LNG STORAGE TANK VAPOR RECOVERY BY NITROGEN CYCLE REFRIGERATION WITH REFRIGERATION MAKE-UP PROVIDED BY SEPARATION OF SAME VAPOR

• US 3,857,251 A
• Filed: 12/18/1972
• Issued: 12/31/1974
• Est. Priority Date: 12/27/1971
• Status: Expired due to Term

• Current Assignee: Jean Alleaume
• Original Assignee: Jean Alleaume
• Inventors: Alleaume, Jean
• Primary Examiner(s): Monacell, A. Louis
• Assistant Examiner(s): Sever, Frank
• Application Number:
  US05/315,931
• Time in Patent Office: 743 Days
• Field of Search: 62/40,54,9,11,27,28,38,39,28,40,23
• US Class Current: 62/623
• CPC Class Codes: F17C 2265/015 by separating
• CPC Class Codes: F17C 9/04 Recovery of thermal energy
• CPC Class Codes: F25J 1/0025 Boil-off gases "BOG" from storages
• CPC Class Codes: F25J 1/0045 by vaporising a liquid return stream
• 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 1/0072 Nitrogen
• CPC Class Codes: F25J 1/0202 in a quasi-closed internal refrigeration loop F25J1/0208, F25J1/0219, F25J1/0224 take precedence
• CPC Class Codes: F25J 1/0204 as a single flow SCR cycle
• CPC Class Codes: F25J 1/0221 using the cold stored in an external cryogenic component in an open refrigeration loop
• CPC Class Codes: F25J 1/0242 Waste heat recovery, e.g. from heat of compression
• 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 1/0251 Intermittent or alternating process, so-called batch process, e.g. "peak-shaving"
• CPC Class Codes: F25J 1/0265 comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
• CPC Class Codes: F25J 1/0277 Offshore use, e.g. during shipping
• CPC Class Codes: F25J 1/0281 characterised by the type of prime driver, e.g. hot gas expander
• CPC Class Codes: F25J 1/0282 Steam turbine as the prime mechanical driver
• CPC Class Codes: F25J 1/0284 Electrical motor as the prime mechanical driver
• CPC Class Codes: F25J 1/0288 using work extraction by mechanical coupling of compression and expansion of the refrigerant, so-called companders
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• 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 2210/62 : Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
• CPC Class Codes: F25J 2210/90 : Boil-off gas from storage
• CPC Class Codes: F25J 2215/04 : Recovery of liquid products
• CPC Class Codes: F25J 2220/62 : Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2230/20 : Integrated compressor and process expander; Gear box arrangement; Multiple compressors on a common shaft
• CPC Class Codes: F25J 2270/06 : with multiple gas expansion loops
• CPC Class Codes: F25J 2270/16 : with mutliple gas expansion loops of the same refrigerant
• CPC Class Codes: F25J 2270/42 : Quasi-closed internal or closed external nitrogen refrigeration cycle
• 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 3/0257 : separation of nitrogen from air F25J3/04, production of nitrogen in general C01B21/00

Abstract

Method and device of treatment of natural gas contained in storage tanks, for producing liquid nitrogen by extraction of nitrogen from the vapours resulting from the evaporation of said liquefied natural gas in said tanks, liquefaction of a portion of said extracted nitrogen and storage thereof for forming a reserve of cold.

Claims

1. A DEVICE FOR TREATMENT OF NATURAL GAS STORED IN LIQUEFIED STATE, COMPRISING:

TANK MEANS CONTAINING SAID LIQUEFIED NATURAL GAS AND INCLUDING A STOP VAPOR SPACE FILLED WITH THE GASEOUS PHASE CONSISTING OF THE VAPORS RESULTING FROM THE BOIL-OFF OF SAID LIQUEFIED-NATURAL GAS;

FRACTIONAL DISTILLATING COLUMN MEANS COMPRISING 9 BOTTOM COLLECTING SUMP PORTION FOR HOLDING RELIQUEFIED-NATURAL-GAS, AN OVERHEAD VAPOR SPACE COLLECTING TOP PORTION FOR CONFINING SEPARATED GASEOUS NITROGEN AND INTERMEDIATE UPPER AND LOWER PORTIONS AND A SUMP PORTION;

