Purification of Carbon Dioxide

• US 20150114033A1
• Filed: 10/25/2013
• Published: 04/30/2015
• Est. Priority Date: 10/25/2013
• Status: Active Application

• Current Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Original Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Inventors: Higginbotham, Paul, Guvelioglu, Galip Hakan, Palamara, John Eugene, White, Vincent
• Granted Patent: US 10,254,042 B2
• Time in Patent Office: Days
• US Class Current: 62/617
• CPC Class Codes: B01D 2257/302 Sulfur oxides
• CPC Class Codes: B01D 2257/304 Hydrogen sulfide
• CPC Class Codes: B01D 2257/306 Organic sulfur compounds, e.g. mercaptans
• CPC Class Codes: B01D 2257/308 Carbonoxysulfide COS
• CPC Class Codes: B01D 2257/404 Nitrogen oxides other than dinitrogen oxide
• CPC Class Codes: B01D 2257/406 Ammonia
• CPC Class Codes: B01D 2257/7022 Aliphatic hydrocarbons
• CPC Class Codes: B01D 53/002 by condensation
• CPC Class Codes: B01D 53/75 Multi-step processes
• CPC Class Codes: C01B 17/167 Separation
• CPC Class Codes: C01B 32/50 Carbon dioxide
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/08 in a triple pressure main column system
• CPC Class Codes: F25J 2200/10 in a quadruple, or more, column or pressure system
• CPC Class Codes: F25J 2200/40 Features relating to the provision of boil-up in the bottom of a column
• CPC Class Codes: F25J 2200/50 using multiple (re-)boiler-condensers at different heights of the column
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• CPC Class Codes: F25J 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/02 : using simple phase separation in a vessel or drum
• CPC Class Codes: F25J 2205/30 : using a washing, e.g. "scrubbing" or bubble column for purification purposes
• CPC Class Codes: F25J 2205/40 : using hybrid system, i.e. combining cryogenic and non-cryogenic separation techniques
• CPC Class Codes: F25J 2205/80 : using membrane, i.e. including a permeation step
• CPC Class Codes: F25J 2215/80 : Carbon dioxide
• CPC Class Codes: F25J 2220/82 : Separating low boiling, i.e. more volatile components, e.g. He, H2, CO, Air gases, CH4
• CPC Class Codes: F25J 2220/84 : Separating high boiling, i.e. less volatile components, e.g. NOx, SOx, H2S
• CPC Class Codes: F25J 2230/80 : the fluid being carbon dioxide
• CPC Class Codes: F25J 2235/02 : using a pump in general or hydrostatic pressure increase
• CPC Class Codes: F25J 2235/80 : the fluid being carbon dioxide
• CPC Class Codes: F25J 2240/40 : Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
• CPC Class Codes: F25J 2245/02 : Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2260/20 : Integration in an installation for liquefying or solidifying a fluid stream
• CPC Class Codes: F25J 2260/80 : Integration in an installation using carbon dioxide, e.g. for EOR, sequestration, refrigeration etc.
• CPC Class Codes: F25J 2270/02 : Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/80 : Quasi-closed internal or closed external carbon dioxide refrigeration cycle
• CPC Class Codes: F25J 2270/88 : Quasi-closed internal refrigeration or heat pump cycle, if not otherwise provided
• CPC Class Codes: F25J 2290/40 : Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.
• CPC Class Codes: F25J 3/0257 : separation of nitrogen from air F25J3/04, production of nitrogen in general C01B21/00
• CPC Class Codes: F25J 3/0266 : separation of carbon dioxide production of carbon dioxide in general C01B32/00
• CPC Class Codes: F25J 3/029 : of helium
• CPC Class Codes: F25J 3/08 : Separating gaseous impurities from gases or gaseous mixtures or from liquefied gases or liquefied gaseous mixturescold traps B01D8/00
• CPC Class Codes: Y02B 30/52 : Heat recovery pumps, i.e. heat pump based systems or units able to transfer the thermal energy from one area of the premises or part of the facilities to a different one, improving the overall efficiency
• CPC Class Codes: Y02C 20/40 : of CO2
• CPC Class Codes: Y02P 20/10 : Process efficiency
• CPC Class Codes: Y02P 20/129 : Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
• CPC Class Codes: Y02P 20/151 : Reduction of greenhouse gas [GHG] emissions, e.g. CO2

