Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
  • F25J3/04436—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using at least a triple pressure main column system
  • F25J3/04448—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using at least a triple pressure main column system in a double column flowsheet with an intermediate 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
  • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
  • F25J3/04284—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
  • F25J3/04309—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams of nitrogen
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2200/00—Processes or apparatus using separation by rectification
  • F25J2200/50—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the 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
  • F25J2200/00—Processes or apparatus using separation by rectification
  • F25J2200/50—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the column
  • F25J2200/52—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the column in the high pressure column of a double pressure main column system
• • 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
  • F25J2200/50—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the column
  • F25J2200/54—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the column in the low pressure column of a double pressure main column system
• • 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
  • F25J2205/00—Processes or apparatus using other separation and/or other processing means
  • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
  • F25J2230/50—Processes or apparatus involving steps for increasing the pressure of gaseous process streams the fluid being oxygen
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
  • F25J2235/02—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams using a pump in general or hydrostatic pressure increase

Definitions

• This invention relates to processes and apparatus for the separation of mixtures of non-condensable gases by fractional distillation at sub-ambient temperatures.
• the invention entails new combinations of steps or equipments which result in more efficient cryogenic distillation. Improved efficiency is more important in cryogenic distillation than in conventional distillation because of the high cost of supplying distillation column reflux at cryogenic temperatures.
• Fulton U.S. Patent 2519451 discloses a liquid recycle distillation configuration which is narrowly applicable to distilling aqueous ammonia at aboveambient temperatures.
• the feed mixture is supplied initially to the lower pressure column, and the liquid overhead from that column is pumped to the higher pressure column. Steam is used to reboil both columns, and cooling water provides reflux to both columns.
• This configuration is not applicable to sub-ambient distillations. It also has the disadvantage that all of the more volatile fraction (NH 3 ) removed by the higher pressure column must first undergo the relatively inefficient total condensation in impure state at the lower pressure column overhead.
• Haselden U.S. Patent 40253908
• Pagani et al. U.S. Patent 4318782 disclose a vapor recycle distillation configuration in which vapor is recycled from the lower pressure column overhead to the higher pressure column.
• Pagani et al. disclose a configuration narrowly applicable to the distillation of aqueous ammonia at above-ambient temperatures, wherein the need for a recycle vapor compressor is avoided by absorbing the lower pressure column overhead vapors into the liquid feed, and then pumping the resulting liquid mixture to the pressure of the higher pressure column.
• Pagani et al. also disclose a lower pressure column that operates only as a stripper, having no reflux other than the liquid from the higher pressure column.
• Haselden discloses a configuration wherein the higher pressure column is solely a rectifier and the lower pressure column is solely a stripper. Feed mixture is supplied to the top of the lower pressure column together with recycle liquid from the higher pressure column, and they form the only reflux for the stripping column. A small amount of reboil is supplied at the bottom of the stripper by indirect application of external heat.
• Additional reboil is supplied at several heights of the stripper by indirect exchange of latent heat with an appropriate height/location of the rectifier (higher pressure column). Since most of the reboil supplied to the stripper is by latent heat exchange and correspondingly supplies reflux to the rectifier, the external reflux requirement is very small, and is only supplied at the top of the rectifier. This configuration is also described in Figure 1 of the AIChE Journal article "Distillation with Secondary Reflux and Vaporization: A Comparative Evaluation" by R.S.H. Mah, J.J. Nicholas, and R.B. Wodnik, September, 1977, p. 652, Vol. 23 No. 5.
• HP column overhead liquid obtained.
• all available liquid nitrogen is required to adequately reflux the LP column. Additionally, it is frequently not desirable to withdraw any liquid at all from a HP column midlength location.
• the apparatus in which the exchange of latent heat between two distillation columns is normally accomplished is generally referred to as a "reboiler/ reflux condenser".
