There are three techniques about gas reliquefaction: nitrogen expansion liquefaction, mixed refrigeration liquefaction and direct refrigeration liquefaction.
● Nitrogen expansion refrigeration liquefaction uses the gas as medium and including four processes: isentropic compression, isobaric cooling, isentropic expansion and isobaric decalescence. Nitrogen does not change its phase during this process. This technology is simple and easy to implement but it is not efficient and high power consuming.
● Mixed refrigeration liquefaction is a secondary cooling liquefaction technique consisting of two refrigeration cycles namely mixed refrigerant system and propane system. This technique is converted from land-based application with advantages of low energy consumption, containerized structure, easy installation and competitive construction cost.
● The direct refrigeration liquefaction technology uses the gas as medium. It gets freezing capacity from processes as follows: isentropic compression by compressor, cooling by after-cooler and regenerator, Isentropic adiabatic expansion in the turbine expander and work externally, obtaining low-temperature air flow and cooling capacity. This is a new marine technology with compact and space saving structure suitable for vessels, famous for low energy consumption and with competitive construction cost.
