Difference between Submerged Arc Furnace and Electric Arc Furnace

What is the difference between submerged arc furnace and electric arc furnace? An electric arc furnace is a kind of power-frequency electric furnace that uses electric arc energy to smelt metal. The electric arc furnaces used in industry can be divided into three types: the first type is the direct heating type. The electric arc occurs between the special electrode rod and the melted furnace charge. The furnace charge is directly heated by the electric arc, which is mainly used for steelmaking, and also used for smelting iron, copper, refractory materials, refining liquid steel, etc. The second type is the indirect heating type. The arc occurs between two special electrode rods. The furnace charge is heated by the radiation of the arc and used for smelting copper, copper alloys, etc. The third type is called submerged arc furnace, which uses high-resistivity ores as raw materials, and the lower part of the electrode is generally buried in the furnace charge during the working process. The heating principle is not only the heat generated by the resistance of the charge when the current passes through the charge, but also the heat generated by the arc between the electrode and the charge.

The submerged arc furnace is a kind of electric arc furnace.

1. Nature

(1) Electric Arc Furnace

It is an electric furnace that uses the high temperature produced by electrode arc to melt ores and metals.

The electric arc furnace is an industrial furnace that generates electric arc heating through metal electrodes or non-metal electrodes. The electric arc furnace can be divided into three-phase electric arc furnaces, consumable electric arc furnaces, single-phase electric arc furnaces, and resistance electric arc furnaces. The furnace body of an electric arc steelmaking furnace is composed of a furnace cover, furnace door, tapping trough, and furnace stack. The furnace bottom and furnace wall are built with alkaline refractory or acid refractory. Electric arc steelmaking furnace is divided into ordinary-power electric arc furnace, high-power electric arc furnace, and ultra-high-power electric arc furnace according to the transformer capacity allocated for each ton of furnace capacity. Electric arc furnace steelmaking is to input electric energy into the electric arc steelmaking furnace through the graphite electrode and uses the electric arc between the electrode end and the furnace charge as the heat source for steelmaking. The electric arc furnace uses electric energy as the heat source, which can adjust the atmosphere in the furnace, and is extremely favorable for smelting steel grades containing more easily oxidized elements. Not long after the invention of electric arc furnace steelmaking, it was used to smelt alloy steel and has been greatly developed.

With the improvement of electric arc furnace equipment and smelting technology, and the development of the electric power industry, the cost of electric arc furnace steelmaking continues to decline. At present, electric arc furnace steelmaking is not only used to produce alloy steel, but also used to produce a large number of ordinary carbon steel. Its output is increasing in proportion to the total steel output of major industrial countries.

(2) Submerged Arc Furnace

A submerged arc furnace is also known as an electric arc furnace or resistance furnace. It is an industrial electric furnace with huge power consumption.

According to the structural characteristics and working characteristics of the submerged arc furnace, 70% of the system reactance of the submerged arc furnace is generated by the short network system, which is a large current working system, and the maximum current can reach tens of thousands of amperes. Therefore, the performance of the short network determines the performance of the submerged arc furnace. For this reason, the natural power factor of the submerged arc furnace is difficult to reach more than 0.85, and the natural power factor of most furnaces is between 0.7 and 0.8, The low power factor not only reduces the efficiency of the transformer and consumes a lot of useless work, but also imposes additional power fines by the power department. At the same time, due to the manual control of electrodes and the stacking process, the power imbalance between the three phases increases, and the maximum imbalance can reach more than 20%, which leads to low smelting efficiency and higher electricity charges. Therefore, improving the power factor of the short grid and reducing the unbalance of the grid has become an effective means to reduce energy consumption and improve smelting efficiency. If proper measures are taken to improve the short network power factor, the power consumption can be reduced by 5~20%, and the yield can be increased by more than 5%~10%.

This will bring good economic benefits to the enterprise, and the transformation costs invested will be recovered in the short and medium term in the saved electricity costs.

In the submerged arc furnace system, the loss of the short network accounts for more than 70% of the system’s own loss, and the short network is a large current operating system, the maximum current can reach tens of thousands of amperes, so the performance of the short network largely determines the performance of the submerged arc furnace

If proper measures are taken to improve the power factor of the short network and the electrode imbalance, the production power consumption will be reduced by 3%~6% and the product output will be increased by 5%~15%.

