水煤浆粒度级配模型和实践的研究进展

水煤浆是一种煤基液态燃料,具有与燃料油相似的物理特性,是煤炭高效清洁利用的一个重要途径,可显著减少NOx和SO2的排放。目前我国水煤浆需求量已突破2.5亿t/a,粒度级配作为影响水煤浆浓度的重要因素,使不同大小的煤颗粒互相填充,尽可能减少空隙,提高颗粒的堆积效率和水煤浆浓度。分析了粒度级配对水煤浆的影响,指出在水煤浆制浆过程中,粒度级配只涉及物理破碎和研磨,能耗相对较小,显著提升浓度,具有广泛的适用性和经济性。论述了近年来新发展的粒度级配理论和模型,特别是隔层堆积理论和分形级配理论,并给出了具体的计算方法和公式,以及假设和适用性。通过举例给出近年来隔层堆积理论的发展和应用,以及对于堆积效率的具体评价;分析了分形级配理论的可行性和新的研究进展,以及在指导烟煤和褐煤级配时的应用效果;给出了三峰级配的工艺流程、级配方案和工业实践案例。在粒度级配提高水煤浆浓度的基础理论和应用实践方面,国内外学者已做大量工作。但在具体的理论细节方面,如隔层堆积对于任意粒度分布的简化计算、分形级配的拟合精度以及三峰级配的粒度堆积评价还需更深入的研究。在级配理论应用于实践过程中,基础理论和工业实践的结合还有待于进一步提高。在粒度级配基础上,建议引入内在水分等影响因素,建立跨煤种的预测模型。     

分级研磨级配制浆技术的研究及应用

以分形理论为基础,推导得出可描述水煤浆粒度分布的分形级配模型,且通过粒度级配模拟软件,模拟煤颗粒堆积效率得出当分形维数Df=2.76时具有较高的堆积效率;以此为指导,综合考虑在工业装置上的可操作性,提出选择性粗磨和超细磨组合的分级研磨级配制浆技术,实现了水煤浆粒度分布优化与控制;同时,介绍了该技术在内蒙古伊泰煤制油有限责任公司的应用效果,即煤浆浓度提高2.8百分点,比煤耗降低29.9 kg/km3,比氧耗降低25.4 m3/km3,有效合成气比例提高2百分点。     

低阶煤煤泥和浮选精煤制备水煤浆的影响机制研究

以低阶煤煤泥(LS)和浮选精煤煤泥(LF)为原料,通过成浆性实验并结合两种煤泥煤样的粒度分布、表面特性、灰分特征、润湿特性及对分散剂吸附性的测试结果,对LS和LF制备水煤浆的影响机制进行研究。结果表明:分别使用LS和LF作为原料制备水煤浆,当分散剂添加量(干基分散剂与干基原料的质量比)从0%增加至0.7%时,LS的最高成浆浓度(干基煤粉与煤浆的质量比)从58%提高至59%;LF的最高成浆浓度从51%提高至57%;LF与LS相比,灰分质量分数从37.05%降低至13.62%,有机组成无变化,无机矿物中石英含量降低显著,粒度分布范围较窄,对分散剂的饱和吸附量降低;LS和LF煤样中颗粒的径距分别为2.22和1.51,LF中颗粒的堆积效率较低,粒度分布是造成LS和LF成浆性差异显著的主要因素,LF的颗粒较细且尺寸较为接近,煤样颗粒表面的静电力使LF颗粒容易团聚在一起,分散剂作用于粒度较细且粒径相近的LF时,主要用于抵抗分子间的作用力,从而造成LF分散剂消耗量大,采用LF制备水煤浆,需充分考虑粒度分布的影响,选用分散性能较优的水煤浆分散剂。     

不定形耐火材料颗粒级配的优化

针对生产实际情况 ,结合紧密堆积理论 ,建立了在给定的条件下如何选取最优配比的优化模型 ,并求解最优配比。通过将所配出坯料的粒度分布和按照经验配比给出的坯料的粒度分布与紧密堆积时 (Dinger-Funk方程 )的粒度分布进行比较 ,说明按最优配比配出的坯料 ,其粒度分布与紧密堆积时的粒度分布接近程度较好     

