Integrated nitrogen liquefier for a cryogenic air separation unit producing nitrogen and argon

Abstract

This invention provides a nitrogen liquefaction unit and a nitrogen liquefaction method configured to be integrated with a cryogenic air separation unit that generates argon and nitrogen. The integrated nitrogen liquefaction unit and related method can operate in at least three different modes, including: (i) a liquid nitrogen-free mode; (ii) a low liquid nitrogen mode; and (iii) a high liquid nitrogen mode. The system and method of this invention are further characterized in that the oxygen-enriched stream from the low-pressure tower of the air separation unit is an oxygen-enriched condensing medium used in the argon condenser.

Description

Technical Field

[0001] This invention relates to enhancing the recovery of liquid nitrogen from cryogenic air separation units that produce nitrogen and argon, and more specifically, to an integrated nitrogen liquefaction unit capable of operating in liquid nitrogen-free, low-liquid-nitrogen, and high-liquid-nitrogen modes. Background Technology

[0002] Industrial gas customers in the electronics industry often seek argon and nitrogen product distributions at varying volumes and pressures, typically generated from cryogenic air separation units, as described in technical publications. Cheung, Moderate Pressure Cryogenic Air Separation Process,Gas Separation&Purification,Vol 5, March 1991 This is disclosed in U.S. Patent No. 4,822,395 (Cheung). Similarly, U.S. Patent Application Serial Nos. 15 / 962205, 15 / 962245, 15 / 962292, and 15 / 962358, filed April 25, 2018, and U.S. Patent Application Serial No. 16 / 662193, filed October 24, 2019, disclose novel air separation cycles that represent improvements over the system disclosed in Cheung. This improvement to the air separation unit that produces medium-pressure argon and nitrogen uses an oxygen-rich stream taken from a low-pressure tower as the condensing medium in the argon condenser to condense the argon-rich stream, thereby improving argon and nitrogen recovery. However, these novel air separation cycles are typically pure gaseous devices, which may be operationally limited in cryogenic air separation applications requiring large-volume liquid nitrogen production or variable liquid nitrogen production.

[0003] While many electronics industry applications focus on pure gas air separation unit designs, some customers seek additional product requirements that may include some oxygen production (in liquid and / or gaseous form) and liquid nitrogen backup. Traditionally, secondary sources of oxygen and liquid nitrogen have been used to meet these additional product requirements.

[0004] There is a need for a cryogenic air separation unit capable of providing basic argon and nitrogen products, as well as oxygen and liquid nitrogen products. Such an air separation unit should preferably have the flexibility to operate in argon and nitrogen-only modes and in one or more liquid nitrogen modes (including a high liquid nitrogen mode) at liquid production rates up to approximately 10% of the incoming air. In other words, further improvements are needed to the medium-pressure cryogenic air separation unit and its circulation for argon and nitrogen production to efficiently produce variable amounts of liquid nitrogen while maintaining overall high nitrogen and high argon recovery from the distillation column system within the cryogenic air separation unit's cold chamber. Summary of the Invention

[0005] The present invention can be characterized as an air separation unit comprising (i) a main air compression system configured to receive an incoming feed air stream and generate a compressed air stream; (ii) an adsorption-based pre-purifier unit configured to remove water vapor, carbon dioxide, nitrous oxide, and hydrocarbons from the compressed air stream and generate a compressed and purified air stream; (iii) a main heat exchange system configured to cool the compressed and purified air stream to a temperature suitable for fractionation; and (iv) a distillation column system having a heat transfer connection via a condenser-reboiler. The distillation system includes a high-pressure column and a low-pressure column, and further includes an argon column arrangement operatively connected to the low-pressure column, the argon column arrangement having at least one argon column and an argon condenser. The distillation system is configured to receive a cooled, compressed, and purified air stream and generate at least two or more oxygen-enriched streams from the low-pressure column; an argon product stream; a gaseous nitrogen product stream; and (v) a nitrogen liquefaction unit, which includes a nitrogen feed compressor; a nitrogen recirculation compressor; a hot booster compressor, a hot turbine with a booster, a cold booster compressor, and a cold turbine with a booster, and is integrated with the main heat exchange system and the distillation system, wherein the nitrogen liquefaction unit is arranged or configured to receive a portion of the gaseous nitrogen product stream and generate a liquid nitrogen product stream.

[0006] Alternatively, the present invention can be characterized as a method for separating air, the method comprising the steps of: (a) compressing an incoming feed air stream in a main air compression system to produce a compressed air stream; (b) purifying the compressed air stream in an adsorption-based pre-purifier unit to produce a compressed and purified air stream; (c) cooling the compressed and purified air stream to a temperature suitable for fractionation in a main heat exchange system; and (d) fractionating the cooled, compressed, and purified air stream in a distillation column system having a high-pressure column and a low-pressure column connected via a condenser-reboiler heat transfer relationship, the distillation column system further comprising... An argon column arrangement is operationally connected to a low-pressure column, the argon column arrangement having at least one argon column and an argon condenser, the distillation column system being configured to generate at least two or more oxygen-enriched streams from the low-pressure column; an argon product stream, a gaseous nitrogen product stream; and (e) liquefying a portion of the gaseous nitrogen product stream in a nitrogen liquefaction unit comprising a nitrogen feed compressor; a nitrogen recirculation compressor; a hot booster compressor, a hot turbine with a booster, a cold booster compressor, and a cold turbine with a booster, and being integrated with a main heat exchange system and a distillation column system, wherein the nitrogen liquefaction unit is arranged or configured to receive a portion of the gaseous nitrogen product stream and generate a liquid nitrogen product stream.

[0007] In both the system and method, the nitrogen liquefier is configured to operate in three modes, including: (1) a liquid nitrogen-free mode, wherein no portion of the gaseous nitrogen product stream is transferred to the nitrogen liquefier and no liquid nitrogen product stream is generated in the nitrogen liquefier; (2) a low liquid nitrogen mode, wherein the gaseous nitrogen feed stream bypasses the nitrogen feed compressor and is transferred to the nitrogen recirculation compressor; and (3) a high liquid nitrogen mode, wherein the gaseous nitrogen feed stream is directed to the nitrogen feed compressor of the nitrogen liquefier. The system and method of the present invention are further characterized in that at least one of the oxygen-enriched streams from the low-pressure tower is an oxygen-enriched condensing medium directed to the argon condenser.

