Ethylene and gas/chemical carriers construction, capacity and temperature control
Ethylene carriers are the most sophisticated of the semi-pressurized tankers and have the ability to carry not only most other liquefied gas cargoes but can also transport ethylene fully-refrigerated at its
atmospheric pressure boiling point of -104°C. Designed to carry most liquefied gas cargoes except LNG.
Of this ethylene carrier fleet, about one dozen form a special sub-group of ships able to handle a wide range of liquid chemicals and liquefied gases simultaneously. The ships can load or discharge at virtually all pressurized and refrigerated terminals, making them the most versatile gas carriers in terms of cargo-handling ability.
Many ethylene carriers can also carry LPG cargoes,
which increases their flexibility.They feature cylindrical or bi-lobe, insulated, stainless or low
temperature nickel steel cargo tanks able to carry cargoes at minimum
temperatures of -104ºC and at tank pressures of up to about 6 bar.
The ships can load and discharge at virtually all pressurised and
refrigerated terminals, making them the most versatile LPG carriers in
terms of cargo handling ability. Powerful reliquefaction units are
installed.
Cargo Capacity
Cargo capacitiy depends on the trade for which the
vessel was constructed and range from 1,500 - 15,000
cubic metres.
Fig: Ethylene carrier underway
Temperature Control
Thermal insulation and a high capacity reliquefaction
plant is fitted on this type of vessel.
Construction
Ethylene Carriers have Containment systems can either
be Type C, Type B or Type A prismatic free-standing.
If Type C pressure vessel tanks are used, then no
secondary barrier is required
If Type B is used a partial secondary barrier is required
If Type A is used a full secondary barrier is required.
Because of the cargo temperature of -104°C, the hull
cannot be used as a secondary barrier in this case and a
separate secondary barrier must be fitted.
For reasons of economy, Type C tanks have
predominated in this trade.
Ballast is carried in a full double bottom and wing tank
ballast system.
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