AU2010329766B2 - Process and unit for the separation of air by cryogenic distillation - Google Patents

Process and unit for the separation of air by cryogenic distillation Download PDF

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Publication number
AU2010329766B2
AU2010329766B2 AU2010329766A AU2010329766A AU2010329766B2 AU 2010329766 B2 AU2010329766 B2 AU 2010329766B2 AU 2010329766 A AU2010329766 A AU 2010329766A AU 2010329766 A AU2010329766 A AU 2010329766A AU 2010329766 B2 AU2010329766 B2 AU 2010329766B2
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low
pressure column
chamber
pressure
stream
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AU2010329766A1 (en
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Benoit Davidian
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Classifications

    • 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
    • F25J3/04436—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 at least a triple pressure main column system
    • F25J3/04454—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 at least a triple pressure main column system a main column system not otherwise provided, e.g. serially coupling of columns or more than three pressure levels
    • 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
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04048—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams
    • F25J3/04066—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams of oxygen
    • 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
    • F25J3/04151—Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04163—Hot end purification of the feed air
    • F25J3/04169—Hot end purification of the feed air by adsorption of the impurities
    • F25J3/04181—Regenerating the adsorbents
    • 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
    • F25J3/04151—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
    • F25J3/04193—Division of the main heat exchange line in consecutive sections having different functions
    • F25J3/04206—Division of the main heat exchange line in consecutive sections having different functions including a so-called "auxiliary vaporiser" for vaporising and producing a gaseous product
    • 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
    • F25J3/04284—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
    • F25J3/04309—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 nitrogen
    • 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
    • F25J3/04406—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
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/04—Mixing or blending of fluids with the feed stream
    • 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
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/42—Processes or apparatus involving steps for increasing the pressure of gaseous process streams the fluid being nitrogen
    • 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
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/40—Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
    • F25J2240/46—Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval the fluid being oxygen
    • 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
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/42—Processes or apparatus involving steps for recycling of process streams the recycled stream being nitrogen
    • 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
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/50—Processes or apparatus involving steps for recycling of process streams the recycled stream being oxygen
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/02—Bath type boiler-condenser using thermo-siphon effect, e.g. with natural or forced circulation or pool boiling, i.e. core-in-kettle heat exchanger
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/30—External or auxiliary boiler-condenser in general, e.g. without a specified fluid or one fluid is not a primary air component or an intermediate fluid
    • F25J2250/40—One fluid being air
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/30—External or auxiliary boiler-condenser in general, e.g. without a specified fluid or one fluid is not a primary air component or an intermediate fluid
    • F25J2250/50—One fluid being oxygen

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Emergency Medicine (AREA)
  • Separation By Low-Temperature Treatments (AREA)
  • Oxygen, Ozone, And Oxides In General (AREA)

Abstract

An air separation unit comprises a medium-pressure column (39), a low-pressure column (41), an enclosure (141), a heat exchanger (13), a bottom condenser (25) of the low-pressure column and a condenser (15) placed in the enclosure, a line for sending compressed, purified and cooled air from the heat exchanger to the medium-pressure column, a line for sending a heat-generating gas to the condenser placed in the enclosure, a line for sending a nitrogen-enriched gas from the medium-pressure column to the condenser of the low-pressure column, a line for sending an oxygen-enriched stream from the bottom of the medium-pressure column to the low-pressure column, a line for sending oxygen-rich liquid from the bottom of the low-pressure column to the enclosure, a line for withdrawing from the enclosure a fluid richer in oxygen than that sent to the enclosure, a line for sending a gas from the enclosure to the low-pressure column, and a line for withdrawing an overhead gas from the low-pressure column, characterized in that the unit includes an expansion means (51) for expanding the oxygen-rich liquid downstream of the bottom of the low-pressure column and upstream of the enclosure and a compressor (21) for compressing the gas from the enclosure, said compressor being downstream of the enclosure and upstream of the low-pressure column.

