Abstract: A plate heat exchanger, having a multiplicity of plates which run parallel to one another, wherein in each case a fin is arranged between two adjacent plates, with the result that a multiplicity of parallel ducts are formed, and an optical waveguide for measuring the temperature of the plate heat exchanger. The optical waveguide is arranged in a groove in a fin or a groove in a plate of the plate heat exchanger. A method for determining the temperature of a plate heat exchanger using the structure described.

Abstract: A process is described for removing a nitrogen-rich fraction from a feed fraction containing essentially nitrogen and hydrocarbons, wherein the feed fraction is partially condensed and fractionated by rectification into a nitrogen-rich fraction and a methane-rich fraction. According to the invention during an interruption in the supply of the feed fraction, the separation column(s) (T1/T2) used for the fractionation by rectification and also the heat exchangers used for the partial condensation (E1) of the feed fraction and the cooling and warming of process streams occurring in the fractionation by rectification (E2) are kept by means of one or more differing cooling media (6-11) at temperature levels which correspond essentially to the temperature levels during standard operation of the separation column(s) (T1/T2) and the heat exchangers (E1, E2).

Abstract: A process is described for removing a nitrogen-rich fraction from a feed fraction containing essentially nitrogen and hydrocarbons, wherein the feed fraction is partially condensed and fractionated by rectification into a nitrogen-rich fraction and a methane-rich fraction. According to the invention during an interruption in the supply of the feed fraction, the separation column(s) (T1/T2) used for the fractionation by rectification and also the heat exchangers used for the partial condensation (E1) of the feed fraction and the cooling and warming of process streams occurring in the fractionation by rectification (E2) are kept by means of one or more differing cooling media (6-11) at temperature levels which correspond essentially to the temperature levels during standard operation of the separation column(s) (T1/T2) and the heat exchangers (E1, E2).