US20150000334A1 - Liquefaction of Natural Gas - Google Patents
Liquefaction of Natural Gas Download PDFInfo
- Publication number
- US20150000334A1 US20150000334A1 US13/941,045 US201313941045A US2015000334A1 US 20150000334 A1 US20150000334 A1 US 20150000334A1 US 201313941045 A US201313941045 A US 201313941045A US 2015000334 A1 US2015000334 A1 US 2015000334A1
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- US
- United States
- Prior art keywords
- lng
- natural gas
- vessel
- vapour
- heat exchanger
- 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.)
- Abandoned
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 156
- 239000003345 natural gas Substances 0.000 title claims abstract description 72
- 239000003949 liquefied natural gas Substances 0.000 claims abstract description 174
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 103
- 239000007788 liquid Substances 0.000 claims abstract description 63
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 51
- 239000002826 coolant Substances 0.000 claims abstract description 28
- 238000000034 method Methods 0.000 claims abstract description 24
- 238000003860 storage Methods 0.000 claims description 46
- 239000007789 gas Substances 0.000 claims description 25
- 238000009835 boiling Methods 0.000 claims description 10
- 238000001816 cooling Methods 0.000 claims description 10
- 239000000446 fuel Substances 0.000 description 16
- 239000000969 carrier Substances 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 238000001704 evaporation Methods 0.000 description 4
- 230000008020 evaporation Effects 0.000 description 4
- 238000002485 combustion reaction Methods 0.000 description 3
- 230000005611 electricity Effects 0.000 description 3
- 238000010926 purge Methods 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000005086 pumping Methods 0.000 description 2
- 238000004887 air purification Methods 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 238000004821 distillation Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000005057 refrigeration Methods 0.000 description 1
- 239000006200 vaporizer Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
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- 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
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- 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
- F25J1/007—Primary atmospheric gases, mixtures thereof
- F25J1/0072—Nitrogen
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- 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
- F25J1/0025—Boil-off gases "BOG" from storages
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- 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
- F25J1/0204—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 single flow SCR cycle
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- 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
- F25J1/0222—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 intermediate heat exchange fluid between the cryogenic component and the fluid to be liquefied
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- 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
- F25J1/0228—Coupling of the liquefaction unit to other units or processes, so-called integrated processes
- F25J1/0234—Integration with a cryogenic air separation unit
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- 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
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS 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
- F17C2221/00—Handled fluid, in particular type of fluid
- F17C2221/03—Mixtures
- F17C2221/032—Hydrocarbons
- F17C2221/033—Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS 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
- F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
- F17C2223/01—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
- F17C2223/0146—Two-phase
- F17C2223/0153—Liquefied gas, e.g. LPG, GPL
- F17C2223/0161—Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS 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
- F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
- F17C2223/03—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the pressure level
- F17C2223/033—Small pressure, e.g. for liquefied gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS 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
- F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
- F17C2225/04—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by other properties of handled fluid after transfer
- F17C2225/042—Localisation of the filling point
- F17C2225/043—Localisation of the filling point in the gas
- F17C2225/044—Localisation of the filling point in the gas at several points, e.g. with a device for recondensing gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS 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
- F17C2265/00—Effects achieved by gas storage or gas handling
- F17C2265/03—Treating the boil-off
- F17C2265/032—Treating the boil-off by recovery
- F17C2265/033—Treating the boil-off by recovery with cooling
- F17C2265/034—Treating the boil-off by recovery with cooling with condensing the gas phase
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS 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
- F17C2265/00—Effects achieved by gas storage or gas handling
- F17C2265/06—Fluid distribution
- F17C2265/066—Fluid distribution for feeding engines for propulsion
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS 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
- F17C2270/00—Applications
- F17C2270/01—Applications for fluid transport or storage
- F17C2270/0102—Applications for fluid transport or storage on or in the water
- F17C2270/0105—Ships
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS 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
- F17C5/00—Methods or apparatus for filling containers with liquefied, solidified, or compressed gases under pressures
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- 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
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- 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
- F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
- F25J2290/34—Details about subcooling of liquids
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- 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
- F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
- F25J2290/62—Details of storing a fluid in a tank
Definitions
- the present invention relates to liquefaction of natural gas vapour, particularly during the transport and storage of liquefied natural gas (LNG).
- LNG liquefied natural gas
- the present invention relates to the handling of boil off gas in a bunker vessel used to refuel LNG-powered vessels.
- Liquefied natural gas is natural gas (typically methane—CH4) that has been liquefied, typically to make it more manageable during storage and/or transport. At atmospheric pressure, this means the temperature of the LNG is reduced to around ⁇ 163 degrees centigrade or below.
- LNG carriers are vessels used to carry LNG across large distances, particularly to carry LNG from gas producing nations to gas consuming nations.
- the journey times of such vessels are significant, measured in days, weeks and even months.
- the LNG is stored at low temperature in order that it does not vaporise.
- Another type of propulsion system used in LNG carriers is a dual fuel diesel electric propulsion system which can operate off either diesel or LNG itself
- the BOG can be used as fuel for the engines to provide propulsion and electrical load. If there is insufficient engine load it is necessary to burn the excess BOG in a GCU.
- a bunker vessel is a smaller vessel designed to carry fuel to the carrier from shore. The bunker vessel must dock with the carrier and transfer fuel from its tanks to that of the carrier.
- the bunker vessel must cope with the fact that the process of fuel transfer is likely to involve an increased production of BOG as the LNG is transferred between the vessels. Even if this were not the case the base level production of BOG would still need to be handled. However, as both vessels are stationary during this process, the BOG created cannot be used for propulsion and must be handled in some other manner.
- a re-liquefaction plant is impractical for a relatively small vessel such as a bunker vessel due to its large energy requirements and, as mentioned above, burning off excess BOG is both wasteful and environmentally unsound. There remains a need to find a method of handling BOG in bunker vessels that is both practical and effective.
