Control of Ash-Related Problems During Pf-Combustion: Drop-Tube Observations with Additives and Blending of Low-Rank Coals

Coal switching from high- or medium- to low-rank categories is massively practiced. However, coal consumers, especially from power plant, often experience problems such as slagging and fouling. To overcome these problems, adding additives and coal blending can be carried out. In this study, five different low-rank coals were tested in a drop-tube combustor to grade the coals from the best to the lowest grade according to their ash deposition. Furthermore, the effect of adding four different compositions of additives and coal blending on ash deposition of the lowest grade coal was investigated. The study comprised theoretical calculation prediction, drop tube furnace (DTF) combustion, ash morphology analysis, and ash mineralogy analysis. The test results showed that MgO-rich coal is the best grade coal among the five tested coals, while sodium-rich coal being the lowest grade coal. Additionally, addition of aluminum-based additives at 0.05 wt% into the low-grade coal revealed less ash deposition propensities compared to the addition of other additives (0.05 wt% MgO, 0.1 wt% MgO, and 0.05 wt% MgO + 0.05 wt% Al₂O₃) and coal blending method. This result is consistent with the results of probe observations, ash morphology, and ash mineralogy which show clean probe surface with unfused particles predominantly containing quartz.