Effect of charcoal addition on the properties of a coke subjected to simulated blast furnace conditions

- Charcoal addition significantly increased the coke surface area.
- Charcoal addition enhanced the coke reactivity upon gasification in blast furnace.
- Charcoal did not affect the microstructure and microstrength of IMDC and RMDC.
- Charcoal addition did not reduce coke strength upon thermal load in blast furnace.
- Charcoal addition reduced coke strength upon gasification in blast furnace.

A pilot oven produced coke with the addition of 7.5 wt% charcoal (bio-coke) and the similarly produced base blend coke were subjected to gasification and annealing under the simulated blast furnace conditions. The effect of charcoal addition on the coke properties after gasification and annealing was characterised using Raman spectroscopy, ultra-micro indentation and tensile testing. The addition of charcoal significantly increased the coke reactivity with CO2 as a result of its increased surface area by charcoal. The addition of charcoal made no further contribution to the devolatilisation or mineral reactions of coke during annealing. The charcoal particles were well preserved after annealing at 2273 K, but preferentially consumed in the gasification. Annealing temperature had less effect on the graphitisation of the charcoal component compared to the coexisting inert maceral derived component (IMDC) and reactive maceral derived component (RMDC). The charcoal addition had no effect on the microstructure and microstrength of coexisting microtextural types during annealing and gasification. The charcoal presented a higher resistance to fracture than IMDC and RMDC under annealing conditions. The addition of charcoal did not deteriorate the coke resistance to strength degradation under the thermal load of blast furnace. However, charcoal addition caused more severe degradation by gasification as demonstrated by more reduction in the tensile strength of the bio-coke. This was attributed to the preferential solution loss reaction of the charcoal particles leaving voids which coalesced the pores in coke, thereby increasing the defects that cause stress concentration under loading.