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Agglomerates in Iron-Making Processes
Published in Ram Pravesh Bhagat, Agglomeration of Iron Ores, 2019
Merits The usage of pellets in comparison to lump ore or sinter results in improved furnace productivity and reduction in coke. This is on account of: Slag volume and thermal load of the furnace decreases when pellets are charged. This is on account of their higher iron content (more than 63 wt. %) and uniform chemical composition.Bed permeability of the stack zone is improved through the usage of pellets. This results in the improved furnace productivity. The contributing factors are: The pellets have spherical shapes, are uniform, and have a close size range (9-15 mm in diameter). Compared to sinter, the low angle of repose (see Table 16.1) has been observed in the case of ore pellets. These provide conducing conditions for minimal segregation and an even charge distribution in the furnace, extending more toward the axis. However, when charged along with sinter, pellets have some drawbacks (see next paragraph).Pellets have sufficient and high mechanical strength during transportation and are also able to withstand the impact on its charging. The effect is lesser fines content in pellets when these are charged into the furnace. Besides, the pellets can withstand more thermal stress under reducing conditions (lower RDI). The effect is less fines generation within the blast furnace stack.Figure 4.1 shows the JIS reducibility of different burden materials.[2a] The reducibility has been determined according JIS M8713.[2b] Pellets have greater reducibility compared to sinter and lump ore (Figure 4.1)[2a] due to: Their uniform mineralogical composition in the form of an easily reducible hematite or hematite-bearing compounds. The basic pellets have higher reducibility (Figure 4.1) due to the formation of calcium ferrites and hematite phases through diffusion.High and even micro-porosity 25–30% as compared to lump ore. The reducing gas, carbon monoxide, enters the pellets via the pores and affects the removal of oxygen.Higher bulk density of pellets (3–3.5 t/m³) helps in improved heat exchange due to the longer duration of gas solid contact.A better solid-gas contact is experienced in the case of pellets. This facilitates reduction, especially with pulverized coal injection (PCI), which is widely practiced in the Chinese mini blast furnaces.
Energy Optimization Studies for Integrated Steel Plant Employing Diverse Steel-Making Route: Models and Evolutionary Algorithms-Based Approach
Published in Mineral Processing and Extractive Metallurgy Review, 2021
Sagnik Chowdhury, Nirupam Chakraborti, Prodip Kumar Sen
Referring to Equation 1, the energy values for BF-BOF system are calculated per ton of crude steel (TCS) from BOF, considering only HM is processed to produce steel without any scrap or DRI addition. This consideration retains the true essence of total fuel energy requirement for a given PCI rate of blast furnace without any dilution. Fuel energy enters the BF-BOF system as coking coal in CO and coal for injection in blast furnace. Fuel gas energy is available in the form of blast furnace gas (BFG), coke oven gas (COG), and basic oxygen furnace gas (BOFG). The effect of PCI rate of BF on energies of BF-BOF system is shown in Figure 3. Total input fuel energy is found to decrease from 23.90 GJ/TCS to 22.36 GJ/TCS with change of PCI rate from 150 to 200 kg/THM. Increasing PCI rate lowers the BF coke rate and as a result requirement of coking coal and the upstream energy demand for coke making decreases. Better % CO utilization with increasing PCI rate as mentioned earlier indicates lesser requirement of reducing gas and saving of fuel. Total available fuel gas energy downstream also decreases along with PCI rate from 8.06 to 7.19 GJ/TCS. Due to lower coke production at high PCI rates, available COG energy decreases. Better % CO utilization with increasing PCI rate as mentioned earlier also lowers available BFG energy.
A reduced order mathematical model of the blast furnace raceway with and without pulverized coal injection for real time plant application
Published in International Journal of Modelling and Simulation, 2018
D. C. Sau, S. K. Das, G. K. Mandal, D. Bandyopadhyay
Maximizing PCI, as a supplement to expensive coke has become the order of the day in blast furnace iron making. However, successful assimilation of this technology needs thorough understanding on the impact of PCI on the behavior of raceway as well as the overall blast furnace process. If the pulverized coal is not completely consumed in the raceway, the unburnt char would tend to get accumulated in the lower part of the furnace. This may severely affect the dripping zone permeability and would disturb the stable operation of the furnace. This situation may arise due to inappropriate blast conditions for a given rate of injection or may be due to injection of PC beyond the acceptable limit, dictated by the operating conditions. Figure 6 shows the temperature distribution in the raceway as a function of rate of PCI. It is imperative to note that the radial locations of PGT shift toward the tuyere nose with increase in the rate of PC. It signifies that conversion rate of O2 to CO2 becomes faster because of combustion of PC close to tuyere nose. This finding is in accordance with the plant observation that higher PCI promotes chances of tuyere burning, unless proper care is exercised. It may be also noted from Table 1 that an increase of PCI rate by 10 kg/thm reduces both the PGT and EGT by approximately 15–20 °C.