Abstract

In a process for separating at least one “heavy” impurity such as hydrogen sulfide from crude carbon dioxide comprising significant quantities of at least one “light” impurity such as non-condensable gases, involving at least one heat pump cycle using carbon dioxide-containing fluid from the process as the working fluid, the “light” impurity is removed from the crude carbon dioxide and carbon dioxide is subsequently recovered from the removed “light” impurity, thereby improving overall carbon dioxide recovery and efficiency in terms of energy consumption.

Claims

1. A process for purifying crude carbon dioxide fluid comprising at least one “

light”

impurity and at least one “

heavy”

impurity, said process comprising;

cooling said crude carbon dioxide fluid above the triple point pressure of carbon dioxide by indirect heat exchange to produce cooled crude carbon dioxide fluid;

feeding said cooled crude carbon dioxide fluid to a first column system for mass transfer separation to produce “

light”

impurity-enriched overhead vapor and “

light”

impurity-depleted carbon dioxide bottoms liquid comprising said “

heavy”

impurity;

re-boiling said first column system by vaporizing “

light”

impurity-depleted bottoms liquid by indirect heat exchange to provide vapor for said first column system;

feeding “

light”

impurity-depleted bottoms liquid from said first column system to a second column system for mass transfer separation to produce carbon dioxide-enriched overhead vapor and “

heavy”

impurity-enriched bottoms liquid;

providing carbon dioxide-enriched liquid as reflux for said second column system;

re-boiling said second column system by indirect heat exchange to provide vapor for said second column system;

wherein said first and second column systems operate above the triple point pressure and below the critical pressure of carbon dioxide;

wherein said process comprises at least one heat pump cycle using as working fluid carbon dioxide-containing fluid from said second column system;

wherein said second column system is re-boiled by at least partially vaporizing at least one “

heavy”

impurity-enriched liquid in or taken from said second column system by indirect heat exchange against carbon dioxide-containing vapor from said second column system; and

wherein said overhead vapor from said first column system comprises carbon dioxide and at least a portion of said carbon dioxide is recovered from said overhead vapor to produce “

light”

impurity-rich residual gas and recovered carbon dioxide.

2. The process of claim 1, wherein said recovered carbon dioxide is fed to said second column system for mass transfer separation.

3. The process of claim 1, wherein said cooled crude carbon dioxide fluid is expanded prior to being fed to said first column system.

4. The process of claim 3, wherein said cooled crude carbon dioxide fluid is below the critical pressure of carbon dioxide prior to expansion.

5. The process of claim 3, wherein said cooled crude carbon dioxide fluid is above the critical pressure of carbon dioxide prior to expansion.

6. The process of claim 1, wherein said overhead vapor from said first column system is cooled prior to carbon dioxide recovery.

7. The process of claim 6, wherein said overhead vapor is cooled by indirect heat exchange to condense carbon dioxide in the vapor which is recovered by phase separation.

8. The process of claim 1, wherein carbon dioxide and said at least one “

heavy”

impurity are washed out of said overhead vapor from said first column system in a wash column using as washing liquid carbon dioxide-enriched liquid from said second column system.

9. The process of claim 8, wherein said overhead vapor from said first column system is cooled but not condensed prior to being fed as cooled vapor to said wash column.

10. The process of claim 8, wherein said overhead vapor from said first column system is cooled by direct heat exchange with said washing liquid in said wash column.

11. The process of claim 8, wherein said overhead vapor from said first column system is cooled by indirect heat exchange.