- a method for condensing natural gas vapour to generate liquefied natural gas (LNG), comprising:
- liquid coolant wherein the liquid coolant has a boiling point less than that of natural gas
- a system for condensing natural gas vapour to generate liquefied natural gas (LNG); comprising
- a first heat exchanger arranged to cool LNG using a liquid coolant to generate sub-cooled LNG, wherein the liquid coolant has a boiling point less than that of natural gas;
- a second heat exchanger arranged to condense natural gas vapour using the sub-cooled LNG to liquefy the natural gas vapour and thereby generate further LNG.
- the present invention can provide an efficient method of condensing natural gas vapour to provide LNG.
- Existing LNG is cooled at a first heat exchanger to create sub-cooled LNG that can be used to condense the natural gas vapour. This is significantly more energy efficient than provision of a plant for generating LNG directly from the natural gas vapour.
- the use of a liquid coolant to first sub-cool existing available LNG reduces the need for energy intensive refrigeration cycles to generate a coolant to directly cool the natural gas vapour.
- Boil-off gas is natural gas vapour that has arisen through the evaporation of an LNG source.
- the boil-off gas is likely not to be significantly warmer than the boiling temperature of natural gas, and furthermore LNG is likely to be available for sub-cooling.
- the natural gas vapour is boil-off gas.
- the method may comprise receiving the LNG for cooling at the first heat exchanger from at least one LNG storage tank and returning the sub-cooled LNG to the at least one storage tank after it is used at the second heat exchanger.
- LNG may be re-used for subsequent condensing of natural gas vapour.
- the sub-cooled LNG is likely to have warmed somewhat, but the method is preferably arranged such that it remains in liquid form for returning to the LNG storage tank.
- the method may further comprise delivering the further LNG to the at least one storage tank.
- the LNG that is created through the method may subsequently be used for condensing further natural gas vapour in future cycles.
- the system is compact and efficient in that there is no requirement for separate tanks for the coolant used at the second heat exchanger and the generated LNG.
- the liquid coolant used at the first generator has a boiling point less than that of the natural gas vapour.
- the natural gas vapour is preferably predominantly methane, more preferably at least 90 Mole % methane, at least 95 Mole % methane or over 97% Mole methane.
- Methane has a boiling point at atmospheric pressure of around ⁇ 163 degrees centigrade.
- the liquid coolant has a boiling point at atmospheric pressure of less than that of methane (i.e. less than ⁇ 163 degrees centigrade), more preferably less than ⁇ 170 degrees centigrade, and most preferably less than ⁇ 190 degrees centigrade.
- the liquid coolant is liquid nitrogen.
- the boiling point of nitrogen is around ⁇ 193 degrees centigrade at atmospheric pressure. References to atmospheric pressure refer to a pressure equal to the understood unit of one atmosphere, rather than to prevailing climatic conditions.
- the system may comprise a storage facility for the liquid coolant.
- the system may comprise at least one storage tank for storing the liquid coolant.
- the system may additionally or alternatively comprise a generator for generating the liquid coolant.
- the method may comprise a step of generating the liquid coolant.
- an initial supply of liquid coolant may be provided to the storage facility from an on-shore facility while the vessel is docked, but when the vessel is at sea additional liquid coolant may be provided as needed by the generator.
- a vessel may be provided comprising the system of the second aspect.
- the vessel may comprise a flow boom arranged to transfer LNG to a second vessel and to receive natural gas vapour from the second vessel.
- the method may further comprise transferring LNG from a first vessel to a second vessel, and receiving the natural gas vapour from the second vessel.
- one or both vessels are maritime vessels.
- the vessel comprising the system i.e. the first vessel
- the second vessel may be an LNG fuelled vessel.
- the second vessel may be a carrier, particularly an LNG carrier.
- a bunker vessel is a vessel arranged to re-fuel other vessels while at sea.
- one or both vessels are LNG powered vessels.
- FIG. 1 is a schematic diagram showing a bunker vessel comprising a system or handling LNG;
- FIG. 2 is a schematic diagram showing the connection between various elements of the system in more detail.
- FIG. 3 is a schematic diagram illustrating the components of a re-condenser unit.
- FIG. 1 a schematic diagram is provided showing the principle elements of a LNG handling system aboard a bunker vessel 1 for re-fuelling larger ships.
- the system comprises two LNG storage tanks 10 , port and starboard manifolds 20 , a liquid nitrogen tank 30 , a gaseous nitrogen tank 40 , a liquid nitrogen generator 50 , a re-condenser unit 60 , engines 70 and a flow boom 80 .
- FIG. 1 illustrates functional connections between the various illustrated elements of the system for the transfer of LNG (indicated as “L”, dotted lines), natural gas vapour (indicated as “V”, thick lines) and nitrogen (both liquid and gaseous indicated as “N”, thin lines).
- the port and starboard manifolds 20 are arranged to allow transfer of LNG, natural gas vapour, and nitrogen between the bunker vessel and an on-shore facility.
- LNG received from the port and starboard manifolds is stored in the storage tanks 10 .
- the storage tanks are pressurised, C-class, storage tanks which may operate at up to 10 bar, but the skilled person will recognize that alternative tanks may be used.
- the storage tanks may be any type of chamber or container suitable to act as a reservoir for LNG. Pressurised tanks, particularly pressurised “C” Type tanks, allow a wider range of operating temperature and pressure within the bunker vessel.
- the storage tanks store LNG at around ⁇ 163 degrees centigrade.
- Liquid nitrogen received from the manifolds 20 is stored in liquid nitrogen tank 30 .
