EP3916330A1 - Process for start-up of a cryogenic distillation air separation unit - Google Patents

Process for start-up of a cryogenic distillation air separation unit Download PDF

Info

Publication number
EP3916330A1
EP3916330A1 EP20212567.0A EP20212567A EP3916330A1 EP 3916330 A1 EP3916330 A1 EP 3916330A1 EP 20212567 A EP20212567 A EP 20212567A EP 3916330 A1 EP3916330 A1 EP 3916330A1
Authority
EP
European Patent Office
Prior art keywords
column
liquid
sent
normal operation
air
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Withdrawn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
EP20212567.0A
Other languages
German (de)
French (fr)
Inventor
Terry SUDRE
Eric Hendrickx
Cédric BUYSSE
Sieger STUER
Kurt MEERT
Luigi MARCON
Felix COCK
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.)
Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Original Assignee
Air Liquide SA
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 Air Liquide SA, LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude filed Critical Air Liquide SA
Priority to EP20212567.0A priority Critical patent/EP3916330A1/en
Publication of EP3916330A1 publication Critical patent/EP3916330A1/en
Withdrawn legal-status Critical Current

Links

Images

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
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04254—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using the cold stored in external cryogenic fluids
    • 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
    • F25J3/04763—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
    • F25J3/04818—Start-up of the process
    • 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
    • F25J3/04824—Stopping of the process, e.g. defrosting or deriming; Back-up procedures
    • 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
    • F25J3/04854—Safety aspects of operation
    • F25J3/0486—Safety aspects of operation of vaporisers for oxygen enriched liquids, e.g. purging of liquids
    • 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
    • F25J2210/42—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
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/50—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
    • F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream

Definitions

  • the present invention relates to a process for the start up of a cryogenic distillation air separation unit. It also relates to a cryogenic distillation air separation unit capable of being started up according to the process.
  • the EIGA document 65/30 "Safe Operation of Reboilers/Condensers in Air Separation Unit" sets out a definition of cold standby as being the condition where equipment is held at cryogenic conditions for immediate service on demand.
  • the section on “cold standby” reads as follows: "Following a plant shutdown, the liquid contained in the packing or trays drains to the low point of the column. At this point, the level in the reboilers can be well greater than 100% of the level indicators. This liquid is generally preserved to permit a quick restart of the plant. This mode is referred to as cold standby.
  • liquid When the liquid has been reduced to half of its normal level, either liquid shall be added using liquid nitrogen or oxygen injection or all liquid in the plant shall be drained.
  • liquid nitrogen rather than liquid oxygen in particular for a long-term cold standby.
  • liquid oxygen is used, extra hydrocarbons, carbon dioxide, nitrous oxide, and contaminants in general are added to the system and could accumulate to exceed the maximum contaminant levels.”
  • the present invention proposes a procedure to speed up the start up process by accelerating the transition from the cold standby where the bottom of the low pressure column contains liquid nitrogen and normal operation where the bottom of the low pressure column contains oxygen enriched liquid.
  • a process for restarting an air separation unit for the separation of air by cryogenic distillation comprising a first column operating in normal operation at a first pressure and a second column operating in normal operation at a second pressure lower than the first pressure, the first and second columns being thermally linked and provided with conduits for transferring liquid enriched in oxygen and liquid enriched in nitrogen from the first column to the second column under normal operation, conduits for removing oxygen enriched fluid and nitrogen enriched gas from the second column in normal operation and a conduit for feeding gaseous air to the first column under normal operation wherein
