Exergy-based estimation and comparison of urea and ammonium nitrate production efficiency and environmental impact

The modern low-energy production processes of urea and ammonium nitrate (AN) are analysed and compared regarding to the natural resources consumption efficiency and GHG emissions generation. The comparison is based on the thermodynamically grounded minimum real attainable consumption of energy and feedstock in each stage of the overall production routes of both fertilizers. The results based on the energy and exergy indices of both production processes are similar and show higher efficiency of the urea production, as the exergy of the product urea is much higher than the exergy of ammonium nitrate. However, as both products are used mainly as fertilizers, their application in the field does not concern their energy and exergy content. Hence, from the comparison based on the exergy consumed in the production processes and exergy of the exported by-products, the ammonium nitrate production process seems to be more efficient. The results from the comparison of GHG emissions also depend on the application features of both products. Urea is a short-time option for CO2 capture and the emissions from the field dissipate into the air, whereas the same quantity of CO2 emitted from ammonium nitrate production is concentrated (99%) and can be used and/or stored. (C) 2017 Elsevier Ltd. All rights reserved.