JP6354516B2 - Cryogenic air separation device and cryogenic air separation method - Google Patents

Description

  The present invention relates to a cryogenic air separation apparatus and a cryogenic air separation method for separating oxygen, nitrogen and argon from raw air.

  Conventionally, in an air liquefaction separation system, for example, a so-called chilled air separation system installed in a steel plant, for example, raw air compressed by an air compressor is pre-cooled in a water-washing cooling tower, and then oxygen and oxygen are separated from the raw air in a rectification tower Nitrogen separation takes place. The oxygen separated from the fractionator is supplied to the customer as product oxygen, and nitrogen is supplied to the customer as product nitrogen.

  In such a cryogenic air separation system, various operation methods have been proposed for stable operation of the rectification column.

  For example, in Patent Document 1, when the temperature of liquid air is reduced at the bottom of a high-pressure column among rectification columns composed of a low-pressure column and a high-pressure column, the flow rate of nitrogen refluxed to the low-pressure column is increased. It has been proposed to stabilize the extraction portion of the argon source gas by maintaining the cold balance of the entire distillation column.

JP-A-6-3048

  By the way, according to the present inventors, the oxygen concentration in the raw material air supplied from the air compressor temporarily decreases, in other words, the nitrogen concentration in the raw material air may temporarily increase. Has been confirmed. This is presumably due to the effects of off-gas from other facilities in the steelworks.

  In such a case, the amount of product oxygen produced in the rectification column is reduced, resulting in insufficient supply. Therefore, when the concentration of nitrogen in the raw material air increases, the amount of oxygen supplied to the rectification tower can be increased by temporarily increasing the supply amount of raw material air from the air compressor and increasing the amount of exhaust as waste nitrogen. It is conceivable to maintain an absolute amount of.

  However, since the time constant from the supply of raw material air to the rectification column until the production of product oxygen is large, the product oxygen can be detected even if the amount of raw material air is increased after the increase in the nitrogen concentration in the raw material air is detected. It is not possible to cope with the shortage. Therefore, at present, in order to cope with a temporary shortage of product oxygen, the amount of raw material air is constantly increased from the planned value.

  And if you try to increase the supply amount of raw material air to increase product oxygen, several times as much nitrogen is also supplied from the air compressor at the same time, so to cope with the temporary increase in product oxygen The power of the air compressor needs to be greatly increased. Further, as the absolute amount of nitrogen supplied to the rectification column increases due to the increase in the supply amount of the raw air, the amount of waste nitrogen released to the outside from the rectification column also increases. As a result, waste nitrogen with no use is produced in large quantities, which is not preferable from the viewpoint of running cost and energy.

  The present invention has been made in view of such points, and in a cryogenic air separation device, particularly when the production amount of product oxygen is reduced, it is quickly returned to a stable state, and the production amount of product oxygen is stabilized. It is an object.

The present invention for achieving the above object includes a high pressure column and low pressure column to produce product nitrogen and product oxygen from the feed air compressed by the air compressor, to condense the separated nitrogen by the high pressure column liquefied And a main condenser for refluxing nitrogen liquefied in the heat exchanger to a high-pressure tower, wherein the nitrogen concentration in the raw material air is increased. as the part of the feed air supplied from the air compressor, a first bypass pipe that teapot subjected to the main condenser by bypassing the high pressure column, provided in the first bypass pipe, A bypass valve for adjusting a flow rate of the raw air supplied from the air compressor flowing through the first bypass pipe, and the raw air after being cooled by the main condenser, bypassing the high pressure column, and the low pressure column A second bypass pipe for supplying to Serial provided in the second bypass pipe, have a, and an expansion mechanism for expanding the cooled feed air in said main condenser, the main condenser, feed air supplied from the first bypass pipe Is cooled by exchanging heat with liquid oxygen in the main condenser to increase the amount of evaporation of liquid oxygen from the main condenser before the nitrogen concentration in the raw material air increases .

