RHEOLOGICAL BEHAVIOR OF LOW-RANK COAL-WATER SLURRIES

The rheological behavior of low-rank coal-water slurries was studied using a Brookfleld Rheolog viscometer. A Sarpy Creek subbituminous coal from Montana, with particle sizes ranging from 0.044 mm to 0.223 mm, was used. The solids concentration in the slurry varied from 15 to 65 weight % and the temperature was maintained constant at 82°F. The rheological behavior of the slurry made from as received coal was compared with that of the slurry made from hot water dried coal

Coal-water slurries, made from both as received and hot water dried coal exhibited pseudoplastic behavior. The shear stress was found to be related to the shear rate by the power law model. As expected, the apparent viscosity was found to increase sharply with solids loading. It was also observed that the apparent viscosities of the slurries made from hot water dried coal were lower than those made from as received coal.     

石油磺酸盐表面活性剂在水煤浆制备中的应用

提出利用廉价易得的石油磺酸盐表面活性剂制备水煤浆。通过FTIR光谱分析了5种不同工艺的石油磺酸盐产品的结构,并考察了各种石油磺酸盐所成浆体的流变性、静态稳定性等因素。研究发现,原料馏分油中芳香类物质含量越多、对其磺化程度越高,所得的石油磺酸盐产品分散降黏性能越好,更适合作为水煤浆分散剂。结果表明,F#石油磺酸盐的成浆性能最好,当w(F#)=1 5%时,水煤浆中w(煤粉)可达65%,在25℃下剪切速率为100s-1时浆体的表观黏度为620mPa·s,可稳定贮存20d以上,达到了工业上对水煤浆性能的要求。     

Influence of sewage sludge on the slurryability of coal-water slurry

In this study, the maximum solids loading, stability and rheological properties of coal-sludge slurries were investigated and compared with those of coal-water slurries. The maximum solids content of coal-sludge slurry was much lower than that of coal-water slurry because of the ∼82% water in sewage sludge. NaOH addition as a pre-treatment of sewage sludge improved the maximum solids content to 61% and 60% for dispersants A₁ and A₂, respectively, for a sludge-coal mass ratio of 22.1:100. Compared to coal-water slurries, the stability of coal-sludge slurries was better, with no solid deposition after 96 h. Coal particles and sewage sludge formed a stable medium and settlement of large coal particles was prevented. All the coal-sludge slurries exhibited pseudo-plastic behavior; this type of fluid is shear-thinning and is easy to transport.     

Experimental study on the rheological behavior of tetrafluoroethane (R-134a) hydrate slurry

Information on the rheological characteristics of clathrate hydrate slurry is vital due to its diverse applications including hydrate slurry transportation as in seawater desalination by gas hydrate process, gas delivery through slurry pipelines, cold thermal energy storage, and secondary refrigeration by hydrate slurries. The current study experimentally investigated the rheological behavior of Tetrafluoroethane (Freon) hydrate slurry formed from R-134a and water serving as a medium for sea water desalination. Experiments were performed in a flow loop with a volume of 5.68?L and an inner pipe diameter of 21.5?mm, which was immersed in a constant temperature bath to maintain hydrate stable condition. Experiments were conducted with two phases in the loop; solid hydrate particles and liquid water. The hydrate solid volume fraction ranged from 15.8 to 31.7?vol%. Pressure drops along the straight section of the pipe were monitored while temperature, solid volume fraction and flow rate were kept constant at desired values. The experimental results indicated that Freon slurry can be considered as a pseudo-plastic fluid. The shear-thinning characteristics of Freon slurry became more pronounced as the hydrate solid fraction increased. An empirical power law type equation that relates the apparent viscosity of the Freon slurry to the hydrate solid volume fraction and shear rate was developed and compared with experimental values. The experimental results well supported the values of the apparent viscosity calculated from the modeled equations.     

