Technical Methods for Energy Conservation in Electric Arc Furnaces

Technical Methods for Energy Conservation in Electric Arc Furnaces

From the perspective of thermal equilibrium, energy conservation in electric steelmaking encompasses two aspects: firstly, reducing heat loss and minimizing thermal downtime;  secondly, adopting new technologies and equipment to shorten smelting time.  It can be argued that electric arc furnace (EAF) steelmaking technology has primarily evolved around the core principle of reducing the smelting cycle.

In light of the current technological trends, the following methods are primarily employed to conserve energy in electric steelmaking:

Substitute electric energy with inexpensive primary energy sources such as oil, natural gas, and coal.

(2) To enhance the efficiency of electric energy utilization and reduce reactive power, the primary measure is to increase the power factor.  To this end, optimize the power supply wiring and conduct high-voltage long-arc operations during the melting period.

(3) Enhance oxygen utilization by equipping oxygen burners to combust the overflowing CO and recycle the chemical heat from the flue gas.

(4) Utilize the physical and chemical heat from the flue gas of electric steelmaking to preheat scrap steel.

(5) The eccentric bottom tapping (EBT) technology is employed to facilitate the operation of retaining steel and slag.  On one hand, it ensures that a substantial amount of hot slag remains within the furnace.

Simultaneously, the residual slag and molten steel contribute to the early stabilization of the electric arc during the initial stage of electrification, thereby enhancing the power factor and reducing the time required for melting.

The fundamental direction of modern electric arc furnace steelmaking is towards high productivity, low production costs, and excellent and stable product quality.  In the control of the production process, electrical operation is an extremely critical aspect.

In the process of steelmaking using electric arc furnaces, a rational electrical operation regime constitutes the fundamental technological system. This rational electrical operation regime hinges on fully exploiting the transformer's capabilities, which is not only essential for the smooth progression of operations but also instrumental in reducing power consumption, electrode wear, and refractory erosion, thereby shortening the smelting cycle.

The principle of optimizing the power supply system lies in maximizing the power supply capacity of the transformer during the smelting process, with the most direct objective being to achieve the maximum arc power.  Therefore, within the permissible range of rated power and under the premise of ensuring stable arc combustion, efforts should be made to enhance the power factor, thereby increasing productivity and reducing power consumption and total energy consumption.

In addition to accelerating the decarburization rate, the intensified use of oxygen can fully utilize the heat released by the chemical reaction between oxygen and the easily oxidizable elements in the raw materials, achieving the effect of energy conservation and consumption reduction.  In modern electric arc furnace steelmaking, the extensive use of oxygen, coupled with the shortened smelting cycle to 40-60 minutes, has led to the term "electric arc furnace steelmaking becoming converter-like." Among them, oxygen blowing oxidizes various elements in the molten pool, and the heat released generally accounts for 25-30% of the total energy supply.  At the same time, the stirring effect of oxygen advances the melting of scrap steel at the bottom of the furnace, homogenizes the temperature of the molten steel, and suppresses the boiling phenomenon during the refining period.  Intensified oxygen use has become an important technical direction in electric arc furnace steelmaking.  For ordinary molten iron, the theoretical heat value of each element reacted at 1600℃ is approximately 4 kWh per lms of oxygen supplied.  Generally, the energy supplied by intensified oxygen use accounts for 25-30% of the total energy supply.

In order to shorten the smelting cycle and enhance productivity, electric arc steelmaking employs a higher secondary voltage for long arc smelting. Due to the strong radiation capability of the long arc, foam slag technology is utilized to shield the electric arc.

Foam slag technology involves the process of injecting carbon powder into the molten bath during oxygen blowing in electric furnace smelting, creating a vigorous carbon-oxygen reaction. This results in the formation of a substantial amount of CO gas foam within the slag layer, which increases the slag thickness to 25 to 30 times the arc length.  This technique effectively shields the electric arc entirely, reducing arc radiation, extending the lifespan of the electric furnace, and enhancing its thermal efficiency.

Excellent foam slag aids in enhancing the heat transfer from the electric arc to the molten steel, reducing gas absorption by the steel, mitigating the erosion from furnace dust, and diminishing noise levels.  Additionally, by increasing the contact area between steel and slag, it greatly facilitates the dephosphorization of oxidized slag.  The application of foam slag technology in large-capacity ultra-high power electric furnaces significantly enhances heat transfer efficiency, shortens smelting time, reduces electricity consumption for smelting, prolongs the lifespan of the electric furnace, and decreases the consumption of furnace lining materials.

The oxygen combustion nozzle technology for electric arc furnaces is a technique aimed at enhancing heat supply to the molten bath. By supplementing electrical energy with other fuels, it ensures the melting of scrap steel, reduces the smelting time of the electric furnace, thereby enhancing production efficiency and lowering the power consumption for smelting.  The utilization of oxygen combustion nozzles to provide auxiliary energy is crucial in heating the cold zone and improving the thermal balance within the furnace, ultimately achieving energy conservation and efficiency enhancement.  

In electric furnace production, the primary functions of using oxygen combustion nozzles can be summarized as follows:

(1) Increase the total heat quantity within the furnace;

(2) Reduce the temperature variation across various parts within the furnace;

(3) Reduce electrical energy consumption;

(4) The reduction of smelting time enhances productivity;

(5) Reduce the consumption of electrodes and refractory materials.

Oxy-fuel burners are the most significant source of electrical energy compensation. However, when utilizing oxy-fuel burners to conserve energy, attention should be paid to the prices of natural gas and fuel oil, and the overall benefits should be considered.