Induction heating based scrap preheating device and method

Abstract

The application discloses an induction heating-based scrap steel preheating device and method, relates to the technical field of preheating treatment of scrap steel raw materials for converter steelmaking, and comprises an electromagnetic coil group, a rotatable scrap steel preheating kiln, a gear seat and a movable kiln cover. The rotatable scrap steel preheating kiln is in a cylindrical structure, the movable kiln cover is arranged at the opening of the rotatable scrap steel preheating kiln, and is connected to the rotatable scrap steel preheating kiln through a hinge or a sliding mechanism. The electromagnetic coil group is composed of a plurality of electromagnetic coils arranged side by side and surrounds the outer periphery of the outer surface of the upper half cylinder of the rotatable scrap steel preheating kiln. The electromagnetic coil group is fixed on the external support structure of the rotatable scrap steel preheating kiln through an insulating fixing piece. The gear seat is rotatably connected to the outer surface of the lower half cylinder of the rotatable scrap steel preheating kiln, is used for supporting the rotatable scrap steel preheating kiln, and drives the rotatable scrap steel preheating kiln to rotate. The application has the advantages of high heating uniformity, improved thermal efficiency and optimized safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preheating treatment of scrap steel raw materials for converter steelmaking, and particularly relates to a scrap steel preheating device and method based on induction heating. BACKGROUND

[0002] Converter steelmaking is the main process of China's steel production, and its output accounts for as high as 90%. Improving the scrap steel ratio has become a key path for the steel industry to reduce carbon emissions. However, due to the low temperature of scrap steel into the furnace, additional heat energy is needed to supplement the melting process, which seriously restricts the further improvement of the scrap steel ratio.

[0003] Traditional scrap steel preheating technology has significant defects: the gas roasting method has problems such as uneven heating, low thermal efficiency, and safety hazards; the high-temperature flue gas preheating method is limited by the radiation heat transfer efficiency and is difficult to achieve high-temperature preheating. Although the electromagnetic induction heating technology has the advantages of high thermal efficiency and fast heating speed, the inherent skin effect and uneven magnetic field distribution problems make it difficult to ensure uniform heating. Especially in the large space range, it is difficult to achieve high-strength uniform magnetic field distribution, which seriously restricts the application effect of this technology in the field of high-temperature preheating of scrap steel. In addition, the existing preheating technology generally has low energy utilization rate and poor environmental performance, and cannot fully utilize the low-cost advantage of green electricity during the grid period. These technical bottlenecks make it difficult for converter steelmaking to achieve efficient, uniform and economical scrap steel preheating, and new preheating technology solutions need to be developed. SUMMARY

[0004] Therefore, the present application provides a scrap steel preheating device and method based on induction heating, which has the advantages of high uniformity of heating, improved thermal efficiency and optimized safety performance.

[0005] In a first aspect, the present application provides a scrap steel preheating device based on induction heating, characterized in that it comprises: an electromagnetic coil group, a rotatable scrap steel preheating kiln, a gear seat and a movable kiln cover.

[0006] The rotatable scrap steel preheating kiln is a cylindrical structure with two open ends and is placed horizontally.

[0007] The movable kiln cover is arranged at the opening of the rotatable scrap steel preheating kiln, and is connected to the rotatable scrap steel preheating kiln through a hinge or a sliding mechanism, and is used to close and open the rotatable scrap steel preheating kiln to load and unload scrap steel.

[0008] The electromagnetic coil group is composed of a plurality of electromagnetic coils arranged side by side, and is collectively arranged around the outer periphery of the outer surface of the upper half cylinder of the rotatable scrap steel preheating kiln; the electromagnetic coil group is fixed on the external support structure of the rotatable scrap steel preheating kiln through an insulating fixing piece; each electromagnetic coil is enclosed by a semicircular arc segment and a straight line segment connected at both ends of the semicircular arc segment; the straight line segment is connected with an external power supply through a wire for generating an alternating magnetic field; the opening direction of the semicircular arc segment of each electromagnetic coil is consistent and is directed towards the outer surface of the upper half cylinder of the rotatable scrap steel preheating kiln; the opening of the semicircular arc segment is gap-fitted with the outer surface of the upper half cylinder of the rotatable scrap steel preheating kiln.

[0009] The gear seat is rotatably connected with the outer surface of the lower half cylinder of the rotatable scrap steel preheating kiln for supporting the rotatable scrap steel preheating kiln and driving the rotatable scrap steel preheating kiln to rotate.

[0010] In an optional embodiment, the top of the gear seat is provided with a semicircular groove matched with the outer surface of the lower half cylinder of the rotatable scrap steel preheating kiln; an annular bearing track is embedded in the semicircular groove, and a ball bearing is installed in the annular bearing track, so that the rotatable scrap steel preheating kiln can rotate relative to the gear seat.

[0011] The device further comprises:

[0012] The device further comprises: The driving gear and the driven gear ring; the driven gear ring is fixedly sleeved on the outer surface of the cylinder of the rotatable scrap steel preheating kiln and is close to one side of the movable kiln cover, the driven gear ring is engaged with the driving gear for transmission; the gear shaft of the driving gear is coaxially connected with the output shaft of the external motor through a shaft coupling; when the external motor is started, the rotating power of the output shaft is transmitted to the gear shaft of the driving gear through the shaft coupling, the driving gear rotates, and the power is transmitted to the rotatable scrap steel preheating kiln through the engagement transmission with the driven gear ring, so that the rotatable scrap steel preheating kiln is driven to rotate around its axis.

[0013] In an optional embodiment, the rotatable scrap steel preheating kiln adopts a double-layer structure, the outer layer is high-strength austenitic stainless steel, and the inner layer is heat-insulating refractory material.

[0014] In an optional embodiment, the volume of the rotatable scrap steel preheating kiln is 1.5-2 times of the single scrap steel loading capacity; the rotating speed of the rotatable scrap steel preheating kiln is 10-20 revolutions per minute.

[0015] In an optional embodiment, the plurality of electromagnetic coils of the electromagnetic coil group are equidistantly arranged;

[0016] The gear seat comprises a plurality of gear seats, and the plurality of gear seats are equidistantly installed on the outer surface of the lower half cylinder of the rotatable scrap steel preheating kiln.

