再生镁钙砖在水泥窑中应用的基础研究

发布时间：2018-08-08 11:12

【摘要】：水泥窑用镁铬砖中的Cr3+极易转变为剧毒的Cr6+,因此急需寻找一种环保的代替品。镁钙砖被认为是一种最可能替代镁铬砖的环保耐火材料,但是其易水化性,限制了其在水泥窑中的应用。用后镁钙砖中含有较多的Si02、Fe2O3、Al2O3等杂质,再生过程中这些杂质能够改善镁钙砖的抗水化性,从而制备成抗水化性能极强的再生镁钙砖。因此,再生镁钙砖不仅充分利用了用后镁钙砖的组成解决了水泥窑用镁钙砖的易水化问题,还减少了镁铬砖的污染问题。本论文将整块用后镁钙砖破碎混匀后,经煅烧处理并与电熔镁砂混合,以石蜡为粘结剂,合成了MgO含量分别为80wt.%、70wt.%、60wt.%的再生镁钙砖生坯,将其在1873K保温2h的条件下烧成,制备出相应的再生镁钙砖,实现了用后镁钙砖的大量利用,且再生镁钙砖结构致密,常温力学性能优良。对比分析在通空气条件和密闭条件下烧成制备的成再生镁钙砖,发现密闭条件下的烧成气氛为还原性气氛,导致了MgO的部分还原,再生镁钙砖的整体结构受到破坏。因此,氧化性烧成气氛较还原性气氛,更有利于提高再生镁钙砖的致密性、常温力学性能。在通空气条件下烧成制备了再生镁钙砖,并系统研究了其抗水化性能和水化机理。发现空气静置实验和热水实验后,再生镁钙砖最大的质量增加率分别为0.60wt.%和0.90wt.%,表现出了非常优良的抗水化性能。证明了游离氧化钙(f-CaO)的水化反应是导致再生镁钙砖水化的主要原因,再生镁钙砖中杂质SiO2、Fe2O3、 Al2O3等固定了部分f-CaO并提高了样品的致密性,二者共同提高了其抗水化性能。再生镁钙砖水化反应的控速环节为扩散控速,其扩散速度常数为0.70x10-6s-1,扩散速度常数很低。进而研究了再生镁钙砖在水泥窑中的使用性能,包括高温力学性能、抗热震性、挂窑皮性能。发现MgO含量为80wt.%的再生镁钙砖具有非常优良的高温抗折性能,而MgO含量为70wt.%、60wt.%的再生镁钙砖的高温抗折性能相对较差。MgO含量分别为80wt.%、70wt.%的再生镁钙砖具有优良的抗热震性能,而MgO含量分别为60wt.%的再生镁钙砖,由于其中含有较多的4CaO·Al2O3·Fe2O3,在实验中期大量断裂,导致其抗热震性能大幅下降。MgO含量分别为80wt.%、70wt.%的再生镁钙砖表现出了优良的挂窑皮性能,而MgO含量分别为60wt.%的再生镁钙砖的挂窑皮性能相对较差。再生镁钙砖的挂窑皮性能由水泥熟料与再生镁钙砖中MgO反应面积和反应层厚度共同决定。综合考察,MgO含量分别为80wt.%、70wt.%的再生镁钙砖较为适合使用在水泥窑中,其中用后镁钙砖的最大利用率为66.97wt.%。向MgO含量为70wt.%的再生镁钙砖混合料中添加总质量1.5wt.%、3.0wt.%的分析纯SiO2或Fe2O3,分别考察再生镁钙砖中主要杂质SiO2和Fe2O3对再生镁钙砖性能的影响。发现随着再生镁钙砖中SiO2含量的增加,导致3CaO·SiO2含量增加,而3CaO·SiO2的生成会固溶部分的Fe\Al元素形成固溶体,由此降低再生镁钙砖中4CaO·Al203·Fe203的含量,进而导致了再生镁钙砖体积密度、常温抗折强度的下降,而高温抗折强度和挂窑皮强度的提升。随着再生镁钙砖中Fe2O3含量的增加,再生镁钙砖中低熔点相2CaO·Fe2O3含量增加,导致了再生镁钙砖体积密度、常温抗折强度的提升,而高温抗折强度下降,挂窑皮强度呈先降低后升高的趋势。综合上看,再生镁钙砖中Si02的最大含量不应超过4.17wt.%, Fe2O3的最大含量不应超过1.57wt.%。再生镁钙砖中杂质元素的走向为：杂质Si元素以3CaO·SiO2的形式存在,Fe元素以2CaO·Fe2O3和4CaO·Al2O3·Fe2O3的形式存在,Al2O3以4CaO·Al2O3·Fe2O3的形式存在。其中,部分Al、Fe元素固溶在3CaO·SiO2中,部分的Fe元素固溶在MgO中。
[Abstract]:The Cr3+ in the magnesia chrome brick used in cement kiln is easily transformed into a highly toxic Cr6+, so it is urgent to find a kind of environmentally friendly substitute. Magnesia calcium brick is considered as a kind of environmentally friendly refractory material which is most likely to replace magnesia chrome brick, but its easy hydration property restricts its application in cement kiln. There are more Si02, Fe2O3, Al2O3 and other impurities in the magnesia calcium brick. In the course of birth, these impurities can improve the hydration resistance of magnesia calcium brick and make the regenerated magnesia calcium brick with very strong hydration resistance. Therefore, the regenerated magnesia calcium brick not only fully utilizes the composition of the magnesia calcium brick after use, but also solves the problem of the easy hydration of magnesia calcium brick used in the cement kiln, and also reduces the pollution problem of the magnesia chrome brick.
In this paper, after the whole block of magnesia calcium brick was crushed and mixed, the regenerated magnesia calcium brick with MgO content of 80wt.%, 70wt.% and 60wt.% was synthesized by calcining and mixed with electric fused magnesia, and using paraffin as binder. The regenerated magnesia calcium brick was prepared under the condition of 1873K insulation 2h, and the mass utilization of magnesia calcium brick was realized. The recycled magnesia calcium brick has compact structure and excellent mechanical properties at room temperature.
By comparing and analyzing the regenerated magnesia calcium brick prepared under the air condition and the airtight condition, it is found that the burning atmosphere under the closed condition is the reductive atmosphere, which leads to the partial reduction of MgO, and the overall structure of the regenerated magnesia calcium brick is destroyed. Therefore, the oxidation atmosphere is more conducive to the improvement of the density of the regenerated magnesium calcium brick. Mechanical properties at normal temperature.
