|
A gas carrier (or gas tanker) is a ship designed to transport LPG, LNG or liquefied chemical gases in bulk.〔Gas Carrier definition as per DNV http://www.dnv.com/industry/maritime/shiptypes/gascarrier/index.asp〕 ==Types== Fully pressurized gas carrier〔Fully Pressurised Ships http://www.liquefiedgascarrier.com/fully-pressurized-ships.html〕 The seaborne transport of liquefied gases began in 1934 when a major international company put two combined oil/LPG tankers into operation. The ships, basically oil tankers, had been converted by fitting small, riveted, pressure vessels for the carriage of LPG into cargo tank spaces. This enabled transport over long distances of substantial volumes of an oil refinery by-product that had distinct advantages as a domestic and commercial fuel. LPG is not only odourless and non-toxic, it also has a high calorific value and a low sulphur content, making it very clean and efficient when being burnt. Today, most fully pressurised oceangoing LPG carriers are fitted with two or three horizontal, cylindrical or spherical cargo tanks and have typical capacities between 3,500 and 7,500 m3. However, in recent years a number of larger-capacity fully pressurised ships have been built, most notably a series of 10,800 m3 ships, built in Japan between 2003 and 2013. Fully pressurised ships are still being built in numbers and represent a cost-effective, simple way of moving LPG to and from smaller gas terminals. Semi-pressurised ships〔Semi-Pressurised Ships http://www.liquefiedgascarrier.com/semi-pressurized-ships.html〕 These ships carried gases in a semi-pressurized/semi-refrigerated state however due to further development semi-pressurised/fully refrigerated gas carriers had become the shipowners' choice by providing high flexibility in cargo handling. These carriers, incorporating tanks either cylindrical, spherical or bi-lobe in shape, are able to load or discharge gas cargoes at both refrigerated and pressurised storage facilities. Ethylene and gas/chemical carriers〔Ethylene and gas/chemical carriers http://www.liquefiedgascarrier.com/ethylene-carriers.html〕 Ethylene carriers are the most sophisticated of the gas tankers and have the ability to carry not only most other liquefied gas cargoes but also ethylene at its atmospheric boiling point of −104 °C. These ships feature cylindrical, insulated, stainless steel cargo tanks able to accommodate cargoes up to a maximum specific gravity of 1.8 at temperatures ranging from a minimum of −104 °C to a maximum of +80 °C and at a maximum tank pressure of 4 bar. Fully refrigerated ships〔Fully refrigerated ships http://www.liquefiedgascarrier.com/Fully-Refrigerated-Ships.html〕 They are built to carry liquefied gases at low temperature and atmospheric pressure between terminals equipped with fully refrigerated storage tanks. However, discharge through a booster pump and cargo heater makes it possible to discharge to pressurized tanks too. The first purpose-built, fully refrigerated LPG carrier was constructed by a Japanese shipyard, to a United States design, in 1962. Prismatic tanks enabled the ship's cargo carrying capacity to be maximised, thus making fully refrigerated ships highly suitable for carrying large volumes of cargo such as LPG, ammonia and vinyl chloride over long distances. Today, fully refrigerated ships range in capacity from 20,000 to 100,000 m3. LPG carriers in the 50,000 - 80,000 m3 size range are often referred to as VLGCs (Very Large Gas Carriers). Although LNG carriers are often larger in terms of cubic capacity, this term is normally only applied to fully refrigerated LPG carriers. The main type of cargo containment system utilised on board modern fully refrigerated ships are independent tanks with rigid foam insulation. The insulation used is quite commonly polyurethane foam. Older ships can have independent tanks with loosely filled perlite insulation. In the past, there have been a few fully refrigerated ships built with semi-membrane or integral tanks and internal insulation tanks, but these systems have only maintained minimal interest. The large majority of such ships currently in service have been constructed by shipbuilders in Japan and Korea. Liquefied natural gas LNG carrier The majority of LNG carriers are between 125,000 and 135,000 m3 in capacity. In the modern fleet of LNG carriers, there is an interesting exception concerning ship size. This is the introduction of several smaller ships of between 18,000 and 19,000 m3 having been built in 1994 and later to service the needs of importers of smaller volumes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gas carrier」の詳細全文を読む スポンサード リンク
|