Air separation device, and method for manufacturing liquid oxygen and liquid nitrogen

Abstract

To provide an air separation device and an air separation method for manufacturing liquid nitrogen and liquid oxygen as a product with less electric power.SOLUTION: An air separation device 1 includes: a first compressor 11 of raw material air; a first heat exchanger 21 for cooling compressed air; a single rectification tower 31 in which the compressed and cooled air is introduced; a nitrogen liquefying part 40 for nitrogen gas separated from air; and a liquid nitrogen storing tank 51. The first heat exchanger is provided with: a first cooled heat supply pipe 80 through which liquid hydrogen flows; and a raw material air pipe 12 through which the compressed air flows. The nitrogen liquefying part includes: second compressors 41 to 43 for nitrogen gas from the rectification tower; and a second heat exchanger 44 for cooling compressed nitrogen gas from the second compressor. The second heat exchanger is provided with: a nitrogen gas pipe 37 through which the compressed nitrogen from the second compressor flows; and a second cooled heat supply pipe 82 through which liquid hydrogen flows. A nitrogen reflow pipe 53 for reflowing liquid nitrogen from the liquid nitrogen storing tank to the single rectification tower, the nitrogen reflow pipe being connected to the liquid nitrogen storing tank and the single rectification tower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to air separation units and methods for producing liquefied oxygen and liquefied nitrogen. [Background technology]

[0002] Air separation units for separating and purifying components contained in air are known. Patent Document 1, for example, discloses a low-purity oxygen production system that uses the cold energy of liquefied hydrogen to perform low-temperature distillation of feed air. The production system disclosed in Patent Document 1 includes a feed air compressor that compresses the feed air, a low-temperature compressor that compresses a portion of the purified feed air at a low temperature, and an expansion turbine that expands the remaining purified feed air. In the main heat exchanger of the air separation unit of Patent Document 1, heat is exchanged between the expanded low-pressure feed air and the low-temperature compressed high-pressure feed air, and the fluid obtained by the low-temperature distillation and liquefied hydrogen, which is a cold energy supply source.

[0003] Patent Document 2 discloses an air separation unit that uses liquefied hydrogen as an external refrigeration source. The air separation unit in Patent Document 2 includes a double column rectification column. Reflux nitrogen extracted from the high-pressure rectification column of the double column rectification column is liquefied by passing it through a heat exchanger that uses liquefied hydrogen as an external refrigeration source. This heat exchanger has an intermediate-temperature flow path, through which hydrogen gas produced by evaporation of the liquefied hydrogen passes, between a high-temperature flow path through which the reflux nitrogen passes and a low-temperature flow path through which the liquid hydrogen passes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 10-274474 [Patent Document 2] Japanese Patent Application Publication No. 11-51558 Summary of the Invention [Problem to be solved by the invention]

[0005] An air separation unit is equipped with multiple compressors, such as a feed air compressor and a nitrogen recycle compressor, and requires a large amount of electricity to operate these compressors. Since electricity costs account for a large portion of the cost of an air separation unit, an air separation unit with low power consumption is desirable. In light of this current situation, one object of the present disclosure is to provide an air separation unit that extracts liquid nitrogen and liquid oxygen as products and that consumes low power. Another object of the present disclosure is to provide a method for producing liquefied oxygen and liquefied nitrogen that can be implemented with low power consumption. [Means for solving the problem]

[0006] An air separation unit according to the present disclosure comprises a first compressor that compresses feed air, a first heat exchanger that cools the feed air compressed in the first compressor, a single-column rectification column into which the cooled feed air that has passed through the first heat exchanger is introduced through a cooled feed air inlet pipe, a nitrogen liquefaction section that liquefies nitrogen gas separated from the cooled feed air and withdrawn from the single-column rectification column, and a liquefied nitrogen storage tank that stores the nitrogen liquefied in the nitrogen liquefaction section. The first heat exchanger is provided with a first cold heat supply pipe through which liquefied hydrogen flows, and a feed air pipe through which compressed feed air compressed in the first compressor flows. The nitrogen liquefaction section includes a second compressor that compresses nitrogen gas withdrawn from the top of the single-column rectification column, and a second heat exchanger that cools the nitrogen gas compressed in the second compressor. The second heat exchanger is provided with a nitrogen gas pipe through which compressed nitrogen gas compressed in the second compressor flows, and a second refrigeration supply pipe through which liquefied hydrogen flows. The air separation unit is provided with a nitrogen reflux pipe connected to the liquefied nitrogen storage tank and the single column rectification column, for supplying liquefied nitrogen taken out of the liquefied nitrogen storage tank to the single column rectification column as nitrogen reflux liquid.