The regenerated magnesia calcium brick was prepared by burning through air, and its hydration resistance and hydration mechanism were studied systematically. It was found that the maximum mass increase rate of the regenerated magnesia calcium brick was 0.60wt.% and 0.90wt.% after the air static test and the hot water test, showing the excellent hydration resistance. The hydration of free calcium oxide (f-CaO) was proved to be hydrated. The reaction is the main reason for the hydration of regenerated magnesia calcium brick. The impurity SiO2, Fe2O3, Al2O3 in the regenerated magnesia calcium brick fixed some f-CaO and increased the densification of the sample. The two all increased its hydration resistance. The rate of control of the hydration reaction of regenerated magnesia calcium brick was diffusion rate, the diffusion rate constant was 0.70x10-6s-1, and the diffusion rate was constant. The number is very low.
Then the performance of regenerated magnesia calcium brick in cement kiln was studied, including high temperature mechanical properties, thermal shock resistance and kiln skin performance. It was found that the MgO content of regenerated magnesia calcium brick with 80wt.% content was very good at high temperature resistance, while the content of MgO was 70wt.%, and the relatively poor flexural performance of 60wt.% was 80wt,.MgO content was 80wt, respectively. %, 70wt.% regenerated magnesia calcium brick has excellent thermal shock resistance, while the MgO content of regenerated magnesia calcium brick is 60wt.% respectively. Because it contains more 4CaO. Al2O3. Fe2O3, it has a large number of fracture in the middle of the experiment, resulting in a significant decrease in thermal shock resistance and.MgO content of 80wt.%. The performance of the kiln skin of the regenerated magnesium calcium brick with MgO content of 60wt.% is relatively poor. The performance of the kiln skin of the regenerated magnesia calcium brick is determined by the reaction area and the thickness of the reaction layer in the cement clinker and the regenerated magnesia calcium brick. The comprehensive investigation, the MgO content of the magnesia calcium brick is 80wt.%, and the 70wt.% calcium magnesia calcium brick is more suitable for use in the cement kiln. The maximum utilization ratio of the post - used magnesia - calcium brick is 66.97wt.%.
The total mass 1.5wt.% was added to the regenerated magnesia calcium brick mixture with MgO content of 70wt.%. The analysis of pure SiO2 or Fe2O3 in 3.0wt.% was studied. The effects of the main impurities, SiO2 and Fe2O3 on the properties of the regenerated magnesia calcium brick were investigated respectively. It was found that with the increase of SiO2 content in the regenerated magnesia calcium brick, the lead 3CaO. SiO2 content increased, and the generation of 3CaO. The solid solution part of the FeAl element forms a solid solution, thus reducing the content of 4CaO Al203 / Fe203 in the regenerated magnesia calcium brick, which leads to the volume density of the regenerated magnesia calcium brick, the decrease of the bending strength at normal temperature, and the increase of the flexural strength and the strength of the kiln skin. With the increase of the Fe2O3 content in the regenerated magnesia calcium brick, the low melting point phase 2CaO in the regenerated magnesia calcium brick The increase of Fe2O3 content leads to the volume density of the regenerated magnesia calcium brick, the increase of the bending strength at normal temperature and the decrease of the flexural strength at high temperature. The strength of the kiln skin decreases first and then increases. The maximum content of the Si02 in the regenerated magnesia calcium brick should not exceed 4.17wt.%, and the maximum content of the Fe2O3 should not exceed 1.57wt.%..
The trend of impurity elements in the regenerated magnesia calcium brick is that the impurity Si element exists in the form of 3CaO. SiO2, and the Fe element exists in the form of 2CaO. Fe2O3 and 4CaO. Al2O3. Fe2O3, and Al2O3 is in the form of 4CaO Al2O3.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ172.6;TQ175.71

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