Refractory bricks for hot blast furnaces
The hot blast furnace is one of the main facilities in blast furnace ironmaking production. With the large-scale blast furnace, the improvement of raw fuel quality, the development of injection technology, and the improvement of blast furnace operation level, the required wind temperature is higher. The general requirement for the hot blast furnace is to achieve high wind temperature and long life. For this reason, a reasonable hot blast furnace structure and refractory materials for building the hot blast furnace must be selected in the design.
1 Performance of refractory bricks for hot blast furnaces.
The refractory bricks used in hot blast furnaces are: clay bricks, silica bricks and high-alumina refractory bricks (including mullite bricks, sillimanite bricks, andalusite bricks, kyanite bricks and cocoon bluestone bricks). The general requirements for refractory bricks in hot blast furnaces are: small creep rate, good high temperature strength, and good thermal shock resistance. In addition to the above requirements, the checker bricks for hot blast furnaces should also have a large heat capacity. When we design hot blast furnaces, in order to be able to reasonably select refractory bricks, we must first understand their performance. Because accurate refractory material characteristic parameters are the basis for ensuring correct and reliable design.
1.1 Silica Bricks
Silica bricks have a low creep rate and are relatively stable in volume when used for a long time at high temperatures. However, the volume of tridymite, cristobalite and residual quartz in silica bricks changes greatly (expands) due to changes in crystal form at low temperatures, so the thermal stability at low temperatures is very poor. During use, it should be heated or cooled slowly to avoid cracks, so it is not suitable for use in areas with sudden temperature changes below 80C. Because of its relatively low price, it is widely used in the vaults, connecting pipes, combustion chambers and high-temperature areas above the regenerator of hot blast furnaces and the high-temperature areas above the checker bricks. It should be pointed out that due to several characteristics of silica bricks, there are strict requirements in all aspects of design, manufacturing, construction and production, so silica bricks should be used with great caution. Silica bricks should be used in the high-temperature areas of large (diameter ≥ 8m) hot blast furnaces with high wind temperatures, while small and medium-sized (diameter < 8m) hot blast furnaces should not be used.
1.2 Clay Bricks
Clay bricks have low refractoriness, load softening point and creep temperature, and strong thermal shock stability. Widely used in the low temperature zone of the hot blast furnace with a temperature below 1000°C, high-density and low-alkali metal clay bricks can also be used as bricks for the lower part of the ceramic burner.
1.3 High-alumina refractory bricks
(1) High-alumina bricks for hot blast furnaces
High-alumina bricks are dense, hard, high in specific gravity, high in mechanical strength, good in wear resistance and thermal conductivity, stable in volume at high temperatures, and have a low creep rate. They are suitable for use in the high and medium temperature zones of hot blast furnaces. If used for the vault, they require a low creep rate and high volume stability; if used as checker bricks, they must have sufficient thermal stability and high volume stability; if used in the lower part of the combustion chamber, they require good thermal stability.
(2) Mullite bricks. Mullite bricks are low-creep bricks made of mullite as the main raw material. They have the advantages of high density, high high-temperature structural strength, low creep rate, low thermal expansion rate, strong resistance to chemical erosion and thermal shock, etc. They can be laid in the vault of the hot blast furnace and the middle and upper parts of the combustion chamber, and can also be used as bricks for ceramic burners. It is suitable for large-scale high-temperature hot blast furnace vault, combustion chamber, upper part and hot blast outlet combination bricks.
(3) Sillimanite bricks, andalusite refractory bricks and kyanite bricks. Sillimanite bricks are low creep bricks made of high-alumina bauxite clinker with part of sillimanite ore added. Andalusite is a low creep brick made of andalusite ore and other raw materials. Kyanite bricks are low creep bricks made of high-alumina bauxite clinker and kyanite ore. Sillimanite bricks and andalusite bricks have high refractoriness and load softening temperature, and have good high temperature stability and thermal shock resistance. They can be used to build hot blast furnace vaults, combustion chambers, the upper part of heat storage chambers and the upper part of checker bricks, as well as ceramic burners and the cold air inlet of mixing chambers (or mixed air pipes). Kyanite bricks have high refractoriness and load softening temperature, low creep rate, and are cheaper than mullite bricks, sillimanite bricks and andalusite bricks. They are very suitable for high-temperature areas of small and medium-sized (diameter <8m) hot blast furnaces with high wind temperature (1100-1150°C).
With the advantages of strong erosion resistance and thermal shock resistance, they can be built in the middle and upper parts of the hot blast furnace vault and combustion chamber, and can also be used as bricks for ceramic burners. However, it is expensive and should be used with caution. It is suitable for large (diameter) 8m) and high-temperature (120°C) hot blast furnace vaults, the middle and upper parts of the combustion chamber and the hot blast outlet combination bricks. my country can now manufacture mullite bricks required for large high-temperature hot blast furnaces according to advanced foreign standards without importing.
