Energy Saving and Emission Reduction Technology for Ladle Refining Furnace

Energy Saving and Emission Reduction Technology for Ladle Refining Furnace

This article provides a detailed introduction to a refining equipment - LF (ladle furnace) and its refining process. LF refining mainly relies on the white slag in the ladle. In a low oxygen atmosphere, argon gas is blown into the ladle for stirring, and the molten steel in the primary refining furnace is heated by graphite electrodes for refining. LF uses three-phase electrodes for heating, and inserts the electrodes into the slag layer through submerged arc heating method to achieve energy conservation, emission reduction, and improve the quality of molten steel. At the same time, LF can also replace a refining furnace for reduction period operations, heating, deoxidation, desulfurization, degassing, alloying, argon blowing, and stirring of molten steel, making the composition and temperature of the molten steel uniform. In addition, the structure and process layout of LF can be adjusted and optimized as needed to improve energy utilization efficiency and equipment production efficiency.

LF (ladle furnace) is a refining equipment developed by Japan in the early 1970s. LF refining mainly relies on the white slag in the ladle. Under a low oxygen atmosphere (with an oxygen content of about 5%), argon gas is blown into the ladle for stirring, and the molten steel in the primary refining furnace is refined by heating it with graphite electrodes. LF uses three-phase electrodes for heating. During the heating process, the electrode is inserted into the slag layer using the submerged arc heating method. This method has low radiation and has a protective effect on the furnace lining (which is particularly important for LF furnaces). Meanwhile, the heating efficiency is relatively high and the thermal efficiency is good. LF can replace a refining furnace for reduction period operations, heating, deoxidation, desulfurization, degassing, alloying, argon blowing, and stirring of molten steel, making the composition and temperature of the molten steel uniform and improving its quality.

According to the electrode adjustment form, the LF structure is divided into three-phase single arm electrode lifting adjustment and three-phase three arm three-phase electrode adjustment; According to the structural form, it can be divided into heating base frame and heating bridge frame; According to the process layout, it can be divided into steel ladle cars (single car dual station, double car three station, electrode rotation dual station) and ladle turntable.

LF Energy-saving and Emission Reduction Technology

(1) Adopting optimized process layout form

In short process steelmaking, the process layout in the form of conductive Conductive Cross Arm rotating electrode or ladle turret with higher efficiency and lower resource allocation is preferred to improve the utilization rate of energy medium and the production and smelting efficiency of equipment;

(2) The main circuit adopts reasonable electrical parameters

Reasonably select the primary voltage and transformer capacity of the transformer

For transformers of 8000 kVA and above, a primary voltage of 35 kV is preferred to reduce primary line losses. Reasonably select the rated capacity of the transformer to avoid investment waste and reactive power and furnace busbar losses caused by blind expansion.

Prioritize the use of copper steel composite new conductive arm materials instead of copper pipes for conductivity, reducing the impedance value of the system and lowering energy consumption.

Optimization Design of Busbar System

The furnace busbar adopts a spatial triangular layout. Using computer-aided technologies such as programming and related electromagnetic analysis software to establish a three-phase power model, accurately calculate furnace bus impedance and three-phase imbalance, improve power input, and reduce power losses.

(3) Adopting an automatic argon blowing device

According to the requirements of the smelting process, an automatic ladle bottom argon blowing device is adopted. Based on the set argon blowing process curve, argon is blown throughout the entire process to achieve stable and safe output of soft blowing, stirring, insulation, strong blowing melting, and room temperature argon blowing, reducing argon consumption.

(4) Adopting intelligent electrode adjustment technology

The electrode regulator system is designed based on single-phase considerations and three-phase correlation. Although past experience has shown that this is feasible, the current ladle furnace process continuously blows argon during the smelting process, resulting in significant changes in the boiling situation on the steel surface. Practical experience has shown that the electrode arc current on one side of the bias direction of the argon blowing port varies greatly. The regulator system usually operates in an unbalanced or sub balanced state, and pure PI regulators have slow response and long adjustment time. The use of intelligent electrode adjustment technology can overcome this drawback.

(5) Adopting a secondary automation system

Based on relevant process models, estimate relevant process indicators, guide furnace operators, achieve energy consumption reduction, ensure product quality and production rhythm.

The relevant models mainly include: temperature prediction model, automatic argon blowing model, optimized alloy feeding model, metallurgical database, and energy calculation model.

(6) Adopting an automatic feeding system

Using an automatic feeding system, the materials added to the furnace are fed into the weighing bin through a vibrating feeder controlled by frequency conversion in the bin. Then, the accurately weighed material is fed into the furnace through a feeding belt conveyor or feeding truck. Ensure feeding accuracy, reduce material waste, and improve smelting efficiency. Combining the feeding data model can achieve automation of feeding operations, reduce manual labor intensity, improve the working environment, and enhance the quality of molten steel.

(7) Adopt foam slag process

Foam slag process is an effective means to improve thermal efficiency and reduce energy consumption. Remove slag by adjusting the composition of the materials added to the furnace. Usually, alkaline slag is used to bubble the slag, envelop the arc, achieve full arc heating, stabilize the arc, improve the input efficiency of transformer power, greatly improve heating efficiency, accelerate the temperature rise of molten steel, shorten smelting time, and reduce the consumption of electrode materials and lining refractory materials.