Optimised Use of Fossil Primary Energies in Integrated Steel Plants for Crude Steel Production in Regards to Technical, Economical and Ecological Aspects

摘要

Instead of sending excess of coke oven gases (COG), converter gases and blast furnace (BF) top gases from integrated steel mills to power stations, as is mainly today's practice, there are technical and feasible possibilities for use of these gases in metallurgical processes, i.e., for direct reduction (DR) of iron ores and crude steel-production. The additional production of direct reduced iron (DRI) to the hot metal (HM) production, and further use of DRI as metallic charge to BF or in EAF's, allows - without increasing the capacities of the coke oven plant and BF and without changes in the quality of the crude steel -an increase in production of crude steel or alternatively, a significant reduction of fossil fuels specific consumption. In the way the production is increased, the specific consumption of fossil primary energy is lowered. Processing the DRI in an EAF also enables, by optimising the DRI/scrap ratio with respect to quality and costs, to produce a much wider product range than would be possible by only charging scrap. An analysis of the most adequate process scheme for an HYL DR plant, based on a simplified Mini-Module concept to be incorporated in integrated steel facilities, is included. The economical evaluation is based on a typical material and energy balance of an integrated steel mill, including thin slab casting and rolling mill for the production of hot rolled coils. The production of DRI in an integrated steel mill is possible at costs that can be below world market prices for DRI/HBI and premium scrap prices. Examples for economical impact are given for use of DRI in BF as well as in EAF The optimised utilisation of primary fossil energy also has the effect of significantly reducing the specific CO_2 emissions per ton of crude steel. The specific CO_2 emission via the conventional BF/BOF route is about 1.6 tonnes (t) of CO_2/t crude steel, even on an optimised process route basis. Utilising the DRI-being produced with COG and BF top gas- as metallic charge to BF or in an EAF, allows significant reductions in absolute and/or specific CO_2 emissions.