- Nitrogen that evaporates from liquid nitrogen tank 30 may be received in gas nitrogen tank 40 from where it is passed to the ship's systems for use in for purging of cargo/fuel lines, inerting tanks and hold spaces and so on. Alternatively or additionally, nitrogen may be vented to the atmosphere or re-used by liquid nitrogen generator 50 .
- the liquid nitrogen tank 30 and the gas nitrogen tank 40 may be any suitable container or chamber suitable to act as a reservoir for liquid nitrogen and gaseous nitrogen respectively.
- the liquid nitrogen generator 50 passes generated liquid nitrogen back to the liquid nitrogen tank 30 .
- the liquid nitrogen generator 50 may be a compression cooling system, and is preferably powered by the vessel's electrical systems.
- the liquid nitrogen generator 50 may be arranged to filter and compress atmospheric air before carbon dioxide water and residual hydrocarbons are removed in an air purification unit. The air is then passed to a cold box where it is cooled and liquefied. The liquid air is distilled then in a distillation column to yield pure nitrogen gas which is condensed in a condenser to yield pure liquid nitrogen.
- the system comprises a flow boom 80 for transferring LNG to another vessel, such as an LNG carrier.
- the flow boom 80 is a transfer boom in this embodiment.
- the transfer boom 80 receives LNG from LNG storage tank 10 and may also receive natural gas vapour from the other vessel. Natural gas vapour received by the transfer boom is passed to the re-condenser unit 60 .
- the re-condenser unit 60 also receives natural gas vapour from the LNG storage tank 10 .
- the re-condenser unit 60 is arranged to re-liquefy the natural gas vapour to return it to an LNG state. Once re-liquefied the LNG may be passed back to the LNG storage tank 10 .
- the re-condenser unit 60 also receives liquid nitrogen from the liquid nitrogen tank 30 and LNG from the LNG tanks 10 . These liquids are used during the processes of cooling the natural gas vapour at the re-condenser unit, as will be explained in greater detail below with reference to FIG. 3 .
- the engines 70 of the bunker vessel use the stored LNG as a fuel source.
- natural gas vapour is used for combustion in the engines.
- the natural gas vapour used for this purpose may be boil-off gas (BOG) spontaneously occurring in the LNG storage tanks 10 , or may be deliberately vaporised LNG from the LNG storage tanks.
- LNG from the storage tank may be vaporised by a forcing vaporizer, for example.
- FIG. 2 shows in more detail the connections between various elements of the system of FIG. 1 .
- FIG. 2 illustrates the LNG storage tanks 10 and the port and starboard manifolds 20 .
- a variety of valves are provided to control the flows and pressures of gas and liquid in the system.
- FIG. 2 also illustrates various connection points to other elements of the system.
- connection points 201 are provided for LNG returning from the re-condenser unit 60
- connection points 202 are provided for natural gas vapour passed to the re-condensing unit 60 .
- connection point 210 for passing LNG to the re-condensing unit 60 for use during a re-liquefaction process implemented by the re-condensing unit 60 and a connection point 214 for receiving LNG from the re-condensing unit that has been used for this purpose.
- LNG that is extracted from the LNG storage tanks 10 but is not ultimately used in the engine 70 or the re-condensing unit 60 may be returned to the LNG storage tanks via connection points 215 .
- Connection point 203 is shown for passing LNG to the transfer boom 80 , while connection point 204 receives natural gas vapour from the transfer boom 80 .
- LG can be transferred to another vessel, while excess boil-off as from the vessel can be retrieved for handling on the bunker vessel.
- Connection point 205 is provided for passing gas vapour to the engines 70 .
- connection point 206 for transferring natural gas vapour to a gas combustion unit (GCU). In an emergency situation, this GCU may be used to burn and thus dispose of natural gas vapour that is not otherwise handled by the system.
- GCU gas combustion unit
- this GCU may be used to burn and thus dispose of natural gas vapour that is not otherwise handled by the system.
- vent 208 to vent natural gas vapour to the atmosphere where this is appropriate.
- Connection point 207 is provided for the receipt of nitrogen vapour for purging of lines, and inerting spaces as required. Excess vapour would be vented via the GCU. The vapour may be received from the gas nitrogen tank 40 which receives boil-off from the liquid nitrogen tank 30 . Connection point 210 is for supply of liquid nitrogen via the manifolds 20 from shore for charging the liquid nitrogen storage tank 30 .
- Each LNG storage tank is provided with a discharge pump 11 for pumping LNG to the transfer boom 80 and a LNG fuel pump 12 for pumping LNG to the engines 70 .
- Various connections allow the LNG pumped by either the discharge pump 11 or the LNG fuel pump 12 to be re-directed as appropriate.
- Each LNG storage tank 10 also comprises a first LNG inlet 13 and a second LNG inlet 14 .
- LNG can be received at the LNG storage tanks 10 from the re-condenser unit 60 via connection points 201 and from the port and starboard manifolds 20 .
- the LNG storage tanks also comprise a gas dome 15 above the storage tanks, where boil off gas (BOG) from the stored LNG is collected.
- the LNG storage tanks 10 comprise a gas outlet 17 for passing this natural gas vapour to other elements of the system.
- the LNG storage tanks 10 also comprise a return spray header 16 .
- the spray header returns a proportion of the LNG extracted from the LNG storage tank 10 as a spray applied to the surface of the stored LNG in the tank. This helps to maintain uniform temperature within the stored LNG and thereby reduces the rate of generation of boil off gas.
- the port and starboard manifolds 20 comprise a first LNG interface 21 .
- a second LNG interface 22 a natural gas vapour interface 23 and a nitrogen interface 24 .
- LNG may be provided to the LNG storage tanks 10 via the LNG interfaces 21 , 22 while natural gas vapour may be returned to shore via the gas vapour interface 23 .
- Liquid nitrogen may also be provided to the liquid nitrogen tank 30 via the nitrogen interface 24 .
