The role of residual char on ash flow behavior, Part 3: Effect of Fe2O3 content on ash fusibility and carbothermal reaction

Residual char shows an obvious influence on ash fusibility through carbothermal reaction. Besides of SiO2, Fe2O3 can also react with residual char to produce metallic iron (Fe) and Fe3Si by Fe-char reaction at high temperatures. Effects of Fe2O3 content on fusibility and carbothermal reaction of ash with residual char were investigated in this work. The results showed that refractory mineral, metallic iron (Fe), Fe3Si and SiC, are formed by Fe-char reaction and carbothermal reaction between mineral and residual char. When Fe2O3 content of ash is lower than 12%, ash fusion temperatures (AFTs) of ash ascend with the increasing residual char content. However, when Fe2O3 content in ashes is more than 12%, flow temperature (FT) of ashes shows a decrease when residual char content increases from 10% to 15%. In the former case, residual char mainly engages in carbothermal reaction, and ash fusibility is largely dependent on SiC content which increases with the increasing residual char content. In the latter case, most of residual char is involved in Fe-char reaction. The AFTs of ashes largely depends on Fe3Si at high temperatures. An increase in Fe2O3 content is favorable to formation of Fe3Si. Besides, Fe2O3 in ash lowers temperature of carbothermal reaction from 1500 degrees C to 1300-1400 degrees C, while the increase of Fe2O3 content is detrimental to formation of SiC.