Comparative Computer Modelling of Geothermal Power Plant Fluid Chemistry, Leyte Geothermal Production Field, Philippines

Abstract

This report describes computer modeling results of the power plant fluid chemistries in the Malitbog, Mahanagdong, and Upper Mahiao geothermal power plants in Leyte, Philippines. The computer program CNDSR was used to model the fluid chemistry based on the gas chemistry of the steam input to the turbine. The program used input data for the gas and water composition and calculates pH, gas fiactions in the vapor and liquid phases. A comparison of the resulting fluid chemistry is made for three methods of steam condensation in a geothermal plant, namely direct-contact condenser (Malitbog), non-contact condenser (Mahanagdong), and by heat exchanger (Upper Mahiao). Modeling showed that the pH of the fluid is controlled by the distribution of gaseous components, primarily H2S, NH3 and C02. Further, the fluids in the direct contact condenser are more acidicithan those in noncontact condenser because of more contact with the gases. Most of the gases are discharged as primary gas emission in the exhaust of the gas extractor and the dissolved gases are discharged as secondary emission in the cooling tower.