Removing Silica from Geothermal Water - Year One of Pilot Plant Operation with a Focus on Carbonate and Silica Analysis

摘要

Amorphous silica and carbonate depositions as intractable sinters on the surface of pipework, valves and heat exchangers and in reinjection wells are major worldwide problems in geothermal energy utilization. The formation of the sinters from supersaturated geothermal brine limits the amount of energy that can be generated and leads to down times and considerable clean-up and remediation costs. Current approaches to alleviate the problem are only partially successful, particularly for high enthalpy resources. The dissolved silica also represents a potentially useful material resource. Our technology which transforms unwanted silica into novel nanostructured calcium silicate hydrate turns the issue of silica formation into an opportunity through controlled formation of a competing material from geothermal brine that prevents sinter formation. Carbonate can be captured in the silicate and is removed along with it. A test rig was built on site at MB Century, New Zealand, sourcing geothermal brine from the Wairakei resource. The test rig was commissioned in August/September 2017 and has been in operation since. We present data from the operation of the pilot plant focusing on the analysis of the incoming brine and the products recovered from it. Various methods for analyzing and tracking carbonate throughout the treatment procedure will be illustrated and compared. Titration is the primary tool for analyzing the brine for carbonate content. While titration can also be used to analyze the carbonate content in the solids recovered from the brine, it is a comparatively expensive and work intensive method. X-ray diffraction patterns can provide similar information. However, as the silicate and silica components are amorphous or polycrystalline, evaluation of relative amounts in the sample is difficult. Thermogravimetric analysis is shown to allow the analysis of several samples in parallel delivering satisfactory accuracy reducing the amount of work required per sample.