Steel heating in an arc smelting furnace and a ladle-furnace unit

Abstract

Two-stage arc heating of ferrocarbon melts in smelting equipment and casting ladles is very widely used in ferrous metallurgy [1‐3]. The efficiency of steel smelting in this case may be judged from the reduced total power consumption when heating the melt in the arc smelting furnace and the ladle‐furnace unit. The energy-saving potential of the smelting technology depends significantly on the efficient integration of the operations within a steel-casting module that includes an arc furnace, a ladle‐furnace unit, and a high-speed continuous-casting machine [4, 5]. Obviously, the efficiency of two-stage melt heating by an electric arc largely depends on the harmonization of its parameters: the discharge temperature of the steel from the smelting unit, the duration and the initial and final temperatures of ladle treatment, and the temperature at which steel is supplied to the continuous-casting machine. To improve the production parameters, practically all electrosmelting shops, regardless of their development strategy, are equipped with ladle‐furnace units [6]. We also know that there are significant technological and energy differences between melt heating in an arc furnace and in a ladle‐furnace unit. This suggests the need for quantitative analysis of heating in each unit. In the present work, we investigate the heating rate of the metal, the thermal-energy consumption, and the efficiency of energy utilization from the electric arc and alternative sources in arc furnaces of classical and updated design and also in the ladle‐furnace unit. In experiments conducted in an arc furnace with a reduction period and in a casting ladle, the steel is reduced for at least 15‐20 min before the first measurement. The homogeneity of the refined slag and the operation of the injection nozzles are visually checked. In all the experiments, the transformer is switched off prior to the measurements, and the metal is held for 1.0‐1.5 min so as to average out the temperature. Then the steel temperature ( t 1 , ° C) is measured by an immersion thermocouple. Before switching the transformer on, the meter readings for the active electrical energy ( p 1 , kW-h) are recorded. Immediately after the first temperature measurement, the furnace transformer is turned on, and its operation is monitored in terms of the instrument readings. (In the heating period, no switching of the power stages, large jumps in the current, or changes in the conditions of inert-gas injection are permitted.) In addition, in the experiments, nothing is added to the melt bath. At the end of heating ( τ = 5‐ 15 min) and averaging of the temperature (1.0‐ 1.5 min), the steel temperature is measured again ( t 2 , ° C), and the readings of the electrical-energy meter are recorded ( p 2 , kW-h). The heating rate v ( ° C/min) and the power consumption ∆ p (kW-h/t ° C) are calculated from the formulas