| Keywords |
nanostructured calcium silicate, CaSil, disruptive technology, silica scaling, scale prevention, enhanced energy recovery, reduced maintenance, business opportunities |
| Abstract |
This paper presents an overview of a novel nanostructured calcium silicate hydrate (CaSil) technology, its implementation at pilot scale operation and the nature and uses of the CaSil products. It is part 1 of 5 papers from our group covering this technology: 1 - Overview of the Technology (this paper), 2 – Precipitation of CaSil (Fraser et al.), 3 – Integration of the technology (Schweig et al.); 4 - CaSil technology under pressure (Borrmann et al; and 5 - Applications of CaSil products (Cairns et al.). The polymerisation and precipitation of silica from separated geothermal brine supersaturated in dissolved silica which results in the formation of intractable silica sinter deposits in pipes, heat exchangers and reinjection wells is a major problem in geothermal resource utilisation worldwide. This sinter compromises the heat energy recoverable in binary cycle electricity generation, blocks reinjection wells and increases maintenance. Current approaches attempt to address the problem by using higher steam/water separation temperatures to reduce silica saturation, acid dosing and additives to retard silica polymerisation. However these are not wholly satisfactory, silica still precipitates and the problem remains. We have developed a disruptive new technology and are demonstrating it at pilot scale operation, whereby we rapidly react the supersaturated dissolved silica entities in the separated brine with calcium ions under controlled conditions to form a novel nanostructured calcium silicate hydrate (CaSil) material, before the silica entities can polymerise and deposit the problematic sinter material. The technology is applicable to any brine temperature and pressure, and the residual level of dissolved silica entities in the brine is controlled by the relevant chemistry rather than by temperature dependent solubility. Hence sufficient dissolved silica can be removed to just prevent silica sinter formation, or essentially all removed to facilitate the recovery of other dissolved mineral species such as lithium and base metals by selective membrane, adsorbent or other methodologies. A key feature is that the CaSil particle surface morphology and chemistry are distinctly different from those of problematic silica particles and as such the CaSil particles do not accrete or deposit on metal surfaces or in reinjection wells, thereby eliminating silica sinter formation. This attribute enables lower steam/water separation temperatures and lower exit temperatures in binary plant heat exchangers to be used, in turn enabling more heat energy to be extracted from a geothermal resource. There is no further propensity for silica to deposit in pipework, heat exchangers, or in reinjection wells. The CaSil particles are recovered continuously as useful products. The CaSil material has a unique 3D framework structure, providing it with high liquid absorbent and surface area properties. By careful control of the calcium silicate chemistry and hence the composition and properties of the material, the technology generates CaSil products which are ideal for high volume use applications in the building, paper, paint, polymer, absorbent, mining and environmental remediation industries. The CaSil technology therefore provides the attractive opportunities to potentially: • eliminate the current worldwide problem of silica deposition from geothermal brine and intractable silica sinter formation in geothermal resource utilisation; • enhance the utilisable heat energy and hence electricity generated; • facilitate reinjection of the treated brine from which silica precipitation cannot occur; • reduce maintenance costs; • provide useful CaSil products for industrial and environmental applications which generate additional revenue. This paper presents an overview of the technology, its implementation at pilot scale operation and the nature and uses of the CaSil products. New business opportunities are also discussed. |