[0007] A method for producing liquefied oxygen and liquefied nitrogen according to the present disclosure is carried out in an air separation unit comprising: a first compressor that compresses feed air; a feed air pipe through which the compressed feed air compressed in the first compressor flows; and a first cold heat supply pipe through which liquefied hydrogen flows, the first heat exchanger cooling the compressed feed air flowing through the feed air pipe with the cold heat of the liquefied hydrogen flowing through the first cold heat supply pipe; a single column rectification column into which the cooled feed air that has passed through the first heat exchanger is introduced through a cooled feed air inlet pipe; a nitrogen liquefaction section for liquefying nitrogen gas separated from the cooled feed air and withdrawn from the single column rectification column; and a liquefied nitrogen storage tank for storing nitrogen liquefied in the nitrogen liquefaction section. The method for producing liquefied oxygen and liquefied nitrogen includes the steps of: pressurizing the feed air to 50 kPaG to 70 kPaG in the first compressor; introducing cooled feed air cooled in the first heat exchanger at −183°C to −188°C and 30 kPaG to 50 kPaG into the single rectification column; a nitrogen gas liquefaction step of withdrawing nitrogen gas separated from the cooled feed air in the single rectification column from the top of the single rectification column and liquefying the nitrogen gas in the nitrogen liquefaction section; and a liquefied oxygen withdrawal step of withdrawing liquefied oxygen separated from the cooled feed air in the single rectification column from the bottom of the single rectification column. [Effects of the Invention]

[0008] An air separation unit that extracts liquid nitrogen and liquid oxygen as products and consumes little power is provided. Also provided is a method for producing liquefied oxygen and liquefied nitrogen that can be carried out with little power consumption. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing a piping system of an air separation unit according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a flowchart showing an outline of a method for producing liquefied oxygen and liquefied nitrogen according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Outline of the embodiment] First, an outline of an air separation unit and a method for producing liquefied oxygen and liquefied nitrogen according to the present disclosure will be described. The air separation unit according to the present disclosure comprises a first compressor for compressing feed air, a first heat exchanger for cooling the feed air compressed in the first compressor, a single-column rectification column into which the cooled feed air that has passed through the first heat exchanger is introduced through a cooled feed air inlet pipe, a nitrogen liquefaction section for liquefying nitrogen gas separated from the cooled feed air and removed from the single-column rectification column, and a liquefied nitrogen storage tank for storing the nitrogen liquefied in the nitrogen liquefaction section. The first heat exchanger is provided with a first cold energy supply pipe through which liquefied hydrogen flows, and a feed air pipe through which compressed feed air compressed in the first compressor flows. The nitrogen liquefaction section comprises a second compressor for compressing nitrogen gas removed from the top of the single-column rectification column, and a second heat exchanger for cooling the nitrogen gas compressed in the second compressor. The second heat exchanger is provided with a nitrogen gas pipe through which compressed nitrogen gas compressed in the second compressor flows, and a second refrigeration supply pipe through which liquefied hydrogen flows. The air separation unit is provided with a nitrogen reflux pipe connected to the liquefied nitrogen storage tank and the single column rectification column, for supplying liquefied nitrogen taken out of the liquefied nitrogen storage tank to the single column rectification column as nitrogen reflux liquid.

