EP1956287A2 - LNG tank and method of treating boil-off gas - Google Patents

LNG tank and method of treating boil-off gas Download PDF

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Publication number
EP1956287A2
EP1956287A2 EP07007423A EP07007423A EP1956287A2 EP 1956287 A2 EP1956287 A2 EP 1956287A2 EP 07007423 A EP07007423 A EP 07007423A EP 07007423 A EP07007423 A EP 07007423A EP 1956287 A2 EP1956287 A2 EP 1956287A2
Authority
EP
European Patent Office
Prior art keywords
lng
storage tank
boil
lng storage
gas
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.)
Pending
Application number
EP07007423A
Other languages
German (de)
French (fr)
Other versions
EP1956287A3 (en
Inventor
Jung Ho Choi
Sung Kon Han
Dong Kyu Choi
Jung Han Lee
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hanwha Ocean Co Ltd
Original Assignee
Daewoo Shipbuilding and Marine Engineering Co Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Daewoo Shipbuilding and Marine Engineering Co Ltd filed Critical Daewoo Shipbuilding and Marine Engineering Co Ltd
Publication of EP1956287A2 publication Critical patent/EP1956287A2/en
Publication of EP1956287A3 publication Critical patent/EP1956287A3/en
Pending legal-status Critical Current

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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B63SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63BSHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B25/00Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby
    • B63B25/02Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods
    • B63B25/08Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid
    • B63B25/12Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid closed
    • B63B25/16Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid closed heat-insulated
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C13/00Details of vessels or of the filling or discharging of vessels
    • F17C13/004Details of vessels or of the filling or discharging of vessels for large storage vessels not under pressure
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B63SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63BSHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B25/00Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby
    • B63B25/02Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods
    • B63B25/08Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2201/00Vessel construction, in particular geometry, arrangement or size
    • F17C2201/01Shape
    • F17C2201/0147Shape complex
    • F17C2201/0157Polygonal
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2201/00Vessel construction, in particular geometry, arrangement or size
    • F17C2201/05Size
    • F17C2201/052Size large (>1000 m3)
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2203/00Vessel construction, in particular walls or details thereof
    • F17C2203/06Materials for walls or layers thereof; Properties or structures of walls or their materials
    • F17C2203/0634Materials for walls or layers thereof
    • F17C2203/0636Metals
    • F17C2203/0639Steels
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2203/00Vessel construction, in particular walls or details thereof
    • F17C2203/06Materials for walls or layers thereof; Properties or structures of walls or their materials
    • F17C2203/0634Materials for walls or layers thereof
    • F17C2203/0636Metals
    • F17C2203/0648Alloys or compositions of metals
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2221/00Handled fluid, in particular type of fluid
    • F17C2221/03Mixtures
    • F17C2221/032Hydrocarbons
    • F17C2221/033Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/01Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
    • F17C2223/0146Two-phase
    • F17C2223/0153Liquefied gas, e.g. LPG, GPL
    • F17C2223/0161Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/03Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the pressure level
    • F17C2223/033Small pressure, e.g. for liquefied gas
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/04Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by other properties of handled fluid before transfer
    • F17C2223/042Localisation of the removal point
    • F17C2223/043Localisation of the removal point in the gas
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/04Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by other properties of handled fluid before transfer
    • F17C2223/042Localisation of the removal point
    • F17C2223/046Localisation of the removal point in the liquid
    • F17C2223/047Localisation of the removal point in the liquid with a dip tube
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/01Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the phase
    • F17C2225/0146Two-phase
    • F17C2225/0153Liquefied gas, e.g. LPG, GPL
    • F17C2225/0161Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/03Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the pressure level
    • F17C2225/033Small pressure, e.g. for liquefied gas
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/03Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the pressure level
    • F17C2225/035High pressure, i.e. between 10 and 80 bars
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/04Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by other properties of handled fluid after transfer
    • F17C2225/042Localisation of the filling point
    • F17C2225/043Localisation of the filling point in the gas
    • F17C2225/044Localisation of the filling point in the gas at several points, e.g. with a device for recondensing gas
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/04Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by other properties of handled fluid after transfer
    • F17C2225/042Localisation of the filling point
    • F17C2225/046Localisation of the filling point in the liquid
    • F17C2225/047Localisation of the filling point in the liquid with a dip tube
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2227/00Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/01Propulsion of the fluid
    • F17C2227/0128Propulsion of the fluid with pumps or compressors
    • F17C2227/0135Pumps
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2227/00Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/01Propulsion of the fluid
    • F17C2227/0128Propulsion of the fluid with pumps or compressors
    • F17C2227/0171Arrangement
    • F17C2227/0178Arrangement in the vessel
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2250/00Accessories; Control means; Indicating, measuring or monitoring of parameters
    • F17C2250/06Controlling or regulating of parameters as output values
    • F17C2250/0605Parameters
    • F17C2250/0631Temperature
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2260/00Purposes of gas storage and gas handling
    • F17C2260/03Dealing with losses
    • F17C2260/035Dealing with losses of fluid
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2265/00Effects achieved by gas storage or gas handling
    • F17C2265/03Treating the boil-off
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2265/00Effects achieved by gas storage or gas handling
    • F17C2265/03Treating the boil-off
    • F17C2265/032Treating the boil-off by recovery
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2265/00Effects achieved by gas storage or gas handling
    • F17C2265/03Treating the boil-off
    • F17C2265/032Treating the boil-off by recovery
    • F17C2265/033Treating the boil-off by recovery with cooling
    • F17C2265/034Treating the boil-off by recovery with cooling with condensing the gas phase
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2265/00Effects achieved by gas storage or gas handling
    • F17C2265/03Treating the boil-off
    • F17C2265/032Treating the boil-off by recovery
    • F17C2265/037Treating the boil-off by recovery with pressurising
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2265/00Effects achieved by gas storage or gas handling
    • F17C2265/05Regasification
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2270/00Applications
    • F17C2270/01Applications for fluid transport or storage
    • F17C2270/0102Applications for fluid transport or storage on or in the water
    • F17C2270/0105Ships
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2270/00Applications
    • F17C2270/01Applications for fluid transport or storage
    • F17C2270/0102Applications for fluid transport or storage on or in the water
    • F17C2270/011Barges
    • F17C2270/0113Barges floating
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2270/00Applications
    • F17C2270/01Applications for fluid transport or storage
    • F17C2270/0102Applications for fluid transport or storage on or in the water
    • F17C2270/0118Offshore
    • F17C2270/0123Terminals

