# Thermodynamic Analysis of Partitioned Combined Cycle using Simple Gases
## 3 Model Description  
The GE 9 HA.02 (General Electric, USA) combined cycle gas turbine is modeled and discussed in detail [54]. The errors in the model were dealt with by defining a range of parametric analysis, as shown in Table 1. Gas turbines have extensive moving machinery and offer a variety of loads. The flexibility in operation comes at a cost of efficiency loss. This decrease in efficacy is usually because of the process dynamics (discrepancy in mechanical losses is usually negligible because of the preventive maintenance schedules). Moreover, the ambient conditions also change frequently. Therefore, simulating such processes with fixed parameters may lead to erroneous conclusions. The best and worst process conditions were defined as upper and lower efficiency limits, respectively. Part load conditions can also be restrained in the same respective limits.  
The high pressure and temperatures in the process required a reasonable thermodynamic model to calculate the properties. Ideal gas assumption was therefore not appropriate. For the partitioned cycle five fluids were selected--air, argon, hydrogen, nitrogen, and carbon dioxide. The choice depended on  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameters** & **Upper Limit** & **Mean Operating Conditions** & **Lower Limit** \\ \hline Gas Turbine Output (MW) & 577 & 564 & 551 \\ Air Intake (kg/h) \(\times\) 10\({}^{-6}\) & 3.342 & 3.51 & 3.695 \\ Fuel Intake (kg/h) \(\times\) 10\({}^{-3}\) & 89.57 & 92.93 & 96.650 \\ Gas Turbine Exhaust & 608 & 630 & 652 \\ Temperature (\({}^{\circ}\)C) & 410 & 444 & 482 \\ Air Compressor work (MW) & 178 & 191 & 204 \\ Rankine cycle out Put (MW) & 61.8 & 59.57 & 57.27 \\ Overall Efficiency (\%) & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Expected full load operating conditions range to confine the simulation errors and variations in real operating conditions.  
Figure 2: Novel proposed partitioned Brayton and Rankine cycles (PCGT) to efficiently recover cycle exhaust energy. Contrary to the main cycle, the partitioned Brayton cycle is a closed one.  
the range of thermodynamic properties. The Peng Robinson equation of state was used to estimate the properties. Other thermodynamic models may also be used, with expected discrepancies from Peng Robinson. As an example, for the Soave-Redlich-Kwong model, the maximum difference in compressibility factor for all the considered gases (at 30 bar and 25-1500 \({}^{\circ}\)C) was around \(\pm\)1.7%. The validity of the calculation may be limited by the accuracy/applicability of the Peng-Robinson Equation of State (EoS). However, ASPEN HYSYS process simulator modified the critical properties to avoid substantial errors in the case of hydrogen and helium. Other quantities, like thermal conductivity and viscosity, were calculated by the polynomials regression based on the experimental data. According to our experience with industry, ASPEN HYSYS algorithms give reasonable accuracy for high pressure and temperature processes with hydrogen and carbon dioxide. Nevertheless, the results were accurate enough to draw a conclusion at least at qualitative level.  
The compressor was intercooled by the help of jackets. A separate intercooler is usually not employed because of excessive pressure drops. The jacket/intercooler affect was inculated in the model by defining the adiabatic efficiency. Hot spots in combustion chamber may produce excessive NOx. Therefore, their equilibrium amount in flue gases was considered. The waste heat boiler temperature approach must be adjusted to avoid excessive backpressure and a huge boiler size. This temperature approach was around \(\approx\)200 \({}^{\circ}\)C. However, depending on the overall heat transfer coefficients defined by different gases, this should be adjusted. Parameters were carefully selected to keep relative simulation errors the same for CCGT and PCGT.