Chemical properties of solid biofuels—significance and impact

The chemical composition of solid biofuels (as defined in [Directive 2000/76/EC of the European Parliament and of the Council on the Incineration of Waste. In: European Commission, editor. Official Journal of the European Communities, vol. L 332; 2000. p. 91–111] and [CEN/TC 335—WG2 N94. Final draft. European Committee for standardization, editor. Solid biofuels—fuel specifications and classes. Brussels, Belgium; 2003.] has manifold effects on their thermal utilisation. C, H and O are the main components of solid biofuels and are of special relevance for the gross calorific value, H in addition also for the net calorific value. The fuel N content is responsible for NOx formation. NOx emissions belong to the main environmental impact factors of solid biofuel combustion. Cl and S are responsible for deposit formation and corrosion and are therefore relevant for a high plant availability. Furthermore, Cl causes HCl as well as PCDD/F and S SOx emissions and both elements are involved in the formation of aerosols (submicron particle emissions). The ash content influences the choice of the appropriate combustion technology and influences deposit formation, fly ash emissions and the logistics concerning ash storage and ash utilisation/disposal. Major ash forming elements (Al, Ca, Fe, K, Mg, Na, P, Si, Ti) are of relevance for the ash melting behaviour, deposit formation and corrosion. In addition, volatile elements such as Na and K are main constituents of aerosols. Volatile minor elements (As, Cd, Hg, Pb, Zn) play a major role in gaseous and especially aerosol emissions as well as in deposit formation, corrosion and ash utilisation/disposal. Either partly or non-volatile minor elements (Ba, Co, Cr, Cu, Mo, Mn, V) are of special relevance for ash utilisation. The present paper discusses the influence of chemical fuel properties on biomass combustion plants as well as possibilities and recommendations for controlling them.