FIRST VAPOR COVEYING DUCT MEANS CONNECTING SAID TOP VAPOR

2. A method of progressively cryogenically purifying a stored stationary body of liquefied-natural-gas containing at least a major portion of methane and a substantial amount of nitrogen mixed therewith by continuous cyclic process comprising the steps of:

providing a stored stationary body of liquid nitrogen;

collecting the boil-off forming the gaseous phase built up on the top of said body of liquefied-natural-gas;

effecting a fractional distillation of said boil-off through heat exchange with a boiling refrigerant by using a cold reflux liquid previously separated and reliquefied-nitrogen whereby the nitrogen contained in said boil-off is separated as a gas therefrom and the so purified remaining boil-off is reliquefied;

collecting the purified hydrocarbon-enriched reliquefied natural gas resulting as the bottoms from said fractional distillation and returning It to said body of liquefied-natural-gas which is thus also gradually enriched;

collecting the separated overhead gaseous nitrogen and the gaseous nitrogen resulting from evaporation of said reflux liquid and conveying same in a confined condition into said body of liquid-nitrogen in heat exchanging relationship therewith so as to condense at least a part of said gaseous nitrogen, the nitrogen condensate serving as said reflux liquid;

recovering the cold gaseous nitrogen evaporated from said body of liquid-nitrogen and that resulting from said nitrogen distillate;

reliquefying said recovered gaseous nitrogen and feeding the reliquefield-nitrogen back to said body of liquid-nitrogen, reboiling at least one portion of said collected reliquefied-natural-gas at the boiling temperature of a nitrogen-free liquid-natural-gas through heat exchange with hot gaseous nitrogen derived from the nitrogen reliquefaction cycle and feeding the vapors of liquefied-natural-gas resulting from said reboiling step to said fractional distillation step to supply reboiling heat thereto, said hot gaseous nitrogen being cooled thereby, while the reboiled substantially nitrogen-free liquid-natural-gas is returned to said body of liquefied-natural-gas;

whereas said reliquefying of said recovered gaseous nitrogen comprises the steps of;

reheating said cold recovered gaseous nitrogen through heat exchange with hot compressed gaseous nitrogen which is cooled thereby;

compressing said heated gaseous nitrogen in at least one stage and after cooling same at least through said heat exchange with said cold recovered gaseous nitrogen and with said reboiling purified liquid natural gas;

subjecting said cooled compressed gaseous nitrogen to at least one first cold phase separation for condensing at least a part of said gaseous nitrogen;

collecting and returning said condensed liquid-nitrogen to said body of liquid-nitrogen;

said method also comprising the steps of;

collecting the cold compressed gaseous nitrogen which has not been condensed during said cold phase separation;

expanding at least one portion thereof in at least one stage while recovering work produced by said expansion and using said work as power for assisting the compression step;

preheating at least one portion of said expanded gaseous nitrogen through heat exchange with that compressed gaseous nitrogen which is about to undergo said cold phase separation thereby further cooling said last-named compressed gaseous nitrogen; and

mixing said preheated compressed gaseous nitrogen with the stream of said recovered gaseous nitrogen arriving from said body of liquid-nitrogen before further preheating same.

3. A method of progressively cryogenically purifying a stored stationary body of liquefied natural gas containing at least a major portion of methane and a substantial amount of nitrogen mixed therewith by a continuous cyclic process comprising the steps of:

providing a stored stationary body of liquid-nitrogen;

collecting the boil-off forming the gaseous phase built up on the top of said body of liquefied-natural-gas;

effecting a fractional distillation of said boil-off through heat exchange with a boiling refrigerant by using a cold reflux liquid previously separated and reliquefied nitrogen whereby the nitrogen contained in said boil-off is separated as a gas therefrom and the sopurified remaining boil-off is reliquefied;

collecting the purified hydrocarbon-enriched reliquefied natural gas resulting as the bottoms from said fractional distillation and returning it to said body of liquefied-natural-gas which is thus also gradually enriched;

