Brine Fouling Risk Assessment Template (Silica, Calcite, Anhydrite) – Field-Deployable Calculator

Brine fouling—caused by precipitation of sparingly soluble minerals—is a critical reliability and efficiency challenge in geothermal binary plants, where hot, chemically complex brines transfer heat across titanium or stainless-steel heat exchangers. Silica scaling dominates at high temperatures (>150°C) due to decreasing solubility upon cooling; calcite precipitates near neutral pH when CO₂ degasses or pH rises during depressurization; anhydrite forms at elevated sulfate and calcium concentrations, especially above 100°C and under confined flow paths. The template implements empirically validated, temperature-corrected solubility models (e.g., Rimstidt for amorphous silica, Plummer & Busenberg for calcite, and Wolery’s EQ3/6-derived anhydrite constants) coupled with activity coefficient corrections (Davies equation or Pitzer-based approximations for high-ionic-strength brines). Users input field-measured parameters—including total dissolved silica, Ca²⁺, SO₄²⁻, HCO₃⁻/CO₃²⁻ alkalinity, pH, TDS, temperature, and pressure—at key process points (production wellhead, preheater inlet/outlet, evaporator inlet, etc.)—and the calculator outputs saturation indices (SI = log₁₀(Q/K), where Q is ion activity product and K is equilibrium constant), supersaturation thresholds, and qualitative risk ratings (Low/Medium/High) based on SI magnitude and kinetic considerations (e.g., SI > 0.5 suggests imminent scaling for silica under typical residence times). The tool is intentionally simplified for field use: it avoids full speciation modeling but applies robust, peer-reviewed simplifications validated against field scaling incidents and laboratory brine aging studies across global geothermal fields (e.g., Cerro Prieto, Reykjanes, The Geysers).