Impact of Direct Reduced Iron (DRI) on Electric Arc Furnace Steelmaking Process

Impact of Direct Reduced Iron (DRI) on Electric Arc Furnace Steelmaking Process

Impact on Productivity and Yield

In practical production, the addition of DRI has a significant impact on the productivity and yield of electric arc furnaces (EAF). In recent years, the number of large EAF steel plants in China has continued to increase. However, the quality of scrap steel entering these plants is often poor, with density ranging from 0.3 to 0.7 t/m³. Typically, EAFs require multiple feedings (usually 3-4 times) to complete a single refining cycle. However, using DRI can reduce the number of feedings, shorten the refining cycle, and improve production efficiency. By continuously adding 20% to 50% DRI, the productivity of the EAF can be significantly increased. Furthermore, with the application of oxygen-fuel assist, foam slag, and scrap preheating technologies, as long as DRI replaces low-density scrap, the productivity of the EAF will increase accordingly.

The yield of molten steel is influenced by factors such as the metallization rate, gangue content, and carbon content of the DRI. To achieve a higher yield, it is necessary to use DRI with a higher metallization rate and possibly add carbon to promote the reduction of iron. Additionally, the characteristics and amount of slag also impact the yield. Under the same basicity, the use of foam slag technology can effectively reduce slag volume.

Changes in Material Consumption

Electrode Consumption

DRI generally has a low carbon content. Therefore, when DRI is added to the EAF, it is necessary to add carbonaceous materials to maintain a reducing atmosphere inside the furnace, which helps reduce electrode oxidation and decrease electrode consumption. However, when the carbon content of the molten steel is high, the EAF may adopt foam slag technology for submerged arc operations. In this case, the increased concentration of the arc may lead to electrode breakage. Overall, the consumption of electrodes does not significantly increase due to the use of DRI.

Refractory Material Consumption

When DRI is added in batches, the feeding method does not change significantly, and refractory material consumption remains stable. However, during continuous feeding, a "splashing" phenomenon may occur, exposing the electric arc and increasing the consumption of refractory materials. After DRI is introduced, the slag tends to have a higher FeO content, and the C-O reaction time is longer, which can increase the chemical erosion of the refractory materials. Nevertheless, by optimizing the foam slag process and adjusting other parameters, the consumption of refractory materials can be maintained at the original level.

Flux Consumption

The use of DRI increases the acid gangue content in the slag, which requires more flux to maintain the slag's basicity. Research shows that for every 1% increase in DRI usage, the flux consumption increases by about 1 kg/t. However, when DRI is used as the raw material, the levels of phosphorus (P) and sulfur (S) in the steel are lower, meaning that excessively high slag basicity is not required, and the overall flux consumption does not increase significantly.

Changes in Energy Consumption

The addition of DRI to the EAF increases energy consumption. The main reasons for this are:

Energy Consumption for DRI Melting

The lower the metallization rate of DRI, the higher the FeO content. During the refining process, the reduction of FeO is an endothermic reaction. At refining temperatures, reducing 1 ton of FeO requires approximately 800 kWh of electrical energy.

Impact of Gangue Content on Energy Consumption

The higher the content of gangue (such as SiO2) in DRI, the greater the energy consumption. To maintain the slag's basicity, an increase in SiO2 content requires more lime to be added, which in turn increases the amount of slag. Melting this slag requires additional electrical energy, approximately 530 kWh/t.

Impact of Carbon Content

The carbon content in DRI also affects energy consumption. The reaction [C] + [O] → CO is exothermic. When an appropriate amount of oxygen is introduced, each additional Nm³ of oxygen reduces energy consumption by 2~4 kWh.

Impact of Feeding Method on Energy Consumption

When DRI is added continuously, if the feeding rate is matched with the power supply (e.g., cold charging at 28-38 kg/MW·min, hot charging at 50 kg/MW·min), it can significantly shorten the refining cycle and improve EAF production capacity. On the other hand, in batch feeding, improper feeding (such as DRI accumulation or positioning near the furnace wall) can lead to prolonged melting time and increased energy consumption.

Impact of DRI Temperature on Energy Consumption

The temperature of the DRI has a considerable effect on energy consumption. When using fully cold DRI, energy consumption will be 100-150 kWh/t higher than when using only scrap steel. However, when using fully hot DRI, energy consumption is comparable to that of scrap steel.

To reduce energy consumption, steel plants have implemented various measures, such as preheating the DRI while preventing secondary oxidation. Overall, to minimize energy usage, it is recommended to use DRI with a high metallization rate, low SiO2 content, and to adopt hot continuous feeding practices.

Improvement in Steel Quality

DRI is primarily used in EAFs to produce high-quality steel products, including petroleum casing, drill rods, deep-drawing automotive sheets, special-purpose steel wires, and other specialty steels such as spring steel, bearing steel, turbine generator rotors, gun barrels, and steels used in the aerospace and nuclear industries. Since DRI does not contain residual elements, it allows for the direct production of steel with minimal impurities. This leads to a significant reduction in the number of inclusions in the steel, thereby improving the hot and cold rolling properties, especially tensile properties. Additionally, using DRI can effectively lower the sulfur (S) content in steel, improving the overall quality of the steel and enhancing the steel's resistance to expansion and torsion.