[0008] Finally, the present invention can be characterized as a nitrogen liquefaction unit configured to be integrated with a cryogenic air separation unit that generates argon and nitrogen, the nitrogen liquefaction unit comprising: (i) a gaseous nitrogen product stream generated by the cryogenic air separation unit and a gaseous nitrogen feed stream comprising 1% to 10% by volume of the gaseous nitrogen product stream; (ii) a nitrogen feed compressor configured to receive and compress the gaseous nitrogen feed stream via a first flow control valve; (iii) a nitrogen recirculation compressor configured to receive the compressed gaseous nitrogen feed stream or receive the gaseous nitrogen feed stream via a second bypass valve, and further compress the received stream; and (iv) a thermal booster compressor configured to further compress the gaseous nitrogen feed stream. (v) A first portion of a compressed hot nitrogen stream to produce a cold nitrogen stream; (vi) a cold booster compressor configured to further compress the cold nitrogen stream to produce a primary nitrogen liquefaction stream; (vi) a hot turbine loaded with a booster configured to expand a second portion of the further compressed hot nitrogen stream to produce a hot recirculation stream; (vii) a cold turbine loaded with a booster configured to expand a recirculation portion of the primary nitrogen liquefaction stream and produce a cold recirculation stream; and (viii) a heat exchanger configured to cool the primary nitrogen liquefaction stream to produce a liquid nitrogen product stream by indirect heat exchange with the hot and cold recirculation streams, wherein the hot and cold recirculation streams are recirculated back to the recirculation compressor after leaving the heat exchanger. Attached Figure Description

[0009] Although the conclusions of this invention are those of the claims that the applicant considers to be their inventive content and clearly indicate the subject matter of the invention, it is believed that the invention will be better understood when considered in conjunction with the accompanying drawings, wherein:

[0010] Figure 1 This is a schematic process flow diagram of a cryogenic air separation unit capable of operating at medium pressure and featuring high nitrogen and high argon recovery; and

[0011] Figure 2 It is constructed to be with Figure 1A partial schematic process flow diagram of a nitrogen liquefaction unit that integrates a low-temperature air separation unit. Detailed Implementation

[0012] The system and method disclosed in this invention provide cryogenic separation of air in a medium-pressure air separation unit with an integrated nitrogen liquefaction unit, characterized by very high nitrogen recovery, high argon recovery, and configured to operate efficiently in liquid nitrogen-free mode, low liquid nitrogen mode, and high liquid nitrogen mode.

[0013] As discussed in more detail below, the disclosed cryogenic air separation unit comprises a three-tower arrangement, and achieves high argon and nitrogen recovery by condensing the argon-rich stream using a portion of the high-purity oxygen-enriched stream taken from the low-pressure tower or a lower-purity oxygen-enriched stream taken from the low-pressure tower as the condensing medium in the argon condenser. The oxygen-enriched vapor from the argon condenser is then used as a purge gas to regenerate the adsorbent bed in the adsorption-based pre-purifier unit. The disclosed air separation system and method are further capable of limited oxygen production and variable liquid nitrogen production as described in the following paragraphs.

[0014] Nitrogen, argon and oxygen recovery in medium-pressure air separation unit

[0015] Go to Figure 1 A schematic diagram of a cryogenic air separation unit 10 that generates argon and nitrogen with high nitrogen recovery and argon recovery is shown.

[0016] In a broad sense, the air separation unit described includes a main feed air compressor unit or system 20, a turbine air circuit 30, an optional booster air circuit 40, a primary heat exchanger system 50, and a distillation column system 70. As used herein, the main feed air compressor unit, the turbine air circuit, and the booster air circuit together constitute the “hot end” air compression circuit. Similarly, portions of the main heat exchanger, the turbine-based refrigeration circuit, and the distillation column system are referred to as “cold end” equipment, typically housed in an insulated cold box.

[0017] exist Figure 1In the main feed compressor unit shown, the incoming feed air 22 is typically drawn through an air intake filter housing (ASFH) and compressed in a multi-stage intercooled main air compressor arrangement 24 to a pressure between about 6.5 bar(a) and about 11 bar(a). The main air compressor arrangement 24 may include integral geared compressor stages or direct-drive compressor stages arranged in series or parallel. The compressed air stream 26 exiting the main air compressor arrangement 24 is fed to an aftercooler (not shown) with an integrated demister to remove free moisture from the incoming feed air stream. The heat of compression from the final compression stage of the main air compressor arrangement 24 is removed in the aftercooler by cooling the compressed feed air with cooling tower water. Condensate from this aftercooler and some of the intercoolers in the main air compressor arrangement 24 is preferably delivered to a condensate tank and used to supply water to other parts of the air separation unit.

[0018] The cooled and dried compressed air stream 26 is then purified in a pre-purification unit 28 to remove high-boiling-point contaminants from the cooled and dried compressed air feed. As is well known in the art, the pre-purification unit 28 typically comprises two beds of alumina and / or molecular sieves operating according to a temperature-switching adsorption cycle in which moisture and other impurities (such as carbon dioxide, water vapor, and hydrocarbons) are adsorbed. One of these beds is used to pre-purify the cooled and dried compressed air feed, while the other bed is preferably regenerated using a portion of waste nitrogen from an air separation unit. The two beds periodically exchange functions. In a dust filter located downstream of the pre-purification unit 28, particles are removed from the compressed, pre-purified feed air to generate a compressed, purified air stream 29.

[0019] The compressed and purified air stream 29 is separated into oxygen-rich, nitrogen-rich, and argon-rich fractions in multiple distillation columns, including a high-pressure column 72, a low-pressure column 74, and an argon column 129. However, prior to this distillation, the compressed and pre-purified air stream 29 is typically split into multiple feed air streams, which may include a boiler air stream and a turbine air stream 32. The boiler air stream may be further compressed in a booster compressor arrangement, then cooled in an aftercooler to form a booster air stream 360, which is then further cooled in a main heat exchanger 52. Preferably, the cooling or partial cooling of the air stream is accomplished in the main heat exchanger 52 by indirect heat exchange with a heated stream including oxygen streams 197, 386 and a nitrogen stream 195 from the distillation column system 70, to produce a cooled feed air stream.

