Potassium capture by coal fly ash: K2CO3, KCl and K2SO4

The potassium capture behavior of two coal fly ashes at well-controlled suspension-fired conditions was investigated through entrained flow reactor (EFR) experiments and chemical equilibrium calculations. The impact of local reaction conditions, i.e., the type of K-salts (K2CO3, KCl or K2SO4), K-concentration in flue gas (molar K/(Al + Si) ratio in reactants), reaction temperature, and coal ash type on the reaction was studied. The results show that the K-capture level of coal fly ash at a K-concentration of 500 ppmv (K/(Si + Al) = 0.481) was considerably lower than the equilibrium data as well as the measured K-capture level of kaolin. However, at 50 ppmv K (with a molar K/(Si + Al) ration of 0.048), no obvious difference between kaolin and coal fly ash was observed in this work. Comparison of results for different K-species showed that coal fly ash captured KOH and K2CO3 more effectively than KCl and K2SO4. Additionally, a coal fly ash with higher content of Si and a lower melting point captured KCl more effectively than the reference coal fly ash.