Mathematical model for the exergy of the system ammonium nitrate-water

The exergy balance has recently been used more frequently for the energy analysis of technological processes and represents a considerable improvement over the evaluation according to the First law of thermodynamics, in which completely convertible and incompletely convertible forms of energy are taken into account equally. In order to carry out the exergy balance, the exergy values of the material flows involved in the process must be known. This article presents a mathematical model for calculating the exergy of ammonium nitrate in aqueous solution in the production of fertilizers. When carrying out the exergy model, it was assumed that the conditions are: ambient temperature 20 degrees C, pressure 101.325 kPa and that it consists of liquid water and crystalline ammonium nitrate, which has an exergy value of zero under these conditions. The model is based on Pitzer's ion- interaction type equations for the dependence of the activity coefficient on the composition of the solution at a given temperature and pressure. This mathematical model is valid for aqueous solutions of ammonium nitrate up to saturation in the temperature range from 20 degrees C to 170 degrees C and offers the possibility to estimate the NH4NO3(aq) enthalpies at different temperatures and different compositions.