[0011] Air separation units that utilize the cold energy of liquefied hydrogen as a cold energy source are known. For example, the air separation unit disclosed in Patent Document 1 is equipped with a liquefied hydrogen evaporation heating path. In the air separation unit disclosed in Patent Document 1, the cold energy of the liquefied hydrogen is first used in a nitrogen gas condenser to cool a portion of the nitrogen gas extracted from the top of the distillation column. The cold energy of the hydrogen gas, which has been heated through a nitrogen gas condenser and turned into a gaseous form, is further used in a supercooling unit and a main heat exchanger to cool a portion of the nitrogen gas extracted from the top of the distillation column. The cooled nitrogen gas becomes liquefied nitrogen and is refluxed to the distillation column as nitrogen reflux. In the main heat exchanger, the feed air is cooled using hydrogen gas that has been slightly heated through the nitrogen gas condenser and supercooling unit. In the air separation unit disclosed in Patent Document 2, the cold energy of the liquefied hydrogen is used to liquefy reflux nitrogen extracted from the distillation column.

[0012] The inventors have conducted research into reducing power consumption by utilizing the cold energy of liquefied hydrogen in an air separation unit. The inventors have arrived at a configuration in which the cold energy of liquefied hydrogen is utilized in the nitrogen liquefaction process, as well as for cooling feed air in the main heat exchanger. They have also arrived at a configuration in which a portion of the liquefied nitrogen stored as a product in a liquefied nitrogen storage tank is utilized as nitrogen reflux liquid to be refluxed to the rectification column. They have found that these configurations make it possible to introduce low-pressure (e.g., 100 kPaG or less) feed air into the rectification column and separate oxygen and nitrogen. These configurations enable the air separation unit according to the present disclosure to reduce the power consumption required for compressing feed air.

[0013] The air separation unit may include a liquefied hydrogen supply pipe and a hydrogen gas recovery pipe. The first cold heat supply pipe and the second cold heat supply pipe may both be connected to the liquefied hydrogen supply pipe and the hydrogen gas recovery pipe. The first cold heat supply pipe may include a first flow control valve between the hot end of the first heat exchanger and the hydrogen gas recovery pipe. The second cold heat supply pipe may include a second flow control valve between the hot end of the second heat exchanger and the hydrogen gas recovery pipe.

[0014] According to the above configuration, liquefied hydrogen is supplied to the first cold heat supply pipe and the second cold heat supply pipe via the liquefied hydrogen supply pipe. Furthermore, a portion of the cold heat is released in the first heat exchanger and the second heat exchanger, and the hydrogen gas that has risen in temperature and turned into gas is supplied to the supply destination (customer) via the hydrogen gas recovery pipe. This configuration makes it possible to maximize the cold heat of the liquefied hydrogen at its liquefaction temperature (-253°C (at atmospheric pressure)), and then supply the evaporated hydrogen gas to the supply destination (customer).

[0015] The air separation unit may be configured such that the nitrogen reflux pipe is provided with a pump for delivering liquefied nitrogen extracted from the liquefied nitrogen storage tank. With this configuration, when there is a pressure difference between the liquefied nitrogen storage tank and the rectification column, the liquefied nitrogen can be appropriately pressurized and supplied to the rectification column as nitrogen reflux liquid.

[0016] In the air separation unit, a regeneration air outlet pipe for taking out regeneration air may be connected to the single rectification column below the connection point of the nitrogen reflux pipe and above the connection point of the cooled feed air introduction pipe. This configuration makes it possible to take out gas for regenerating a feed air dryer while reducing losses of high-purity nitrogen gas (liquefied nitrogen product) and liquefied oxygen (liquefied oxygen product).

[0017] A method for producing liquefied oxygen and liquefied nitrogen according to the present disclosure is carried out in an air separation unit comprising: a first compressor that compresses feed air; a feed air pipe through which the compressed feed air compressed in the first compressor flows; and a first cold heat supply pipe through which liquefied hydrogen flows, the first heat exchanger cooling the compressed feed air flowing through the feed air pipe with the cold heat of the liquefied hydrogen flowing through the first cold heat supply pipe; a single column rectification column into which the cooled feed air that has passed through the first heat exchanger is introduced through a cooled feed air inlet pipe; a nitrogen liquefaction section for liquefying nitrogen gas separated from the cooled feed air and withdrawn from the single column rectification column; and a liquefied nitrogen storage tank for storing nitrogen liquefied in the nitrogen liquefaction section. The method for producing liquefied oxygen and liquefied nitrogen includes the steps of: pressurizing the feed air to 50 kPaG to 70 kPaG in the first compressor; introducing cooled feed air cooled in the first heat exchanger at −183°C to −188°C and 30 kPaG to 50 kPaG into the single rectification column; a nitrogen gas liquefaction step of withdrawing nitrogen gas separated from the cooled feed air in the single rectification column from the top of the single rectification column and liquefying the nitrogen gas in the nitrogen liquefaction section; and a liquefied oxygen withdrawal step of withdrawing liquefied oxygen separated from the cooled feed air in the single rectification column from the bottom of the single rectification column.

