Gas tankers | Off shore

Extra space means extra money: gas safely and economically underway

Refrigeration technology for marine systems-LNG gas tanker

The import of liquefied natural gas (LNG), delivered by ship, is on the increase. One reason is that the gas reserves of some countries are dwindling. Another is that countries would like to free themselves from dependence on single importers of gas. Depending on the route, gas transport by ship can even be more economical than via pipeline – and the required infrastructure has grown accordingly. More and more facilities, for example, are now required for regasification – and the demand for refrigeration technology placed on GEA has accordingly grown as well.

When gas is cooled to - 163 °C, it liquefies and shrinks to 1/600th of its uncompressed volume. Transport of the energy-laden liquid takes place in LNG tankers in special, insulated pressurized tanks (today, frequently preferred in the form of membrane tanks). In contrast to traditional spherical tanks, membrane tanks have the advantage that they fit more completely into the ship structure and optimally utilize the available cargo space. They consist of Invar®, a nickel-steel alloy that is especially tolerant to temperature fluctuations. Membrane tanks are not subject to deformation, even if below- zero temperatures prevail inside and tropical heat, outside.

GEA Refrigeration Technologies offers cryotechnology for gas liquefaction systems, refrigeration technology for gas storage in ship tanks, and temperature monitoring for regasification. We also deliver the required valves and fittings.

The sophisticated insulation of membrane tanks, however, cannot entirely prevent their contents from slowly warming, with part of the cargo evaporating. It is necessary to vent the evaporated gas to prevent the pressure in the tank from exceeding a safe level. As a rule, this vented gas is used as fuel for the ship. For this reason, many LNG tankers are turbine ships that can use natural gas as fuel. At the present time, it is not yet economical to re-cool this gas: i.e., to return the evaporated gas to a liquid state. Naturalgas prices, however, are rising, and experts assume that motor-driven ships with gas re-liquefaction systems will in the near future replace the present turbine ships. A number of advanced LNG tankers have already been designed for installation of gas re-liquefaction facilities, with the result that it will be possible to retrofit these ships at relatively little expense.