No abstract

Coal-water slurry has received considerable research nowadays due to its ability in substituting energy sources. The present work reports the formulation of highly concentrated coal-water slurry using a natural occurring surface active compound, saponin, extracted from the fruits of plant Sapindous laurifolia. The isolation of saponin from the plant and its surface activity has been discussed. The rhelogical characteristics of coal-water slurry have been investigated as a function of coal loading, ash content of coal, pH, temperature, and amount of saponin. The viscosity of the slurry and zeta potential are substantially decreased with concomitant shift of the isoelectric point of coal on adsorption of saponin to it. In the presence of 0.8% of saponin, coal-water slurry containing 64% weight fraction of coal could be achieved. The slurry is stable for a period of as long as 1 month in contrast to 4-5 h in the case of bare coal-water slurry. The results confirm the use of saponin as a suitable additive for coal-water slurry similar to the commercially available additive such as sodium dodecyl sulfate. Basing on the effect of pH on the zeta potential and viscosity of slurry, a suitable mechanism for saponin-coal interaction and orientation of saponin at the coal-water interface has been proposed.

The present work involves the preparation of a highly concentrated coal-water slurry employing three different low-rank coals of Indian origin having variable ash content. The formulation, rheology, and stabilization of the slurry have been investigated using saponin extracted from the seeds and pericarps (mods) of the Acacia concinna plant as a dispersant. The saponins extracted from both the seeds and pericarps of the plant are found to stabilize the slurry. The rheological characteristics of the slurry have been analyzed by varying pH and coal loading in the presence and absence of saponin. The coal-water slurry follows the Bingham plastic model and behaves as a non-Newtonian fluid in the presence of saponin. The stabilization of the coal-water slurry has been attributed primarily to the diminution of the coal particle-particle interaction because of steric hindrance offered by adsorbed saponin. The measurements of ζ potential, yield stress, and viscosity of coal in the presence of saponin further provide evidence to this effect.