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1. A method for oxygen production by low-temperature separation of air with variable energy consumption in a distillation column system having a high-pressure column, a low-pressure column as well as a main condenser and a side condenser which are both in the form of condenser-evaporators, wherein in the method
atmospheric air is compressed to a total air pressure in a main air compressor, cooled in a main heat exchanger and fed at least in part to the high-pressure column, in the main condenser, gaseous nitrogen from the high-pressure column is at least partially liquefied, at least a portion of the liquid nitrogen generated in the main condenser is used as reflux in at least one of the columns of the distillation column system, a first liquid oxygen stream from the bottom of the low-pressure column is introduced into the side condenser and is at least partially evaporated therein in indirect heat exchange with at least a portion of the compressed and cooled feed air, at least a portion of the evaporated first liquid oxygen stream is obtained as a gaseous oxygen product, in a first operating mode with higher energy consumption a first amount of the first liquid oxygen stream from the bottom of the low-pressure column is introduced into the side condenser and a first amount of air is compressed in the main air compressor to a first outlet pressure,in a second operating mode
a second amount of air, which is smaller than the first amount of air, is compressed in the main air compressor, a second amount of the first liquid oxygen stream from the bottom of the low-pressure column, which is smaller than the first amount, is introduced into the side condenser, and a second liquid oxygen stream is fed to the side condenser in addition to the first liquid oxygen stream,characterized in that
in both operating modes an intermediate liquid from an intermediate point of the low-pressure column is introduced into the evaporation space of the main condenser, and at least a portion of the vapor generated in the main condenser is introduced into the low-pressure column, an oxygen stream is removed from the lower region of the low-pressure column and passed into the evaporation space of an additional condenser which is in the form of a condenser-evaporator, at least a portion of the gas formed in the evaporation space of the additional condenser is introduced as rising vapor into the low-pressure column, the oxygen evaporated in the side condenser is heated in the main heat exchanger and obtained as the gaseous oxygen product, a first nitrogen stream from the distillation column system is compressed in a cold compressor and then introduced at least in part into the liquefaction space of the additional condenser, and at least a portion of the liquid nitrogen generated in the additional condenser is used as reflux in at least one of the columns of the distillation column system, wherein in the first operating mode a first amount of nitrogen is compressed in the cold compressor, a first amount of gaseous nitrogen from the high-pressure column is introduced into the main condenser, and the first amount of air is compressed in the main air compressor to a first total air pressure, and in the second operating mode a second amount of nitrogen, which is greater than the first amount of nitrogen, is compressed in the cold compressor, a second amount of gaseous nitrogen from the high-pressure column, which is smaller than the first amount, is introduced into the main condenser, and the second amount of air is compressed in the main air compressor to a second total air pressure which is lower than the first total air pressure. |
