Lamella Separators for Recovering Nano-Structured Calcium Silicate Hydrate from Geothermal Brine

摘要

One of the major challenges in geothermal energy utilization is the formation of silica scale from supersaturated geothermal brine. Over time silica scale blocks pipes, valves, heat exchangers and reinjection wells, which need to be regularly cleaned, serviced or replaced. High costs and downtimes for maintenance and replacement are the result. Many of the current technologies that address this challenge only attenuate the problem but can't solve it wholly. The formation of silica scale in supersaturated geothermal brine can be fully prevented with the competitive transformation of dissolved silica into nano-structured calcium silicate hydrate (NCaSilH) particles. The NCaSilH-particles form within milliseconds and don't stick to metal surfaces. Dissolved silica can be reduced to safe levels at which no polymerization takes place, even at room temperature. This allows for an increased energy production of the geothermal power plant, reduces maintenance and replacement costs and can even create additional revenue for a useful NCaSilH-product. The particles agglomerate over time and are too big to be reinjected into the geothermal reservoir risking blockage of the porous rock structure. This means, that they need to be separated from the spent brine prior to reinjection of the brine. In order to identify a suitable separation technology to separate NCaSilH-particles from geothermal brine settling experiments were conducted. Lamella separators were identified and investigated as a promising technology for the recovery of the silicate. We have constructed multiple laboratory models in a rapid prototyping approach to develop a suitable separator. An up-scaled version was built for pilot plant operation to demonstrate the technology to industry. We present data from the settling behavior as well as the design process of the separator.