GEOFLEXHeat: Spike’s System for Silica Reduction at Bagnore
The GEOFLEXHeat project addresses one of the major challenges of high-enthalpy geothermal energy: silica precipitation during the cooling of geothermal brine. At the Amiata Energia site, supplied by 90 °C and 200 °C brines from the ENEL Green Power Bagnore 3 and 4 geothermal plants, fluid cooling generates supersaturation that leads to silica and stibnite deposits, damaging heat exchangers, pipelines, and reinjection wells.
Managing Stibnite: Injection of Inhibitors at High Temperature
The first phase of brine treatment focuses on managing stibnite, which tends to precipitate as the brine begins to cool in high-pressure heat exchangers. To prevent this phenomenon, Sb₂S₃ inhibitors are injected directly into the 200 °C line, before entering the first exchanger. This approach protects the system’s metallic surfaces, prevents clogging, and ensures the continuous operation of the geothermal line, without interfering with the subsequent silica-reduction process.
Fluid Preparation: Controlled Cooling to 80 °C
After inhibitor injection, the brine is cooled from 200 °C to approximately 80 °C using a high-pressure heat exchanger based on heat-pipe technology. This temperature is an optimal balance: low enough to trigger controlled silica precipitation, yet high enough to avoid premature formation of unwanted deposits. Around 80 °C is the ideal temperature to ensure efficient reaction with Ca(OH)₂ in the next step.
The Key Reaction: Adding Ca(OH)₂ to Precipitate Silica
Once the target temperature is reached, Ca(OH)₂ is introduced, rapidly increasing the pH and initiating the conversion of excess silica into calcium-silicate phases. This controlled precipitation reduces the silica concentration below the saturation threshold, lowering the risk of scaling along the reinjection circuit. Project simulations and tests show that precipitation occurs within minutes and is completed in 20–30 minutes—dramatically faster than traditional methods based on simple retention tanks.
The Scaling Reactor: Spike’s New Technology
The core of the system is a 1.5 m³ scaling reactor designed by Spike, featuring a cyclone-type geometry that ensures high mixing and a uniform pH throughout the volume. This design promotes the growth of precipitates and their separation from the fluid, reducing the formation of deposits in the piping and improving operational continuity. The kinetic model developed within GEOFLEXHeat also enables precise definition of process parameters such as pH, Ca/Si ratio, temperatures, and retention times, allowing the system to be adapted to the actual conditions of the Bagnore brine.
Expected Benefits for Amiata Energia and Technology Validation
The installation at Bagnore represents a key milestone for the industrial demonstration of GEOFLEXHeat technologies and serves as a replicable model for other geothermal districts across Europe.