Abstract
The blast furnace still dominates the production and supply of metallic units for steelmaking. Coke and coal used in the blast furnace contribute substantially to CO2 emissions from the steel sector. Therefore, blast furnace operators are making great efforts to lower the fossil CO2 emissions and transition to fossil-free steelmaking. In previous studies the use of pre-treated biomass has been indicated to have great potential to significantly lower fossil CO2 emissions. Even negative CO2 emission can be achieved if biomass is used together with carbon capture and storage. Blast furnace conditions will change at substantial inputs of biomass but can be defined through model calculations when using a model calibrated with actual operational data to define the key blast furnace performance parameters. To understand the effect, the modelling results for different biomass cases are evaluated in detail and the overall performance is visualised in Rist- and carbon direct reduction rate (CDRR) diagrams. In this study injection of torrefied biomass or charcoal, top charging of charcoal as well as the use of a combination of both methods are evaluated in model calculations. It was found that significant impact on the blast furnace conditions by the injection of 142 kg/tHM of torrefied biomass could be counteracted by also top-charging 30 kg/tHM of charcoal. With combined use of the latter methods, CO2-emissions can be potentially reduced by up to 34% with moderate change in blast furnace conditions and limited investments.
Highlights
The analysis and higher heating value (HV) of pulverised coal (PC), TB1, TB2 and CC used in this study are shown in Table 1, where the PC and CC are carbonaceous materials with high C content and HV
The weighed amount of pellets, the slag basicity (B2) and the specific blast volume in the operational data can be quite closely estimated in the model calculation for the reference case (Ref.)
A comparative evaluation of introduction of pre-treated biomass to the blast furnace (BF) through injection and top charging using a BF model calibrated with actual BF data has been conducted
Summary
In a previous study the potential to reduce CO2 emissions by applying different methods as e.g., top gas recycling [1], use of pre-reduced burden as hot briquetted iron (HBI)/direct reduced iron (DRI) [2], injection of hydrogen-rich gases (coke oven gas, H2 ) [2,3,4,5,6,7] or introduction of pre-treated biomass (torrefied biomass (TB) and charcoal (CC)) [4]. Comparing the above-mentioned methods, it was apparent that the introduction of pre-treated biomass in the form of TB and CC has the largest potential for avoiding fossil CO2 emissions when considering the total process system with production of heat and power from process gases. Through CO2 capture and storage, both fossil and renewable CO2 is captured, which results in a significantly higher total CO2 capture than the generated fossil CO2
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