JP2018096645A - Air liquefaction separation method and air liquefaction separation unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep a manufacturing amount of product oxygen and its purity in a stable manner even if oxygen concentration in raw material air is decreased at a deep cold air liquefaction separation unit with a crude argon tower for manufacturing high yield oxygen.SOLUTION: This invention relates to an air liquefaction separation method for supplying raw material air compressed by a raw material air compressor 11 to a water washed cooling tower 12, MS adsorber 13, a main heat exchanger 14 and a rectification column 15 having a high pressure part 15a and a low pressure part 15b in this order through a raw material air pipe 20 to generate product oxygen, product nitrogen and crude argon at the rectification column 15. When an average value of oxygen concentration at a specified time in raw material air is lower than a preset threshold, a supplying amount of raw material air is increased and at the same time an extraction quantity of crude argon from the rectification column 15 is increased in response to an increased quantity of raw material air and when the average value of oxygen concentration recovers to its original value, the raw material air supplying quantity and the extraction quantity of crude argon are recovered to their original values.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an air liquefaction separation method and an air liquefaction separation apparatus for separating oxygen, nitrogen, and argon gas from raw material air. In particular, the present invention stably supplies product oxygen even when the oxygen concentration of raw material air is lowered. The present invention relates to a method and an apparatus that can be supplied.

  For example, in an air liquefaction / separation apparatus installed at an ironworks or the like, so-called chilled air liquefaction / separation apparatus, the raw air is compressed by a raw air compressor, pre-cooled in a washing cooling tower, and further, moisture and Carbon dioxide gas is removed and cooled by the main heat exchanger. The cooled raw material air is separated into oxygen, nitrogen, and argon raw material gas in a rectification column having a high-pressure part and a low-pressure part, and oxygen is supplied as a product oxygen and nitrogen is supplied as a product nitrogen to customers. The argon source gas is sent to a crude argon column provided outside the rectification column, and further rectification is performed.

  If there are multiple such air liquefaction separation plant plants on the premises of a steelworks, etc., the concentration of nitrogen in the raw material air is temporarily affected by the influence of nitrogen diffused by other adjacent plants. And the oxygen concentration may temporarily decrease. In an air liquefaction separation apparatus for producing high-yield oxygen used in recent years, if the nitrogen concentration in the raw material air temporarily increases and the oxygen concentration decreases, the rectification balance is lost and rectification becomes unstable. In particular, in an air liquefaction separation apparatus that separates and purifies argon, rectification becomes impossible or the product oxygen purity is likely to decrease.

  On the other hand, there is a method to respond by temporarily reducing the amount of product oxygen to be supplied. However, if the oxygen concentration of the raw material air frequently decreases, the product oxygen amount must be adjusted each time, and the operation is complicated. become. Moreover, there arises a problem that the required amount of product oxygen cannot be supplied.

  Therefore, Patent Document 1 discloses a method for injecting liquid oxygen in the main condenser into the high-pressure section as a means for preventing the rectification from becoming unstable due to a decrease in oxygen concentration in the raw material air. .

Japanese Patent Laid-Open No. 2006-80297

  However, in the case of an air liquefaction separation apparatus having a crude argon tower, as in Patent Document 1, in the method of increasing only oxygen without changing the supply amount of argon, the oxygen concentration in the crude argon increases, and the argon purification apparatus In some cases, the amount of oxygen reaction in the deoxygenation tower increases and overheats, resulting in excess capacity.

  An object of the present invention is to maintain a production amount and purity of product oxygen stably even in a cryogenic air liquefaction / separation apparatus for producing high yield oxygen having a crude argon column even if the oxygen concentration in the raw material air is lowered. There is.

  In order to solve the above problems, the present invention includes raw water air compressed by a raw air compressor, a water washing cooling tower, an MS adsorber, a main heat exchanger, a high pressure part and a low pressure part via a raw material air pipe. An air liquefaction separation method in which product oxygen, product nitrogen, and crude argon are generated in the rectification column by supplying them in the order of the rectification column, and an average value of oxygen concentration in the raw material air in a predetermined time is previously When less than the set threshold value, the supply amount of the raw material air is increased, and the amount of crude argon extracted from the rectification column is increased according to the increase amount of the raw material air, and the average value is restored. And a method for liquefying and separating air, wherein the supply amount of the raw material air and the extraction amount of the crude argon are restored.

