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LNG Carrier Type
The flower of ship technology, LNG carrier
Since LNG carriers need to design and build tanks that can withstand ultra-low temperatures of minus 163 degrees Celsius, the highest level of drying technology in the overall shipbuilding industry is required. do. LNG carriers can be largely classified into two types: MEMBRANE method and independent tank method MOSS type. of these methods The GAZTRANSPORT method and the TECHINIGAZ method are used in the MEMBRANE method, and the old TANK method is used in the independent TANK method. It has been established as a cargo containment system and is currently used in LNG carriers for maritime transportation.
Independent MOSS old TYPE-B TANK method Hyundai Merchant Marine, SK Shipping
A high degree of stress analysis is possible because of the simple structure supported by a cylindrical skirt without a heat shield. AL alloy A5083 or
9% NI steel is used, and the heat dissipation material, POLYSTYRANE foam or POLYURETHANE foam, is applied to the outer surface of the spherical tank and the cylindrical shape.
It is attached to the upper part of the skirt. The secondary barrier is reduced by partial isolation. This is done with enough time before the great destruction of the tank occurs.
This is because it has been proven in the tank fatigue mechanism analysis that a small amount of gas leakage can be detected. Independent spherical shape with thermal expansion measures
The tank is supported by a cylindrical skirt.
has been Because of this, the tank and skirt can be gently stretched.
MEMBRANE-type TANK method Hanjin Shipping, SK Shipping, Korea Shipping
Membrane is a very thin membrane of about 0.5 to 1.2 mm and has strength as an independent tank, and has only liquid tightness to prevent leakage of cargo.
There is no strength as a TANK. That is, the load of the cargo is transferred from the heat shield to the hull. There are two ways to do this, one is a thermal expansion countermeasure.
The TECHNIGAZ method uses wrinkled membranes, and the other uses the characteristics of INVAR and uses flat membranes.
There is a GAZTRANSPORT method.
TECHINIGAZ method
The characteristic of this method is the STAINLESS Membrane with 1.2mm thick corrugation used as the primary barrier, and the shrinkage caused by low temperature is the corrugated part.
Absorbed in wrinkles, almost no large stress occurs in the membrane. BALSA material was used as a heat dissipation material, and special plywood with a thickness of 2.4 mm was used as the secondary bulkhead.
The chosen one is called MARK I type and has many achievements. On the other hand, for the purpose of cost reduction and material reliability,
POLYURETHANE FOAM with GLASS fibers and GLASSCLOTH attached to both sides of the TRIPLEX CAL BOX as a secondary barrier)
The one used is called the MARK III type.
GAZ TRANSPORT MEMBRANE method Hanjin Pyeongtaek, Hanjin Muscat, Hanjin Suho, Hanjin Ras Lappan TYPE
The feature of the GT Membarane method is that it uses 36% Ni (INVAR INVARIABLE STEEL) with a thickness of 0.5 to 0.7 mm like the primary barrier.
there is. Since this INVAR has the characteristic of having a very small coefficient of thermal expansion, it is hardly affected by thermal expansion or contraction. As a heat insulator
Plywood boxes filled with PERLITE are being used. The feature of this method is that the primary barrier has almost the same level of liquid tightness and strength, so in case of leakage of the primary barrier,
The point is that the secondary barrier alone can safely support the cargo for a considerable period of time.
SPB method SELF-SUPPORTING PRISMATIC TYPE-B
This method is characterized by adopting an AL TANK with a track record in the same way as the square independent TANK used in conventional LPG carriers.
As the primary barrier, aluminum alloy 4508301 is used, and the inner wall of the tank has heat shields of the same aluminum alloy vertically and horizontally. This method is MOSS
Recognized as IMO TYPE B like TYPE, the secondary barrier has been reduced. Polyurethane foam was used as the heat dissipation material. TANK body
Several support blocks are put in to align with the hull, and the thermal expansion and contraction of the tank is absorbed by the slide structure of this support block. this
The method was independently developed by Japan's IHI, and two ships are currently being built and operating.
Comparison of characteristics between stand-alone TANK and MEMBRANE TANK method
| division | Moss Type (Independent tank type) | Membrane Type (TG/GT) |
|---|---|---|
| TANK function | It has the functions of TANK self-support and LNG load support. regardless of hull strength. | It has liquid-tightness and thermal expansion and contraction for LNG. |
| Heat insulation function | Has only the function of heat dissipation material itself. | There is no self-supporting and LNG load-bearing function. In addition to the heat dissipation function, it has the strength of LNG load bearing (function to transmit LNG load to the hull) |
| INNER HULL function (other than hull strength) |
Support tank load and LNG load at the bottom of the ship. | Supports insulation load and LNG load on the front side of the HOLD part. |
| Others | The cargo area is located on the upper deck, so the navigator's blind sector is large, and the windage area is wide, which hinders the turning performance of the ship. | The cargo area is located below the deck, so the viewing area is wide, and the windage area is smaller than that of general cargo ships, so the ship's maneuverability is less affected. |
LNG (Liquefied Natural Gas) A liquid state made by atmospheric pressure cooling of natural gas
| component | Boiling point (the temperature at which it liquefies under 1 atm) | Gas specific gravity (air=1) | Liquid specific gravity (boiling point/4℃ water) | gas volume/liquid volume | Exploded (to-air mixture ratio) | Fever (Kcal/kg) |
|---|---|---|---|---|---|---|
| Methane (CH4) | -161.5℃ | 0.555 | 0.425 | 630배 | 5~15 | 13,270 |
| Remarks | cryogenic | lighter than air | lighter than water | expands greatly when vaporized | flammable gas | high energy |
<Reference> Household propane gas is LPG (liquefied petroleum gas, which is different from LNG. Propane gas is heavier than air.
Liquefied natural gas (LNG) is consumed in huge quantities. A ship that carries such LNG is called an LNG tanker [LNG ship]. LNG is very
Because of the low temperature, the LNG tanker must be equipped with special facilities to maintain the low temperature. For this reason, the inner surface of the tank is made of stainless steel and aluminum alloy that are resistant to low temperatures.
materials are used. In addition, for insulation and explosion prevention, the hull is surrounded by a double cover. Connect several spherical tanks or use a metal film to
There is a method of embedding a sealed tank inside the hull. LNG does not cause environmental pollution like crude oil because it evaporates even if accidentally spilled into the sea.
LNG that leaks from the ranks little by little during transportation is not discharged, but is brought to the boiler and used to operate the steam turbine. Recently, fuel cells have been
An LNG tanker is being developed, which converts LNG directly into electric power without burning it to drive a motor. Motor ships are easy to control and operate with a small number of people.
There are advantages that can be