Rheology Of Coal-water Slurries Research Articles

Influence of particle size gradation on the preparation of highly concentrated coal-water slurry and the development of a gradation model

ABSTRACT Aiming at the problem that low-rank coal is unsuitable for making CWS (coal-water slurry) and lacks an accurate particle size gradation prediction model. This paper expounds on the effects of ball milling time and speed on the concentration and rheology of CWS under different grinding conditions. After size grading, the slurry’s bimodal parameters and particle size distribution are studied. Based on the BP neural network, a particle size distribution model more suitable for low-rank coal is established in this paper. The results show that the slurry concentration in the graded coal sample increases by 4% higher than that of the ungraded coal sample. The BP neural network model accurately predicts the relationship between bimodal parameters and slurry concentration based on bimodal parameters. In the context of grain size gradation, the optimized particle size cumulative distribution model, denoted as y = x n − x K n x 100 n − x K n + K { ( K + 10 % > x > K% } , demonstrates enhanced alignment with the attributes of low-rank coal. This underscores the paper’s contribution in providing a more fitting particle size distribution model for low-rank coal in the context of CWS production.

Selection of Appropriate Model for the Synthesis of Coal Water Slurry (CWS) Using PVA and TEA

Coal-Water Slurry (CWS) is an attractive alternative fuel with lower cost and reliable in terms of transportation and handling. The efficiency of CWS gasification depends on the preparation of CWS to ensure the higher carbon contents and low viscosity which will enhance the heating rates along with the atomization of CWS. In this paper, the rheology of CWS was studiedwith coal loading 30 to 60% and the rheological behavior was discussed with the help of Power-law, Casson and Herschel Buckley models which shows that CWS exhibits pseudo-plastic (shear thinning) behavior. The CWS was prepared by using Poly-Vinyl Alcohol (PVA) and Triethanol Amine (TEA) as dispersants and Xanthan gum as a stabilizer. The experimental results showed that for a constant coal loading viscosity decreases as the shear rate increases and out of these rheological models, power-law fits best on the experimental data with the highest R2 of 0.99

Effects of hydrothermal dewatering of lignite on rheology of coal water slurry

AbstractMaximizing the dry‐based solid loading of coal particles in water is essential in increasing the burning efficiency of coal water slurry, which has been widely used as a liquid fuel. Understanding the rheology of coal water slurry could provide fundamental guidance on designing and optimizing coal water slurry formulation. The rheological studies have shown that coal water slurries made with lignite samples after hydrothermal dewatering (HTD) exhibit a stronger shear thinning behaviour as compared with those made with raw lignite samples. The viscosity of coal water slurry at the shear rate of 100 s−1 decreases with an increasing HTD temperature, which is probably due to the decrease of volume of lignite particles caused by the permanent reduction of both bound and non‐freezable water (inherent moisture) after the HTD process. The reduction of the inherent moisture of lignite samples after HTD treatment was elucidated by differential scanning calorimetry (DSC) under the temperature well below the freezing point. A lignite water slurry with a solid loading of 62 wt% db (dry basis) is obtained after hydrothermal dewatering at 300 °C with the addition of 1.2 wt% of polycarboxylate ether (PCE). Our findings indicated that hydrothermal dewatering of lignite has profound impacts on the inherent moisture of lignite and the rheological properties of coal water slurry.

Secondary breakup of coal water slurry drops

To investigate secondary atomization of coal water slurry (CWS), deformation and breakup of eight kinds of CWS drops are presented using high speed digital camera. Based on morphology, deformation and breakup regimes of CWS drops can be termed some different modes: deformation, multimode breakup (including two sub-modes: hole breakup and tensile breakup), and shear breakup. Correlations on the ranges of breakup modes are also obtained. The conventional Weber number and Ohnesorge number are found to be insufficient to classify all breakup modes of CWS drops, so two other non-dimensional numbers based on rheology of CWS are suggested to use in the deformation and breakup regime map. Finally, total breakup time is studied and correlated, which increases with Ohnesorge number.

Rheology of coal-water slurries

The costs of preparation and burning of coal slurries, in particular, coal-water fuel (CWF), considerably exceed the cost of coal utilization according to the conventional technology. CWF technology projects suggest that additional expenditures will be compensated for by the profitability of their pipeline transport in the laminar regime. Energy consumptions for the preparation and pipeline or tanker transportations is determined to a considerable extent by the viscosity and stability of these slurries. Thus, the rheology of slurries has become a subject of comprehensive experimental study. The results of theoretical investigation of the rheology of concentrated slurries are reported. The theory adequately describes all of the experimental data relevant to the issue.

Rheological Behavior of Coal-Water Slurry

The rheological behavior of some Indian coal-water slurry (CWS) was investigated using a HAAKE RV30 viscometer. The objective was to study the effect of solid concentration, ash content, pH, and temperature on the rheology of CWS. It was found that CWS exhibits pseudoplastic behavior. The apparent viscosity varies with the amount of coal in the slurry, pH, and temperature, which is the highest around pH 6 and the lowest near pH 8. The effect of temperature on the viscosity could be described using an Arrhenius type of relation.

98/02764 Effect of humic acids and coal surface properties on rheology of coal-water slurries: Pawlik, M. et al. Coal Prep., 1997, 18, (3/4), 129–149

98/02764 Effect of humic acids and coal surface properties on rheology of coal-water slurries: Pawlik, M. et al. Coal Prep., 1997, 18, (3/4), 129–149

98/02795 Sedimentation stability and rheology of coal-water slurries: Usui, H. et al. Coal Prep., 1997, 18, (3/4), 201–214

98/02795 Sedimentation stability and rheology of coal-water slurries: Usui, H. et al. Coal Prep., 1997, 18, (3/4), 201–214

Effect of Humic Acids and Coal Surface Properties on Rheology of Coal-Water Slurries

In the tests described in this paper, humic acids were used to modify coal surface properties and to study the effect of such modification on the rheology of coal-water slurries (CWS). Adsorption of humic acids onto a hydrophobic bituminous coal surface renders the surface hydrophilic; also the electric charge on such a surface becomes more negative. Such a modified surface of a bituminous coal resembles very closely the surface of an oxidized and/or low rank coal as indicated by the results of our contact angle and electrokinetic measurements. The presence of humic acids results in improved dispersion of bituminous coal and increases the coal loading of CWS. Slurries prepared from hydrophobic coals in distilled water exhibit high yield stress values and high apparent viscosities. In the presence of humic acids the yield stress values decrease almost to zero and the apparent viscosity is lowered as well. Since oxidized and/or lower rank coals contain large quantities of humic acids, the addition of humic acids does not affect markedly the rheological behavior of such coals. In the absence of humic acids, the hydrophobic attractive interactions between hydrophobic particles apparently dominate in the system and lead to particle aggregation. In the absence of such hydrophobic interactions, hydrophilic particles are stabilized by electrostatic repulsion and remain well dispersed in the aqueous phase.

Sedimentation Stability and Rheology of Coal Water Slurries

Sedimentation of coal particles should be avoided during the transportation of coal water mixtures (CWMs) by sea in tankers. The sedimentation of coal particles under shear flow plays an important role in the stability of CWMs. It is important to understand how the theological characteristics of CWMs are related to the sedimentation stability. In this study, the stability of CWMs prepared with and without a stabilizer was evaluated using test equipment developed at Yamaguchi University. The Theological measurements of CWMs were also conducted, and the results obtained were correlated with the sedimentation stability of CWMs.

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.