  In the air liquefaction separation method, when the average value of oxygen concentration in the raw material air is less than 20.5%, the supply amount of the raw material air is increased by 2%, and the average value is 20.9. When it becomes%, the supply amount of the raw material air may be restored. When increasing the supply amount of the raw material air, the extraction amount of the crude argon may be increased by 2%.

  It is preferable to measure the oxygen concentration in the raw material air in real time.

  In addition, the present invention includes a raw material air compressor that compresses raw material air, and a water-washing cooling tower, an MS adsorber, a main heat exchanger, a high-pressure part, and a low-pressure part from the raw material air compressor through a raw material air pipe. A rectifying column is arranged in order, and is an air liquefaction separation device that generates product oxygen, product nitrogen, and crude argon in the rectifying column, and an oxygen concentration detection unit that detects an oxygen concentration in the raw material air; and A control unit that controls the supply amount of the raw material air and the extraction amount of the crude argon in accordance with the oxygen concentration, and the control unit has an average value of the oxygen concentration for a predetermined time that is lower than a preset threshold value. And increasing the supply amount of the raw material air, increasing the amount of crude argon extracted from the rectification tower according to the increase amount of the raw material air, and returning the average value to the original value, Feed rate and crude argon And returning to the original can retracted amount, to provide an air separation plant.

  In the air liquefaction separation apparatus, the oxygen concentration detection unit may be a zirconia oxygen concentration meter provided between the MS adsorber and the main heat exchanger.

  According to the present invention, even if the oxygen concentration of the raw air is temporarily reduced, product oxygen can be rectified stably while suppressing an increase in oxygen concentration in the crude argon.

It is a figure which shows the structure of the air liquefaction separation apparatus concerning this Embodiment. It is explanatory drawing which shows the state of the normal time in the low pressure part of the rectification column of the air liquefaction separation apparatus of FIG. It is explanatory drawing which shows a state when oxygen concentration in the low pressure part of the rectification column of the air liquefaction separation apparatus of FIG. 1 falls. It is explanatory drawing of embodiment of this invention which shows the state when the supply amount of raw material air is increased after the oxygen concentration falls in the low pressure part of the rectification column of the air liquefaction separation apparatus of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  The air liquefaction separation apparatus 1 cools and removes the raw material air by bringing the raw material air compressor 11 that compresses the air sucked through the suction filter 10 and supplies it as the raw material air with the cooling water and the raw material air. A water washing cooling tower 12 that performs the above, an MS (Molecular Sieve) adsorber 13 that removes water and carbon dioxide from the raw air that has passed through the water washing cooling tower 12, and a main heat exchanger 14 that cools the raw air to a predetermined temperature, And a packing tray type rectification column 15 for separating the raw material air into product oxygen and product nitrogen. These devices are connected in series via the raw material air pipe 20 in this order. Further, on the downstream side of the rectifying column 15, a crude argon column 16 that generates a crude argon gas from the argon source gas separated in the rectifying column 15 is provided.

  Between the MS adsorber 13 and the main heat exchanger 14 of the raw material air pipe 20, an oxygen concentration meter 21 as an oxygen concentration detector for detecting the oxygen concentration of the raw material air and the flow rate of the raw material air are measured. A flow meter 22 is provided. The oxygen concentration meter 21 is preferably one that has quick response and can be measured in real time. For example, a zirconia oxygen concentration meter is used. As the flow meter 22, for example, an orifice flow meter is used.

