| abstract |
The method and the apparatus extract oxygen by separating air at a low temperature with variable energy consumption. A distillation column system having a high pressure column (34), a low pressure column (35) and a main condenser (36), an auxiliary condenser (26) and an additional condenser (37). The gaseous nitrogen (41, 42) extracted from the high pressure column (34) is liquefied in the main condenser (36) by indirect heat exchange with the intermediate liquid (43) of the lower pressure column (35). The first liquid oxygen stream (70) extracted from the bottom layer of the lower pressure column (35) is vaporized in the auxiliary condenser (26) by indirect heat exchange with the air used (25b) to extract the gaseous oxygen product (72). The additional condenser is used as a bottom heating device for the lower pressure column (35) and is heated by a first nitrogen stream (44) extracted from the distillation column system, which was previously compressed in a cold compressor (45). Compared to the first mode of operation with higher energy consumption, in the second mode of operation with lower energy consumption, less air used (1) is compressed to a lower pressure in the main air compressor (3) of the device, Less liquid oxygen (70) is introduced into the auxiliary condenser (26) from the lower pressure column (35) and more nitrogen is compressed within the cold compressor (45). Additionally, the second mode of operation further delivers a second liquid oxygen stream (73) to the auxiliary condenser (26). |