[0018] According to this production method, liquefied oxygen and liquefied nitrogen can be produced by cooling low-pressure (50 kPaG to 70 kPaG) feed air using the cold energy of liquefied hydrogen and introducing it into a single column rectification column, thereby reducing the power consumption required to compress the feed air.

[0019] In the method for producing liquefied oxygen and liquefied nitrogen, the nitrogen liquefaction section may include a second compressor that compresses nitrogen gas extracted from the top of the single-column rectification column, and a second heat exchanger that cools the nitrogen gas compressed by the second compressor. The second heat exchanger may be provided with a nitrogen gas pipe through which the compressed nitrogen gas compressed in the second compressor flows, and a second cold heat supply pipe through which liquefied hydrogen flows. The nitrogen gas liquefaction step may include a step of cooling the compressed nitrogen gas with the cold energy of liquefied hydrogen in the second heat exchanger. By utilizing the cold energy of liquefied hydrogen to liquefy nitrogen gas, the effect of reducing power consumption is further enhanced.

[0020] In the method for producing liquefied oxygen and liquefied nitrogen, the air separation unit may include a nitrogen reflux pipe connected to the liquefied nitrogen storage tank and the single column rectification column, for supplying liquefied nitrogen removed from the liquefied nitrogen storage tank to the single column rectification column as nitrogen reflux. The method may include a nitrogen reflux liquid supply step of supplying liquefied nitrogen removed from the liquefied nitrogen storage tank to the single column rectification column as nitrogen reflux liquid.

[0021] By using the liquefied nitrogen extracted from the liquefied nitrogen storage tank as the nitrogen reflux liquid, the nitrogen reflux liquid can be supplied to the single-column rectification column more stably than in a method in which liquefied nitrogen obtained by cooling nitrogen gas extracted from the rectification column is immediately refluxed.

[0022] [Specific example of embodiment] Next, specific embodiments of an air separation unit according to the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and their description will not be repeated. Note that in this specification, the "upstream side" and "downstream side" of a pipe are referred to based on the direction of fluid flow through the pipe in the air separation method described in the specification, but in actual operation, the flow direction of the fluid is not limited to this.

[0023] [Air separation unit] 1 is a system diagram showing a piping system of an air separation unit according to one embodiment of the present disclosure. Air separation unit 1 introduces feed air into the unit from feed air acquisition unit S. Air separation unit 1 includes a feed air compressor 11 as a first compressor, a main heat exchanger 21 as a first heat exchanger, a distillation column 31 which is a single column rectification column, a nitrogen liquefaction unit 40, and a liquefied nitrogen storage tank 51. Air separation unit 1 also includes a hydrogen piping system 80 which supplies and recovers the cold energy of liquefied hydrogen.

[0024] Feed air compressed by feed air compressor 11 passes through pipe 12 and dryer 13A before being introduced into main heat exchanger 21. Pipe 12 connects compressor 11 to main heat exchanger 21. Specifically, compressor 11 may be, for example, a blower. Compressor 11 does not have to be a positive displacement or turbo compressor, but may also be a positive displacement or turbo compressor. Pipe 12 is connected to pipe 14. Pipe 14 is a pipe for feed air that passes through main heat exchanger 21. Feed air that has passed through pipe 14 and been cooled in main heat exchanger 21 is introduced into distillation column 31 through pipe 15, which serves as a cooled feed air introduction pipe. Pipe 15 is connected to pipe 14 and is arranged between main heat exchanger 21 and distillation column 31.

