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EP2783176A2 - Process and apparatus for separating air by cryogenic distillation - Google Patents

Process and apparatus for separating air by cryogenic distillation

Info

Publication number
EP2783176A2
EP2783176A2 EP12806557.0A EP12806557A EP2783176A2 EP 2783176 A2 EP2783176 A2 EP 2783176A2 EP 12806557 A EP12806557 A EP 12806557A EP 2783176 A2 EP2783176 A2 EP 2783176A2
Authority
EP
European Patent Office
Prior art keywords
pressure
liquid
air
frequency
compressor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP12806557.0A
Other languages
German (de)
French (fr)
Inventor
Frédéric BONNE
Nicolas FOIRIEN
Alain Guillard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Original Assignee
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude filed Critical LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Publication of EP2783176A2 publication Critical patent/EP2783176A2/en
Withdrawn legal-status Critical Current

Links

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
    • 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
    • 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
    • F25J3/04012—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling
    • F25J3/04018—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling of main feed 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
    • 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
    • F25J3/04012—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling
    • F25J3/04024—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling of purified feed air, so-called boosted 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
    • 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
    • F25J3/04054—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 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
    • 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
    • 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
    • F25J3/04109—Arrangements of compressors and /or their drivers
    • F25J3/04115—Arrangements of compressors and /or their drivers characterised by the type of prime driver, e.g. hot gas expander
    • F25J3/04133—Electrical motor as the prime mechanical driver
    • 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
    • F25J3/0429—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
    • 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
    • F25J3/0429—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
    • 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
    • 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
    • F25J3/0446—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 the heat generated by mixing two different phases
    • F25J3/04466—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 the heat generated by mixing two different phases for producing oxygen as a mixing column overhead gas by mixing gaseous air feed and liquid 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/04—Processes or apparatus using separation by rectification in a dual pressure main column system
    • F25J2200/06—Processes or apparatus using separation by rectification in a dual pressure main column system in a classical double column flow-sheet, 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
    • F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
    • F25J2235/50—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being oxygen

