J.H. Johnston
Victoria University of Wellington and CaSil Technologies Ltd,
New Zealand
Keywords: geothermal, green energy, climate change mitigation, clean water, calcium silicate, sustainable
Summary:
Geothermal energy is a natural, sustainable, 24/7 energy resource that is harnessed for industrial “green” heat energy and electricity generation. Superheated geothermal water in the subsurface geothermal reservoir is supersaturated in dissolved silica which polymerises and precipitates as the water is cooled in the heat extraction and electricity generation processes. The silica deposits as an intractable sinter which blocks pipes, heat exchangers and reinjection wells. This severely restricts the lower temperature to which the water can be safely cooled, thereby limiting the amount of heat energy that can be extracted and electricity generated from the resource. This is a major problem worldwide that has not been addressed satisfactorily. We have developed and demonstrated a world first proprietary technology (CaSil technology) at automated continuous pilot plant scale operation in different New Zealand geothermal resources, to capture the problematic dissolved silica as a unique nanostructured calcium silicate (CaSil) material, before silica can polymerise and deposit. The CaSil material CaSiO3-x(OH)2x.yH2O, is separated continuously. The removal of the problematic dissolved silica enables significantly more heat energy to be extracted and electricity generated from the same superheated geothermal water flow, than is possible with existing resource utilisation practices. The technology is applicable to geothermal energy resources world wide. The CaSil material comprises non-planar platelets a few hundred nanometres in size by a few nanometres thick, which are stacked together in a unique 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 liquid absorbency of up to 400 g oil g-1. We have utilised the unique structure and properties of nanostructured calcium silicate material to develop and demonstrate environmentally beneficial applications including: • The recovery and capture of environmentally problematic phosphate and other species from surface waters and effluent streams. • The recovery of base and heavy metals from industry and mining waste water streams. • Lightweight CaSil-based building products with inherent thermal and sound insulation, moisture control and fire-retardant properties. • An adsorbent to capture base and heavy metals from mining and industrial waste streams. • An ink absorbent filler in the paper industry to enhance the print and optical properties of paper. • A functional filler in rubber, plastics and paint. The production of this CaSil material from geothermal water and the consequent prevention of silica deposition in the geothermal resource utilisation, enables more heat energy to be recovered and more electricity to be generated from a sustainable, natural geothermal energy resource. Also, the environmental remediation and beneficiation applications will contribute to reducing algal pollution of waterways and preserving our clean water resources for the future. The CaSil technology and CaSil products, collectively address Climate Change mitigation and Clean Water protection and restoration. This paper presents an overview of the CaSil technology and the CaSil products, and their environmentally beneficial applications. New business opportunities are discussed.