Inhibition of calcium carbonate scaling by precipitation using secondary nucleation coupled to degassing with atmospheric air

Scaling by calcium carbonate precipitation is an important challenge during exploitation of geothermal water or geothermal district heating systems. Water decarbonation is a promising solution to mitigate calcium carbonate precipitation and reduce the scaling risks. In the current work, the decarbonation of geothermal water by coupling atmospheric air bubbling with seeding was investigated. For that, several operating conditions were studied and optimized such as air and water flows, hydrodynamics, residence time, and bubbling rate. Synthetic and real solutions were tested. To reveal the efficiency of the proposed process, the addition of chemicals was avoided. Results showed that, using continuously operating reactor and under optimized operating conditions, the decarbonation rate of a calcium carbonate solution tested (4 mmol/L of CaCO3, T = 50 °C) can exceed 30% without using chemicals. It was also shown that he residence time in the reactor is relatively short (2.5 min) and the protection of the walls from precipitate adherence was guaranteed.