Definitions

  • power grids are not sufficiently “strong” and meshed to avoid major disturbances in the frequency of their network during high demand or during hot weather, both of which are often concomitant.
  • Air separation devices (ASUs) on such networks are severely disrupted.
  • ASUs Air separation devices
  • the invention makes it possible, for example when the customer is a steel industry, to continue to produce the flow rate of oxygen and / or nitrogen requested, even during the important changes of frequency, while having a conservation of a good energy. specific on outgoing products.
  • the invention is also of particular interest in cases where the pressure of gas production by the separating apparatus is not the same as the pressure of use of the gas by the customer, for example, thanks to the presence interposed a buffer capacity.
  • US-A-5471843 discloses an air separation process in which the vapor pressure of liquid oxygen is reduced, if the oxygen demand is reduced. At the same time, it reduces the air flow to be treated but the motor is driven by a constant speed motor. Thus, the logical sequence of events is the opposite of that of our invention and is not conditioned by the observation of a decrease in frequency.
  • EP-A-1845323 describes an air separation process in which the vaporization pressure of the liquid oxygen is a function of the pressure of which the tank containing the vaporized oxygen. Neither the motorization of the compressor nor the regulation according to the frequency of the electricity are mentioned.
  • rich in oxygen means that the fluid contains at least 70 mol% of oxygen.
  • a flow of air is compressed in a compressor, is cooled by an exchange line and sent to a column system where it separates to form a nitrogen-enriched flow and an oxygen-enriched flow rate
  • the compressor is driven by a motor powered by electricity having a first frequency
  • a liquid flow is withdrawn from the column system, pressurized at a first pressure by a pump and vaporized by indirect heat exchange with air from the compressor to produce a gaseous product substantially at the first pressure; a case of a liquid flow rich in oxygen, sent at the first pressure to the head of an auxiliary column supplied in the tank with air coming from the compressor, oxygen gas being withdrawn at the top of the column as product and an intermediate liquid of the auxiliary column of the auxiliary column being sent to the column system.
  • the pressurization pressure of the liquid flow is reduced to a second pressure lower than the first pressure.
  • the compressor compresses air from the atmospheric pressure.
  • the compressor compresses air from a pressure greater than
  • the oxygen-rich liquid flow is sent at the first pressure to the head of the auxiliary column fed in the tank with air coming from the compressor, oxygen gas being drawn off at the top of the column as product and at least one liquid being sent from the auxiliary column to the column system.
  • the liquid flow rate has a flow rate V and if the frequency is lower than the given threshold lower than the first frequency at the first frequency the liquid flow rate at least equal to 0.9V, or even at least equal to at 0.95V or even equal to V.
  • the pressure of the pressurization of the liquid is lowered if the measured air flow passes below a threshold with respect to the air flow required to reach the nominal value of the liquid flow rate at the first pressurization pressure.
  • the pressurization pressure of the liquid is lowered if the measured air pressure falls below a threshold with respect to the air pressure required to reach the nominal value of the liquid flow rate at the first pressurization pressure.
  • the pressurization pressure of the liquid is reduced only by modifying the operation of the pressurizing pump.
  • the output pressure of the pump is equal to the vaporization pressure of the liquid pressurized by the pump.
  • the vaporized liquid serves as a product for the vaporization pressure without undergoing expansion downstream of the vaporization.
  • an air separation installation by cryogenic distillation comprising a compressor, an exchange line, a column system, an electric motor for driving the compressor, a pipe for withdrawing a column system liquid, a pump for pressurizing the withdrawn liquid and means for permitting direct or indirect heat exchange between compressed air by the compressor and the pressurized liquid, optionally the means also allowing a mass exchange if the pressurized liquid is rich in oxygen, characterized in that it comprises means for regulating the pressure of the pressurized liquid in the pump as a function of the frequency of the electricity supplying the electric motor.
  • the installation comprises:
  • means for regulating the pressure of the pressurized liquid by action of the control system on the flow and / or the outlet pressure of the pump means for measuring the frequency supplying the electric motor, the means for regulating the pressurization pressure of the liquid being able to be turned on if the frequency falls below a threshold.
  • a booster means for sending air from the compressor to the booster and booster to the exchange line, the booster being driven by the or a motor powered by electricity having one or frequency.
  • the separation apparatus comprises a compressor 100, an exchange line 4, a booster 7, a turbine 27, a pump 6 and a double distillation column 1 comprising a medium pressure column 2 and a low pressure column 3.
  • a double column could be replaced by a triple column or that other columns could be added such as a column of argon mixture etc.
  • the thermal coupling means shown is to heat the bottom of the low pressure column with nitrogen from the medium pressure column, but other means of thermal coupling can be envisaged.
  • the booster illustrated is a cold booster having an inlet temperature lower than that of the hot end of the exchange line 4.
  • the invention also applies to cases using a booster having an inlet temperature equal to or greater than that hot end of the exchange line 4.
  • Air is compressed in the compressor 100, which is driven by an electric motor powered by a source of electricity having a nominal frequency, for example 50Hz (in Europe) or 60Hz (in the United States).
  • the compressed air is cooled and purified to form the flow 19 and then sent to the exchange line 4.
  • the air cools in the exchange line and is then divided in two, a part 20 continuing to cool to the cold end of the exchanger and being sent to the medium pressure column 2 in gaseous form.
  • the rest of the air 21 is sent to a cold booster 7, is supercharged at high pressure and then returned to the exchange line as a flow 22.
  • Part of the pressurized air 23 is expanded in a turbine 27 and sent to the medium pressure column then that the rest of the supercharged air continues cooling to the cold end, is expanded in a valve 28 and sent to the medium pressure column.
  • Rich liquid 1 1 is sent from the tank of the medium pressure column via the valve 12 and the subcoolers 5A, 5B and liquid nitrogen 13 is sent to the top of the low pressure column 3 via the valve 14. the low pressure nitrogen is heated in the subcoolers 5A, 5B and the exchange line 4.
  • Liquid oxygen 16 is withdrawn in the bottom of the low pressure column 3, pressurized by the pump 6 and vaporized at a first high pressure in the exchange line 4.
  • the booster 7 is also driven by an electric motor M powered by an electric current.
  • the flow and / or the pressure of the compressed air may be insufficient to vaporize the oxygen at the first high pressure.
  • the pressurizing pressure of the pump 6 is reduced to vaporize the oxygen at a lower pressure.
  • the triggering of this pressure reduction can be done by measuring the frequency of electricity supplied to the motor and / or by measuring the compressed air flow 19, 22 and / or the pressure of the compressed air flow 19, 22.
  • the frequency and / or the flow rate and / or the pressure pass below a given threshold (of given thresholds)
  • the pressure of the oxygen can be reduced while keeping a production flow "close" to the nominal flow rate. .
  • the apparatus can still operate despite the reduced frequency, at the cost of producing vaporized oxygen at lower pressure.
  • the invention is also applicable to the vaporization of liquid nitrogen.
  • a flow of oxygen gas 37 is withdrawn at the top of the column 33 and heated in the exchanger 4.
  • An oxygen-enriched liquid 37 is withdrawn from the tank of the column 33, expanded in a valve 43 and sent to the lower column pressure 3. It is also necessary to withdraw a liquid 39 at an intermediate level of the auxiliary column 33, to relax in a valve 41 and send it to the column system.
  • the mixing column 33 operates at a reduced pressure, to compensate for the reduction in pressure of the air flow 31.
  • the reduction of the frequency for all the cases of application of the invention, can last a few minutes, a few hours or even a few days. It goes without saying that the decision to lower the pressure of pressurization will be made according to the needs of the customer and if a reduction of product due to the reduction of frequency can be tolerated, it will not be necessary necessarily to use the process of the 'invention.
  • the pressurization pressure is increased again by reversing the actions taken to reduce the pressure in case of frequency reduction.
  • the pressurized liquid flow will remain constant, regardless of the frequency, but a decrease of up to 5%, or even up to 10% of the flow at normal frequency can sometimes be tolerated.
  • the reduction of the pressurization pressure in the event of a drop in frequency can be triggered by detecting that an air flow to be separated decreases. Often a reduction with respect to the nominal flow rate can be compensated at least partially by adjusting the compressors.
  • the reduction of the pressurization pressure in the event of a drop in frequency can be triggered by detecting that the pressure of an air flow to be separated decreases. Often a reduction from the nominal pressure can be at least partially compensated by adjusting the compressors. On the other hand, at a given threshold below the nominal pressure, it will be necessary to proceed according to the invention since the regulation of the compressors can no longer suffice to fill the pressure drop.

