Influence of co-processing of coal and oil shale on combustion characteristics, kinetics and ash fusion behaviour

Highlights: • Combustion and ash fusion of oil shale and coal blends were investigated. • Notable synergistic interactions were found that are dependent on blending ratio. • Activation energy was determined and was the lowest for 10 wt% oil shale in blend. • Combustion mechanism and reaction kinetics were determined. • The addition of oil shale lowers the slagging and fouling propensities. Combustion characteristics and ash fusion behaviours of Qinghai coal (QH) and Fushun oil shale (FS) and their blends were investigated. It was found that ignition index and burnout index of the blends reached maximum for the blend with 10 wt% FS, while its comprehensive combustibility index remained nearly unchanged when compared with the coal sample. With the increase in heating rates, combustion performance of the samples improved significantly. The statistical analysis demonstrated that combustion temperature contributed significantly (about 73% of the impact ratio) to the thermogravimetric mass loss, followed by oil shale blending ratio and heating rate. In addition, there is noticeable deviation between the experimental and theoretical curves of the blends in the temperature range of 410–480 °C, which indicates the existence of synergistic interactions. Moreover, the lowest apparent activation energy, determined using two model-free integral methods, was found to be 64.1 kJ/mol for the blend with 10 wt% FS. In addition, slag formation and mineral transformation of different samples were determined using the thermochemical database package FactSage 6.3. For the blend with 10 wt% of FS, anorthite, hematite, diopside and quartz were found to be the main crystalline phases at high temperatures. It is shown that the addition of FS mitigated the slagging and fouling tendency of the QH coal combustion.