Method for controlling the internal pressure of a cryogenic tank

A method for controlling the internal pressure of a cryogenic tank (100) containing a liquid fraction (1002) and a gaseous fraction (1004) of a fluid, the enthalpy of which can be lowered during isothermal compression in the liquid phase, the method comprising the following steps:

• withdrawal of a portion of the liquid fraction to obtain a withdrawn portion defined in state A by:
• a first temperature T1,
• a first pressure P1,
• a first enthalpy E1, and
• a first density D1,
• substantially isothermal compression of the withdrawn portion to obtain a compressed portion defined in state B by:
• a second temperature T2 substantially equal to the first temperature T1,
• a second pressure P2 greater than the first pressure P1, and
• a second density D2 greater than the first density D1,
• said compression being intended to lead to a decrease in enthalpy between the first enthalpy E1 in state A and a second enthalpy E2 in state B,
• expansion of the compressed portion to obtain an expanded portion defined in state C by:
• a third temperature T3 less than the second temperature T2,
• a third pressure P3 less than the second pressure P2, and
• a third density D3 less than the second density D2 and greater than the first density D1,
• injection of the compressed portion or of the expanded portion into the tank (100),
• said expansion being carried out after the injection step when the compressed portion is injected into the tank (100), or
• said expansion being carried out between the compression step and the injection step when the expanded portion is injected into the tank (100).