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Abstract

The invention relates to an apparatus for separating air by cryogenic distillation comprising a compressor (100), an exchange line (4), a system of columns (1), an electric motor (M) for driving the compressor, a duct for extracting a liquid from the system of columns, a pump (6) for applying pressure to the extracted liquid, means enabling heat exchange between the air compressed by the compressor and the liquid (16) pressurized by the pump, and means for lowering the output pressure of the pump depending on the frequency of the electricity powering the electric motor.

Description

Procédé et installation de séparation d'air par distillation cryogénique  Process and installation of air separation by cryogenic distillation
Dans un certain nombre de pays, les réseaux électriques ne sont pas suffisamment « solides » et maillés pour éviter des perturbations importantes sur la fréquence de leur réseau lors de fortes demandes ou lors de grosses chaleurs, les deux étant d'ailleurs souvent concomitantes. In a number of countries, power grids are not sufficiently "strong" and meshed to avoid major disturbances in the frequency of their network during high demand or during hot weather, both of which are often concomitant.
Les appareils de séparation d'air (ASU) qui se trouvent sur de tels réseaux se trouvent fortement perturbés. Pour pouvoir continuer à produire aux spécifications demandées en terme de débit, pression, voire pureté sur l'oxygène comme sur l'azote, il est nécessaire lors de leur conception d'intégrer dans le choix des différentes machines ces contraintes de fréquence, ce qui est très pénalisant en terme de rendement du compresseur sur le point nominal même, plusieurs points de rendements peuvent être ainsi perdus, ce qui induit une mauvaise énergie spécifique sur les produits sortant de l'ASU.  Air separation devices (ASUs) on such networks are severely disrupted. In order to be able to continue to produce the required specifications in terms of flow rate, pressure, and even purity on oxygen and nitrogen, it is necessary during their design to integrate the frequency constraints into the choice of the different machines. is very penalizing in terms of compressor efficiency on the nominal point itself, several yield points can be lost and this leads to a bad specific energy on the products coming out of the ASU.
L'invention permet, par exemple lorsque le client est une industrie sidérurgique, de continuer de produire le débit d'oxygène et/ou d'azote demandé, même lors des changements importants de fréquence, tout en ayant une conservation d'une bonne énergie spécifique sur les produits sortants.  The invention makes it possible, for example when the customer is a steel industry, to continue to produce the flow rate of oxygen and / or nitrogen requested, even during the important changes of frequency, while having a conservation of a good energy. specific on outgoing products.
L'invention présente également un intérêt particulier dans les cas où la pression de production de gaz par l'appareil de séparation n'est pas la même que la pression d'utilisation du gaz par le client, par exemple, grâce à la présence interposée d'une capacité-tampon.  The invention is also of particular interest in cases where the pressure of gas production by the separating apparatus is not the same as the pressure of use of the gas by the customer, for example, thanks to the presence interposed a buffer capacity.
US-A-5471843 décrit un procédé de séparation d'air dans lequel on réduit la pression de vaporisation de l'oxygène liquide, si la demande d'oxygène réduit. Par la même occasion, on réduit le débit d'air à traiter mais le moteur est entraîné par un moteur à vitesse constante. Ainsi, la suite logique des événements est le contraire de celle de notre invention et n'est pas conditionnée par l'observation d'une baisse de fréquence.  US-A-5471843 discloses an air separation process in which the vapor pressure of liquid oxygen is reduced, if the oxygen demand is reduced. At the same time, it reduces the air flow to be treated but the motor is driven by a constant speed motor. Thus, the logical sequence of events is the opposite of that of our invention and is not conditioned by the observation of a decrease in frequency.
EP-A-1845323 décrit un procédé de séparation d'air dans lequel la pression de vaporisation de l'oxygène liquide est fonction de la pression dont le réservoir contenant l'oxygène vaporisé. Ni la motorisation du compresseur ni la régulation en fonction de la fréquence de l'électricité ne sont mentionnées. EP-A-1845323 describes an air separation process in which the vaporization pressure of the liquid oxygen is a function of the pressure of which the tank containing the vaporized oxygen. Neither the motorization of the compressor nor the regulation according to the frequency of the electricity are mentioned.
Dans ce contexte, « riche en oxygène » veut dire que le fluide contient au moins 70% mol d'oxygène.  In this context, "rich in oxygen" means that the fluid contains at least 70 mol% of oxygen.
Selon un objet de l'invention, il est prévu un procédé de séparation d'air par distillation cryogénique dans lequel  According to an object of the invention, there is provided a method for separating air by cryogenic distillation in which
i) un débit d'air est comprimé dans un compresseur, est refroidi d'une ligne d'échange et envoyé à un système de colonnes où il se sépare pour former un débit enrichi en azote et un débit enrichi en oxygène  i) a flow of air is compressed in a compressor, is cooled by an exchange line and sent to a column system where it separates to form a nitrogen-enriched flow and an oxygen-enriched flow rate
ii) le compresseur est entraîné par un moteur alimenté par de l'électricité ayant une première fréquence  ii) the compressor is driven by a motor powered by electricity having a first frequency
iii) un débit liquide est soutiré du système de colonnes, pressurisé à une première pression par une pompe et soit vaporisé par échange de chaleur indirect avec de l'air provenant du compresseur pour produire un produit gazeux substantiellement à la première pression soit, dans le cas d'un débit liquide riche en oxygène, envoyé à la première pression à la tête d'une colonne auxiliaire alimentée en cuve par de l'air provenant du compresseur, de l'oxygène gazeux étant soutiré en tête de la colonne comme produit et un liquide intermédiaire de la colonne auxiliaire de la colonne auxiliaire étant envoyé au système de colonnes. caractérisé en ce que  iii) a liquid flow is withdrawn from the column system, pressurized at a first pressure by a pump and vaporized by indirect heat exchange with air from the compressor to produce a gaseous product substantially at the first pressure; a case of a liquid flow rich in oxygen, sent at the first pressure to the head of an auxiliary column supplied in the tank with air coming from the compressor, oxygen gas being withdrawn at the top of the column as product and an intermediate liquid of the auxiliary column of the auxiliary column being sent to the column system. characterized in that
