Experimental study on ash fusion characteristics and slagging potential using simulated biomass ashes

Ash fusion characteristics (AFC) affect biomass slagging significantly. Due to the complexity of biomass ash composition, simulated ashes have been used for investigating AFC. Considering the practical ash components used in power plants, the mixture of SiO₂, CaO, K₂O and Al₂O₃ were used as simulated ashes. Deformation temperature (DT) changes remarkably as the ash components of biomass change, and thus is selected as an index. The results are presented by SiO₂-CaO-K₂O ternary diagrams with three different ratios of Al₂O₃. The ternary diagrams are divided as high-temperature zone (HZ, >1400 °C), medium-temperature zone (MZ, 900–1400 °C) and low-temperature zone (LZ, <900 °C). Results also show that without Al, low melting products (K₄CaSi₃O₉) of the eutectic reactions among K₂O, CaO and SiO₂ led to a DT of 1290 °C in MZ. With the addition of Al₂O₃, DT can increase from LZ to MZ at high K content condition because Si-Al-K compounds such as KAlSi₂O₆ and KAlSi₃O₈ formed. However, DT decreased and moved from HZ to MZ with the addition of Al while Ca or Si content is high because of Si-Al-Ca compounds such as Ca₂Al₂SiO₇ and CaAl₂Si₂O₈. Besides, the difference (DSD) between deformation temperature and softening temperature has been used to predict the slagging potential. Long slag tends to occur in the zone of high K content, where SiO₂ leads to a larger DSD than CaO does. Al₂O₃ can decrease DSD and form short slag, which is suitable as additive for relieving slagging.