Method and installation for fractionating gas derived from pyrolysis of hydrocarbons

• US 20040237581A1
• Filed: 03/15/2004
• Published: 12/02/2004
• Est. Priority Date: 09/13/2001
• Status: Active Grant

• Current Assignee: Technip France (Technip)
• Original Assignee: Technip France (Technip)
• Inventors: Paradowski, Henri
• Granted Patent: US 7,185,514 B2
• Time in Patent Office: Days
• US Class Current: 62/620
• 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 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/02 Multiple feed streams, e.g. originating from different sources
• CPC Class Codes: F25J 2210/04 Mixing or blending of fluids with the feed stream
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2210/62 Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
• CPC Class Codes: F25J 2235/60 the fluid being (a mixture of) hydrocarbons
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2245/90 the recycled stream being boil-off gas from storage
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/04 Internal refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 2270/60 Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• CPC Class Codes: F25J 2270/904 by liquid or gaseous cryogen in an open loop
• CPC Class Codes: F25J 3/0219 Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0252 separation of hydrogen production of hydrogen containing gas in general C01B3/00, e.g. separation of hydrogen or hydrogen containing gases form gaseous mixtures at low temperatures C01B3/506

Abstract

The invention relates to a method for fractionating a gas produced by the pyrolysis of hydrocarbons (1) for the recovery of C₂ and higher hydrocarbons, in particular ethylene and ethane, comprising an operation (70) for compressing and drying gas (1) as a result of it passing into a series of compressors (3, 10, 17, 24, 36), an operation (80) for progressively cooling and partially liquefying the gas produced by compression and drying operation (70) as a result of it successively passing into a cryogenic exchanger (62), and a distillation operation (90) in a column (64), and the corresponding installation.

According to the invention, cryogenic exchanger (62) is cooled by at least one cooling liquid (400) which is liquid natural gas (LNG).

Claims

1. A method of fractionating a gas (1) produced by the pyrolysis of hydrocarbons, encompassing hydrogen and hydrocarbons, in particular C₁ to C₄ hydrocarbons including ethylene, ethane and methane, possibly water and CO₂, into at least a first current (76) enriched in hydrogen and methane, possibly at least a second current (31) essentially consisting of water, comprising:

a) an operation (70) for compressing and drying gas (1) as a result of it passing into a series of compressors (3, 10, 17, 24, 36) each connected to a cooler respectively (4, 11, 18, 25, 37) and a separator respectively (5, 12, 19, 26, 39), and further comprising a CO₂-removal stage, should gas (1) contain a surplus thereof, in order to obtain a compressed gas (73),

b) an operation (80) for progressively cooling and partially liquefying a gas (73) produced by the compression and drying operation a), as a result of it successively passing into a cryogenic exchanger (62) and being separated in separators (44, 46, 49, 52, 55) into

(i) liquids respectively (71, 48, 51, 54, 56) enriched in C₂ and higher hydrocarbons, in particular in ethylene and ethane, but low in hydrogen and methane, and into

(ii) gases respectively (45, 47, 50, 53, 59) depleted in C₂ and higher hydrocarbons, in particular in ethylene and ethane, each successive passage into cryogenic exchanger (62) bringing the gases (73, 45, 47, 50, 53) to a relatively lower temperature and therefore allowing the hydrocarbons to be liquefied in a more complete manner, gas (59) produced by last separator (55) making up first current (76) essentially containing hydrogen and methane and a very small amount of ethylene and ethane, this gas (59) then being collected, the cryogenic exchanger (62) being cooled by at least one cooling fluid (400) which is liquid natural gas (LNG),

c) a distillation operation (90),

characterized in that;

d) gas (73) undergoing the progressive cooling and partial liquefaction operation b) is formed with the gas produced in the compression and drying operation a),

e) the distillation operation c) is performed in a column (64), supplied at various levels with liquids (71, 48, 51, 54, 56) collected during operation b) and partially expanded, said column (64) allowing the separation, into a relatively colder upper part, of a gaseous top current (65) enriched in methane and depleted in ethylene and ethane, and, into a relatively less cold lower part, of a liquid bottom current (66) depleted in methane and enriched in ethylene and ethane, top current (65) being recycled during operation a) upstream of the compressor, the feed pressure of which is closest to the operating pressure of column (64), bottom current (66) and collected and making up a third current (77) containing most of the other C₂ and higher hydrocarbons, in particular ethylene and ethane,

f) the temperature of LNG (400) upon entering cryogenic exchanger (62) can vary from minus 89°

C. to minus 160°

C.;

g) gas (59) produced by last separator (55), top current (65) and bottom current (66) are heated in cryogenic exchanger (62).

2. Method of fractionating a gas produced by the pyrolysis of hydrocarbons according to claim 1, characterised in that gas (59) produced by last separator (55) is divided into a stream (60) heated in cryogenic exchanger (62) and a stream (61) expanded and cooled in a turbine (68) then heated in cryogenic exchanger (62).