Definitions

  • the present invention relates generally to a liquefied natural gas (LNG) storage tank and a method of treating boil-off gas using the same, and more particularly to an LNG storage tank that can store natural gas in a liquid state and a method of treating boil-off gas using the same.
  • LNG liquefied natural gas
  • liquefied natural gas is produced by cooling natural gas (NG) into a cryogenic liquid state at a production location and is transported by LNG carriers to a distant destination.
  • LNG is regasified through a floating storage and regasification unit (FSRU) or an unloading terminal on land and then supplied to consumers.
  • FSRU floating storage and regasification unit
  • LNG is transported by an LNG regasification vessel (LNG-RV)
  • LNG is regasified in the LNG-RV itself not through the FSRU or the unloading terminal.
  • LNG Since the liquefaction of natural gas occurs at a cryogenic temperature of approximately -163 °C at ambient pressure, LNG is likely to be vaporized if the temperature of LNG increases slightly above -163 °C at ambient pressure.
  • LNG carriers although an LNG storage tank is equipped with thermal insulation structure, it is impossible to completely prevent heat ingress to LNG through the storage tank, so that LNG is continuously vaporized and boil-off gas is generated in the LNG storage tank during the transportation of LNG by the LNG carrier.
  • a steam turbine propulsion system driven by steam generated in boilers by burning boil-off gas and heavy fuel oil has a problem of low propulsion efficiency.
  • boil-off gas generation in the LNG storage tank is suppressed by maintaining the LNG storage tank at a high pressure of about 200 bars without installing an insulation wall on the LNG storage tank.
  • the LNG storage tank must have a significantly high thickness to withstand a high pressure of about 200 bars, there are problems of high manufacturing costs and requirement of additional components, such as a high-pressure compressor.
  • an object of the present invention is to provide an LNG storage tank configured to maintain the LNG storage tank at a safe level without separately treating the boil-off gas, and a method of treating boil-off gas using the same.
  • an LNG storage tank comprising a thermal insulation wall and having strength to withstand a pressure increment caused by boil-off gas generated in the LNG storage tank to permit a pressure increase resulting from boil-off gas generation in the LNG storage tank.
  • a method of treating boil-off gas comprising: permitting a pressure increase caused by boil-off gas generation in an LNG storage tank without treating boil-off gas generated in the LNG storage tank, so that the boil-off gas is accumulated in the LNG storage tank.
  • An LNG storage tank of the present invention is applicable to an LNG carrier, a floating storage and regasification unit (FSRU), an unloading terminal on land, and an LNG regasification vessel (LNG-RV), etc.
  • FSRU floating storage and regasification unit
  • LNG-RV LNG regasification vessel
  • Fig. 1 is a schematic view illustrating the conception of heat ingress and absorption of heat in an LNG storage tank for LNG carriers according to the present invention.
  • the pressure of the LNG storage tank for the LNG carrier is maintained in a predetermined range, so that most of heat ingress into the LNG storage tank contributes to boil-off gas generation, all of which should be treated in the LNG carrier.
  • an LNG storage tank for an LNG carrier is constructed to permit a pressure increase therein, causing an increase in saturation temperature, whereby most of heat ingress is absorbed by large heat capacity of LNG and natural gas (NG) vapor in the storage tank, noticeably reducing the boil-off gas generation.
  • NG natural gas
  • Fig. 2 is a schematic view illustrating an LNG storage tank for an LNG carrier according to an exemplary embodiment of the invention.
  • the LNG storage tank 1 for the LNG carrier comprises an insulation wall built thereon and has an inner pressure of approximately 0.06 bars (gauge pressure) at the point of departure when LNG is loaded in an LNG production terminal. Then, as boil-off gas is generated in the LNG storage tank during the LNG carrier's voyage, the pressure of the LNG storage tank gradually increases. For example, when LNG is loaded into the LNG storage tank 1 of the LNG carrier at the location where LNG is produced, the LNG storage tank 1 has an inner pressure of 0.06 bars, and, when the LNG carrier arrives at a destination after a voyage of about 15 ⁇ 20 days, the inner pressure of the LNG storage tank 1 can increase to 0.7 bars (gauge pressure).
  • the LNG storage tank 1 for the LNG carrier comprises the thermal insulation wall and is designed by taking account the pressure increase caused by boil-off gas generation, that is, to have sufficient strength to withstand a pressure increment caused by the boil-off gas generation.
  • the boil-off gas generated in the LNG storage tank 1 is accumulated therein without any loss or extraction from the LNG tank during the LNG carrier's voyage.
  • the LNG storage tank 1 for the LNG carrier comprises the thermal insulation wall, and, preferably has construction capable of withstanding a pressure of 0.4 to 2 bars (gauge pressure), and more preferably a pressure of 0.6 to 1.5 bars (gauge pressure). Since such an LNG storage tank 1 of the present invention can be sufficiently embodied by constructing the storage tank 1 to have a high thickness or by suitably reinforcing a conventional LNG storage tank for LNG carriers through addition of a reinforcing steel structure thereto without significantly changing the design and construction of the conventional LNG storage tank, it is very economical in view of manufacturing costs.
  • the LNG storage tank for the LNG carriers can be classified into an independent type tank and a membrane type tank. This classification of the LNG storage tank depends on whether or not the load of cargo directly acts on the thermal insulation wall, and is described in detail hereinafter.
  • GTT No. 96-2 and GTT Mark III have been renamed from GT and TGZ, respectively, when the names of Gaz Transport (GT) Corporation and Technigaz (TGZ) Corporation was changed to GTT (Gaz Transport & Technigaz) Corporation in 1999.
  • Table 1 Classification Membrane Type Independent Type GTT Mark ⁇ GTT No. 96-2 MOSS IHI-SPB Material-thickness of tank SUS 304L-1.2 mm Invar steel-0.7 mm Al alloyed steel (5083)-50 mm Al alloyed steel (5083) Max. 30 mm Material for heat dissipation-thickness Reinforced Polyurethane Foam-250 mm Plywood Box+Perlite-530 mm Polyurethane Foam-250 mm Polyurethane Foam-250 mm Polyurethane Foam-250 mm
  • GT type and TGT type tanks are disclosed in US Patent Nos. 6,035,795 , 6,378,722 , and No. 5,586,513 , US Patent Publication No. 2003-0000949 , Korean Patent Laid-open Publication Nos. 2000-0011347 and 2000-0011346 , etc.
  • Korean Patent Nos. 499710 and 0644217 discloses thermal insulation walls embodied according to other conceptions.
  • the present invention can be applied to the conventional LNG storage tank for the LNG carriers that have various shapes of thermal insulation walls, as described above.
  • Most of the conventional LNG storage tanks for the LNG carrier are constructed to withstand a pressure of 0.25 bars or less, and to allow boil-off gas generated in the LNG storage tank to be consumed as the fuel for propulsion of the system or to be re-liquefied to maintain the LNG storage tank at 0.2 bars or less and to be discharged outside through a safety valve when the pressure of the storage tank increases over 0.2 ⁇ 0.25 bars.
  • the LNG storage tank according to the present invention is constructed to reduce the LNG tank pressure by reducing the local temperature and pressure increase.
  • the LNG storage tank is maintained at a uniform temperature distribution by injecting boil-off gas having a higher temperature from an upper portion of the LNG storage tank toward a lower portion of the LNG storage tank and by spraying LNG from the lower portion of the LNG storage tank toward the upper portion of the LNG storage tank having a higher temperature.
  • the LNG storage tank 1 is provided at the lower portion with an LNG pump 11 and a boil-off gas injection nozzle 21, and is provided at the upper portion with an LNG spray 13 and a boil-off gas compressor 23.
  • the boil-off gas having the higher temperature in the upper portion of the LNG storage tank 1 is injected into the lower portion of the LNG storage tank 1 through the boil-off gas nozzle 21 at the lower portion of the LNG storage tank 1 by the boil-off gas compressor 23.
  • LNG having the lower temperature in the lower portion of the LNG storage tank 1 can be sprayed toward the upper portion of the LNG storage tank 1 through the LNG spray 13 at the upper portion of the LNG storage tank 1 by the LNG pump 11.
  • the temperature distribution of the LNG storage tank 1 can be uniformly maintained, which enables a reduction in the boil-off gas generation.
  • a vapor region of an LNG storage tank may be filled with nitrogen.
  • an LNG storage tank 1 permits a pressure increase in the LNG storage tank 1 caused by heat influx and boil-off gas generation therein without treating the boil-off gas, so that most of the heat influx to the LNG tank can be absorbed as internal energy of LNG and NG vapor in the LNG storage tank 1, and so, the LNG tank pressure increases only by a small portion corresponding to the saturation pressure at the increased LNG temperature by the increase in internal energy. Then, when the LNG carrier arrives at a destination, the boil-off gas accumulated in the LNG storage tank is treated at an unloading terminal.
  • Fig. 3 is a schematic diagram illustrating the construction for treating boil-off gas at an unloading terminal with the LNG storage tank for LNG carriers according to the exemplary embodiment of the present invention.
  • the unloading terminal is installed with a plurality of LNG storage tanks 2, a plurality of compressor 3, a re-condenser 4, a high pressure LNG pump P and a vaporizer 5.
  • the generated boil-off gas can be supplied to consumers after being compressed in multiple stages by a high pressure mode of the compressor 3 at the unloading terminal.
  • the boil-off gas compressed by a low pressure mode of the compressor 3 can be supplied to the consumers after being re-condensed by the re-condenser 4 and vaporized.
  • LNG in the LNG storage tank 1 of the LNG carrier may be directly supplied to the re-condenser 4 so as not to generate boil-off gas due to higher LNG pressure than that of the LNG storage tank of the unloading terminal.
  • LNG can be directly supplied to a suction side of the high pressure LNG pump P.
  • the boil-off gas generation can be minimized in the respective LNG storage tanks 2 due to dispersion of the boil-off gas generation to the plurality of LNG storage tanks 2, so that the boil-off gas can be accommodated in the respective LNG storage tanks 2 themselves at the unloading terminal.
  • the LNG storage tank of the LNG carrier is operated at higher pressure than an existing design pressure, it is possible to omit a process of filling boil-off gas or NG vapor, which is required to maintain the inner pressure of the LNG storage tank of the LNG carrier when unloading LNG from the LNG carrier to the unloading terminal as the flash gas is generated in the LNG tank of the LNG carrier.
  • the boil-off gas management for the LNG- FSRU can be more flexible and the re-condensing unit may not be required.
  • an LNG-RV (Regasification vessel) can have above mentioned advantages of the LNG carrier and the LNG-FSRU.
  • boil-off gas in the case of LNG carriers, during the voyage, boil-off gas can be accumulated in the LNG storage tank which is designed to withstand the increased pressure caused by boil-off gas generation and the accumulated boil-off gas can be treated at an unloading terminal when unloading. In this way, there is much flexibility in selection of propulsion system and system simplicity can be attained by the independency of the propulsion system.
  • the LNG storage tank of the present invention can be very efficiently used along with the existing systems of treating boil-off gas or the re-liquefaction apparatus.
  • the boil-off gas generation exceeds the capacity of a propulsion system or re-liquefaction plant, the surplus boil-off gas can be preserved in the LNG storage tank without any loss by burning, thereby providing cost savings in an LNG carrier operation.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
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  • General Engineering & Computer Science (AREA)
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Abstract

