(DRI) Impact on electric arc furnace steelmaking

1. Productivity and yield

Production practice shows that adding DRI has a great impact on the productivity and yield of the electric arc furnace. In recent years, the number of large electric arc furnace plants newly built and put into operation in China has gradually increased

However, due to various reasons, the quality of scrap steel entering the plant is particularly poor, with densities ranging from 0.3 to 0.7 t/m3. Many electric arc furnaces need to add 3 to 4 times of steel scrap to make one furnace of steel. If DRI is used, the number of feedings can be significantly reduced, thereby shortening the smelting cycle. Continuous addition of 20-50% DRI can greatly increase productivity.

Moreover, with the introduction of oxy-fuel smelting, foamed slag and scrap preheating technology, as long as DRI replaces low-density scrap, the productivity of electric arc furnaces will increase. The yield of molten steel is related to the metallization rate, gangue content and carbon content of DRI. If you want to get a high yield, you must add DRI with a higher metallization rate to the electric arc furnace or add a recarburizer to promote iron reduction.

The properties of slag and the amount of slag also affect the yield of molten steel. Under the same alkalinity, foaming slag can reduce the amount of slag.

 2. Consumption of production materials

1) The carbon content of the electrode consumed by the DRI is generally low. After adding DRI to the electric arc furnace, a recarburizer will be appropriately added to make the electric arc furnace present a reducing atmosphere, reducing the oxidation of the electrode and reducing the consumption; but the carbon content in the molten steel is higher. At high temperatures, electric arc furnaces often use foamed slag technology for submerged arc operation. At this time, the concentration of arcs increases the possibility of electrode fracture. In general, the consumption of electrodes will not increase due to the adoption of DRI.

2) Consumption of refractory materials When adding DRI in batches, there is no change to the original feeding method, and the consumption of refractory materials will not increase; “splashing” will be formed during continuous feeding, and the slag surface will be opened to expose the arc, and the refractory materials will be somewhat increase. After applying DRI, the FeO content in the slag is higher, and the C-O reaction time is longer, which may also increase the chemical attack of the refractory material. However, the foam slag process and the adjustment of other parameters can keep the refractory material consumption at the original level.

3) Flux consumption and the use of DRI will increase the acid gangue content. To maintain the original slag alkalinity will obviously increase the consumption of flux. Studies have shown that for every increase of 1% DRI, the flux will increase by 1 kg/t. However, when DRI is used as a raw material, the content of [P] and [S] in molten steel is low, and the slag basicity does not need to be too high, so the flux consumption does not increase.

 3. Changes in energy consumption After the addition of DRI, the energy consumption of electric arc furnace steelmaking increases. 

The main reasons for the increase in energy consumption of electric arc furnace steelmaking are as follows:

The melting of DRI increases energy consumption. The lower the DRI metallization rate, the higher the FeO content. The reduction reaction of FeO during electric furnace steelmaking is an endothermic reaction. At the steelmaking temperature, reducing 1tFeO will require about 800kWh of electricity. 

1) The content of gangue in DRI has a significant impact on energy consumption. The higher the content of SiO2, the higher the power consumption. In order to maintain the alkalinity of the slag, with the increase of SiO2, the added quicklime will inevitably increase, which will cause an increase in the slag. The melting of 1 ton of slag requires about 530 kWh of electricity, and both SiO2 and tempered quicklime need to be melted. Consume energy.

2) DRI with high carbon content also affects power consumption. Because the reaction of [C] + [O] -> CO in the molten pool is an exothermic reaction, if the oxygen is blown in the appropriate amount of oxygen, every additional 1Nm3 of oxygen will reduce the power consumption by 2~4 kWh.

3) When the continuous DRI addition method is adopted, the smelting time can be greatly shortened and maintained under the condition that the power supply and the DRI addition rate (28-38kg/MW.min for cold charging and 50kg/MW.min for hot charging) are matched. The electric arc furnace operates with the maximum input power, which is beneficial to increase the output of the electric arc furnace. When the DRI is added in batches, improper feeding (such as DRI too concentrated or DRI close to the furnace wall) will cause DRI to accumulate or stick to Furnace wall, thereby greatly extending the melting time and increasing power consumption.

4) DRI's charge temperature has a greater impact on power consumption and less impact on the smelting cycle. When using fully cold loaded sponge iron, the power consumption will be 100~150kwh/t higher than that of all scrap steel smelting, and if it is fully hot loaded, the power consumption is equivalent to that of scrap steel.

 At present, in order to reduce the energy consumption of electric arc furnace steelmaking when DRI is added, various steel mills have adopted many measures, such as preheating the added DRI, but need to prevent secondary oxidation.

All in all, in order to reduce power consumption, DRI with high metallization rate and low SiO2 should be used, carbon can be increased appropriately during the smelting process, and the charging system should be hot charging and continuous charging.

4. Steel quality

At present, DRI is mainly used to smelt high-quality products in electric arc furnace applications at home and abroad, such as oil casing and drill pipes in the petroleum industry; deep-drawn automotive sheets in the mechanical industry, special-purpose steel wires and special-purpose steels, such as Spring steel, bearing steel, steam turbine generator rotor, gun barrel, and steel materials for aviation, aerospace, and atomic energy industries.

 Because DRI does not contain residual elements, steel without residual elements can be directly produced, and the number of inclusions in the steel is significantly reduced, thereby improving the hot rolling and cold rolling properties of the steel, especially the tensile properties; the use of DRI can significantly reduce the steel The S content in the steel, the shape of the steel sulfur inclusions can also be controlled, which improves the quality of the steel and changes the expansion and torsion resistance of the steel.