Chars from agricultural wastes as greener fuels for electric arc furnaces

The thermochemical properties of two chars obtained from agricultural residues, grape seed and pumpkin seed chars, have been studied in order to address their suitability to be used in electric arc furnace (EAF) steelmaking. Four coals (a metallurgical coal and three different anthracites), currently employed in an EAF process, were used for comparison. Proximate analyses of the four coals and the two chars were determined and compared. Isothermal CO2 reactivity and relative combustion reactivity of the carbonaceous samples were evaluated in a thermogravimetric analyser. Pyrolysis and gasification behaviour of these coal and char samples was studied in a wire mesh reactor in order to compare them at the high heating rate (1000 °C s−1) typical of EAF and short residence times (5 and 10 s). The two biomass chars exhibited markedly different properties, which matched those of their coal counterparts. Pumpkin seed char and the metallurgical coal were found to present similar and thermochemical properties. Thermal behaviour of grape seed char was closer to that of the anthracite coals. Nevertheless, it was established that grape seed char was more volatile and presented higher combustion and gasification reactivities. The stages of the steelmaking process which are more appropriate to feed the chars were also proposed.