A clean technology for decarbonation of geothermal waters from Chott El Fejjej using a three-phase fluidized bed reactor — modelling aspects Original Research Article

Cecarbonation is considered in the context of research on the prevention of scaling. To apply it to the geothermal waters of Chott El Fejjej in El Hamma (Gabes, Tunisia), we examined water characteristics having a high permanent calcic hardness (100°F) accelerating the scaling and a high temperature at emergence (65°C) favouring the exhaust of CO2. In addition to these natural factors which predispose water to scaling, we introduced air bubbling with a distributor, permitting transport of CO2 (leading quickly to the oversaturation in calcium carbonate) and injected seeds that contribute, by adsorption, to the acceleration of calcium carbonate precipitation. This is a clean technology of decarbonation without chemical reagents. This research links our previous work in 2002 where we used a pilot reactor having a capacity of 50 L. We achieved a continuous pilot reactor having a capacity of about 1 m3 higher performance. This reactor was conceived in order to allow the study of some key parameters of importance in scaling at different radial and axial levels. It determined reactor efficiency by its output (fundamental objective) and characterization of the flow state. Decarbonation was performed to reach a target residual complete alcalimetric title (CAT) 6°F (1°F = 12.2 mg HCO3− /L), which stemmed from our previous experimental work. The target output was reached and was even exceeded under specific conditions where working parameters were optimised. We investigated the reactor output at its gradual filling up. This method showed an evolutionary aspect and a study of modelling kinetics according to two methods: a gait according to diffusional and Reddy models, and a gait adopting two approaches — first-order kinetics and the Haas and Karra model. The preferred model was the one of Haas and Karra that was perfectly applied (R2 0.99) and that is original in the domain of decarbonation under the complex, specific conditions of water characteristics such as temperature, etc.