Silicate Scale Prevention in Geothermal Brine Systems: Comparing the Mechanism and Performance of Two Polymer-Based Inhibitors/Dispersants

Silica scaling is a potential issue in geothermal fields. In this work, a static bottle test methodology was developed to assist in identifying efficient silicate inhibitors/dispersants with high inhibition performance (80-90%), applicable for low enthalpy geothermal heat recovery systems. To investigate products to control amorphous silicate and magnesium silicate scale, the inhibition efficiency (IE) and mechanism of two sulphonated polymer-based scale inhibitors/dispersants, denoted A5 and SI B were studied over an active concentration range of 20-200ppm at 60ºC/95ºC, and at pH 8.5. Then, the inhibition mechanism was evaluated via two different methods, determining the concentration of sulphur (S) contained within the A5 and SI B structure by Inductively Coupled Plasma-Optical Emissions Spectrometer (ICP-OES) and detecting inhibitors as a polymer product by matrix-matching Hyamine technique. At 60ºC, a minimum inhibitor concentration (MIC) of 20-50ppm A5 and SI B was identified as being able to prevent scaling. At 95ºC, although a higher MIC of 50-100ppm was required for A5 to control silicate scale, it remained at 50ppm for SI B. Despite the differences between the two analytical methods for the SI consumption profiles, an investigation showed that the decline in scale inhibitor concentrations was more accurately identified by the Hyamine analysis.