  Since the present inventor stores liquid oxygen as a refrigerant in the main condenser, when temporarily increasing the volume of product oxygen in the low-pressure column, if the liquid oxygen in the main condenser can be used, We thought that the delay time until recovery due to the increase in the amount of raw material air supplied from the air compressor could be reduced. The present invention is based on such knowledge, the first bypass pipe that heat-exchanges a part of the raw material air supplied from the air compressor by the main condenser and cools the raw material air after cooling, Since the second bypass pipe that bypasses the high-pressure column and supplies the low-pressure column is provided, the oxygen in the main condenser can be evaporated by the raw air and the oxygen volume in the low-pressure column can be recovered in a short time. . In such a case, when the volume of the product oxygen is increased, the supply amount of the raw air from the air compressor may be increased so that the oxygen in the main condenser is evaporated by an amount corresponding to the volume increase. Therefore, compared with the case where the total amount of raw material air is supplied from the high pressure column to the low pressure column to increase the volume of product oxygen, the amount of raw material air supplied from the air compressor can be greatly reduced. In particular, it is possible to quickly cope with a decrease in the production amount of product oxygen. As a result, the production amount of product oxygen can be efficiently stabilized in the cryogenic air separation device.

  In addition, since it has an expansion mechanism that expands the raw air flowing through the second bypass pipe, the cold balance in the low pressure column is maintained, and the high pressure column is bypassed and the raw air is supplied directly to the low pressure column. Even if it exists, the stable operation of the low pressure column can be maintained.

    In the low-pressure column, provided in a position between a waste nitrogen pipe provided in the upper part of the low-pressure column and a product oxygen pipe provided in the lower part of the low-pressure column, the nitrogen temperature in the low-pressure column is detected. An increase in the amount of nitrogen gas in the low-pressure column is detected based on the detection temperature of the low-pressure column nitrogen temperature detection mechanism and the low-pressure column nitrogen temperature detection mechanism, and flows through the bypass valve based on the increase amount of the nitrogen gas amount And a control device that controls the flow rate of the raw material air.

  The first bypass pipe may be connected to a position between the waste nitrogen pipe provided in the upper part of the low pressure column and the product oxygen pipe provided in the lower part of the low pressure column in the low pressure column. Good.

  A gas-liquid heat exchanger for cooling the raw air supplied from the first bypass pipe may be provided inside the main condenser.

The present invention according to another aspect, a heat exchanger for liquefying and condensing the high pressure column and low pressure column to produce product nitrogen and product oxygen from the feed air compressed by the air compressor, the separated nitrogen by the high pressure column A chilled air separation method in a chilled air separation device having a main condenser for refluxing nitrogen liquefied in the heat exchanger to a high pressure tower, wherein the temperature of nitrogen in the raw material air is increased in a portion of the feed air supplied from the air compressor, the high pressure column by bypassing supplied to the main condenser, to cool with liquid oxygen and heat exchange in the main condenser, The amount of evaporation of liquid oxygen from the main condenser is increased from before the nitrogen concentration in the raw material air is increased , the raw material air after being cooled by the main condenser is expanded, and the expanded raw material air is Feed to the low pressure column .

  In the low-pressure column, the temperature in the low-pressure column is detected at a position between a waste nitrogen pipe provided in the upper part of the low-pressure column and a product oxygen pipe provided in the lower part of the low-pressure column. Based on the detected temperature, an increase in the amount of nitrogen gas in the low pressure column is detected, and according to the amount of increase in the amount of nitrogen gas, the raw material air is supplied from the main condenser to the low pressure column by bypassing the high pressure column The flow rate may be controlled.

  The raw material air expanded after cooling in the main condenser is between the waste nitrogen pipe provided in the upper part of the low pressure column and the product oxygen pipe provided in the lower part of the low pressure column in the low pressure column. The position may be supplied.

  A gas-liquid heat exchanger for cooling the raw material air may be provided inside the main condenser, and the raw material air may be cooled by the gas-liquid heat exchanger.

  According to the present invention, in the cryogenic air separation device, even if the production amount of product oxygen is reduced due to the influence of off-gas or the like, it can be quickly returned to a stable state, and the production amount of product oxygen can be stabilized.

It is a process flow figure which shows the structure of the cryogenic air separation system concerning this Embodiment. It is explanatory drawing which shows typically the distribution condition of the gas in the low pressure tower at the time of normal. It is explanatory drawing which shows typically the distribution condition of the gas in the low-pressure tower at the time of abnormality.

  Embodiments of the present invention will be described below. FIG. 1 is a process flow diagram showing a configuration of a cryogenic air separation system 1 including a cryogenic air separation device according to the present embodiment.

  The cryogenic air separation system 1 cools the raw material air and removes dust by bringing the cooling air and the raw material air into contact with an air compressor 11 that compresses the air sucked through the suction filter 10 and supplies it as raw material air. A washing / cooling tower 12 to be performed, an MS (Molecular Sieve) adsorber 13 for removing water and carbon dioxide from the raw material air that has passed through the washing / cooling tower 12, a main heat exchanger 14 for cooling the raw air to a predetermined temperature, And a rectifying column 15 for separating product oxygen and product nitrogen from the raw air.

