 1 shown in Fig. 4, when the operation of the cryogenic air separation plant is stopped, the liquefied gas remaining in the lower part of the rectification tower 31 is vaporized due to heat intrusion from outside the cold box, etc., and the pressure in the tower increases. In order to suppress this pressure increase, it was necessary to release the liquefied gas in the rectification tower 31 through the liquefied air discharge line 72, the pressure reducing valve 34, the condenser 32, the exhaust gas discharge line 76, the pressure adjustment line 37, and the gas release valve 36. In this method, in order to suppress the pressure increase in the tower, it is necessary to vaporize a part of the liquefied gas remaining in the tower and release it to the outside of the system, and there is room for improvement in terms of maintaining the coldness in the apparatus.

[0011] Furthermore, when starting up after shutting down the operation, it is necessary to cool the device from the room temperature state after the full heating operation, and the exhaust gas flowing through the exhaust gas discharge path 76 is introduced into the expansion turbine 35, and the rectification tower is gradually cooled by the cold energy generated in the expansion turbine 35. During startup operation, the operating temperature of the rectification tower is higher than during normal operation, so that it is not possible to ensure a sufficient flow rate of exhaust gas flowing through the exhaust gas discharge path 76 (the fluid density is low / the fluid volume is large, and exhaust gas does not easily flow through piping with a small diameter), which was one of the reasons why startup time took a relatively long time.

[0012] Therefore, an object of the present invention is to provide a cryogenic air separation unit, a method for shutting down the unit, and a method for starting up the unit, which are capable of significantly extending the low-temperature standby time of the unit and further shortening the total heating time and start-up time without damaging carbon steel piping for normal temperature gas due to low-temperature brittleness. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention provides a cryogenic air separation unit as a first configuration, comprising a heat exchanger for cooling compressed and purified feed air, and a double rectification column combining a high-pressure column and a low-pressure column for liquefying and rectifying the feed air, wherein a first pressure adjustment path for discharging a fluid outside the system is branched off from a path connecting the low-pressure column and the heat exchanger, and the first pressure adjustment path is provided with a first gas release valve controlled so that the pressure of the low-pressure column does not exceed a preset pressure, and a second pressure adjustment path for discharging a fluid outside the system is branched off from a path connecting the high-pressure column and the heat exchanger, and the second pressure adjustment path is provided with a second gas release valve controlled so that the pressure of the high-pressure column does not exceed a preset pressure, and a bypass path is provided connecting the upstream side of the first gas release valve of the first pressure adjustment path to the upstream side of the second gas release valve of the second pressure adjustment path. The passage connecting the low pressure tower and the heat exchanger is an exhaust gas discharge passage for extracting exhaust gas from the low pressure tower. It is characterized by the following.

[0014] Furthermore, in the air liquefaction separation plant of the first configuration, ,before The present invention is characterized in that the path connecting the low-pressure tower and the heat exchanger is a path for introducing feed air, and that valves for closing each path are provided in the path for introducing feed air to the heat exchanger and the path of an outlet system from the low-pressure tower.

[0015] A second configuration of the air cryogenic separation unit of the present invention is an air cryogenic separation unit including a heat exchanger for cooling compressed and purified feed air, and a single rectification column combining a rectification column and a condenser for liquefying, rectifying and separating the feed air, wherein a first pressure adjustment path for discharging a fluid outside the system is provided branching off from a path connecting the condenser and the heat exchanger, and the first pressure adjustment path is provided with a first gas release valve controlled so that the pressure in the first pressure adjustment path does not exceed a preset pressure, and a second pressure adjustment path for discharging a fluid outside the system is provided branching off from a path connecting the rectification column and the heat exchanger, and the second pressure adjustment path is provided with a second gas release valve controlled so that the pressure in the rectification column does not exceed a preset pressure, and a bypass path is provided connecting the upstream side of the first gas release valve of the first pressure adjustment path to the upstream side of the second gas release valve of the second pressure adjustment path. a path connecting the condenser and the heat exchanger is an exhaust gas discharge path for extracting exhaust gas from the condenser, and a path connecting the distillation column and the heat exchanger is a path for introducing feed air. It is characterized by:

[0016] Furthermore, in the air liquefaction separation plant of the second configuration, ,before The present invention is characterized in that a valve for closing each of the paths for introducing feed air into the heat exchanger and the path of the outlet system from the rectification column is provided.