[0020] The partially cooled feed airflow 38 expands in turbine 35 to produce an exhaust flow 64 directed to low-pressure tower 74. A portion of the cooling for air separation unit 10 is also typically generated by turbine 35. A fully cooled airflow 47, along with a high-pressure airflow, is introduced into high-pressure tower 72. Optionally, a small portion of the air flowing in turbine air circuit 30 is not extracted from the turbine feed flow 38. An optional booster flow 48 is extracted at the cold end of heat exchanger 52, causing it to condense completely or partially, reducing its pressure in valve 49, and feeding it into high-pressure tower 72 several stages from the bottom. Flow 48 is utilized only when the pumped oxygen flow 386 is sufficiently high.

[0021] The main heat exchanger 52 is preferably a brazed aluminum plate-fin heat exchanger. Such heat exchangers are advantageous because they have a compact design, high heat transfer rates, and the ability to handle multiple flows. They are manufactured as fully brazed and welded pressure vessels. For small air separation units, a heat exchanger with a single core may be sufficient. For larger air separation units handling higher flow rates, the heat exchanger may be constructed from several cores that must be connected in parallel or series.

[0022] Turbine-based refrigeration circuits, often referred to as lower tower turbine (LCT) or upper tower turbine (UCT) arrangements, are used to provide refrigeration to dual-tower or triple-tower cryogenic air distillation systems. Figure 1 In the illustrated UCT arrangement, the compressed and cooled turbine airflow 32 is preferably at a pressure between about 6 bar(a) and about 10.7 bar(a). The compressed and cooled turbine airflow 32 is directed to or introduced into the main heat exchanger or primary heat exchanger 52, where the compressed and cooled turbine airflow is partially cooled to a temperature between about 140 K and about 220 K to form a partially cooled and compressed turbine airflow 38, which is introduced into the turbine 35 to produce a cold exhaust flow 64, which is then introduced into the low-pressure column 74 of the distillation column system 70. The supplemental cooling generated by the expansion of the flow 38 is thus applied directly to the low-pressure column 72, thereby relieving some of the cooling load on the main heat exchanger 52. In some embodiments, the turbine 35 may be coupled to a booster compressor 34 for further compression of the turbine airflow 32, either directly or via a suitable gear mechanism.

[0023] Although Figure 1The turbine-based refrigeration circuit shown is illustrated as an upper column turbine (UCT) circuit (where turbine exhaust flow is directed to a low-pressure column), but it is conceivable that a turbine-based refrigeration circuit could alternatively be a lower column turbine (LCT) circuit or a partial lower column turbine (PLCT) circuit (where expanded exhaust flow is fed to the high-pressure column 72 of the distillation column system 70). Furthermore, the turbine-based refrigeration circuit can be some variation or combination of LCT arrangements, UCT arrangements, and / or heat recirculation turbine (WRT) arrangements commonly known to those skilled in the art.

[0024] The aforementioned components (i.e., oxygen, nitrogen, and argon) of the incoming feed air stream are separated within a distillation column system 70 comprising a high-pressure column 72, a low-pressure column 74, an argon column 129, a condenser-reboiler 75, and an argon condenser 78. The high-pressure column 72 typically operates at a pressure between about 6 bar(a) and about 10 bar(a), while the low-pressure column 74 operates at a pressure between about 1.5 bar(a) and about 2.8 bar(a). The high-pressure column 72 and the low-pressure column 74 are preferably connected in a heat transfer relationship such that all or part of the nitrogen-rich vapor overhead distillate extracted as stream 73 from near the top of the high-pressure column 72 is condensed in the condenser-reboiler 75 located at the base of the low-pressure column 74 by the oxygen-rich liquid bottom distillate 77 residing at the bottom of the low-pressure column 74. The boiling of the oxygen-rich liquid bottom distillate 77 initiates the formation of an upward vapor phase within the low-pressure column 74. The condensation produces a liquid nitrogen-containing stream 81, which is divided into a clean shelf reflux stream 83 and a nitrogen-rich stream 85. The clean shelf reflux stream can be used to reflux into the low-pressure tower 74 to initiate the formation of a descending liquid phase in the low-pressure tower 74, and the nitrogen-rich stream is refluxed into the high-pressure tower 72.

[0025] The cooled feed air stream 47 is preferably a vapor air stream slightly above its dew point, but may be at or slightly below its dew point. This cooled feed air stream is fed into the high-pressure column, whereby distillation is achieved through mass transfer between the rising vapor phase and the descending liquid phase induced by the reflux stream 85 within multiple mass transfer contact elements (shown as tray 71). This produces a crude liquid oxygen column bottom distillate 86 (also called bottom liquid, which is taken out as stream 88) and a nitrogen-enriched column top distillate 89 (taken out as clean shelf liquid stream 83).

[0026] In the low-pressure column, the rising vapor phase comprises vaporized gas from the condenser-reboiler and exhaust stream 64 from turbine 35, which is subcooled in subcooling unit 99B and introduced as a vapor stream at the midpoint of low-pressure column 72. The descending liquid is initiated by nitrogen reflux stream 83, which is sent to subcooling unit 99A, where it is subcooled and then expanded in valve 96 before being introduced into low-pressure column 74 near the top of the column.

[0027] The low-pressure column 74 is also provided with multiple mass transfer contact elements, which can be trays, structured packing, or other known elements in the field of cryogenic air separation. These contact elements in the low-pressure column 74 are shown as structured packing 79. The separation occurring within the low-pressure column 74 produces an oxygen-enriched liquid bottom distillate 77, which is extracted as an oxygen-enriched liquid stream 377 with an oxygen concentration greater than 99.5%. The low-pressure column also produces a nitrogen-enriched vapor overhead distillate extracted as a gaseous nitrogen product stream 95.