  The rectification column 15 has a high pressure column 15a and a low pressure column 15b. The high-pressure column 15a is disposed below the low-pressure column 15b. A main condenser 15c is provided between the high pressure column 15a and the low pressure column 15b. The MS adsorber 13, the main heat exchanger 14, and the high-pressure tower 15 a are connected in series by a raw material air pipe 20. A branch pipe 20 a is provided between the MS adsorber 13 and the main heat exchanger 14 of the raw material air pipe 20. The branch pipe 20a is connected near the middle stage of the low-pressure column 15b, and an expansion turbine 21 is provided between the branch pipe 20a and the low-pressure column 15b. The raw air sent to the low pressure column 15b by the branch pipe 20a is compressed by a compressor (not shown) provided coaxially with the expansion turbine 21, cooled by the main heat exchanger 14, and then adiabatically expanded again by the expansion turbine. At low temperature and low pressure. Thereby, the rectifying column 15 is replenished with cold.

  A plurality of shelves (not shown) are provided inside the high-pressure column 15a and the low-pressure column 15b. The shelves accommodate packing materials for ensuring the contact area between the gas and the liquid. In the high-pressure tower 15a and the low-pressure tower 15b, a low-temperature liquid supplied from the upper part of the towers 15a and 15b and a gas having a higher temperature than the liquid supplied from the lower parts of the towers 15a and 15b are separated. By making the liquid contact, heat exchange between the gas and the liquid is performed.

  The bottom of the low pressure column 15b and the main condenser 15c are connected by a liquid oxygen pipe 22, and the liquid oxygen at the bottom of the low pressure column 15b flows into the main condenser 15c through the liquid oxygen pipe 22. Inside the main condenser 15c, heat is exchanged between the nitrogen supplied from the high pressure column 15a via the top nitrogen pipe 23 connected to the top of the high pressure column 15a and the liquid oxygen in the main condenser 15c. A plurality of exchangers 24 are provided, two in FIG. The nitrogen cooled by exchanging heat in the heat exchanger 24 is refluxed to the high pressure column 15a and also refluxed to the upper portion of the low pressure column 15b through the top reflux pipe 25 connected to the top of the high pressure column 15a.

  A lower part of the high pressure column 15a below the top reflux pipe 25 is connected to a middle reflux pipe 26 that communicates below the position of the low pressure tower 15b to which the top reflux pipe 25 is connected. Gas is refluxed to the low pressure column 15b.

  Further, inside the main condenser 15c, a gas-liquid heat exchanger 27 that performs heat exchange between the raw material air supplied via the first bypass pipe 40 described later and liquid oxygen in the main condenser 15c, In FIG. 1, one is provided. Liquid oxygen evaporated by heat exchange in the heat exchanger 24 and the gas-liquid heat exchanger 27 is refluxed to the vicinity of the bottom of the low-pressure column 15b through an oxygen reflux pipe 28 connected to the top of the main condenser 15c. The number and arrangement of the heat exchanger 24 and the gas-liquid heat exchanger 27 are not limited to the contents of the present embodiment, and can be arbitrarily set.

  In addition, a liquid air pipe 30 is connected to the bottom of the high pressure tower 15a to recirculate the liquid air accumulated at the bottom of the high pressure tower 15a to a position below the middle reflux pipe 26 in the low pressure tower 15b. Note that the liquid air pipe 30 is a supply pipe (not shown) for supplying liquid air to a crude argon tower (not shown) that generates crude argon from an argon source gas containing oxygen and argon accumulated in the rectification tower 15. (Not shown) are branched. In addition, expansion valves (not shown) are provided in the vicinity of the low pressure column 15b in the top reflux pipe 25, the middle reflux pipe 26, and the liquid air pipe 30, respectively, and fluid flowing through the pipes 25, 26, and 30 is caused by the expansion valves. It is adiabatically expanded and refluxed to the low pressure column 15b.

  In the low-pressure column 15b, the raw air roughly rectified in the high-pressure column 15a is further rectified, and nitrogen accumulates in the upper portion of the low-pressure column 15b. At this time, the purity of nitrogen becomes higher at the upper part of the low pressure column 15b. Further, product oxygen accumulates in the lower part of the low pressure column 15b. And the product nitrogen extraction pipe | tube 31 which extracts product nitrogen with high purity from the low pressure column 15b is provided in the top part of the low pressure column 15b. Product nitrogen extracted by the product nitrogen extraction pipe 31 is sent to the main heat exchanger 14, and heat exchange with the raw material air is performed in the main heat exchanger 14.