Description

Process and unit for the separation of air by cryogenic distillation The present invention relates to a process and to a unit for separating air by cryogenic distillation. It is known to separate air in a unit comprising one medium pressure column and two low-pressure columns operating at the same pressure, one of the low-pressure columns being fed at the ) top with the bottoms liquid from the other column and each low pressure column having a bottom condenser. One aspect of the invention is to reduce the separation energy for producing impure oxygen, in particular in the case where 5 there is no co-production of nitrogen. Another aspect of the invention is to reduce the cost of at least some elements of the unit. ) All the percentages relating to purities are molar percentages. The invention involves the use of a cold compressor for compressing an oxygen-rich gas, originating from a chamber operating at a pressure below that of the low-pressure column, '5 the gas being intended for the bottom of a low-pressure column. This makes it possible to decouple the pressure at the bottom of the medium-pressure column with the top of the low-pressure column. 0 The invention is particularly advantageous for the case where air partially condenses in the condenser of the chamber operating at lower pressure than the low-pressure column.
-2 The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these 5 matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. D Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, 5 integers, steps or components, or group thereof. According to one subject of the invention, a process is provided for separating air by cryogenic distillation, wherein: i) a stream of compressed and purified air is cooled in a 0 heat exchanger and sent to a column operating at medium pressure; ii) the stream of air is separated into a nitrogen-enriched stream and an oxygen-enriched stream; iii) a portion of the nitrogen-enriched stream is sent to a 25 low-pressure column; iv) at least one portion of the oxygen-enriched stream is sent to the low-pressure column; v) a nitrogen-rich stream is withdrawn from the top of the low-pressure column; 30 vi) an oxygen-rich stream is withdrawn from the bottom of the low-pressure column and sent to a chamber containing at least one condenser-reboiler; vii) a gaseous stream originating from the chamber is -3 withdrawn therefrom and sent back to the first low pressure column, preferably at the bottom; viii) a portion of the nitrogen-enriched stream from step ii) condenses at least partially in a condenser fed by 5 liquid originating from the low-pressure column and is sent to the medium-pressure column and/or the low pressure column; ix) a stream of warming gas, optionally at least one portion of the compressed, purified air that is cooled in the 3 heat exchanger from step i), condenses at least partially in the condenser-reboiler of the chamber; x) withdrawn from the chamber is a fluid that is richer in oxygen than the stream withdrawn from the bottom of the low-pressure column; 5 characterized in that the oxygen-rich stream withdrawn from the bottom of the low-pressure column is expanded upstream of the chamber and the gaseous stream from the chamber is pressurized upstream of the first low-pressure column. o Preferably: - the gaseous stream originating from the chamber is compressed in a compressor having an inlet temperature below -50 0 C, preferably no heating step takes place between the chamber and the compressor; 5 - the oxygen-rich stream withdrawn from the low-pressure column is expanded to a pressure at most 1 bar below the pressure at the bottom of the low-pressure column, preferably at most 0.5 bar, or even at most 0.2 bar below this pressure and/or the gaseous stream originating from the chamber is compressed 30 in order to increase its pressure by at most 