Separation device for separating a liquid/gas mixture in a heavy fraction mainly containing liquid and a light fraction mainly containing gas, comprising: - a separation vessel comprising at least one inlet, at least a first outlet for the discharge of the heavy fraction and at least a second outlet for the discharge of the light fraction, - separator for separating the mixture into the heavy and light fraction; - a vane type inlet device connected to the inlet for admitting the gas/liquid mixture to the vessel en for distributing the admitted gas/liquid mixture in the vessel, the inlet device comprising: an elongated support structure; is - a plurality of curved guiding vanes placed one behind the other and attached to the support structure, the guiding vanes being arranged so as intercept and deflect the admitted gas/liquid mixture sideways; - at least an agglomerator arranged close to the guiding vanes for agglomerating the liquid in the gas/liquid mixture.