  A product oxygen extraction pipe 32 for extracting product oxygen from the low pressure column 15b is provided at the lower portion of the low pressure column 15b. Product oxygen extracted by the product oxygen extraction pipe 32 is also sent to the main heat exchanger 14, and heat exchange with the raw material air is performed in the main heat exchanger 14. Product nitrogen and product oxygen after heat exchange in the main heat exchanger 14 are supplied into, for example, an ironworks.

  A waste nitrogen extraction pipe 33 for extracting waste nitrogen having a purity lower than that of product nitrogen is provided below the product nitrogen extraction pipe 31 of the low-pressure column 15b. The waste nitrogen extracted by the waste nitrogen extraction pipe 33 is sent to the MS adsorber 13 after heat exchange with the raw material air in the main heat exchanger 14. In the MS adsorber 13, a regeneration process is performed in which carbon dioxide and moisture adsorbed on the MS adsorber 13 are removed by waste nitrogen.

  From between the main heat exchanger 14 and the high-pressure tower 15a in the raw material air pipe 20, a first bypass pipe 40 is branched to supply a part of the raw material air to the main condenser 15c by bypassing the high-pressure tower 15a. Is provided. The first bypass pipe 40 is connected to the gas-liquid heat exchanger 27, and the raw material air supplied from the first bypass pipe 40 is heat-exchanged (cooled) with the liquid oxygen in the main condenser 15c. Further, the first bypass pipe 40 is provided with a bypass valve 41 that controls the flow rate of the raw material air flowing through the first bypass pipe 40.

  In the gas-liquid heat exchanger 27, the raw material air cooled by the gas-liquid heat exchanger 27 is supplied to a position lower than, for example, the waste nitrogen extraction pipe 33 and higher than the product oxygen extraction pipe 32 in the low-pressure column 15b. Two bypass pipes 42 are connected. An expansion valve 43 as an expansion mechanism for adiabatically expanding the raw material air flowing inside the second bypass pipe 42 is provided in the vicinity of the low pressure column 15 b in the second bypass pipe 42. As a result, the pressure and temperature of the raw air flowing through the second bypass pipe 42 are reduced, and the rectification column 15 is replenished with cold. As a result, even when the raw air is supplied from the first bypass pipe 40 and heat is brought into the rectification tower 15, it is offset by the cold replenished from the second bypass pipe 42, and the rectification tower The cold balance as a whole is maintained.

  A low pressure column nitrogen temperature detection mechanism 50 for detecting the atmospheric temperature (nitrogen temperature) in the low pressure column 15b is provided in the vicinity of the branch pipe 20a in the low pressure column 15b. The arrangement of the low-pressure column nitrogen temperature detection mechanism 50 is not limited to the contents of the present embodiment. If the nitrogen temperature in the low-pressure column 15b, particularly the temperature of nitrogen mixed with oxygen, can be measured, the arrangement is not limited. It can be set arbitrarily. However, as will be described later, in order to detect an increase in the nitrogen concentration in the low pressure column 15b from the temperature detected by the low pressure column nitrogen temperature detection mechanism 50, the product oxygen is provided below the waste nitrogen extraction pipe 33. It is preferable to provide it above the extraction pipe 32.

  Further, the cryogenic air separation apparatus according to the present embodiment includes a rectifying column 15, that is, a high-pressure column 15a, a low-pressure column 15b, and a main condenser 15c, and a high-pressure column 15a, a low-pressure column 15b, and a main condenser 15c. It is comprised by the various pipes which connect.

  As shown in FIG. 1, the above-described cryogenic air separation system is provided with a control device 100. The control device 100 is constituted by a computer including, for example, a CPU and a memory, and monitors the operation result of various devices such as a temperature detection result in the low-pressure column nitrogen temperature detection mechanism 50 and the bypass valve 41 and the expansion valve 43. By controlling the operation of various devices, the cryogenic air separation method in the cryogenic air separation system 1 is realized.

  The cryogenic air separation system 1 according to the present embodiment is configured as described above. Next, a cryogenic air separation method in the cryogenic air separation system 1 will be described.

  The raw material air that has been compressed by the air compressor 11 to become a high temperature and high pressure is first supplied to the washing cooling tower 12. In the water-washing cooling tower 12, the raw air is cooled and dedusted, and then supplied to the MS adsorber 13. In the MS adsorber 13, water and carbon dioxide are removed from the raw air in order to prevent the generation of ice in the rectification column 15.