Slip flow of coal water slurries in pipelines

Experiments were carried out on a pilot scale slurry transport apparatus to investigate slip flow behavior of coal water slurries (CWSs) in pipes with various diameters (25, 32, 40 and 50 mm). The effects of volume concentration, particle size and slurry temperature on wall slip behavior (wall slip velocity, critical wall shear stress and slippage contribution) were investigated. A numerical technique based on Tikhonov regularization was applied to determine the wall slip behavior. As the slurry temperature or the particle size increased, the critical wall shear stress was observed to decrease and the wall slip velocity was observed to increase significantly, while when the solid concentration was very close to the maximum packing fraction, a slight increase in volume concentration would lead to a rapid decrease in wall slip velocity and a sharp increase in critical wall shear stress. The temperature influence on critical wall shear stress and yield stress increased as volume concentration increased. At low wall shear stress, the slippage contribution was mainly dependent on the difference between yield stress and critical shear stress. While at high wall shear stress, it was dependent on both of the shear viscosity of the bulk slurries and the wall slip velocity.     

Egg White as an Environmentally Friendly Low-Cost Binder for Gelcasting of Ceramics

Slurries with different solids loading (34–50 vol%) of alumina were made with egg white (ovalbumin)–water premix. The ovalbumin content in the premix was decreased with increase in solids loading to lower slurry viscosity. The slurries were cast into bulk shapes and heated to 80°C, resulting in denaturation of ovalbumin forming a gel. The gelled samples were dried under controlled humidity and sintered in air to densities 94%–97% of theoretical. Alumina slurries formed with egg white (no water) were used to form tapes as thin as 60 μm in the sintered state.     

Preparation and rheology of biochar, lignite char and coal slurry fuels

Slurries of an Oil Mallee biomass char, a low rank coal char and sub-bituminous coals were prepared by mixing the finely milled solids with water and a range of additives including polyacrylic acid, charged copolymers D101 and D102, and sucrose. The resultant slurries were subjected to rheological characterizations including apparent viscosity and yield stress. The effect of the solid type, particle size distribution, and the additives on preparation of highly loaded slurries with the desired rheological behaviour were systematically examined in terms of apparent viscosity and yield stress. The additives D101 and D102 were found to be most effective in producing highly loaded suspensions with a low apparent viscosity and yield stress. Particle size distributions were manipulated to improve the solid loading. Suspensions produced by powder mixture containing equal weight precent of 30 min and 1 min milled powders gave a broad size distribution and is very effective in increasing the solid loading in slurries. The significant improvement in the solid loading was shown to be achieved by (i) increasing particle packing density via size distribution control and (ii) minimising the strength and number of the interactions between colloidal particles. The maximum solid loading of flowable (or relatively low apparent viscosity) slurries achieved with the Oil Mallee char is ∼40 wt.%, with the sub-bituminous coals 56-63 wt.%, and with the lignite char ∼65 wt.%. This study has shown that for low rank coals such as lignite, thermal and densification treatment is essential to achieve the solid loading of slurry fuel.     

湿法超细研磨中无机材料浆体的流变性研究

概述了无机材料超细粉体机械研磨制备中浆体的流变性能、流变性能的表征方法和流变学行为的经验方程模型.对影响超细粉浆体流变性能的参数(如固相含量、颗粒粒径和分布、形状、温度、pH值及分散剂)进行了讨论.对浆料流变学性能进行最优化以提高超细粉体的产量,降低能耗,提高产品细度.提出了今后的研究重点应放在湿法超细研磨过程中分散剂种类及用量对浆体流变学性能改变机理的研究,并建立可描述浆体流变性能与粉碎参数、分散剂用量、能耗和颗粒大小的数学关系.     

生物质水煤浆流变特性研究

以福建无烟煤、水葫芦、添加剂等制备生物质水煤浆,研究了其流变特性。结果表明：添加3％～3．5％的水葫芦及1％的分散剂制得的生物质水煤浆粘度在0．8～1．2Pa·s之间,且稳定性较好。生物质含量提高,生物质水煤浆的粘度逐渐上升;分散剂含量为1％时,能够制得流变性较佳的生物质水煤浆;搅拌强度的增加能够使生物质水煤浆的粘度降低;当温度低于60℃时生物质水煤浆的粘度随温度升高而下降;当温度高于60℃时,生物质水煤浆的粘度随温度升高而上升。     

Spray drying water soluble organic dyes: Effect of morphology and crystal habit on process and product properties

Water soluble reactive dyes for cellulose are spray dried from high solids brine slurries and are commercially available in granular form. The physical form, size and structure of the grains directly affects the bulk density, friability and solubility parameters and may be significantly influenced by the parent dye morphology and habit. Isolated dye paste solids and the rheological behaviour of the slurry prior to drying are also affected.The interactions, control and influence of dye morphology and habit on the process, drying and resultant grain properties are discussed.     