Thereby bringing good economic benefits to the enterprise, and the investment in the transformation cost can be recovered in the short and medium term of the comprehensive benefits created. Under normal circumstances, in order to solve the problem of low natural power factor of submerged arc furnaces, our country mostly adopts the method of reactive power compensation on the high-voltage side. The high-voltage compensation only improves the power factor of the high-voltage side. The reactive power generated by the huge inductive reactance still flows in the short grid system, and the three-phase imbalance is due to the strong phase of the short grid (the short grid is short, so the inductive reactance is small, so the loss is small, and the output is large. Therefore, the high-voltage compensation cannot solve the problem of three-phase balance, nor does it achieve the effect of offsetting the reactive power of the short-line system and improving the power factor of the low-voltage side. More than 70% of the power supply, so it cannot reduce the loss of the low-voltage side, nor can it increase the output of the transformer, but it can avoid fines, which is only meaningful to the power supply department.
Compared with high-voltage compensation, the advantages of low-voltage compensation are mainly reflected in the following aspects in addition to improving the power factor:
1) Improve the utilization rate of transformers and high-current lines, and increase the effective input power of smelting.
For arc smelting, the generation of reactive power is mainly caused by the arc current. Move the compensation point forward to the short grid to compensate for the large reactive power consumption of the short grid on the spot, increase the input voltage of the power supply, increase the output of the transformer, and increase the smelting effective input power. The melting power of the material is a function of the electrode voltage and the material-specific resistance, which can be simply expressed as P=U2/Z material. As the load capacity of the transformer is improved, the power input from the transformer to the furnace is increased, thereby increasing production and reducing consumption.
2) Compensate for unbalance and improve the strong and weak phase conditions of three phases.
Because the layout of the three-phase short grid and the furnace body and charge are always unbalanced, the different voltage drops and different powers of the three phases leading to the formation of strong and weak phases. Single-phase parallel connection is adopted for reactive power compensation, the compensation capacity of each phase is comprehensively adjusted, the power density of the furnace core and the uniformity of the crucible are improved, the effective working voltage of the three-phase electrodes is consistent, the electrode voltage is balanced, the three-phase feed is balanced, and the three-phase electrode is balanced. The strong and weak phase conditions of the phase can achieve the purpose of increasing production and reducing consumption. At the same time, the three-phase unbalance phenomenon is improved, the working environment of the furnace is improved, and the service life of the furnace is prolonged.
3) Reduce high-order harmonics, reduce the harm of harmonics to the entire power supply equipment, and reduce additional losses of transformers and networks.
4) The power quality is improved, the electrical parameters of the system are improved, and the product quality is improved.

However, due to the traditional compensation switching technology (such as switching with AC contactor), the number of switching switches is high, and the cost is high. At the same time, due to the harsh working environment, service life is greatly affected. The service life of the low-voltage compensation of the switching method is difficult to exceed one year, so it brings a lot of maintenance to the enterprise, and the investment recovery period is prolonged. Due to the high follow-up maintenance cost, the comprehensive benefit is not good. BWKN-3500 type reactive power compensation controller (special type for submerged arc furnace short network) is a reactive power compensation controller for submerged arc furnace system specially developed and designed to adapt to the working characteristics of submerged arc furnace (submerged arc furnace short network special type), the controller has the ideal function of improving power quality, mainly has the functions of improving the power factor of a submerged arc furnace, saving energy, providing voltage support, reducing flicker and so on. The controller has the following salient features:
1) The three phases are compensated separately to reduce the unbalance of the three phases and effectively increase production and reduce consumption.
2) Greatly improve voltage drop and flicker.
3) Achieving free switching at any time.
4) With high reliability, it can realize maintenance-free and unattended operation.
5) Multiple protection design to avoid the damage of capacitors and electronic switches to the greatest extent. (made according to different customers)
6) Significantly improve the utilization rate of the power supply system.
7) Main technical parameters: the main basis of the controller
Design specification: DL/T597-1996; rated voltage: 220V; fundamental frequency: 50Hz; control physical quantity: reactive power Q; power factor COSΦ; Continuous work; Ambient temperature: -5℃~+70℃; Relative humidity: daily average not more than 95%, monthly average not more than 90% (indoor), no condensation; compensation method: compensation by phase and grade. (can be customized according to customer needs.) 8) Performance characteristics can be divided into phases, grading, circulation, and electronic switch switching; can be divided into grading compensation. Equipped with complete protection functions; automatic control of switching, no manual intervention is required for the operation of the device, which is safe and efficient.

2. Features

What’s the difference between a submerged arc furnace and an electric arc furnace?

(1) Electric Arc Furnace

The electric arc furnace is more flexible than other steelmaking furnaces, and can effectively remove impurities such as sulfur and phosphorus. The furnace temperature is easy to control, and the equipment occupies a small area. It is suitable for the melting of high-quality alloy steel.

(2) Submerged Arc Furnace

Its working characteristics are that it uses carbon or magnesia refractory material as the furnace lining and uses self-cultivation electrodes. The electrode is inserted into the charge for submerged arc operation, using the energy and current of the arc to pass through the charge, and generate energy due to the resistance of the charge to smelt metal.