  The raw material air that has passed through the MS adsorber 13 is supplied to the main heat exchanger 14, and is cooled to about −170 ° C. by the main heat exchanger 14, for example. The cooled raw material air is supplied to the high pressure tower 15a in a partially liquefied state, and liquid air gradually accumulates at the bottom of the high pressure tower 15a. At this time, the pressure in the high-pressure tower 15a is maintained at about 0.4 to 0.5 MPa. A part of the raw material air that has passed through the MS adsorber 13 is guided to the expansion turbine 21 by the branch pipe 20a, and the raw material air adiabatically expanded by the expansion turbine 21 is supplied to the low-pressure column 15b. At this time, the pressure in the low pressure column 15b is maintained at about 0.04 MPa.

  The liquid air collected at the bottom of the high pressure column 15a is supplied to the intermediate portion of the low pressure column 15b in a gas-liquid mixed state via the liquid air pipe 30 and an expansion valve (not shown) provided in the liquid air pipe 30. As a result, oxygen having a boiling point higher than that of nitrogen gradually accumulates at the bottom of the low pressure column 15b as liquid oxygen.

  Liquid oxygen collected at the bottom of the low-pressure column 15b flows down to the main condenser 15c through the liquid oxygen pipe 22, and accumulates in the main condenser 15c. In the main condenser 15c, the nitrogen supplied from the high pressure column 15a to the heat exchanger 24 via the top nitrogen pipe 23 and the liquid oxygen in the main condenser 15c are heat-exchanged, and the evaporated oxygen is supplied to the oxygen reflux pipe 28. To the low pressure column 15b. Further, the nitrogen cooled in the main condenser 15c is caused by the pressure difference between the high pressure column 15a and the low pressure column 15b through the top reflux pipe 25 and the expansion valve (not shown) provided in the top reflux pipe 25 to the low pressure column 15b. While refluxing to the upper part, it liquefies by cooling and heat exchange with the gas in the high-pressure tower 15a is performed.

  Further, the gas in the vicinity of the intermediate portion of the high-pressure column 15 a is refluxed to the vicinity of the intermediate portion of the low-pressure column 15 b through the middle reflux pipe 26. When this state continues, the insides of the high pressure column 15a and the low pressure column 15b are in an equilibrium state. For example, liquid air at the bottom of the high pressure column 15a is maintained at approximately -175 ° C, and liquid oxygen at the bottom of the low pressure column 15b is maintained at approximately -180 ° C. Is done. Product oxygen and product nitrogen are supplied to the customer from the product oxygen extraction pipe 32 and the product nitrogen extraction pipe 31 as needed, and the flow rate of waste nitrogen discharged from a control valve (not shown) provided in the waste nitrogen extraction pipe 33 is reduced. By controlling, the pressure in the low pressure column 15b is maintained at about 0.04 MPa. In this state (normal time), for example, as shown in FIG. 2, product nitrogen, waste nitrogen (oxygen-containing nitrogen), air (oxygen and nitrogen), and product oxygen flow from the top to the bottom in the low pressure column 15b. It stays in this order. In this state, the temperature detected by the low-pressure column nitrogen temperature detection mechanism 50 is about -184 ° C.

  Thereafter, when the oxygen concentration in the raw material air supplied from the air compressor 11 decreases for some reason, that is, when the nitrogen concentration in the raw material air increases, the amount of nitrogen in the low-pressure column 15b also increases. Then, as the nitrogen concentration in the low-pressure column 15b increases and the oxygen concentration decreases, the distribution of the gas staying in the low-pressure column 15b changes. Specifically, as shown in FIG. 3, for example, the waste nitrogen region spreads downward and the product oxygen region decreases. Then, the temperature in the vicinity of the low-pressure column nitrogen temperature detection mechanism 50, which was about −184 ° C. in a normal operation state, decreases as the nitrogen concentration increases, for example, about −186 ° C. to 188 ° C. .

