2017 Volume 57 Issue 10 Pages 1788-1796
Growing concerns over fossil CO2 emissions has created a considerable interest in an efficient utilization of renewable biomass in steel industry. Biomass lignin can be used as binder and reducing agent in the blast furnace briquettes. The traditional briquettes consist of various iron oxide-containing residues and cement is used as binder to give the proper mechanical strength. In the present study, cement (C) has been partially and totally substituted with lignin (L) to produce briquettes containing 0–12 wt.% lignin (L/C: 0, 10, 25, 50 and 100%). The mechanical strength has been evaluated based on drop test and tumbler index measurement. The partial replacement of cement with lignin up to 25% (3.0 wt.% lignin in briquettes) was exhibited adequate briquettes strength for blast furnace application. At higher substitution rate (L/C: 50 and 100%), the briquettes strength was sharply decreased. The briquettes with proper mechanical strength (L/C: 0, 10 and 25%) were subjected to self-reduction under inert atmosphere using thermogravimetric technique (TGA). The reduction rate of briquettes increased when increasing the cement substitution with lignin. The reduction took place in two main steps at 500–800°C and 800–940°C. Combined effect of gas diffusion and interfacial reaction were the rate determining step at the first stage while carbon gasification was controlling the second step of reduction. Interrupted reduction tests have been conducted to evaluate the compression strength after reduction. For all briquettes, the increased reduction temperature and lignin content deteriorated the briquette’s mechanical strength due to the effect of dehydration and lignin gasification.