Method for controlling impurities in an installation for the separation of air

In a method for controlling operation of an installation for separation of air by cryogenic distillation comprising a double distillation column wherein a top of a medium pressure column and a base of a low pressure column are thermally interconnected by a vaporizer-condenser supplied with liquid oxygen from a bath of liquid oxygen in the base of the low pressure column and impurities are purged from the bath by removal of liquid oxygen from the bath through a purge line;

• the improvement comprising continuously measuring nitrous oxide in said bath, and upon detection of a rise in nitrous oxide content of the bath when the installation is operating under equilibrium conditions, increasing a flow of liquid oxygen through said purge line to lower the measured nitrous oxide content of the bath.

In a method for controlling operation of an installation for separation of air by cryogenic distillation comprising a plurality of switching adsorbers through at least one of which air passes at an adjustable pressure and for an adjustable time whilst at least one other said adsorber undergoes purging, thus-purified air then passing to a double distillation column wherein a top of a medium pressure column and a base of the low pressure column are thermally interconnected by a vaporizer-condenser supplied with liquid oxygen from a bath of liquid oxygen in the base of the low pressure column;

• the improvement comprising continuously measuring nitrous oxide in said bath, and upon detection of a rise in nitrous oxide content of the bath when the installation is operating under equilibrium conditions, changing at least one of said adjustable pressure and adjustable time so as to lower the measured nitrous oxide content of the bath.