[0028] The oxygen-enriched liquid stream 377 can be separated into a first oxygen-enriched liquid stream 380 pumped in pump 385, and the resulting pumped oxygen stream 386 is directed to the main heat exchanger 52, where it is heated to produce a high-purity gaseous oxygen product stream 390. A second portion of the oxygen-enriched liquid stream 377 is transferred to a second oxygen-enriched liquid stream 90. The second oxygen-enriched liquid stream 90 is preferably pumped via pump 180, then subcooled in subcooling unit 99B via indirect heat exchange with the oxygen-enriched waste stream 196, and then passed to the argon condenser 78, where it is used to condense the argon-enriched stream 126 taken from the top 123 of the argon column 129. Figure 1 As shown, a portion of the supercooled second oxygen-enriched liquid flow 90 or a portion of the first liquid oxygen flow can serve as a liquid oxygen product. However, as Figure 1 The extraction of liquid oxygen product 185, as shown, adversely affects the operational efficiency and recovery of argon and nitrogen from the air separation unit. Alternatively, some embodiments may extract a lower purity oxygen-enriched stream (not shown) from several stages of low-pressure towers above condenser 75, instead of using a portion of the high-purity oxygen-enriched stream as a condensing medium to condense the argon-enriched stream.

[0029] The vaporized oxygen stream from the argon condenser 78 is heated as an oxygen-enriched waste stream 196 within the subcooler 99B. The heated oxygen-enriched waste stream 197 is directed to the main heat exchanger or primary heat exchanger and then used as purge gas to regenerate the adsorption-based pre-purifier unit 28. Additionally, a waste nitrogen stream 93 can be extracted from a low-pressure column to control the purity of the gaseous nitrogen product stream 95. Preferably, the waste nitrogen stream 93 is combined with the oxygen-enriched waste stream 196 upstream of the subcooler 99B. Furthermore, in some cases, when there is more available oxygen than is required to operate the argon condenser 78, typically when argon production is reduced, a vaporized waste oxygen stream 97 may be necessary.

[0030] Liquid stream 130 is drawn from argon condenser container 120, passing through gel trap 370 and returning to or near the base of low-pressure tower 74. Gel trap 370 is used to remove carbon dioxide, nitrous oxide, and certain heavy hydrocarbons that might otherwise accumulate in the system. Alternatively, a small flow rate can be drawn from stream 130 as an exhaust stream from the system, thereby eliminating gel trap 140 (not shown).

[0031] Preferably, Figure 1 The argon condenser shown is a downflow argon condenser. The downflow configuration results in a smaller effective temperature difference (ΔT) between the condensing and boiling streams. As indicated above, a smaller ΔT leads to lower operating pressures within the argon column, low-pressure column, and high-pressure column, which translates into reduced power required to generate the various product streams and increased argon recovery. The use of a downflow argon condenser also allows for a potential reduction in the number of column stages, particularly for the argon column. From a capital perspective, the use of a downflow argon condenser is also advantageous, partly because pump 180 is already required in the air separation cycle disclosed in this invention. Furthermore, since liquid stream 130 provides a continuous liquid flow exiting the argon condenser housing, this liquid flow also provides the necessary wetting of the reboiling surfaces to prevent the argon condenser from 'drying up'.

[0032] The nitrogen product stream 95 is passed through subcooling unit 99A to subcool the nitrogen reflux stream 83 and the reactor liquid stream 88 via indirect heat exchange. As described above, the subcooled nitrogen reflux stream 83 expands in valve 96 and is introduced to the highest position of the low-pressure column 74, while the subcooled reactor liquid stream 88 expands in valve 107 and is introduced to the middle position of the low-pressure column 74. After passing through subcooling unit 99A, the heated nitrogen stream 195 is further heated in the main heat exchanger 52 to produce a heated gaseous nitrogen product stream 295.

[0033] The flow rate of the first oxygen-enriched liquid stream 380 can be up to about 20% of the total oxygen-enriched stream leaving the system. The argon recovery rate of this arrangement is between about 75% and 96%, which is greater than that of prior art medium-pressure air separation systems. (Although not shown, taken from the reference...) Figure 2 The nitrogen liquefier 500, or the liquid nitrogen stream 400 taken from an external source (not shown), can be combined with a second oxygen-enriched liquid stream 90 and a combined stream for condensing an argon-enriched stream 126 in an argon condenser 78 to enhance argon recovery.

[0034] With the addition of liquid nitrogen, the boiling refrigerant in the argon condenser is a mixture of liquid oxygen and liquid nitrogen, and is typically colder than the boiling refrigerants disclosed in the following U.S. patent application serial numbers: 15 / 962205; 15 / 962245; 15 / 962292; and 15 / 962358. As a result, the distillation column system pressure can naturally be lower. In other words, the cryogenic air separation unit, and specifically the compressor and distillation column system, can be designed to utilize this lower operating pressure, resulting in overall power savings. Alternatively, if it is not advisable to design the compressor and distillation column of the cryogenic air separation unit for the desired pressure range, the exhaust gas from the argon condenser can be back-pressurized at the hot end of the main heat exchanger. With this back-pressurization, the temperature of the boiling fluid in the argon condenser does not change, and the pressure of the distillation column system will also remain constant. This alternating back-pressurization method is a possible operating method for the cryogenic air separation unit if higher liquid oxygen production is desired infrequent or discontinuous.

[0035] Turn now Figure 2 The core of the improved cryogenic air separation unit is the integration of the liquefaction cycle into the main heat exchange system and cold box of the argon and nitrogen cryogenic air separation unit, which contains only gases. In this way, the integrated liquefaction unit can be a source of liquid nitrogen product for refilling or standby purposes, and can also be used to replace any liquid nitrogen removed from the shelf transfer lines in the distillation column system, ensuring that the nitrogen reflux to the low-pressure distillation column is the same as the nitrogen reflux in the case where the air separation cycle does not produce any liquid nitrogen at all. This ensures that the distillation column system performance in terms of argon and nitrogen recovery is substantially the same in high liquid nitrogen mode, low liquid nitrogen mode, and no (absent) liquid nitrogen mode.