1 bar, preferably at most 0.5 bar, or even at most 0.2 bar upstream of the low-pressure column; - 3a - the chamber does not contain any mass-exchange means, nor does it contain any packings or distillation plates; - the chamber constitutes a second low-pressure column and contains mass-exchange means, such as packings or i distillation plates, placed at least above the condenser. According to another subject of the invention, an air separation unit is provided comprising a medium-pressure column, a low-pressure column, a chamber, a heat exchanger, a ) condenser of the low-pressure column and a condenser placed in the chamber, a line for sending compressed, purified air that is cooled in the heat exchanger to the medium-pressure column, a line for sending a warming gas to the condenser placed in the chamber, a line for sending a nitrogen-enriched gas from the 5 medium-pressure column to the condenser of the low-pressure column, a line for sending an oxygen- WO 2011/070257 PCT/FR2010/052099 -4 enriched stream from the bottom of the medium-pressure column to the low-pressure column, a line for sending oxygen-rich liquid from the bottom of the low-pressure column to the chamber, a line for withdrawing from the 5 chamber a fluid that is richer in oxygen than that sent to the chamber, a line for sending a gas from the chamber back to the low-pressure column, a line for withdrawing an overhead gas from the low-pressure column, characterized in that it comprises an expansion 10 means for expanding the oxygen-rich liquid downstream of the bottom of the low-pressure column and upstream of the chamber and a compressor for compressing the gas from the chamber downstream of the chamber and upstream of the low-pressure column. 15 Optionally: - the chamber comprises mass-exchange means above the condenser; - the chamber does not comprise any mass-exchange means 20 above the condenser; - the unit comprises a turbine and a line for sending a nitrogen-rich gas from the medium-pressure column to the turbine; - the unit comprises a pump for pressurizing a stream 25 of liquid oxygen originating from the low-pressure column and/or from the chamber upstream of the heat exchanger. The invention will be described in greater detail with 30 reference to the figures, which represent units according to the invention. In figure 1, the air 1 is compressed between 3 and 5 bar in a compressor 3, purified in a purification 35 unit 5 and split in two. One portion 9 is cooled in the heat exchanger 13 and is sent to the bottom condenser 15 of a chamber 141 where it partially condenses before WO 2011/070257 PCT/FR2010/052099 -5 being sent to the medium-pressure column 39 of a double column. The double column comprises the medium-pressure column 5 39 and a low-pressure column 41 which surmounts it, the thermal link between the two columns being provided by a condenser 25 in the bottom of the low-pressure column 41. 10 The other portion of the air 7 is compressed in a compressor 11, cooled in the heat exchanger 13 and used for vaporizing pressurized liquid oxygen. As the oxygen is vaporized at a low pressure, the vaporization takes place in an external reboiler 27, different from the 15 heat exchanger 13. The liquefied air thus formed is sent to the medium-pressure column 39 after expansion in a valve 19. The liquid air may also be sent to the low-pressure column. 