- Time:Sep 04, 2023
China's refractory materials started late, and the development of related technologies was relatively slow. Until the 21st century, China's refractory material enterprises gradually began to imitate the production of magnesia-aluminum spinel bricks, but restricted by factors such as raw materials, processes, equipment and technology, in cement. The service life of the transition zone of the rotary kiln is generally 3-4 months, and the longest time is no more than 6 months. The kiln lining of the transition zone needs to be replaced 2-3 times a year. Affected by this factor, magnesia-alumina spinel bricks for cement rotary kilns in China have been monopolized by international brands such as Austrian Magnesium and Rayfa.
Until 2006, the ZJMA magnesia-aluminum spinel brick produced by Zhenjin Refractories broke this monopoly. In terms of raw material selection, production process, production equipment and production technology, it is synchronized with the international advanced level, so that the service life of the product in the second gear belt area of the transition zone of the new dry process cement kiln can reach more than one year, and it can be used with the firing belt kiln lining Maintaining synchronous operation reduces the number of kiln shutdown maintenance and creates considerable economic benefits for customers.
1. Why does the kiln use magnesia-alumina spinel bricks in the transition zone of the cement rotary kiln?
Magnesia-alumina spinel bricks are generally used in the transition zone of cement rotary kiln. This is because the temperature field in the transition zone of cement rotary kiln is easily affected by the change of coal injection pipe and fuel. Thermal fatigue phenomenon, general materials cannot withstand the rapid cooling and rapid heating caused by changes in the temperature field, resulting in damage to the lining bricks in the transition zone. Therefore, the refractory materials in the transition zone of cement rotary kiln must not only have high strength to resist mechanical stress, strong thermal shock resistance to prevent thermal fatigue damage, but also have good high temperature performance and corrosion resistance. At present, magnesia-aluminum spinel bricks account for 30-40% of the refractory materials used in cement kilns.
2. Why does the magnesia-alumina spinel brick produced by Zhenjin reach the advanced level in the world?
We demonstrate through use cases.
China Huaxin Wuxue Cement Company’s 6000t/d cement rotary kiln uses ZJMA8 magnesia-alumina spinel bricks made of domestic zhenjin refractories at 19-24 meters; R2CB magnesia-alumina spinel bricks of an internationally renowned brand are used at 27-35 meters. It will be ignited on July 27, 2022, and the annual maintenance will be carried out as planned until June 12, 2023, with a total of 320 days of operation. During the inspection of the kiln, it was found that the thickness of the remaining bricks of ZJMA8 magnesia-alumina spinel brick and R2CB magnesia-alumina spinel brick were both 180-200mm. And the ZJMA8 magnesia-aluminum spinel brick has no fault phenomenon.
The magnesia-aluminum spinel bricks produced by the two companies use the same raw materials and production process, and are used in the same position of the same cement kiln. It can be seen that the two are comparable in terms of technical strength and service life. Since China Refractories has adopted a new intelligent production line, the product cost has been well controlled, and the price of ZJMA8 is about 400 US dollars/ton cheaper than R2CB.
Not only that, the service life of ZJMA magnesia-alumina spinel bricks in the transition zone of various cement rotary kilns in the world has also reached more than 12 months. Among them, Huaxin Cement, the 17th largest cement company in the world by market value, has 14 cement kilns with a capacity of more than 5,000 t/d using domestic ZJMA magnesia-alumina spinel bricks and other refractory products of the company. In particular, the 6500t/d production line of Huaxin (Yangxin) Cement has been in safe operation for 456 days. This record has created the record for the longest safe use period in China's refractory industry.
Domestic magnesia-alumina spinel bricks can completely replace the magnesia-alumina spinel bricks of internationally renowned refractory companies, and become a new choice for global cement companies.
3. Advantages of ZJMA magnesia-aluminum spinel bricks produced by zhenjin refractories
3.1. Good thermal shock stability
Periclase and spinel in magnesia-alumina-spinel bricks have different thermal expansion coefficients, so some micro-cracks are formed during the firing process of the bricks. The formation of these micro-cracks plays a role in improving the thermal shock stability of the bricks. very important role. Utilizing the interaction between periclase and magnesia-aluminum spinel and adopting an appropriate ratio, the thermal shock stability of the brick can be optimized.
During use, it reacts with clinker to form a thin layer of calcium aluminate protective layer on the surface of spinel bricks, which makes the liquid phase not easy to penetrate, has good anti-stripping performance, and improves the service life.
3.2. Good corrosion resistance
The liquid phase in the cement clinker is mainly C4AF and C3A, and the component in the clinker that first penetrates into the brick is mainly C4AF. In the batching of bricks, multi-level batching is used to optimize the matrix in the bricks. When the liquid phase in the clinker enters the surface of the brick, it forms a high-temperature refractory phase to prevent the further infiltration of the liquid phase, which solves the problem of penetration and improves the corrosion resistance of the brick.
3.3. Good thermal expansion performance
The lining of the new dry-process cement kiln is basically a single-layer structure. The high thermal conductivity of the lining brick will cause the shell to overheat and deform, and cause serious energy loss.
Magnesia-aluminum spinel bricks have a low coefficient of thermal expansion and have little influence on temperature changes. The low coefficient of thermal expansion can reduce the thermal stress of the furnace lining itself and the shell, reduce refractory spalling and damage to the kiln body, thereby creating better conditions for reducing the kiln load and improving the operating rate and service life of the rotary kiln.
3.4. Good corrosion resistance and wear resistance
By optimizing the selection of raw materials, the magnesia-alumina spinel brick reduces the SiO2 and Fe2O3 that affect its stability to a reasonable range, improves the corrosion resistance of the spinel brick, and at the same time increases the strength at high temperature.
Through the adjustment of particle critical particle size and particle gradation and the use of high-tonnage brick press and ultra-high temperature sintering technology, the strength and wear resistance of magnesia-alumina spinel bricks have been improved, and the problem of spinel bricks in high temperature conditions has been solved. The problem of structural spalling caused by the infiltration and deterioration of cement clinker.
