Enhanced oxygen recovery and energy efficiency in a reconfigured single column air separation unit producing pure and impure oxygen simultaneously

Abstract

Oxygen produced at 99.5 % purity and 30−40 bar pressure is used for converting pig iron to steel in integrated steel and iron plants. But oxygen at 90 % purity and 8−10 bar is sufficient for enriching air for the blast furnace that converts iron ore to pig iron. However, the same high purity and pressure oxygen enriches air that is a waste of purification and internal compression energy. Although basic configuration having a single air distillation column has low absolute power consumption than a double column plant, its low 70 % oxygen recovery due to impure reflux (liquid air) leads to higher specific power. Oxygen recovery of reconfigured single column plant is enhanced to 99 % by switching to pure liquid nitrogen reflux generating low and high purity oxygen simultaneously at the required pressures by internal compression. The reconfigured process of the single column plant consumes 15–25 % and 23–40 % lower specific power than basic single and double column plants respectively. Similarly, the Levelized total hourly cost (capital and operating) of producing oxygen reduces by 10 % and 14 %. Producing pure and impure oxygen at required pressures and proportions demand appropriate flexibility of operation of compressors and turbines that ought to be planned and incorporated right at the design stage.