EP1848946A1 - Process for conditioning liquefied natural gas - Google Patents

Process for conditioning liquefied natural gas

Info

Publication number
EP1848946A1
EP1848946A1 EP06709671A EP06709671A EP1848946A1 EP 1848946 A1 EP1848946 A1 EP 1848946A1 EP 06709671 A EP06709671 A EP 06709671A EP 06709671 A EP06709671 A EP 06709671A EP 1848946 A1 EP1848946 A1 EP 1848946A1
Authority
EP
European Patent Office
Prior art keywords
stream
natural gas
produce
heat exchanger
feed
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.)
Withdrawn
Application number
EP06709671A
Other languages
German (de)
French (fr)
Inventor
Lee Alan Phillips
Lee Scott
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.)
BP Exploration Operating Co Ltd
Original Assignee
BP Exploration Operating 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 BP Exploration Operating Co Ltd filed Critical BP Exploration Operating Co Ltd
Publication of EP1848946A1 publication Critical patent/EP1848946A1/en
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0242—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 3 carbon atoms or more
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • 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
    • F17C9/00—Methods or apparatus for discharging liquefied or solidified gases from vessels not under pressure
    • F17C9/02—Methods or apparatus for discharging liquefied or solidified gases from vessels not under pressure with change of state, e.g. vaporisation
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
    • F25J3/0209—Natural gas or substitute natural gas
    • F25J3/0214—Liquefied natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0238—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 2 carbon atoms or more
    • 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
    • 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
    • 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
    • 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
    • F17C2225/01—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the phase
    • F17C2225/0107—Single phase
    • F17C2225/0123—Single phase gaseous, e.g. CNG, GNC
    • 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
    • F17C2225/03—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the pressure level
    • F17C2225/036—Very high pressure, i.e. above 80 bars
    • 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
    • F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/01—Propulsion of the fluid
    • F17C2227/0128—Propulsion of the fluid with pumps or compressors
    • F17C2227/0135—Pumps
    • 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
    • F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/03—Heat exchange with the fluid
    • F17C2227/0302—Heat exchange with the fluid by heating
    • F17C2227/0306—Heat exchange with the fluid by heating using the same fluid
    • 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
    • F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/03—Heat exchange with the fluid
    • F17C2227/0367—Localisation of heat exchange
    • F17C2227/0369—Localisation of heat exchange in or on a vessel
    • F17C2227/0376—Localisation of heat exchange in or on a vessel in wall contact
    • F17C2227/0379—Localisation of heat exchange in or on a vessel in wall contact inside the vessel
    • 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
    • F17C2265/01—Purifying the fluid
    • F17C2265/015—Purifying the fluid by separating
    • F17C2265/017—Purifying the fluid by separating different phases of a same fluid
    • 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
    • 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
    • F17C2265/05—Regasification
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/70—Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
    • 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
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
    • F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
    • 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
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/90—Mixing of components
    • 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
    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/02—Mixing or blending of fluids to yield a certain product
    • 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
    • F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
    • F25J2235/60—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being (a mixture of) hydrocarbons
    • 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
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/90—Processes or apparatus involving steps for recycling of process streams the recycled stream being boil-off gas from storage
    • 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
    • F25J2290/12—Particular process parameters like pressure, temperature, ratios
    • 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

