Application of the exergy method to the environmental impact estimation: The nitric acid production as a case study

In this work the exergy method is used to compare various methods for removal of NO_x from waste (tail) gas released into the atmosphere from nitric acid production plants with respect to their overall environmental impact. Three basic methods for NO_x abatement are analysed: selective catalytic reduction (SCR), non-selective catalytic reduction (NSCR) and extended absorption. The positive and negative effects and the net effect from the NO_x abatement are calculated. The following exergy-based indicators are used for comparing the energy efficiency and the environmental impact of different treatment processes as a result from pollutants removal: reduction of the exergy of the emissions from the whole process route (ammonia and nitric acid production units); exergy of the additional emissions, arising as a result of the treatment process; total net reduction of the exergy consumption, Cumulative Energy Consumption (CEnC) and Cumulative Exergy Consumption (CExC) of natural resources as a result of the waste flows treatment.