Method for liquefying a methane-rich gas to be processed, and corresponding facility

A method for liquefying a gas to be processed comprising at least 50% by volume of methane, the method comprising the following steps:

• purification of the gas to be processed to obtain a purified gas,
• precooling of the purified gas to obtain a precooled gas having a temperature less than or equal to −15° C., the precooling being performed by heat exchange with a precooling refrigeration cycle,
• liquefaction of the precooled gas, in a liquefaction unit, to obtain a liquid stream, with a subcooling of the liquid stream of less than or equal to 5° C. at the outlet of the liquefaction unit, the liquefaction unit including a Stirling refrigeration cycle distinct from said precooling refrigeration cycle and implementing a first refrigerant, the Stirling refrigeration cycle comprising a precooling of the first refrigerant by heat exchange with a second refrigerant of a precooling refrigeration cycle distinct from a Stirling cycle,
• subcooling of the liquid stream to obtain a subcooled liquid stream, and
• expansion of the subcooled liquid stream to obtain a liquefied gas.