An LNG storage tank and a method of treating boil-off gas using the same are disclosed. The LNG storage tank and the method of treating boil-off gas enable the pressure of the LNG storage tank to be maintained in a stable state without consuming boil-off gas generated in the LNG tank as propulsion fuel or without re-liquefying the boil-off gas. The storage tank comprises a thermal insulation wall, and has strengthened structure to permit a pressure increase resulting from heat influx to the LNG tank and boil-off gas generation. The method comprises permitting a pressure increase by the boil-off gas generation and LNG cargo temperature increase in the storage tank without treating the generated boil-off gas in the storage tank, so that the boil-off gas is accumulated without extracting or loss in the storage tank.

Description

    BACKGROUND OF THE INVENTION 1. Field of the Invention
  • The present invention relates generally to a liquefied natural gas (LNG) storage tank and a method of treating boil-off gas using the same, and more particularly to an LNG storage tank that can store natural gas in a liquid state and a method of treating boil-off gas using the same.
  • 2. Description of the Related Art
  • Generally, liquefied natural gas (LNG) is produced by cooling natural gas (NG) into a cryogenic liquid state at a production location and is transported by LNG carriers to a distant destination. At the destination, LNG is regasified through a floating storage and regasification unit (FSRU) or an unloading terminal on land and then supplied to consumers.
  • In the case where LNG is transported by an LNG regasification vessel (LNG-RV), LNG is regasified in the LNG-RV itself not through the FSRU or the unloading terminal.
  • Since the liquefaction of natural gas occurs at a cryogenic temperature of approximately -163 °C at ambient pressure, LNG is likely to be vaporized if the temperature of LNG increases slightly above -163 °C at ambient pressure. For example, in the case of LNG carriers, although an LNG storage tank is equipped with thermal insulation structure, it is impossible to completely prevent heat ingress to LNG through the storage tank, so that LNG is continuously vaporized and boil-off gas is generated in the LNG storage tank during the transportation of LNG by the LNG carrier.
  • When boil-off gas is generated in the LNG storage tank as described above, the pressure of the LNG storage tank increases and becomes dangerous.
  • Conventionally, to maintain the pressure of the LNG storage tank in a stable state, boil-off gas generated in the LNG storage tank is consumed as fuel for propulsion of the LNG carrier.
  • A steam turbine propulsion system driven by steam generated in boilers by burning boil-off gas and heavy fuel oil has a problem of low propulsion efficiency.
  • On the other hand, there is a dual fuel diesel electric propulsion system which uses compressed boil-off gas as fuel for the diesel engine and the system has higher propulsion efficiency than the steam turbine propulsion system. But there are many difficulties in maintenance due to a complicated integration of medium speed diesel engines and units for electric propulsion in the system. Furthermore, since boil-off gas must be supplied as fuel, this system employs a gas compression method which is more expensive in initial and operational costs compared with liquid compression.
  • In addition, such conventional methods using boil-off gas as fuel fails to achieve the highest efficiency of two-stroke slow speed diesel engine, which is generally adopted for marine use.
  • There is another method which re-liquefies the boil-off gas from the LNG tank and returns it to the tank. For this system, however, complicated and expensive re-liquefaction plant must be installed.
  • Furthermore, when the boil-off gas amount exceeds the capacity of the propulsion system or the re-liquefaction plant, the surplus must be burnt by a gas combustion unit or the like. And so, auxiliary units such as gas combustion units are installed and the valuable gas is lost by burning.
  • According to techniques disclosed in Korean Patent Laid-open Publication Nos. 2001-0014021 , 2001-0014033 , 2001-0083920 , 2001-0082235 , and 2004-0015249 , etc., boil-off gas generation in the LNG storage tank is suppressed by maintaining the LNG storage tank at a high pressure of about 200 bars without installing an insulation wall on the LNG storage tank. However, since the LNG storage tank must have a significantly high thickness to withstand a high pressure of about 200 bars, there are problems of high manufacturing costs and requirement of additional components, such as a high-pressure compressor.
  • SUMMARY OF THE INVENTION
  • Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an LNG storage tank configured to maintain the LNG storage tank at a safe level without separately treating the boil-off gas, and a method of treating boil-off gas using the same.
  • In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of an LNG storage tank comprising a thermal insulation wall and having strength to withstand a pressure increment caused by boil-off gas generated in the LNG storage tank to permit a pressure increase resulting from boil-off gas generation in the LNG storage tank.
  • In accordance with another aspect of the present invention, a method of treating boil-off gas is provided, comprising: permitting a pressure increase caused by boil-off gas generation in an LNG storage tank without treating boil-off gas generated in the LNG storage tank, so that the boil-off gas is accumulated in the LNG storage tank.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:
    • Fig. 1 is a schematic view illustrating the conception of heat ingress and absorption of heat in an LNG storage tank for LNG carriers according to the present invention;
    • Fig. 2 is a schematic view illustrating an LNG storage tank for LNG carriers according to an exemplary embodiment of the present invention; and
    • Fig. 3 is a schematic diagram illustrating an LNG unloading method at an unloading terminal by using the LNG storage tank for the LNG carriers according to the present invention.
    DETAILED DESCRIPTION OF THE INVENTION
  • Exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings hereinafter.
  • An LNG storage tank of the present invention is applicable to an LNG carrier, a floating storage and regasification unit (FSRU), an unloading terminal on land, and an LNG regasification vessel (LNG-RV), etc.
  • Hereinafter, an LNG storage tank applicable to the LNG carrier will be described as an example.
  • Fig. 1 is a schematic view illustrating the conception of heat ingress and absorption of heat in an LNG storage tank for LNG carriers according to the present invention. In the prior art, the pressure of the LNG storage tank for the LNG carrier is maintained in a predetermined range, so that most of heat ingress into the LNG storage tank contributes to boil-off gas generation, all of which should be treated in the LNG carrier. On the other hand, according to the present invention, an LNG storage tank for an LNG carrier is constructed to permit a pressure increase therein, causing an increase in saturation temperature, whereby most of heat ingress is absorbed by large heat capacity of LNG and natural gas (NG) vapor in the storage tank, noticeably reducing the boil-off gas generation. For example, when the pressure of the LNG storage tank for the LNG carrier according to an exemplary embodiment becomes 0.7 bars from initial pressure of 0.06 bars, the saturation temperature is increased by about 6 K.
