MAN B&W ME-C series for LNG Carriers. Reliquefaction technology
While reliquefaction is widely used in gas handling on land, it has been used on board ship so far only on LNG carriers.
Recently, the technology for reliquefying LNG on board ship has been matured and commercialised. The present analysis is based on the Moss Reliquefaction, sold worldwide by Hamworthy KSE.
The patented system (Moss RS) for reliquefying boil-off gas, establishes a solution for pumping LNG back to the tanks and selling more LNG to the buyers of gas.
The boil-off gas reliquefaction concept is based on a closed nitrogen cycle extracting heat from the boil-off gas. Several novel features such as separation and removal of incondensable components have resulted in a compact system with low power consumption.
The concept has the following technical merits:
The process can be described as follows.
The LNG boil-off os compressed by the low duty (LD) compressor (BOG compressor), and sent directly to the so-called cold box.
The cold box in which the boil-off is reliquefied is cooled by a closed refrigeration loop (Brayton cycle). Nitrogen is the working medium. Fig. 2 shows the standard Moss RS reliquefaction system.
Fig. 2. Standard Moss RS reliquefaction system.