CN108474616B - Method and system for providing supplemental refrigeration to an air separation plant - Google Patents

Method and system for providing supplemental refrigeration to an air separation plant Download PDF

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Publication number
CN108474616B
CN108474616B CN201680078814.4A CN201680078814A CN108474616B CN 108474616 B CN108474616 B CN 108474616B CN 201680078814 A CN201680078814 A CN 201680078814A CN 108474616 B CN108474616 B CN 108474616B
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compressed
refrigeration
stream
air stream
feed air
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CN108474616A (en
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Z·徐
Y·罗
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Praxair Technology Inc
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Praxair Technology Inc
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04278—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using external refrigeration units, e.g. closed mechanical or regenerative refrigeration units
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04769—Operation, control and regulation of the process; Instrumentation within the process
    • F25J3/04812—Different modes, i.e. "runs" of operation
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    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04078—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression
    • F25J3/0409—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression of oxygen
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
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    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04151—Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04187—Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams
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    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
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    • F25J3/04284—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/0429—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams of feed air, e.g. used as waste or product air or expanded into an auxiliary column
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    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
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    • F25J3/04284—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/0429—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams of feed air, e.g. used as waste or product air or expanded into an auxiliary column
    • F25J3/04296—Claude expansion, i.e. expanded into the main or high pressure column
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
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    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
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    • F25J3/04284—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/0429—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams of feed air, e.g. used as waste or product air or expanded into an auxiliary column
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
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    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04375—Details relating to the work expansion, e.g. process parameter etc.
    • F25J3/04381—Details relating to the work expansion, e.g. process parameter etc. using work extraction by mechanical coupling of compression and expansion so-called companders
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
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    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
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    • F25J3/04393—Details relating to the work expansion, e.g. process parameter etc. using multiple or multistage gas work expansion
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04406—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system
    • F25J3/04412—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04642—Recovering noble gases from air
    • F25J3/04648—Recovering noble gases from air argon
    • F25J3/04654—Producing crude argon in a crude argon column
    • F25J3/04666—Producing crude argon in a crude argon column as a parallel working rectification column of the low pressure column in a dual pressure main column system
    • F25J3/04672—Producing crude argon in a crude argon column as a parallel working rectification column of the low pressure column in a dual pressure main column system having a top condenser
    • F25J3/04678—Producing crude argon in a crude argon column as a parallel working rectification column of the low pressure column in a dual pressure main column system having a top condenser cooled by oxygen enriched liquid from high pressure column bottoms
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    • F25J3/04866—Construction and layout of air fractionation equipments, e.g. valves, machines
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Abstract

A method and system for cryogenic air separation employing both a primary refrigeration circuit and an auxiliary refrigeration circuit is provided. The auxiliary refrigeration circuit is configured in such a way that it can be easily accessed or modified to existing air separation plants.

Description

Method and system for providing supplemental refrigeration to an air separation plant
Technical Field
The present invention relates to a method and system for cryogenic air separation involving the production of liquid products by using an integrated refrigeration system comprising a primary refrigeration loop and an auxiliary refrigeration loop. More particularly, the present invention relates to an auxiliary refrigeration circuit that can be easily incorporated into existing cryogenic air separation plants and their existing refrigeration systems.
Background
Oxygen, nitrogen and argon are separated from air in an air separation plant by cryogenic rectification. Typically, the gaseous and/or liquid products are prepared for an on-site customer or pipeline customer, and any excess product tends to be converted to a commodity liquid product for a nearby customer. For some cryogenic air separation plants, the demand for gaseous products (such as gaseous oxygen or gaseous nitrogen) by field or pipeline customers may diminish over time, whether long-term or temporary or intermediate. To meet the lower gaseous product demand, cryogenic air separation plants can be operated to discharge some of the economically inefficient undesirable gaseous products, as such discharge ultimately wastes the power/energy costs for producing the discharged gaseous products. Alternatively, the air separation plant may be operated in a conditioning mode that produces less gaseous product, but less than the full plant capacity and separation efficiency. A third option is to adjust the product slate of the cryogenic air separation plant to produce more liquid product instead of the reduced gaseous product demand.
There have been a number of prior art cryogenic air separation processes designed to address this third option of producing additional liquid products to offset the need for gaseous product reduction. See, e.g., U.S. patent 6,125,656, U.S. patent 6,666,048, U.S. patent 6,945,076, and U.S. patent 8397535; and U.S. patent application publication 2010-0058805, U.S. patent application publication 2013-0192301, U.S. patent application publication 2007-0101763, and european patent publication EP1544559a 1. As shown in these prior art references, refrigeration must be provided to offset ambient heat leaks, warm end heat exchange losses and to allow extraction or production of liquid products, including liquid oxygen, liquid nitrogen or liquid argon, from one or more air separation units. The conventional or main refrigeration source for the cryogenic rectification plant is typically supplied by a turbine-based refrigeration system that is capable of expanding a portion of the feed air stream or waste stream to form a refrigeration stream that is then introduced into the main heat exchanger or distillation column system of the cryogenic air separation plant. The supplemental refrigeration required to produce additional liquid product may be supplied with additional turbine-based refrigeration sources. Such additional turbine-based refrigeration systems involve additional capital costs and are often not optimized or fully integrated with the primary refrigeration source of the cryogenic air separation plant.