  • an air separation unit for the separation of air by cryogenic distillation, the unit comprising a first column operating in normal operation at a first pressure and a second column operating in normal operation at a second pressure lower than the first pressure, the first and second columns being thermally linked and provided with a conduit for transferring liquid enriched in oxygen from the first column to the second column under normal operation and a conduit for transferring liquid enriched in nitrogen from the first column to the second column under normal operation, conduits for removing oxygen enriched fluid and nitrogen enriched gas from the second column in normal operation and a conduit for feeding gaseous air to the first column under normal operation characterized in that it comprises means for sending liquid oxygen from an external source connected to the bottom of the second column and a conduit for sending liquid from the bottom of the second column to the bottom of the first column.
  • the unit comprises:
  • Figure 1 shows a cryogenic air separation unit comprising a first column K1 operating in normal operation at a first pressure and a second column K2 operating in normal operation at a second pressure lower than the first pressure.
  • the first and second columns are thermally linked and provided with a conduit 2 for transferring liquid enriched in oxygen from the first column to the second column under normal operation and a conduit 4 for transferring liquid enriched in nitrogen from the first column to the second column under normal operation.
  • Conduit 7 serves to remove oxygen enriched fluid from the bottom of the second column K2 and conduit 8 removes nitrogen enriched gas from the second column K2 in normal operation.
  • Conduit 3 does not serve during normal operation.
  • a conduit 1 feeds gaseous air to the first column K1 under normal operation.
  • the air in conduit 1 has previously been purified and cooled. It is possible to cool the air using a refrigeration unit upstream of the purification step.
  • valve V3 is opened, liquid is removed from the bottom of the second column K2 via conduit 3 and sent to the bottom of the first column K1.
  • valve V3 is closed and no more liquid is removed via conduit 3. Instead liquid oxygen from a second external source S is sent via conduit 5 to the bottom of the second column K2 by opening valve V5.
  • the amount of liquid drained via conduit 3 depends on the purity of the liquid drained and the purity of the liquid oxygen to be added by conduit 5.
  • the aim is to establish a liquid bath at the bottom of the second column K2 having an oxygen purity greater than that existing during shutdown so as to approach to some degree the oxygen purity existing during distillation.
  • the liquid purity at the bottom of the column could reach between 40 and 50% mol oxygen due to the addition of liquid oxygen. This value will depend on the type of air separation unit.
  • the temperature of the liquid in the bath will increase with the oxygen content.
  • the temperature on the nitrogen side (column K1) will also increase.
  • the product that will be condensed is air.
  • the temperature on the nitrogen side must be high enough so that the corresponding pressure (point on the boiling curve of air) is high enough to transfer the condensed liquids from K1 to K2 by pressure differential.
  • valve V1 opens and gaseous air is sent to column K1 to enable distillation to begin.
  • the unit includes means for detecting the liquid level at the bottom of the first column and means for sending air to start up the distillation in response to a signal from the means for detecting the liquid level.
  • the unit may comprise means for detecting the pressure difference between the first and second columns and means for sending liquid oxygen to the bottom of the second column once the pressure difference is sufficient.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