12. The process of claim 1, wherein said overhead vapor from said first column system is warmed by indirect heat exchange prior to carbon dioxide recovery.

13. The process of claim 1, wherein carbon dioxide is recovered from said overhead vapor from said first column system using a process selected from the group consisting of adsorption;

absorption;

membrane separation; and

solidification.

14. The process of claim 1, wherein said second column system comprises at least two distillation sections and said “

light”

impurity depleted carbon dioxide bottoms liquid from said first column system is fed to said second column system at an intermediate zone between adjacent distillation sections.

15. The process of claim 14, wherein said second column system is re-boiled by vaporizing liquid in or taken from said or another intermediate zone.

16. The process of claim 1, wherein said crude carbon dioxide fluid is either a vapor that is at least partially condensed during said cooling, or a supercritical fluid that is “

pseudo-condensed”

during said cooling, to produce said cooled crude carbon dioxide fluid.

17. The process of claim 16, wherein said cooled crude carbon dioxide fluid is expanded prior to being fed to said first column system.

18. The process of claim 16, wherein re-boil duty for said first column system is provided at least in part by indirect heat exchange against condensing, or pseudo-condensing, crude carbon dioxide fluid.

19. The process of claim 16, wherein re-boil duty for said first column system is provided at least in part by indirect heat exchange against condensing recycle fluid in said heat pump cycle.

20. The process of claim 1, wherein said first column system comprises a distillation column system, said cooled crude carbon dioxide fluid being fed to said distillation column system for distillation to produce said “

light”

impurity-enriched overhead vapor and said “

light”

impurity-depleted carbon dioxide bottoms liquid.

21. The process of claim 1, wherein said crude carbon dioxide fluid comprises at least one first “

light”

impurity and at least one second “

light”

impurity, said first “

light”

impurity being more volatile than said second “

light”

impurity.

22. The process of claim 21, wherein said first column system comprises a first distillation column system and a second distillation column system, said process comprising:

feeding said cooled crude carbon dioxide fluid to said first distillation column system to produce overhead vapor enriched in said first “

light”

impurity, and bottoms liquid depleted in said first “

light”

impurity;

re-boiling said first distillation column system by indirect heat exchange to provide vapor for said first distillation column system;

feeding bottoms liquid from said first distillation column system to said second distillation column system to produce said “

light”

impurity-enriched overhead vapor and said “

light”

impurity depleted carbon dioxide bottoms liquid; and

feeding bottoms liquid from said second distillation column system to said first distillation column system, preferably as reflux.

23. The process of claim 22, wherein said bottoms liquid from said second distillation column system is pumped prior to being fed to said first distillation column system.

24. The process of claim 22, wherein reflux to said first distillation column system is provided using carbon dioxide-enriched liquid from said second column system.

25. The process of claim 24, wherein said carbon dioxide-enriched liquid from said second column system is pumped prior to being fed to said first distillation column system.

26. The process of claim 22, wherein said bottoms liquid from said first distillation column system is expanded prior to being fed to said second distillation column system.

27. The process of claim 22, wherein helium is a first “

light”

impurity and wherein methane, ethane and nitrogen are second “

light”

impurities.

28. The process of claim 1, wherein said “

light”

impurity depleted carbon dioxide bottoms liquid from said first column system is subcooled prior to being fed to said second column system.

29. The process of claim 1, wherein said “

light”

impurity depleted carbon dioxide bottoms liquid from said first column system is expanded prior to being fed to said second column system.

30. The process of claim 29, wherein said “

light”

impurity depleted carbon dioxide bottoms liquid from said first column system is subcooled by indirect heat exchange prior to being expanded.

31. The process of claim 1, wherein said “

light”

impurity depleted carbon dioxide bottoms liquid from said first column system is at least partially vaporized prior to being fed to said second column system.

