Co-firing biomass with coal on ash deposition behavior at various temperatures in a Down-Fired furnace

The ash fouling and slagging caused by biomass combustion limits its extensive utilization, and biomass/coal co-firing is considered a promising way to alleviate this issue. In this study, the ash deposition characteristics at various flue gas temperatures during biomass/coal co-firing were investigated in a high-temperature down-fired furnace. The results indicated that an increase in flue gas temperature caused less deposition mass and intensified sintering of the deposited particles, which elevated the compactness and strength of deposits. As the flue gas temperature rose to 1100 °C, the deposited particles in the initial layer exhibited significant melting deformation and tightly adhered to the probe surface. The amounts of sintered particles in the outer and inner layers had a pronounced increase. The slagging indicators suggested that the slagging propensity of the deposits was enhanced remarkably at the flue gas temperature of 1100 °C. The influence of higher flue gas temperature on ash deposition formation was summarized as enhancing the melting degree of deposited particles, promoting the thermophoresis of low-melting fine ash particles and the condensation of SO2 and alkali vapor, as well as accelerating the formation reaction of low-melting Ca, Fe-bearing silicates.