Settling stability of coal slurries prepared by wet grinding in the szego mill

Static sedimentation experiments on coal-#2 oil and coal-water slurries, wet ground in a Szego mill, were conducted. These slurries contain more flaky particles as compared to those conventionally ground. Concentration and size distribution of the coal, diameter and height of the settling columns and settling time were the independent variables. Coal concentration and particle size distribution along the columns, and settling rates were measured. Despite their particle shape differences, these slurries were similar to others in terms of settling stability due to particle flocculation.     

Clusters Formation during Sedimentation of Dilute Suspensions

Abstract

Particle interactions in dilute monodispersed sedimenting suspensions of spherical particles are studied as a function of solid concentration. It is shown that in suspensions with solid concentrations below 0.83%, the interactions are too insignificant to effect the use of Stokes' law in sedimentation results. Beyond this concentration, however, a definite change in suspension behavior occurs, as particles come close enough to form clusters of varying sizes causing faster settling rates. Optimum clustering takes place around 4.5%-solid concentration, corresponding to mean interspacing of 2.2 particle diameter within suspension and giving settling rates 1.58 times faster than the Stokes' velocity for a mean particle. Clusters start breaking beyond this concentration as the sedimentation becomes more hindered and the return upward flow of liquid becomes increasingly tortuous. The probability of clusters formation and their stability as a function of particle size, concentration, and the Reynolds number of suspensions are also investigated. The studies are further extended to demonstrate the effect of “immobile” liquid within the clusters in interpreting the sedimentation results.     

Properties and rheology of coal-water mixtures using different coals

The properties, settling rates, and the rheology of coal-water mixtures (CWM) made up from different coals were investigated. Test suspensions containing different concentrations of suspended particles were made up from each of four different pulverized parent coals: a Pittsburgh Seam No. 8 coal, an Illinois coal, and the product and feed from a flotation process using an Illinois coal. All the parent coals had broad particle-size distributions. In addition, the Pittsburgh Seam No. 8 coal was classified into four different size fractions using sieving, resulting in three coarser, narrow particle size cuts and the fine residual fraction passing 325-mesh, which had a broad size distribution. The property characterizations for all coals included the following: elemental analyses, heating values, particle size analyses, particle surface areas and pore sizes, solid heat capacities, and thermal conductivities. Tests on the suspensions included detailed supernatant ion analyses, and measurements of pH values and zeta potentials. For each test coal maximum-packing volume fractions were estimated using centrifugation, and the settling rates and directly measured yield stresses, using the vane method, were determined for every concentration of coal-water mixtures (CWM) used. The shear-stress/shear-rate dependences of the test suspensions, covering the shear-rate range from 0.1 to 10⁵ s⁻¹, were determined using a capillary rheometer. For some of the test suspensions, correction for a pronounced wall-slip effect was required. Apart from the directly measured yield stresses using the vane method, yield stresses were estimated indirectly by extrapolation and rheological model-fitting. Extrapolation of directly measured yield stresses to infinite limit was used to estimate maximum packing for comparison with those determined from the irreducible sediment volumes using centrifugation. The two-parameter power-law, Bingham plastic and Casson empirical rheological models, and the three-parameter Herschel-Bulkley and Sisko models were used to fit the shear-stress/shear-rate data. In general, the shear-stress/shear-rate dependence was found to be shear-thinning, power-law, over the lower ranges of shear, and to tend to Newtonian limit at high shear; a dependence which is best described by the three-parameter Sisko model.     

Jamming rheology of model cementitious suspensions composed of comb‐polymer stabilized magnesium oxide particles

The colloidal microstructure of concentrated suspensions containing anionic comb‐polymer‐stabilized magnesium oxide (MgO) particles in water was analyzed by shear rheometry for indications of changes in particle microstructure based on particle size and comb‐polymer usage. As the suspensions were sheared at different rates, jamming in the sheared MgO suspensions was observed as shear stress overshoots. The shear‐induced evolution of the suspension's microstructure was strongly related to the perceived interactions between neighboring MgO particles in the suspension. In the jammed state, interactions are believed to be enhanced by the formation of entanglements between opposing comb‐polymer side‐chains. Steric repulsion between side‐chains was lessened for large particles on account of their diameters, which further enabled side‐chain entanglement during close particle contact under shear. Suspensions with relatively wide particle size distributions (0.5–400 μm) were theorized to form hydrocluster aggregates, while suspensions with narrower particle size distributions (0.5–40 μm) most likely resulted in networked microstructures under the influence of the chain entanglements from the adsorbed comb‐polymer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40429.     

