Low energy recycling of salt from process water

Abstract

The objective of this Master´s thesis was to study the total energy consumption for salt recovery from fly ash. The treatment water (Brine) from neutralizing of fly ash contains salts that could be worth recovering. The study included a feasibility study of utilizing high-temperature heat pumps and stram compressors to increase the quality of waste heat streams. New technology for upgrading low-quality heat streams can become a part of salt production in the future. By recovering energy from the cooling water stream at Hydro, it could save the salt production by 19.4GWh per year of electrical power. The salt concentration of the brine at Langøya fluctuates through the year. The processing plant must have the robustness to handle the fluctuation of salt concentration. The larges component in the process is the MVR crystallizer, which must handle the fluctuation. If the MVR Crystallizer is designed for a high solid suspension, it can probably handle the fluctuation of NaCl and KCl in the salt composition, but increased CaCl2 concentration will reduce the efficiency. NOAH has installed a pilot crystallizer at Herøya Industripark. The results from the pilot experiment are supposed to give input to a full-scale plant. Some of the results from the pilot operation might be worthless for the design of a full-scale plant due to high specific circulation flow and low-temperature increase over the heat exchanger. The crystal size from the salt produced in step 1 in the pilot (similar to full-scale MVR) has been studied for two different temperature increases over the heat exchanger. The size of the crystals is probably within the range of what the industry can utilize

The objective of this Master´s thesis was to study the total energy consumption for salt recovery from fly ash. The treatment water (Brine) from neutralizing of fly ash contains salts that could be worth recovering. The study included a feasibility study of utilizing high-temperature heat pumps and stram compressors to increase the quality of waste heat streams. New technology for upgrading low-quality heat streams can become a part of salt production in the future. By recovering energy from the cooling water stream at Hydro, it could save the salt production by 19.4GWh per year of electrical power. The salt concentration of the brine at Langøya fluctuates through the year. The processing plant must have the robustness to handle the fluctuation of salt concentration. The larges component in the process is the MVR crystallizer, which must handle the fluctuation. If the MVR Crystallizer is designed for a high solid suspension, it can probably handle the fluctuation of NaCl and KCl in the salt composition, but increased CaCl2 concentration will reduce the efficiency. NOAH has installed a pilot crystallizer at Herøya Industripark. The results from the pilot experiment are supposed to give input to a full-scale plant. Some of the results from the pilot operation might be worthless for the design of a full-scale plant due to high specific circulation flow and low-temperature increase over the heat exchanger. The crystal size from the salt produced in step 1 in the pilot (similar to full-scale MVR) has been studied for two different temperature increases over the heat exchanger. The size of the crystals is probably within the range of what the industry can utilize