iv) si la fréquence de l'électricité passe en dessous d'un seuil donné inférieur à la première fréquence, on réduit la pression de pressurisation du débit liquide à une deuxième pression inférieure à la première pression.  iv) if the frequency of the electricity falls below a given threshold lower than the first frequency, the pressurization pressure of the liquid flow is reduced to a second pressure lower than the first pressure.
Selon des caractéristiques optionnelles :  According to optional features:
- le compresseur comprime de l'air depuis la pression atmosphérique. le compresseur comprime de l'air à partir d'une pression supérieur à - the compressor compresses air from the atmospheric pressure. the compressor compresses air from a pressure greater than
2 bars. 2 bars.
le débit liquide se vaporise dans la ligne d'échange.  the liquid flow vaporizes in the exchange line.
le débit liquide riche en oxygène est envoyé à la première pression à la tête de la colonne auxiliaire alimentée en cuve par de l'air provenant du compresseur, de l'oxygène gazeux étant soutiré en tête de la colonne comme produit et au moins un liquide étant envoyé de la colonne auxiliaire au système de colonnes. si la fréquence est égale à la première fréquence, le débit liquide a un débit V et si la fréquence est inférieure au seuil donné inférieur à la première fréquence à la première fréquence le débit liquide au moins égale à 0,9V, voire au moins égale à 0,95V ou même égale à V. the oxygen-rich liquid flow is sent at the first pressure to the head of the auxiliary column fed in the tank with air coming from the compressor, oxygen gas being drawn off at the top of the column as product and at least one liquid being sent from the auxiliary column to the column system. if the frequency is equal to the first frequency, the liquid flow rate has a flow rate V and if the frequency is lower than the given threshold lower than the first frequency at the first frequency the liquid flow rate at least equal to 0.9V, or even at least equal to at 0.95V or even equal to V.
- on baisse la pression de pressurisation du liquide si le débit d'air mesuré passe en dessous d'un seuil par rapport au débit d'air requis pour atteindre la valeur nominale du débit liquide à la première pression de pressurisation.  the pressure of the pressurization of the liquid is lowered if the measured air flow passes below a threshold with respect to the air flow required to reach the nominal value of the liquid flow rate at the first pressurization pressure.
on baisse la pression de pressurisation du liquide si la pression d'air mesurée passe en dessous d'un seuil par rapport à la pression d'air requise pour atteindre la valeur nominale du débit liquide à la première pression de pressurisation.  the pressurization pressure of the liquid is lowered if the measured air pressure falls below a threshold with respect to the air pressure required to reach the nominal value of the liquid flow rate at the first pressurization pressure.
on réduit la pression de pressurisation du liquide seulement en modifiant le fonctionnement de la pompe de pressurisation.  the pressurization pressure of the liquid is reduced only by modifying the operation of the pressurizing pump.
- la pression de sortie de la pompe est égale à la pression de vaporisation du liquide pressurisé par la pompe.  - The output pressure of the pump is equal to the vaporization pressure of the liquid pressurized by the pump.
le liquide vaporisé sert de produit à la pression de vaporisation, sans subir de détente en aval de la vaporisation.  the vaporized liquid serves as a product for the vaporization pressure without undergoing expansion downstream of the vaporization.
Selon un autre objet de l'invention, il est prévu une installation de séparation d'air par distillation cryogénique comprenant un compresseur , une ligne d'échange, un système de colonnes, un moteur électrique pour entraîner le compresseur, une conduite pour soutirer un liquide du système de colonnes, une pompe pour pressuriser le liquide soutiré et des moyens pour permettre un échange de chaleur direct ou indirect entre de l'air comprimé par le compresseur et le liquide pressurisé, éventuellement les moyens permettant également un échange de masse si le liquide pressurisé est riche en oxygène, caractérisée en ce qu'elle comprend des moyens pour réguler la pression du liquide pressurisé dans la pompe en fonction de la fréquence de l'électricité alimentant le moteur électrique.  According to another object of the invention, there is provided an air separation installation by cryogenic distillation comprising a compressor, an exchange line, a column system, an electric motor for driving the compressor, a pipe for withdrawing a column system liquid, a pump for pressurizing the withdrawn liquid and means for permitting direct or indirect heat exchange between compressed air by the compressor and the pressurized liquid, optionally the means also allowing a mass exchange if the pressurized liquid is rich in oxygen, characterized in that it comprises means for regulating the pressure of the pressurized liquid in the pump as a function of the frequency of the electricity supplying the electric motor.
Eventuellement l'installation comprend :  Possibly the installation comprises:
des moyens pour réguler la pression du liquide pressurisé par action du système de contrôle sur le débit et/ou la pression de sortie de la pompe. des moyens pour mesurer la fréquence alimentant le moteur électrique, les moyens pour réguler la pression de pressurisation du liquide étant capables d'être mis en marche si la fréquence passe en dessous d'un seuil. means for regulating the pressure of the pressurized liquid by action of the control system on the flow and / or the outlet pressure of the pump. means for measuring the frequency supplying the electric motor, the means for regulating the pressurization pressure of the liquid being able to be turned on if the frequency falls below a threshold.