Determination of the characteristics of agglomerates in aqueous suspensions using nonlinear optimization

Measurement of characteristics of particles in suspensions without dilution has a practical interest in formulation, mineral processing, material sciences and environmental technologies.These characteristics are the size, shape, and surface properties of the primary particles, and also the size, structure and the number of primary particles in the agglomerates.In this work, the multiple light-scattering model through the optical analyzer, Turbiscan MA 2000 is used to determine the mean settling velocities of monodisperse glass beads and two polydisperse samples of powders, kaolin D and alumina, differing by their particle size distribution, their shape and their surface properties.Beyond the experimental validation of theoretical and empirical predictions, the nonlinear adjustment of experimental settling data gives the number of primary particles per agglomerate and the agglomerate size. These two characteristics lead to the determination of the fractal dimension of the agglomerates. The latter was found in the range of 2.5-2.7 for all suspensions examined. The calculation of permeability and spherical factor reveals the nonspherical impermeable agglomerates.     

旋流内循环厌氧反应器中厌氧颗粒污泥特性研究

厌氧颗粒污泥是厌氧反应器高效、稳定运行的核心。在实验条件下,以旋流内循环厌氧反应器处理酒精废水为例,对厌氧颗粒污泥的形态、粒径、沉速以及产甲烷活性做进一步的研究。反应器运行120d后测各项指标,下反应室的厌氧颗粒污泥粒径集中在1.50mm～2.50mm之间,最大比产甲烷速率为328 mL/gVSS.d;上反应室的厌氧颗粒污泥粒径集中在0.5mm～1.00mm之间,最大比产甲烷速率为206 mL/gVSS.d。颗粒污泥的沉降速度最大近140 m/h,VSS/SS由启动时的0.60提高到了0.85。试验表明,旋流传质的水力条件较好,有利于形成沉降性能好和产甲烷活性高的颗粒污泥。     

Porous acrylonitrile/itaconic acid copolymers prepared by suspended emulsion polymerization

Porous acrylonitrile (AN)/itaconic acid (IA) copolymers were successfully prepared by suspended emulsion polymerization for the first time, with potassium peroxydisulfate (KPS) as an initiator, poly(vinyl alcohol) (PVA) as a dispersant agent, and Span80 as an emulsifier. The effects of the water/monomer mass ratio, agitation conditions, KPS concentration, PVA concentration, Span80 concentration,s and IA concentration on the average particle size and size distribution, particle morphology, and porosity of the AN/IA copolymers were investigated. The results show that the final AN/IA copolymers formed with agglomerates of primary particles had a porous structure, low particle density, and uniform particle size and did not agglomerate easily between the particles. The preparation conditions for the AN/IA copolymers were optimized as follows: (1) the water/monomer mass ratio was 0.3 : 1; (2) the concentrations of KPS, IA, PVA, and Span80 were 0.5, 12.4, 0.1, and 0.5 wt %, respectively, based on the weight of AN separately; (3) the agitation rate was 400 rpm; (4) the polymerization temperature was 70°C; and (5) the reaction time was 3 h. The size of the final AN/IA copolymer particles was in the range 200–400 μm. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

ENHANCEMENT OF THE SEDIMENTATION RATES OF FIBROUS SUSPENSIONS

The settling of suspensions of slender rod-like particles with large aspect ratios was studied. The novel technique of enhancement of sedimentation rates by the addition of buoyant particle promoters was applied to such suspensions. The settling rates could be increased by many times by this simple technique. Sedimentation velocity increases of between 5 to 7 times have been observed for fibrous suspensions of concentrations of about 0.5%. A statistical analysis of the experimental data was performed to establish a correlation for the enhancement in settling velocities. The sediment volume was unaffected by the presence of buoyant particles. The buoyant parjticles were found to adsorb some surfactants onto their surfaces.     