[0025] The dryer 13A may be provided in parallel with a similar dryer 13B. Specifically, the dryers 13A and 13B may be, for example, column-type adsorption / desorption devices containing molecular sieves. One of the dryers 13A and 13B can be used to dry the feed air while the other can be used to regenerate the feed air.

[0026] Main heat exchanger 21 is provided with pipe 81 as a first cold energy supply pipe through which liquefied hydrogen supplied from a liquefied hydrogen supply source (for example, a liquefied hydrogen tank) through pipe 88, which is a liquefied hydrogen supply pipe. Pump 87 is provided midway along liquefied hydrogen supply pipe 88. In main heat exchanger 21, feed air circulating through pipe 14 exchanges heat with liquefied hydrogen circulating through pipe 81, and is cooled by the cold energy of the liquefied hydrogen.

[0027] Distillation column 31 is a single-column rectification column and has a feed air inlet 35 near the vertical center. In other words, pipe 15 is connected to the distillation column 31 near the center. For example, when distillation column 31 is divided into three regions vertically, the "near the center" refers to the region sandwiched between the upper and lower regions. Distillation column 31 has a liquefied oxygen outlet at or near the lower end in the vertical direction. Liquefied oxygen LO2 separated from the feed air is extracted from distillation column 31 through pipe 32 and stored in a liquefied oxygen storage tank. Pipe 32 is equipped with pump 33.

[0028] Distillation column 31 has a nitrogen gas outlet port 36 at its top. Pipe 37, which is a nitrogen gas outlet pipe, is connected to the top of distillation column 31. Pipe 37 passes through main heat exchanger 21 to compressor 41. The nitrogen gas passing through pipe 37 is cooled, compressed, and liquefied in nitrogen liquefaction section 40. Nitrogen liquefaction section 40 includes multiple compressors 41, 42, and 43 serving as second compressors, and a heat exchanger 44 serving as a second heat exchanger.

[0029] A pipe 82 for supplying liquefied hydrogen is disposed in the heat exchanger 44. The pipe 82 is connected to a liquefied hydrogen supply pipe 88. In the heat exchanger 44, the cold energy of the liquefied hydrogen is supplied to the nitrogen gas flowing through the pipe 45, thereby cooling the nitrogen gas. That is, in the heat exchanger 44, heat is exchanged between the liquefied hydrogen and the nitrogen gas.

[0030] In the air separation unit 1 according to the present disclosure, a liquefied hydrogen supply pipe 88 is connected to a pipe 81 that passes through the main heat exchanger 21 and a pipe 82 that passes through the heat exchanger 44. Pipes 81 and 82 are also connected to a pipe 83 that serves as a hydrogen gas recovery pipe. The hydrogen that has been heated by releasing cold energy in the heat exchangers 21 and 44 becomes hydrogen gas and is extracted from the pipe 83. A flow rate control valve 84 is provided in the pipe 81. A flow rate control valve 85 is provided in the pipe 82. The flow rate control valves 84 and 85 adjust the hydrogen gas that has passed through the heat exchangers 21 and 44 to an appropriate temperature and pressure.

[0031] The nitrogen liquefaction section 40 will now be described. The nitrogen liquefaction section 40 includes a pipe 45 connected to the pipe 37. Compressors 42 and 43 are provided along the pipe 45, and sequentially pressurize the nitrogen gas flowing through the pipe 45. A pipe 46 branches off from the pipe 45 downstream of the heat exchanger 44. The pipe 46 is provided with a valve 61. The pipe 46 passes through the heat exchanger 44 and connects to the pipe 45 between the compressors 42 and 43. That is, a portion of the nitrogen gas flowing through the pipe 45 circulates through the pipe 46. The air separation unit 1 includes three stages of compressors 41, 42, and 43, but the number of compressors can be changed depending on the performance of the compressors and the size of the entire unit.

