Method of and arrangement for processing through low temperature heat exchanges and in particular for treating natural gases and cracked gases

• US 4,072,485 A
• Filed: 10/04/1976
• Issued: 02/07/1978
• Est. Priority Date: 01/30/1976
• Status: Expired due to Term

• Current Assignee: Compagnie Francaise D'Etudes et de Construction Technip
• Original Assignee: Compagnie Francaise D'Etudes et de Construction Technip
• Inventors: Paradowski, Henri, Kaiser, Victor, Becdelievre, Charles
• Primary Examiner(s): Bernstein, Hiram H.
• Application Number:
  US05/729,182
• Time in Patent Office: 491 Days
• Field of Search: 62/40, 62/9, 62/23, 62/114
• US Class Current: 62/612
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0092 Mixtures of hydrocarbons comprising possibly also minor amounts of nitrogen
• CPC Class Codes: F25J 1/0267 using flash gas as heat sink
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2270/12 External refrigeration with liquid vaporising 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 2270/66 Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• CPC Class Codes: F25J 2270/902 Details about the refrigeration cycle used, e.g. composition of refrigerant, arrangement of compressors or cascade, make up sources, use of reflux exchangers etc.
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• 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 3/061 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/062 Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• CPC Class Codes: F25J 3/0635 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/064 separation of CnHm with 2 carbon atoms or more

Abstract

A method of processing through low temperature heat exchanges natural gases and cracked gases consisting in using a cooling cycle including compressing and then cooling a cycle mixture of gases consisting of C1 hydrocarbons, C2 hydrocarbons and C3 hydrocarbons through outer coolers with attendant total liquefaction of the cycle mixture under pressure; subsequently effecting a sub-cooling of the mixture within heat exchanges in counter-current relation to one expanded part thereof and/or cold returns and rejects of products processed in the cycle and finally expanding said sub-cooled mixture in at least one exchanger where various cooling processes of the treated products are carried out at successive temperature levels.

Claims

1. In a method for refrigerating a natural gas or a cracked gas by indirect heat exchange with a cycle gas mixture at temperatures ranging from -40°

C. to -140°

C., the improvement comprising the sequence of steps

compressing a cycle gas mixture consisting essentially of C₁, C₂ and C₃ hydrocarbons,

cooling said compressed cycle gas mixture in a plurality of successive staged external, indirect heat exchanges with coolants selected from the group consisting of water, air, propane and propylene to about 40°

C., whereby said cycle mixture is fully condensed,

dividing the fully condensed cycle mixture into at least an auxiliary stream and a remaining stream,

passing said auxiliary stream through an auxiliary heat exchanger countercurrently in indirect heat exchange with a colder stream employed in refrigerating the natural gas, whereby said auxiliary stream is sub-cooled,

passing said remaining stream through a main heat exchanger countercurrently in indirect heat exchange with a combined liquefied sub-cooled cycle mixture as defined below after the latter has been expanded and passed into said main heat exchanger, whereby said remaining stream is sub-cooled,

combining said sub-cooled auxiliary and remaining streams to form said combined liquefied sub-cooled cycle mixture,

expanding said combined sub-cooled stream and passing it at a temperature of from about -100°

C. to about -140°

C. countercurrently into said main heat exchanger in indirect heat exchange with said remaining stream and with a warmer stream employed in refrigerating the natural gas.

2. A method according to claim 1, comprising the step of making said cycle mixture work between staged absolute pressures ranging from 1 bar to 3 bars at the suction side of the compressors and from 30 bars to 50 bars at the delivery side of the compressors.

3. A method according to claim 1, comprising the step of using as a cycle mixture a mixture comprising about 7% to 12% of C₁ hydrocarbon, 30% to 45% of C₂ hydrocarbons and 50% to 60% of C₃ hydrocarbons.

4. A method according to claim 3, wherein the cycle mixture is a mixture comprising about 8% of C₁ hydrocarbon, 37% to 42% of C₂ hydrocarbons and 50% to 55% of C₃ hydrocarbons.

