Behavior Of Coal Water Slurry Research Articles

Effect of mixture of a non-ionic and a cationic surfactant for preparation of stabilized high concentration coal water slurry

ABSTRACT The rheological behavior of high ash Indian coal samples was investigated by blending fines (<38 µm) with four distinct coarse fractions (212–300 µm, 90–300 µm, 150–212 µm,75–150 µm). The blended four representative samples were labeled as S-1, S-2, S-3, and S-4, respectively for the study. The flow behavior of coal water slurry (CWS) was characterized with a mixture of non-ionic surfactant saponin from shikakai and a cationic surfactant di-docyl ammonium bromide (DDAB) at different coal loadings, Ph, and dispersant dosages. The concentration of DDAB in saponin was optimized on the basis of surface tension and apparent viscosity values. The non-Newtonian flow behavior of CWS in the studied range of concentrations (58–70% by weight) was fitted well to Bingham plastic model. A suitable mechanism of interaction between mixture of saponin and DDAB on coal surfaces was given on the basis of Zeta potential measurement.

Effect of mixture of natural and synthetic surfactant and particle size distribution for stabilized high-concentrated coal water slurry

ABSTRACT A medium ash coal is used for the study. Four different samples have prepared by blending fine fraction (<38 µm) with four distinct coarse fractions (212 µm – 300 µm, 90 µm – 300 µm, 150 µm – 212 µm,75 µm – 150 µm) in the ratio of 40:60 and named as sample 1, sample 2, sample 3, sample 4, respectively. These four samples mixed with mixture of natural and chemical additive solution, i.e. saponin from shikakai and SDBS (sodium dodecyl benzene sulfonate) to reduce the viscosity and increase the stability of the slurry. The flow behavior of coal water slurry were characterized at different coal loadings, pH, dispersant contents with and without presence of mixture of bio and chemical additive. The flow behavior of the slurry studied in the solid concentration range of (58–68) % by weight and the behavior is well fitted to the Bingham plastic model which indicates non-Newtonian behavior in nature. Out of four samples, sample 1 shows maximum coal loading, i.e. 68% in the presence of mixture of additive, i.e. saponin and SDBS. For the solid loading of 68% by weight the apparent viscosity is 1.3 PaS for the shear rate 147 S−1. The ratio of saponin and SDBS is optimized on the basis of surface tension measurement and apparent viscosity of coal water slurry. During surface tension measurement the value of surface tension is 14 mN/m at the point of optimization of surfactant mixture percentage, i.e. saponin:SDBS = 92:8 and the viscosity of the surfactant/additive mixture at this optimization point is 0.403 Pa.S. The rheological behavior of the slurry has been measured. Effect of zeta potential of the coal particle has been studied in the presence of mixture of additive solution (saponin and SDBS). A suitable mechanism has given to explain the interaction between additive solution and coal surface.

Rheological behavior of coal-water slurries of Indian coals using carboxymethylcellulose as dispersant- a comparative study

ABSTRACT The rheological nature of coal-water suspensions of two Indian coal samples (namely coal 1 and coal 2) was reported and compared in the shear rate range of 60–160 s−1 at constant pH of 8. Proximate and ultimate analysis were used to characterize the coal, and zeta potential and turbidity measurements were carried out to test the suitability and selection of carboxymethylcellulose (CMC) as a dispersant for the Coal Water Slurry (CWS). The effects of percentage solid loading, dispersant dosage on the rheological nature were studied. The rheological data was fitted for the power law model to categorize the slurry flow nature with reference to the calculated flow behavior index of the model. At lower solid loadings (10%, 20%), the shear stress-shear rate relation did not alter with the dispersant dosage and the slurries exhibited shear thickening behavior. The effects of the slurry parameters were quite predominant at 30%, 40%, and 50% solid loadings as they exhibited the shear thinning behavior. The slurry with 30% solid loading showed transition from shear thickening to shear thinning with the increase in dispersant dosage. For a given percentage of solids, a lower magnitude of shear stress versus shear rate, a wider distribution of flow behavior index and favorable pumpable characteristics were seen for coal 1 in comparison to coal 2 owing to their chemical nature and amount of ash-bearing mineral constituents.

Rheological behavior of coal-water slurry using sodium tripolyphosphate as a ​dispersant

ABSTRACT The rheological nature of coal-water suspensions of an Indian coal variety is reported in the shear rate range of 60–160 s−1. Sodium tripolyphosphate (STPP) is used as a dispersant or chemical additive for the slurries. The effects of percentage solid loading, dispersant dosage and pH on the rheological nature are comprehensively studied. The rheological data is fitted for power-law model to categorize the slurry flow nature with reference to the calculated flow behavior index of the model. At lower solid loadings (10% 20%), the shear stress-shear rate relation did not alter with the dispersant dosage or pH and the slurries of exhibited dilatant behavior. The effects of the slurry parameters are quite predominant at higher solid loadings (30%, 40%, and 50%). For pH ≥ 8.0, dilatancy of the slurries were observed for 30% solids loadings with dispersant in some cases. Excluding this, the higher percent solid loadings exhibited shear thinning behavior. For a fixed shear rate, the shear stress decreased with increasing pH at higher dispersant dosages which confirms the sharp effect of pH on the slurry rheology with the dispersant addition. The increased adsorption of the anionic dispersant (STPP) on the solids at higher pH values is the reason for this trend.

