Abstract
Most modern blast furnaces (BFs) operate with Pulverized Coal Injection (PCI), but renewable and carbon neutral biochar could be applied to reduce the fossil CO2 emission in the short term. In the present study, heat and mass balance-based model (MASMOD) is applied to evaluate the potential of biochar in partial and full replacement of injected pulverized coal (PC) in the ironmaking BF. The impact of biochar injection on the raceway adiabatic flame temperature (RAFT) and top gas temperature (TGT) is evaluated. Three grades of biochar, produced from the pyrolysis of sawdust, were evaluated in this study. The total carbon content was 79.2%, 93.4% and 89.2% in biochar 1, 2 and 3, respectively, while it was 81.6% in the reference PC. For each type of biochar, 6 cases were designed at different injection levels from 30 kg/tHM up to 143 kg/tHM, which represent 100% replacement of PC in the applied case, while the top charged coke is fixed in all cases as reference. The oxygen enrichment, RAFT, and TGT are fixed for certain cases, and have been calculated by MASMOD in other cases to identify the optimum level of biochar injection. The MASMOD calculation showed that as the injection rate of biochar 1 and biochar 2 increased, the RAFT increased by ~190 °C, while TGT decreased by ~45 °C at 100% replacement of PC with biochar. By optimizing the moisture content of biochar and the oxygen enrichment in the blast, it is possible to reach 100% replacement of PC without much affecting the RAFT and TGT. Biochar 3 was able to replace 100% of PC without deteriorating the RAFT or TGT.
Highlights
Steel is the most used metal and most recycled material, with 1.95 billion metric tons produced in 2021, according to the World Steel Association [1]
The oxygen enrichment, raceway adiabatic flame temperature (RAFT), and top gas temperature (TGT) are fixed for certain cases, and have been calculated by mass balance-based model (MASMOD) in other cases to identify the optimum level of biochar injection
The production rate of hot metal kept constant; RAFT (Raceway adiabatic flame temperature) kept constant or varied; thermal reserve zone temperature (TRZT) kept constant; TGT was varied; Shaft efficiency was assumed to be constant as the reference; Slag basicity kept the same by adjusting the amount of limestone to blast furnaces (BFs), the slag rate varied; Pulverized Coal Injection (PCI) was varied, coke rate was kept constant; Pellets and briquettes rate kept constant; The generated dust and sludge kept constant at 15 kg/tHM of dust and 5.0 kg/tHM
Summary
Steel is the most used metal and most recycled material, with 1.95 billion metric tons produced in 2021, according to the World Steel Association [1]. The results of mathematical modelling indicated an increase in the blast furnace productivity by about 25% when 100 kg/tHM of charcoal is injected with 150 kg/tHM pulverized coal with an optimization of the oxygen enrichment [18]. Multi-dimensional (2D and 3D) and multi-phase (4, 5 and 6 phases) mathematical models based on chemical kinetics and transport phenomena have been greatly developed to evaluate the effect of injections (e.g., pulverized coal, natural gas, coke oven gas and waste plastics) and innovative burden materials (e.g., carbon composite agglomerate) on the BF performance [25,26,27,28,29]. The oxygen enrichment in the blast and moisture content of biochar were optimized to reach the highest injection rate of biochar
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