| Title | NANOSTRUCTURED CALCIUM SILICATE HYDRATE – A POTENTIAL SOLUTION TO PROBLEMATIC SILICA DEPOSITION FROM GEOTHERMAL BRINE AND A USEFUL PRODUCT |
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| Authors | J.H. Johnston and T. Borrmann |
| Year | 2017 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | geothermal, silica, silica deposition, calcium silicate, nanostructured, geothermal energy, filler, fire retardant |
| Abstract | The deposition of amorphous silica as an intractable sinter on the surfaces of pipework, valves and heat exchangers and in reinjection wells, from separated geothermal brine supersaturated in dissolved silica, is a major problem in geothermal energy utilisation. It limits the amount of energy that can be recovered from the steam and especially the brine. Current approaches to alleviate the problem are not fully successful. The dissolved silica also represents a potentially useful material resource. We have turned this problem into an opportunity through the controlled formation of a novel nanostructured calcium silicate hydrate material from geothermal brine. We utilise the rapid reaction of the dissolved silica species with calcium cations under particular conditions to precipitate the nanostructured calcium silicate hydrate. Our technology allows the silica solubility to be controlled by the chemistry and not by the temperature as silica precipitation is. There is no further propensity for silica to precipitate and form the intractable sinter deposits. The nanostructured calcium silicate hydrate is separated from the brine leaving a low silica-containing water which is amenable for reinjection. Lower steam-water flash temperatures and lower binary plant heat exchanger exit temperatures can be used, enabling more heat and electrical energy to be recovered. Nanostructured calcium silicate hydrate has excellent whiteness, chemical reactivity, adsorbent and absorbent properties. Potential large volume applications are being explored. They include its use as a functional filler in tyres, plastics, paper, concrete, thermal insulation and fire retardancy; in the recovery of dissolved phosphate from waterways and lakes, and base metals from mine waters; and as a general absorbent and soil conditioning agent. We are developing the technology at a pilot scale operation in New Zealand geothermal fields, and are optimising the product characteristics for these uses. We are seeking expressions of interest as we move the technology to commercialisation. |