Modern technologies for preheating scrap before charging it into electric arc steelmaking furnace

There are a number of technical solutions to utilize the waste gases of electric arc furnaces (EAF) for scrap preheating thus returning back the heat into the technological process. The waste gases can be utilized also for steam or hot water production. The preliminary scrap heating before charging it into EAF is more perspective. Technical features of various types scrap heaters considered, including conveyer and shaft scrap heating technologies with continuous (Contiarc, Consteel, Comelt, BBC-Brusa) and periodic charging (Fuchs Systemtechnik, COSS, backet). It was shown that application of scrap heaters for EAF ensures saving of electric energy, increase of metal yield, decrease of dust and gases level in the shop, decrease of negative impact on environment. The disadvantages include frequent and costly repairs of the facilities, impossibility to control some factors having effect on the process of scrap heating. It was shown that when designing new EAFs with a charge exceeding 100 t, horizontal facilities are more preferrable, while for EAFs of small volumes shaft heaters suit better. At EAF modernizing it is recommended to use shaft heaters and back­et-thermos, since it is easier to construct a vertical furnace than a horizontal one with minimal length of 100 m. It was noted that hor­izontal heaters operate better in terms of technology, since ensure continuous charging by scrap, but at that occupy a considerable space in the shop. When comparing vertical heaters and backet by all the characteristics including heat-engineering and designingones, vertical shaft heaters prevail.

Drying and heating of scrap metal at steelmaking: industrial safety, economics, ecology

At steel production based on scrap metal utilization, the scrap heating before charging into a melting facility is an important way of energy efficiency increase and ecological parameters improving. In winter time scrap metal charging with ice inclusions into a metal melt can result in a considerable damage of equipment and even accidents. Therefore, scrap preliminary drying is necessary to provide industrial safety. It was shown, that in countries with warm and low-snow climate with no risk of scrap metal icing up during its transportation and storing in the open air, the basic task being solved at the scrap drying is an increase of energy efficiency of steelmaking. InRussiathe scrap metal drying first of all provides the safety of the process and next - energy saving. Existing technologies of scrap metal drying and heating considered, as well as advantages and drawbacks of technical solutions used at Russian steel plants. In winter time during scrap metal heating at conveyers (Consteel process) hot gases penetrate not effectively into its mass, the heat is not enough for evaporation of wetness in the metal charge. At scrap heating by the furnace gases, a problem of dioxines emissions elimination arises. Application of shaft heaters results in high efficiency of scrap heating. However, under conditions of Russian winter the upper scrap layers are not always heated higher 0 °С and after getting into a furnace bath the upper scrap layers cause periodical vapor explosions. The shaft heaters create optimal conditions for dioxines formation, which emit into atmosphere. It was shown, that accounting Russian economic and nature conditions, the metal charge drying and heating in modified charging buckets by the heat of burnt natural gas or other additional fuel is optimal. The proposed technical solution enables to burnt off organic impurities ecologically safely, to melt down ice, to evaporate the wetness in the scrap as well as to heat the charge as enough as the charging logistics enables it. The method was implemented at several Russian steel plants. Technical and economical indices of scrap metal drying in buckets under conditions of EAF-based shop, containing two furnaces ДСП-100, presented.