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5 Factors Affecting Energy Consumption of Electric Arc Furnace Steelmaking


Electric Arc Furnace,DRI

Source: internal company

1. Metalization rate and w (FeO)
Internationally, the metallization rate of DRI used in electric arc furnaces is generally >90%. The melting of DRI increases energy consumption. At the same time, for DRI, the lower the metallization rate, the higher w (FeO), and the reduction reaction of FeO is an endothermic reaction. At steelmaking temperature, when it takes 1t of FeO to be reduced, the electricity consumption is about 800kWh. The influence of different metallization rates on the power consumption of DRI melting is shown in Figure 1. It can be seen from Figure 1 that as the metallization rate increases, the smelting power consumption gradually decreases. When all raw materials are DRI, the smelting power consumption changes approximately linearly. For every 1% decrease in metallization rate, the smelting power consumption increases by about 9kWh/t. When the raw material uses 65% DRI and the metallization rate is >90%, the power consumption increases by about 8kWh/t for every 1% decrease in the metallization rate. When the metallization rate continues to decrease, the power consumption increases significantly.


Fig. 2 Effect of metallization rate on the power consumption of DRI melting

2. Gangue content and alkalinity
The gangue content of DRI (SiO2+Al2O3) is ≤10%. Generally, the SiO2 content of DRI used in electric arc furnaces should be controlled not to exceed 6%. The content and alkalinity of gangue not only determine the amount of slag-making material added during the smelting process, but also affect the final slag amount, which in turn affects the smelting energy consumption. The influence of gangue content and alkalinity on the energy consumption required to smelt 1 ton of molten steel is shown in Figure 2. Among them, the alkalinity of the final smelting slag is 2, w (FeO) in the slag is 20%, and DRI w (C) is 1.2%. It can be seen that the gangue content and alkalinity in DRI have a significant impact on energy consumption. The higher w (SiO2), the higher the power consumption. In order to maintain the alkalinity of the slag, the amount of quicklime and other fluxes added into the furnace also increases accordingly, which leads to an increase in the amount of slag. Melting 1 ton of steel slag to 1600°C consumes about 530kWh, and the melting of SiO2 and calcined quicklime requires energy. Research shows that for every 1% increase in the amount of DRI, the flux amount needs to be increased by 1kg/t. When the slag basicity is reduced from 2.0 to 1.4-1.7, the slag amount can be reduced to a certain extent, the iron loss is reduced, and the power consumption is reduced by 8-17kWh/t. Experiments have shown that when 10% to 30% DRI is continuously added, the energy consumption is reduced compared with all scrap steel. The reason is that the DRI must be of high quality and the gangue content is low (metalization rate ≥ 94%, gangue Content ≤3%), and if DRI exceeds 30%, energy consumption will increase.


Fig. 3 Effect of the content and alkalinity of gangue on the energy consumption required for smelting1 t steel liquid

3. P and S content (mass fraction) in DRI
The P and S of DRI do not exceed 0.1% and 0.04%. Different grades of steel have different requirements for P and S during tapping. P and S in steel are generally less than 0.03%, and some high-quality steels require less than 0.015% or even lower. Dephosphorization requires the production of oxidized slag. If the FeO content of the slag is constant during the process, to reduce the P content, more quicklime must be added, which also leads to an increase in power consumption and a decrease in yield. Removal of S requires the production of slag, and electric arc furnace steelmaking is a typical alkaline oxidation slag. When the added quicklime removes part of the S, it will not only have no effect, but also increase power consumption. Therefore, in order to reduce energy consumption, dephosphorization is carried out in electric arc furnaces, while desulfurization should be carried out in ladle furnaces.

4. C content (mass fraction) in DRI
Depending on the process, DRI C is about 1% to 4.5%. DRI contains high C, which can react chemically with the remaining oxides. The gas produced causes the slag to foam. The use of high voltage and long arc operation is beneficial to reducing power consumption. In addition, the carbon-oxygen reaction in the molten pool is an exothermic reaction. If the oxygen blowing amount is within the appropriate range, for every additional 1m3 of oxygen (standard state), the power consumption will be reduced by 2 to 4kWh.

5. Hot charging of DRI
In order to reduce the energy consumption of electric arc furnace steelmaking, DRI hot charging and hot feeding technology has attracted much attention. However, attention needs to be paid to the problem of oxidation. Hot DRI can be sent directly into the electric arc furnace through a sealed system. Usually the hot charging and transporting temperature of DRI is between 500 and 700°C. The hot charging and transporting methods of gas-based shaft furnace-electric arc furnace mainly include Hytemp pneumatic conveying system, Hotlink thermal connection method, etc. The DRI produced by the gas-based shaft furnace can be hot discharged and added to the electric arc furnace for smelting through hot charging. Based on relevant statistical data, the impact of different thermal DRI ratios and temperatures on power saving is shown in Figure 4. Mexico's Hylsa Company uses DRI 650℃ hot charging, which greatly reduces power consumption compared with cold charging. When 70% is added, 112kWh/t steel can be saved and the smelting time can be shortened by 20 minutes. When 100% DRI is added to the electric arc furnace, 140kWh of electricity can be saved per ton of steel. Generally speaking, for every 100°C increase in hot charging of DRI, 20 to 30kWh can be saved.


Fig. 4 Effect of the hot direct reduction iron ratio and temperature on energy saving


In summary, in order to reduce power consumption, w [C] should be controlled to 1%~4.5%, metallization rate ≥90%, w [SiO2] ≤6%, w [P] ≤0.1%, w [S] ≤0.04% , using high C, high metallization rate, low SiO2, low P, low S and higher temperature thermal DRI.

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