5. A method according to claim 1, wherein the cycle mixture is a mixture comprising about:

N₂ ;

0% to 3%

C₁ ;

5% to 25%

C₂ ;

30% to 60%

C₃ ;

30% to 60%.

6. A method according to claim 1, wherein the cycle mixture is a mixture comprising:

C₁ ;

20% to 40%

C₂ ;

30% to 60%

C₃ ;

5% to 15%

C₄ ;

5% to 15%.

7. A method according to claim 6, wherein said cycle mixture has the following composition:

methane;

30%

ethylene;

30%;

ethane;

20%

propane;

10%

isobutane;

10%.

8. A method according to claim 1, wherein the cycle mixture is a mixture having the following composition:

N₂ >

0.5%

c₁ ;

20% to 40%

C₂ ;

30% to 60%

C₃ ;

20% to 35%.

9. A method according to claim 8, wherein said cycle mixture has the following composition:

nitrogen;

1.5%

methane;

30%

ethylene;

20%;

ethane;

20%

propane;

28.5%.

10. A method according to claim 1, wherein said cycle mixture contains at least one of ethylene and propylene.

11. A system for refrigerating a natural gas or a cracked gas with a fluid cycle comprising multi-component refrigerant fluid at a low temperature of from -40°

C. to -140°

C., the multi-component refrigerant fluid consisting essentially of C₁, C₂ and C₃ hydrocarbons, the system comprising;

compression means for compressing said refrigerant fluid in the gaseous condition from an absolute pressure of about 1 bar to 3 bars at the suction side of the compression means to an absolute pressure of about 30 bars to 50 bars at the delivery side of the compression means;

successive stage external coolers coupled to said compression means and operating with coolants selected from the group consisting of water, air, propane and propylene for providing at least full condensation of said refrigerant fluid after compression;

at least one main heat exchanger coupled to at least one of said successive stage external cooler for receiving therefrom a first part of said condensed refrigerant fluid, and including inlet means and cold outlet means for said first part of said condensed refrigerant fluid, an expansion means at its cold end at a temperature of from about -100°

C. to about -140°

C. for expansion of said refrigerant fluid to the pressure at the suction side of the compression means, a vapor passage coupled to the expansion means for passing vaporized refrigerant fluid through the main exchanger for sub-cooling said first part of said condensed refrigerant fluid in indirect heat exchange therewith, and further inlet and further outlet means containing a warmer stream than said refrigerant vapor in indirect heat exchange relation with vapor in said exchanger;

at least one auxiliary heat exchanger having an inlet means and a cold outlet means, the inlet means thereof being coupled to said at least one of said successive stage external coolers for receiving a second part of said condensed refrigerant fluid, and having further inlet and further outlet means containing a colder stream than said second part of said condensed refrigerant fluid for sub-cooling said second part of said condensed refrigerant fluid;

means for coupling said vapor passage at its warm end to the suction side of said compression means; and

a conduit connected to and joining the cold outlet means of said main and auxiliary heat exchangers for combining said sub-cooled first and second parts of said condensed refrigerant fluid, and connected to said expansion means.

12. A system according to claim 11, wherein at least one portion of said cycle mixture is liquefied after having flown through said outer coolers operating with at least one of water and air.

13. A system according to claim 11, wherein said main exchanger is used for sub-cooling at least one portion of said cycle mixture in counter-current relationship with itself prior to expansion and vaporization within said exchanger.

14. A system according to claim 11, further comprising a secondary exchanger for carrying out through heat exchange with cold process rejects issuing from said main exchanger the sub-cooling of at least one part of said cycle mixture before expansion and vaporization within said main exchanger.

15. A system according to claim 11, wherein said exchangers are of plate-type construction.

16. A system according to claim 15, wherein said main exchanger is divided on the refrigerated side into several independent components for the separate treatment of various products at given temperature levels.