Multi-objective Optimization of Ironmaking in the Blast Furnace with Top Gas Recycling

Abstract

Concern about the growing carbon dioxide content in the atmosphere has induced increasing research activities in the search for means to suppress the emissions of CO 2 in primary steelmaking. Blast furnace top gas recycling, combined with CO 2 stripping, has been proposed as a promising concept. The paper presents a numerical analysis of top gas recycling under massive oxygen enrichment of the blast based on a simulation of the process chain from coal and ore to liquid steel. Because of the conflicting goals of reducing both production costs and emissions, the task is formulated as a multi-objective optimization problem. The optimal states of the system studied were found to vary significantly on the Pareto frontier, which demonstrates that fundamentally different states of operation may be selected to strongly reduce the emissions, still keeping the steelmaking economically feasible. The findings stress the importance of selecting a proper state of operation for achieving a cost-efficient production of steel with reduced environmental impact. The results also show how emissions can be "artificially" reduced by minimizing the arising emissions within the system boundary.KEY WORDS: sustainable steelmaking; CO 2 emissions; top gas recycling; multi-objective optimization.gen enrichment of the blast would be economically feasible by optimizing the recycling conditions with respect to rate of auxiliary reductant, blast volume, temperature and oxygen content. The investigators concluded that the CO 2 emissions and stripping costs strongly affected the optimal recycling policy. A problem with this approach is, however, that it is difficult to provide realistic estimates of the future price of reductants and emissions, and, in particular, of the CO 2 stripping costs. The present paper therefore analyzes the economy and emissions of steelmaking by a multi-objective approach, where the two goals are treated as independent objectives: A similar approach, but for the system with conventional BF operation, was studied by Pettersson et al. 15) and Wang et al. 16) Like in the earlier analysis, 14) the simulations in the present paper consider the coke plant, sinter plant, hot stoves, blast furnace, stripping unit, the basic oxygen furnace and power plant, with the main attention focused on the blast furnace, for which a more detailed model is applied. The analysis shows how minimizing the conflicting goals results in different optimal states, where, e.g., maximum top gas recycling or maximum externally produced raw materials (coke and pellets) can be preferred despite increased costs due to the low emission rates within the plant, or, vice versa, how the steel production price can be reduced at the expense of increased emissions. The study also throws light on the effect of the steel production rate on the costs and emissions in the optimal states. The System StudiedThe entity comprised in this study is an integrated steel works, considering the main units starting from the raw material processing (sintermaking and cokema...

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