超净煤分选过程中絮团形成机理的研究

发布时间：2018-08-26 14:14

【摘要】：我国煤炭行业目前处于转型的关键性时期,煤炭工作者们已经清楚的认识到煤炭的深度加工、精加工才是使煤炭行业重新焕发生命力的发展方向。超净煤(Ultra-clean coal)正是煤炭清洁利用中一个具有研究价值的领域,根据实际生产使用的需要,超净煤的灰分可以控制在1%以内甚至更低,超低灰的特征使超净煤不仅可以做为能源供给,也可以制备超级电容、石墨替代产品、电极以及应用于其他行业领域。目前,基于环保和节能的角度考虑最常使用的超净煤的加工方法是物理分选法中的疏水絮团-浮选法。对于疏水絮凝生成絮团已经有了系统的理论研究,但是缺乏关于超净煤制备过程中絮团形成机理的研究。因此,论文围绕着超净煤制备过程,从四个方面进行了研究和分析:探究了准备阶段煤样的解离方式对煤样几何特征、物理化学性质、机械力化学方面的影响;验证了絮团形成过程微细煤粒疏水絮凝发生的理论基础;研究了能量场中能量输入和药剂使用制度对絮团品质的影响;浮选过程中絮团的形态特征对其与气泡的碰撞及吸附的作用。第一部分的研究针对制备超净煤的基础工作:煤样的准备。为了研究超细粉碎方式对超净煤品质的作用机理并选择最适合超净煤加工需要的超细粉碎设备,考虑到超净煤制备超细粉碎加工需要及现有的超细粉碎加工设备,选用搅拌磨、胶体磨、气流磨和球磨四种超细粉碎设备对煤样进行加工,对超细粉碎加工后煤样的解离度、表面形貌、官能团含量、比表面积、孔径分布、表面电位等的变化进行了进一步的研究和分析,试验分析发现最适合的超细粉碎加设备是胶体磨。对煤粒的几何特征分析表明,胶体磨加工后煤样粒度分布范围大,粗细粒含量最均匀,表面呈现沟状形貌,起伏不平,无明显断裂痕迹,具有最大的平均粗糙度2.27nm,表明胶体磨使样品新生成表面增多,更多的官能团和分子簇显露,有利于絮团形成。对煤样的界面化学性质的分析表明,胶体磨加工后煤样固液界面张力最大,为62.22m J/m2,接触角最大,为109.70°,表明煤粒之间的水分子更容易被排开而形成絮团。对煤样表面的官能团分析发现,胶体磨加工的煤样表面疏水基团与亲水基团吸收峰面积相对含量的比值最大,为0.229,可以使煤样更有效地细化,使表面官能团更充分的暴露;胶体磨加工使煤样具有更大的比较面积和较大的孔隙直径,药剂更容易在煤样表面铺展和吸附;同时,胶体磨加工后煤样与非极性油反应的润湿热最大,为-1.384J/kg,与非极性油作用效果的最强烈,不仅利于非极性油药剂在煤颗粒表面吸附和铺展,并且提高颗粒表面的疏水性使颗粒间的油桥连接作用更紧密。对于煤样表面机械力化学性质的研究表明,煤样的微晶参数呈现一定的规律性变化,其中d(002)由小到大依次为:胶体磨、气流磨、搅拌磨和球磨,胶体磨和气流磨加工后的煤样,煤晶核堆砌高度较高,平均直径较大。胶体磨加工后的煤样显现出更接近石墨晶格形态的特征,有较高的变质程度相关参数,利于后续絮团的形成。此外,胶体磨在不同的酸碱环境中具有较低的Zeta电位,等电点略高,颗粒表面的电负性大,颗粒间的静电排斥力大,因此在形成絮团的初期过程需要更多的机械能的输入才能显现出优势。第二部分的研究是针对煤粒疏水絮凝过程的理论分析,测算絮团的絮凝率发现煤样自身的疏水性是发生疏水絮凝的基础,通过控制絮团形成过程中机械能的输入以及添加非极性油的方法强化煤粒的疏水絮凝效果。对煤粒发生疏水絮凝形成絮团过程中体系内势能的变化过程进行了定量计算,发现传统的胶体稳定性理论理论并不能合理解释体系内势能变化,需要使用EDLVO理论,引入疏水势能才能合理的解释微粒发生絮凝的过程。在计算体系能势能过程中,需要使用表征煤粒表面荷电作用范围的德拜长度,而目前有关于混合物煤炭表面的该常数并没有明确的数值,德拜长度关系到煤泥水沉降、煤样的选择性絮凝、疏水絮凝、煤样的表面改性、成浆性质的影响、微细煤粒在溶液中的分散与聚集状态等的理论研究和计算。论文选用原子力显微镜(AFM)进行力-距离曲线的测量,通过EDLVO理论反推煤样表面的德拜长度。为了使力-距离曲线精确反映同种煤样之间作用力随距离之间的变化过程,采用探针修饰技术,对氮化硅探针进行修饰,使用抛光后的同种煤片做为基底,置于溶液环境中进行试验测试,选用变质程度不同的鄂尔多斯长焰煤、神木不粘煤、淮南气煤和太西无烟煤在水溶液、酸溶液、碱溶液中分别进行测试。试验发现样品在不同酸碱环境中德拜长度的变化范围在1.12-9.78×10-9m之间,对于同种煤样,随着溶液PH值的增加,德拜长度增加;对于不同种类的煤样,随着煤样变质程度的增加,德拜长度减小。因为随着溶液环境中OH-离子含量的增加,更多的H+离子向煤样表面靠拢、聚集、吸附,导致形成的双电层厚度增加;随着煤样变质程度的增加,煤样表面含氧官能团和带负电官能团减少,煤样表面的负电性降低,在相同的酸碱环境中,煤样表面的双电层厚度较小。第三部分的研究针对絮团形成过程中能量输入以及各种药剂的添加对疏水絮凝的强化作用机理。有关机械能输入作用机理的研究,通过分析微粒疏水絮凝过程体系能势能变化曲线的方法,从理论上证明机械能为微粒提供的动能是煤粒越过能垒发生絮凝的必不可少的条件。通过在流场中对煤粒受力进行分析,从理论上分析了适量的机械能输入可以促进絮团的生成,过量的机械能反而会破坏已经形成的絮团,即存在最合适的机械能输入量。使用数学量纲分析的方法,使用搅拌速度表征机械能输入,建立了絮团形态特征与机械能输入量之间的关系,基于分形维数的分析方法,分析机械能输入过程中絮团形态的变化特征及规律。分析发现,分形维数随着搅拌速度的增加而增加,在2000r/min处达到峰值为1.762,随后,搅拌速度继续增加,分形维数迅速减少最终维持在1.74左右。由于絮团的分形维数体现了絮团的密度,即絮团的密实程度,在搅拌速度为2000r/min处,絮团具有最大的分形维数,结构紧实粒径合适。多重分形分形图谱显示在500-2000r/min之间,f(αmax)从0.677增加到0.796,f(αmin)从1.483减少到1.202,表明小概率对象即大颗粒的数量在此阶段显著增加,大概率对象即小颗粒的数量在此阶段显著减少,在2000r/min之后,f(αmax)明显减少后平稳,f(αmin)明显增加后平稳,表明在此阶段体系内大絮团碎裂成小絮团,直至絮团的生成和碎裂达到动态平衡。结合机械能输入与超净煤分选效果的试验结果,认为悬浮液体系内絮团平均粒径较大,大颗粒含量较高,絮团形态较均一时,最利于超净煤的分选。有关药剂种类对疏水絮凝影响的研究发现非极性油珠与煤粒之间总势能曲线存在一个很小的能垒及一个较大的能谷,非极性油可以自发在煤粒表面顺利的吸附和铺展,此时适量的机械能的输入可以加速非极性油和煤粒相互靠近,使之成功发生粘附。通过对比不同接触角的煤样添加非极性油前后聚团效率的变化,发现随着接触角的增加,非极性对煤粒聚团效率的促进作用增加,在接触角大于80°以后这种促进作用涨幅开始变小,表明只有当矿物表面的疏水性足够显著时,非极性油对矿物的疏水絮凝效果才能有效体现,即非极性油对疏水絮凝促进作用的本质是煤粒自身的疏水性加快疏水絮凝的进程。此外非极性油的用量与絮团形态密切相关,合适的非极性油在煤粒之间的起到桥联作用使絮团体积迅速增长的同时,填充于絮团之间的空隙中,使絮团的结构接近规则的球状。其他药剂添加对煤样疏水絮凝效果的研究表明:(1)在强酸性溶液中,煤样表面荷正电,随着PH值的增加,煤样表面荷负电并且绝对值逐渐增加,煤粒之间的分散性逐渐增加,煤样表面Zeta电位小易发生絮凝,但同时高灰部分的矿物微粒也易发生絮凝,造成精煤产品产率增加的同时灰分也增高。通过分选试验发现超净煤产率和灰分随PH值的变化均呈现出一致的规律,即PH值越低,精煤灰分和产率均降低。