Liquefying natural gas, comprises cooling natural gas by exchanging heat with first refrigerant mixture flowing in first circuit, injecting natural gas into separation system, and withdrawing first refrigerant mixture from first circuit

摘要

The method comprises cooling natural gas by exchanging heat with a first refrigerant mixture flowing through a first refrigeration circuit, injecting a portion of natural gas into a separation system, withdrawing the first refrigerant mixture from the first refrigeration circuit, injecting a portion of discharged first refrigerant mixture into the separation system, separating the portion of natural gas and the portion of discharged first refrigerant mixture in the separation system to obtain two components, and cooling natural gas by exchanging heat with a second refrigerant mixture. The method comprises cooling natural gas by exchanging heat with a first refrigerant mixture flowing through a first refrigeration circuit, injecting a portion of natural gas into a separation system, withdrawing the first refrigerant mixture from the first refrigeration circuit, injecting a portion of discharged first refrigerant mixture into the separation system, separating the portion of natural gas and the portion of discharged first refrigerant mixture in the separation system to obtain two components, cooling natural gas by exchanging heat with a second refrigerant mixture flowing in a second refrigeration circuit and the first refrigeration circuits, and injecting the obtained components into the first and/or second refrigerant circuits to modify the composition of the first and/or second refrigerant mixtures. The first refrigerant mixture is compressed and then condensed by cooling, is expanded and sprayed for cooling the natural gas, and is stored in a storage unit before expanded and vaporized to cool the vaporized natural gas. The portion of first refrigerant mixture is withdrawn from the storage unit before the injection of the first mixture into the separation system. The natural gas is cooled until to obtain liquid natural gas. The second refrigerant mixture is compressed and cooled using an external fluid cooling before the second mixture is cooled by exchanging heat with the second refrigerant mixture. The step of withdrawing the portion of the refrigerant mixture is carried out in the first and/or second refrigeration circuit. The refrigerant mixture is withdrawn from the storage unit when the step of withdrawing the refrigerant mixture is carried out in the first and second refrigeration circuits. The refrigerant mixture is subcooled by exchanging heat with the first refrigerant circuit before the mixture is injection into the separation system. The liquefied natural gas is denitrogenated in a denitrogenation unit to obtain a nitrogen-rich fraction and a poor-nitrogen liquefied natural gas, where a portion of the nitrogen-rich fraction is injected into a refrigeration circuit.