РОЗВИТОК КОНЦЕПЦІЇ ПІДВИЩЕННЯ ЕНЕРГОЕФЕКТИВНОСТІ ДУГОВОЇ СТАЛЕПЛАВИЛЬНОЇ ПЕЧІ ШЛЯХОМ УТИЛІЗАЦІЇ ТЕПЛОТИ ДИМОВИХ ГАЗІВ ДЛЯ ПОПЕРЕДНЬОГО НАГРІВУ СКРАПУ

Abstract

An important factor in improving the energy efficiency of the electric arc steelmaking furnace (EAF) is utilization of the flue gas energy to preheat the initial charge. Implementation of the process in existing EAF requires the measures to synchronize with the carbon monoxide post combustion and to prevent of the toxic PCDD/F formation when conventional scrap heating, which is significantly complicated in a traditional scheme of CO afterburning with a single-stage air inflow through a temperature and concentration factors. The technological basics of medium-temperature scrap preheating by EAF flue gas have been developed and substantiated. Numerical study of carbon monoxide burning thermodynamics and kinetics shown that implementation of two-stage inflow of air into postcombustion chamber for stoichiometric combustion of CO and cooling the heat carrier provides a comprehensive solution of mentioned problems. The ratio of primary and secondary flows 1 to 3.5 provides allowable concentration of carbon monoxide in the ducts; obtaining gas mixture with a temperature of up to 500 °C, which prevents PCDD/F formation; acceptable temperature operating conditions of bag fabric filters of the gas cleaning system within 100 °C regardless of scrap preheating. Numerical simulation of the heat exchange process between the charge layer and the gaseous heat carrier reveal that shredder scrap of standard bulk density 0.9 t/m3 and mass of half EAF capacity can be preheated up to temperature of 450 °C in 18-20 minutes. Given value corresponds to the duration of technological period in the EAF heat cycle, characterizing by comparatively stable emission and maximal temperature of the flue gas flow. Reduction of the scrap fragments bulk density and the average size, as well as increasing the ratio of the heating chamber height to its diameter in the range from 0.7 to 2.0, promotes the heating rate magnification. The technology provides specific energy savings within 20-30 kW.h per ton of steel and can be implemented in existing electric steelmaking shop of the mini-mill without additional CO2 emissions. The payback period for a 50-ton EAF with annual productivity of 400-450 thousand tons of steel is 14-18 months.