Liquefied Petroleum Gas (LPG) Carriers are designed to carry mainly butane, propane, butadiene, propylene, and are also able to carry anhydrous ammonia. All gas cargoes are transported in liquid form. Gas Carriers are generally grouped as follows:
a) Fully pressurized:
The simplest of the gas carriers, they are generally fitted with two or three pressure vessel tanks operating at ambient temperature. No re-liquefaction plant is fitted and the cargo tank pressure will fluctuate according to the product carried and ambient temperature. Such vessels vary in capacity from 100 m3 up to 10,000 m3.
b) Fully refrigerated:
Designed to carry liquefied gases at low temperature and at, or slightly above, atmospheric pressure. The onboard re-liquefaction plant maintains these conditions. These ships typically vary in size from 15,000 m3 to 100,000 m3, with three common sizes for LPG/ Ammonia Trades: 30,000 m3, 52,000 m3 and 80,000 m3.
c) Semi-pressurized and refrigerated:
A combination of both. Most semi-pressurized LPG/ chemical Gas Carriers are in the 2,000 m3 – 20,000 m3 size range.