In a process for restarting an air separation unit for the separation of air by cryogenic distillation, the unit comprising a first column (K1) operating in normal operation at a first pressure and a second column (K2) operating in normal operation at a second pressure lower than the first pressure, the first and second columns being thermally linked and provided with conduits (2,4) for transferring liquid enriched in oxygen and liquid enriched in nitrogen from the first column to the second column under normal operation, conduits for removing oxygen enriched fluid (7) and nitrogen enriched gas (8) from the second column in normal operation and a conduit for feeding gaseous air (1) to the first column under normal operation, during restart of the air separation unit, liquid (3) is removed from the bottom of the second column and sent to the bottom of the first column and liquid oxygen (5) from a second external source (S) is sent to the bottom of the second column.

Description

  • The present invention relates to a process for the start up of a cryogenic distillation air separation unit. It also relates to a cryogenic distillation air separation unit capable of being started up according to the process.
  • All air separation units for the cryogenic distillation of air need to be closed down from time to time, either for maintenance work or because their products are not required. If the unit no longer operates, heat penetrates into the cold box and the columns warm up. This means that once the unit restarts, considerable time is wasted while the cold box cools down in order for distillation to resume and for the necessary purities to be established.
  • For this reason, it is known to maintain the cold box at cryogenic temperatures by processes known as "cold standby" or "cold hold".
  • The EIGA document 65/30 "Safe Operation of Reboilers/Condensers in Air Separation Unit" sets out a definition of cold standby as being the condition where equipment is held at cryogenic conditions for immediate service on demand.
  • The section on "cold standby" reads as follows:
    "Following a plant shutdown, the liquid contained in the packing or trays drains to the low point of the column. At this point, the level in the reboilers can be well greater than 100% of the level indicators. This liquid is generally preserved to permit a quick restart of the plant. This mode is referred to as cold standby.
  • During a one day or two day cold standby period, flow is circulated through liquid oxygen adsorbers if installed. The following shall be followed to maintain a more extended cold standby in a safe manner:
    • close inlet and outlet valves of the recirculation pumps;
    • drain pumps and suction filters; and
    • drain and regenerate liquid oxygen adsorbers. The regeneration should be done soon after complete draining of the liquid and purging of the adsorber with nitrogen to avoid the release of contaminants in gaseous oxygen atmosphere.
  • Due to the heat leak into the coldbox, vaporization eventually reduces the amount of liquid in the reboiler to well less than the normal operating level.
  • When the liquid has been reduced to half of its normal level, either liquid shall be added using liquid nitrogen or oxygen injection or all liquid in the plant shall be drained.
  • When injecting liquid into the plant, it is advisable to use liquid nitrogen rather than liquid oxygen in particular for a long-term cold standby. When liquid oxygen is used, extra hydrocarbons, carbon dioxide, nitrous oxide, and contaminants in general are added to the system and could accumulate to exceed the maximum contaminant levels."
  • It is thus known to maintain the temperature in the columns within the coldbox by adding liquid nitrogen to the air separation unit. Since no distillation takes place and no air enters the columns during cold standby, the liquid nitrogen sent to the top of the low pressure column accumulates at the bottom of that column and is vaporised to a certain extent, due to the heat ingress. This vaporization helps to ensure that the columns remain under a positive pressure and limits the possibility that fluids should enter the columns through the conduits normally used to introduce air or remove products.
  • The present invention proposes a procedure to speed up the start up process by accelerating the transition from the cold standby where the bottom of the low pressure column contains liquid nitrogen and normal operation where the bottom of the low pressure column contains oxygen enriched liquid.
  • According to the present invention, there is provided a process for restarting an air separation unit for the separation of air by cryogenic distillation, the unit comprising a first column operating in normal operation at a first pressure and a second column operating in normal operation at a second pressure lower than the first pressure, the first and second columns being thermally linked and provided with conduits for transferring liquid enriched in oxygen and liquid enriched in nitrogen from the first column to the second column under normal operation, conduits for removing oxygen enriched fluid and nitrogen enriched gas from the second column in normal operation and a conduit for feeding gaseous air to the first column under normal operation wherein
    • when the air separation unit is shut down, no air is sent to the first column and liquid nitrogen from a first external source is sent at least occasionally to the second column and
    • during restart of the air separation unit:
      1. a) Liquid is removed from the bottom of the second column and sent to the bottom of the first column,
      2. b) Liquid nitrogen is no longer sent to the second column and liquid oxygen from a second external source is sent to the bottom of the second column and
      3. c) Gaseous air is sent to the first column.
  • According to other optional features:
    • no gaseous air is sent to the first column during restart until a given quantity of liquid has been sent from the bottom of the second column to the bottom of the first column.
    • no gaseous air is sent to the first column during restart until liquid oxygen has been sent to the bottom of the second column.
    • no liquid oxygen is sent to the bottom of the second column until a given quantity of liquid has been sent from the bottom of the second column to the bottom of the first column.
    • liquid nitrogen is sent to the second column during normal operation.
    • the liquid nitrogen sent to the second column during normal operation provides at least 90% of the refrigeration needed for the process.