32. The process of claim 31, wherein said “

light”

impurity depleted carbon dioxide bottoms liquid from said first column system is subcooled by indirect heat exchange and optionally expanded prior to being at least partially vaporized.

33. The process of claim 31, wherein said “

light”

impurity depleted carbon dioxide bottoms liquid from said first column system is expanded prior to being at least partially vaporized.

34. The process of claim 1, wherein said heat pump cycle comprises:

after optionally at least partially vaporizing said carbon dioxide-containing working fluid from said second column system by indirect heat exchange, warming said optionally at least partially vaporized carbon dioxide-containing working fluid to produce warmed carbon dioxide-containing gas;

compressing said warmed carbon dioxide-containing gas to form compressed carbon dioxide-containing recycle gas;

cooling and optionally at least partially condensing said compressed carbon dioxide-containing recycle gas by indirect heat exchange to produce cooled carbon dioxide-containing recycle fluid; and

recycling at least a portion of said cooled carbon dioxide-containing recycle fluid to said second column system,

wherein said working fluid is expanded as required either prior to said optional vaporization and warming to produce said warmed carbon dioxide-containing gas, or after said cooling and optional condensation to produce said cooled carbon-dioxide containing recycle fluid prior to recycling said recycle fluid to said second column system.

35. The process of claim 1, wherein said working fluid is carbon dioxide-enriched overhead vapor, said heat pump cycle comprising:

warming said carbon dioxide-enriched overhead vapor by indirect heat exchange to produce warmed carbon dioxide-enriched gas;

compressing said carbon dioxide-enriched gas to produce compressed carbon dioxide-enriched recycle gas;

using said compressed carbon dioxide-enriched recycle gas to provide at least a part of the reboil duty required to vaporize said “

heavy”

impurity-enriched liquid(s) thereby cooling and at least partially condensing said compressed carbon dioxide-enriched recycle gas to produce carbon dioxide-enriched liquid;

expanding said carbon dioxide-enriched liquid to produce expanded carbon dioxide-enriched liquid; and

using at least a portion of said expanded carbon dioxide-enriched liquid to provide said reflux to said second column system.

36. The process of claim 1, wherein said working fluid is an “

heavy”

impurity-enriched liquid from said second column system, said heat pump cycle comprising;

expanding said “

heavy”

impurity-enriched liquid to produce expanded “

heavy”

impurity-enriched liquid;

at least partially vaporizing said expanded “

heavy”

impurity-enriched liquid by indirect heat exchange against said carbon dioxide-enriched overhead vapor to produce “

heavy”

impurity-enriched vapor and at least partially condensed carbon dioxide-enriched overhead vapor;

compressing said “

heavy”

impurity-enriched vapor to produce compressed “

heavy”

impurity-enriched recycle vapor;

cooling said compressed “

heavy”

impurity-enriched recycle vapor by indirect heat exchange to produce cooled “

heavy”

impurity-enriched recycle vapor; and

feeding said cooled “

heavy”

impurity-enriched recycle vapor to said second column system,

wherein said at least partially condensed carbon dioxide-enriched overhead vapor is used at least in part as said carbon dioxide-enriched liquid providing said reflux to said second column system.

37. The process of claim 36, wherein said “

heavy”

impurity-enriched vapor is warmed by indirect heat exchange to produce warmed “

heavy”

impurity-enriched vapor prior to compression.

38. The process of claim 1, wherein said “

light”

impurity-rich residual gas is warmed by indirect heat exchange and purged from said process.

39. The process of claim 1, wherein said “

light”

impurity-rich residual gas is warmed by indirect heat exchange and added to carbon dioxide gas removed as product from said second column system.

40. The process of claim 1, wherein at least one “

light”

impurity is selected from the group consisting of hydrogen;

methane;

C₂ hydrocarbons; and

mixtures thereof, said “

light”

impurity-rich residual vapor being used as a fuel for combustion to produce combustion product gas.

