半晶态硅酸盐固液分离及介尺度下分子流动机理研究

发布时间：2018-06-14 21:23

本文选题：硅酸盐 + 结晶状态　；参考：《天津大学》2015年博士论文

【摘要】：随着矿业和煤炭行业的发展进步,各种不同类型的半晶态硅酸盐材料层出不穷,由于硅源的提取工艺以及硅酸盐的合成工艺直接影响了硅酸盐材料的结晶状态和分子结构,进而会影响到固液分离效果。因此,研究宏观水平的过滤效果、介尺度水平的滤饼结构和毛细作用以及分子水平的结晶状态的耦合机制,并结合介尺度流场下的分子迁移理论及模拟方法,揭示半晶态硅酸盐材料的强化脱水机理,具有重要的理论意义和研究价值。本文针对高铝粉煤灰颗粒的特殊结构,即以莫来石和刚玉为基本构架,表面包覆着大量的无定形硅,在充分利用工业废热的前提下,提出了温度梯度脱硅工艺。温度梯度脱硅工艺原理是利用低温反应抑制高硅含量的羟基方钠石的产生,进而将高铝粉煤灰表面的非晶态硅充分脱除。应用该工艺可将脱硅粉煤灰中的铝硅比从1.92提高至2.51。由于温度梯度脱硅工艺得到的脱硅粉煤灰过滤困难,为此本文进一步研究了添加表面活性剂的强化脱水工艺与机理。结果表明,在添加量为浆液质量的0.6‰阳离子表面活性剂十六烷基三甲基氯化铵时,过滤速度可以提高至原来的2倍,滤饼含水率下降了13%左右。添加表面活性剂之所以能够强化脱水,是由于脱硅粉煤灰物料的分散度和滤饼毛细作用得到改善,同时水的表面张力得到降低,进而加速了滤饼孔道中的液体流动,最终改善了过滤效果。针对硅酸钙水热合成法生产工艺,研究了合成温度和合成时间对结晶状态的影响规律。通过跟踪从活性硅酸钙转化为硬硅钙石的过程,基于结晶状态、微观形貌以及化学成分分析构建了硅酸钙晶须的生长模型,该模型可用于指导不同结晶状态硅酸盐材料的过滤分离方法。依据硅酸钙晶须生长模型,研究了铝晶核促进硅酸盐结晶过程的工艺,结果表明加入铝晶核后可以显著提高结晶度,最高结晶度能够达到95%左右。在此基础上,从宏观水平、介尺度水平和分子水平分析研究了结晶状态与强化脱水之间的耦合作用机理。结果表明,半晶态硅酸盐材料结晶的过渡阶段,由于受到微观形貌、层间水释放、比表面积和水分赋存状态的影响,具有较优的过滤性能,而结晶状态良好的硬硅酸钙属于难过滤的物料。在强化脱水过程中,分子水平的结晶状态与宏观水平的脱水效果之间的耦合可以通过介尺度水平的滤饼结构进行研究,而处于介尺度条件下滤饼内的微孔通道,其内部流场的流动特性不同于与宏观流场,不仅需要考虑宏观的重力和压力作用,还需要考虑微孔中的毛细作用、分子间作用力、界面张力等。基于此,本文开展了介尺度流场中分子的流动特性研究。研究中定义了一个新的无量纲参数梯度数Gr,用来描述分子大小与速度梯度之间的关系。基于两相流模型和稀溶液模型,构建了分子迁移微扰理论,即以梯度数展开的动量方程、维森堡数展开的本构方程以及皮勒数展开的质量传递方程为基础,利用泰勒公式和微扰方法对分子在介尺度流场中的流动进行数学演绎分析,得到分子的应力张量和浓度分布的理论计算方法。以泰勒涡流场为计算流场,对比了分子迁移微扰理论解析解与布朗动力模拟解,验证了介尺度条件下分子迁移微扰理论的正确性并得到分子迁移微扰理论的应用范围,即分子迁移微扰理论可以应用于梯度数Gr低于0.208,韦森堡数Wi低于0.012,皮勒数Pe低于10的流场中。以含有附加电场的微孔流场为研究背景,从流场的流体动力相互作用以及对流扩散程度两个方面,对比分析了布朗动力模拟和随机旋转动力模拟在介尺度分子迁移流场中的应用,得到了布朗动力模拟在介尺度分子迁移计算中的适用范围,即在流体动力相互作用h*小于0.27时,Pe数低于500时,可以使用布朗动力模拟方法,而当流体相互作用和对流强度较高时,必须采用计算成本较高的随机旋转动力模拟方法。本文的研究结果为硅酸盐的合成工艺和过滤分离方法提供了理论依据,为介尺度水平下分子迁移规律提供了计算方法,对半晶态硅酸盐材料的固液分离工艺及微孔流场内颗粒流动规律的研究具有重要的意义。
[Abstract]:With the development and progress of the mining and coal industry, various types of semicrystal silicate materials emerge in endlessly. Because the extraction process of silicon source and the synthesis process of silicate have a direct effect on the crystalline and molecular structure of silicate materials, it will affect the effect of solid-liquid separation. Therefore, the filtration effect of macro level is studied. The coupling mechanism of mesoscale filter cake structure and capillary action and molecular level crystallization state, combined with the molecular migration theory and simulation method under the mesoscale flow field, reveals the strengthening dehydration mechanism of the semicrystal silicate material, which has important theoretical significance and research value. This paper is aimed at the special junction of high alumina fly ash particles. With mullite and corundum as the basic framework, a large number of amorphous silicon is coated on the surface, and a temperature gradient desilication process is put forward on the premise of making full use of industrial waste heat. The principle of temperature gradient desilication is the production of hydroxyl sodium stone with high silicon content by low temperature reaction, and then the amorphous silicon on the surface of high aluminum fly ash. The application of this process can increase the ratio of aluminum and silicon in desilicon fly ash from 1.92 to 2.51. due to the temperature gradient desilication process, which is difficult to filter. Therefore, this paper further studies the strengthening dehydration process and mechanism of adding surfactants. The results show that the addition amount of 0.6 per thousand cationic surface is added to the slurry quality. When the active agent is sixteen alkyl three methyl ammonium chloride, the filtration speed can be raised to 2 times, and the water content of the filter cake is reduced by 13%. The reason that adding surfactants can strengthen the dehydration is due to the improvement of the dispersity of the silica fly ash material and the capillary action of the filter cake, the surface tension of the same water is reduced, and then the filtration is accelerated. The liquid flow in the cake channel eventually improved the filtration effect. According to the process of calcium silicate hydrate hydrothermal synthesis, the influence of the synthesis temperature and time on the crystallization state was studied. The silicic acid was constructed on the basis of the crystallization state, micromorphology and chemical composition analysis by