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Blast Furnace Refractory

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blast furnace and refractory lining

The blast furnace is an industrial equipment widely used in smelting industrial metals thanks to its easy processing, large productivity, high efficiency, and low energy consumption. Hot air is blown into the furnace to heat the materials including iron ore, the limestone, and the coke. Metals are obtained because of the chemical reduction. The carbon takes away the oxide from the iron ore and the metallic iron is kept.

Shaped and unshaped refractories are used for the blast furnace lining to withstand high temperatures and a series of chemical and physical reactions. The refractory quality is essential to the life span of the blast furnace.

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refractory lining in blast furnace

blast furnace lining structure

The working conditions are quite different in varied sections of the blast furnace. For example, in the upper body, mechanical wear or abrasion often happens because of the charging materials and the gases. High thermal loads are a primary factor in the lower body and the belly regions. In the hearth region, horizontal and vertical flow of hot metal combined with thermal stresses often form undesirable elephant foot shapes. Therefore, the BF body (upper middle and lower), belly, bosh, hearth and bottom, and taphole all require different quality refractories depending on the respective application conditions.

Throat

The furnace throat plays the role of protecting the upper lining, evenly distributing the furnace material, and limiting the amount of ash carried away by gas. As the upper part of the blast furnace, the temperature at the throat is low. The common refractory for the furnace throat is high alumina bricks.

Furnace Body

The furnace body is a long part of the blast furnace. The preheating, heating, reduction, and slagging take place here. The upper and middle parts of the furnace body are usually built with fire clay bricks or fire clay based monolithics. The lower part of the body always chooses premium fire clay bricks, high alumina bricks with good slag resistance, or corundum bricks which possess higher thermal conductivity and better slag resistance.

Belly

The temperature of the furnace belly is 1400-1600°C, which is relatively high. The furnace charge has been partially reduced to slag, and the air permeability is poor. The slag erosion is serious. At the same time, the rising airflow in the lower part is severely eroded, and the coke friction is serious. Therefore, the furnace lining in this part is seriously damaged. So, high-quality clay bricks, high-alumina bricks, corundum bricks, and carbon bricks are often used.

Bosh

The furnace bosh is connected to the furnace belly and the furnace hearth. To adapt to the expansion of high-temperature furnace gas and the contraction of molten materials, it is usually designed to be larger at the top and smaller at the bottom. At the same time, this part is close to the tuyere and will be affected by the washing of hot air, and erosion caused by slag and iron separation and the dripping process of slag iron. So this area is the most vulnerable area to damage during the operation of the blast furnace. The furnace bosh is usually made of high alumina bricks or corundum bricks.

Hearth & bottom

The furnace hearth and furnace bottom mainly play the role of burning coke and storing molten iron. The hot air blown in from the tuyere reacts with the coke at this location to produce gas with a temperature as high as 2000°C or more. Therefore, the use temperature of the refractory materials in the tuyere area is above 1700°C. The molten steel contained in the furnace is regularly discharged from the taphole. The high-speed hot air will also blow the molten iron in the furnace, causing the molten iron to form a swirling flow in the furnace. Therefore, the furnace refractory materials will be washed and eroded by the high-temperature molten iron, so carbon bricks are generally used as refractory materials. The molten iron in the dead iron layer at the bottom of the furnace will penetrate the refractory material. At the same time, the carbon in the molten iron will also cause the refractory material to embrittle. Therefore, the furnace bottom is prone to erosion like an elephant feet shape. The furnace bottom is generally made of high-quality clay bricks or High alumina bricks.

Requirements of blast furnace lining

Generally speaking, refractory materials for blast furnaces should meet the following requirements. They should not soften, melt, or volatilize at high temperatures while maintaining the complete strength of the furnace body under high temperatures and high-pressure conditions. They must be able to withstand the temperature changes in the furnace. It must also have chemical stability against molten iron, slag, and furnace gas.

  1. High refractoriness

Refractoriness refers to the temperature at which refractory materials begin to soften. It represents the ability of refractory materials to withstand high temperatures.

  1. High RUL (refractoriness under load)

The load softening point can more accurately evaluate the performance of refractory materials.

  1. Low potential for after-contraction

A scale that indicates the likelihood of cracks occurring in refractory materials when they rise to high temperatures.

  1. Low porosity

Under blast furnace smelting conditions, if the porosity of the brick lining material is large, it will create conditions for the deposition of graphite and zinc, thus causing furnace lining damage.

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