| Abstract: | A study was made to determine the effect of an electrolyte, namely sodium chloride(NaCl), on the apparent viscosity of coal suspensions in water. This required a fundamental study of the behavior of the second electro-viscous effect on suspensions of larger particle size and more solids volume loading than has previously been done. A long term application may be in economical coal slurry pipeline development. A reduction in slurry viscosity would reduce pipeline pressure drops and power requirements. Studies of the viscosity of coal suspensions ranging in solids volume fraction from 0.20 to 0.50 and electrolyte concentration from 10⁻⁴ to 10⁻¹ molar were made using the Model R-17 Weissenberg Rheogoniometer. The variables; electrolyte concentration, solids volume fraction, and shear rate, were independently studied to determine their affect on overall suspension viscosity. In addition, tests were made to determine the charge of the ions adsorbed on the coal particle surface, and to determine the conductivity of the electrolytic solution and suspension. The results showed that at a low solids volume fraction, the suspension viscosity decreased with increasing electrolyte concentration to a minimum, then increased upon further electrolyte addition. The minimum occured at an electrolyte concentration of 10⁻³ molar. At a high solids volume fraction, just the opposite behavior occured. The viscosity increased to a maximum with an electrolyte concentration of 10⁻³ molar, then decreased as further electrolyte was added. Intermediate values of solids volume fraction showed no dependence on electrolyte concentration. It was also shown that the negative ion Cl⁻ was adsorbed by the coal particles. This indicates that further study should focus on the negatively charged ion that is added to the suspension. Some of the negative charge on the coal particles was due to the high clay content of the coal sampled. In a natural state, the clay is negatively charged. Another study of interest would look at using coal samples with varying clay content. |
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