Energy Performance Versus Exergy Performance of MRU Processes

Abstract

The interrelationship between energy performance and exergy performance of a chemical process is somewhat subtle and commonly not well interpreted in general. For instance, it is possible to keep the same level of energy performance of a given operating process, but adopting some modifications—characteristically based on investing some capital into the process—to operate with a better exergy performance, as demonstrated in this chapter. In other words, an upgrade of the exergy performance does not necessarily mean that the process now uses less energy, albeit a better exergy performance usually leads to better energy usage and less energy expenditures. Another obvious fact is that making the process more costly does not necessarily imply in better exergy performance. The truth is that the achievement of a better exergy performance of a process always implies, on the one hand, that some monetary investment has to be injected into the process increasing its capital expenditure (CAPEX), size and possibly operational complexity, but, on the other hand, with the counterpart that some benefit can be expected in one or more of the following contexts related to the process performance as a whole: (1) energy degradation and energy usage; (2) energy consumption; (3) health, safety and environmental (HSE) impacts; (4) durability of equipment; (5) maintenance costs of equipment; (6) energy costs; (7) operation costs (OPEX); (8) product degradation costs; (9) waste production costs; (10) pollutant emissions; and (11) atmospheric emissions of CO₂.