Combustibility of Portuguese shrubland species: analysis of corrosion, fouling, and slagging indices

The increasing utilization of shrubland biomass for energy production in Portugal necessitates a comprehensive understanding of combustion-related challenges, particularly corrosion, fouling, and slagging phenomena. This study presents a detailed analysis of combustion indices for thirty-eight Portuguese shrubland species, including representatives from major botanical families such as Cistaceae, Ericaceae, and Leguminosae. Through proximate and ultimate analysis, ash composition determination, and advanced statistical evaluation, we calculated and analyzed nine key combustion indices: Base/Acid Ratio, Slagging Index, Silica Ratio, Fouling Index, Alkali Index, Chlorine Index, Alkali Chloride Index, Corrosion Index, and Ash Fusion Temperature. Statistical analysis revealed that none of the combustion indices followed normal distributions, indicating the diverse nature of shrubland biomass composition. Principal component analysis identified four main factors explaining 86.7% of the variance in combustion behavior. The Base/Acid Ratio ranged from 1.39 to 168.62, with 94.7% of species showing very high slagging tendency. Fouling Index values varied from 0.36 to 2.71, with 68.4% of species showing medium fouling potential. Multiple regression analysis demonstrated that ash composition parameters can predict combustion indices with R2 values ranging from 0.433 to 0.871. Significant differences between species groups were observed for Alkali Index, Alkali Chloride Index, and Corrosion Index (p < 0.05). These findings provide essential data for optimizing shrubland biomass combustion systems and developing mitigation strategies for operational challenges in Portuguese biomass power plants.