Production method for smelting clean steel from full-scrap steel using duplex electric arc furnaces

A production method for smelting clean steel from full-scrap steel using duplex electric arc furnaces, comprising:

• performing smelting by combining a decarbonization electric arc furnace and 1-3 dephosphorization electric arc furnaces, a specific process of performing the smelting comprises:
• (1) in a charging period of the 1-3 dephosphorization electric are furnaces, adding the full-scrap steel for the smelting, lime, slag in the decarbonization electric arc furnace, auxiliary materials and carbon powder or a carbon block into the dephosphorization electric arc furnace;
• wherein, the full-scrap steel is brought into the dephosphorization electric are furnace using any one or several ways selected from the group consisting of continuous charging, shaft charging and basket charging;
• the lime, the slag in the decarburization electric arc furnace, the auxiliary materials and the full-scrap steel are all added into the 1-3 dephosphorization electric arc furnaces;
• an amount of addition of the lime is 0-50 kg per ton of steel;
• an amount of addition of the slag in the decarburization electric arc furnace is 0-50 kg per ton of steel;
• the carbon powder or the carbon block is added into a furnace hearth of the dephosphorization electric arc furnace through a charging bin, and an amount for adding or injecting the carbon block or the carbon powder is 0-200 kg per ton of steel;
• (2) in a melting period of the full-scrap steel, melting the full-scrap steel in the dephosphorization electric arc furnace through power-on and switching a furnace wall cluster oxygen lance to a burner mode, to increase a temperature in the furnace hearth to melt the full-scrap steel;
• injecting powder-air flow of a carrier gas and the carbon powder to an interior of molten steel by a submerged spray lance to reduce a melting point of the full-scrap steel;
• controlling a time of the melting period of the full-scrap steel within 10-150 min, and entering a dephosphorization period once the full-scrap steel is melted down;
• wherein, the furnace wall cluster oxygen lance in the burner mode has a first main oxygen flow rate of 100-2000 Nm3/h, a first gas flow rate of 50-1000 Nm3/h, and a first epoxy flow rate of 50-1000 Nm3/h:
• the carrier gas and a seam protection gas of the submerged spray lance are both any one selected from the group consisting of nitrogen, a fuel gas, carbon dioxide, and a mixture gas of any two of the nitrogen, the fuel gas, and carbon dioxide;
• a flow rate of the carrier gas is 50-1000 Nm3/h, an injection rate of the carbon powder is 0-200 kg/min, a flow rate of injecting the seam protection gas is 10-1000 Nm3/h, and a particle diameter of the carbon powder is 15 μm-3.0 mm;
• (3) in the dephosphorization period in the dephosphorization electric arc furnace, forming the slag to perform dephosphorization using characteristics of the furnace hearth in an earlier stage of the smelting;
• switching the furnace wall cluster oxygen lance to an oxygen supply mode to form foam slag;
• continuing to inject the carbon powder by the submerged spray lance, and controlling a temperature in the decarburization electric arc furnace at 1530-1580° C.;
• adopting an automatic operation of flowing the slag out of a furnace door, and adding the lime into the decarburization electric arc furnace in a middle stage of the smelting to control basicity of the slag at 2.5-3.5;
• wherein, the furnace wall cluster oxygen lance in the oxygen supply mode has a second main oxygen flow rate of 50-2000 Nm3/h, a second gas flow rate of 50-1000 Nm3/h, and a second epoxy flow rate of 50-1000 Nm3/h the injection rate of the carbon powder of the submerged spray lance is 0-200 kg/min, and the amount of addition of the lime is 5-50 kg per ton of steel;
• (4) performing a terminal output of the 1-3 dephosphorization electric arc furnaces to an inside of a semisteel ladle, comprising the following steps:
• sampling the molten steel to measure a phosphorus content and a carbon content in a later stage of the smelting in the 1-3 dephosphorization electric arc furnaces, outputting steel from a bottom of an eccentric furnace when a predetermined standard for the steel is satisfied, and adopting a steel reserve operation to prevent dephosphorization oxidation slag from entering into the decarbonization electric arc furnace;
• wherein, a smelting time of the 1-3 dephosphorization electric arc furnaces is controlled at 60-120 min;
• after a dephosphorization process is finished, the carbon content in the molten steel is controlled between 0.4%-2_wt %, the phosphorus content in the molten steel is controlled below 0.010%, a tapping temperature is greater than 1540° C., and remaining steel in the 1-3 dephosphorization electric arc furnaces is 10%-30% of the total amount of the molten steel;
• (5) in a charging period of the decarbonization electric arc furnace, adding the molten steel in the semisteel ladle into the decarburization electric arc furnace, and adding the lime and the auxiliary materials into the decarburization electric arc furnace;
• wherein, the molten steel is added into the decarbonization electric arc furnace for charging by ways of a furnace door, a charging tank of a furnace wall or unscrewing a furnace cover;
• if a special circumstance occurs in a process of entering into the decarbonization electric arc furnace, and the molten steel fails to enter into the furnace, the molten steel is directly cast to steel blocks for use:
• the amount of addition of the lime in the decarburization electric arc furnace is 2-50 kg per ton of steel;
• (6) in a period of decarbonization degassing, detecting a temperature of the molten steel after the molten steel enters into the decarburization electric arc furnace;
• calculating an oxygen consumption and a power consumption during decarbonization by calculating modules and in combination of a predetermined tapping temperature for the molten steel and the carbon content:
• forming the slag continuously in the decarburization electric arc furnace, and controlling the basicity of the slag to be 2-3.5;
• injecting, by the furnace wall cluster oxygen lance and the submerged spray lance, oxygen to the interior of the molten steel according to results of a calculation, blowing argon from the bottom of the eccentric furnace and stirring carbon dioxide;
• deeply removing [N], [H] and impurities in the molten steel through stirring bubbles generated by a carbon-oxygen reaction, argon, or carbon dioxide in a process of floatation;
• wherein, an oxygen supply flow rate of the furnace wall cluster oxygen lance is 50-3000 Nm3/h, an oxygen supply flow rate of the submerged spray lance is 50-2000 Nm3/h, the second gas flow rate of the furnace wall cluster oxygen lance is 50-1000 Nm3/h, a flow rate for blowing argon or carbon dioxide from the bottom of the eccentric furnace is 1-100 NL/min, a power-on time for electrodes is 0-100 min, and a converting time is 10-100 min;
• (7) performing an end point control of the decarbonization electric arc furnace, comprising the following steps:
• sampling the molten steel to measure the phosphorus content, the carbon content and the temperature of the molten steel in the later stage of the smelting, outputting steel, and adopting the steel reserve operation to prevent the slag from entering into the molten steel, and controlling the tapping temperature of the molten steel at 1550-1700° C.;
• wherein, the carbon content of the molten steel is controlled above 0.1 wt % after a decarburization process is finished;
• the phosphorus content of the molten steel is controlled below 0.003%;
• the slag discharged from the decarbonization electric arc furnace returns back to the 1-3 dephosphorization electric are furnaces for continuing use.