Part of the liquefied gas is pumped out (18) and super-cooled in a heat exchange system (22) before it is re-injected into t tank (10). In addition, part of the evaporated gas (16) is extracted intermittently, compressed in a compressor (36) and injecte into the extracted liquid to form a mixture which is then fully liquefied and super-cooled in the heat exchange system. The heat exchanger is designed to treat a fluid that is mainly liquid on entry. The liquid/compressed gas mixture injected the heat exchanger is in molar ratio 50-100% liquid, preferably 70-100%. The system applies to several tanks, with the mixture b taken from at least one tank and re-injected into at least one tank after passing through the heat exchanger. The heat exchanger uses a cooling fluid such as gaseous nitrogen or the products from the tanks and cools the liquid/gas mixture by 1-20 degrees C, preferably 3-17 degrees C. An intermediate storage capacity for the super-cooled liquid (30) is placed betw the heat exchanger and a control valve (26). The super-cooled liquid is re-injected into the tank at the liquid level and/or the level. The liquefied gas is a gas which cannot be distributed in liquid form at 15 degrees C, whatever the pressure, such as liquefied natural gas (LNG) or hydrogen. Alternatively the liquefied gas is liquefied petroleum gas (LPG). The cooling liquid in heat exchanger can be polypropylene, a freon, an HCFC or the product in the tank.
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