[0036] exist Figure 2 The integrated nitrogen liquefaction unit 500 associated with the aforementioned air separation unit is shown in more detail. As seen therein, the nitrogen liquefaction unit preferably includes a nitrogen feed compressor 404, a nitrogen recirculation compressor 410, a hot booster compressor 420, a cold booster compressor 430, a hot turbine 425 loading the booster, a cold turbine 435 loading the booster, a heat exchanger 52, multiple aftercoolers 405, 411, 421, 431, and at least two valves, including a first flow control valve 403 and a second bypass valve 407.

[0037] The nitrogen feed compressor 404 is configured to receive a gaseous nitrogen feed stream 402 via a first flow control valve 403 and compress the gaseous nitrogen feed stream to produce a compressed gaseous nitrogen feed stream 406. The nitrogen recirculation compressor 410 is configured to receive the compressed gaseous nitrogen feed stream 406 from the nitrogen feed compressor 404 or a transferred gaseous nitrogen feed stream 409 via a second bypass valve 407, and further compress the received stream 408 to produce a further compressed hot nitrogen stream or discharge stream. The gaseous nitrogen feed stream 402 preferably comprises about 1% to 10% by volume of the gaseous nitrogen product stream 295, wherein the remainder of the gaseous nitrogen product stream 298 is delivered to the end-user customer as gaseous nitrogen product.

[0038] A hot booster compressor 420 is located downstream of the nitrogen recirculation compressor 410 and is configured to further compress the first portion 412 of the further compressed hot nitrogen stream to produce a further compressed cold nitrogen stream 422. A cold booster compressor 430 receives the cold nitrogen stream 422 and further compresses it to produce a primary nitrogen liquefaction stream 432, which is liquefied in a heat exchanger 52 to produce a liquid nitrogen product stream 400, which is preferably directed to a liquid nitrogen storage tank (not shown) or recirculated back to the distillation column system of the air separation unit.

[0039] A hot turbine 425, loaded with a booster, is operatively coupled to and driven by a hot booster compressor 420. The hot turbine 425 expands a second portion 414 of the further compressed hot nitrogen stream, which has been partially cooled in a heat exchanger 52 to produce a hot recirculation stream 428. A cold turbine 435, loaded with a booster, is operatively coupled to and driven by a cold booster compressor 430 and is configured to expand a transferred recirculation portion 434 of the primary nitrogen liquefaction stream 432, which has been partially cooled in the heat exchanger 52, to produce a cold recirculation stream 438. The heat exchanger 52 is further arranged to cool the primary nitrogen liquefaction stream 432 through indirect heat exchange with the hot recirculation stream 428 and the cold recirculation stream 438 to produce a liquid nitrogen product stream 400, while the hot recirculation stream 428 and the cold recirculation stream 438 return as a recirculation stream 440 to the recirculation compressor 410 after exiting the hot end of the heat exchanger 52.

[0040] The nitrogen liquefier 500 of the present invention is configured to operate in at least three different operating modes, including a first liquid nitrogen-free mode, wherein both the first flow control valve 403 and the second bypass valve 407 are oriented in the closed position, such that no portion of the gaseous nitrogen product stream 295 is transferred to the nitrogen liquefier, and no liquid nitrogen product stream is generated in the nitrogen liquefier. The second operating mode is a low liquid nitrogen mode, wherein the first flow control valve 403 is oriented in the closed position and the second bypass valve 407 is oriented in the open position, such that a portion of the gaseous nitrogen product stream 295 is transferred as a gaseous nitrogen feed stream 409 to the nitrogen recirculation compressor 410 and bypasses the nitrogen feed compressor 404. The third operating mode is a high liquid nitrogen mode, wherein the first flow control valve 403 is oriented in the open position and the second bypass valve 407 is oriented in the closed position, such that a portion of the gaseous nitrogen product stream 295 is transferred as a gaseous nitrogen feed stream 402 to the nitrogen feed compressor 404. In low liquid nitrogen operation mode, the portion of the gaseous nitrogen product stream transferred to the nitrogen recirculation compressor 410 by volume is between approximately 1% and 5% of the gaseous nitrogen product stream 295. However, in high liquid nitrogen operation mode, the portion of the gaseous nitrogen product stream 295 transferred to the nitrogen feed compressor 410 by volume is between approximately 5% and 10% of the gaseous nitrogen product stream 295.

[0041] In the absence of liquid nitrogen, the air separation unit can operate with the nitrogen liquefier completely shut off; however, this may require some liquid nitrogen to be added from the liquid nitrogen storage tank to the air separation unit's distillation column system to provide any necessary cooling.

[0042] In high liquid nitrogen mode, gaseous nitrogen feed stream 402 is fed into nitrogen feed compressor 404, where it is discharged at a pressure equal to that of nitrogen liquefaction recirculation stream 440. The further compressed discharge stream 406 from nitrogen feed compressor 404 mixes with recirculation stream 440 to form stream 408, which is further compressed to an intermediate pressure in recirculation compressor 410. The discharge stream from recirculation compressor 410 is split into two streams, including a first portion further compressed in series in both hot boost compressor 420 and cold boost compressor 430 before cooling in heat exchanger 52. The second portion 414 of the discharge stream is cooled midway through heat exchanger 52 and then expanded in hot turbine 425. Exhaust stream 428 from hot turbine returns to heat exchanger 52 at an intermediate location and mixes with the returning cold recirculation stream 438.

[0043] In low liquid nitrogen mode or liquid-lowering mode, the gaseous nitrogen feed stream 402 is diverted via bypass valve 407 and directed to the nitrogen recirculation compressor 410. In this low liquid nitrogen mode, the turbine machinery is maintained at a substantially constant pressure ratio and actual volumetric flow rate. To achieve this, the total head of the nitrogen liquid product stream is reduced while maintaining a substantially constant pressure ratio across the turbine until the recirculation stream 440 enters the recirculation compressor 410 at a pressure just above atmospheric pressure. In this low liquid nitrogen mode, a feed compressor is not required because the gaseous nitrogen feed stream 402 is at a higher pressure than the feed pressure to the recirculation compressor. In addition to reducing the total pressure in the nitrogen liquefaction unit, the recirculation flow rate is reduced until the volumetric flow rate through the compressor is equal to the volumetric flow rate under high liquid nitrogen conditions.

