Electric Arc Furnace Energy Saving Technology

author: Anna

2024-11-18

Electric Arc Furnace Energy Saving Technology

Electric arc furnace energy saving can start from the following three aspects:

One is to use new technologies to reduce heat loss;
The second is to reduce the power loss of electric arc furnace-related electrical equipment;
The third is to strengthen production management and reduce energy consumption.

1. Strengthen the Oxygen System

The purpose of the oxygen blowing operation of the electric furnace is to blow oxygen to promote melting and decarburization, in conjunction with the injection of carbon powder, to create foamy slag. Using an oxygen lance to replace the oxygen blowing pipe operation can achieve significant results. The oxygen lance uses cheap carbon powder, oil, natural gas, etc. to replace electric energy to heat and flux the cold area of the electric arc furnace, improving production efficiency.

The oxygen lance jet airflow is concentrated, It has a strong ability to penetrate the metal molten pool, strengthen the stirring effect of molten steel, speed up oxygen blowing decarburization and foaming slag, strengthen the use of oxygen in electric arc furnace steelmaking, and extend the carbon-oxygen reaction time.

2. Foamed Slag Technology

Artificial oxygen blowing generates foam slag, which is labor-intensive and ineffective. Using a carbon-oxygen gun to blow oxygen and carbon powder into the slag layer will easily generate foamy slag in the slag layer.

By controlling metallurgical conditions such as slag basicity, oxidation, and fluidity to meet process requirements, the best effect of generating foamed slag is when the slag basicity is 2.0~2.5 and the iron oxide content in the slag is 15%~20%.

Oxygen is blown into the molten pool to generate carbon monoxide, which foams the electric furnace slag, thereby achieving submerged arc operation.

The arc heat is efficiently transferred into the molten steel through the slag. The ultra-high power transformer operates with long arc and high power, achieving high voltage and low current, further improving the arc. heat transfer efficiency.

3. Ultra-high Power Supply Technology

Electric arc furnace steelmaking adopts ultra-high power smelting, which increases the energy input density of the molten pool, accelerates the melting of the charge, and greatly shortens the smelting time, thereby improving the thermal efficiency of the electric arc furnace and significantly reducing the unit power consumption. The ultra-high-power electric arc furnace has a unique power supply system.

High-power power supply is used throughout the smelting process. High voltage and long arc are used to quickly melt materials during the melting period.

Submerged arc foam slag operation is used at the end of the melting period to promote heating and stirring of the molten pool to ensure the melt composition and temperature are uniformized; and the thermal load of the furnace lining is reduced at the same time, thereby improving the productivity of electric arc furnace steelmaking and reducing power consumption.

4. Waste Heat Utilization Technology

The fundamental measure to reduce the total energy consumption of electric arc furnace steelmaking is to reduce the total energy demand, the most important of which is the reuse of waste heat from waste gas.

(1) Reuse of chemical waste heat - secondary combustion

The secondary combustion technology injects an appropriate amount of auxiliary oxygen through the secondary combustion device to burn CO and other gases generated during operation, and releases a large amount of heat to preheat the surrounding scrap steel and return it to the inside of the molten pool, thus shortening the smelting time and achieving energy saving and consumption reduction. effect.
Secondary combustion technology mainly includes three technologies: water-cooled oxygen lance, oxygen flow control and gas analysis system.
Secondary combustion is an emerging technology aimed at reducing energy costs and increasing the productivity of electric arc furnaces. This is a direct continuation of foam slag technology.

The secondary combustion of electric arc furnace gas can achieve the following effects:

Reduce power consumption;
Improve production intensity;
Increase the carbon content of the furnace charge;
Conducive to waste gas treatment.

2) Physical waste heat utilization - scrap steel preheating

The latest development of electric arc furnace steelmaking combined with scrap steel waste heat is the vertical furnace-electric arc furnace developed by Fuchs, which moves the traditional scrap steel preheating device outside the furnace to the upper part of the furnace to preheat the scrap steel in the furnace, fully convert the chemical energy of secondary combustion and recover the physical waste heat of high-temperature furnace gas, while filtering smoke dust. Before the electric arc melts the scrap steel, the sensible heat and chemical heat of the furnace gas are used to preheat the scrap steel, thereby saving the input energy in the furnace.

The scrap steel temperature can rise by 200~300℃, and the maximum can rise to 600~800℃, saving 15~40kWh/t of electricity.
The productivity and processing cost of this process are improved due to the following reasons:
1. The waste heat is obtained before the scrap steel is melted, which shortens the melting time;
2. The power input is improved, which increases the productivity of the furnace;
3. The metal recovery rate is improved; electrodes and refractory materials are saved; environmental pollution is reduced.

5. Transformer Capacity Preservation Transformation

Replacing the transformer can achieve the goal of energy saving and consumption reduction, but it is difficult for enterprises with financial difficulties to achieve it. At this time, the method of capacity preservation transformation can be adopted, which can not only achieve the goal of energy saving and consumption reduction, but also alleviate financial difficulties.