    • steps a) and b) do not take place during a common time period.
  • According to another object of the invention, there is provided an air separation unit for the separation of air by cryogenic distillation, the unit comprising a first column operating in normal operation at a first pressure and a second column operating in normal operation at a second pressure lower than the first pressure, the first and second columns being thermally linked and provided with a conduit for transferring liquid enriched in oxygen from the first column to the second column under normal operation and a conduit for transferring liquid enriched in nitrogen from the first column to the second column under normal operation, conduits for removing oxygen enriched fluid and nitrogen enriched gas from the second column in normal operation and a conduit for feeding gaseous air to the first column under normal operation characterized in that it comprises means for sending liquid oxygen from an external source connected to the bottom of the second column and a conduit for sending liquid from the bottom of the second column to the bottom of the first column.
  • According to optional features, the unit comprises:
    • means for detecting the amount of liquid sent from the bottom of the second column to the bottom of the first column and means for sending liquid oxygen to the bottom of the second column once a given amount of liquid has been sent from the bottom of the second column to the bottom of the first column.
    • means for detecting the liquid level at the bottom of the first column and means for sending air to start up the distillation in response to a signal from the means for detecting the liquid level.
    • means for detecting the pressure difference between the first and second columns and and means for sending liquid oxygen to the bottom of the second column once the pressure difference is sufficient.
  • The invention will be described in greater detail with reference to the figure.
  • Figure 1 shows a cryogenic air separation unit comprising a first column K1 operating in normal operation at a first pressure and a second column K2 operating in normal operation at a second pressure lower than the first pressure.
  • The first and second columns are thermally linked and provided with a conduit 2 for transferring liquid enriched in oxygen from the first column to the second column under normal operation and a conduit 4 for transferring liquid enriched in nitrogen from the first column to the second column under normal operation.
  • Conduit 7 serves to remove oxygen enriched fluid from the bottom of the second column K2 and conduit 8 removes nitrogen enriched gas from the second column K2 in normal operation.
  • Conduit 3 does not serve during normal operation.
  • A conduit 1 feeds gaseous air to the first column K1 under normal operation. The air in conduit 1 has previously been purified and cooled. It is possible to cool the air using a refrigeration unit upstream of the purification step.
  • When the air separation unit is shut down, no air is sent to the first column K1 and liquid nitrogen 9 from a first external source is sent at least occasionally to the second column K2. This allows the columns K1, K2 to remain at a low temperature even though distillation is not taking place. Whilst the air separation unit is shut down, liquid from within the column drains to the bottom of the column and accumulates. This liquid is much richer in nitrogen than the liquid which accumulates at the bottom of the column during normal operation.
  • During restart of the air separation unit, valve V3 is opened, liquid is removed from the bottom of the second column K2 via conduit 3 and sent to the bottom of the first column K1.
  • Once sufficient liquid has been sent to the bottom of the first column K1, valve V3 is closed and no more liquid is removed via conduit 3. Instead liquid oxygen from a second external source S is sent via conduit 5 to the bottom of the second column K2 by opening valve V5.
  • The amount of liquid drained via conduit 3 depends on the purity of the liquid drained and the purity of the liquid oxygen to be added by conduit 5. The aim is to establish a liquid bath at the bottom of the second column K2 having an oxygen purity greater than that existing during shutdown so as to approach to some degree the oxygen purity existing during distillation. For example, the liquid purity at the bottom of the column could reach between 40 and 50% mol oxygen due to the addition of liquid oxygen. This value will depend on the type of air separation unit.
  • The temperature of the liquid in the bath will increase with the oxygen content. For a given Delta T (design value) of the bottom condenser of the second column K1, the temperature on the nitrogen side (column K1) will also increase. During start up, the product that will be condensed is air. The temperature on the nitrogen side must be high enough so that the corresponding pressure (point on the boiling curve of air) is high enough to transfer the condensed liquids from K1 to K2 by pressure differential.
  • Consequently the sending of liquid oxygen to the bottom of second column K2 continues until the pressure in the first column K1 is sufficient to ensure that the liquid reflux flows can overcome the hydrostatic pressure and arrive in the second column K2.
  • This is checked by measuring the liquid level at the bottom of the first column K1 using level detector LIC. If, on opening the valve V3, the liquid level at the bottom of the first column K1 decreases, then it can be concluded that the pressure is sufficient to cause the bottom liquid to rise through conduit 2 to the second column K2.
  • Finally once a certain level of liquid oxygen is established at the bottom of the second column K2, valve V1 opens and gaseous air is sent to column K1 to enable distillation to begin.
  • Thus the unit includes means for detecting the liquid level at the bottom of the first column and means for sending air to start up the distillation in response to a signal from the means for detecting the liquid level.
  • Optionally, the unit may comprise means for detecting the pressure difference between the first and second columns and means for sending liquid oxygen to the bottom of the second column once the pressure difference is sufficient.
  • It is useful before starting the distillation to send an air stream to the refrigeration unit in series with the purification unit. Since the minimum flow for the refrigeration unit to operate is higher than the minimum flow for the purification unit to operate, the excess air from the refrigeration unit can be sent to the atmosphere.