20 An oxygen-enriched liquid 17 is withdrawn from the bottom of the medium-pressure column 39, cooled in the heat exchanger 43, expanded in a valve and sent to the low-pressure column 41. A liquid 49 having substantially the composition of air is withdrawn at an 25 intermediate level of the medium-pressure column 39, cooled in the heat exchanger 43, expanded in a valve and sent to the low-pressure column 41. A nitrogen enriched liquid 47 is withdrawn from the top of the medium-pressure column 39, cooled in the heat exchanger 30 43, expanded in a valve and sent to the top of the low pressure column 41. A nitrogen-rich gas 45 is withdrawn from the top of the low-pressure column, heated in the heat exchanger 43 35 and then in the heat exchanger 13. A portion of this gas may be compressed in the compressor 35 in order to form the stream 37 that participates in the WO 2011/070257 PCT/FR2010/052099 -6 regeneration of the purification unit 5. A medium-pressure nitrogen stream 33 is withdrawn from the top of the medium-pressure column 39, heated in the 5 heat exchanger 13, expanded in the turbine 23 and heated again in the heat exchanger 13 before being used for the regeneration of the purification unit 5. An oxygen-rich stream 53 containing between 45 and 75% 10 of oxygen is withdrawn from the bottom of the low pressure column 41, expanded in a valve 51 and sent to the top of the chamber 141 which, in this variant, is a distillation column with a bottom condenser 15. Found above the condenser are heat- and mass-exchange means 15 143, for example structured or unstructured packings, or plates. The valve 51 only lowers the pressure of the liquid by 0.15 bar approximately. The liquid 53 is separated in the chamber in order to 20 form a liquid 29 that is richer in oxygen as bottoms. It is this liquid 29 that is sent to the reboiler 27 after pressurization in the pump 63. A purge liquid 61 is withdrawn from the reboiler 27. Alternatively, an oxygen-rich gas may be withdrawn from the chamber 141. 25 An overhead gas 145 is withdrawn from the chamber, compressed at the withdrawal temperature in a compressor 21 which increases its pressure by at most 0.15 bar. The gas produced is reinjected into the 30 bottom of the low-pressure column at the outlet pressure of the compressor 21. With a temperature difference in the heat exchanger 13 of 2 0 C at the hot end, a saving of around 2.5% is 35 obtained compared to the same layout without the cold compressor at the bottom of the low-pressure column.
Wo 2011/070257 PCT/FR2010/052099 -7 The unit from figure 2 differs from that from figure 1 in that the chamber 141 does not contain any packings or plates. There is also ascending partial condensation in the reboiler 15. Thus the difference in composition 5 between the liquid 53 sent to the chamber and the liquid 29 withdrawn from the chamber is very reduced even if the liquid 29 is however richer in oxygen than the liquid 53. The gas 145 is the gas produced by partial vaporization of the liquid 53 in the chamber 10 141 by heat exchange with the air 9. If the temperature difference at the hot end of the heat exchanger 13 is kept at 2 0 C, there is a saving of around 1.5% compared to the same layout without an LP 15 bottom cold compressor. An energy is obtained that is very slightly better than that of the process from WO-A-2007/129152 with the heat exchanger kept at 2 0 C at the hot end. Even if a cold 20 compressor is used in the two processes, in the variant of the invention the power of the cold compressor is ten times smaller than in the prior art variant and the nitrogen turbine is two times smaller. It is also observed that the compression ratio in the variant 25 according to the invention is very low and that a technology similar to a fan should suffice for the compressor 21: these elements make it possible to state that the cold compressor 21 and the turbine 23 will be less expensive than in the prior art process. 30 The cryogenic compression of a fluid that is relatively rich in oxygen should not pose a safety problem. The concept of compression of the vapor portion in the 35 low-pressure column may be extended to the case of layouts with three condensers in the low-pressure column, with one or two cold compressors to be placed WO 2011/070257 PCT/FR2010/052099 -8 between the three condensers of the low-pressure column.

