Characterisation of Dendromass Ash Fractions Captured in Power Plant with a View to their Further Utilization

Small and larger dendromass-burning power plants entrust the management of the ash waste to companies which guarantee its ecological disposal. In order to specify the correct disposal or further utilization of the dendromass ash, the various slag and fly ash fractions from a power plant combusting waste wood were analyzed and compared in this work. The plant produces approximately 660 t of ash waste/year. The efficiency of combustion depends on the season, dendromass quality and plant operating conditions. The proportion of carbon residue (incomplete burnt wood-chips) in slag and ash fractions increases in the winter months. Except for the seasonal carbon residue, the crumble slag and fine ashes captured in the flue channel and cyclone are similar in chemical composition and phase (28 - 44 wt.% CaO; 25 - 35 % SiO2; similar to 7 % Al2O3; similar to 5 % K2O; similar to 4.5 % MgO). The finest ash captured in the fabric filter contains less silicon and alumina compounds (<7 % SiO2; similar to 2 % Al2O3) and a significantly higher portion of potassium and sulphur, and chlorine compounds (approx. 13 % K2O; 3.5 % S; <1.5 % Cl) which are well soluble in water. All ash fractions produce strongly alkaline leaches in first contact with water. The differences in the chemical composition of captured ashes provide an impulse for considering the possibility of effective re-utilization of individual fractions.