The air contains 0.932% argon. When 99.6% oxygen is to be produced from the upper tower, 1.05% argon must be contained in the nitrogen discharge. From the perspective of separation process, the distillation section of the upper tower (below the liquid inlet) is basically oxygen-argon separation, while in the distillation section (above the liquid inlet) then it is basically nitrogen-oxygen (argon) separation. The boiling point of argon and oxygen is relatively close (the boiling point of oxygen under 0.1013MPa is-182.97 ℃, and that of argon is-185.7 ℃), so it is relatively difficult to separate. In the distillation section, such a situation often occurs. In the process of nitrogen-oxygen separation, the oxygen component is not separated clean, and the argon component basically escapes together with the oxygen component in the nitrogen discharge, reduce the purity of nitrogen. If it is required to produce high purity nitrogen, the oxygen component should be completely separated from the nitrogen, then the argon component and the oxygen component may be condensed by the downstream liquid together. The result is that while reducing the oxygen component in the nitrogen discharge, the argon component in the product oxygen increases and the purity of oxygen decreases.
In order to produce nitrogen with high purity while improving the purity of oxygen, a certain amount of gas containing high argon concentration should be extracted from the distillation section as the distillation gas.