un surpresseur, des moyens pour envoyer de l'air du compresseur au surpresseur et du surpresseur à la ligne d'échange, le surpresseur étant entraîné par le ou un moteur alimenté par de l'électricité ayant une ou la fréquence.  a booster, means for sending air from the compressor to the booster and booster to the exchange line, the booster being driven by the or a motor powered by electricity having one or frequency.
une ligne d'échange où le liquide pressurisé se vaporise contre de l'air à séparer  a line of exchange where the pressurized liquid vaporizes against air to separate
une colonne auxiliaire alimenté par un liquide pressurisé riche en oxygène et de l'air.  an auxiliary column fed by a pressurized oxygen-rich liquid and air.
L'invention sera décrite en plus de détail en se référant à la figure qui illustre schématiquement un appareil selon l'invention.  The invention will be described in more detail with reference to the figure which schematically illustrates an apparatus according to the invention.
L'appareil de séparation comprend un compresseur 100, une ligne d'échange 4, un surpresseur 7, une turbine 27, une pompe 6 et une double colonne de distillation 1 comprenant une colonne moyenne pression 2 et une colonne basse pression 3. Il sera compris que la double colonne pourrait être remplacée par une triple colonne ou que d'autres colonnes pourraient être rajoutées tells qu'une colonne de mixture argon etc. Le moyen de couplage thermique montré est de chauffer la cuve de la colonne basse pression au moyen d'azote de la colonne moyenne pression, mais d'autres moyens de couplage thermique peuvent être envisagés.  The separation apparatus comprises a compressor 100, an exchange line 4, a booster 7, a turbine 27, a pump 6 and a double distillation column 1 comprising a medium pressure column 2 and a low pressure column 3. It will be understanding that the double column could be replaced by a triple column or that other columns could be added such as a column of argon mixture etc. The thermal coupling means shown is to heat the bottom of the low pressure column with nitrogen from the medium pressure column, but other means of thermal coupling can be envisaged.
Le surpresseur illustré est un surpresseur froid ayant une température d'entrée inférieure à celle du bout chaud de la ligne d'échange 4. L'invention s'applique également aux cas utilisant un surpresseur ayant une température d'entrée égale ou supérieure à celle du bout chaud de la ligne d'échange 4.  The booster illustrated is a cold booster having an inlet temperature lower than that of the hot end of the exchange line 4. The invention also applies to cases using a booster having an inlet temperature equal to or greater than that hot end of the exchange line 4.
De l'air est comprimé dans le compresseur 100, qui est entraîné par un moteur électrique alimentée par une source d'électricité ayant une fréquence nominale, par exemple 50Hz (en Europe) ou 60Hz (aux Etats-Unis). L'air comprimé est refroidi et épuré pour former le débit 19 puis envoyé à la ligne d'échange 4.  Air is compressed in the compressor 100, which is driven by an electric motor powered by a source of electricity having a nominal frequency, for example 50Hz (in Europe) or 60Hz (in the United States). The compressed air is cooled and purified to form the flow 19 and then sent to the exchange line 4.
L'air se refroidit dans la ligne d'échange puis est divisé en deux, une partie 20 poursuivant son refroidissement jusqu'au bout froid de l'échangeur et étant envoyé à la colonne moyenne pression 2 sous forme gazeuse. Le reste de l'air 21 est envoyé à un surpresseur froid 7, est surpressé à une pression élevée puis renvoyé à la ligne d'échange en tant que débit 22. Une partie de l'air surpressée 23 est détendue dans une turbine 27 et envoyé à la colonne moyenne pression alors que le reste de l'air surpressé poursuit son refroidissement jusqu'au bout froid, est détendu dans une vanne 28 et envoyé à la colonne moyenne pression. The air cools in the exchange line and is then divided in two, a part 20 continuing to cool to the cold end of the exchanger and being sent to the medium pressure column 2 in gaseous form. The rest of the air 21 is sent to a cold booster 7, is supercharged at high pressure and then returned to the exchange line as a flow 22. Part of the pressurized air 23 is expanded in a turbine 27 and sent to the medium pressure column then that the rest of the supercharged air continues cooling to the cold end, is expanded in a valve 28 and sent to the medium pressure column.
Du liquide riche 1 1 est envoyé de la cuve de la colonne moyenne pression via la vanne 12 et les sous-refroidisseurs 5A, 5B et de l'azote liquide 13 est envoyé en tête de la colonne basse pression 3 via la vanne 14. De l'azote basse pression 15 se réchauffe dans les sous-refroidisseurs 5A, 5B et la ligne d'échange 4.  Rich liquid 1 1 is sent from the tank of the medium pressure column via the valve 12 and the subcoolers 5A, 5B and liquid nitrogen 13 is sent to the top of the low pressure column 3 via the valve 14. the low pressure nitrogen is heated in the subcoolers 5A, 5B and the exchange line 4.
De l'oxygène liquide 16 est soutiré en cuve de la colonne basse pression 3, pressurisé par la pompe 6 et vaporisé à une première haute pression dans la ligne d'échange 4.  Liquid oxygen 16 is withdrawn in the bottom of the low pressure column 3, pressurized by the pump 6 and vaporized at a first high pressure in the exchange line 4.
Le surpresseur 7 est également entraîné par un moteur électrique M alimenté par un courant électrique.  The booster 7 is also driven by an electric motor M powered by an electric current.
Si la fréquence de l'électricité alimentant un des deux moteurs entraînant le compresseur ou le surpresseur, le débit et/ou la pression de l'air comprimé peut être insuffisant pour vaporiser l'oxygène à la première haute pression.  If the frequency of the electricity supplying one of the two motors driving the compressor or booster, the flow and / or the pressure of the compressed air may be insufficient to vaporize the oxygen at the first high pressure.
Dans ce cas, selon l'invention, la pression de pressurisation de la pompe 6 est réduite pour vaporiser l'oxygène à une pression plus basse. Le déclenchement de cette réduction de pression peut être fait en mesurant la fréquence de l'électricité alimentant le moteur et/ou en mesurant le débit d'air comprimé 19, 22 et/ou la pression du débit d'air comprimé 19, 22. Ainsi si la fréquence et/ou le débit et/ou la pression passe en dessous d'un seuil donné (de seuils donnés), la pression de l'oxygène peut être réduite tout en conservant un débit de production « proche » du débit nominal.  In this case, according to the invention, the pressurizing pressure of the pump 6 is reduced to vaporize the oxygen at a lower pressure. The triggering of this pressure reduction can be done by measuring the frequency of electricity supplied to the motor and / or by measuring the compressed air flow 19, 22 and / or the pressure of the compressed air flow 19, 22. Thus, if the frequency and / or the flow rate and / or the pressure pass below a given threshold (of given thresholds), the pressure of the oxygen can be reduced while keeping a production flow "close" to the nominal flow rate. .