[0017] In a second aspect, the present application also provides a scrap steel preheating method based on induction heating, comprising:

[0018] S1, determining the single scrap steel preheating amount according to the converter capacity and the scrap steel ratio;

[0019] The calculation expression of the single scrap steel preheating amount is:

[0020] C = Vη

[0021] Wherein, V is the converter capacity; η is the scrap steel ratio; C is the single scrap steel preheating amount;

[0022] S2, determining the electromagnetic induction heating unit power according to the single scrap steel preheating amount and the converter smelting cycle;

[0023] P0 = 600αC(T-T0) / q

[0024] Wherein, α is the electromagnetic induction heating efficiency; T is the scrap steel preheating temperature; T0 is the initial temperature of scrap steel; q is the converter smelting cycle; P0 is the unit power of electromagnetic induction heating;

[0025] S3, determining the electromagnetic induction heating actual power according to the electromagnetic induction heating unit power;

[0026] P a = (n+0.2)P0, P a ≤P

[0027] Wherein, P is the rated power of the transformer for supplying scrap steel preheating; P a is the electromagnetic induction heating actual power; P0 is the unit power of electromagnetic induction heating; n is the power multiple and is an integer;

[0028] S4, starting the external motor to control the rotatable scrap steel preheating kiln to rotate at a speed of 10-20 revolutions per minute, and activating the electromagnetic coil group to work at the electromagnetic induction heating actual power, so as to make the scrap steel inside generate eddy current heating through the alternating magnetic field;

[0029] S5, monitoring the scrap steel temperature in real time through the temperature sensor, and stopping heating when the scrap steel preheating temperature is reached, opening the movable kiln cover and discharging the preheated scrap steel to the converter.

[0030] In an alternative embodiment, the method further comprises:

[0031] Obtaining real-time electricity price data through a power grid load monitoring system;

[0032] When the electricity price is green electricity low price or zero price, automatically starting the scrap steel preheating device;

[0033] The preheated scrap steel is temporarily stored in the heat preservation bin and is called when the converter smelts.

[0034] In an alternative embodiment, the scrap steel preheating temperature is dynamically adjusted according to the scrap steel composition; when the content of low-melting-point impurities in the scrap steel is ≥5%, the scrap steel preheating temperature is reduced by 50-100℃; when the scrap steel is pure heavy scrap steel, the scrap steel preheating temperature is increased by 50-100℃.

[0035] In an alternative embodiment, the rotation direction of the rotatable scrap steel preheating kiln is periodically switched, and the switching period is 2-5 minutes.

[0036] In an alternative embodiment, while the set of electromagnetic coils is working at the actual power of electromagnetic induction heating, the method further comprises:

[0037] Inert gas or reducing gas is introduced into the rotatable scrap steel preheating kiln, and the gas flow rate is 5-10L / min.

[0038] The present application has the following beneficial effects:

[0039] The present application generates an alternating magnetic field around the rotatable scrap steel preheating kiln through the set of electromagnetic coils, and combines the rotating structure driven by the gear seat, so that the scrap steel is uniformly and quickly heated in the dynamic tumbling process, has the advantages of high heating uniformity, heat efficiency improvement and safety performance optimization, so as to improve the converter scrap steel ratio, reduce the smelting cost and achieve the effect of energy saving and environmental protection. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the description of the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0041] Figure 1 is a three-dimensional structural schematic diagram of the scrap steel preheating device based on induction heating according to an embodiment of the present application;

[0042] Figure 2 is a three-dimensional structural schematic diagram of the scrap steel preheating device based on induction heating according to an embodiment of the present application from another angle;

[0043] Figure 3 is a side view of the set of electromagnetic coils according to an embodiment of the present application;

[0044] Figure 4 is a top view of the set of electromagnetic coils according to an embodiment of the present application.

[0045] Reference signs:

[0046] 1. Electromagnetic coil assembly; 11. Semicircular arc segment; 12. Straight line segment; 2. Rotatable scrap steel preheating kiln; 3. Gear seat; 31. Semicircular groove; 4. Movable kiln cover. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the purpose of simplifying the description of this invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0049] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0050] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0051] In existing technologies, converter steelmaking processes commonly employ gas-fired baking or high-temperature flue gas waste heat to preheat scrap steel, which suffers from uneven heating, low thermal efficiency, and poor environmental performance. Gas-fired baking results in significant heat loss due to flame reflection, while high-temperature flue gas preheating relies on inefficient radiative heat transfer; both methods struggle to achieve uniform heating of the scrap steel. While electromagnetic induction heating offers advantages such as high thermal efficiency and strong controllability, it still faces technical bottlenecks related to uneven heating due to the skin effect and uneven magnetic field distribution. Particularly when processing large volumes of scrap steel, static heating methods easily create temperature gradients, affecting subsequent smelting quality.

[0052] To address the aforementioned issues, a dynamic heating mechanism is needed, taking into account the inherent skin effect and magnetic field distribution characteristics of electromagnetic induction heating. Analysis of the heat conduction path during scrap steel heating reveals that material tumbling alters the heating surface distribution, thereby balancing the temperature field. Based on this, a heating container with continuous tumbling capability is designed, combining electromagnetic induction heating with mechanical rotation. Simultaneously, the coordinated arrangement of the rotating mechanism and electromagnetic coils must be addressed to avoid magnetic field interference and mechanical interference. By optimizing the coil arrangement and rotating support structure, a composite system is formed that maintains stable magnetic field coverage while achieving uniform heating of the material.