Capacity preservation transformation mainly reduces the internal loss of the transformer, reduces the working temperature rise, increases the working current, and shortens the smelting period through the transformation of the iron core and coil, thereby achieving the goal of energy saving and consumption reduction. After the capacity preservation transformation of a 3t electric arc furnace, the smelting period was shortened by 30min, and 28.58kW·h of electricity was saved per ton of steel, and the investment could be recovered in one and a half years.

6. Short Network Transformation

The short network refers to a section of wire from the low-voltage end of the electric furnace transformer to the electric furnace electrode. It is mainly composed of rectangular copper busbars, compensators, flexible cables, water-cooled copper tubes, electrode clamps and graphite electrodes. Among them, flexible cables generally use copper core cables, and water-cooled cables can be used for large-capacity electric furnaces.

Due to the complex structure of the short-circuit network and the large current passing through it, the power loss is relatively large, generally accounting for about 9% to 13% of the total power transmitted. Therefore, it is an effective way to save electricity to transform the short-circuit network and reduce the short-circuit network loss.

(1) Reduce the resistance of the short-circuit network

The resistance of the short-circuit network mainly consists of three parts: effective resistance, contact resistance and additional resistance.

The effective resistance of the short-circuit network is related to the length and cross-section of the short-circuit network. The effective resistance can be reduced by reasonably selecting the cross-section and number of wires.

When selecting the cross-section of the wire, the main consideration should be to reduce the influence of the skin effect. When the cross-section of the wire exceeds 600mm2, more than two conductors should be selected.

There are many joints in the arc furnace short net, and the current passing through the short net is very large. If the joint is not connected well, the contact resistance will increase, which will not only increase the power loss of the short net, but also may burn the joint. Therefore, the joints should be reduced as much as possible. For the joints that are not disassembled, welding should be used or the contact area should be increased.

The contact surface should be kept clean and flat so that there is sufficient contact pressure. In recent years, with the advent of electrical contact conductive paste, applying conductive paste to the joints has become a new method to reduce contact resistance. Conductive paste is a fluid paste conductive coating containing conductive fillers and adhesives. The use of conductive paste can not only reduce the contact resistance value of the joint, but also reduce the temperature rise.
According to the information: After using conductive paste, the contact resistance of the joint can be reduced by 25% to 75%, and the temperature rise can be reduced by 25% to 75%. The generation of additional resistance is related to the eddy current and hysteresis loss generated by the ferromagnetic components near the short net under the action of electromagnetic induction. The loss of these components accounts for about 15% to 20% of the total resistance loss.

The methods to reduce the additional resistance are:
1. Avoid using ferromagnetic materials around the short network as much as possible;
2. Steel objects should be kept away from the short network;
3. Create air gaps and add insulating pads in closed steel objects.

(2) Reduce the imbalance of short network reactance and three-phase impedance.

When wiring the short network, double-wire layout should be used as much as possible. This wiring method can achieve flux compensation, reduce short network reactance, and increase the three-phase impedance balance coefficient.

When arranging the three-phase short network in space, the middle phase should be raised to form a regular triangle.

This also helps to improve the three-phase reactance balance coefficient. After a factory adopted a double-wire layout, the power factor increased from 0.76 to about 0.84, achieving a good power saving effect.

(3) Use a new type of water-cooled conductive cross arm to transform the short network.

The cross arm is an important component of the arc furnace short network and electrode lifting mechanism.

One of its main functions is to support the conductive steel pipe; the other function is to connect with the column and the electrode clamp to form an electrode lifting mechanism to realize the up and down movement of the electrode.
The two functions of the ordinary short-net cross arm are separate, namely, the conduction and support of the electrode, which have problems such as high failure rate and large power loss.

In recent years, with the large-scale and high-power arc furnace, the resistance and reactance values of the entire short-net part have continued to increase, which has deteriorated the electrical efficiency and power factor of the main circuit of the arc furnace; on the other hand, with the continuous increase in the working current of the arc furnace, it has also brought many troublesome problems to the conductive copper pipe section of the short net.

The new electrode cross arm - water-cooled conductive cross arm combines the conductive function of the original water-cooled copper tube and the support function of the cross arm, and is equipped with a large-section water-cooled cable. Its short-net impedance is low and has good energy-saving benefits.

Most of the short-net soft cables of small and medium-sized arc furnaces are air-cooled bare cables, which have the disadvantages of large contact resistance, short service life, large maintenance workload, increased thermal downtime and three-phase reactance imbalance. The large-section water-cooled cable absorbs foreign advanced technology.

The conductors are twisted into strands. Each strand is connected to the copper using a one-time crimping process. The two ends of the cable are flat joints to reduce contact resistance. Each strand is separated by soft insulating material to avoid mutual friction.

The cable life can be extended by 2 to 3 times. It can give full play to the transformer capacity and increase the transformer output power by 10%. The use of large-section water-cooled cables can save 2% to 5% of electricity. The water-cooled conductive cross arm is shown in Figure 14. It cancels the traditional conductive copper tube and its supporting structure.

All devices are installed in the overall box-shaped cross arm. The short-circuit resistance will increase with the increase of temperature, which will increase the power loss of the short-circuit. For example, for a short-circuit under 10kA operation, the temperature increases by 1℃, and the loss per meter of busbar increases by about 3 to 6W.