What is needed is an improvement over these prior art supplemental liquid manufacturing solutions that enables additional liquid manufacturing systems to be configured as additional functions of an air separation plant that can be easily added to a cryogenic air separation plant/unit after initial plant construction. Such additional supplemental liquid manufacturing functions should be integrated with the main refrigeration source of the cryogenic air separation plant and must also have both high efficiency and operational flexibility. In other words, the supplemental or auxiliary refrigeration system should be able to and allow the apparatus to easily switch between the high liquid production cycle and the original high gaseous product production cycle. Finally, the additional supplemental or auxiliary refrigeration system should be portable and preferably skid mounted.
Disclosure of Invention
The invention may be characterized as a method of separating air in an air separation unit. The air separation unit preferably comprises a main heat exchanger configured to cool the compressed and purified feed air stream to a temperature suitable for rectification and a distillation column system configured to rectify the compressed, purified and cooled air stream to produce at least one liquid product stream. In such an air separation unit, the method comprises the steps of: (a) compressing and purifying a feed air stream to produce a compressed and purified feed air stream; (b) transferring a first portion of the compressed and purified feed air stream to a first refrigeration loop configured to produce a first cooled refrigeration stream; (c) diverting a second portion of the compressed and purified feed air stream to a main heat exchanger to cool the second portion of the compressed and purified feed air stream, and wherein the cooled second portion of the compressed and purified feed air stream is subsequently directed into a higher pressure column of a distillation column system; (d) diverting a third portion of the compressed and purified feed air stream to a charge air compression circuit configured to prepare a further compressed feed air stream, and wherein the portion of the further compressed feed air stream is directed to a main heat exchanger where the further compressed feed air stream is cooled to prepare a liquid air stream that is directed to a distillation column system; (e) diverting a fraction of the further compressed feed air stream from the charge air compression circuit to an auxiliary refrigeration circuit configured to produce a second refrigeration stream, the auxiliary refrigeration circuit comprising a second turboexpander and an auxiliary heat exchanger; (f) transferring a fourth portion of the compressed and purified feed air stream to an auxiliary heat exchanger; (g) transferring part of the first refrigeration stream from the first refrigeration loop to an auxiliary heat exchanger, and heating the transferred part of the first refrigeration stream in the auxiliary heat exchanger via indirect heat exchange with the transferred fourth part of the compressed and purified feed air stream; (h) directing a fourth portion of the compressed and purified feed air stream exiting the auxiliary heat exchanger to a distillation column system; (i) directing the remaining portion of the first refrigeration stream to a lower pressure column of the distillation column system to impart a first portion of the refrigeration required by the distillation column system; and (j) directing the cooled second refrigeration stream to the higher pressure column of the distillation column system to impart a desired second portion of refrigeration to the distillation column system.
The invention can also be characterized as an air separation unit configured to produce at least one liquid product stream. Characterized in that the air separation unit comprises: (i) an inlet air compression and purification train configured to produce a compressed and purified feed air stream; (ii) a primary refrigeration circuit having a first turboexpander, the primary refrigeration circuit being operatively coupled to the intake air compression and purification train and configured to receive a first portion of the compressed and purified feed air stream and expand the first portion of the compressed and purified feed air stream in the first turboexpander to produce a first cooled refrigeration stream; (iii) a main heat exchanger operably coupled to the inlet air compression and purification train and configured to receive a second portion of the compressed and purified feed air stream and to cool the second portion of the compressed and purified feed stream to a temperature suitable for rectification of the compressed and purified feed air stream; (iv) a charge air compression circuit operably coupled to the inlet air compression and purification train and the main heat exchanger, the charge air compression circuit configured to receive a third portion of the compressed and purified feed air stream, further compress the third portion, and direct the further compressed third portion to the main heat exchanger to produce a liquid air stream; (v) a second turboexpander configured to receive the further compressed third portion of the fraction and expand the further compressed third portion of the fraction to produce a second refrigeration stream; (vi) an auxiliary heat exchanger operatively coupled to the inlet air compression and purification train, the charge air compression circuit, and the primary refrigeration circuit, the auxiliary heat exchanger configured to receive a fourth portion of the compressed and purified feed air stream and cool the fourth portion of the compressed and purified feed air stream via indirect heat exchange with the diverted portions of the second and first refrigeration streams; and (vii) a distillation column system operably coupled to the primary refrigeration loop, the charge air compression loop, and the auxiliary heat exchanger, the distillation column system configured to rectify, by a cryogenic rectification process, some or all of the first refrigeration stream, the second refrigeration stream, the liquid air stream, and the cooled second portion of the compressed and purified feed air stream to produce at least one liquid product stream.
In some embodiments, the first refrigeration loop may comprise a compressor for further compressing a first portion of the compressed and purified feed air stream; cooling means, such as an aftercooler and/or a main heat exchanger, configured to cool the further compressed first portion of the compressed and purified feed air stream; and a first turboexpander disposed within the first refrigeration circuit and configured to expand a further compressed first portion of the compressed and purified feed air stream to produce a first refrigeration stream. Similarly, the auxiliary refrigeration circuit may also include an auxiliary compressor and a cooling device.
