| Title | TURNING THE PRESSURE ON FOR THE NANO-STRUCTURED CALCIUM SILICATE HYDRATE (CASIL) SOLUTION TO SILICA SCALING |
|---|---|
| Authors | T. Borrmann, J.H. Johnston and M. Schweig |
| Year | 2021 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Silica, silica scale prevention, calcium silicate hydrate, solid liquid separation, lamellar separation, steam carry-over |
| Abstract | The nano-structured calcium silicate hydrate (CaSil) technology has been shown to prevent the formation of hard intractable silica scale. Such scale forms due to the supersaturation and precipitation of silica from geothermal water during energy production. Using the CaSil technology suspended silica is converted and precipitated as calcium silicate hydrate, which does not stick to surfaces and can be recovered via solid-liquid separation to yield useful products. Additionally, CaSil can capture and trap calcium carbonate species formed in parallel. So far, this technology has been employed after flashing processes with the recovery happening at atmospheric pressure and below boiling temperatures. Feedback from the geothermal industry suggested that it would be very interesting to capture and transform the silica prior or during the flashing process. Doing so would offer a significant advantage. Currently during flashing silica can be carried over with the steam and damage sensitive equipment. Transformation of the silica into a non-volatile and particulate silicate hydrate reduces the carryover. Furthermore, applying the CaSil technology under pressure would allow to retain elevated pressure at the end of the process, which aids in the transport of liquids over distances and reinjection. In this article we present preliminary findings regarding employing the technology at elevated pressures. We have investigated and answered several research questions. The CaSil process does not significantly change the vapour pressure or lower the temperature of the geothermal water. It significantly reduces the carry-over of silica into the vapour phase depending on the extent of treatment. Lastly, the lamellar separation process can be carried out at elevated pressure. Elevated temperature has a larger impact on the efficiency of a lamella separator than pressure. |