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The best way to transport gases is in liquid form. Gases are liquefied by means of cooling or overpressure. Liquefied gases can be transported merely on special-purpose ships, so called LPG/LEG tankers.
These ships are almost floating chemical plants, looking at the complex technology of the gas plant, the tanks and the piping system. Shipyard staff involved in the construction of the ships need special know-how, not only in terms of construction, but also of the initial operation. Meyer Werft has these experts: since 1961 the shipyard has built more than 47 LPG/LEG tankers for carrying liquefied gases and chemicals.
On an international scale Meyer Werft has a top reputation for building both LPG/LEG tankers and separate tanks. But the shipyard also gained a lot of experience and expertise in the construction of pressure vessels and gas tanks so that gas tanks for various applications could be built from a large variety of materials.
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It is a vessel of Ship Type 2G, and it has been built to transport LPG/NH3/VCM. It has three independent Prismatic IMO type-A cargo tanks of the fully-refrigerated type.
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For gas- and chemical transportation the inert gas needs to be of high purity. For many applications, oxygen levels of 0.5% or even 0.1% are required, in combination with a water dew-point of about -45 °C and sometimes lower
(-65 °C). Also here, the burner is the heart of the system as the inert gas needs to be absolutely soot free in the first place. This is achieved with the Ultramizing® Combustion system. When the gas leaves the generator, it has the right composition, but it is saturated with 100% water and has to be dried. The drying process takes place in two steps. In the first step of the refrigerant cooler, the gas temperature is lowered to 5 °C which results in condensation of a great quantity of water. In the second stage the inert gas is dehumidified further in a double vessel type drying-unit using activated alumina or adsorbent. The whole process operates under a pressure of about 0.3 bar(g).
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For lower capacities and for applications where high delivery pressure is required, like for instance on LPG carriers, the inert gas is compressed by a rotary screw type compressor. The compressor is working at the same time as a dryer by condensing most of the water in the after cooler. However, for low dew-point an absorption dryer will be required where the inert gas is dried to the final dew-point.
Combustion type nitrogen generators:
Nitrogen can be generated by the same high pressure type inert gas generator by adding a CO2 stripper. This stripper removes the CO2 in the inert gas (originally N2 + CO2) by in a double vessel type adsorption system by means of molecular sieves. This type of nitrogen generator is specially used in cases of high capacities and high purity.
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