The use of scrap preheating technology can effectively shorten the smelting cycle and reduce smelting consumption; so far, the existing technology mainly uses electric furnace high-temperature flue gas to preheat scrap steel; there are two main ways to use electric furnace high-temperature flue gas to preheat scrap steel: direct Preheating method and indirect preheating method; the direct preheating method is characterized by connecting the flue gas extracted from the electric furnace to preheat the scrap steel, while the indirect preheating method uses the extracted flue gas to first heat the air and then use it to be heated Preheated steel scrap with the cooled air. Obviously, in terms of the effective utilization of the heat contained in the flue gas of the electric furnace, the direct method is better than the indirect method. At present, the relatively advanced scrap preheating technology mainly has the following 6 methods:
①Basket preheating: This method introduces high-temperature exhaust gas from the furnace of the electric furnace into the preheating tank, and then preheats the scrap in the basket. In order to extend the service life of the basket, the temperature in the basket must be controlled, and the temperature cannot be too high. Generally, the inlet temperature is 700°C to 800°C, and the outlet temperature is 200°C to 300°C. The energy-saving effect of this preheating method is 25kwh/t on average, but the disadvantage is that the preheating process is accompanied by smoke and odor.
② One electric two furnace type: This method is characterized by using one power source and two furnaces, one of which is used for steelmaking, and the exhaust gas generated by it is introduced into another furnace containing scrap steel for preheating, and then cycle operation . This not only solves the pollution problem caused by the preheating basket method, but also enables the preheated steel scrap to reach a high temperature above 1000 ℃, and the preheating effect is more efficient; in addition, this technology also omits the tapping, furnace repair and the first time Non-energized time such as furnace installation, thereby improving productivity. The energy saving effect of this process is obvious: when the preheating rate of scrap steel is 60%, the electric energy saving is 35-40kwh/t steel; when the preheating rate reaches 100%, the electric energy saving can reach 65kwh/t steel.
③Shaft furnace method: The structural characteristics of the shaft furnace method preheating process are: the water-cooled shaft furnace and the electric furnace cover are connected as a whole, and scrap steel is loaded inside, and the high temperature exhaust gas rising in the electric furnace hearth is used for preheating. In order to achieve the purpose of continuously preheating the scrap of each heat, hooks are installed at the lower part of the shaft furnace to support and control the falling scrap; the disadvantage is that in order not to affect the position of the furnace top electrode in the center of the furnace, the shaft can only be biased toward the electric furnace On one side, the scrap steel in the furnace is heated unevenly and the melting is not synchronized. The energy saving effect of this technology is about 30kwh/t steel.
④Preheating in the continuous conveying layer: This process is referred to as the NSCF process, which aims to solve the problem of uneven preheating of scrap steel on the conveyor belt in the CONSTEEL process. Therefore, an exhaust gas outlet is installed at the lower part of the enclosed conveyor belt, so that the exhaust gas preheats the scrap from top to bottom, so that the temperature of the scrap at a distance of 600mm～700mm from the surface of the conveyor belt is increased from <100℃ to >400℃; the energy saving effect can be achieved. 65kwh/t steel.
⑤Shaft furnace continuous installation: The structural feature of this process is that the top of the device such as the receiving hopper, exhaust pipe, preheating tank and pusher are all located on the upper part of the furnace center; the scrap steel is preheated by high temperature exhaust gas. The feeder is pushed to the center of the top of the electric furnace and then falls into the furnace; its energy saving effect can reach 138kwh/t steel, which has attracted wide attention.
⑥Filling layer electric furnace method: This technical feature is: the scrap steel is continuously charged around the top electrode of the electric furnace to form a filling layer in the furnace, and then it is preheated by the rising high temperature exhaust gas. Specifically, the scrap steel transported by the conveyor belt is loaded into the surrounding direction of the electric furnace furnace with a rotating magnet; in order to ensure that the exhaust gas can flow evenly and preheat in the filling layer scrap steel, an annular pipe is installed on the upper part of the furnace. The disadvantage is that this process is easily restricted by the geometry of the scrap steel; another key point is to ensure the heat resistance and reliability of the scrap steel loading equipment.