## 6 Results and Discussion
### Multi-Objective Optimization Results
In addition, the comparison of results in the Table 17 (optimum case) and Table 8 (base case) indicates that the optimization process leads to a decrease in the exergy unit cost of products and systems total cost and an increase in the exergetic efficiency. Therefore, improvement for all objectives has been achieved using optimization process. Accordingto this table, optimization process improves the total performance of the system in a way that the exergy efficiency is increased from 48.76% to 49.6% for the first configuration, from 47.92% to 48.28% for the second configuration, and from 39.29% to 43% for the third configuration. Exergy unit cost of generated electricity is reduced from 23.66 \[Minimize\ \dot{C}_{tot}\big{(}P_{r,comp},GTT,\ \eta_{gt},\eta_{comp},\ \epsilon_{rg},\ \Delta T_{PP,gg},\ P_{cond}\big{)} \tag{39}\]4/GJ for the first configuration, from 22.93 \[Minimize\ \dot{C}_{tot}\big{(}P_{r,comp},GTT,\ \eta_{gt},\eta_{comp},\ \epsilon_{rg},\ \Delta T_{PP,gg},\ P_{cond}\big{)} \tag{39}\]5/GJ for the second configuration, and from 24.89 \[Minimize\ \dot{C}_{tot}\big{(}P_{r,comp},GTT,\ \eta_{gt},\eta_{comp},\ \epsilon_{rg},\ \Delta T_{PP,gg},\ P_{cond}\big{)} \tag{39}\]6/GJ for the third configuration. In addition, this table indicates that the exergoeconomic factor for the studied systems is increased from 7.53 to 14.47 for the first configuration, from 9.59 to 14.78 for the second configuration, and from 10.63 to 17.96 for the third configuration. Although these improvements achieve with 38.87%, 16.38% and 57.58% increase in the capital investment cost of the first, the second and the third configurations, respectively, from studied combined cycle systems. Moreover, environmental emmision costs decrease 57.7%, 6.7% and 29.52% in the optimum cases for the first, the second and the third configuration, respectively. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Design Variables** & **Config. 1** & **Config. 2** & **Config. 3** \\ \hline Compressor pressur ratio, \(\Pr_{t}\) & 19 & 10 & 16.47 \\ Gas turbine inlet temperature, GTT (\({}^{\circ}\)C) & 1213 & 1171 & 181 \\ Isentropic efficiency of gas turbine, \(\eta_{gt}\) & 0.88 & 0.88 & 0.88 \\ Isentropic efficiency of compressor, \(\eta_{comp}\) & 0.844 & 0.869 & 0.856 \\ Effectiveness of regenerator, \(\varepsilon_{reg}\) & - & 0.8 & 0.7 \\ Pinch point temperature of steam generator, \(\Delta T_{pp,g}(^{\circ}\mathrm{C})\) & 10 & 10 & 10 \\ Condenser pressure, \(P_{cond}(kPa)\) & 10 & 10 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 16: Design variables of configurations shown in Figures 1–3 in the optimum case. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Output Parameter** & **Config. 1** & **Config. 2** & **Config. 3** \\ \hline Exergy efficiency, \(\eta_{ext,tot}(\%)\) & 49.6 & 48.28 & 43 \\ Total cost, \(\hat{C}_{tot}(\$/s)\) & 10.81 & 8.315 & 6.83 \\ Total energy unit cost of produced electricity, \(c_{el,tot}(\$/\mathrm{GJ})\) & 22.36 & 21.13 & 23.28 \\ Inlet air temperature to combustion chamber, \(T_{init,CC}(^{\circ}\mathrm{C})\) & 468.8 & 619.5 & 736.3 \\ Inlet steam temperature to steam turbine, \(T_{init,st}(^{\circ}\mathrm{C})\) & 550 & 381.4 & 327.7 \\ Fuel mass flow rate, \(\dot{m}_{fuel}(kg/s)\) & 9.69 & 7.22 & 5.18 \\ Steam mass flow rate, \(\dot{m}_{\mathrm{steam}}(kg/s)\) & 69.95 & 31.03 & 15.88 \\ Gas turbine power, \(\dot{W}_{gt}(MW)\) & 170.4 & 151.8 & 117.6 \\ Steam turbine power, \(\dot{W}_{gt}(MW)\) & 78.76 & 28.54 & 13.48 \\ Net power, \(\dot{W}_{net}(MW)\) & 249.2 & 180.2 & 131.1 \\ Fuel energy, \(\dot{E}x_{fc,cc}(MW)\) & 502.5 & 373.48 & 304.96 \\ Exergy destruction, \(Ex_{D,tot}(MW)\) & 227.8 & 157.4 & 133.3 \\ Capital investment cost, \(\dot{Z}_{tot}(\$/s)\) & 0.582 & 0.405 & 0.46 \\ Exergy destruction cost, \(\dot{C}_{D,tot}(\$/s)\) & 3.44 & 2.34 & 2.1 \\ Fuel cost, \(\dot{C}_{fuel}(\$/s)\) & 5.817 & 4.33 & 3.53 \\ Environmental cost, \(\dot{C}_{env,tot}(\$/s)\) & 0.968 & 1.24 & 0.74 \\ Exergoeconomic factor, \(f\) (\%) & 14.47 & 14.78 & 17.96 \\ \hline \hline \end{tabular}
\end{table}