  • This invention relates to a process for conditio . ning liquefied natural gas.
  • Liquefied natural gas needs to be vaporized before being fed into a pipeline for distribution.
  • the LNG is fed into a storage tank. This inevitably results in some boil-off of vapour; typically this off-gas is compressed and then passed to a boil-off condenser where it is condensed, for example by passing a quantity of LNG from the tank into the boil-off condenser where the boil-off gas, at increased pressure, is combined with the LNG stream to produce an all-liquid stream which may then be combined with an outflow stream from the tank.
  • the resultant LNG is then passed from the tank to a pump which discharges the LNG, at a suitable pressure, to a pipeline, via one or more heat exchangers which vaporize the LNG.
  • the LNG does not meet required product or pipeline specifications because of the presence of excess quantities of hydrocarbons containing two or more carbon atoms, and various additional processing steps are required.
  • US 6,564,579 describes a process for the removal of natural gas liquids (NGLs), typically hydrocarbons containing two or more carbon atoms, from LNG, in order to provide a natural gas product with a reduced heating value which meets pipeline or other commercial specifications.
  • This process which is of a type which may be referred to as conditioning, includes the following steps: vaporizing at least a major portion of a stream of the liquefied natural gas to produce an at least partially vaporized natural gas stream; fractionating- the at least partially vaporized natural gas stream to produce a gas stream and a natural gas liquids stream; compressing the gas stream to increase the pressure of the gas stream by about 50 to about 150 psi to produce a compressed gas stream and cooling the compressed gas stream by heat exchange with the stream of liquefied natural gas to produce a liquid compressed gas stream; pumping the liquid compressed gas stream to produce a high-pressure liquid stream at a pressure from about 800 to about 1200 psig; vaporizing the high-pressure liquid stream to produce a conditioned natural gas
  • US 6,604,380 also describes a process for the recovery of natural gas liquids from LNG. This process is a complex, multi-step process which involves splitting the feed stream and using at least one portion as reflux elsewhere in the process.
  • US 6,510,706 describes a process which is specific for the processing of pressurized liquid natural gas. According to US 6,510,706, "It has been proposed to transport natural gas at temperatures above -112°C (-170 0 F) and at pressures sufficient for the liquid to be at or below its bubble point temperature. This pressurized liquid natural gas is referred to as "PLNG” to distinguish it from LNG, which is transported at near atmospheric pressure and at a temperature of about -162°C (-260 0 F)." The processing of LNG and PLNG present different engineering challenges.
  • the present invention provides a process for the conditioning of liquefied natural gas, which comprises the following steps: i) supplying a feed stream of liquefied natural gas at a pressure in the range of from 15 to 35 barg and a temperature of -12O 0 C or lower to a heat exchanger to produce an at least partially vaporized natural gas stream; ii) passing at least part of the stream from step (i) to a distillation vessel operated without reflux to produce a natural gas liquids stream and a stream rich in methane; iii) passing the stream rich in methane from step (ii), without additional compression, to a heat exchanger and cooling by heat exchange with at least part of the feed stream of liquefied natural gas to produce a liquid natural gas stream; iv) vaporizing the liquid natural gas stream from step (iii) to produce a conditioned natural gas; and v) recovering the natural gas liquids.
  • the process according to the invention produces a conditioned natural gas which is suitable for delivery to a pipeline, or for other commercial use, together with natural gas liquids.
  • the natural gas liquids comprise hydrocarbons having 2 or more carbon atoms.
  • the initial natural gas liquids product obtained by the process of the invention can be further processed to separate hydrocarbons by the difference in the number of their carbon atoms.
  • the initial step of the process of the present invention requires that the feed stream of LNG is provided at a sufficiently high pressure so that a compressor is not required to be applied to the stream rich in methane obtained from step (ii). of the process prior to the heat exchange of step (iii). In most circumstances, this will involve pumping the LNG to achieve the desired pressure in the range from 15 to 35 barg, preferably 15 to 30 barg, for entry of the feed stream to the heat exchanger.
  • the feed stream of LNG must be supplied at a temperature of -120°C or less, for example -130°C or less.
  • the temperature is -170 0 C or greater, especially -163°C or greater.
  • the temperature is in the range of from around -170 0 C to -120 0 C, especially from -163°C to -120 0 C, for example from -163 0 C to - 13O 0 C.
  • the LNG feed to the process may be provided from an LNG storage tank, usually by pumping.
  • a small quantity of the feed may be separated off as a slip stream and used to perform certain functions within the process.
