GB1596330A - Gas liquefaction - Google Patents

Gas liquefaction Download PDF

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Publication number
GB1596330A
GB1596330A GB2361078A GB2361078A GB1596330A GB 1596330 A GB1596330 A GB 1596330A GB 2361078 A GB2361078 A GB 2361078A GB 2361078 A GB2361078 A GB 2361078A GB 1596330 A GB1596330 A GB 1596330A
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United Kingdom
Prior art keywords
gas
liquefied
natural gas
compressed
gaseous
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB2361078A
Inventor
Thompson Jack
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BP PLC
Worley Field Services Ltd
Original Assignee
BP PLC
Constructors John Brown Ltd
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Publication date
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Priority to GB2361078A priority Critical patent/GB1596330A/en
Publication of GB1596330A publication Critical patent/GB1596330A/en
Expired legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0012—Primary atmospheric gases, e.g. air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0012—Primary atmospheric gases, e.g. air
    • F25J1/0015—Nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/004—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by flash gas recovery
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/008—Hydrocarbons
    • F25J1/0085—Ethane; Ethylene
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/008—Hydrocarbons
    • F25J1/0087—Propane; Propylene
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0203—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle
    • F25J1/0205—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle as a dual level SCR refrigeration cascade
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0221—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using the cold stored in an external cryogenic component in an open refrigeration loop
    • F25J1/0223—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using the cold stored in an external cryogenic component in an open refrigeration loop in combination with the subsequent re-vaporisation of the originally liquefied gas at a second location to produce the external cryogenic component
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0221—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using the cold stored in an external cryogenic component in an open refrigeration loop
    • F25J1/0224—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using the cold stored in an external cryogenic component in an open refrigeration loop in combination with an internal quasi-closed refrigeration loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0275—Construction and layout of liquefaction equipments, e.g. valves, machines adapted for special use of the liquefaction unit, e.g. portable or transportable devices
    • F25J1/0277—Offshore use, e.g. during shipping
    • F25J1/0278—Unit being stationary, e.g. on floating barge or fixed platform
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/40—Air or oxygen enriched air, i.e. generally less than 30mol% of O2
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/42—Nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/62—Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/62—Separating low boiling components, e.g. He, H2, N2, Air

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Ocean & Marine Engineering (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Description