通过上述分析认为,适当的增加矿浆的PH值,可以在一定程度上提高絮团品质达到降灰的效果,但是要同时考虑精煤产率的损失;(2)分散剂的使用,在一定程度上使降低了煤样中Al、Si元素的含量,表明添加分散剂脱除了絮团内部分黏土类矿物,改善了絮团的选择性;(3)抑制剂用量对Al、Si、S三种元素的重量百分比含量的影响只有在用量达到较高程度时才能体现,分选试验发现超净煤产品的产率及灰分变化较小。以超净煤制备过程中机械能的输入条件以及药剂用量做为因素,以超净煤的产率及灰分做为响应值,使用变质程度不同的三种煤样做为试验煤样,基于BBD试验设计法进行响应面分析,发现对于超净煤的产率及灰分,显著性依次排列为:药剂用量搅拌时间搅拌速度,交互作用的分析表明,对于超净煤产率,搅拌时间与药剂用量的交互作用起主导作用;对于超净煤的灰分,搅拌速度与药剂用量的交互作用起主导作用。第四部分的研究针对絮团在浮选过程中与气泡的矿化过程,通过建立图像捕捉分析系统,基于概率学统计分析针对疏水絮团与气泡的吸附及碰撞情况进行了研究。结果表明,碰撞效率随着絮团粒度的增加持续增加;当絮团粒径小于200μm时,吸附效率随着粒径的增加而增大,当絮团粒径大于200μm时,吸附效率反而随着粒径的增加而减小;絮团密度与絮团粒度之间存在关联,在10-170μm左右的范围内,絮团的密度随着粒径的增加而增大,增幅也显著增加,当絮团粒径大于170μm后,随着絮团粒径的增加,絮团的密度开始略微下降。絮团密度在170μm左右开始随粒度的增加而下降,而絮团与气泡的吸附效率在200μm左右开始随粒度的增加而下降,认为两者出现差异的原因是由于絮团粒径增加对吸附效率的促进作用在一定程度上抵消了絮团密度降低对吸附效率的阻碍作用。因此,絮团与气泡的碰撞效率主要由絮团的粒径决定,而絮团与气泡的吸附效率是絮团粒度与密度共同作用的结果,其中絮团的密度起主导作用。概率学统计分析数据表明,絮团与气泡的碰撞效率及概率呈现出相同的变化趋势,均随着絮团粒度级的增加而增加,只是增幅在逐渐变缓,吸附效率及概率呈现先增长后减小的变化趋势。出现这种现象的原因是,随着絮团粒度的增加絮团与接触的面积也随之增大,碰撞次数增加。对于较大的絮团,其惯性力较大,不易受流体影响,容易与气泡发生接触。此外,对于下落的絮团而言,促进其与气泡接触主要是惯性力的作用,惯性力的大小取决于絮团的粒度与密度,当粒度相同时,密度越大惯性力越大,颗粒受水力阻力的影响越小。由于随着粒度的增加,絮团的密度呈现先增加后略微减小的变化趋势。因此,在絮团长大到某一粒度,碰撞概率/效率的增加趋势开始变缓,吸附概率/效率开始出现减小的转折点。
[Abstract]:At present, the coal industry in China is in a critical period of transformation. Coal workers have clearly realized that the deep processing of coal and the fine processing are the development direction of revitalizing the coal industry. Ultra-clean coal can be used not only as an energy supply, but also as a supercapacitor, graphite substitutes, electrodes and other industries. Hydrophobic flocculation-flotation method in physical separation method. There is a systematic theoretical study on the formation of flocs by hydrophobic flocculation, but there is a lack of research on the formation mechanism of flocs in the preparation process of ultra-clean coal. Therefore, this paper studies and analyzes the preparation process of ultra-clean coal from four aspects: exploring the dissociation of coal samples in the preparation stage. The effects of different flocculation modes on the geometric characteristics, physical and chemical properties, mechanochemistry of coal samples, the theoretical basis of hydrophobic flocculation of fine coal particles during flocculation formation, the effects of energy input and reagent application system on the quality of flocs, and the collision and adsorption of flocs with bubbles during flotation were studied. In order to study the mechanism of ultra-fine pulverization on the quality of ultra-clean coal and select the most suitable ultra-fine pulverizing equipment for the processing of ultra-clean coal, considering the needs of ultra-fine pulverizing for ultra-clean coal preparation and the existing ultra-fine pulverizing processing equipment, the selection of ultra-fine pulverizing equipment is made. The dissociation degree, surface morphology, functional group content, specific surface area, pore size distribution, surface potential and other changes of ultra-fine pulverized coal samples were further studied and analyzed by stirring mill, colloid mill, pneumatic mill and ball mill. The most suitable equipment for ultra-fine pulverized coal samples was found to be ultra-fine pulverized equipment. Geometric characteristics of coal particles show that the particle size