LPG/LNG cargo handling

1. 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)

2. 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)

3. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Inerting by displacement method vapour liquid

4. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Inerting of cargo tanks by ship's plant vapour liquid

5. 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

6. 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

7. Gassing-up • Compressors for reliquefaction can be started after gas concentration into tank reach at least 90%

8. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Gassing-up cargo tanks using liquid fm. shore vapour liquid

9. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Gassing-up cargo tanks using vapour fm. shore vapour liquid

10. 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)

11. 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)

12. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Cool-down using liquid from shore: vapour returned to shore vapour liquid

13. 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)

14. 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

15. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Loading with vapur return to shore vapour liquid

16. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Loading without vapour return vapour liquid

17. 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

18. 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

19. 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)

20. 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

21. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Cargo refrigiration at sea vapour liquid

22. 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

23. Cargo refrigiration at sea • Reliquefaction plant run on more than one tank simultaneosly – carefully controled condensate return (to avoid overfilling of any one tank)

24. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Discharge without vapour return vapour liquid

25. 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

26. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Discharge with vapour return vapour liquid

27. 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

28. VENT HEADER INERT GAS HEADER CONDENSATE RETURN LINE VAPOUR HEADER LIQUID HEADER L.P.G. Heater Reliquefaction L.P.G. Vaporizer Vapour Compressor Inert Gas Generator Air Blower Aeration of cargo tanks vapour liquid

29. 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

30. 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)

31. 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

37. Cargo compatibilities