Abstract
Coke corresponds to 2/3–3/4 of the reducing agents in BF, and by the partial replacement of coking coals with 5–10% of bio-coal, the fossil CO2 emissions from the BF can be lowered by ~4–8%. Coking coal blends with 5% and 10% additions of bio-coals (pre-treated biomass) of different origins and pre-treatment degrees were carbonized at laboratory scale and with a 5% bio-coal addition at technical scale, aiming to understand the impact on the bio-coal properties (ash amount and composition, volatile matter content) and the addition of bio-coke reactivity. A thermogravimetric analyzer (TGA) connected to a quadrupole mass spectroscope monitored the residual mass and off-gases during carbonization. To explore the effect of bio-coal addition on plasticity, optical dilatometer tests were conducted for coking coal blends with 5% and 10% bio-coal addition. The plasticity was lowered with increasing bio-coal addition, but pyrolyzed biomass had a less negative effect on the plasticity compared to torrefied biomasses with a high content of oxygen. The temperature for starting the gasification of coke was in general lowered to a greater extent for bio-cokes produced from coking coal blends containing bio-coals with higher contents of catalyzing oxides. There was no significant difference in the properties of laboratory and technical scale produced coke, in terms of reactivity as measured by TGA. Bio-coke produced with 5% of high temperature torrefied pelletized biomass showed a similar coke strength as reference coke after reaction.
Highlights
The iron-ore-based blast furnace (BF) process is still the most dominant method for producing metallic iron units for steelmaking [1]
The results show that the max. dilatation of CC5 and HTT5 was quite similar to BB but dropped for the other coking coal blends
This study aimed to understand the impact of different bio-coal types from different origins and pyrolysis degrees, with added amounts of 5% or 10% to an industrially used coal blend, on carbonization and quality of bio-coke structure and reactivity
Summary
The iron-ore-based blast furnace (BF) process is still the most dominant method for producing metallic iron units for steelmaking [1]. Besides working as a reducing agent for iron ore, coke serves as the structural support for the burden in the furnace and provides passages for the upward movement of reducing gases [1]. The total consumption of coke is about 300 kg/t hot metal [1], depending on the amount of auxiliary reducing agents used (coke, coal, oil natural gas, etc.) [2]. The iron and steel industry aims to decrease the use of fossil carbon to minimize CO2 emissions. According to the World Steel Association, the iron and steel industry accounts for approximately 7–9% of total world CO2 emissions [3]
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