Characterization of Binary Plant Heat Exchanger Scale Deposits under Different Treatment Conditions

Abstract

Mineral scaling insights in a geothermal binary plant can be from geochemical simulation, sidestream testing and actual plant operations. The information gathered from these studies can help provide a clearer picture of the scale deposition behavior. This study investigates the characteristics of scale deposits formed under different binary plant treatment conditions. The conditions considered were untreated, treated with polymer-based inhibitor and treated with pH modification. The collected scale samples were analyzed using x-ray fluorescence (XRF), gravimetry, scanning electron microscopy (SEM) and x-ray diffraction (XRD) to determine their mineralogical composition, morphology and elemental content. From the results, the scales treated with polymer-based inhibitor exhibited a relatively consistent composition of amorphous silica (majority at more than 90% w/w). Untreated and treated with pH modification conditions showed combination of amorphous silica, metal silicates and metal sulfides. Aside from quantitative results, qualitative observations showed that the deposited scales also differ on the physical characteristics like hardness, color and tenacity. The resulting deposits from polymer-based treated system were relatively softer and easier to remove compared to the deposits from either untreated or treated with pH modification. The study of these deposits can also provide an additional decision criteria in selecting the appropriate treatment option.