【摘要】：水泥窯用鎂鉻磚中的Cr3+極易轉(zhuǎn)變?yōu)閯《镜腃r6+,因此急需尋找一種環(huán)保的代替品。鎂鈣磚被認(rèn)為是一種最可能替代鎂鉻磚的環(huán)保耐火材料,但是其易水化性,限制了其在水泥窯中的應(yīng)用。用后鎂鈣磚中含有較多的Si02、Fe2O3、Al2O3等雜質(zhì),再生過程中這些雜質(zhì)能夠改善鎂鈣磚的抗水化性,從而制備成抗水化性能極強(qiáng)的再生鎂鈣磚。因此,再生鎂鈣磚不僅充分利用了用后鎂鈣磚的組成解決了水泥窯用鎂鈣磚的易水化問題,還減少了鎂鉻磚的污染問題。 本論文將整塊用后鎂鈣磚破碎混勻后,經(jīng)煅燒處理并與電熔鎂砂混合,以石蠟為粘結(jié)劑,合成了MgO含量分別為80wt.%、70wt.%、60wt.%的再生鎂鈣磚生坯,將其在1873K保溫2h的條件下燒成,制備出相應(yīng)的再生鎂鈣磚,實(shí)現(xiàn)了用后鎂鈣磚的大量利用,且再生鎂鈣磚結(jié)構(gòu)致密,常溫力學(xué)性能優(yōu)良。 對(duì)比分析在通空氣條件和密閉條件下燒成制備的成再生鎂鈣磚,發(fā)現(xiàn)密閉條件下的燒成氣氛為還原性氣氛,導(dǎo)致了MgO的部分還原,再生鎂鈣磚的整體結(jié)構(gòu)受到破壞。因此,氧化性燒成氣氛較還原性氣氛,更有利于提高再生鎂鈣磚的致密性、常溫力學(xué)性能。 在通空氣條件下燒成制備了再生鎂鈣磚,并系統(tǒng)研究了其抗水化性能和水化機(jī)理。發(fā)現(xiàn)空氣靜置實(shí)驗(yàn)和熱水實(shí)驗(yàn)后,再生鎂鈣磚最大的質(zhì)量增加率分別為0.60wt.%和0.90wt.%,表現(xiàn)出了非常優(yōu)良的抗水化性能。證明了游離氧化鈣(f-CaO)的水化反應(yīng)是導(dǎo)致再生鎂鈣磚水化的主要原因,再生鎂鈣磚中雜質(zhì)SiO2、Fe2O3、 Al2O3等固定了部分f-CaO并提高了樣品的致密性,二者共同提高了其抗水化性能。再生鎂鈣磚水化反應(yīng)的控速環(huán)節(jié)為擴(kuò)散控速,其擴(kuò)散速度常數(shù)為0.70x10-6s-1,擴(kuò)散速度常數(shù)很低。 進(jìn)而研究了再生鎂鈣磚在水泥窯中的使用性能,包括高溫力學(xué)性能、抗熱震性、掛窯皮性能。發(fā)現(xiàn)MgO含量為80wt.%的再生鎂鈣磚具有非常優(yōu)良的高溫抗折性能,而MgO含量為70wt.%、60wt.%的再生鎂鈣磚的高溫抗折性能相對(duì)較差。MgO含量分別為80wt.%、70wt.%的再生鎂鈣磚具有優(yōu)良的抗熱震性能,而MgO含量分別為60wt.%的再生鎂鈣磚,由于其中含有較多的4CaO·Al2O3·Fe2O3,在實(shí)驗(yàn)中期大量斷裂,導(dǎo)致其抗熱震性能大幅下降。MgO含量分別為80wt.%、70wt.%的再生鎂鈣磚表現(xiàn)出了優(yōu)良的掛窯皮性能,而MgO含量分別為60wt.%的再生鎂鈣磚的掛窯皮性能相對(duì)較差。再生鎂鈣磚的掛窯皮性能由水泥熟料與再生鎂鈣磚中MgO反應(yīng)面積和反應(yīng)層厚度共同決定。綜合考察,MgO含量分別為80wt.%、70wt.%的再生鎂鈣磚較為適合使用在水泥窯中,其中用后鎂鈣磚的最大利用率為66.97wt.%。 向MgO含量為70wt.%的再生鎂鈣磚混合料中添加總質(zhì)量1.5wt.%、3.0wt.%的分析純SiO2或Fe2O3,分別考察再生鎂鈣磚中主要雜質(zhì)SiO2和Fe2O3對(duì)再生鎂鈣磚性能的影響。發(fā)現(xiàn)隨著再生鎂鈣磚中SiO2含量的增加,導(dǎo)致3CaO·SiO2含量增加,而3CaO·SiO2的生成會(huì)固溶部分的Fe\Al元素形成固溶體,由此降低再生鎂鈣磚中4CaO·Al203·Fe203的含量,進(jìn)而導(dǎo)致了再生鎂鈣磚體積密度、常溫抗折強(qiáng)度的下降,而高溫抗折強(qiáng)度和掛窯皮強(qiáng)度的提升。隨著再生鎂鈣磚中Fe2O3含量的增加,再生鎂鈣磚中低熔點(diǎn)相2CaO·Fe2O3含量增加,導(dǎo)致了再生鎂鈣磚體積密度、常溫抗折強(qiáng)度的提升,而高溫抗折強(qiáng)度下降,掛窯皮強(qiáng)度呈先降低后升高的趨勢(shì)。綜合上看,再生鎂鈣磚中Si02的最大含量不應(yīng)超過4.17wt.%, Fe2O3的最大含量不應(yīng)超過1.57wt.%。 再生鎂鈣磚中雜質(zhì)元素的走向?yàn)椋弘s質(zhì)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.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ172.6;TQ175.71

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