Claims (10)

  1. Process for restarting an air separation unit for the separation of air by cryogenic distillation, the unit comprising a first column (K1) operating in normal operation at a first pressure and a second column (K2) operating in normal operation at a second pressure lower than the first pressure, the first and second columns being thermally linked and provided with conduits (2,4) for transferring liquid enriched in oxygen and liquid enriched in nitrogen from the first column to the second column under normal operation, conduits for removing oxygen enriched fluid (7) and nitrogen enriched gas (8) from the second column in normal operation and a conduit for feeding gaseous air (1) to the first column under normal operation wherein
    - when the air separation unit is shut down, no air is sent to the first column and liquid nitrogen (9) from a first external source is sent at least occasionally to the second column
    - and during restart of the air separation unit:
    a) Liquid (3) is removed from the bottom of the second column and sent to the bottom of the first column,
    b) Liquid nitrogen is no longer sent to the second column and liquid oxygen (5) from a second external source (S) is sent to the bottom of the second column and
    c) Gaseous air is sent to the first column.
  2. Process according to Claim 1 wherein no gaseous air is sent to the first column (K1) during restart until a given quantity of liquid (3) has been sent from the bottom of the second column to the bottom of the first column.
  3. Process according to Claim 1 or 2 wherein no gaseous air (1) is sent to the first column (K1) during restart until liquid oxygen (5) has been sent to the bottom of the second column (K2).
  4. Process according to any preceding claim wherein no liquid oxygen (5) is sent to the bottom of the second column (K2à until a given quantity of liquid has been sent from the bottom of the second column (3) to the bottom of the first column (K1).
  5. Process according to any preceding claim wherein liquid nitrogen (9) is sent to the second column during normal operation.
  6. Process according to any preceding claim wherein the liquid nitrogen (9)sent to the second column during normal operation provides at least 90% of the refrigeration needed for the process.
  7. Process according to any preceding claim wherein steps a) and b) do not take place during a common time period.
  8. Air separation unit for the separation of air by cryogenic distillation, the unit comprising a first column (K1) operating in normal operation at a first pressure and a second column (K2) operating in normal operation at a second pressure lower than the first pressure, the first and second columns being thermally linked and provided with a conduit for transferring liquid enriched in oxygen (2) from the first column to the second column under normal operation and a conduit (4) for transferring liquid enriched in nitrogen from the first column to the second column under normal operation, conduits for removing oxygen enriched fluid (7) and nitrogen enriched gas (8) from the second column in normal operation and a conduit for feeding gaseous air (1) to the first column under normal operation characterized in that it comprises means for sending liquid oxygen (5) from an external source (S) connected to the bottom of the second column and a conduit (3) for sending liquid from the bottom of the second column to the bottom of the first column.
  9. Unit according to Claim 8 comprising means for detecting the amount of liquid (3) sent from the bottom of the second column (K2) to the bottom of the first column (K1) and means for sending liquid oxygen (5) to the bottom of the second column once a given amount of liquid has been sent from the bottom of the second column to the bottom of the first column.
  10. Unit according to Claim 8 or 9 including means (LIC) for detecting the liquid level at the bottom of the first column and means for sending air (1) to start up the distillation in response to a signal from the means for detecting the liquid level.
EP20212567.0A 2020-12-08 2020-12-08 Process for start-up of a cryogenic distillation air separation unit Withdrawn EP3916330A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP20212567.0A EP3916330A1 (en) 2020-12-08 2020-12-08 Process for start-up of a cryogenic distillation air separation unit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP20212567.0A EP3916330A1 (en) 2020-12-08 2020-12-08 Process for start-up of a cryogenic distillation air separation unit

Publications (1)

Publication Number Publication Date
EP3916330A1 true EP3916330A1 (en) 2021-12-01

Family

ID=73789806

Family Applications (1)

Application Number Title Priority Date Filing Date
EP20212567.0A Withdrawn EP3916330A1 (en) 2020-12-08 2020-12-08 Process for start-up of a cryogenic distillation air separation unit

Country Status (1)

Country Link
EP (1) EP3916330A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2026008184A1 (en) 2024-07-04 2026-01-08 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Method for starting a cryogenic distillation air separation unit

