Sea transport of bulk natural liquefied gases - LNG & LPG carriers Safety & operational matters
Carrying liquefied gases in bulk
A liquefied gas is the liquid form of a substance which, at ambient temperature and at atmospheric pressure, would be a gas.The same liquefied gas at the same temperature, in a closed container, will always have the same pressure. Therefore, butane at the same temperature has an identical pressure irrespective of whether the container is the tank of a gas carrier, a simple gas cigarette lighter, a storage tank, or a domestic gas bottle All are pressurised containers.
Most liquefied gases are hydrocarbons and the key property that makes hydrocarbons the world’s primary energy source – combustibility – also makes them inherently hazardous. Because these gases are handled in large quantities, it is imperative that all practical steps are taken to minimize leakage and to limit all sources of ignition.
Gases are always liquefied for transportation in bulk simply because more cargo can be fitted in a given volume. Typically, but dependent upon the product, 1 volume of liquefied petroleum gas (LPG) is equivalent to over 250 volumes of vapour and 1 volume of liquefied natural gas (LNG) equivalent to 600 volumes of vapour. Carrying and handling liquefied gas cargo onboard poses significant potential hazards including risk of injury or death,threats to environment and each person working on a gas carrier and terminal ashore needs to understand the risks involved, obtain the necessary training and take all the needed precautions.
LNG used as fuel for ships gas engines is the best choice as far as the emissions of CO2, SOx and NOx are concerned. When considering the life-time cost for a gas engine , LNG is also the best fuel. Our site is based on trans-ocean transport of liquefied gases in bulk , various gas carrier operation, onboard safety procedure, safe cargo loading , unloading , care at sea passage & other industry relevant safe practices .
The Principal Products - Whilst the hydrocarbon gases methane, ethane, propane and butane may be regarded principally as fuels, the LPGs are also important as feedstock in the production of the chemical gases.
All gas cargoes are transported in liquid form (ie they are not carried as a gas in its vapour form) and, because of their physical and chemical properties, they are carried either at:
pressures greater than atmospheric, or at
temperatures below ambient, or a combination of both.
Therefore, gas carriers are generally grouped as follows:
i) Fully Pressurised
ii) Semi-pressurised and Refrigerated
iii) Fully Refrigerated
Gas carriers are divided into two main groups:
Liquefied Petroleum Gas (LPG) Carriers, which are designed to carry mainly butane, propane, butadiene, propylene, vinyl chloride monomer (VCM) and are able to carry anhydrous ammonia.
Liquefied Natural Gas (LNG) Carriers, which are designed to carry liquefied natural gas (which is mostly methane).
On the basis of Tank Types used gas carriers may be classified as below:
Type ‘A’: Constructed of plain surfaces (prismatic tanks)
Type ‘B’: Spheres
Type ‘C’: Cylindrical pressure vessels
(Note. These tanks are used where appropriate, regardless of gas carrier type)
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