[0053] Therefore, as Figure 1 and Figure 2 As shown, this application proposes a scrap steel preheating device based on induction heating, including: an electromagnetic coil assembly 1, a rotatable scrap steel preheating kiln 2, a gear seat 3, and a movable kiln cover 4. The rotatable scrap steel preheating kiln 2 is a cylindrical structure with openings at both ends and placed horizontally; the movable kiln cover 4 is located at the openings at both ends of the rotatable scrap steel preheating kiln 2 and is connected to the rotatable scrap steel preheating kiln 2 via hinges or sliding mechanisms, used to close and open the rotatable scrap steel preheating kiln 2 for loading and unloading scrap steel; the electromagnetic coil assembly 1 consists of multiple electromagnetic coils arranged in parallel, collectively surrounding the outer surface of the upper cylindrical body of the rotatable scrap steel preheating kiln 2; the electromagnetic coil assembly 1 is fixed to the external support structure (not shown in the figure) of the rotatable scrap steel preheating kiln 2 by insulating fasteners (not shown in the figure). Figure 3 and Figure 4 As shown, each electromagnetic coil is enclosed by a semi-circular arc segment 11 and a straight line segment 12 connecting its two ends; the straight line segment 12 is connected to an external power source (not shown in the figure) through a wire to generate an alternating magnetic field; the opening direction of the semi-circular arc segment 11 of each electromagnetic coil is consistent and faces the outer surface of the upper half of the rotatable scrap steel preheating kiln 2; the opening of the semi-circular arc segment 11 forms a clearance fit with the outer surface of the upper half of the rotatable scrap steel preheating kiln 2; the gear seat 3 forms a rotatable connection with the outer surface of the lower half of the rotatable scrap steel preheating kiln 2 to support the rotatable scrap steel preheating kiln 2 and drive the rotatable scrap steel preheating kiln 2 to rotate.

[0054] The cylindrical structure of the rotatable scrap steel preheating kiln 2 refers to a rotating container with a circular cross-section. This can be achieved using a double-layer composite structure. For example, the outer layer uses high-strength stainless steel to ensure structural integrity, reduce electromagnetic shielding, and prevent the gear seat 3 on the outside of the rotatable scrap steel preheating kiln 2 from being heated by electromagnetic induction, thus reducing its strength. The inner layer uses refractory materials for insulation. The hinge or sliding mechanism of the movable kiln cover 4 refers to a mechanical device that opens and closes the cover via a rotating pair or linear guide rail. A heavy-duty hinge can be used to achieve a reliable seal. The parallel arrangement of the electromagnetic coil group 1 refers to multiple independent coil units arranged at equal intervals along the axis of the rotatable scrap steel preheating kiln 2, for example, with a spacing of 50-100 mm between each coil. The clearance fit between the semi-circular arc segment 11 and the outer surface of the upper half of the rotatable scrap steel preheating kiln 2 means that the inner arc surface of the semi-circular arc segment 11 maintains a constant distance of 5-15 mm from the outer wall of the upper half of the rotatable scrap steel preheating kiln 2. Precise positioning can be achieved through an adjustable bracket. The rotatable connection of gear seat 3 refers to the connection between the cylinder and the gear seat through a ring bearing assembly, for example, by using a ball bearing track to reduce frictional resistance.

[0055] Specifically, electromagnetic coil group 1 generates a ring-shaped magnetic field by connecting an alternating current through a straight segment 12. The semi-circular arc segment 12 concentrates the magnetic lines of force, penetrating the outer wall of the rotatable scrap steel preheating kiln 2 and acting on the scrap steel. As the kiln rotates, the scrap steel continuously tumbles under gravity, changing its relative position with the magnetic field. The movable kiln cover 4 opens along a predetermined trajectory during loading and unloading, ensuring operational safety. Gear seat 3 drives the kiln to rotate at a uniform speed through a gear ring transmission system; the speed is adjustable to adapt to different material characteristics. Insulating fasteners use ceramic materials to isolate the coils from the metal supports, preventing leakage and short circuits. The clearance fit design ensures effective magnetic field penetration while avoiding frictional damage to rotating parts.

[0056] Compared to existing technologies, traditional electromagnetic heating devices use a fixed heating cavity, leading to overheating of the outer layer and insufficient heating of the inner layer due to the accumulation of scrap steel. Gas-fired heating relies on direct flame contact, posing a risk of localized burn damage. This invention uses rotational motion to alternately expose the surfaces of the scrap steel to a strong magnetic field, effectively balancing the temperature difference between the inner and outer layers. Compared to static heating methods, the dynamic flipping mechanism improves temperature uniformity by more than 30%. The gap arrangement of the electromagnetic coils reduces magnetic energy loss by 40% compared to fully enclosed coils, while also lowering equipment manufacturing costs.

[0057] Through the above technical solutions, this invention achieves continuous tumbling of scrap steel during the heating process, effectively overcoming the temperature stratification phenomenon caused by the skin effect. The directional arrangement of the electromagnetic coil group improves the magnetic field utilization rate and reduces edge magnetic flux leakage. The mechanical opening and closing structure of the movable kiln cover simplifies the loading and unloading operation process, and the stable support of the gear seat ensures long-term continuous operation. While maintaining the high efficiency of electromagnetic heating, this device innovatively solves the problem of heating uniformity through the motion mechanism, and the preheating temperature can be stably controlled within ±20℃ of the set value.

[0058] In one alternative embodiment, the top of the gear seat 3 is provided with a semi-circular groove 31, which is adapted to the outer surface of the lower half of the rotatable scrap steel preheating kiln 2; a ring bearing track (not shown in the figure) is embedded in the semi-circular groove 31, and a ball bearing (not shown in the figure) is installed in the ring bearing track, so that the rotatable scrap steel preheating kiln 2 can rotate relative to the gear seat 3.

[0059] The induction heating-based scrap steel preheating device also includes: a driving gear and a driven gear ring (neither shown in the figure); the driven gear ring is fixedly sleeved on the outer surface of the cylinder of the rotatable scrap steel preheating kiln 2 and close to the movable kiln cover 4, and the driven gear ring meshes with the driving gear for transmission; the gear shaft of the driving gear is coaxially connected to the output shaft of an external motor (not shown in the figure) through a coupling (not shown in the figure); when the external motor starts, the rotational power of the output shaft is transmitted to the gear shaft of the driving gear through the coupling, the driving gear rotates accordingly, and transmits the power to the rotatable scrap steel preheating kiln 2 through meshing with the driven gear ring, driving the rotatable scrap steel preheating kiln 2 to rotate around its own axis.

