Abstract
Substitution of coal in coking coal blend with bio-coal is a potential way to reduce fossil CO2 emissions from iron and steelmaking. The current study aims to explore possible means to counteract negative influence from bio-coal in cokemaking. Washing and kaolin coating of bio-coals were conducted to remove or bind part of the compounds in the bio-coal ash that catalyzes the gasification of coke with CO2. To further explore how the increase in coke reactivity is related to more reactive carbon in bio-coal or catalytic oxides in bio-coal ash, ash was produced from a corresponding amount of bio-coal and added to the coking coal blend for carbonization. The reaction behavior of coals and bio-coals under carbonization conditions was studied in a thermogravimetric analyzer equipped with a mass spectrometer during carbonization. The impact of the bio-coal addition on the fluidity of the coking coal blend was studied in optical dilatometer tests for coking coal blends with and without the addition of bio-coal or bio-coal ash. The result shows that the washing of bio-coal will result in lower or even negative dilatation. The washing of bio-coals containing a higher amount of catalytic components will reduce the negative effect on bio-coke reactivity, especially with acetic acid washing when the start of gasification temperature is less lowered. The addition of bio-coal coated with 5% kaolin do not significantly lower the dilatation-relative reference coking coal blend. The reactivity of bio-cokes containing bio-coal coated with kaolin-containing potassium oxide was higher in comparison to bio-coke containing the original bio-coal. The addition of ash from 5% of torrefied bio-coals has a moderate effect on lowering the start of gasification temperature, which indicates that the reactive carbon originating from bio-coal has a larger impact.
Highlights
Most of the iron units used for steelmaking are produced by reduction and smelting in the blast furnace (BF)
A great challenge for steel producers is to lower the CO2 emissions that are mainly related to the use of fossil coal for the injection or production of the coke to be used for reduction and smelting in the BF
The aim of this study is to find out if higher added amounts, with less effects on bio-coke reactivity, can be reached by using (1) washed bio-coals with lowered contents of catalytic ash oxides or (2) bio-coal coated with kaolin aiming to bind the catalytic oxides in the bio-coal ash
Summary
Most of the iron units used for steelmaking are produced by reduction and smelting in the blast furnace (BF). The BF is a counter-current process where top-charged iron ore, coke and fluxes descending through the shaft meet ascending reducing gas generated in the lower part by partial combustion of tuyere-injected auxiliary reducing agents and some coke in oxygen-enriched hot blast air. A great challenge for steel producers is to lower the CO2 emissions that are mainly related to the use of fossil coal for the injection or production of the coke to be used for reduction and smelting in the BF. The biomass generation time is comparatively short, and as the carbon cycle is closed the contribution to global warming is lowered [7]
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