[0044] When using an integrated nitrogen liquefier, supplemental cooling is preferably provided by the integrated nitrogen liquefier, thus requiring almost no UCT arrangement. However, it is preferable to still install a UCT, and the air separation unit can operate in pure gas mode with the liquefier off (i.e., no liquid nitrogen mode), as described above.

[0045] From a heat exchanger perspective, the feed flow and / or heat exchange channels for both the nitrogen liquefaction unit and the main heat exchanger in an air separation unit can be integrated into a single core, or, in the case of a larger air separation unit, integrated into all cores. Alternatively, these two heat exchange functions can be separated or independent in cores of various possible configurations, depending on the size of the air separation unit and the total number of heat exchange cores required.

[0046] This is another hybrid operating mode, which will be referred to as Hybrid Mode 4. To reduce operating costs (i.e., power costs) in the process of producing only gaseous argon and nitrogen in the cryogenic air separation unit, the operator can alternately operate the air separation unit in a low liquid nitrogen mode (Mode 2) and a liquid nitrogen-free mode (Mode 1), where any required liquid nitrogen needed by the distillation column system is added from a liquid nitrogen tank or other liquid nitrogen source. During this liquid nitrogen-free mode, the liquid nitrogen tank is depleted and periodically refilled by switching the operating mode back to the low liquid nitrogen mode. With this switching technique between liquid nitrogen-free and low liquid nitrogen modes, the liquid nitrogen tank would have to be designed or sized with additional volume to allow for switching between the different operating modes.

[0047] Example

[0048] To demonstrate the practicality of the integrated liquefaction unit of the present invention, computer model simulations were performed to compare different operating modes of cryogenic air separation units for producing nitrogen and argon with integrated nitrogen liquefaction units as generally disclosed above. The operating parameters of the various air separation units were compared with those of a baseline cryogenic air separation unit for producing nitrogen and argon, generally shown and described in U.S. Patent Application Serial No. 15 / 962,358.

[0049] Table 1 presents data from computer model simulations for three different operating modes of the cryogenic air separation unit producing nitrogen and argon: a liquid nitrogen-free operating mode (Mode 1, referred to here as the non-liquid nitrogen mode); a low liquid nitrogen mode (Mode 2); and a high liquid nitrogen mode (Mode 3). To compare with a baseline air separation unit without a nitrogen liquefaction unit, the operating pressure, temperature, and flow rate of various feed streams are... Figure 2 The pressure ratios of the turbomachinery used in the nitrogen liquefaction unit shown are presented in a table.

[0050] For comparative purposes, the baseline system and all operating modes used similar inlet feed air conditions, approximately 53,000 Nm. 3 / h to 60,000 Nm 3 The flow rate was [flow rate] / h and the incoming compressed pre-purified air pressure was approximately 116.1 psia. As shown in Table 1, each different operating mode produced similar volumes of gaseous nitrogen and gaseous oxygen products compared to the baseline air separation unit. However, argon production increased compared to the baseline air separation unit when operating in the low liquid nitrogen mode (Mode 2) and high liquid nitrogen mode (Mode 3). In Mode 2, argon production increased by 2.5%, the incoming gas flow increased by only 1.8%, and the main air compressor (MAC) power consumption increased by 2.0%, while in Mode 3, argon production increased by approximately 12.4%, the incoming gas flow increased by 11.7%, and the main air compressor (MAC) power consumption increased by 12.0%.

[0051]

[0052]

[0053]

[0054] Table 1

[0055] More importantly, it can be predicted that liquid nitrogen production will be significantly increased when operating in both low liquid nitrogen mode (Mode 2) and high liquid nitrogen mode (Mode 3). Specifically, this is achieved when the first flow control valve is closed (see...). Figure 2 In mode 2 (low-pressure, low-liquid-nitrogen mode, i.e., liquid nitrogen reduction mode) of valve 403, the second bypass valve is open (see...). Figure 2 Valve 407), and the pressure of the gaseous nitrogen feed stream is from approximately 27.5 psia (see valve 407). Figure 2 The flow rate (402) decreased to approximately 16.5 psia (see [link]). Figure 2 The liquid nitrogen product production rate (in the flow 409) is approximately 750 Nm³ at a pressure of approximately 180 psia. 3 / h, while the nitrogen liquefaction unit consumes approximately 519kW of power. In contrast, when the first flow control valve opens (see... Figure 2 In mode 3 (high pressure, high liquid nitrogen operation mode) of valve 403, the second bypass valve is closed (see...). Figure 2 Valve 407 in the middle), and the pressure of the gaseous nitrogen feed stream is about 27.5 psia (see valve ...). Figure 2 The liquid nitrogen product production rate (in the flow 404) is approximately 4885 Nm³ at a pressure of approximately 750 psia. 3 / h, while the nitrogen liquefaction unit consumes 2467kW of power.

[0056] For comparison, the operating mode 1 shown in Tables 1 and 2 is the operating mode without liquid nitrogen, where the first flow control valve (see...) Figure 2 Valve 403) and the second bypass valve (see Figure 2 All valves (407) are closed. In this operating mode, a small amount of liquid nitrogen can be extracted from the air separation unit as a fraction of the nitrogen flow transferred to the subcooled shelf. Furthermore, as described above, the baseline mode represents the operation of a cryogenic air separation unit for the production of nitrogen and argon, as generally shown and described in U.S. Patent Application Serial No. 15 / 962,358.

[0057] Turning now to Table 2, a further comparison of the corresponding product output and power consumption between the operating modes 1 and 2 as described above and different anticipated operating modes 4, which switch between mode 1 and operating mode 2 over time based on local liquid nitrogen demand and power costs. For example, when utility power costs are high and / or the demand for liquid nitrogen is low, the operator may choose to operate in mode 1 (i.e., liquid nitrogen-free operating mode), while when utility power costs are low and / or there is some demand for liquid nitrogen, the operator may choose to operate the air separation unit in mode 2 (i.e., liquid nitrogen-lowering mode). Mode 4 represents a shared operating mode or an average of mode 1 and mode 2 operation.

