To study the influence of local conditions on the reaction between gaseous KCl and kaolin or coal fly ash experiments were done on CHECs electrically heated entrained flow reactor, which can simulate the local conditions in suspension fired boilers. The experimental results were compared with model calculations to support the interpretation. The extent of the reaction between KCl vapor and coal minerals was evaluated by the amount of formed water insoluble potassium in the product. The effects of reaction temperature, residence time and potassium load on the potassium capture by coal minerals were studied. Due to not completely well controlled conditions during the experiments only preliminary conclusions can be provided. For experiments done at 1100°C with a molar ratio of K/Si=0.3 and a residence time of 1.07s approximately 80% of potassium from KCl reacted with kaolin. A changed temperature (1100-1300 °C) or a changed amount of KCl (K/Si = 0.1 – 0.34) did only change the KCl conversion slightly. Si and Al rich coal ash seems to be less efficient to react with KCl compared to kaolin. However the applied coal ash had a larger particle size (d50 = 22μm) compared to the kaolin (d50 = 10μm).