NATURAL GAS PROCESSING METHOD

• US 20080163645A1
• Filed: 01/03/2008
• Published: 07/10/2008
• Est. Priority Date: 01/09/2007
• Status: Abandoned Application

• Current Assignee: JGC Corporation (JGC Holdings Corporation)
• Original Assignee: JGC Corporation (JGC Holdings Corporation)
• Inventors: Konishi, Hitoshi, Omori, Hidefumi
• Application Number:
  US11/968,819
• Publication Number:
  US 20080163645A1
• Time in Patent Office: Days
• US Class Current: 62/620
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0035 by gas expansion with extraction of work
• CPC Class Codes: F25J 1/0037 of a return stream
• CPC Class Codes: F25J 1/004 by flash gas recovery F25J1/0267 takes precedence
• CPC Class Codes: F25J 1/0042 by liquid expansion with extraction of work
• CPC Class Codes: F25J 1/005 by expansion of a gaseous refrigerant stream with extraction of work
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0082 Methane
• CPC Class Codes: F25J 1/0087 Propane; Propylene
• CPC Class Codes: F25J 1/0208 in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop F25J1/021 takes precedence
• CPC Class Codes: F25J 1/021 using a deep flash recycle loop
• CPC Class Codes: F25J 1/0229 Integration with a unit for using hydrocarbons, e.g. consuming hydrocarbons as feed stock
• CPC Class Codes: F25J 1/0237 integrating refrigeration provided for liquefaction and purification/treatment of the gas to be liquefied, e.g. heavy hydrocarbon removal from natural gas details related to rectification F25J3/02; details related to partial condensation F25J3/06; working-up natural gas C10L3/10
• CPC Class Codes: F25J 1/025 Details related to the refrigerant production or treatment, e.g. make-up supply from feed gas itself
• CPC Class Codes: F25J 1/0254 controlling particular process parameter, e.g. pressure, temperature
• CPC Class Codes: F25J 1/0264 Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams F25J1/0272 takes precedence
• CPC Class Codes: F25J 1/0274 Retrofitting or revamping of an existing liquefaction unit
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2220/62 Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2220/64 : Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
• CPC Class Codes: F25J 2230/24 : Multiple compressors or compressor stages in parallel
• CPC Class Codes: F25J 2230/30 : Compression of the feed stream
• CPC Class Codes: F25J 2230/32 : Compression of the product stream
• CPC Class Codes: F25J 2230/60 : the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2260/20 : Integration in an installation for liquefying or solidifying a fluid stream
• CPC Class Codes: F25J 2270/06 : with multiple gas expansion loops
• 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 2290/80 : Retrofitting, revamping or debottlenecking of existing plant
• CPC Class Codes: F25J 3/0209 : Natural gas or substitute natural gas
• 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 3/0242 : separation of CnHm with 3 carbon atoms or more

Abstract

A natural gas processing method includes: a pretreatment process of obtaining a treated natural gas; an NGL recovery process of cooling the treated natural gas obtained in the pretreatment process to recover an NGL product composed of ethane and heavier hydrocarbons and to separate a lean gas; a sales gas production process of compressing a part of the lean gas separated in the NGL recovery process to obtain a high-pressure gas; and a natural gas liquefying process of cooling the high-pressure gas after the high-pressure gas is obtained by compressing the lean gas separated in the NGL recovery process, to thereby obtain the LNG product. In the natural gas processing method, a gas compressor used in the sales gas production process is used as a gas compressor in the natural gas liquefying process.

Claims

1. A natural gas processing method of recovering a natural gas liquid (NGL) and a high-pressure sales gas (sales gas) as major products and recovering a liquefied natural gas (LNG) as a co-product from a natural gas, the method comprising:

a pretreatment process of removing impurities from a feed natural gas to obtain a treated natural gas;

an NGL recovery process of cooling the treated natural gas obtained in the pretreatment process to a temperature at which ethane and heavier hydrocarbons are condensed and liquefied to recover an NGL product and separating a lean gas which mainly contains methane;

a sales gas production process of compressing a part of the lean gas separated in the NGL recovery process by a gas compressor to obtain a high-pressure gas which is delivered as a sales gas; and

a natural gas liquefying process of compressing the remaining part of the lean gas separated in the NGL recovery process by a gas compressor to obtain a high-pressure gas which exceeds critical pressure, and cooling the high-pressure gas up to a temperature at which methane is condensed and liquefied to thereby obtain an LNG product,

the gas compressor used in the sales gas production being used in the natural gas liquefying process as the gas compressor.

