CFB Combustion of alkali-laden biomass: Agglomeration and fouling resistance

• The maximum allowance of specific accumulating potassium weight in the bed was addressed. • Agglomeration tests were performed in both low and high bed temperature. • In-line two deposit probes were provided to examine deposition fluxes and fouling resistances. • Effects of K-content on IDT and TDT were clearly described. Biomass co-firing in circulating fluidized bed (CFB) boilers offers a promising pathway toward sustainable power generation. However, biomass fuels rich in alkali metals—particularly potassium—pose significant operational challenges such as bed agglomeration and superheater fouling. This study presents the first experimental investigation into the combustion behavior of two under-researched tropical biomass fuels—oil palm empty fruit bunch (EFB) and palm kernel shell (PKS)—in a 100 kWth CFB reactor. The work focuses on three objectives: (i) to examine fired-side problems, including bed agglomeration and fouling; (ii) to determine the critical potassium accumulation level leading to defluidization; and (iii) to quantify the evolution of fouling thermal resistance using a simplified thermal model to support optimized soot-blowing strategies. Bed material and agglomerate samples were analyzed using SEM/EDX, revealing the formation of low-melting potassium silicates responsible for agglomeration. Results indicate that EFB and PKS co-firing significantly increases the risk of agglomerate formation through both reactive (coating-induced) and non-reactive (melt-induced) mechanisms. Additionally, time-dependent fouling resistance data highlight the need for adaptive cleaning schedules to maintain heat transfer efficiency. These findings are particularly valuable for tropical Asian countries where these fuels are abundantly available but remain underexplored in CFB applications. This work provides foundational insights for improving the reliability and efficiency of biomass CFB systems through better fuel management and fouling mitigation strategies.