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 mu m) with four distinct coarse fractions (212 mu m - 300 mu m, 90 mu m - 300 mu m, 150 mu m - 212 mu m,75 mu m - 150 mu m) 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 1.3PaS for the shear rate 147S(-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 14mN/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.