[0017] In addition, the method for temporarily stopping operation of a cryogenic air separation unit in the first and second configurations of the present invention is characterized in that, when operation is stopped, fluid is discharged from the first pressure adjustment path to the outside of the system, and fluid is discharged from the second pressure adjustment path to the outside of the system.

[0018] Furthermore, the method for starting up operation of a cryogenic air separation unit in the first and second configurations of the present invention is characterized in that, during full heating operation before start-up, a portion of heated feed air is introduced from the second pressure adjustment path through the bypass path into the first pressure adjustment path.

[0019] Furthermore, the method for starting up the operation of an air cryogenic separation unit in the second configuration of the present invention is characterized in that a portion of the feed air is introduced from the second pressure adjustment path through the bypass path and the first pressure adjustment path into an expansion turbine. Effect of the Invention

[0020] According to the present invention, by providing a pressure adjustment path in the path connecting the high-pressure column (rectification column) and the heat exchanger, gas can be released without passing through a pressure reducing valve or a heat exchanger, thereby reducing the amount of liquefied gas released to the outside and enabling the liquefied gas to be retained inside the column for a longer period of time, thereby making it possible to extend the low-temperature standby time.

[0021] Furthermore, during the full heating operation, a portion of the heated feed air can be introduced from the second pressure adjustment path through the bypass path into the first pressure adjustment path, thereby making it possible to shorten the full heating operation time.

[0022] Furthermore, at the time of startup, a portion of the feed air can be introduced from the second pressure regulation path through the bypass path and the first pressure regulation path into the expansion turbine, thereby making it possible to shorten the startup time. [Brief description of the drawings]

[0023] [Figure 1] 1 is a system diagram showing a first embodiment of a cryogenic air separation unit to which the shutdown method and startup method of the present invention can be applied. [Diagram 2] FIG. 2 is a system diagram showing a main part of a second embodiment of a cryogenic air separation unit to which the shutdown method and startup method of the present invention can be applied. [Diagram 3] FIG. 1 is a system diagram of a cryogenic air separation plant using a conventional double rectification column. [Figure 4] FIG. 1 is a system diagram of a cryogenic air separation plant using a conventional single column rectification column. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 1 is a system diagram showing a first embodiment of a cryogenic air separation unit of the present invention, and shows an embodiment in which the present invention is applied to a cryogenic air separation unit using a double column rectification column. Note that in the following description, high pressure, medium pressure, and low pressure indicate relative pressure differences in each embodiment, and do not specify a pressure range.

[0025] The air cryogenic separation unit shown in this embodiment comprises, as its main equipment, a compressor 11 that compresses the feed air, a purifier 12 that removes impurities from the feed air, a heat exchanger 13 that cools the purified feed air by heat exchange with a low-temperature gas, a double rectification column 16 that combines a high-pressure column 14 and a low-pressure column 15 that liquefy and rectify the cooled feed air, a condenser 17 that liquefies the high-pressure nitrogen gas separated at the top of the high-pressure column 14 by heat exchange with the low-pressure liquid oxygen separated at the bottom of the low-pressure column 15 to produce liquid nitrogen, and a supercooler 18 that exchanges heat between the liquefied gas (oxygen-enriched liquefied air) extracted from the bottom of the high-pressure column 14 and the gas (product nitrogen gas, exhaust gas) extracted from the top of the low-pressure column 15.

[0026] In addition, the low pressure column 15 is provided with a crude argon column 20 equipped with an argon condenser 19. Furthermore, each device and path through which each low temperature gas flows is housed in a cold box 21 to suppress the intrusion of heat from the outside.

[0027] In this embodiment of the cryogenic air separation unit having such a configuration, a first pressure adjustment path 24 is provided in the exhaust gas discharge path 22, which discharges the exhaust gas from the upper part of the low-pressure column 15, and which branches off from a position before the introduction into the heat exchanger 13 and has a first gas release valve 23 for discharging the exhaust gas to the outside. The first gas release valve 23 is controlled so that the valve opening degree is adjustable so that the pressure in the low-pressure column 15 does not exceed a preset pressure, and a first pressure transmission path 25 is provided between the first gas release valve 23 and the upper part of the low-pressure column 15.