  As a result, the control device 100 detects that the nitrogen concentration in the low-pressure column 15b has increased (the amount of nitrogen gas has increased) and also detects that the amount of product oxygen produced is insufficient. Therefore, the control device 100 opens the bypass valve 41 to a predetermined opening, and causes the main condenser 15c to bypass a part of the raw material air flowing through the raw material air pipe 20. Thereby, raw material air is supplied to the gas-liquid heat exchanger 27 in the main condenser 15c, and heat exchange with raw material air and liquid oxygen is performed. As a result, the amount of oxygen evaporated from the main condenser 15c increases, and the amount of oxygen refluxed from the oxygen reflux pipe 28 into the low pressure column 15b increases. Thereby, the upward flow of oxygen gas increases in the low pressure column 15b, and the oxygen concentration in the low pressure column 15b increases. As a result, the distribution of the gas in the low-pressure column 15b returns from the state shown in FIG. 3 which is an abnormal state to the normal state shown in FIG. The change in the gas distribution in the low-pressure column 15b is confirmed by the detection temperature of the low-pressure column nitrogen temperature detection mechanism 50, which has been, for example, about −186 ° C. to 188 ° C. being about −184 ° C. again. At this time, by increasing the amount of waste nitrogen from the waste nitrogen extraction pipe 33, the increase in the amount of oxygen refluxed to the low pressure column 15b is offset, and the pressure in the low pressure column 15b is maintained at about 0.04 MPa.

  The raw material air cooled by liquid oxygen in the gas-liquid heat exchanger 27 of the main condenser 15c is adiabatically expanded by the expansion valve 43 and supplied to the low-pressure column 15b. The low-pressure column 15b is replenished with cold by the raw air that has become low-temperature and low-pressure due to adiabatic expansion, and the heat of the increased amount of oxygen evaporation from the main condenser 15c is offset. Thereby, even if it is a case where raw material air is supplied from the bypass valve 41, the cold balance in the rectification tower 15 is maintained. In addition, when the supply amount of the raw material air to the rectification tower 15 decreases with the opening operation of the bypass valve 41, the supply amount of the raw material air from the air compressor 11 is increased as necessary. The increase in the supply amount from the air compressor 11 is suppressed to the flow rate of the raw material air supplied from the bypass valve 41 at the maximum.

  Thereafter, the opening degree of the bypass valve 41 is controlled so as to maintain the detected temperature of the low-pressure column nitrogen temperature detecting mechanism 50 at −184 ° C., for example. When the oxygen concentration in the raw material air supplied from the air compressor 11 is restored, the detected temperature of the low-pressure tower nitrogen temperature detecting mechanism 50 becomes slightly higher than −184 ° C., so that the control device 100 opens the bypass valve 41. The degree is gradually closed and it becomes a fully closed state. Thereby, the cryogenic air separation system 1 returns to a normal operation state, and the operation is continued as it is.

  According to the above embodiment, even if the nitrogen concentration in the raw material air rises temporarily, a part of the raw material air supplied from the air compressor 11 is cooled by exchanging heat with the main condenser 15c. 1 and the second bypass pipe 42 for supplying the raw air cooled by the main condenser 15c to the low pressure tower 15b by bypassing the high pressure tower 15a. The oxygen in 15c can be evaporated and the volume of oxygen in the low pressure column 15b can be recovered in a short time. In this case, when the volume of product oxygen is increased, the amount of increase in the raw material air supplied from the air compressor 11 is sufficient to additionally evaporate a desired amount of oxygen in the main condenser 15c. Therefore, the supply amount of the raw material air from the air compressor 11 can be greatly reduced as compared with the case where the total amount of the raw material air is supplied from the high pressure column 15a to the low pressure column 15b to recover the volume of product oxygen. As a result, the production amount of product oxygen can be efficiently stabilized in the cryogenic air separation system.

  In addition, since the expansion valve 43 is provided in the second bypass pipe 42, the cold balance in the low pressure column 15b is maintained, and the high pressure column 15a is bypassed so that part of the raw air is directly supplied to the low pressure column 15b. Even when it is supplied, the stable operation of the rectification column 15 can be maintained.

  Furthermore, by cooling the raw material air flowing in the first bypass pipe 40 in the main condenser 15c, a part of the raw material air is condensed in the gas-liquid heat exchanger 27, and the first bypass pipe 40 is condensed. As the internal pressure decreases, a gas flow from the raw material air pipe 20 to the first bypass pipe 40 is formed. In other words, the apparent pressure loss at the outlet of the air compressor 11 decreases. As a result, even if the supply amount of the raw material air flowing through the bypass valve 41 is increased, the increase in the power of the air compressor 11 is extremely small.

