Application of high alumina bricks and magnesia-chrome bricks in lead metallurgical furnaces
Application of high alumina bricks in lead metallurgical furnaces
High alumina bricks belong to the aluminum silicate refractory system. According to their chemical properties, they are called neutral refractory materials. They are the most widely used refractory bricks in the refractory industry. High alumina bricks have the advantages of small high-temperature creep, strong corrosion resistance, and good thermal shock stability. Therefore, high alumina bricks can be seen in high-temperature kilns in various industries such as steel smelting, non-ferrous metals, glass, cement, ceramics, petrochemicals, and electricity. Today, we mainly take the lead smelting kiln as an example to briefly describe the application of high alumina bricks in metallurgical furnaces used in the lead smelting process.
The working environment of the metallurgical furnace used for lead smelting is very complex. Not only do refractory bricks have sufficient high temperature resistance, but they also have certain resistance to slag and lead liquid corrosion, as well as resistance to slag and flue gas scouring. In the selection of refractory bricks, lead metallurgical furnaces mainly use magnesia-chrome bricks, high alumina bricks, and high alumina refractory ramming materials. Among them, high-alumina bricks and high-alumina refractory ramming materials are mainly used in the permanent layer area of the furnace bottom.
In the design of the lining of the lead metallurgical furnace, the choice of refractory materials varies according to the different positions in the furnace body. Taking the fixed horizontal metallurgical furnace body as an example, the furnace bottom generally uses magnesia-chrome bricks, high-alumina bricks, aluminum-chrome spinel, high-alumina ramming materials, magnesium ramming materials, etc., and some use high-strength anti-seepage ramming materials, which also belong to the AL2O3-SiO2 system, and the content of AL2O3 is >75%. The specific gravity of liquid lead is 10.6g/cm3, and the permeability is extremely strong. Therefore, the refractory material of the furnace bottom must have the function of heat dissipation and a high ability to prevent lead seepage.
At present, the widely used practice is to first lay high-aluminum bricks on the furnace bottom steel plate. High-aluminum bricks have higher compressive strength (compressive strength at room temperature 40~60MPa), and thermal conductivity (2.09+1.861×10-3t) is also higher than magnesia-chrome bricks (1.28+0.407×10-3t). It is more reasonable to use them as a cushion at the bottom of the furnace; a layer of refractory material with lead penetration resistance should be set on the upper part of the furnace bottom cushion. Currently, magnesium ramming material or high-strength anti-seepage ramming material (high-aluminum) is used, both of which can act as a barrier. The ratio of magnesia ramming material is: magnesia: magnesium powder = 7:3, with brine, magnesia particle size: 0.2~0.5mm70%, 1.5~3.0mm30%; the composition of high-strength anti-seepage ramming material is: high-aluminum aggregates of various particle sizes and bone powder.
After high-temperature baking, aggregates of various particle sizes expand and combine tightly to achieve the ideal purpose of anti-seepage lead. It must be noted that after the ramming of magnesium and magnesium-chrome ramming materials is completed, low-temperature baking is required. After the free water is baked out, the expansion joints are filled with fine magnesium powder to ensure the strength and density of the ramming layer. The thickness of the ramming material is recommended to be 150~300mm, which is convenient for one-time completion during ramming and can be baked more evenly to form an overall layer with good anti-seepage effect.
Application of magnesia-chrome bricks in lead smelting industry kilns
The requirements for refractory materials in lead smelting are relatively complex. They must have sufficient high temperature resistance and certain high-temperature mechanical strength. At the same time, they must have good resistance to slag erosion and resistance to slag and flue gas scouring. Therefore, the selection of refractory materials in the furnace is very strict. Therefore, magnesia-chrome bricks are mainly selected in its high-temperature working area. The selection of refractory materials in the working area (furnace wall and furnace top) in the furnace chamber of the lead smelting furnace is divided into two areas, one is the magnesia-chrome bricks in the molten pool area (especially the slag line area), and the other is the magnesia-chrome bricks in the meteorological area.
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01 Molten pool area in the furnace
The refractory bricks in the molten pool area (especially the slag line area) will be corroded and washed by the slag. The composition of lead smelting slag is relatively complex, and high-aluminum refractory materials will participate in the slag-making reaction. Therefore, it is inappropriate to use high-aluminum refractory bricks. Magnesia-chrome refractory bricks should be used. At the same time, considering the slag corrosion and scouring resistance of refractory bricks, electric melting recombination magnesia-chrome bricks should be used. Bricks of this material are better than semi-recombined magnesia-chrome bricks in slag corrosion resistance. Increasing the content of Cr2O3 can improve the slag corrosion resistance of bricks, so try to choose magnesia-chrome bricks with a higher Cr2O3 content.
02 Meteorological zone in the furnace
The refractory bricks in the meteorological zone will not be corroded by slag, but only by a small amount of splashing erosion from the molten edge and scouring of dusty flue gas. Therefore, magnesia-chrome bricks with a lower Cr2O3 content can be selected.
The magnesia-chrome bricks used in the lead reduction furnace of a domestic factory used direct-bonded magnesia-chrome bricks with a high content of Cr2O3 in the early stage of production. The magnesia-chrome bricks in the meteorological zone had no metal and slag on the surface, the bricks were broken into two sections, and the structure was loose. According to the analysis results, it was judged that the Fe3+ and Fe2+ in the refractory bricks were reduced to elemental Fe in large quantities, resulting in a loose brick structure. Therefore, during maintenance, fused re-bonded magnesia-chrome bricks with a low content of Cr2O3 (Cr2O3 containing 12% S) were used. The main reason for this improvement is that the apparent porosity of fused re-bonded magnesia-chrome bricks is low, and at the same time, the content of Fe3+ and Fe2+ in the refractory bricks is reduced, so that it is more suitable for the strong reducing atmosphere in the meteorological zone and prolongs the service life. After switching to this type of fused re-bonded magnesia grid bricks, the service life has been greatly extended and good results have been achieved.
In order to ensure the normal operation of metallurgical furnaces, ensure a reasonable furnace life, and enable enterprises to obtain economic benefits, correct and reasonable refractory design is also necessary, including structural design, expansion calculation, and masonry heating and baking, which all affect the normal use of refractory materials. Therefore, on the basis of existing development, it is necessary to further study and improve the erosion resistance, slag erosion resistance, stress analysis, baking system and other aspects of refractory materials. It requires the joint efforts of refractory suppliers, design units and users in many aspects to achieve better application effects of refractory materials.