[0028] In addition, a second pressure adjustment path 80 is provided, which branches off from a gas piping (low-temperature feed air path 52 described later) that introduces feed air from the heat exchanger 13 to the high-pressure column 14, and is equipped with a second gas release valve 81 for discharging the gas in the high-pressure column 14 to the outside. The second gas release valve 81 is controlled so that the valve opening degree is adjustable so that the pressure in the high-pressure column 14 does not exceed a preset pressure, and a second pressure transmission path 90 is provided between the second gas release valve 81 and the high-pressure column 14.

[0029] The first pressure regulation path 24 and the second pressure regulation path 80 may join at the outlet side. Furthermore, a bypass path 84 is provided that connects the upstream side of the first gas release valve 23 of the first pressure regulation path 24 to the upstream side of the second gas release valve 81 of the second pressure regulation path 80. The bypass path 84 includes a valve 85.

[0030] First, in the air cryogenic separation unit during normal operation, feed air compressed to a set pressure by compressor 11 is introduced into one of a pair of purifiers that are used switchably between the purification process and the regeneration process, and after impurities such as moisture and carbon dioxide in the feed air are adsorbed and removed by an adsorbent to purify the air, it is introduced into heat exchanger 13 in cold box 21 via feed air path 51 equipped with feed air inlet valve 51a. In heat exchanger 13, the feed air is cooled to a predetermined low temperature state by exchanging heat with a feed air cooling fluid consisting of low-temperature fluids such as product oxygen gas, product nitrogen gas, and exhaust gas.

[0031] Low-temperature feed air is introduced into the lower part of the high-pressure column 14 through low-temperature feed air passage 52 and rises within the column, where high-pressure nitrogen gas is separated at the top of the column by a rectification operation within the column, and high-pressure liquefied air with concentrated oxygen is separated at the bottom of the column. The liquefied air at the bottom of the high-pressure column is extracted into liquefied air outlet passage 53 and cooled to a subcooled state in the subcooler 18, then passes through liquefied air introduction passage 54 and is reduced in pressure by pressure reducing valve 54a to a low-pressure state corresponding to the low-pressure column pressure, before being introduced as a descending liquid into the middle stage of the low-pressure column 15.

[0032] A portion of the liquefied air passes through argon cooling path 55 branched off from liquefied air outlet path 53, is depressurized by pressure reducing valve 55a, is introduced into argon condenser 19, is vaporized, and is introduced as ascending gas into the upper middle stage of low-pressure column 15 through vaporized air path 56. Meanwhile, high-pressure nitrogen gas in the upper part of high-pressure column 14 is liquefied in condenser 17, and then a portion of it is introduced as descending liquid into the upper part of high-pressure column 14, and the remainder passes through liquid nitrogen path 57 and supercooler 18, is depressurized by pressure reducing valve 57a, and is introduced as descending liquid into the upper part of low-pressure column 15.

[0033] In the low-pressure column 15, low-pressure nitrogen gas is separated at the top of the column by the rectification operation within the column, and low-pressure liquid oxygen is separated at the bottom of the column. The low-pressure nitrogen gas at the top of the column is extracted to a low-pressure nitrogen outlet line 58, passes through a subcooler 18, and is further heated by heat exchange with the feed air in a heat exchanger 13, and is then extracted as product nitrogen gas from a product nitrogen extraction line 59 equipped with a product nitrogen extraction valve 59a.

[0034] Meanwhile, the liquid oxygen at the bottom of the tower is vaporized by heat exchange with high-pressure nitrogen gas in the condenser 17, and then extracted into the oxygen discharge line 60. The liquid oxygen is then heated by heat exchange with the feed air in the heat exchanger 13, and is then collected as product oxygen gas from a product oxygen collection line 61 equipped with a product oxygen collection valve 61a.

[0035] Furthermore, low-purity nitrogen is extracted from the upper middle stage of the low-pressure column 15 into the exhaust gas discharge line 22 as an exhaust gas, which is a fluid for cooling the feed air, passes through the subcooler 18 and the heat exchanger 13 to be heated, and then passes through the external exhaust gas discharge line 22a to be used as a regeneration gas for the purifier 12.

[0036] In addition, in the middle stage of the low-pressure column 15, a part of the ascending gas is extracted into the argon feed line 62 and introduced as ascending gas into the crude argon column 20, and liquefied gas from the bottom of the crude argon column 20 passes through the liquefied gas return line 63 and is introduced as descending liquid into the low-pressure column 15.