  In addition, since the raw air is supplied from the bypass valve 41 to evaporate the oxygen in the main condenser 15c, the volume of the oxygen gas in the low pressure column 15b can be recovered in an extremely short time. Therefore, even if the bypass valve 41 is closed during normal operation and the bypass valve 41 is opened only in an emergency when the oxygen concentration in the raw material air is lowered, there is no shortage of product oxygen. In addition, it is not necessary to constantly increase the supply amount of the raw material air from the air compressor 11 in order to cope with a temporary shortage of product oxygen. Therefore, the cryogenic air separation system 1 can be operated extremely efficiently.

  In the above embodiment, the supply amount of the raw material air from the air compressor 11 is increased with the opening operation of the bypass valve 41, but the supply amount from the air compressor 11 is not necessarily increased. The extent to which the supply amount from the air compressor 11 is increased as the nitrogen concentration in the raw material air rises (decrease in the oxygen concentration) depends on the supply amount of product nitrogen and the like. It is determined according to the balance, and the supply amount from the air compressor 11 may not be increased. In particular, when the increase amount of oxygen is small or the period is short, the liquid oxygen stored in the main condenser 15c can be evaporated to cover the shortage. In such a case, the air compressor 11 can continue operation with a constant load.

  In the above embodiment, the second bypass pipe 42 is provided at a position lower than the waste nitrogen extraction pipe 33 and higher than the product oxygen extraction pipe 32 in the low pressure column 15b. About the connection position to 15b, the location where the composition of the gas in the low pressure column 15b is comparable to air is preferable. Specifically, it is preferable to connect to the same height as the branch pipe 20a is connected. By doing so, after the raw air is supplied into the low-pressure column 15b, it can be quickly separated into oxygen and nitrogen, and the disturbance given to the low-pressure column 15b can be minimized.

  As an example, when the amount of oxygen produced during normal operation is about 60000 Nm3 / hr, the amount of product oxygen produced is temporarily about 0.6% using the chilled air separation system 1 according to the present embodiment. The increase in power of the air compressor 11 when increased was confirmed. Note that the power of the air compressor 11 during normal operation is, for example, about 20000 kW / hr.

  In the cryogenic air separation system 1 according to the present embodiment, when oxygen of about 360 Nm3 / hr corresponding to 0.6% of about 60000 Nm3 / hr is increased, about 450 Nm3 / hr of raw air is supplied from the bypass valve 41. By supplying, the amount of evaporation of oxygen from the main condenser 15c can be increased by about 360 Nm3 / hr. In such a case, the increase in power of the air compressor 11 for increasing the feed air of 450 Nm 3 / hr is approximately 30 kW / hr, which is suppressed to an increase of about 0.15%. Further, when the load of the air compressor 11 is kept constant and the amount of oxygen evaporated from the main condenser 15c can be covered only by operating the bypass valve 41, the power of the air compressor 11 does not naturally increase.

  On the other hand, when a conventional cryogenic air separation system that does not have the first bypass pipe 40 and the second bypass pipe 42 is used, for example, in order to increase the oxygen concentration by 0.6%, the raw material air is reduced to 3%. % Need to be increased. In that case, it is necessary to increase the power of the air compressor 11 by about 3%. Therefore, according to the chilled air separation system 1 of the present invention, it was confirmed that an increase in the power of the air compressor 11 can be suppressed to a very low level even when the production amount of product oxygen is increased.

  Further, as in the present embodiment, when the raw material air is supplied through the bypass pipe 40 and the bypass valve 41 to increase the evaporation amount of the liquid oxygen from the main condenser 15c, it takes approximately 5 to 6 minutes. It was confirmed that the volume of oxygen in the low pressure column 15b can be increased. On the other hand, in the conventional cryogenic air separation system that does not have the first bypass pipe 40 and the second bypass pipe 42, the low pressure column 15b is increased after the supply amount of the raw air from the air compressor 11 is increased. It has been confirmed that it takes about 30 to 40 minutes to increase the volume of oxygen inside. Therefore, according to the cryogenic air separation system 1 of the present invention, even when the oxygen concentration in the raw material air is reduced due to the influence of off-gas or the like, the volume of oxygen in the low-pressure column 15b is recovered in a short time, It was also confirmed that the production amount of product oxygen could be stabilized.

  The present invention is useful for stable operation in a cryogenic air separation system.