collecting the separated overhead gaseous nitrogen and the gaseous nitrogen resulting from evaporation of said reflux liquid and conveying same in a confined condition into said body of liquid-nitrogen in heat exchanging relationship therewith so as to condense at least a part of said gaseous nitrogen, the nitrogen condensate serving as said reflux liquid;

recovering the cold gaseous nitrogen evaporated from saId body of liquid-nitrogen and that resulting from said nitrogen distillate;

reliquefying said recovered gaseous nitrogen and feeding the reliquefied nitrogen back to said body of liquid-nitrogen, reboiling at least one portion of said collected reliquefied-natural-gas at the boiling temperature of a nitrogen-free liquid natural gas through heat exchange with hot gaseous nitrogen derived from the nitrogen reliquefaction cycle and feeding the vapors of liquefied-natural-gas resulting from said reboiling step to said fractional distillation step to supply reboiling heat thereto, said hot gaseous nitrogen being cooled thereby, while the reboiled substantially nitrogen-free liquid-natural-gas is returned to said body of liquefied natural gas;

whereas said reliquefying of said recovered gaseous nitrogen comprises the steps of;

reheating said cold recovered gaseous nitrogen through heat exchange with hot compressed gaseous nitrogen which is cooled thereby;

compressing said heated gaseous nitrogen in at least one stage and aftercooling same at least through said heat exchange with said cold recovered gaseous nitrogen and with said reboiling purified liquid-natural-gas;

subjecting said cooled compressed gaseous nitrogen to at least one first cold phase separation for condensing at least a part of said gaseous nitrogen;

collecting and returning said condensed liquid-nitrogen to said body of liquid nitrogen; and

said method comprising further the steps of collecting the cold compressed gaseous nitrogen which has not been condensed during said cold phase separation;

preheating at least one portion thereof through heat exchange with that compressed gaseous nitrogen which is about to undergo said cold phase separation thereby further cooling said last-named compressed gaseous nitrogen; and

mixing said preheated compressed gaseous nitrogen with the stream of said recovered gaseous nitrogen arriving from said body of liquid nitrogen before further preheating same;

expanding another portion of said non-condensed gaseous nitrogen and recovering the work produced thereby as power for assisting the compression step; and

mixing said expanded portion with said one portion before preheating the same.

4. A device according to claim 1, comprising aftercooling means inserted in series between the outlet of each stage of said compressor means and the inlet of the heating medium flow path of said main heat exchanger means and extraneous coolant circulating means, said aftercooler means being cooled by the circulation of extraneous coolant of said extraneous coolant circulating means.

5. A device according to claim 1, comprising work-producing gas expansion means having its inlet connected to another outlet of the vapor holding portion of said cold phase separator means and its outlet connected to an inlet of the refrigerating medium flow path of said main heat exchanger means.

6. A device according to claim 5, wherein said work-producing gas expansion means comprises a tubular thermal separator.

7. A device according to claim 5, wherein said work-producing gas expansion means comprising at least one reciprocating piston engine coupled to at least one piston compressor forming compressor means and motor means, said compressor means also being operatively connected to motor means.

8. A device according to claim 7 wherein said work-producing gas expansion means comprises turbine means having at least one stage, compressor means which comprise multiple stages, interstage cooler means separating said multiple stages and extraneous coolant means for said stages said turbine means and said compression means being directly coupled and operatively connected to said motor means.

9. A device according to claim 1, wherein said main heat exchanger means comprise first and second heat exchangers whose said pipe coil means are interconnected.

10. A device according to claim 5, comprising further gas flow heat exchanger means having a heating medium flow path connected in series between the outleT of the heating medium flow path of said main heat exchanger means and said inlet of the vapor holding portion of said cold phase separator means and a refrigerating medium flow path connected in series between said inlet of the refrigerating medium flow path of said main heat exchanger means and on the other hand said one outlet of the vapor holding portion of said cold phase separator means and said outlet of said work-producing gas expansion means.

11. A device according to claim 10, wherein said cold phase separator means consist of first and second cold phase separators, the outlet of the condensate holding portion of said first cold phase separator being connected to the inlet of the vapor holding portion of said second cold phase separator whereas the outlet of the heating medium flow path of said further heat exchanger means is connected to an inlet of the vapor holding portion of said first cold phase separator and the outlet of said first cold phase separator is connected to the inlet of said work-producing gas expansion means, the outlet of the vapor holding portion of said second cold phase separator being connected to the inlet of the refrigerating medium flow path of said further heat exchanger means.