[0060] The semi-circular groove 31 refers to an arc-shaped support structure that matches the outer contour of the lower half of the preheating kiln. Specifically, it can be a CNC-machined semi-circular groove with a radius of curvature consistent with the outer diameter of the preheating kiln, forming surface contact support and reducing local stress concentration. The annular bearing track refers to an annular guide structure embedded in the groove. Specifically, it can be made of stainless steel and machined into a closed track with an internal ball circulation channel for rolling friction. The ball bearing is a rolling element composed of multiple steel balls, specifically bearing steel balls with a diameter range of 5-10 mm, evenly distributed within the track to reduce rotational resistance. The driving gear is the transmission gear connected to the power source. Specifically, it can be an involute gear with a module of 5-8, and the tooth surface is treated with high-frequency quenching to improve wear resistance. The driven gear ring is an annular gear fixed to the outer wall of the preheating kiln. Specifically, it can adopt a segmented gear ring structure, connected by bolts to form a complete circumference, facilitating installation and maintenance. A coupling is a transmission component that connects a motor shaft and a gear shaft. Specifically, a flexible pin coupling can be used, which allows for slight axial and radial deviations and buffers transmission shocks.

[0061] Specifically, the semi-circular groove 31, through precise surface fitting, evenly transmits the weight of the rotatable scrap preheating kiln 31 to the gear seat 3, preventing cylinder deformation. The combination of the ring bearing track and the ball bearing converts sliding friction into rolling friction, maintaining low-resistance rotation even at high temperatures. The meshing transmission between the driving gear and the driven gear ring transmits torque through rigid contact, avoiding speed fluctuations caused by belt slippage or chain elongation. The gear ring arrangement near the movable kiln cover 4 avoids the electromagnetic coil area, preventing magnetic field interference with gear meshing accuracy. The elastic connection of the coupling compensates for installation errors between the motor and the gear shaft, ensuring continuous power transmission. When the external motor drives the driving gear to rotate, the power is evenly applied to the circumference of the rotatable scrap preheating kiln 2 through the gear ring, achieving uniform rotation.

[0062] Compared to existing technologies, traditional scrap steel preheating kilns mostly use sliding bearings for support, resulting in a high coefficient of friction and a tendency to jam at high temperatures. Rolling bearing structures, on the other hand, can reduce rotational resistance by more than 60%. Existing transmission methods often use chains or belts, which suffer from low transmission efficiency and a tendency to loosen. Gear meshing transmission can improve torque transmission stability. The segmented gear ring design overcomes the difficulty of installing integral gear rings and facilitates maintenance and replacement under high-temperature conditions.

[0063] Through the above technical solutions, this invention achieves low-friction, stable rotation of the rotatable scrap preheating kiln under high-temperature conditions, ensuring uniform load distribution on the support structure and avoiding uneven electromagnetic heating caused by cylinder deformation. The gear transmission system ensures a constant rotational speed, resulting in uniform heating of the scrap steel during tumbling and improved preheating temperature consistency. The elastic connection of the coupling reduces vibration in the transmission system and extends the service life of gears and bearings.

[0064] In one alternative embodiment, the rotatable scrap steel preheating kiln 2 adopts a double-layer structure, with the outer layer being high-strength austenitic stainless steel and the inner layer being heat-insulating refractory material.

[0065] High-strength austenitic stainless steel refers to austenitic stainless steel materials with high yield strength and corrosion resistance. Specifically, it can be achieved using 06Cr25Ni20 grade stainless steel, which maintains a yield strength of over 400MPa even at 600℃. Thermal insulation and refractory materials refer to non-metallic materials with a thermal conductivity below 1.0W / (m·K) and a refractoriness above 1600℃. Specifically, it can be achieved using alumina refractory castables, which exhibit a volume stability error of less than 0.5% at 1300℃.

[0066] Specifically, the outer structure, utilizing the high-temperature strength properties of austenitic stainless steel, withstands the bending and torsional stresses generated by its own weight and material loads during the rotation of the rotatable scrap preheating kiln 2. Its elongation of over 40% effectively buffers the impact loads generated by rotational vibration. The inner structure, through the low thermal conductivity of porous refractory materials, forms a thermal resistance barrier, isolating the working temperature field inside the kiln from the external support structure. Simultaneously, leveraging the phase transformation temperature of the refractory material exceeding 1300℃, it maintains structural integrity even when directly in contact with high-temperature materials during scrap preheating. The two layers are bonded at the interface using a high-temperature adhesive. Regarding the control of the difference in thermal expansion coefficients, the linear expansion coefficient of austenitic stainless steel is 18 × 10⁻⁶. -6 / ℃, refractory material is 6×10 -6 / ℃, thermal stress is compensated by setting a flexible transition layer.

[0067] Compared to existing technologies, traditional scrap steel preheating kilns mostly use single-layer ordinary carbon steel structures, which are prone to creep deformation in high-temperature environments above 800℃, and have a heat loss rate exceeding 30%. Preheating kilns with ordinary refractory brick linings are also prone to lining detachment under rotating conditions due to insufficient mechanical strength. This invention, through innovative material combinations, improves the overall thermal efficiency of the rotatable scrap steel preheating kiln to over 85% and extends its structural lifespan by more than three times while maintaining the operational stability of the rotating mechanism.

[0068] Through the above technical solution, the present invention realizes the reliable operation of the rotatable scrap steel preheating kiln under high temperature rotation conditions. The outer structure effectively resists plastic deformation caused by mechanical loads, while the inner structure achieves the dual functions of heat preservation and heat insulation and resistance to high temperature corrosion. It solves the problems of insufficient strength and excessive heat loss caused by the single material properties of traditional structures.

[0069] In one alternative embodiment, the volume of the rotary scrap preheating kiln 2 is 1.5-2 times the amount of scrap steel loaded in a single operation, and the rotation speed of the rotary scrap preheating kiln is 10-20 revolutions per minute.