  • At least part of the stream from step (i) is separated into a natural gas liquids stream and a gas stream in the distillation vessel of step (ii), and the resulting gas stream is sent to a heat exchanger where it is cooled against the LNG feed stream (step (iii)).
  • the heat exchanger used is a plate-fin exchanger or other type of compact heat exchanger (plate in shell or printed circuit heat exchangers); these are very compact, and permit small temperature approaches between the "net” cooling and warming streams, which in turn, leads to high process efficiency.
  • the high-pressure feed stream is heated by heat exchange with the stream exiting step (ii) of the process.
  • the distillation vessel of step (ii) contains distillation trays or packing, and produces a stream rich in methane. If the distillation, vessel is a demethaniser, the majority of the methane sent to the vessel is routed overhead as gas, while the liquid stream contains hydrocarbons having two or more carbon atoms. If the vessel is a deethaniser, the stream rich in methane will also contain the majority of the ethane sent to the vessel, and the liquid product will contain predominantly hydrocarbons having 3 or more carbon atoms.
  • the use of LNG as a feed at the temperatures and pressures used in the process of the present invention provides a number of advantages.
  • a mixed commercial LPG product can be used as such, or may for example be fractionated downstream to produce commercial propane and commercial butane.
  • a recondenser is incorporated into the front end of the process.
  • boil-off gases from the LNG storage tank are compressed, typically to a pressure of from 8 to 12 barg, prior to entering a recondenser.
  • a slip-stream from the main LNG stream exiting the LNG storage tank is also passed to the recondenser, where is absorbs the condensed boil-off gases.
  • the output from the recondenser, which is liquid, is then combined with the main exit stream from the LNG storage tank, and the combined stream, normally after pumping to raise the pressure to the desired level, forms the feed to the process.
  • a preferred embodiment of the process of the invention comprises a process in which an exit stream of liquefied natural gas is pumped from a storage tank; said exit stream is split into at least a first portion and a second portion; boil-off gases from said storage tank are compressed and subsequently fed to a recondenser; the first portion of the exit stream is also passed to the recondenser, where it absorbs the condensed boil-off gases; the output from the recondenser is combined with the second portion of the exit stream from the storage tank; and the resulting combined stream is used as the feed stream of step (i).
  • an additional separator generally containing no internals other than minor items such as a feed device or a demister pad), may be used.
  • the process may incorporate an ⁇ additional separation step, in which the stream from step (i) is passed to a separator to produce a first stream which is rich in methane, and a second stream which is rich in hydrocarbons having two or more carbon atoms, the second stream becoming the input stream for step (ii) of the process, i.e. the input to the distillation vessel, while the first stream is passed to a heat exchanger and cooled by heat exchange with at least part of the feed stream of LNG to produce an LNG stream.
  • the process may be characterised as a process for the conditioning of liquefied natural gas, which comprises the following steps: i) supplying a feed stream of liquefied natural gas at a pressure in the range of from 15 to 35 barg and a temperature of -120°C or lower to a heat exchanger to produce an at least partially vaporized natural gas stream; ia) separating the at least partially vaporized natural gas stream to produce a first stream which is rich in methane and a second stream which is rich in hydrocarbons having two or more carbon atoms; ii) passing the second stream from step (ia) to a distillation vessel operated without reflux to produce a natural gas liquids stream and a stream rich in methane; iii) passing the stream rich in methane from step (ii), optionally after combining with the first stream from step (ia), without additional compression, to a heat exchanger and cooling by heat exchange with at least part of the feed stream of liquefied natural gas to produce a liquid
  • the heat exchange is preferably carried out on the two separate gas streams using two different heat exchangers or using a multi-stream heat exchanger.
  • the heat exchanger used is a plate-fin exchanger or other type of compact heat exchanger, for example a plate in shell where a single combined gas stream feed is present, or a printed circuit heat exchanger.
  • this embodiment of the process of the invention may also incorporate the front end recondenser as described above.
  • optional pumping may be applied to further increase the pressure, followed by vaporization to produce the desired conditioned natural gas.
  • the two streams from steps (iii) and (iiia) may if desired be combined prior to this pumping step.
  • the process of the present invention provides a number of advantages relative to the process described in US 6,564,579.
  • the process of the present invention gives operability improvements over US 6,564,579 because the scheme has increased turndown potential whilst still maximising LNG recovery.