- FIG. 2 also illustrates a forcing vaporiser 211 on the line between the LNG storage tanks and connection point 205 to the engines 70 .
- This is used to vaporise LNG to produce natural gas vapour which can be combusted by the engines 70 to generate power for the bunker vessel's propulsion and electrical systems.
- the system further comprises a compressor 212 for compressing gas passed through the vaporiser 211 before it reaches the engines 70 .
- a further compressor 213 may also be provided for natural gas vapour being returned to the port and starboard manifolds 20 .
- FIG. 3 illustrates the re-condensing unit 60 in more detail.
- various functionally equivalent connections portions are shown in FIG. 3 using the same reference numerals as used in FIG. 2 .
- FIG. 3 shows connection points 202 for providing natural gas vapour, particularly BOG, to the re-condensing unit 60 .
- connection points 201 for receiving the re-liquefied LNG from the re-condensing unit 60 and returning this to the LNG storage tanks 10 are also shown.
- FIG. 3 also illustrates liquid nitrogen tank 30 and gaseous nitrogen tank 40 .
- the liquid nitrogen tank 30 is filled from the port and starboard manifolds via connection point 209 (also shown in FIG. 2 ) and may also be filled from bunker vessel's liquid nitrogen generator 50 via connection point 301 .
- Nitrogen which evaporates from the liquid nitrogen tank 30 may be passed to the gaseous nitrogen tank 40 , from where it may be vented via connection point 302 or passed to consumers via connection point 303 .
- Consumers in this case may include systems aboard the vessel; for example, nitrogen vapour may be used for purging of cargo/fuel lines, inerting tanks and hold spaces and so on.
- the re-condensing unit 60 comprises a first heat exchanger 62 , a second heat exchanger 64 and a compressor 66 .
- the first heat exchanger 62 is an LNG sub-cooler and is coupled to the liquid nitrogen tank 30 and to LNG outlets of the LNG tanks 10 .
- LNG from the LNG tanks 10 is cooled using liquid nitrogen from the liquid nitrogen tank 30 to below its temperature in the LNG tanks 10 .
- the LNG cooled in this manner is referred to as “sub-cooled”.
- the second heat exchanger 64 is coupled to the first heat exchanger 62 so as to receive the sub-cooled LNG therefrom.
- the second heat exchanger 64 is also arranged to receive natural gas vapour.
- the natural gas vapour may originate either at the LNG tanks 10 or be received from another vessel via the transfer boom 80 .
- the natural gas vapour is BOG that has occurred by evaporation of LNG.
- the second heat exchanger 64 is a condenser arranged to cool the natural gas vapour using the sub-cooled LNG received from the first heat exchanger such that it is liquefied.
- the second heat exchanger thus generates LNG which is returned to the LNG tanks 10 . Furthermore, once it has passed through the second heat exchanger, the sub-cooled LNG is returned to the LNG tanks 10 .
- the re-condensing unit also comprises a compressor 66 .
- the compressor 66 is used to compress natural gas vapour prior to its injection into the second heat exchanger 64 . This is found to increase the efficiency of heat exchange at the second heat exchanger 64 .
- the bunker vessel comprising the system illustrated in FIG. 1 is docked with another vessel which it is to re-fuel.
- this other ship is an LNG fuelled vessel.
- the transfer boom 80 is used to transfer LNG from the LNG tanks 10 to the LNG carrier.
- natural gas vapour is displaced from the tanks aboard the LNG carrier, and boil-off gas is also generated from the LNG tanks 10 on the bunker vessel and at other points in the system.
- This natural gas vapour is directed towards the re-condensing unit, where it first encounters 60 the compressor 66 .
- the compressor 66 acts to increase the pressure within the natural gas vapour by compressing the vapour, and the compressed vapour is then passed to the second heat exchanger 64 .
- the second heat exchanger 64 transfers heat between sub-cooled LNG and the compressed vapour, thereby cooling the compressed vapour until it condenses (i.e. liquefies), and creating LNG.
- This LNG is then passed to the LNG storage tanks 10 .
- the sub-cooled LNG used in the second heat exchanger 64 is also passed to the LNG storage tanks 10 after passing through the second heat exchanger 64 .
- the sub-cooled LNG is generated by cooling using liquid nitrogen at the first heat exchanger 62 .
- the preferred embodiment is designed for use upon a bunker vessel used to refuel another ship.
- a bunker vessel used to refuel another ship.
- variations may be proposed for alternative types of marine vessels, and indeed to shore-based transport and storage.
Abstract
A method and apparatus for liquefying natural gas vapour is provided. Firstly, liquid natural gas is sub-cooled at a first heat exchanger using a liquid coolant such as liquid nitrogen. The sub-cooled liquid natural gas is then used to condense the natural gas vapour at a second heat exchanger.
Description
- The present invention relates to liquefaction of natural gas vapour, particularly during the transport and storage of liquefied natural gas (LNG). In particular, but not exclusively, the present invention relates to the handling of boil off gas in a bunker vessel used to refuel LNG-powered vessels.
- Liquefied natural gas (LNG) is natural gas (typically methane—CH4) that has been liquefied, typically to make it more manageable during storage and/or transport. At atmospheric pressure, this means the temperature of the LNG is reduced to around −163 degrees centigrade or below.
- LNG carriers are vessels used to carry LNG across large distances, particularly to carry LNG from gas producing nations to gas consuming nations. The journey times of such vessels are significant, measured in days, weeks and even months. During such time, the LNG is stored at low temperature in order that it does not vaporise.
- Notwithstanding the efforts made to maintain this low temperature, there is in practice some evaporation of LNG during the vessel's journey. This evaporation creates boil-off gas (BOG) which must be handled by the vessel in some way. Indeed, this has been a factor in the continuing use of steam-turbine propulsion on LNG carriers. Carriers that use such a propulsion system are able to use BOG to drive turbines for propulsion and electricity generation.
