Integration of the Calcium Silicate Hydrate (CaSil) Technology into Geothermal Power Generation – An Overview of the State-of-Art and Potential Applications

Silica polymerisation and precipitation from supersaturated separated geothermal brine results in the formation of intractable silica sinter deposits in pipes, heat exchangers and reinjection wells. Silica scale is a major problem in geothermal resource utilisation worldwide. This sinter compromises the heat energy recoverable for binary cycle electricity generation, blocks reinjection wells and increases maintenance costs. We have developed the new nanostructured calcium silicate hydrate, CaSil, technology and are demonstrating it at pilot scale operation, whereby we rapidly react supersaturated dissolved silica entities in the brine with calcium ions under controlled conditions to form a CaSil material. The formation of CaSil prevents silica entities from polymerising and depositing the problematic sinter scale. The technology is applicable to any brine temperature and pressure conditions, and the residual level of dissolved silica entities in the brine is controlled by the relevant chemistry rather than by temperature dependent solubility. The silica saturation index (SSI) is lowered to far below 1. Sufficient dissolved silica can be removed to just prevent silica sinter formation, or essentially all of it can be removed to facilitate the recovery of other dissolved mineral species such as lithium and base metals by selective membrane or adsorbent methodologies. The removal of problematic silica enables lower steam/water separation temperatures and lower exit temperatures in binary plant heat exchangers. More heat energy can be extracted from a geothermal resource. CaSil particles are recovered continuously as a useful product. Its applications are based on the unique 3D framework structure of CaSil, which provide it with high liquid absorbent and surface area properties. New CaSil materials are generated with properties suitable for high volume applications in the building, paper, paint, polymer, absorbent, mining and environmental remediation industries.