geothermal power plant projects in central america - Orkustofnun

pressures (kPa) in the separator for SF and DF cases and in the boiler for the ORC case. In order tosimplify reading from the graphs, the optimum net power output (kW) for a unit mass flow rate isused; the total power output can be obtained for each specific case simply by multiplying this by theactual mass flow rate in kg/s.4.3.1 Single flashThe selection of the separatorpressure has an important effect onthe overall plant performance interms of power output (Figure 19).High separator pressures result inhigher working potential steam atthe turbine inlet, a lower quality ofsteam in the turbine exhaust andhigher injection temperature.Lower separator pressures increasethe mixture quality in the separator,which means that more steam canbe produced, but the specificavailable energy of the steam flowwould decline.The optimization routine isrelatively simple since there is onlyone optimization variable and it canbe determined by varying the valueof the wellhead pressure to locatethe power output maximum(Karlsdóttir, 2008). The results ofthe optimization process arepresented in Figure 20 as theoptimum specific net output and theseparator pressure (kPa) as afunction of the resourcestemperature. The specific net poweroutput is directly proportional tothe resource temperature. Theseparator pressure increases for aresource temperature ranging from160 to 280°C; for higher resourcevalues it is constant as the constraints of the steam quality of the turbine exhaust cannot be lower than0.85, as seen in Figure 20.4.3.2 Double flashSpecific power output [ kW/kg/s ]Specific net power output [ kW/kg/s ]3002502001501005030025020015010000160 180 200 220 240 260 280 300 320 340Resource temperature [°C]50Specific net power outputSeparator pressureFIGURE 4: Specific net power output and separatorpressure of SF cycleSpecific net power outputSteam quality at turbine output00.70160 180 200 220 240 260 280 300 320 340Resource temperature [ °C ]In the optimization process of a DF cycle, the maximum power output is gotten by adjusting the valueof the high-pressure (HP) and low-pressure (LP) separators. Also, in a DF cycle, as in a SF cycle, thesteam quality of the turbine exhaust is a constraint in the optimization process, in this case for twostations at the exhaust of LP and HP turbines (Figure 22).Figure 21 shows the optimum specific net output and pressure separation for different resourcetemperatures. The specific net power output and the optimum pressure value of the HP separator aredirectly proportional to the temperature resource. In the DF system, as shown in Table 3, themaximum well head pressure was set at 3500 kPa, corresponding to the HP separator pressure at340°C. Where limits for the maximum well head pressure are set lower, the pressure increases until it8007006005004003002001001.000.950.900.850.800.75FIGURE 4: Specific net power output and steam qualityof turbine output of SF cycleSeparator pressure [ kPa ]Steam quality [ - ]24