## 6 Results and Discussion
### Exergoeconomic and Environmental Results
In the third configuration, expanding of the gas mixture is such that only the required work of the compressor needs to be supplied (in the first and second configurations, the mixture of gases expands to near atmospheric pressure), and this causes a rise in the inlet air temperatures into the regenerator and the combustion chamber and a decrease in the required fuel flow rate in the third configuration than the second configuration. However, the output power of the Brayton cycle in the first and second configurations is close to each other and the greater than the third configuration. In addition, in the third configuration, Rankine cycle output power is substantially less than the first and second configurations due to the lower steam turbine inlet temperature and reduced steam generation rate. In the first configuration, due to the absence of a regenerator, the temperature of the exhaust gas is high enough such that the maximum inlet temperature to the steam turbine (550 \({}^{\circ}\)C) is always provided. In the third configuration, the exhaust gases temperature decreases in three stages (first gas turbine, second gas turbine and regenerator) compared to the second configuration that is in two stages. For this reason, the temperature of the generated steam in the steam generator of the third configuration is lower than the other two configurations and this reduces the steam turbine output power. In the case of exergy efficiency, although the fuel consumption of the combustion chamber in the third configuration is lower than the other two configurations, the significant reduction in the output power reduces exergy efficiency more than the other configurations examined. On the other hand, the reduction in fossil fuel consumption and consequently the reduction of environmental pollutants in the third configuration has been a factor in reducing of the fuel cost rates, environmental cost rates and overall cost rates which is significantly less than the other two configurations. In addition, the less overall exergy destruction and the associated cost rate is another contributing factor in the reduction of overall cost of the third configuration in comparison to the other two configurations. Finally, the lowest exergy unit cost of generated electricity in the base case is obtained using the second configuration. \begin{table}
\begin{tabular}{l c} \hline \hline
**Parameter** & **Value** \\ \hline Ambient temperature (\({}^{\circ}\)C) & 25 \\ Ambient pressure (kPa) & 101.3 \\ Inlet air mass flow rate (kg/s) & 491.55 \\ Compressor pressure ratio & 10 \\ Isentropic efficiency of compressor and gas turbine & 0.86 \\ Regenerator effectiveness & 0.7 \\ Inlet temperature of the first gas turbine (\({}^{\circ}\)C) & 1200 \\ Lower heating value of fuel \(\left(\frac{kI}{kknM}\right)\) & 802,361 \\ Fuel inlet temperature (\({}^{\circ}\)C) & 25 \\ Fuel inlet pressure (kPa) & 1200 \\ Saturation temperature of steam generator (\({}^{\circ}\)C) & 290 \\ Steam side temperature difference of the steam generator in the sec and third configurations (\({}^{\circ}\)C) & 20 \\ Steam turbine inlet temperature in the first configuration (\({}^{\circ}\)C) & 550 \\ Condenser pressure (kPa) & 10 \\ Isentropic efficiency of pump & 0.8 \\ Isentropic efficiency of steam turbine & 0.85 \\ Pinch point temperature difference of steam generator and condenser (\({}^{\circ}\)C) & 10 \\ Cooling water inlet temperature to condenser (\({}^{\circ}\)C) & 25 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Input data to simulate the combined cycle systems shown in Figures 1–3. If a comparison is made between the results of exergy, exergoeconomic and environmental analysis calculated in Table 8 and energy analysis results presented in [9].