• a "reboiler/ reflux condenser” usually higher pressure gas con denses on one side of the heat exchange surface while lower pressure liquid boils or evaporates on the other side. It may physically be located internal or external to either column it services.
• Reboilers and/or reflux condensers which connect to a midlength location or tray height of a distillation column rather than the respective top or bottom are sometimes referred to as “side” or “intermediate” reboilers or refluxers.
• the mixture being separated by a fractional distillation column may be either binary or multicomponent.
• distillation column signifies an apparatus with at least one feed entry point, at least one zone of countercurrent vapor-liquid contact both above and below the feed point, plus an overhead and bottom.
• Rectifier and “stripper” refer to columns in which the countercurrent vapor-liquid contact only occurs respectively above and below the feed entry point.
• the contacting section can be of any known type-bubble caps, sieve trays, packing, etc.
• a midlength location signifies a location between the feed point and either the overhead or bottom where there is countercurrent vapor-liquid contact both above and below the location.
• Cryogenic temperatures are those temperatures at which non-condensable gases, i.e., gases which are incapable of being liquefied at ambient temperature, can be liquefied.
• a process which comprises: a) supplying the mixture to be separated in fluid state to a first distillation column; b) distilling the mixture to overhead product and enriched bottom product liquid; c) transporting the enriched bottom product liquid to a second distillation column d) distilling the enriched bottom product liquid to bottom product fluid and enriched over head fluid; e) transporting the enriched overhead fluid to the first distillation column; f) reboiling the first and second distillation columns by latent heat exchange with a condensing gas; g) refluxing the second distillation column by latent heat exchange with a boiling liquid; h) with drawing said bottom product fluid and said overhead product.
• Sub-ambient distillation is frequently accomplished by supplying the mixture as a compressed gas to a high pressure rectification column which reboils a lower pressure distillation column.
• the rectification column also supplies enriched liquid feed to the midlength of the distillation column and liquid overhead product as direct injection reflux to the overhead of the distillation column.
• the pressure ratio between the rectifier and the distillation column is indicative of the energy consumed by the distillation process, i.e., the amount the supply mixture must be compressed.
• Substituting the liquid recycle distillation columns for the single distillation column is one way of reducing the required pressure ratio between the rectifier and the two columns. Incorporating multiple latent heat exchanges between the rectifier and distillation column is a second way of reducing the required pressure ratio.
• Two essential aspects of the disclosed improvement of recycle distillation at sub-ambient temperatures are that the feed mixture be supplied initially to the higher pressure column of the two distillation columns, and that the lower pressure column have a zone of countercurrent vapor-liquid contact plus a supply of reflux located above the point at which recycle liquid from the higher pressure column is introduced. It is imis portant to minimize the amount of fluid which /recycled from the lower pressure column to the higher pressure column, as that step is inherently inefficient. Any of the more volatile fraction that is introduced into the lower pressure column must be removed overhead. Thus by introducing the feed initially to the higher pressure column, at least some more volatile fraction is removed there, reducing the amount introduced to the lower pressure column.
• the two aspects described above combine to greatly reduce the overhead product flow rate which is recycled from the lower pressure column to the higher pressure column compared to prior art processes.
• the lower pressure column overhead product which is recycled can be in any fluid state, i.e., gas and/or liquid.
• gas and/or liquid For the separation of close boiling components, it will normally be liquid, to avoid the need for compression.
• the gas becomes progressively more enriched in the more volatile component than the liquid, and hence withdrawing the product as gas reduces the required flow rate. In some cases this advantage will more than offset the disadvantage of supplying a small compressor and adding a small amount of work inside the cold box.
• FIG. 1 illustrates the basic configuration of sub-ambient liquid recycle distillation with feed supplied to the higher pressure distillation column and reflux supplied to the lower pressure distillation column. It also shows a high pressure rectifier which reboils both recycle columns and generates the feed for the higher pressure recycle column and reflux for both recycle columns.
• Figure 2 illustrates a recycle distillation configuration wherein in addition to the latent heat exchange between the rectifier overhead and the two recycle columns, there is also a latent heat exchange between a rectifier midlength location and the bottom of one of the recycle columns, in this case the higher pressure one.
• Figure 3 illustrates a recycle distillation configuration wherein the two recycle columns exchange latent heat. In this case the heat flow is from the lower pressure column to the higher pressure column.