粒度级配对煤成浆质量分数的影响

水煤浆受煤的粒度、添加剂、不同煤种的内水分、煤种孔隙结构、含氧官能团和可磨性指数影响,成浆性能差别较大[1]。近几年由于油价和能源紧张,企业利润率较低,提高水煤浆浓度再次受到关注,水煤浆的粒度分布要求达到较高的堆积效率,即要求颗粒堆积时空隙小,而固体容积的浓度高,制备时使用单一粒径的煤颗粒很难达到高的最佳堆积效率。     

棉秸秆—水煤浆制备工艺的研究

分析了棉桔杆、水煤浆原料成分及煤炭的粒度分布情况,介绍了煤粉、水、棉秸秆粉、添加剂用量及棉秸秆—水煤浆制备试验流程,对浆体的测定结果表明,添加棉桔杆后,可以提高水煤浆的pH值和水煤浆的反应活性;分析认为,由于棉秸秆中大量纤维物质为网状结构,加入水煤浆中,降低了水煤浆的浓度和流动性,减缓了颗粒沉降,提了水煤浆的粘度和稳定性。     

城市污泥掺混水煤浆体系对粒度和浆体流变性能的影响

为了研究城市污泥(污泥)掺混水煤浆体系对粒度和浆体流变性能的影响,通过成浆实验考察了污泥水煤浆和同样实验条件下水煤浆的粒度分布和中位径。研究表明,两种浆体的粒度均呈双峰分布,污泥的加入能明显增加细颗粒的生成,并且随着分散剂添加量和湿法球磨时间的增加,细颗粒分布增加。此外,污泥水煤浆浆体中颗粒越小,累积分布含量的增长率越大,使得成浆浓度降低,表观粘度增大。     

级配粒度对宁东煤成浆性影响的研究

以宁东煤为研究对象,采用正交试验法进行了煤粉粒度分布对水煤浆成浆性能影响的分析研究。自制了不同颗粒区间的煤粉,并将各种粒径的煤粉配制成相同浓度的水煤浆,以水煤浆的黏度和流动性作为试验指标,探讨了不同粒度级配对宁东煤成浆性的影响。采用超声衰减粒度仪进行了粒度分布测定,并得到了分布曲线。试验结果表明:双峰级配的煤粉粒度级配合理,大颗粒和小颗粒之间相互填充,煤粉堆积效率达到最大,煤粉空隙中的水量最小,表现为浆体的黏度低、流动性好。     

贵州无烟煤制备水煤浆的研究

通过向无烟煤中加入4种不同分散剂制备水煤浆,优选出最佳的分散剂和添加量,然后通过Alfred模型研究了不同粒度分布对水煤浆性能的影响,并且与相同条件下烟煤制备的水煤浆性能进行对比。结果表明:萘系聚合物和磺化木质素是较好的分散剂,最优的添加量为1%,当Alfred模型参数N等于0.2时的粒度级配最佳,并且无烟煤的成浆性能明显优于烟煤。     

超硫酸盐水泥实际与最密集堆积的灰色关联度与抗压强度的关系

本文采用激光粒度分析仪测试超硫酸盐水泥粉体粒径,用以反映超硫酸盐水泥的粒径分布;采用机械压力法制备的超硫酸盐水泥干粉压实体,其空隙率可以宏观上反映颗粒间的物理堆积密实度;根据Dinger-Funk数学模型得出粉体最佳颗粒群分布即最紧密堆积颗粒群分布;运用灰色关联分析原理考察粉体实际颗粒群分布与最紧密堆积颗粒群分布的相关性;基于以上分析建立水泥净浆抗压强度与超硫酸盐水泥堆积效应的关系.试验结果表明:超硫酸盐水泥粉体实际颗粒群分布与最紧密堆积颗粒群分布的相关性越高,压实体空隙率越低,抗压强度越高.     

基于可压缩堆积模型的透水混凝土配合比设计

基于可压缩堆积模型,以全孔隙率为设计指标,提出了一种考虑成型过程和集料级配影响的透水混凝土配合比设计方法.该方法首先根据可压缩堆积模型挑选出干堆积密实度较高的级配集料,引入反映成型过程影响的比例因子λ建立了集料在透水混凝土中的堆积密实度与其干堆积密实度之间的关系,进而确定出单位体积透水混凝土的集料用量;然后根据集料用量和水灰比,计算得到透水混凝土的水泥浆体体积和水泥用量.对依据该方法设计的透水混凝土性能验证试验表明,实测全孔隙率与设计全孔隙率非常吻合,达到预设目标;透水混凝土强度随小粒径集料体积分数的变化趋势与集料干堆积密实度的相近,但是并非干堆积密实越高则强度越高,强度还受到集料粒径的影响.     

