Integration of the Calcium Silicate (CASIL) Technology into Geothermal Power Generation to Prevent Silica Deposition

Abstract

Silica supersaturation in geothermal brine results in the formation of intractable silica scale deposits in pipes, heat exchangers and reinjection wells. This scale prevents the full effective utilisation of geothermal resources for electricity generation and heat recovery applications. It is a major problem worldwide. Also, process equipment and reinjection wells can be blocked, which necessitate costly maintenance and plant downtime. Current approaches attempt to address the problem by using higher steam/water separation temperatures to reduce silica saturation, acid dosing or additives to retard silica polymerisation. However, the use of these is not wholly satisfactory; silica still precipitates and electricity generation and heat recovery remain compromised.
We have developed our proprietary new nanostructured calcium silicate, CaSil, technology to address the problem and are demonstrating it in an automated pilot scale operation at Wairakei. We remove the problematic dissolved silica as a novel CaSil material. This lowers the silica saturation index (SSI) substantially below 1. The technology is applicable to a range of brine compositions, temperature and pressure conditions. The technology opens up opportunities for further mineral extraction (e.g. lithium, base metals). Additionally, more heat energy can be safely extracted from the brine without causing silica scaling during electricity generation or industrial direct use applications. Because of its unique surface chemistry the CaSil material does not stick to metal pipes, significantly reducing maintenance costs for process equipment and reinjection wells, and plant downtime.
The CaSil material is a useful product that has a range of industrial and environmental remediation applications. These applications utilise the unique 3D framework structure of CaSil, which provide it with high liquid absorbent and surface area properties. By careful control of the calcium silicate chemistry and some post-separation treatment, new CaSil materials are generated with properties suitable for high volume applications in the building, paper, paint, absorbent, mining and environmental remediation industries.