- However, steam turbine propulsion is a relatively inefficient means to drive a large ship. As a result, a move towards slow speed diesel engine powered vessels has been apparent. The diesel engine in such a ship is unable to handle BOG and instead an independent LNG re-liquefaction plant is provided on the vessel. Typically nitrogen vapour is compressed and expanded in a “compander” in such a way as to lower its temperature so that it can be used as a coolant during the re-liquefaction process. The re-liquefaction plant is typically powered by the electricity generated on-board and has significant requirements in this regard, with ratings of 5 MW or above not uncommon. Furthermore, as well as high power requirements, the re-liquefaction plant is typically unable to handle high boil-off rates. Excess BOG that the LNG re-liquefaction plant is unable to handle is burnt in a gas combustion unit (GCU) and thereby wasted.
- Another type of propulsion system used in LNG carriers is a dual fuel diesel electric propulsion system which can operate off either diesel or LNG itself In such a vessel, the BOG can be used as fuel for the engines to provide propulsion and electrical load. If there is insufficient engine load it is necessary to burn the excess BOG in a GCU.
- There has been an increasing drive towards the use of LNG as a primary fuel in vessels of all types, driven at least partially by the relative cost of LNG in comparison to other fuels. As mentioned above, while this offers a potential method for handling BOG needed to provide propulsion and/or electricity, there remains the issue of handling such BOG when the required load does not match the BOG present.
- Simply burning the BOG in a GCU is both wasteful and polluting. Nor can the BOG simply be vented to the atmosphere, for similar reasons. Indeed, environmental regulations in many territories prohibit the handling of BOG in this way within close proximity to shore. Furthermore, using LNG as a primary fuel source creates its own challenges. For example, in many circumstances it may be desirable to re-fuel an LNG fuelled vessel using a bunker vessel. A bunker vessel is a smaller vessel designed to carry fuel to the carrier from shore. The bunker vessel must dock with the carrier and transfer fuel from its tanks to that of the carrier.
- As well as having to handle BOG during general operation, the bunker vessel must cope with the fact that the process of fuel transfer is likely to involve an increased production of BOG as the LNG is transferred between the vessels. Even if this were not the case the base level production of BOG would still need to be handled. However, as both vessels are stationary during this process, the BOG created cannot be used for propulsion and must be handled in some other manner.
- A re-liquefaction plant is impractical for a relatively small vessel such as a bunker vessel due to its large energy requirements and, as mentioned above, burning off excess BOG is both wasteful and environmentally unsound. There remains a need to find a method of handling BOG in bunker vessels that is both practical and effective.
- According to a first aspect of the present invention there is provided a method for condensing natural gas vapour to generate liquefied natural gas (LNG), comprising:
- providing a liquid coolant, wherein the liquid coolant has a boiling point less than that of natural gas;
- cooling LNG at a first heat exchanger using the liquid coolant to generate sub-cooled LNG; and
- condensing natural gas vapour at a second heat exchanger using the sub-cooled LNG to liquefy the natural gas vapour and thereby generate further LNG.
- According to a second aspect of the present invention, there is provided a system for condensing natural gas vapour to generate liquefied natural gas (LNG); comprising
- a first heat exchanger arranged to cool LNG using a liquid coolant to generate sub-cooled LNG, wherein the liquid coolant has a boiling point less than that of natural gas; and
- a second heat exchanger arranged to condense natural gas vapour using the sub-cooled LNG to liquefy the natural gas vapour and thereby generate further LNG.
- The present invention can provide an efficient method of condensing natural gas vapour to provide LNG. Existing LNG is cooled at a first heat exchanger to create sub-cooled LNG that can be used to condense the natural gas vapour. This is significantly more energy efficient than provision of a plant for generating LNG directly from the natural gas vapour. The use of a liquid coolant to first sub-cool existing available LNG reduces the need for energy intensive refrigeration cycles to generate a coolant to directly cool the natural gas vapour.
- The present invention finds particular utility in circumstances in which boil-off gas is present. Boil-off gas is natural gas vapour that has arisen through the evaporation of an LNG source. In such circumstances, the boil-off gas is likely not to be significantly warmer than the boiling temperature of natural gas, and furthermore LNG is likely to be available for sub-cooling. Thus, in a preferred embodiment, the natural gas vapour is boil-off gas.
- The method may comprise receiving the LNG for cooling at the first heat exchanger from at least one LNG storage tank and returning the sub-cooled LNG to the at least one storage tank after it is used at the second heat exchanger. In this manner, LNG may be re-used for subsequent condensing of natural gas vapour. After use at the second heat exchanger the sub-cooled LNG is likely to have warmed somewhat, but the method is preferably arranged such that it remains in liquid form for returning to the LNG storage tank.
- Preferably, the method may further comprise delivering the further LNG to the at least one storage tank. Accordingly, the LNG that is created through the method may subsequently be used for condensing further natural gas vapour in future cycles. Furthermore, the system is compact and efficient in that there is no requirement for separate tanks for the coolant used at the second heat exchanger and the generated LNG.
- As mentioned above, the liquid coolant used at the first generator has a boiling point less than that of the natural gas vapour. The natural gas vapour is preferably predominantly methane, more preferably at least 90 Mole % methane, at least 95 Mole % methane or over 97% Mole methane. Methane has a boiling point at atmospheric pressure of around −163 degrees centigrade. Preferably, the liquid coolant has a boiling point at atmospheric pressure of less than that of methane (i.e. less than −163 degrees centigrade), more preferably less than −170 degrees centigrade, and most preferably less than −190 degrees centigrade. In preferred embodiments, the liquid coolant is liquid nitrogen. The boiling point of nitrogen is around −193 degrees centigrade at atmospheric pressure. References to atmospheric pressure refer to a pressure equal to the understood unit of one atmosphere, rather than to prevailing climatic conditions.
