lpg/lng cargo handling inerting (izlaz iz doka) gassing-up cooling-down (tanks) loading...
TRANSCRIPT
![Page 1: LPG/LNG cargo handling Inerting (izlaz iz doka) Gassing-up Cooling-down (tanks) Loading Refrigiration (for LPG Carriers) Discharging Inerting (if changing](https://reader035.vdocument.in/reader035/viewer/2022081420/56649ce15503460f949aaf4f/html5/thumbnails/1.jpg)
LPG/LNG cargo handling
• Inerting (izlaz iz doka)• Gassing-up• Cooling-down (tanks)• Loading• Refrigiration (for LPG Carriers)• Discharging• Inerting (if changing cargo or aerating) (ulaz u
d.)• Aerating (degazation)
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Inerting
• By displacement method • low speed of inert gas• abt. 4 changing of tank volume• entering of IG on top or bottom of tank (depending
of specific density)
• By mixing of inert gas and gas residues• high speed of IG entering (mixing)
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VENT HEADER
INERT GAS HEADER
CONDENSATE RETURN LINE
LIQUID HEADER
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
VAPOUR HEADER
liquid vapour
Inerting by displacement method
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VAPOUR HEADER
LIQUID HEADER
VENT HEADER
INERT GAS HEADER
CONDENSATE RETURN LINE
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
liquid vapour
Inerting of cargo tanks by ship's plant
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Gassing-up
• For passing fm.inerted to loaded condition
• Inert gas has uncondensable gases (Nitrogen and CO2 can not be condensed by ship’s reliquefaction plant)
• problem w. reliquifaction plant (condenser)
• Venting to atmosphere or return to shore until tank is full with next cargo vapour
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Gassing-up
• Gassing-up at sea (available to fully or semi-pressurised ships) – often with deck tanks
• Gassing-up using cargo from shore
• Before commencing gasing-up O2 contents must be less then 5% for LPG-s, and for some terminals less than 0.5%, or even less – for Vinyl Cloride
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Gassing-up
• Compressors for reliquefaction can be started after gas concentration into tank reach at least 90%
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CONDENSATE RETURN LINE
VENT HEADER
INERT GAS HEADER
LIQUID HEADER
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
VAPOUR HEADER
liquid vapour
Gassing-up cargo tanks using liquid fm. shore
![Page 9: LPG/LNG cargo handling Inerting (izlaz iz doka) Gassing-up Cooling-down (tanks) Loading Refrigiration (for LPG Carriers) Discharging Inerting (if changing](https://reader035.vdocument.in/reader035/viewer/2022081420/56649ce15503460f949aaf4f/html5/thumbnails/9.jpg)
VENT HEADER
INERT GAS HEADER
CONDENSATE RETURN LINE
LIQUID HEADER
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
VAPOUR HEADER
liquid vapour
Gassing-up cargo tanks using vapour fm. shore
![Page 10: LPG/LNG cargo handling Inerting (izlaz iz doka) Gassing-up Cooling-down (tanks) Loading Refrigiration (for LPG Carriers) Discharging Inerting (if changing](https://reader035.vdocument.in/reader035/viewer/2022081420/56649ce15503460f949aaf4f/html5/thumbnails/10.jpg)
Cooling-down
• For preventing excesive pressure during loading or transporting
• Spraying cargo liquid into a tank at a slow rate – evaporation/expansion
• Cooling-down rate depends of the tanks design and size – abt. 10oC per hour
• Inert gas – cargo vapour mixture goes to vent riser (atmosphere) or reliquefaction plant (problem with noncondensable gases – constant condenser venting)
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Cooling-down
• Cargo tank cooling-down reduces temperature into hold space or interbarrier spaces – pressure drop
• Pressure drop into interbarrier or hold space should be compensated with inert gas or dry air
• During coolin-down water (moisture) or remain inert gas could couse big problems (pumps, valves and other equipment could stuck up)
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LIQUID HEADER
VENT HEADER
INERT GAS HEADER
CONDENSATE RETURN LINE
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
VAPOUR HEADER
liquid vapour
Cool-down using liquid from shore: vapour returned to shore
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Loading the cargobefore
• Ship / shore preloading plan • Cargo characteristics, inhibitors and inert
gas to be used• Before loading attention to be paid:
• safety valves settings and h.p. alarm settings • remotely operated valves• reliquefaction equipment• gas detection system• alarms and controls• ESD (Emergency Shut Down)
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Loading
• Vapourisation control (LPG ships):• vapour return line connected to gas compressor• reliquefaction plant – liquid return to tanks• combination of above
• Vapourisation control (LNG ships):• return to shore is normal procedure (no reliq. plant)• return by ship’s compressors or compressors from
shore – max. loading rate limitation
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VAPOUR HEADER
LIQUID HEADER
VENT HEADER
INERT GAS HEADER
CONDENSATE RETURN LINE
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
liquid vapour
Loading with vapur return to shore
![Page 16: LPG/LNG cargo handling Inerting (izlaz iz doka) Gassing-up Cooling-down (tanks) Loading Refrigiration (for LPG Carriers) Discharging Inerting (if changing](https://reader035.vdocument.in/reader035/viewer/2022081420/56649ce15503460f949aaf4f/html5/thumbnails/16.jpg)
VAPOUR HEADER
LIQUID HEADER
VENT HEADER
INERT GAS HEADER
CONDENSATE RETURN LINE
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
liquid vapour
Loading without vapour return
![Page 17: LPG/LNG cargo handling Inerting (izlaz iz doka) Gassing-up Cooling-down (tanks) Loading Refrigiration (for LPG Carriers) Discharging Inerting (if changing](https://reader035.vdocument.in/reader035/viewer/2022081420/56649ce15503460f949aaf4f/html5/thumbnails/17.jpg)
