Ethylene is one of the basic raw materials of the petrochemical industry that is used to produce plastics. One
of the largest producers of this compound is the USA, and a substantial increase in the demand for ethylene
has also been recently observed in the Middle East, the Far East, and China. This requires the transport of this
cargo by sea. Ethylene carriers are a type of LPG ships and are equipped with a cascade cycle that uses propylene
or refrigerant R404A as a coolant medium. These vessels have been designed to withstand the minimum
temperature of ethylene of –104°C for fully-cooled cargo. A mixture of ethylene and air (from concentrations
of 2.75–2.6%) becomes explosive during heating under elevated pressures. Hence, it is necessary to form an
inert atmosphere in the tanks using mostly nitrogen before the ethylene cargo is loaded. The process of aerating,
inerting, gassing-up, and cooling cargo tanks and cargo is constantly repeated during the operation of
LPG carriers. Due to the large amounts of ethylene lost during gassing-up, which results in significant financial
losses and disruptions in cargo compressors during the cooling of the tanks and cargo, this operation is the
most problematic of all. In this article, a solution is proposed for performing the gassing-up procedure which
prevents excessive ethylene loss.
