Abstract: A method and system for producing liquefied and sub-cooled natural gas by means of a refrigeration assembly using a single phase gaseous refrigerant comprising: at least two expanders (1-3); a compressor assembly (5-7); a heat exchanger assembly (8) for heat absorption from natural gas; and a heat rejection assembly (10-12). The novel features according to the present invention are arranging the expanders (1-3) in expander loops; using only one and the same refrigerant in all loops; passing an expanded refrigerant flow from the respective expander into the heat exchanger assembly (8), each being at a mass flow and temperature level adapted to de-superheating, condensation or cooling of dense phase and/or sub-cooling of natural gas; and serving the refrigerant to the respective expander in a compressed flow by means of the compressor assembly having compressors or compressor stages enabling adapted inlet and outlet pressures for the respective expander.

Abstract: A method and system for producing liquefied and sub-cooled natural gas by means of a refrigeration assembly using a single phase gaseous refrigerant comprising: at least two expanders (1-3); a compressor assembly (5-7); a heat exchanger assembly (8) for heat absorption from natural gas; and a heat rejection assembly (10-12). The novel features according to the present invention are arranging the expanders (1-3) in expander loops; using only one and the same refrigerant in all loops; passing an expanded refrigerant flow from the respective expander into the heat exchanger assembly (8), each being at a mass flow and temperature level adapted to de-superheating, condensation or cooling of dense phase and/or sub-cooling of natural gas; and serving the refrigerant to the respective expander in a compressed flow by means of the compressor assembly having compressors or compressor stages enabling adapted inlet and outlet pressures for the respective expander.

Abstract: A system for cooling a boil-off gas (BOG) stream prior to compression in a boil-off reliquefaction plant, comprising a line (10) for feeding BOG into a compressor (11; 11?) prior to heat exchange with a closed-loop refrigeration system. The refrigeration system comprising compressors (2, 3, 4) and expanders(8, 9) and a number of heat ex-changers for heat exchange with the BOG stream. The expanders (8, 9) are arranged in series. A precooler in the feed line (10) is fluidly connected (32, 33) to the closed-loop refrigeration system, whereby said BOG is pre-cooled in heat exchange with a portion of the coolant in the closed-loop refrigeration system prior to said compression.