Exergy and energy analysis of a load regulation method of CVO of air separation unit

• Novel regulation method of ASU to reduce the electricity consumption was proposed.
• General exergy efficiency of ASU used the new method increased by 11%.
• Overall consumption of unit oxygen was used to evaluate energy-saving potential.
• Overall consumption of unit oxygen used CVO method reduces about 4.47–6.22%.

Generally in the Chinese iron and steel industry, the electricity consumption of cryogenic air separation unit (ASU) is about 14% of the overall electricity use. To reduce the electricity consumption, the combined variable oxygen (CVO) supply method for ASU is proposed. The exergy calculation program for ASU was developed and the detailed analysis of CVO method was performed. The results show that the general exergy efficiency (GEE) of ASU combined with a liquefaction unit is increased by 11 %–31 %. The consumption of unit oxygen, the total electricity consumption and the overall consumption of unit oxygen (OCUO) was compared. The OCUO is a suitable method to evaluate the energy-saving potential of CVO. Compared with the load regulation method of Automatic Load Control (ALC), the OCUO and the unit consumption of compression of CVO reduced more than 4.47% and 30%, respectively. It means that CO2 emission of every reduction 1% of gaseous oxygen release in a year in Chinese iron and steel industry will contribute approximately 0.75% to the 2020s CO2 emission reduction target of China.

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