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 a first 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 with a second energy consumption lower than the first energy consumption
- 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 of the first liquid oxygen from the bottom of the low-pressure column, 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 an 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 a lower region of the low-pressure column and passed into an 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 a 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 of gaseous nitrogen, 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.