[0037] In the crude argon column 20, a crude argon gas in which argon is concentrated is separated at the top of the column by the rectification operation within the column, and this crude argon gas is liquefied to become liquid crude argon by heat exchange with a part of the liquefied air in the argon condenser 19. A part of this liquid crude argon is extracted to an argon outlet line 64 via an argon outlet valve (not shown), and the remainder passes through a descending liquid line 65 and is introduced as a descending liquid into the upper part of the crude argon column 20.

[0038] In such a double column rectification column, when operation is temporarily stopped for inspection of compressor 11 or the like, feed air inlet valve 51a is closed, and the product nitrogen sampling valve 59a, product oxygen sampling valve 61a, argon outlet valve, and each valve provided in purifier 12, which are provided in the path for extracting low-temperature gas from inside cold box 21, are also closed to cut off the flow of gas inside and outside cold box 21. This prevents low-temperature fluid from flowing out to the outside, making it possible to maintain the inside of cold box 21 in a predetermined low-temperature standby state.

[0039] If the operation of the cryogenic air separation unit is stopped for a long time and the temperature inside the cold box 21 rises due to a slight intrusion of heat from the outside, the various liquefied gases held inside the high-pressure column 14 and the low-pressure column 15 will evaporate, and the pressure inside the system will gradually rise.

[0040] When the pressure in the system, in this embodiment, the pressure at the top of the low-pressure tower 15 reaches a preset pressure lower than the design pressure due to evaporation of the liquefied gas, the valve aperture of the first gas release valve 23 is adjusted by a pressure signal transmitted from the first pressure transmission path 25, and the low-temperature gas in the low-pressure tower 15 and the exhaust gas in the exhaust gas discharge path 22 are released to the outside through the first pressure adjustment path 24. When the pressure in the high-pressure tower 14 reaches a preset pressure lower than the design pressure, the valve aperture of the second gas release valve 81 is adjusted by a pressure signal transmitted from the second pressure transmission path 90, and the low-temperature gas in the high-pressure tower 14 is released to the outside through the second pressure adjustment path 80. This makes it possible to maintain the pressure in the system in the cold box 21 at or below the design pressure of the equipment, and to prevent various equipment including the rectification tower from being damaged due to an excessive increase in pressure.

[0041] In addition, because the exhaust gas is discharged before being introduced into the heat exchanger 13, the low-temperature exhaust gas does not flow into the external exhaust gas discharge path 22a at a low temperature without being heated. Therefore, the external exhaust gas discharge path 22a and the outlet of the refiner 12 are not cooled by the low-temperature exhaust gas, and there is no need to form them from low-temperature compatible materials, which reduces costs.

[0042] On the other hand, the first pressure adjustment path 24 can be formed from piping of a smaller diameter and shorter length than the product nitrogen sampling path 59, etc., so the increase in cost is slight compared to making the product nitrogen sampling path 59, etc. compatible with low temperatures. Also, it is possible to branch off the pressure adjustment path from the low pressure nitrogen outlet path 58 or the oxygen outlet path 60, but since releasing gas from the product system may have an adverse effect on the product purity after operation is resumed, it is preferable to branch off the first pressure adjustment path 24 from the exhaust gas outlet path 22. Also, since the second pressure adjustment path 80 branches off from the low temperature feed air path 52 through which the feed air flows, there is no risk of adversely affecting the product purity after operation is resumed.

[0043] In this way, by releasing the exhaust gas to the outside in accordance with the pressure at the top of the low-pressure column 15, the inside of the cold box 21 can be kept at a low temperature for a longer period of time than in the past, and liquefied gas can be retained in each rectification column, so that the start-up time when restarting operation can be significantly shortened.

[0044] On the other hand, if the cryogenic air separation unit is completely shut down, when the cryogenic air separation unit is started up, it is necessary to first carry out full warming operation of the unit. This full warming operation involves compressing and purifying the feed air, warming it using a heater or steam, and then flowing this warmed purified air into various equipment and piping such as the rectification tower to remove the moisture and carbon dioxide inside.

[0045] In this embodiment, since the second pressure adjustment path 80 and the first pressure adjustment path 24 are connected by the bypass path 84, by opening the valve 85, a part of the raw air can be introduced from the second pressure adjustment path 80 to the first pressure adjustment path 24 during the full heating operation. Therefore, a part of the heated raw air can be introduced into the exhaust gas discharge path 22 immediately after the start of the full heating operation without passing through the liquefied air discharge path 53 or the liquid nitrogen path 57, which are usually assumed to be flowing liquefied gas. Therefore, it is possible to efficiently heat the heat exchanger 13, which has a particularly large heat capacity among the various devices. This makes it possible to reduce the full heating time and the power required for the full heating operation.