tracking the conversion from active calcium silicate to hard silica. The growth model of calcium whisker can be used to guide the filtration and separation of silicate materials with different crystalline states. Based on the growth model of calcium silicate whisker, the process of promoting the crystallization of silicate by aluminum nucleation is studied. The results show that the crystallinity can be significantly increased after adding aluminum nucleation, and the highest crystallinity can reach about 95%. On the basis of the analysis, the coupling mechanism between the crystallization state and the intensification dehydration is studied from the macro level, the mesoscale level and the molecular level. The results show that the transition stage of the crystallization of the semicrystal silicate material has a better filtration performance due to the influence of the micromorphology, the release of interlayer water, the specific surface area and the water distribution state. In the process of strengthening dehydration, the coupling between the crystalline state of the molecular level and the dehydration effect at the macro level can be studied through the mesoscale filter cake structure during the process of strengthening dehydration, while the microporous channel in the filter cake under the mesoscale condition is different in the flow characteristics of the internal flow field. In the macroscopic flow field, it is necessary to consider not only the macroscopic gravity and pressure effects, but also the capillary action, the intermolecular force and the interfacial tension in the micropores. Based on this, the flow characteristics of the molecules in the mesoscale flow field are studied. A new dimensionless parameter gradient Gr is defined to describe the molecular size and the size of the molecules. The relationship between the velocity gradient. Based on the two phase flow model and the dilute solution model, the theory of the molecular migration perturbation is constructed, which is based on the momentum equation expanded by the ladder number, the constitutive equation of the expansion of the Vivien number and the mass transfer equation of the Peeler number expansion, and the flow of molecules in the mesoscale flow field by the Taylor formula and the perturbation method. The theoretical calculation method of molecular stress tensor and concentration distribution is obtained by mathematical deductive analysis. The Taylor eddy field is used to calculate the flow field. The analytical solution of molecular migration perturbation theory and the Brown dynamic simulation solution are compared. The correctness of the molecular migration perturbation theory under the mesoscale condition is verified and the application scope of the molecular migration perturbation theory is obtained. The theory of molecular migration perturbation can be applied to the flow field in which the number of ladder numbers Gr is below 0.208, the number of Weisenberg is less than 0.012 and the Peeler number Pe is less than 10. With the microporous flow field containing the additional electric field as the research background, the Brown dynamic simulation and the random rotation movement are compared and analyzed from the fluid dynamic interaction of the flow field and the convective diffusion degree in two aspects. The application of force simulation in mesoscale molecular migration flow field is obtained. The application range of Brown dynamic simulation in mesoscale molecular migration is obtained. That is, when the fluid dynamic interaction h* is less than 0.27 and the Pe number is less than 500, the Brown dynamic simulation method can be used. When the fluid phase interaction and convective intensity are high, the calculation must be used. The results of this paper provide a theoretical basis for the synthesis of silicate and the filtration separation method, and provide a calculation method for the molecular migration under the mesoscale level. The study on the solid-liquid separation process and the particle flow law in the micropore flow field of the semi crystalline silicate material is heavy. The meaning of it.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ170.1

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