Claims (18)

1. A process for separating air by cryogenic distillation, wherein: i) a stream of compressed and purified air is cooled in a heat exchanger and sent to a column operating at medium pressure; ii) the stream of air is separated into a nitrogen enriched stream and an oxygen enriched stream; ) iii) a portion of the nitrogen-enriched stream is sent to a low-pressure column; iv) at least one portion of the oxygen-enriched stream is sent to the low-pressure column; v) a nitrogen-rich stream is withdrawn from the top of 5 the low-pressure column; vi) an oxygen-rich stream is withdrawn from the bottom of the low-pressure column and sent to a chamber containing at least one condenser-reboiler; vii) a gaseous stream originating from the chamber is O withdrawn therefrom and sent back to the low pressure column; viii) a portion of the nitrogen-enriched stream from step ii) condenses at least partially in a condenser fed by liquid originating from the low-pressure column !5 and is sent to the medium-pressure column and/or the low-pressure column; ix) a stream of warming gas, optionally at least one portion of the compressed, purified air that is cooled in the heat exchanger from step i), condenses at least partially in the condenser reboiler of the chamber; x) withdrawn from the chamber is a fluid that is richer in oxygen than the stream withdrawn from the bottom of the low-pressure column; - 10 xi) wherein the oxygen-rich stream withdrawn from the bottom of the low-pressure column is expanded upstream of the chamber and the gaseous stream from the chamber is pressurized upstream of the first 5 low-pressure column.
2. The process as claimed in claim 1, wherein the gaseous stream originating from the chamber is withdrawn therefrom and sent back to the bottom of the low pressure ) column.
3. The process as claimed in claim 1 or claim 2, wherein the gaseous stream originating from the chamber is compressed in a compressor having an inlet temperature below -50 0 C. 5
4. The process as claimed in claim 3, wherein no heating step takes place between the chamber and the compressor.
5. The process as claimed in any one of the preceding D claims, wherein the oxygen-rich stream withdrawn from the low-pressure column is expanded to a pressure at most 1 bar below the pressure at the bottom of the low-pressure column and/or the gaseous stream originating from the chamber is compressed in order to increase its pressure 5 by at most 1 bar upstream of the low-pressure column.
6. The process as claimed in claim 5, wherein the low pressure column is expanded to a pressure at most 0.5 bar below the pressure at the bottom of the low-pressure 30 column.
7. The process as claimed in claim 6, wherein the low pressure column is expanded to a pressure at most 0.2 bar below the pressure at the bottom of the low-pressure - 11 column.
8. The process as claimed in any one of claims 5 to 7, wherein the gas stream originating from the chamber is 5 compressed in order to increase its pressure by at most 0.5 bar.
9. The process as claimed in claim 8, wherein the gas stream originating from the chamber is compressed in order to ) increase its pressure by at most 0.2 bar.
10. The process as claimed in any one of the preceding claims, wherein the chamber does not contain any mass exchange means, nor does it contain any packings or 5 distillation plates.
11. The process as claimed in any one of claims 1 to 9, wherein the chamber constitutes a second low-pressure column and contains mass-exchange means such as packings ) or distillation plates at least above the condenser.
12. An air separation unit comprising a medium-pressure column, a low-pressure column, a chamber, a heat exchanger, a condenser of the low-pressure column and a 5 condenser placed in the chamber, a line for sending compressed, purified air that is cooled in the heat exchanger to the medium-pressure column, a line for sending a warming gas to the condenser placed in the chamber, a line for sending a nitrogen-enriched gas from the medium-pressure column to the condenser of the low pressure column, a line for sending an oxygen-enriched stream from the bottom of the medium-pressure column to the low-pressure column, a line for sending oxygen-rich liquid from the bottom of the low-pressure column to the - 12 chamber, a line for withdrawing from the chamber a fluid that is richer in oxygen than that sent to the chamber, a line for sending a gas from the chamber back to the low pressure column, a line for withdrawing an overhead gas 5 from the low-pressure column, wherein it comprises an expansion means for expanding the oxygen-rich liquid downstream of the bottom of the low-pressure column and upstream of the chamber and a compressor for compressing the gas from the chamber downstream of the chamber and 2 upstream of the low-pressure column.
13. The unit as claimed in claim 12, wherein the chamber comprises mass-exchange means above the condenser. 5
14. The unit as claimed in claim 12, wherein the chamber does not comprise any mass-exchange means above the condenser.
15. The unit as claimed in any one of the preceding claims 12 to 14, comprising a turbine and a line for sending a 0 nitrogen-rich gas from the medium-pressure column to the turbine.
16. The unit as claimed in any one of claims 12 to 15, comprising a pump for pressurizing a stream of liquid 25 oxygen originating from the low-pressure column and/or from the chamber upstream of the heat exchanger.
17. The process as claimed in claim 1, substantially as hereinbefore described with reference to any one of the 30 Figures.
18. The unit as claimed in claim 12, substantially as hereinbefore described with reference to any one of the Figures.
AU2010329766A 2009-12-11 2010-10-05 Process and unit for the separation of air by cryogenic distillation Ceased AU2010329766B2 (en)

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FR0958880A FR2953915B1 (en) 2009-12-11 2009-12-11 METHOD AND APPARATUS FOR AIR SEPARATION BY CRYOGENIC DISTILLATION
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PCT/FR2010/052099 WO2011070257A1 (en) 2009-12-11 2010-10-05 Process and unit for the separation of air by cryogenic distillation

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ES2486260T3 (en) 2014-08-18
CN102652247A (en) 2012-08-29
AU2010329766A1 (en) 2012-07-05
WO2011070257A1 (en) 2011-06-16
FR2953915A1 (en) 2011-06-17
CA2782958A1 (en) 2011-06-16
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FR2953915B1 (en) 2011-12-02
CN102652247B (en) 2014-09-24

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