[0046] Furthermore, since the feed air passage 51 introduced into the heat exchanger 13 is provided with the feed air introduction valve 51a, it is possible to prevent the fluid in the high-pressure column 14 from flowing back into the feed air passage 51. Furthermore, since the product nitrogen collection passage 59 and the product oxygen collection passage 61, which are outlet systems for discharging gas from the low-pressure column 15 to the outside of the system, are provided with the product nitrogen collection valve 59a and the product oxygen collection valve 61a, respectively, the system of the low-pressure nitrogen discharge passage 58 from the top of the low-pressure column 15 is maintained at the same pressure as in the operating state, and by closing the product nitrogen collection passage 59 and the product oxygen collection passage 61 with the product nitrogen collection valve 59a and the product oxygen collection valve 61a, the pressure distribution inside the high-pressure column 14 and the low-pressure column 15 is maintained at the same pressure distribution as in the operating state, and the air separation unit can be started up in a state in which the composition distribution of the liquid and gas is maintained, so that the air separation unit can be started up in a short time.

[0047] Fig. 2 shows a second embodiment of the cryogenic air separation unit of the present invention, which illustrates an embodiment in which the present invention is applied to a cryogenic air separation unit using a single column rectification column. In the following explanation, the system of the main parts housed in a cold box is illustrated.

[0048] The cryogenic air separation unit shown in this embodiment extracts product nitrogen gas using a single rectification tower which combines a rectification tower 31 operated at high pressure with a condenser 32 operated at medium pressure. Feed air compressed by a compressor (not shown) and purified by a purifier (not shown) is cooled to a predetermined temperature by heat exchanger 33 housed in a cold box with the product nitrogen gas and exhaust gas, which are feed air cooling fluids, and is introduced into the lower part of the rectification tower 31 through low-temperature feed air passage 71.

[0049] In the rectification tower 31, nitrogen gas is separated at the top of the tower by rectifying the feed air, and liquefied air with concentrated oxygen is separated at the bottom of the tower. The liquefied air at the bottom of the tower is discharged to a liquefied air discharge line 72 and is introduced into the condenser 32 after being reduced in pressure to a medium pressure state by the pressure reducing valve 34. A portion of the nitrogen gas at the top of the tower is extracted to a nitrogen product collection line 73 and is collected as high-pressure product nitrogen after being heated in the heat exchanger 33, and the remaining nitrogen gas is introduced into the condenser 32 through a condensation line 74.

[0050] In the condenser 32, the liquefied air and the nitrogen gas exchange heat, and the nitrogen gas is liquefied to become liquid nitrogen, which is introduced as a descending liquid into the upper part of the rectification tower 31 through the descending liquid path 75. The liquefied air is vaporized to become a medium-pressure exhaust gas, which is discharged to an exhaust gas discharge path 76 as a feed air cooling fluid, and during normal operation, a part of the exhaust gas passes through a turbine path 77, is heated to an intermediate temperature in the heat exchanger 33, is introduced into the expansion turbine 35, and is expanded to a low-pressure state to generate refrigeration, is merged with the remaining exhaust gas, which has been reduced in pressure to the same pressure as the exhaust gas after the expansion, through a pressure reducing valve 78a of a pressure reducing path 78, is passed through a merging path 79, and is introduced into the heat exchanger 33 as a feed air cooling fluid, is discharged to the outside after being heated, and is used as a regeneration gas for the refiner, etc.

[0051] In the air cryogenic separation unit equipped with the single column rectification column thus formed, a first pressure adjustment path 37 equipped with a first gas release valve 36 is branched off from a position in the exhaust gas discharge path 76 before the introduction into the heat exchanger 33. The first gas release valve 36 is controlled so that the pressure in the first pressure adjustment path 37 on the primary side of the first gas release valve 36, the pressure in the exhaust gas discharge path 76, or the pressure of the gas phase in the condenser 32 does not exceed a preset pressure, and a first pressure transmission path 38 is provided between the first gas release valve 36 and the exhaust gas discharge path 76.

