(752f) In-Situ pH Control for Selective Removal of Toxic Elements to Sustain Water Supply for Cooling and Process Water

Water quality determines the feasibility of using non-traditional water for current cooling equipment in thermoelectric power plants. The “tough toxic impurities” in low quality water are the most frequent existing species in cooling water that limits the number of water recycle. Selective separation remove the key saline constitutes selectively for the recycled water therefore reduces the energy consumption. One of the toxic elements in impaired water heat-exchanger is the silica. Conventionally, it was removed by adding chemicals to adjust aqueous pH. The toleration of silica in cooling is around 20 - 100 ppm depending on the heat-exchange efficiency. However, acidification of the feed cooling water is applied to filtrate silica in coagulation was not an efficient process. Silica will form multiple compounds with other constitutes in aqueous at different pHs. At high pH, ~10, silica will stay as ionic form that opens an opportunity to use electrochemical driven force to selectively separate silica from aqueous. However, raise the feed water pH using chemicals is not a viable solution because the cost as well as the increase of TDS that needs more energy to treat. Electrodeionization (EDI) offers the prospect of desalination with a low energy footprint. It is a modular technology based on electrically driven membrane separations platform and is capable of producing clean water fit for consumption and numerous industrial processes such as energy production, semiconductors, and pharmaceuticals. ANL’s resin wafer electrodeionization (RW-EDI) is developed from commercial EDI technology with higher energy efficient and better economic viability in producing portable water. A bench-scale RW-EDI has been demonstrated capable to desalinate brackish water (i.e., one of the sources of impaired water) with 90% water recovery at 0.70 kwh/m³ or ~ 30% energy efficiency. In-situ pH control of the process stream during desalination is a unique capability using the RW-EDI that enables low cost removal of “tough toxic impurities” in cooling system. We use RW-EDI technology to extract silica from aqueous.