Influence of the consumption of pellets with different basicity on indicators of blast-furnace smelting

The results of the analysis of production data on the operation of blast furnace No. 1 (useful volume 1007 m3) of Ural Steel JSC for the period from 2013 to 2018 are presented. During this period, pellets from the Mikhailovsky GOK were used with varying degrees of fluxing: pellets of natural basicity in the ratio of CaO/SiO2 equal to 0.08 ± 0.02 units. (2013-2015) and partially fluxed pellets with a basicity of 0.52 ± 0.05 units. (from 2016 to the present). It has been established that the effectiveness of the use of pellets of various basicities is determined by their behavior in the blast furnace and depends on the proportion of pellets in the iron ore part of the charge. The gas-dynamic conditions of the smelting worsen with an increase in the proportion of pellets in the charge, which is accompanied by an increase in the specific pressure drop and forces the flow rate to be adjusted. There is an optimal level of specific pressure drop (53–55 Pa per 1 m3 of blast per minute) for the operating conditions of blast furnace No. 1 of Ural Steel, which ensures the optimum combination of the melting characteristics. Deviation from the optimal level of pressure drop leads to an increase in coke rate and a decrease in the degree of CO use, which is associated with gas distribution disturbance. Due to the increase in high-temperature properties, the replacement of non-fluxed pellets with off-fluxed pellets improves the gas-dynamic conditions in the lower part of the mine (in the cohesive zone). This leads to a decrease in the total pressure drop and specific pressure drop at a constant flow rate of the blast, and is a reserve for melting intensification. To minimize coke rate and maintain the high-performance operation of blast furnaces of Ural Steel JSC, it is necessary to work on 40–45 % of fluxed or 20–25 % acid pellets in a charge. An increase in pellet consumption while maintaining the efficiency of blast-furnace smelting is possible only if their high-temperature properties are improved. The improvement of these properties is possible as a result of optimizing the basicity and increasing the MgO content, which affects the structure and properties of the silicate bond. This work is carried out within a framework of the government order (No. FZRU-2020-0011) of the Ministry of Science and Higher Education of the Russian Federation.

Attempts to replace nut coke with semi-coke for blast furnace ironmaking

Low coke rate for blast furnace operation has been required in response to the rising cost of coking coals. To extend the utilisation of coal resources, semi-coke has been introduced to blast furnace ironmaking process in recent years, however, there are still many issues unclear about the effect of semi-coke on ironmaking process. In this study, the possibilities of using semi-coke as alternative fuel for nut coke were studied. The characteristics of semi-coke including mechanical strength, high-temperature strength/reactivity, carbon gasification as well as direct reduction were studied and compared with small size metallurgical cokes (nut cokes). The results showed that semi-coke has higher CRI values, especially at higher temperatures and in a mix-charging pattern. Semi-coke was found to have a higher gasification reaction rate and depleted at lower temperatures. The reduction results showed that with participating of semi-coke the reaction starts at lower temperatures. In addition, the study suggested that semi-coke exhibits the advantages of low ash and sulphur contents, although it has lower mechanical strength, it would protect the lump coke by shifting the carbon gasification to itself, therefore, mixing semi-coke would benefit the blast furnace operation and lower the coke rate.

Energy Conservation and CO2 Abatement Potential of a Gas-injection Blast Furnace

The gas-injection blast furnace (BF) is a new iron-making technology with an injecting gas instead of traditional pulverized coal injection (PCI) and recycling of the BF top gas through a gasifier. In contrast to traditional all-coke and PCI BFs, the coke rate will depend mostly on the heat consumption in a gas-injection BF with abundant injected gas, which results in a large coke-saving potential. Based on energy conservation, carbon recycling, CO2 abatement and fuel cost, the degree of direct reduction should be between 0.2 and 0.3. In addition, in terms of the effects of the gas injected and the rich oxygen rate in the tuyere region, the optimum injection parameters were obtained, which can reduce the coke rate to 273.36 kg/tHM, carbon recycling to 100.72 kg/tHM and abate carbon dioxide emissions by 94.00 Nm3/tHM. Theoretically, the minimum total carbon consumption value is 399.73 kg/tHM. These results illustrate the great potential for carbon recycling and coke saving in gas-injection BFs without increasing total carbon consumption.

Study on the Appropriate Production Parameters of a Gas-injection Blast Furnace

The change regulations of the smelting parameters in a gas-injection blast furnace are investigated using theoretical calculations. The results show that when the volume of gas injected, the oxygen enrichment rate and the theoretical combustion temperature of tuyere are 600 m3/tHM, 10% and 1950~2200∘C, respectively, the conditions meet the smelting requirements of a blast furnace. With the increase of the oxygen enrichment rate, the required air volume decreases, the contents of CO and H2 in the top gas increase, and the content of CO2 first increases and then decreases.With an increase of the volume of gas injected, the coke rate decreases. In addition, when the oxygen enrichment rate and the volume of gas injected are 10% and 600 m3/tHM, respectively, the CO content of the top gas constantly increases with the increase of the coke rate, while the H2 and CO2 contents both decrease. With the increase of the H2 content in the gas, the direct reduction degree of iron gradually decreases and the volume shrinkage burden increases. Apparently, injecting gas into the blast furnace can prevent the theoretical combustion temperature from being too high and solve the contradiction between the upper cooling and lower heating of the blast furnace.

Measurement of Process Conditions Present in Pilot Scale Iron Ore Sintering

An improved experimental technique has been developed to measure, concurrently, the oxygen partial pressures and temperatures within a pilot scale iron ore sinter pot as a function of time. The measurements and thermodynamic calculations have demonstrated that the oxygen partial pressure at peak bed temperature and during cooling can be oxidising or reducing relative to hematite. Examples of typical microstructures and phase assemblages observed in product sinters are presented. Potential mechanisms of hematite and magnetite formation at sub-liquidus and sub-solidus conditions are demonstrated. The relative impacts of changes to coke rate and draft pressure drop on the process conditions and proportions of the phases formed in the sinter have been measured. Increasing coke rate was shown to result in a faster sinter heating rates, higher peak bed temperatures and times at peak temperature. Higher draft pressures across the sinter bed resulted in faster sinter heating rates and shorter times at peak temperature.