Dependence of Compaction Efficiency in Dry Pressing on the Particle Size Distribution

The compact densification with pressing pressure (compaction efficiency) was determined to be sensitive to the particle size distribution. For the three types of alumina powders used in this research, the compaction efficiency increased with increasing particle size. It has been demonstrated that if the compact density versus log (pressure) has a linear relationship for any two types of powders, so do the blends of the two powders. A model is proposed which can predict the compaction efficiency of a binary particle system based on the Furnas particle packing model and consider the packing efficiency as a function of forming pressure. The composition of the binary mixture at which the highest density is obtained under high pressures is also the composition having the largest compaction efficiency. When coarse particles were added to this composition, the compaction efficiency slowly decreased, and when fine particles were added, the compaction efficiency rapidly decreased. For a continuous particle size distribution, the highest compaction efficiency is related to the average value of -log (porefraction).     

高密实粉煤灰混凝土的配制与性能研究

探讨了高密实粉煤灰混凝土的配合比设计方法。依据骨料密实堆积观念 ,利用粗细骨料与粉煤灰按照大小粒径致密堆积在一起 ,获得混凝土中骨料间的最小空隙Vv ,再利用Vv来控制混凝土中的浆体用量Vp ,从而减少混凝土中的水泥用量和单位用水量。高密实粉煤灰混凝土由于其骨料颗粒搭配情况良好 ,堆积密实 ,有助于减少骨料间的滑动阻力 ,在高效减水剂作用下 ,能拌制出高流动性、易泵送的混凝土。同时 ,只需少量水泥浆 ,通过骨料间传递应力即可达到致密堆积混凝土的设计强度。工程试验表明 ,高密实粉煤灰混凝土技术性能优异 ,成本低 ,具有很好的应用前景     

Highly filled thermoplastic composites. II: Effects of particle size distribution on some properties

The effect of irregularly shaped glass particle size and size distribution on the packing density and flexural mechanical properties of highly-filled composites with a rubbery thermoplastic matrix was studied. Increasing the particle's median size and size distribution width significantly increases the packing density of the composites. Compression molding causes the glass particles to fracture at a decreasing level with an increasing distribution width. Particle median size, rather than size distribution, affects the mechanical properties; The flexural modulus and strength increase and the ultimate deflection in flexure decreases with a decreasing median size. A “glass network” is formed in the compression molded composites because of the mechanical interlocking of particles. The nature of this continuous glass phase predominates the composites mechanical behavior. The particle's size and shape determine the nature of the glass network and, thus, have a dominating effect on the mechanical properties. The latter are significantly affected by the particle's surface properties. A specific silane treatment of the glass particles acts to reduce the particle/particle friction, resulting in a higher packing density. The treatment also acts as a cohesive liquid to increase the strength of the glass network, and to increase the particle/polymer adhesion, increasing the composites' strength and ductility.     

Prediction of the porosity of multi-component mixtures of cohesive and non-cohesive particles

This paper presents an experimental and theoretical study of the packing of mixtures of cohesive (fine) and non-cohesive (coarse) particles. The experimental results, produced by means of a standard funnel packing method with glass beads as experimental materials, are first used to depict the similarity between the packings of fine and coarse particles. On this basis, the so-called linear packing model is extended to estimate the porosity of mixtures of fine and coarse particles with a wide size range. Its interaction functions and equivalent packing size are determined empirically. The applicability of the resultant model is demonstrated by the good agreement between the predicted and measured results for typical packing systems, including particles with the Gaudin–Schuhmann distribution or with a mixture size distribution. Finally, the packing of particles with a lognormal distribution, involving both cohesive and non-cohesive particles, is investigated in detail. This example also demonstrates how the proposed model can be used to solve a packing problem.     