[0058]

[0059] Table 2

[0060] As shown in the data and tables generated in the computer model simulation, the air separation unit for producing argon and nitrogen described above can operate in a pure gas product state mode or according to a high liquid nitrogen mode (i.e., LIN sprint mode or refill mode) or even in a low liquid nitrogen mode, without any performance loss in argon and nitrogen recovery rates from the distillation column system in any of these three modes.

[0061] Although the invention has been described with reference to one or more preferred embodiments, it should be understood that various additions, changes and omissions may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. An air separation unit, the air separation unit comprising: A main air compression system, which is configured to receive an incoming feed airflow and generate a compressed airflow; An adsorption-based pre-purifier unit is configured to remove water vapor, carbon dioxide, nitrous oxide and hydrocarbons from the compressed air stream and produce a compressed and purified air stream. A main heat exchange system configured to cool the compressed and purified air stream to a temperature suitable for fractionation; A distillation column system having a high-pressure column and a low-pressure column connected via a condenser-reboiler in a heat transfer relationship, the distillation column system further including an argon column arrangement operatively connected to the low-pressure column, the argon column arrangement having at least one argon column and an argon condenser, the distillation column system being configured to receive a cooled, compressed and purified air stream and generate at least two or more oxygen-enriched streams from the low-pressure column as well as generate an argon product stream and a gaseous nitrogen product stream; At least one of the oxygen-enriched streams from the low-pressure tower is an oxygen product stream, and at least one of the oxygen-enriched streams from the low-pressure tower is an oxygen-enriched condensing medium guided to the argon condenser. and A nitrogen liquefaction unit, comprising a nitrogen feed compressor, a nitrogen recirculation compressor, a hot booster compressor, a hot turbine loaded with a booster, a cold booster compressor and a cold turbine loaded with a booster, a flow control valve disposed upstream of the nitrogen feed compressor, and a bypass valve configured to transfer gaseous nitrogen feed to the nitrogen recirculation compressor; The nitrogen liquefaction unit is integrated with the main heat exchange system and the distillation column system, and the nitrogen liquefaction unit is arranged or configured to receive a portion of the gaseous nitrogen product stream and generate a liquid nitrogen product stream. The nitrogen liquefier is configured to operate in three modes, the three modes being: (i) a first non-liquid nitrogen mode, wherein the bypass valve and the flow control valve are closed such that no portion of the gaseous nitrogen product stream is transferred to the nitrogen liquefier and no liquid nitrogen product stream is generated in the nitrogen liquefier; (ii) a second low liquid nitrogen mode, wherein a portion of the gaseous nitrogen product stream is transferred to the nitrogen liquefier as the gaseous nitrogen feed stream, wherein the flow control valve is closed and the gaseous nitrogen feed stream bypasses the nitrogen feed compressor via the open bypass valve and is transferred to the nitrogen recirculation compressor; and (iii) a third high liquid nitrogen mode, wherein the bypass valve is closed and a portion of the gaseous nitrogen product stream is transferred to the nitrogen feed compressor of the nitrogen liquefier as the gaseous nitrogen feed stream via the open flow control valve.

2. The air separation unit of claim 1, wherein the nitrogen liquefaction unit further comprises wherein the bypass valve is an expansion valve configured to reduce the pressure of the gaseous nitrogen feed stream transferred to the nitrogen recirculation compressor.

3. The air separation unit according to claim 1, wherein the portion of the gaseous nitrogen product stream transferred to the nitrogen recirculation compressor section accounts for between 1% and 5% of the gaseous nitrogen product stream by volumetric flow rate.

4. The air separation unit according to claim 1, wherein the portion of the gaseous nitrogen product stream transferred to the nitrogen liquefaction unit accounts for between 5% and 10% of the gaseous nitrogen product stream.

5. The air separation unit according to claim 1, wherein: The argon column is configured to receive an argon-rich oxygen stream from the low-pressure column and to generate a third oxygen-rich stream that is returned to or released into the low-pressure column, as well as an argon-rich overhead distillate that is directed to the argon condenser; and The argon condenser is configured to condense the argon-rich column overhead distillate from the low-pressure column using the oxygen-rich condensing medium to produce a crude argon stream, an argon reflux stream, and an oxygen-rich waste stream.

6. The air separation unit of claim 5, wherein the argon condenser is configured to condense the argon-rich overhead distillate by means of a mixture of the oxygen-rich condensing medium and the liquid nitrogen source taken from the low-pressure column, to produce the crude argon stream, the argon reflux stream, and the oxygen-rich waste stream.

7. The air separation unit according to claim 6, wherein the liquid nitrogen source is a portion of the liquid nitrogen product stream taken from the nitrogen liquefaction unit.

8. The air separation unit of claim 5, wherein the oxygen-rich waste stream is heated in the main heat exchange system and used to regenerate the adsorption-based pre-purification unit.

9. The air separation unit of claim 8, wherein the oxygen-rich waste stream is further compressed upstream of the adsorption-based pre-purification unit.

