Transforming Silica into Silicate - Pilot Scale Removal of Problematic Silica from Geothermal Brine

摘要

The condensation of dissolved silica speciesto form a hard silica scale is a major issue inthe generation of electrical energy and heatrecovery from geothermal hot water and wetsteam resources. In previous publications wehave shown that nano-structured calcium silicatehydrate (NCaSilH) forms readily from dissolvedsilica species in the separated geothermal brineand, therefore, provides an attractive solutionto the world-wide problem of the formation ofsilica scale. NCaSilH is placed into context withsilica species and other calcium silicate hydratesto demonstrate why the controlled formation anduses of this material are of interest in geothermalresource operation and management and invarious end user applications. The formation andremoval of this novel precipitated silicate fromthe brine is discussed in the early stages of pilotscale trials. A pilot scale test rig for such trials wasconstructed on site at MB Century, Taupo, NewZealand, and commissioned in September 2017.The test rig uses lamella separation technologyfor recovery of NCaSilH and other species frombrine. The development and implementation ofthis technology in the test rig is outlined. Earlyresults showed that the source of silica is quitevariable and comparatively low in silica andhigh in carbonate content. However, it served toshow that our NCaSilH approach to removingproblematic supersaturated dissolved silicaspecies from a geothermal brine works. Removalefficiencies for various species were between 95%and 99%, slightly lower than laboratory resultsdue to low silica levels. The test rig demonstratesthat the technology is very robust in operationand offers a novel disruptive approach to facilitatethe reduction in silica scale-forming species byremoving most or all of the problematic dissolvedsilica species from such geothermal brines, alongwith calcium carbonate and some other species.