  • the process of the present invention operates by supplying a feed stream of LNG at a sufficiently high initial pressure so that there is no requirement for gas compression at any stage of the process. This leads to low power consumption, reduced capital cost, reduced operating cost and high
  • the liquid stream from step (ia) may be let down into the distillation vessel: no pump is required to transfer the natural gas liquids stream from step (ia) to the distillation vessel, in addition to the fact that no compressor is needed to compress the gas stream exiting from the separator in step (ia).
  • the pressure of the feed stream is in the range of from 15 to 35 barg, preferably from 15 to 30 barg, especially from 20 to 30 barg, and this pressure is substantially maintained (subject to small pressure losses across the various pieces of equipment) throughout the process.
  • the preferred pressures used are generally lower than envisaged by the process of US 6,510,706, and because no compressor is needed to carry out the process of the invention (unless, optionally, a compressor is incorporated prior to step (i) of the process to handle boil off gases from the LNG storage tank) the process is significantly simplified over that of US 6,564,579.
  • the heat recovery efficiency of the process is high, especially if a compact heat exchanger is used and, when an additional separator is used and the gas streams from steps (ia) and (ii) are kept separate rather than combining them prior to heat exchange, the heat recovery efficiency is particularly improved over that of US 6,564,579.
  • the process of the invention may be integrated with existing LNG handling facilities. The process may also form part of an integrated energy recovery system as described in US 6,564,579.
  • FIG. 1 illustrates a flow scheme which represents the process according to the invention
  • Figure 2 represents an embodiment of the process of Figure 1 incorporating a recondenser at the front end of the process
  • FIG. 3 represents an embodiment of the process of Figure 1 incorporating an additional separator.
  • a cryogenic tank 1 contains LNG forming the feed to the process.
  • An in-tank pump 2 pumps the LNG at a temperature of -12O 0 C or lower from tank 1 via a pump 3 which increases the pressure to around 15 to 35, preferably 20 to 30, barg.
  • the LNG is passed to a heat exchanger 4, preferably of the compact, e.g. plate- fin, type.
  • a line 5 carries the partially vaporized LNG to distillation vessel 11 which separates the input stream into a liquid stream comprising natural gas liquids which are removed via line 12 to a cooler (not shown) and a gas stream which is removed via line 13 and fed back to the heat exchanger 4.
  • the distillation vessel 11 is provided with a reboiler 20 comprising a heat exchanger 21 and a line 22 forming a closed loop back to the distillation vessel 11.
  • FIG. 1 shows the process of Figure 1 incorporating a recondenser at the front end.
  • Boil-off gases leave the tank 1 via stream 41 and are compressed in compressor 42 to a pressure typically of from 8 to 12 barg.
  • the output from the compressor 42 is passed to recondenser 43.
  • a slip-stream 44 of the LNG stream pumped from the tank 1 by pump 2 is also passed to recondenser 43 where it absorbs the compressed boil off gases from stream 41.
  • the liquid stream 45 exiting the recondenser 43 is combined at mixing point 46 with the LNG stream from pump 2, and the resulting stream forms the feed stream entering pump 3.
  • a cryogenic tank 1 contains LNG forming the feed to the process.
  • An in-tank pump 2 pumps the LNG at a temperature of -12O 0 C or lower from tank 1 via a pump 3 which increases the pressure to around 15 to 35, preferably 20 to 30, barg.
  • the LNG is passed to a multi-channel heat exchanger 4, preferably of the plate- fin type.
  • a line 5 carries the partially vaporized LNG to a separation vessel 6 having two outlet lines.
  • Outlet line 7 carries a gas stream from the separation vessel 6 to one channel 30 of the multi-channel heat exchanger 4.
  • Outlet line 10 carries a liquid stream from the separation vessel to a distillation vessel 11 which separates the input stream into a liquid stream comprising natural gas liquids which are removed via line 12 to a cooler (not shown) and a gas stream which is removed via line 13 and fed back to the multi-channel heat exchanger 4 using a separate channel 31 from that used by line 7.
  • the distillation vessel 11 is provided with a reboiler 20 comprising a heat exchanger 21 and a line 22 forming a closed loop back to the distillation vessel 11.
  • the streams exiting channels 30 and 31 are carried by lines 14 and 16 to mixing point 15 where the streams are combined.
  • the combined stream is then passed to pump 17 and subsequently vaporised in heat exchanger 18 before being discharged.
  • the whole process is carried out at cryogenic temperatures, for example, the feed stream of LNG is typically at a temperature of around -170 to -12O 0 C, for example -163 to -13O 0 C.
  • the exact temperatures and pressures used will naturally depend upon the exact set-up details of the process and the quality of the LNG feed.
  • pump 3 may be omitted if, unusually, the LNG feed stream is at a sufficiently high initial pressure.
  • An additional pump may be added to the line feeding distillation column 11 if equipment configuration requires the pressure to be raised at this point.
  • An additional heat exchanger may be employed to warm (but not to vaporise) the LNG feed prior to pumping by pump 3.