[0032] Pipe 45 is connected to gas-liquid separation tank 47. Pipe 45 is equipped with valve 62, which is a Joule-Thomson valve. Nitrogen gas extracted from distillation column 31 passes through main heat exchanger 21, compressors 41, 42, and 43, heat exchanger 44, and valve 62 and reaches gas-liquid separation tank 47, where it is separated into gas and liquid in a liquefied state. Pipe 48 is connected to the top of gas-liquid separation tank 47. Nitrogen gas filling the gas phase of gas-liquid separation tank 47 is discharged through pipe 48. Pipe 48 passes through heat exchanger 44 and connects to pipe 45 on the upstream side of compressor 42.

[0033] The gas-liquid separation tank 47 is connected to a liquefied nitrogen storage tank 51 by a pipe 49. A flow rate adjustment valve 63 is provided midway along the pipe 49. The liquefied nitrogen storage tank 51 stores the product liquefied nitrogen LN2.

[0034] A pipe 53 is disposed between the liquefied nitrogen storage tank 51 and the distillation column 31. The pipe 53 is equipped with a pump 52. The liquefied nitrogen taken out from the liquefied nitrogen storage tank 51 is introduced into the distillation column 31 through the pipe 53 as a nitrogen reflux liquid.

[0035] Pipe 71 is disposed between distillation column 31 and dryers 13A and 13B. Pipe 71 passes through main heat exchanger 21. Pipe 71 is connected to distillation column 31 above feed air inlet 35. Pipe 71 is also connected to distillation column 31 below nitrogen reflux liquid supply port 54. That is, pipe 71, which is the regeneration air outlet pipe for extracting regeneration air, is connected below the connection to the nitrogen reflux pipe and above the connection to the cooled feed air inlet pipe. The gas extracted from pipe 71 is heated by heat exchange with the feed air passing through pipe 14 in heat exchanger 21 and is used as regeneration gas for dryers 13A and 13B.

[0036] (Method of producing liquefied oxygen and liquefied nitrogen) The method for producing liquefied oxygen and liquefied nitrogen according to the present disclosure can be implemented using the air separation unit described above. An example of implementing the method for producing liquefied oxygen and liquefied nitrogen according to the present disclosure using the air separation unit 1 will be described below. Figure 2 is a flowchart showing an outline of the method for producing liquefied oxygen and liquefied nitrogen according to an embodiment of the present disclosure.

[0037] 1 and 2, air at room temperature (for example, -5°C to 30°C) taken in from the feed air intake section S is first compressed by a compressor 11 in a pressure increase step (S10). The feed air may be pressurized to 30 kPaG to 100 kPaG. Typically, the feed air may be pressurized to 50 kPaG to 70 kPaG. The degree of compression of the feed air does not necessarily require a positive displacement or turbo compressor, and the pressure can be obtained using a blower.

[0038] The feed air leaving compressor 11 passes through pipe 12 and dryer 13A (or dryer 13B), where moisture is removed. The feed air passes through pipe 12 to main heat exchanger 21. In main heat exchanger 21, the feed air passing through pipe 14 exchanges heat with the cold of liquefied hydrogen passing through pipe 81, and the feed air is cooled to approximately -190°C to -180°C. Typically, the feed air is cooled to approximately -188°C to -183°C. The temperature of liquefied hydrogen is -253°C (at atmospheric pressure), which is sufficient to supply cold to the feed air.

[0039] The feed air cooled in main heat exchanger 21 is introduced into distillation column 31 through pipe 15 (S11). Distillation column 31 is a low-pressure rectification column, and the pressure inside the distillation column may be 10 kPaG to 100 kPaG. Conventionally, air separation units mainly use a combined distillation column composed of a high-pressure distillation column and a low-pressure distillation column. In this regard, the air separation unit according to the present disclosure uses feed air with a low compression ratio and cooled to a lower temperature, and can separate liquid nitrogen and liquid oxygen in a single rectification column.

[0040] In distillation column 31, oxygen and nitrogen are each separated from the cooled feed air. At this time, liquefied nitrogen extracted from liquefied nitrogen storage tank 51 is introduced into distillation column 31 via pipe 53 as nitrogen reflux liquid. The oxygen separated from the feed air is extracted as liquefied oxygen from the bottom of distillation column 31 (S13). The nitrogen separated from the feed air is extracted as nitrogen gas from the top of distillation column 31. The temperature and pressure of the extracted nitrogen gas are not particularly limited, but may be, for example, a pressure of about 25 kPaG and a temperature of about −196° C. The nitrogen gas extracted from distillation column 31 is liquefied in nitrogen liquefaction section 40 (S12).