  The rectification column 15 has a high pressure portion 15a having a high pressure and a high temperature, and a low pressure portion 15b having a lower pressure and a lower temperature than the high pressure portion. In the present embodiment, the low-pressure part 15b is arranged above the high-pressure part 15a. However, the present invention is not limited to such a mode, and various modes such as making the low-pressure part 15b and the high-pressure part 15a separate types are used. It is also possible. The raw material air pipe 20 connected to the high pressure section 15 a of the rectification column 15 through the main heat exchanger 14 is partially branched, and the branch pipe 20 a is connected to the low pressure section 15 b via the expansion turbine 23. ing. The raw material air sent to the low-pressure part 15b is depressurized by the expansion turbine 23, so that the temperature is lower than that of the raw material air sent to the high-pressure part 15a.

  A nitrogen extraction pipe 31 for extracting high-purity product nitrogen from the low-pressure part 15b is provided above the low-pressure part 15b. Product nitrogen extracted by the nitrogen extraction pipe 31 passes through the supercooler 51 and is then sent to the main heat exchanger 14 where heat exchange with the raw material air is performed.

  In addition, an oxygen extraction pipe 32 for extracting product oxygen from the low pressure part 15b is provided below the low pressure part 15b. Product oxygen extracted by the oxygen extraction pipe 32 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 waste nitrogen extraction pipe 33 for extracting waste nitrogen having a purity lower than that of product nitrogen is provided below the junction with the nitrogen extraction pipe 31 at the upper part of the low pressure part 15b. The waste nitrogen extracted by the waste nitrogen extraction pipe 33 passes through the supercooler 52, further heat-exchanges with the raw air in the main heat exchanger 14, and then sent to the MS adsorber 13. 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. The waste nitrogen extraction pipe 33 is provided with a pressure regulating valve 43. The pressure regulating valve 43 keeps the pressure in the low pressure part 15b constant, and discharges excess waste nitrogen when the pressure increases.

  A liquid air extraction pipe 34 is provided at the bottom of the high pressure section 15a. The liquid air extracted from the liquid air extraction pipe 34 is decompressed to the pressure of the low pressure part 15b by the supercooler 51 and the expansion valve 44, and then introduced into the center in the height direction of the low pressure part 15b.

  A top reflux nitrogen extraction pipe 35 is provided on the upper portion of the high pressure section 15a. The medium pressure nitrogen gas extracted from the top reflux nitrogen extraction pipe 35 is decompressed to the pressure of the low pressure part 15b by the supercooler 51 and the expansion valve 45, and then introduced into the upper part of the low pressure part 15b to become reflux liquefied nitrogen. . Further, a middle reflux nitrogen extraction pipe 36 is provided at the center in the height direction of the high pressure section 15a. Nitrogen gas extracted from the middle reflux nitrogen extraction pipe 36 is supplied to the low pressure section 15b by the supercooler 52 and the expansion valve 46. After being reduced to the pressure, it is introduced below the introduction portion from the top reflux nitrogen extraction pipe 35 at the top of the low pressure portion 15b to become reflux liquefied nitrogen.

  The high pressure part 15 a and the low pressure part 15 b are connected via the main condenser 30. The main condenser 30 may be incorporated between the high pressure part 15a and the low pressure part 15b in the rectification column 15.

  An argon source gas extraction pipe that has a relatively high argon gas concentration above the lower oxygen concentration portion at the lower portion of the low-pressure portion 15b, extracts the argon source gas from that portion, and supplies it to the crude argon column 16 37 is provided. The argon source gas extraction pipe 37 is connected to the lower part of the crude argon column 16. The argon source gas supplied to the crude argon column 16 becomes an ascending gas, is liquefied by a condenser 53 (described later) provided at the upper part of the crude argon column 16 and descends as a reflux liquid. Liquid oxygen stays.

  The liquid oxygen staying at the bottom of the crude argon column 16 is introduced, for example, below the argon source gas extraction tube 37 in the low pressure unit 15b by the second liquid air extraction tube 38 connected to the bottom of the crude argon column 16. . Further, a condenser 53 that cools and condenses the argon source gas in the crude argon column 16 is provided at the upper portion of the crude argon column 16. A part of the liquid air extracted from the liquid air extraction pipe 34 provided at the bottom of the high pressure part 15 a is supplied to the condenser 53. The argon source gas condensed in the condenser 53 is refluxed toward the lower part of the crude argon column 16, and heat exchange is performed with the argon source gas rising in the crude argon column 16.