2. The natural gas processing method according to claim 1, wherein the natural gas liquefying process comprises:

a process A of cooling a part of the LNG feed gas, which is the high-pressure lean gas being supplied in the natural gas liquefying process and exceeding the critical pressure, by heat exchanging with a low-temperature gas generated when the LNG product is produced, and adiabatically expanding the part by a liquid expander;

a process B of cooling the remaining part of the LNG feed gas supplied in the process A by heat exchanging with a propane refrigerant, and adiabatically expanding the remaining part by a gas expander to liquefy the remaining part; and

merging LNG produced in the process A with LNG produced in the process B to obtain an LNG product.

3. The natural gas processing method according to claim 2, wherein the low temperature gas generated when the LNG product is produced, and used to perform the cooling in the process A is returned to the gas compressor in the sales gas production process.

4. The natural gas processing method according to claim 1, wherein the LNG feed gas supplied in the natural gas liquefying process is pressurized to a pressure higher than in the sales gas production process to be used in a state where the LNG feed gas exceeds the critical pressure.

5. The natural gas processing method according to claim 1, wherein the natural gas liquefying process comprises:

a process A1 of cooling a part of the high-pressure lean gas being supplied in the natural gas liquefying process and exceeding the critical pressure by heat exchanging with a low temperature gas generated when the LNG product is produced to perform adiabatic expansion by a liquid expander;

a process C of cooling some of the remaining part of the high-pressure lean gas supplied in the process A1 by heat exchanging with a propane refrigerant, cooling the some of the remaining part by heat exchanging with a self-cooling medium which is formed by cooling a fluid comprised of an LNG feed gas containing the remainder of the remaining part of the high-pressure lean gas supplied to the process A1, and liquefying the remainder of the remaining part by adiabatic expansion by the gas expander to obtain LNG; and

merging LNG produced in the process A1 with LNG produced in the process C to obtain an LNG product.

6. The natural gas processing method according to claim 5, wherein the self-cooling medium comprises a part of a gas which is cooled by heat exchanging between the remainder of the remaining part of the high-pressure lean gas supplied in the process A1 and a propane refrigerant, and

wherein the remainder of the remaining part is cooled by heat exchanging, merged with the part of the gas, followed by adiabatically expanded by the gas expander, and the resulting expanded fluid is heat-exchanged as the self-cooling medium with the remaining part of the gas cooled by the heat exchanging with a propane refrigerant.

7. The natural gas processing method according to claim 6, wherein the self-cooling medium is returned to the gas compressor in the sales gas production process after the remainder of the remaining part of the LNG feed gas supplied in the process A1 is cooled by heat exchanging and compressed by a gas compressor.

8. The natural gas processing method according to claim 5, wherein the low temperature gas generated when the LNG product used to perform the cooling in the process A1 is returned to the gas compressor in the sales gas production process.

9. The natural gas processing method according to claim 1, wherein the natural gas liquefying process comprises:

a process A1 of cooling a part of an LNG feed gas which is the high-pressure lean gas being supplied in the natural gas liquefying process and exceeding the critical pressure, by heat exchanging with a low-temperature gas generated when the LNG product is produced, liquefying the part of the LNG feed gas, followed by adiabatic expansion by a liquid expander;

a process D of cooling the remaining part of the LNG feed gas supplied in the process A1 by heat exchanging with a propane refrigerant, separating the gas into a gas for an LNG feed gas and a cooling medium gas, cooling the LNG feed gas by heat exchanging with a self-cooling medium obtained by adiabatically expanding the cooling medium gas, and liquefying the LNG feed gas by adiabatic expansion by a gas expander to obtain LNG; and

merging LNG produced in the process A1 with LNG produced in the process D to obtain an LNG product.

10. The natural gas processing method according to claim 9, wherein the cooling medium gas is adiabatically expanded by a gas expander and the resulting adiabatically expanded fluid is heat-exchanged with the LNG feed gas.

11. The natural gas processing method according to claim 9, wherein the self-cooling medium forms a circulation cycle in which a part of a gas obtained by compressing the self-cooling medium by gas compressors is cooled by heat exchanging and adiabatically expanded by a gas expander, and the resulting adiabatically expanded fluid is heat-exchanged with the LNG feed gas, followed by heating by heat exchanging, and compressing by the gas compressors.

12. The natural gas processing method according to claim 11, wherein the part of the gas compressed by the gas compressors is heat-exchanged with the cooling medium gas and merged with the remaining part of the gas cooled by the heat exchanging with the propane refrigerant, and the remaining part is merged with the remaining part of the LNG feed gas supplied in the process A1.

13. The natural gas processing method according to claim 5, wherein the LNG feed gas supplied in the natural gas liquefying process is pressurized to a pressure higher than in the sales gas production process to be used in a state where the LNG feed gas exceeds the critical pressure.

14. The natural gas processing method according to claim 1, wherein the pressure of the high-pressure gases supplied in the natural gas liquefying process is in the range of 40 bara to 150 bara.