ABSTRACT In this paper, energy, exergy, and sustainability analyses are performed on the Karun petrochemical nitric acid plant in Mahshahr at varying ambient temperatures to reveal realistic optimization opportunities. All plant components have been analyzed individually by using mass, energy, and exergy balance equations. Results regarding energy, exergy, and sustainability evaluations of the equipment have been presented in the individual table. The energy analysis indicates that the system’s energy efficiency is 30.9% and introduces the absorber column as the equipment with the highest heat transfer to the environment in the entire plant (6889 kW). The exergy analysis revealed that the exergy efficiency of the entire system had variations ranging from 13.39% to 14.72%, which is inversely proportional to the increase in dead state temperatures. The maximum amount of exergy destruction is calculated for the converter (5129 kW at 45°C). In addition, exergy analysis identified the converter as the component with the most potential for improvement (2918 kW at 45°C). On the other hand, the highest sustainability index is found for the absorber column (1.616 at 15°C). Moreover, by selecting the optimal intermediate pressure for the compressors, the power consumption of the air compression system has been reduced by 185.9 kW, and its exergy efficiency has increased by 3%.