41. The process of claim 40, wherein heat is recovered from said combustion product gas by indirect heat exchange.

42. The process of claim 1, wherein said crude carbon dioxide fluid comprises carbon dioxide in an amount of at least about 50 mol %.

43. The process of claim 1, wherein said crude carbon dioxide fluid comprises said at least one “

light”

impurity in an amount of no more than about 50 mol % in total.

44. The process of claim 1, wherein said crude carbon dioxide fluid comprises said at least one “

heavy”

impurity in an amount of no more than about 50 mol % in total.

45. The process of claim 1 wherein at least one “

light”

impurity is selected from the group consisting of nitrogen;

oxygen;

argon;

neon;

xenon;

krypton;

carbon monoxide;

nitric oxide;

nitrous oxide;

hydrogen;

helium;

methane; and

C₂ hydrocarbons.

46. The process of claim 1, wherein at least one “

heavy”

impurity is selected from the group consisting of hydrogen sulfide;

methanol;

C₃ to C₈ hydrocarbons;

carbon disulfide;

carbon oxysulfide;

dimethyl sulfide and other organic sulfur compounds;

nitrogen dioxide, sulfur dioxide;

sulfur trioxide; and

ammonia.

47. The process of claim 1, wherein at least one “

heavy”

impurity is hydrogen sulfide.

48. The process of claim 47, wherein at least one “

light”

impurity is selected from the group consisting of nitrogen;

argon;

helium;

methane; and

ethane.

49. The process of claim 1, wherein said “

light”

impurity-rich residual gas comprises methane, nitrogen and helium, said process comprising rejecting nitrogen and helium from methane and recovering helium from the rejection process.

50. The process of claim 1, wherein the operating pressure(s) of said first column system is from about 10 bar to about 60 bar, and preferably from about 30 bar to about 50 bar.

51. The process of claim 1, wherein the operating pressure(s) of said second column system is from about 5.2 bar to about 40 bar, and preferably from 15 bar to about 25 bar.

52. The process of claim 1, wherein the process is auto-refrigerated.

53. Apparatus for purifying crude carbon dioxide fluid comprising at least one “

light”

impurity and at least one “

heavy”

impurity, said apparatus comprising;

a first heat exchanger for cooling said crude carbon dioxide fluid by indirect heat exchange to produce cooled crude carbon dioxide fluid;

a first column system in fluid flow communication with said first heat exchanger for separating said cooled crude carbon dioxide fluid by mass transfer separation to produce “

light”

impurity-enriched overhead vapor and “

light”

impurity-depleted carbon dioxide bottoms liquid comprising said “

heavy”

components, said first column system comprising a first re-boiler for re-boiling by indirect heat exchange bottoms liquid produced by said first column system;

a second column system in fluid flow communication with said first column system for separating said bottoms liquid from said first column system by mass transfer separation to produce carbon dioxide-enriched overhead vapor and bottoms liquid enriched with said heavy impurity;

a second heat exchanger in fluid flow communication with said second column system for warming carbon dioxide-enriched overhead vapor from said second column system by indirect heat exchange to produce warmed carbon dioxide-enriched gas;

a first compressor in fluid flow communication with said second heat exchanger for compressing said warmed carbon dioxide-enriched gas to produce compressed carbon dioxide-enriched recycle gas;

a third heat exchanger in fluid flow communication with said first compressor for cooling and at least partially condensing said compressed carbon dioxide-enriched recycle gas by indirect heat exchange to form at least partially condensed carbon dioxide-enriched liquid;

a first pressure reduction arrangement in fluid flow communication with said third heat exchanger for expanding said at least partially condensed carbon dioxide-enriched liquid;

a conduit arrangement for providing at least partially condensed carbon dioxide-enriched liquid from said first pressure reduction arrangement to said second column system as reflux; and

a carbon dioxide recovery system in fluid flow communication with said first column system for recovering carbon dioxide from said overhead vapor from said first column system to produce “

light”

impurity-rich residual gas and recovered carbon dioxide,

wherein said third heat exchanger is arranged to re-boil said second column system by vaporizing “

heavy”

impurity-enriched liquid in or taken from said second column system by said indirect heat exchange against said condensing carbon dioxide recycle gas.