[0052] In addition, a second pressure adjustment path 82 is provided, which branches off from the low-temperature feed air path 71 that introduces feed air from the heat exchanger 33 to the rectification tower 31 and is equipped with a second gas release valve 83 for discharging the gas in the rectification tower 31 to the outside. The second gas release valve 83 is controlled so that the valve opening degree is adjustable so that the pressure in the rectification tower 31 does not exceed a preset pressure, and a second pressure transmission path 91 is provided between the second gas release valve 83 and the rectification tower 31. .

[0053] The first pressure regulation path 37 and the second pressure regulation path 82 may join at the outlet side. Furthermore, a bypass path 86 is provided that connects the upstream side of the first gas release valve 36 of the first pressure regulation path 37 to the upstream side of the second gas release valve 83 of the second pressure regulation path 82. The bypass path 86 includes a valve 87.

[0054] As a result, when the operation of the cryogenic air separation unit is stopped, with the feed air introduction valve, product nitrogen collection valve, and exhaust gas discharge valve closed to block the flow of gas inside and outside the cold box, when the liquefied gas held in the rectification tower 31 and the condenser 32 evaporates due to heat intrusion from the outside and the pressure in the rectification tower 31 and the condenser 32 rises, the first gas release valve 36 and the second gas release valve 83 are opened by the pressure signals transmitted from the first pressure transmission path 38 and the second pressure transmission path 91, respectively, and exhaust gas is released from the first pressure adjustment path 37 and the second pressure adjustment path 82, so that the pressure in the rectification tower 31 and the condenser 32 can be maintained below the design pressure, and damage to the rectification tower and the like due to an excessive rise in pressure can be prevented. Furthermore, as in the first embodiment, low-temperature gas that is not heated by the heat exchanger 33 does not flow into external piping, so there is no need to form external equipment such as room-temperature piping from materials suitable for low temperatures.

[0055] Furthermore, during full heating operation after the cryogenic air separation unit in this embodiment is completely stopped, the second pressure adjustment path 82 and the first pressure adjustment path 37 are connected by the bypass path 86, so that by opening the valve 87, a part of the heated feed air can be introduced from the second pressure adjustment path 82 through the first pressure adjustment path 37 into the pressure reduction path 78 and the junction path 79 immediately after the start of the full heating operation. This makes it possible to efficiently heat the heat exchanger, which has a particularly large heat capacity. This makes it possible to reduce the full heating time and the power required for the full heating operation.

[0056] Furthermore, when starting up the unit after full heating operation, by bypassing part of the feed air in the low-temperature feed air passage 71 from the second pressure adjustment passage 82 to the first pressure adjustment passage 37, the feed air can be introduced into the expansion turbine 35 through the turbine passage 77, making it possible to shorten the normal temperature start-up time. In other words, it is possible to introduce more feed air into the expansion turbine 35 than in the conventional unit without passing part of the feed air through piping and valves that are assumed to allow low-temperature liquefied gas to flow, such as the liquefied air discharge passage 72 and the pressure reducing valve 34, and by introducing the feed air, which has a higher pressure than the exhaust gas flowing through the exhaust gas discharge passage 76, into the expansion turbine 35, more refrigeration can be generated.

[0057] In order to avoid problems such as the impurities in the product gas piping being difficult to reduce when the apparatus is started up, it is preferable that the second pressure adjustment path 82 branch off from the low-temperature feed air path 71, as in this embodiment, rather than branching off from the product nitrogen sampling path 73 of the product system.

[0058] The present invention is not limited to the double rectification column and single rectification column in the above-mentioned embodiment, but can be applied to, for example, a double rectification column that does not have the crude argon column 20, and can be applied to rectification columns of various configurations to which paths having other functions are added. [Explanation of symbols]

