Water Eductors for LNG Tankers

LNG Tankers are specialized ships used to transport Liquified Natural gas (LNG) throughout the world. LNG is a specialized cargo and needs careful handling due to its very low temperature and tendency to ignite.
That’s why loading and un-loading of LNG is done as per set guidelines and procedures and vacuum plays an important role in it.

Water Eductors are essentially Liquid jet Vacuum Ejectors that operate on the basis of the jet Venturi principle.
Water Eductors utilize the energy in pumped water for their operation and can be put to use to create vacuum conditions at its suction inlet.

LNG Tankers utilize water eductors to create Vacuum for following purposes:

  1. In the inerting process followed for the LNG tanks.
    Before loading the LNG into tanks it is important to remove the oxygen and moisture present inside the tanks. To accomplish it the air inside the LNG tanks is evacuated by the Water Eductor and inert gas is filed in inside the tank through repeated processes.
  2. Vacuum as insulating layer for the LNG tank
    LNG is stored at a very low temperature in the LNG tankers. Maintaining the tanks at low temperature is important during transport. Hence the Tank are adequately insulated using multiple methods. As part of the insulation, a vacuum gap is maintained between the outside and inside shells of the tank. Water Eductors are used to create and maintain this vacuum.

Water Eductors tend to have large suction flows at ambient & low vacuum pressures, this helps the Water Eductor in performing rapid evacuation initially. This ability to generate large suction flows are particularly suited in evacuating the LNG tanks quickly during the inerting process.

A Water Eductor or Liquid jet Vacuum ejector can develop ultimate vacuum upto 30 Torr i.e 40mbar which is useful in achieving very high vacuum in the insulating gap of the LNG Tank.

Most importantly the same Water Eductor can be used for both the objectives.

Water Eductors are perfectly suited for LNG Tankers because of their below inherent characteristics
• Available in Bronze material – makes it possible to operate with Sea-water which is abundantly available on a LNG tanker
• The water Eductor commonly operates with wide range of motive water pressure from 2.5 bar(a) to 7 bar(a). The required pressure can be easily provided by the Ballast pumps / Fire Pumps onboard a LNG Tanker – hence no additional infrastructure is required for operation.
• Low Evacuation time during inerting process of LNG tanks
• Ability to develop high vacuum for the insulating layer of the LNG tanks
• Water Eductors do not contain any moving parts and have large internal passage areas, hence are not vulnerable to liquid entry or clogging by solid particles.
• As they have no moving parts, maintenance requirements are very less. Also it reduces largely the risk of abrupt breakdowns, helps in maintaining the regular production schedule