Analysis of an integrated energy system under variable loads through the symbolic exergoeconomics. 2

In this paper, the natural gas depressurization plant of the previous paper, containing a turboexpander and two cogeneration engines, is still considered. The aim of the work is to seek to what extent the Symbolic Exergoeconomic procedure can operate independently of a thermodynamic simulator. For this purpose, the results obtained by the two methodologies have to be compared when varying significant thermodynamic parameters of the system. In particular, the isentropic efficiency of the first stage turbine has been modified in a wide range. The results are very close in the hypothesis of linear variations of the symbolic parameters as a function of the turbine efficiency, whereas are not acceptable under the hypotheses of independence of the efficiencies and stability of the exergy bifurcation rations. A close correspondence between the results of the thermodynamic simulator and the symbolic procedure allows the Symbolic Exergoeconomics algorithms to be used as a basis of an optimization process. As already pointed out in previous analyses, the comparison has t be carried out for each step of the annual discretized duration curve of the gas flow rate, since the behavior of the system is very different from one step to another