Air separation unit

An air separation unit for delivering a regeneration gas for a regeneration process in a pre-purification unit, the air separation unit comprising:

• the pre-purification unit;
• a rectification column;
• a main heat exchanger;
• means for sending air to be purified in the pre-purification unit;
• means for sending purified airfrom the pre-purification unit to the main heat exchanger to be cooled;
• means for sending cooled air from the main heat exchanger to the rectification column;
• means for delivering a first waste gas from the rectification column to the main heat exchanger to be warmed;
• means for delivering a second waste gas from the rectification column to the main heat exchanger to be warmed;
• a first waste gas pipe configured to send warmed at least part of the first waste gas from the main heat exchanger to a mixing point;
• a second waste gas pipe configured to send at least part of the warmed second waste gas from the main heat exchanger to the mixing point;
• a regeneration gas pipe configured to send a mixture of the at least part of the first waste gas and the at least part of the second waste gas as regeneration gas to the pre-purification unit;
• a first waste gas control valve which is provided in the first waste gas pipe downstream of a main heat exchanger, a degree of valve opening thereof being adjustable;
• a first waste gas flow rate control unit configured to measure a gas flow rate in the first waste gas pipe downstream of the main heat exchanger, and to adjust the degree of opening of the first waste gas control valve so that a measured value which has been measured reaches a preset first waste gas flow rate set value;
• a second waste gas control valve which is provided in a second waste gas pipe downstream of the main heat exchanger, a degree of valve opening thereof being adjustable;
• a regeneration gas flow rate control unit configured to measure the gas flow rate in the regeneration gas pipe for circulating the regeneration gas, and to output a first output value based on a measured value which has been measured and a preset regeneration gas flow rate set value;
• and
• a control unit configured to use, as a target set value of the flow rate of a second waste gas, a value obtained by subtracting the first waste gas flow rate set value of the first flow rate measuring unit F7 from the flow rate set value of the regeneration gas flow rate, the control unit further configured to compare the first output value with a second output value based on a value obtained by subtracting the measured value of the first flow rate control unit from the measured value of the regeneration gas flow rate control unit, further configured to control the degree of opening of the second waste gas control valve on the basis of the lower of the values, and then further configured to adjust the second waste gas flow rate.