10. A nitrogen liquefaction unit, said nitrogen liquefaction unit being configured to be integrated with a cryogenic air separation unit that generates argon and nitrogen, said nitrogen liquefaction unit comprising: The gaseous nitrogen product stream generated by the cryogenic air separation unit and the gaseous nitrogen feed stream, which accounts for 1% to 10% of the gaseous nitrogen product stream by volume; A nitrogen feed compressor, the nitrogen feed compressor being configured to receive the gaseous nitrogen feed stream and compress the gaseous nitrogen feed stream via a flow control valve disposed upstream of the nitrogen feed compressor; A nitrogen recirculation compressor, the nitrogen recirculation compressor being configured to receive a compressed gaseous nitrogen feed stream from the nitrogen feed compressor or via a bypass valve, and to further compress the received stream to produce a further compressed hot nitrogen stream; A hot pressurization compressor, located downstream of the nitrogen recirculation compressor and configured to further compress a first portion of the further compressed hot nitrogen stream to produce a further compressed cold nitrogen stream; A cold booster compressor, configured to further compress the cold nitrogen stream to produce a primary nitrogen liquefaction stream; A hot turbine for loading a supercharger is operatively coupled to the hot supercharger compressor and configured to expand a second portion of the further compressed hot nitrogen stream to generate a hot recirculation stream. A cold turbine for loading a supercharger is operatively coupled to the cold supercharger compressor and configured to expand the recirculation portion of the primary nitrogen liquefaction stream and generate a cold recirculation stream. A heat exchanger configured to cool the primary nitrogen liquefaction stream by indirect heat exchange with the hot recirculation stream and the cold recirculation stream to produce a liquid nitrogen product stream; The hot recirculation stream and the cold recirculation stream are recirculated back to the recirculation compressor after leaving the heat exchanger; The nitrogen liquefaction unit is configured to operate in a first liquid nitrogen-free mode, wherein the flow control valve and the bypass valve are oriented in a closed position such that no portion of the gaseous nitrogen product stream is transferred to the nitrogen liquefaction unit and no liquid nitrogen product stream is generated in the nitrogen liquefaction unit. The nitrogen liquefaction unit is configured to operate in a second low liquid nitrogen mode, wherein the flow control valve is oriented in a closed position and the bypass valve is oriented in an open position, such that a portion of the gaseous nitrogen product stream is transferred as a gaseous nitrogen feed stream to the nitrogen recirculation compressor and bypasses the nitrogen feed compressor. as well as The nitrogen liquefier is configured to operate in a third high liquid nitrogen mode, wherein the flow control valve is oriented in the open position and the bypass valve is oriented in the closed position, such that a portion of the gaseous nitrogen product stream is transferred as a gaseous nitrogen feed stream to the nitrogen feed compressor.

11. The nitrogen liquefaction device of claim 10, wherein the heat exchanger is further configured to partially cool the second portion of the further compressed hot nitrogen stream and partially cool the recirculation portion of the primary nitrogen liquefaction stream.

12. The nitrogen liquefaction unit of claim 10, wherein the portion of the gaseous nitrogen product stream transferred to the nitrogen recirculation compressor section accounts for between 1% and 5% of the gaseous nitrogen product stream by volumetric flow rate.

13. The nitrogen liquefaction unit of claim 10, wherein the portion of the gaseous nitrogen product stream transferred to the nitrogen feed compressor section accounts for between 5% and 10% of the gaseous nitrogen product stream by volumetric flow rate.

14. A method for generating a liquid nitrogen product stream from an air separation unit, the method comprising the steps of: The incoming feed airflow is compressed in the main air compression system to produce a compressed airflow; The compressed air stream is purified in an adsorption-based pre-purifier unit to produce a compressed and purified air stream; The compressed and purified air stream is cooled to a temperature suitable for fractionation in the main heat exchange system; The distillation system fractionates a cooled, compressed, and purified air stream, the distillation system having a high-pressure column and a low-pressure column connected by a heat transfer relationship via a condenser-reboiler, the distillation system further including an argon column arrangement operatively connected to the low-pressure column, the argon column arrangement having at least one argon column and an argon condenser, the distillation system being configured to generate at least two or more oxygen-enriched streams from the low-pressure column and to generate an argon product stream and a gaseous nitrogen product stream; At least one of the oxygen-enriched streams from the low-pressure tower is an oxygen product stream, and at least one of the oxygen-enriched streams from the low-pressure tower is an oxygen-enriched condensing medium guided to the argon condenser. and A portion of the gaseous nitrogen product stream is liquefied in a nitrogen liquefaction unit, the nitrogen liquefaction unit including a nitrogen feed compressor, a nitrogen recirculation compressor, a hot booster compressor, a hot turbine with a booster, a cold booster compressor and a cold turbine with a booster, a flow control valve located upstream of the nitrogen feed compressor, and a bypass valve configured to transfer the gaseous nitrogen feed stream to the nitrogen recirculation compressor. The nitrogen liquefaction unit is integrated with the main heat exchange system and the distillation column system, and the nitrogen liquefaction unit is arranged or configured to receive a portion of the gaseous nitrogen product stream and generate a liquid nitrogen product stream. The nitrogen liquefier is configured to operate in three modes, the three modes being: (i) a first non-liquid nitrogen mode, wherein the bypass valve and the flow control valve are closed such that no portion of the gaseous nitrogen product stream is transferred to the nitrogen liquefier and no liquid nitrogen product stream is generated in the nitrogen liquefier; (ii) a second low liquid nitrogen mode, wherein a portion of the gaseous nitrogen product stream is transferred to the nitrogen liquefier as a gaseous nitrogen feed stream, wherein the flow control valve is closed and the gaseous nitrogen feed stream bypasses the nitrogen feed compressor via the open bypass valve and is transferred to the nitrogen recirculation compressor; and (iii) a third high liquid nitrogen mode, wherein the bypass valve is closed and a portion of the gaseous nitrogen product stream is transferred to the nitrogen feed compressor of the nitrogen liquefier as the gaseous nitrogen feed stream via the open flow control valve.

15. The method of claim 14, wherein the portion of the gaseous nitrogen product stream transferred to the nitrogen recirculation compressor section accounts for between 1% and 5% of the gaseous nitrogen product stream by volumetric flow rate.

16. The method of claim 14, wherein the portion of the gaseous nitrogen product stream transferred to the nitrogen liquefaction unit accounts for between 5% and 10% of the gaseous nitrogen product stream.

17. The method of claim 14, further comprising the step of: In the argon condenser, the oxygen-enriched overhead distillate is condensed from the oxygen-enriched condensing medium taken from the low-pressure column to produce a crude argon stream, an argon reflux stream, and an oxygen-enriched waste stream.

18. The method of claim 17, wherein the step of condensing the argon-rich overhead distillate in the argon condenser further comprises condensing the argon-rich overhead distillate in the argon condenser due to the oxygen-enriched condensing medium and liquid nitrogen source taken from the low-pressure column, to generate the crude argon stream, the argon reflux stream, and the oxygen-enriched waste stream.

19. The method of claim 18, wherein the liquid nitrogen source is a portion of the liquid nitrogen product stream taken from the nitrogen liquefaction unit.

20. The method of claim 17, further comprising the step of: The adsorption-based pre-purification unit is regenerated using the oxygen-enriched waste stream.

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