55. The apparatus of claim 53 or claim 54, wherein the apparatus further comprises a conduit arrangement for feeding recovered carbon dioxide from said carbon dioxide recovery system to said second column system for mass transfer separation.

56. The apparatus of claim 53 or claim 54, wherein said apparatus comprises a second pressure reduction arrangement provided in said fluid flow communication between said first heat exchanger and said first column system for expanding said cooled crude carbon dioxide fluid.

57. The apparatus of claim 53 or claim 54, wherein said apparatus comprises a fourth heat exchanger provided in said fluid flow communication between said first column system and said carbon dioxide recovery system for cooling said overhead vapor from said first column system by indirect heat exchange.

58. The apparatus of claim 53 or claim 54, wherein said carbon dioxide recovery system comprises:

a fifth heat exchanger in fluid flow communication with said first column system for partially condensing said overhead vapor from said first column system by indirect heat exchange; and

a phase separator in fluid flow communication with said fifth heat exchanger for separating said “

light”

impurity-rich residual gas from said recovered carbon dioxide in the form of condensate.

59. The apparatus of claim 53 or claim 54, wherein said carbon dioxide recovery system comprises:

a wash column in fluid flow communication with said first column system for washing carbon dioxide and said “

heavy”

impurity from said overhead vapor from said first column system to produce said “

light”

impurity-rich residual gas and said recovered carbon dioxide; and

a conduit arrangement for feeding carbon dioxide-enriched liquid from said second column system to said wash column.

60. The apparatus of claim 53 or claim 54, wherein said second column system comprises:

at least two distillation sections;

an intermediate zone between adjacent distillation sections; and

an inlet for feeding bottoms liquid from said first column system to said second column system at said intermediate zone.

61. The apparatus of claim 59, wherein said third heat exchanger is arranged to re-boil liquid in or taken from said or another intermediate zone of said second column system.

62. The apparatus of claim 53 or claim 54, wherein said apparatus comprises a third pressure reduction arrangement in said fluid flow communication between said first heat exchanger and said first column system for expanding said crude carbon dioxide fluid.

63. The apparatus of claim 53 or claim 54, wherein said first re-boiler is at least a part of said first heat exchanger, said first heat exchanger being arranged to re-boil said bottoms liquid produced by said first column system by said indirect heat exchange against said condensing crude carbon dioxide fluid.

64. The apparatus of claim 53 or claim 54, wherein said first re-boiler is at least a part of said third heat exchanger, said third heat exchanger being arranged to re-boil said bottoms liquid produced by said first column system by said indirect heat exchange against said condensing carbon dioxide fluid.

65. The apparatus of claim 53 or claim 54, wherein said first column system comprises a distillation column system.

66. The apparatus of claim 53 or claim 54, wherein said first column system comprises:

a first distillation column system for separating crude carbon dioxide fluid into overhead vapor enriched in a first “

light”

impurity, and bottoms liquid depleted in said first “

light”

impurity, wherein said first distillation column system comprises a second re-boiler for re-boiling by indirect heat exchange bottoms liquid produced by said first distillation column system;

a second distillation column system in fluid flow communication with said first distillation column system for separating bottoms liquid from said first distillation column system into said “

light”

impurity-enriched overhead vapor and said “

light”

impurity-depleted carbon dioxide bottoms liquid; and

a conduit arrangement for providing bottoms liquid from said second distillation column system to said first distillation column system, preferably as reflux,

wherein said first re-boiler is arranged to re-boil said second distillation column system.

67. The apparatus of claim 66, wherein said conduit arrangement for providing bottoms liquid from said second distillation column system to said first distillation column system comprises a first pump for pumping bottoms liquid from said second distillation column system to said first distillation column system.

