Phosphorus removal from high-phosphorus hot metal in the converter

Abstract

The introduction of Korshunsk concentrate in the sintering batch at OAO Chelyabinskii Metallurgicheskii Kombinat (OAO ChMK) increased the mean phosphorus content in the hot metal from 0.10 to 0.17‐ 0.18% (in some periods, 0.20‐0.22%). This is due to the phosphorus content of 0.1% in such concentrate, which is an order of magnitude higher than in the batch materials previously employed, and also to the addition of converter slag to the batch (about 3% in the batch and the blast-furnace melt). On account of phosphorus accumulation in the converter slag, its content in the hot metal is constantly increasing. In view of the expanded production of continuous-cast billet, effective removal of phosphorus is required in order to produce converter steel with of required composition from high-phosphorus hot metal. In the oxygen-converter shop, most steel is smelted in three 160-t converters with a tar‐dolomite lining. Hot metal is supplied to the converter shop from the blast-furnace shop in portable ladles of capacity 100 and 140 t, decanted into two mixers in the mixer department, and then supplied through a special ladle to the converters. Oxygen is injected into the converter through a five-nozzle tuyere, with a nozzle aperture angle of 20 ° , at 400‐450 m 3 /min. Processing hot metal with up to 0.2% P increases the required duration of injection of the intermediate product in the converter, which considerably increases the loss of iron and the reducing-agent consumption and reduces the lining life. To determine the optimal phosphorus-removal parameters for oxygen-converter melt, an experimental series of 35 melts is considered, with three basicity values B = (CaO + MgO)/SiO 2 : less than 3.0, 3.0‐3.5, and more than 3.5. In the experimental melts, the chemical composition of the hot metal is as follows (wt %): 0.57‐ 1.07 Si (0.87, on average), 0.10‐0.24 Mn (0.15), and 0.10‐0.17 P (0.14). The hot-metal temperature fluctuates from 1323 to 1368 ° C (1345 ° C, on average). The proportion of hot metal in the metal batch is 80%. A single-slag smelting process is employed, with standard injection (mean rate 400‐450 m 3 /min); the height of the tuyere above the level of the quiescent bath is 1.1‐1.3 m during most of injection. The MgO content in the final slag is 4.9‐15.9% (8.9%, on average), and the FeO content is 11.3‐23.3% (16.2%). For some melts, at the end of injection, the tuyere is raised by 0.5 m, to increase slag oxidation. The end of injection is recorded visually in terms of the shape of the flame, the injection time, and the volume of oxygen consumed.