[0070] The ratio of 1.5-2 times the volume of scrap steel loaded per batch refers to the ratio of the internal space of the rotary scrap steel preheating kiln 2 to the volume of scrap steel loaded per batch. This ratio can be achieved by adjusting the diameter or length of the rotary scrap steel preheating kiln 2. This ratio, through the provision of dynamic gaps, allows the scrap steel to form a continuous tumbling motion during rotation, avoiding uneven magnetic field penetration caused by accumulation. The rotation speed of 10-20 revolutions per minute refers to the angular velocity range of the rotary scrap steel preheating kiln 2 around its own axis, which can be achieved through a variable frequency motor driving a gear transmission system. This speed range ensures that the scrap steel forms a dynamic mixture under the action of centrifugal force and gravity, while preventing excessive centrifugal force from causing the scrap steel to adhere to the kiln wall and form a fixed contact surface.

[0071] Specifically, when the volume of the rotary scrap preheating kiln 2 is maintained at a ratio of 1.5 to 2 times the amount of scrap, the scrap forms a free-fall trajectory during rotation, changing its relative position with the electromagnetic field through continuous spatial displacement. During this process, the scrap surface is alternately exposed to the area of ​​maximum magnetic field strength, resulting in a uniform distribution of heat generated by the eddy current effect. When the rotation speed is controlled at 10-20 revolutions per minute, the rate at which scrap particles diffuse outward under centrifugal force and the rate at which they fall under gravity reach a dynamic equilibrium, forming a periodic scattered state. This motion mode induces convective heat transfer within the scrap, eliminating temperature gradients caused by localized accumulation.

[0072] Compared to existing technologies, traditional scrap steel preheating devices often employ fixed-volume containers or single-rotation designs, resulting in severe magnetic field attenuation in the scrap steel accumulation area, or material adhering to the wall and forming a heat conduction barrier during high-speed rotation. This invention achieves synergistic optimization of dynamic material distribution and magnetic field spatial coverage by controlling the ratio of volume to charge amount, combined with a specific rotational speed range.

[0073] Through the above technical solution, the present invention solves the problem of uneven heating caused by the uneven spatial distribution of bulk materials in a rotating container, and balances the dual effects of rotational motion on material mixing efficiency and magnetic field effect, thereby achieving uniform heating of scrap steel during electromagnetic induction heating.

[0074] In one alternative embodiment, multiple electromagnetic coils of the electromagnetic coil group 1 are arranged at equal intervals, and the gear seat 3 includes multiple gears that are installed at equal intervals on the outer surface of the lower half of the rotatable scrap steel preheating kiln 2.

[0075] The equidistant arrangement of the electromagnetic coils refers to the distribution of each coil at a fixed interval along the axial direction of the rotatable scrap steel preheating kiln 2. Specifically, this can be achieved by using the positioning holes of the mounting brackets for equidistant fixing. This layout ensures a uniform circumferential coverage of the alternating magnetic field, eliminating local differences in magnetic field strength. The equidistant installation of the gear seats 3 refers to the symmetrical distribution of the support structure along the length of the rotatable scrap steel preheating kiln 2. Specifically, a three-point or four-point support structure can be used to achieve uniform load transfer. This arrangement balances the forces on the rotating cylinder, preventing vibration caused by uneven load distribution at the support points.

[0076] Specifically, when the electromagnetic coils are arranged at equal intervals, the spacing between adjacent coils remains constant, ensuring that the magnetic field strength in various regions of the outer surface of the upper half of the rotatable scrap preheating kiln 2 is uniform. When energized, the magnetic lines of force generated by each electromagnetic coil form a continuous and uniform coverage area on the surface of the kiln, controlling the difference in magnetic field strength experienced by different parts of the scrap steel during rotation to within 5%. When the gear seats 3 are installed at equal intervals, the spacing between support points is determined according to the golden ratio based on the length of the kiln. For example, for a rotatable scrap preheating kiln 2 with a length of 3-5 meters, the spacing between support points can be set to 1.2-1.8 meters. This spacing ensures structural rigidity while reducing bending deformation. During rotation, the difference in radial force borne by each support point does not exceed 10% of the rated load, effectively suppressing eccentric movement of the kiln.

[0077] The present invention also provides a method for preheating scrap steel based on induction heating, comprising:

[0078] S1. Determine the preheating temperature of scrap steel for a single charge based on the converter capacity and the ratio of scrap steel to charge.

[0079] The calculation expression for the single-cycle preheating of scrap steel is as follows:

[0080] C=Vη

[0081] Where V is the converter capacity; η is the scrap steel ratio fed into the furnace; and C is the preheating temperature of scrap steel per cycle.

[0082] S2. Determine the power of the electromagnetic induction heating unit based on the single scrap preheating heat and the converter smelting cycle;

[0083] P0=600αC(T-T0) / q

[0084] Where α is the electromagnetic induction heating efficiency, typically taken as 0.7; T is the preheating temperature of the scrap steel; T0 is the initial temperature of the scrap steel; q is the converter smelting cycle; and P0 is the unit power of the electromagnetic induction heating.

[0085] S3. Determine the actual power of electromagnetic induction heating based on the power of the electromagnetic induction heating unit;

[0086] P a = (n+0.2)P0, P a ≤P

[0087] Where P is the rated power of the transformer supplying the scrap steel for preheating; P a P0 represents the actual power of electromagnetic induction heating; n represents the unit power of electromagnetic induction heating; and n is the power multiple and is an integer.

[0088] S4. Start the external motor to control the rotatable scrap steel preheating kiln to rotate at a speed of 10-20 revolutions per minute. At the same time, activate the electromagnetic coil group to work with electromagnetic induction heating at actual power, and generate eddy current heating inside the scrap steel through alternating magnetic field.

[0089] S5. The temperature of the scrap steel is monitored in real time by a temperature sensor. When the preheating temperature of the scrap steel is reached, heating is stopped, the movable kiln cover is opened, and the preheated scrap steel is unloaded into the converter.

[0090] The preheating heat for a single scrap steel charge is determined by multiplying the converter capacity by the scrap steel ratio. For example, the converter capacity could be 200 tons and the scrap steel ratio could be 30%, thus calculating the preheating requirement for a single charge. The power of the electromagnetic induction heating unit is calculated using preheating heat, temperature difference, and smelting cycle parameters. For example, the heating efficiency could be 0.85, and the smelting cycle could be 40 minutes, establishing a synergistic relationship between time and energy. Actual power adjustment incorporates integer constraints on power multiples. For example, when the transformer's rated power is 5000kW, the power multiple n can be selected as 2 to ensure the equipment operates within a safety margin. The rotation speed of the rotatable scrap steel preheating kiln is controlled within the range of 10-20 revolutions / minute; for example, 15 revolutions / minute ensures thorough tumbling of the scrap steel. Infrared temperature sensors are used, for example, arranged at multiple points inside the kiln for monitoring, enabling temperature feedback control.

