Cryogenic air separation units are widely used in industry, which consume a large energy and need to produce a huge amount of need of nitrogen, oxygen and argon products with high purity. High purity distillation columns are critical unit operations in cryogenic air separation plants. In this paper the low pressure distillation column is investigated by using a steady state model. The first principles mathematic model of the column is firstly developed, and the pressure, temperature and static liquid nitrogen, oxygen and argon concentrations in the upper column are presented. The obtained results give important information on the variation of temperature, pressure, component concentrations and molar flows within the distillation column. The study highlighted the importance of considering air as ternary mixture. The separation process performance is significantly influenced by the location of side draw of argon and reflux ratio at the top of the column

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