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3709588A1 (en) * 1986-04-02 1987-10-08 Voest Alpine Ag DEVICE FOR THE DISASSEMBLY OF GASES BY MEANS OF COAXIAL INTERLECTED RECTIFICATION COLONES
JP2002168561A (en) * 2000-11-30 2002-06-14 Kobe Steel Ltd Method and system for separating air
JP2009299930A (en) * 2008-06-10 2009-12-24 Air Water Inc Air separating method and device used for the same

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3709588A1 (en) * 1986-04-02 1987-10-08 Voest Alpine Ag DEVICE FOR THE DISASSEMBLY OF GASES BY MEANS OF COAXIAL INTERLECTED RECTIFICATION COLONES
JP2002168561A (en) * 2000-11-30 2002-06-14 Kobe Steel Ltd Method and system for separating air
JP2009299930A (en) * 2008-06-10 2009-12-24 Air Water Inc Air separating method and device used for the same

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
"Fast Startup of Cryogenic Gas Separation Plants ED - Darl Kuhn", IP.COM, IP.COM INC., WEST HENRIETTA, NY, US, 14 September 2006 (2006-09-14), XP013115821, ISSN: 1533-0001 *
"Safe Operation of Reboilers/Condensers in Air Separation Units = SECURITE D'EXPLOITATION DES REBOUILLEURS/CONDENSEURS DANS LES UNITES DE SEPARATION DES GAZ DE L'AIR = Sicherer Betrieb von Kondensatoren in Muftzerlegungsanlagen", EUROPEAN INDUSTRIAL GASES ASSOCIATION, IGC DOCUMENT DOC 65/99/EFD, IGC, vol. 65/99/EFD, 1 January 1999 (1999-01-01), pages 78pp, XP009183353, ISBN: 978-2-85701-330-3 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2026008184A1 (en) 2024-07-04 2026-01-08 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Method for starting a cryogenic distillation air separation unit
FR3164275A1 (en) * 2024-07-04 2026-01-09 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Method for starting an air separation device by cryogenic distillation

Similar Documents

Publication Publication Date Title
US8647409B2 (en) Air compression system and method
EP3625509A1 (en) Apparatus and process for liquefying gases
US5546766A (en) Air separation
US4934147A (en) Cryogenic gas purification process and apparatus
JPH0861844A (en) Method and equipment for restarting sub-column for separating argon and oxygen by distilation
JPS6146747B2 (en)
US5651271A (en) Process for the separation of a gas mixture by cryogenic distillation
EP3916330A1 (en) Process for start-up of a cryogenic distillation air separation unit
JPS6148072B2 (en)
US20120279239A1 (en) Method and Device for Low-Temperature Cooling/Liquefaction
US6272884B1 (en) Rapid restart system for cryogenic air separation plant
US2908144A (en) Process and apparatus for separating gas mixtures
US5421164A (en) Process and installation for the production of ultra-pure nitrogen under pressure
JP2002168561A (en) Method and system for separating air
CN119686711B (en) Oilfield wellhead gas circulation injection system and process
CN103282732B (en) By the apparatus and method of separating air by cryogenic distillation
JP7385800B1 (en) Heat exchanger control system and method for low temperature equipment, and air separation device equipped with the system
US20230392862A1 (en) Krypton recovery and purification from customer processing
EP4455588A1 (en) Process and apparatus for the separation of air by cryogenic distillation
JP7608386B2 (en) Cryogenic air separation unit, and method for shutting down and starting up a cryogenic air separation unit
JP2012159285A (en) Plant for liquefying gas or gas mixture by cryogenic technique, and refining method belonging thereto
US7284395B2 (en) Cryogenic air separation plant with reduced liquid drain loss
CA2329490A1 (en) Distillation separation apparatus and method of cleaning a reboiler/condenser of the apparatus
EP4242568A1 (en) Air separation apparatus
EP4425078A1 (en) Process and apparatus for purifying air and cryogenic air separation process and plant

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION HAS BEEN PUBLISHED

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

B565 Issuance of search results under rule 164(2) epc

Effective date: 20210506

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION HAS BEEN WITHDRAWN

18W Application withdrawn

Effective date: 20211202