Other embodiments contemplate transferring the partially cooled portion of the second refrigeration stream from the auxiliary refrigeration circuit to the first refrigeration circuit, and mixing the transferred portion with the first portion of the compressed and purified feed air stream in the first refrigeration circuit.
Finally, in some embodiments employing a multi-stage compression system within the charge air compression circuit, transferring the fraction of the further compressed feed air stream to the auxiliary refrigeration circuit preferably further comprises transferring one or more fractions of the third portion of the compressed and purified feed air stream from one or more interstage locations of the plurality of compression stages to the auxiliary refrigeration circuit. One or more flow control valves are interposed between the charge air compression circuit and the second turboexpander in the auxiliary refrigeration circuit to control the flow of the diverted one or more fractions and the inlet pressure into the second turboexpander in the auxiliary refrigeration circuit.
Drawings
While the applicants regard the present invention as their summary and distinctly claim the subject matter of the invention, it is believed that the invention will be better understood when considered in connection with the accompanying drawings, wherein:
FIG. 1 is a schematic process flow diagram of a cryogenic air separation plant integrated with an additional supplemental or auxiliary refrigeration circuit in accordance with the present invention; and is
Fig. 2 is a schematic process flow diagram of a cryogenic air separation plant also integrated with an alternative embodiment of an additional supplemental or auxiliary refrigeration circuit in accordance with the present invention.
Detailed Description
Referring to fig. 1-2, the air separation unit 10 generally includes an inlet air compression and purification train or circuit (not shown); a primary refrigeration circuit 20; a charge air compressor train or circuit 30; a primary heat exchanger 40; and a distillation column system 50.
The feed air is compressed in a multi-stage intercooled main air compressor arrangement to a pressure which may be between about 5 bar (a) and about 15 bar (a) in an inlet air purification and compression train or circuit. The main air compressor arrangement may be an integrally geared compressor or a direct drive compressor arrangement. The compressed air feed is then purified in a pre-purification unit to remove high boiling contaminants from the feed air. As is well known in the art, prepurification units typically contain beds of alumina and/or molecular sieves operating according to a temperature and/or pressure swing adsorption cycle in which water and other impurities (such as carbon dioxide, water vapor and hydrocarbons) are adsorbed.
As described in detail below, compressed and purified feed air stream 12 is divided into portions, which are further compressed and/or cooled. Different portions of the compressed and purified air stream are then separated into oxygen-rich, nitrogen-rich and argon-rich fractions in a plurality of distillation columns, including distillation column system 50. Preferably, distillation column system 50 may include a thermally linked higher pressure column 54 and a lower pressure column 56, and an optional argon rectification column 58.
Prior to such distillation, however, a portion of the compressed and purified feed air stream 12 may be further compressed and/or cooled in a charge air compressor train or circuit 30 to a temperature suitable for rectification within a primary or main heat exchanger 40 cooling is typically accomplished by refrigeration using the various oxygen, nitrogen and/or argon gas streams produced by the air separation unit 10 and refrigeration formed by one or more refrigeration circuits, often due to turboexpansion of the various air streams in an Upper Column Turbine (UCT) arrangement, a lower column turbine (L CT) arrangement, and/or a thermal cycle turbine (WRT) arrangement as is known to those skilled in the art.
Air separation unit with primary and auxiliary refrigeration circuits
Turning now to fig. 1, there is illustrated an embodiment of the present invention comprising a plurality of separate portions of a compressed and purified feed air stream. A first portion 13 of the compressed and purified feed air stream resulting from the compression and pre-purification of the incoming feed air is diverted to a first or primary refrigeration circuit 20, which is shown as an Upper Column Turbine (UCT) arrangement configured to produce a first cooled refrigeration stream 22. Preferably, within the first or primary refrigeration loop 20, the first portion 13 of the compressed and purified feed air stream is further compressed in compressor 24 and cooled in aftercooler 25 and/or main heat exchanger 40. The compressed and cooled (or partially cooled) stream is then expanded in a first turboexpander 26 to produce a first refrigerant stream 22. As described in detail below, a portion of the first refrigeration stream is directed to the low pressure column, while a second portion of the first refrigeration stream is diverted to an auxiliary or second refrigeration loop 60.
The second portion 15 of the compressed and purified feed air stream is directed or diverted to the primary heat exchanger 40 to cool this portion of the compressed and purified feed air stream. The resulting cooled second portion 42 of the compressed and purified feed air stream is then directed to a higher pressure column 54 of a distillation column system 50, as is well known in the art and practiced in many cryogenic air separation units.
Additionally, a third portion 17 of the compressed and purified feed air stream is diverted to a charge air compression circuit 30 configured to produce a further compressed high pressure feed air stream 32. As shown, the charge air compression circuit 30 employs a charge air compressor arrangement 33 having a plurality of compression stages with intercoolers and aftercoolers 31, and forming a high pressure air stream 32 that is supplied to a main heat exchanger 40. After cooling in the main heat exchanger, the high pressure air stream forms a liquid phase or dense fluid if its pressure exceeds a critical pressure. The liquid air stream 34 is then split into two portions 35, 36, with the first portion 35 being directed through an expansion valve 37 and into a higher pressure column 54 of the distillation column system 50, and the second portion 36 being expanded through another expansion valve 38 and introduced into a lower pressure column 56 of the distillation column system 50.