- The system may comprise a storage facility for the liquid coolant. For example, the system may comprise at least one storage tank for storing the liquid coolant. The system may additionally or alternatively comprise a generator for generating the liquid coolant. Equally, the method may comprise a step of generating the liquid coolant. For example, where the system is provided on a maritime vessel, an initial supply of liquid coolant may be provided to the storage facility from an on-shore facility while the vessel is docked, but when the vessel is at sea additional liquid coolant may be provided as needed by the generator.
- According to a further aspect, a vessel may be provided comprising the system of the second aspect. The vessel may comprise a flow boom arranged to transfer LNG to a second vessel and to receive natural gas vapour from the second vessel. The method may further comprise transferring LNG from a first vessel to a second vessel, and receiving the natural gas vapour from the second vessel. In preferred embodiments, one or both vessels are maritime vessels. In particular, the vessel comprising the system (i.e. the first vessel) may be a bunker vessel while the second vessel may be an LNG fuelled vessel. Alternatively or additionally, the second vessel may be a carrier, particularly an LNG carrier. A bunker vessel is a vessel arranged to re-fuel other vessels while at sea. Preferably, one or both vessels are LNG powered vessels.
- A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, in which:
-
FIG. 1 is a schematic diagram showing a bunker vessel comprising a system or handling LNG; -
FIG. 2 is a schematic diagram showing the connection between various elements of the system in more detail; and -
FIG. 3 is a schematic diagram illustrating the components of a re-condenser unit. - Referring to
FIG. 1 , a schematic diagram is provided showing the principle elements of a LNG handling system aboard a bunker vessel 1 for re-fuelling larger ships. The system comprises twoLNG storage tanks 10, port and starboard manifolds 20, aliquid nitrogen tank 30, agaseous nitrogen tank 40, aliquid nitrogen generator 50, are-condenser unit 60,engines 70 and aflow boom 80.FIG. 1 illustrates functional connections between the various illustrated elements of the system for the transfer of LNG (indicated as “L”, dotted lines), natural gas vapour (indicated as “V”, thick lines) and nitrogen (both liquid and gaseous indicated as “N”, thin lines). - The port and starboard manifolds 20 are arranged to allow transfer of LNG, natural gas vapour, and nitrogen between the bunker vessel and an on-shore facility. LNG received from the port and starboard manifolds is stored in the
storage tanks 10. In this embodiment, the storage tanks are pressurised, C-class, storage tanks which may operate at up to 10 bar, but the skilled person will recognize that alternative tanks may be used. Indeed, the storage tanks may be any type of chamber or container suitable to act as a reservoir for LNG. Pressurised tanks, particularly pressurised “C” Type tanks, allow a wider range of operating temperature and pressure within the bunker vessel. The storage tanks store LNG at around −163 degrees centigrade. - Liquid nitrogen received from the
manifolds 20 is stored inliquid nitrogen tank 30. Nitrogen that evaporates fromliquid nitrogen tank 30 may be received ingas nitrogen tank 40 from where it is passed to the ship's systems for use in for purging of cargo/fuel lines, inerting tanks and hold spaces and so on. Alternatively or additionally, nitrogen may be vented to the atmosphere or re-used byliquid nitrogen generator 50. Theliquid nitrogen tank 30 and thegas nitrogen tank 40 may be any suitable container or chamber suitable to act as a reservoir for liquid nitrogen and gaseous nitrogen respectively. - The
liquid nitrogen generator 50 passes generated liquid nitrogen back to theliquid nitrogen tank 30. Theliquid nitrogen generator 50 may be a compression cooling system, and is preferably powered by the vessel's electrical systems. For example, theliquid nitrogen generator 50 may be arranged to filter and compress atmospheric air before carbon dioxide water and residual hydrocarbons are removed in an air purification unit. The air is then passed to a cold box where it is cooled and liquefied. The liquid air is distilled then in a distillation column to yield pure nitrogen gas which is condensed in a condenser to yield pure liquid nitrogen. - The system comprises a
flow boom 80 for transferring LNG to another vessel, such as an LNG carrier. Theflow boom 80 is a transfer boom in this embodiment. Thetransfer boom 80 receives LNG fromLNG storage tank 10 and may also receive natural gas vapour from the other vessel. Natural gas vapour received by the transfer boom is passed to there-condenser unit 60. - The
re-condenser unit 60 also receives natural gas vapour from theLNG storage tank 10. There-condenser unit 60 is arranged to re-liquefy the natural gas vapour to return it to an LNG state. Once re-liquefied the LNG may be passed back to theLNG storage tank 10. - The
re-condenser unit 60 also receives liquid nitrogen from theliquid nitrogen tank 30 and LNG from theLNG tanks 10. These liquids are used during the processes of cooling the natural gas vapour at the re-condenser unit, as will be explained in greater detail below with reference toFIG. 3 . - In the embodiment shown in
FIG. 1 , theengines 70 of the bunker vessel use the stored LNG as a fuel source. In practice, natural gas vapour is used for combustion in the engines. The natural gas vapour used for this purpose may be boil-off gas (BOG) spontaneously occurring in theLNG storage tanks 10, or may be deliberately vaporised LNG from the LNG storage tanks. LNG from the storage tank may be vaporised by a forcing vaporizer, for example. -
FIG. 2 shows in more detail the connections between various elements of the system ofFIG. 1 . In particular,FIG. 2 illustrates theLNG storage tanks 10 and the port and starboard manifolds 20. As shown, a variety of valves are provided to control the flows and pressures of gas and liquid in the system.FIG. 2 also illustrates various connection points to other elements of the system. In particular, connection points 201 are provided for LNG returning from there-condenser unit 60, while connection points 202 are provided for natural gas vapour passed to there-condensing unit 60. There is also providedconnection point 210 for passing LNG to there-condensing unit 60 for use during a re-liquefaction process implemented by there-condensing unit 60 and aconnection point 214 for receiving LNG from the re-condensing unit that has been used for this purpose. LNG that is extracted from theLNG storage tanks 10 but is not ultimately used in theengine 70 or there-condensing unit 60 may be returned to the LNG storage tanks via connection points 215. -