distribution of coal samples after colloidal grinding is large, the content of coarse and fine particles is the most uniform, the surface presents groove shape, uneven undulations, no obvious breaking marks, with the largest average roughness of 2.27 nm, indicating that colloidal grinding makes the sample generated more surface, more functional groups and molecular clusters appear. The analysis of the interfacial chemical properties of coal samples shows that the maximum interfacial tension is 62.22 mJ/m2, and the maximum contact angle is 109.70 degrees. This indicates that the water molecules between coal particles are easier to be separated and form flocs. The ratio of absorption peak area of water group to hydrophilic group is the largest, 0.229, which can make coal sample more refined and surface functional groups more fully exposed; colloid grinding makes coal sample have larger area and larger pore diameter, and the reagent is easier to spread and adsorb on the surface of coal sample; at the same time, coal after colloid grinding can be more effectively refined. The wetting heat of the reaction between the sample and the non-polar oil is - 1.384J/kg, and the effect of the interaction between the non-polar oil and the non-polar oil is the strongest. It is not only conducive to the adsorption and spreading of the non-polar oil on the coal particle surface, but also to the enhancement of the hydrophobicity of the particle surface, which makes the oil bridge connection between the particles closer. The micro-crystal parameters of the samples showed a certain regularity change, and the order of d(002) from small to large was: colloid mill, airflow mill, agitating mill and ball mill, colloid mill and airflow mill. The coal samples processed by colloid mill had higher stacking height and larger average diameter. In addition, the gel mill has lower Zeta potential, higher isoelectric point, larger electronegativity on the surface of particles, and greater electrostatic repulsion between particles. Therefore, more mechanical energy input is needed in the initial process of flocculation to show the advantages. According to the theoretical analysis of coal particle hydrophobic flocculation process, the calculation of flocculation rate shows that the hydrophobicity of coal sample itself is the basis of hydrophobic flocculation. By controlling the mechanical energy input in the process of flocculation formation and adding non-polar oil, the hydrophobic flocculation effect of coal particle is strengthened. It is found that the traditional colloid stability theory can not explain the change of potential energy in the system reasonably. It is necessary to use EDLVO theory and introduce hydrophobic potential energy to explain the flocculation process of particles reasonably. The Debye length of the surface charge range has no definite value about the surface constant of the coal mixture at present. The Debye length is related to the settling of slime water, the selective flocculation of coal samples, the hydrophobic flocculation, the surface modification of coal samples, the influence of slurry properties, the dispersion and aggregation of fine coal particles in solution and so on. In this paper, atomic force