Transportation Performance of Highly Concentrated Coal-Water Slurries Prepared from Indian Coals

The rheological behaviour of concentrated coal-water slurries prepared from three different Indian coals were investigated using an Anton Paar rheometer. The perspective was laid in to study the effect of solids concentration on the rheological behaviour of coal water slurry. It was observed that coal water slurry exhibited non-Newtonian pseudoplastic fluid behaviour at concentrations above 30 % by weight. The apparent viscosity varied with the amount of coal in the slurry. The rheological data were utilized to predict the pressure drop characteristics of coal water slurry flowing through a 53 mm diameter slurry pipeline using ANSYS Fluent 14.0 computational fluid dynamics code.

Effect of the Interfacial Agents with Different Types of Hydrophilic Functional Groups on the Rheological Properties of Coal-Water Slurry

Five interfacial agents with different hydrophilic groups (DBS, SDS, SO, TX, CTAB) are used as model additives to prepare coal-water slurry (CWS). The effects of different interfacial agents on the rheological properties of CWS are systemically investigated, the microscopic aggregation behavior of coal particles in the suspensions and the zeta potentials in coal-water interface are also studied. Based on the interpretation of the results, the rheological behavior of CWS is greatly influenced by the adsorption pattern of the interfacial agents in coal-water interface. The adsorption patterns of anionic interfacial agents on coal surface are mainly influenced by the combining force between the anionic hydrophilic groups with Ca2+, the stronger combining force with Ca2+ leads to the apparent viscosity increase and heavier pseudo-plastic property of CWS. The adsorption pattern of nonionic interfacial agent on coal surface is seldom influenced by the hydrophilic polyoxyethylene chain, and the addition of nonionic interfacial agent reduces the apparent viscosity of CWS. The adsorption pattern of cationic interfacial agent on coal surface is determined by its cationic head, and the addition of cationic interfacial agent increases the apparent viscosity of CWS. The concluded adsorption models of the interfacial agents with different hydrophilic groups can be guidance for the molecular design of high-performance additives of CWS.

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.

97/01769 Adsorptive characteristics of dispersant on coal surface and its corresponding electrochemical properties and their effect on rheological behavior of coal water slurry

97/01769 Adsorptive characteristics of dispersant on coal surface and its corresponding electrochemical properties and their effect on rheological behavior of coal water slurry

97/00270 Surface properties of thermally upgraded low-rank coals and their effect on the rheological behavior of coal water slurry

The rheological behaviour of a low-rank coal-water slurry from Lochiel, South Australia, has been studied as a function of solids concentration, particle size and size distribution. Coal slurries consisting of particles finer than 45 μm suspended in water were found to exhibit a wide spectrum of flow behaviour ranging from Newtonian as low solids concentrations to shear-thinning and viscoplastic with a yield stress at higher concentrations. By adding a narrow-sized coarse coal fraction (208–279 μm) to the fine coal slurry, the flow characteristic of the slurry, at a fixed total solids concentrations, could be changed significantly with a substantial reduction in the slurry viscosity. An optimum coarse-to-fine particle ratio of 40:60 exists at which the slurry is Newtonian with a minimum viscosity of a about 5 times lower than the viscosity of a slurry containing only fine particles at the same solids concentration. A further reduction in the slurry viscosity of 50% was achieved by adding a second coarse coal particle (279–325 μm) to the bimodal slurry. The significant improvement in the rheological behaviour with changing the particle size distribution may be explained in terms of spatial rearrangement of the particles, and an apparent dilution effect. The results obtained in this study indicate that, with a careful control of the particle size distribution, it is possible to prepare an optimum coal-water slurry which has a low viscosity but with high solids loadings.

The Influence of Fluid Physical Properties on Coal-Water Slurry Atomization

This study reports the atomization behavior of coal-water slurries (CWS) at conditions typical of a gas turbine combustor. Slurry atomization characteristics were determined for a plain-jet airblast research nozzle and six slurries. Atomization quality is reported in terms of the spray’s Sauter mean diameter (SMD) and the radial distribution of fuel mass flux (patternization). The drop size data demonstrate that SMD can be predicted from a knowledge of slurry velocity, the relative velocity between the airblast air and the slurry, the air-to-fuel mass flow ratio (AFR), and the slurry rheology. Slurry rheology is represented here by a power law expression.

Viscometry and rheology of coal water slurry

This paper presents the results of a detailed experimental study on rheological behaviour of coal water slurry (CWS). In contrast to earlier rheological studies at shear rates of rather narrow ranges, this study covered a much wider range of shear rates: 0–800 s −1 in a rotational viscometer and 400–10000 s −1 in a capillary viscometer. While the gap width of a rotational viscometer had no effect on the apparent viscosity of CWS, it was found that selection of proper tube dimensions in a capillary viscometer was important, Thus, the viscosities of CWS measured in both viscometers at the overlapping shear rates of 400–800 s −1 were in good agreement. Consequently, it was possible to study the effect of shear rate higher than 800 s −1 on slurry rheology. In addition, the effects of coal content, coal particle size and size distribution, and temperature on the slurry rheology were investigated. The slurry, a dispersion of coal particles in a pseudoplastic fluid, became more viscous and less pseudoplastic as the coal content was increased. The pseudoplasticity of a highly concentrated utility grind CWS approached that of a concentrated suspension of 40–50 μm solids in a Newtonian fluid. Also, the slurry pseudoplasticity was enhanced at a slightly elevated temperature, but significantly reduced as the shear rate exceeded a threshold dependent on coal content and particle size and size distribution.