Ainsi l'appareil peut toujours fonctionner malgré la fréquence réduite, au prix de produire de l'oxygène vaporisé à pression moins élevée.  Thus the apparatus can still operate despite the reduced frequency, at the cost of producing vaporized oxygen at lower pressure.
L'invention s'applique également à la vaporisation d'azote liquide.  The invention is also applicable to the vaporization of liquid nitrogen.
Comme illustré dans la Figure 2, il est également possible d'effectuer un échange de chaleur et de masse entre l'air et l'oxygène pressurisé dans une colonne auxiliaire appelée « colonne de mélange ». Ici l'oxygène liquide 16 provenant de la pompe 6 est envoyé en tête d'une colonne 33. La colonne auxiliaire 33 est alimentée en bas par un débit d'air 31 à la pression de la colonne moyenne pression. As illustrated in Figure 2, it is also possible to perform a heat and mass exchange between air and pressurized oxygen in an auxiliary column called "mixing column". Here the liquid oxygen 16 from the pump 6 is sent to the top of a column 33. The column auxiliary 33 is supplied at the bottom by a flow of air 31 at the pressure of the medium pressure column.
Toutefois, d'autres pressions d'opération plus élevées ou plus basses peuvent être utilisées. Un débit d'oxygène gazeux 37 est soutiré en tête de la colonne 33 et réchauffé dans l'échangeur 4. Un liquide 37 enrichi en oxygène est soutiré de la cuve de la colonne 33, détendu dans une vanne 43 et envoyé à la colonne basse pression 3. Il est également nécessaire de soutirer un liquide 39 à un niveau intermédiaire de la colonne auxiliaire 33, de le détendre dans une vanne 41 et de l'envoyer au système de colonnes.  However, other higher or lower operating pressures may be used. A flow of oxygen gas 37 is withdrawn at the top of the column 33 and heated in the exchanger 4. An oxygen-enriched liquid 37 is withdrawn from the tank of the column 33, expanded in a valve 43 and sent to the lower column pressure 3. It is also necessary to withdraw a liquid 39 at an intermediate level of the auxiliary column 33, to relax in a valve 41 and send it to the column system.
Dans ce cas, en cas de fréquence réduite, la colonne de mélange 33 opère à une pression réduite, pour compenser la réduction de pression du débit d'air 31 .  In this case, in the case of a reduced frequency, the mixing column 33 operates at a reduced pressure, to compensate for the reduction in pressure of the air flow 31.
La réduction de la fréquence, pour tous les cas d'application de l'invention, peut durer quelques minutes, quelques heures, voire quelques jours. Il va de soi que la décision de baisser la pression de pressurisation sera prise en fonction des besoins du client et si une réduction de produit dû à la réduction de fréquence peut être tolérée, ce ne sera pas forcément nécessaire d'utiliser le procédé de l'invention.  The reduction of the frequency, for all the cases of application of the invention, can last a few minutes, a few hours or even a few days. It goes without saying that the decision to lower the pressure of pressurization will be made according to the needs of the customer and if a reduction of product due to the reduction of frequency can be tolerated, it will not be necessary necessarily to use the process of the 'invention.
Une fois la fréquence normale rétablie, la pression de pressurisation est de nouveau augmentée en inversant les actions prises pour réduire la pression en cas de réduction de fréquence.  Once the normal frequency is restored, the pressurization pressure is increased again by reversing the actions taken to reduce the pressure in case of frequency reduction.
Idéalement le débit liquide pressurisé restera constant, quelle que soit la fréquence, mais une baisse de jusqu'à 5%, voire jusqu'à 10% du débit à fréquence normale peut parfois être tolérée.  Ideally the pressurized liquid flow will remain constant, regardless of the frequency, but a decrease of up to 5%, or even up to 10% of the flow at normal frequency can sometimes be tolerated.
La réduction de la pression de pressurisation en cas de baisse de fréquence peut être déclenchée en détectant qu'un débit d'air à séparer baisse. Souvent une réduction par rapport au débit nominal peut être compensée au moins partiellement en réglant les compresseurs.  The reduction of the pressurization pressure in the event of a drop in frequency can be triggered by detecting that an air flow to be separated decreases. Often a reduction with respect to the nominal flow rate can be compensated at least partially by adjusting the compressors.
Par contre à un seuil donné en dessous du débit nominal, il sera nécessaire de procéder selon l'invention car la régulation des compresseurs ne peut plus suffire pour combler la baisse de débit.  On the other hand, at a given threshold below the nominal flow rate, it will be necessary to proceed according to the invention since the regulation of the compressors can no longer be sufficient to compensate for the drop in flow.
De même, en combinaison avec la méthode ci-dessous ou seul, la réduction de la pression de pressurisation en cas de baisse de fréquence peut être déclenchée en détectant que la pression d'un débit d'air à séparer baisse. Souvent une réduction par rapport à la pression nominale peut être compensée au moins partiellement en réglant les compresseurs. Par contre à un seuil donné en dessous de la pression nominale, il sera nécessaire de procéder selon l'invention car la régulation des compresseurs ne peut plus suffire pour combler la baisse de pression. Similarly, in combination with the method below or alone, the reduction of the pressurization pressure in the event of a drop in frequency can be triggered by detecting that the pressure of an air flow to be separated decreases. Often a reduction from the nominal pressure can be at least partially compensated by adjusting the compressors. On the other hand, at a given threshold below the nominal pressure, it will be necessary to proceed according to the invention since the regulation of the compressors can no longer suffice to fill the pressure drop.