(3) Sillimanite bricks, andalusite bricks and kyanite bricks. Sillimanite bricks are low creep bricks made of high-alumina bauxite clinker with part of sillimanite ore. Andalusite bricks are low creep bricks made of andalusite ore and other raw materials. Kyanite bricks are low creep bricks made of high-alumina bauxite clinker and kyanite ore. Sillimanite bricks and andalusite bricks have high refractoriness and load softening temperature, and have good high temperature stability and thermal shock resistance. They can be used to build hot blast furnace vaults, combustion chambers, the upper part of heat storage chambers and the upper part of checker bricks, as well as ceramic burners and the cold air inlet of mixing chambers (or mixed air pipes). Kyanite bricks have high refractoriness and load softening temperature, low creep rate, and are cheaper than mullite bricks, sillimanite bricks and andalusite bricks. They are very suitable for the high temperature area of small and medium-sized (diameter <8m) hot blast furnaces with high wind temperature (1100-1150°C).
(4) Azurite bricks are high-alumina bricks containing azurite components. They have low thermal expansion rate and good thermal shock resistance, and are suitable as bricks for the upper part of ceramic burners.
2 Performance of insulation bricks for hot blast furnaces
2.1 Lightweight silica bricks
The refractoriness, compressive strength, slag resistance, erosion resistance and thermal conductivity of lightweight silica bricks are not as good as those of silica refractory bricks. They should be laid on the back of silica refractory bricks as a heat insulation layer.
2.2 Diatomaceous earth bricks
Diatomaceous earth bricks are lightweight refractory materials made of diatomaceous earth. They have good heat insulation performance and can be laid on the back of clay bricks as a heat insulation layer. For the performance indicators of diatomaceous earth bricks in my country, please refer to the relevant provisions of GB9396-83 standards.
2.3 Lightweight clay bricks
Lightweight clay bricks are porous lightweight thermal insulation materials. They can be laid on the back of clay bricks or lightweight high-alumina bricks as a heat insulation layer.
2.4 Lightweight high-alumina bricks
Lightweight high-alumina bricks are good heat insulation materials and can be used to lay on the back of high-alumina refractory bricks or lightweight silica bricks.
3 Selection of refractory bricks and insulation bricks for hot blast furnaces
In order to achieve high wind temperature and long life of hot blast furnaces, it is necessary to reasonably select refractory materials for hot blast furnace masonry. The selection of refractory materials is mainly determined by the design hot blast temperature and the size of the hot blast furnace. In addition, the price of refractory bricks should also be considered. According to design practice, the author believes that refractory bricks and insulation bricks for hot blast furnaces can be selected according to the following scheme.
(1) Large blast furnace hot blast furnace (diameter ≥ 8m, wind temperature 1200℃): silica bricks are used for the arch, upper part of the combustion chamber, upper part of the regenerator and upper part of the checker bricks; mullite bricks are used in the arch part and the middle part of the combustion chamber (high temperature zone) adjacent to silica bricks; andalusite bricks or sillimanite bricks are used in the middle and high temperature zones of the regenerator and checker bricks adjacent to silica bricks and the lower area of the combustion chamber above the top surface of the burner; andalusite bricks or sillimanite bricks are suitable for the checker bricks above the grate; clay bricks are used in the low temperature zone below 1000℃.
(2) Large blast furnace hot blast furnace (diameter ≥ 8m, wind temperature 1150℃): silica bricks are used for the vault, the upper part of the combustion chamber, the upper part of the regenerator and the upper part of the checker bricks. Andalusite bricks or sillimanite bricks are used in the vault part immediately adjacent to the silica bricks, the middle part of the combustion chamber, the medium and high temperature areas of the regenerator and checker bricks, and the lower area of the combustion chamber above the top surface of the burner; andalusite bricks or sillimanite bricks are also suitable for the 15 layers of checker bricks above the grate; clay bricks are used in the low temperature area with a temperature below 1000℃.
(3) Small and medium-sized blast furnace hot blast furnace (diameter <8m, wind temperature 1100-1150℃): kyanite bricks are used for the dome, the middle and upper parts of the combustion chamber, the heat storage chamber and the upper part of the checker bricks. The lower area of the combustion chamber above the top surface of the burner is made of andalusite bricks. Clay bricks are used for the low temperature zone (including checker bricks) with a temperature below 100℃.
(4) Ceramic burner: cocoon bluestone bricks or andalusite bricks are used for the upper part, and dense clay bricks with low alkali metal content are used for the lower part.
(5) Selection of insulation bricks: The type of insulation bricks used for the hot blast furnace is determined by the type of refractory bricks used in the working layer. When the working layer is built with silica bricks, lightweight silica bricks should be laid on the back of the silica bricks. When the working layer is built with high-alumina refractory bricks, lightweight high-alumina bricks should be laid on the back of the refractory bricks. When the working layer is built with clay bricks, lightweight clay bricks or diatomaceous earth bricks should be laid on the back of the clay bricks.
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