  The argon gas in the crude argon column 16 is extracted as crude argon from the crude argon gas extraction tube 39 and sent to the argon purification device 55 via the heat exchanger 54. An argon amount detector 62 is provided in the middle of a pipe 61 for sending crude argon from the heat exchanger 54 to the argon purification device 55, and sends the purified argon from the argon purification device 55 to the heat exchanger 54. A thermometer 64 is provided in the middle of the pipe 63.

  The above air liquefaction separation apparatus 1 is provided with a control unit 100. The control unit 100 is configured by a computer including, for example, a CPU and a memory, and performs operation state monitoring and operation control of various devices, calculation using measurement values of each measuring device, valve opening / closing control, and the like.

  Next, an air liquefaction separation method according to this embodiment using the air liquefaction separation apparatus 1 will be described.

  In producing product oxygen and product nitrogen in the air liquefaction separation device 1, first, the raw material air compressed to a high temperature and high pressure by the raw material air compressor 11 is supplied to the water cooling tower 12. At this time, the temperature of the raw material air at the outlet of the raw material air compressor 11 is approximately 100 ° C.

  In the washing / cooling tower 12, the raw air is cooled to about 10 ° C. and dust is removed. The raw material air removed from the dust is supplied to the MS adsorber 13. In the MS adsorber 13, moisture and carbon dioxide are removed from the raw air in order to prevent generation of ice and dry ice in the main heat exchanger 14 and the rectification tower 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, for example, about −170 ° C. by the main heat exchanger 14. The cooled raw material air is supplied to the high pressure portion 15a in a partially liquefied state, and liquid air gradually accumulates at the bottom of the high pressure portion 15a. Further, part of the raw material air that has passed through the MS adsorber 13 is guided to the expansion turbine 23 by the branch pipe 20a, and the raw material air decompressed by the expansion turbine 23 is supplied to the low pressure portion 15b.

  In the high-pressure part 15a, the raw material air is roughly rectified and separated into liquid air and nitrogen. A part of the nitrogen separated by the high-pressure part 15a is condensed and liquefied by the main condenser 30, and the liquefied nitrogen is refluxed to the upper part of the low-pressure part 15b. Further, the liquid air separated by the high pressure portion 15a passes through the liquid air extraction pipe 34 and is supplied to the intermediate portion of the low pressure portion 15b through the expansion valve 44 in a gas-liquid mixed state.

  In the low-pressure part 15b, the raw air is further rectified, nitrogen is accumulated in the upper part of the low-pressure part 15b, and the purity of nitrogen becomes higher as the upper part of the low-pressure part 15b. In addition, product oxygen accumulates in the lower portion of the low pressure portion 15b. The high-purity product nitrogen collected in the upper part of the low-pressure part 15b is sent to the main heat exchanger 14 through the nitrogen extraction pipe 31, and heat is exchanged with the raw air in the main heat exchanger 14 to raise the temperature. The compressor is compressed to a predetermined pressure by a compressor (not shown) and supplied to the customer.

  The product oxygen accumulated in the lower part of the low pressure part 15b is sent to the main heat exchanger 14 through the oxygen extraction pipe 32, and heat is exchanged with the raw air in the main heat exchanger 14 to raise the temperature. It is compressed to a predetermined pressure by a compressor that does not, and supplied to the customer.

  The crude argon gas extracted from the crude argon column 16 is sent to the argon purification device 55 via the heat exchanger 54, and oxygen is removed by adding hydrogen gas in the deoxygenation tower provided in the argon purification device 55. Then, it is sent again through the heat exchanger 54 to a purifier (not shown) for further final purification of argon. The amount of argon sent to the argon purification device 55 is measured by the argon amount detector 62, and the temperature of the argon gas sent from the argon purification device 55 is measured by the thermometer 64, whereby the argon purification processing is performed by the argon purification device 55. Monitor not to exceed the ability of.

