Steelmaking production is progressing towards more clean and more high efficiency along with many technologies put into practical application.
Scrap is mixed with ferrous metals, non-ferrous metals, non-metals, and should be crushed and sorted before charging into the furnace. Apart from separation, the paint and coating on the surface of scrap steel can be removed mostly.
There is double-shell EAF and vertical EAF and consteel EAF able to preheating scrap because of the low waste heat utilization, large maintenance of equipment the double shell and vertical electric arc furnace have been used less.
Consteel arc furnace of continuous feeding system features small impact of power grid, reliable and controllable feeding, high efficiency of waste heat utilization of flue gas, but its disadvantages are the dynamic sealing air leakage, too long production line and high operating cost.
As scrap generally contains grease, paint, cutting waste oil and other impurities, the gas containing certain amount of dioxins will be produced in the process of EAF steelmaking, thus causing environmental pollution. Generally to treat this problem adopts source inhibition and Synthesis inhibition solution. The source inhibition is through online detection and manual selection to minimize or even eliminate the scrap containing chlorine source material into the furnace. The Synthesis inhibition plan is to rapidly cool and add catalytic/inhibitor to inhibit dioxin regeneration. This solution needs high equipment investment.
A large amount of high temperature dust-containing flue is produced during EAF smelting process, and the heat taken away is about 11% of the total energy input by the electric furnace, and some are even as high as 20%. EAF steelmaking is periodic. Only the recovered heat can be stored then stable and continuous used to ensure stable power generation. The molten salt heat storage system or concrete heat energy storage system is used to store excess heat from the EAF.
The batching is the key link to determine the production cost and product quality of EAF steelmaking. According to the parameters of EAF equipment, the production process, the constraint of raw material usage and the chemical composition of the charge, the mathematical model of optimizing batching is established, and the standard charging structure with optimal cost is calculated by mathematical programming method to realize intelligent batching.
Now electrode lifting automatic control system can set different smelting periods and may achieve the best in response time, three-phase unbalanced control, reactor input or removal, basically meet flexible control need of the electrode and furnace condition.
Advanced automatic sampling robot can realize automatic on-line replacement of the temperature measuring probe and the temperature and oxygen activity of the liquid steel in the electric arc furnace can be measured in real time, and then the carbon content can be calculated through the program under one-key operation.
It is difficult to accurately measure the temperature of molten steel due to harsh environment during the EAF run. USTB non-contact liquid steel temperature measuring system developed by Beijing University of Science and Technology installed measuring device in the furnace wall, obtains the characteristic signal of liquid steel temperature by using multi-element temperature measuring gas injection. The established model can realize the temperature measurement and prediction of molten steel pool.
The foam slag operation in the process of EAF steelmaking can isolate the molten steel from air, cover the arc, reduce the heat loss of radiation to the furnace wall and cover, efficiently convert electric energy into heat energy to transport to the molten pool, meanwhile shorten the smelting period. To control foam slag level and existence time is to ensure thickness of slay layer in the furnace at melting period.
The modern electric arc furnace gas analysis system can accurately measure the temperature, flow rate and CO、CO2、H2、O2、H2O and CH4 components of the furnace gas, analyze the smelting process by using the collected information and its own control model, determine the utilization rate of chemical energy in the furnace, the degree of imbalance between carbon and oxygen, the explosion hazard of the exhaust system and whether the ventilation system is over-extracted, and at the same time, realize the dynamic input control of oxygen to ensure full combustion of the gas.
The process information comes from various sensors such as exhaust gas analysis, electric harmonics, current and voltage, etc. The data bank is set up based on the history record of the process, then select the best history data which have similar the charging and working surroundings, finally the optimal process procedure with low cost and short melting time is determinate.
