How the LF Ladle Refining Furnace Performs Secondary Refining Treatment Using Scrap Steel

How the LF Ladle Refining Furnace Performs Secondary Refining Treatment Using Scrap Steel

China generates approximately 200 million tons of steel scrap annually (e.g., trimmings, machining waste, discarded machinery, and household metal scrap). The LF (Ladle Furnace) is a secondary refining unit installed downstream of primary melting furnaces (converters or electric arc furnaces). It utilizes electrode-arc heating to raise the temperature of molten steel, replacing the reduction phase typically carried out in the primary furnace. During LF treatment, the steel is heated, deoxidized, desulfurized, degassed, alloyed, and stirred with argon to improve its quality.

To make effective use of the abundant scrap resources, a scrap preheating system can be integrated with the LF furnace. Waste gas from blast furnaces or converters is used to preheat scrap to 450–600°C, after which the hot scrap is continuously charged into the LF. The preheated scrap is added to molten steel at approximately 1500°C in the ladle. Combined with the arc heating capability of the LF, the scrap melts rapidly and undergoes full refining, producing molten steel that meets the required specifications.

During each refining cycle, 10%–20% scrap steel can be added, increasing daily molten steel output by 10%–20%. This approach recycles valuable iron and steel elements from waste, forming a sustainable, circular-economy process that supports resource efficiency.

By leveraging both the inherent heat of the incoming molten steel and the LF’s arc heating—along with low-cost furnace off-gas as a preheating energy source—resource waste is minimized, production costs per ton of steel are significantly reduced, and overall plant economics are improved.

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Technical Features of the LF Scrap Preheating and Charging System

The scrap preheating and feeding system is an integrated mechatronic unit designed to heat crushed scrap steel. Scrap size is controlled to 50–100 mm. Inside the preheating furnace, the scrap is heated to a process temperature typically between 450°C and 600°C, suitable for steelmaking.

The system consists of a steel-structure furnace lined with refractory material. Configurations can include 1 to 4 preheating stations, each mounted on a structural frame. A single station can preheat 5 to 10 tons of scrap per hour.

Scrap is loaded into bottom-opening containers in the stockyard and lifted by crane into the preheating furnace. The upper section serves as a charging bin equipped with a pneumatic gate valve. The middle and lower sections form the scrap heating chamber. At the base, a vibratory feeder continuously transfers the heated scrap via a chute into the LF furnace. The preheating unit includes a weighing device for precise charge control, and the vibratory feeder uses variable-frequency drive to allow adjustable feed rates.

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