  • Fig. 2 is a schematic view illustrating an LNG storage tank for an LNG carrier according to an exemplary embodiment of the invention. The LNG storage tank 1 for the LNG carrier comprises an insulation wall built thereon and has an inner pressure of approximately 0.06 bars (gauge pressure) at the point of departure when LNG is loaded in an LNG production terminal. Then, as boil-off gas is generated in the LNG storage tank during the LNG carrier's voyage, the pressure of the LNG storage tank gradually increases. For example, when LNG is loaded into the LNG storage tank 1 of the LNG carrier at the location where LNG is produced, the LNG storage tank 1 has an inner pressure of 0.06 bars, and, when the LNG carrier arrives at a destination after a voyage of about 15~20 days, the inner pressure of the LNG storage tank 1 can increase to 0.7 bars (gauge pressure).
  • The LNG storage tank 1 for the LNG carrier according to the invention comprises the thermal insulation wall and is designed by taking account the pressure increase caused by boil-off gas generation, that is, to have sufficient strength to withstand a pressure increment caused by the boil-off gas generation. Thus, the boil-off gas generated in the LNG storage tank 1 is accumulated therein without any loss or extraction from the LNG tank during the LNG carrier's voyage.
  • For example, the LNG storage tank 1 for the LNG carrier according to the embodiment of the invention comprises the thermal insulation wall, and, preferably has construction capable of withstanding a pressure of 0.4 to 2 bars (gauge pressure), and more preferably a pressure of 0.6 to 1.5 bars (gauge pressure). Since such an LNG storage tank 1 of the present invention can be sufficiently embodied by constructing the storage tank 1 to have a high thickness or by suitably reinforcing a conventional LNG storage tank for LNG carriers through addition of a reinforcing steel structure thereto without significantly changing the design and construction of the conventional LNG storage tank, it is very economical in view of manufacturing costs.
  • Various conventional LNG storage tanks for LNG carriers with a thermal insulation (heat dissipation) wall built on the storage tank are known in the related art as described below. The thermal insulation wall is not shown in Fig. 1.
  • First, the LNG storage tank for the LNG carriers can be classified into an independent type tank and a membrane type tank. This classification of the LNG storage tank depends on whether or not the load of cargo directly acts on the thermal insulation wall, and is described in detail hereinafter.
  • In the following Table 1, GTT No. 96-2 and GTT Mark III have been renamed from GT and TGZ, respectively, when the names of Gaz Transport (GT) Corporation and Technigaz (TGZ) Corporation was changed to GTT (Gaz Transport & Technigaz) Corporation in 1999. Table 1
    Classification Membrane Type Independent Type
    GTT Mark □ GTT No. 96-2 MOSS IHI-SPB
    Material-thickness of tank SUS 304L-1.2 mm Invar steel-0.7 mm Al alloyed steel (5083)-50 mm Al alloyed steel (5083) Max. 30 mm
    Material for heat dissipation-thickness Reinforced Polyurethane Foam-250 mm Plywood Box+Perlite-530 mm Polyurethane Foam-250 mm Polyurethane Foam-250 mm
  • GT type and TGT type tanks are disclosed in US Patent Nos. 6,035,795 , 6,378,722 , and No. 5,586,513 , US Patent Publication No. 2003-0000949 , Korean Patent Laid-open Publication Nos. 2000-0011347 and 2000-0011346 , etc.
  • Korean Patent Nos. 499710 and 0644217 discloses thermal insulation walls embodied according to other conceptions.
  • As such, there are many conventional LNG storage tanks for the LNG carriers having variously shaped thermal insulation walls, all of which are designed to suppress the boil-off gas generation as much as possible.
  • The present invention can be applied to the conventional LNG storage tank for the LNG carriers that have various shapes of thermal insulation walls, as described above. Most of the conventional LNG storage tanks for the LNG carrier are constructed to withstand a pressure of 0.25 bars or less, and to allow boil-off gas generated in the LNG storage tank to be consumed as the fuel for propulsion of the system or to be re-liquefied to maintain the LNG storage tank at 0.2 bars or less and to be discharged outside through a safety valve when the pressure of the storage tank increases over 0.2 ~ 0.25 bars.
  • In addition, the LNG storage tank according to the present invention is constructed to reduce the LNG tank pressure by reducing the local temperature and pressure increase. The LNG storage tank is maintained at a uniform temperature distribution by injecting boil-off gas having a higher temperature from an upper portion of the LNG storage tank toward a lower portion of the LNG storage tank and by spraying LNG from the lower portion of the LNG storage tank toward the upper portion of the LNG storage tank having a higher temperature.
  • In Fig. 2, the LNG storage tank 1 is provided at the lower portion with an LNG pump 11 and a boil-off gas injection nozzle 21, and is provided at the upper portion with an LNG spray 13 and a boil-off gas compressor 23. The boil-off gas having the higher temperature in the upper portion of the LNG storage tank 1 is injected into the lower portion of the LNG storage tank 1 through the boil-off gas nozzle 21 at the lower portion of the LNG storage tank 1 by the boil-off gas compressor 23. Additionally, LNG having the lower temperature in the lower portion of the LNG storage tank 1 can be sprayed toward the upper portion of the LNG storage tank 1 through the LNG spray 13 at the upper portion of the LNG storage tank 1 by the LNG pump 11. As a result, the temperature distribution of the LNG storage tank 1 can be uniformly maintained, which enables a reduction in the boil-off gas generation.
  • Further, if LNG is loaded in a sub-cooled state into an LNG carrier at a production terminal where LNG is produced, it is possible to further reduce the boil-off gas generation during LNG transportation to a destination. To prevent the pressure of an LNG storage tank for the LNG carrier from being lowered to a negative pressure (0 atm or less) after LNG is loaded in the sub-cooled state at the production terminal, a vapor region of an LNG storage tank may be filled with nitrogen.
  • Next, a method of treating boil-off gas using an LNG storage tank for LNG carriers according to the present invention will be described.
