Abstract
Problem Statement (Relevance): To achieve a high-perfomance iron smelting process in a blast furnace, it is necessary to ensure an even peripheral distribution of charge materials by type and size. Because the blast furnace burden is comprised of multiple components, which, in addition to sinter and pellets, may include flushing materials, fuel additives and kish forming components, achieving an even peripheral distribution of the сharge may be a challenging task. In connection with the above, it would be necessary to study how different charging parameters influence the charging pattern in terms of the size distribution of the components, which are fed from the bell-less top (BLT) charging system hopper into the furnace top. The objective is to identify the charging patterns in terms of the size distribution of the charge components, which are fed from the BLT charging hopper into the furnace top, aimed at the development of efficient iron ore charging regimes delivering an enhanced smelting performance. Methods Applied (Experiments): A series of experiments was carried out using a laboratory installation of a single-track compact charging device with a chute, which is a 1:5 scale copy of the BLT charging systems installed on MMK’s Blast Furnaces No. 4 and No. 6. The first series of experiments focused on monitoring how the size uniformity index of the charged sinter was changing depending on the concentration of 1–5 mm particles in the range from 1 to 18%, which were loaded into the charging hopper blended with the (–10) mm sinter. At the same time a finer sinter was placed below the +10 mm class, above it and in the middle layer. The +10 mm sinter was also placed in the layer of the (–10) mm sinter. The following +10 to (–10) mm ratios were used: 90:10; 70:30; 50:50; 30:70; 10:90. In the second series of experiments, the authors looked at how the charging sequence can influence the size uniformity of the charged sinter and pellets as they are fed from the BLT charging hopper onto the chute. For this, pellets were charged in the bottom of the hopper under the sinter, above it and in the layer between the sinter portions at different ratios: 25:75; 50:50 and 75:25 %, which were placed in the hopper underneath and above the pellets correspondingly. This was compared with the regimes when sinter was fed into the layer of pellets at different ratios: 25:75; 50:50 and 75:25 %, which were placed in the hoрреr underneath and above the sinter correspondingly. The share of pellets varied from 0.1 to 0.9 with a 0.2 step. The materials were released with the chute door open at 50 degrees. Samples were taken during the release, the materials were sieved to form the following classes: 1–3; 3–5; 5–8; 8–10; 10–12; 12–15; 15–17.5; 17.5–25; > 25. After that, the authors analysed the distribution of the charge components being fed from the hopper into the chute. Originality: The authors established how the charging conditions can influence the size distribution patterns of the charge components being fed from the BLT charging hopper into the furnace top. Findings: The authors established mathematical dependencies for the charging sequence and the size distribution of iron ore fed from the charging hopper under different charging regimes. To ensure a higher uniformity index, when loading materials into the BLT charging hopper it would be advisable to place the material that is consumed most at the bottom of the hopper, while the material seeing the lowest rate of consumption should be placed above the former. A higher percent of the 1–5 mm particles in the sinter in the range from 1 to 10% and an increased concentration of the (–10) mm particles from 10 to 90% due to a lower share of the +10 mm sinter did not produce any significant effect on the 1–5 mm sinter redistribution in the charged portions. The average uniformity index was 0.88. An increase in the concentration of the 1–5 mm material from 10 to 18 % would considerably affect the hopper-to-furnace top charging uniformity. The fines averaged 10% in the first portions and 25 % when the release time was 60% over. The uniformity index dropped from 0.88 to 0.62. Consequently, the concentration of the 1–5 mm material exceeding 10% will impact the gas dynamics in particular zones of a blast furnace and, therefore, will affect the furnace performance. To ensure an even size distribution of iron ore being fed from the BLT charging hopper into the furnace top to maintain an optimum peripheral distribution of gas travelling through the burden, the material with a higher equivalent surface area should be in the layer of smaller size material. The best size distribution of the charge components being fed from the BLT charging hopper is achieved when pellets are fed in the the middle of the sinter layer. When pellet accounted to 38% of the iron ore charge, the uniformity index was 0.90. Practical Relevance: The developed charging regimes applied to MMK’s blast furnaces equipped with compact BLT charging systems with a chute will enhance the peripheral size distribution of the charge materials, which will lead to enhanced furnace performance.
Keywords
Blast furnace, BLT charging system with a chute, charge size, peripheral distribution, sinter, pellets.
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