J.H. Johnston
CaSil Technologies Ltd,
New Zealand
Keywords: geothermal energy, calcium silicate, silica, silica scale, sustainability, environmental, electricity generation
Summary:
This paper presents the exciting journey from discovery to commercialisation of a new technology (CaSil technology) that enables more electricity to be generated from geothermal resources, and at the same time produce an advanced nanostructured calcium silicate product. 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 the superheated geothermal brine. 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 from the brine flow. This silica scaling is a major problem in geothermal resource utilisation world-wide. Our CaSil technology captures the H3SiO4- species present at supersaturated levels in the geothermal brine by the rapid formation of a proprietary nanostructured calcium silicate material (CaSil) with a generalised composition of CaSiO3-x(OH)2x.yH2O. The material does not form a scale deposit like silica does and is separated continuously as an advanced CaSil product. 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 practices and operations. Substantially more “green” heat energy can now be recovered, and more electricity generated from the geothermal resource. The CaSil technology can be interfaced into existing geothermal infrastructures, thereby increasing the overall electricity generation from the resource. The CaSil material comprises non-planar platelets a few hundred nanometres in size by a few nanometres thick, which are 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 which is chemically active, together with a pore structure that has a high liquid absorbency of up to 400 g oil g-1. These chemical and physical properties have been utilised in environmentally beneficial applications. The technology has been developed and demonstrated at a fully automated pilot plant scale operation in four geothermal fields is New Zealand. 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.