Abstract

A process for the conditioning of liquefied natural gas comprising the following steps: supplying (3) a feed stream of liquefied natural gas at a pressure in the range of from 15 to 35 barg to a heat exchanger (4) to produce an at least partially vaporized natural gas stream (5) ; passing at least part of the stream from step (i) to a distillation vessel (11) operated without reflux to produce a natural gas liquids stream (12) and a stream rich in methane (13) ; passing the stream rich in methane from step (ii) , without additional compression, to a heat exchanger (4) and cooling by heat exchange with at least part of the feed stream of liquefied natural gas to produce a liquid natural gas stream (14) ; vaporizing (18) the liquid natural gas stream from step (iii) to produce a conditioned natural gas; and recovering the natural gas liquids (12) .

Description

PROCESS FOR CONDITIONING LIQUEFIED NATURAL GAS
This invention relates to a process for conditio.ning liquefied natural gas.
Liquefied natural gas (LNG) needs to be vaporized before being fed into a pipeline for distribution. In a typical vaporization process, the LNG is fed into a storage tank. This inevitably results in some boil-off of vapour; typically this off-gas is compressed and then passed to a boil-off condenser where it is condensed, for example by passing a quantity of LNG from the tank into the boil-off condenser where the boil-off gas, at increased pressure, is combined with the LNG stream to produce an all-liquid stream which may then be combined with an outflow stream from the tank. The resultant LNG is then passed from the tank to a pump which discharges the LNG, at a suitable pressure, to a pipeline, via one or more heat exchangers which vaporize the LNG.
However, in many cases, the LNG does not meet required product or pipeline specifications because of the presence of excess quantities of hydrocarbons containing two or more carbon atoms, and various additional processing steps are required.
US 6,564,579 describes a process for the removal of natural gas liquids (NGLs), typically hydrocarbons containing two or more carbon atoms, from LNG, in order to provide a natural gas product with a reduced heating value which meets pipeline or other commercial specifications. This process, which is of a type which may be referred to as conditioning, includes the following steps: vaporizing at least a major portion of a stream of the liquefied natural gas to produce an at least partially vaporized natural gas stream; fractionating- the at least partially vaporized natural gas stream to produce a gas stream and a natural gas liquids stream; compressing the gas stream to increase the pressure of the gas stream by about 50 to about 150 psi to produce a compressed gas stream and cooling the compressed gas stream by heat exchange with the stream of liquefied natural gas to produce a liquid compressed gas stream; pumping the liquid compressed gas stream to produce a high-pressure liquid stream at a pressure from about 800 to about 1200 psig; vaporizing the high-pressure liquid stream to produce a conditioned natural gas suitable for delivery to a pipeline or for commercial use; and recovering the natural gas liquids. 50 to 150 psi corresponds to about 3.5 to about 10.3 bar, while 800 to 1200 psig corresponds to about 55.2 to about 82.8 barg.
As well as providing a natural gas product which meets pipeline specifications, the process of US 6,564,579 provides separated natural gas liquids which may have greater commercial value than if they were constituents of the natural gas product, and is relatively simple and economical. However, the process has disadvantages. In particular, the process requires the use of a compressor located at the vapour outlet of the separation (fractionating) column to enable complete condensation of the vapour stream.
US 6,604,380 also describes a process for the recovery of natural gas liquids from LNG. This process is a complex, multi-step process which involves splitting the feed stream and using at least one portion as reflux elsewhere in the process.
US 6,510,706 describes a process which is specific for the processing of pressurized liquid natural gas. According to US 6,510,706, "It has been proposed to transport natural gas at temperatures above -112°C (-1700F) and at pressures sufficient for the liquid to be at or below its bubble point temperature. This pressurized liquid natural gas is referred to as "PLNG" to distinguish it from LNG, which is transported at near atmospheric pressure and at a temperature of about -162°C (-2600F)." The processing of LNG and PLNG present different engineering challenges.
We have now found an efficient, simple and flexible process which can be used to condition LNG.
Accordingly the present invention provides a process for the conditioning of liquefied natural gas, which comprises the following steps: i) supplying a feed stream of liquefied natural gas at a pressure in the range of from 15 to 35 barg and a temperature of -12O0C or lower to a heat exchanger to produce an at least partially vaporized natural gas stream; ii) passing at least part of the stream from step (i) to a distillation vessel operated without reflux to produce a natural gas liquids stream and a stream rich in methane; iii) passing the stream rich in methane from step (ii), without additional compression, to a heat exchanger and cooling by heat exchange with at least part of the feed stream of liquefied natural gas to produce a liquid natural gas stream; iv) vaporizing the liquid natural gas stream from step (iii) to produce a conditioned natural gas; and v) recovering the natural gas liquids.
The process according to the invention produces a conditioned natural gas which is suitable for delivery to a pipeline, or for other commercial use, together with natural gas liquids. In general, the natural gas liquids comprise hydrocarbons having 2 or more carbon atoms. If desired, the initial natural gas liquids product obtained by the process of the invention can be further processed to separate hydrocarbons by the difference in the number of their carbon atoms. The initial step of the process of the present invention requires that the feed stream of LNG is provided at a sufficiently high pressure so that a compressor is not required to be applied to the stream rich in methane obtained from step (ii). of the process prior to the heat exchange of step (iii). In most circumstances, this will involve pumping the LNG to achieve the desired pressure in the range from 15 to 35 barg, preferably 15 to 30 barg, for entry of the feed stream to the heat exchanger.
' The feed stream of LNG must be supplied at a temperature of -120°C or less, for example -130°C or less. Within this constraint, preferably the temperature is -1700C or greater, especially -163°C or greater. Preferably the temperature is in the range of from around -1700C to -1200C, especially from -163°C to -1200C, for example from -1630C to - 13O0C.
