An electric arc furnace is a specialized device that utilizes the intense heat generated by an electric arc between the electrode tip and the charge to produce steel. The evolution of electric arc furnace technology has centered around the adoption of high-power operations, leading to the development of direct current electric arc furnaces, furnace bottom gas agitation systems, and furnace bottom tapping mechanisms. The fundamental components of an electric arc furnace include the furnace roof, furnace wall, furnace bottom, and tapping trough (or tap hole in modern designs).
The roof of an electric arc furnace is typically constructed using high-alumina bricks, with an alumina content ranging from 75% to 85%. These bricks offer superior refractoriness, excellent thermal shock resistance, and high compressive strength compared to silica bricks. Given the abundance of domestic bauxite resources, high-alumina bricks have become the primary refractory material for electric arc furnace roofs, boasting a lifespan approximately two to three times longer than that of silica brick roofs.
However, with the advent of large-scale ultra-high-power electric furnaces, the service life of high-alumina bricks has diminished, prompting the further utilization of basic bricks such as fired or unfired magnesia bricks and magnesia-chrome bricks. Additionally, commercial cast refractory preforms can be hoisted into place, offering advantages such as convenient construction, enhanced integrity, robust resistance to arc radiation, and resilience to rapid temperature changes.
The furnace wall is divided into several sections, including the general furnace wall, slag line area, and hot spots near the arc. Generally, magnesia bricks, dolomite bricks, and periclase bricks are the primary materials used for constructing the furnace walls, along with unburned magnesia alkaline bricks and asphalt-bonded magnesia and dolomite ramming materials. For ultra-high-power or special steel smelting electric arc furnaces, magnesia-chrome bricks and high-quality magnesia bricks are preferred.
The slag line area and hot spots represent the weakest links in the furnace wall, as the lifespan of the wall largely depends on the degree of damage sustained at these hot spots. Initially, magnesia-chrome bricks were used for masonry in these areas, achieving a lifespan of 100-250 heats. Nowadays, magnesia-carbon bricks are widely employed, exhibiting exceptional high-temperature resistance and slag resistance, significantly extending the service life to over 300 heats.
To balance the wear and tear on the furnace wall and prolong its lifespan, water-cooled boxes or water-cooled jackets are installed. The inner surface is coated with a layer of refractory material to form a protective slag layer, effectively reducing the unit consumption of refractory materials, albeit at the cost of increased energy consumption.
The furnace bottom and the slope of the embankment form the melting pool, where the charge and molten steel accumulate. When the furnace bottom lining reacts with molten slag and iron oxide, a metamorphic layer forms, which can become loose due to the reduction of some components during the reduction process, often leading to floating caused by molten steel intrusion.
Therefore, the masonry or knotted lining of this part should possess uniform overall performance, tight masonry, excellent high-temperature properties, high strength, corrosion resistance, erosion resistance, thermal shock resistance, and stable volume. Good-quality magnesia or fused magnesia is selected for the knotted lining, with careful attention paid to the joints between each layer during construction to ensure consistent thickness and density. Beneath the ramming layer, there are working layers and permanent linings. The working layer is typically made of tar pitch-bonded magnesia bricks, while magnesia bricks are mostly used for the permanent lining.
At the slag line on the upper part of the embankment slope, due to severe slag erosion, lining bricks similar to those used at the hot spots of the furnace wall are often employed, such as cast magnesia-chrome bricks or combined magnesia-chrome bricks. Magnesia-carbon bricks are preferred for their superior performance.
The currently adopted furnace bottom eccentric tapping method transforms the furnace body from a tilting type to a fixed type, featuring a tap hole at the eccentric position of the furnace bottom to replace the traditional tapping trough. This design offers several advantages, including the elimination of tilting equipment, expansion of the water wall area, alleviation of furnace lining damage, appropriate reduction in tapping temperature, and shortening of tapping time, thereby reducing costs.
The eccentric tap hole bricks are pitch-impregnated and fired magnesia bricks, while the pipe bricks are made of magnesia-carbon bricks with a resin-bonded carbon content of 15%. The end bricks are magnesia-carbon bricks with a resin-bonded carbon content of 10%-15% or 15% AlO-C-SiC bricks. For smooth tapping, coarse sand with olivine as the matrix is often used as drainage material.
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