Air separation unit

Abstract

To provide an air separation unit capable of reducing the risk of combustion of a heat exchanger connected to an oxygen turbine. An air separation unit A 1 including a main heat exchanger 1 ; an intermediate-pressure rectification column 2 ; a low-pressure rectification column 4 ; a crude-argon column 5 ; a nitrogen condenser 3 ; a crude-argon condenser 6 ; an oxygen turbine 9 ; an oxygen turbine inlet pipe L 32 for feeding oxygen gas drawn out from a bottom section of the low-pressure rectification column 4 or a gas phase in a refrigerant storage section of the nitrogen condenser 3 into the oxygen turbine 9 via the main heat exchanger 1 , and feeding the oxygen gas to the main heat exchanger 1 again; an oxygen bypass pipe L 321 which branches from the oxygen turbine inlet pipe L 32 ; and a dilution stream pipe L 42 for drawing out a nitrogen-containing gas.

What is claimed is: 
     
         1 . An air separation unit comprising:
 a main heat exchanger in which feed air is introduced from a warm end and drawn out from a cold end;   an intermediate-pressure rectification column into which feed air drawn out from the main heat exchanger is introduced;   a nitrogen condenser in which a vapor stream is introduced from the intermediate-pressure rectification column, and is condensed and drawn out as a reflux liquid;   a low-pressure rectification column into which an oxygen-rich liquid drawn out from the intermediate-pressure rectification column is introduced;   an oxygen turbine, which expands and cools oxygen gas drawn out from a bottom section of the low-pressure rectification column or a gas phase in a refrigerant storage section of the nitrogen condenser, after the oxygen gas has undergone heat exchange in the main heat exchanger;   an oxygen turbine inlet pipe for feeding the oxygen gas to the oxygen turbine via the main heat exchanger, and feeding the oxygen gas to the main heat exchanger again;   an oxygen bypass pipe which branches from the oxygen turbine inlet pipe; and   a dilution stream pipe for drawing out a nitrogen-containing gas, in which the oxygen concentration is lower than the oxygen concentration in the oxygen gas drawn out from the bottom section of the low-pressure rectification column or the gas phase in the refrigerant storage section, as a dilution stream, and introducing the dilution stream into the oxygen turbine inlet pipe.   
     
     
         2 . The air separation unit according to  claim 1 , comprising:
 a gas flowmeter and a first flow rate regulation valve, which are provided in the oxygen turbine inlet pipe on the upstream side of the main heat exchanger and the oxygen bypass pipe;   a second flow rate regulation valve, which is provided in the oxygen bypass pipe on the upstream side of the main heat exchanger;   a third flow rate regulation/check valve, which is provided in the dilution stream pipe;   an oxygen concentration analyzer for measuring oxygen concentration and a fourth flow rate regulation valve, which are provided in the oxygen turbine inlet pipe downstream of the main heat exchanger; and   a liquid level sensor, which senses the liquid level of a refrigerant phase in the nitrogen condenser.   
     
     
         3 . The air separation unit according to  claim 1 , comprising:
 an oxygen concentration adjustment unit, which sets a target oxygen concentration corresponding to operation of a nozzle of the oxygen turbine, sets a dilution flow rate and an oxygen bypass flow rate so as to attain the target oxygen concentration, and adjusts the oxygen concentration of the oxygen gas flowing through the oxygen turbine inlet pipe.   
     
     
         4 . The air separation unit according to  claim 2 , comprising:
 an oxygen gas stream shut-off control unit, which, in a case where the oxygen concentration measured by the oxygen concentration analyzer exceeds a threshold at which it is determined that there is a severe risk of combustion in the oxygen turbine, performs control so as to interrupt an oxygen gas stream by closing the first flow rate regulation valve, open the third flow rate regulation/check valve, and introduce a dilution stream into the oxygen turbine inlet pipe as an inert gas.   
     
     
         5 . The air separation unit according to  claim 2 , comprising:
 an interlock which stops the oxygen turbine in a case where the oxygen concentration measured by the oxygen concentration analyzer exceeds a threshold at which it is determined that there is a severe risk of combustion in the oxygen turbine.