Ash characteristics investigation from co-firing of Calliandra calothyrsus and Gliricidia sepium with a high-sulfur and -iron coal in drop tube furnace

Calliandra calothyrsus and Gliricidia sepium ash characteristics as co-firing fuel to high-sulfur and -iron coal were investigated through theoretical prediction, FactSage modelling, and combustion experiment in drop tube furnace. The results show that the addition of Calliandra and Gliricidia were able to mitigate the slagging risk according to theoretical prediction and FactSage modelling. Slag formations were predicted to occur at higher combustion temperature compared to coal which was reflected in higher ash fusion temperature. The results of combustion experiment showed an agreement with less ash deposition and cleaner probe surface. The addition of Calliandra and Gliricidia increased the high-melting minerals and decreased Fe-based minerals. However, domination of Ca2SO4 in addition of 25 wt% Gliricidia can be detrimental with presence of strongly adhered ash and material degradation. This research provides an important insight of Calliandra and Gliricidia utilization as co-firing fuel that improve the ash characteristics of high-sulfur and -iron coal.