Chemical Forms of Ash-Forming Matter in Woody Fuels for FBC

The prediction of the ash behavior in combustion processes is enhanced by the determination of the ash-forming matter in the fuel. The scope of this work was to characterize Scandinavian wood fuels by studying the wood, bark and leaves from a spruce and an aspen. Chemical Fractionation, a step-wise leaching procedure that treat the fuel in water, ammonium acetate and hydrochloric acid, was used to determine the solubility of the ash elements. The resulting solutions were further analyzed on ionic species, which was coupled to the presence of salt compounds in the original biomass tissues. The leaching procedure dissolved nearly 100% of the ash-forming matter. The phosphorus (P), chlorine (Cl) and some of the sulfur (S) were readily leached with water and found present as HPO₄²⁻, SO₄²⁻ and Cl⁻ in the solutions. The simultaneous dissolving of potassium (K) in this step proved the presence of water soluble potassium salts in the biomasses. The remaining K after the water treatment and all magnesium (Mg) dissolved completely in the ammonium acetate step together with a large part of the tissues’ calcium (Ca) and manganese (Mn). The remaining Ca after the second step was leached in hydrochloric acid together with equivalent amounts of oxalate ions, C₂O₄²⁻. This proved the presence of acid soluble calcium oxalate in the tissues, a salt with low solubility in neutral pH.