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

The reaction of kaolin powder with K₂CO₃, KCl, and K₂SO₄ 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 K₂CO₃ and KCl by kaolin generally followed the equilibrium predictions at temperatures above 1100 °C, when using a kaolin particle size of D₅₀ = 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 K₂SO₄ by kaolin was much lower than the equilibrium predictions. Kaliophilite (KAlSiO₄) product was predicted by the equilibrium calculations of the K₂SO₄ capture reaction; however the XRD results revealed that leucite (KAlSi₂O₆) was formed. Compared with the C_K of KOH reacting with kaolin, the C_K of K₂CO₃ was similar, while the C_K values of KCl and K₂SO₄ were both lower.