[0059] 11...compressor, 12...purifier, 13...heat exchanger, 14...high pressure column, 15...low pressure column, 16...double rectification column, 17...condenser, 18...subcooler, 19...argon condenser, 20...crude argon column, 21...cold box, 22...exhaust gas discharge path, 22a...external exhaust gas discharge path, 23...first gas release valve, 24...first pressure adjustment path, 25...first pressure transmission path, 31...rectification column, 32...condenser Compressor, 33... heat exchanger, 34... pressure reducing valve, 35... expansion turbine, 36... first gas release valve, 37... first pressure adjustment path, 38... first pressure transmission path, 51... feed air path, 51a... feed air introduction valve, 52... low-temperature feed air path, 53... liquefied air discharge path, 54... liquefied air introduction path, 54a... pressure reducing valve, 55... argon cooling path, 55a... pressure reducing valve, 56... vaporized air path, 57... liquefied low pressure nitrogen outlet path, 57a...pressure reducing valve, 58...low pressure nitrogen outlet path, 59...product nitrogen collection path, 59a...product nitrogen collection valve, 60...oxygen outlet path, 61...product oxygen collection path, 61a...product oxygen collection valve, 62...argon raw material path, 63...liquefied gas return path, 64...argon outlet path, 65...descending liquid path, 71...low temperature raw air path, 72...liquefied air outlet path, 73...product nitrogen collection path path, 74... condensation path, 75... descending liquid path, 76... exhaust gas discharge path, 77... turbine path, 78... pressure reduction path, 78a... pressure reduction valve, 79... merging path, 80... second pressure adjustment path, 81... second gas release valve, 82... second pressure adjustment path, 83... second gas release valve, 84... bypass path, 85... valve, 86... bypass path, 87... valve, 90... second pressure transmission path, 91... second pressure transmission path

Claims

1. An air liquefaction separation unit including a heat exchanger for cooling compressed and purified feed air, and a double rectification column combining a high-pressure column and a low-pressure column for liquefying and rectifying the feed air, A first pressure adjustment path for discharging a fluid to the outside of the system is provided by branching off from a path connecting the low pressure column and the heat exchanger, and the first pressure adjustment path is provided with a first gas release valve that is controlled so that the pressure of the low pressure column does not exceed a preset pressure, a second pressure regulation path for discharging a fluid to the outside of the system, the second pressure regulation path being branched off from a path connecting the high pressure column and the heat exchanger, the second pressure regulation path including a second gas release valve that is controlled so that the pressure of the high pressure column does not exceed a preset pressure; a bypass path is provided that connects the upstream side of the first gas release valve of the first pressure adjustment path and the upstream side of the second gas release valve of the second pressure adjustment path, The path connecting the low pressure tower and the heat exchanger is an exhaust gas discharge path for extracting exhaust gas from the low pressure tower. A cryogenic air separation unit comprising:

2. 2. The air cryogenic separation unit according to claim 1, wherein the passage connecting the high pressure column and the heat exchanger is a passage for introducing feed air.

3. 3. The air cryogenic separation unit according to claim 1, wherein a valve for closing each of the paths is provided in the path for introducing feed air into the heat exchanger and the path of an outlet system from the low pressure column.

4. An air liquefaction separation system including a heat exchanger for cooling compressed and purified feed air, and a single column rectification column combining a rectification column and a condenser for liquefying and rectifying the feed air, a first pressure regulation path for discharging a fluid to the outside of the system, the first pressure regulation path being branched off from a path connecting the condenser and the heat exchanger, the first pressure regulation path including a first gas discharge valve that is controlled so that the pressure of the first pressure regulation path does not exceed a preset pressure; a second pressure adjustment path for discharging a fluid to the outside of the system is provided branching off from a path connecting the rectification column and the heat exchanger, the second pressure adjustment path including a second gas release valve that is controlled so that the pressure in the rectification column does not exceed a preset pressure; A bypass path is provided that connects the upstream side of the first gas release valve of the first pressure adjustment path and the upstream side of the second gas release valve of the second pressure adjustment path. a path connecting the condenser and the heat exchanger is an exhaust gas discharge path for extracting exhaust gas from the condenser, The passage connecting the rectification column and the heat exchanger is a passage for introducing feed air. A cryogenic air separation unit comprising:

5. 5. The air cryogenic separation unit according to claim 4, wherein a valve for closing each of the paths is provided in the path for introducing feed air into said heat exchanger and the path of an outlet system from said rectification column.

6. 6. A method for temporarily stopping operation of a cryogenic air separation unit according to claim 1, characterized in that, when operation is stopped, fluid is discharged from the first pressure adjustment path to the outside of the system, and fluid is discharged from the second pressure adjustment path to the outside of the system.

7. 6. The method for starting up a cryogenic air separation unit according to claim 1, wherein during full heating operation before start-up, a portion of heated feed air is introduced from the second pressure adjustment path through the bypass path into the first pressure adjustment path.

8. 6. The method for starting up a cryogenic air separation unit according to claim 4 or 5, characterized in that a portion of the feed air is introduced from the second pressure adjustment path through the bypass path and the first pressure adjustment path into an expansion turbine.

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