3. Method of fractionating a gas produced by the pyrolysis of hydrocarbons according to claim 1, characterised in that cryogenic exchanger (62) is fed with two streams of LNG, a high pressure stream (402) at a first, relatively higher pressure and a medium pressure stream (401) at a second, relatively lower pressure.

4. Method of fractionating a gas produced by the pyrolysis of hydrocarbons according to claim 3, characterised in that medium pressure stream (401) of LNG feeding cryogenic exchanger (62) is produced by deriving a part of high pressure stream (402) and expanding said stream in order to reduce its temperature, the flow rate of medium pressure stream (401) depending on the temperature of LNG stream (400) and being all the more large since this temperature is high.

9. Method of fractionating a gas produced by the pyrolysis of hydrocarbons according to claim 2, characterised in that cryogenic exchanger (62) is fed with two streams of LNG, a high pressure stream (402) at a first, relatively higher pressure and a medium pressure stream (401) at a second, relatively lower pressure.

5. Installation for fractionating a gas (1) produced by the pyrolysis of hydrocarbons, encompassing hydrogen and hydrocarbons, in particular C₁ to C₄ hydrocarbons including ethylene, ethane and methane, possibly water and CO₂, into at least a first current (76) enriched in hydrogen and methane, possibly at least a second current (31) essentially consisting of water, comprising:

a) a unit (70) for compressing and drying gas (1) as a result of it passing into a series of compressors (3, 10, 17, 24, 36) each connected to a cooler respectively (4, 11, 18, 25, 37) and a separator respectively (5, 12, 19, 26, 39), further comprising a CO₂-removal stage, should gas (1) contain a surplus thereof, in order to obtain a compressed gas (73),

b) a unit (80) for progressively cooling and partially liquefying a gas (73) produced by compression and drying unit (70) as a result of it passing successively into a cryogenic exchanger (62) and being separated in separators (44, 46, 49, 52, 55) into (i) liquids respectively (71, 48, 51, 54, 56) enriched in C₂ and higher hydrocarbons, in particular in ethylene and ethane, but low in hydrogen and methane, and

(ii) gases respectively (45, 47, 50, 53, 59) depleted in C₂ and higher hydrocarbons, in particular in ethylene and ethane, each successive passage into cryogenic exchanger (62) bringing gases (73, 45, 47, 50, 53) to a relatively lower temperature and therefore allowing the hydrocarbons to be liquefied in a more complete manner, gas (59) produced by last separator (55) making up first current (76) essentially containing hydrogen and methane and a very small amount of ethylene and ethane, this gas (59) then being collected, the cryogenic exchanger (62) being cooled by at least one cooling fluid (400) which is liquid natural gas (LNG),

c) a distillation unit (90);

characterized in that;

d) gas (73) undergoing the progressive cooling and partial liquefaction is formed with the gas produced in the compression and drying unit (70);

e) said distillation unit (90) essentially comprises a column (64), supplied at various levels with liquids (71, 48, 51, 54, 56) collected in progressive cooling and partial liquefaction unit (80) and partially expanded, said column (64) allowing the separation, into a relatively colder upper part, of a gaseous top current (65) enriched in methane and depleted in ethylene and ethane, and, into a relatively less cold lower part, of a liquid bottom current (66) depleted in methane and enriched in ethylene and ethane, top current (65) being recycled in unit (70) upstream of the compressor, the feed pressure of which is closest to the operating pressure of column (64), bottom current (66) being collected and making up third current (77) containing most of the other C₂ and higher hydrocarbons, in particular ethylene and ethane,

f) the temperature of LNG (400) upon entering cryogenic exchanger (62) can vary from minus 89°

C. to minus 160°

C.; and

g) gas (59) produced by last separator (55), top current (65) and bottom current (66) are heated in cryogenic exchanger (62).

6. Installation for fractionating a gas produced by the pyrolysis of hydrocarbon according to claim 5, characterised in that gas (59) produced by last separator (55) is divided into a stream (60) heated in cryogenic exchanger (62) and a stream (61) expanded and cooled in a turbine (68) then heated in cryogenic exchanger (62).

7. Installation for fractionating a gas produced by the pyrolysis of hydrocarbons according to claim 5, characterised in that cryogenic exchanger (62) is fed with two streams of LNG, a high pressure stream (402) at a first, relatively higher pressure and a medium pressure stream (401) at a second, relatively lower pressure.

8. Installation for fractionating a gas produced by the pyrolysis of hydrocarbons according to claim 7, characterised in that medium pressure stream (401) of LNG feeding cryogenic exchanger (62) is produced by deriving a part of high pressure stream (402) and expanding said stream to reduce its temperature, the flow rate of medium pressure stream (401) depending on the temperature of LNG stream (400) and being all the more large since this temperature is high.

10. Installation for fractionating a gas produced by the pyrolysis of hydrocarbons according to claim 6, characterised in that cryogenic exchanger (62) is fed with two streams of LNG, a high pressure stream (402) at a first, relatively higher pressure and a medium pressure stream (401) at a second, relatively lower pressure.