The invention relates to a system for separating a mixture of gas and liquid into a heavy fraction and a light fraction, the system comprising: - a separation vessel having a vessel inlet for the supply of the mixture to be separated, an upper vessel outlet for the discharge of the light fraction and a lower vessel outlet for the discharge of the heavy fraction; - at least one inlet device for pretreatment of the incoming mixture, the inlet device, comprising a casing having a liquid outlet for the discharge of a first mixture part mainly containing liquid to a lower compartment of the separation vessel; and at least one demister element arranged at a position below the liquid outlet for separating liquid from the gas in the first mixture part flowing from the liquid output.