Loading fully refrigirated ships
• Usually from fully refrigirated storage (jetty)
• Long distance btw. shore storage and ship and high ambient temperature can couse tank pressure remaining problem, specially in early stages;
• loading rate must be reduced to give a time reliq. plant for cooling down cargo tank
• loading limited quantities of liquid into the tank via the top sprays – helping condensate some cargo
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Loading pressurised ships
• Arriving at a loading terminal at atmospheric pressure
• Need vapour from shore to purge remaining nitrogen or contaminants from tanks – equalise pressures btw. ship and terminal
• Tank and pipeline temperature must not fall bellow design temperature – slow rate at the beginning
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Loading pressurised ships from refrigirated storage
• Tanks suitable for min. temperature btw. 0 and –5oC
• Cargo should be heated (pumping through cargo heater on board or shore)
• Attention to be paid for topping of (max. 98% at max. temperature reached during the voyage)
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Loading semi-pressurised ships from refrigirated storage
• Cargo tanks constructed of low temperature steels – able to accomodate fully refrigirated propan (-40 and –50oC) or for ethylene -104oC
• Refrigirated cargo can be loaded without heating• Cargo temperature can be maintained during
loaded voyage by reliq. plant – if discharged to refrigirated storage
• Cargo can be heated during loaded voyage if discharged into pressurised facilities
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VENT HEADER
INERT GAS HEADER
CONDENSATE RETURN LINE
LIQUID HEADER
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
VAPOUR HEADER
liquid vapour
Cargo refrigiration at sea
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Cargo refrigiration at sea
• By reliquefaction plant • Compressor should not be run during heavy
rolling• Condensate is passed through the top sprayes –
cooling down the liquid surface (the bulk of the liquid has not been cooled)
• To cool down bulk of the liquid condensate return should be through the bottom connection of the tank to ensure proper circulation
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Cargo refrigiration at sea
• Reliquefaction plant run on more than one tank simultaneosly – carefully controled condensate return (to avoid overfilling of any one tank)
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VENT HEADER
INERT GAS HEADER
CONDENSATE RETURN LINE
LIQUID HEADER
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
VAPOUR HEADER
liquid vapour
Discharge without vapour return
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Discharging
• Method depends on type of ship, cargo specification and terminal storage;
• Discharge by pressurising the vapour space– shore vapor suply or vaporiser and compressor on board
• Discharge with or without booster pumps– discharging limited by pipeline diametar– booster pump – for long distances or higher levels
• Discharge via booster pump and cargo heater– when discharged from refrigirated ship to pressurised
terminals
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VENT HEADER
INERT GAS HEADER
CONDENSATE RETURN LINE
LIQUID HEADER
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
VAPOUR HEADER
liquid vapour
Discharge with vapour return
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After discharge
• Draining tanks and pipelines• Pump discharge valve should not be throtteled for
flow control if the pump is operating with a booster pump (can damage pump)
• Cargo must be drained from all deck lines and cargo hoses or hard arms – by compressor (from ship to shore) or by blowing the liquid into ship’s tanks using nitrogen injected at the base or apex of the hard arm
• Only after depressuring all deck lines and purging with nitrogen ship/shore connection can be broken
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liquid vapour
CONDENSATE RETURN LINE
VENT HEADER
INERT GAS HEADER
LIQUID HEADER
Reliquefaction
VapourCompressor
L.P.G.Vaporizer
Inert Gas Generator
L.P.G.Heater
Air Blower
VAPOUR HEADER
Aeration of cargo tanks
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Ballast voyage
• Small quantity of cargo retain on bord (heel)• only if the same grade of cargo will be loaded
• For large LNG carriers 2000 to 3000 m3
may be retained in the tanks – fitted with spray cool-down pumps in each cargo tank to minimise tank thermal gradients
• On LPG-s small amount of liquid remaining to provide necessary cooling during ballast voyage – by using reliquefaction plant
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Amonia – special procedures• When changing from amonia to LPG most traces of vapours
must be removed (remaining volume quantity - 20ppm)• Amonia – when evaporating to air is particulary likely to
reach super-cooled condition – all liquid must be removed• For amonia the inert gas plant must not be used as the
ship’s inert gas plant is not suitable – carbamate formation• Blowing warm fresh air into system – disperzing amonia
vapour• Sometimes washing with fresh water (amonia is highly water
soluble) – not suitable for prismatic tanks (for tanks with minimum internal structure - full drainage, clean and rust free tanks)
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Amonia – special procedures
• All traces of water must be removed (preventing formation of ice or hydrats) – fixed or portable pumps
• High solubility of amonia in water (300:1) can lead to dangerous vacum condition in tank – to ensure essential air entry into the tank during water washing proces – air dew point must be lower than the tank atmosphere
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Cargo compatibilities
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