As shown in fig. 1, fractions 62A, 62B of the third portion 17 of the compressed and purified feed air stream are further transferred from the charge air compression circuit 30 to the auxiliary refrigeration circuit 60, which is configured to produce a second refrigeration stream 66. The auxiliary refrigeration circuit 60 preferably includes an auxiliary compressor 63, a second turboexpander 64 and an auxiliary heat exchanger 65. This fraction 62A, 62B of the further compressed feed air stream from the charge air compression circuit 30 is diverted to the auxiliary compressor 63 via one or more flow control valves 67A, 67B where the diverted fraction stream is further compressed (as stream 61), optionally cooled or partially cooled, and then expanded in the turboexpander 64. After expansion in the turboexpander 64, the diverted fraction stream is then cooled in an auxiliary heat exchanger 65 via indirect heat exchange with one or more cooling streams, preferably the diverted portion of the first refrigeration stream 28, to produce a cooled second refrigeration stream 66 leaving the auxiliary heat exchanger 65 and the heating stream 29. The cooled second refrigerant stream 66 is then mixed with the cooled second portion 34 of the compressed and purified feed air stream and the resulting mixed stream 68 is then directed to the higher pressure column 54 to impart the other or second portion of the refrigeration required by the distillation column system 50. As briefly discussed above, a portion of the first refrigeration stream 22 is preferably diverted as a cooled stream 28 to the auxiliary heat exchanger 65 where it cools the diverted fraction 62A, 62B of the further compressed feed air stream in the auxiliary refrigeration loop 60. The remainder of the first refrigerant stream 22 is directed to the lower pressure column 56 to impart a portion of the refrigeration required by the distillation column system 50. In this arrangement, supplemental refrigeration generated by expansion of the first portion 13 of the compressed and purified air stream in the first or primary refrigeration circuit 20 is thus imparted in part to the lower pressure column 56 and in part to the auxiliary heat exchanger 65, thereby mitigating some of the cooling duty of the main heat exchanger 40.
This embodiment also shows a fourth portion 19 of the compressed and purified feed air stream, which may also be transferred as a carrier fluid from the incoming air purification and compression loop (not shown) to an auxiliary heat exchanger 65 where it is cooled and then directed to the higher pressure column 54 of the distillation column system 50 to capture auxiliary refrigeration. As shown, the cooled fourth portion 69 of the compressed and purified feed air stream can be mixed with the heated second refrigerant stream 66 and/or the cooled second portion 42 of the compressed and purified feed air stream exiting the main heat exchanger 40, with the resulting mixed stream 68 then being directed to the higher pressure column 54.
In a preferred embodiment, the first portion of the compressed and purified feed air stream directed to the primary refrigeration loop represents about 8% to 20% of the incoming feed air stream. In this first portion, 0% to 12% of the incoming feed air stream is diverted as a second portion to the auxiliary heat exchanger to balance the temperature in the auxiliary heat exchanger. Varying the amount of transfer air from the first refrigeration circuit to the auxiliary refrigeration circuit enables the air separation unit to be easily switched between a high gaseous product manufacturing cycle and a high liquid product manufacturing cycle.
The third portion of the compressed and purified feed air stream represents approximately 25% to 32% of the incoming feed air stream, with approximately 5% to 10% of the incoming feed air stream being diverted to the auxiliary refrigeration loop.
The second and fourth portions of the combined compressed and purified feed air stream represent the remaining portion of the incoming feed air stream, which is about 48% to 67% of the incoming feed air stream. The exact split between the second and fourth portions of the compressed and purified feed air stream depends on the heat exchange duty in the main and auxiliary heat exchangers.
The primary heat exchanger 40 and the secondary heat exchanger 65 are preferably brazed aluminum plate fin heat exchangers. Such heat exchangers are advantageous because they have a compact design, high heat transfer rates, and they are capable of handling multiple streams. They are manufactured as fully brazed and welded pressure vessels. The brazing operation involves stacking corrugated fins, separator sheets, and end rods to form a core matrix. The substrate is placed in a vacuum brazing furnace where it is heated and maintained at brazing temperature in a clean vacuum environment. For small devices, a heat exchanger with a single core may be sufficient. For higher flows, the heat exchanger may be constructed from several cores, which may be connected in parallel or in series.
The turbo- expanders 26 and 64 are preferably linked to the charge air compressors 24 and 63, respectively, either directly or through suitable gearing. Although not shown, the turboexpander may also be connected or operably coupled to an electrical generator. Such generator-loaded turboexpander arrangements allow the speed of the turboexpander to remain constant even at very high or low loads. This arrangement may be desirable in certain applications because the speed of the turboexpander will maintain a substantially constant desired efficiency throughout the operating range. In such an arrangement, the generator load may be connected to the turboexpander using a high speed generator. Alternatively, the generator load may be connected to the turboexpander using a high speed coupling connected to an internal or external gearbox and a low speed coupling from the gearbox to the generator.