Claims

REVENDICATIONS
1 . Procédé de séparation d'air par distillation cryogénique dans lequel i) un débit d'air est comprimé dans un compresseur (7, 100), est refroidi d'une ligne d'échange (4) et envoyé à un système de colonnes (1 ) où il se sépare pour former un débit enrichi en azote et un débit enrichi en oxygène 1. A method of separating air by cryogenic distillation in which i) a flow of air is compressed in a compressor (7, 100), is cooled by an exchange line (4) and sent to a column system (1 ) where it separates to form a nitrogen-enriched flow and an oxygen-enriched flow
ii) le compresseur (7, 100) est entraîné par un moteur (M) alimenté par de l'électricité ayant une première fréquence  ii) the compressor (7, 100) is driven by a motor (M) powered by electricity having a first frequency
iii) un débit liquide (16) est soutiré du système de colonnes, pressurisé à une première pression par une pompe (6) et soit vaporisé par échange de chaleur indirect avec de l'air provenant du compresseur pour produire un produit gazeux substantiellement à la première pression soit, dans le cas d'un débit liquide riche en oxygène, envoyé à la première pression à la tête d'une colonne auxiliaire (33) alimentée en cuve par de l'air provenant du compresseur, de l'oxygène gazeux (37) étant soutiré en tête de la colonne comme produit et un liquide intermédiaire (39) de la colonne auxiliaire de la colonne auxiliaire étant envoyé au système de colonnes  iii) a liquid flow (16) is withdrawn from the column system, pressurized at a first pressure by a pump (6) and vaporized by indirect heat exchange with air from the compressor to produce a gaseous product substantially at the first pressure is, in the case of a liquid flow rich in oxygen, sent to the first pressure at the head of an auxiliary column (33) supplied in the tank with air from the compressor, oxygen gas ( 37) being withdrawn at the top of the column as product and an intermediate liquid (39) of the auxiliary column of the auxiliary column being sent to the column system
caractérisé en ce que  characterized in that
iv) si la fréquence de l'électricité passe en dessous d'un seuil donné inférieur à la première fréquence, on réduit la pression de pressurisation du débit liquide à une deuxième pression inférieure à la première pression.  iv) if the frequency of the electricity falls below a given threshold lower than the first frequency, the pressurization pressure of the liquid flow is reduced to a second pressure lower than the first pressure.
2. Procédé selon la revendication 1 , dans lequel le compresseur (100) comprime de l'air depuis la pression atmosphérique. The method of claim 1, wherein the compressor (100) compresses air from atmospheric pressure.
3. Procédé selon la revendication 1 , dans lequel le compresseur (7) comprime de l'air à partir d'une pression supérieur à 2 bars. 3. The method of claim 1, wherein the compressor (7) compresses air from a pressure greater than 2 bar.
4. Procédé selon la revendication 1 à 3, dans lequel le débit liquide (16) se vaporise dans la ligne d'échange (4). 4. The method of claim 1 to 3, wherein the liquid flow (16) vaporizes in the exchange line (4).
5. Procédé selon l'une des revendications 1 à 3, dans lequel le débit liquide riche en oxygène est envoyé à la première pression à la tête de la colonne auxiliaire alimentée en cuve par de l'air provenant du compresseur, de l'oxygène gazeux étant soutiré en tête de la colonne comme produit et au moins un liquide étant envoyé de la colonne auxiliaire au système de colonnes. 5. Method according to one of claims 1 to 3, wherein the oxygen-rich liquid flow is sent to the first pressure at the head of the auxiliary column supplied in the tank with air from the compressor, oxygen gaseous product being withdrawn at the top of the column and at least one liquid being sent from the auxiliary column to the column system.
6. Procédé selon l'une des revendications précédentes, dans lequel si la fréquence est égale à la première fréquence, le débit liquide a un débit V et si la fréquence est inférieure à la première fréquence le débit liquide est au moins égale à 0,9V, voire au moins égale à 0,95V ou même égale à V. 6. Method according to one of the preceding claims, wherein if the frequency is equal to the first frequency, the liquid flow has a flow rate V and if the frequency is lower than the first frequency the liquid flow rate is at least equal to 0, 9V, or at least equal to 0.95V or even equal to V.
7. Procédé selon l'une des revendications précédentes, dans lequel on baisse la pression de pressurisation du liquide si le débit d'air mesuré passe en dessous d'un seuil par rapport au débit d'air requis pour atteindre la valeur nominale du débit liquide (16) à la première pression de pressurisation. 7. Method according to one of the preceding claims, wherein the pressurization pressure of the liquid is lowered if the measured air flow passes below a threshold with respect to the air flow required to reach the nominal value of the flow rate. liquid (16) at the first pressurization pressure.
