Cargo Heating Systems On Board Ships
Heavy fractions, such as fuel oil become very thick and sluggish when cold, and in order that such oils can be loaded and discharged without delay it is necessary to keep them heated. Today the oil trade is so vast and wide spread that the average oil tanker may be trading in the tropics one voyage and the Artic conditions in the next. It is therefore necessary that cargo heating systems be designed to cope with extreme conditions.
Due to the fact that a loaded tanker has comparatively little freeboard, the temperature of the seawater through which the vessel is passing is of major significance. Cold water washing around the ship's side, bottom and across the decks rapidly reduces the temperature of the cargo and makes the task of heating it much harder. Warm seawater, however, has the reverse effect and can be very useful in helping to maintain the temperature of the cargo with a minimum amount of steam. Steam is used to heat the oil inside ship's tank. It is piped from the boilers along the length of the vessel's deck. Generally the catwalk or flying bridge is used for this purpose.
The main cargo heating steam and exhaust pipes being secured to either the vertical or horizontal girder work immediately below the foot treads. At intervals, manifold is arranged from which the steam for he individual cargo tanks is drawn. Each tank has its own steam and exhaust valves, which enables the steam to be shut off or reduced on any of the tanks at will. Generally the main steam lines are well lagged, but it is obviously impractical to lag the individual lines leading from the manifold to the cargo tanks.
The heating arrangements in the actual cargo tanks consist of a system of coils, which are spread over the bottom of the tank at a distance of six to eighteen inches from the bottom plating. In wing tanks it is usual practice to extend the coil system as far as the turn on the bilge but not up the ship's side.
