Patent ID: 7370494

Claim:
A method of producing, in gaseous form and under high pressure, at least one fluid chosen from oxygen, argon and nitrogen, in which method, in stable operation, the air is compressed in a compressor, the compressed air is purified and sent into a heat exchange line of the installation in which it is cooled, the compressed, purified and cooled air is separated in a system of columns of the installation comprising at least one distillation column, a fluid is withdrawn in the liquid state from one column of the system of columns, the said fluid in the liquid state is brought to the high pressure, vaporized by heat exchange with air and the vaporized liquid is warmed at this high pressure in the heat exchange line of the installation: a) a flow of compressed nitrogen in the process of cooling in the heat exchange line is extracted from the latter at an intermediate temperature of the exchange line; b) the nitrogen is supercharged at the intermediate temperature in a cold blower up to the high pressure; c) the supercharged nitrogen is reintroduced into the heat exchange line; d) at least a portion of the supercharged nitrogen is sent into an expansion turbine, the expanded nitrogen then being sent into one column of the system of columns, wherein, during start-up of the installation and/or when the inlet temperature of the turbine inlet falls below a predetermined threshold and/or during a change of operation, at least one portion of the nitrogen extracted from the exchange line and supercharged in the cold blower is sent upstream of the expansion turbine without passing through the exchange line.