In the air liquefaction separation apparatus 1 as described above, FIG. 2 shows the internal state of the low pressure section 15b of the rectification column 15 when the raw material air is normal air, that is, when the oxygen concentration is 20.9%. The nitrogen concentration of the raw air is 78.1% and the argon concentration is 0.93%. The upper portion of the low-pressure portion 15b is an area 151 having a high nitrogen concentration, the lower portion is an area 153 having a high oxygen concentration, and the middle portion is an area 152 having a high argon concentration. In FIG. 2, the boundaries of the areas 151, 152, and 153 are shown in a straight line, but in reality, there is a range where a plurality of types of gases are mixed in the boundary part, and the same applies to FIGS. 3 and 4 described later. It is. In this state, the amount of oxygen in the raw air of the raw air of 293,000 Nm ³ / H is
^{293,000 (Nm 3 /H)×20.9%=61,230(Nm 3 / H} )
When the oxygen yield of the air liquefaction separation apparatus 1 is 98%,
61,230 (Nm ³ / H) × 98% = 60,000 (Nm ³ / H)
Thus, the production capacity of product oxygen is 60,000 Nm ³ / H.

FIG. 3 shows that the nitrogen concentration in the raw material air is increased by increasing the nitrogen concentration in the vicinity of the raw material air inlet (78.5%), whereby the oxygen concentration is 20.5% and the argon concentration is 0.91. When the ratio is reduced to%, the internal state of the low-pressure part 15b is shown in the case where the supply amount of the raw material air and the extraction amount of oxygen, nitrogen and argon gas are set as usual. In this case, the nitrogen-oxygen balance is changed, the nitrogen concentration in the low pressure part 15b is increased, the amount of nitrogen mixed in the argon source gas supplied to the crude argon column 16 is increased, and the rectification of the crude argon column 16 is performed. It becomes unstable. Moreover, the temperature in the low-pressure part 15b falls due to the increase in the concentration of nitrogen having a low boiling point, and the area 152 having a high argon concentration falls downward. When argon comes into contact with the reflux liquid in the low-pressure part 15b, the temperature of the low-pressure part 15b is lowered, so that argon is easily dissolved in the reflux liquid, and the purity of the liquid oxygen at the lower part of the low-pressure part 15b is reduced. . That is, the oxygen amount decreases and the oxygen purity decreases. In this state, the oxygen amount in the raw air of the raw air of 293,000 Nm ³ / H is
^{293,000 (Nm 3 /H)×20.5%=60,000(Nm 3 / H} )
When the oxygen yield of the air liquefaction separation apparatus 1 is 98%,
60,000 (Nm ³ / H) x 98% = 58,800 (Nm ³ / H)
Thus, the production capacity of product oxygen is 2% lower than in the case of FIG. That is, both oxygen purity and oxygen amount are reduced.

  FIG. 4 shows an internal state of the low-pressure part 15b when the supply amount of the raw material air is increased by 2% when the oxygen concentration of the raw material air is lowered to 20.5%. The raw material air at this time has a high nitrogen concentration as in the case of FIG. In this case, although the absolute amount of oxygen supplied to the air liquefaction separation apparatus 1 returns, the nitrogen concentration in the raw material air is high, so the nitrogen-oxygen balance in the low pressure part 15b remains poor, and the oxygen purity remains as it is. descend. Therefore, by increasing the extraction amount of the argon source gas by 2%, it is possible to suppress the area 152 having a high argon concentration from being lowered, and to secure the oxygen amount and the oxygen concentration. Moreover, since the amount of nitrogen in the low pressure part 15b naturally increases by increasing the supply amount of the raw air, the amount of waste nitrogen released is increased so that the pressure in the low pressure part 15b becomes constant. The amount of waste nitrogen released is adjusted by a pressure adjusting valve 43 provided in the waste nitrogen extraction pipe 33 so that the pressure in the low pressure portion 15b is maintained constant.

