With the increasing global emphasis on renewable energy, the generation of biomass fly ash is anticipated to rise substantially in the coming years. This trend highlights the urgent need for effective strategies to manage and utilize this byproduct sustainably. This study reviews and classifies selected types of biomass ashes, treating them as representative examples that illustrate the wide variability in chemical compositions and physical properties across different biomass sources. These include ashes derived from woody biomass, agricultural residues, animal-origin biomass, and sewage sludge. Biomass ashes exhibit significant heterogeneity compared to coal ashes, which makes understanding their chemical composition—particularly the major components such as calcium (Ca), silicon (Si), and phosphorus (P)—critical for identifying suitable industrial applications. Special categories of ashes with elevated heavy metals and chlorine (Cl) levels are also identified and discussed. This approach enables the identification of sustainable utilization pathways, ranging from traditional uses, such as agricultural fertilizers and construction materials, to emerging applications in advanced engineering materials. Additionally, this paper addresses the assessment and mitigation of potential risks related to hazardous metals in biomass ashes.

The use of poultry litter (PL) as a sustainable fuel is gaining more attention due to its wide availability and carbon neutrality. However, this type of feedstock is rich in ash and typically contains a high concentration of chlorine (Cl) and alkali elements (Na, K). Therefore, it is likely to cause unwanted issues during combustion and co-combustion, such as chlorine-induced corrosion, ash deposition, and bed agglomeration. In this study, for the first time, the influence of aluminosilicate additives on the above problems of poultry litter was investigated. Three aluminosilicate minerals are under consideration: kaolin, halloysite, and bentonite. Their influence on the chemical composition and meting tendencies of two poultry litter ashes are determined. The investigated ashes, PL1 and PL2, are characterized by different chlorine contents of 6.38% and 0.42%, respectively. The results show that in the case of the chlorine-rich PL1 ash, the additives reduced the chlorine content by up to 45%, resulting in a 3.93% of chlorine in the case of halloysite, 3.48% in the case of kaolin, and 4.25% in the case of bentonite. The additives also positively influenced the shrinkage starting temperature and the deformation temperature of the PL1 ash.

Biomass and waste contain elevated concentrations of chlorine and alkali metals that promote the problem of high-temperature chlorine corrosion in power boilers. The results are rapid metal loss, increased maintenance costs, and reduced operational availability. This review paper provides a comprehensive overview of the high-temperature chlorine corrosion in biomass- and waste-fired boilers. The occurrence and chemical speciation of chlorine in these fuels are discussed together with its transformation during thermal conversion. Particular attention is devoted to the mechanisms of active oxidation, the role of ash deposits and their chemistry. The corrosion performance of conventional boiler steels, nickel-based alloys, and protective coatings is evaluated. Laboratory investigation methods, including gravimetric measurement and microstructural characterization are reviewed alongside recent advances in computational modelling, such as thermodynamic equilibrium calculations and computational fluid dynamics. The review shows that corrosion severity is governed by the coupled effects of chlorine speciation, alkali metals, deposit chemistry, temperature, combustion conditions, and material properties. Advanced alloys and protective coatings can substantially improve corrosion resistance, but cannot completely eliminate degradation under prolonged exposure. The analysis also indicates that effective corrosion mitigation requires a combination of fuel modification, combustion optimization, deposit control, appropriate material selection, and surface engineering.