Air separation system

An air separation system comprising:

• a main heat exchanger;
• a higher-pressure column into which feed air that has passed through the main heat exchanger is introduced,
• a first condensing unit for condensing gas discharged from a column top portion of the higher-pressure column,
• a lower-pressure column into which oxygen-enriched liquid discharged from a column bottom portion of the higher-pressure column is introduced, and
• a crude argon column into which an argon-containing oxygen-enriched gas-liquid substance discharged from an argon extraction portion, which is an intermediate stage of a distillation portion of the lower-pressure column, is introduced, and also provided with:
• a process control unit for controlling components constituting the air separation system;
• an oxygen concentration estimating unit for estimating, by calculation, the oxygen concentration of the oxygen-enriched liquid that accumulates in the column bottom portion of the higher-pressure column;
• a flow rate estimating unit for estimating, by calculation, the flow rate of the oxygen-enriched liquid that has been discharged from the column bottom portion of the higher-pressure column and that is to be introduced into the distillation portion of the lower-pressure column;
• and
• a target temperature calculating unit for calculating a target temperature of the argon extraction portion on the basis of the flow rate of the feed air that has passed through at least a portion of the main heat exchanger and that is to be sent to the expansion turbine, the oxygen concentration of the oxygen-enriched liquid, and the flow rate of the oxygen-enriched liquid.