The LNG feed to the process may be provided from an LNG storage tank, usually by pumping. Preferably in excess of 90% or 95% of the LNG feed to the process, preferably all of the LNG, is processed in steps (i) and (ii) of the process. If desired, a small quantity of the feed may be separated off as a slip stream and used to perform certain functions within the process. However, it is an advantage of the process according to the invention that none of the feed is required to act as a reflux in columns used in the process, as is common in processes for processing LNG, for example the process described in US 6,604,380. 100% of the LNG feed can be processed, and 90% or more of the NGL liquids recovered as a product. At least part of the stream from step (i) is separated into a natural gas liquids stream and a gas stream in the distillation vessel of step (ii), and the resulting gas stream is sent to a heat exchanger where it is cooled against the LNG feed stream (step (iii)). Preferably the heat exchanger used is a plate-fin exchanger or other type of compact heat exchanger (plate in shell or printed circuit heat exchangers); these are very compact, and permit small temperature approaches between the "net" cooling and warming streams, which in turn, leads to high process efficiency.
In the process of the invention, the high-pressure feed stream is heated by heat exchange with the stream exiting step (ii) of the process. In some circumstances, it may be desirable to provide additional heating to the feed stream, using a heating fluid other than this exit stream.
The distillation vessel of step (ii) contains distillation trays or packing, and produces a stream rich in methane. If the distillation, vessel is a demethaniser, the majority of the methane sent to the vessel is routed overhead as gas, while the liquid stream contains hydrocarbons having two or more carbon atoms. If the vessel is a deethaniser, the stream rich in methane will also contain the majority of the ethane sent to the vessel, and the liquid product will contain predominantly hydrocarbons having 3 or more carbon atoms. The use of LNG as a feed at the temperatures and pressures used in the process of the present invention provides a number of advantages. In particular, it is possible to use a conventional LNG feed which is substantially free from pentanes and heavier hydrocarbons, leading to a high-value NGL product requiring no downstream processing. A mixed commercial LPG product can be used as such, or may for example be fractionated downstream to produce commercial propane and commercial butane.
In a preferred embodiment of the process according to the invention, a recondenser is incorporated into the front end of the process. In this embodiment, when an LNG storage tank is providing the feed to the process, boil-off gases from the LNG storage tank are compressed, typically to a pressure of from 8 to 12 barg, prior to entering a recondenser. A slip-stream from the main LNG stream exiting the LNG storage tank is also passed to the recondenser, where is absorbs the condensed boil-off gases. The output from the recondenser, which is liquid, is then combined with the main exit stream from the LNG storage tank, and the combined stream, normally after pumping to raise the pressure to the desired level, forms the feed to the process. Thus, a preferred embodiment of the process of the invention comprises a process in which an exit stream of liquefied natural gas is pumped from a storage tank; said exit stream is split into at least a first portion and a second portion; boil-off gases from said storage tank are compressed and subsequently fed to a recondenser; the first portion of the exit stream is also passed to the recondenser, where it absorbs the condensed boil-off gases; the output from the recondenser is combined with the second portion of the exit stream from the storage tank; and the resulting combined stream is used as the feed stream of step (i). In a further embodiment of the process of the invention, an additional separator, generally containing no internals other than minor items such as a feed device or a demister pad), may be used. In this embodiment, the process may incorporate an ■ additional separation step, in which the stream from step (i) is passed to a separator to produce a first stream which is rich in methane, and a second stream which is rich in hydrocarbons having two or more carbon atoms, the second stream becoming the input stream for step (ii) of the process, i.e. the input to the distillation vessel, while the first stream is passed to a heat exchanger and cooled by heat exchange with at least part of the feed stream of LNG to produce an LNG stream. Thus, in this embodiment, the process may be characterised as a process for the conditioning of liquefied natural gas, which comprises the following steps: i) supplying a feed stream of liquefied natural gas at a pressure in the range of from 15 to 35 barg and a temperature of -120°C or lower to a heat exchanger to produce an at least partially vaporized natural gas stream; ia) separating the at least partially vaporized natural gas stream to produce a first stream which is rich in methane and a second stream which is rich in hydrocarbons having two or more carbon atoms; ii) passing the second stream from step (ia) to a distillation vessel operated without reflux to produce a natural gas liquids stream and a stream rich in methane; iii) passing the stream rich in methane from step (ii), optionally after combining with the first stream from step (ia), without additional compression, to a heat exchanger and cooling by heat exchange with at least part of the feed stream of liquefied natural gas to produce a liquid natural gas stream; iiia) passing the first stream from step (ia), optionally after combining with the stream rich in methane from step (ii), without additional compression, to a heat exchanger and cooling by heat exchange with at least part of the feed stream of liquefied natural gas to produce a liquid natural gas stream; iiib) if the output from steps (iii) and (iiia) comprises two separate streams, optionally combining them; iv) vaporizing the liquid natural gas streams from steps (iii), (iiia) and/or (iiib) to produce a conditioned natural gas; and v) recovering the natural gas liquids. In this embodiment it is possible to combine the two gas streams from the separator and the distillation vessel prior to cooling, and hence use a single channel heat exchanger. However, to optimise process efficiency, the heat exchange is preferably carried out on the two separate gas streams using two different heat exchangers or using a multi-stream heat exchanger. Preferably the heat exchanger used is a plate-fin exchanger or other type of compact heat exchanger, for example a plate in shell where a single combined gas stream feed is present, or a printed circuit heat exchanger.
Naturally, this embodiment of the process of the invention may also incorporate the front end recondenser as described above. Following the heat exchange of step (iii), optional pumping may be applied to further increase the pressure, followed by vaporization to produce the desired conditioned natural gas. When using an additional separator, the two streams (from steps (iii) and (iiia)) may if desired be combined prior to this pumping step.