  • During the voyage of an LNG carrier, an LNG storage tank 1 according to the present invention permits a pressure increase in the LNG storage tank 1 caused by heat influx and boil-off gas generation therein without treating the boil-off gas, so that most of the heat influx to the LNG tank can be absorbed as internal energy of LNG and NG vapor in the LNG storage tank 1, and so, the LNG tank pressure increases only by a small portion corresponding to the saturation pressure at the increased LNG temperature by the increase in internal energy. Then, when the LNG carrier arrives at a destination, the boil-off gas accumulated in the LNG storage tank is treated at an unloading terminal.
  • Fig. 3 is a schematic diagram illustrating the construction for treating boil-off gas at an unloading terminal with the LNG storage tank for LNG carriers according to the exemplary embodiment of the present invention.
  • The unloading terminal is installed with a plurality of LNG storage tanks 2, a plurality of compressor 3, a re-condenser 4, a high pressure LNG pump P and a vaporizer 5.
  • When LNG is unloaded from the LNG storage tank of the LNG carrier to an LNG storage tank of the unloading terminal, additional boil-off gas can be generated due to inflow of LNG having a higher pressure into the LNG storage tank of the unloading terminal since the pressure of the LNG storage tank of the LNG carrier is higher than that of the LNG storage tank of the unloading terminal.
  • The generated boil-off gas can be supplied to consumers after being compressed in multiple stages by a high pressure mode of the compressor 3 at the unloading terminal. Here, the boil-off gas compressed by a low pressure mode of the compressor 3 can be supplied to the consumers after being re-condensed by the re-condenser 4 and vaporized.
  • Instead of being supplied into the LNG storage tank 2 of the unloading terminal, LNG in the LNG storage tank 1 of the LNG carrier may be directly supplied to the re-condenser 4 so as not to generate boil-off gas due to higher LNG pressure than that of the LNG storage tank of the unloading terminal.
  • On the other hand, if the re-condenser 4 is not installed at the unloading terminal, LNG can be directly supplied to a suction side of the high pressure LNG pump P.
  • In the case where the plurality of LNG storage tanks 2 are installed at the unloading terminal as described above, when LNG is sent to the plural LNG storage tanks 2 of the unloading terminal, the boil-off gas generation can be minimized in the respective LNG storage tanks 2 due to dispersion of the boil-off gas generation to the plurality of LNG storage tanks 2, so that the boil-off gas can be accommodated in the respective LNG storage tanks 2 themselves at the unloading terminal.
  • Further, according to the invention, since the LNG storage tank of the LNG carrier is operated at higher pressure than an existing design pressure, it is possible to omit a process of filling boil-off gas or NG vapor, which is required to maintain the inner pressure of the LNG storage tank of the LNG carrier when unloading LNG from the LNG carrier to the unloading terminal as the flash gas is generated in the LNG tank of the LNG carrier.
  • Furthermore, if a conventional LNG storage tank of the unloading terminal or a floating storage and regasification unit (FSRU) or an LNG regasification vessel (LNG-RV) is modified or a new LNG storage tank of the unloading terminal or floating storage and regasification unit (FSRU) or LNG regasification vessel (LNG-RV) is built such that the storage pressure of the LNG storage tank corresponds to the pressure of the LNG storage tank of the LNG carrier according to the invention, it is possible to employ an existing unloading technique to these LNG storage tanks since there is no additional flash gas generation during unloading of LNG from the LNG carrier to any of these LNG storage tanks at the unloading terminal or FSRU or LNG-RV.
  • According to a conventional operating method, most of the boil-off gas generated in the LNG storage tank of the LNG carrier should be consumed as fuel for propulsion system or re-liquefied to lower the pressure of the LNG storage tank. According to the present invention, however, since the pressure of the LNG storage tank of the LNG carrier can be maintained by consuming or re-liquefying only reduced capacity or a portion of the boil-off gas, it is possible to apply the present invention to conventional LNG carriers configured to use the boil-off gas as propulsion fuel or with onboard re-liquefaction system.
  • According to the present invention, since restrictions on the LNG storage tank pressure maintenance during transportation of LNG are lifted, application of the present invention is not restricted to the case where the LNG carrier is operated without any boil-off gas treating apparatus and it can be used for conventional LNG carriers with boil-off gas treating equipment as well.
  • If the storage tank of an LNG-FSRU (Floating Storage and Regasification Unit) is constructed based on the present invention, the boil-off gas management for the LNG- FSRU can be more flexible and the re-condensing unit may not be required.
  • According to the present invention, an LNG-RV (Regasification vessel) can have above mentioned advantages of the LNG carrier and the LNG-FSRU.
  • As apparent from the above, according to the present invention, in the case of LNG carriers, during the voyage, boil-off gas can be accumulated in the LNG storage tank which is designed to withstand the increased pressure caused by boil-off gas generation and the accumulated boil-off gas can be treated at an unloading terminal when unloading. In this way, there is much flexibility in selection of propulsion system and system simplicity can be attained by the independency of the propulsion system.
  • Further, according to the present invention, in the case of the LNG carriers, it becomes unnecessary to employ various components for boil-off gas related equipment and propulsion system (such as a boiler/steam turbine, a re-liquefaction apparatus, a gas-based engine, a compressor for fuel gas supply etc.), which have been required in the prior art for treating the boil-off gas. Moreover, according to the present invention, it is possible to employ a high efficiency general purpose marine engine as a propulsion system.
  • Further, in the case of the LNG carriers, the LNG storage tank of the present invention can be very efficiently used along with the existing systems of treating boil-off gas or the re-liquefaction apparatus. In particular, even when the boil-off gas generation exceeds the capacity of a propulsion system or re-liquefaction plant, the surplus boil-off gas can be preserved in the LNG storage tank without any loss by burning, thereby providing cost savings in an LNG carrier operation.
  • Although particular embodiments of the present invention have been shown and described herein, it should be understood that various modifications, variations or corrections may readily occur to those skilled in the art, and thus, the description and drawings herein should be interpreted by way of illustrative purpose without limiting the scope and sprit of the present invention.

