Reduction of CO2 emissions from integrated steelmaking by optimised scrap strategies: Application of process integration models on the BF-BOF system

Abstract

In integrated steelmaking there are a number of means to reduce CO 2 emissions. One approach is to increase the metallic Fe input to the production system. A common belief is that scrap works as a CO2 diluent when introduced in iron ore based steelmaking. It is not necessarily so. Scrap is a key supplementary charge material in oxygen steelmaking converters, but scrap can also be utilised in ironmaking where it will decrease the use of reducing agents and with that also the specific CO2 emissions. By the use of a process integration model which basically includes the primary processes of cokemaking, sintering, ironmaking and oxygen steelmaking the overall influence of scrap input on CO2 emissions is demonstrated and commented. The influence of hot metal silicon content is elucidated by calculations with different material and process constraints. The results show that at moderate scrap rates, the reduction of CO2 emissions is favoured by increased scrap additions to the oxygen converter. When the scrap additions to the converter balances the actual heat capacity of the bath, other means to achieve an increased scrap melting capacity can be taken into account. This include combinations of scrap addition to the blast furnace, increased silicon content in tapped hot metal, and/or addition of Ferro-silicon combined with further scrap additions to the oxygen converter. Different strategies for CO2 emission reduction have to be suggested depending on if the objective is to minimise the site (direct) emissions or the global (indirect+direct) emissions. © 2006 ISIJ.