Comparative study of thermal properties of bio-coal from aromatic spent with low rank sub-bituminous coals

[Display omitted] •Bio-char were prepared from various aromatic spent.•Their fuel properties depend upon the pyrolysis temperature.•Probable fouling and slagging potentials.•Can be used as fuel with sub-bituminous Indian coals. In present investigation, biocoal samples were prepared from aromatic plant waste of two perennial grasses, i.e. Cymbopogon flexuosus (lemongrass) and Vetiveria zizanioides (khus) after oil extraction, root of Rosa damascene (rose), bark of Eucalyptus citriodora. These biocoals were characterized by proximate, ultimate, metal, thermogravimetric analysis (TGA), Fourier Transform Infra Red (FTIR) spectroscopy and ash analyses. Activation energies, initial temperature of devolatilization, maximum rate of weight loss (Rmax), fouling, slagging and alkali index were determined on the basis of TGA and ash analysis. These biocoals have good calorific values. There is possibility of slagging and fouling in combustion system but it is not severe. Owing to their similar fuel properties as high sulphur sub-bituminous coal, they can be good candidates for co-firing. Blending of these biocoals with high sulphur coals will serve dual purpose as (i) alternate fuel, and (ii) reduction in SO2 emission.