Distillation column system 50 preferably includes a thermally linked higher pressure column 54 and a lower pressure column 56, and an optional argon rectification column 58. Within the column, vapor and liquid are countercurrently contacted to effect separation of the respective feed streams based on gas/liquid mass transfer. Such columns will preferably employ structured packing or trays or a combination thereof. The higher pressure column 54 is typically operated in the range of between about 20 bar (a) and about 60 bar (a), while the lower pressure column 56 is typically operated at a pressure of between about 1.1 bar (a) and about 1.5 bar (a).
As indicated above, the higher pressure column 54 and the lower pressure column 56 are linked in heat transfer relationship such that the nitrogen-rich vapor column overhead extracted as stream 71 from the top of the higher pressure column is condensed in the main condenser-reboiler 55 located at the base of the lower pressure column 56, rather than boiling the oxygen-rich liquid column bottoms 72. The boiling of the oxygen-rich liquid column bottoms 72 is initiated by the formation of an ascending vapor phase within the lower pressure column 56. The condensation produces a liquid nitrogen-containing stream 73 which is divided into streams 74 and 75 which reflux the higher pressure column 54 and the lower pressure column 56, respectively, to initiate the formation of a descending liquid phase in such columns. Stream 76 can also be recovered if a liquid nitrogen product is desired.
Streams 34,66 and 69 are introduced into higher pressure column 54 along with expanded liquid air stream 39 for rectification by contacting the ascending vapor phase of such mixture within a plurality of mass transfer contacting elements with the descending liquid phase induced by reflux stream 74. This produces a crude liquid oxygen column bottoms 77 (also referred to as kettle liquid) and a nitrogen-rich column overhead 78. Stream 79, representing a portion of nitrogen-rich column overhead 78, can be directed to main heat exchanger 40 to provide refrigeration to the feed air stream. Additionally, stream 101 of the crude liquid oxygen column bottoms 77 can be directed to the argon column 58 as reflux to assist in the recovery of argon product 93. Alternatively, although not shown, the stream at the bottom of the crude liquid oxygen column may be expanded in an expansion valve to a pressure at or near the pressure of the lower pressure column and introduced into the lower pressure column for further rectification.
The lower pressure column 56 is also provided with a plurality of mass transfer contacting elements which may be trays or structured packing or random packing or other elements known in the art of cryogenic air separation. As previously described, this separation produces an oxygen-rich liquid 80 and a nitrogen-rich vapor column overhead 82 that is extracted as a nitrogen product stream 84. In addition, a waste stream 85 is also extracted to control the purity of nitrogen product stream 84. Both nitrogen product stream 84 and waste stream 85 pass through subcooling unit 90, which is designed to subcool reflux stream 75. A portion of the reflux stream can optionally be considered liquid product stream 76 and the remaining portion (shown as stream 75B) can be introduced into lower pressure column 56 after passing through expansion valve 99.
After passing through subcooling unit 90, nitrogen vapor product stream 84 and waste stream 85 are fully heated within main heat exchanger 40 to produce a heated nitrogen product stream 94 and a heated waste stream 95. Although not shown, heated waste stream 95 can be used to regenerate the sorbent within the pre-purification unit. Additionally, an oxygen-enriched liquid stream 80 is withdrawn from the bottom 72 of the oxygen-enriched liquid column near the bottom of the lower pressure column 56. Oxygen-rich liquid stream 80 can be pumped by pump 83 to form a pumped product stream shown as pumped liquid oxygen stream 86. A portion of the pumped liquid oxygen stream 86 can optionally be withdrawn directly as liquid oxygen product stream 88, with the remainder, stream 87, being directed to main heat exchanger 40 where it is heated and vaporized to produce pressurized oxygen product stream 97. While only one such stream is shown, there may be multiple such streams fed into the primary heat exchanger 40. The pumped liquid oxygen stream 86 can be pressurized above or below the critical pressure so that the oxygen product stream 97 will be a supercritical fluid when discharged from the main heat exchanger 40. Alternatively, the pressurization of the pumped liquid oxygen stream 86 can be lower to produce the oxygen product stream 97 in vapor form.
Turning now to the illustrated embodiment of fig. 2, an alternative embodiment of an additional supplemental or auxiliary refrigeration circuit 60 is shown. Fig. 2 differs from fig. 1 in that all or a portion of the partially heated expanded working fluid 27 in the auxiliary refrigeration circuit 60 is circulated back to the first refrigeration circuit 20 at a location upstream of the first turboexpander 26. In this manner, the working fluid 27 undergoes two-stage expansion in a series arrangement. In other words, the turboexpander 64 of the auxiliary refrigeration circuit 60 is arranged in series with the turboexpander 26 of the first refrigeration circuit 20, and the resulting expanded working fluid is directed into the lower pressure column 56 and/or the auxiliary heat exchanger 65.