The process of the present invention provides a number of advantages relative to the process described in US 6,564,579. Thus, the process of the present invention gives operability improvements over US 6,564,579 because the scheme has increased turndown potential whilst still maximising LNG recovery. In particular, the process of the present invention operates by supplying a feed stream of LNG at a sufficiently high initial pressure so that there is no requirement for gas compression at any stage of the process. This leads to low power consumption, reduced capital cost, reduced operating cost and high
"availability" due to the absence of a major machinery duty, in comparison to the process of US 6,564,579, which does require gas compression. In addition, the process of US 6,564,579 is inherently less efficient than that of the present invention, because in the prior art process the compressor used generates a lot of heat, which has to be removed. In effect, the process of the present invention replaces gas compression by liquid pumping, so reducing power, cost and complexity.
When using an additional separator, because the process is operated at a substantially uniform pressure, i.e. following the initial pumping step no significant increase in pressure is required at any point, and because there is no requirement to merge two separate gas streams at different pressures prior to heat exchange as there is in the process of US 6,564,579, the liquid stream from step (ia) may be let down into the distillation vessel: no pump is required to transfer the natural gas liquids stream from step (ia) to the distillation vessel, in addition to the fact that no compressor is needed to compress the gas stream exiting from the separator in step (ia).
The pressure of the feed stream, usually generated by an* initial pumping step, is in the range of from 15 to 35 barg, preferably from 15 to 30 barg, especially from 20 to 30 barg, and this pressure is substantially maintained (subject to small pressure losses across the various pieces of equipment) throughout the process. The preferred pressures used are generally lower than envisaged by the process of US 6,510,706, and because no compressor is needed to carry out the process of the invention (unless, optionally, a compressor is incorporated prior to step (i) of the process to handle boil off gases from the LNG storage tank) the process is significantly simplified over that of US 6,564,579. The heat recovery efficiency of the process is high, especially if a compact heat exchanger is used and, when an additional separator is used and the gas streams from steps (ia) and (ii) are kept separate rather than combining them prior to heat exchange, the heat recovery efficiency is particularly improved over that of US 6,564,579. The process of the invention may be integrated with existing LNG handling facilities. The process may also form part of an integrated energy recovery system as described in US 6,564,579.
The invention is further illustrated in the accompanying drawings, in which:
Figure 1 illustrates a flow scheme which represents the process according to the invention;
Figure 2 represents an embodiment of the process of Figure 1 incorporating a recondenser at the front end of the process; and
Figure 3 represents an embodiment of the process of Figure 1 incorporating an additional separator. In Figure 1, a cryogenic tank 1 contains LNG forming the feed to the process. An in-tank pump 2 pumps the LNG at a temperature of -12O0C or lower from tank 1 via a pump 3 which increases the pressure to around 15 to 35, preferably 20 to 30, barg. From the pump 3 the LNG is passed to a heat exchanger 4, preferably of the compact, e.g. plate- fin, type. A line 5 carries the partially vaporized LNG to distillation vessel 11 which separates the input stream into a liquid stream comprising natural gas liquids which are removed via line 12 to a cooler (not shown) and a gas stream which is removed via line 13 and fed back to the heat exchanger 4. The distillation vessel 11 is provided with a reboiler 20 comprising a heat exchanger 21 and a line 22 forming a closed loop back to the distillation vessel 11.
The stream exiting heat exchanger 4 is carried by line 14 to pump 17 and subsequently vaporised in heat exchanger 18 before being discharged. Figure 2 shows the process of Figure 1 incorporating a recondenser at the front end.
Boil-off gases leave the tank 1 via stream 41 and are compressed in compressor 42 to a pressure typically of from 8 to 12 barg. The output from the compressor 42 is passed to recondenser 43. A slip-stream 44 of the LNG stream pumped from the tank 1 by pump 2 is also passed to recondenser 43 where it absorbs the compressed boil off gases from stream 41. The liquid stream 45 exiting the recondenser 43 is combined at mixing point 46 with the LNG stream from pump 2, and the resulting stream forms the feed stream entering pump 3.
In Figure 3, a cryogenic tank 1 contains LNG forming the feed to the process. An in-tank pump 2 pumps the LNG at a temperature of -12O0C or lower from tank 1 via a pump 3 which increases the pressure to around 15 to 35, preferably 20 to 30, barg. From the pump 3 the LNG is passed to a multi-channel heat exchanger 4, preferably of the plate- fin type. A line 5 carries the partially vaporized LNG to a separation vessel 6 having two outlet lines. Outlet line 7 carries a gas stream from the separation vessel 6 to one channel 30 of the multi-channel heat exchanger 4. Outlet line 10 carries a liquid stream from the separation vessel to a distillation vessel 11 which separates the input stream into a liquid stream comprising natural gas liquids which are removed via line 12 to a cooler (not shown) and a gas stream which is removed via line 13 and fed back to the multi-channel heat exchanger 4 using a separate channel 31 from that used by line 7.
The distillation vessel 11 is provided with a reboiler 20 comprising a heat exchanger 21 and a line 22 forming a closed loop back to the distillation vessel 11.
The streams exiting channels 30 and 31 are carried by lines 14 and 16 to mixing point 15 where the streams are combined. The combined stream is then passed to pump 17 and subsequently vaporised in heat exchanger 18 before being discharged.
In the Figures, the whole process is carried out at cryogenic temperatures, for example, the feed stream of LNG is typically at a temperature of around -170 to -12O0C, for example -163 to -13O0C. The exact temperatures and pressures used will naturally depend upon the exact set-up details of the process and the quality of the LNG feed. Various modifications of the flow scheme shown in the Figures are likewise possible. For example, pump 3 may be omitted if, unusually, the LNG feed stream is at a sufficiently high initial pressure. An additional pump may be added to the line feeding distillation column 11 if equipment configuration requires the pressure to be raised at this point. An additional heat exchanger may be employed to warm (but not to vaporise) the LNG feed prior to pumping by pump 3.