[0041] Nitrogen gas extracted from distillation column 31 and passing through pipe 37 is introduced into main heat exchanger 21. The nitrogen gas passing through pipe 37 is used as a cold heat source for cooling feed air in main heat exchanger 21. Next, the nitrogen gas passing through pipe 45 is pressurized in stages by compressors 41, 42, and 43. For example, the pressure can be increased to 0.4 MPaG in compressor 41, to 3.0 MPaG in compressor 42, and to 5.0 MPaG in compressor 43. The compressed nitrogen gas is generally at room temperature.

[0042] The nitrogen gas passing through pipe 45 is then cooled in heat exchanger 44 by the cold energy of the liquefied hydrogen passing through pipe 82. The nitrogen gas that has passed through heat exchanger 44 is cooled to, for example, about −150° C. The nitrogen gas, whose pressure is adjusted by Joule-Thomson valve 62, is liquefied and stored in gas-liquid separation tank 47. The liquefied nitrogen extracted from gas-liquid separation tank 47 through pipe 49 has its flow rate adjusted by valve 63 and is stored in liquefied nitrogen storage tank 51.

[0043] A portion of the nitrogen gas leaving heat exchanger 44 flows into pipe 46, is heated through heat exchanger 44, and joins the nitrogen gas passing through pipe 45 downstream of compressor 43. Nitrogen gas extracted from the gas phase of gas-liquid separation tank 47 through pipe 48 is heated through heat exchanger 44 and joins the nitrogen gas passing through pipe 45 downstream of compressor 41. In other words, the cold energy of the nitrogen gas passing through pipe 48 is recovered and utilized by heat exchanger 44. Nitrogen gas is liquefied by nitrogen liquefaction unit 40, which includes compressors 41, 42, 43 and heat exchanger 44 that utilizes the cold energy of liquefied hydrogen, and liquefied nitrogen is obtained as a product.

[0044] A portion of the liquefied nitrogen stored in liquefied nitrogen storage tank 51 is supplied as nitrogen reflux liquid to distillation column 31 through pipe 53. The liquefied nitrogen as nitrogen reflux liquid is pumped out by pump 52. The pressure of the liquefied nitrogen as nitrogen reflux liquid is adjusted to match the pressure inside distillation column 31, for example, to about 30 KPaG.

[0045] The embodiments disclosed herein are illustrative in all respects and should not be construed as limiting. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0046] 1 air separation unit, 11 compressor, 12 piping, 13A, 13B dryer, 14, 15, 32, 37, 45, 46, 48, 49, 53, 71 piping, 21 main heat exchanger, 31 distillation column, 33, 52 pump, 35 feed air inlet, 36 nitrogen gas outlet, 40 nitrogen liquefaction section, 41, 42, 43 compressor, 44 heat exchanger, 47 gas-liquid separation tank, 51 liquefied nitrogen storage tank, 52 pump, 54 supply port, 61, 62, 63 valve, 80 Hydrogen piping system, 81, 82, 83, 88 Piping, 84, 85 Flow control valve, 87 Pump.

Claims

1. a first compressor that compresses the feed air; a first heat exchanger that cools the raw air compressed in the first compressor; a single rectification column into which the cooled feed air that has passed through the first heat exchanger is introduced through a cooled feed air inlet pipe; a nitrogen liquefaction section for liquefying the nitrogen gas separated from the cooled feed air and removed from the single column rectification column; a liquefied nitrogen storage tank for storing the nitrogen liquefied in the nitrogen liquefaction unit; Equipped with The first heat exchanger includes: a first cold energy supply pipe through which liquefied hydrogen flows; a raw air pipe through which the compressed raw air compressed in the first compressor flows; is arranged, The nitrogen liquefaction section a second compressor for compressing nitrogen gas taken out from the top of the single column rectification column; a second heat exchanger that cools the nitrogen gas compressed by the second compressor; Including, The second heat exchanger has: a nitrogen gas pipe through which the compressed nitrogen gas compressed in the second compressor flows; a second refrigeration supply pipe through which liquefied hydrogen flows; is arranged, a nitrogen reflux pipe connected to the liquefied nitrogen storage tank and the single column rectification column for supplying the liquefied nitrogen taken out from the liquefied nitrogen storage tank to the single column rectification column as a nitrogen reflux liquid; Air separation unit.