microscopy (AFM) is used to measure the force-distance curve, and the Debye length of coal sample surface is deduced by EDLVO theory. In order to accurately reflect the force-distance curve between the same coal samples with the change of distance, the silicon nitride probe is modified by probe modification technology, and polished. The same kind of coal slices were used as the basement and put into solution environment for testing. Ordos long flame coal, Shenmu non-stick coal, Huainan gas coal and Taixi anthracite were tested in water solution, acid solution and alkali solution respectively. The results showed that the Debye length of the samples varied from 1.12 to 9.78 in different acid-alkali environments. For the same kind of coal sample, the Debye length increases with the increase of solution PH value; for different kinds of coal sample, the Debye length decreases with the increase of coal sample metamorphism degree. With the increase of coal sample metamorphism, the oxygen-containing functional groups and charged functional groups on the surface of coal sample decrease, and the negative electrical properties on the surface of coal sample decrease. The mechanism of coagulation is studied. The kinetic energy provided by mechanical energy is proved theoretically to be the necessary condition for coagulation of coal particles crossing energy barrier by analyzing the variation curve of energy potential energy in the process of particulate hydrophobic flocculation. It is analyzed that a proper amount of mechanical energy input can promote the formation of flocs, but excessive mechanical energy will destroy the flocs that have been formed, that is, there is the most suitable mechanical energy input. The fractal dimension increases with the increase of stirring speed and reaches a peak value of 1.762 at 2000 r/min. Then, the stirring speed continues to increase, and the fractal dimension decreases rapidly and finally maintains around 1.74. The dimension reflects the density of the floc, i.e. the density of the floc. At the stirring speed of 2000 r/min, the floc has the largest fractal dimension and the compact particle size is suitable. The multifractal spectrum shows that between 500-2000 r/min, f (alpha max) increases from 0.677 to 0.796, f (alpha min) decreases from 1.483 to 1.202, indicating that the small probability object is the large particle. After 2000 R / min, f (alpha max) decreased significantly and then stabilized, and f (alpha min) increased significantly, indicating that the large flocs were fragmented into small flocs until the formation and fragmentation of flocs reached a dynamic equilibrium. The experimental results of separation efficiency of super-clean coal show that when the average size of flocs in suspension system is larger, the content of large particles is higher, and the morphology of flocs is more uniform, it is most advantageous to the separation of super-clean coal. In large energy valley, non-polar oil can spontaneously adsorb and spread on the surface of coal particles smoothly. At this time, appropriate mechanical energy input can accelerate the non-polar oil and coal particles close to each other, so that they can successfully adhere to each other. The effect of polarity