PATENT SPECIFICATION
( 21) Application No 23610/78 ( 22) Filed 26 May 1978 ( 44) Complete Specification published 26 Aug 1981 ( 51) INT CL 3 F 25 J 1/02 ( 52) Index at acceptance F 4 P AB ( 72) Inventor JACK THOMPSON () 1 596 330 ( 54) GAS LIQUEFACTION ( 71) We, CONSTRUCTORS JOHN BROWN LIMITED, a British Company, of CJB House, Eastbourne Terrace, Paddington, London W 2 6 LE, and the BRITISH PETROLEUM COMPANY LIMITED, a British Company of Britanic House, Moor Lane, London EC 2 do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the
following statement:-
The present invention relates to a process for the production of a liquefied natural gas, preferably offshore.
Offshore gas may be available either from subsea natural gas fields or as associated gas obtained during the course of oil production The latter may be disposed of in various ways including re-injection to the field, flaring, or pipe lining to land, but often none of these methods is acceptable.
There has for some time been a need for an alternative method of disposing of offshore natural gas which is acceptable to all the parties involved It has been suggested that an alternative is to convert the gas to liquefied natural gas (LNG) on the offshore production facilities, but this has its disadvantages, some of which are:
(i) unacceptable space requirements on platforms.
(ii) the difficulties of storage of LNG at sea, (iii) the difficulties of transfer at sea of cryogenic liquids to LNG tankers, (iv) the varying production rate of a field and hence the inability to obtain a good load factor on a natural gas liquefaction plant over the field life, and (v) the difficulty of re-using the capital plant at the end of the field life.
We have now developed a process which may be used for converting such offshore gas to liquefied natural gas which does not suffer from the above disadvantages and which should be acceptable to all the parties involved It should be appreciated, however, that the present process is as equally applicable to whatever the ship location e g dockside use as it is to use offshore.
According to the present invention, there is provided a process for the production of a liquefied natural gas, which process comprises the steps of: (a) supplying gaseous natural gas to a sea-going vessel which is adapted to store and transport liquefied natural gas, and (b) passing the said gaseous natural gas and a liquefied gas through a heat exchanger situated on board the said sea-going vessel so that the said gaseous natural gas is liquefied and the said liquefied gas is gasified, the said liquefied gas having a boiling point at atmospheric pressure which is lower than the critical temperature of methane.
As will be appreciated by those skilled in the art, before its liquefaction each gas has to be pretreated to remove therefrom impurities, such as water and carbon dioxide, to an extent which is sufficient to avoid blockages Desirably, hydrogen sulphide is also removed from natural gas at this pretreatment stage.
The liquefied natural gas produced by the process according to the present invention may be used to assist by heat exchange in the production of other liquefied gases, such as liquid air or liquid nitrogen, depending on the economics of the situation including the cost of fuel and the ratio of LNG price to gas price.
According to a further aspect of the present invention, therefore, there is provided a process for the production of liquefied gas, which gas has a boiling point at atmospheric pressure which is lower than the critical temperature of methane, comprising passing through a liquefaction plant, which plant includes a heat exchanging means and is situated on land, a liquefied natural gas produced by the process according to the invention, and the gas to be liquefied.
Alternatively, the liquefied natural gas may be sold as such.
Whilst any gas which satisfies the above c Dl 2 1,9633 criteria can be used at the liquefied gas, in practice the preferred gases are air and nitrogen It will be seen from the Table below that both air and nitrogen are cold enough at atmospheric pressure to cool methane (which is by far the main constituent of natural gas) to -259 o 1 F and hence liquefy it at atmospheric pressure.
-.Furthermore, both air and nitrogen are readily available, although to produce liquid nitrogen one has to incur the further expense of distilling liquid air However, liquid air is, in relative terms, more dangerous to use than liquid nitrogen which is non-combustible, although in practice it only becomes dangerous if safety standards are not met Another advantage of using air or nitrogen is that either may be discharged to the atmosphere after use without pollution problems This is not so with ethylene, although in practice it would be possible to liquefy natural gas using ethylene under pressure.
TABLE
Boiling Point at Atmospheric Critical Pressure Temperature Gas OF OF Methane (C,) -259 -116 Air -318 -221 Nitrogen -320 -233 Oxygen -297 -182 Ethylene -155 + 50 Hereinafter reference will be made to the use of liquid air or liquid nitrogen as the liquefied gas, although such should not be read as limiting the present invention.
