A systematic dynamic exergy method is proposed for identifying exergy performance dynamically to achieve efficient operation, and then examined through its applications for air compression process and CO2 compression and purification unit (CPU). In this method, the dynamic exergy calculation is based on complicated coupling procedures among steady-state simulation, dynamic simulation, and exergy calculation. Then, dynamic exergy property, energy consumptions for operating conditions, sensitivity of operating parameters, and the effect of control system can be acquired in the dynamic exergy evaluation. It is found that the proposed dynamic exergy method would be a powerful tool to uncover important information for operators and engineers. From the results of CPU, flue gas composition ramp up process runs more effectively than that of flow rate ramp down and composition ramp down processes. CPU is more sensitive to the variation of flue gas composition than that of flue gas flow rate since smaller sensitive factor is obtained in the latter case. Control system saves energy during flue gas composition ramp down process however consumes energy in flow rate ramp down and composition ramp up processes. Meanwhile, smaller control costs are required for flue gas flow rate ramp case than that of composition ramp case. (C) 2016 Elsevier Ltd. All rights reserved.