| Title | Reykjanes Geothermal Field: Clarification of Brine for Reinjection and Production of Precipitated Silica |
|---|---|
| Authors | Trausti HAUKSSON, Ãrmann E. LUND, KristÃn V. MATTHÃASDÓTTIR, Kiflom G. MESFIN, Þór GÃSLASON, Albert ALBERTSSON |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | silica production, brine reinjection, precipitation, flocculation, clarification, filtration |
| Abstract | In the Reykjanes geothermal power plant, the steam is separated from brine at high pressure and the hot brine disposed off. Bottoming unit is now being developed in which the hot brine will be flashed in two stages and the medium- and low-pressure steam used in a dual stage turbine to generate 30 MW of electricity. The brine flowing at atmospheric pressure from the separators contains 940 mg/kg SiO2 and silica will rapidly precipitate out of solution making it impossible to inject the brine into wells. A process for clarifying the brine for reinjection and production of precipitated silica was developed and tested in a pilot unit which is able to treat 20 kg/s of brine. In the process the brine is rapidly mixed with silica slurry in a solid contact reactor at optimal pH for silica precipitation. In the reactor the concentration of dissolved SiO2 is reduced almost to saturation. The brine then flows into a flocculator where the small silica particles are flocculated by adding alkali and with slow stirring. The flocculated silica is separated from the brine by settling in a clarifier and after dilution with condensate below silica saturation the brine containing less than 20 mg/kg suspended silica particles is finally filtered in a drum filter and is then suitable for reinjection. The silica slurry which settles in the clarifier is recirculated to the solid contact reactor. Sufficient silica slurry is removed from the process to balance the precipitation of inflowing SiO2 and at the same time keeping the slurry concentration high enough in the solid-contact reactor. The full-size process will handle 300 kg/s of brine and as a valuable byproduct, produce 14 tons per day of precipitated silica. The silica has great potential for various uses which are being investigated. |