## 2 Modelling, Analysis and Optimization of a System
### Description of the Sinem GPP as a Case Study  
Turkey's geothermal fields have a wide regional distribution linked to tectonic and volcanic activity. In this situation, the majority of high enthalpy or high temperature geothermal fields are compressed in the continental rift zones of the Menderes Massif and are due to later expanding tectonic activity. As a result, these high temperature geothermal fields are found within the continental rift belt of the Buyuk Menderes basin. One of these fields is the Hidrbeyli region of Germencik county in Aydin province/Turkey with five geothermal power plants (GPP) operating under the names Irem GPP (20 MW), Sinem GPP (24 MW), Deniz GPP (24 MW), Kerem GPP (24 MW) and Ken 1 GPP (24 MW) belonging to the Maren Maras Electricity Generation Inc. with 116 MW capacity [45]. In this study it is chosen the Sinem GPP operating at 24 MW installed power within this geothermal field. The schematic flow diagram for Sinem GPP is given in Figure 1.  
This GPP works in accordance with an air-cooled geothermal binary organic Rankine cycle. It started operating in July 2012. From Figure 1, the Sinem GPP with the air-cooled binary organic Rankine cycle comprises evaporators (VAP 1, VAP 2, PREHE 1, PREHE 2 and RECUP), turbines (TURB 1 and TURB 2), generator (GEN), condensers (CON 1 and CON 2), fans (FAN 1 and FAN 2) and pumps (PU 1 and PU 2) components at level I and II. The heat input rate at the GPP system currently obtains mixed geothermal fluids from 3 artesian production wells (GM3, GM5 and GM8), with each well-head installed with a vertical separator to divide two phase fluid into geofluid (liquid brine) and saturated steam. These production wells have temperatures of 165 \({}^{\circ}\)C-170 \({}^{\circ}\)C, pressure of 10 bar-14 bar and flow rate of 1100 ton/h-1500 ton/h. Figure 1: A schematic flow diagram of the Sinem GPP. Initially high pressure steam with 165 \({}^{\circ}\)C temperature, 8.33 kg/s flow and 1040 kPa is obtained from the separators. This steam comprises 30% non-condensable gases (NCG). The remaining 70% is geothermal fluid steam. Then geofluid with 165 \({}^{\circ}\)C, 1040 kPa and 445 kg/s is obtained from separators. Only the power plant of Sinem GPP is only examined as it can be seen from Figure 1. The production wells, separators, automation/safety systems, re-injection wells, piping and fittings of the GPP are outside the scope of the study. Steam and liquid geofluids are prepared with the properties mentioned above reach the power plant. Thus, the binary organic Rankine cycle of the GPP begins the operation. The binary ORC comprises two different classic Rankine cycles alongside and separates each other. The Sinem GPP, like all these systems, is operated in accordance with the T-s flow diagrams as illustrated in Figure 2. The temperatures, pressures, mass flow rates of the system are listed in Table 1, based on the thermodynamic states indicated in Figure 1, for the chosen day. As can be seen in Figure 2 and Table 1, the cycles are called as level I with 160 kg/s flow rate (high pressure of 1261 kPa) and level II with 196 kg/s flow rate (low pressure of 687 kPa). As follows from Figure 1 and Table 1, the geofluid first compresses the vaporizer VAP 1 on level I heating n-pentane as working fluid of the ORC. Later the geofluid passes to the vaporizer VAP 2 on level II and heats _n_-pentane. As the geofluid in VAP 2 on level II has low temperature and pressure, the stream of geofluid obtained from the separators is inputted here. Both the geofluid and steam pass through VAP 2 without mixing. In the output from VAP 2, the NCG and steam is released to the atmosphere, and the condensed geofluid is compressed for re-injection. The geofluid emerges from VAP 2. Here it passes through the pre-heaters PREHE 1 and PREHE 2 simultaneously. However, for safety reasons, the pre-heaters are taken offline when a certain temperature is reached.