Another difference between the embodiment shown in fig. 2 and the embodiment shown in fig. 1 is in the auxiliary refrigeration loop 60. In the embodiment of fig. 2, all or a portion of the transferred fraction stream may optionally bypass the auxiliary compressor 63 and directly enter the second turboexpander 64 and continue to the auxiliary heat exchanger 65. When the flow control valve 67C is opened and the flow control valve 67D is closed, the mixed streams 62A and 62B are further compressed in the auxiliary compressor 63, then expanded in the second turbo expander 64, and heated in the auxiliary heat exchanger 65. Conversely, when flow control valve 67C is closed and flow control valve 67D is open, the mixed working fluid streams 62A and 62B bypass the auxiliary compressor 63 and are directed to the second turbo-expander 64 and then heated in the auxiliary heat exchanger 65. This arrangement allows the pressure of the working fluid in the auxiliary refrigeration circuit 60 to be regulated.
Integrating an auxiliary refrigeration circuit with an air separation unit
As indicated above, the air separation unit 10 is capable of producing liquid products, namely the nitrogen-rich liquid stream 76 and the liquid oxygen product stream 88. To increase the production of such liquid products, additional refrigeration is provided by an additional or auxiliary refrigeration loop. In the presently disclosed air separation unit or air separation plant, the additional refrigeration circuit is an auxiliary refrigeration circuit 60 that is preferably configured to be added to or bolted to the cryogenic air separation unit 10 after initial plant construction. Accordingly, the design of the auxiliary refrigeration circuit 60 is customized for such late-stage addition or retrofit applications and minimizes access points to the cryogenic air separation unit 10.
In the illustrated embodiment, there are four or five key access points between the cryogenic air separation unit 1 and the auxiliary or second refrigeration loop 60. The first access point 110 preferably occurs downstream of the main air compressor train or main circuit where the fourth portion 19 of the compressed and purified feed air stream 12 is diverted to an auxiliary or second refrigeration circuit, and more specifically to the auxiliary heat exchanger 65. The first access point 110 is configured to provide a carrier fluid (i.e., compressed and purified air) provided by auxiliary refrigeration from the auxiliary refrigeration circuit 60.
The second access point 120 is within the charge air compression circuit 30 and is configured to divert a fraction of the further compressed third portion of the compressed and purified stream to the auxiliary refrigeration circuit 60 as compressed streams 62A, 62B. The second access point 110 provides a working fluid (i.e., pressurized compressed air) that is to be expanded to provide a portion of the auxiliary refrigeration from the auxiliary refrigeration circuit 60.
The third access point 130 is located within the distillation column system 50 and is configured to return the cooled carrier fluid 69 (i.e., compressed and purified air) and the heated working fluid 66 (i.e., fully warmed, expanded working fluid) to the higher pressure column 54.
The fourth access point 140 is located within the first refrigeration circuit 20 and is configured to divert a portion 28 of the first refrigeration stream 22 to the auxiliary refrigeration circuit 60 where it provides further cooling or refrigeration to the carrier stream 19 via indirect heat exchange in the auxiliary heat exchanger 65.
A fifth access point 150 is also required in the embodiment shown in fig. 2. The fifth access point 150 is also located within the first refrigeration circuit 20 and is configured to return a portion of the partially heated, expanded working fluid 27 to the first refrigeration circuit 20 upstream of the first turboexpander 26.
Preferably, the supplemental or auxiliary refrigeration system is configured and constructed as a portable, skid-mounted refrigeration system that can be easily added to the cryogenic air separation plant/unit after initial plant construction in a manner that minimizes cold box entry. A preferred skid-mounted supplemental or auxiliary refrigeration system will include: (i) one or more auxiliary compressors 63; (ii) a heated second turboexpander 64; (iii) an auxiliary heat exchanger 65; (iv) associated pipes for the four to five access points; and (v) one or more control valves 67A, 67B, 67C and 67D configured to control the flow of air to the one or more auxiliary compressors 63, second turboexpanders 64 and auxiliary heat exchangers 65 as described above with reference to fig. 1 and 2. In some embodiments, some of the flow control valves 67A, 67B, 67C, and 67D configured to control the air flow to the one or more auxiliary compressors 63, second turbo-expanders 64, and auxiliary heat exchangers 65 may be configured as part of a cryogenic air separation plant, and where a skid-mounted supplemental or auxiliary refrigeration system is incorporated downstream of such control valves.
By controlling the flow to the supplemental or auxiliary refrigeration circuit via one or more flow control valves, the presently disclosed system can easily switch between a high gaseous product cycle (when the flow control valves are closed) and a high liquid product production cycle to produce more refrigeration and related liquid product production.
An advantage of the present system and method for providing supplemental refrigeration to a cryogenic air separation plant is that the amount of refrigeration and associated liquid product production can be increased in a cost-effective manner. The amount of refrigeration and liquid production produced is regulated by varying the pressure and flow of the heated turbine inlet in the supplemental or auxiliary refrigeration circuit. Regulation of the pressure and flow to the heated turbine inlet is achieved by selectively opening and/or closing one or more flow control valves 67A, 67B, 67C and 67D. The discharge stream from the heated second turboexpander passes through the auxiliary heat exchanger and is then directed to the higher pressure column (i.e., the cooled second portion of the compressed and purified feed air stream) along with the main air and the fourth portion of the compressed and purified feed air stream exiting the auxiliary heat exchanger.