DESCRIPTION OF SYMBOLS 1 Cryogenic air separation system 10 Suction filter 11 Raw material air compressor 12 Flushing cooling tower 13 MS adsorber 14 Main heat exchanger 15 Rectification tower 15a High pressure part 15b Low pressure part 15c Main condenser 20 Raw material air pipe 20a Branch pipe 21 Expansion Turbine 22 Liquid oxygen pipe 23 Top nitrogen pipe 24 Heat exchanger 25 Top reflux pipe 26 Central reflux pipe 27 Gas-liquid heat exchanger 28 Oxygen reflux pipe 30 Liquid air pipe 31 Product nitrogen extraction pipe 32 Product oxygen extraction pipe 33 Waste nitrogen extraction pipe 40 First bypass pipe 41 Bypass valve 42 Second bypass pipe 43 Expansion valve 50 Low-pressure tower nitrogen temperature detection mechanism

Claims (8)

Comprising a high pressure column and low pressure column to produce product nitrogen and product oxygen from the feed air compressed by an air compressor, a heat exchanger for liquefying and condensing the separated nitrogen by the higher pressure column, in the heat exchanger A main condenser for refluxing the liquefied nitrogen to the high-pressure column, and a cryogenic air separation device comprising:
As a configuration when the nitrogen concentration in the raw material air is increased,
The portion of the feed air supplied from the air compressor, a first bypass pipe that teapot subjected to the main condenser by bypassing the high pressure column,
A bypass valve that is provided in the first bypass pipe and adjusts the flow rate of the raw material air supplied from the air compressor that flows through the first bypass pipe;
A second bypass pipe for supplying the raw material air after being cooled by the main condenser to the low pressure column by bypassing the high pressure column;
An expansion mechanism provided in the second bypass pipe for expanding the raw material air cooled by the main condenser ;
I have a,
The main condenser cools the raw material air supplied from the first bypass pipe by heat exchange with the liquid oxygen in the main condenser, thereby reducing the amount of evaporation of liquid oxygen from the main condenser. A cryogenic air separation device that increases the nitrogen concentration in the feed air before it increases . In the low-pressure column, provided in a position between a waste nitrogen pipe provided in the upper part of the low-pressure column and a product oxygen pipe provided in the lower part of the low-pressure column, the nitrogen temperature in the low-pressure column is detected. A low-pressure column nitrogen temperature detection mechanism;
A controller that detects an increase in the amount of nitrogen gas in the low-pressure column based on the detected temperature of the low-pressure column nitrogen temperature detection mechanism, and controls the flow rate of the raw air flowing through the bypass valve based on the detection result; having, cryogenic air separation unit as claimed in claim 1. The first bypass pipe is connected to a position between a waste nitrogen pipe provided in an upper portion of the low pressure column and a product oxygen pipe provided in a lower portion of the low pressure column in the low pressure column . The cryogenic air separation device according to claim 1 or 2. Inside of the main condenser, the first gas-liquid heat exchanger for cooling the feed air supplied from the bypass pipe is provided, cryogenic according to any one of claims 1 to 3 Air separation device. Comprising a high pressure column and low pressure column to produce product nitrogen and product oxygen from the feed air compressed by an air compressor, a heat exchanger for liquefying and condensing the separated nitrogen by the higher pressure column, in the heat exchanger A main condenser for refluxing liquefied nitrogen to a high-pressure column, and a cryogenic air separation method in a cryogenic air separation apparatus,
When the nitrogen concentration in the raw material air increases,
Wherein a portion of the feed air supplied from the air compressor, said bypass the higher pressure column is supplied to the main condenser, to cool with liquid oxygen and heat exchange in the main condenser, the main Increasing the evaporation amount of liquid oxygen from the condenser before the nitrogen concentration in the raw material air increases,
It said main condenser feed air that has cooled inflated with, for supplying feed air obtained by the expansion to the low pressure column, a cryogenic air separation process. In the low-pressure column, the temperature in the low-pressure column is detected at a position between a waste nitrogen pipe provided in the upper part of the low-pressure column and a product oxygen pipe provided in the lower part of the low-pressure column,
Detecting an increase in the amount of nitrogen gas in the low-pressure column based on the detected temperature;
Depending on the amount of increase in the amount of nitrogen gas, to bypass the high pressure column to control the flow rate of the feed air supplied to the lower pressure column from the main condenser, cryogenic air separation method according to claim 5. The raw material air expanded after cooling in the main condenser is between the waste nitrogen pipe provided in the upper part of the low pressure column and the product oxygen pipe provided in the lower part of the low pressure column in the low pressure column. The cryogenic air separation method according to claim 5 , wherein the method is supplied to a position. Inside the main condenser, a gas-liquid heat exchanger for cooling the raw material air is provided,
The cryogenic air separation method according to any one of claims 5 to 7 , wherein the raw material air is cooled by the gas-liquid heat exchanger.

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