High-temperature melting behavior of urban wood fuel ash

Ashes from commercial wood fuel blends show wide compositional ranges that in part can be related to an admired soil component. To evaluate agglomerat ion potentials and to formulate predictive models, an experimental study wa s conducted of an urban wood waste fuel ash from an operating power plant i n California. The melting relations were investigated from the liquidus at 1276 degrees C to the near solidus at about 1130 degrees C. The liquidus ph ase is melilite composed of a solid solution dominated by akermanite and so dium melilite. A phosphate phase appears at 1207 degrees C and can be descr ibed as a solid solution of calcium phosphate, sodium phosphate, and calciu m disilicate. Garnet appears at 1159 degrees C and is composed of an andrad ite, pyrope, and grossular solid solution. The alkali metals are partially lost to the atmosphere during the experimental duration. Sodium loss is mod erate and dependent on the liquid remaining. Potassium shows very low parti tioning into the solid phases and is strongly lost from the slag. The exper imental results have been used to formulate a calculation procedure for eva luating the high-temperature compositional behavior of urban wood fuel slag . The results predict strong potassium volatilization tendencies for relati vely pure wood fuel ashes with less than about 47 wt % SiO2. Because the Si O2 content increases with increasing soil component, the effect of soil is to retain potassium in the solid residue, In addition, the effect of an adm ired soil component on wood fuel slag behavior is principally to increase v iscosity and has little effects on the surface tension. Because of the inve rse effect of viscosity on agglomeration, the result is that an admired soi l to wood fuel will reduce alkali losses and agglomeration potential.