68. The apparatus of claim 66, wherein said apparatus comprises a conduit arrangement for providing carbon dioxide-enriched liquid from said second column system as reflux to said first distillation column system.

69. The apparatus of claim 68, wherein said conduit arrangement for providing carbon dioxide-enriched liquid from said second column system to said first distillation column system comprises a second pump for pumping carbon dioxide liquid from said second column system to first distillation column system.

70. The apparatus of claim 66, wherein said apparatus comprises a fourth pressure reduction arrangement in said fluid flow communication between said first and second distillation column systems for expanding said bottoms liquid from said first distillation column system prior to being fed to said second distillation column system.

71. The apparatus of claim 53 or claim 54, wherein said apparatus comprises a sixth heat exchanger in said fluid flow communication between said first column system and said second column system for subcooling bottoms liquid from said first column system by indirect heat exchanger prior to feeding to said second column system.

72. The apparatus of claim 53 or claim 54, wherein said apparatus comprises a fifth pressure reduction arrangement in said fluid flow communication between said first column system and said second column system for expanding bottoms liquid from said first column system prior to feeding to said second column system.

73. The apparatus of claim 53 or claim 54, wherein said apparatus comprises a seventh heat exchanger in said fluid flow communication between said first column system and said second column system for vaporizing bottoms liquid from said first column system prior to feeding to said second column system.

54. Apparatus for purifying crude carbon dioxide fluid comprising at least one “

light”

impurity and at least one “

heavy”

impurity, said apparatus comprising;

a first heat exchanger for cooling said crude carbon dioxide fluid by indirect heat exchange to produce cooled crude carbon dioxide fluid;

a first column system in fluid flow communication with said first heat exchanger for separating said cooled crude carbon dioxide fluid by mass transfer separation to produce “

light”

impurity-enriched overhead vapor and “

light”

impurity-depleted carbon dioxide bottoms liquid comprising said “

heavy”

components, said first column system comprising a first re-boiler for re-boiling by indirect heat exchange bottoms liquid produced by said first column system;

a second column system in fluid flow communication with said first column system for separating said bottoms liquid from said first column system by mass transfer separation to produce carbon dioxide-enriched overhead vapor and bottoms liquid enriched with said heavy impurity;

a first pressure reduction arrangement in fluid flow communication with said second column system for expanding “

heavy”

impurity-enriched liquid from said second column system to produce expanded “

heavy”

impurity-enriched liquid;

a second heat exchanger in fluid flow communication with said first pressure reduction arrangement for at least partially vaporizing said expanded “

heavy”

impurity-enriched liquid by indirect heat exchange to produce expanded “

heavy”

impurity-enriched gas;

a first compressor in fluid flow communication with said second heat exchanger for compressing said expanded “

heavy”

impurity-enriched gas to produce compressed “

heavy”

impurity-enriched recycle gas;

a third heat exchanger in fluid flow communication with said first compressor for cooling said compressed “

heavy”

impurity-enriched recycle gas by indirect heat exchange to form cooled “

heavy”

impurity-enriched recycle gas;

a conduit arrangement for feeding said cooled “

heavy”

impurity-enriched recycle gas from said third heat exchanger to said second column system; and

a carbon dioxide recovery system in fluid flow communication with said first column system for recovering carbon dioxide from said overhead vapor from said first column system to produce “

light”

impurity-rich residual gas and recovered carbon dioxide,

wherein said second heat exchanger is arranged to at least partially condense carbon dioxide-enriched overhead vapor from said second column system by said indirect heat exchange against said vaporizing expanded “

heavy”

impurity-enriched liquid.

74. The apparatus of claim 54, comprising an eighth heat exchanger in said fluid flow communication between said second heat exchanger and said first compressor for warming said expanded “

heavy”

impurity-enriched gas to produce warmed expanded “

heavy”

impurity-enriched gas for compression.