• Figure 4 illustrates a recycle distillation configuration which incorporates both of the improvements illustrated in Figures 2 and 3, and which is particularly advantageous in the application of air separation.
• the higher pressure distillation column 1 and lower pressure distillation column 2 are interconnected by means for transporting overhead fluid 4.
• Means for transport 3 may be a pump, valve, check valve, or simply a conduit or the like;
• means for transport 4 may be a pump, a com pressor, or a barometric leg with one way valve or the like.
• the barometric leg will suffice when liquid is being transported and the absolute pressure difference between the columns is suitably low, such as for low pressure air separation.
• Feed mixture in fluid state gas and/or liquid
• the basic recycle distillation configuration as described above can be caused to operate by compressing the gas obtained from the boiling liquid which refluxes both columns back to the pressure required in reboilers 7 and 8, in a heat pump configuration.
• a high pressure rectification column 11 may be employed in what can be termed a "feed heat pumped" configuration.
• the mixture to be separated, in a cleaned, cooled, pressurized gaseous state, is supplied to the bottom of column 11; the overhead gas condenses in reboiler/reflux condensers 7 and 8, and the condensate is divided in three parts: part refluxes column 11, part refluxes column 1, and part is used to generate reflux for column 2.
• Bottom liquid from column 11 is transported to column 1 via means for transport and pressure reduction 5, as previously described.
• liquid or gaseous supply or withdrawal points may be located at any point on the several columns and interconnections described.
• air separatio processes frequently part of the gaseous N 2 in column 11 overhead is withdrawn and routed to an expander which generates refrigeration required for the process.
• the point at which overhead from column 2 is reintroduced into column 1 is not necessarily below the column 1 feed point (means for feeding 5) as shown. It may be at the same feed point, or above the feed point. The only stipulation is that it will be at some midlength location of the entire column. This applies to all the configurations illustrated.
• Figure 2 additionally illustrates an exchange of latent heat between a midlength location of column 11 and the bottom of column 1.
• Column 1 bottom liquid flows to reboiler/reflux condenser 12, and the resulting vapor liquid mixture is separated by separator 14 so as to return the vapor as reboil to column 1.
• An additional zone of countercurrent vapor-liquid contact 13 is incorporated in column 1 to take advantage of the additional reboil.
• the additional latent heat exchange could be between columns 11 and 2 vice 11 and 1.
• Figure 3 additionally illustrates an exchange of latent heat between column 1 and column 2.
• Gas from column 2 communicates with reboiler/reflux condenser 15, and liquid reflux returns to column 2.
• part of the downflowing liquid in column 1 is vaporized in reboiler/reflux condenser 15 and flows back up the column.
• the heat flow is from column 2 to column 1.
• the latent heat interchange illustrated is from a midlength location to another midlength location, but this is not generally required, as in some cases it will be from or to a bottom or overhead location, and/or in the other direction.
• Figure 4 combines the improvements of both Figures 2 and 3, and has the same numbered components 1 through 15. This configuration is particularly advantageous for separating air to an oxygen product of about 97% purity or more.
• Both the liquid recycle configuration as in Figures 1 or 2, and the prior art multiply latent heat exchanged dual pressure columns suffer from the fact that only a limited amount of reboil is available at the bottom of the oxygen producing distillation column. This makes it impossible to separate out very much of the argon in the feed air from the oxygen, and an oxygen purity of 95 to 96% results, with argon as the major impurity.
• substantially greater reboil is provided at the bottom of column 2, resulting in much greater oxygen purity.
• Reboiler/reflux condenser 12 also causes the rectifier 11 to operate more efficiently, provided most or preferably all of the reflux it generates is returned to column 11.
• the reboil to column 1 can be comprised of 9 m/m vapor from separator 14, 16 m/m vapor to reboiler 8, and 22 m/m vapor to reboiler 15, or other suitable combination.
• the pressure ratio between the two recycle distillation columns in this disclosure will be approximately the fourth root of the relative volatility of the two fractions separated. For air, the relative volatility between oxygen and nitrogen at 90K is about 3.5, and the fourth root is 1.37. The pressure ratio will always be less than the square root of the relative volatility with the disclosed configuration.

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

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• 1984
  • 1984-03-30 WO PCT/US1984/000477 patent/WO1984003934A1/en not_active Application Discontinuation
  • 1984-03-30 BR BR8406508A patent/BR8406508A/pt unknown
  • 1984-03-30 EP EP19840901556 patent/EP0141826A4/de not_active Withdrawn
  • 1984-03-30 JP JP50149184A patent/JPS60500972A/ja active Pending

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