高岭土悬浮液的流变性质

<正>1引言高岭土在水中分散形成絮凝悬浮液,此体系中固相的体积分率、粒子形状和粒径分布、表面电荷和流动类型等,都在不同程度上影响其流变特性。有关此问题的研究工作尚不多。文献中已有的悬浮液流变模型大都是针对刚性球形粒子形成的悬浮液,粒于之间无相互作用,此时影响悬浮液表观粘度的主要因素是固相体积分率。     

Effect of particle size on the rheology of Athabasca clay suspensions

The success of the separation process conventionally used in Alberta for oil sands extraction is highly influenced by the rheology of the oil sands slurry. In the gravity separation vessel, high slurry viscosities can hinder the rise of aerated bitumen and reduce the efficiency of the recovery process. In this study, the effect of particle size on the viscosity of oil sands slurries is investigated. Solids from mature fine tails (MFT) obtained from tailings pond were fractionated into three fractions of different particle size distributions and their rheological properties were studied. The solids in each fraction were characterized by XRD analysis which showed the presence of different types of clays in each fraction. For the rheological measurements, dispersions of the three fractions were prepared in the supernatant water decanted from centrifuged MFT to maintain the solution chemistry of the solids. Suspensions of each fraction showed a non‐Newtonian shear thinning behaviour as well as yield stress that is characteristic of structure formation within the suspensions. For all solids fractions, increasing solids concentration led to higher viscosities and higher yield stress values. Viscoelastic properties of the suspensions showed stronger solid‐like behaviour at higher particle concentrations. Among the three fractions numbered from 1 to 3, solids in fraction 3 were coated with organic matters, exhibiting the highest suspension viscosities. Also for fraction 3, higher gelling potency was observed at much lower weight fractions of solids as compared to the other fractions.     

Laboratory studies of the grinding and rheology of coal—water slurries

The laboratory ball mill grinding of coal—water slurries is described for three coals. Emphasis is placed on the measurement of specific rates of breakage for various operating conditions. Corresponding rheological information is also presented based on data collected using a rotational viscometer. A rheological explanation of the influence of various slurry fluidity conditions on the specific rates of breakage is presented. This rheological approach has proved useful in both the identification of suitable chemicals for increasing breakage rates in coal—mineral slurry grinding and in the plant scale implementation of dense slurry grinding systems.     

Hydrothermal dewatering of lower rank coals. 1. Effects of process conditions on the properties of dried product

The hydrothermal dewatering of a Loy Yang Low Ash Victorian brown coal has been studied under a wide range of process conditions. The intra-particle porosity (<1 μm pore radius) determined by mercury porosimetry of the resulting dried products, a proxy for the maximum solids concentration of coal-water slurries, is reported as a function of reaction time, processing temperature, autoclave size and configuration and slurry concentration. Of these variables only the process temperature had a significant influence on the product intra-particle porosity, which decreased with increasing temperature. Other product variables were affected by a wider range of process conditions; increase in temperature and residence time and decrease in slurry concentration led to marked increase in loss of organic material to waste water, and the elemental composition of the product changed significantly with e.g. residence time. Drying of coal samples of particle sizes >50 μm gave products of constant intra-particle porosity but smaller coal particles gave products with higher intra-particle porosities as a result of agglomeration. Milling of the coal reduced the porosity of the dried coal at constant particle size.     

Rheological Behavior of Slurries and Consolidated Bodies Containing Mixed Silicon Nitride Networks

Two particle networks, each formulated with a different interparticle potential, were mixed to control the rheological properties of ceramic slurries and to develop claylike plasticity in consolidated bodies. A weakly attractive network, containing silicon nitride powder, alkylated with hexadecanol, was mixed with a second slurry containing flocculated (nonalkylated) silicon nitride powder. The elastic modulus and apparent yield stress of concentrated suspensions containing each constituent and their mixtures were found to increase with volume fraction according to a previously reported power law function (exponents of 4.8 and 3.75, respectively). Because of the large difference in the relative strengths of the two networks, the flocculated network overwhelmingly controlled the behavior of the mixed slurries when its volume fraction (relative to total solids) exceeded 0.30. Slurries were consolidated by pressure filtration, and the saturated bodies were tested in uniaxial compression. Bodies containing only alkylated powder packed to a high volume fraction and deformed at a low flow stress. The addition of small amounts of the flocculated network increased the flow stress to produce a body with rheological properties similar to clay.     

