a float 16 which makes it possible to follow the changes in level in the closed processing tank 1 the crude petroleum once processed is stored until the time of its leaving via the outlet pipe 8 in static or dynamic manner the processing gas 3 is compressed by a compressor 4 a current of the processing gas 3 being projected via the injector 4 a onto and tangentially to the free surface of the crude petroleum the current of the processing gas 3 making a particular angle with the free surface of the crude petroleum above the plate 2 b before reaching the surface which angle can vary between zero and thirty degrees the angle being preferably between 0 and eight degrees but preferably five degrees the injector 4 a is also joined and connected to the plate 2 b so that it can follow the level of the crude petroleum in the tank 1 the compressor 4 is fed by the gas present in the tank after it circulates through the exchanger 14 with addition adding if necessary of compatible gas 21 coming from the outside the exchanger 14 receives the gaseous mixture 6 through the pipe 14 a which is cooled by an outside refrigerant 15 the condensates of the exchanger 14 are sent on through the pipe 19 for subsequent processing.