Claims

Claims:
1. A process for the conditioning of liquefied natural gas, which comprises the following steps: i) supplying a feed stream of liquefied natural gas at a pressure in the range of from 15 to
35 barg to a heat exchanger to produce an at least partially vaporized natural gas stream; ii) passing at least part of the stream from step (i) to a distillation vessel operated without reflux to produce a natural gas liquids stream and a stream rich in methane; iii) passing the stream rich in methane from step (ii), without additional compression, to a heat exchanger and cooling by heat exchange with at least part of the feed stream of liquefied natural gas to produce a liquid natural gas stream; iv) vaporizing the liquid natural gas stream from step (iii) to produce a conditioned natural gas; and v) recovering the natural gas liquids.
2. A process according to claim 1, in which an exit stream of liquefied natural gas is pumped from a storage tank; said exit stream is split into at least a first portion and a second portion; boil-off gases from said storage tank are compressed and subsequently fed to a recondenser; the first portion of the exit stream is also passed to the recondenser, where it absorbs the condensed boil-off gases; the output from the recondenser is combined with the second portion of the exit stream from the storage tank; and the resulting combined stream is used as the feed stream of step (i).
3. A process as claimed in claim 2, in which the boil-off gases are compressed to a pressure of from 8 to 12 barg in the compressor.
4. A process as claimed in any one ofclaims 1 to 3, which comprises the following steps: i) supplying a feed stream of liquefied natural gas at a pressure in the range of from 15 to 35 barg and a temperature of -120°C or lower to a heat exchanger to produce an at least partially vaporized natural gas stream; ia) separating the at least partially vaporized natural gas stream to produce a first stream which is rich in methane and a second stream which is rich in hydrocarbons having two or more carbon atoms; ii) passing the second stream from step (ia) to a distillation vessel to produce a natural gas ■ liquids stream and a stream rich in methane; iii) passing the stream rich, in methane from step (ii), optionally after combining with the
First stream from step (ia), without additional compression, to a heat exchanger and cooling by heat exchange with at least part of the feed stream of liquefied natural gas to produce a liquid natural gas stream; iiia) passing the first stream from step (ia), optionally after combining with the stream rich in methane from step (ii), without additional compression, to a heat exchanger and cooling by heat exchange with at least part of the feed stream of liquefied natural gas to produce a liquid natural gas stream; iiib) if the output from steps (iii) and (iiia) comprises two separate streams, optionally combining them; iv) vaporizing the liquid natural gas streams from steps (iii), (iiia) and/or (iiib) to produce a conditioned natural gas; and v) recovering the natural gas liquids.
5. A process as claimed in claim 4, in which the heat exchange of steps (iii) and (iiia) is carried out on two separate gas streams using two different heat exchangers of using a multi-stream heat exchanger.
6. A process as claimed in either claim 4 or claim 5, in which the two streams exiting steps (iii) and (iiia) are combined prior to vaporization to produce conditioned natural gas.
7. A process as claimed in any one of claims 1 to 6, in which the feed stream is supplied at a pressure in the range of from 15 to 30 barg.
8. A process as claimed in claim 7, in which the feed stream is supplied at a pressure in the range of from 20 to 30 barg.
9. A process as claimed in any one of claims 1 to 8, in which the feed stream is raised to the required pressure by pumping.
10. A process as claimed in any one of claims 1 to 9, in which any heat exchanger used in the process is a compact heat exchanger.
11. A process as claimed in claim 10, in which any heat exchanger used in the process is a plate-fin exchanger.
12. A process according to any one of claims 1 to 11, in which the temperature of the feed stream of liquefied natural gas is in the range of from -170° to -12O0C.
13. A process as claimed in claim 12, in which the temperature of the feed stream of liquefied natural gas is in the range of from -163° to -13O0C.
14. A process as claimed in any one of claims 1 to 13, in which in excess of 90% of the liquefied natural gas feed to the process is processed in steps (i) and (ii).
EP06709671A 2005-02-16 2006-02-07 Process for conditioning liquefied natural gas Withdrawn EP1848946A1 (en)

Applications Claiming Priority (2)

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GBGB0503213.1A GB0503213D0 (en) 2005-02-16 2005-02-16 Process for conditioning liquefied natural gas
PCT/GB2006/000429 WO2006087520A1 (en) 2005-02-16 2006-02-07 Process for conditioning liquefied natural gas

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EP1848946A1 true EP1848946A1 (en) 2007-10-31

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CA2663060C (en) 2006-09-11 2014-08-12 Exxonmobil Upstream Research Company Transporting and managing liquefied natural gas
CN106609914A (en) * 2015-10-26 2017-05-03 安徽华尔泰化工股份有限公司 Hose ammonia recovery device
KR102117852B1 (en) * 2018-07-02 2020-06-03 주식회사래티스테크놀로지 Fluid Tank Having Internal Vaporizers

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US6510706B2 (en) * 2000-05-31 2003-01-28 Exxonmobil Upstream Research Company Process for NGL recovery from pressurized liquid natural gas
US6941771B2 (en) * 2002-04-03 2005-09-13 Howe-Baker Engineers, Ltd. Liquid natural gas processing
US6564579B1 (en) * 2002-05-13 2003-05-20 Black & Veatch Pritchard Inc. Method for vaporizing and recovery of natural gas liquids from liquefied natural gas
EA008337B1 (en) * 2003-06-05 2007-04-27 Флуор Корпорейшн Liquefied natural gas regasification plant
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GB0503213D0 (en) 2005-03-23
KR20070121673A (en) 2007-12-27
CN101128712A (en) 2008-02-20

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