12. A device according to claim 1, including a conduit connecting the outlet of the refrigerating medium flow path of said main exchanger means to the inlet of said compressor means and controllable vent pipe means branched off said conduit.

13. A device according to claim 1, including third liquid pump means at least the suction side of which is immersed in the liquefied-natural-gas contained in said tank means;

pipe line means leading from the discharge side of said third liquid pump means to the outside of said tank means towards a consumer station and auxiliary heat exchanger means comprising a heating medium flow path connected to the coolant outlet of said aftercooling means and a refrigerating medium flow path inserted in series in said pipe line means.

14. A device according to claim 13, including additional heat exchanger means comprising a heating medium flow path having an inlet connected through branch duct means to said pipe line means downstream of said auxiliary heat exchanger means and an outlet connected to the top vapor space of said tank means, and a refrigerating medium flow path inserted in series into said pipe line means upstream of said auxiliary heat exchanger means.

15. A device according to claim 1, wherein said power driven compressor means comprise a plurality of separate, respectively low intermediate and high pressure turbine-motor-compressor sets having each one a workproducing gas expansion turbine, a motor and a compressor, and drive shaft means, said drive shaft means operatively and mechanically coupling each set, the gas flow path of said compressors being interconnected in series and inserted between the outlet of the refrigerating medium flow path entering the low pressure compressor and the inlet of the heating medium flow path fed by the final high pressure compressor to said main heat exchanger means, with interstage extraneous gas coolant supplied cooler means connected in series between any two successive compressors and gas aftercooler means cooled by said extraneous coolant connected in series between the outlet of said high pressure compressor and the inlet of the heating medium flow path of said main heat exchange means;

said cold phase separator means comprising a primary cold phase separator whose vapor holding portion is connected through an outlet to the inlet of the turbine of the final high pressure turbine-motor-compressor set and a like plurality of secondary cold phase separators associated with said plurality of turbine-motor-compressor sets, respectively;

a like plurality of further gas flow heat exchangers also associated with said turbine-motor-compressor sets, respectively, the heating medium flow paths of which are interconnected in series and inserted between the outlet of the hEating medium flow path of said main heat exchanger means and an inlet of the vapor holding portion of said primary cold phase separator;

the condensate holding portion of said primary cold phase separator being connected to an inlet of the vapor holding portion of the first secondary cold phase separator;

the vapor holding portion of each secondary cold phase separator being connected through an outlet to the inlet of the refrigerating medium path of the associated further heat exchanger, the outlet of which is connected to the inlet of the turbine of the next successive turbine-motor-compressor set, except for the corresponding outlet of the further heat exchanger associated with the first or low pressure turbine-motor-compressor set which outlet is connected to the inlet of the refrigerating medium flow path of said main heat exchanger means;

the condensate holding portion of each secondary cold phase separator being connected through an inlet to the outlet of the turbine of the associated turbine-motor-compressor set through an outlet to an inlet of the vapor holding portion of the next secondary cold phase separator, except for the outlet of the last secondary cold phase separator associated with the first or low pressure turbine-motor-compressor set which outlet is connected to said fourth liquid-conveying duct means.

16. A device according to claim 15, wherein each turbine-motor-compressor set comprises multiplying gear means with two output shafts operatively coupled to drive shafts of said turbine and said compressor, respectively, and with an input shaft operatively coupled to said motor, said compressor having an axially directed gas inlet and a tangentially directed gas outlet.

17. A device according to claim 15, mounted on board a ship and wherein the turbine-motor and compressor of each turbine-motor-compressor set are housed in a same casing and said motor comprises a steam turbine whose steam pressure is slightly lower than the gas pressure in said gas flow path.

18. A method according to claim 3, wherein said cold phase separation comprises a first separation producing liquid nitrogen which is subject to a second separation producing liquid nitrogen which is returned to said body of liquid nitrogen whereas the non-condensed gaseous nitrogen resulting from said first separation is expanded and mixed with the non-condensed gaseous nitrogen resulting from said second separation.