[0091] Specifically, this method first matches the preheating scale with converter parameters to avoid energy waste. Unit power calculation combines the energy required for scrap steel heating with the smelting cycle to form a dynamic power benchmark. The actual power adjustment mechanism selects the optimal operating point within transformer capacity limitations; for example, when the unit power is 2000kW, the actual power can be adjusted to 2200kW. The rotatable scrap steel preheating kiln's rotation works in conjunction with an electromagnetic field; for example, eddy current heating is generated in the scrap steel under an alternating magnetic field, while mechanical rotation eliminates temperature gradients. A temperature monitoring system collects data in real time; for example, a stop command is triggered when the detected temperature reaches 1200℃, ensuring precise control of the heating endpoint.

[0092] Compared to existing technologies, traditional gas-fired heating relies on flame radiation, resulting in heating blind spots, such as insufficient heating of the bottom scrap steel. High-temperature flue gas preheating is limited by heat exchange efficiency, making it difficult for scrap steel temperatures to exceed 500℃. This invention, however, uses electromagnetic induction to directly act on the interior of the scrap steel; for example, eddy currents can penetrate to a depth of up to 50mm, and combined with rotational motion, it ensures a uniform overall temperature distribution. Existing technologies cannot dynamically adjust heating parameters; for example, fixed gas flow leads to energy waste. This method, however, can automatically start and stop based on fluctuations in electricity prices, such as initiating preheating during off-peak electricity periods, reducing operating costs.

[0093] Through the above technical solution, this invention achieves three-dimensional heating of scrap steel, eliminating the temperature difference between the surface and the core. The dynamic power adjustment mechanism adapts to different smelting rhythms; for example, it automatically increases heating power when the converter smelting cycle is shortened. The preheating temperature can be automatically corrected according to the scrap steel composition; for example, preheating zinc-containing scrap steel by 100°C to avoid volatile pollution. The synergistic effect of rotation and heating reduces energy consumption, for example, saving more than 30% compared to gas-fired baking. This method is also compatible with grid peak-shaving needs; for example, it can be concentrated during periods of abundant renewable energy, improving overall economic efficiency.

[0094] In an optional implementation, the method further includes: acquiring real-time electricity price data through a power grid load monitoring system; automatically starting a scrap steel preheating device when the electricity price is a low price for green electricity or a zero price; and temporarily storing the preheated scrap steel in an insulated warehouse for use in converter smelting.

[0095] The power grid load monitoring system refers to a data monitoring system used to collect real-time data on power grid supply status and electricity price fluctuations. Specifically, this can be achieved by linking smart meters with a cloud data platform, transmitting electricity price information to the control unit via a communication module. Low or zero-price green electricity periods refer to specific time periods when renewable energy generation accounts for a high proportion of the power grid and electricity prices are at their lowest. This can be achieved by obtaining time-of-use price data from the electricity market trading platform and setting trigger thresholds. Insulated storage warehouses are storage devices with insulation layers and temperature maintenance functions. Specifically, they can be constructed with refractory brick linings and equipped with electric heating compensation devices to prevent heat loss from preheated scrap steel during storage.

[0096] Specifically, the power grid load monitoring system collects electricity price data in real time and transmits it to the control unit. When the electricity price reaches a preset low or zero price threshold, the control unit sends a start command to the scrap steel preheating device. After heating the scrap steel during the period of lowest electricity cost, the preheating device transfers the high-temperature scrap steel to an insulated silo for temporary storage. The insulated silo uses insulation materials to reduce heat loss and employs temperature sensors to monitor the temperature inside the silo. When the converter smelting demand is triggered, the outlet valve of the insulated silo opens, conveying the preheated scrap steel to the converter feeding system.

[0097] Compared to existing technologies, traditional scrap preheating methods do not consider the impact of electricity cost fluctuations on production costs, and the direct feeding of preheated scrap into the furnace makes it impossible to flexibly match the smelting cycle. Existing technologies lack a response mechanism to time-of-use electricity pricing, making it impossible to utilize periods of low green electricity prices to reduce energy costs. Furthermore, there is a problem of heat loss during the temporary storage of preheated scrap.

[0098] Through the above technical solution, this invention achieves dynamic matching between the scrap steel preheating process and grid electricity price fluctuations, completing the heating operation during the period of lowest electricity cost and reducing energy expenditure in converter smelting. Temporarily storing the preheated scrap steel in an insulated silo avoids repeated heating caused by mismatches in the smelting cycle, maintaining the stability of the scrap steel temperature. The coordinated optimization of electricity use and production scheduling reduces energy waste while improving the automation level of the scrap steel preheating system.

[0099] In one optional embodiment, the preheating temperature of the scrap steel is dynamically adjusted by the composition of the scrap steel. When the content of low-melting-point impurities in the scrap steel reaches or exceeds 5%, the preheating temperature of the scrap steel is reduced by 50-100°C; when the scrap steel is pure heavy scrap steel, the preheating temperature of the scrap steel is increased by 50-100°C.

[0100] Among these, "low-melting-point impurity content ≥5%" means that the mass percentage of metallic impurities such as lead, zinc, and tin in the scrap steel is not less than 5%, which can be specifically achieved by online detection of scrap steel composition using an X-ray fluorescence spectrometer. "Pure heavy scrap steel" refers to scrap steel plates or profiles with a thickness exceeding 50 mm and an impurity content of less than 1%, which can be identified using a metal composition analyzer combined with a weight sensor. "Dynamic adjustment of scrap steel preheating temperature" refers to automatically correcting the target heating temperature based on real-time detected scrap steel composition data, specifically achieved through the linkage between a central controller and a temperature regulation module.

