THE INFLUENCE OF BLAST-FURNACE SMELTING INTENSITY ON THE NATURE OF HEAT TRANSFER IN A FURNACE

Abstract

This paper analyzes the relationship between blast furnace smelting intensity and the characteristics of heat exchange processes along the furnace's height. The study was conducted using the operating data of a blast furnace with a useful volume of 2000 m³. Specific furnace productivity, defined as the ratio of daily hot metal output to its useful volume, was used as an intensity indicator. During the analyzed stage of operation, furnace productivity decreased from 3,0 to 1,7 t/(m³·day). The furnace's operation is characterized by the use of combined blast technology, which involves the simultaneous supply of pulverized coal (PC) and natural gas as auxiliary fuel additives. Varying the gas pressure under the furnace throat was the determining factor (control action) for adjusting the blast furnace smelting intensity. Furthermore, regulating the degree of oxygen enrichment in the blast served as an auxiliary tool for controlling the process rate. The technological process was focused on the smelting of pig iron, the chemical composition of which, in terms of silicon content, was maintained in the range of 0,35–0.55%. The structure of the iron ore portion of the charge was formed using pellets, the proportion of which ranged from 30 to 40%. Specific coke consumption ranged from 314–402 kg/t, and the specific slag yield ranged from 235–260 kg/t. The dynamics of key process indicators during the period under review were characterized by the following changes: blast oxygen content decreased from 31 to 28%, specific blast consumption increased from 970 to 1.426 m³/t of hot metal, blast furnace pressure decreased from 2.1 to 0.8 kgf/cm², specific pulverized coal consumption increased from 0 to 143 kg/t of hot metal, and specific natural gas consumption decreased from 154 to 46 m³/t of hot metal. Observations and calculations show that changes in smelting intensity shift the boundaries of the heat exchange zones: an increase in smelting intensity expands the upper zone and contracts the reserve zone, while the lower zone changes nonlinearly, reaching a minimum. This dynamic is determined by the balance between the development of reduction processes in the lower zone, the amount and enthalpy of the gas, and the contact time of the materials with the gas. The size of the reserve zone is determined by the shift in the boundaries of the upper and lower zones.