Geochemistry, Mineralogy and Geochemical Model of Scaling In Cerro Pabellón (northern Chile) Geothermal Power Plant

Understanding the nature and behavior of geothermal fluids is a fundamental step for the design and operation of power plants. However, operational conditions of the geothermal power plants, cause changes in physico-chemical properties of fluids inducing possible precipitation of solid phases both in production and injection pipelines and in heat exchangers. Through chemical monitoring, such as brine and scale sampling, it is possible to understand precipitation mechanisms and put in place strategies to avoid or, at least, diminish it. We studied scaling processes observed in the Cerro Pabellón high enthalpy binary geothermal power plant, Northern Chile, the first geothermal power plant operating in South America. X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) are used to analyze mineralogy, chemistry and precipitation textures of scales. Geochemical modelling software were used to validate thermodynamic processes and assess the tendency of solid phases to precipitate at different operational scenarios. Main scales were found in the ORC preheaters linked to T&P drop of the fluid and subsequent minerals supersaturation. Scaling sequence was identified, starting with thick layer of colloidal and massive amorphous silica (opal-A) and ending with microcrystalline acicular stibnite and granular orpiment. Thermodynamics simulations shows that under acid conditions scale precipitation it is favorable, while at alkaline pH it is reduced. This work helps to understand the mineral precipitation phenomena from geothermal fluids under known operation conditions (P&T) and also giving insights to improve mitigation strategies against scaling inside geothermal power plants.