Performance improvement of air separation unit for an iron-steel industry using enhanced exergy analysis

Abstract

In this study, the thermodynamic performance of a real operating three-stage turbo/centrifugal type main air compressor for the air separation unit in an iron-steel industry was evaluated using both conventional and enhanced exergy analyses. Furthermore, the interaction and the potential for improvement of system components at two different airflow rates, 210,000 Nm3 h−1 and 240,000 Nm3 h−1, were investigated under real operating conditions. The results indicated that the conventional exergy analysis of the system yields efficiency rates of approximately 21.3% and 25.0% for these airflow rates, respectively. It was found that implementing operating conditions proposed by the enhanced exergy analysis could increase the system’s exergy efficiency to about 40.8% and 80.7%, respectively. The primary causes of exergy destruction in the compressor are generally attributed to frictions occurring in the impeller, diffuser, and volute, as well as shock waves and air circulation during the compression process. It was observed that system efficiency could potentially increase to 80.7% with improvements in compressors and pump. The study also determined that enhanced exergy analysis is beneficial for identifying losses in system components and is seen as a tool that complements conventional exergy analysis.