Claims (20)

  1. An LNG storage tank comprising a thermal insulation wall and having strength to withstand a pressure increment caused by boil-off gas generation in the LNG storage tank so as to permit a pressure increase resulting from the generation of the boil-off gas in the LNG storage tank.
  2. The LNG storage tank according to claim 1, designed to withstand a pressure of 0.3 ~ 2 bars (gauge pressure).
  3. The LNG storage tank according to claim 1, designed to withstand a pressure of 0.6 ~ 1.5 bars (gauge pressure).
  4. The LNG storage tank according to claim 1, manufactured by adding a reinforcing steel structure to an existing general LNG storage tank.
  5. The LNG storage tank according to claim 1, wherein a temperature distribution in the LNG storage tank is uniformly maintained.
  6. The LNG storage tank according to any one of claims 1 to 5, wherein boil-off gas having a higher temperature at an upper portion of the LNG storage tank is injected into a lower portion of the LNG storage tank having a lower temperature and LNG having a lower temperature at the lower portion of the LNG storage tank is sprayed into the upper portion of the LNG storage tank having a higher temperature.
  7. The LNG storage tank according to claim 6, further comprising:
    an LNG pump and a LNG spray for LNG pumping; and
    a boil-off gas compressor and boil-off gas injection nozzle for boil-off gas injection.
  8. The LNG storage tank according to claim 1, wherein the LNG storage tank is applicable to an LNG carrier, a floating storage and regasification unit (FSRU), an unloading terminal on land or an LNG regasification vessel (LNG-RV).
  9. A method of treating boil-off gas, comprising: permitting a pressure increase caused by boil-off gas generation in an LNG storage tank without treating the boil-off gas generated in the LNG storage tank, so that the boil-off gas is accumulated in the LNG storage tank.
  10. A method of treating boil-off gas, comprising: allowing most of heat influx into an LNG storage tank to be absorbed by increased internal thermal energy of LNG and NG within the LNG storage tank without treating the boil-off gas generated in the LNG storage tank, so that boil-off gas is accumulated in the LNG storage tank.
  11. The method according to claim 9, wherein the LNG storage tank is permitted to have a pressure of 0.3 ~ 2 bars (gauge pressure).
  12. The method according to claim 9, wherein the LNG storage tank is permitted to have a pressure of 0.6 ~ 1.5 bars (gauge pressure).
  13. The method according to claim 9 or 10, wherein a temperature distribution in the LNG storage tank is uniformly maintained.
  14. The method according to claim 9, wherein the LNG storage tank is applicable to an LNG carrier, a floating storage and regasification unit (FSRU), an unloading terminal on land or an LNG regasification vessel (LNG-RV).
  15. The method according to claim 14, wherein boil-off gas accumulated in the LNG storage tank of the LNG carrier is treated at an unloading terminal after the LNG carrier arrives at a destination.
  16. The method according to claim 15, wherein boil-off gas generated in an LNG storage tank of the unloading terminal when LNG is unloaded from the LNG storage tank for the LNG carrier is supplied to consumers after being compressed by a high pressure compressor at the unloading terminal.
  17. The method according to claim 15, wherein boil-off gas generated in an LNG storage tank of the unloading terminal when LNG is unloaded from the LNG storage tank for the LNG carrier is supplied to consumers after being compressed by a low pressure boil-off gas compressor, re-condensed and vaporized at the unloading terminal.
  18. The method according to claim 15, wherein LNG in the LNG storage tank for the LNG carrier is supplied to consumers after being directly supplied from the LNG storage tank for the LNG carrier to either an inlet of a re-condenser or a suction side of a high pressure pump and vaporized at the unloading terminal.
  19. The method according to claim 15, wherein LNG in the LNG storage tank for the LNG carrier is supplied to a plurality of LNG storage tanks at the unloading terminal, supplied from the plurality of LNG storage tanks of the unloading terminal to reduce flash gas regeneration effects in the unloading terminal.
  20. The method according to claim 14, wherein each of the LNG storage tank of the unloading terminal or a floating storage and regasification unit (FSRU) or an LNG regasification vessel (LNG-RV) is constructed such that a storage pressure of the LNG storage tank of the unloading terminal or the floating storage and regasification unit (FSRU) or the LNG regasification vessel (LNG-RV) is increased to correspond to a storage pressure of the LNG storage tank of the LNG carrier.
EP07007423.2A 2007-02-12 2007-04-11 LNG tank and method of treating boil-off gas Pending EP1956287A3 (en)

