The air contains 0.932% of argon. When the upper tower wants to produce 99.6% of oxygen, it must contain 1.05% of argon in the nitrogen exhaust. From the perspective of the separation process, the stripping section (below the liquid-air inlet) in the upper column is basically an oxygen-argon separation, and the rectification section (above the liquid-air inlet) is basically a nitrogen-oxygen (argon) separation. . The boiling points of argon and oxygen are relatively close (the boiling point of oxygen is -182.97 ° C and the boiling point of argon is -185.7 ° C at 0.1013 MPa), and it is difficult to separate. In the rectification section, such a situation often occurs. In the nitrogen-oxygen separation process, the oxygen component is not cleanly separated, and the argon component basically escapes with the oxygen component in the nitrogen discharge, which reduces the purity of the nitrogen. If high-purity nitrogen is required, the oxygen component must be completely separated from the nitrogen, and the argon component may be condensed by the downstream liquid together with the oxygen component. As a result, while reducing the oxygen component in the nitrogen discharge, the argon component in the product oxygen is increased, and the oxygen purity is reduced.
In order to increase the purity of oxygen while producing high-purity nitrogen, a certain amount of argon-containing gas with a higher concentration in the rectification section must be extracted as the fraction gas.
