This article describes the details about steelmaking production, including the main features and safety technologies of safe production (scrap and blasting safety technology, steel, iron, and slag burn protection technology, steelmaking plant hoisting and transportation safety technology, steelmaking production Accident prevention measures and techniques).
Keywords: steelmaking; safety production; safety technology
Main features of steelmaking safety production
The molten iron contains impurities such as C, S, and P, which affect the strength and brittleness of iron. The molten iron needs to be resmelted to remove the above impurities, and Si, Mn, etc. are added to adjust its composition. The process of re-smelting molten iron to adjust its composition is called steelmaking. The main raw materials for steelmaking are molten iron or pig iron with high carbon content and scrap steel. In order to remove impurities in the molten iron, oxidants, deoxidizers, slagging materials, and ferroalloys and other materials need to be added to the molten iron to adjust the composition of the steel. After the molten iron or pig iron with high carbon content is added to the steel-making furnace, the impurities in the molten iron are oxidized and removed through oxygen supply blowing, ore addition, decarburization and other processes. Finally, alloy is added for alloying, and molten steel is obtained. There are three types of steelmaking furnaces: open hearth, converter and electric furnace. The open hearth steelmaking method has been gradually phased out due to high energy consumption and poor working environment. In converter and open-hearth steelmaking, molten iron is first put into a mixing furnace for preheating, scrap steel is added into the converter or open-hearth furnace, and then the high-temperature molten iron in the mixing furnace is mixed into the converter or open-hearth furnace using a mixing car for melting and heating. When the temperature is appropriate, the oxidation period begins. Electric furnace steelmaking is to add all cold scrap steel into the electric furnace steel, and then enter the oxidation period after a long period of melting and temperature raising.
(1) Melting process. Molten iron and scrap steel contain impurities such as C, Mn, Si, P, and S. During the low-temperature melting process, C, Si, P, and S are oxidized, even if the impurities in the single substance state become combined impurities, which will facilitate further removal in the later stage. Impurities. Oxygen comes from the rust in the charge (composition is Fe2O3·2H2O), iron oxide scale, added iron ore, oxygen in the air and oxygen blowing. The oxidation process of various impurities takes place between the interface of slag and molten steel.
(2) Oxidation process. The oxidation process is a decarburization, phosphorus removal, gas removal, and impurity removal reaction carried out at high temperature.
(3) Deoxidation, desulfurization and tapping. At the end of oxidation, the steel contains a large amount of excess oxygen. The excess oxygen in the molten steel is removed by adding lump or powdered iron alloy or multi-element alloy to the molten steel. The harmful gas CO produced is discharged with the furnace gas, and the generated slag can be Further desulfurization means that during the final tapping process, slag and steel are intensively mixed and flushed to increase the desulfurization reaction.
(4) Refining outside the furnace. The molten steel smelted from the steel-making furnace contains a small amount of gas and impurities. Generally, the molten steel is injected into the refining ladle and subjected to processes such as argon blowing, degassing, and ladle refining to obtain purer steel.
(5) Casting. The pure molten steel coming out of the steelmaking furnace or refining furnace can be tapped when its temperature is appropriate and its chemical composition is adjusted appropriately. The molten steel passes through the molten steel ladle and enters the steel ingot mold or continuous casting machine to obtain the steel ingot or continuous casting billet.
Pouring is divided into two methods: mold casting and continuous casting. Mold casting is divided into two types: upper casting method and lower casting method. The upper casting method is to inject molten steel from the molten steel ladle through the upper opening of the casting mold directly into the mold to form a steel ingot. The pouring method is to pour the molten steel in the molten steel ladle into the injection pipe and flowing steel bricks, and the molten steel enters the mold from the lower opening of the steel ingot mold. The molten steel solidifies in the mold to obtain the steel ingot. After removing the insulation cap, the steel ingot is sent to the soaking furnace of the steel rolling mill for heating, and then the steel ingot mold and other materials are transported back to the steelmaking plant for mold shaping.
In continuous casting, molten steel is poured from a ladle into a tundish and then into a cleaner. After being chilled, the molten steel is pulled out of the crystallizer at a certain speed by the blanking machine. After secondary cooling and forced cooling, after all cooling, it is cut into continuous casting slabs of a certain size and finally sent to the steel rolling workshop.
Main safety technologies in steelmaking production
(1) Prevention of explosion accidents in elbows or reducing pipes. The oxygen pipe bend or reducer in the upper part of the oxygen lance has a large flow rate and a large local resistance loss. If there is slag in the pipe or the degreasing is not clean, it is easy to induce explosion of high-purity, high-pressure, high-speed oxygen. Accidents should be avoided by improving the design, preventing sharp bends, slowing down the flow rate, blowing the pipe regularly, cleaning the filter, and improving degreasing.