Connection point 203 is shown for passing LNG to thetransfer boom 80, whileconnection point 204 receives natural gas vapour from thetransfer boom 80. In this manner, LG can be transferred to another vessel, while excess boil-off as from the vessel can be retrieved for handling on the bunker vessel. - Connection point 205 is provided for passing gas vapour to the
engines 70. There is also provided aconnection point 206 for transferring natural gas vapour to a gas combustion unit (GCU). In an emergency situation, this GCU may be used to burn and thus dispose of natural gas vapour that is not otherwise handled by the system. There is also provided avent 208 to vent natural gas vapour to the atmosphere where this is appropriate. -
Connection point 207 is provided for the receipt of nitrogen vapour for purging of lines, and inerting spaces as required. Excess vapour would be vented via the GCU. The vapour may be received from thegas nitrogen tank 40 which receives boil-off from theliquid nitrogen tank 30.Connection point 210 is for supply of liquid nitrogen via themanifolds 20 from shore for charging the liquidnitrogen storage tank 30. - Each LNG storage tank is provided with a
discharge pump 11 for pumping LNG to thetransfer boom 80 and aLNG fuel pump 12 for pumping LNG to theengines 70. Various connections allow the LNG pumped by either thedischarge pump 11 or theLNG fuel pump 12 to be re-directed as appropriate. - Each
LNG storage tank 10 also comprises afirst LNG inlet 13 and asecond LNG inlet 14. LNG can be received at theLNG storage tanks 10 from there-condenser unit 60 via connection points 201 and from the port and starboard manifolds 20. The LNG storage tanks also comprise agas dome 15 above the storage tanks, where boil off gas (BOG) from the stored LNG is collected. TheLNG storage tanks 10 comprise agas outlet 17 for passing this natural gas vapour to other elements of the system. - The
LNG storage tanks 10 also comprise areturn spray header 16. The spray header returns a proportion of the LNG extracted from theLNG storage tank 10 as a spray applied to the surface of the stored LNG in the tank. This helps to maintain uniform temperature within the stored LNG and thereby reduces the rate of generation of boil off gas. - The port and starboard manifolds 20 comprise a
first LNG interface 21. Asecond LNG interface 22, a naturalgas vapour interface 23 and anitrogen interface 24. When the bunker vessel is docked, LNG may be provided to theLNG storage tanks 10 via the LNG interfaces 21, 22 while natural gas vapour may be returned to shore via thegas vapour interface 23. Liquid nitrogen may also be provided to theliquid nitrogen tank 30 via thenitrogen interface 24. -
FIG. 2 also illustrates a forcingvaporiser 211 on the line between the LNG storage tanks and connection point 205 to theengines 70. This is used to vaporise LNG to produce natural gas vapour which can be combusted by theengines 70 to generate power for the bunker vessel's propulsion and electrical systems. The system further comprises acompressor 212 for compressing gas passed through thevaporiser 211 before it reaches theengines 70. Afurther compressor 213 may also be provided for natural gas vapour being returned to the port and starboard manifolds 20. -
FIG. 3 illustrates there-condensing unit 60 in more detail. In order to facilitate comparison withFIG. 2 , various functionally equivalent connections portions are shown inFIG. 3 using the same reference numerals as used inFIG. 2 . For example,FIG. 3 shows connection points 202 for providing natural gas vapour, particularly BOG, to there-condensing unit 60. Moreover, connection points 201 for receiving the re-liquefied LNG from there-condensing unit 60 and returning this to theLNG storage tanks 10 are also shown. -
FIG. 3 also illustratesliquid nitrogen tank 30 andgaseous nitrogen tank 40. Theliquid nitrogen tank 30 is filled from the port and starboard manifolds via connection point 209 (also shown inFIG. 2 ) and may also be filled from bunker vessel'sliquid nitrogen generator 50 viaconnection point 301. Nitrogen which evaporates from theliquid nitrogen tank 30 may be passed to thegaseous nitrogen tank 40, from where it may be vented via connection point 302 or passed to consumers viaconnection point 303. Consumers in this case may include systems aboard the vessel; for example, nitrogen vapour may be used for purging of cargo/fuel lines, inerting tanks and hold spaces and so on. - The
re-condensing unit 60 comprises afirst heat exchanger 62, asecond heat exchanger 64 and acompressor 66. Thefirst heat exchanger 62 is an LNG sub-cooler and is coupled to theliquid nitrogen tank 30 and to LNG outlets of theLNG tanks 10. LNG from theLNG tanks 10 is cooled using liquid nitrogen from theliquid nitrogen tank 30 to below its temperature in theLNG tanks 10. The LNG cooled in this manner is referred to as “sub-cooled”. - The
second heat exchanger 64 is coupled to thefirst heat exchanger 62 so as to receive the sub-cooled LNG therefrom. Thesecond heat exchanger 64 is also arranged to receive natural gas vapour. The natural gas vapour may originate either at theLNG tanks 10 or be received from another vessel via thetransfer boom 80. Typically, the natural gas vapour is BOG that has occurred by evaporation of LNG. - The
second heat exchanger 64 is a condenser arranged to cool the natural gas vapour using the sub-cooled LNG received from the first heat exchanger such that it is liquefied. The second heat exchanger thus generates LNG which is returned to theLNG tanks 10. Furthermore, once it has passed through the second heat exchanger, the sub-cooled LNG is returned to theLNG tanks 10. - The re-condensing unit also comprises a
compressor 66. Thecompressor 66 is used to compress natural gas vapour prior to its injection into thesecond heat exchanger 64. This is found to increase the efficiency of heat exchange at thesecond heat exchanger 64. - In use, the bunker vessel comprising the system illustrated in
