Installation for processing a stream of LNG obtained by means of cooling using a first refrigeration cycle, the installation, being of the type comprising:
- means for sub-cooling the stream of LNG comprising a first heat-exchanger in order to bring the LNG stream into a heat-exchange relationship with a refrigerating fluid;
- and
- a second semi-open refrigeration cycle which is independent of the first cycle, characterised in that it comprises:
- an intermediate turbine for dynamic expansion of the stream of sub-cooled LNG from the first heat-exchanger;
- means for cooling and expanding the stream from the intermediate turbine;
- a distillation column which is connected to the cooling and expansion means;
- means for recovering a stream of denitrogenated LNG at the bottom of the column, and means for recovering a stream of gas at the top of the column,
- a stage compressor which is connected to the means for recovering the stream of gas at the top of the column;
- and
- means for extracting a first portion of the top stream of gas tapped at an intermediate pressure stage of the compressor in order to form a stream of combustible gas;
- and in that the second refrigeration cycle comprises:
- means for forming an initial stream of refrigerating fluid from a second portion of the top gas compressed to the intermediate pressure;
- means for compressing the initial stream of refrigerating fluid to a high pressure PH which is greater than the intermediate pressure PI in order to form a compressed stream of refrigerating fluid;
- a second heat-exchanger in order to cool the compressed stream of refrigerating fluid;
- means for separating the compressed stream of refrigerating fluid from the second heat-exchanger into a main cooling stream and a sub-cooling stream of the LNG;
- a third heat-exchanger for cooling the sub-cooling stream;
- means for introducing the sub-cooling stream from the third heat-exchanger into the first heat-exchanger;
- means for expanding the sub-cooling stream from the first heat-exchanger to a low pressure PB which is lower than the intermediate pressure PI in order to form a substantially liquid sub-cooling stream of the LNG;
- means for circulating the substantially liquid sub-cooling stream in the first heat-exchanger in order to form a reheated sub-cooling stream;
- a main turbine for expanding the main cooling stream substantially to the low pressure PB;
- means for mixing the cooling stream from the main turbine with the sub-cooling stream which has been reheated in order to form a mixed stream;
- means for circulating the mixed stream successively in the third heat-exchanger then in the second heat-exchanger in order to form a reheated mixed stream;
- means for introducing the reheated mixed stream in the compressor at a low pressure stage which is located upstream of the intermediate pressure stage.