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KR1020070014405A KR100805022B1 (en) 2007-02-12 2007-02-12 Lng cargo tank of lng carrier and method for treating boil-off gas using the same

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EP1956287A2 true EP1956287A2 (en) 2008-08-13
EP1956287A3 EP1956287A3 (en) 2015-12-09

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8821132B2 (en) 2008-03-10 2014-09-02 Burckhardt Compression Ag Device and method for preparing liquefied natural gas (LNG) fuel
DE102016002316A1 (en) 2016-02-29 2017-08-31 Tge Marine Gas Engineering Gmbh Method for operating a liquefied gas tank and liquid gas tank for receiving LNG and boil-off gas

Families Citing this family (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008286211A (en) * 2007-05-15 2008-11-27 Ihi Corp Bog compression installation and its operation method
NO331559B1 (en) * 2010-03-08 2012-01-23 Hamworthy Oil & Gas Systems As System for reducing emissions from volatile liquid cargo
FI121876B (en) * 2010-04-09 2011-05-31 Waertsilae Finland Oy Procedure for operating a watercraft using LNG as fuel and watercraft
US20130333799A1 (en) * 2011-02-28 2013-12-19 Korea Advanced Institute Of Science And Technology Lng refueling system and boil-off gas treatment method
EP2685078A4 (en) * 2011-03-11 2014-09-10 Daewoo Shipbuilding & Marine System for supplying fuel to marine structure having re-liquefying device and high-pressure natural gas injection engine
JP5715479B2 (en) * 2011-05-02 2015-05-07 ジャパンマリンユナイテッド株式会社 Boil-off gas treatment device and liquefied gas tank
JP5818902B2 (en) * 2011-09-28 2015-11-18 三菱重工業株式会社 Direct injection diesel engine equipment
KR101875089B1 (en) * 2011-12-28 2018-07-05 대우조선해양 주식회사 Abnormal pressure protection apparatus for flng storage
KR101422719B1 (en) * 2012-09-27 2014-08-13 삼성중공업 주식회사 Apparatus for loading storage tank with oil and oil carrier having the same
US10088108B2 (en) * 2012-12-14 2018-10-02 Wärtsilä Finland Oy Method of filling a fuel tank with liquefied gas and liquefied gas system
CN103049875B (en) * 2012-12-18 2016-08-24 上海燃气工程设计研究有限公司 FOB with DES mixes the computational methods of the liquefied natural gas day of supply under delivery mode
KR101922271B1 (en) * 2014-02-06 2018-11-26 현대중공업 주식회사 A Treatment System Of Liquefied Gas
CN103912761B (en) * 2014-04-18 2016-03-02 大连理工大学 A kind of LNG ship adjustable thermal insulation bed device
JP6418942B2 (en) * 2014-12-26 2018-11-07 川崎重工業株式会社 Liquefied gas carrier
FR3032258B1 (en) * 2015-01-30 2017-07-28 Gaztransport Et Technigaz STORAGE AND TRANSPORTATION INSTALLATION OF A CRYOGENIC FLUID EMBEDDED ON A SHIP
JP6299037B2 (en) * 2015-03-27 2018-03-28 三菱重工業株式会社 Liquefied gas storage tank and ship
KR101848139B1 (en) * 2015-06-09 2018-04-11 현대중공업 주식회사 Vessel having Gas Treatment System
CN105042323A (en) * 2015-06-30 2015-11-11 柳州市山泰气体有限公司 Manufacturing method of liquefied petroleum gas horizontal storage tank
JP6728025B2 (en) * 2016-11-15 2020-07-22 レール・リキード−ソシエテ・アノニム・プール・レテュード・エ・レクスプロワタシオン・デ・プロセデ・ジョルジュ・クロード Boil-off gas recondensing device and LNG supply system including the same
FR3073602B1 (en) * 2017-11-10 2019-11-22 Gaztransport Et Technigaz METHOD FOR DETERMINING AN OPTIMUM VALUE OF AT LEAST ONE PARAMETER FOR IMPLEMENTING A METHOD FOR COLDING A WATERPROOF AND THEMALLY INSULATING TANK
CN109140225A (en) * 2018-09-05 2019-01-04 中国海洋石油集团有限公司 A kind of LNG Distribution Center

