geothermal power plant projects in central america - Orkustofnun

The net contribution of that power plant to the electric grid can be calculated by subtracting all internalpower consumption to the generator output.Condenser with heat exchangeSteam exhaust from the turbine is cooled without mixing using water from the cooling tower in asurface type condenser. The goal is to condense this steam by extracting energy because it requiresless work to pump an incompressible liquid than compressible gas or steam at state 4. The energyextracted is calculated by using the mass flow of steam and the enthalpy difference at stations 3 and 4,as followsEquation 11, based on the energy balance in the exchanger, is = ( h − h ) (10) ( h − h ) = ( h − h ) (11)The heat exchange is determined by the temperature difference; therefore, the maximum temperatureof the cooling water must not exceed the condensation temperature in the condenser. According toPálsson (2010) there should be at least 5°C difference between those numbers, written as follows = −5 (12)Assuming that condensation takes place at a constant temperature, a simplified equation can be givenas = (13)Since a temperature value is fixed on the design for the inlet cooling water temperature, alltemperature variables can be identified. Therefore, Equation 11 can be used to calculate the requiredflow rate of the cooling water at station c1.Gas extractionThe geothermal steam includes non condensable gases all the time. Carbon dioxide is typically about98% of the gas content and is released to the atmosphere in most geothermal power plants(Thorhallsson, 2006). In this analysis, the composition of the non-condensable gases is assumed to be100 % CO 2 .Non condensable gases cause a problem in the condenser; while the steam is condensed and pumpedout, the gases are kept on in gaseous form producing an increase in the pressure in the condenser. Apossible solution to this problem is to compress the gases and suck them out of the condenser.In the extraction process, some amount of steam will always be included since the steam is mixed withother gases inside. Hence, the gas mixture is then assumed to be saturated with steam when it issucked out from the condenser. According to Pálsson (2010) the mass of steam extracted can bedefined as = ( ) (14)where is the mass molar mass of water and is the mass molar mass of gases, is thesaturation pressure of steam at the gas outlet temperature, is the condenser pressure and is themass flow of gases into the condenser.The energy required for the pump is calculated by an ideal isentropic process between the condenserpressure and the atmospheric pressure. The mixture properties are calculated as follows17