J.H. Johnston
CaSil Technologies Limited,
New Zealand
Keywords: geothermal energy, calcium silicate, silica, clean water, fertiliser, nutrient, environmental
Summary:
Geothermal energy is a natural, renewable, non-fossil fuel, 24/7 energy resource, that is harnessed for industrial “green” heat energy and electricity generation. Electricity is generated by the binary cycle technology using the heat from superheated geothermal brine. Heat energy for industrial and/or consumer applications is harnessed through heat exchangers. The resulting brine is consequently cooled in the process and reinjected back into the reservoir to recharge the resource and ensure sustainability. The superheated geothermal brine contains significant quantities of dissolved silica at supersaturated levels. This polymerises on cooling, depositing an intractable silica scale blocking pipes, heat exchangers and reinjection wells. It severely limits the extent to which the brine can be cooled and hence the amount of heat energy that can be recovered and electricity generated. Silica scaling is a major problem in geothermal resource utilisation world-wide. This problematic silica which is largely present as the H3SiO4- species, has been captured as a unique nanostructured calcium silicate material CaSiO3-x(OH)2x.yH2O, using our proprietary CaSil technology. The material does not form a scale, stick to metal surfaces or block reinjection wells. It is separated continuously as a CaSil product with a unique nanostructure and surface chemistry properties, that have been utilised in environmentally beneficial applications. The CaSil material comprises non-planar platelets a few hundred nanometres in size by a few nanometres thick, stacked together in an open framework structure forming discrete particles of about 1-5 microns in size. This nanostructure provides the CaSil material with a high surface area of up to about 400 m2 g-1 and a high liquid absorbency of up to 400 g oil g-1. This removal of the problematic supersaturated silica from the hot geothermal brine, now enables the brine to be cooled to substantially lower temperatures without silica scale deposition, than are currently possible with existing geothermal energy resource utilisation operations. It enables substantially more “green” heat energy to be recovered and electricity generated from the geothermal resource. The surface discharge of cooled geothermal brine laden with precipitated silica particles, into natural pristine geothermal water such as boiling lakes, that are features of natural beauty and cultural value, undesirably destroys these features. By removing the problematic silica as a useful nanostructured calcium silicate product, this degradation is prevented, and the natural qualities and cultural significance of the water are restored. Also, the unique open framework structure, high surface area and accessible surface chemistry properties of nanostructured calcium silicate material have been used to capture phosphate and nitrate species from excess fertiliser use and prevent them entering the natural water systems. This desirably reduces the extent of environmentally unacceptable algae and weed growth and associated pollution of surface waters. Over time, the pristine quality of the water will be restored. This paper presents an overview of the CaSil technology and the CaSil products, and their environmentally beneficial applications. New business opportunities for the CaSil technology and CaSil products are discussed.