The present invention relates to a feed distribution device in separation columns and a method of operation. In particular it relates to distillation columns in which the feed stream is substantially liquid phase, or a mixture of gas and liquid upstream of the column, but where the feed vaporizes or vaporizes more when it enters the column. More specifically, the feed distribution device contains a plurality of opening which allow the feed to vaporize inside the column and where the openings are maintained in critical condition during operation. Significant advantage is achieved through the implementation and use of the present feed distribution device.