Feeding System for DC Arc Furnaces

Feeding System for DC Arc Furnaces

DC arc furnaces are designed to melt waste material into a molten state. The waste material may be in the form of municipal, industrial or medical waste. The power source of the DC arc furnace comprises a transformer, an AC joule heating system, and a DC arc electrode. The transformer is used to provide the required energy for the metal melting process. A special feature of the transformer is that it is a “U” core transformer whereby all the windings are wound around a magnetic core. This structure ensures a high degree of stability to the DC power supply.

The primary side of the transformer is connected to a grid, and the secondary side is connected to the DC arc furnace via a control circuit. The control circuit provides constant current and constant voltage to the DC arc furnace. This minimizes disturbance to the AC network and the AC joulle heating system.

Various benefits have been claimed by DC EAF operations for their operation, such as reduced electrode consumption (20 % to 50 %) and low voltage flicker at the point of common coupling (PCC). However, large DC furnaces did not achieve these expected results immediately when converted from AC to DC operation. The main problems experienced were refractory wear and bottom electrode life.

In order to address these issues, the present invention discloses a new feeding system for dc arc furnaces that uses diode rectifiers with DC choppers. This feed system is shown to significantly reduce the deviation of the arc power from the specified reference value. It also improves the reactive power absorbed by the feeder.

The DC arc furnace is generally configured to have an anode and a cathode. The anode is usually a metal pin electrode with a non-conductive lining. The cathode is a steel plate electrode and it is configured to have a conducting bottom lining. Several designs of bottom electrodes are available to increase the arc life. However, these designs often create arc flare in the hearth area.

This arc flare causes excessive refractory wear as the arc concentrates on this area of the furnace. In addition, it leads to an increased number of reversals in the electrical circuit of the furnace. Several solutions have been developed to eliminate this problem and to increase the arc life. The most promising solution is the use of a chopper feed. However, this type of solution is expensive. Consequently, other methods for improving the performance of a DC arc furnace are also discussed. These include modifying the anode design, decreasing the arc current, and using a high-power thyristor feeder. The article discusses these methods and compares them with the chopper feed system for DC EAFs. The resulting simulations show that the chopper feeder has lower deviation than the thyristor feeder when using constant current or constant power control. The chopper feeder also has higher reactive power compensation capability than the thyristor feeder. These results indicate that a chopper feed system for DC arc furnaces is preferable to the thyristor feeder.

Tags:blast furnace | electric arc furnace | electric furnace steelmaking