| Title | Moving the Calcium Silicate (CaSil) Pilot Plant to Kawerau |
|---|---|
| Authors | T. Borrmann, M. Schweig, J.H. Johnston, H.P. Fraser |
| Year | 2022 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Silica scale prevention, calcium silicate technology, geothermal energy, enhanced electricity generation, reduced maintenance, molybdenum blue test, molybdenum yellow test, silica analysis |
| Abstract | Silica scale formation due to supersaturation in geothermal brine results in the formation of intractable silica scale deposits in pipes, heat exchangers and reinjection wells. This is a major problem in liquid dominated geothermal fields worldwide. Heat energy extraction and hence electricity generation are adversely affected, and blockages of process equipment and reinjection wells necessitate costly maintenance and plant downtime. We have developed a proprietary technology that definitively prevents the scale formation and enables full utilisation of geothermal resources for electricity generation and direct-heat applications. Our technology addresses the problem by producing a nanostructured calcium silicate (CaSil), which is formed in and recovered from geothermal brine in an automated pilot scale operation. The process lowers the silica saturation index (SSI) substantially below 1 within seconds. Laboratory work and batch field worked showed that the technology is applicable to a range of brine compositions, temperature, and pressure conditions. The CaSil material does not stick to metal surfaces because of its unique surface chemistry, significantly reducing maintenance costs for process equipment and reinjection wells as well as plant downtime. From commissioning of an initial proof-of-concept plant in 2017, through the construction (November 2019) and operation of our pilot plant (2019 to 2021) we were located on the Wairakei geothermal field. Mid 2021 we were invited to relocate the pilot plant to the Kawerau geothermal field. The new field and chemicals in the Kawerau brine posed some challenges and surprises regarding the on-site silica analysis of samples (molybdenum blue and yellow tests) but reconfirmed that our overall process is very robust and can cope with very different brine compositions. We successfully operated the pilot plant for several weeks in 2021 and 2022 and present insights from the operation. |