Potassium Capture by Kaolin, Part 2: K2CO3, KCl, and K2SO4

The reaction of kaolin powder with K 2 CO 3, KCl, and K 2 SO 4 under suspension-fired conditions was studied by entrained flow reactor experiments and equilibrium calculations. The influence of reaction temperature, K-concentration in the flue gas, molar ratio of K/(Al + Si) in the reactants, and gas residence time on the reaction was investigated. The results showed that the K-capture level ( C K ) (g potassium reacted by per g kaolin available) of K 2 CO 3 and KCl by kaolin generally followed the equilibrium predictions at temperatures above 1100 °C, when using a kaolin particle size of D 50 = 5.47 μm and a residence time of 1.2 s. This revealed that a nearly full conversion was obtained without kinetic or transport limitations at the conditions applied. At 800 and 900 °C, the measured conversions were lower than the equilibrium predictions, indicating that the reactions were either kinetically or diffusion controlled. The measured C K of K 2 SO 4 by kaolin was much lower than the equilibrium predictions. Kaliophilite (KAlSiO 4 ) product was predicted by the equilibrium calculations of the K 2 SO 4 capture reaction; however the XRD results revealed that leucite (KAlSi 2 O 6 ) was formed. Compared with the C K of KOH reacting with kaolin, the C K of K 2 CO 3 was similar, while the C K values of KCl and K 2 SO 4 were both lower.