ENHANCEMENT OF THE SEDIMENTATION RATES OF FIBROUS SUSPENSIONS

The settling of suspensions of slender rod-like particles with large aspect ratios was studied. The novel technique of enhancement of sedimentation rates by the addition of buoyant particle promoters was applied to such suspensions. The settling rates could be increased by many times by this simple technique. Sedimentation velocity increases of between 5 to 7 times have been observed for fibrous suspensions of concentrations of about 0.5%. A statistical analysis of the experimental data was performed to establish a correlation for the enhancement in settling velocities. The sediment volume was unaffected by the presence of buoyant particles. The buoyant parjticles were found to adsorb some surfactants onto their surfaces.     

Analysis of dilute solid–liquid suspensions in turbulent stirred tanks

In this work, dilute suspensions of solid particles in stirred tanks are investigated by Particle Image Velocimetry measurements, which were specifically designed to determine the effects of the dispersed phase on mean velocity and turbulence levels of the continuous phase and the local solid–liquid slip velocity. In order to determine the effect of particle size and concentration, glass particles of narrow size distribution were selected; the particle content was increased stepwise up the maximum of 0.2 vol.%. Overall, moderate dampening of liquid turbulent fluctuations was found with the smaller particles, while turbulence enhancement was observed with the bigger ones. Continuous phase turbulence was found to affect the local map of the particle settling velocity, which was also discussed on the basis of a force balance analysis. The reduction of particle settling velocity due to free stream turbulence under specific conditions is confirmed.     

准能选煤厂煤泥水絮凝沉降优化试验研究

为改善准能选煤厂煤泥水沉降效果,在对选煤厂一系统煤泥水中煤泥矿物组成和粒度特性进行研究分析的基础上,对煤泥水进行了絮凝沉降试验,分别比较了絮凝剂类型、分子量(离子度)和用量对煤泥水沉降效果的影响;结果表明:选择阳离子度为70%~80%的阳离子型聚丙烯酰胺,用量为1 g/L时,上清液浊度为12.24 NTU,煤泥水体系Zeta电位最接近于零,煤泥水沉降效果达到最佳。     

Continuous and oscillatory flow properties of concentrated coal/water suspensions

A Theological characterization of coal/water suspensions has been carried out under continuous and oscillatory flow conditions. Shear stress - shear rate data were correlated with the Shangraw-Grim-Mattocks (SGM) equation. The analysis of the SGM parameters indicated that a limiting concentration ?₀ exists above which the suspensions exhibit plastic behavior and suggested that a strong particle aggregation still occurs at high rates of shear. Oscillatory flow tests revealed marked non-linear viscoelastic properties and analogies were found between the continuous and oscillatory flow behaviors of the coal/water suspensions, particularly under limiting flow conditions.     

Calculation of the hindered settling velocity of a bimodal mixture of solid particles of arbitrary shape in a Newtonian fluid

A method for calculating the settling velocity of a bimodal mixture of particles of arbitrary shape is proposed. The method uses the concept of effective particle diameter, which characterizes the particle shape, volume, and midsection area. The method takes into account the contact interaction between particles of different sizes due to their collisions. The calculation results are compared with experimental data on settling of bimodal mixtures of limestone particles of arbitrary shape.     

难沉降煤泥水组成及特点的研究

以山东某选煤厂的难沉降煤泥水为研究对象,利用现代分析测试手段,分析难沉降煤泥水的水质特性、矿物组成、粒度组成、表面电性等。结果表明导致煤泥水难沉降的主要原因是煤泥水中粘土矿物含量较高,泥化现象严重,颗粒粒度小,表面带有很强的负电荷,具有胶体稳定特性,从而导致其难以沉降。     