2. A liquefied hydrogen supply pipe and a hydrogen gas recovery pipe are provided, the first cold heat supply pipe and the second cold heat supply pipe are both connected to the liquefied hydrogen supply pipe and the hydrogen gas recovery pipe; the first cold heat supply pipe includes a first flow rate adjustment valve between the hot end of the first heat exchanger and the hydrogen gas recovery pipe; the second cold heat supply pipe is provided with a second flow rate adjustment valve between the hot end of the second heat exchanger and the hydrogen gas recovery pipe; 10. The air separation unit of claim 1.

3. The nitrogen reflux pipe is provided with a pump that delivers liquefied nitrogen taken out from the liquefied nitrogen storage tank.

3. The air separation unit according to claim 1 or claim 2.

4. In the single column rectification column, a regeneration air outlet pipe for taking out regeneration air is connected to the single rectification column below the connection part of the nitrogen reflux pipe and above the connection part of the cooled feed air inlet pipe.

3. The air separation unit according to claim 1 or claim 2.

5. a first compressor that compresses the feed air; a first heat exchanger including a feed air pipe through which compressed feed air compressed in the first compressor flows and a first cold heat supply pipe through which liquefied hydrogen flows, the first heat exchanger cooling the compressed feed air flowing through the feed air pipe with cold heat of the liquefied hydrogen flowing through the first cold heat supply pipe; a single rectification column into which the cooled feed air that has passed through the first heat exchanger is introduced through a cooled feed air inlet pipe; a nitrogen liquefaction section for liquefying the nitrogen gas separated from the cooled feed air and removed from the single column rectification column; a liquefied nitrogen storage tank for storing the nitrogen liquefied in the nitrogen liquefaction unit; In an air separation plant comprising: pressurizing the feed air to 50 kPaG to 70 kPaG in the first compressor; introducing cooled feed air cooled in the first heat exchanger, the cooled feed air having a temperature of −183° C. to −188° C. and a pressure of 30 kPaG to 50 kPaG, into the single column rectification column; a nitrogen gas liquefaction step of extracting the nitrogen gas separated from the cooled feed air in the single column rectification column from the top of the single column rectification column and liquefying the nitrogen gas in the nitrogen liquefaction section; a liquefied oxygen withdrawing step of withdrawing the liquefied oxygen separated from the cooled feed air in the single rectification column from a lower part of the single rectification column; Including, A method for producing liquefied oxygen and nitrogen.

6. The nitrogen liquefaction section a second compressor for compressing nitrogen gas taken out from the top of the single column rectification column; a second heat exchanger that cools the nitrogen gas compressed by the second compressor; Including, The second heat exchanger has: a nitrogen gas pipe through which the compressed nitrogen gas compressed in the second compressor flows; a second refrigeration supply pipe through which liquefied hydrogen flows; is arranged, The nitrogen gas liquefaction step includes a step of cooling the compressed nitrogen gas with the cold heat of liquefied hydrogen in the second heat exchanger. The method for producing liquefied oxygen and liquefied nitrogen according to claim 5.

7. the air separation unit comprises a nitrogen reflux pipe connected to the liquefied nitrogen storage tank and the single column rectification column, for supplying liquefied nitrogen taken out from the liquefied nitrogen storage tank to the single column rectification column as a nitrogen reflux liquid; The production method includes a nitrogen reflux liquid supplying step of supplying liquefied nitrogen taken out from the liquefied nitrogen storage tank to the single column rectification column as a nitrogen reflux liquid, 7. A method for producing liquefied oxygen and liquefied nitrogen according to claim 5 or 6.

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