To get from the steady state operating point to a dry and cold state, the mass flow of the feed stream and the reboiler duty are gradually reduced to zero. All product valves are opened, and the column is progressively run dry. At the same time, nitrogen with a temperature of 20 °C is introduced into the column. When all the liquid is removed from the column and it is only filled with nitrogen at a pressure of 0.95 bar, as well as a temperature of 20 °C, the inert gas valve and all product valves are closed. This marks the initial point for the start-up operation.