Therefore, reducing the temperature of the short-circuit can also reduce power loss. A factory used a new water-cooled conductive cross arm to transform the arc furnace, and the melting rate increased by 13.3% and the smelting power consumption decreased by 12.7%.

(4) Use a good electrode lifting system.

The power input into the arc furnace is related to the arc length.

During smelting, it is required to maintain the specified arc length under the optimal input power curve. However, due to various reasons, the arc length will change during steelmaking, and the arc power will deviate from the optimal input curve, resulting in increased power loss.

This requires the electrode to adjust its position in time to maintain the specified arc length. The microcomputer-controlled variable frequency electrode regulator has good speed, accuracy and reliability.

It can automatically control the electrode lifting and adjusting the arc length quickly, accurately and smoothly to achieve the purpose of automatically controlling the arc power; and the system has high control accuracy, stable current, low failure rate, and less hot stop time, which shortens the smelting time, reduces electrode consumption, and reduces the impact on the power grid load.

7. Consteel Process:

During tapping, a large amount of steel is retained to form a molten pool. The preheated scrap steel continuously enters the molten pool in the furnace from the transportation channel and is melted.

The transformer starts to work, the electrodes transmit power, and at the same time, the automatic water-cooled carbon-oxygen gun in front of the furnace mixes the carbon powder and Oxygen is injected into the furnace to create foamed slag and perform submerged arc operation.

The Consteel process has working characteristics such as scrap steel preheating, continuous feeding, and full submerged arc foaming slag operation, which are greatly superior to traditional processes, which significantly improves the smelting efficiency and reduces the consumption of electrical and chemical energy, and comprehensive energy consumption. The indicators are very advanced.

1) Due to the continuous feeding operation, there is no need to frequently stop the furnace and open the furnace cover, which reduces heat dissipation loss into the air.

The scrap steel that has been preheated along the closed conveyor channel is added to the molten pool through the hole in the wall of the electric arc furnace via a connecting car. There is no need to open the furnace cover when adding materials.

At the same time, there is always a molten pool in the furnace, and the process of feeding, melting, and smelting can continue without frequent shutdowns of the furnace.

Therefore, in this process, there is no radiant heat loss from the furnace masonry to the surroundings through the open charging port and the furnace shutdown in the traditional process. According to mathematical model calculations, this part of the heat loss can reach 1.43% during traditional top loading. The consteel process can be avoided.

(2) Continuous feeding keeps the molten pool temperature constant, the arc is stable, the load in the circuit is stable and the power loss is reduced. The consteel process retains a large amount of steel, enabling high-efficiency foam slag and submerged arc operations to be realized from the beginning of smelting.

This operation effectively reduces arc damage to refractory materials, so the transformer of the consteel electric arc furnace always operates within the maximum arc power range during the entire smelting cycle.

And, this maximum arc power is achieved through high voltage, low current and high power factor. Due to the small current, the corresponding short network size, flexible cable, busbar size, and electrode diameter can be reduced, and the capacity of the transformer can be 25 to 40% smaller than a traditional electric arc furnace with the same production capacity.

8. Gas Fluxing

Gas fluxing is to send gas and oxygen into the furnace from a lance, and burn it in the furnace to heat the charge. It is made of two stainless steel tubes of different diameters, concentrically sleeved together, and installed on a rotating frame on the front side of the furnace.

The oil-oxygen spray gun can be installed in the low-temperature area of the furnace, and the furnace wall 150 mm to 200 mm above the slag line forms an angle of 13° to 18° with the horizontal line.

Generally, after using gas as flux, 15% to 20% of electricity can be saved, and the effect is remarkable.

9. Furnace Building Materials

The old-fashioned electric arc furnace construction materials mostly use tar magnesia to knot the furnace lining, which consumes a lot of refractory materials and has a service life of only 30 to 50 times. The linings of steelmaking electric arc furnaces are all made of magnesia-carbon bricks.

Although the cost of furnace construction has increased, the lining life has been increased to more than 130 heats, which reduces the consumption of refractory materials and oven power consumption. Generally, power consumption can be reduced by 20kwh/t.

10. Strengthen Furnace Maintenance

The quality of the electric arc furnace body is not only related to the quality of molten steel, but also directly affects the electricity consumption.

To strengthen the maintenance of the furnace body, start with repairing the furnace, pay special attention to shortening the repairing time, and achieve quick repairing and thin repairing after the furnace is repaired; after repairing the furnace, use the slag leaving operation (after tapping, do not remove the remaining slag in the furnace The slag will be repaired), which can shorten the repairing time, reduce heat loss, and is beneficial to the sintering of magnesia.

Secondly, for small electric arc furnaces with intermittent production, "stuffing operation" can be adopted (after the last batch of molten steel comes out of the day, the scrap steel from the first batch of the next day is loaded into the furnace), so that the waste heat in the furnace can be fully utilized to heat the charge.

It has the effect of preheating the furnace charge; in addition, try to avoid turning on the cold furnace and turn on the hot furnace more often.

Steel Induction Furnace for Sale

Electric Arc Furnace Steelmaking Process