Tank, liquid circulation system and operating method

A liquid circulation system comprising:

• a rotor located within a tank,
• an electric component accommodated within the tank,
• a power unit comprising a stator having a plurality of coils, a control unit and an electric terminal box, the power unit is attached outside the tank, and
• an exterior tank wall of the tank that is non-magnetic and that is located next to the rotor and to the stator between the rotor and the stator, the power unit is attached on the exterior tank wall,
• wherein
• the tank is configured as a sub-sea component,
• the rotor faces the electric component so that there is no exterior tank wall between the rotor and the electric component,
• an axis (R) of rotation of the rotor is in parallel with the exterior tank wall next to the rotor,
• the rotor is configured to be rotated by the stator through the exterior tank wall by means of a varying electromagnetic field driven by the stator to circulate a liquid within the tank and a paddle portion of the rotor is configured to rotate around the axis (R) of rotation is distant from the exterior tank wall,
• the coils of the stator are arranged along the axis (R) of rotation of the rotor so that the coils are arranged in a linear manner along a straight line, and
• at least a driving portion of the rotor is of helical shape.