  That is, in the present embodiment, the oxygen concentration in the raw material air is measured online by the oxygen concentration meter 21, and the average value of the oxygen concentration for a certain time, for example, 10 to 30 minutes, falls below a predetermined threshold value, for example, 20.5%. When the control unit 100 detects this, the operating amount of the raw material air compressor 11 is increased and the raw material air amount corresponding to the insufficient oxygen amount is increased by 2%, for example. Then, the opening of the valve 47 provided in the argon source gas extraction pipe 37 for extracting argon from the low pressure part 15b is adjusted, and the crude argon increased by 2% corresponding to the incremental amount of argon contained in the increased source air is extracted. To do. When the oxygen concentration in the raw material air returns to the normal value (20.9%), the supply amount of the raw material air and the amount of extracted crude argon are restored. It is preferable to increase / decrease the supply amount of the raw air at, for example, about 0.5% / min.

  As described above, according to the present invention, even if the oxygen concentration of the raw air is temporarily decreased, the production amount and oxygen purity of product oxygen can be kept constant, and the rectification of the crude argon column can be stabilized. Can be made.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

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

DESCRIPTION OF SYMBOLS 1 Air liquefaction separation apparatus 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 16 Crude argon tower 20 Raw material air pipe 20a Branch pipe 21 Oxygen concentration Total 22 Flow meter 23 Expansion turbine 30 Main condenser 31 Nitrogen extraction pipe 32 Oxygen extraction pipe 33 Waste nitrogen extraction pipe 34 Liquid air extraction pipe 35 Top reflux nitrogen extraction pipe 36 Central reflux nitrogen extraction pipe 37 Argon source gas extraction pipe 38 (No. (Ii) Liquid air extraction pipe 39 Coarse argon gas extraction pipe 43 Pressure regulating valves 44, 45, 46 Expansion valve 47 Valve 100 Controller

Claims (6)

The raw material air compressed by the raw material air compressor is supplied through the raw material air pipe in the order of the washing cooling tower, the MS adsorber, the main heat exchanger, and the rectification tower having the high pressure part and the low pressure part, and An air liquefaction separation method for producing product oxygen, product nitrogen, and crude argon in a distillation column,
When the average value of the oxygen concentration in the raw material air is below a preset threshold value, the supply amount of the raw material air is increased and, depending on the increase amount of the raw material air, from the rectification tower An air liquefaction separation method characterized in that when the amount of crude argon extracted is increased and the average value returns to the original value, the supply amount of raw material air and the amount of crude argon extracted are restored.   When the average value of oxygen concentration in the raw material air for 10 to 30 minutes is less than 20.5%, the supply amount of the raw material air is increased by 2%, and when the average value becomes 20.9%, the raw material The air liquefaction separation method according to claim 1, wherein the supply amount of air is restored.   3. The air liquefaction separation method according to claim 2, wherein when the supply amount of the raw air is increased, the extraction amount of the crude argon is increased by 2%.   The air liquefaction separation method according to any one of claims 1 to 3, wherein the oxygen concentration in the raw material air is measured in real time. A raw material air compressor that compresses raw material air, and a rectification tower having a water washing cooling tower, an MS adsorber, a main heat exchanger, and a high pressure portion and a low pressure portion are arranged in this order from the raw material air compressor through a raw material air pipe. An air liquefaction separation apparatus for producing product oxygen, product nitrogen, and crude argon in the rectification column,
An oxygen concentration detection unit that detects the oxygen concentration in the raw material air, and a control unit that controls the supply amount of the raw material air and the extraction amount of the crude argon in accordance with the oxygen concentration,
The control unit increases the supply amount of the raw material air when the average value of the oxygen concentration in a certain period of time is lower than a preset threshold value, and from the rectification tower according to the increase amount of the raw material air. The air liquefaction separation apparatus is characterized in that when the amount of crude argon extracted is increased and the average value is restored to the original value, the supply amount of raw material air and the amount of crude argon extracted are restored.   The air liquefaction separation apparatus according to claim 5, wherein the oxygen concentration detection unit is a zirconia oxygen concentration meter provided between the MS adsorber and the main heat exchanger.

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