Filtration in coal liquefaction. Influence of filtration conditions in non-hydrogenated systems

A series of experiments has been carried out to study the effects of filtration conditions upon the rate of filtration of non-hydrogenated coal digests. The results show the dependence of cake resistivity on both the filtration temperature and pressure. Filter cakes were found to be compressible, resulting in smaller increases in rate with increasing pressure than with incompressible cakes. The filtration temperature determines the packing of residual solids in the cake which in turn affects the cake resistivity. An empirical relation has been derived between filtration temperature and resistivity. With increasing temperature there is an increase in filtration rate due to the reduced viscosity, but a reduction owing to a higher packing density of solids in the filter cake.     

Experimental study of the packing of mono-sized spheres subjected to one-dimensional vibration

The packing of mono-sized spheres under one-dimensional (1D) vibration is studied experimentally. The effects of operational conditions, such as vibration amplitude A and vibration frequency ω, and feeding method on packing density have been analyzed. The results indicate that there exist optimum values for A and ω to achieve the maximum packing density. The effects of A and ω cannot be represented by a single parameter (i.e. vibration intensity Γ = Aω²), but should be considered separately. The number of particles fed per batch affects the packing density significantly within a range of one to four layers per batch, but otherwise has no visible effect. Through the extrapolation on packing density using different sized containers, packing density can reach 0.636 in the total feeding method and 0.663 using the batch-wise feeding method. The values, however, are affected by material properties. The experimental results have therefore testified our previous numerical work on the transition from random loose packing to random close packing [An et al., Phys. Rev. Lett. 95, 205502 (2005)].     

Measurement of coal particle size and shape with concentrated coal-water mixtures

The behavior of concentrated coal-water mixtures having narrow particle size ssfractions of coal was investigated. The pulverized coal was fractionated into six distinct particle size ranges, i.e. -70+80, -80+120, -120+140,-140+200, -200+400 and -400 mesh sizes by using a series of sieves. Settling rates were determined as functions of solids concentration for suspensions in water of coal particles to establish the measurement of particle size and shape factor and to assess concentration effect upon the observed hindered settling rates. The settling rates were modelled using the Richardson-Zaki model with the exponent n variable to account for the nonspherical shape of the coal particles. The data was also correlated with the Michaels-Bolger model which explicitly account for the excess water which is dragged down along with the particles undergoing sedimentation. In addition, coal particles and suspensions were characterized by coal analysis, heating value, solid heat capacity and thermal conductivity, densities, maximum packing concentrations and pore size distributions.     

Segregation in beds of large particles at high velocities

In some industrial fluidized bed processes, notably coal combustion, the bed contains a very wide size range (50 – 5000 μm) of equal density particles. In others the particles change their density as the reaction proceeds, giving a bed of particles having similar sizes but densities varying by a factor of up to 2.

Experiments have been done in a bed 0.29 m diam. at velocities up to 5 m/s, using coarse particles up to 6 mm. They show that segregation by density difference can be reduced to negligible proportions by using high velocities, but that segregation by size appears to be an intrinsic feature of coarse particle systems at all velocities when a very wide size range is present. A tentative form of equation is proposed for segregation by size; the equations of Rowe are useful predictors for segregation by density difference.     

Picobubble Enhanced Fine Coal Flotation

Abstract

Froth flotation is widely used in the coal industry to clean ?28 mesh fine coal. A successful recovery of particles by flotation depends on efficient particle‐bubble collision and attachment with minimal subsequent particle detachment from bubble. Flotation is effective in a narrow size range beyond which the flotation efficiency drops drastically. It is now known that the low flotation recovery of particles in the finest size fractions is mainly due to a low probability of bubble‐particle collision while the main reason for poor coarse particle flotation recovery is the high probability of detachment. A fundamental analysis has shown that use of picobubbles can significantly improve the flotation recovery of particles in a wide range of size by increasing the probability of collision and attachment and reducing the probability of detachment.

A specially designed column with a picobubble generator has been developed for enhanced recovery of fine coal particles. Picobubbles were produced based on the hydrodynamic cavitation principle. They are characterized by a size distribution that is mostly below 1 µm and adhere preferentially to the hydrophobic surfaces. The presence of picobubbles increases the probability of collision and attachment and decreases the probability of detachment, thus enhancing flotation recovery. Experimental results with the Coalberg seam coal in West Virginia, U.S.A. have shown that the use of picobubbles in a 2″ column flotation increased fine coal recovery by 10–30%, depending on the feed rate, collector dosage, and other flotation conditions. Picobubbles also acted as a secondary collector and reduced the collector dosage by one third to one half.