Another advantage provided by the present systems and methods is that by transferring a portion of the first refrigeration stream from the primary refrigeration circuit to the auxiliary refrigeration circuit and thus bypassing the low pressure column separation, the gaseous oxygen product produced by the distillation column system is reduced, but argon recovery within the distillation column system can be maintained or possibly enhanced.
Furthermore, it is preferred to control the transfer of a portion of the first refrigeration stream to the auxiliary refrigeration circuit to balance the temperature in the auxiliary heat exchanger and maintain recovery in the auxiliary booster-turbine arrangement. The flow and pressure ratio within the primary refrigeration circuit is maximized. In this way, the upper column turbine arrangement acts more as a heat pump to improve the liquid making capacity of the cryogenic air separation plant.
Although the present invention has been discussed with reference to preferred embodiments, those skilled in the art will appreciate that various changes and omissions may be made therein without departing from the spirit and scope of the present invention as set forth in the appended claims.

Claims (15)

1. A method of separating air in an air separation unit comprising a main heat exchanger configured to cool a compressed and purified feed air stream to a temperature suitable for rectification and a distillation column system configured to rectify the compressed, purified and cooled air stream to produce at least one liquid product stream, the method comprising the steps of:
compressing and purifying a feed air stream to produce the compressed and purified feed air stream;
transferring a first portion of the compressed and purified feed air stream to a first refrigeration loop configured to produce a first refrigeration stream;
transferring a second portion of the compressed and purified feed air stream to the main heat exchanger to cool the second portion of the compressed and purified feed air stream, and wherein the cooled second portion of the compressed and purified feed air stream is subsequently directed to a higher pressure column of the distillation column system;
diverting a third portion of the compressed and purified feed air stream to a charge air compression circuit configured to produce a further compressed feed air stream and wherein a portion of the further compressed feed air stream is directed to the main heat exchanger where it is cooled to produce a liquid air stream that is directed to the distillation column system;
transferring a fraction of the further compressed feed air stream from the charge air compression circuit to an auxiliary refrigeration circuit configured to produce a second refrigeration stream, the auxiliary refrigeration circuit comprising a second turboexpander and an auxiliary heat exchanger;
transferring a fourth portion of the compressed and purified feed air stream to the auxiliary heat exchanger;
transferring a portion of the first refrigeration stream from the first refrigeration loop to the auxiliary heat exchanger, and heating the transferred portion of the first refrigeration stream in the auxiliary heat exchanger via indirect heat exchange with the transferred fourth portion of the compressed and purified feed air stream;
directing the fourth portion of the compressed and purified feed air stream exiting the auxiliary heat exchanger to the distillation column system;
directing the remaining portion of the first refrigeration stream to a lower pressure column of the distillation column system to impart a first portion of the refrigeration required by the distillation column system; and
directing a portion of the cooled second refrigeration stream to the higher pressure column of the distillation column system to impart a desired second portion of refrigeration to the distillation column system;
transferring a portion of the second refrigeration stream from the auxiliary refrigeration circuit to the first refrigeration circuit; and
mixing a diverted portion of the second refrigeration stream with the first portion of the compressed and purified feed air stream in the first refrigeration loop.
2. The method of claim 1, further comprising the steps of:
further compressing the first portion of the compressed and purified feed air stream within the first refrigeration loop;
cooling the further compressed first portion of the compressed and purified feed air stream; and
expanding the further compressed first portion of the compressed and purified feed air stream in a first turboexpander disposed within the first refrigeration loop to produce the first refrigeration stream.
3. The method of claim 2, wherein the step of cooling the further compressed first portion of the compressed and purified feed air stream further comprises: cooling the further compressed first portion of the compressed and purified feed air stream in an aftercooler.
4. The method of claim 2, wherein the step of cooling the further compressed first portion of the compressed and purified feed air stream further comprises: partially cooling the further compressed first portion of the compressed and purified feed air stream in the main heat exchanger.
5. The method according to claim 1, wherein the step of directing a cooled fourth portion of the compressed and purified feed air stream to the distillation column system further comprises: directing the cooled fourth portion of the compressed and purified feed air stream to the higher pressure column of the distillation column system.
6. The method of claim 2, further comprising the steps of:
transferring a portion of the second refrigeration stream partially cooled from the auxiliary heat exchanger in the auxiliary refrigeration circuit to the first refrigeration circuit; and
mixing a diverted portion of the second refrigeration stream with the first portion of the compressed and purified feed air stream in the first refrigeration loop upstream of the first turboexpander.
7. The method of claim 1, wherein the step of diverting a fraction of the further compressed feed air stream from the charge air compression circuit to the auxiliary refrigeration circuit further comprises:
further compressing the third portion of the compressed and purified feed air stream in a plurality of compression stages; and
transferring a first fraction of the third portion of the compressed and purified feed air stream from an interstage location of the plurality of compression stages to the auxiliary refrigeration circuit.