on the coagulation efficiency of coal particles increases, and the increase amplitude of polarity on coagulation efficiency decreases when the contact angle is greater than 80 degrees. This indicates that only when the hydrophobicity of mineral surface is significant enough, the hydrophobic flocculation effect of non-polar oil on minerals can be effectively reflected, that is, the nature of non-polar oil on hydrophobic flocculation is coal particles themselves. In addition, the amount of non-polar oil is closely related to the morphology of the flocs. Suitable non-polar oil bridges the coal particles to make the floc volume increase rapidly, and fills the gap between the flocs, making the floc structure close to the regular sphere. The results show that: (1) in strong acidic solution, the surface of coal sample is charged positively. With the increase of PH value, the surface of coal sample is charged negatively and the absolute value increases gradually. The dispersibility of coal particles increases gradually. The Zeta potential of coal sample surface is small and easy to flocculate, but the mineral particles of high ash part are also easy to flocculate, resulting in the increase of the yield of clean coal products. The results show that the lower the PH value is, the lower the ash content and yield of clean coal are. Through the above analysis, it is concluded that increasing the PH value of pulp properly can improve the quality of flocs to a certain extent, but the same is true. When considering the loss of clean coal yield; (2) the use of dispersants, to a certain extent, reduced the content of Al, Si in coal samples, indicating that the addition of dispersants to remove some clay minerals within the floc, improved the floc selectivity; (3) inhibitor dosage on the weight percentage of Al, Si, S three elements only in the dosage reached a relatively high level. The results show that the yield and ash content of super-clean coal have little change. The input conditions of mechanical energy and dosage of reagent are taken as factors, the yield and ash content of super-clean coal as response values, and three coal samples with different deterioration degree are used as test coal samples, based on BBD test design method. Response surface analysis showed that for the yield and ash of super-clean coal, the order of significance was as follows: stirring speed of stirring time of reagent dosage, interaction analysis showed that for the yield of super-clean coal, the interaction between stirring time and reagent dosage played a leading role; for the ash of super-clean coal, the interaction between stirring speed and reagent dosage. The fourth part studies the adsorption and collision between hydrophobic flocs and bubbles by establishing an image capture analysis system based on probability statistical analysis. The results show that the collision efficiency increases with the increase of floc size. When the particle size is less than 200 micron, the adsorption efficiency increases with the increase of particle size. When the particle size is larger than 200 micron, the adsorption efficiency increases with the particle size.
【学位授予单位】：中国矿业大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TD94

【参考文献】