In a preferred embodiment, liquid air or nitrogen is produced on shore and transported in a tanker to the field The tanker is equipped with heat exchangers and other equipment for gas liquefaction At the field are one or more mooring terminals to which the tanker can be moored and connected to a supply of gas from the production facilities, most probably via a subsea flowline, buoy riser, and loading hose After mooring, gas is admitted to the liquefaction plant on or in the tanker and liquefied by heat exchange with the liquid air/nitrogen It is then stored in the cryogenic tanks on the tanker until a full or substantial load is achieved, when the tanker unmoors and returns to port Here, LNG is discharged, liquid air/nitrogen reloaded, and the cycle re-commenced By the use of more than one tanker and mooring terminal, continuous gas liquefaction can be achieved by the field.
On the tankers gas purification plant may be installed and also mechanical refrigeration plant The latter, by doing some of the "easy" cooling in the liquefaction process can substantially decrease the consumption of liquid air/nitrogen, which is relatively expensive to produce The particular balance between mechanical refrigeration and coiling by liquid air/N 2 is determined by a study of the economics of the situation So that mechanical refrigeration can be used thus, the gas to be liquefied is compressed, preferably to a pressure of about 75 ats For similar reasons, onshore, air to be liquefied is compressed, preferably to about 25 ats.
Typically, the quantity (by weight) of liquid air/N 2 used is substantially the same as that of the LNG produced.
Reference will hereinafter be made to the accompanying drawings, in which:
Figure 1 is a flow diagram of a typical liquefaction cycle of the present invention; Figure 2 is a flow diagram of an offshore LNG plant, and Figure 3 is a flow diagram of an onshore liquid air plant.
In Figure 2, natural gas ( 100 tons/hr, 25 atms, 3000 K) is passed into a ship along line 1 Some of this gas ( 7 2 tons/hr) is passed along line 2 to power the compressors, and some ( 4 3 tons/hr) is passed along line 3 to an adsorbant regeneration zone The remainder ( 88 5 tons/hr) is compressed in compressor A ( 6930 Hp) to a pressure of 75 atms and purified by removal therefrom of carbon dioxide and water vapour The purified gas is passed along line 4 through a first heat exchanger 5 through which air ( 88 5 tons/hr 2 atms, 2330 K) travelling along line 6 is being passed The gas (now at 285 K) is passed along line 7 into a conventional refrigeration plant where it is cooled by pronane to 240 OK The gas is then passed along line 8 through a second heat exchanger 9 through which air ( 88 5 tons/hr 2 atms, 1780 K) travelling along line 10 is being passed The cooled gas ( 220 'K) is then passed along line 11 back into the refrigeration plant where it is cooled by ethylene to 185 OK The gas is then passed along line 12 to a third heat exchanger 13 through which liquid air ( 88 5 tons/hr, 2 atms, 78 OK) is being passed along line 14 from a cryogenic tank (not shown) on board the ship In the heat exchanger 13 the gas is cooled by the liquid air to 1100 K i.e to below its normal boiling point, and is pumped into atmospheric pressure cryogenic tanks (not shown) on board the ship along line 15 The liquid air which is vaporised in heat exchanger 13 is cold enough for it to assist in the cooling steps in the heat exchangers 5, 9 before being vented to the atmosphere along line 16 The total power of the compressors A, B and C is 28000 hp.
1,596,330 1,596,330 In Figure 3, fresh air ( 92 8 tons/hr, I atm, 300 K) is taken into the plant along line 17 and compressed in compressor D ( 9300 hp) to a pressure of 7 atms and then in compressor E ( 8700 hp) to 25 atms The air is then cooled by cooling water in cooler F and purified (purification plant not shown) before being passed along line 18 into a multiple heat exchanger 19 In heat exchanger 19 the air is liquefied under pressure by means of LNG ( 46 4 tons/hr, I atm, 111 OK) which enters the heat exchanger 19 along line 20 The natural gas ( 46 4 tons/hr, 1 atm, 2801 K) is passed out of the heat exchanger 19 along line 21 and is compressed in compressor G ( 10900 hp) to a pressure of 22 atms Part of this compressed natural gas ( 8 tons/hr) is passed along line 22 to power the compressors, and the remainder ( 38 4 tons/hr) is further compressed in compressor H ( 2000 hp) to a pressure of 40 atms and passed from the heat exchanger 19 along line 24 and is flashed twice so that liquid air ( 92 8 tons/hr.
1 atm, 780 K) emerges along line 25 and is passed to cryogenic storage tanks (not shown) The cold gases from the two flash drums 26 and 27 are used in heat exchanger 28 and 29 to assist in the cooling of the liquid air and are then re-cycled along lines ( 52 tons/hr, 7 atms 1151 K) and line 31 ( 52 tons/hr, 7 atms, 2800 K), and line 32 ( 30 4 tons/hr, 1 atm, 1151 K) and line 33 ( 30 4 tons/hr, I atm, 280 'K).
The present invention as exemplified by the above specific embodiments offers the following advantages:(i) the natural gas liquefaction plant does not have to be installed on the fixed offshore production facilities; (ii) most of the machinery and plant is onshore where it is easiest and cheapest to build and operate, i e while the refrigeration effect is required offshore it is actually produced onshore.
(iii) by the re-use of the cold of the LNG, energy requirements for production of LNG are minimized.
(iv) the problems of offshore storage and transfer of cryogenic liquids are eliminated.
(v) the facilities can be transferred to other fields for re-use when the field concerned is depleted.
(vi) the scheme can be extended to embrace any number of fields with increased economy in multi-field operation.
Throughout the specification and claims by -natural gas" we intend to cover both gas from a gas well and associated gas resulting from oil production.

