Structure-governed potassium retention mechanism in the slagging and non-slagging gasification condition of corn straw

Understanding the potassium retention mechanism in biomass gasification is the key for mitigating the severe ash-related issues (deposition, low slag viscosity, etc.) to gasifier operation. In this study, the kaolin addition was effective in K retention in both non-slagging and slagging gasification conditions, albeit through distinct mechanisms. In the non-slagging condition, K retention in the dry ash was predominantly governed by the crystallization kinetics of minerals with various K retention abilities. Notably, leucite demonstrated the highest retention ability followed by kalsilite and KAlO2. In contrast, the K retention was mainly thermodynamically controlled in the slagging gasification condition. The charge-compensation effect of K+ to the four-coordinated Al3+ was key for the K retention, and the Si-O-Al bond was converted to Si-O-KAl with kaolin addition. Moreover, a novel method for determining the Gibbs free energy (ΔG) of slag in the K capture reaction was introduced, demonstrating a decrease in ΔG from −16.66 kJ/(mol⋅K−1) to −57.67 kJ/(mol⋅K−1) with a 5 wt% kaolin addition, resulting in a 38.46 % increase in K retention. Finally, the viscosity of the biomass slag was empirically correlated with the K release ratio (R2 = 0.95), providing one stone for two birds strategy for addressing ash deposition and slag mobility issues.