Varieties and properties of magnesium-calcium refractory materials. There are main reasons for the use of dolomite bricks in cement rotary kilns in some Western countries. One is the high operating rate of the kiln (>80%). Second, the price of dolomite bricks is relatively low. Third, there are regulations to prevent chromium pollution and waste magnesia-chrome bricks cannot be discarded casually.
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| advantages of dolomite bricks |
Application advantages of dolomite bricks
The advantages of dolomite bricks are high-temperature resistance, kiln coating, and resistance to clinker chemical erosion. The disadvantage is that it has poor thermal shock resistance, hydration resistance, and gas erosion resistance such as CO2 and SO2. Experiments have proved that dolomite bricks used in the stable section of the kiln skin of the firing zone can obtain a life equivalent to that of magnesia-chrome bricks (about 1 year). However, even if measures such as enriching magnesium, increasing zirconium, and reducing permeability are taken, magnesia-dolomite bricks or dolomite bricks should not be used in sections where the kiln skin is unstable. If used in these sections, magnesia dolomite bricks, especially dolomite bricks only have a lifespan of 3 months. Properties of dolomite bricks, zirconium-containing dolomite bricks, magnesium-rich dolomite bricks, and magnesium-zirconium bricks.
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| zirconium-containing dolomite bricks |
General-purpose products; zirconium-enhanced products, slightly stronger thermal shock resistance; magnesium-rich zirconium-enhanced products, slightly stronger thermal shock resistance, and gas erosion resistance. The former is suitable for the firing zone with stable kiln skin; the latter two are suitable for the firing zone with poor conditions. Magnesium-zirconium bricks have good performance in high-temperature resistance, corrosion resistance, and hanging kiln skin, but the thermal conductivity is too high.
If a large amount of ZrO2 is added to produce MgO-CaO·ZrO2 series materials, refractory products with excellent performance can be obtained. But raw material costs are high, making the product difficult to sell.
Dolomite bricks adopt three technologies of aluminum foil packaging, vacuum pumping, and waterproof coating to prevent hydration. Under normal circumstances, dolomite bricks with the above measures can be preserved for 1 year. Pay attention to the use of dolomite bricks.
- ①Do not damage the waterproof packaging during transportation.
- ②The warehouse must not leak from rain or return to dampness.
- ③ Do not wet the bricks during the kiln-building process.
- ④ Do not use fireclay to build dolomite bricks or refractory materials close to dolomite bricks.
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| magnesia dolomite brick |
Structure and performance analysis of fired magnesia dolomite brick
The high-quality fired magnesia dolomite brick has very little silicate phase and mainly exists in the crystal, and the aggregate is closely combined with the matrix. The fine pores in the matrix are evenly distributed. In the dolomite particles, the pericalcite and periclase crystals are fine and directly bonded; in the fused magnesia particles, the periclase crystals are large and directly bonded, the grain boundaries are relatively straight, and the cleavage seams are straight. Its microstructural characteristics determine that the material has a series of excellent properties such as resistance to high-temperature erosion and peeling. The latter has a lot of silicate phases and mainly exists in the intergranular, the combination of aggregate and matrix is not dense enough, and there are many pores and cracks in the matrix. Therefore, a series of properties such as its high-temperature corrosion resistance and peeling are poor.
The three impurity contents of high-quality fired magnesia dolomite bricks are all below 1.5%. American magnesia dolomite bricks contain 3 impurities above 2.0%. And other magnesia dolomite bricks in China have 3 impurity content above 3.0%. The relative erosion index of high-quality fired magnesia dolomite bricks is 25%~50% of that of the United States, and 16% of other magnesia dolomite bricks in my country. The spalling resistance of high-quality fired magnesia dolomite bricks is significantly better than that of similar products of LWB in the United States and is more than twice that of ordinary magnesia dolomite bricks in China.
"High-quality fired magnesia dolomite bricks for refining low-carbon and ultra-low carbon steel" have been tested by AOD furnaces in many steel factories at home and abroad, and have achieved better results than the current internationally renowned American magnesia dolomite bricks. For example, in a 180t AOD furnace, the service life of high-quality fired magnesia dolomite bricks is 279 times, breaking the world record of 269 times for magnesia dolomite bricks in the United States. The main raw material of this product is magnesia dolomite sand, which is natural dolomite sintered by an ultra-high temperature rotary kiln with heavy oil as fuel. Compared with the traditional coke or white coal firing method, it not only reduces the pollution of the fuel to the magnesium dolomite sand but also reduces the emission of pollutants. The use of high-quality magnesia dolomite bricks can increase the service life of the ladle, reduce the energy consumption and exhaust gas emissions of the ladle, reduce the number of furnace repairs, and reduce the cost per ton of steel. During the stay of molten steel in the ladle furnace, due to the action of free calcium oxide in high-quality magnesia dolomite bricks, the number and size of non-metallic inclusions inside the steel are reduced, and the quality of molten steel is improved. This product is resistant to high-temperature corrosion and peeling, especially for purifying molten steel. Create conditions for iron and steel enterprises to save energy, reduce emissions, reduce costs, and improve quality. This product has a huge demand in domestic and foreign markets, and is one of the development directions of metallurgical refractory materials in the future, with good development prospects.