Family Cites Families (38)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2790307A (en) * 1955-09-12 1957-04-30 Phillips Petroleum Co Storage of volatile liquids
US3453836A (en) * 1967-07-24 1969-07-08 Mcmullen John J Liquefied petroleum gas tanker
CH653262A5 (en) * 1980-03-24 1985-12-31 Buse Kohlensaeure METHOD AND DEVICE FOR DISCHARGING GAS LEAKING IN THE CASE OF EMERGENCY FALLS FROM A STORAGE CONTAINER OR LIQUIDATING VEGETABLES DURING THE DRAINING.
JPS5872800A (en) * 1981-10-23 1983-04-30 Tokyo Gas Co Ltd Bog reducing method of liquefied gas
JPS58140394U (en) * 1982-03-18 1983-09-21 石川島播磨重工業株式会社 Reliquefaction equipment in low-temperature liquefied gas storage facilities
JPS6145837A (en) * 1984-08-09 1986-03-05 Kawasaki Heavy Ind Ltd Secondary lng base system
CA1241890A (en) * 1985-03-05 1988-09-13 Colin G. Young Automatic fuel tank anti b.l.e.v.e. safety apparatus and system
CN85105351B (en) * 1985-07-13 1988-04-13 日本钢管株式会社 Method and system for insulating a cargotank for liquefied gas
JPS6354938U (en) * 1986-09-26 1988-04-13
US4843829A (en) * 1988-11-03 1989-07-04 Air Products And Chemicals, Inc. Reliquefaction of boil-off from liquefied natural gas
JPH02257000A (en) * 1989-03-30 1990-10-17 Toho Gas Co Ltd Pressure control method for adjusting quantity of heat considering fluctuation in flow rate of bog
NO176454C (en) * 1993-01-29 1995-04-05 Kvaerner Moss Tech As Methods and plants for utilizing and providing fuel gas, respectively
NO300288B1 (en) * 1996-02-29 1997-05-05 Kvaerner Maritime As Process for utilizing decoction from liquid gas and plant for carrying out the process
TW444109B (en) * 1997-06-20 2001-07-01 Exxon Production Research Co LNG fuel storage and delivery systems for natural gas powered vehicles
JPH1163396A (en) * 1997-08-18 1999-03-05 Ishikawajima Harima Heavy Ind Co Ltd Boiloff gas condensing device and liquefied gas storage equipment
JPH11153296A (en) * 1997-11-19 1999-06-08 Ishikawajima Harima Heavy Ind Co Ltd Cryogenic liquefied gas storage facility
US6089022A (en) * 1998-03-18 2000-07-18 Mobil Oil Corporation Regasification of liquefied natural gas (LNG) aboard a transport vessel
TW432192B (en) * 1998-03-27 2001-05-01 Exxon Production Research Co Producing power from pressurized liquefied natural gas
JPH11280996A (en) * 1998-03-27 1999-10-15 Ishikawajima Harima Heavy Ind Co Ltd Fluid receiving method and fluid storage equipment
FR2781557B1 (en) * 1998-07-24 2000-09-15 Gaz Transport & Technigaz IMPROVEMENT FOR A WATERPROOF AND THERMALLY INSULATING TANK WITH PREFABRICATED PANELS
JP2000046295A (en) * 1998-07-27 2000-02-18 Ishikawajima Harima Heavy Ind Co Ltd Bog re-liquefying device in low temperature liquefied gas tank
US6237347B1 (en) * 1999-03-31 2001-05-29 Exxonmobil Upstream Research Company Method for loading pressurized liquefied natural gas into containers
CN2400677Y (en) * 1999-10-30 2000-10-11 中原石油勘探局 Self-cooling liquefied natural gas tank
US6230516B1 (en) * 2000-02-04 2001-05-15 Andonian Family Nominee Trust Apparatus for mixing a multiple constituent liquid into a container and method
GB0005709D0 (en) * 2000-03-09 2000-05-03 Cryostar France Sa Reliquefaction of compressed vapour
JP2002295799A (en) * 2001-04-03 2002-10-09 Kobe Steel Ltd Method and system for treating liquefied natural gas and nitrogen
US6829901B2 (en) * 2001-12-12 2004-12-14 Exxonmobil Upstream Research Company Single point mooring regasification tower
JP2003247697A (en) * 2002-02-25 2003-09-05 Kawasaki Shipbuilding Corp Low-temperature liquefied gas agitating device and boat provided with it
WO2003072993A1 (en) * 2002-02-27 2003-09-04 Excelerate Energy, Llc Method and apparatus for the regasification of lng onboard a carrier
US7147124B2 (en) * 2002-03-27 2006-12-12 Exxon Mobil Upstream Research Company Containers and methods for containing pressurized fluids using reinforced fibers and methods for making such containers
CN2630625Y (en) * 2003-06-10 2004-08-04 河南中原绿能高科有限责任公司 Liquified natural-gas cylinder
NO20035047D0 (en) * 2003-11-13 2003-11-13 Hamworthy Kse Gas Systems As Apparatus and method for temperature control of gas condensation
JP4347037B2 (en) * 2003-12-25 2009-10-21 三菱重工業株式会社 Fuel supply apparatus for gas-fired internal combustion engine such as gas turbine and LNG ship equipped with the same
US7165408B2 (en) * 2004-02-19 2007-01-23 General Motors Corporation Method of operating a cryogenic liquid gas storage tank
KR100499710B1 (en) * 2004-12-08 2005-07-05 한국가스공사 Lng storage tank installed inside the ship and manufacturing method the tank
KR100638924B1 (en) * 2005-01-18 2006-10-26 대우조선해양 주식회사 Operating system for sub-cooled liquefaction boil-off gas of LNG ship
CN2833317Y (en) * 2005-07-20 2006-11-01 宝利发展公司 High vacuum thermal-insulating tank for transporting low-temperature liquefied natural gas
CN100489372C (en) * 2005-10-19 2009-05-20 马磊 Liquefied natural gas automatic pressure regulation and gasification and charging device

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
None *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8821132B2 (en) 2008-03-10 2014-09-02 Burckhardt Compression Ag Device and method for preparing liquefied natural gas (LNG) fuel
US9273675B2 (en) 2008-03-10 2016-03-01 Burckhardt Compression Ag Device and method for preparing liquified natural gas (LNG) fuel
DE102016002316A1 (en) 2016-02-29 2017-08-31 Tge Marine Gas Engineering Gmbh Method for operating a liquefied gas tank and liquid gas tank for receiving LNG and boil-off gas
WO2017148571A1 (en) 2016-02-29 2017-09-08 Tge Marine Gas Engineering Gmbh Method for operating a liquefied gas tank and liquefied gas tank for receiving lng and boil-off gas
CN108778921A (en) * 2016-02-29 2018-11-09 塔格海底天然气工程有限公司 Method for running liquid gas storage tank and the liquid gas storage tank for accommodating LNG and boil-off gas

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JP2010261595A (en) 2010-11-18
CN101245897A (en) 2008-08-20
CN101245892B (en) 2014-09-24
CN103398284B (en) 2016-08-10
JP2008196682A (en) 2008-08-28
EP1956287A3 (en) 2015-12-09
CN101245893B (en) 2010-06-02
CN101245892A (en) 2008-08-20
CN101245893A (en) 2008-08-20
CN101245897B (en) 2010-06-02
CN103398284A (en) 2013-11-20

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