8. The method of claim 1, wherein the step of diverting a fraction of the further compressed feed air stream from the charge air compression circuit to the auxiliary refrigeration circuit further comprises:
further compressing the third portion of the compressed and purified feed air stream in a plurality of compression stages; and
transferring one or more fractions of the third portion of the compressed and purified feed air stream from one or more interstage locations of the plurality of compression stages to the auxiliary refrigeration circuit;
controlling the flow of the diverted one or more fractions of the third portion of the compressed and purified feed air stream with one or more flow control valves disposed in the auxiliary refrigeration circuit between the charge air compression circuit and the second turboexpander;
wherein the inlet pressure of the second turboexpander in the auxiliary refrigeration loop is controlled by adjusting the one or more flow control valves which in turn control the second portion of refrigeration required by the distillation column system.
9. The method of claim 1, wherein the auxiliary refrigeration circuit further comprises an auxiliary compressor, the second turboexpander, and the auxiliary heat exchanger, and wherein the method further comprises the steps of:
transferring said fraction of said further compressed feed air stream from said charge air compression circuit to said auxiliary compressor;
further compressing the diverted portion of the compressed feed air stream from the charge air compression circuit;
partially cooling the further compressed transferred fraction in the auxiliary heat exchanger via indirect heat exchange with the transferred portion of the first refrigeration stream;
expanding the partially cooled further compressed diverted fraction in the second turboexpander;
further cooling the expanded transferred fraction in the auxiliary heat exchanger via indirect heat exchange with the transferred portion of the first refrigeration stream to produce the cooled second refrigeration stream; and
said cooled second refrigeration stream is directed to said higher pressure column of said distillation column system to impart said second portion of refrigeration required by said distillation column system.
10. An air separation unit configured to produce at least one liquid product stream, the air separation unit comprising:
an intake air compression and purification train configured to produce a compressed and purified feed air stream;
a primary refrigeration circuit having a first turboexpander, the primary refrigeration circuit being operatively coupled to the intake air compression and purification train and configured to receive a first portion of the compressed and purified feed air stream and expand the first portion of the compressed and purified feed air stream in the first turboexpander to produce a first refrigeration stream;
a main heat exchanger operably coupled to the inlet air compression and purification train and configured to receive a second portion of the compressed and purified feed air stream and cool the second portion of the compressed and purified feed air stream to a temperature suitable for rectification of the compressed and purified feed air stream;
a charge air compression circuit operably coupled to the inlet air compression and purification train and the main heat exchanger, the charge air compression circuit configured to receive a third portion of the compressed and purified feed air stream, further compress the third portion, and direct the further compressed third portion to the main heat exchanger to produce a liquid air stream;
a second turboexpander configured to receive the further compressed third portion of the fraction and expand the further compressed third portion of the fraction to produce a second refrigerant stream; and
an auxiliary heat exchanger operatively coupled to the inlet air compression and purification train, the charge air compression circuit, and the primary refrigeration circuit, the auxiliary heat exchanger configured to receive a fourth portion of the compressed and purified feed air stream and cool the fourth portion of the compressed and purified feed air stream via indirect heat exchange with a diverted portion of the second and first refrigeration streams;
a distillation column system operably coupled to the primary refrigeration circuit, the charge air compression circuit, and the auxiliary heat exchanger, the distillation column system configured to rectify some or all of the first refrigeration stream, the second refrigeration stream, the liquid air stream, and the cooled second portion of the compressed and purified feed air stream by a cryogenic rectification process to produce the at least one liquid product stream; and
a recirculation loop connecting the auxiliary heat exchanger with the primary refrigeration loop, wherein a portion of the second refrigeration stream is recirculated to the primary refrigeration loop.
11. The air separation unit of claim 10, wherein the primary refrigeration circuit further comprises a compressor configured to further compress the first portion of the compressed and purified feed air stream within the primary refrigeration circuit; and wherein the compressor is operably coupled to the main heat exchanger such that the further compressed first portion of the compressed and purified feed air stream in the main heat exchanger is partially cooled.
12. The air separation unit of claim 10, wherein a cooled fourth portion of the compressed and purified feed air stream exiting the auxiliary heat exchanger is directed to a higher pressure column of the distillation column system.
13. The air separation unit of claim 10, wherein a portion of the second refrigeration stream is recycled to the primary refrigeration circuit, partially cooled within the auxiliary heat exchanger, and recycled to a location in the primary refrigeration circuit upstream of the first turboexpander.
14. The air separation unit of claim 10, further comprising an auxiliary refrigeration circuit including an auxiliary compressor configured to receive the portion of the further compressed feed air stream diverted from the charge air compression circuit, the second turboexpander configured to receive the compressed air stream from the auxiliary compressor and expand the compressed air stream, and the auxiliary heat exchanger configured to receive the expanded air stream from the second turboexpander.
15. The air separation unit of claim 14, wherein the charge air compression circuit further comprises a plurality of compression stages and a transfer circuit for transferring one or more fractions of the further compressed feed air stream from one or more interstage locations of the plurality of compression stages to the auxiliary refrigeration circuit.
CN201680078814.4A 2016-01-22 2016-08-26 Method and system for providing supplemental refrigeration to an air separation plant Active CN108474616B (en)

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