FIG. 1 is docked with another vessel which it is to re-fuel. In particular examples, this other ship is an LNG fuelled vessel. - The
transfer boom 80 is used to transfer LNG from theLNG tanks 10 to the LNG carrier. During this process, natural gas vapour is displaced from the tanks aboard the LNG carrier, and boil-off gas is also generated from theLNG tanks 10 on the bunker vessel and at other points in the system. This natural gas vapour is directed towards the re-condensing unit, where it first encounters 60 thecompressor 66. Thecompressor 66 acts to increase the pressure within the natural gas vapour by compressing the vapour, and the compressed vapour is then passed to thesecond heat exchanger 64. Thesecond heat exchanger 64 transfers heat between sub-cooled LNG and the compressed vapour, thereby cooling the compressed vapour until it condenses (i.e. liquefies), and creating LNG. This LNG is then passed to theLNG storage tanks 10. - As mentioned above, the sub-cooled LNG used in the
second heat exchanger 64 is also passed to theLNG storage tanks 10 after passing through thesecond heat exchanger 64. Prior to this, the sub-cooled LNG is generated by cooling using liquid nitrogen at thefirst heat exchanger 62. - As described above, the preferred embodiment is designed for use upon a bunker vessel used to refuel another ship. However, it will be understood that variations may be proposed for alternative types of marine vessels, and indeed to shore-based transport and storage.
- Other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known and which may be used instead of, or in addition to, features described herein. Features that are described in the context of separate embodiments may be provided in combination in a single embodiment. Conversely, features which are described in the context of a single embodiment may also be provided separately or in any suitable sub-combination. It should be noted that the term “comprising” does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality, a single feature may fulfill the functions of several features recited in the claims and reference signs in the claims shall not be construed as limiting the scope of the claims. It should also be noted that the Figures are not necessarily to scale; emphasis instead generally being placed upon illustrating the principles of the present disclosure.
Claims (15)
1. A method for condensing natural gas vapour to generate liquefied natural gas (LNG), comprising:
providing a liquid coolant, wherein the liquid coolant has a boiling point less than that of natural gas;
cooling LNG at a first heat exchanger using the liquid coolant to generate sub-cooled LNG; and
condensing natural gas vapour at a second heat exchanger using the sub-cooled LNG to liquefy the natural gas vapour and thereby generate further LNG.
2. A method according to claim 1 , further comprising:
obtaining the LNG for cooling at the first heat exchanger from at least one LNG storage tank; and
returning the sub-cooled LNG to the at least one LNG storage tank after it is used at the second heat exchanger.
3. A method according to claim 2 , further comprising delivering the further LNG to the at least one LNG storage tank.
4. A method according to claim 1 , wherein the natural gas vapour is boil-off gas.
5. A method according to claim 1 , wherein the liquid coolant is liquid nitrogen.
6. A method according to claim 1 , further comprising compressing the natural gas vapour.
7. A method according to claim 1 , further comprising:
delivering LNG from a first vessel to a second vessel; and
receiving the natural gas vapour from the second vessel.
8. A system for condensing natural gas vapour to generate liquefied natural gas (LNG); comprising:
a first heat exchanger arranged to cool LNG using a liquid coolant to generate sub-cooled LNG, wherein the liquid coolant has a boiling point less than that of natural gas; and
a second heat exchanger arranged to condense natural gas vapour using the sub-cooled LNG to liquefy the natural gas vapour and thereby generate further LNG.
9. A system according to claim 8 , further comprising at least one LNG storage tank, wherein the first heat exchanger is arranged to receive the LNG for cooling at the first heat exchanger from the at least one LNG storage tank, and wherein the system is arranged to return the sub-cooled LNG to the LNG storage tank after it is used at the second heat exchanger.
10. A system according to claim 9 , wherein the system is arranged to deliver the further LNG to the at least one LNG storage tank.
11. A system according to claim 8 , wherein the natural gas vapour is boil-off gas.
12. A system according to claim 8 , wherein the liquid coolant is liquid nitrogen.
13. A system according to claim 8 , further comprising a compressor for compressing the natural gas vapour.
14. A vessel having a system for condensing natural gas vapour to generate liquefied natural gas, the vessel comprising:
a first heat exchange exchanger arranged to cool LNG using a liquid coolant to generate sub-cooled LNG, wherein the liquid coolant has a boiling point less than that of natural gas;
a second heat exchanger arranged to condense natural gas vapour using the sub-cooled LNG to liquefy the natural gas vapour and thereby generate further LNG; and
a transfer boom arranged to transfer LNG to a second vessel and to receive natural gas vapour from the second vessel.
15. A vessel according to claim 14 , wherein the vessel is a bunker vessel.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB1311756.9 | 2013-07-01 | ||
GB1311756.9A GB2515741A (en) | 2013-07-01 | 2013-07-01 | Liquefaction of natural gas |
Publications (1)
Publication Number | Publication Date |
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US20150000334A1 true US20150000334A1 (en) | 2015-01-01 |
Family
ID=48999315
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/941,045 Abandoned US20150000334A1 (en) | 2013-07-01 | 2013-07-12 | Liquefaction of Natural Gas |
Country Status (2)
Country | Link |
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US (1) | US20150000334A1 (en) |
GB (1) | GB2515741A (en) |
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GB2515741A (en) | 2015-01-07 |
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