Ash Vaporization in Circulating Fluidized Bed Coal Combustion

ABSTRACT

In this work, the vaporization of the ash forming constituents in circulating fluidized bed combustion (CFBC) in a full-scale 80 MW_th unit was studied. Ash vaporization in CFBC was studied by measuring the fly ash aerosols in a full-scale boiler upstream of the electrostatic precipitator (ESP) at the flue gas temperature of 125°C. The fuel was a Venezuelan bituminous coal, and a limestone sorbent was used during the measurements. The fly ash number size distributions showed two distinct modes in the submicrometer size range, at particle diameters 0.02 and 0.3 μm. The concentration of the ultrafine 0.02-μm mode showed a large variation with time and it decreased as the measurements advanced. The concentration of the 0.02-μm mode was two orders of magnitude lower than in the submicrometer mode observed earlier in the bubbling FBC and up to three orders of magnitude lower than in the pulverized coal combustion. Scanning electron micrographs showed few ultrafine particles. The intermediate mode at 0.3 μm consisted of particles irregular in shape, and hence in this mode the particles had not been formed via a gas to particle route. We propose that the 0.3-μm mode had been formed from the partial melting of the very fine mineral particles in the coal. The mass size distribution in the size range 0.01–70 μm was unimodal with maximum at 20 μm. Less than 1% of the fly ash particles was found in the submicrometer size range. Ninety percent of Mg in coal was organically bound, and it was found to react with quartz and aluminosilicate minerals inside the coal particle. No Mg was found to be released to the gas phase and Mg mass fraction size distribution was size independent. A fraction of halogens CI, Br and I were found to be in the gas phase after the combustion.     

In‐Line Monitoring of Crystallization Processes Using a Laser Reflection Sensor and a Neural Network Model

Laboratory‐scale experiments were carried out for measuring the chord length distribution of different particle systems using a laser reflection sensor. Samples consisted of monodisperse, polydisperse and bimodal FCC catalyst and PVC particles of different sizes, ranging from about 20 to 500 μm. The particles were dispersed in water, forming suspensions with solid‐phase mass fractions ranging from ca. 0.2 % until ca. 30 %. The experimental results, consisting of the particle number counting per chord length class, were used in fitting a neural network model for estimating the mass concentration of particles in the suspension and the volume‐based size distribution, eliminating the effects of suspension concentration and particle shape. The results indicate the feasibility of using such a model as a software sensor in crystallization processes monitoring.     

RHEOLOGY OF VERY CONCENTRATED COAL SUSPENSIONS

Non-Newtonian viscosity curves of coal slurries were measured over a 3-5 decade shear rate range with a Weissenberg Rheogoniometer, for coal volume fractions up to 0.6 and particle sizes under 62 fim. Suspending media were Aroclor 1254 (a chlorinated biphenyl), glycerin, and glycerin with surfactant; these have densities very close to that of coal, so no settling occurred. Viscosity magnitudes generally exceeded predictions of correlations and theory established for spherical particles; explanations are sought in terms of particle aggregation, shape irregularity, and surface effects.     

RHEOLOGY OF VERY CONCENTRATED COAL SUSPENSIONS

Non-Newtonian viscosity curves of coal slurries were measured over a 3-5 decade shear rate range with a Weissenberg Rheogoniometer, for coal volume fractions up to 0.6 and particle sizes under 62 fim. Suspending media were Aroclor 1254 (a chlorinated biphenyl), glycerin, and glycerin with surfactant; these have densities very close to that of coal, so no settling occurred. Viscosity magnitudes generally exceeded predictions of correlations and theory established for spherical particles; explanations are sought in terms of particle aggregation, shape irregularity, and surface effects.     

Influence of Nanoparticles and Drop Size Distributions on the Rheology of w/o Pickering Emulsions

The rheological behavior of particle/oil suspensions and w/o Pickering emulsions consisting of water, 1‐dodecene and different fumed silica nanoparticles was investigated. The particles varied in hydrophobicity and specific surface area. The influence of particle concentration and water content on rheology was determined and the emulsion drop size distributions were examined. Emulsions with different drop sizes were created by either varying the particle concentration or the water content. It was found that the particles in the continuous oil phase and not the drop size distribution seem to be the major influencing factor on the Pickering emulsion rheology.     

钛磁铁矿的旋流离心连续分级实验

分析了旋流离心连续分选机的作用原理并用其对攀枝花钛磁铁矿进行分级实验. 结果表明,旋流离心连续分选机的给矿浓度、给矿压力、反冲水压力、溢流口压力和沉砂口压力等操作条件对沉砂的粒度分布均有明显影响,在给矿浓度5%、给矿压力70?72 kPa、反冲水压力5 kPa、溢流口压力40?50 kPa、沉砂口压力45?55 kPa的操作条件下,钛磁铁矿分级后0.15?2.00和0.074?0.15 mm粒级的颗粒分别占80%?83%和60%?65%,小于0.074 mm的颗粒仅占22%?28%.