The connotation of electric furnace automatic steelmaking can be divided into two levels: the first level, instead of entering (hand) for oxygen blowing, power supply and feeding operations, and the automatic determination of the smelting end point, this level is still called automatic steelmaking; The second level, instead of entering (brain) for the optimization of the smelting process, such as power curve optimization, power supply optimization, oxygen blowing optimization, etc., this level is called intelligent steelmaking. Therefore, some intelligent electrical parameter adjustment and control systems, such as NAF of NAC, SimeltNEC of SmartARC.SIEMENS of AMIGE, are not all of intelligent steelmaking. At present, the automatic (smart) steelmaking technology of electric arc furnace is still lagging behind converter steelmaking to a large extent, which is related to the fact that the former system is more open, the main raw materials are more diverse, the energy input is more complicated, and the process cycle is longer.
The electric steelmaking control model is divided into a static model and a dynamic model.
The static model is based on the theoretical calculation of heat balance and material balance, or the statistical analysis results of previous heat data to establish some models, and obtain a set of static smelting process curves through the model. The actual smelting process is always in constant change. Especially the modern advanced electric arc furnace is more complicated in terms of energy input and main raw material structure, but it puts forward higher requirements for energy saving and accurate determination of smelting end point. Therefore, the static model is obviously difficult to do. Dynamic models are models built on simple feedback control. The process dynamic control system includes metallurgical database, expert system, intelligent control model, etc., to forecast and optimize the whole process of smelting.
In the production of electric arc furnaces, the steelmaking process has many similarities with the converter, and the main difference is the electrode control. The value of the power delivered to the electric arc furnace is related to the length of the arc; when the secondary voltage of the electric furnace transformer is constant, it is related to the equivalent resistance of the arc.
When the electric furnace is in the working process, especially during the charging period of the furnace, the arc discharge gap often changes, and various deviations from the normal working state (difference from the short circuit of the electrode to the metal until the arc breaking) continuously occur. A change in the length of the arc discharge inevitably results in a change in input power, thereby damaging the process specification. Therefore, the fundamental requirement for the operation of an electric arc furnace is to maintain a specified arc length under optimal power usage specifications.
To maintain the arc length constant, this can be achieved by continuously adjusting the length of the arc gap under each electrode. That is, the most common method of adjusting the power of an electric arc furnace is to take a method of changing the length of the arc by moving the position of the electrode.
Due to the extremely unbalanced electrical system during the melting period of the charge, frequent inrush currents and short circuits occur. In this case, if manual adjustment is taken, the operator is not competent; in addition, manual adjustment is more difficult if the number of electrodes (three electrodes in the three-phase furnace) and the electrode weight of the large furnace are taken into consideration. Therefore, the electric arc furnace must be equipped with an electrode lift automatic regulator.
The regulation conditions and adjustment tasks of the electric arc furnace regulator are quite complicated. When the cold material is melted, an arc of several millimeters in length produces several megawatts of power in a relatively small range. At this point, the arc temperature is several thousand degrees, the molten metal melts rapidly, violently, evaporates, splashes under the electrodes, and the arc moves to a nearby metal block. Therefore, the arc length, arc current, and power constantly change.
When the current is less than the rated value, the electric energy input into the furnace is reduced, the melting time is prolonged, and the electric energy and the electrode consumption are increased. When the current is very large, even a few seconds can greatly increase the line loss, resulting in the input furnace. The internal energy is reduced and the various indicators of the equipment are reduced. At this time, the length of the arc is very short, especially when the electrode is in contact with red or liquid metal, which actually causes the metal to be subjected to carbonization, which is not allowed when smelting various alloys. It can be seen that maintaining the optimal electricity consumption specification in the electric arc furnace is a particularly arduous task, and the quality of the smelted steel and the utilization rate of the equipment are all related to this.
Each phase electrode is equipped with a separate auto regulator. The main part of the regulator includes the prime mover that controls the lift of the electrode and the regulator body. The regulator is an instrument that is very sensitive to changes in the electrical system in the electric furnace. It controls the electrode lift according to the electrical signal of the furnace.