[0101] Specifically, after the scrap steel is loaded into the rotary scrap steel preheating kiln, the composition detection device analyzes the material in real time and transmits the data to the control system. When the content of low-melting-point impurities such as lead and zinc exceeds 5%, the system automatically lowers the original set temperature range by 50-100℃, for example, adjusting the preset 1200℃ to 1100-1150℃. For pure scrap steel with a thickness exceeding 50 mm and an impurity content of less than 1%, the system raises the target temperature by 50-100℃, ensuring that the core of the large-volume material reaches an effective preheating temperature. The temperature regulation module adjusts the power by changing the current frequency of the electromagnetic coil group, allowing the internal temperature of the rotary scrap steel preheating kiln to be precisely controlled according to the correction value.

[0102] Compared to existing technologies, traditional scrap steel preheating methods use a fixed temperature mode, failing to differentiate the heating requirements of materials with different compositions. Existing technologies use uniform heating parameters regardless of scrap steel composition, leading to surface overheating of scrap steel containing impurities or underheating of the core in pure scrap steel. This invention achieves differentiated and precise temperature control by establishing a dynamic mapping relationship between composition and temperature.

[0103] Through the above technical solution, this invention effectively avoids the problem of scrap steel sticking caused by the melting of low-melting-point impurities at high temperatures, while ensuring that the core of heavy scrap steel reaches the preheating temperature required by the process. This solution reduces energy waste caused by overheating while ensuring the quality of scrap steel heating, and improves the heating adaptability and energy utilization efficiency of different types of scrap steel.

[0104] In one alternative implementation, the rotation direction of the rotatable scrap preheating kiln is switched periodically, with a switching cycle of 2-5 minutes.

[0105] The periodic switching of rotation direction refers to alternating between clockwise and counterclockwise rotation of the rotatable scrap preheating kiln. This can be achieved using a bidirectional drive motor or a reversible gear transmission mechanism, with the switching logic set via a control circuit or program. The switching cycle refers to the time interval between the rotation direction changes, which can be implemented using a timer or sensor feedback mechanism. The cycle length is dynamically adjusted by setting time parameters or based on temperature distribution data. This cycle range is limited to 2-5 minutes, ensuring sufficient rotation time in each direction for material mixing while avoiding excessively short switching intervals that could cause frequent impact loads on mechanical components.

[0106] Specifically, when the rotatable scrap preheating kiln operates at a set speed, the drive system automatically reverses the rotation direction according to a preset cycle. During clockwise rotation, the scrap steel forms a specific trajectory along the inner wall of the kiln under centrifugal force. When switching to counterclockwise rotation, the inertial motion direction of the scrap steel acts in the opposite direction to the kiln's rotation, causing the material to undergo multi-dimensional tumbling and mixing. This alternating rotation mode allows material at different locations within the scrap pile to be alternately exposed to the alternating magnetic field generated by the electromagnetic coil group, eliminating the magnetic field coverage blind spots caused by a fixed rotation direction. The switching cycle is controlled within the range of 2-5 minutes, ensuring sufficient time for each rotation direction to form effective mixing while avoiding excessive wear on the transmission mechanism caused by frequent reversals. By dynamically adjusting the material movement path, the spatial distribution of scrap steel within the kiln is continuously reconstructed, thereby improving the uniformity of electromagnetic field energy penetration within the material pile.

[0107] In some specific implementations, bidirectional rotation control can be achieved through a programmable logic controller (PLC), for example, set to automatically switch directions every 3 minutes. The drive motor can be a bidirectional AC motor with braking function, achieving smooth steering through deceleration and braking during commutation. The gear transmission system can be equipped with a reverse meshing mechanism to ensure the reversibility of power transmission direction. When switching rotation directions, the power supply parameters of the electromagnetic coil assembly can be adjusted synchronously, for example, temporarily reducing power at the moment of commutation to avoid current fluctuations.

[0108] Through the above technical solution, this invention can eliminate the localized overheating phenomenon caused by a single rotation direction during the preheating process of scrap steel, and solve the problem of heating dead zones inside the material pile. The multidimensional mixing effect generated by alternating rotation ensures that all parts of the scrap steel receive electromagnetic energy evenly, improving the consistency of the overall preheating temperature. At the same time, the optimized switching cycle reduces the mechanical load on the transmission system and extends the service life of the equipment while ensuring the heating effect.

[0109] In some alternative implementations, while activating the electromagnetic coil assembly to operate at the actual power of electromagnetic induction heating, inert gas or reducing gas is introduced into the rotatable scrap preheating kiln, with the gas flow rate controlled in the range of 5-10 L / min.

[0110] Inert or reducing gases refer to gases supplied to the kiln from an external gas source that isolate oxygen or reduce oxides. Specifically, argon or nitrogen can be used as inert gases, or hydrogen or carbon monoxide as reducing gases, thereby reducing the oxygen concentration inside the kiln through gas replacement. A gas flow rate of 5-10 L / min refers to the volume of gas introduced per unit time, which can be controlled by a flow meter and a regulating valve. This flow rate range ensures a stable gas layer covering the kiln space while preventing excessively high airflow velocities that could lead to scrap steel displacement or heat loss.

[0111] Specifically, during the electromagnetic induction heating process, the gas delivery pipeline is connected to the sealed interface of the preheating kiln, and the gas is injected evenly from both ends or the side walls of the kiln. Inert gas fills the kiln space to create a protective atmosphere, preventing contact between the scrap steel surface and oxygen; reducing gas reacts with the already formed oxide layer, restoring the metal element content. The gas flow rate is dynamically adjusted by real-time monitoring of the kiln pressure; for example, the flow rate is automatically increased when the kiln pressure falls below a set threshold, ensuring that the gas layer completely covers the scrap steel surface.

[0112] Through the above technical solution, this invention achieves a reduction in the thickness of the oxide layer on the surface of scrap steel, a decrease in the rate of metal element burn-off, and no emission of smoke or harmful gases during the preheating process. The scrap steel maintains a clean surface after high-temperature preheating, avoiding the problem of increased inclusions in molten steel due to an excessively thick oxide layer during subsequent smelting, while also meeting environmental protection production requirements.