水基纳米SiC复合料浆的流变性能和稳定性

引言 纳米复相碳化硅陶瓷是在多相复合碳化硅陶瓷基础上发展起来的-种新型碳化硅陶瓷材料,通过引人第二或第三纳米增强相来同时实现细晶结构、梯度残余应力场、裂纹桥联、自增韧等增强增韧机理,从而获得多强韧化机理协同强化碳化硅陶瓷,已成为碳化硅陶瓷的研究方向之一[1-4].其中,纳米增强相在碳化硅基体(包括料浆、复合粉体、陶瓷)中的分布是制备纳米复相碳化硅陶瓷的关键和前提之一[5].     

水焦浆的流变特性与壁面滑移效应

在浆体流动试验系统上采用不同管径的直管考察了水焦浆的流变特性以及壁面滑移效应对水焦浆流动特性的影响。采用Tikhonov 正则化方法确定了水焦浆的真实流变特性和壁面滑移特性。结果表明：浓度为59.8%的水焦浆随剪切速率增大呈现由伪塑性流体到胀塑性流体的转变,浓度增加,水焦浆变为单一的胀塑性流体,当浓度达到63.4%时,水焦浆表现为由胀塑性流体到伪塑性流体的转变;水焦浆的流变特性对滑移速度的变化趋势具有较大影响,滑移速度在水焦浆为胀塑性流体时随剪切应力增加呈加速增加,水焦浆为伪塑性流体时滑移速度随剪切应力的增长速率变化不明显;滑移贡献率的变化趋势迟滞于流变特性曲线。     

Effects of sewage sludge on rheological characteristics of coal-water slurry

The coal-sludge slurry (CSS) containing coal, sewage sludge and water was prepared to study the effects of sewage sludge on rheological characteristics of the CSS. The yield stress, thixotropy and rheological type of CSS were investigated and compared with those of coal-water slurry (CWS). The results showed that the yield stress of CSS appears at the shear rate range from 0.05 to 0.14 s⁻¹. For CSS with the naphthalene sulfonate sodium formaldehyde condensate as dispersant and the sludge/coal mass ratio of 10:100, the yield stress can reach to 22.9 Pa. The thixotropy was quantitatively described by the thixotropy loop area, and sewage sludge can obviously improve the CWS thixotropy. The non-Newtonian behavior of CSS was characterized by a progressive decrease in viscosity with increasing shear rate at the shear rate range from 5 to 180 s⁻¹. By the analysis of FTIR, SEM and optical microscope, hydrophilic functional groups and colloidal structure of sewage sludge play the key roles on the different rheological characteristics of CSS and CWS.     

High-concentration coal–water slurry from Indian coals using newly developed additives

Coal–water slurry (CWS) holds promise to offer a long-term alternative to fuel oil, and also it is being conceived as an attractive fuel for power generation industry in India. The essential requirements of the CWS technology, viz., the additive package, concentration of additives, particle size distribution (PSD) of coal, solids loading, methodology for CWS formulation and its rheological properties, have been discussed and reported here. The effect of the two newly developed anionic additives in the formulation of CWS has been studied. The basic parameters were established taking beneficiated Ledo coal samples with 9.7% ash content. Ball milling of the coal samples in a wet grinding process could produce particle size distributions most suited for highly loaded CWS. Coal loadings to the extent of 70% in the CWS have been achieved using a concentration of 0.8 wt.% (on coal charge) of the naphthalene-based additive referred to as ‘P’. Using 0.9 wt.% of the naphthalene-toluene-based additive denoted as ‘R’, a coal loading of 69% has been achieved. The viscosities of the slurries were found to be below 1000 mPa s. The shelf lives of slurries were found to be 22 and 20 days with the use of additives P and R, respectively, in the CWS formulation. The two additives functioned well in CWS formulation with Sirka coal having relatively higher ash content (14.4%). Using the specified concentration of the additives P and R, the solid loadings of 67% and 65%, respectively, could be obtained under the established parameters. The lower values of solids loading from Sirka coal than that from Ledo coal in CWS formulation may be attributed to the higher percentages of oxygen-containing functional groups (O_OH and O_COOH), ash content and higher O/C ratio of Sirka coal.