Claims (1)

  1. WHAT WE CLAIM IS:-
    1 A process for the production of a liquefied natural gas, which process comprises the steps of: (a) supplying gaseous natural gas to a sea-going vessel which is 65 adapted to store and transport liquefied natural gas, and (b) passing the said gaseous natural gas and a liquefied gas through a heat exchanger situated on board the said sea-going vessel so that the said gaseous 70 natural gas is liquefied and the said liquefied gas is gasified, the said liquefied gas having a boiling point at atmospheric pressure which is lower than the critical temperature of methane 75 2 A process as claimed in claim I which is carried out offshore.
    3 A process as claimed in claim I or claim 2 in which the said liquefied gas is liquid air or liquid nitrogen 80 4 A process as claimed in any one of the preceding claims in which the said gaseous natural gas is compressed, and then cooled by mechanical refrigeration, before liquefaction thereof 85 A process as claimed in claim 4 in which the said gaseous natural gas is compressed to a pressure of about 75 atms.
    6 A process as claimed in any one of claims 1 to 5 in which the said liquefied gas 90 has been compressed before liquefaction thereof.
    7 A process as claimed in claim 6 in which the said liquefied gas has been compressed to a pressure of 25 atms 95 8 A process as claimed in any one of the preceding claims in which the quantity (by weight) of the said liquefied gas used is substantially the same as that of the liquefied natural gas produced 100 9 A process for the production of a liquefied natural gas substantially as hereinbefore described with reference to, and as illustrated in, Figure 1 or Figure 2 of the accompanying drawings 105 A liquefied natural gas which has been produced by a process as claimed in any one of the preceding claims.
    11 A natural gas in the gaseous state which has been produced from a liquefied 110 natural gas as claimed in claim 10.
    12 A process for the production of a liquefied gas, which gas has a boiling point at atmospheric pressure which is lower than the critical temperature of methane, 115 comprising passing through a liquefaction plant, which plant includes a heat exchanging means and is situated on land, a liquefied natural gas as claimed in claim 10 and the gas to be liquefied 120 13 A process as claimed in claim 12 in which the gas to be liquefied is air or nitrogen.
    14 A process as claimed in claim 12 or claim 13 in which the gas to be liquefied is 125 compressed before liquefaction thereof.
    A process as claimed in claim 14 in which the gas is compressed to a pressure of atms.
    I 56 3 A16 A process for the production of a liquefied gas, which gas has a boiling point at atmospheric pressure which is lower than the critical temperature of methane, substantially as hereinbefore described with reference to, and as illustrated in, Figure 1 or Figure 3 of the accompanying drawings.
    17 A liquefied gas which has been produced by a process as claimed in any one of claims 12 to 16.
    BOULT, WADE & TENNANT Chartered Patent Agents 34 Cursitor Street, London EC 4 A 1 PQ Printed for Her Majesty's Stationery Office, by the Courier Press, Leamington Spa, 1981 Published by The Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.
    1,596,330 A
GB2361078A 1978-05-26 1978-05-26 Gas liquefaction Expired GB1596330A (en)

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