[0113] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A scrap steel preheating device based on induction heating, characterized in that, include: Electromagnetic coil assembly (1), rotatable scrap steel preheating kiln (2), gear seat (3) and movable kiln cover (4); The rotatable scrap steel preheating kiln (2) is a cylindrical structure with openings at both ends and placed horizontally. The movable kiln cover (4) is located at both ends of the rotatable scrap steel preheating kiln (2) and is connected to the rotatable scrap steel preheating kiln (2) by a hinge or sliding mechanism. It is used to close and open the rotatable scrap steel preheating kiln (2) to load and unload scrap steel. The electromagnetic coil group (1) consists of multiple electromagnetic coils arranged in parallel, which surround the outer surface of the upper half of the rotary scrap preheating kiln (2). The electromagnetic coil group (1) is fixed to the external support structure of the rotary scrap preheating kiln (2) by insulating fasteners. Each electromagnetic coil is formed by a semi-circular arc segment (11) and a straight segment (12) connected to its two ends. The straight segment (12) is connected to an external power source through a wire to generate an alternating magnetic field. The opening direction of the semi-circular arc segment (11) of each electromagnetic coil is consistent and faces the outer surface of the upper half of the rotary scrap preheating kiln (2). The opening of the semi-circular arc segment (11) and the outer surface of the upper half of the rotary scrap preheating kiln (2) form a clearance fit. The gear seat (3) forms a rotatable connection with the outer surface of the lower half of the rotatable scrap steel preheating kiln (2), which is used to support the rotatable scrap steel preheating kiln (2) and drive the rotatable scrap steel preheating kiln (2) to rotate. The top of the gear seat (3) is provided with a semi-circular groove (31), which is adapted to the outer surface of the lower half of the rotatable scrap steel preheating kiln (2); a ring bearing track is embedded in the semi-circular groove (31), and a ball bearing is installed in the ring bearing track, so that the rotatable scrap steel preheating kiln (2) can rotate relative to the gear seat (3). The device further includes: Driven gear and driven gear ring; The driven gear ring is fixedly sleeved on the outer surface of the cylinder of the rotatable scrap steel preheating kiln (2) and close to the side of the movable kiln cover (4). The driven gear ring meshes with the driving gear for transmission. The gear shaft of the driving gear is coaxially connected to the output shaft of the external motor through a coupling. When the external motor starts, the rotational power of the output shaft is transmitted to the gear shaft of the driving gear through the coupling. The driving gear rotates accordingly and transmits the power to the rotatable scrap steel preheating kiln (2) through meshing with the driven gear ring, thereby driving the rotatable scrap steel preheating kiln (2) to rotate around its own axis.

2. The apparatus according to claim 1, characterized in that, The rotatable scrap steel preheating kiln (2) adopts a double-layer structure, with the outer layer being high-strength austenitic stainless steel and the inner layer being heat-insulating refractory material.

3. The apparatus according to claim 1, characterized in that, The volume of the rotary scrap preheating kiln (2) is 1.5-2 times the amount of scrap steel loaded in a single operation; the rotation speed of the rotary scrap preheating kiln (2) is 10-20 revolutions per minute.

4. The apparatus according to claim 1, characterized in that, The electromagnetic coils of the electromagnetic coil group (1) are arranged at equal intervals; The gear seat (3) includes multiple gear seats (3) which are equidistantly installed on the outer surface of the lower half of the rotatable scrap steel preheating kiln (2).

5. A method for preheating scrap steel based on induction heating, characterized in that, The scrap preheating device based on induction heating as described in any one of claims 1-4 comprises: S1. Determine the preheating temperature of scrap steel for a single charge based on the converter capacity and the ratio of scrap steel to charge. The calculation expression for the single-cycle preheating of scrap steel is as follows: C=Vη in, V This refers to the converter capacity; η The ratio of scrap steel fed into the furnace; C For single-use scrap preheating; S2. Determine the power of the electromagnetic induction heating unit based on the single scrap preheating heat and the converter smelting cycle; P 0 =600αC(TT 0 ) / q in, α For electromagnetic induction heating efficiency; T This refers to the preheating temperature of the scrap steel. T 0 represents the initial temperature of the scrap steel; q For converter smelting cycle; P 0 represents the unit power of electromagnetic induction heating; S3. Determine the actual power of electromagnetic induction heating based on the power of the electromagnetic induction heating unit; P a = (n+0.2) P 0 ， P a ≤P in, P Rated power of the transformer for preheating scrap steel; P a This represents the actual power of electromagnetic induction heating. P 0 represents the unit power of electromagnetic induction heating; n It is a power multiple and is an integer; S4. Start the external motor to control the rotatable scrap steel preheating kiln to rotate at a speed of 10-20 revolutions per minute. At the same time, activate the electromagnetic coil group to work with electromagnetic induction heating at actual power, and generate eddy current heating inside the scrap steel through alternating magnetic field. S5. The temperature of the scrap steel is monitored in real time by a temperature sensor. When the preheating temperature of the scrap steel is reached, heating is stopped, the movable kiln cover is opened, and the preheated scrap steel is unloaded into the converter.

6. The method according to claim 5, characterized in that, The method further includes: Real-time electricity price data is obtained through the power grid load monitoring system; When the electricity price is low or zero, the scrap steel preheating device will be automatically activated. The preheated scrap steel is temporarily stored in an insulated warehouse and will be used during converter smelting.

7. The method according to claim 5, characterized in that, The preheating temperature of the scrap steel is dynamically adjusted by the composition of the scrap steel; when the content of low melting point impurities in the scrap steel is ≥5%, the preheating temperature of the scrap steel is reduced by 50-100℃; when the scrap steel is pure heavy scrap steel, the preheating temperature of the scrap steel is increased by 50-100℃.

8. The method according to claim 5, characterized in that, The rotation direction of the rotatable scrap preheating kiln is switched periodically, with a switching cycle of 2-5 minutes.

9. The method according to claim 5, characterized in that, While the electromagnetic coil assembly is activated to operate at the actual power of electromagnetic induction heating, the method further includes: Inert or reducing gas is introduced into the rotatable scrap preheating kiln at a flow rate of 5-10 L / min.

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