8. Procédé selon l'une des revendications précédentes, dans lequel on baisse la pression de pressurisation du liquide si la pression d'air mesurée passe en dessous d'un seuil par rapport à la pression d'air requise pour atteindre la valeur nominale du débit liquide (16) à la première pression de pressurisation. 8. Method according to one of the preceding claims, wherein the pressurization pressure of the liquid is lowered if the measured air pressure falls below a threshold with respect to the air pressure required to reach the nominal value of the liquid flow (16) at the first pressurization pressure.
9. Procédé selon l'une des revendications précédentes, dans lequel on réduit la pression de pressurisation du liquide seulement en modifiant le fonctionnement de la pompe de pressurisation (6). 9. Method according to one of the preceding claims, wherein the liquid pressurizing pressure is reduced only by modifying the operation of the pressurizing pump (6).
10. Procédé selon l'une des revendications précédentes, dans lequel la pression de sortie de la pompe (6) est égale à la pression de vaporisation du liquide pressurisé par la pompe. 10. Method according to one of the preceding claims, wherein the output pressure of the pump (6) is equal to the vaporization pressure of the liquid pressurized by the pump.
1 1 . Procédé selon l'une des revendications précédentes, dans lequel le liquide vaporisé sert de produit à la pression de vaporisation, sans subir de détente en aval de la vaporisation. 1 1. Method according to one of the preceding claims, wherein the vaporized liquid serves as product to the vaporization pressure, without undergoing expansion downstream of the vaporization.
12. Installation de séparation d'air par distillation cryogénique comprenant un compresseur (7, 100), une ligne d'échange (4), un système de colonnes (1 ), un moteur électrique (M) pour entraîner le compresseur , une conduite pour soutirer un liquide du système de colonnes, une pompe (6) pour pressuriser le liquide soutiré et des moyens (4, 33) pour permettre un échange de chaleur direct ou indirect entre de l'air comprimé par le compresseur et le liquide pressurisé, éventuellement les moyens permettant également un échange de masse si le liquide pressurisé est riche en oxygène, caractérisée en ce qu'elle comprend des moyens pour réguler la pression du liquide pressurisé (16) dans la pompe en fonction de la fréquence de l'électricité alimentant le moteur électrique. 12. Cryogenic distillation air separation plant comprising a compressor (7, 100), an exchange line (4), a column system (1), an electric motor (M) for driving the compressor, a pipe for withdrawing liquid from the column system, a pump (6) for pressurizing the withdrawn liquid and means (4, 33) to allow direct or indirect heat exchange between compressed air by the compressor and the pressurized liquid, optionally the means also allowing a mass exchange if the pressurized liquid is rich in oxygen, characterized in that it comprises means for regulating the pressure of the pressurized liquid (16) in the pump as a function of the frequency of the electricity supplying the electric motor.
13. Installation selon la revendication 12, comprenant des moyens pour réguler la pression du liquide pressurisé (16) par action du système de contrôle sur le débit et/ou la pression de sortie de la pompe (6). 13. Installation according to claim 12, comprising means for regulating the pressure of the pressurized liquid (16) by action of the control system on the flow and / or the outlet pressure of the pump (6).
14. Installation selon la revendication 12 ou 13, comprenant des moyens pour mesurer la fréquence alimentant le moteur électrique (M), les moyens pour réguler la pression de pressurisation du liquide étant capables d'être mis en marche si la fréquence passe en dessous d'un seuil. 14. Installation according to claim 12 or 13, comprising means for measuring the frequency supplying the electric motor (M), the means for regulating the pressurization pressure of the liquid being able to be started if the frequency falls below 'a threshold.
15. Installation selon l'une des revendications 12 à 14, comprenant un surpresseur (7), des moyens pour envoyer de l'air du compresseur (100) au surpresseur et du surpresseur à la ligne d'échange (4), le surpresseur étant entraîné par le ou un moteur alimenté par de l'électricité ayant une ou la fréquence. 15. Installation according to one of claims 12 to 14, comprising a booster (7), means for sending air from the compressor (100) to the booster and booster to the exchange line (4), the booster being driven by the or a motor powered by electricity having one or frequency.
EP12806557.0A 2011-11-25 2012-11-23 Process and apparatus for separating air by cryogenic distillation Withdrawn EP2783176A2 (en)

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FR2983287B1 (en) 2018-03-02

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