From February 2014 to September 2015 an Geo40 pilot plant operated at the Contact Energy Wairakei (NZ) geothermal field where it processed over 25,000 tonnes of geothermal fluid supplied from the feed stream to the Wairakei binary power station. These trials produced over one tonne of colloidal silica product which has been shipped to potential customers in New Zealand, Japan and England. The feedback from potential customers was very positive with New Zealand customers stating that in trials, the samples performed as well as, if not better, than the colloidal silica they presently use.
During the pilot plant’s operation at Wairakei, the silica extraction process evolved. Three provisional patents were filed covering the different processes. Each successive process provided improved economics and product quality. The final process involves initially treating the geothermal fluid to nucleate the colloids and multi-stage concentration through an ultrafiltration process developed by Geo40 and a speciality membrane company in San Diego, USA. In this process incoming geothermal fluids have over 98% of the water removed to produce a 10wt% colloidal silica concentrate. This concentrate is then further processed to grow the colloids and concentrated to a final product with a colloidal silica concentration of at least 30wt%.
The pilot plant is substantial and has been built using full-scale equipment in order to minimise scale-up risk and provide meaningful data for design of the first commercial scale plant. The pilot plant and its scalability have been positively audited by several independent engineering consultancy companies.