(2) Prevention and control of backfire and explosion accidents. The use of low-pressure oxygen leads to negative pressure in the oxygen pipe and clogging of the oxygen lance nozzle holes, which can easily cause the gas generated in the high-temperature molten pool to backfire and cause explosion accidents. Therefore, oxygen pressure should be closely monitored. When multiple furnaces use oxygen, do not rush to use oxygen to avoid backfire in the pipelines.
(3) Prevention of vapor lock explosion accidents. Due to operational errors, the water return to the oxygen lance was blocked. The accumulated water in the oxygen lance vaporized in the high temperature of the molten pool, preventing high-pressure water from entering. When the vapor pressure in the oxygen lance is higher than the strength limit of the lance wall, an explosion occurs.
Scrap steel and blasting safety technology
(1) Possible hazards from blasting: explosion seismic waves; explosion shock waves; hazards from debris and flying blocks; noise.
(2) Safety countermeasures: First, heavy scrap steel blasting. Scrap steel must be carried out in underground blasting pits. The blasting pits must be strong and have pressure relief holes. Column retaining walls must be set up around the pressure relief holes. The second is to dismantle the furnace for blasting, limit the charge amount, and control the blasting energy. The third is to take necessary measures. Prevention.
Steel, iron and slag burn protection technology
The temperature of iron, steel, and slag liquid is very high, the heat radiation is very strong, and it is easy to splash. In addition, the temperature of the equipment and the environment is very high, and burn accidents are very easy to occur.
(1) Burns and their causes: missing equipment, such as overflowing of steel-making furnaces, molten steel tanks, molten iron tanks, iron mixing furnaces, etc.; physical and chemical explosions and secondary explosions when iron, steel, and slag liquids meet water; overheating The steam pipeline is leaking or exposed; hot gas or flame is ejected when changing the direction of the flame and exhaust gas in the open-hearth furnace; violation of operating procedures.
(2) Safety countermeasures: Regularly inspect and repair steel-making furnaces, molten steel tanks, molten iron tanks, mixing furnaces and other equipment; improve safety technical regulations and strictly implement them; do a good job of personal protection; flanges and valves that are prone to air leakage must be regularly inspected and repaired. replace.
Safety technology for hoisting and transportation operations in steelmaking plants
The raw materials, semi-finished products, and finished products required in the steelmaking process all require lifting equipment and locomotives for transportation. There are many dangerous factors during the transportation process.
(1) Existing dangers: lifting objects falling and injuring people; lifting objects colliding with each other; molten iron and molten steel tipping over and injuring people; vehicles hitting people.
(2) Safety countermeasures: consider sufficient space when designing the factory; innovate equipment and strengthen maintenance; improve workers’ operating level; strictly abide by safety production regulations.
Steelmaking production accident prevention measures and technologies
(1) Safety requirements for steelmaking plants. It should be considered that the structure of the steelmaking plant can withstand high-temperature radiation; it has sufficient strength and stiffness to withstand loads and collisions such as ladles, ladles, steel ingots and billets without deformation; it has a spacious working environment, good ventilation and lighting, and It is conducive to heat dissipation and smoke emission, and the safety requirements of personnel during operation must be fully considered.
(2) Explosion-proof safety measures. Molten steel, molten iron, steel slag and the slag at the bottom of the steelmaking furnace are all high-temperature molten materials that will explode when in contact with water. When 1 kg of water is completely turned into steam, its volume will increase approximately 1500 times, which is extremely destructive. The main situations where the molten material explodes when it comes into contact with water in the steelmaking plant include: converter, open-hearth oxygen lance, fume hood of the converter, high- and medium-pressure cooling water leakage of the crystallizer of the continuous casting machine, which penetrates the molten material and explodes; steelmaking The water-cooling parts of furnaces, refining furnaces, and continuous casting crystallizers may explode due to blockage of return water, resulting in continued heating; explosions may occur when steel-making furnaces, molten steel tanks, molten iron tanks, intermediate tanks, and slag tanks leak steel, slag, or tip over. ; An explosion occurs when filling molten steel, molten iron, and liquid slag into wet molten steel tanks, molten iron tanks, tundish tanks, and slag tanks; Discharging hot tanks, discharging slag, and turning over slag into tank pits and slag pits containing moist waste and water. Explosions caused when wet materials are added to the steel-making furnace; explosions occur when leaking steel in the casting steel system comes into contact with wet ground. The main measures to prevent molten materials from exploding when exposed to water are to ensure safe water supply to the cooling water system, purify the water quality, and prevent leakage; materials, containers, and working areas must be dry.