Synergistic effects on the co-combustion of medicinal biowastes with coals of different ranks

In attempt to understand the synergistic mechanisms controlling the co-combustion processes of blended fuels, two medicinal biowastes (lignocellulose and non-lignocellulose) and three different-rank coals (lignite, bituminite and anthracite) were employed in this work. Intrinsic characteristics of parent materials were firstly measured with the help of 13C NMR, FTIR and XRD technologies, followed by the thermogravimetric analysis of mono- and co-combustion behaviors. The results suggested that synergistic processes depended on the amount and properties of light volatiles in biowastes, but both lignocellulose and non-lignocellulose biowastes had positive effects on co-combustion with coals to some extent. Among them, the blends with low-rank coal showed the highest combustion efficiency. The actual HHV of blends with coal A (low-rank coal) exceeded their theoretical one, reaching the increases of 3.1–4.5%, 6.9–7.0% and 11.5–11.6% for 30%, 50% and 70% addition of coal A, respectively. Additionally, the introduction of biowastes also lowered the activation energy to initiate main decomposition of coals, increased the co-combustion reactivity, as well as altered the main combustion profiles to different extends. In general, co-combustion with low-rank coal achieved the best combustion efficiency among the blends. These findings would be beneficial for efficient utilization of organic biowastes as solid fuels in existing co-firing equipment.